Principles and Practice of Endocrinology and Metabolism [2 ed.] 0397514042, 9780397514045

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NATIONAL INSTITUTES OF HE NIH LIBRARY |StP I I 1995 BLDG 10, 10 CENTER DR. BETHESDA, MD 20892-1150

Principles and Practice of

ENDOCRINOL OGY AND

METABOLISM

Principles and Practice of

ENDOCRINOLOGY AND

METABOLISM Second Edition

EDITOR

Kenneth L. Becker ASSOCIATE EDITORS

John P. Bilezikian William J. Bremner Wellington Hung C. Ronald Kahn D. Lynn Loriaux Eric S. Nylen Robert W. Rebar Gary L. Robertson Leonard Wartofsky

328 Contributors

J. B. LIPPINCOTT COMPANY Philadelphia

Acquisitions Editor: Richard Lampert Associate Medical Editor: Wendy Greenberger-Czarnecki Project Editor: Jody E. Gould Production Manager: Caren Erlichman Production Coordinator: David Yurkovich Design Coordinator: Kathy Kelley-Luedtke Cover Designer: Tom Jackson Indexer: Maria Coughlin Compositor: Tapsco, Incorporated Printer/Binder: Courier Book Company/Westford

Second Edition

Copyright © 1995, 1990 by J. B. Lippincott Company. All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission except for brief quotations embodied in critical articles and reviews. Printed in the United States of America. For information write J. B. Lippincott Company, 227 East Washington Square, Philadelphia, PA 19106.

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Library of Congress Cataloging-in-Publication Data Principles and practice of endocrinology and metabolism/editor, Kenneth L. Becker; associate editors, John P. Bilezikian . . . [et al.]; 328 contributors. — 2nd ed. p. cm. Includes bibliographical references and index. ISBN 0-397-51404-2 (alk. paper) 1. Endocrinology. 2. Endocrine glands—Diseases. 3. Metabolism—Disorders. I. Becker, Kenneth L. II. Title: Endocrinology and metabolism. [DNLM: 1. Endocrine Diseases. 2. Metabolic Diseases. WK 100 P957 1995] RC648.P67 1995 616.4—dc20 DNLM/DLC for Library of Congress 94-42416 CIP @ This paper meets the requirements of ANSI/NISO Z39.48-1992 (permanence of paper). Every effort has been made to trace the copyright holders of all reprinted material. If any copyright holder has been inadvertently overlooked, the Publisher will make the appropriate arrangements at the earliest opportunity. The opinions or assertions contained in Chapters 29, 31, 37, 39, 41, and 42 are the private views of the authors and are not to be construed as official or reflecting the views of the Army or the Department of Defense. The authors and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new or infrequently employed drug.

EDITORS

EDITOR Kenneth L. Becker, MD, PhD, FACP Professor of Medicine and Physiology Director of Endocrinology and Metabolism George Washington University School of Medicine and Health Sciences and Veterans Affairs Medical Center Washington, D.C.

D. Lynn Loriaux, MD, PhD Chairman, Department of Medicine Head, Division of Endocrinology, Diabetes and Clinical Nutrition Oregon Health Sciences University Portland, Oregon

Eric S. Nylen, MD

ASSOCIATE EDITORS John P. Bilezikian, MD Professor of Medicine and Pharmacology College of Physicians and Surgeons Columbia University Attending Physician Presbyterian Hospital New York, New York

William J. Bremner, MD, PhD Chief, Medicine Service Seattle Veterans Affairs Medical Center Professor and Vice Chair, Department of Medicine Director, Population Center for Research in Reproduction University of Washington Seattle, Washington

Wellington Hung, MD, PhD Professor of Pediatrics Division of Pediatric Endocrinology and Metabolism Georgetown University Children's Medical Center Washington, DC

C. Ronald Kahn, MD Mary K. Iacocca Professor of Medicine Harvard Medical School Director, Research Division Joslin Diabetes Center Boston, Massachusetts

Assistant Professor of Medicine George Washington University School of Medicine and Health Sciences Division of Endocrinology and Metabolism Veterans Affairs Medical Center Washington, DC

Robert W. Rebar, MD Professor and Director Department of Obstetrics and Gynecology University of Cincinnati College of Medicine Chief, Obstetrics and Gynecology University Hospital Cincinnati, Ohio

Gary L. Robertson, MD Professor of Medicine and Neurology Director, Clinical Research Center Northwestern University Medical School Chicago, Illinois

Leonard Wartofsky, MD Professor of Medicine and Physiology Uniformed Services University of the Health Sciences Clinical Professor of Medicine George Washington University School of Medicine and Georgetown University School of Medicine Chair, Department of Medicine Washington Hospital Center Washington, DC

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CONTRIBUTORS

Thomas Aceto, Jr., md

Neil Aronin, md

James N. Baraniuk, md, frcp(C)

Professor of Pediatrics Chairman Emeritus St. Louis University School of Medicine Medical Staff Cardinal Glennon Children's Hospital St. Louis, Missouri

Professor of Medicine and Cell Biology University of Massachusetts Medical School and the Graduate School of Biomedical Sciences Worcester, Massachusetts

Assistant Professor of Medicine Georgetown University Washington, DC

David S. Baskin, md, facs Louis J. Aronne, md

Zalman S. Agus, md, facp Professor of Medicine and Physiology University of Pennsylvania School of Medicine Attending Physician Renal-Electrolyte and Hypertension Division Hospital of the University of Pennsylvania and VA Medical Center Philadelphia, Pennsylvania

Andrew J. Ahmann, md Assistant Professor Department of Medicine Division of Endocrinology Oregon Health Sciences University Portland, Oregon

Bilal Ahmed, mbbs Staff Endocrinologist Liaquat National Hospital Karachi, Pakistan

Associate Professor of Clinical Medicine Cornell University Medical College Assistant Attending Physician Medical Director, Comprehensive Weight Control New York Hospital New York, New York

Gilbert P. August, md Professor of Pediatrics George Washington University School of Medicine and Health Sciences Chairman, Department of Endocrinology Children's National Medical Center Washington, DC

Professor of Medicine University of Newcastle Upon Tyne United Kingdom

Lloyd Axelrod, md Associate Professor of Medicine Harvard Medical School Physician and Chief of the James Howard Means Firm Massachusetts General Hospital Boston, MA

Associate Director, Clinical Research Bone Metabolism/Endocrinology Rhone-Poulenc Rorer Central Research Collegeville, Pennsylvania

Richard G. Allen, PhD

Melvin G. Alper, md, facs Clinical Professor of Ophthalmology and Neurological Surgery The George Washington University Senior Attending in Ophthalmology, George Washington University School of Medicine and Health Sciences and Washington Hospital Center Washington, DC

Senior Research Fellow University of Melbourne Department of Obstetrics & Gynecology Royal Women's Hospital Carlton, Victoria Australia

James R. Baker, Jr., md Associate Professor of Internal Medicine and Pathology Department of Internal Medicine and Pathology Chief, Allergy Division University of Michigan Medical School Ann Arbor, Michigan

William A. Banks, md Donna M. Arab, md, frcp(C) Endocrinology Fellow Dalhousie University CompHill Medical Center Halifax, Nova Scotia, Canada

Professor of Experimental Medicine The Medical School, University of Newcastle Upon Tyne Consultant Physician Royal Victoria Infirmary Newcastle Upon Tyne, England

Professor of Radiology and Medicine Cornell University Medical College Director, Division of Nuclear Medicine New York Hospital New York, New York

Dorothy J. Becker, mb Bch (FCP) Professor of Pediatrics University of Pittsburgh Director, Diabetes Section Children's Hospital of Pittsburgh Pittsburgh, Pennsylvania

Kenneth L. Becker, md, PhD, facp H. W. Gordon Baker, md, PhD, fracp

Assistant Professor/Scientist Oregon Health Sciences University Portland, Oregon

Peter H. Baylis, BSc, ms, frcp

David V. Becker, md

Daiva R. Bajorunas, md K. George M. M. Alberti, FRCP, DPhil

Professor of Neurosurgery and Anesthesiology Baylor College of Medicine Attending Physician The Methodist Hospital Houston, Texas

Associate Professor, Tulane University School of Medicine Staff Physician, Veterans Affairs Medical Center New Orleans, Louisiana

Professor of Medicine and Physiology Director of Endocrinology and Metabolism George Washington University School of Medicine and Health Sciences and Veterans Affairs Medical Center Washington, DC

Margery C. Beinfeld, PhD Professor of Pharmacological & Experimental Therapeutics Tufts University School of Medicine Boston, Massachusetts

Norman H. Bell, md Professor of Medicine and Pharmacology Director, Division of Bone and Mineral Metabolism Medical University of South Carolina Staff Physician, Veterans Affairs Medical Center Charleston, South Carolina wti

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CONTRIBUTORS

John P. Bilezikian, md Professor of Medicine and Pharmacology College of Physicians and Surgeons Columbia University Attending Physician Presbyterian Hospital New York, New York

Richard E. Blackwell, PhD, md Professor of Obstetrics and Gynecology Director, Division of Reproductive Biology and Endocrinology University of Alabama at Birmingham Birmingham, Alabama

Henry B. Burch, md Assistant Professor of Medicine Uniformed Services University of the Health Sciences Bethesda, Maryland Walter Reed Army Medical Center Department of Medicine Endocrine-Metabolic Service Washington, DC

Eberhard Blind, md Research Assistant Department of Medicine I— Endocrinology and Metabolism University of Heidelberg Heidelberg, Germany

Kenneth D. Burman, md Clinical Professor of Medicine George Washington University School of Medicine and Health Sciences Washington, DC Professor of Medicine (Affiliated) Uniformed Services University of the Health Sciences Bethesda, Maryland Director of Endocrinology Washington Hospital Center Washington, DC

Stephen R. Bloom, ma, md Professor of Endocrinology Endocrine Unit Royal Postgraduate Medical School Hammersmith Hospital London, England

William J. Burtis, md, PhD Associate Professor of Medicine Yale University School of Medicine Staff Physician West Haven Veterans Affairs Medical Center West Haven, Connecticut

Manfred Blum, md, facp Professor of Clinical Medicine and Radiology Director of Nuclear Endocrine Division Attending in Medicine New York University Medical Center New York, New York

Nanci Bobrow, PhD Psychologist Cardinal Glennow Children's Hospital St. Louis, Missouri

Susan Bonner-Weir, PhD Associate Professor of Medicine Harvard Medical School Senior Investigator Joslin Diabetes Center Boston, Massachusetts

William J. Bremner, md, PhD Chief, Medicine Service Seattle Veterans Affairs Medical Center Professor and Vice Chair, Department of Medicine Director, Population Center for Research in Reproduction University of Washington Seattle, Washington

Edward M. Brown, md Associate Professor Harvard Medical School Endocrine-Hypertension Unit Brigham and Women's Hospital Boston, Massachusetts

Peter H. Byers, md Professor of Pathology and Medicine (Medical Genetics) University of Washington Seattle, Washington Robert E. Canfield, md Irving Professor of Medicine Director, Irving Center for Clinical Research Columbia University College of Physicians and Surgeons Attending Physician The Presbyterian Hospital New York, New York Thomas O. Carpenter, md Associate Professor of Pediatrics Yale University School of Medicine Attending Physician Yale-New Haven Hospital New Haven, Connecticut Bruce R. Carr, md Paul C. MacDonald Professor of Obstetrics & Gynecology Director, Division of Reproductive Endocrinology Senior Attending Physician Parkland Memorial Hospital Zale Lipshy Hospital Dallas, Texas Robert E. Carraway, PhD Professor of Physiology University of Massachusetts Medical Center Worcester, Massachusetts

Patricia B. Carroll, md Assistant Professor of Medicine, Surgery and Pediatrics University of Pittsburgh Medical Center Pittsburgh, Pennsylvania Veronica M. Catanese, md Assistant Professor of Medicine New York University School of Medicine Attending Physician New York University Medical Center New York, New York Donald Chakeres, md Professor of Radiology Ohio State University College of Medicine Division Head of Neuroradiology Clinical Director of Magnetic Resonance Imaging Ohio State University Hospital Columbus, Ohio John R. G. Challis, PhD Scientific Director Lawson Research Institute Director, MRC Group in Fetal and Neonatal Health and Development University of Toronto Toronto, Ontario Canada Charles H. Chesnut, III, md, facp Professor, Medicine and Radiology Director, Osteoporosis Research Center Division of Nuclear Medicine University of Washington Medical Center Seattle, Washington William W. Chin, md Professor of Medicine, Harvard Medical School Investigator, Howard Hughes Medical Institute Chief, Division of Genetics and Senior Physician Brigham and Women's Hospital Boston, Massachusetts Richard V. Clark, md, PhD Associate Professor of Medicine Director, Clinical and Educational Programs Division of Endocrinology and Metabolism Duke University Medical Center Durham, North Carolina Thomas L. Clemens, PhD Associate Professor of Medicine Division of Endocrinology and Metabolism Cedars-Sinai Medical Center University of California, Los Angeles School of Medicine Los Angeles, California

CONTRIBUTORS Fredric L. Coe, md Professor of Medicine and Physiology Director, Nephrology Section, Department of Medicine University of Chicago Chicago, Illinois

Joshua L. Cohen, md Associate Professor of Medicine Division of Endocrinology and Metabolism George Washington University School of Medicine and Health Sciences Washington, DC

Regis Cohen, md, PhD University of Paris XIII Dept, of Endocrinology Hopital Avicenne Bobigny, France

Warren E. Cohen, md Associate Professor of Pediatrics and Neurology Case Western Reserve University School of Medicine Chief, Division of Rehabilitative Pediatrics and Developmental Disabilities, Rainbow Babies and Childrens Hospital Medical Director, Health Hill Hospital for Children Cleveland, Ohio

Richard J. Comi, md Residency Training Program Director Associate Professor of Medicine Staff Physician Dartmouth-Hitchcock Medical Center Co-Medical Director Diabetes Centers of New Hampshire Lebanon, New Hampshire

Paul E. Cooper, md Associate Professor Department of Clinical Neurological Sciences and Department of Medicine University of Western Ontario Chief, Clinical Neurological Sciences Vice President, Medical Affairs St. Joseph's Health Centre London, Ontario, Canada

Felicia Cosman, md Assistant Professor of Clinical Medicine Columbia University College of Physicians and Surgeons Endocrinologist-Metabolic Bone Specialist Helen Hayes Hospital West Haverstraw, New York

Brian M. Cox, PhD Professor and Chairman (Acting) Department of Pharmacology Uniformed Services University of the Health Sciences Bethesda, Maryland

Glenn R. Cunningham, md Professor of Medicine and Cell Biology Baylor College of Medicine Chief, Division of Endocrinology and Metabolism Department of Medicine Baylor College of Medicine Associate Chief of Staff for Research and Development Veterans Affairs Medical Center Houston, Texas

Gordon B. Cutler, Jr., md Chief, Section on Developmental Endocrinology Developmental Endocrinology Branch National Institute of Child Health and Human Development National Institutes of Health Bethesda, Maryland

David C. Dahl, md Assistant Professor of Medicine University of Minnesota Attending Physician Hennepin County Medical Center Minneapolis, Minnesota

Mary F. Dallman, PhD Professor and Vice-Chair Department of Physiology University of California, San Francisco San Francisco, California

Daniel N. Darlington, PhD Assistant Professor Departments of Surgery and Physiology University of Maryland School of Medicine Baltimore, Maryland

Faith B. Davis, md Professor of Medicine Albany Medical College Attending Physician, Endocrinology Albany Medical Center Hospital Albany, New York

Paul J. Davis, md Professor and Chairman Department of Medicine Albany Medical College Physician-in-Chief Albany Medical Center Hospital Staff Physician, Stratton Veterans Affairs Medical Center Albany, New York

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Ralph A. DeFronzo, md Professor of Medicine Chief, Diabetes Division Member, Endocrine and Nephrology Divisions University of Texas Health Sciences Center San Antonio, Texas David M. de Kretser, md, fracp Professor and Director Institute of Reproduction & Development Monash University Melbourne, Australia Nicola de Maria, md Clinical Research Fellow Oklahoma Transplantation Institute Baptist Medical Center Oklahoma City, Oklahoma David W. Dempster, PhD Associate Professor of Clinical Pathology Columbia University College of Physicians and Surgeons New York, New York Director, Regional Bone Center Helen Hayes Hospital West Haverstraw, New York

Ralph G. DePalma, md, facs Vice Chairman Professor of Surgery Associate Dean Department of Surgery University of Nevada Reno, Nevada Richard N. Dexter, md Professor of Medicine Indiana University School of Medicine Chief, Endocrinology and Metabolism Wishard Memorial Hospital Indianapolis, Indiana

Gerard M. Doherty, md Assistant Professor of Surgery Washington University School of Medicine Staff Surgeon, Barnes Hospital St. Louis, Missouri John L. Doppman, md Department of Radiology National Institutes of Health Bethesda, Maryland

Allan L. Drash, md Professor of Pediatrics and Epidemiology University of Pittsburgh Director of Research Division of Pediatric Endocrinology The Children's Hospital of Pittsburgh Pittsburgh, PA

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CONTRIBUTORS

Marc K. Drezner, md Professor of Medicine Chief, Division of Endocrinology, Metabolism and Nutrition Director, Sarah W. Stedman Nutrition Center Duke University Medical Center Durham, North Carolina Raghvendra K. Dubey, PhD Assistant Professor, Department of Medicine School of Medicine Center for Clinical Pharmacology University of Pittsburgh Medical Center Pittsburgh, Pennsylvania Alan Dubrow, md Clinical Assistant Professor Mount Sinai School of Medicine Director, Hemodialysis Unit Beth Israel Medical Center New York, New York D. Robert Dufour, md Associate Professor of Pathology The George Washington University School of Medicine and Health Sciences Clinical Associate Professor of Pathology Uniformed Services University of the Health Sciences Chief, Pathology and Laboratory Medicine Services Veterans Affairs Medical Center Washington, DC Roberta P. Durschlag, PhD, rd Assistant Professor of Nutrition Boston University Boston, Massachusetts Richard C. Eastman, md Director, Division of Diabetes, Endocrinology and Metabolic Diseases National Institute of Diabetes, Digestive and Kidney Diseases National Institutes of Health Bethesda, Maryland

Gregory F. Erickson, PhD Professor, Department of Reproductive Medicine University of California, San Diego La Jolla, California Stefano Fagiuoli, md Clinical Fellow Oklahoma Transplantation Institute Baptist Medical Center Oklahoma City, Oklahoma

Jan Fahrenkrug, md, dmSc Professor of Clinical Neurochemistry University of Copenhagen Head, Department of Clinical Biochemistry Bispebjerg Hospital Copenhagen, Denmark

Kenneth R. Falchuk, md Assistant Professor of Medicine Harvard Medical School Director, Gastrointestinal Endoscopy Unit Deaconess Hospital Boston, Massachusetts

Murray J. Favus, md Professor of Medicine University of Chicago Pritzker School of Medicine Program Director General Clinical Research Center Chicago, Illinois

Jo-David Fine, md, mph Professor of Dermatology, School of Medicine Adjunct Professor of Epidemiology, School of Public Health The University of North Carolina at Chapel Hill Attending Physician, UNC Hospitals Chapel Hill, North Carolina

George S. Eisenbarth, md, PhD Executive Director Barbara Davis Center for Childhood Diabetes Professor of Pediatrics, Medicine and Immunology University of Colorado Health Sciences Center Denver, Colorado

James D. Finkelstein, md Professor of Medicine George Washington University School of Medicine and Health Sciences and Howard University College of Medicine Clinical Professor of Medicine Georgetown University School of Medicine Chief, Medical Service Veterans Affairs Medical Center Washington, DC

George M. Eliopoulos, md Associate Professor of Medicine Harvard Medical School Assistant Chairman, Department of Medicine Deaconess Hospital Boston, Massachusetts

Lorraine A. Fitzpatrick, md Associate Professor of Medicine Mayo Medical School Consultant in Endocrinology and Metabolism Mayo Clinic and Mayo Foundation Rochester, Minnesota

Jeffrey S. Flier, md Professor of Medicine Harvard Medical School Chief, Division of Endocrinology and Metabolism Beth Israel Hospital Boston, Massachusetts

Ruth C. Fretts, md, mph Instructor in Obstetrics, Gynecology and Reproductive Biology Harvard University Beth Israel Hospital Boston, Massachusetts

Om P. Ganda, md Senior Physician Joslin Diabetes Center Associate Clinical Professor of Medicine Harvard Medical School Attending Physician New England Deaconess Hospital Boston, Massachusetts

Luigi Garibaldi, md Associate Professor of Pediatrics St. Louis University School of Medicine Cardinal Glennon Children's Hospital St. Louis, Missouri

David A. Gelber, md Assistant Professor of Neurology Southern Illinois University School of Medicine Springfield, Illinois

Gary W. Gibbons, md Associate Clinical Professor of Surgery Harvard Medical School Clinical Chief Division of Vascular Surgery New England Deaconess Hospital Boston, Massachusetts

John R. Gill, Jr., md Scientist Emeritus Hypertension-Endocrine Branch National Heart Lung and Blood Institute National Institutes of Health Bethesda, Maryland

Joel S. Glaser, md Professor, Neuro-Ophthalmology Bascom Palmer Eye Institute University of Miami School of Medicine Miami, Florida

Allen M. Glasgow, md Professor of Pediatrics George Washington University School of Medicine and Health Sciences Children's National Medical Center Washington, DC

CONTRIBUTORS Allan R. Glass, md Professor of Medicine Uniformed Services University of Health Sciences Assistant Chief, Endocrinology Walter Reed Army Medical Center Washington, DC

W. Reid Glaws, DO Associate of Medicine University of Illinois at Chicago College of Medicine Gastroenterology Fellow University of Illinois Hospital and Clinics Chicago, Illinois

Philip W. Gold, md Chief, Clinical Neuroendocrinology Branch National Institute of Mental Health National Institutes of Health Bethesda, Maryland

Stuart L. Goldberg, md Assistant Professor of Medicine Assistant Director, Bone Marrow Transplantation Program Temple University Health Science Center Philadelphia, Pennsylvania

Allison B. Goldfine, md Instructor in Medicine Harvard Medical School Research Associate Joslin Diabetes Center Boston, Massachusetts

Allan L. Goldstein, PhD Professor and Chairman Department of Biochemistry and Molecular Biology George Washington University School of Medicine and Health Sciences Washington, DC

David S. Goldstein, md Senior Investigator National Institute of Neurological Disorders and Stroke Bethesda, Maryland

David Goltzman, md Professor and Chairman McGill University Physician-in-Chief Royal Victoria Hospital Montreal, Quebec, Canada

Michael N. Goodman, PhD Professor of Medicine, University of California School of Medicine, Davis University of California Medical Center Sacramento, California

Phillip Gorden, md Director, National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health Bethesda, Maryland Fredric D. Gordon, md Instructor in Medicine Harvard Medical School Gastroenterologist Deaconess Hospital Boston, Massachusetts Daryl K. Granner, md Professor and Chairman Department of Molecular Physiology and Biophysics Professor of Internal Medicine Vanderbilt University Medical School Nashville, Tennessee Maria B. Grant, md Associate Professor Division of Endocrinology and Metabolism Department of Medicine University of Florida College of Medicine Shands Teaching Hospital Gainesville, Florida Douglas A. Greene, md Professor of Internal Medicine Chief, Division of Endocrinology and Metabolism University of Michigan Medical School Director, Michigan Diabetes Research and Training Center University of Michigan Ann Arbor, Michigan David Allen Gruenewald, md Acting Assistant Professor of Medicine University of Washington School of Medicine Staff Physician, Gerontology Research Education and Clinical Center Veterans Affairs Medical Center Seattle, Washington Philippe A. Halban, PhD Louis Jeantet Professor of Medicine University of Geneva Geneva, Switzerland

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Peter J. Hammond, bm, Bch, ma, mrcp Senior Registrar, Department of Diabetes and Endocrinology St. James University Hospital Leeds, United Kingdom John W. Harmon, md Professor of Surgery George Washington University School of Medicine Georgetown University School of Medicine Uniformed Services University of the Health Sciences Clinical Professor of Surgery Howard University School of Medicine Chief of Surgery Veterans Affairs Medical Center Washington, DC Stephen G. Harner, md Professor of Otolaryngology Mayo Medical School Consultant in Otolaryngology Mayo Clinic Rochester, Minnesota J. Fielding Hejtmancik, md, PhD Medical Officer National Eye Institute National Institutes of Health Bethesda, Maryland Geoffrey N. Hendy, PhD Associate Professor of Medicine McGill University Medical Scientist Royal Victoria Hospital Montreal, Quebec, Canada Jules Hirsch, md Sherman Fairchild Professor Rockefeller University Physician-in-Chief Rockefeller University Hospital New York, New York Max Hirshkowitz, PhD Associate Professor Baylor College of Medicine Department of Psychiatry Sleep Research Center Director Veterans Affairs Medical Center Houston, Texas

Nicholas R. S. Hall, PhD Professor and Director, Division of Psychoimmunology University of South Florida College of Medicine Tampa, Florida

Gary D. Hodgen, PhD Professor and President The Jones Institute of Reproductive Medicine Dept, of Obstetrics and Gynecology Eastern Virginia Medica' School Norfolk, Virginia

Allan G. Halline, md Assistant Professor, Department of Medicine University of Illinois at Chicago Attending Physician, University of Illinois Hospital Chicago, Illinois

David I. Hoffman, md Medical Staff Northwest Center for Infertility and Reproductive Endocrinology Medical Staff North Broward Medical Center Margate, Florida

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CONTRIBUTORS

Edward W. Holmes, md Frank Wister Thomas Professor of Medicine Chairman, Department of Medicine Professor of Genetics University of Pennsylvania School of Medicine Chief of Medicine Hospital of the University of Pennsylvania Philadelphia, Pennsylvania Robert N. Hoover, md, ScD Chief, Environmental Epidemiology Branch Epidemiology and Biostatistics Program Division of Cancer Etiology National Cancer Institute, National Institutes of Health Rockville, MD Gabriel N. Hortobagyi, md, facp Professor of Medicine Chairman, Department of Breast and Gynecologic Medical Oncology Internist, University of Texas M. D. Anderson Cancer Center Houston, Texas Richard Horton, md Professor of Medicine University of Southern California Los Angeles, California Eva Horvath, PhD Associate Professor of Pathology Department of Pathology University of Toronto Research Associate Department of Pathology St. Michael's Hospital Toronto, Ontario, Canada Barbara V. Howard, PhD President, Medlantic Research Institute Research Professor of Medicine University of Maryland and George Washington University School of Medicine and Health Sciences Washington, DC

Wellington Hung, md, PhD Professor of Pediatrics Division of Pediatric Endocrinology and Metabolism Georgetown University Children's Medical Center Washington, DC

Edwin L. Kaplan, md Professor of Surgery The University of Chicago Pritzker School of Medicine The University of Chicago Medical Center Chicago, Illinois

Philip M. Iannaccone, md, PhD Professor of Pathology Northwestern University Medical School Pathologist Northwestern Memorial Hospital Chicago, Illinois

Abba J. Kastin, md Professor, Department of Medicine Tulane University School of Medicine Chief of Endocrinology Veterans Affairs Medical Center New Orleans, Louisiana

Koichi Ito, MD, PhD Visiting Research Fellow Department of Surgery, University of Chicago Medical Center Chicago, Illinois

Laurence Katznelson, md Instructor in Medicine Harvard Medical School Assistant in Medicine Neuroendocrine Unit Massachusetts General Hospital Boston, Massachusetts

Ivor M. D. Jackson, md Professor of Medicine Director, Division of Endocrinology Brown University School of Medicine Physician-in-Charge Division of Endocrinology, Rhode Island Hospital Providence, Rhode Island

Lois Jovanovic-Peterson, md Senior Scientist Sansum Medical Research Foundation Attending Physician Director, Diabetes Program Santa Barbara, California Clinical Professor of Medicine University of Southern California, Los Angeles Los Angeles, California

William A. Jubiz, md Director of Endocrinology, Metabolism and The Diabetes Center Universidad de Valle Cali, Colombia

Wm. James Howard, md Professor of Medicine George Washington University School of Medicine and Health Sciences Senior Vice President and Medical Director Medlantic Research Institute Washington, DC

C. Ronald Kahn, md Mary K. Iacocca Professor of Medicine Harvard Medical School Director, Research Division Joslin Diabetes Center Boston, Massachusetts

Willa A. Hsueh, md Professor of Medicine Chief, Division of Endocrinology, Diabetes and Hypertension University of Southern California Medical Center Los Angeles, California

Cynthia G. Kaplan, md Associate Professor of Pathology State University of New York, Stony Brook Pediatric Pathologist University Medical Center Stony Brook, New York

Harry R. Keiser, md Clinical Director, National Heart, Lung and Blood Institute Chief, Hypertension Endocrine Branch, NHLBI National Institutes of Health Bethesda, Maryland

Robert P. Kelch, md Dean and Professor of Pediatrics University of Iowa College of Medicine Iowa City, Iowa

Ellie Kelepouris, md Associate Professor of Medicine Division of Nephrology and Hypertension Temple University of Health Sciences Philadelphia, Pennsylvania

John W. Kendall, md Professor of Medicine Oregon Health Sciences University Distinguished Physician Portland Veterans Affairs Medical Center Portland, Oregon

Daniel Kenigsberg, md Co-Director Long Island IVF Chief, Section of Reproductive Endocrinology J. T. Mather Memorial Hospital Port Jefferson, New York Clinical Associate Professor Department of Obstetrics and Gynecology State University of New York at Stonybrook Stonybrook, New York

CONTRIBUTORS

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Craig M. Kessler, md Professor of Medicine Director of the Division of HematologyOncology George Washington University School of Medicine and Health Sciences Washington, DC

Andrzej S. Krolewski, md Associate Professor of Medicine Harvard Medical School Chief, Section on Epidemiology and Genetics Research Division Joslin Diabetes Center Boston, Massachusetts

Hoyle Leigh, md, facp, fapa Professor and Vice-Chair, Department of Psychiatry University of California, San Francisco Chief of Psychiatry, Fresno VA Medical Center Lecturer in Psychiatry, Yale University Fresno, California

Paul L. Kimmel, md Professor of Medicine, Division of Renal Diseases and Hypertension George Washington University School of Medicine and Health Sciences Washington, DC

Robert J. Kurman, md The Richard W. TeLinde Professor of Gynecologic Pathology Professor of Pathology and Gynecology and Obstetrics Department of Pathology Johns Hopkins University School of Medicine Baltimore, Maryland

Derek LeRoith, md, PhD Chief of Section on Molecular and Cellular Physiology Diabetes Branch National Institute of Diabetes, Digestive and Kidney Diseases National Institutes of Health Bethesda, Maryland

George L. King, md Senior Investigator and Section Head Section on Vascular Cell Biology, Joslin Diabetes Center Associate Professor Harvard Medical School and Brigham & Women's Hospital Boston, Massachusetts

Anne Klibanski, md Associate Professor of Medicine Harvard Medical School Associate Physician in Medicine Chief, Neuroendocrine Unit Massachusetts General Hospital Boston, Massachusetts

Mitchel A. Kling, md Chief, Unit on Affective Disorders Clinical Neuroendocrinology Branch National Institute of Mental Health Bethesda, Maryland

Edward J. Kosinski, md Assistant Professor of Medicine Yale University New Haven, Connecticut Chief, Division of Cardiology St. Vincent's Medical Center Bridgeport, Connecticut

Kalman Kovacs,

md, PhD, DSc, frcp(C),

FCAP, FRC(Path)

Ann M. Labriola, md Assistant Professor of Medicine George Washington University School of Medicine and Health Sciences Attending Physician in Infectious Diseases Washington Veterans Affairs Medical Center Washington, DC

Preston Lamberton, md Clinical Associate Professor of Medicine Division of Biology and Medicine Brown University Attending Physician Rhode Island Hospital Attending Physician Miriam Hospital Providence, Rhode Island

John C. LaRosa, md Chancellor, Tulane University Medical Center Professor of Medicine, Tulane University School of Medicine New Orleans, Louisiana

Robert B. Layzer, md Professor of Neurology University of California, San Francisco School of Medicine San Francisco, California

Professor, Department of Pathology University of Toronto Staff Pathologist Department of Pathology St. Michaels Hospital Toronto, Ontario, Canada

Jacques LeBlanc, PhD Professor of Physiology School of Medicine Laval University Quebec City, Canada

Sumner C. Kraft, md Professor of Medicine Department of Medicine Section of Gastroenterology University of Chicago University of Chicago Hospitals Chicago, Illinois

Peter A. Lee, md, PhD Professor of Pediatrics University of Pittsburgh School of Medicine Attending Physician Children's Hospital of Pittsburgh Pittsburgh, Pennsylvania

Michael A. Levine, md Professor of Medicine and Pathology Johns Hopkins University School of Medicine Physician Johns Hopkins Hospital Baltimore, Maryland

Jonathan J. Li, PhD Professor and Director Department of Pharmacology, Toxicology and Therapeutics Division of Etiology & Prevention of Hormonal Cancers University of Kansas Cancer Center University of Kansas Medical Center Kansas City, Kansas

Sara Antonia Li, PhD Associate Professor Department of Pharmacology, Toxicology and Therapeutics University of Kansas Cancer Center University of Kansas Medical Center Kansas City, Kansas

Robert D. Lindeman, md Professor and Chief, Division of Gerontology Department of Medicine University of New Mexico School of Medicine University of New Mexico Hospitals Albuquerque, New Mexico

Robert Lindsay, mb, ChB, PhD Professor of Clinical Medicine Columbia University College of Physicians and Surgeons New York, New York Chief of Internal Medicine Helen Hayes Hospital West Haverstraw, New York

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CONTRIBUTORS

Timothy O. Lipman, md Associate Professor of Medicine Georgetown University School of Medicine Associate Chief, GI-HepatologyNutrition Section Department of Veterans Affairs Medical Center Washington, DC

Burt A. Littman, md Associate Clinical Professor George Washington University School of Medicine and Health Sciences Washington, DC Director, Center for Reproductive Medicine Rockville, Maryland

Virginia A. Livolsi, md Professor, Department of Pathology and Laboratory Medicine University of Pennsylvania Vice Chair, Anatomic Pathology Hospital of the University of Pennsylvania Philadelphia, Pennsylvania

Rogerio A. Lobo, md Professor of Obstetrics and Gynecology Chief, Division of Reproductive Endocrinology and Infertility University of Southern California School of Medicine Women's and Children's Hospital Los Angeles, California

D. Lynn Loriaux, md, PhD Chairman, Department of Medicine Head, Division of Endocrinology, Diabetes and Clinical Nutrition Oregon Health Sciences University Portland, Oregon

Karl Lubsch, RPh Staff Pharmacist Cardinal Glennon Children's Hospital St. Louis, Missouri

Thomas F. Liischer, md Professor of Medicine Division of Cardiology University Hospital Bern, Switzerland

Michael L. Lydic, md Clinical Instructor Fellow in Reproductive Endocrinology and Infertility Department of Obstetrics and Gynecology University of Cincinnati College of Medicine Cincinnati, Ohio

Kenneth W. Lyles, md Associate Professor of Medicine Duke University Medical Center Clinical Director, GRECC Veterans Affairs Medical Center Durham, North Carolina Ruth S. MacDonald, rd, PhD Associate Professor Department of Food Science and Human Nutrition University of Missouri-Columbia Columbia, Missouri Michelle Fischmann Magee,

Alvin M. Matsumoto, md Associate Professor Department of Medicine Division of Gerontology and Geriatric Medicine University of Washington School of Medicine Chief, Gerontology Associate Director, Geriatric Research, Education and Clinical Center Associate Chief of Staff for Geriatrics and Extended Care Department of Veterans Affairs Medical Center Seattle, Washington

md, mb,

Bch, BAO

Staff Physician, Medlantic Research Institute Assistant Clinical Professor of Medicine George Washington University School of Medicine and Health Sciences Washington, DC

Ernest L. Mazzaferri, md, facp Professor and Chairman The Ohio State University Medical Center Columbus, Ohio

Robert W. Mahley, md, PhD Director, Gladstone Institute of Cardiovascular Disease Professor of Pathology and Medicine University of California, San Francisco San Francisco, California

Alan M. McGregor, md Professor of Medicine King's College School of Medicine and Dentistry London, England

Andrea Manni, md Professor of Medicine Pennsylvania State University College of Medicine University Hospital Hershey, Pennsylvania

Minesh P. Mehta, md Associate Professor Department of Human Oncology Consultant Radiation Oncologist University of Wisconsin Medical School Madison, Wisconsin

Eleftheria Maratos-Flier, md Assistant Professor of Medicine Harvard Medical School Investigator, Joslin Diabetes Center Associate Physician, Brigham and Women's Hospital Boston, Massachusetts

James C. Melby, md Professor of Medicine and Physiology Director of Endocrine Hypertension Boston University Medical Center Hospital Boston, Massachusetts

Joseph B. Martin, md, PhD Chancellor and Professor of Neurology University of California, San Francisco San Francisco, California Kevin J. Martin, mb BCh, facp Professor, Internal Medicine Director, Division of Nephrology St. Louis University Health Sciences Center St. Louis, Missouri William D. Mathers, md Associate Professor Department of Ophthalmology University of Iowa Hospitals and Clinics Iowa City, Iowa Paul N. Maton, md, frcp Oklahoma Foundation for Digestive Research Presbyterian Hospital Oklahoma City, Oklahoma

Thomas J. Merimee, md Professor of Medicine Head, Division of Endocrinology and Metabolism University of Florida College of Medicine Gainesville, Florida

Susan E. Meyers, md Assistant Professor of Pediatrics St. Louis University School of Medicine Cardinal Glennon Children's Hospital St. Louis, Missouri

Donald L. Miller, md Professor of Radiology Uniformed Services University of the Health Sciences Chief, Vascular/Interventional Radiology National Naval Medical Center Bethesda, Maryland

CONTRIBUTORS Michael M. Miller, md Associate Professor and Director Department of Obstetrics and Gynecology Division of Reproductive Endocrinology and Infertility University of Arkansas for Medical Sciences Little Rock, Arkansas Mark E. Molitch, md Professor of Medicine Center for Endocrinology, Metabolism and Molecular Medicine Northwestern University Medical School Attending Physician Northwestern Memorial Hospital Chicago, Illinois Arshag D. Mooradian, md Professor of Internal Medicine Director of Endocrinology St. Louis University School of Medicine St. Louis University Health Sciences Center St. Louis, Missouri Gregory P. Mueller, PhD Associate Professor Department of Physiology and Program in Neuroscience Uniformed Services University of the Health Sciences Bethesda, Maryland Satyabrata Nandi, PhD Professor Department of Molecular and Cell Biology University of California, Berkeley Berkeley, California David J. Nashel, md, facp Professor of Medicine Georgetown University Chief, Rheumatology Section Veterans Affairs Medical Center Washington, DC Isaac Neuhaus, ba National Institute of Mental Health Clinical Neuroendocrinology Branch Bethesda, Maryland

Georg Noll, md Division of Cardiology University Hospital Bern, Switzerland Jeffrey A. Norton, md Professor of Surgery Washington University School of Medicine Chief of Endocrine and Oncologic Surgery Barnes Hospital St. Louis, Missouri Robert H. Noth, md Associate Professor of Clinical Internal Medicine University of California, Davis School of Medicine Chief, Endocrinology Veterans Affairs Northern California System of Clinics Martinez, California Jennifer A. Nuovo, md Endocrinologist and Internist Medical Clinic of Sacramento, Inc. Mercy Medical Foundation Sacramento, California Eric S. Nylen, md Assistant Professor of Medicine George Washington University School of Medicine and Health Sciences Division of Endocrinology and Metabolism Veterans Affairs Medical Center Washington, DC Mary Oehler, md Assistant Professor of Radiology Ohio State University Staff Radiologist Ohio State University Hospital Columbus, Ohio Joseph E. Oesterling, md Professor and Urologist-in-Chief Director, The Michigan Prostate Center The University of Michigan Ann Arbor, Michigan

Director, Institute of Reproductive Medicine of the University Muenster, Germany

Maureen P. O'Grady, PhD Assistant Professor Psychoimmunology Division Department of Psychiatry University of South Florida College of Medicine Tampa, Florida

Robert A. Nissenson, PhD Adjunct Professor of Medicine and Physiology University of California, San Francisco Research Career Scientist Veterans Affairs Medical Center San Francisco, California

James A. O'Hare, md, frcpi, mrcp Consultant Physician-Endocrinologist Limerick Regional General Hospital Limerick, Ireland College Lecturer in Medicine University College Cork Cork, Ireland

Prof. Dr. med. Eberhard Nieschlag, FRCP

Professor Jeffrey L. H. O'Riordan, Professor of Metabolic Medicine University College London Consultant Physician The Middlesex Hospital London, England

XV

dm

Steven J. Ory, md Associate Professor Chairman Division of Reproductive Endocrinology Department of Obstetrics and Gynecology Mayo Graduate School of Medicine Consultant, Mayo Clinic

Harry Ostrer, md Associate Professor of Pediatrics and Pathology Director, Human Genetics Program Department of Pediatrics New York University Medical Center Associate Attending Tisch Hospital New York, New York

Louis N. Pangaro, md Associate Professor of Clinical Medicine Uniformed Services University of the Health Sciences Walter Reed Army Medical Center Washington, DC

Yogesh C. Patel,

md, PhD, fracp,

FRCP(C), FRSC

Professor, Departments of Medicine, Neurology and Neurosurgery McGill University Senior Physician, Director Fraser Laboratories for Diabetes Research Director, Neuroendocrine Clinic Royal Victoria Hospital Montreal, Quebec, Canada

Gary R. Peplinski, md Resident in Surgery Washington University School of Medicine Barnes Hospital St. Louis, Missouri

Ora Hirsch Pescovitz, md Director of Pediatric Endocrinology Professor of Physiology and Biophysics James Whitcomb Riley Children's Hospital Indiana University Medical Center Indianapolis, Indiana

Charles M. Peterson, md Director, Research Sansum Medical Research Foundation Santa Barbara, California

XVI

CONTRIBUTORS

Michael A. Pfeifer, MD, cde Associate Professor of Medicine Director, Diabetes Research & Treatment Center at SIU Southern Illinois University School of Medicine Springfield, Illinois Kristina C. Pfendler, bs Graduate Student Northwestern University Medical School Chicago, Illinois Mark R. Pittelkow, md Associate Professor, Mayo Medical School Department of Dermatology and Biochemistry and Molecular Biology Mayo Clinic Rochester, Minnesota Stephen R. Plymate, md Research Associate Professor Department of Medicine University of Washington Deputy Associate Director Geriatric Research Education and Clinical Center Seattle/American Lake Veterans Affairs Medical Center Tacoma, Washington Julia M. Polak, DSc, md, FRCPath Professor of Endocrine Pathology Department of Histochemistry, Royal Postgraduate Medical School Consultant Pathologist, Hammersmith Hospital London, England Ralph Rabkin, md, MBChB Professor of Medicine Stanford University School of Medicine Chief, Nephrology Section Veterans Affairs Medical Center Palo Alto, California

Robert W. Rebar, md Professor and Director Department of Obstetrics and Gynecology University of Cincinnati College of Medicine Chief, Obstetrics and Gynecology University Hospital Cincinnati, Ohio Robert S. Redman, dds, msd, PhD Clinical Associate Professor Department of Oral Pathology Baltimore College of Dental Surgery Dental School, University of Maryland Baltimore, Maryland Chief, Oral Diagnosis Section, Dental Service Chief, Oral Pathology Research Laboratory Veterans Affairs Medical Center Washington, DC Lester Reed, md, col, mc Associate Professor of Medicine Uniformed Services University of the Health Sciences Assistant Chief, Endocrine-Metabolic Service Walter Reed Army Medical Center Washington, DC Domenico C. Regoli, md Professor, Department of Pharmacology Medical School, Universite de Sherbrooke Sherbrooke, Quebec, Canada Jens F. Rehfeld, md, DSc, DMSc Professor of Clinical Biochemistry University of Copenhagen Head, Department of Clinical Biochemistry Rigshospitalet (National University Hospital) Copenhagen, Denmark

Lawrence G. Raisz, md Professor of Medicine Head, Division of Endocrinology and Metabolism Program Director, General Clinical Research Center University of Connecticut Health Center John Dempsey Hospital Farmington, Connecticut

Robert L. Reid, md, frcs[C] Head of Reproductive Endocrinology Professor Department of Obstetrics and Gynecology Queen's University Kingston, Ontario, Canada

Lawrence I. Rand, md Assistant Clinical Professor of Ophthalmology Harvard Medical School Boston, Massachusetts

Russel J. Reiter, PhD, D.med Professor of Neuroendocrinology Department of Cellular and Structural Biology University of Texas Health Science Center San Antonio, Texas

Robert E. Ratner, md Director, Medlantic Clinical Research Center Associate Clinical Professor of Medicine George Washington University School of Medicine and Health Sciences Washington, DC

Roger S. Rittmaster, md Professor of Medicine Dalhousie University Active Staff Camp Hill Medical Center Halifax, Nova Scotia, Canada

Charles T. Roberts, Jr., md Professor of Pediatrics Department of Pediatrics Oregon Health Sciences University Portland, Oregon

Gary L. Robertson, md Professor of Medicine and Neurology Director, Clinical Research Center Northwestern University Medical School Chicago, Illinois

R. Paul Robertson, md Professor of Medicine and Cell Biology Director, Division of Diabetes, Endocrinology and Metabolism Pennock Chair for Diabetes Research Department of Medicine University of Minnesota Minneapolis, Minnesota

Simon P. Robins, PhD, DSc Biochemical Sciences Division Rowett Research Institute Aberdeen, United Kingdom

Alan D. Rogol, md, PhD Professor of Pediatrics and Pharmacology University of Virginia School of Medicine Chief, Division of Pediatric Endocrinology University of Virginia Hospital Charlottesville, Virginia

Prashant K. Rohatgi, mbbs Director, Division of Pulmonary Diseases and Allergy Professor of Medicine George Washington University School of Medicine and Health Sciences Chief, Pulmonary Section, Veterans Affairs Medical Center Washington, DC

Mikael Rorth, md Professor, Physician in Chief The National University Hospital Copenhagen, Denmark

David Rosen, md, mph Assistant Professor of Pediatrics and Lecturer in Internal Medicine University of Michigan Medical Center Ann Arbor, Michigan

Robert L. Rosenfield, md Professor of Pediatrics and Medicine The University of Chicago Pritzker School of Medicine Head, Section of Pediatric Endocrinology Wyler Children's Hospital Chicago, Illinois

CONTRIBUTORS Jack M. Rozental, md, PhD Associate Professor of Neurology Northwestern University Medical School Director of Medical Neuro-Oncology Northwestern Memorial Hospital Chief, Neurology Service Veterans Affairs Lakeside Medical Center Chicago, Illinois

Robert K. Rude, md Professor of Medicine University of Southern California School of Medicine Los Angeles County Medical Center Los Angeles, California Neil B. Ruderman, md, d Phil. Professor of Medicine and Physiology Boston University School of Medicine Director, Diabetes Unit, Boston University Medical Center Boston, Massachusetts

Sami I. Said, md Professor of Medicine and Physiology Chief, Pulmonary Critical Care University Medical Center Stony Brook, New York, and Veterans Affairs Medical Center Northport, New York

Lester B. Salans, md Vice President, Scientific and Academic Affairs Sandoz Research Institute East Hanover, New Jersey Adjunct Professor The Rockefeller University Clinical Professor Mt. Sinai School of Medicine New York, New York

Richard J. Santen, md Professor and Chairman Department of Internal Medicine Harper Hospital Wayne State University School of Medicine Interim Director for the Michigan Cancer Foundation Detroit, Michigan

Salil D. Sarkar, md Associate Professor of Clinical Radiology State University of New York Health Science Center Brooklyn, New York

David H. Same, md, facp Associate Professor of Medicine Department of Medicine University of Illinois at Chicago College of Medicine at Chicago Veterans Affairs Westside Medical Center Chicago, Illinois

Ernst J. Schaefer, md Professor of Medicine Tufts University School of Medicine Director, Lipid & Heart Disease Prevention Clinic and Lipid Research Laboratory New England Medical Center, and Chief, Lipid Metabolism Laboratory Jean Mayer USDA Human Research Center on Aging at Tufts University Boston, Massachusetts Isaac Schiff, md Joe Vincent Meigs Professor of Gynecology at Harvard Medical School Chief of Vincent Memorial Obstetrics and Gynecology Service at Massachusetts General Hospital Boston, Massachusetts R. Neil Schimke, md, facp, facmg Professor of Medicine and Pediatrics Director, Division of Endocrinology, Metabolism and Genetics Kansas University Medical Center Kansas City, Kansas James R. Schreiber, md Professor and Head Department of Obstetrics and Gynecology Washington University School of Medicine Chief of Obstetrics and Gynecology Barnes Hospital St. Louis, Missouri David E. Schteingart, md Professor of Internal Medicine Division of Endocrinology and Metabolism University of Michigan Medical School University of Michigan Hospitals Ann Arbor, Michigan Ellen W. Seely, md Director of Clinical Research Endocrine-Hypertension Division Brigham and Women's Hospital Assistant Professor of Medicine Harvard Medical School Boston, Massachusetts

XVii

Lawrence E. Shapiro, md Associate Professor of Medicine Albert Einstein College of Medicine Attending Physician Internal Medicine and Endocrinology Montefiore Medical Center Bronx, New York Meeta Sharma, md, cde Assistant Clinical Professor of Medicine Division of Endocrinology and Metabolism George Washington University School of Medicine and Health Sciences Consultant, Veterans Affairs Medical Center, Washington, DC R. Michael Siatkowski, md Assistant Professor, Clinical Ophthalmology University of Miami School of Medicine Bascom Palmer Eye Institute Miami, Florida Omega L. Silva, md Professor of Oncology Howard University College of Medicine Professor of Medicine George Washington University School of Medicine and Health Sciences Assistant Chief, Endocrinology and Metabolism Chief, Diabetes Clinic Veterans Affairs Medical Center Washington, DC Shonni J. Silverberg, md Assistant Professor of Medicine College of Physicians and Surgeons Columbia University Assistant Attending Physician Presbyterian Hospital New York, New York Joe Leigh Simpson, md Ernst W. Bertner Chairman and Professor Department of Obstetrics and Gynecology Professor of Molecular and Human Genetics Baylor College of Medicine Houston, Texas

Markus J. Seibel, md Department of Medicine Division of Endocrinology and Metabolism University of Heidelberg Medical School Heidelberg, Germany

Ethel S. Siris, md Professor of Clinical Medicine Columbia University College of Physician and Surgeons Attending Physician Presbyterian Hospital New York, New York

Elizabeth Shane, md Associate Professor of Clinical Medicine Columbia University College of Physicians and Surgeons Associate Attending Physician Columbia Presbyterian Medical Center New York, New York

Glen W. Sizemore, md Professor of Medicine Loyola University of Chicago Stritch School of Medicine Loyola University Medical Center Maywood, Illinois

XViii

CONTRIBUTORS

Niels E. Skakkebaek, md Professor of Growth and Reproduction University of Copenhagen National University Hospital, Rigshospitalet Copenhagen, Denmark

Celia D. Sladek, PhD Professor of Physiology and Neurology Finch University of Health Sciences Chicago Medical School North Chicago, Illinois

John R. Sladek, Jr., PhD Professor and Chairman of Neuroscience Finch University of Health Science Chicago Medical School North Chicago, Illinois

Eduardo Slatopolsky, md, facp Professor of Internal Medicine Director, Chromalloy American Kidney Center Washington University Medical Center St. Louis, Missouri

Robert C. Smallridge, md Colonel, Medical Corps. Director, Division of Medicine Walter Reed Army Institute of Research Professor of Medicine and Director Division of Endocrinology Uniformed Services University of the Health Sciences Bethesda, Maryland

Robert J. Smith, md Associate Professor of Medicine Harvard Medical School Assistant Director of Research, Head of Metabolism Section Elliott P. Joslin Research Laboratories Boston, Massachusetts

David B. Smotrich, md Instructor Division of Reproductive Endocrinology and Fertility Department of Obstetrics and Gynecology George Washington University School of Medicine and Health Sciences Washington, DC

Richard H. Snider Jr., PhD Research Chemist Veterans Affairs Medical Center Washington, DC

Phyllis W. Speiser, md Associate Professor of Pediatrics Cornell University Medical College Chief, Division of Pediatric Endocrinology and Metabolism North Shore University Hospital Manhasset, New York

Harvey J. Stern, md, PhD Director, Biochemical and Molecular Genetics Children's National Medical Center Assistant Professor of Pediatrics and Pathology George Washington University School of Medicine and Health Sciences Washington, DC Andrew F. Stewart, md Professor of Medicine Yale University School of Medicine Chief, Endocrinology West Haven Veterans Affairs Medical Center West Haven, Connecticut Robert J. Stillman, md Professor of Obstetrics and Gynecology Director, Division of Reproductive Endocrinology and Fertility George Washington University School of Medicine and Health Sciences Washington, DC

Christopher J. Thompson, Lecturer in Endocrinology Edinburgh University Department of Medicine Royal Infirmary Edinburgh, Scotland Department of Medicine Ninewells Hospital Dundee, Scotland

mb, mrcp

Jack F. Tohme, md Assistant Clinical Professor of Medicine Columbia University College of Physicians and Surgeons Attending Physician Presbyterian Hospital New York, New York

Keith Tornheim, PhD Associate Professor of Biochemistry Boston University School of Medicine Boston, Massachusetts

Elizabeth A. Streeten, md Assistant Professor of Medicine Division of Endocrinology and Metabolism Johns Hopkins Hospital Baltimore, Maryland

Carmelita U. Tuazon, md Professor of Medicine George Washington University School of Medicine and Health Sciences Washington, DC

Gordon J. Strewler, md Professor of Medicine University of California, San Francisco Chief, Endocrine Unit Veterans Affairs Medical Center San Francisco, California

Michael L. Tuck, md Professor of Medicine University of California, Los Angeles School of Medicine Chief, Endocrinology and Metabolism UCLA-San Fernando Valley Medical Program Los Angeles, California

Martin I. Surks, md Professor of Medicine and Pathology Albert Einstein College of Medicine Head, Division of Endocrinology and Metabolism Montefiore Medical Center Bronx, New York Reiko Tanaka, md Visiting Research Fellow University of Chicago Department of Surgery University of Chicago Hospitals Chicago, Illinois Robert J. Tanenberg, md, facp Clinical Associate Professor of Medicine Georgetown University School of Medicine Medical Director, Diabetes Treatment Center Washington Hospital Center Washington, DC Kamal Thapar, md Resident, Division of Neurosurgery Department of Surgery University of Toronto Resident, Division of Neurosurgery St. Michael's Hospital Toronto, Ontario, Canada

Stephen Jon Usala, md, PhD Associate Professor Department of Medicine East Carolina University School of Medicine Greenville, North Carolina

Judith L. Vaitukaitis, md Director, The National Center for Research Resources National Institutes of Health Bethesda, Maryland

Eve Van Cauter, PhD Research Associate Professor The University of Chicago Department of Medicine Chicago, Illinois

David H. Van Thiel, md Medical Director, Transplant Medicine Oklahoma Transplant Institute Medical Director of Transplantation Baptist Medical Center of Oklahoma Oklahoma City, Oklahoma

CONTRIBUTORS

XIX

Gilberto A. Vera, md Fellow, Division of Renal Diseases and Hypertension Department of Medicine George Washington University School of Medicine and Health Sciences Washington, DC

Stephen I. Wasserman, md The Helen M. Ranney Professor of Medicine Chairman, Department of Medicine University of California, San Diego School of Medicine San Diego, California

Michael P. Whyte, md Professor of Medicine and Pediatrics Washington University School of Medicine Medical Director and Metabolic Research Shriners Hospital for Crippled Children St. Louis, Missouri

Joseph G. Verbalis, md Professor and Chief, Division of Endocrinology and Metabolism Georgetown University Medical Center Washington, DC

Albert C. Watson, md Assistant Professor of Pediatrics Christie Clinic Champaign, Illinois

Gordon H. Williams, md Professor of Medicine Harvard Medical School Chief, Endocrine-Hypertension Division Brigham and Women's Hospital Boston, Massachusetts

Robert Volpe,

md, frcp(C), facp,

FRCP(Edin)

Professor Emeritus, Department of Medicine University of Toronto Director, Endocrinology Research Laboratory The Wellesley Hospital Toronto, Ontario, Canada Brian Walsh, md Assistant Professor of Obstetrics, Gynecology, and Reproductive Biology Harvard Medical School Director, Menopause Center Brigham & Women's Hospital Boston, Massachusetts Robert M. Walter, Jr., md Professor of Internal Medicine Department of Internal Medicine University of California, Davis School of Medicine Attending Physician University of California, Davis Medical Center Sacramento, California James H. Warram, md, Investigator Research Division Joslin Diabetes Center Boston, Massachusetts

Anthony Peter Weetman, md, DSc Professor of Medicine University of Sheffield Honorary Consultant Physician Northern General Hospital United Kingdom

Stephen Weinroth, md Division of Infectious Disease George Washington University School of Medicine and Health Sciences Washington, DC

Gordon C. Weir, md Professor of Medicine Harvard Medical School Joslin Diabetes Center Boston, Massachusetts

Laura S. Welch, md Associate Professor of Medicine George Washington University School of Medicine and Health Sciences Director of the Division of Occupational and Environmental Medicine Washington, DC

ScD

Michelle P. Warren, md Associate Professor of Clinical Obstetrics and Gynecology and Clinical Medicine Columbia College of Physicians and Surgeons Head, Reproductive Endocrinology St. Luke's-Roosevelt Hospital New York, New York Leonard Wartofsky, md Professor of Medicine and Physiology Uniformed Services University of the Health Sciences Clinical Professor of Medicine Georgetown University School of Medicine George Washington University School of Medicine and Health Sciences Chairman, Department of Medicine Washington Hospital Center Washington, DC

Samuel A. Wells, Jr., md Bixby Professor and Chairman Department of Surgery Washington University School of Medicine Surgeon-in-Chief Barnes Hospital St. Louis, Missouri

Jon C. White, md Assistant Professor of Surgery George Washington University School of Medicine and Health Sciences Director of Surgical Intensive Care Veterans Affairs Hospital Washington, DC

Perrin C. White, md Professor of Pediatrics University of Texas Southwestern Medical Center Chief of Endocrinology Children's Medical Center of Dallas Dallas, Texas

Karen Winchester, md Fellow in Cornea and External Disease Department of Ophthalmology University of Iowa Hospitals and Clinics Iowa City, Iowa

Stephen J. Winters, md Professor of Medicine University of Pittsburgh Pittsburgh, Pennsylvania

Kai H. Yang, md Associate Research Scientist Yale University School of Medicine Staff Physician West Haven Veterans Affairs Medical Center West Haven, Connecticut

I-Tien Yeh, md Clinical Assistant Professor University of Pennsylvania Philadelphia, Pennsylvania Assistant Pathologist Abington Memorial Hospital Abington, Pennsylvania

James E. Zadina, PhD Associate Professor Department of Medicine and Neuroscience Tulane University School of Medicine Research Physiologist Veterans Affairs Medical Center New Orleans, Louisiana

Charles Zaloudek, md Professor of Clinical Pathology Department of Pathology University of California, San Francisco University of California Medical Center San Francisco, California

Gerald I. Zatuchni, md, MSc Professor of Obstetrics and Gynecology Northwestern University Prentice Women's Hospital Chicago, Illinois

■

PREFACE

This textbook is a complete update of the first edition. All chapters have been revised or rewritten, and there is much important new material. In addition, several topics have been added or have been given greater emphasis, such as growth factors and cytokines, endocrine disease in pregnancy, endocrine aspects of prostate hyperpla¬ sia, thyroid hormone resistance syndromes, parathyroid hormone-related peptide, markers of bone metabolism, lipid abnormalities in diabetes mellitus, and the endocrine endothelium. The immunologic basis of endocrine disor¬ ders has been expanded into a separate section. Many new references have been provided, even while the chapters were being assembled into the textbook. As in the prior edition, this book is written primarily for the clinician. It is intended to be a practical, clinically relevant textbook that is disease-oriented. The emphasis is on the manifestations, diagnosis, and treatment of endo¬ crine and metabolic dysfunction. Laboratory information has been carefully selected for its strong applicability to

human illness. Throughout, we have strived to blend the two disciplines of basic endocrinology and clinical endo¬ crinology into a single, informative, useful sourcebook for the physician. Conveniently placed at the end of the book, and framed in gray for rapid consultation, are several updated lexicon-like chapters that pertain to endocrine-related drugs, the effects of other drugs on endocrine function and values, reference values in endocrinology, the DNA diag¬ nosis of endocrine disease, and dynamic procedures in en¬ docrinology. It is our hope that these compendiums, as well as the very detailed index to the entire textbook, will enable the reader to rapidly locate pertinent information. I wish to acknowledge my appreciation to Richard H. Snider, Jr., PhD, for his biochemical expertise and his out¬ standing editorial assistance and advice.

Kenneth L. Becker,

md, PhD

XXI

PREFACE

TO

THE

Although there are several excellent large textbooks of endocrinology, we have felt the need for a book which would ain't at encompassing all aspects of the field, a book which would be disease-oriented, would have practical applicability to the care of the adult and pediatric patient, and could be consulted to obtain a broad range of patho¬ physiologic, diagnostic, and therapeutic information. To fulfill this goal we called upon not only eminent specialists in endocrinology but also upon experts in many fields of medicine and science. The first part of the book surveys general aspects of endocrinology. The eight suc¬ ceeding parts deal with specific fields of endocrinology: The Endocrine Brain and Pituitary Gland, The Thyroid Gland, Calcium and Bone Metabolism, The Adrenal Glands, Sex Determination and Development, Endocri¬ nology of the Female, Endocrinology of the Male, and Dis¬ orders of Fuel Metabolism. Each of these parts contains relevant anatomic, physiologic, diagnostic, and therapeu¬ tic information and, when indicated, pediatric coverage of the topic. Diffuse Hormonal Secretion expounds upon the fact that endocrine function is not confined to anatomically discrete endocrine glands but is also intrinsic to all tissues and organs. This part is divided in two; it first presents a discussion of hormones which have a diffuse distribution and are not reviewed elsewhere in the book, and subse¬ quently it deals with body constituents which are impor¬ tant sites of hormonal secretion. Heritable Abnormalities of Endocrinology and Metab¬ olism underlines the importance of genetics in the causa¬ tion of many endocrine and metabolic abnormalities. En¬ docrine and metabolic dysfunction in the young and in the aged is the subject of a separate part, because in both of these age groups hormonal function as well as endocrine disorders differ profoundly from those of individuals in their middle decades. Interrelationships Between Hormones and the Body discusses the impact of hormones on the soma and ad¬ dresses clinical aspects of the disorders they may engen¬ der. Hormones and Cancer examines the phenomenon of hormone-induced neoplasms, elaborating on the fact that all neoplasms secrete hormones, that several of these hor¬ mones can cause additional clinical disorders, and that some neoplasms respond therapeutically to hormonal manipulation. The ensuing part, entitled Endocrine and Metabolic Effects of Toxic Agents deals with the sometimes subtle, sometimes profound influence of four nearly omnipresent agents: medication, alcohol, tobacco, and cannabis; it also addresses the consequences of environmental toxins on the endocrine system. The last part deals with the thera¬ peutic use of drugs in endocrinology and the proper inter¬

FIRST

EDITION

pretation of laboratory values. It offers an extensive table on the clinical use of endocrine-related drugs, a table on reference values, and an outline of the dynamic proce¬ dures used in endocrinology. The goal of these tabular chapters is to facilitate the day-to-day evaluation and ther¬ apy of the endocrine patient. As a rule, the emphasis of this textbook is on the en¬ docrinology of the human being. Animal data are pre¬ sented only when contributing to a better understanding of human physiology and pathology. To maximize current relevance, historical information is kept to a minimum. While efforts were made to avoid repetition, the coverage of certain topics may recur when viewed from different standpoints. It is hoped that this will provide a wider di¬ mension of the understanding of endocrine and metabolic function and dysfunction. In order not to interrupt continuity, bibliographic ref¬ erences are grouped at the end of each part. Finally, with the interest of the reader in mind, particular attention was given to composing an index as detailed as possible. I wish to thank the associate editors of this text for their skill, their enthusiasm, and their hard work. We all are very grateful for the expertise of our many eminent contributors. During the preparation of the manuscripts, there was considerable intercommunication between these contributors and their respective editors concerning both content and presentation. I wish to acknowledge the participation of Richard H. Snider, PhD, and Eric S. Nylen, MD, who have provided outstanding editorial assistance throughout the prepara¬ tion of the textbook. The field of endocrinology and metabolism is evolv¬ ing rapidly. New data are being developed continuously, and with this in mind, all contributors were encouraged to add up-to-date information until nearly the date of publication. There are numerous matters upon which there is no current common agreement, and logical arguments can be marshaled to buttress diametrically different viewpoints. This textbook is written by many authors; though most of the beliefs and conclusions of the contributors tend to re¬ flect those of the editors, no attempt was made to impose a uniformity of pathophysiologic, diagnostic, or therapeutic viewpoints, and the book does not lack for differences of opinion. We hope that the Principles and Practice of Endocrinol¬ ogy and Metabolism will be a relevant sourcebook for those interested in the science and the practice of this fascinating discipline, whether they be clinicians, basic scientists, al¬ lied health personnel, or students. Kenneth L. Becker,

MD, PhD

XXIII

.

5

■

CONTENTS

P A R T 1

2 3 4

5

I

ENDOCRINOLOGY AND THE ENDOCRINE PATIENT 2 KENNETH L. BECKER, ERIC S. NYLEN, and RICHARD H. SNIDER, JR. BIOSYNTHESIS AND SECRETION OF PEPTIDE HORMONES 8 WILLIAM W. CHIN HORMONAL ACTION 20 DARYL K. GRANNER FEEDBACK CONTROL IN ENDOCRINE SYSTEMS 34 DANIEL N. DARLINGTON and MARY F. DALLMAN ENDOCRINE RHYTHMS 41 EVE VAN CAUTER

PART II 10

11

12 13

GENERAL PRINCIPLES OF ENDOCRINOLOGY Kenneth L. Becker, Editor

7

8 9

16

17 18 19 20

21

A

ADENOHYPOPHYSIS 14

15

VITAMINS: HORMONAL AND METABOLIC INTERRELATIONSHIPS 50 TIMOTHY O. LIPMAN TRACE MINERALS: HORMONAL AND METABOLIC INTERRELATIONSHIPS 56 ROBERT D. LINDEMAN EXERCISE: ENDOCRINE AND METABOLIC EFFECTS 64 JACQUES LEBLANC GROWTH AND DEVELOPMENT IN THE NORMAL INFANT AND CHILD 69 GILBERT P. AUGUST

THE ENDOCRINE BRAIN AND PITUITARY GLAND Gary L. Robertson, Editor

MORPHOLOGY OF THE ENDOCRINE BRAIN, HYPOTHALAMUS, AND NEUROHYPOPHYSIS 84 JOHN R. SLADEK, JR., and CELIA D. SLADEK PHYSIOLOGY AND PATHOPHYSIOLOGY OF THE ENDOCRINE BRAIN AND HYPOTHALAMUS 90 PAUL E. COOPER and JOSEPH B. MARTIN THE PINEAL GLAND 98 RUSSEL J. REITER MORPHOLOGY OF THE PITUITARY IN HEALTH AND DISEASE 103 KAMAL THAPAR, KALMAN KOVACS, and EVA HORVATH

SECTION

6

GROWTH HORMONE AND ITS DISORDERS 129 THOMAS J. MERIMEE and MARIA B. GRANT PROLACTIN AND ITS DISORDERS LAURENCE KATZ NELSON and ANNE KLIBANSKI

22 23 140

ADRENOCORTICOTROPIN AND RELATED PEPTIDES, AND THEIR DISORDERS 147 JOHN W. KENDALL and RICHARD G. ALLEN THYROID-STIMULATING HORMONE AND ITS DISORDERS 153 JOSHUA L. COHEN PITUITARY GONADOTROPINS AND THEIR DISORDERS 163 WILLIAM J. BREMNER HYPOPITUITARISM 169 RICHARD N. DEXTER HYPOTHALAMIC AND PITUITARY DISORDERS IN INFANCY AND CHILDHOOD 180 ALAN D. ROGOL THE OPTIC CHIASM IN ENDOCRINOLOGIC DISORDERS 193 R. MICHAEL SIATKOWSKI and JOEL S. GLASER DIAGNOSTIC IMAGING OF THE SELLAR REGION 207 MARY OEHLER and DONALD CHAKERES MEDICAL TREATMENT OF PITUITARY TUMORS AND HYPERSECRETORY STATES 223 DAVID H. SARNE XXV

XXVI

24

25

CONTENTS

RADIOTHERAPY OF PITUITARYHYPOTHALAMIC TUMORS 229 MINESH P. MEHTA and JACK M. ROZENTAL NEUROSURGICAL MANAGEMENT OF PITUITARY-HYPOTHALAMIC NEOPLASMS 238 DAVID S. BASKIN

SECTION B NEUROHYPOPHYSIAL SYSTEM 26

27

28

PART

III

PHYSIOLOGY OF VASOPRESSIN, OXYTOCIN, AND THIRST 248 GARY L ROBERTSON DIABETES INSIPIDUS AND HYPEROSMOLAR SYNDROMES 257 PETER H. BAYLIS and CHRISTOPHER J. THOMPSON INAPPROPRIATE ANTIDIURESIS AND OTHER HYPOOSMOLAR STATES 265 JOSEPH G. VERBALIS

THE THYROID GLAND Leonard Wartofsky, Editor

29

30

31

32

33 34 35

36

37

THE APPROACH TO THE PATIENT WITH THYROID DISEASE 278 LEONARD WARTOFSKY MORPHOLOGY OF THE THYROID GLAND 281 VIRGINIA A. LIVOLSI PHYSIOLOGY OF THE THYROID GLAND I: SYNTHESIS AND RELEASE, IODINE METABOLISM, AND BINDING AND TRANSPORT 285 LESTER REED and LOUIS N. PANGARO PHYSIOLOGY OF THE THYROID GLAND II: RECEPTORS, POSTRECEPTOR EVENTS, AND HORMONE RESISTANCE SYNDROMES 292 STEPHEN JON USALA THYROID FUNCTION TESTS 299 ROBERT C. SMALLRIDGE THYROID UPTAKE AND IMAGING 307 SAUL D. SARKAR and DAVID V. BECKER THYROID SONOGRAPHY, COMPUTED TOMOGRAPHY, AND MAGNETIC RESONANCE IMAGING 313 MANFRED BLUM ABNORMAL THYROID FUNCTION TEST RESULTS IN EUTHYROID PERSONS 323 HENRY B. BURCH ADVERSE EFFECTS OF IODIDE 332 JENNIFER A. NUOVO and LEONARD WARTOFSKY

38 39

40 41 42

43

44

45

46

NONTOXIC GOITER 338 PAUL J. DAVIS and FAITH B. DAVIS THE THYROID NODULE 345 LEONARD WARTOFSKY and ANDREW J. AHMANN THYROID CANCER 354 ERNEST L. MAZZAFERRI HYPERTHYROIDISM 367 KENNETH D. BURMAN ENDOCRINE OPHTHALMOPATHY 385 MELVIN G. ALPER and LEONARD WARTOFSKY SURGERY OF THE THYROID GLAND 399 EDWIN L. KAPLAN, KOICHI ITO, and REIKO TANAKA HYPOTHYROIDISM 404 LAWRENCE E. SHAPIRO and MARTIN I. SURKS THYROIDITIS 412 PRESTON LAMBERTON and IVOR M.D. JACKSON THYROID DISORDERS OF INFANCY AND CHILDHOOD 421 WELLINGTON HUNG

CONTENTS

PART

IV

XXVII

CALCIUM AND BONE METABOLISM John P. Bilezikian, Editor

47

MORPHOLOGY OF THE PARATHYROID GLANDS 432 VIRGINIA A. LIVOLSI 48 PHYSIOLOGY OF CALCIUM METABOLISM 437 EDWARD M. BROWN 49 PHYSIOLOGY OF BONE 447 LAWRENCE G. RAISZ 50 PARATHYROID HORMONE 455 DAVID GOLTZMAN and GEOFFREY N. HENDY 51 PARATHYROID HORMONE-RELATED PROTEIN 467 EBERHARD BUND, ROBERT A. NISSENSON, and GORDON J. STREWLER 52 CALCITONIN GENE FAMILY OF PEPTIDES 474 KENNETH L. BECKER, ERIC S. NYLEN, REGIS COHEN, OMEGA L. SILVA, and RICHARD H. SNIDER, JR. 53 VITAMIN D 483 THOMAS L. CLEMENS and JEFFREY L.H. O’RIORDAN 54 BONE QUANTIFICATION AND DYNAMICS OF TURNOVER 491 DAVID W. DEMPSTER and ELIZABETH SHANE 55 MARKERS OF BONE METABOLISM 498 MARKUS J. SEIBEL, SIMON P. ROBINS, and JOHN P. BILEZIKIAN 56 BONE IMAGING TECHNIQUES 508 CHARLES H. CHESNUT III 57 PRIMARY HYPERPARATHYROIDISM 512 SHONNI J. SILVERBERG, LORRAINE A. FITZPATRICK, and JOHN P. BILEZIKIAN

PART

V

58

59

60

61

62 63

64

65

66

67 68 69

NONPARATHYROID HYPERCALCEMIA 520 WILLIAM J. BURTIS, KAI H. YANG, and ANDREW F. STEWART HYPOPARATHYROIDISM AND OTHER CAUSES OF HYPOCALCEMIA 532 ELIZABETH A. STREETEN and MICHAEL A. LEVINE RENAL OSTEODYSTROPHY 547 KEVIN J. MARTIN and EDUARDO SLATOPOLSKY SURGERY OF THE PARATHYROID GLANDS 554 GERARD M. DOHERTY, JEFFREY A. NORTON, and SAMUEL A. WELLS, JR. OSTEOMALACIA AND RICKETS 559 NORMAN H. BELL OSTEOPOROSIS 567 JACK F. TOHME, FELICIA COSMAN, and ROBERT LINDSAY PAGET DISEASE OF BONE 585 ETHEL S. SIRIS and ROBERT E. CANFIELD RARE DISORDERS OF SKELETAL FORMATION AND HOMEOSTASIS 594 MICHAEL P. WHYTE DISEASES OF ABNORMAL PHOSPHATE METABOLISM 606 KENNETH IV. LYLES and MARC K. DREZNER MAGNESIUM METABOLISM 616 ROBERT K. RUDE NEPHROLITHIASIS 622 MURRAY J. FAVUS and FREDRIC L. COE DISORDERS OF CALCIUM AND BONE METABOLISM IN INFANCY AND CHILDHOOD 631 THOMAS O. CARPENTER

THE ADRENAL GLANDS D. Lynn Loriaux, Editor

70

71

MORPHOLOGY OF THE ADRENAL CORTEX AND MEDULLA 640 ROGER S. RITTMASTER and DONNA M. ARAB SYNTHESIS AND METABOLISM OF CORTICOSTEROIDS 647 PERRIN C. WHITE, ORA HIRSCH PESCOVITZ, and GORDON B. CUTLER, JR.

72

73 74

TESTS OF ADRENOCORTICAL FUNCTION 662 D. LYNN LORIAUX CUSHING SYNDROME 667 DAVID E. SCHTEINGART ADRENOCORTICAL INSUFFICIENCY 682 D. LYNN LORIAUX

XXVlii

75

76 77

78 79 80

81

CONTENTS

CONGENITAL ADRENAL HYPERPLASIA 686 PHYLLIS W. SPEISER CORTICOSTEROID THERAPY 695 LLOYD AXELROD ALDOSTERONE AND THE RENINANGIOTENSIN SYSTEM 706 WILLA A. HSUEH and MICHAEL L. TUCK HYPERALDOSTERONISM 716 JOHN R. GILL, JR. HYPOALDOSTERONISM 729 JAMES C. MELBY ENDOCRINE ASPECTS OF HYPERTENSION 734 MICHAEL L. TUCK ADRENOCORTICAL DISORDERS IN INFANCY AND CHILDHOOD 744 ROBERT L ROSENFIELD and ALBERT C. WATSON

PART

VI

82

83

84

85

86

PHYSIOLOGY OF THE ADRENAL MEDULLA AND THE SYMPATHETIC NERVOUS SYSTEM 753 DAVID S. GOLDSTEIN PHEOCHROMOCYTOMA AND OTHER DISEASES OF THE SYMPATHETIC NERVOUS SYSTEM 762 HARRY R. KEISER ADRENOMEDULLARY DISORDERS OF INFANCY AND CHILDHOOD 770 WELLINGTON HUNG DIAGNOSTIC IMAGING OF THE ADRENAL GLAND 773 DONALD L. MILLER and JOHN L. DOPPMAN SURGERY OF THE ADRENAL GLANDS 778 GARY R. PEPLINSKI and JEFFREY A. NORTON

SEX DETERMINATION AND DEVELOPMENT Robert W. Rebar and William J. Bremner, Editors

87

88

NORMAL AND ABNORMAL SEXUAL DIFFERENTIATION AND DEVELOPMENT 788 JOE LEIGH SIMPSON and ROBERT W. REBAR PHYSIOLOGY OF PUBERTY 822 PETER A. LEE

PART

VII

89

90

PRECOCIOUS AND DELAYED PUBERTY 830 DAVID ROSEN and ROBERT P. KELCH MICROPENIS, HYPOSPADIAS, AND CRYPTORCHIDISM IN INFANCY AND CHILDHOOD 843 WELLINGTON HUNG

ENDOCRINOLOGY OF THE FEMALE Robert W. Rebar, Editor

91

92

93

94

MORPHOLOGY AND PHYSIOLOGY OF THE OVARY 852 GREGORY F. ERICKSON and JAMES R. SCHREIBER THE NORMAL MENSTRUAL CYCLE AND THE CONTROL OF OVULATION 868 ROBERT W. REBAR, DANIEL KENIGSBERG, and GARY D. HODGEN DISORDERS OF MENSTRUATION, OVULATION, AND SEXUAL RESPONSE 880 ROBERT W. REBAR OVULATION INDUCTION 900 MICHAEL M. MILLER and DAVID I. HOFFMAN

95

96 97 98

99

ENDOMETRIOSIS 906 BURT A. LITTMAN, DAVID B. SMOTRICH, and ROBERT J. STILLMAN PREMENSTRUAL SYNDROME 909 ROBERT L. REID and RUTH C. FRETTS MENOPAUSE 915 ISAAC SCHIFF and BRIAN WALSH HIRSUTISM, ALOPECIA, AND ACNE 924 ROGERIO A. LOBO FUNCTIONING TUMORS AND TUMOR-LIKE CONDITIONS OF THE OVARY 940 I-TIEN YEH, CHARLES ZALOUDEK, and ROBERT J. KURMAN

CONTENTS

100

101 102

103

104

THE DIFFERENTIAL DIAGNOSIS OF FEMALE INFERTILITY 947 STEVEN J. ORY FEMALE CONTRACEPTION 954 GERALD I. ZATUCHNI KNOWN AND POTENTIAL COMPLICATIONS OF STEROIDAL CONTRACEPTION 963 GERALD I. ZATUCHNI MORPHOLOGY OF THE NORMAL BREAST AND ITS HORMONAL CONTROL 968 RICHARD E. BLACKWELL PATHOPHYSIOLOGY OF THE orpACT

105

106

107

108

109

Q79

RICHARD E. BLACKWELL 110

PART

111

112

113

114 115

116

VIII

117

118 119

120 121

122

123

PART

IX

CONCEPTION, IMPLANTATION, AND EARLY DEVELOPMENT 977 PHILIP M. IANNACCONE and KRISTINA C. PFENDLER THE MATERNAL-FETAL-PLACENTAL UNIT 987 BRUCE R. CARR ENDOCRINOLOGY OF PARTURITION 1001 JOHN R. G. CHALLIS ENDOCRINE DISEASE IN PREGNANCY 1005 MARK E. MOLITCH TROPHOBLASTIC TISSUE AND ITS ABNORMALITIES 1019 CYNTHIA G. KAPLAN ENDOCRINOLOGY OF TROPHOBLASTIC TISSUE 1025 JUDITH L. VAITUKAITIS and MICHAEL L. LYDIC

ENDOCRINOLOGY OF THE MALE William /. Bremner, Editor

MORPHOLOGY AND PHYSIOLOGY OF THE TESTIS 1032 DAVID M. DE KRETSER TESTICULAR STEROID TRANSPORT, METABOLISM, AND EFFECTS 1042 RICHARD HORTON EVALUATION OF TESTICULAR FUNCTION 1048 STEPHEN J. WINTERS MALE HYPOGONADISM 1056 STEPHEN R. PLYMATE TESTICULAR DYSFUNCTION IN SYSTEMIC DISEASE 1083 H. W. GORDON BAKER IMPOTENCE 1089 GLENN R. CUNNINGHAM and MAX HIRSHKOWITZ

IMPOTENCE DUE TO VASCULAR DISEASE 1099 RALPH G. DEPALMA MALE INFERTILITY 1102 RICHARD V. CLARK CLINICAL USE AND ABUSE OF ANDROGENS AND ANTI ANDROGENS 1110 ALVIN M. MATSUMOTO GYNECOMASTIA 1123 ALLAN R. GLASS ENDOCRINE ASPECTS OF BENIGN PROSTATIC HYPERPLASIA 1129 JOSEPH E. OESTERLING TESTICULAR TUMORS 1134 NIELS E. SKAKKEBAEK and MIKAEL R0RTH MALE CONTRACEPTION 1144 EBERHARD NIESCHLAG

DISORDERS OF FUEL METABOLISM C. Ronald Kahn, Editor

SECTION A FOOD AND ENERGY

125

124 PRINCIPLES OF NUTRITIONAL MANAGEMENT 1148 ROBERTA P. DURSCHLAG and ROBERT J. SMITH

126

XXIX

OBESITY 1155 JULES HIRSCH, LESTER B. SALANS, and LOUIS J. ARONNE STARVATION 1164 RUTH S. MACDONALD and ROBERT J. SMITH

XXX

127

128

129

130

131

CONTENTS

ANOREXIA NERVOSA AND OTHER EATING DISORDERS 1169 MICHELLE P. WARREN FUEL HOMEOSTASIS AND INTERMEDIARY METABOLISM OF CARBOHYDRATE, FAT, AND PROTEIN 1174 NEIL B. RUDERMAN, KEITH TORNHEIM, and MICHAEL N. GOODMAN MORPHOLOGY OF THE ENDOCRINE PANCREAS 1187 SUSAN BONNER-WEIR ISLET CELL HORMONES: PRODUCTION AND DEGRADATION 1191 PHILIPPE A. HALBAN and GORDON C. WEIR GLUCOSE HOMEOSTASIS AND INSULIN ACTION 1198 C. RONALD KAHN

SECTION B DIABETES MELLITUS

141

142

143

144 145 146 147

148 149

132

133

134

135

136

137

138

139

140

CLASSIFICATION, DIAGNOSTIC TESTING, AND PATHOGENESIS OF TYPE I DIABETES MELLITUS 1202 GEORGE S. EISENBARTH ETIOLOGY AND PATHOGENESIS OF TYPE II DIABETES MELLITUS AND RELATED DISORDERS 1210 C. RONALD KAHN NATURAL HISTORY OF DIABETES MELLITUS 1216 ANDRZEJ S. KROLEWSKI and JAMES H. WARRAM SECONDARY FORMS OF DIABETES MELLITUS 1220 VERONICA M. CATANESE and C. RONALD KAHN EVALUATION OF METABOLIC CONTROL IN DIABETES 1228 ALLISON B. GOLDFINE DIET AND EXERCISE IN DIABETES 1231 OM P. GANDA ORAL AGENTS FOR THE TREATMENT OF TYPE II DIABETES MELLITUS 1235 ELEFTHERIA MARATOS-FLIER INSULIN THERAPY AND ITS COMPLICATIONS 1238 GORDON C. WEIR and JAMES A. O’HARE SYNDROMES OF INSULIN RESISTANCE 1249 JEFFREY S. FLIER

150

151

CARDIOVASCULAR COMPLICATIONS OF DIABETES 1259 GEORGE L. KING and EDWARD J. KOSINSKI DIABETIC NEUROPATHY 1270 DOUGLAS A. GREENE, DAVID A. GELBER, MICHAEL A. PFEIFER, and PATRICIA B CARROLL GASTROINTESTINAL COMPLICATIONS OF DIABETES 1280 FREDRIC D. GORDON and KENNETH R. FALCHUK DIABETIC NEPHROPATHY 1283 RALPH A. DEFRONZO DIABETES AND THE EYE 1297 LAWRENCE I. RAND DIABETES AND INFECTION 1303 GEORGE M. ELIOPOULOS DIABETES AND THE SKIN 1307 RICHARD C. EASTMAN and ROBERT J. TANENBERG THE DIABETIC FOOT 1313 GARY W. GIBBONS DIABETIC ACIDOSIS, HYPEROSMOLAR COMA, AND LACTIC ACIDOSIS 1316 K. GEORGE M.M. ALBERTI DIABETES MELLITUS AND PREGNANCY 1329 LOIS JOVANOVIC-PETERSON and CHARLES M. PETERSON DIABETES MELLITUS IN THE INFANT AND CHILD 1337 ALLAN L. DRASH and DOROTHY J. BECKER

SECTION C HYPOGLYCEMIA 152

153

154

155

HYPOGLYCEMIC DISORDERS IN THE ADULT 1342 RICHARD J. COMI and PHILLIP GORDEN LOCALIZATION OF ISLET CELL TUMORS 1351 DONALD L. MILLER and JOHN L. DOPPMAN SURGERY OF THE ENDOCRINE PANCREAS 1355 JON C. WHITE and JOHN W. HARMON HYPOGLYCEMIA OF INFANCY AND CHILDHOOD 1360 ALLEN M. GLASGOW

CONTENTS

SECTION

D

158

LIPID METABOLISM 156

157

BIOCHEMISTRY AND PHYSIOLOGY OF LIPID AND LIPOPROTEIN METABOLISM 1369 ROBERT W. MAHLEY LIPOPROTEIN DISORDERS 1378 ERNST J. SCHAEFER

PART

X

159

XXXI

THERAPY OF THE HYPERLIPOPROTEINEMIAS 1395 JOHN C. LAROSA LIPID ABNORMALITIES IN DIABETES MELLITUS 1402 ROBERT E. RATNER, BARBARA V. HOWARD, and WM. JAMES HOWARD

DIFFUSE HORMONAL SECRETION_ Eric S. Nylen, Editor

SECTION

A

SECTION

B

SEVERAL HORMONES INVOLVED IN DIFFUSE SECRETION

SEVERAL SITES OF DIFFUSE HORMONAL SECRETION

160

171

161 162 163 164 165

166 167

168

169

170

CHARACTERISTICS OF DIFFUSE PEPTIDE HORMONE SYSTEMS 1412 JENS F. REHFELD BOMBESIN-LIKE PEPTIDES 1415 JAMES N. BARANIUK CHOLECYSTOKININ 1420 MARGERY C. SEINFELD KININS 1421 DOMENICO C. REGOLI NEUROTENSIN 1424 ROBERT E. CARRAWAY ENDOGENOUS OPIOID PEPTIDES 1430 BRIAN M. COX and GREGORY P. MUELLER SOMATOSTATIN 1436 YOGESH C. PATEL SUBSTANCE P AND THE TACHYKININS 1446 NEIL ARONIN VASOACTIVE INTESTINAL PEPTIDE 1449 SAMI I. SAID GROWTH FACTORS AND CYTOKINES 1451 DEREK LEROITH and CHARLES T. ROBERTS, JR. PROSTAGLANDINS AND OTHER ARACHIDONIC ACID METABOLITES 1466 R. PAUL ROBERTSON

172 173

174

175

176

177 178

179 180

THE DIFFUSE NEUROENDOCRINE SYSTEM 1472 ERIC S. NYLEN and KENNETH L. BECKER THE ENDOCRINE LUNG 1479 KENNETH L BECKER THE ENDOCRINE HEART 1487 ELLEN W. SEELY and GORDON H. WILLIAMS THE ENDOCRINE ENDOTHELIUM 1491 THOMAS F. LUSCHER, RAGHVENDRA K. DUBEY, and GEORG NOLL THE ENDOCRINE GASTROINTESTINAL TRACT: PATHOPHYSIOLOGY 1499 STEPHEN R. BLOOM and JULIA M. POLAK ENDOCRINE TUMORS OF THE GASTROINTESTINAL TRACT 1512 STEPHEN R. BLOOM, PETER J. HAMMOND, and JULIA M. POLAK THE ENDOCRINE KIDNEY 1518 ALAN DUBROW THE ENDOCRINE GENITOURINARY TRACT 1523 JAN FAHRENKRUG THE ENDOCRINE SKIN 1526 MARK R. PITTELKOW THE ENDOCRINE MAST CELL 1537 STEPHEN I. WASSERMAN

xxxii

CONTENTS

PART XI HERITABLE ABNORMALITIES OF ENDOCRINOLOGY _AND METABOLISM_ Kenneth L. Becker, Editor 181

182

183

GENETIC DISORDERS OF ENDOCRINOLOGY AND METABOLISM 1544 ft NEIL SCHIMKE MULTIPLE ENDOCRINE NEOPLASIA 1555 GLEN IV. SIZEMORE HERITABLE DISEASES OF COLLAGEN AND FIBRILLIN 1564 PETER H. BYERS

PART

XII

184

185

186

HERITABLE DISEASES OF LYSOSOMAL STORAGE 1576 WARREN E. COHEN HERITABLE DISEASES OF AMINO ACID METABOLISM 1586 HARVEY J. STERN and JAMES D. FINKELSTEIN HERITABLE DISEASES OF PURINE METABOLISM 1595 EDWARD W. HOLMES and DAVID J. NASH EL

IMMUNOLOGIC BASIS OF ENDOCRINE DISORDERS Leonard Wartofsky, Editor

187

188

189

THE ENDOCRINE THYMUS 1606 NICHOLAS R.S. HALL, ALLAN L. GOLDSTEIN, and MAUREEN P. O’GRADY IMMUNOGENETICS, THE HLA SYSTEM, AND ENDOCRINE DISEASE 1612 JAMES R. BAKER, JR. T CELLS IN ENDOCRINE DISEASE 1617 ANTHONY PETER WEETMAN

PART

XIII

190

191

B CELLS AND AUTOANTIBODIES IN ENDOCRINE DISEASE 1624 ALAN M. MCGREGOR THE IMMUNE SYSTEM AND ITS ROLE IN ENDOCRINE FUNCTION 1629 ROBERT VOLPE

ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED Wellington Hung, Editor

192 SHORT STATURE AND SLOW GROWTH IN THE INFANT AND CHILD 1644 THOMAS ACETO, JR., LUIGI GARIBALDI, SUSAN E. MEYERS, NANCI BOBROW, and KARL LUBSCH

193 AGING AND ENDOCRINOLOGY DAVID A. GRUENEWALD and ALVIN M. MATSUMOTO

1664

PART XIV INTERRELATIONSHIPS BETWEEN HORMONES _AND THE BODY Kenneth L. Becker, Editor 194 INFLUENCE OF HORMONES AND MESSENGER PEPTIDES ON NORMAL BRAIN FUNCTION 1682 ABBA J. KASTIN, WILLIAM A. BANKS, BILAL AHMED, and JAMES E. ZADINA

195

CEREBRAL EFFECTS OF ENDOCRINE DISEASE 1691 HOYLE LEIGH

CONTENTS

196

197

198

199

200

201

202

203

PSYCHIATRIC-HORMONAL INTERRELATIONSHIPS 1696 MITCHEL A. KLING, ISAAC NEUHAUS, and PHILIP W. GOLD RESPIRATION AND ENDOCRINOLOGY 1703 PRASHANT K. ROHATGI and KENNETH L. BECKER THE CARDIOVASCULAR SYSTEM AND ENDOCRINE DISEASE 1713 ELLEN W. SEELY and GORDON H. WILLIAMS GASTROINTESTINAL MANIFESTATIONS OF ENDOCRINE DISEASE 1721 ALLAN G. HALLINE, W. REID GLAWS, and SUMNER C. KRAFT THE LIVER AND ENDOCRINE DYSFUNCTION 1726 STEFANO FAGIUOLI, NICOLA DE MARIA, and DAVID H. VAN THIEL EFFECTS OF NONRENAL HORMONES ON THE NORMAL KIDNEY 1740 PAUL L KIMMEL and GILBERTO A. VERA RENAL METABOLISM OF HORMONES 1746 RALPH RABKIN and DAVID C. DAHL EFFECTS OF ENDOCRINE DISEASE ON THE KIDNEY 1754 ELLIE KELEPOURIS and ZALMAN S. AGUS

PART

213

214

215

XV

204

205

206

207

208

209

210

211

212

XXXIII

ENDOCRINE DYSFUNCTION DUE TO RENAL DISEASE 1759 ARSHAG D. MOORADIAN NEUROMUSCULAR MANIFESTATIONS OF ENDOCRINE DISEASE 1762 ROBERT B. LAYZER RHEUMATIC MANIFESTATIONS OF ENDOCRINE DISEASE 1770 DAVID J. NASH EL HEMATOLOGIC ENDOCRINOLOGY 1776 STUART L. GOLDBERG and CRAIG M. KESSLER INFECTIOUS DISEASES AND ENDOCRINOLOGY 1784 CARMELITA U. TUAZON, ANN M. LABRIOLA, and STEPHEN WEINROTH THE EYE IN ENDOCRINOLOGY 1793 KAREN WINCHESTER and WILLIAM D. MATHERS OTOLARYNGOLOGY AND ENDOCRINE DISEASE 1817 STEPHEN G. HARNER DENTAL ASPECTS OF ENDOCRINOLOGY 1821 ROBERT S. REDMAN THE SKIN AND ENDOCRINE DISORDERS 1830 JO-DAVID FINE and KENNETH L. BECKER

HORMONES AND CANCER Kenneth L. Becker, Editor

PARANEOPLASTIC ENDOCRINE SYNDROMES 1842 KENNETH L. BECKER and OMEGA L. SILVA THE CARCINOID TUMOR AND THE CARCINOID SYNDROME 1853 PAUL N. MATON HORMONES AND CARCINOGENESIS: LABORATORY STUDIES 1856 JONATHAN J. LI, SATYABRATA NANDI, and SARA ANTONIA LI

216

217

218

219

SEX HORMONES AND HUMAN CARCINOGENESIS: EPIDEMIOLOGY 1861 ROBERT N. HOOVER ENDOCRINE TREATMENT OF BREAST CANCER 1868 GABRIEL N. HORTOBAGYI ENDOCRINE ASPECTS OF PROSTATE CANCER 1875 ANDREA MANN! and RICHARD J. SANTEN ENDOCRINE CONSEQUENCES OF CANCER THERAPY 1884 DAIVA R. BAJORUNAS

XXXIV

CONTENTS

PART

XVI

ENDOCRINE AND METABOLIC EFFECTS OF TOXIC AGENTS Kenneth L. Becker, Editor

220 ENDOCRINE-METABOLIC EFFECTS OF ALCOHOL 1892 ROBERT H. NOTH and ROBERT M. WALTER, JR.

PART

223

224

225

XVII

221

222

METABOLIC EFFECTS OF TOBACCO, CANNABIS, AND COCAINE 1897 OMEGA L. SILVA ENVIRONMENTAL TOXINS AND ENDOCRINE FUNCTION 1900 LAURA S. WELCH

ENDOCRINE DRUGS AND VALUES Kenneth L. Becker, Editor

COMPENDIUM OF ENDOCRINE-RELATED DRUGS 1908 ERIC S. NYLEN and MICHELLE FISCHMANN MAGEE EFFECTS OF DRUGS ON ENDOCRINE FUNCTION AND VALUES 1937 MEETA SHARMA REFERENCE VALUES IN ENDOCRINOLOGY 1957 D. ROBERT DUFOUR

226

227

DNA DIAGNOSIS OF ENDOCRINE DISEASE 2006 J. FIELDING HEJTMANCIK and HARRY OSTRER DYNAMIC PROCEDURES IN ENDOCRINOLOGY 2013 D. ROBERT DUFOUR and WILLIAM A. JUBIZ

INDEX

2035

Principles and Practice of

ENDOCRINOL OGY AND METABOLISM

PART

I

GENERAL PRINCIPLES OF ENDOCRINOLOGY KENNETH L.

1. 2. 3. 4. 5.

.

6

7.

.

8

9.

BECKER, editor

ENDOCRINOLOGY AND THE ENDOCRINE PATIENT. BIOSYNTHESIS AND SECRETION OF PEPTIDE HORMONES. HORMONAL ACTION FEEDBACK CONTROL IN ENDOCRINE SYSTEMS. ENDOCRINE RHYTHMS. VITAMINS: HORMONAL AND METABOLIC INTERRELATIONSHIPS. TRACE MINERALS: HORMONAL AND METABOLIC INTERRELATIONSHIPS. EXERCISE: ENDOCRINE AND METABOLIC EFFECTS. GROWTH AND DEVELOPMENT IN THE NORMAL INFANT AND CHILD.

2

8 20 34 41 50 56 64 69

2

PART I: GENERAL PRINCIPLES OF ENDOCRINOLOGY Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

1_

ENDOCRINOLOGY AND THE ENDOCRINE PATIENT KENNETH L. BECKER, ERIC S. NYLEN, AND RICHARD H. SNIDER, JR.

DEFINITIONS Endocrinology is the study of communication and control within a living organism by means of chemical messengers that are synthesized in whole or in part by that organism. Metabolism, which is part of the science of endocrinology, is the study of the biochemical control mechanisms that occur within living organisms. The term includes such diverse activities as gene expression; biosynthetic pathways and their enzymatic catalysis; the modification, transformation, and degradation of biologic substances; the biochemical mediation of the actions and interactions of such substances; and the means for obtaining, storing, and mobilizing energy. The chemical messengers of endocrinology are the hormones, endogenous informational molecules that are involved in both intracellular and extracellular communication.

ROLE OF THE ENDOCRINE SYSTEM The mammalian organism, including the human, is multi¬ cellular and highly specialized toward sustaining life and repro¬ ductive processes. Reproduction requires gametogenesis, fertil¬ ization, and implantation. Subsequently, the new intrauterine conception must undergo cell proliferation, organogenesis, and differentiation into a male or female. After parturition, the new¬ born must grow and mature sexually, so that the life cycle may be repeated. To a considerable extent, the endocrine system in¬ fluences or controls all of these phenomena. Hormones partici¬ pate in all physiologic functions, such as muscular activity, respi¬ ration, digestion, hematopoiesis, sense organ function, thought, mood, and behavior. The overall purpose of the coordinating, regulating, integrating, stimulating, suppressing, and modulating effects of the many components of the endocrine system is ho¬ meostasis, which is the maintenance of a healthy internal milieu in the presence of a continuously changing and sometimes threatening external environment.

HORMONES CHEMICAL CLASSIFICATION Most hormones can be classified into one of several chemical categories: amino acid derivatives (e.g., tryptophan -*■ serotonin and melatonin; tyrosine -*■ dopamine, norepinephrine, epineph¬ rine, triiodothyronine, and thyroxine; L-glutamic acid -*• yaminobutyric acid; histidine histamine), peptides or polypep¬ tides (e.g., thyrotropin releasing hormone, insulin, growth hormone, nerve growth factor), steroids (e.g., progesterone, androgens, estrogens, corticosteroids, vitamin D and its metabo¬ lites), and fatty acid derivatives (e.g., prostaglandins, leukotrienes, thromboxane).

SOURCES, CONTROLS, AND FUNCTIONS It was previously thought that hormones were synthesized and secreted predominantly by anatomically discrete and cir¬ cumscribed glandular structures, called ductless glands (e.g., pi¬ tuitary, thyroid, adrenals, gonads). However, many microscopic organoid-like groups of cells and innumerable other cells of the body contain and secrete hormones (see Chap. 171). The classic “glands” of endocrinology have lost their exclu¬ sivity, and although they are important on physiologic and pathologic levels, the widespread secretion of hormones throughout the body by "nonglandular" tissues is of equal impor¬ tance. Most hormones are known to have multiple sources. More¬ over, the physiologic stimuli that release these hormones are of¬ ten found to differ according to their locale. The response to a secreted hormone is not stereotyped but varies according to the nature and location of the target cells or tissues. TRANSPORT TYPES OF SECRETORY TRANSPORT

Hormones have various means of reaching target cells. In the early decades of the development of the field of endocrinol¬ ogy, hormones were conceived to be substances that traveled to distal sites through the blood. This is accomplished by release into the extracellular spaces and subsequent entrance into blood vessels by way of capillary fenestrations. The most appropriate term for such blood-bone communication is hemocrine (Fig. 1-1). However, there are several alternative means of hormonal communication. Paracrine communication involves the extrusion of hormonal contents into the surrounding interstitial spaces; the hormone then interacts with receptors on nearby cells (see Fig. 1-1 and see Chaps. 3 and 171).1 Direct paracrine transfer of cyto¬ plasmic messenger molecules into adjacent cells may occur through specialized gap junctions.2 Unlike hemocrine secretion, in which the hormonal secretion is diluted within the circulatory system, paracrine secretion delivers a very high concentration of hormone to its target site, juxtacrine communication is a form of paracrine secretion in which the messenger molecule does not traverse a fluid phase to reach another cell but instead remains associated with the plasma membrane of the signaling cell while acting directly on an immediately adjacent receptor cell.3 Hormones may be secreted and subsequently interact with the same cell that released the substance; this process is autocrine secretion (see Fig. 1-1).4 The secreted hormone stimulates, sup¬ presses, or otherwise modulates the activity of the secreting cell. Autocrine secretion is a form of self-regulation of a cell by its own product. When peptide hormones or other neurotransmitters or neu¬ romodulators are produced by neurons, the term neurocrine se¬ cretion is used (see Fig. 1-1).5 This specialized form of paracrine release may be synaptic (i.e., the messenger traverses a structured synaptic space) or nonsynaptic (i.e., the messenger is carried to its local or distal site of action by way of the extracellular fluid or the blood). Nonsynaptic neurocrine secretion has also been called neurosecretion. An example of neurosecretion is the release of va¬ sopressin and oxytocin into the circulatory system by nervous tissue of the pituitary (see Chap. 26). Several peptides and amines are secreted into the lumi¬ nal aspect of the gut (e.g., gastrin, somatostatin, luteinizing hormone-releasing hormone, calcitonin, secretin, vasoactive in¬ testinal peptide, serotonin, substance P).6 This process may be called solinocrine secretion (see Fig. 1-1), from the Greek word for a hollow tube. Solinocrine secretion also occurs into the bronchi, the urogenital tract, and other ductal structures.7 Commonly, the same hormone can be transported by more than one of these means.8 Extracellular transportation may not always be necessary for hormones to exert their effects. For example, some known hor-

Ch. 1: Endocrinology and the Endocrine Patient

3

HEMOCRINE

NEUROCRINE

Synaptic

EXOCRINE GLANDS

Non-synaptic

mortal secretions that are transported by one or more of these mechanisms are also found in extremely low concentrations within the cytoplasm of many cells. In such circumstances, these hormones do not appear to be localized to identifiable secretion granules and probably act primarily within the cell. This phe¬ nomenon may be called intracrine secretion. OVERLAP OF EXOCRINE AND ENDOCRINE TYPES OF SECRETION

Classically, an exocrine gland is a specialized structure that secretes its products at an external or internal surface (e.g., sweat glands, sebaceous glands, salivary glands, oxyntic or gastric glands, pancreatic exocrine glandular system, prostate gland). An exocrine gland may be unicellular (e.g., mucous or goblet cells of the epithelium of mucous membranes) or multicellular (e.g., salivary glands). Many multicellular exocrine glands possess a structured histologic organization that is suited to the production and delivery of secretions that are produced in relatively large quantities. A specialized excretory duct or system of ducts usually constitutes an intrinsic part of the gland. Some exocrine glandu¬ lar cells secrete their substances by means of destruction of the cells themselves (i.e., holocrine secretion); an example is the se¬ baceous glands. Other exocrine glandular cells secrete their sub¬ stances by way of the loss of a portion of the apical cytoplasm along with the material being secreted (i.e., apocrine secretion); an example is the apocrine sweat glands. Alternatively, in many forms of exocrine secretion, the secretory cells release their prod¬ ucts through the cell membrane, and the cell remains intact (i.e., merocrine secretion); an example is the salivary glands. The con¬ stituents of some exocrine glands, particularly those opening on the external surface of the body, sometimes function as phero¬ mones, which are chemical substances that act on other members of the species.9 Many exocrine glands contain cells of the diffuse neuroen¬ docrine system (see Chap. 171) and neurons; both cell types se¬ crete peptide hormones. Peptide hormones and prostaglandins are found in all exocrine secretions (e.g., sweat, saliva, milk, bile, seminal fluid; see Chap. 103).10,11 Although they usually are not directly produced in such glands, thyroid and steroid hormones are found in exocrine secretions as well.12-15

FIGURE 1-1. Types of hormonal communication. The darkened areas on the cell membrane represent receptors.

It is preferable to view the term exocrine as a histologicanatomic entity and not as a term that is meant to be antithetical to or to contrast with the term endocrine. Endocrinologists are concerned clinically and experimentally with all means of hor¬ monal communication. The word endocrine is best used in a global sense, indicating any and all means of communication by messenger molecules.

TYRANNY OF HORMONE TERMINOLOGY Hormones usually are named at the time of their discovery. Sometimes, the names are based on the locations where they were first found or on their presumed effects. However, with time, other locations and other effects are discovered, and these new locations or effects often are more physiologically relevant than the initial findings. Hormonal names are often overly restric¬

tive, confusing, or misleading. In many instances, such hormonal names have become in¬ appropriate. For example, atrial natriuretic hormone is present in the brain, hypothalamus, pituitary, autonomic ganglia, and lungs as well as atrium, and it has effects other than natriuresis (see Chap. 173). Gastrin-releasing peptide is found in semen, far from the site of gastrin release. Somatostatin, which was found in the hypothalamus and named for its inhibitory effect on growth hor¬ mone, occurs in many other locations and has multiple other functions (see Chap. 166). Calcitonin, which initially was thought to play an important role in regulating serum calcium and was named accordingly, appears to exert many other effects, and its influence on serum calcium may be quite minor (see Chap. 52). Growth hormone-releasing hormone and arginine vaso¬ pressin are found in the testis, where effects on growth hormone release or on the renal tubular reabsorption of water are most unlikely. Vasoactive intestinal peptide is found in multiple tis¬ sues other than the intestines (see Chap. 168). Insulin, named for the pancreatic islets, is found in the brain and elsewhere Prostaglandins have effects that are far more widespread than those exerted in the secretions of the prostate, from whxc‘ .iieir name derives (see Chap. 170). There are also so-called hormones in the endocrine lexicon that are not hormones. In the human, melanocyte-stimulating

4

PART I: GENERAL PRINCIPLES OF ENDOCRINOLOGY

TABLE 1-1 Modulation of the Hormone Message and its Subsequent Physiologic or Pathologic Metabolic Effects* Modulation

Explanation

Examples

Gene mutations

Alteration of one or more nucleotides within the DNA gene sequence may result in a missense gene, nonsense gene, a gene deletion, or a gene conversion.19,20 The mutation may affect hormone synthesis, enzymatic processing of the hormone, or synthesis of a receptor for a hormone.

Mutant proinsulin syndrome (a structurally abnormal proinsulin resulting in diminished bioactivity and diabetes).21 Growth hormone resistance (i.e., Laron syndrome) is caused by point mutations in the gene coding for the human growth hormone receptor.22,23

Chromosomal deletion

Loss of chromosomal material, with an associated loss of genes

WAGR syndrome (Wilms tumor, aniridia, genitourinary malformations, mental retardation). The syndrome may have an associated chromosomal deletion involving the gene coding for the /3-subunit of follicle-stimulating hormone; its deficiency during embryonic development may cause the genitourinary abnormalities.24 Ovarian dysgenesis (Turner syndrome) is the result of the loss of all or part of an X chromosome (see Chap. 87).

Alternative gene processing

Alternative splicing of the primary RNA transcript gives rise to multiple messenger RNAs, each encoding a different hormone (see Chap. 2). A similar phenomenon can occur during the synthesis of a hormonal receptor.

The alternative exon selection that gives rise to the hormone calcitonin or the very differently structured hormone calcitonin gene-related peptide (CGRP), a phenomenon that may be altered by a physiologic or pathologic change of the biosynthetic milieu (see Chap. 52).25 Many patients with medullary thyroid cancer have a greater CGRP to calcitonin secretion ratio than do normal persons. Alternative splicing can also produce different forms of receptors (e.g., thyroid receptors.26,27

Posttranslational processing

Most or all peptide hormones are synthesized in the form of large polypeptide precursors,28 some of which contain more than one functionally distinct hormone (see Chap. 2). Subsequent proteolytic enzymatic processing releases these hormones in their bioactive state.29

In the paraneoplastic ACTH syndrome in which there is biosynthesis of ACTH by an extrapituitary tumor (see Chap. 213), much of the hormone that is detectable in the serum is of high molecular mass, incompletely processed bioinactive material (see Chaps. 16 and 73)

Alterations of transporting molecules

Many hormones are transported in the blood in association with protein carrier molecules. These substances facilitate transport and may provide a means of temporary storage of the hormone, protecting it from degradation or retarding its clearance.

Sex hormone binding globulin (see Chap. 98) progressively decreases in concentration from infancy to prepuberty, gradually increasing the amount of unbound testosterone and estradiol; this augments the free, tissue-available sex hormones prior to puberty.30 In familial dysalbuminemic hyperthyroxinemia, a variant albumin possesses a high affinity for thyroxine; as a result, these euthyroid persons have a spuriously high total serum thyroxine.31

Endogenous antihormones

Circulating antihormones antagonize hormone action.32 These substances, which differ slightly in structure from the hormones they antagonize, bind to the appropriate hormonal receptors but lack some or all bioactivity.

Some men with idiopathic azoospermia or oligospermia may have relatively inactive folliclestimulating hormone isoforms.33

Antibodies to hormones or to their receptors

Although not present normally, antibodies to endogenous hormones may develop. Antibodies also may develop to a hormone receptor.38

Antiinsulin antibodies are found in the blood of patients with previously untreated type 1 diabetes.34 In first-degree relatives of type I diabetics, the presence of such antibodies may be a predictive marker for the disease.35 Antiinsulin receptor antibodies may produce hypoglycemia through their continuous receptor stimulatory activity.36 Autoantibodies to the thyrotropin receptor of the thyroid follicular cell appear in Graves disease (see Chap. 41) and may cause the hyperthyroidism.37

hormone (MSH) is not a functional hormone, but it comprises mino acid sequences within the proopiomelanocortin (POMC) molecule: a-MSH within the adrenocorticotropic hormone (ACTH) moiety, /3-MSH within 5-lipotropin, and 5-MSH within the N-terminal fragment of POMC (see Chap. 16).

There are numerous peptide hormones that, because of their effects on DNA synthesis, cell growth, and cell proliferation, have been called growth factors and cytokines (see Chap. 169). These substances, which act locally and at a distance, often do not have the sharply delimited target cell selectivity attributed to

Ch. 1: Endocrinology and the Endocrine Patient

5

TABLE 1-1 (continued) Modulation

Explanation_Examples

Receptor or postreceptor mediation of hormone action

Hormones reversibly bind to specific high-affinity protein receptors, leading to intracellular events that culminate in the appropriate cellular response (see Chaps. 3, 32, and 71). Altered receptor function or altered transduction (i.e., the biochemical events beyond receptor binding) plays a role in the pathogenesis of several endocrine disorders. Some of these defects are the result of antibodies to receptors (as above) and others result from heritable or acquired (e.g., druginduced) defects in the receptor or its subsequent transduction. These congenital or acquired conditions may be called target cell resistance disorders.

Steroid hormone resistance: vitamin D-dependent rickets type 2 (see Chaps. 62 and 69),39 primary glucocorticoid resistance,40 pseudohypoaldosteronism,41 androgen resistance (see Chap. 93).42 Thyroid hormone resistance: pituitary or generalized resistance to thyroid due to a receptor abnormality (see Chap. 32). Peptide hormone resistance: resistant ovary syndrome due to decreased responsivity to gonadotropins (see Chap. 93),43,44 type A syndromes of insulin resistance and acanthosis nigricans (see Chap. 140),45 congenital nephrogenic diabetes insipidus due to resistance to vasopressin.46,47

Hormone inactivation and clearance

A hormone must be inactivated or removed from its target site so that its effect may terminate. Depending on the hormone, various mechanisms for such termination include hydrolysis by degradative enzymes, oxidation, reduction, aromatization, deiodination, conjugation with glucuronide, and other methods.48-52 Depending on the hormone, various tissues or organs are involved in their degradation or their clearance from the circulation or from the body (e.g., liver, kidney, muscle,

Ineffective hepatic degradation of endogenous estrogens may result in gynecomastia (see Chap. 120). Renal disease may result in poor degradation of the exogenous insulin administered to a type I diabetic, resulting in hypoglycemia. A deficiency of the 11/3-hydroxysteroid dehydrogenase enzyme results in poor clearance of cortisol and a syndrome of mineralocorticoid excess (see Chap. 78).

lung).

them when they first were discovered. Their terminology also is confusing and often misleading. Aside from occasional readjustments of hormonal nomen¬ clature, there appears to be no facile solution to the quandary of terminology, other than to be aware of the pitfalls into which the terms may lead us.

ENDOCRINE SYSTEM INTERACTION WITH ALL BODY SYSTEMS Although it is convenient to speak in terms of the cardiovas¬ cular, respiratory, gastrointestinal, and nervous systems, the en¬ docrine system anatomically and functionally overlaps with all body systems (see Part X). There is an extensive overlap between the endocrine system and the nervous system (see Chaps. 171 and 194). Hormonal peptides are synthesized in the cell bodies of neurons, are transported along axons to nerve terminals, and are released at the nerve endings. Within these neurons, they coexist with classic neurotransmitters and often are co-released with them. These substances play a role in neuromodulation or neurosecretion by means of the extracellular fluid. The nerves in which peptide hormones appear to play a role in the transmission of information are called peptidergic nerves.17 It is the ample sim¬ ilarity of ultrastructure, histochemistry, and hormonal contents of nerve cells and of many peptide-secreting endocrine cells that has led to the concept of the diffuse neuroendocrine system.

GENETICS AND ENDOCRINOLOGY The rapid application of new discoveries and new tech¬ niques in genetics has revolutionized medicine, including the field of endocrinology. DNA probes have been targeted to se¬ lected genes, and the chromosomal locations of many hormones and their receptors have been determined. An extensive map of the human genome is gradually emerging.18 This approach has led to new knowledge about hormone biosynthesis and has pro¬

vided important information concerning species differences and evolution. The elucidation of the chromosomal loci for genes controlling the biosynthesis of hormone receptors should pro¬ vide insights into the physiologic effects of hormones. Clinically, these techniques have potential significance as a diagnostic aid for afflicted patients, a means of identifying asymptomatic het¬ erozygotes, and a method for identification of unborn subjects at risk (i.e., prenatal diagnosis; see Chap. 226). Delineation of processes of genetic expression is revealing the mechanisms of hormonal disease.

NORMAL AND ABNORMAL EXPRESSION OR MODULATION OF THE HORMONAL MESSAGE AND ITS METABOLIC EFFECT A sophisticated and faultless machinery is required for ap¬ propriate hormonal expression. The hormonal messenger is sub¬ ject to modifications that may occur anywhere from its initial syn¬ thesis to its final arrival at its target site. Subsequently, the expression of the message at this site (i.e., its action) may also be modified (see Chap. 3). The modulations or alterations of the hormonal message or its final action may be physiologic or patho¬ logic. Table 1-1 summarizes some of the normal or abnormal modulations of a hormone message and its subsequent metabolic effect. On a physiologic level, the first steps in the genetic ordering of hormonal synthesis, the subsequent posttranslational process¬ ing of the hormone, the postsecretory extracellular transport, the receptor mediation of the hormone and subsequent transduction, and the inactivation and clearance of the hormone all contribute to expressing, diversifying, focalizing, and specifying the hormonal message and its ultimate action. On a pathologic level, all of these steps are subject to malfunction, causing endocrine disease. Our increased knowledge of endocrine systems has made it necessary to rethink many traditional concepts. To dispe’ some common misconceptions, it may be worthwhile to list several "nots" of endocrinology (Table 1-2).

6

PART I: GENERAL PRINCIPLES OF ENDOCRINOLOGY

TABLE 1-2 Several “Nots” of Modern Endocrinology 1. Endocrinology is not only the study of internal secretions by ductless glands. It also deals with the secretions of groups of cells, of individual cells, and of the exocrine glands. 2. The secretion of a gland is not unihormonal. There is no gland and probably no hormone-secreting cell that secretes only one active substance. 3. Most hormones do not have a single source. With very few exceptions, hormones are produced by more than one locale in the body and by more than one cell type. 4. In view of the extensive tissue distribution of most hormones, with some exceptions, the extirpation of any single gland or tissue that produces large amounts of a specific hormone usually does not remove that hormone from the body. 5. A hormone is not a substance that acts only at a distal site in the body. Its action often is within the immediate environs, and sometimes it acts on the very cell that secretes the hormone. 6. The term endocrine should not be used to connote a means of transport (i.e., the blood). A hormone is not only blood borne. It also may be borne by extracellular fluid, in lymph, across synapses, or in external secretions, and it may be carried in a functioning state within the confines of the cell itself. 7. A hormone does not in itself exert a specific action. It depends on arriving and interacting with an appropriate receptor that commences the transduction of the hormone message into an action. 8. The receptor-mediated actions of most hormones are not stereotyped. They often differ according to the site-specific characteristics of the receptors and their function at that time. 9. The name of a hormone does not necessarily indicate its exclusive site of production or its predominant physiologic action. 10. The endocrine system is not under the control of a separate and independent nervous system. Instead, the nervous and endocrine systems overlap on both a biochemical and a physiologic level. 11. The effects of hormones are not independent of their concentrations. They vary according to the quantity present at the site of action; an excess may cause effects entirely different from a physiologically sufficient amount. 12. The effects of hormones are not independent of the age of the individual. They vary with the developmental stage of an individual and with his or her age.

of diabetes, the health care expenditure is staggering. Patients with diabetes comprised almost 5% of the U.S. population in 1992 and accounted for 105 billion dollars in health care expen¬ ditures, which amounts to almost 15% of the total spent on health care.55 One of seven U.S. health care dollars was spent on this disease.

FACTORS THAT INFLUENCE TEST RESULTS In clinical medicine, hormonal concentrations usually are as¬ certained from two of the most easily obtained sources: blood and urine. The diagnosis of an endocrinopathy often depends on the demonstration of increased or decreased levels of these blood or urine constituents. However, several factors must be kept in mind when attempting to interpret a result that appears to be abnormal. These may include age, gender, time of day, exercise, posture, emotional state, hepatic and renal status, presence of other illness, and concomitant drug therapy (see Chaps. 224 and 225). RELIABILITY OF THE LABORATORY DETERMINATION

The practice of clinical endocrinology far from a large medi¬ cal center was previously hindered by the difficulty in obtaining blood and urine tests essential for appropriate diagnosis and follow-up care. However, accurate and rapid analyses now are provided by commercial laboratories. Nevertheless, wherever performed, some tests are unreliable because of methodologic difficulties. Other tests may be difficult to interpret because of a particular susceptibility to alteration by physiologic or pharma¬ cologic factors (e.g., plasma catecholamines; see Chap. 83). Al¬ though many tests are sensitive and specific, they all have innate interassay and intraassay variations that may be particularly mis¬ leading when a given value is close to the clinical “medical deci¬ sion point" (see Chap. 225). DETERMINING ABNORMAL TEST RESULTS

THE ENDOCRINE PATIENT FREQUENCY OF ENDOCRINE DISORDERS In a survey of the subspecialty problems seen by endocrinol¬ ogists, the six most common, in order of frequency, were found to be diabetes mellitus, thyrotoxicosis, hypothyroidism, nontoxic nodular goiter, diseases of the pituitary gland, and diseases of the adrenal gland.53 Some conditions seen by endocrinologists are infrequent or rare (e.g., congenital adrenal hyperplasia, pseudo¬ hypoparathyroidism), others are relatively common (e.g.. Graves disease, Hashimoto thyroiditis), and some are among the most prevalent diseases in general practice (e.g., diabetes mellitus, obesity, hyperlipoproteinemia, osteoporosis, Paget disease). In one study, the third most common medical problem encountered by general practitioners was diabetes mellitus, and the tenth most frequent problem was obesity.53 Of the total deaths in the United States (i.e., both sexes, all races, and all ages combined), diabetes mellitus is the seventh most common cause. The most common cause of death (i.e., heart disease) and the third most common (i.e., cerebrovascular acci¬ dents) are greatly influenced by metabolic conditions such as di¬ abetes mellitus and hyperlipemia.54

COST OF ENDOCRINE DISORDERS In considering the frequency and morbidity of endocrine diseases such as osteoporosis, obesity, hypothyroidism, and hyperihvroidism and the grave consequences of other endocrine disorders such as Cushing syndrome and Addison disease, it is apparent that the expense to society is considerable. In the case

Not uncommonly, the intellectual or commercial enthusi¬ asm engendered by a new diagnostic procedure of presumed im¬ portance is found to be unjustified, because the “test" was based on an invalid premise, because of a paucity of ill patients studied, because of insufficient normative data to establish reference val¬ ues, or because subsequent studies are not confirmatory (see Chaps. 225 and 227). The increased sophistication of medical testing has made the physician and the patient aware of the presence of "abnormali¬ ties" that may be harmless: physiologic deviations from that which is most common, or pathologic entities that commonly re¬ main asymptomatic. Such findings may cause considerable worry, lead to the expense and risk of further diagnostic proce¬ dures, and even cause needless therapeutic intervention. Some “abnormalities" are the result of methods of imaging. For example, sonography of the thyroid may demonstrate the presence of small nodules within the thyroid gland of a person without any oalpable abnormality of that region of the gland; most such microlesions are benign or behave as if they were. Another “abnormality" revealed by imaging is the occa¬ sional heterogeneous appearance of a normal pituitary gland on a computed tomography (CT) examination. Intermingled CTlucent and CT-dense areas are seen on the scan, and such nonhomogeneous areas may be confused with a microadenoma.56,57 The increasing use of magnetic resonance imaging (MRI) of the brain may reveal a bona fide asymptomatic microadenoma of the pituitary gland, but extensive endocrine workup often reveals many such lesions to be nonfunctional. They occur in as much as 10% of the normal population.58 Rathke cleft cysts of the anterior sella turcica or the anterior suprasellar cistern often are seen by MRI.59 Although an occa¬ sional patient may have a large and symptomatic lesion, most

Ch. 1: Endocrinology and the Endocrine Patient of these lesions are small and asymptomatic. During MRI or CT examination of the brain, the examiner often incidentally en¬ counters a “primary empty sella," an extension of the subarach¬ noid space into the sella turcica with a resultant flattening of the pituitary gland in a patient without any pituitary lesion or any prior surgery of that region (see Chap. 13). Although some of these patients may be symptomatic, most have no associated symptoms or hormonal deficit. Another, albeit rare, lesion of the pituitary region seen on MRI is a sellar spine. This asymptomatic anatomic variant is an osseous spine arising in the midline from the dorsum sella that protrudes into the pituitary fossa; it may be an ossified remnant of the cephalic tip of the notochord.60 MRI or CT scanning of the abdomen may reveal the pres¬ ence of harmless morphologic variations of the adrenal gland (i.e., incidentalomas) that sometimes leads to unnecessary surgery.61

RISKS OF ENDOCRINE TESTING Endocrine testing is not always benign. Many procedures can cause mild to marked side effects.62-65 Other diagnostic ma¬ neuvers, particularly angiography, may result in severe illness.66 The expected benefit of any procedure that is contemplated for a patient clearly should be greater than the risk.

COST AND PRACTICABILITY OF ENDOCRINE TESTING In addition to being aware of the many factors that influence hormonal values, the limitations of laboratory determinations, and the potential risks of some of these procedures, the endocri¬ nologist must be aware of their expense, particularly because medical costs have increased at an annual rate that is almost twice the rate of overall inflation during the last several years. A hypertensive patient with hypokalemia, who is taking nei¬ ther diuretics nor laxatives, should undergo studies of the reninangiotensin-aldosterone system along with appropriate pharma¬ cologic or dietary manipulations of sodium balance (see Chap. 78). But what should be done with the hypertensive patient who is normokalemic? Occasionally, such a person may have an aldosteronoma.67 Should such normokalemic patients be studied? Similarly, should the approximately 25 million hypertensive pa¬ tients in the United States undergo urinary collections for de¬ terminations of catecholamine metabolites to find the rare pa¬ tient with pheochromocytoma? In the context of the individual physician-patient relationship, the answers to such questions may not be difficult, but they become more controversial when placed within the framework of fiscal guidelines.

CONCLUSION The complexity of the endocrine system presents a profound intellectual challenge. The macrosystem of endocrine glands se¬ cretes its hormones under the influence of other glandular-based releasing factors or neural influences or both. The very act of se¬ cretion alters subsequent secretion by means of feedback controls (see Chap. 4). Superimposed on this already complex arrange¬ ment, the microsystem of dispersed, somewhat independent, but overlapping units throughout the body, as well as the continuous modulation of the receptors for the secreted hormones, allow general or focal actions that are coordinated with other body functions, tempered to the occasion, and appropriate to the needs of the individual. It is not surprising that such a complex system may go awry and that a dysfunction may have a considerable impact on the patient. Because endocrinology and metabolism are broad subjects that incorporate much, if not all, of normal body functions and disease states, they defy easy categorization. However, these enormous complexities, rather than deterring the clinician, re¬ searcher, or student, should provide a stimulus to probe deeper

7

into areas difficult to understand and should hasten the eventual application of new developments to patient care.

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8

PART I: GENERAL PRINCIPLES OF ENDOCRINOLOGY

cretion of FSH antagonists by women treated with a GnRH analog. Science 1988;239:72. 33. Wang C, Dahl KD, Leung A, et al. Serum bioactive follicle-stimulating hormone in men with idiopathic azoospermia and oligospermia. J Clin Endocrinol Metab 1987;65:629. 34. Palmer JP, Asplin CM, Clemons P, et al. Insulin antibodies in insulindependent diabetics before insulin treatment. Science 1983; 222:1337. 35. Gorus FK, Vandevalle CL, Dorchy H, et al: Influence of age on the asso¬ ciations among insulin autoantibodies, islet cell antibodies, and HLA DAQ1 0301DQBI0302 in siblings of patients with type 1 (insulin-dependent) diabetes mellitus. Belgian Diabetes Registry. J Clin Endocrinol Metab 1994; 78:1172. 36. Di Paolo S, Georgino R. Insulin resistance and hypoglycemia in a patient with systemic lupus erythematosus: description of antiinsulin receptor antibodies that enhance insulin binding and inhibit insulin action. J Clin Endocrinol Metab 1991; 73:650. 37. Chiovato L, Santini F, Vitti P, et al. Appearance of thyroid stimulating antibody and Graves disease after radioiodine therapy for toxic nodular goitre. Clin Endocrinol 1994; 40:803. 38. Bach JF. Antireceptor or antihormone autoimmunity and its relationship with the idiotype network. Adv Nephrol 1987; 16:251. 39. Liberman UA, Eil C, Marx SJ. Clinical features of hereditary resistance to 1,25-dihydroxyvitamin D (hereditary hypocalcemic vitamin D resistant rickets type II). Adv Exp Med Biol 1986; 196:391. 40. Chrousos GP, Detera-Wadleigh SD, Karl M. Syndromes of glucocorticoid resistance. Ann Intern Med 1993; 119:1113. 41. Zennoro MC, Borensztein P, Seubrier F, et al. The enigma of pseudohypoaldosteronism. Steroids 1994;59:96. 42. Zoppi S, Wilson CM, Harbison MD, et al. Complete testicular feminiza¬ tion caused by an amino-terminal truncation of the androgen receptor with down¬ stream initiation. J Clin Invest 1993;91:1105. 43. Talbert LM, Raj MIT, Hammond MG, Greer T. Endocrine and immuno¬ logic ovary syndrome. Fertil Steril 1984;42:7411. 44. Fraser IS, Russell P, Greco S, Robertson DM. Resistant ovary syndrome and premature ovarian failure in young women with galactosemia. Clin Reprod Fertil 1986;4:133. 45. Suzuki Y, Hashimoto N, Shimada F, et al. Defects in insulin binding and receptor kinase in cells from a human with type A insulin resistance and from her family. Diabetologia 1991; 34:. 46. Bichet DG, Razi M, Lonergan M, et al. Hemodynamic and coagulation responses to 1-desamino (8-D-arginine) vasopressin in patients with congenital nephrogenic diabetes insipidus. N Engl ] Med 1988; 318:881. 47. Singer I, Forrest JN Jr. Drug-induced states of nephrogenic diabetes in¬ sipidus. Kidney Int 1976; 10:82. 48. Visser TJ, Kaptein E, Terpstra OT, Krenning EP. Deiodination of thyroid hormone by human liver. J Clin Endocrinol Metab 1988;67:17. 49. Bunnett NW. Postsecretory metabolism of peptides. Am Rev Respir Dis 1987; 136:S27. 50. Roupas P, Herington AC. Receptor-mediated endocytosis and degradative processing of growth hormone by rat adipocytes in primary culture. Endocri¬ nology 1987; 120:2158. 51. Benzi L, Ceechetti P, Ciccarone A, et al. Insulin degradation in vitro and in vivo: a comparative study in men. Evidence that immunoprecipitable, partially rebindable degradation products are released from cells and circulate in blood. Dia¬ betes 1994; 43:297. 52. Yamaguchi T, Fukase M, Kido H, et al. Meprin is predominantly involved in parathyroid hormone degradation by the microvillar membranes of rat kidney. Life Sci 1994;54:381. 53. Mendenhall RC. Medical practice in the United States. Princeton, NJ: Robert Wood Johnson Foundation, 1981. 54. National Center for Health Statistics. Monthly Vital Statistics Report 1985; 33:13. 55. Rubin RJ, Altman WM, Mendelson BN. Health care expenditures for peo¬ ple with diabetes mellitus 1992. J Clin Endocrinol Metab 1994; 78:809A. 56. Roppolo HMN, Latchaw RE, Meyer JD, Curtin HD. Normal pituitary gland: 1. Macroscopic anatomy—CT correlation. Am J Neuroradiol 1983; 4:927. 57. Tihansky DP, Crossen J, Markowitz H. Pseudotumor artifact of the dor¬ sum sella in CT scanning. Comput Radiol 1987; 11:241. 58. Hall WA, Luciano MG, Doppman JL, et al. Pituitary magnetic resonance imaging in normal human volunteers: occult adenomas in the general population. Ann Intern Med 1994; 120:817. 59. Kucharczyk W, Peck WW, Kelly WM, et al. Rathke cleft cysts: CT, MR imaging, and pathologic features. Radiology 1987,165:491. 60. Fujisawa I, Asato R, Togashi K, et al. MR imaging of the sellar spine. J Comput Assist Tomogr 1988; 12:644. 61. The adrenal incidentaloma. A pediatric perspective. Am J Dis Child 1993; 147:1274. 62. Ratzmann GW, Zollner H. Hypomagnesemia and hypokalemia in the in¬ sulin hypoglycemia test. Z Gesamte Inn Med 1985; 40:567. 63. Read RC, Doherty JE. Cardiovascular effects of induced insulin hypogly¬ cemia in man during the Hollander test. Am J Surg 1972; 104:573. 64. Sobel RJ, Ariad S. Adverse cardiovascular responses to thyrotropin¬ releasing hormone (200 micrograms) in cardiac patients. Isr J Med Sci 1987; 23:1107. . 65. Boice JD Jr. The danger of x-rays—real or apparent. N Engl J Med I986;315:828. 66. Porter GA. Contrast medium-associated nephropathy. Recognition and manage'nent. Invest Radiol 1993;28(suppl 4):S11. 67. Bravo EL, Tarazi RC, Dustan HP, et al. The changing clinical spectrum of primary aldosteronism. AmJ Med 1983; 74:641.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

2_

BIOSYNTHESIS AND SECRETION OF PEPTIDE HORMONES WILLIAM W. CHIN

In the traditional endocrine system, hormones are factors produced by groups of cells clustered in specific tissues, com¬ monly known as glands, and are released into the general circu¬ lation to affect the function of distant target cells. Because hor¬ mones are responsible for the control of a complex metabolic milieu, they, along with the hormone-producing and target cells, participate in intricate regulatory networks (see Chaps. 3 and 4). An important feature is positive regulation of hormone syn¬ thesis and secretion. For example, gonadotropin-releasing hor¬ mone (GnRH) from the hypothalamus stimulates production and release of the pituitary gonadotropins. Another common theme is regulation by negative feedback, by which a trophic hormone stimulates the production and secretion of a second hormone in a target cell that acts on the original gland to decrease secretion of the trophic hormone. For example, thyroid-stimulating hormone (TSH) is produced and secreted from the thyrotrope in the ante¬ rior pituitary gland. It stimulates the thyroid gland to synthesize and secrete thyroid hormones, which act on the thyrotrope to decrease further production and release of TSH. Thus, hormones may regulate the biosynthesis and release of other hormones. Moreover, hormones may control other cellular activities by de¬ termining the amount and activity of other proteins. This regula¬ tion occurs largely at the gene transcriptional level, although some regulation occurs at posttranscriptional, translational, and posttranslational levels. In addition to the broader distribution of the endocrine sys¬ tem, factors secreted from a given cell can influence cellular ac¬ tivities in adjacent or neighboring cells (i.e„ paracrine effects) or within itself (i.e., autocrine effects; see Chap. 1). Intracellular communication effected by hormonal factors is critical for the integrated function of an organism. The pivotal and ubiquitous nature of hormones in these tasks make understanding their syn¬ thesis and release essential. This chapter describes the events that occur in the biosyn¬ thesis of polypeptide hormones in hormone-secretory cells, from the gene to the final, bioactive protein hormone, including the intracellular structures involved in this process. Insights about the regulation of the hormone-producing cell derived from stud¬ ies involving recombinant DNA technology and molecular and cellular biology are highlighted.

OVERVIEW OF PEPTIDE HORMONE SYNTHESIS AND SECRETION Proteins are important as the backbones of polypeptide hor¬ mones and as integral components of enzymes that participate in the biosynthetic pathways of steroid and thyroid hormones and those that participate in intracellular synthetic and degradative actions and in energy generation. They are critical membrane, receptor, and cytoskeletal molecules, and an appreciation of the pathways for polypeptide synthesis and their associated cellular structures is important. This section describes the general path¬ ways of polypeptide synthesis, with an emphasis on the infor¬ mational flow from the gene to the final functional protein and

9

Ch. 2: Biosynthesis and Secretion of Peptide Hormones the cell structures involved in each of the steps in this highway of biochemical events.1-3 The production of a functional protein hormone requires numerous steps, each one involving modifi¬ cations or processing of precursor molecules. The eukaryotic cell consists of two major compartments, the nucleus and cytoplasm (Figs. 2-1 and 2-2), which are delimited by plasma membranes that are topologically contiguous with one another (see Fig. 2-2). The nucleus is surrounded by a nuclear envelope consisting of an outer and inner membrane encom¬ passing a cisternal space.4 The nuclear envelope is perforated by nuclear pore complexes that permit communication of the nu¬ cleoplasm with the cytoplasm. The nucleus contains much of the cellular nucleic acid or genetic material in the form of genes, which harbor the informa¬ tion necessary for the initial production of precursor RNAs and hence functional proteins. The cytoplasm contains multiple or¬ ganelles that are involved in the synthesis of proteins and their processing. These events occur through an assembly-line ar¬ rangement, by which the initial protein precursors are altered by changes in their primary structures and by glycosylation and other chemical modifications. These organelles include the endo¬ plasmic reticulum (ER), where initial protein synthesis occurs, and a complex membranous structure known as the Golgi stack, where further protein processing and posttranslational modifi¬ cations, sorting, and translocation occur. The secretory cell is differentiated from other cell types by the presence of secretory granules that emerge from the Golgi stack. These granules are specialized, membrane bound organ¬ elles that contain polypeptide hormones in high concentration that may be stored for long periods. Stimulus-secretion coupling allows release of the hormone from the granule on physiologic demand. The informational flow from the gene to the final protein is shown in Figure 2-3. Each protein produced by a cell is encoded

FIGURE 2-2. Diagram of the secretory cell. The secretory cell contains two major compartments: nucleus and cytoplasm. The nucleus is delim¬ ited by a nucleoplasmic membrane that is perforated by nuclear pore complexes. The nuclear membrane is contiguous with the endoplasmic reticulum (ER). Transport of polypeptides from the ER to the next organ¬ elle, the Golgi stack, is accomplished by way of transport vesicles or tran¬ sitional elements. Polypeptide hormones exit from the Golgi stack by for¬ mation of secretory vesicles and granules. The stored polypeptide hormone in the secretory granule is released in the process emiocytosis or exocytosis on receipt of the appropriate extracellular stimuli. The shaded areas represent topologically extracellular spaces. The lumen of the ER and Golgi are contiguous with the extracellular space.

POLYPEPTIDE HORMONE GENE

£V

TRANSCRIPTION




300

c

O E

w

* 200

100

Hypopituitary

Controls

Hypopituitary

Controls

FIGURE 14-5. Insulin-like growth factor I (SmC, somatomedin C) con¬ centrations in fasting serum samples are shown for normal and hypopi¬ tuitary adults and children. Note particularly the overlap of values be¬ tween normal children and those with growth hormone deficiency.

134

PART II: THE ENDOCRINE BRAIN AND PITUITARY GLAND

Nearly one third of children whose size is outside the 95% confidence limits of normal have a growth pattern that is a varia¬ tion of normal. These children do not have pathologic problems relevant to GH and IGF-I. This should be suspected when chil¬ dren have more prominent disturbances of height-age than bone-age, and when the weight is inappropriate for the heightage. Various multisystem disorders also can cause short stature; these can be related to chromosomal abnormalities, endocrine disease of nonpituitary origin, and connective tissue aberrations. Problems in growth not only may relate to circulating con¬ centrations of GH and IGF-I, but also may result from defects of GHRH, pituitary responses to GHRH, or tissue responses to IGFI. For example, along with an absence of GH receptors (Laron dwarfism; see Chap. 20),53 receptor and postreceptor defects that simulate GH deficiency are now being reported for IGF-I. The occurrence of IGF-I receptor deficiency has been described, and there are reports of short stature, despite normal or increased se¬ rum concentrations of GH and IGF-I, and despite normal binding of IGF-I to cell receptors. When fibroblasts, isolated from some patients, are exposed to high concentrations of IGF-I, the intra¬ cellular transport of amino acids may not occur in a normal man¬ ner.54-60 Although this initially suggested a postreceptor defect in responsiveness to IGF-I,54'55 it has been shown that such pa¬ tients produce an abnormal binding protein, which interferes with binding of IGF-I to its appropriate receptor61 (Table 14-2, item IIC). Table 14-2 presents an overview of short stature, with an emphasis on the nature of the IGF-I deficiency state. A large, national cooperative study has shown that GH therapy is effi¬ cacious in patients with GH deficiency (Fig. 14-6), idiopathic short stature, and Turner syndrome. However, GH is much less effective in corticosteroid-treated patients and is useless in pa¬ tients with Laron dwarfism.62

HYPERSECRETION OF GROWTH HORMONE (ACROMEGALY) PATHOPHYSIOLOGY

Acromegaly is a disease of insidious onset that usually is not recognized until the progressive overgrowth of connective tissue and bone has caused striking changes of appearance. Although the initiating cause of hypersecretion of GH in acromegaly was disputed for years, it now has been noted that many GHsecreting tumors contain a mutant form of the chain of Gs protein, which is a stimulatory regulator of adenylate cyclase. Gproteins transduce signals from hormone receptors and regulate effector enzymes and ion channels, essentially functioning to amplify the hormonal signal. Mutations of the Gs protein in the somatotrope bypass the need for GHRH for GH stimulation. In one study, 10 of 25 pituitary adenomas associated with acromegaly (40%) contained this mutant. In general, patients with such mutations have clinical characteristics similar to those without the mutant Gs protein.5 Other GH-secreting tumors may result from the deletion of a tumor repressor gene on chromo¬ some ll.62 Accurate identification of the cells causing the pituitary ade¬ noma can be made only by morphologic techniques, and these have become more sophisticated. Most tumors produce only GH. However, immunohistochemical investigation now indicates that, occasionally, tumors causing acromegaly may be capable of producing two or more hormones; such tumors can be divided into monomorphous and plurimorphous adenomas. The former consist of one cell type with two or more hormones present in the same cell type, whereas the latter consist of two or more cell types, each with separate hormones. The most common variant produces GH and prolactin, but TSH also may be produced. The pattern of discharge from such tumors may vary widely, but this

TABLE 14-2 Insulin-Like Growth Factor I (IGF-I) Deficiency States Associated With Short Stature* Inheritance

Growth Hormone (GH) Levels

Characteristics

I PRIMARY DEFICIENCY IGF-I (THEORETIC) II SECONDARY DEFICIENCY IGF-I A. Hypothalamic-Pituitary 1. Isolated GH Deficiency (IGHD)26,57

AR, AD; sex-linked

4.5 mg/dL Carpal tunnel syndrome Hypertension (blood pressure > 150/95 mmHg) Fasting plasma glucose >110 mg/dL Testosterone (males) < 300 ng/mL Prolactin > 25 ng/mL 8 am cortisol < 8.0 ^g/dL

% 100 96 91 91 88 72 68 68 58 48 44 37 30 23 16 0.4

From Clemmons DR, Van Wyk JJ, Ridgway EC, et al. Evaluation of acromegaly by radioimmunoassay of somatomedin-C. N Engl J Med 1979;301:1138.

may be surprisingly difficult. Often, the changes in appearance occur slowly, and sometimes only an examination of old pho¬ tographs allows one to suspect the disease and determine its time of onset. A delay in diagnosis is unfortunate because the more prominent connective tissue and bone changes are irreversible. However, a delay in diagnosis has other critical implications for the surgical and medical treatment of these patients. The success of surgery, particularly by the transsphenoidal approach, closely relates to the size of the tumor producing the GH. The larger is the adenoma, the greater is the chance for expansion to adjacent structures; this most commonly involves an erosion inferiorly to the sphenoid sinus, or superiorly, where it stretches and finally destroys the dorsum sella, often with compression of the overly¬ ing optic nerves or chiasm (see Chaps. 13 and 21). Pituitary tumors usually do not have a well-defined capsule; often, over a protracted period, such tumors form pockets of tis¬ sue in the inner lining of the fossa. This behavior of pituitary tumors is extremely common in acromegaly, and almost certainly is the major reason for surgical failure, further emphasizing the need for early diagnosis. CLINICAL AND LABORATORY MANIFESTATIONS

The major clinical evidence of acromegaly usually relates to the hormonal effects of GH and IGF-I, and occasionally, locally, to the size of the tumor. Table 14-3 tabulates the major clinical and laboratory findings recorded in a large series of patients with acromegaly.63 The clinical symptoms of acromegaly can be con-

136

PART II: THE ENDOCRINE BRAIN AND PITUITARY GLAND

FIGURE 14-7. A 64-year-old man with acromegaly. Note the prominent, "lantern-like" jaw, the large zyg°matic arches and supraorbital ridges, and the sloping "beetle brow." The bony overgrowth often results in a comparative hollowing of the temporal region. The nose and ears are enlarged, and the latter may be calcified. The skin folds are exaggerated, the skin is tough and oily, and there is enlargement of the sebaceous glands and pores.

sidered in three categories: (1) symptoms caused by local effects of the pituitary tumor, (2) metabolic results of excessive amounts of GH, and (3) physical changes related to excessive amounts of GH. Because of the growth and location of the tumor mass, head¬ aches, visual abnormalities (most commonly a bitemporal hemi¬ anopsia), hypopituitarism (rare), and, occasionally, galactorrhea are encountered. Headaches may increase in severity and be¬ come almost continuous, and then suddenly cease. The pain of

the headaches is caused by stretching of the dura, and the cessa¬ tion of headaches is thought to result from tearing of the dura overlying the sella, thus relieving tension. Because GH inhibits the peripheral action of insulin on glu¬ cose uptake and also increases hepatic glucose production, it is not surprising that glucose intolerance is common in acromegaly, although frank diabetes (serum glucose value >140 mg/dL) oc¬ curs in less than 15% of patients (see Chap. 135). A more useful

FIGURE 14-8. Progressive acromegalic changes in a 58-year-old man. Old photographs are useful to evaluate clinically whether a diagnosis of acromegaly should be considered or to document progression of the disease.

Ch. 14: Growth Hormone and Its Disorders

137

FIGURE 14-9. A, Lateral skull radiograph of a patient with acromegaly. Note the large ramus of the mandible, the eroded sella turcica (arrowhead), and the large frontal sinus (arrow). B, Hands of an acromegalic man. Note the thickened soft tissue, the dense bones, and the large sesamoid bones (black arrows). Note also the arrowhead tufting of the distal phalanges (white arrows).

finding in acromegaly than glucose intolerance is the presence of extreme hyperinsulinism with only modest or no deterioration of glucose tolerance. During the diagnostic evaluation of this condi¬ tion, the basal concentration of insulin and the concentration 1 hour after glucose ingestion frequently are measured. The find¬ ing of grossly elevated insulin values (with basal levels often ex¬ ceeding 100 pU/mL) accompanied by nonsuppressible GH levels is virtually always indicative of acromegaly. This is seen neither in obesity nor in Cushing disease. The connective tissue abnormalities listed in Table 14-3 are usually the most obvious. These include hypertrophy of the tongue and skin, the latter usually being coarse and not readily movable; enlargement of extremities; classic changes of the con¬ formation of the skull; prognathism; and thickening of soft tis¬ sues. The patients may have noted an increase in their hat, shirt collar, glove, or shoe size, and increasingly tight fit of a ring. The teeth may be widely separated (see Chap. 211). Carpal tunnel

syndrome may occur early in the development of acromegaly. At the Mayo Clinic, 35 of 100 patients with acromegaly had carpal tunnel syndrome, which in every case disappeared when re¬ mission was obtained.64 GH excess also may cause hyperhidrosis and increased sebaceous secretion. In acromegaly, bony overgrowth of the skull is apparent. The bony ridges become extremely prominent and the calvarium is thickened (Figs. 14-7 through 14-10). Cartilaginous tissues may enlarge, and the vocal cords may thicken, causing a coarse deepening of the voice. The ribs thicken and the cartilage of the costochondral junctions may hypertrophy. Arthropathies result¬ ing from changes in the synovium are common, particularly in the weight-bearing joints (see Chap. 206). The excessive secretion of GH probably is responsible for the major cardiovascular abnormalities of acromegaly.63 Cardiac enlargement commonly occurs in this disease, and there invari¬ ably are gross abnormalities on tests of dynamic cardiac func-

138

PART II: THE ENDOCRINE BRAIN AND PITUITARY GLAND

FIGURE 14-10. Enlarged hands of an elderly man with acromegaly. The fingers are sausage-like in appearance, the skin is thickened, and the veins are prominent. In spite of this man's muscular appearance, he had considerable muscular weakness. There is a large fibroma of the right deltoid region.

tion66 (see Chap. 198). Before effective means of treating acro¬ megaly were available, death resulting from cardiac disease was the usual terminal event, often occurring as early as the fourth decade in patients who had active disease for 20 years or more. GH excess also causes enlargement of many other visceral or¬ gans, including the lungs, liver, brain, and kidneys. Its effect on skeletal muscle results in hypertrophy, commonly accompanied by surprising weakness, and a diminution of fat mass67 (see Chap. 205). There may be an increased incidence of colon carcinoma. In addition, GH can increase the tubular reabsorption of phosphate and, although hyperphosphatemia is common, serum phosphate levels correlate poorly with the level of activity of the GH excess. Urinary calcium and hydroxyproline levels are in¬ creased. GH also may increase the metabolic rate. Few entities can be confused with true acromegaly. Pachy¬ dermoperiostosis (see Chap. 213) and phenytoin-induced facial thickening only superficially resemble the complete picture of ac¬ romegaly. Benign familial prognathism is a more common cause for referral (Fig. 14-11). However, the total absence of other stig¬ mata of acromegaly in this last condition should make this dis¬ tinction readily apparent. Paraneoplastic Secretion of GHRH. On rare occasions, acro¬ megaly may be associated with tumors arising at a site other than the pituitary. A so-called ectopic GHRH syndrome was noted ini¬ tially with bronchial carcinoid tumors, but also has been reported with hypothalamic hamartomas containing GHRH and with pancreatic islet cell adenomas, which may contain high concen¬ trations of this hormone as well.68,69 Such tumors are extremely rare. Attempts to distinguish these last patients on the basis of pituitary histology, GH responses to stimulatory or inhibitory agents, and measurements of serum GHRH have proved unsat¬ isfactory (see Chap. 213). These tumors are rich in somatostatin receptors and occasionally may be visualized with labeled octreotide.68 DIAGNOSTIC TESTING The diagnosis of acromegaly, or the confirmation of this di¬ agnosis, has been greatly improved by the development of im¬

FIGURE 14-11. Patient with benign familial prognathism. Growth hor¬ mone testing was normal.

munoassays for IGF-I. In a large series evaluated at the Massa¬ chusetts General Hospital and at the University of North Carolina at Chapel Hill, 57 patients with acromegaly had serum IGF-I values substantially above normal levels. The mean value of IGF-I in the patients with acromegaly was 10-fold higher than that in normal control patients, and there was virtually no over¬ lap in values.63 The authors' experience is similar: in 16 patients with acromegaly, the lowest value of IGF-I was 3-fold the highest value recorded in nearly 100 control patients. The results of all other studies are consistent with these findings. Occasionally in acromegaly, however, cases are reported with normal plasma immunoreactive GH levels despite clear-cut stigmata of acromeg¬ aly. It appears that alleged large forms of GH in these cases are not GH, but anti-GH receptor antibodies that act to stimulate the GH-receptor and interfere with the GH radioimmunoassay.68 Serum IGF-I values should be determined in all patients sus¬ pected of having acromegaly. If values are significantly higher than normal, these patients should be admitted to the hospital for a more definitive evaluation. This includes (1) repeated mea¬ surement of serum IGF-I, (2) basal determinations of GH for two consecutive mornings, and (3) on the second morning, a 100-g glucose tolerance test with serum samples collected at 60 minutes and 2 hours for GH and insulin assay. High-resolution computed tomographic scanning or magnetic resonance imaging of the pituitary-hypothalamic region also should be performed. The combination of these techniques has proved highly effective, and other previously advocated measurements for the diagnosis of acromegaly, such as the measurement of skin thickness, are prob¬ ably of little value. TREATMENT Three alternative forms of therapy for acromegaly are avail¬ able: (1) selective transsphenoidal adenectomy, (2) high-voltage x-ray therapy, and (3) proton beam treatment. Most centers favor the operative procedure (see Chap. 25). In a large study of 110 patients with acromegaly operated on by the transsphenoidal ap¬ proach, 94 were cured, 20 were improved, and only 6 remained unchanged.70 The rate of recurrence after surgery may approach 20%, but varies widely among centers. This appears to increase with time.

Ch. 14: Growth Hormone and Its Disorders Conventional radiation therapy can be effective, but the slowness of response to treatment as well as the failure to achieve a cure in 25% of cases make this a less satisfactory approach. The progressive disfigurement and other complications may be brought under control only slowly with the latter treatment (see Chap. 24). Proton beam irradiation is not widely available, and the number of patients cured is not established. Several pharma¬ cologic agents, including bromocriptine, suppress GH, but opin¬ ions vary widely on the advisability of their long-term use.70-72 The definition of “cure" of acromegaly after surgery has changed in recent years. Initially, the criterion often used was a postoperative serum GH concentration that decreased after glu¬ cose administration to less than 5 ng/mL. This has been amended to include normalization of the circulating IGF-I level, decrease of the mean 24-hour GH level to 3 ng/mL or less, or disappearance of the paradoxic increase of GH after thyrotropin¬ releasing hormone administration. Using such strict biochemi¬ cal criteria, a cure rate of less than 50% of patients with acro¬ megaly appears common, making additional medical therapy a consideration. The use of octreotide, as well as other long-acting analogues of somatostatin, may prove beneficial in some cases of acromeg¬ aly.73-75 The following four indications for octreotide have been recommended and approved74: (1) for the treatment of patients with active disease, in whom surgery and radiotherapy have been unsuccessful or contraindicated; (2) for the treatment of pa¬ tients with active disease during the period when the clinical effects of radiotherapy have not yet taken place; and (3) as a pri¬ mary treatment in elderly patients with a relatively short life ex¬ pectancy, especially if they have hypertension, congestive heart failure, or diabetes mellitus, or if they are incapacitated by a stroke. In summarizing the advances that have been made in our knowledge of GH during the last several years, three stand out. First, a more complete understanding of the genetic control of the development of pituitary cells and hormones is available, partic¬ ularly the roles of the Pit-1 gene, the tumor suppressor genes, and the G-proteins as amplifiers of gene action. Second, the role of GH-receptors and GHBP derived from these receptors is better appreciated. Finally, the evidence is strong that IGF-I, which me¬ diates many of the actions of GH, is involved with a complex system of carrier proteins that modulate many of its biologic effects on specific tissues.

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Growth hormone release in man revis¬ ited: spontaneous versus stimulus-initiated tides. In: Pecile A, Muller EE, eds. Growth and growth hormone. Amsterdam: Excerpta Medica, 1972:371. 19. Hammer RE, Brinster RL, Rosenfeld MG, et al. Expression of GH-releasing factor in transgenic mice results in increased somatic growth. Nature 1985; 315: 413. 20. Schally AV, Arimura A, Bowers CY, et al. Hypothalamic neurohormones regulating anterior pituitary function. Recent Prog Horm Res 1968; 24:497. 21. Brazeau P, Vale W, Burgus R, et al. Hypothalamic polypeptide that inhib¬ its secretion of immunoreactive growth hormone. Science 1973; 179:77. 22. Koerker DJ, Ruch W, Chideckel E. Somatostatin: hypothalamic inhibitor of the endocrine pancreas. Science 1974; 184:482. 23. Stachura ME. Basal and dibutyryl cyclic AMP stimulated release of newly synthesized and stored GH from perfused rat pituitaries. Endocrinology 1976; 98: 580. 24. Stachura ME. Potassium modification of the somatostatin effect on stim¬ ulated rat growth hormone release. Endocrinology 1981; 108:1027. 25. Stachura ME, Tyler JM. Growth hormone releasing factor-44 specifically for components of somatotroph and lactotroph immediate release pool substruc¬ tures. Endocrinology 1987; 120:1719. 26. Merimee TJ, Rabinowitz D. Isolated human growth hormone deficiency and related disorders. Isr J Med Sci 1973; 9:1599. 27. Abe H, Molitch M, Van Wyk JJ, Underwood LE. Human growth hormone and somatomedin C suppress the spontaneous release of growth hormone in un¬ anesthetized rats. Endocrinology 1983; 113:1319. 28. Miki N, Ono M, Miyoshi H, et al. Hypothalamic growth hormone-releas¬ ing factor (GRF) participates in the negative feedback regulation of growth hormone secretion. Life Sci 1989; 44:469. 29. Masuda A, Shibasaki T, Nakahara M, et al. Effect of glucose on GHreleasing factor mediated GH secretion in man. J Clin Endocrinol Metab 1985; 60: 523. 30. Kitajima N, Chihar K, Abe H, et al. Galanin stimulates GH-releasing fac¬ tor secreting from rat hypothalamic slices in vitro. Life Sci 1990;47:2371. 31. Bowees CY, Momany FA, Reynolds GA, et al. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release GH. Endocrinology 1984,-114:1537. 32. Ellis S, Huble J, Simpson ME. Influence of hypophysectomy and growth hormone on cartilage sulfate metabolism. Proc Soc Exp Biol Med 1953;84:603. 33. Salmon WD Jr, Daughaday WH. A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro. J Lab Clin Med 1957; 49: 825. 34. Salmon WD Jr, Duvall MR. In vitro stimulation of leucine incorporation into muscle and cartilage protein by a serum fraction with SF activity: differentiation of effects from those of growth hormone and insulin. Endocrinology 1970; 87:1168. 35. Drops S, Schuller A, Lindenberg-Kortleve D, et al. Structural aspects of IGFBP family. Growth Regul 1992;2:80. 36. Welbourne TC, Cronin MJ. Growth hormone accelerates tubular acid se¬ cretion. Am J Physiol 1991;261:R1036. 37. Rogers SA, Hammerman MR. GH activates phospholipase C on proximal tubular basolateral membranes from canine kidney. Proc Natl Acad Sci USA 1989:86:6363. 38. Zezulad KM, Green H. The generation of insulin-like growth factor I sen¬ sitive cells by growth hormone. Science 1986,-233:551. 39. Nielson A, Isgaard J, Lindahl A, et al. Regulation by GH of the number of chondrocytes containing IGF I. Science 1986;233:571. 40. Davison BL, Mathews LS, Norstedt G, et al. Expression of growth factor genes in transgenic mice. In: Puett D, ed. Advances in gene technology. Cambridge: Cambridge Univ Press, 1986:78. 41. Laron Z, Anin S, Klinger B. Long term IGF, treatment of children with Laron syndrome. Pediatr Adolesc Endocrinol 1992; 24:226. 42. Merimee TJ, Hail JG, Rimoin DL, et al. Sexual ateliotic dwarfism. J Clin Invest 1969;38:59(A). 43. Guillemin R, Ling N, Esch F, et al. Growth hormone-releasing factor. An update. In: Labrie F, Prouix L, eds. Endocrinology. Amsterdam: Elsevier Science Publishing, 1984:823. 44. Arimura A, Merchenthaler I, Culler MD, Iwasaki K. Distribution and re¬ lease of GRF. In: Labrie F, Prouix L, eds. Endocrinology. Amsterdam: Elsevier Sci¬ ence Publishing, 1984:827. 45. Thorner MO, Evans WS, Vance ML, et al. Clinical studies with growth hormone releasing factor. In: Labrie F, Prouix L, eds. Endocrinology. Amsterdam: Elsevier Science Publishing, 1984:831.

140

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46. Chihara K, Kashio Y, Abe H, et al. Effect of single and repeated admin¬ istration of human GH-releasing factor on plasma GH. J Clin Endocrinol Metab 1985;60:269. 47. Borges JLC, Blizzard RM, Gelato MC, et al. Effects of human pancreatic tumor growth hormone releasing factor on GH and SmC levels in patients with idiopathic growth hormone deficiency. Lancet 1983; 2:119. 48. Rinderknecht E, Humbel RE. The amino acid sequence of human insulin¬ like growth factor I and its structural homology with proinsulin. J Biol Chem 1978;253:2769. 49. Rinderknecht E, Humbel RE. Primary structure of human insulin-like growth factor II. FEBS Lett 1978; 89:283. 50. Rimoin DL, Schimke RN. Genetic disorders of the pituitary. In: Rimoin DL, Schimke RN, eds. Genetic disorders of the endocrine glands. St Louis: CV Mosby, 1971:19. 51. Underwood LE, Clemmons DR, Van Wyk JJ. Plasma immunoreactive so¬ matomedin C/IGF in the evaluation of short stature. In: Martin Spencer E, ed. Insulin-like growth factors/somatomedins. Berlin-New York: Walter de Gruyter, 1983:235. 52. Gourmelen M, Girard F, Binoux M. Age related variations of IGF (insulin¬ like growth factor) and IGF BP (IGF binding protein) serum levels in normal chil¬ dren and adolescents. Comparison with levels in children with constitutional short stature. In: Martin Spencer E, ed. Insulin-like growth factors/somatomedins. Berlin-New York: Walter de Gruyter, 1983:255. 53. Laron Z, Pertzelan A, Mannheimer S. Genetic pituitary dwarfism with high serum concentration of human growth hormone—a new inborn error in me¬ tabolism. Isr] Med Sci 1966; 2:152. 54. Bierich JR, Moeller H, Ranke MB, Rosenfeld RG. Pseudopituitary dwarfism due to resistance to somatomedin: a new syndrome. Eur J Pediatr 1984; 142:186. 55. Heath-Mannig E, Wohltmann HJ, Daughaday WH. Short stature associ¬ ated with a post receptor defect in IGF I responsiveness of isolated skin fibroblasts. (Abstract) Program of the Endocrine Society. 1985:1068. 56. Rogel AD, Blizzard RM, Foley TP Jr. GH releasing hormone and growth hormone. Genetic studies in familial growth hormone deficiency. Pediatr Res 1985; 19:489. 57. Phillips JA III, Frandez A, Frisch H, et al. Defects of GH genes. Clinical syndrome. In: Raiti S, ed. Human growth hormone. New York: Plenum Press, 1986: 266. 58. Daughaday WH, Trivedi B. Absence of serum GH binding protein in pa¬ tients with GH receptor deficiency (Laron dwarfism). Proc Natl Acad Sci USA 1987;84:4636. 59. Laron Z, Pentzelon A, Mannhermen S. Genetic pituitary dwarfism with high serum concentrations of GH: a new inborn error of metabolism? Is J Med Sci 1966;2:152. 60. Merimee TH, Baumann G, Daughaday W. Growth hormone binding pro¬ tein II studies in pygmies and normal statured subjects. J Clin Endocrinol Metab 1990;71:1183. 61. Tollefsen SE, Heath-Manning E, Cascienis MA, et al. Endogenous insulin-like growth factor (IGF) binding proteins cause IGF| resistance in cultured fibroblasts from a patient with short stature. J Clin Invest 1991; 87:1241. 62. Thakker RV, Pook MA, Wooding C, et al. Association of somatinomas with loss of alleles on chromosome 11 and with gsp mutations. J Clin Invest 1993; 91:2815. 63. Clemmons DR, Van Wyk JJ, Ridgway EC, et al. Evaluation of acromegaly by radioimmunoassay of somatomedin-C. N Engl J Med 1979;301:1138. 64. O'Duffy JD, Randall RV, MacCarry CS. Median neuropathy (carpaltunnel syndrome) in acromegaly. Ann Intern Med 1973; 78:379. 65. Savage DD, Henry WL, Eastman RC, et al. Echocardiographic assessment of cardiac anatomy and function in acromegalic patients. Am J Med 1979; 67:823. 66. Martin JB, Kerber RE, Sherman MB, et al. Cardiac size and function in acromegaly. Circulation 1977;56:863. 67. O'Sullivan AJ, Kelly JJ, Hoffman DM, et al. Body composition and energy expenditure in acromegaly. J Clin Endocrinol Metab 1994; 78:381. 68. Faglio G, Arosio M, Bazzoni N. Ectopic acromegaly. Endocrinol Metab Clin North Am 1992;21:575. 69. Caplan RH, Koob L, Abellar RM, et al. Cure of acromegaly by operative removal of an islet cell tumor of the pancreas. Am J Med 1978; 64:874. 70. Hardy J. Transsphenoidal microsurgical treatment of pituitary tumors. In: Linfood JA, ed. Recent advances in the diagnosis and treatment of pituitary tumors. New York: Raven Press, 1979:375. 71. Wass JAH, Thorner MO, Morris DV, et al. Long-term treatment of acro¬ megaly with bromocriptine. BMJ 1977; 1:875. 72. Moses AE, Molitch ME, Sawin CT, et al. Bromocriptine therapy in acro¬ megaly: use in patients resistant to conventional therapy and effect on serum levels of somatomedin-C. J Clin Endocrinol Metab 1981;53:752. 73. Gorden P, Comi RJ, Maton PN, Go VLW. Somatostatin and somatostatin analogue (SMS 201-995) in treatment of hormone-secreting tumors of the pituitary and gastrointestinal tract and non-neoplastic diseases of the gut. Ann Intern Med 1989; 110:35. 74. Lamberts SW, Reubi JC, Krenning EP. Somatostatin analogs in the treat¬ ment of acromegaly. Endocrinol Metab Clin North Am 1992;21:737. 75. Johnson MR, Chowdrey HS, Thomas F, et al. Pharmacokinetics and efficacy of the long-acting somatostatin analogue somatuline in acromegaly. Eur J Endocrinol 1994; 130:229.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

15

PROLACTIN AND ITS DISORDERS LAURENCE KATZNELSON AND ANNE KLIBANSKI

NORMAL CONTROL OF PROLACTIN SECRETION Prolactin secretion is controlled by dual inhibitory and stim¬ ulatory factors (Fig. 15-1). This hormone is unique among ante¬ rior pituitary hormones, because it is primarily regulated through tonic inhibition. Two decades of investigation have demon¬ strated the presence of one or more prolactin-inhibiting fac¬ tors (PIF).1

Higher centers

Serotonin (+)

Dopamine (-)

(Suckling Stimulus) FIGURE 15-1.

Regulation of prolactin secretion. Prolactin release is un¬ der tonic inhibition by prolactin inhibiting factors (P/Fs), predominantly dopamine. Prolactin release is stimulated by a number of factors, includ¬ ing vasoactive intestinal peptide (VIP), thyroid-releasing hormone (TRH), and gonadotropin-releasing hormone (GnRH). Estrogens, preg¬ nancy, and breast suckling stimulate prolactin release. Within the hypo¬ thalamus, serotinergic and dopaminergic pathways are stimulatory and inhibitory, respectively, to prolactin release. (Modified from Molitch ME. Pathologic hyperprolactinemia. Endocrinol Metab Clin North Am 1992; 21: 877.)

Ch. 15: Prolactin and Its Disorders Dopamine is the most important PIF described. There are multiple studies that support this hypothesis. In vitro studies demonstrate that high-affinity dopamine receptors (D2) are pres¬ ent on lactotrope membranes, and after binding occurs, inhibi¬ tion of adenylate cyclase is demonstrated.2,3 This results in a de¬ crease in cyclic AMP production and the release of prolactin. Dopamine also directly inhibits prolactin biosynthesis at the level of RNA transcription. Dopamine is produced in higher nuclei in the brain and secreted into the portal circulation to reach the pi¬ tuitary. Infusion of dopamine in humans, resulting in serum do¬ pamine concentrations similar to those found in portal blood, causes a reduction in prolactin secretion.4 Dopamine receptor blockade results in prolactin elevations.5 After dopamine is re¬ moved, as during pituitary stalk section, prolactin is rapidly re¬ leased. These studies all point to a direct inhibitory effect of do¬ pamine on pituitary lactotrope secretion. Most pharmacologic agents that cause prolactin release act by blockade of dopamine receptors (e.g., haloperidol, phenothiazines) or by dopamine de¬ pletion in the tuberoinfundibular neurons (e.g., reserpine, amethyldopa). Another potential PIF includes a 56-amino acid prolactininhibiting factor identified within the precursor for gonadotro¬ pin-releasing hormone (GnRH). This GnRH-associated peptide (GAP) inhibits prolactin secretion and reduces prolactin secretion in rats, but the role of GAP in modulating prolactin secretion in humans remains unconfirmed.6 Data also support y-aminobutyric acid (GABA) as a PIF. GABA is secreted into the portal circula¬ tion, with a resulting inhibitory effect on prolactin secretion, and GABA receptors have been detected on lactotropes.7 ITowever, the physiologic importance of GABA in prolactin regulation is unclear. Stimulatory factors also regulate prolactin secretion. These substances may act directly on the pituitary or may act indirectly by means of dopaminergic blockade or depletion at the level of the hypothalamus. Estrogens are important physiologic stimula¬ tors of prolactin release.8 In vitro studies show that estradiol in¬ creases prolactin biosynthesis, consistent with a direct stimula¬ tory effect of estrogen on lactotrope function.9 Chronic exposure to estrogens increases lactotrope number and size (i.e., “preg¬ nancy cells"), and acute administration increases prolactin secre¬ tion within hours.10 Estrogens may also indirectly increase pro¬ lactin levels by altering dopaminergic tone and by increasing responsiveness to other neuromodulators. Thyrotropin-releasing hormone (TRH) stimulates the synthe¬ sis and release of prolactin in vivo and in vitro from normal and neoplastic lactotropes. Although pharmacologic doses of TRFI re¬ sult in a rapid release in prolactin after intravenous administra¬ tion in humans, the physiologic role of TRH in modulating pro¬ lactin secretion is not established.11 For example, suckling leads to release of prolactin without an accompanying heightened re¬ lease of TRH. Hypothyroidism results in an increase in the TSH and prolactin response to TRH, and elevations in basal prolactin levels may be seen in primary hypothyroidism. It has been sug¬ gested that decreased hypothalamic dopamine may play a role in the hyperprolactinemia associated with hypothyroidism. Vasoactive intestinal peptide (VIP) may selectively stimulate or potentiate the TRH effect on prolactin release.12 There is evi¬ dence for VIP receptors on lactotropes and VIP may stimulate prolactin release in vitro. Immunoneutralization of VIP effects through administration of anti-VIP antisera diminishes the pro¬ lactin response to stimuli including suckling, again suggesting a role of VIP as a stimulatory factor.13 Data suggest that VIP may be produced in the pituitary and may stimulate prolactin release through a paracrine or autocrine mechanism.14 The clinical sig¬ nificance of VIP in prolactin regulation in humans is unknown. GnRH may also have stimulatory properties. The admin¬ istration of GnRH induces the acute release of prolactin in nor¬ mally cycling women and hypogonadal patients.15 Moreover, in¬ cubation of human lactotropes with GnRH in vitro results in

141

prolactin secretion.16 These investigations suggest that GnRH di¬ rectly or through a paracrine mechanism involving gonadotropes may be important in evoking prolactin release. Investigations have suggested a role for galanin as a potent stimulator of prolactin release. Galanin is a 29-amino acid pep¬ tide widely distributed in the central and peripheral nervous sys¬ tem. In the rat, intracerebroventricular injections of galanin may increase prolactin levels.17 However, intravenous administration of galanin in humans does not stimulate serum prolactin levels.18 The physiologic role of galanin in human prolactin regulation remains controversial. Serotonin is another factor that may stimulate prolactin se¬ cretion.19 Administration of serotonin antagonists decreases pro¬ lactin levels. Serotonin agonists appear to enhance prolactin se¬ cretion through specific serotonin receptors, which may explain why only specific serotonin antagonists are capable of lowering prolactin secretion.20 Other factors that may have stimulatory roles includes bombesin, angiotensin II, histamine (H2) antagonists, and opiates. Human prolactin structure has partial structural homology with growth hormone, which may account for the lactotropic ac¬ tivity of growth hormone. There are heterogeneous forms of pro¬ lactin in the circulation. Eighty-five percent of prolactin (23 kilodaltons [kd]) detected in the pituitary and secreted into serum is nonglycosolated, but glycosolated forms have been detected.21 Approximately 8% of prolactin extractable from the pituitary is dimeric, and an additional 1% to 5% is polymeric, linked by di¬ sulfide bonds.22 These forms include "big," "big-big," and "lit¬ tle" or "native" prolactins. The significance of these forms is un¬ known. These larger forms of prolactin may have decreased rates of binding to the prolactin receptor and possess diminished bio¬ activity relative to monomeric, nonglycosolated prolactin. These forms may represent nonspecific hormonal aggregates or binding of prolactin to serum proteins. Some patients have normal repro¬ ductive function but elevated serum prolactin values; the prolac¬ tin in these patients is composed of a relatively increased compo¬ nent of polymeric prolactin.23 In such patients, the elevated prolactin levels may reflect increased levels of polymeric prolac¬ tin with decreased bioactivity. It has been suggested that certain isotypes of prolactin, specifically the iso-B prolactin, may be ele¬ vated in the sera of patients with infertility and pregnancy wast¬ age.24 This isotype may be more resistant to bromocriptine ther¬ apy than native prolactin. However, these reports need to be confirmed. The significance of the remaining fraction of glycoso¬ lated prolactin is unknown.

CLINICAL ASPECTS OF PROLACTIN PHYSIOLOGY The physiologic causes of hyperprolactinemia are summa¬ rized in Table 15-1. The following sections describe clinical as¬ pects of prolactin physiology.

TABLE 15-1 Physiologic Causes of Hyperprolactinemia Pregnancy Postpartum Nonnursing: days 1-7 Nursing: with suckling Newborn Estrogen therapy Stress Sleep Hypoglycemia Intercourse Nipple stimulation Exercise

142

PART II: THE ENDOCRINE BRAIN AND PITUITARY GLAND

DIURNAL AND MENSTRUAL CYCLE VARIATION Prolactin is secreted in a pulsatile fashion with 4 to 14 pulses per day (60% occur during sleep).25 Prolactin secretory pulses begin about 60 to 90 minutes after the onset of sleep.26 The am¬ plitude of pulses varies greatly among individuals, with peak lev¬ els occurring during the late hours of sleep. Such rises are not clearly associated with any specific stage of sleep. Although some studies have suggested that prolactin varies during the menstrual cycle, the precise nature of this relationship remains unclear. Sev¬ eral investigators have shown that prolactin levels are signifi¬ cantly higher during the ovulatory and luteal phases, particularly at midcycle.2. This midcycle rise may be the result of increased circulating periovulatory estradiol levels. However, other studies have not confirmed this finding. Prolactin is probably not neces¬ sary for ovulation, because ovulatory periods may occur in women taking bromocriptine, a medication that suppresses prolactin.

FOOD Abrupt rises in serum prolactin levels occur within an hour of eating in normal and pregnant hyperprolactinemic individu¬ als, but they do not rise in those with prolactinomas. Amino acids metabolized from protein components of meals appear to be the main stimulants to prolactin secretion.28

STRESS Prolactin rises during stress, including physical exertion, sur¬ gery, sexual intercourse, insulin hypoglycemia, and seizures. The nature and teleologic significance of these changes are unknown. Nipple stimulation, chest wall trauma or surgery, and herpes zos¬ ter infection of the breast may result in increases in prolactin lev¬ els, in part through afferent neural pathways.29 In contrast, nip¬ ple stimulation in men does not cause increased prolactin levels.

AGE Mean levels of prolactin are slightly higher in premeno¬ pausal women than men, probably because of a direct effect of estrogen on pituitary prolactin secretion or estrogen-induced al¬ terations in dopaminergic tone. Some studies suggest that there is a progressive decline in prolactin levels in women with age, particularly after the menopause.30 The responsiveness of pro¬ lactin to various pharmacologic agents (e.g., TRH) declines with age in women, probably because of postmenopausal estrogen deficiency.

NORMAL STATES The only established role of prolactin is to initiate and main¬ tain lactation. Prolactin levels increase progressively with preg¬ nancy. Estrogens play a major role in stimulation of prolactin lev¬ els, which peak at term (100-300 ng/mL).31 Lactation begins when estradiol levels fall at parturition. During the first 4 to 6 weeks after delivery, prolactin levels increase to 60 times higher than baseline levels in the circulation within 20 to 30 minutes of nursing.32 This elevation is associated with enhanced prolactin pulse amplitude without alteration of pulse frequency.33 The nursing stimulus effectively promotes acute prolactin release through afferent spinal neural pathways. With continued nurs¬ ing, the nipple stimulation itself elicits progressively less prolac¬ tin release, and in the weeks after initiation of lactation, basal and nursing-induced prolactin pulses decrease, although lactation continues.32 Within 4 to 6 months after delivery, basal prolactin levels are normal, without a nursing-induced rise. However, the

full explanation for the attenuation in basal and nursing induced prolactin levels with continued nursing is unknown.

CLINICAL MANIFESTATIONS OF HYPERPROLACTINEMIA The amenorrhea-galactorrhea syndrome is the classic de¬ scription of the clinical manifestation of hyperprolactinemia. However, a spectrum of reproductive disorders may be seen. Prolactin elevations are found in approximately 20% of patients with secondary amenorrhea.34 Women with hyperprolactinemia may have more subtle abnormalities in gonadal function, includ¬ ing oligomenorrhea or alterations in luteal phase function. A sub¬ set of infertile women have been described with mild hyperpro¬ lactinemia in whom fertility was restored with bromocriptine therapy. Galactorrhea affects only approximately 30% of female patients with hyperprolactinemia, but galactorrhea in a woman with an ovulatory disorder greatly increases the chance that hy¬ perprolactinemia is the underlying etiology of the amenorrhea.35 Patients with primary amenorrhea and delayed puberty may have hyperprolactinemia.36 Galactorrhea occurs in as many as 25% of women with nor¬ mal serum prolactin levels. However, patients with idiopathic ga¬ lactorrhea may demonstrate intermittent hyperprolactinemia. In a study of 9 normoprolactinemic women with galactorrhea, 8 pa¬ tients had elevated levels of prolactin during sleep.37 Several studies have shown that infertile, normoprolactinemic women with luteal phase defects may show improved luteal function or fertility after administration of bromocriptine therapy.37 Unrec¬ ognized hyperprolactinemia may occur in a subset of patients with presumed normoprolactinemic galactorrhea and luteal phase defects. Hypogonadism is frequently found in patients with hyper¬ prolactinemia. In women, hypogonadism includes abnormal menstrual function, dry vaginal mucosa, and dyspareunia, and in men and women, the features include fatigue and diminished libido. There are multiple potential mechanisms hypothesized for the induction of hypogonadism by prolactin, and the antigonadotropic actions of prolactin may occur at multiple levels. Fre¬ quently, the hypogonadism is associated with decreased or inap¬ propriately normal LH and FSH levels relative to the state of estrogen deficiency. Multiple investigations suggest that prolac¬ tin may suppress spontaneous LH release through decreases in endogenous GnRH levels. In castrated rats, graded doses of prolactin suppress LH levels, and prolactin appears to exert a negative-feedback effect on its own secretion by means of a short-loop negative feedback at the level of the hypothala¬ mus.38 39 This feedback may be mediated through an increase in dopamine inhibitory tone. This increased hypothalamic dopa¬ mine tone, along with opiates and other factors, may suppress GnRH with a resultant decrease in LH pulses. The restoration of ovulatory menstrual periods in hyperprolactinemic women with pulsatile exogenous GnRH administration confirms the impor¬ tance of endogenous GnRH abnormalities as the key mechanism of hypogonadism in these women.40 Prolactin may modulate an¬ drogen secretion at the level of the adrenal gland and ovary, re¬ sulting in increased secretion of dehydroepiandrosterone sulfate and testosterone.41 Altered ratios of estrogens and androgens may result in further abnormal gonadal function, with evidence of clinical hyperandrogenism. If the underlying cause of the increased prolactin is a pitu¬ itary macroadenoma, the adenoma could cause compression of the normal, adjacent pituitary gland with a resultant decrease in gonadotrope function. Men with hyperprolactinemia may have clinical manifesta¬ tions of hypogonadism, such as decreased libido, impotence, in¬ fertility due to oligospermia, and gynecomastia. Galactorrhea is

Ch. 15: Prolactin and Its Disorders rare in hyperprolactinemic men because of a lack of estrogen priming of the breast.

DIFFERENTIAL DIAGNOSIS AND CLINICAL APPROACH TO HYPERPROLACTINEMIA As shown in Tables 15-1 and 15-2, there are multiple causes of hyperprolactinemia. The prolactin level should be repeated in a nonstimulated state, and, if possible, after an overnight fast in a nonstressed state. Because prolactin may be secreted to a modest degree after a breast examination, a subsequent mild increase in prolactin levels would warrant a repeat determination. Although Table 15-2 demonstrates that there are several pathologic causes of prolactin elevation, pituitary tumors are clinically the most im¬ portant. Prolactin secreting pituitary adenomas are the most common type of pituitary tumors and may account for as many as 40% to 50% of all pituitary tumors.42 Hyperprolactinemia may be detected in as many as 40% of patients with acromegaly and has been reported in patients with Cushing disease. Acromegaly and Cushing disease should be evaluated in hyperprolactinemic patients with suggestive clinical manifestations. Substantial elevations in prolactin (> 150 ng/mL) in a nonpuerperal state usually indicate a pituitary tumor. There is good correlation between radiographic estimates of tumor size and prolactin levels, and very high levels of prolactin are associated with larger tumors. Prolactinomas are classified as microadeno¬ mas (< 10 mm) and macroadenomas (> 10 mm). The finding of a substantial elevation in serum prolactin in association with a pituitary lesion larger than 10 mm by radiographic analysis sup¬ ports the diagnosis of a macroprolactinoma. Modest levels of prolactin elevation (25-100 ng/mL) may be associated with several diagnoses. All causes of hyperprolactin¬ emia should be excluded before a tumor is considered. It is im¬ portant to exclude primary hypothyroidism and pregnancy. Chronic renal disease is associated with elevations in prolactin, probably because of altered metabolism or clearance of prolactin or decreases in dopaminergic tone.43 Hemodialysis does not usu¬ ally reverse the hyperprolactinemia. There are multiple pharmacologic causes of hyperprolactin¬ emia. Ingestion of phenothiazines and other neuroleptics is a common cause for elevations in serum prolactin. One diagnostic problem is the evaluation of patients with psychiatric disease who are receiving phenothiazines and are found to have an ele¬ vated prolactin level. A magnetic resonance image (MRI) should be obtained for patients whose prolactin levels are above 100 ng/ mL. Levels lower than 100 ng/mL are consistent with neuroleptic administration, and a scan is unnecessary unless other symptoms suggest a pituitary tumor. This strategy is based on the finding that most patients receiving neuroleptics with modest prolactin elevations have no evidence of a pituitary abnormality on MRI. Other pharmacologic agents associated with hyperprolactinemia include reserpine, a-methyldopa, cimetidine, and opiates. Estrogen may increase prolactin levels, as is seen in preg¬ nancy. However, estrogen concentrations in typical oral contra¬ ceptives (e.g., 35 ng of ethinyl estradiol) are not associated with hyperprolactinemia, and there is no evidence that postmeno¬ pausal replacement estrogen causes elevations in serum prolac¬ tin. Any intra-suprasellar mass may lead to modest prolactin ele¬ vations through stalk compression, and the evaluation should include an MRI. These masses include primary pituitary tumors or meningiomas and craniopharyngiomas. Hypothalamic disor¬ ders, including destructive lesions such as tumors and granulo¬ matous diseases, may lead to hyperprolactinemia by interfering with normal dopaminergic tone. If an elevated serum prolactin level is not associated with primary hypothyroidism, pregnancy, or pharmacologic agents, a pituitary radiographic scan should be performed to rule out the

143

presence of a prolactin-secreting pituitary tumor or other lesions. It is important to differentiate microprolactinomas from macro¬ prolactinomas. An MRI is the most sensitive tool for evaluating the sellar and suprasellar areas. If the scan shows normal sellar and extrasellar contents and there is no clear secondary cause of the elevated prolactin, the diagnosis of idiopathic hyperprolac¬ tinemia is made. This syndrome may be the result of a small tu¬ mor that is beyond the sensitivity of the scanning technique. The evaluation should include assessment of gonadal status, such as the presence of oligomenorrhea or amenorrhea in women and of sexual dysfunction in men. This impacts therapy, as is described later. There are no stimulatory or suppressive endo¬ crine tests that aid in the evaluation of elevated prolactin levels. For example, a TRH test cannot be used to diagnose a pituitary tumor; although tumors typically have blunted responses after TRH stimulation, this response can be seen with other disorders.

TREATMENT FOR PROLACTINOMAS Treatment depends on whether the patient has hyperprolac¬ tinemia due to an underlying cause such as drugs or hypothy¬ roidism or caused by a prolactinoma. If the evaluation suggests the presence of a microprolactinoma, there are three treatment options: medical therapy with a dopamine agonist, careful follow-up without treatment, and rarely, surgery. All patients with macroadenomas should be treated.

MEDICAL THERAPY Almost all patients with hyperprolactinemia due to pituitary disease can be effectively treated medically with the dopamine agonist bromocriptine (see Chap. 23). Bromocriptine lowers se¬ rum prolactin in patients with pituitary tumors and all other causes of hyperprolactinemia. A review of early studies of bro¬ mocriptine therapy for more than 400 hyperprolactinemic pa¬ tients showed that normoprolactinemia or return of ovulatory menses occurred in 80% to 90% of patients.44 Bromocriptine effectively decreases prolactin levels, normalizes reproductive function, and reverses galactorrhea. In this series, return of men-

TABLE 15-2 Pathologic and Pharmacologic Causes of Hyperprolactinemia PITUITARY DISEASE Prolactin-secreting tumors Acromegaly Cushing disease Empty sella syndrome PITUITARY STALK SECTION Clinically nonfunctioning pituitary tumors Trauma HYPOTHALAMIC INFILTRATIVE OR DEGENERATIVE DISEASE Craniopharyngiomas Meningiomas Dysgerminomas Gliomas Lymphoma Metastatic disease Tuberculosis Sarcoidosis Eosinophilic granuloma Irradiation

NEUROGENIC CAUSES Chest wall trauma Chest wall lesions Herpes zoster Breast stimulation MEDICATIONS Phenothiazines Tricyclic-antidepressants Metoclopramide Cimetidine Methyldopa Reserpine Calcium-channel blockers Cocaine OTHER Renal failure Liver disease Primary hypothyroidism Ectopic hormone production Seizures

(Adapted from Molitch ME. Pathologic hyperprolactinemia. Endocrinol Metab Clin North Am 1992;21:877.)

144

PART II: THE ENDOCRINE BRAIN AND PITUITARY GLAND

strual function was accompanied in some patients by prolactin levels that were significantly reduced but not normal. This sug¬ gests that the reduction of prolactin in some patients to slightly elevated levels may be sufficient for return of gonadal function. Bromocriptine is also useful in treating galactorrhea in patients with normoprolactinemic galactorrhea. The onset of the effects of bromocriptine is rapid, usually occurring within 1 to 2 hours. The greatest decrease in prolactin levels occurs at the initiation of therapy; but normalization may take weeks. The biologic half-life of bromocriptine is similar to its plasma half-life. Discontinuation of the drug is typically fol¬ lowed by a return of prolactin to elevated values. Bromocriptine decreases prolactin production and secretion, with a resultant re¬ duction in lactotrope size and a subsequent decrease in tumor size.45 Therapy should be initiated slowly because side effects, in¬ cluding nausea, headache, dizziness, nasal congestion, and con¬ stipation, may occur. Gastrointestinal side effects may be mini¬ mized by starting with a very low dose at night (e.g., 1.25 mg (one-half tablet) with a snack, and increasing the dose by 1.25 mg over 4- to 5-day intervals, as tolerated. This progression is continued until a dose that normalizes prolactin levels is reached. The rate of dose escalation is dictated by the clinical situation, such as the presence of mass effects. Side effects usually improve by continuing the medication at the same dose or by temporarily reducing the dose. If patients stop taking the medication for a few days, therapy should be reinstituted at a lower dose, because these side effects may return. Rarely, chronic therapy may result in side effects, including painless cold-sensitive digital vaso¬ spasm, alcohol intolerance, dyskinesia, and psychiatric reactions, including fatigue, depression, and anxiety. To reduce the gastrointestinal side effects, bromocriptine has been administered intravaginally. Reductions in prolactin similar to that attained by oral bromocriptine have been achieved with the intravaginal route.46 Gastrointestinal side effects are less common, and therapy may be more effective with vaginal bromocriptine.47 There are other dopamine agonists under investigation, in¬ cluding CV 205-502 and the long-acting preparations, Parlodel LAR and cabergoline. CV 205-502 is a nonergot, long-acting do¬ pamine agonist that appears to have heightened D2-receptor binding compared with bromocriptine. CV 205-502 or bromo¬ criptine was administered in a randomized double-blind fashion to 22 patients with microprolactinomas.48 In this study, 91% of the patients who received CV 205-502 and 56% of those who received bromocriptine had normalization of prolactin levels. Side effects were less common in the CV 205-502 group, and the drug may be useful in those patients intolerant to bromocriptine.49 CV 205-502 also is effective in the management of macro¬ prolactinomas. CV 205-502 was administered to 26 patients with macroprolactinomas for 24 weeks; a significant decrease in pro¬ lactin levels was observed in all patients, and normalization oc¬ curred in 58%.50 This was accompanied by resumption of regular menses in 73% of premenopausal women and a decrease in tu¬ mor size in 81% of patients. Cabergoline is an ergoline derivative with selective, potent, and long-lasting dopaminergic properties and is highly effective in the management of hyperprolactinemia. Because of the ease of administration of cabergoline (i.e., once or twice weekly) and its improved side-effect profile relative to bromocriptine, patients have a high rate of compliance. Administration of cabergoline at doses as high as 1.0 mg twice weekly to 113 patients with micro¬ prolactinomas resulted in normalization of prolactin levels in 95%.51 When cabergoline was administered to 14 patients with macroprolactinomas, tumor shrinkage was observed in 13 (93%) and complete disappearance was documented in 2 patients.52 Ca¬ bergoline appears to be better tolerated than bromocriptine and may play an important role in the management of patients resis¬ tant to or intolerant of bromocriptine.523

Pergolide is a dopamine agonist approved by the U.S. Food and Drug Administration for the treatment of Parkinson disease. Although not approved for use in the management of hyperpro¬ lactinemia, studies have shown that pergolide has a comparable side-effect profile to bromocriptine and may reduce prolactin lev¬ els in patients unresponsive to bromocriptine.53

SURGERY Although surgery is not a primary mode of management for patients with prolactinomas, it may be indicated in several set¬ tings. These include large tumors with visual field deficits unre¬ sponsive to bromocriptine, an inability to tolerate bromocriptine because of its side effects, cystic tumors that do not respond to medical therapy, and tumor apoplexy. A transsphenoidal ap¬ proach is used almost exclusively. When performed by experi¬ enced surgeons, the morbidity rate is negligible. The mortality rate is less than 0.27%, and the major morbidity rate is 3%.54 A theoretic advantage of curative surgery is avoidance of long-term medication. However, clinical evidence is lacking. Among 28 patients with microprolactinomas, 24 were cured with transsphenoidal surgery based on normalization of serum pro¬ lactin levels. After approximately 4 years, 50% of these initially "cured" patients had recurrence of hyperprolactinemia, al¬ though none had radiographic evidence of tumor growth.55 An¬ other study found a recurrence rate of 39% after approximately 5 years.56 These data suggest that, although surgery may result in normalization of prolactin levels initially in patients with micro¬ prolactinomas, there is a relatively high risk of recurrence. A se¬ rum prolactin level greater than 9 ng/mL 1 to 3 days after surgery may be associated with early recurrence and probably indicates failed surgery.55 Surgical cure rates for macroprolactinomas are approxi¬ mately 32%, with cure defined as normal prolactin levels after surgery.44 Surgical cure is inversely proportional to serum prolac¬ tin levels and tumor size. Unfortunately, the recurrence rate in macroprolactinomas is as high as 80% after curative surgery.55

RADIATION THERAPY Conventional radiotherapy (4500-5000 rad) or, rarely, proton-beam therapy may be indicated in patients with larger tumors in whom immediate control of symptoms and fertility is not a high priority and in patients who are not able to tolerate medical therapy.

MANAGEMENT OF MICROPROLACTINOMAS The decision to institute medical therapy in patients with microprolactinomas is based on the metabolic consequences of hyperprolactinemia and tumor size. Patients with hyperprolac¬ tinemia are usually hypogonadotropic and have accompanying menstrual irregularities. Bromocriptine therapy can restore men¬ strual function in most patients with amenorrhea. Luteal phase defects associated with hyperprolactinemia can also be reversed with bromocriptine therapy. Ovulation rates greater than 90% have been reported, with induction of pregnancy in more than 80% of patients.57 Galactorrhea is not an absolute indication for bromocriptine therapy, unless the degree of galactorrhea is sig¬ nificantly bothersome to the patient. The presence of amenorrhea is an indication for medical therapy because of the risk of osteo¬ porosis associated with hyperprolactinemic amenorrhea. Some women with microprolactinomas may choose not to have ther¬ apy if they show no evidence of hypogonadism or amenorrhea and if they do not desire fertility. Reduction of prolactin levels frequently restores libido and increases sperm counts in hyper¬ prolactinemic men. Patients with microprolactinomas and those without radiographic evidence of pituitary tumors can sometimes be followed without therapy. Studies investigating the natural history of such tumors have shown that prolactin elevations usually remain sta-

Ch. 15: Prolactin and Its Disorders ble and, in some cases, spontaneously normalize.58 In a study of 41 patients with idiopathic hyperprolactinemia, based on normal computed tomography scans for 5.5 years, 67% of patients whose initial prolactin values were less than 57 ng/mL had nor¬ malization of prolactin levels.59 None of the patients with initial prolactin values above 60 ng/mL normalized. These and other data suggest that the degree of prolactin elevation is a prognostic factor for spontaneous resolution. When 38 untreated patients with microprolactinomas were followed for an average of 50.5 months, 36.6% had an increase, 55.3% had a spontaneous decrease, and 13.1% had no change in prolactin levels.60 A prospective study of untreated hyperprolactinemic women showed that basal menstrual function is an important variable in predicting progression of the prolactin level.6f In this study, patients with normal initial menstrual function were more likely to have normalization of prolactin levels, and patients with oligomenorrhea or amenorrhea were more likely to have no change or increases in prolactin levels. Most microprolactinomas do not exhibit evidence of further growth, and prolactin levels may spontaneously normalize. An important aspect of the natural history of microprolacti¬ nomas is that most tumors do not significantly increase in size. Although many of these studies used insensitive radiographic techniques, such as skull films and tomograms, they demon¬ strated that in patients with microprolactinomas and no radiographic evidence of a tumor, tumor size increased in 0% to 22% of patients.57,59 62 In a study of 43 patients with presumed mi¬ croadenomas with a mean follow-up period of 5.4 years, only 2 patients showed evidence of tumor progression.62 In a pro¬ spective study, 27 women were followed for an average of 5.2 years.61 Of 14 women with normal baseline radiographic studies, 4 developed evidence of an adenoma, although none developed a macroadenoma. Of the 13 women with evidence of a tumor at baseline, only 2 showed worsening of radiographic findings. This study suggests that, although tumor growth may occur in as many as 22% of cases, it is rarely accompanied by clinical symp¬ toms from mass effects. Follow-up of untreated patients should include serial prolactin levels and periodic MR scans, because tu¬ mor progression may not be accompanied by increasing prolactin levels. The presence of osteoporosis is a key factor in the decision to institute therapy. Hyperprolactinemia is associated with tra¬ becular and cortical osteopenia. Fourteen young hyperprolacti¬ nemic women with prolactin levels ranging from 22 to 99 ng/ mL and amenorrhea for 1 to 18 years had significantly decreased cortical bone density compared with normal women.63 Addi¬ tional studies have shown that hyperprolactinemic women may have trabecular osteopenia with spinal bone density 10% to 25% below normal.64-66 Spinal bone density in hyperprolactinemic women correlates with serum androgen levels and relative per¬ centage of ideal body weight.64,67,68 The cause of decreased bone density is thought to be hypogonadism and not a direct effect of prolactin, because hyperprolactinemic women with normal men¬ strual function do not have associated bone loss.64 Figure 15-2 shows that hyperprolactinemic patients with hypogonadism have lower bone density than eugonadal hyperprolactinemic women. The decreased bone density in the hyperprolactinemic women with amenorrhea also correlates with the duration of amenorrhea.66 An important question is whether therapy of hyperprolacti¬ nemic amenorrhea may result in improvement in bone density. A prospective series of 32 women with hyperprolactinemic amenorrhea randomized to medical therapy or no therapy showed that resumption of menses with medical therapy was associated with a significant increase in cortical bone density, mostly during the first 12 months of therapy.66 However, the cor¬ tical bone density in this series remained below that of normal women. Of 38 women with prolactinomas 2 to 5 years after sur¬ gery, cortical bone mass was below normal in cured and uncured patients, suggesting that remission of hyperprolactinemia may

145

220 200 ISO 180 140

z

LD I-

o o

120 100 SO

60 I

0 X.. 20

_l

25

J_ _L.

_l_,_i_,_._i

30

35

40

45

30

35

40

45


T3

T4 > rT3

t3,t4

Location

Liver, kidney, thyroid

Brain, brown adipose tissue, pituitary, pineal

Brain, skin, placenta

Selenium active site

Yes

No

No (?)

Optimal pH

Outer ring, 6.5-7.5; inner ring, 8.0-8.5

6.5-7.5

8.0-8.5

Response to f T4

f Activity

I Activity

f Activity

Response to 1 T4

I Activity

f Activity

i Activity

Response to fasting

| Activity

Little effect

Little effect

Response to propylthiouracil

I Activity

Little to no effect

Little effect

Iopanoic acid

I Activity

| Activity

Characterized

27-kd subunit; cloned

29-kd subunit; not cloned

NA

* Inner ring deiodination may increase Vmax/Km by 50- to 200-fold under the influence of the sulfate substrate (see Fig. 31-3). •f Substrate preference may be changed for type I deiodination with sulfation of the substrate.

It does not prevent goiter but is a competitive inhibitor of 5'D-I. Therefore, the 5-deiodination pathway catalyzed both by 5'D-I, at a different pH optima from that for phenolic ring deiodination, and by a type III enzyme (see Table 31-3) that is found in pla¬ centa, brain, and skin constitutes an inactivation. Substrate con¬ jugation with sulfate can increase the tyrosyl ring deiodination of T4 and T3 by 5'D-I several hundred-fold, thereby inactivating these hormones.18,18a The sequential deiodination continues, as in Figure 31-3, to yield thyronine and a family of diiodothyronines and monoiodothyronines that have uncertain bioactivity. Peripheral T4 deiodination contributes 80% to 85% of the T3 plasma appearance rate. This conversion occurs mostly in the liver and kidney. The thyroid gland may secrete about 15% of the T3 total plasma appearance rate directly in the form of T3. The role of thyroidal 5'D-I as a contributing mechanism of peripheral T4 deiodination is under investigation. Nearly 100% of rT3 comes from peripheral T4 deiodination, although not necessarily from hepatic or renal sources.

T4

^

\

Tj-3,5,3’

rT3-3,3',5'

i/

V

Tr3,5

t/

Tr3',5'

T2-3,3'

*l/

\

\

\ T,-3'

Tr3

\

^

THYRONINE FIGURE 31-3.

Iodothyronine deiodination. Sequential deiodination of thyroxine by outer (phenolic) ring (-*■) 5'-D-I and 5-D-II, and inner (ty¬ rosyl) ring (-*-) 5'-D-III and 5'-D-I deiodination is indicated. The iodine locations for the named compounds given are referenced. The increase in activities mediated by 5'-D-I that are influenced by sulfation of the sub¬ strate are indicated with an asterisk (*).

5'D-I is a selenium-dependent enzyme found in human thy¬ roid, liver, and kidney; it has decreased activity in hypothyroid¬ ism, malnutrition, nonthyroidal illness, selenium deficiency, and after PTU administration.31314 When phenolic ring deiodination (5'D-I) activity is decreased, both the production of T3 and the degradation of rT3 decline14 (see Fig. 31-3). These changes result in an increase in plasma rT3 and decrease in T3 concentration, as is found with fasting and some nonthyroidal illnesses for which human kinetic studies have validated the mechanism de¬ scribed.1314 Many other situations may also have a similar profile, consisting of a low serum T3 and high rT3, including: drug ad¬ ministration (e.g., glucocorticoids, /3-blockers, thionamides, oral cholecystographic dyes); chronic illness (e.g., cirrhosis, renal fail¬ ure, malignancy); and acute illness (e.g., myocardial infarc¬ tion, sepsis, uncontrolled diabetes mellitus, severe burns; see Chap. 36). In central Africa, myxedematous cretinism associated with iodine deficiency predominates, with little incidence of neuro¬ logic cretinism.3 Some of these regions have coexistent iodine and selenium deficiency. The resultant hypothyroidism that occurs in these locations is associated with decreased selenium-dependent activity of 5'D-I that may attenuate the frequency of neurologic cretinism.3 Fetal brain T4 acts as the major source of brain T3 con¬ verted by 513-11, a selenium-independent enzyme (see Table 31-3). Because circulating fetal T4 has not been converted to T3 by 5'D-I, the selenium-dependent enzyme, T4 is more available for uptake by the fetal brain during early pregnancy. Thus, the selenium-mediated decrease in T4 peripheral deiodination may help reduce the incidence of neurologic cretinism. The iodine should be replaced first in this particular circumstance to avoid premature activation of 5'D-I by selenium replacement, predis¬ posing to a further lowering of serum T4.3 Other pathways for the disposal of thyroid hormones exist. The ether bond may be broken, leading to splitting of the two rings, although the clinical importance of this mechanism is un¬ certain. The alanine side chain of T4 and T3 may be oxidized to form the acetic acid derivatives tetraiodoacetic acid (tetrac) and triiodoacetic acid (Triac). These compounds have some metabolic activity; their clinical role is being investigated. Sulfoconjugation of iodothyronines facilitates tyrosyl (inner ring) deiodination, with the possible exception of rT3, which is already a favored substrate for phenolic (outer ring) deiodination. Glucuronide conjugates of iodothyronines are more hydrophilic and are con-

290

PART III: THE THYROID GLAND

sequently excreted more readily in the bile. The intestinal flora in rats may mediate deconjugation of some of these compounds and facilitate reuptake of the hormones: thus, the term enterohepatic circulation. In humans, changing this enterohepatic circulation with an anion exchange resin (cholestyramine) has been shown to lower serum T4 both in postabsorptive states after excessive T4 ingestion19 and in Graves disease,20 further highlighting its clini¬ cal importance. The intrapituitary generation of T3 from T4 by 5'D-II helps maintain regulation of TSH release. In contradistinction to 5'D-I, as the substrate level of T4 declines, the activity of this form of phenolic ring deiodination increases, and fasting does not appear to inhibit its activity. Pharmacologic inhibition of 5'D-I conversion of T4 to T3 with the use of iodinated radiographic contrast agents (e.g., iopanoic acid) and thiourea compounds (e.g., PTU) is an effective means of rapidly decreasing T3 production and its serum concentration in hyperthyroid patients (see Table 31-1 and Chap. 41).

NEUROTRANSMITTERS

REGULATION OF THYROID HORMONE ECONOMY Thyroid hormone regulation is directed through the hypothalamic-pituitary-thyroid-peripheral tissue axis (Fig. 31-4). The system extends "higher” to neuroendocrine modulation at the hypothalamus and "lower" to peripheral thyroid hormone metabolism. This system has autocrine (e.g., enzyme autoregula¬ tion), paracrine (e.g., somatostatin, thyrotropin-releasing hor¬ mone [TRH]), and hemocrine (e.g., T4, T3) autoregulation that is also influenced by environmental factors (e.g., energy balance, circadian variation, illness).

TARGET ORGANS (heart, Gl Tract, etc)

PERIPHERAL MONODEIODINATION

NEUROENDOCRINE MODULATION Serum TSH secretion has a diurnal rhythm: values peak af¬ ter midnight and are lowest in midafternoon. Advancing age may blunt this nocturnal surge in TSH.21 In rodents and human in¬ fants, cold stimulates TSH. Hypothyroid patients administered a constant T4 dose have a slight decline in serum T4, unchanged T3, and increased TSH response to TRH in winter months.22 Sev¬ eral factors are well recognized to increase (e.g., estrogens, a-adrenergic agonists, dopamine antagonists) or decrease (e.g., thyroid hormones, glucocorticoids, dopamine, growth hormone, somatostatin) the release of TSH.23

FIGURE 31 -4. Major steps in thyroid hormone regulation. Thyrotropin¬ releasing hormone (TRH) from the hypothalamus stimulates and so¬ matostatin inhibits thyroid-stimulating hormone (TSH) release from the pituitary, leading to regulation of the thyroid gland. Peripheral monodeiodination yields T3 and other iodothyronines (see Fig. 31-3). T3 initiates action in target tissues. Circulating T4 and T3 have inhibitory action (-), primarily on the pituitary, but also on the hypothalamus (From Smallridge RC. Thyroid hormone metabolites, a review of diiodo thyronines and monoiodothyronines. Am Assoc Clin Chem 1985;3:1. Reprinted with per¬ mission from Clinical Chemistry).

PITUITARY HYPOTHALAMIC To maintain thyroid hormone production, the tonic stimula¬ tion by TRH is required. Severe hypothalamic injury or separa¬ tion of the pituitary from the hypothalamus by stalk section re¬ sults in hypothyroidism. TRH is a tripeptide (Glu-His-Pro) synthesized in the paraventricular nucleus of the hypothalamus, and its mRNA concentration is inversely related to concentra¬ tions of circulating thyroid hormones. TRH is transported down nerve endings to the median eminence and reaches the anterior pituitary through the portal capillary plexus. Somatostatin, found in the anterior periventricular region, inhibits TSH release. Administration of somatostatin decreases the TSH response to TRH, nocturnal TSH rise, and the TSH elevations seen in primary hypothyroidism (see Chap. 17). TRH binds to high-affinity receptors on the surface of TSHproducing cells (thyrotropes) and leads to a prompt release of stored TSH. With more prolonged stimulation, new synthesis and release of TSH occurs. As a diagnostic procedure, the provo¬ cation of TSH secretion by injecting TRH has limited utility be¬ cause free T4 assays and sensitive TSH assays are readily avail¬ able24 (see Chap. 33). Direct measurement of serum TRH is not yet clinically feasible.

Thyroid-stimulating hormone is a glycoprotein synthesized in the anterior pituitary gland. It has a molecular mass of 28-kd and is composed of two subunits, designated as the a and /3 chains, whose bioactivity may depend on the attached carbohy¬ drate moiety. This two-subunit structure is similar to that of follicle-stimulating hormone, luteinizing hormone, and human chorionic gonadotropin (see Chaps. 17, 18, and 110); in fact, these regulatory hormones all share a common structure for the a subunit. Excess a subunit is synthesized by the pituitary cells. The rate-limiting step in TSH synthesis is production of the /? subunit, which also confers specificity in stimulation of target organs. Only intact TSH is routinely measured in the serum, but measurement of subunits may be useful in syndromes of inap¬ propriate TSH secretion. TSH-producing pituitary tumors may be associated with disproportionately elevated serum a-subunit levels (see Chaps. 17 and 41). Two major factors regulate TSH synthesis and secretion: in¬ hibitory, negative feedback at the anterior pituitary, from circu¬ lating thyroid hormones and hypothalamic mediators, such as somatostatin and dopamine; and stimulation by TRH from the hypothalamus.

Ch. 31: Physiology of the Thyroid Gland I: Synthesis and Release, Iodine Metabolism, and Binding and Transport High circulating levels of T4 or T3 suppress TSH synthesis and release by negative feedback. Either excess endogenous hor¬ mone from primary hyperthyroidism or exogenous T4 or T3 from hormone administration should lead to low serum TSH levels; otherwise, a measurable TSH concentration in the face of ele¬ vated levels of T4 and T3 is considered inappropriately elevated and may suggest a TSH-secreting pituitary tumor. Physiologi¬ cally, small changes in the levels of free T4 or T3 lead to a small inverse-logarithmic change in serum TSH concentration, suffi¬ cient to return the free hormone level to its prior level.24 Intrapituitary T3 and, thus, TSH regulation are derived prin¬ cipally by 5'D-II (see Table 31-3) from circulating T4. TSH, there¬ fore, may be seen to rise if serum T4 is decreased, even though serum T3 is in the normal or slightly elevated range. This situation is found during primary hypothyroidism or iodine deficiency. However, with excess T3 administration, TSH secretion and thy¬ roidal iodine uptake can be greatly inhibited; this inhibition is the basis for the T3 suppression test (see Chap. 34). Consequently, most T3 used by the pituitary is generated locally. This concept is in contrast to most other human tissues that obtain their supplies of T3 from the circulation. A noted exception is the brown adipose tissue that is found in human infants and in both adult and infant rodents, which has a high activity of 5'D-II. Hypothyroidism due to an absent or failing thyroid gland leads to an elevated serum TSH (see Chaps. 33 and 44). In pri¬ mary hypothyroidism, the TSH production rate may increase 20fold.

THYROID GLAND Production of T3 and T4 by the thyroid gland is regulated primarily by circulating TSH. A small fraction of thyroidal activ¬ ity and T4 release, however, has been described as non-TSHdependent.25 TSH binds to specific membrane receptors on the surface of thyroid cells, activates intracellular adenylate cyclase, and mediates most of its action through increased cyclic adeno¬ sine monophosphate. TSH stimulation induces thyroid growth and differentiation and all phases of iodine metabolism from up¬ take to secretion of T3 and T4. Additionally, there is some auto¬ regulation of thyroid cells by iodide; however, the principal reg¬ ulation of the thyroid gland is from the pituitary. Recombinant human TSH has been commercially manufactured and has a longer half-life than endogenous TSH. This difference is proba¬ bly due to increased sialylation of the recombinant form. When available for clinical use, recombinant human TSH will expand our understanding of thyroid gland responses to TSH and be of major benefit in the management of thyroid cancer patients.

PERIPHERAL THYROID METABOLISM Many disease states result in decreased T4 to T3 conver¬ sion.13,26 Although T3 levels may be markedly depressed, serum TSH does not rise in this setting. A dissociation of peripheral (he¬ patic, 5'D-I) and central (pituitary, 5'D-II) generation of T3, as out¬ lined in Table 31-3, may help explain this observation. Severe nonthyroidal illness may depress total T4 to nearly undetectable levels and elevate free T4, suggesting a decreased binding to car¬ rier proteins (see Chap. 36). Increased tissue requirements of thy¬ roid hormones may occur during pregnancy in hypothyroid women27 and also may occur with extensive exercise.28 These variations in normal physiology depend on energy balance, tis¬ sue hormone use, and systemic and local responses, allowing thyroid hormone delivery to fluctuate over a wide range.

REFERENCES 1. DeGroot LJ. Kinetic analysis of iodine metabolism. J Clin Endocrinol Metab 1966;26:149. 2. Danforth E, Burger AG. The impact of nutrition on thyroid hormone phys¬ iology and action. Annu Rev Nutr 1989;9:201.

291

3. Berry MJ, Larsen PR. The role of selenium in thyroid hormone action. Endocr Rev 1992; 13:207. 3a. Le Mar H], Georgitis WJ, McDermott MT. Thyroidal adaptation to chronic tetraglycine hydroperiodide water purification tablet use. J Clin Endocrinol Metab 1994 (in press). 4. Namba H, Yamashita S, Kimura H, et al. Evidence of thyroid volume in¬ crease in normal subjects receiving excess iodide. J Clin Endocrinol Metab 1993; 76: 605. 5. Arntzenius AB, Smit LJ, Schipper J, et al. Inverse relation between iodine intake and thyroid blood flow: color doppler flow imaging in euthyroid humans. J Clin Endocrinol Metab 1991;73:1051. 6. Woeber KA. Iodine and thyroid disease. Med Clin North Am 1991; 75:169. 7. Toyoda N, Nishikawa M, Mori Y, et al. Identification of a 27-kilodalton protein with the properties of the type I iodothyronine 5'-deiodinase in human thy¬ roid gland. J Clin Endocrinol Metab 1992; 74:533. 8. Lever EG, Medeiros-Neto GA, DeGroot IJ. Inherited disorders of thyroid metabolism. EndocrRev 1983;4:213. 9. Burmeister LA, Goumaz MO, Mariash CN, Oppenheimer JH. Levothyroxine dose requirements for thyrotropin suppression in the treatment of differen¬ tiated thyroid cancer. J Clin Endocrinol Metab 1992; 75:344. 9a. Ozata M, Suzuki S, Miyamoto T, et al. Serum thyroglobulin in the follow¬ up of patients with treated differentiated thyroid cancer. J Clin Endocrinol Metab 1994; 79:98. 10. Kohrle J. Thyrotropin (TSH) action on thyroid hormone deiodination and secretion: one aspect of thyrotropin regulation of thyroid cell biology. Horm Metab Res 1990;23S:18. 11. Engler D, Burger AG. The deiodination of the iodothyronines and of their derivatives in man. Endocr Rev 1984; 5:151. 12. McGuire RA, Hays MT. A kinetic model of human thyroid hormones and their conversion products. J Clin Endocrinol Metab 1981;53:852. 13. Kaptein EM, Robinson WJ, Grieb DA, Nicoloff JT. Peripheral serum thy¬ roxine, triiodothyronine and reverse triiodothyronine kinetics in the low thyroxine state of acute nonthyroidal illnesses: a noncompartmental analysis. J Clin Invest 1982;69:526. 14. LoPresti JS, Gray D, Nicoloff JT. Influence of fasting and refeeding on 3,3',5'-triiodothyronine metabolism in man. J Clin Endocrinol Metab 1991; 72:130. 15. Mendel CM, Weisiger RA, Jones AL, Cavalieri RR. Thyroid hormone¬ binding proteins in plasma facilitate uniform distribution of thyroxine within tis¬ sues: a perfused rat liver study. Endocrinology 1987; 120:1742. 16. Cavalieri RR, Steinberg M, Searle GL. The distribution kinetics of triiodo¬ thyronine: studies of euthyroid subjects with decreased plasma thyroxine-binding globulin and patients with Graves' disease. J Clin Invest 1970;49:1041. 17. Bianchi R, Iervasi G, Pilo A, et al. Role of serum carrier proteins in the peripheral metabolism and tissue distribution of thyroid hormones in familial dysalbuminemic hyperthyroxinemia and congenital elevation of thyroxine-binding globulin. J Clin Invest 1987; 80:522. 18. Mol JA, Visser TJ. Rapid and selective inner ring deiodination of thyrox¬ ine sulfate by rat liver deiodinase. Endocrinology 1985; 117:8. 18a. LoPresti JS, Nicoloff JT. 3,5,3'-triiodothyronine (T3) sulfate: a major me¬ tabolite in T3 metabolism in man. J Clin Endocrinol Metab 1994; 78:688. 19. Shakir KM, Michaels RD, Hays JH, Potter BB. The use of bile acid sequestrants to lower serum thyroid hormones in iatrogenic hyperthyroidism. Ann Intern Med 1993; 118:112. 20. Solomon BL, Wartofsky L, Burman KD. Adjunctive cholestyramine ther¬ apy for thyrotoxicosis. Clin Endocrinol 1993; 38:39. 21. Greenspan SL, Klibanski A, Rowe JW, Elahi D. Age-related alterations in pulsatile secretion of TSH: role of dopaminergic regulation. Am J Physiol 1991; 260: E486. 22. Konno N, Morikawa K. Seasonal variation of serum thyrotropin concen¬ tration and thyrotropin response to thyrotropin-releasing hormone in patients with primary hypothyroidism on constant replacement dosage of thyroxine. J Clin En¬ docrinol Metab 1982; 54:1118. 23. Morley JE. Neuroendocrine control of thyrotropin secretion. Endocr Rev 1981;2:396. 24. Spencer CA, LoPresti JS, Patel A, et al. Applications of a new chemiluminometric thyrotropin assay to subnormal measurement. J Clin Endocrinol Metab 1990; 70:453. 25. Nicoloff JT, Spencer CA. Non-thyrotropin-dependent thyroid secretion. J Clin Endocrinol Metab [Editorial] 1992; 75:343. 26. Kaptein EM, Kaptein JS, Chang El, et al. Thyroxine transfer and distribu¬ tion in critical nonthyroidal illnesses, chronic renal failure, and chronic ethanol abuse. J Clin Endocrinol Metab 1987; 65:606. 27. Mandel SJ, Larsen PR, Seely EW, Brent GA. Increased need for thyroxine during pregnancy in women with primary hypothyroidism. N Engl J Med 1990; 323: 91. 28. Rone JK, Dons RF, Reed HL. The effect of endurance training on serum triiodothyronine kinetics in man: physical conditioning marked by enhanced thy¬ roid hormone metabolism. Clin Endocrinol (Oxf) 1992; 37:325.

292

PART III: THE THYROID GLAND Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

TABLE 32-1 Genes Regulated by Thyroid Hormone Receptors Gene Regulation

CHAPTER

32_

PHYSIOLOGY OF THE THYROID GLAND II: RECEPTORS, POSTRECEPTOR EVENTS, AND HORMONE RESISTANCE SYNDROMES STEPHEN JON USALA

MECHANISMS OF NORMAL THYROID HORMONE ACTION REGULATION OF GENE EXPRESSION THROUGH NUCLEAR RECEPTORS The thyroid hormone 3,5,3'-triiodothyronine (T3) has pro¬ found and diverse effects on the growth, development, and met¬ abolic processes of many different human tissues. For example, thyroid hormone is crucial for normal brain development in the neonate and for linear growth and bone differentiation in the neonate and adolescent. In adults, thyroid hormone has striking effects on basal metabolic rate, and cardiac and hepatic functions. Since the mid-1960s, significant progress has been made in un¬ derstanding the bases of thyroid hormone action, aiding elucida¬ tion of the genetic bases of thyroid hormone resistance syndromes. An important advance in understanding thyroid hormone action was the concept of receptors as high-affinity, thyroid hor¬ mone binding proteins that reside in the nucleus and bind tightly to DNA, governing gene expression (i.e., mRNA levels). Early work indicated that thyroid hormone increased RNA synthesis, and experimental efforts shifted to the nucleus as the primary site of thyroid hormone action.1,2 Specific nuclear binding sites were first demonstrated in 1972.3 T3 receptors were found to have a

Reference

UP-REGULATED WITH T3 Sarcoplasmic reticulum calcium ATPase

7

a-Myosin heavy chain

8

Spot 14

5

Lysozyme

9

Rat growth hormone

10

Prolactin

11

Apolipoprotein A1 (Spot 11)

12

Malic enzyme

5

Na+,K+-ATPase

13

DOWN-REGULATED WITH T3 /3-Myosin heavy chain

8

Epidermal keratin

14

/3-Subunit of thyroid-stimulating hormone

15, 16

a-Subunit

15, 16

physiologic association constant of approximately 4 X 1011 M-1.2 Subsequently, it was demonstrated that the T3 receptors, which could be extracted from the nuclei of various organs and tissue culture cells, were nonhistone proteins.4 The identification of nuclear T3 receptors as the “first mes¬ sengers" in thyroid hormone action was based on the following experimental data5: Nuclear T3 receptors are high-affinity and low-capacity pro¬ teins, an attribute of hormonal receptors in general. Nuclear T3 receptors are found in all thyroid hormoneresponsive tissues; there is a general correlation between receptor concentration and sensitivity to thyroid hormone (e.g., T3-sensitive hepatic nuclei have ~4000 sites/nu¬ cleus; T3-insensitive testes nuclei have only ~16 sites/ nucleus). The affinity of nuclear receptors for thyroid hormone ana¬ logues correlates with the relative degree of thyroid hor¬ mone action induced by the analogues. The interval between T3 occupation and nuclear response is short (< 1-24 hours) There is a direct correlation between the level of occupancy of the nuclear receptors and bioeffects.

GENE EXPRESSION AND THYROID HORMONE ACTION

FIGURE 32-1. The proportion of saturated (T3 occupied) receptors is approximately 50% in euthyroid liver nuclei. Data come from studies of rats with varying T3 concentrations (euthyroid concentration is 0.6 ng/ mL). (From Oppenheimer JH, Schwartz HL, Surks MI, et at. Nuclear receptors and the initiation of thyroid hormone action. Recent Prog Horm Res 1976;32: 529.)

The model of thyroid hormone action hinges on the notion that the level of T3 binding to the nuclear receptors is directly related to the level of gene activation. In the rat, it was established that, at euthyroid levels of thyroid hormone, T3 nuclear receptors were approximately 50% saturated6 (Fig. 32-1). There is ample room in the basal state for further T3 occupancy and consequent receptor activation with stimulation of gene expression. Several specific genes that were isolated were found to be up-regulated or down-regulated by thyroid hormone (Table 32-1). Only a handful of genes have been identified from the hundreds that are regulated by thyroid hormone in diverse cell types. The partial list in Table 32-1 provides some of the bettercharacterized genes, the study of which have contributed to our understanding of the molecular mechanisms of thyroid hormone action. Thyroid hormone regulation of gene expression can be divided into two broad categories: augmented or reduced gene expression resulting from T3-receptor effects on the rate of transcription (i.e., rate of nuclear RNA synthesis) and increased gene expression resulting from stabilization of mRNA. Many thyroid hormone-

Ch. 32: Physiology of the Thyroid Gland II: Receptors, Postreceptor Events, and Hormone Resistance Syndromes

nh2

100 200 300 400 500 600 700 800 J_I_I_I_I-1-1-1-COOH

hGR

hc-erbAp 152% |

I

17%

ESTRADIOL

CYS

hER

FIGURE 32-2. Thyroid hormone receptors are members of a nuclear receptor gene superfamily. The amino acid sequence of the (31 thyroid hormone receptor (hc-erbA/3) is compared with those of the glucocorti¬ coid (hGR) and estrogen (hER) receptors. These receptors belong to a gene superfamily that includes receptors for vitamin A, vitamin D, androgen, progesterone, and rnineralocorticoid. The receptors are characterized by a DNA binding domain that is cysteine (CVS) rich and highly homologous among different members. The hormone or ligand binding domain is much less homologous among different members. The immunogenic re¬ gion is in the amino-terminal domain of the hGR. (From Weinberger C, Thompson CC, Ong ES, et al. The c-erbA gene encodes a thyroid hormone receptor. Nature 1986;324:641.)

regulated genes such as the malic enzyme gene demonstrate tran¬ scriptional and posttranscriptional (i.e., stabilization) modes of control.5 The latter mechanism, although quite important, is poorly understood. However, with the identification of the nuclear thyroid hormone receptors as the c-erbA protoonco¬ genes, considerable details are available concerning the tran¬ scriptional mode of regulation.

THYROID HORMONE RECEPTORS AS MEMBERS OF A RECEPTOR SUPERFAMILY In 1986, two related protooncogenes were identified that en¬ coded proteins with the properties of high affinity and specificity for T3, characteristics that were expected for the T3 nuclear recep¬ tor. These two forms of c-erbA genes were c-erbA(3 on chromo¬ some 3 and c-erbAa on chromosome 17.17,18 The c-erbA/31 and cerbAal proteins that were predicted to be expressed by these genes were closely related on the basis of primary structure to the glucocorticoid and estrogen receptors (Fig. 32-2). Subsequent studies, including the elucidation of the molecular pathology of thyroid hormone resistance syndromes, have convincingly dem¬ onstrated that c-erbA/3 and c-erbAa function as thyroid hormone receptor genes in humans. There are several isoforms of c-erbA involved in modulating

1_159

TRp2

293

thyroid hormone action (Fig. 32-3). Two isoforms of the (3 recep¬ tor exist, c-erbAl31 and c-erbA/32, which are alternatively spliced variants from the same gene.19 Both bind thyroid hormone and can mediate thyroid hormone action, but the (82 receptor is found predominantly in pituitary, and the (81 receptor is found in all thyroid hormone-responsive tissues.19 At least two isoforms of the a receptor exist, c-erbAal and c-erbAa2; however, c-erbAa2 does not bind thyroid hormone, and it has been speculated that this protein may antagonize (i.e., act as a dominant negative) cerbA/3 and c-erbAal function.20'23 The c-erbAal receptor is pres¬ ent in all thyroid hormone-responsive tissue, and c-erbAa2 is particularly abundant in brain and testes.24'26 The specific functions of c-erbA/3 and c-erbAal in terms of regulating specific genes are being investigated, but some conclu¬ sions can be drawn regarding this question from the data on thy¬ roid hormone resistance syndromes. Localization studies by in situ hybridization histocytochemistry indicate a different distri¬ bution of a and (3 receptors in neuroanatomic regions of the rat brain.27 The /3 and al receptors have a modular structure: one por¬ tion of these proteins is cysteine rich and binds with zinc to form zinc fingers (see Fig. 32-2). The zinc finger or DNA binding do¬ main is highly conserved among members of the steroid and thy¬ roid hormone receptor gene superfamily (see Chap. 71). The par¬ ticular structure of this domain in the (8 and a receptors is critical in recognizing the cognate DNA sequences, called thyroid hor¬ mone response elements (TREs), that are present in the promoters of thyroid hormone-regulated genes (Fig. 32-4). Hexameric DNA sequences of the type AGGT(C/A)A, as single or multiplex configurations in promoters, bind thyroid hormone receptors and confer thyroid hormone sensitivity to gene expression28"30 (Fig. 32-5). These TREs are often “positive” in that the binding of T3occupied /3 or a receptor induces gene expression. However, some TREs are “negative,” because the T3-occupied receptor re¬ presses and the unoccupied receptor transactivates the gene that contains negative elements (e.g., hTSH/8).3132 The other critical portion of the thyroid hormone receptors is the ligand binding domain (see Figs. 32-3 and 32-4). During the past several years, it has become evident that this domain has several different and convoluted functions33,34 (see Fig. 32-4). There is much less conservation between the ligand binding do¬ main of the thyroid hormone receptors and that of other mem¬ bers of the steroid and thyroid hormone receptor gene superfamily.

TRANSCRIPTIONAL REGULATION OF GENE EXPRESSION BY THYROID HORMONE The DNA binding and ligand binding domains of the c-erbA proteins are critical for up-regulating (i.e., transactivation

227_514 " — -

HI lJ \ A

== FIGURE 32-3.

Different isoforms of the c-erbAa and c-erbA/3 receptors. (SI and /32 receptors are alternatively spliced variants from the c-erbA/3 gene on chromosome 3, and al and a2 receptors are alternatively spliced variants from c-erbAa on chromosome 17. The cerbAa2 protein does not bind thyroid hormone, but the al, (81, and @2 proteins function as bona fide thyroid hormone receptors. Amino acid sequences that are identical or different are indicated by shading. The DNA binding domain is highly conserved among all these isoforms; the thyroid hormone binding domain is also highly conserved between the /SI//S2 receptor and the al receptors. (From Lazar MA. Thyroid hormone re¬ ceptors: multiple forms, multiple possibilities. Endocr Rev 1993:14:184.)

294

PART III: THE THYROID GLAND 1

106

174

240

461

ABNORMAL THYROID HORMONE ACTION IN RESISTANCE SYNDROMES GENERALIZED RESISTANCE TO THYROID HORMONE

DNA-Binding

Thyroid Hormone-Binding Transactivation (Up-regulation) Homodimerization Heterodimerization Silencing/Active Repression (Down-regulation)

FIGURE 32-4.

Functions of the DNA binding domain (amino acids 106-174) and T3 binding domain (amino acids ~240-461) of c-erbA/31.

function) and down-regulating (i.e., repression function) gene expression. The co-regulatory proteins that interact with the /? and a receptors are called thyroid hormone auxiliary proteins (TRAPs)34-41 (Fig. 32-6). The existence of these transcription fac¬ tors-was first discerned by the ability of nuclear extracts to in¬ crease c-erbA binding to TREs on electrophoretic mobility shift assay (gel-shift).35 Subsequently, retinoid X receptors (RXRs), which are members of the thyroid, steroid, and retinoic acid re¬ ceptor gene superfamily, were shown to heterodimerize with the thyroid hormone receptors and behave as TRAPs, and RXRs can increase the level of T3-induced gene expression.34,37 However, proteins other than the RXRs are TRAPs as well.38 A domain within the T3 binding region that is critical for heterodimer formation has been identified by in vitro mutagene¬ sis studies.36 A segment of the T3 binding region (boilnded by amino acids 349-428 in the /SI receptor) contains a series of heptad repeats that form a leucine zipper structure, which mediates dimerization activity.39 Thyroid hormone receptors form hetero¬ dimers on artificial and native TREs and form homodimers.34,40,41 It is thought that the heterodimer structure is more important in mediating transactivation, although some TREs (e.g., F2 element; see Fig. 32-6) preferentially bind receptor homodimers.41 Thy¬ roid hormone occupancy causes dissociation of homodimers from some TREs, possibly making the heterodimer the predomi¬ nant DNA binding species in the hyperthyroid state.40 The exact mechanisms of up-regulation of transcription rate after thyroid hormone activation of c-erbA homodimers or heterodimers are not understood. However, one mechanism that may explain the down-regulation and up-regulation of certain T3-regulated genes is active repressic (i.e., silencing) by unoccupied thyroid hor¬ mone receptor ar relief of repression with T3 occupancy42-44 (see Fig. 32-6). Un .cupied thyroid hormone receptor can repress reporter gene expression below basal rates. Studies suggest that unoccupied c-erbA proteins, which bind to TREs in certain pro¬ moters, may block the formation of a preinitiation complex (PIC) of basal transcription factors near the start site of transcription. Thyroid hormone occupancy of receptor would relieve this hin¬ drance; in some manner, PIC formation would increase, with a consequent increase in transcription rate. A

B

-190 _^

C

^_

-160

AAAGGTAAGATCAGGGACGTGACCGCAGGAGA FIGURE 32-5.

Promoter element from the rat growth hormone gene that is up-regulated by thyroid hormone. A, B, and C (arrows) are the hexameric half-site DNA sequences that bind thyroid hormone receptors and confer thyroid hormone inducibility to the gene. The direct repeat of half-sites (A and B) separated by four base pairs binds receptor homodi¬ mers or heterodimers most tightly and is thought to be the strongest reg¬ ulatory component. Different numbers and configurations of half-sites are thought to result in thyroid hormone-responsive promoters; the structural motif of a direct repeat of half-sites (AGGTCA) separated by four base pairs has been reported in natural promoters. (Redrawn from Brent GA, Moore DD, Larsen PR. Thyroid hormone regulation of gene expres¬ sion. Annu Rev Physiol 1991;53:17.)

In 1967, a bizarre finding in two young deaf-mutes was re¬ ported by Refetoff and coworkers.45 These patients had delayed bone ages and stippled epiphyses consistent with juvenile hypo¬ thyroidism but, paradoxically, significantly elevated levels of cir¬ culating thyroid hormones. It was concluded that these Refetoff patients had a tissue-specific combination of hypothyroidism, hyperthyroidism, and euthyroidism. Because tissues such as bone and brain were judged to lack the appropriate sensitivity to the high levels of thyroid hormone and the patients failed to manifest other common symptoms and signs of hyperthyroid¬ ism, it was proposed that the Refetoff patients were the first ex¬ ample of thyroid hormone resistance. Time has validated this conclusion. Many kindreds and spo¬ radic patients with thyroid hormone resistance syndromes have been studied. The most common form of thyroid hormone resis¬ tance is called generalized resistance to thyroid hormone46 (Fig. 32-7) Patients with this form must satisfy three criteria: elevated serum levels of free thyroid hormones (i.e., free T3 and free thy¬ roxine [T4]), inappropriately normal levels of serum TSH, and clinical euthyroidism. Patients with the syndrome of generalized resistance to thyroid hormone manifest a proportional decrease in sensitivity to thyroid hormone in the pituitary and many of the peripheral tissues. As manifested by the Refetoff patients, there may be variable degrees of tissue sensitivity to thyroid hormone. In other examples, patients with generalized resistance to thyroid hormone are affected in the brain (i.e., reduced intelligence quo¬ tient resulting in part from resistance) but have no evidence of resistance in the bone compartment (i.e., normal final adult height).46 The variable tissue resistances are reflected in the different phenotypes of generalized resistance to thyroid hor-

DR+4

+T3 Activation of transcription or relief of repression TH - regulated gene

(released with T3) FIGURE 32-6. Model of thyroid hormone receptor regulation of tran¬ scription. A schematic thyroid hormone (TH)-regulated gene is shown with a promoter region containing preinitiation complex (PIC) and thy¬ roid hormone-response element (TRE). Heterodimer (T-R) or homodimer (R-R) of TRAP (f) and thyroid hormone receptor (R) molecules are shown binding to two different TREs: a direct repeat of half-sites separated by 4 base pairs (DR+4) and reversed half-sites separated by 6 base pairs (F2). The arrows indicate half-sites with the sequence AGGTCA; the stoichi¬ ometry is such that one half-site binds one molecule of a receptor or TRAP. The DR+4 and F2 TREs have been identified in different thyroid hormone-regulated genes. Heterodimers of TRAP-thyroid hormone re¬ ceptor bind preferentially to DR+4, and homodimers of thyroid hormone receptors bind preferentially to F2. Structural studies indicate the con¬ figuration of TRAP-receptor heterodimers is with the TRAP molecule at the 5' side of the promoter. In the presence of thyroid hormone, the level of transcription is increased (i.e., transactivation) or repression is relieved. Thyroid hormone occupancy of homodimers appears to induce dissocia¬ tion from certain TREs but does not result in dissociation of receptor TRAP heterodimers.

Ch. 32: Physiology of the Thyroid Gland II: Receptors, Postreceptor Events, and Hormone Resistance Syndromes T4.T3 I.

TSH

Pituitary

T4.T3

Thyroid

Peripheral Tissues

Generalized Resistance to Thyroid Hormone

295

tion is not increased to compensate for the increased peripheral resistance (see Fig. 32-7). One well-studied patient on large doses of exogenous T3 had clinical hypothyroidism and suppressed TSH.48 It may be that selective peripheral resistance to thyroid hormones is more common than this one patient and escapes diagnosis. Making this diagnosis is difficult, because the markers of thyroid hormone action in humans, with the exception of TSH levels, lack quantitativeness.

T4T3

f II.

Pituitary

TSH

■ Thyroid

T4.T3

Peripheral Tissues

Selective Pituitary Resistance to Thyroid Hormone

T4J3

III.

Pituitary

TSH

Thyroid

T4T3

Peripheral Tissues

Selective Peripheral Resistance to Thyroid Hormone FIGURE 32-7.

Three clinical forms of thyroid hormone resistance in humans. The first shows blockage of the biologic responses to thyroxine (T4) and triiodothyronine (T3) in the pituitary and peripheral tissues, which is characteristic of generalized resistance to thyroid hormone. The second shows selective blockage at the pituitary, which is characteristic of selective pituitary resistance to thyroid hormone. The third shows se¬ lective blockage at the peripheral tissues, as described in one patient with selective peripheral resistance to thyroid hormone. Patients with identi¬ cal mutations in the c-erbA/3 thyroid hormone receptor can present clini¬ cally with generalized or selective pituitary resistance. (Modified from Usala S], Weintraub BD. Familial thyroid hormone resistance: clinical and molecular studies. In: Mazzaferri E, Kreisberg RA, Bar RS, eds. Advances in endocrinology and metabolism, vol 2. Chicago: Mosby-Year Book, 1991:59.)

mone. However, by definition, the patients lack the clinical stig¬ mata of hyperthyroidism, such as weight loss, heat intolerance, nervousness, and hyperkinesis, and the compensatory elevation of thyroid hormone is such that the patients do not have com¬ plaints of hypothyroidism. In 108 different kindreds with gener¬ alized resistance to thyroid hormone, most patients were identi¬ fied after screening for goiter.46

SELECTIVE PITUITARY RESISTANCE TO THYROID HORMONE A less common form of resistance is selective pituitary resis¬ tance to thyroid hormone, in which the sensitivity to thyroid hor¬ mone is decreased in the pituitary relative to peripheral tissues (see Fig. 32-7). Most of the patients with this syndrome have in¬ appropriately normal TSH at elevated levels of free thyroid hor¬ mone, similar to generalized resistance to thyroid hormone, but with signs and symptoms of hyperthyroidism.46,4' The last crite¬ rion is often a subjective one; the assignment of selective pituitary or generalized resistance to thyroid hormone may be less than rigorous. Because the phenotypic borders are often not sharp, differentiating selective pituitary from generalized resistance to thyroid hormone can be a problem.46,47

SELECTIVE PERIPHERAL RESISTANCE TO THYROID HORMONE Another form of resistance is selective peripheral resistance to thyroid hormone, which is of more theoretical than therapeutic significance.46,48 In this form, the sensitivity of peripheral tissues to thyroid hormones is decreased relative to the pituitary, to the point of clinical hypothyroidism; thyrotropic resistance to thy¬ roid hormone is nonexistent or inadequate, and the TSH secre-

GENETIC MUTATIONS IN THYROID HORMONE RESISTANCE SYNDROMES Generalized resistance to thyroid hormone is a genetic dis¬ ease. Most reported cases belong to families with multiple affected members, and inspection of these pedigrees reveals that, in all but the original Refetoff kindred, the abnormal trait is transmitted dominantly.46 Compelling evidence that generalized resistance to thyroid hormone is a disease of the c-erbA/3 thyroid hormone receptor gene has come from linkage studies.46,50 Re¬ striction fragment length polymorphisms (RFLPs) have been used to establish tight linkage between the /3 receptor gene and the syndrome of generalized resistance to thyroid hormone. There is no counterexample to linkage between this condition and c-erbA/3; there is not yet a case of an a receptor gene mutation associated with thyroid hormone resistance. Given the dominant inheritance pattern of pedigrees of gen¬ eralized resistance to thyroid hormone, it was originally postu¬ lated that resistance occurred because mutant /3 receptors inhib¬ ited the activity of the normal (3 and al receptors (from one and two alleles, respectively).46 This hypothesis was convincingly proved in humans from the recessive kindred that has been ex¬ tensively studied by Refetoff and coworkers.51,52 At least 28 mu¬ tations in the T3 binding domain of the c-erbAfi gene have been isolated from different families with generalized resistance to thyroid hormone46 (Fig. 32-8). These mutations exist as single (i.e., heterozygous) alleles, except in the Refetoff and Bercu pa¬ tients.51,52,57,59 With the exception of one mutation, all congregate in subregions of the penultimate and final exons of the c-erbA/3 gene.53 These exons comprise the C-terminal portions of the T3 binding domain (see Fig. 32-8).

HOMOZYGOUS EftBA/3 MUTATIONS IN REFETOFF AND BERCU PATIENTS Two human mutants, the Refetoff and Bercu patients, pro¬ vide important information on the interrelationships of the a and /3 receptors in mediating thyroid hormone action in humans (Fig. 32-9). These human mutants are homozygous for very different abnormalities in c-erbA/3 and have very different phenotypes. The resistance syndrome of the Refetoff patient is consider¬ ably milder that of the Bercu patient (see Fig. 32-9). Although the original bone x-ray films of the first Refetoff patient suggested juvenile hypothyroidism, the final adult height in affected mem¬ bers was above the parental mean. The intelligence quotients of the Refetoff patients were normal compared with the ranges seen in hearing-impaired individuals.58 The Refetoff patients have a major deletion in both /3 receptor alleles and have only functional a receptors.51,52 Significantly, the obligate heterozygotes in the Refetoff kindred are phenotypically normal; these heterozygotes have normal TSH and thyroid hormone levels. It is possible to draw several conclusions from the Refetoff patients that only one /3-receptor allele is necessary (with two a receptor alleles) for nor¬ mal thyroid hormone action in humans; most or at least life-sus¬ taining thyroid hormone action can be mediated solely through the a receptor; and the heterozygous, mutant c-erbA/3 alleles in resistance patients act as dominant negative genes. The obligate heterozygotes demonstrate that it is not the loss of function 01 a 0 receptor allele that results in thyroid hormone resistance. The Bercu patient (see Fig. 32-9) has a complex pattern of

236

PART III: THE THYROID GLAND

SERUM [mean ± SD] (percent of the mean) FAMILY

FIGURE 32-8. Mutations in the c-erbAp thy¬ roid hormone receptor gene responsible for gen¬ eralized thyroid hormone resistance. The rela¬ tive sites of the mutations in the T3 binding domain of the receptor with the alterations in amino acids are indicated. The last three exons of the p gene comprise amino acids 247-295, 296381, and 382-461. The relative deficiencies in the T3 binding affinities of the mutant receptors measured in vitro (1.0 = no defect, 0.01 = 100fold reduction in Ka) are shown (Ka mutant/ Ka wild-type). The mean total T4, total T3, and thyroid-stimulating hormone levels for the pa¬ tients are listed; the results in brackets are mean values expressed as a percent of the correspond¬ ing mean levels of unaffected family members or the mean value for the laboratory. F100, F102, and F108 had prior (inappropriate) ablative ther¬ apy and were on T3 therapy. F68 values are free T4 arid free T3 given in picomoles per liter. The T3 binding domain of c-erbAp spans amino acids ~243-461, at the COOH terminus. The black bars represent areas that interact with thyroid hormone auxiliary proteins (TRAPs) and stabi¬ lize TRAP-receptor heterodimers. Some of these regions may stabilize homodimers of c-erbA/3 as well. The 349-428 region contains heptad re¬ peats (gray boxes) with hydrophobic amino acids that form a leucine zipper structure, which is in¬ volved in receptor dimerization. Some of these heptads appear to be critical for the dominant negative function of mutant c-erbApl receptors, although other domains may be involved. (From Refetoff S, Weiss RE, Usala SJ. The syndrome of re¬ sistance to thyroid hormones. Endocr Rev 1993;14348.)

hyperthyroidism and hypothyroidism resulting from homozy¬ gosity of a dominant negative allele.57 S9 This patient manifested severe pituitary resistance with strikingly elevated TSH levels in the setting of high free thyroid hormone levels. Significant growth and profound bone retardation suggested hypothyroid¬ ism. However, this patient was tachycardic and appeared to be hypermetabolic, consistent with hyperthyroidism. The patient

CODON

MUTATION

310

Met -»Thr

317

Ala - Thr

b

__ TT4

Ka wild type

^g/dl

tt3 ng/dl

15.8 ± 3.7 (190)

253 ± 72 (171)

4.7 ± 2.1

28.0 (350)

205

4.2

(173)

Ka mutant

“

TSH ,uU/ml

317

Ala - Thr

0.22 ± 0.07

_c

-C

320

Arg -»Cys

0.49 ±0.10

15.3 ± 2.3d (180)

246 ± 35d (141)

3.2 ± 1.4d

320

Arg -* His

0.51 ± 0.29

14.9 ± 1.8 (165)

286 ± 53

2.2 ± 1.3

22.1e

334s

332

Gly -» Arg

“

337

Thr deletion

2000 rad) are not well defined because of relatively short follow-up in reported series. Although low-dose irradiation does not produce hypothyroidism, larger doses, such as those used for Hodgkin disease, are associated with a high rate of thy¬ roid dysfunction, as manifested by elevated serum TSH levels, with or without hypothyroxinemia.22 Despite a postulated in¬ ducer effect of elevated TSH levels, and despite some reports of nodular thyroid disease, including carcinoma, in patients who have received high-dose irradiation, there is no definitive evi¬ dence of an increased incidence of carcinoma in this group. Con¬ sideration of isodose curves, penumbra effect, backscatter, and specifics of the employed field suggests that many of the reported thyroid lesions occurring after higher dose radiation therapy ac¬ tually have been associated with low-dose exposure of the thyroid.23

347

As with high-dose external irradiation, iodine-131 (131I) therapy does not appear to be causally related to subsequent thy¬ roid carcinoma. In both cases, the high-dose thyroid exposure with attendant cell destruction, fibrosis, and hypothyroidism may serve to attenuate any carcinogenic effect.

DIAGNOSTIC EVALUATION OF THE THYROID NODULE Because most thyroid nodule morbidity is related to cancer¬ ous lesions, clinical evaluation focuses on the identification of malignant nodules. Numerous methods have evolved to better define the probability of cancer in a given lesion.

HISTORY AND PHYSICAL EXAMINATION The single most important historical risk factor for cancer is irradiation. It is important to determine the age at exposure, the type and site of therapy, and if possible, the radiation dose to the thyroid. A family history of pheochromocytoma, hypercalcemia, mucosal abnormalities, or medullary thyroid carcinoma should raise suspicion of the latter diagnosis as part of the multiple en¬ docrine neoplasia syndrome (see Chap. 182). A family history of benign goiter may be reassuring, although the rare Pendred syndrome (familial goiter and deaf-mutism) is associated with a higher cancer risk 1-3 Nodules in men are more likely to be malig¬ nant than in women; nodules in children are more likely to be malignant than in adults. The diagnosis of thyroid lymphoma should be considered in patients with a previous diagnosis of Hashimoto thyroiditis, especially in women older than 50 years of age. The following clinical findings are thought to be more com¬ mon in malignant than benign nodules: a history of radiation therapy, a family history of multiple endocrine neoplasia type 2A or 2B, rapid growth, hoarseness, pain, dysphagia, respiratory obstructive symptoms, and growth of the nodule despite T4 med¬ ication; and physical examination findings of cervical lymphadenopathy, firmness, documented nodule growth, vocal cord pa¬ ralysis, fixation, and Horner syndrome. In general, signs and symptoms alone are not sufficiently sensitive or specific to allow selection of candidates for surgery. However, patients with ad¬ vanced disease may present with lymphadenopathy, recent growth of hard nodules, and vocal cord paralysis, all of which suggest malignancy; the presence of obstructive symptoms is less reliable.1-24 As indicated, identification of a single nodule renders the patient at higher risk than does multinodularity.25

LABORATORY TESTS The commonly employed blood thyroid function tests often are of limited value in the evaluation of thyroid nodules. Func¬ tional thyroid parameters, including serum T3 and T4 or TRH stimulation (see Chaps. 17 and 33), are useful in evaluating pos¬ sible toxic adenomas. Thyroglobulin levels may be elevated in patients with thyroid malignancy but do not differentiate malig¬ nant from benign adenomas or from thyroiditis. Serum antithyroglobulin and antimicrosomal antibodies also are of limited value.1-3 An increased basal plasma calcitonin level is reasonably sensitive and specific for medullary thyroid carcinoma in the set¬ ting of a thyroid nodule, although abnormal calcium and pentagastrin stimulation tests provide the greatest sensitivity (see Chaps. 40, 52, and 182). In one large series, an elevated plasma calcitonin level was found in 0.5% of all thyroid nodules and in 15.7% of all thyroid carcinomas, leading the authors to recom¬ mend routine measurement in the evaluation of thyroid nod¬ ules.26 Serum carcinoembryonic antigen levels are also elevated in most patients with medullary thyroid carcinoma but they may be increased in patients with other thyroid carcinomas as well.1-5-27 None of these tests intended to detect medullary thy-

348

PART III: THE THYROID GLAND

roid carcinoma is cost-effective for the initial evaluation of the nodular thyroid.

THYROID SCANNING RADIONUCLIDE UPTAKE Based on the pattern of radionuclide uptake (see Chap. 34), nodules may be classified as hot (hyperfunctioning) or cold. Hy¬ perfunctioning nodules rarely represent malignancy, nondelineated or hypofunctioning lesions carry an intermediate risk, and nonfunctioning (cold) nodules have the highest risk.2,28 More than 80% of nonfunctioning nodules, however, still represent benign pathology. Therefore, radioisotope scans are of low diag¬ nostic specificity despite their high sensitivity for nodules more than 1 cm in diameter.29 Scanning usually is done with 123I or technetium-99m (99mTc) pertechnetate. Despite some limitations, the advantages of low radiation dose, low cost, short scanning time, and reliability have led to the wide use of "mTc. 123I also delivers low radiation and is the preferred iodine scanning agent. In addition to functional information, scans may reveal multi¬ nodularity in up to one third of clinically palpable solitary le¬ sions, a finding that decreases the likelihood of malignancy. 8 FLUORESCENT THYROID SCANNING Fluorescent thyroid scanning employs americium-241, which can excite thyroidal iodine, causing the release of x-rays, which quantitatively correlates with iodine content of the imaged tissue. Fluorescent scanning is rapid and provides minimal radi¬ ation exposure, thereby offering special advantages for children and pregnant women. The procedure is nearly 100% sensitive but only 64% specific when areas of low iodine content are taken as positive results.29 However, a large series has indicated that the converse analysis may be more reliable because areas with an iodine content ratio above 0.60 yielded 63% sensitivity and 99% specificity for benign lesions.30 Unfortunately, the required equipment is not widely available, and accumulated data remain too limited for this technique to be used routinely. The utility of other radionuclides in differentiating benign from malignant lesions of the thyroid has been investigated, in¬ cluding thallium-201, selenomethionine-75, gallium-67, and cesium-131. None of these has proved to be a reliable indicator of malignancy.2 OTHER THYROID IMAGING TECHNIQUES Radiography. Routine x-ray techniques have long been used in an attempt to identify calcifications characteristic of malig¬ nancy, but they are of limited value. Shell-like calcifications are most typical of benign cysts, stippled (psammomatous) calcifica¬ tions have high specificity for papillary carcinoma, and flocculent deposits are more characteristic of medullary carcinoma, but other descriptive terms of calcification have minimal predictive value.1,2 Ultrasonography. Ultrasonography is frequently used to evaluate the thyroid. Conventional US techniques are most valu¬ able in differentiating solid from cystic lesions.31 This differenti¬ ation is important because solid lesions have a higher malignant potential and require different therapy. However, cystic lesions larger than 4 cm in diameter may pose a significant cancer risk.1 Modern high-resolution US provides detailed information and can demonstrate lesions as small as 2 mm; this increased sensi¬ tivity has revealed that pure simple cysts are exceedingly rare because most cystic lesions contain some solid components.32 Al¬ though high-resolution US discloses multinodularity in up to 40% of glands presumed to have a single palpable nodule, it is unclear whether this "subclinical" multinodularity has the same favorable connotation as multinodularity detected with the less sensitive techniques of physical examination or radionuclide scanning (see Chap. 35).

US may be used for the following purposes: to differentiate solid from cystic nodules, to detect multinodularity, to detect oc¬ cult thyroid malignancy in cases of metastatic cervical lymphadenopathy from an unknown primary, to monitor the size of a nod¬ ule (including any response to suppressive therapy), to differentiate solid from hemorrhagic expansion in fast-growing thyroid lesions, to guide needle biopsy in selected cases, to mon¬ itor irradiated thyroids, and to monitor the local recurrence of thyroid carcinoma. Unfortunately, the value of US in specifically identifying malignancy is limited. Carcinomas are usually hypoechoic, but many adenomas have a similar echogenicity. The ap¬ pearance of a 1- to 2-mm, decreased echogenic halo surrounding nodules strongly favors follicular adenoma as the diagnosis, but this also has been found in a few carcinomas.32 Other Imaging Techniques. Two other imaging techniques deserve mention. Computed tomography (CT) can provide de¬ scriptive information similar to that achieved with US but offers no advantages except in cases of mediastinal extension.33 CT is associated with high doses of ionizing radiation, is more expen¬ sive, and requires iodine contrast media for maximal visualiza¬ tion. US is preferable to CT as a thyroid imaging method in most cases. Magnetic resonance imaging of the thyroid does not require iodine contrast or involve radiation exposure and provides supe¬ rior vascular imaging and substernal views as compared with CT, but both CT and magnetic resonance imaging are useful for substernal goiter and for both initial presentation and recurrence of thyroid malignancies (see Chap 35). Use of positron emission to¬ mography scanning in the assessment of thyroid nodules is still being evaluated.34

THYROID HORMONE SUPPRESSION Thyroid hormone has been used for many years to reduce the size of thyroid lesions thought to be dependent on TSH stim¬ ulation. As a diagnostic test for thyroid nodules, the assumption is that benign lesions will show preferential reduction in size. Typically, patients are given a 3- to 6-month trial of T4 at a dose titrated to result in undetectable serum TSH in an ultrasensitive assay or unresponsiveness of TSH to TRH stimulation, but with¬ out inducing clinical hyperthyroidism. Continued growth of a nodule or lack of reduction in size during therapy increases the suspicion of malignancy. However, an absolute reduction in size sufficient to denote benignancy has not been determined, and various investigators have adopted different criteria for response, rendering the interpretation of results more difficult. A partial response to treatment is not particularly reassuring because there may be inconsistency in palpated size and/or a misleading ap¬ parent reduction in size of a nodule due to regression of sur¬ rounding normal tissue. About 7% to 16% of nonresponding le¬ sions harbor carcinoma, and an occasional carcinoma has exhibited partial regression.2 Largely uncontrolled studies have suggested that a complete response to suppressive therapy occurs in less than 10% of cases, while a 50% reduction in size is seen in about 30% of cases.4 However, a recent double-blind controlled study found no significant difference in sonographically mea¬ sured colloid nodule size reduction between a group of patients treated with suppressive doses of T4 and those treated with pla¬ cebo.35 Although 21% of thyroid hormone-treated nodules de¬ creased more than 30% in volume over 6 months, equivalent size reductions were noted in nodules in the placebo-treated group. Some confirmation of these findings was provided by the failure to observe significant shrinkage of nodules on T4 therapy in two other studies.36,37 On the other hand, other workers continue to suggest that suppressive therapy may shrink both nontoxic goi¬ ter38 and thyroid nodules.39”42 Additional carefully controlled studies of large numbers of patients are required to clarify the management of thyroid nodules with suppression therapy. The increasing concern about possible risk of osteopenia after long¬ term suppressive doses of thyroid hormone has been allayed

Ch. 39: The Thyroid Nodule somewhat by careful analyses of the data.43 Use of prudent sup¬ pression doses of T4 has not been shown to contribute to osteope¬ nia.44 Moreover, supplementation of T4 with estrogen replace¬ ment in postmenopausal women may totally obviate any potential risk of osteopenia.45 It appears that failure of suppression minimally increases the probability of cancer, while successful suppression reduces the probability by about 25%.4 An unusual category of lesions that may carry an exceptionally high risk of carcinoma are those that respond initially to thyroid hormone but later grow.4 A trial of thyroid hormone suppression alone is neither sensitive nor spe¬ cific but may have utility as an adjunct to other modalities of evaluation. This therapy requires periodic and regular follow-up.

THYROID NEEDLE ASPIRATION AND BIOPSY Obtaining tissue or cells from a thyroid nodule by some form of biopsy technique is the best single method to identify malig¬ nancy. Biopsies can be performed by fine-needle (22- to 27gauge) aspiration (FNA), large-needle (16- to 18-gauge) aspira¬ tion, or cutting-needle biopsy (14-gauge Tru-cut or Silverman needle). Most clinicians have found FNA to provide the highest incidence of successful samples and the lowest incidence of com¬ plications while yielding a diagnostic precision equal to or better than that of other methods.2 This technique is shown in Figure 39-1. In selected large lesions for which FNA has failed to pro¬ vide a satisfactory diagnosis, some other aspiration method may be used. FNA has been popular in Europe for decades but only re¬ cently has attained similar acceptance in the United States. The

349

ability to obtain adequate samples improves with experience, and the success rate approaches 95%. However, the collecting tech¬ nique appears less critical than the ability of the pathologist to interpret the cytologic specimens correctly. Because of these two primary factors, this procedure is best limited to situations in which the operator and pathologist each have considerable ex46-48 penence. FNA may yield a variety of descriptive diagnoses.49'50 The most common and important categories are typically benign, sus¬ picious for malignancy, malignancy, or inadequate for diagnosis. Ex¬ amples of cytologic and histologic features are shown in Figure 39-2. At least 60% of aspirates are benign. The determination of sensitivity and specificity depends on whether suspicious lesions are considered positive. This latter group is primarily composed of highly cellular lesions, which represent about 20% of aspira¬ tions, of which 20% are cases of malignancy.51 When all suspi¬ cious lesions are taken to surgery, the sensitivity of FNA exceeds 90%, with specificity approximating 70%.29-51,52 The specificity of FNA for the malignant aspirates probably exceeds 95%. The use of FNA has decreased the frequency of surgery by 50% while doubling the rate of finding carcinoma in patients operated on. The relative economic advantage of this technique has been documented.5 29 Difficulties in interpretation of FNA biopsy specimens in¬ volve the differentiation of cellular specimens from possible Hurthle cell tumors, low-grade carcinomas, cellular adenomas, and Hashimoto thyroiditis. A few clinicians have performed quantitative DNA analyses on aspirated thyroid cells in an at¬ tempt to distinguish benign from malignant lesions.53 DNA mea¬ surements have been unsuccessful, although the technique may provide prognostic indications of malignant tumor aggressive¬ ness, with correlation to outcome and survival. Another ap¬ proach being evaluated is to perform immunohistochemistry on the FNA sample.54 Hashimoto disease also may be difficult to differentiate from lymphoma or from carcinoma with background Hashimoto changes. Anaplastic carcinomas may resemble poorly differen¬ tiated lymphoma or granulomatous thyroiditis. Cysts pose several diagnostic difficulties.31 Attempts to cor¬ relate characteristics of aspirated fluid with pathologic diagnosis have proved unreliable, although the occasional finding of clear, colorless fluid is typical of parathyroid cysts.2 Cystic fluid may be difficult to aspirate unless a large needle is used. Cells obtained by centrifugation of cyst fluid may provide insufficient or confusing information.49 Any solid remnant that follows initial cyst aspira¬ tion should be subjected to cautious follow-up and consideration for repeat aspiration. Finally, solid nodules less than 1 cm or more than 4 cm in diameter may be associated with an increased sam¬ pling error. FNA carries minimal risk when properly performed. Con¬ cerns have been raised as to the possibility of severe local hemor¬ rhage with airway obstruction and recurrent laryngeal nerve damage, but such complications are not documented in large re¬ ported series of FNA.2'51 Bleeding complications are unusual and almost always self-limited. However, core biopsies have been as¬ sociated with occasional severe bleeding and rare reports of tu¬ mor seeding.

INTEGRATED APPROACH TO THYROID NODULES

FIGURE 39-1.

Technique for fine-needle aspiration biopsy. A, Aspirate 1 to 2 mL of air into syringe to loosen plunger and facilitate expiration of contents after aspiration. B, Insert needle into lesion without aspiration. C, Retract syringe piston to provide maximum suction. D, Make several passes at different angles, withdrawing needle to near the surface before redirecting. E, Release suction passively. F, Withdraw needle. G, Express needle contents onto a glass slide.

The clinical challenge in thyroid nodule management is to define a diagnostic protocol that will produce the most accurate and cost-effective use of the various diagnostic methods. The im¬ plementation of decision analysis appears to highlight the diffi¬ culty in attaining this goal because consideration of all possible combinations of tests would require unmanageable decision trees, and the calculation of individual occurrence probabilities depends on an inconsistent literature. Limited decision analysis

350

PART III: THE THYROID GLAND

FIGURE 39-2.

(See legend on opposite page)

has suggested that FNA biopsy, the most accurate single evalua¬ tion technique, provides a minimal advantage in quality-adjusted life expectancy over the use of the usually inexact trial of thyroid suppression in patients already known to have solid, cold thyroid nodules. Either of these latter approaches appear slightly supe¬ rior to a decision tree selecting immediate surgery when life ex¬ pectancy is used as the gauge, but the differences may not be significant.4 On the other hand, analysis of the selection of radio¬ nuclide scanning indicates questionable benefit because initial aspiration can provide equal sensitivity and specificity at a lower cost.29 Figure 39-3 suggests an algorithm that may be useful in a practice in which FNA biopsy is frequently used and experienced cytopathology support is available. Many factors may alter the

protocol for individual patients or clinical practice situations. At present there is no right or wrong approach, and many physici¬ ans prefer radionuclide imaging as the initial step. However, this may increase costs because only 5% to 10% of scans obviate the need for aspiration, whereas 60% of 80% of FNA biopsies elimi¬ nate scan requirements. The utility of scans in identifying multi¬ nodularity is largely replaced by the high incidence of benign cytology results in these cases. Aspiration and biopsy identify predominantly cystic lesions, which rarely are simple cysts; therefore, US has limited utility initially but may be of significant value in monitoring the results of suppressive therapy, especially in patients with suspicious lesions and in practices in which the patient may see different clinicians on follow-up. It can be argued that the 20% to 25% cancer risk in suspicious lesions should lead

Ch. 39: The Thyroid Nodule

351

asp^srrstf* FIGURE 39-2. A, Fine-needle aspirate (FNA) of follicular neoplasm showing hypercellular specimen consisting of fol¬ licular epithelium (X150). B, Microfollicular structures with centrally located colloid (arrow). Follicular cell nuclei are en¬ larged and pleomorphic (FNA of follicular neoplasm, X540). C, Follicular carcinoma (histology). Note well-defined cap¬ sule with invasion (arrow). Residual normal thyroid gland is present at top of the field (X95). D, Papillary carcinoma (FNA). Specimen is hypercellular, with numerous papillary clusters (X150). E, Papillary cluster with diagnostic intra¬ nuclear inclusions at arrow (X960). F, Hashimoto thyroiditis (FNA). Note chronic inflammatory background with reactive lymphocytes. A follicular epithelial group showing oxyphilic metaplasia is seen in the background. Note enlarged nuclei and granular cytoplasm of these cells (arrow) (X480). (Slides and legend text courtesy of Dr. Sanford Robbins. Photography courtesy of Charles Brown, M.S. From the Department ofPathology, Walter Reed Army Medical Center, Washington, DC.)

352

PART III: THE THYROID GLAND Single Nodule on Examination

FNA*

Probably malignantf

Probable follicular neoplasm:}:

Radionuclide scan

Surgery

I Hot

I Evaluate for hyperthyroidism

I Cold

I Surgery"

Inadequate specimen lnconclusive§

Benign

1. Repeat FNA^J (consider large needle) 2. Trial of suppressive therapy with follow-up at 6 mo

Size reduction

Follow

No size change

Reaspirate^J Follow if negative

T4 suppression Reevaluate every 6 mo Repeat FNA at least once^l

Repeat FNA (consider large needle)

Enlargement

Surgery

Growth or p0s. aspirate

Surgery FIGURE 39-3. Approach to the solitary nodule. *22- to 25-gauge needle, repeated with 18-gauge nee¬ dle if fluid is obtained. -(Evidence of carcinoma (papillary, medullary, poorly differentiated, follicular) or lymphoma. fFor example, sheets of follicular cells. §For example, small groups of uniform follicular cells with little colloid. ||Selected patients with above normal surgical risk or other extenuating circumstances may be followed closely with suppressive therapy. IfChanges in cytologic findings redirect clinician to the appropriate arm of the algorithm. FNA, fine-needle aspiration.

to immediate surgery in all cases, but a trial of suppressive ther¬ apy may still be warranted in selected patients. In many border¬ line clinical situations, the patient's strong preference or surgical risk factors may be important considerations. When a trial of sup¬ pressive therapy is undertaken, the approximate dosage required is greater than 1.7 jug/kg/day of T4.55 The dose is increased in¬ crementally by 0.025 mg/day every 5 to 6 weeks with TSH mon¬ itoring until a suppressed TSH is observed. Nodules are assessed for change in size by physical examination (or US if required) every 6 weeks for the first 6 months. The follow-up intervals may be more prolonged when significant decreases in size are ob¬ served, extending eventually to annual follow-up. FNA biopsy should be repeated immediately when a nodule is found to be enlarging on suppressive therapy, with surgical exploration likely to be inevitable unless cystic fluid or hemor¬ rhage with benign cytology is obtained. FNA should also be re¬ peated when there is failure to obtain significant reduction in nodule size after 6 to 12 months of suppressive therapy. Of re¬ peat FNA biopsies, 95% confirm the original diagnosis.51 Lesions with benign cytology on initial FNA biopsy may be identified as malignancies in a few cases on subsequent repeat aspiration.47'51 However, the prognosis for neoplasms discovered during a later evaluation is unlikely to be different from the prog¬ nosis for neoplasms discovered earlier. The authors believe that reaspiration is preferable to the requirement of nodule size re¬ duction as a confirmation of benignity in such cases and that this management approach will significantly reduce the frequency of unnecessary surgery. Patients with a history of irradiation present a special situa¬ tion.56 Historically, these patients have been immediately re¬ ferred for surgery because of their high cancer rate. Some clini¬ cians now advocate FNA biopsy in the management of these patients, although sufficient evidence for the reliability of benign results is still lacking.5,51 The surgical approach to thyroid nodules varies. An ipsilateral lobectomy and isthmusectomy are commonly used for single nodules when the preoperative diagnosis is uncertain. Fre¬ quently, histologic evaluation of frozen sections is inconclusive

or unreliable, and the final diagnosis requires careful examina¬ tion of permanent sections. When the ultimate diagnosis is carci¬ noma, it is customary to complete a near-total thyroidectomy within 1 week of the first operation.57 Near-total thyroidectomy is the initial procedure of choice in patients with thyroid nodules and a history of thyroid irradiation (see Chap. 43). When only a lobectomy, or lobectomy and isthmusectomy, is adequate (i.e., with benign histopathology), a question of indication for postop¬ erative T4 therapy often arises. In one group of patients with a history of neck irradiation who underwent partial thyroidectomy for nodules, the T4-treated patients had a nodule recurrence rate of 8.4%, compared with a rate of 35.8% in untreated patients.58 However, T4 therapy may not prevent postoperative recurrence of nontoxic goiter. 60

MANAGEMENT OF THYROID CYSTS Simple thyroid cysts are often successfully drained by thy¬ roid aspiration. In many cases, a single aspiration is curative; in other cases, cysts recur even after multiple aspirations. If the ini¬ tial aspiration leaves no solid residual, the risk of cancer is very low; an additional therapeutic effect can be obtained in recurrent lesions by instilling sclerosing agents such as tetracycline61 or eth¬ anol.62 There is no convincing evidence that thyroid hormone therapy reduces the likelihood of recurrence. Surgery is usually reserved for cysts more than 4 cm in diameter or for recurrent cysts that produce local symptoms. In cysts defined only by nee¬ dle aspiration of at least 1 mL of fluid, it may be prudent to con¬ sider surgery in lesions that recur after two or more aspirations, especially if the fluid is hemorrhagic, if the nodules are more than 3 cm in diameter, or if a residual abnormality remains after max¬ imum drainage.63

MANAGEMENT OF AUTONOMOUS NODULES Hot nodules are commonly identified by thyroid scanning.64 The need for definitive treatment is determined by the degree of functional activity of the nodules rather than by their malignant

Ch. 39: The Thyroid Nodule potential. Nontoxic hot nodules are most often followed clini¬ cally. Toxic nodules may be treated with antithyroid drugs tem¬ porarily but require definitive therapy with 13II or surgery. The choice between these two modalities remains controversial. Sur¬ gery is recommended if there is a history of radiation and in chil¬ dren or women who are of childbearing age. The use of 13II usu¬ ally reduces the nodule's functional activity, but palpable nodules often persist.65 For patients with toxic nodules, doses of 131I (5-20 mCi) appear to be successful in rendering patients euthyroid,36 while higher doses, especially when given to euth¬ yroid patients with autonomous nodules, produce hypothyroid¬ ism66 (see Chap. 41). Percutaneous injection of ethanol has also been employed with some success.67

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30. Patton JA, Sandler MP, Partain CL. Prediction of benignancy of the soli¬ tary "cold" thyroid nodule by fluorescent scanning. J Nucl Med 1985,-26:461. 31. de los Santos ET, Keyhani-Rofagha S, Cunningham JJ, Mazzaferri EL. Cystic thyroid nodules: the dilemma of malignant lesions. Arch Intern Med 1990:150:1422. 32. Simeone JF, Daniels GH, Mueller PR, et al. High-resolution real-time so¬ nography of the thyroid. Radiology 1982; 145:431. 33. Radecki PD, Arger PH, Arenson RL, et al. Thyroid imaging: comparison of high resolution real time ultrasound and computed tomography. Radiology 1984; 153:145. 34. Bloom AD, Adler LP, Shuck JM. Determination of malignancy of thyroid nodules with positron emission tomography. Surgery 1993; 114:728. 35. Gharib H, James EM, Charboneau JW, et al. Suppressive therapy with levothyroxine for solitary nodules. N Engl J Med 1987;317:70. 36. Cheung PSY, Lee JMH, Boey JH. 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Changes in serum thyroid hor¬ mone, thyrotropin and thyroglobulin concentrations during thyroxine therapy in patients with solitary thyroid nodules. J Clin Endocrinol Metab 1989;69:227. 42. Hamburger JI, Husain M. In: Hamburger JI, ed. Diagnostic methods in clinical thyroidology. New York: Springer-Verlag, 1989:232. 43. Wartofsky L. Does replacement L-thyroxine therapy cause osteoporosis? Adv Endocrinol Metab 1993;4:157. 44. Marcocci C, Golia F, Bruno-Bossio G, et al. Carefully monitored levoth¬ yroxine suppressive therapy is not associated with bone loss in premenopausal women. J Clin Endocrinol Metab 1994;78:818. 45. Schneider DL, Barrett-Connor EL, Morton DJ. Thyroid hormone use and bone mineral density in elderly women. JAMA 1994,-271:1245. 46. Hall TL, Layfield LJ, Philippe A, Rosenthal DL. Sources of diagnostic er¬ ror in fine needle aspiration of the thyroid. Cancer 1989;63:718. 47. Hamburger JI, Husain M, Nishiyama R, et al. Increasing the accuracy of fine-needle biopsy for thyroid nodules. Arch Pathol Lab Med 1989; 113:1035. 48. Caraway NP, Sneige N, Samaan NA. Diagnostic pitfalls in thyroid fineneedle aspiration: a review of 394 cases. Diagn Cytopathol 1993;9:345. 49. Wartofsky L, Oertel Y. Fine needle aspiration biopsy of thyroid nodules. In: Van Nostrand D, ed. Nuclear medicine atlas. Philadelphia: JB Lippincott, 1987. 50. Tani EM, Skoog L, Lowhagen T. Clinical utility of fine-needle aspiration cytology of the thyroid. Annu Rev Med 1988; 39:255. 51. Hamburger JI, Hamburger SI. Fine needle biopsy of thyroid nodules: avoiding the pitfalls. NY State J Med 1986;86:241. 52. Grant CS, Hay ID, Gough IR, et al. Long-term follow-up of patients with benign thyroid fine-needle aspiration cytologic diagnoses. Surgery 1989; 106:980. 53. Backdahl M, Wallin G, Lowhagen T, et al. Fine-needle biopsy cytology and DNA analysis. Surg Clin North Am 1987; 67:197. 54. Davila RM, Bedrossian CWM, Silverberg AB. Immunocytochemistry of the thyroid in surgical and cytologic specimens. Arch Pathol Lab Med 1988; 42:51. 55. Hennessey JV, Evaul JE, Tseng YL, et al. L-thyroxine dosage: a reevalua¬ tion of therapy with contemporary preparations. Ann Intern Med 1986; 105:11. 56. DeGroot LJ. Clinical review 2: diagnostic approach and management of patients exposed to irradiation to the thyroid. J Clin Endocrinol Metab 1989; 69:925. 57. Brooks JR, Starnes HF, Brooks DC, Pelkey JN. Surgical therapy for thy¬ roid carcinoma: a review of 1249 solitary thyroid nodules. Surgery 1988; 104:940. 58. Fogelfeld L, Wiviott MBT, Shore-Freedman E, et al. Recurrence of thyroid nodules after surgical removal in patients irradiated in childhood for benign condi¬ tions. N Engl J Med 1989;320:835. 59. Anderson PE, Hurley PR, Rosswick P. Conservative treatment and long term prophylactic thyroxine in the prevention of recurrence of multinodular goiter. Surg Gynecol Obstet 1990; 171:309. 60. Hegedus L, Hansen JM, Veiergang D, Karstrup S. Does prophylactic thy¬ roxine treatment after operation for non-toxic goitre influence thyroid size? Br Med J 1987;294:801. 61. Treece GL, Georgitis WJ, Hofeldt FD. Resolution of recurrent thyroid cysts with tetracycline instillation. Arch Intern Med 1983; 140:2285. 62. Monzani F, Lippi F, Goletti O, et al. Percutaneous aspiration and ethanol sclerotherapy for thyroid cysts. J Clin Endocrinol Metab 1994; 78:800. 63. Rosen IB, Provias JP, Walfish PG. Pathologic nature of cystic thyroid nod¬ ules selected for surgery by needle aspiration biopsy. Surgery 1986; 100:606. 64. Hamburger JI. The autonomously functioning thyroid nodule: Goetsch's disease. Endocr Rev 1987; 8:439. 65. Goldstein R, Hart IR. Follow-up of solitary autonomous thyroid nodules treated with 131I. N Engl J Med 1983;309:1473. 66. Ross DS, Ridgway EC, Daniels GH. Successful treatment of solitary toxic thyroid nodules with relatively low-dose iodine 131, with low prevalence of hypo¬ thyroidism. Ann Intern Med 1984; 101:458. 67. Mazzeo S, Toni MG, DeGaudio C, et al. Percutaneous injection of ethanol to treat autonomous thyroid nodules. AJR 1993; 161:871.

354

PART III: THE THYROID GLAND Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

40

THYROID CANCER ERNEST L. MAZZAFERRI About 12,000 new cases of thyroid carcinoma are diagnosed annually in the United States, and an estimated 1000 deaths are due to this disease each year.1 Thyroid carcinoma creates consid¬ erable public reaction and concern among physicians because it sometimes occurs after external head and neck irradiation and is sometimes familial. Thyroid carcinoma is classified into four major types: papil¬ lary, follicular, medullary, and anaplastic. Papillary and follicular carcinomas arise from follicular cells and tend to be slowgrowing tumors. Medullary carcinoma, which originates from the C cells of the thyroid, may be sporadic or familial. Anaplastic carcinoma usually arises from well-differentiated thyroid tumors and is almost invariably fatal within a short time. The concept of a dual histogenesis of thyroid carcinoma has been challenged by studies using immunohistochemical techniques to stain tumors that show calcitonin (a C-cell marker) in some follicular tumors and thyroglobulin (Tg; a follicular cell marker) in some medullary carcinomas. Thyroid carcinoma today is usually diagnosed at an early stage, making therapy for many patients extremely effective. The optimal treatment of well-differentiated tumors is controversial. Many thyroid carcinomas grow slowly and indolently over a span of decades, making accurate assessment of the impact of therapy difficult; others grow aggressively and, despite vigorous treatment, metastasize to distant sites, causing death within a few years. Nevertheless, with an understanding of the factors influ¬ encing prognosis, one can avoid unnecessarily extensive therapy for those tumors that are likely to follow a benign course and inadequate therapy for others that are anticipated to be more aggressive.

PAPILLARY THYROID CARCINOMA PREVALENCE Papillary thyroid carcinoma accounts for about 80% of all thyroid cancers in the United States,1'3 including more than 85%

of those induced by radiation.4 In countries with endemic goiter, a greater proportion are follicular or anaplastic carcinomas.1 In the United States, thyroid carcinoma is diagnosed in about 1 in 27,000 people annually. Ten percent of thyroid glands carefully studied at autopsy contain clinically unimportant, occult micro¬ scopic papillary carcinomas that occur with much the same fre¬ quency throughout adult life and with about the same prevalence in men and women.5 In contrast, although clinically detectable papillary thyroid carcinoma can occur at any age, it peaks in the third and fourth decades, when it is two to three times more fre¬ quent in women than in men. In children, the sex ratio is nearly equal, which may reflect the occurrence of radiation-induced disease.

PATHOLOGY Papillary and follicular carcinomas behave differently and should be considered as separate diagnostic entities. Most mixed papillary and follicular neoplasms behave and should be classi¬ fied as papillary carcinomas.6'8 The pathologic term mixed papillary-follicular carcinoma has no clinical value9'11 because the relative follicular component of mixed tumors cannot be used to predict outcome or iodine-131 (131I) uptake.9 On occasion, pure papillary carcinomas may metastasize in a predominantly follic¬ ular form.8 Papillary carcinomas usually are nonencapsulated, sharply circumscribed tumors. About 5% to 10%, however, extend di¬ rectly through the thyroid capsule into surrounding structures and are associated with high recurrence and mortality rates2,9 (Fig. 40-1 A). Another 10% are encapsulated and have an excep¬ tionally favorable prognosis.8 Papillary carcinomas usually are firm and solid, but hemorrhagic necrosis may develop in larger tumors, yielding a thick brownish fluid on needle biopsy that can be mistaken for a benign hemorrhagic cyst. The size of the primary lesion is important for prognosis. Clinically apparent tumors 1.5 cm or smaller in diameter rarely metastasize to distant sites and virtually never cause death1213 (see Fig. 40-1B). Larger tumors are associated with higher recur¬ rence and mortality rates.10,12 Histologically, papillary carcinoma usually shows both pap¬ illary and follicular components (Fig. 40-2A), but it occasionally has a pure papillary or trabecular appearance and less often has a pure follicular pattern (see Fig. 40-2B). Microscopic sclerosing tumors have a stellate appearance. Regardless of its architecture, papillary carcinoma has distinct cellular features that distinguish it from other thyroid neoplasms, permitting an accurate cytologic diagnosis to be made by fine-needle aspiration (FNA) biopsy (see Fig. 40-2C). The cells are large and contain pink to amphophilic

FIGURE 40-1. Papillary thyroid carcinoma: gross pathology. A, Large papillary thyroid carcinoma completely replacing right thyroid lobe and extending beyond the thyroid capsule. Such lesions are associated with high recurrence and mortality rates. B, Occult papillary thyroid carcinoma found inci¬ dentally at surgery. This lesion almost invariably has a benign clinical course.

Ch. 40: Thyroid Cancer

355

FIGURE 40-2. Papillary thyroid carcinoma: histology. A, Microscopic papillary thyroid carcinoma (ar¬ row) showing a mixed papillary and follicular architecture, and encapsulation. Isolated microscopic pap¬ illary carcinomas, found in about 10% of the general population, are incidental findings at surgery or autopsy and almost never are of clinical significance (X20). B, Papillary thyroid carcinoma with typical papillae containing a fibrovascular core, and cells with large, pale-staining nuclei that appear crowded and overlapping (XI00). C, Fine-needle aspiration biopsy specimen of papillary thyroid carcinoma showing typical cytologic features of the tumor (X400). D, High-power magnification of typical papillary thyroid carcinoma showing characteristic cellular features, including nuclear inclusions, irregularly placed, pale-staining nuclei, and abundant cytoplasm (X400).

finely granular cytoplasm and large pale nuclei ("Orphan Annie eye" nuclei), which identify the papillary nature of mixed tumors with a predominantly follicular pattern (see Fig. 40-2D). Psammoma bodies (Fig. 40-3), which are calcified, concen¬ tric, lamellated spheres within or near the tumor and in nearby lymph nodes, are seen in about half of cases and are virtually pathognomonic of papillary carcinoma.8 Papillary carcinoma often shows lymphocytic infiltration ranging from focal areas of lymphocytes and plasma cells to clas¬ sic Hashimoto disease1 (see Chap. 45). However, thyroid carci¬ noma does not occur with increased frequency in patients with Hashimoto disease.14 A lobe or the entire gland may be involved, with papillary carcinoma infiltrated with lymphocytes, which may be mistaken for thyroiditis. Multiple tumor foci, generally thought to be intraglandular metastases, are seen in 20% to 80% of cases, depending on the degree to which the gland is examined (Fig. 40-4). Their clinical importance is debated: some investiga¬ tors report almost no tumor recurrences in the thyroid remnant after subtotal thyroidectomy,8,15 while others note a substantial number of recurrences.2'9 Anaplastic transformation occurs in well-differentiated thy¬ roid carcinoma, dramatically altering the course of the disease and resulting in aggressive local invasion of tumor and wide¬ spread, rapidly fatal metastases that do not concentrate 131I.

Gross cervical lymph node metastases occur in about half of patients, while even more have microscopic nodal metastases.1 Recurrence rates are higher in patients with cervical lymph node metastases, and mortality rates may be higher.3'10'1" Mediastinal and bilateral cervical node metastases carry a more serious prognosis. Distant metastases, seen in fewer than 5% of patients at the time of initial diagnosis but eventually developing in up to 10% of patients, are usually found in lung or bone but occasionally appear in other soft tissues. Pulmonary metastases may be large discrete nodules or may have a "snowflake" appearance owing to diffuse lymphangitic spread of tumor16 (Fig. 40-5A and B). Rarely, pulmonary metastases cannot be seen on radiographs and are detected only with serum Tg measurement or 131I scan¬ ning. Although many patients with distant metastases eventually die of disease, long-term survival is fairly common, especially in children and young adults, who may live for years with pulmo¬ nary metastases16"18 (see Fig. 40-5C). Papillary thyroid carcinoma may arise within a thyroglossal duct. In such cases, it is almost always small, sometimes locally metastatic, and usually has a benign course.1 Papillary carcinomas that occur after childhood irradiation for benign conditions have a survival rate similar to that of spon¬ taneously occurring papillary carcinomas. Some investigators,

356

PART III: THE THYROID GLAND *

FIGURE 40-3. Psammoma bodies of papillary carcinoma (arrows) are calcified, dark-staining, lamellated spheres that are virtually pathogno¬ monic of papillary thyroid carcinoma (X400).

however, suggest that radiation-induced tumors are larger, more often multicentric, and associated with more frequent recurrence than are spontaneously occurring tumors.4'12

DIAGNOSIS Papillary carcinoma may manifest as a neck mass or may be discovered in an asymptomatic patient during a routine exami¬ nation. It also may be found in screening programs of patients

FIGURE 40-5. Distant metastases of papillary thyroid carcinoma. A, Pap¬ illary thyroid carcinoma with diffuse lymphangitic spread of tumor giving a typical "snowflake" appearance on the chest radiograph. Such tumors typi¬ cally concentrate 131I in younger patients and tend to have a good prognosis. B, Papillary thyroid carcinoma with diffuse nodular infiltrates that concen¬ trated 131I poorly. This patient had pulmonary metastases at the time of initial diagnosis. C, Left, Papillary thyroid carcinoma in a young woman that did not concentrate 131I and grew steadily over a 4-year period (right).

FIGURE 40-4. Microscopically multifocal papillary thyroid carcinoma (arrows) usually represents intraglandular metastases (X20).

with a history of head and neck irradiation. In the past, many of these tumors were large and invasive when first diagnosed; with the contemporary use of FNA, most are smaller at diagnosis. External irradiation to the head and neck for benign disease during childhood or adolescence may cause thyroid carcinoma that can appear 30 or more years after exposure.4 Such a history is not an absolute indication that the nodule is malignant because

Ch. 40: Thyroid Cancer only 30% of patients develop thyroid nodules after irradiation and only one third of these are malignant.4 Papillary thyroid carcinoma usually becomes apparent as a palpably discrete thyroid nodule that moves as the patient swal¬ lows, or it may become apparent first as enlarged lateral cervical lymph nodes without a palpable thyroid tumor. A midline mass above the thyroid isthmus may be a metastatic lymph node—a “Delphian" node—or may be carcinoma within a thyroglossal duct, identified from its upward movement when the tongue is protruded. Although it is usually a firm, nontender, discrete mass, papillary carcinoma can also be soft and cystic or can diffusely infiltrate one lobe or the entire thyroid. Occasionally, it causes symptoms of pain, hoarseness, dysphagia, or hemoptysis, or it can appear to infiltrate surrounding structures or grow rap¬ idly—findings associated with high subsequent recurrence rates.9 Unlike follicular carcinoma, distant metastases of papil¬ lary carcinoma rarely are seen less often at the time of presenta¬ tion; when they are, the primary tumor is almost invariably large and easily palpated19 (see Fig. 40-5B). Usually, neither the history nor the physical examination findings, except perhaps for the presence of large cervical lymph nodes or vocal cord paralysis, offer enough evidence to indicate surgery, and further testing must be done (see Chaps. 34, 35, and 39). The usual tests include radionuclide scanning, thyroid ultrasonography, and fine- or large-needle biopsies. Papil¬ lary carcinomas as small as 5 mm can be detected on 123I or technetium-99m pertechnetate scanning with a gamma camera and a pinhole collimator. Most carcinomas of this size appear as nonfunctional ("cold") lesions. Because many pathologic pro¬ cesses can produce such scan defects, this nonspecific finding is insufficient evidence for surgical extirpation.20 Thyroid ultraso¬ nography also detects tumors as small as 5 mm, although it too is of low specificity (see Chap. 35). Papillary carcinomas usually appear as well-defined solid lesions, although larger necrotic tu¬ mors can present as complex cystic and solid lesions.20 Simple cysts are rarely malignant, but well-documented examples of cancer in cystic lesions have been reported.21 Because neither radionuclide scanning nor ultrasonography is sufficiently specific for the diagnosis of cancer, most thyroid nodules, except hyperfunctional (“hot") nodules, require needle biopsy before surgery is performed.20 Although large-needle cut¬ ting biopsies can be done, papillary carcinoma, owing to its dis¬ tinctive cytologic features, usually can be readily identified by the safer FNA biopsy technique20 (see Chap. 39). In many centers, FNA biopsy is the first procedure to be performed because of its cost-effectiveness. Nodules that yield diagnostic or highly suspi¬ cious aspirates are excised; the others are scanned to exclude hot nodules (which rarely are malignant), and those remaining are simply observed or sometimes are treated with thyroxine sup¬ pressive therapy. Thyroxine suppression as a diagnostic test must be done with extreme caution because thyroid carcinomas initially may appear to shrink.20 Unless the tumor (or scan defect in patients with nonpalpable lesions and a history of radiation exposure) completely disappears, the patient must be followed up indefi¬ nitely. Usually, thyroxine suppression should not be done with¬ out prior FNA. Special diagnostic problems arise in the patient with a his¬ tory of prior head and neck irradiation. Some physicians prefer immediate surgery for all irradiated patients with palpable nod¬ ules,4 while others perform FNA and excise only malignant or suspicious nodules.20 A strong argument in favor of FNA is that radiation-induced cancers are associated with a mortality similar to that of spontaneously occurring tumors. Also controversial is the use of thyroid scans in previously irradiated patients without palpable abnormalities, about 15% of whom have “cold" defects; however, of these, only about one fourth are occult carcinomas. Because most evidence suggests that these tiny lesions are not clinically important, many prefer not to scan those with palpably normal glands. Thyroid hormone is sometimes given to pre¬

357

viously irradiated patients with palpably normal thyroid glands, but it does not prevent the appearance of subsequent nodules.4

FACTORS INFLUENCING PROGNOSIS Most patients can be cured of papillary carcinoma, and many others have a long survival with palliative therapy, even with distant metastases. Typically, papillary thyroid carcinoma follows a leisurely course associated with low mortality from can¬ cer, which makes analysis of the impact of therapy difficult.915 With current therapy, the net mortality appears to be well under 10% during the first decade and not more than 20% during the second decade.1 Recurrences can occur many years after therapy, when some patients have distant metastases or serious local recurrences.1,12 The relapse and mortality rates are influenced by factors other than therapy. Age at the time of diagnosis clearly is one of the most important factors. In older series, children often were reported to have a more unfavorable prognosis than adults,22 but recently, because the tumors in children are less advanced at the time of diagnosis and often are treated more aggressively, their prognosis is excellent.23,24 Generally, death rates are greatest in adults older than 40 years of age at the time of diagnosis. There is a good correlation between age at diagnosis and mortality from carcinoma, with the adverse effect of age increasing smoothly and gradually from younger patients to age 60, after which it sharply increases. The response to therapy generally is more fa¬ vorable in younger patients, most of whom have tumors that concentrate 131I.16 Other factors, summarized in Table 40-1, in¬ fluence the clinical course of this disease and must be taken into account when planning therapy.25-29 In addition to the clinical features listed in Table 40-1, tumors that have a high proportion of DNA aneuploid cells,30 or tall-cell variants of papillary carci¬ noma,31 and tumors with metaplastic cellular features25 have a poor prognosis, while tumor encapsulation is associated with a less aggressive course.30 Several oncogenes have been identified in thyroid carcinomas,33-35 but none clearly identifies welldifferentiated tumors with aggressive behavior.

SURGERY Although surgery usually is the initial treatment of choice, there is considerable controversy concerning the optimal proce¬ dure. Some prefer lobectomy and regional lymph node dissection as the initial treatment for nearly all patients, whereas others treat most patients with total or near-total thyroidectomy.11315 3* After more aggressive thyroid surgery, fewer cancer recurrences and deaths can be expected,36 37 but the incidence of serious com¬ plications rises. The best approach is to tailor the procedure to fit the anticipated aggressiveness of the neoplasm. Subtotal lobectomy is inadequate therapy, except for iso¬ lated microscopic tumors found incidentally during surgery for other benign disorders. Unilateral total lobectomy and isthmusthectomy may be adequate for well-circumscribed, isolated le¬ sions smaller than 1.5 cm in diameter without metastases in patients not previously exposed to radiation therapy. Complica¬ tions with this procedure are few, and survival in this group is virtually assured.1'1213 Near-total thyroidectomy (total lobec¬ tomy on the involved side, isthmusthectomy, and on the opposite side near-total lobectomy, leaving the posterior thyroid capsule intact) is performed for more extensive unilateral tumors (larger than 1.5 cm in diameter) or for tumors that are locally metastatic. Total thyroidectomy is done in cases of extensive multifocal dis¬ ease, large bilateral lymph node metastases, and tumors that di¬ rectly invade contiguous neck structures or are metastatic to dis¬ tant sites. Involved cervical lymph nodes should be excised, preserving thp sternocleidomastoid muscle, because radical neck dissection offers no therapeutic advantage except for tumors ex¬ tensively invading the strap muscles.1'1*38 The principal disad¬ vantage of total thyroidectomy is the higher incidence of compli-

358

PART III: THE THYROID GLAND

cations, especially hypoparathyroidism, which now occurs in fewer than 5% of patients when the posterior thyroid capsule is left intact on the contralateral side.1,9 9 Patients with large tumors treated by lobectomy alone have a recurrence rate in the opposite lobe of about 5% to 10%1,9,19 and have the highest frequency of subsequent pulmonary metastases. In one study, recurrence, in the form of pulmonary metastases, as a function of initial therapy of papillary or follicular car¬ cinomas, was reported to be as follows: thyroidectomy plus 13!I (131I ablation dose of 100 mCi), 1.3%; thyroidectomy alone, 3%; partial thyroidectomy plus I31I, 5%; partial thyroidectomy alone, 11%.36 Recurrence rates after near-total or total thyroidectomy are about half those seen after less extensive thyroidectomy,1'9,39 and fewer patients develop pulmonary metastases.36 Extensive lymph node metastases are likely to be associated with multifocal papillary carcinomas.3' The higher recurrence rates observed in patients with cervical node metastases and multicentric tumors12

TABLE 40-1 Factors Influencing the Prognosis of Papillary and Follicular Thyroid Cancer PAPILLARY THYROID CANCER Most Aggressive Tumor Behavior

FIGURE 40-6. Differentiated thyroid carcinoma recurrence rates after different types of medical therapy. (Adapted from data published in Mazzaferri EL, Jhiang SM. Long term impact of initial surgical and medical ther¬ apy on papillary and follicular thyroid cancer. Am J Med 1994;97:418.)

would appear to justify a more aggressive approach, particularly in patients older than 40 years of age (see Chap. 43).

Large primary tumors (>2.5-3 cm in diameter) Tumor invasion of cervical structures Symptomatic primary tumors that initially display aggressive growth characteristics Anaplastic transformation of tumor Age > 40 years at the time of diagnosis Distant tumor metastases Bone metastases Large solitary pulmonary metastases Distant metastases that do not effectively concentrate 131I

Less Aggressive but More Unpredictable Tumor Behavior Primary tumors of intermediate size (1.5-2.5 cm) Microscopic multicentric primary tumors* Cervical lymph node metastases* Male patients* (slight preponderance) Tumors occurring after head and neck irradiation* Pulmonary metastases that are diffuse and concentrate 131I

Least Aggressive Tumor Behavior Small primary tumors (5 cm in diameter)! Tumor invasion of cervical structures Moderate to extensive vascular and capsular invasion! Oxyphilic tumors (Hurthle cell carcinoma)! Anaplastic transformation or marked cellular atypia Age > 40 years at the time of diagnosis Male patients (slight preponderance)! Distant metastases

Least Aggressive Tumor Behavior Medium-sized or large tumor follicles Minimal vascular or capsular tumor invasion! * Features about which the most controversy or uncertainty exists concerning the influence on prognosis. | See text for explanation.

RADIOIODINE THERAPY Compelling arguments have been made for using 131I to treat patients with residual or recurrent neoplasm in the neck that is not amenable to surgical excision. However, the prophylactic use of radioactive iodine in patients with aggressive tumors with no evidence of residual disease and only 131I uptake in the thyroid bed postoperatively is controversial. Reduced recurrence rates have been reported in several studies in which 131I was used rou¬ tinely in the postoperative treatment of papillary carci¬ noma117,39,40 (Fig. 40-6). Moreover, the lowest incidence of sub¬ sequent pulmonary metastases occurs after total thyroidectomy and 131I. It has been shown that prophylactic 131I reduces the mortality rate from cancer. Patients with tumors that are anticipated to be aggressive often are given 131I postoperatively to ablate uptake in the thyroid bed.1 36 39 40 Occult thyroid cancer metastases may not be de¬ tected. They accumulate 131I optimally only in the absence of nor¬ mal thyroid tissue, and high levels of circulating thyrotropin (thyroid-stimulating hormone, TSH) are necessary to enhance tumor 1311 uptake. Neither can be achieved if considerable func¬ tioning thyroid tissue remains. If postoperative 131I treatment is selected, studies should be done 6 weeks after surgery to allow serum TSH to rise to levels sufficient (>30 /uU/mL) to stimulate neoplastic and normal thy¬ roid tissue to concentrate 131I maximally. The optimal procedure is to give triiodothyronine (Cytomel), 1 /rg/kg/d (about 25 pg orally, three times daily), for the first 4 weeks after surgery, then to discontinue it for 2 weeks. The patient must carefully avoid iodine during this period, especially in the form of drugs. During the last week, a low iodine diet should be ingested, and the serum TSH and Tg levels should be measured. Endogenous TSH ordi¬ narily rises to over 30 /mL unless a substantial amount of nor¬ mal thyroid tissue remains.41 Diuretics are sometimes necessary to reduce the iodine pool and enhance tumor 131I uptake. Recom¬ binant human TSH is now available and, pending Food and Drug Administration approval, is likely to alter this general diagnostic approach.42 Whole body scans are obtained at 24 to 72 hours. Although some use 131I scanning doses as large as 10 mCi, smaller amounts are sufficient because focal abnormalities that are seen with 10 but not 2 mCi are not likely to be ablated successfully.43 Because it is virtually impossible to perform a true total thyroidectomy, uptake of 131I is almost always seen in the thyroid bed and must

Ch. 40: Thyroid Cancer be ablated before 131I will optimally concentrate in metastatic de¬ posits. If only partial lobectomy has been performed, it may be best to consider further surgery for lesions that are anticipated to have an aggressive behavior because large thyroid remnants are more difficult to ablate with 131I. Because the complication rate is higher with second operations, however, many prefer 131I abla¬ tion for smaller thyroid remnants. The choice of an appropriate 131I dose for the ablation of thy¬ roid remnants is also controversial. No studies show whether lower doses are preferable to higher ones with regard to survival. Nonetheless, it appears reasonable, considering the large differ¬ ences in cost and radiation exposure, to use a 30-mCi dose for patients without known residual disease in whom the only aim of therapy is to ablate uptake in the thyroid bed or to destroy a small normal thyroid remnant to facilitate follow-up.44 Residual or metastatic disease should be treated with 131I, but 13II uptake can be induced in only about half of these tumors. In one large series, 10-year survivals were 83% or 0%, depending on whether pulmonary metastases did or did not concentrate 131I.16 The pulmonary metastases that concentrate 131I best are snowflake metastases, seen most often in younger patients.16 Tumor 131I uptake in amounts adequate for imaging is usu¬ ally sufficient for 131I therapy, with doses from 100 to 200 mCi either given empirically or calculated to deliver an optimal tumor dose without exceeding 200 rad to the blood. The most effective tumor dose appears to be at least 8,000 rad.43 There is consider¬ able difficulty in estimating tumor size, however, particularly of deep metastatic deposits, which is necessary to calculate the tu¬ mor radiation dose. Lesions that receive only a few hundred rad from 150 to 200 mCi 131I should be considered for alternative surgical, external radiation, or medical therapy. Usually, there are no immediate risks of 131I therapy except in patients with brain and spinal cord metastases in whom edema and sudden hemorrhage into the tumor can develop 1 to 2 weeks after treatment. Widespread pulmonary metastases should usu¬ ally be treated with no more than 150 mCi 1311 because larger doses can cause pulmonary fibrosis. Mild radiation thyroiditis, sialadenitis, and a slight drop in the number of platelets can oc¬ cur, but ordinarily, these effects are inconsequential. Radiation cystitis does not occur if the patient is well hydrated. As long as metastatic deposits concentrate 131I, treatment should be continued every 6 to 12 months until maximal doses of 131I are reached or adverse affects are seen. Repeat doses of 131I should not be given until the bone marrow has fully recovered from the previous dose. Total cumulative doses of 13'I generally are kept below 500 mCi in children and 800 mCi in adults when¬ ever possible because larger doses are more likely to be associated with serious long-term adverse effects such as leukemia or blad¬ der cancer. In practice, this is usually not a problem because tu¬ mor tissue that concentrates 131I is likely to be ablated by the first few doses of radionuclide, leaving either no residual tumor or metastases that do not concentrate 131I. Some patients, however, who have extensive metastatic disease that continues to concen¬ trate 131I after multiple doses of 131I, are given cumulative doses greater than 800 mCi because the risk of thyroid cancer might outweigh that due to radiation. Trivial uptake of radioiodine in the neck or elsewhere is not a reason for using large cumulative doses of 131I. With this approach to 131I therapy, few side effects, such as permanent bone marrow depression, leukemia, or pulmonary fibrosis, are noted.19 44 Gonadal damage and infertility are of con¬ cern after large doses of 131I but are infrequently observed.44 Po¬ tential long-term systemic, oncologic, and genetic effects require ongoing investigative studies.

THYROID HORMONE THERAPY Abundant evidence is available that differentiated thyroid tumors contain TSH receptors and that TSH stimulates their growth. Thyroxine should always be given in normal replace¬

359

ment doses; this substantially reduces recurrence rates (see Fig. 40-6) but probably does not alter the mortality rate.1,9 No advan¬ tage is conferred by toxic doses of thyroid hormone. The Lthyroxine dosage associated with an undetectable basal serum TSH is about 2.7 ± 0.4 (SD) ^g/kg/d after total thyroidectomy;45 but the dose is age-dependent, and should be adjusted to main¬ tain the serum TSH as low as possible without causing thyrotox¬ icosis. Prolonged suppression of TSH to undetectable levels may cause a loss in bone mineral density, particularly in postmeno¬ pausal women.

OTHER THERAPY Focal lesions that do not concentrate 131I adequately and iso¬ lated skeletal metastases should be considered for surgical exci¬ sion or external irradiation.9 Patients with life-threatening tu¬ mors refractory to all other forms of therapy may be given palliation therapy with doxorubicin (Adriamycin).

FOLLOW-UP Subsequent care depends on the extent and aggressiveness of the lesion and the initial therapy but generally consists of pe¬ riodic examination, chest radiography, whole body 131I scans, ul¬ trasonography, and, if postoperative thyroidal radioablation has been performed, serum Tg determinations. Patients with clini¬ cally significant tumors (>1.5 cm) should be evaluated at 6- to 12-month intervals for the first 10 years. In many patients, complete tumor ablation can be docu¬ mented by whole body scan within 12 to 18 months after surgery and 131I therapy. Thereafter, scanning can be done at infrequent intervals unless there is a change in the examination or the chest radiograph or if there is a rise in the yearly Tg measurement. Low serum Tg concentrations ( jejunum) and portions of the colon. Because these segments of the GI tract are anatomically much longer than the duodenum, they may contribute significantly to overall calcium absorption. After administration of l,25(OH)2D to vitamin D-deficient animals, there is an increase in the GI absorption of calcium over several hours, which generally is paralleled by the induction in the intestinal mucosal cells of several vitamin D-dependent pro¬ teins, including a calcium binding protein, alkaline phosphatase, and Ca2+-Mg2+-ATPase.37 These proteins may be involved in the mechanism by which vitamin D enhances calcium absorption. Probably, calcium ions in the intestinal lumen move down their electrochemical gradient across the brush border of the epithe¬ lium and are pumped out of the basolateral aspect of the cell on their way to the extracellular fluid. l,25(OH)2D appears to stimulate both the influx and the egress of calcium from the in¬ testinal epithelial cells.38,39

Most phosphate absorption from the intestine occurs in the small bowel through a vitamin D-responsive mechanism, dis¬ tinct from that for calcium.4,5 Even in vitamin D deficiency, how¬ ever, about half of dietary phosphorus is absorbed. The less strin¬ gent regulation of phosphate absorption in the gut is consonant with the ubiquity of this ion in the diet and the looser control of the serum phosphate concentration. An important aspect of the calcium homeostatic system is its capacity to adapt the efficiency of calcium absorption to its di¬ etary intake. Patients placed on a low calcium diet increase their serum levels of l,25(OH)2D by 50% within 24 to 48 hours, whereas exposure to a high calcium diet produces a 50% decrease in this metabolite over this period.40 In experimental animals, the increase in l,25(OH)2D levels on a low calcium diet is largely abolished by prior parathyroidectomy,41 suggesting that dietary calcium-induced changes in l,25(OH)2D concentration arise from changes in serum calcium concentration that alter vitamin D metabolism through alterations in the rate of PTH secretion. Because of this adaptive mechanism, the calcium absorption var¬ ies much less than dietary calcium content. Absorption of sup¬ plemental calcium may be predominantly through the vitamin D-independent route.42 Phosphate intake also modulates the production of l,25(OH)2D, with hypophosphatemia stimulating and hyperphosphatemia inhibiting its renal synthesis.

CONTROL OF RENAL CALCIUM EXCRETION Although PTH produces only modest changes in calcium ex¬ cretion, the effects of the hormone on renal calcium handling nevertheless play an important role in overall fine-tuning of calcium balance43,44 (see Chap. 201). Conversely, vitamin D and its metabolites have only minor direct effects on the renal han¬ dling of calcium. Of about 10 g of calcium filtered daily by the kidney, some 65% is reabsorbed in the proximal tubule.44 Calcium reabsorp¬ tion in this site is closely linked to sodium transport, as evidenced by the effects of sodium diuresis in enhancing calcium excretion. PTH has little effect on calcium transport in this segment of the nephron. In fact, in some studies, PTH inhibits the proximal tu¬ bular reabsorption of calcium, perhaps because the hormone re¬ duces sodium reabsorption. Of the more distal portions of the renal tubule, the descend¬ ing and ascending thin limbs of Henle loop transport little calcium. Conversely, the thick ascending limb of the loop and the distal convoluted tubule reabsorb about 20% and 10%, respec¬ tively, of the filtered load of calcium. In experimental animals, PTH rapidly increases the reabsorption of calcium in both seg¬ ments of the nephron by increasing transport of the ion from lumen to plasma.4,5,44 It exerts this effect, like its other actions in the kidney and in other tissues, by interacting with a recently cloned G-protein-coupled cell-surface receptor that couples to activation of adenylate cyclase and phospholipase C. Several lines of evidence support a role for cAMP in mediating this effect. In microdissected portions of the mammalian renal tubule, PTHsensitive adenylate cyclase is present in the proximal tubule, thick ascending limb of Henle loop, and portions of the distal tubule.45 The location of the enzyme in the proximal tubule is thought to be linked to the well-known PTH-induced phosphaturia. The PTH-activated adenylate cyclase in the latter two loca¬ tions correlates well with the sites of action of the hormone in promoting calcium reabsorption. Moreover, the exposure of renal tubules to analogues of cAMP mimics the effects of PTH on calcium transport, further supporting the mediatory role of cAMP. Although the detailed cellular mechanisms by which PTH modifies calcium transport in the kidney are unknown, the vitamin D-dependent calcium binding protein, which is local¬ ized in the distal but not in the proximal tubules, may play some role.46 Another small amount of calcium (about 5% of the filtered load) is reabsorbed in the collecting ducts, but transport at this site is not regulated by PTH.

Ch. 48: Physiology of Calcium Metabolism The net action of PTH on the renal handling of calcium is to reduce the calcium excreted at any given level of serum calcium.43 This relationship has been demonstrated in vivo by examining renal calcium excretion as a function of serum calcium concen¬ tration in subjects with underactive, normal, and overactive parathyroid function (Fig. 48-5). In patients with primary hyper¬ parathyroidism, although total calcium excreted over 24 hours may be elevated, less calcium is excreted in the urine than in a normal person whose serum calcium concentration is equally el¬ evated. Conversely, hypoparathyroid patients have a renal calcium "leak,” excreting more calcium than normal at a given serum calcium concentration. Therefore, during therapy with vi¬ tamin D, patients with hypoparathyroidism should have their se¬ rum calcium concentration maintained in the range of 8 to 9 mg/ dL to avoid hypercalciuria (see Chap. 59). Along with its effects on renal calcium handling in the distal nephron, PTH also inhibits phosphate reabsorption in both prox¬ imal and distal sites and enhances the synthesis of l,25(OH)2D in the proximal tubule.4,5 The first of these effects, like the actions of the hormone on calcium reabsorption, appears to be mediated by cAMP. PTH is also known to activate PI turnover,47 and evi¬ dence has implicated this pathway in the PTH-mediated stimu¬ lation of the synthesis of l,25(OH)2D.48

ROLE OF THE SKELETON IN CALCIUM HOMEOSTASIS During the constant remodeling of the skeleton, there is a close coupling of osteoclastic bone breakdown to osteoblastic bone formation.49 This constant turnover and renewal of bone (see Chap. 49) presumably plays an important role in maintain¬ ing the structural integrity of this tissue. The precision of the cou¬ pling between resorption and formation is dramatically illus¬ trated in Paget disease of bone, in which 10-fold increases in the rate of skeletal turnover are often unassociated with alterations in the serum calcium concentration or calcium balance (see Chap. 64). Along with its structural role, however, the skeleton also serves as a reservoir for calcium and phosphate ions.4”6 Because the skeletal content of calcium is 1000-fold that of the extracellu¬ lar fluid, this function can be subserved by the net movement of relatively small amounts of calcium into or out of bone. After

FIGURE 48-5. Urinary excretion of calcium expressed as a function of serum calcium in normal individuals (area enclosed by the dotted lines [mean ± 2 SD]) and in hypoparathyroid (A, A; solid triangles represent basal values) and hyperparathyroid (•) subjects. The shaded area is the normal physiologic situation. (From Nordin BEC, Peacock M. Role of the kidney in regulation of plasma calcium. Lancet 1969;2:1280.)

443

administration of PTH to animals, there is an alteration in the structure of osteoclasts, osteoblasts, and osteocytes (those bone cells trapped within the calcified matrix) within minutes.4 Those morphologic changes are accompanied by an increased activity of osteoclasts and an inhibition of osteoblastic function, leading to an increase in net skeletal calcium release within 2 to 3 hours. The PTH-induced increase in the size of the periosteocytic lacu¬ nae also has been considered presumptive evidence for a role for this cell type in skeletal calcium release. Continued exposure to PTH causes an increase in the number and activity of osteoclasts that is ultimately accompanied by an increase in osteoblastic ac¬ tivity through the coupling of bone formation to resorption. The mechanisms by which PTH modulates bone cell func¬ tion remain to be fully elucidated. The hormone raises skeletal levels of cAMP50 but may also act through other second messen¬ ger systems, including the activation of PI turnover. Although PTH was originally thought to act directly on bone-resorbing cells, data suggest that it acts initially on other cell types, such as osteoblasts, which subsequently modulate the activity of osteo¬ clasts and other bone cells through physical contact, the release of soluble mediators, or both.51

REGULATION OF CIRCULATING CALCIUM CONCENTRATION The information in Figure 48-2 does not delineate the tem¬ poral sequence of response to perturbations in the ionized calcium concentration. Actually, there is a hierarchy of responses by both the parathyroid gland and the effector systems that reg¬ ulate calcium transport in the skeleton, kidney, and intestine.6 The initial alteration in the secretory rate of PTFI—release of pre¬ formed stores of hormone—occurs within seconds of the change in calcium concentration. Within 15 to 30 minutes, there is an increase in the net synthesis of PTH, without any change in the levels of messenger RNA (mRNA), perhaps because of reduced intracellular degradation of PTH. If the hypocalcemic stimulus persists, there is an increase in the levels of PTH mRNA over the ensuing 1 to 3 days.25,26 Eventually, chronic hypocalcemia is associated with enhanced parathyroid cellular proliferation over days to weeks,52 further increasing the secretory rate for the hor¬ mone. Reduced levels of l,25(OH)2D are also a potent stimulus for parathyroid cellular proliferation and contribute to the severe hyperparathyroidism that can be encountered in chronic renal insufficiency. The most rapid changes in the handling of calcium by the effector organs of the homeostatic system occur in the skeleton and kidney. Alterations in distal tubular calcium reabsorption take place within minutes in vitro,44 whereas the skeletal release of calcium occurs within 2 to 3 hours.53 If these two functional changes are insufficient to restore normocalcemia, the continued hypersecretion of PTH stimulates increased synthesis of l,25(OH)2D within 1 to 2 days,40 enhances the activity of existing osteoclasts, and promotes the appearance of new osteoclasts within days to weeks. Only rarely (e.g., in severe vitamin D de¬ ficiency) is the full complement of homeostatic responses in¬ sufficient to restore normocalcemia. Exposure of the homeostatic system to a calcium load pro¬ duces responses that are largely the opposite of those seen with hypocalcemia. The suppression of parathyroid function induces a renal leak of calcium, reduces the release of skeletal calcium, and ultimately suppresses GI absorption of calcium by inhibiting the synthesis of l,25(OH)2D. The remarkable sensitivity of the system is illustrated by its response to the ingestion of the calcium in a glass of milk. A minute rise in serum calcium causes about a 30% reduction in PTH secretion, which leads to prompt excretion of much of the extra calcium in the urine.4 In response to severe loads of calcium, the skeleton can buffer substantial quantities of calcium, and the kidney can excrete up to 1 g of calcium over 24

444

PART IV: CALCIUM AND BONE METABOLISM

hours; however, hypercalcemia may ensue, particularly if renal impairment develops. One of the most elegant features of the homeostatic system for calcium is that it simultaneously contributes to the regulation of serum phosphate concentration. With calcium deficiency lead¬ ing to secondary hyperparathyroidism, the excess phosphate mo¬ bilized into the extracellular fluid from intestine and bone is ex¬ creted in the urine (mild hypophosphatemia may ensue). Conversely, with oral calcium loading, reduced GI and skeletal availability of phosphate are managed by decreased renal phos¬ phate clearance because of reduced PTH secretion. Primary abnormalities in phosphate metabolism also elicit changes in the calcium homeostatic system that tend to correct both serum phosphate and calcium concentrations. Hypophos¬ phatemia, for example, enhances the synthesis of l,25(OH)2D, which then increases intestinal absorption and skeletal release of phosphate and calcium41 (Fig. 48-6). The increased movement of calcium into the extracellular fluid suppresses PTH release, thereby enhancing the excretion of the excess calcium, as well as retaining the phosphate mobilized from intestine and bone. The net result of these adaptations is some normalization of serum phosphate without any change in serum calcium concentration. Through poorly defined mechanisms, the kidney also retains phosphate more avidly in states of phosphate depletion indepen¬ dent of alterations in PTH secretion.

IMPORTANCE OF ION-SENSING IN MINERAL ION HOMEOSTASIS The recent cloning of an extracellular Ca2+-sensing receptor from parathyroid gland10 further supports an accumulating body of evidence that ion sensing plays a key role in mineral ion ho¬ meostasis.6 Calcium, phosphate, and magnesium ions also regu¬ late the function of target tissues for these hormones, in addition to their actions in modulating the synthesis and secretion of the calciotropic hormones, PTH, calcitonin, and l,25(OH)2D. Ele¬ vated extracellular Ca2+ or Mg2+ concentrations, for example, in¬ hibit the renal tubular reabsorption of calcium and magnesium in the thick ascending limb of the loop of Henle,54 inhibit vaso¬ pressin action at this site,55 directly inhibit osteoclastic bone re¬ sorption,56 57 and may stimulate bone formation.58 Some or all of these actions may be mediated by Ca2+-sensing receptors similar to or related to those in parathyroid cells and may provide for local regulation of mineral ion homeostasis by modulating calci¬ otropic hormone action (or by hormone-independent effects on

target tissues). Variations in extracellular phosphate concentra¬ tion also modulate ion homeostasis. For example, elevated phos¬ phate levels inhibit bone resorption and stimulate bone forma¬ tion, while hypophosphatemia has the opposite actions.58 In a sense, therefore, mineral ions themselves may be thought of as calciotropic factors, transmitting information about the state of calcium, phosphate, and, perhaps, magnesium homeostasis be¬ tween the cells and tissues involved in regulating the metabolism of these ions. Figure 48-7 illustrates this concept schematically, showing the additional layers of homeostatic control offered by the actions of these ions on ion-sensing tissues.

CLINICAL ASSESSMENT OF CALCIUM HOMEOSTASIS The clinical evaluation of normal and abnormal calcium ho¬ meostasis requires an accurate assessment of serum calcium and phosphate concentrations as well as the function of the parathy¬ roid glands and the effector systems regulating calcium homeo¬ stasis. Total serum calcium and phosphate measurements are usually reliable. Although it would be desirable to measure ion¬ ized calcium concentration in many disorders of calcium homeo¬ stasis, the precision and reproducibility of measuring total calcium is generally better than for the ionized calcium concen¬ tration. Both dip-type and flow-through electrodes of improved quality are becoming increasingly available for measuring ion¬ ized calcium and may be useful when changes in serum protein levels make the accurate estimation of ionized from total calcium levels difficult.

DIRECT ASSAYS OF CALCIUM-REGULATING HORMONES IN BLOOD PARATHYROID HORMONE Most of the immunoreactive PTH in the circulation repre¬ sents inactive fragments of the hormone comprising the mid¬ molecule and carboxy terminal portions of the molecule59 (see Chap. 50). The amount of biologically active PTH (1-84) in the blood represents less than 10% of the total immunoreactivity. The advent of specific and sensitive double antibody (e.g., immunoradiometric or immunochemiluminescent) assays specific for intact PTH has largely supplanted previously used, so-called mid-molecule and carboxy terminal assays.60 The intact PTH as-

*ECF P04

t1,25(OH)2D

INTESTINE

FIGURE 48-6. Response of the homeostatic system to hypo¬ phosphatemia. Hypophosphatemia per se stimulates synthe¬ sis of l,25(OH)2D. Excess calcium mobilized with phosphate from bone and intestine suppresses parathyroid hormone (PTH) release, facilitating calciuresis. Decreased renal phos¬ phate clearance resulting from reduced circulating levels of PTH retains phosphate available from intestine and bone. ECF, extracellular fluid.

BONE

Ch. 48: Physiology of Calcium Metabolism

445

FIGURE 48-7. Selected direct effects of calcium and phosphate ions on tissues involved in maintaining mineral ion homeostasis, illustrating the role of these ions as extracellular, first messengers. These are superimposed on the diagram of the homeostatic system shown in Figure 48-2 and indicate additional layers of regulatory control. For example, in addition to the well-known direct inhibitory action of extra¬ cellular calcium ions on parathyroid hormone secretion, elevated calcium concentrations have suppres¬ sive effects on the synthesis of l,25(OH)2D in the proximal tubule, the tubular reabsorption of calcium ions in the thick ascending limb of loop of Henle, and the resorptive activities of osteoclasts. Thus, calcium ions modulate their own homeostasis not only through direct actions on the secretion of calciotropic hormones but also through effects on target tissues mediated through modulation of the actions of these hormones as well as through hormone-independent actions. In effect, calcium and phosphate ions act as calciotropic factors or “hormones" because they transmit information about the state of min¬ eral ion metabolism from one part of the homeostatic system to other parts.

says permit reliable diagnosis of primary and secondary hyper¬ parathyroidism when interpreted in the context of a simulta¬ neously measured serum calcium concentration. Furthermore, in hypercalcemia due to nonparathyroid causes, intact PTH levels are generally frankly suppressed, greatly facilitating the differ¬ ential diagnosis of hypercalcemia. There is seldom any need, therefore, for the measurement of PTH by the older immunoas¬ says or more cumbersome bioassays. Because high-quality assays for parathyroid hormone-related protein are also routinely avail¬ able,61 measurement of urinary cAMP excretion is usually not required to diagnose parathyroid hormone-related proteinmediated hypercalcemia of malignancy.

VITAMIN D METABOLITES Assays are available for measuring 25(OH)D and l,25(OH)2D. The former is measured to assess circulating stores of the vitamin. Serum is extracted and purified chromatographically; 25(OH)D is then measured either directly by its absorption of ultraviolet light, by a radioligand binding assay that uses en¬ dogenous binding proteins, or by radioimmunoassay. Because of the low levels of 1,25(QH)2D in blood (about 30 pg/mL), this metabolite generally must be extensively purified before assay and then measured using the naturally occurring cellular receptor in radioligand assays or by radioimmunoassay. The clinical set¬ tings in which the measurement of this metabolite is useful are discussed in Chapters 62, 69, and 213.

CALCITONIN The determination of immunoreactive calcitonin is most useful in screening patients suspected of harboring medullary thyroid carcinoma.62 In this setting, calcitonin is determined both before and after the administration of a secretagogue, such as calcium or pentagastrin. Most calcitonin assays detect multiple immunoreactive forms of calcitonin that, unlike those of PTH, are larger than the native hormone. A useful way to assess secre¬ tory function of the C cells is to extract calcitonin monomer from blood and measure it by radioimmunoassay. It is uncertain how or to what extent serum calcitonin influences calcium homeosta¬ sis in humans (see Chap. 52).

ASSESSMENT OF THE FUNCTION OF TARGET ORGANS FOR CALCIUM-REGULATING HORMONES KIDNEY Along with urinary cAMP excretion, determination of the tubular reabsorption of phosphate (TRP) is another indirect as¬ sessment of PTH action on the kidney that is seldom required now that high-quality assays for intact PTH are widely available.

446

PART IV: CALCIUM AND BONE METABOLISM

This parameter is calculated from the equation TRP = 1 — [l/p X SCT/ticr X Sp], where Up = urinary phosphate excretion, UCI = urinary creatinine excretion, and Sp and Scr = serum phosphate and creatinine excretion, respectively. A particularly useful ex¬ pression of renal phosphate handling is the tubular maximum for phosphate corrected for glomerular filtration rate, which can be calculated using an appropriate nomogram.63 This parameter is particularly useful in assessing the contribution of renal leak of phosphate to hypophosphatemic, osteomalacic disorders (see Chaps. 62 and 69). The measurement of the relationship between serum calcium and urine calcium excretion provides some indi¬ rect information about the PTH-calciferol axis (see Fig. 48-5). Calcium excretion is often expressed in terms of the calcium/ creatinine excretion ratio.

INTESTINE The direct measurement of calcium absorption provides an indication of the intestinal response to circulating levels of l,25(OH)2D and, indirectly, PTH. Calcium absorption may be assessed by determining the difference between oral calcium in¬ take and fecal calcium excretion or by isotopic techniques.64 The former is laborious and requires equilibration of mineral homeo¬ stasis to a constant diet over weeks. The latter is accomplished by administering a tracer dose of 47Ca or other isotopes of calcium with a fixed amount of stable calcium (40Ca, usually 100 mg) and measuring the appearance of the isotope in blood samples during the following 0.5 to 6 hours. Unfortunately, neither technique is widely available.

BONE Alkaline phosphatase in serum originates from many sources, of which bone and liver are the two principal forms in adult humans.65 Circulating alkaline phosphatase of skeletal ori¬ gin derives primarily from osteoblasts and can be a useful indica¬ tor of osteoblastic activity. A crude way of distinguishing skeletal from hepatic alkaline phosphatase is the greater lability of the former to heat. As immunoassays specific for the skeletal isoen¬ zyme become more widely available, the utility of this marker will increase.65 Recent data also suggest that a bone-derived se¬ rum protein, bone Gla protein or osteocalcin, may be a marker of osteoblast function. This protein contains 7-carboxyglutamic acid (Gla) synthesized through a vitamin K-dependent carboxylation of glutamate, and it may be measured by radioimmunoas¬ say.66 When bone resorption and formation are coupled, it is a marker of bone turnover; if they are not well coupled (i.e., during therapy with glucocorticoids), it is a marker of bone formation.65 Urinary hydroxyproline arises from the turnover of collagen. Because about 60% of total body collagen resides in bone, the determination of urinary hydroxyproline excretion can provide information about the turnover of the bone matrix. Although much of urinary hydroxyproline appears as small peptides and probably reflects bone resorption, larger peptides containing hy¬ droxyproline may arise during bone formation. Thus, urinary hy¬ droxyproline is not a direct measure of bone resorption or forma¬ tion, but it does provide a measurement of bone turnover that may be useful in monitoring changes in skeletal metabolism, for instance, during the treatment of Paget disease of bone. Methods have been developed for measuring the breakdown products of collagen cross-links in bone (hydroxylysyl pyridinolines = pyridinolines; lysyl pyridinolines = deoxypyridinolines).67 As clinical experience accumulates, it appears that these will be useful, rela¬ tively specific urinary (and perhaps serum) markers of bone re¬ sorption that are superior, in this regard, to hydroxyproline (see Chap. 55).

REFERENCES 1. Rasmussen H. Calcium messenger system. N Engl J Med 1986,-314:1089. 2. Pietrobon D, DiVirgilio F, Pozzan T. Structural and functional aspects of calcium homeostasis in eukaryotic cells. Eur J Biochem 1990; 120:599. 2a. Nathanson MH. Cellular and subcellular calcium signaling in gastroin¬ testinal epithelium. 1994;106:1349. 3. Parfitt AM, Kleerkoper M. The divalent ion homeostatic system: physiol¬ ogy and metabolism of calcium, phosphorous, magnesium, and bone. In: Maxwell MH, Kleeman CR, eds. Clinical disorders of fluid and electrolyte metabolism, ed 3. New York: McGraw-Hill, 1980:269. 4. Stewart AF, Broadus AE. Mineral metabolism. In: Felig P, Baxter JD, Broadus AE, Frohman LA, eds. Endocrinology and metabolism. New York: McGraw-Hill, 1987:1317. 5. Aurbach GD, Marx SJ, Spiegel AM. Parathyroid hormone, calcitonin, and the calciferols. In: Wilson JD, Foster DW, eds. Williams textbook of endocrinology. Philadelphia: WB Saunders, 1986:1137. 6. Brown EM. Extracellular Ca2+-sensing, regulation of parathyroid cell func¬ tion, and role of calcium and other ions as extracellular (first) messengers. Physiol Rev 1991; 71:371. 7. Walser M. Ion association. VI. Interactions between calcium, magnesium, inorganic phosphate, citrate, and protein in normal human plasma. J Clin Invest 1961;40:723. 8. Lindgarde F, Zettervall D. Hypercalcemia and normal ionized serum calcium in a case of myelomatosis. Ann Intern Med 1973; 78:396. 9. Heaney RP, Gallagher JC, Johnston CC, et al. Calcium nutrition and bone health in the elderly. Am J Clin Nutr 1982; 36:986. 10. Brown EM, Gamba G, Riccardi D, et al. Cloning and characterization of an extracellular Ca2+-sensing receptor from bovine parathyroid. Nature 1993; 366: 575. 11. Weisinger JR, Favus MJ, Langman CB, Bushinsky DA. Regulation of 1,25dihydroxy vitamin D3 by calcium in the parathyroidectomized, parathyroid hormone-replete rat. J Bone Mineral Res 1989;4:929. 12. Fraser DR, Kodicek E. Regulation of 25-hydroxy-cholecalciferol-hydroxylase activity in kidney by parathyroid hormone. Nature New Biol 1973;241:163. 13. Reichel H, Koeffler HP, Norman AW. The role of the vitamin D endocrine system in health and disease. N Engl J Med 1989;320:980. 14. Brown EM, LeBoff MS, Oetting M, et al. Secretory control in normal and abnormal parathyroid tissue. Recent Progr Horm Res 1987;43:337. 15. Gittes RF, Radde JC. Experimental model for hyperparathyroidism: effect of excessive numbers of transplanted isologous parathyroid glands. J Urol 1966;95: 595. 16. Adami S, Muirhead N, Manning RM, et al. Control of secretion of para¬ thyroid hormone in secondary hyperparathyroidism. Clin Endocrinol 1982; 16:463. 17. Grant FD, Conlin PR, Brown EM. Rate and concentration dependence of parathyroid hormone dynamics during stepwise changes in serum ionized calcium in normal humans. J Clin Endocrinol Metab 1990;71:370. 18. Poliak M, Brown EM, Chou Y-HW, et al. Mutations in the human Ca2+sensing receptor gene cause familial hypocalciuric hypercalcemia and neonatal se¬ vere hyperparathyroidism. Cell 1993; 75:1297. 18a. Poliak MR, Brown EM, Estep HL, et al. Autosomal dominant hypocal¬ cemia caused by a Ca2+-sensing receptor gene mutation. Nature Genet 1994;8:303. 19. Nakanishi S. Molecular diversity of glutamate receptors and implications for brain function. Science 1992; 258:597. 20. Habener JT, Potts JT Jr. Relative effectiveness of calcium and magnesium on the secretion and biosynthesis of parathyroid hormone in vitro. Endocrinology 1976;98:197. 21. Anast CS, Mohs JM, Kaplan SL, Burns TW. Evidence for parathyroid fail¬ ure in magnesium deficiency. Science 1972; 177:606. 22. Brown EM. Parathyroid secretion in vivo and in vitro: regulation by calcium and other secretagogues. Miner Electrolyte Metab 1982; 8:130. 23. Russell J, Silver J, Sherwood LM. The effects of calcium and vitamin D metabolites on cytoplasmic mRNA coding for preproparathyroid hormone in iso¬ lated parathyroid cells. Trans Assoc Am Physicians 1984; 97:269. 24. Chan YK, McKay C, Dye E, Slatopolsky E. The effect of 1,25 dihydroxycholecalciferol on parathyroid hormone secretion by monolayer cultures of bovine parathyroid cells. Calcif Tissue Int 1986;38:27. 25. Yamamoto M, Igarishi T, Muramatsu M, et al. Hypocalcemia increases and hypercalcemia decreases the steady-state level of parathyroid hormone mes¬ senger RNA in the rat. J Clin Invest 1989; 83:1053. 26. Silver J, Naveh-Many T, Mayer J, et al. Regulation by vitamin D metabo¬ lites of parathyroid hormone gene transcription in vivo in the rat. J Clin Invest 1986; 78:1296. 27. Kremer R, Bolivar I, Goltzman D, Hendy GN. Influence of calcium and 1,25-dihydroxycholecalciferol on proliferation and proto-oncogene expression in primary cultures of bovine parathyroid cells. Endocrinology 1989; 125:935. 28. Heath H III, Biogenic amines and the secretion of parathyroid hormone and calcitonin. Endocr Rev 1980; 1:319. 29. Heath H III, Fox J, Fryer M. Electrical and chemical stimulation of cervical sympathetic nerves in the dog does not affect secretion of parathyroid hormone. Endocrinology 1985,-116:1977. 30. Mallette LE, Khouri K, Zengolita H, et al. Lithium treatment increases midregion parathyroid hormone and parathyroid volume. J Clin Endocrinol Metab 1989;68:654. 31. Brown EM. Lithium induces abnormal calcium-regulated PTH release in dispersed bovine parathyroid cells. J Clin Endocrinol Metab 1981;52:1046.

Ch. 49: Physiology of Bone 32. Habener JF, Rosenblatt M, Potts JT. Parathyroid hormone; biochemical aspects of biosynthesis, secretion, action, and metabolism. Physiol Rev 1984; 64: 985. 33. Nemeth EF, Scarpa A. Cytosolic Ca++ and the regulation of secretion in parathyroid cells. FEBS Lett 1986;213:15. 34. Kifor O, Kifor I, Brown EM. Effects of high extracellular calcium concen¬ trations on phosphoinositide turnover and inositol phosphate in dispersed bovine parathyroid cells. ] Bone Mineral Metab 1992;7:1327. 35. Marx SJ, Lasker R, Brown E, et al. Secretory dysfunction in parathyroid cells from a neonate with severe primary hyperparathyroidism. J Clin Endocrinol Metab 1986; 62:445. 36. Bronner F. Intestinal calcium absorption and transport. In: Carafoli E, ed. Membrane transport of calcium. New York: Academic Press, 1982:237. 37. DeLuca HF, Schnoes HR. Vitamin D: recent advances. Annu Rev Biochem 1983; 52:411. 38. Rasmussen H, Fontaine O, Max EE, Goodman DBP. The effect of lahydroxyvitamin D3 administration on calcium transport in chick intestine brush border membrane vesicles. J Biol Chem 1979; 25:2993. 39. Bikle DD. Regulation of intestinal calcium transport by vitamin D: role of membrane structure. In: Aloia RC, Curtain KC, Gordon LM, eds. Membrane transport and information storage. New York: Wiley Ross, 1990:191. 40. Adams ND, Gray RW, Lemann J. The effect of oral CaC03 loading and dietary calcium deprivation on plasma 1,25-dihydroxyvitamin D concentrations in healthy adults. J Clin Endocrinol Metab 1979;48:1008. 41. Hughes MR, Brumbaugh PF, Haussler MR, et al. Regulation of serum la25-dihydroxy vitamin D3 by calcium and phosphate in the rat. Science 1975; 190: 578. 42. Sheikh MS, Ramirez A, Emmett M, et al. Role of vitamin D-independent mechanisms in absorption of food calcium. J Clin Invest 1988;81:126. 43. Nordin BEC, Peacock M. Role of the kidney in regulation of plasma calcium. Lancet 1969; 2:1280. 44. Rouse D, Suki W. Renal control of extracellular calcium. Kidney Int 1990;38:700. 45. Morel F, Chabardes D, Imbert-Teboul M, et al. Multiple hormonal control of adenylate cyclase in distal segments of the rat kidney. Kidney Int 1982; 1 l(Suppl): 555. 46. Sonneberg J, Pansini AR, Christakos S. Vitamin D-dependent rat renal calcium-binding proteins: development of a radioimmunoassay, tissue distribution, and immunologic identification. Endocrinology 1984; 115:640. 47. Farese RV. Phosphoinositide metabolism and hormone action. Endocr Rev 1983;4:78. 48. Ro HK, Tembe V, Favus MS. Evidence that activation of protein kinase C can stimulate 1,25-dihydroxyvitamin D3 secretion by rat proximal tubules. Endocri¬ nology 1992; 131:1424. 49. Raisz LG. Bone metabolism and calcium regulation. In: Avioli LV, Krane OM, eds. Metabolic bone disease, vol 1. New York: Academic Press, 1977:1. 50. Chase LR, Fedak SA, Aurbach GD. Activation of skeletal adenyl cyclase by parathyroid hormone in vitro. Endocrinology 1969;84:761. 51. Rodan GA, Martin TJ. Role of osteoblasts in hormonal control of bone resorption: a hypothesis. Calcif Tissue Int 1981;33:349. 52. Lee MJ, Roth SI. Effect of calcium and magnesium on deoxyribonucleic acid synthesis in rat parathyroid glands in vitro. Lab Invest 1975;33:72. 53. Robertson WG, Peacock M, Alkins D. The effect of parathyroid hormone on the uptake and release of calcium by bone in tissue culture. Clin Sci 1972;43: 715. 54. Quamme G. Control of magnesium transport in the thick ascending limb. Am J Physiol 1989;256(Renal Fluid Electrolyte Physiol 25):F197. 55. Takaichi K, Kurokawa K. Inhibitory guanosine triphosphate-binding pro¬ tein-mediated regulation of vasopressin action in isolated single medullary tubules of mouse kidney. J Clin Invest 1988;82:1437. 56. Zaidi M, Datta HK, Patchell A, et al. "Calcium-activated" intracellular calcium elevation: a novel mechanism of osteoclast regulation. Biochem Biophys Res Commun 1989; 163:1461. 57. Malgaroli A, Meldolesi J, Zambonin-Zallone A, Teti A. Control of cyto¬ solic free calcium in rat and chicken osteoclasts: the role of extracellular calcium and calcitonin. J Biol Chem 1989;264:14349. 58. Raisz LG, Kream BE. Regulation of bone formation. N Engl J Med 1983;309:35. 59. Martin KJ, Hruska KA, Freitag JJ, Slatopolsky E. The peripheral metabo¬ lism of parathyroid hormone. N Engl J Med 1979,-301:1092. 60. Nussbaum SR, Zahradnik RJ, Lavigne JR. Highly sensitive two-site immunoradiometric assay of parathyrin, and its clinical utility in evaluating patients with hypercalcemia. Clin Chem 1987;33:1364. 61. Burtis WJ, Brady TG, Orloff JJ, et al. Immunochemical characterization of hypercalcemia of malignancy. N Engl J Med 1990;322:1106. 62. Austin LA, Heath H III. Calcitonin physiology and pathophysiology. N Engl J Med 1981;304:269. 63. Walton RJ, Bijvoet OLM. Nomogram for determination of renal threshold phosphate concentration. Lancet 1975;2:309. 64. Heaney RP, Recker RR, Hinders SM. Variability of calcium absorption. Am J Clin Nutr 1988; 47:262. 65. Delmas PD. Biochemical markers of bone turnover: methodology and clinical use in osteoporosis. Am J Med 1991;91(Suppl 5B):59S. 66. Price PA, Baukol SA. 1,25-Dihydroxyvitamin D3 increases synthesis of the vitamin K-dependent bone protein by osteosarcoma cells. J Biol Chem 1980,-255:11660. 67. Eyre D. New biomarkers of bone resorption. J Clin Endocrinol Metab [Editorial] 1992;74:470A.

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Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

49

PHYSIOLOGY OF BONE LAWRENCE G. RAISZ

Understanding of the physiology of skeletal tissue has ad¬ vanced remarkably during the past few decades. Studies of the various cell types in bone and their interactions have led to the concept of a system involving not only systemic hormones but also local factors that regulate bone turnover. Also, molecular biology techniques are now being applied to bone cells and are likely to provide even more rapid advances. Fundamental to any description of physiologic regulation is an understanding of the functions of the skeleton. Structurally, bone must provide a framework for muscle movement, must pro¬ tect internal organs and marrow, and must be able to adapt to changing physical stress. Metabolically, the skeleton functions as a storehouse and as a homeostatic buffer system. Presumably, bone evolved to fulfill both its structural and metabolic roles as our ancestors moved from the calcium-rich, buoyant ocean to fresh water, and then to dry land. Although the major reservoir function of bone is to supply calcium and phosphorus, the skele¬ ton also serves as a source of other ions, such as magnesium and sodium, and as a buffer to deal with ion excess. Also, the ability of the skeleton to take up a variety of trace elements may serve as an important safeguard against their toxicity. To achieve its mechanical functions, the skeleton needs to be light, of high ten¬ sile strength, and rigid but not brittle.1 This is achieved by an orderly, slightly deformable, mineralized collagen structure dis¬ tributed as a combination of dense cortical bone and spongy trabec¬ ular bone.

EMBRYOLOGY AND ANATOMY OF BONE The formation of the skeleton begins with condensation and differentiation of mesenchymal cells into cartilage. These provide the template for subsequent bone formation in two ways. Bone may begin to form by differentiation of osteoblasts around the cartilage rudiments. This occurs in the membranous bones, such as the skull and the periosteum of long bones. Here, the mesen¬ chyme condenses, and osteoblasts differentiate on the surface of the cartilaginous template, which then degenerates. Endochon¬ dral bone formation occurs at the cartilage growth plate. Here, the osteoblasts differentiate directly on calcified cartilage and form spicules of bone with a cartilaginous core. Long bones lengthen by the proliferation of cartilage cells. The cartilage un¬ dergoes an orderly change, in which the columns of cells in the proliferative zone become hypertrophied and the matrix between these columns becomes mineralized. This probably involves both breakdown of the highly hydrated high-molecular-weight pro¬ teoglycans of cartilage matrix and the release of matrix vesicles from hypertrophic chondrocytes. After the cartilage is mineral¬ ized, new bone formation by osteoblasts begins on the surface of the calcified cartilage spicules; this is called the primary spongiosa. Subsequently, the spicules are resorbed and replaced by bone, termed the secondary spongiosa. Early in fetal bone formation, col¬ lagen is laid down in a woven and irregular pattern, but soon the osteoblasts deposit an orderly lamellar arrangement of collagen. The combination of a smooth, dense outer layer of cortical (compact) bone and spongy trabecular (cancellous) bone provides both the necessary strength without excessive weight and an ex¬ tended surface on which rapid changes in formation or resorp-

448

PART IV: CALCIUM AND BONE METABOLISM

FIGURE 49-1.

Haversian remodeling. This is a longitudinal section through a cortical bone remodeling unit (X400). The haversian canal is formed by an osteoclast-cutting cone. After the canal reaches maximal diameter, mesenchymal cells differentiate into osteoblasts and begin to form an osteon made of concentric lamellae of new matrix. (Courtesy of Dr. Robert Schenk.)

tion can respond to changing metabolic needs. The metabolic re¬ sponses of the skeleton mainly occur on the trabecular bone surfaces and the endosteal (inner) surface of the cortex. However, even the periosteal (outer) surface of the cortex can be affected by calcium-regulating hormones, as evidenced by the development of subperiosteal bone resorption in severe hyperparathyroidism.

MODELING AND REMODELING The term modeling refers to the process by which bone grows and alters its shape through resorption and formation at different sites. For example, the long bones enlarge by periosteal formation and endosteal resorption. As they lengthen, the large amount of bone formed at the growth plate is resorbed to maintain a hollow tubular structure. The flat bones of the skull and pelvis grow and change their shape by this process of formation at one site and resorption at another. Modeling can be influenced by mechanical stress. For example, bone mass increases in the most used long bones of athletes by both periosteal and endosteal apposition. Bone formation on one surface and resorption on the other per¬ mit teeth to be moved by mechanical forces. Even soft tissues can produce modeling changes. For example, increased endosteal resorption and periosteal apposition can occur in response to bone marrow hyperplasia. The term remodeling refers to the process in which resorption is followed by formation at the same site; hence, the two pro¬ cesses are “coupled." This process is important for the overall health and functional integrity of skeletal tissues as well as for

the metabolic responses of the bone mineral reservoir. In large mammals, the cortical bone is remodeled by the development of a haversian system of osteons (Fig. 49-1). These structures are formed by osteoclastic removal of a cylinder of bone. Behind these osteoclasts are a vascular loop and mesenchymal cells that differentiate into osteoblasts and form concentric lamellae of new bone around the central vascular canal. The major importance of this system of osteons may be that it enables the cortex to partic¬ ipate in the metabolic functions of the skeleton without excessive loss of strength. Haversian remodeling may also be important in the repair of fatigue damage in bone.2 Remodeling also occurs on the trabecular bone surface. Here, osteoclasts excavate scalloped areas called Howship lacunae, which are then replaced by packets of new lamellar bone laid down by osteoblasts. Although much is known about the anatomic sequence and time course of cycles of cortical and trabecular remodeling (Fig. 49-2), the cellular mechanisms are poorly understood.3,4 The initial activation in¬ volves a change in the lining cells or resting osteoblasts on the surface of bone, which may normally protect it from attack by osteoclasts. These may not only change shape but also release factors that stimulate osteoclastic activity. Once osteoclasts have removed the bulk of bone mineral and matrix, a reversal phase occurs that involves the removal of additional elements of bone matrix by macrophages and the preparation of the bone surface for new osteoblastic formation. In the formation phase, succes¬ sive generations of osteoblasts synthesize lamellar bone and re¬ place the resorbed bone with a packet of new bone, called a bone structural unit (BSU).

NATURAL HISTORY OF THE SKELETON In humans, the skeleton continues to grow until about 25 to 35 years of age. Before puberty, the bones grow largely by peri¬ osteal apposition and endosteal resorption, but during and after puberty, there is a period of endosteal apposition and thickening of the trabeculae, so that bone mass increases by 10% to 20% even after linear growth has ceased.5 Later in life, bone mass be¬ gins to decrease. Age-related bone loss appears to be more rapid in women than in men, greater for trabecular than for cortical bone, and accelerated at menopause. Remodeling is important in age-related bone loss. The formation of new BSU both in the cor¬ tex and on the surface of trabecular bone continues throughout life. Bone mass can decrease simply because there are more BSU formed (increased turnover), and there is a time gap between re¬ sorption and formation even though the processes are coupled. This deficit is theoretically reversible if the rate of turnover de¬ creases and the formation phase is allowed to proceed to com¬ plete replacement. Moreover, remodeling can be uncoupled be¬ cause so much endosteal or trabecular bone is removed that there is no longer a template for osteoblastic replacement. Thus, there may be areas in which trabecular plates develop holes or are con¬ verted to attenuated rods. Finally, the ability of successive popu-

FIGURE 49-2.

Bone remodeling cycle. Activation of this cycle begins with a change in the resting osteo¬ blasts (also called lining cells) on the bone surface, which permits and perhaps stimulates osteoclastic bone resorption. Osteoclasts and macrophages are probably derived from different immediate precur¬ sors, but both originate from hematopoietic stem cells. During the reversal phase in trabecular bone remod¬ eling, macrophages are seen on the bone surface, but their role is not established. Osteoblasts come from a separate mesenchymal stem cell population, probably related to stromal stem cells in the marrow. Deter¬ mined osteoprogenitor cells or preosteoblasts repli¬ cate and differentiate into mature osteoblasts that lay down lamellar bone and replace the bone lost during the resorption phase. (From Raisz LG. Local and sys¬ temic factors in the pathogenesis of osteoporosis. N Engl J Med 1988;318:818.)

Hematopoietic Stem Cel

Mesenchymal Stem Cell

Monocyte Preosteoblast

Osteoblasts Macrophage

'//I;//!///////////////////////,//////////^

ACTIVATION ► RESORPTION ► REVERSAL ► FORMATION

Ch. 49: Physiology of Bone lations of osteoblasts to complete the formation process is im¬ paired with age so that haversian canals remain enlarged and trabecular surfaces show only partial replacement of resorbed bone with thinner packets of new bone.

449

phate, mineralization appears to be normal.9 Moreover, there is little evidence that parathyroid hormone (PTH) or calcitonin are essential for mineralization. The more important direct effects of the calcium-regulating hormones appear to be on matrix forma¬ tion and bone resorption.

BONE CHEMISTRY AND MINERALIZATION Bone mineral consists largely of hydroxyapatite (Ca10[P04]6[0H]2) together with transition forms and other minerals absorbed on the surface. The hydroxyapatite crystals are small and often have lattice defects, although these crystals become more complete as bone matures. The major absorbed minerals are carbonate, magnesium, and sodium. Ninety-nine percent of body calcium, 90% of phosphorus, 80% of carbonate, 80% of citrate, 60% of magnesium, and 35% of sodium are in the skeleton. All these ions may be accessed when there are deficits and stored when there are excesses. Hydrogen ion is generated when hydroxyapatite is formed from circulating Ca2+ and HPO|_. When there is a hydrogen ion excess, this can be buffered by demineralization, releasing carbonate and phosphate from bone. Moreover, there are many bone-seeking elements, such as alu¬ minum, fluoride, lead, and strontium. Deposition of these ele¬ ments in the skeleton can prevent soft-tissue damage but is likely to alter bone cell function. The organic matrix of bone is made up largely of type I colla¬ gen, which consists of tightly coiled, long, triple helical molecules containing two c^- and one a2-chains. The collagen molecules are strengthened by covalent intramolecular and intermolecular cross-links and are assembled in ordered fibers. The other colla¬ gen types, such as types III, IV, and V, are not deposited in the matrix but are present in interstitial and vascular structures. Type II collagen predominates in cartilage. Although 95% of the matrix is collagen, the noncollagenous components that constitute the remaining 5% are also important in providing bone with some of its physical and chemical prop¬ erties.6,7 The proteoglycan of bone is of lower molecular weight and is more compact than that in cartilage. There are also small amounts of proteolipid, which can form complexes with calcium phosphate. Noncollagen proteins include a calcium-binding, ycarboxyglutamic acid-containing protein (BGP or osteocalcin) and osteonectin, a highly phosphorylated glycoprotein that binds to collagen and calcium. Osteopontin and sialoprotein are highly acidic, have a high affinity for calcium, and have binding sites for integrin receptors. All these proteins are probably important in regulating mineralization, and their distribution may account for the delay between matrix deposition and mineralization. These proteins may also be involved in bone resorption. Osteocalcin is chemotactic for osteoclasts and their precursors; and osteopon¬ tin, as well as other proteins, may be involved in the adhesion of osteoclasts to mineralized matrix. Mineralization may also be controlled by cellular elements.8 Matrix vesicles have been identified in calcifying cartilage and fetal bone, contain cell membrane elements, are rich in alkaline phosphatase, and may initiate mineralization by increasing local phosphate concentration or providing membrane proteolipids. The concept that phosphatase activity is essential for mineraliza¬ tion has been with us for more than 50 years, but its precise role is uncertain. Such enzymes may increase the local inorganic phosphate concentration by acting on organic phosphates, or they may cleave pyrophosphate, a potent inhibitor of calcification. The delay between the deposition of matrix by osteoblasts and its mineralization is probably essential for extracellular mod¬ ifications of matrix, such as collagen cross-linking, formation of large collagen fibers, and deposition of noncollagen proteins, all of which may increase the strength of mineralized tissues. There is little evidence for direct hormonal control of these steps, but adequate supplies of calcium and phosphate are essential. Thus, in vitamin D-deficient animals given enough calcium and phos¬

CELL BIOLOGY OF BONE The lineages of bone-forming cells (osteoblasts) and boneresorbing cells (osteoclasts) probably become separate early in de¬ velopment. Their function is controlled by a complex system of intercellular signals that involve not only systemic calcium¬ regulating and growth-regulating hormones but also local fac¬ tors. Bone disease occurs when there is an imbalance between the functions of forming and resorbing cells. Thus, accelerated resorption and diminished formation exacerbate decreased bone mass in osteoporosis. Excessive bone mass occurs because bone resorption is impaired, as in congenital osteopetrosis, or because formation is excessive and disorderly, as in virally induced avian osteopetrosis and Paget disease.

OSTEOBLASTS The osteoblast, a highly specialized bone matrix-synthesiz¬ ing cell, is derived from precursor cells in the periosteum or the stroma of the bone marrow called determined osteoprogenitor cells.10 Bone can also form in ectopic sites from undifferentiated mesenchymal cells in response to certain inducing agents, partic¬ ularly demineralized bone matrix.11 This may be due to the effects of specific proteins produced by bone cells and deposited in matrix. Under these conditions, the sequence of endochondral bone formation is recapitulated; that is, cartilage is formed, min¬ eralized, and then replaced by bone. The mature osteoblast is a plump polygonal cell that has an eccentric nucleus, a prominent Golgi apparatus, and abundant rough endoplasmic reticulum (Fig. 49-3). These cells deposit a collagenous matrix and extend cytoplasmic processes into this matrix. As they complete their synthetic activity, they become buried in their own matrix and are called osteocytes. Osteoblasts may also stop producing matrix but remain on the bone surface; these lining cells or resting osteoblasts can be the sites for new remodeling cycles of activation, resorption, and formation. Osteoblasts produce most of the constituents of bone matrix; however, many proteins are taken up by matrix from the circula¬ tion, including a2-HS-glycoprotein and albumin.12 Osteoblasts produce alkaline phosphatase and release it systemically. Hence, serum alkaline phosphatase activity correlates with osteoblastic activity. BGP is also released into the circulation from osteoblasts and provides another marker of their activity.13 When procolla¬ gen is converted to collagen, large N- and C-terminal peptides are released. These can be measured in the circulation and reflect the overall rate of collagen synthesis in the body. Osteoblasts have receptors for PTH and 1,25-dihydroxyvitamin D (l,25[OH]2D3) and for systemic growth regulators.14 They apparently are the major source of the autocrine factors that regulate local bone turnover, including prostaglandins and bonederived growth factors. Osteoblasts may trigger bone resorption in the remodeling process. This activation step may involve shape changes or secretion of collagenase and related metalloproteinases as well as other proteolytic enzymes, such as plas¬ minogen activator.13 The changes may enhance the access of os¬ teoclasts to the mineralized bone surface. Osteoblasts may also release factors that activate osteoclasts.

OSTEOCLASTS Osteoclasts resorb bone and calcified cartilage. These large multinucleated cells are formed by the fusion of mononuclear precursors. Osteoclasts presumably are derived from a hemato-

450

PART IV: CALCIUM AND BONE METABOLISM

■

v„-

FIGURE 49-3. Osteoblasts shown on electron mi¬ crograph. A layer of plump cells rich in rough endo¬ plasmic reticulum and with a large Golgi apparatus is seen forming an osteoid seam consisting of a col¬ lagenous matrix that subsequently mineralizes. (Courtesy of Dr. Marijke E. Holtrop.)

poietic stem cell rather than from the mesenchymal precursor of the osteoblast. The osteoclast cell line is related to the monocytemacrophage lineage, but many of the surface markers for macro¬ phages are missing from osteoclasts, and the osteoclast and monocyte precursor cell lines probably separate early in differ¬ entiation.16 The stimulation of osteoclast precursor replication may be an important mechanism for increasing bone resorption. Once fusion has occurred, however, the nuclei in an osteoclast do not undergo further cell division. The osteoclast cytoplasm contains abundant mitochondria, many lysosomes, and relatively little rough endoplasmic reticu¬ lum. The unique feature of the osteoclast is the ruffled border, which is the site of active resorption (Fig. 49-4). This is sur¬ rounded by a clear or sealing zone, which functions to attach the osteoclast to bone and isolate the ruffled border from extracellu¬ lar fluid so that a high local concentration of hydrogen ions and lysosomal enzymes can be maintained.17 Osteoclasts are rich in acid phosphatase as well as other lysosomal enzymes, and in car¬ bonic anhydrase, which facilitates hydrogen ion secretion. Thus, the ruffled border area simulates a giant exteriorized phagolyso¬ some. Hydrogen ions are important not only in mobilizing min¬ eral but also in activating lysosomal enzymes that can degrade all components of bone matrix, including collagen at a low pH. The proton pump that transports hydrogen ions into the

ruffled border area is similar but not identical to the vacuolar pro¬ ton pump found in lysosomes and kidney cells.18 Other impor¬ tant features of the osteoclast are the cell attachment apparatus, which involves vitronectin receptors that can bind a wide variety of proteins containing Arg-Gly-Asp sequences.19 The osteoclast also has receptors that mediate the inhibition of osteoclastic ac¬ tivity by high calcium concentrations.

OTHER CELL TYPES IN BONE Macrophages may be found at resorption sites after the initial removal of bone osteoclasts.3 Their function is uncertain, but they may remove residual matrix that has not been completely digested because macrophages can secrete collagenase as well as lysosomal enzymes. Macrophages may also be a source of interleukin-1 (IL-1) and prostaglandin E2 (PGE2), which not only are potent stimulators of bone resorption but also can stimulate the replication of osteoblast precursors and may be involved in initiating the formation phase of the remodeling cycle. Lympho¬ cytes may also play a role by secreting bone-resorbing factors. Moreover, calcium-regulating hormones can act on these hema¬ topoietic cells. For example, l,25(OH)2D3 increases the differen¬ tiation of monocyte precursors into macrophages.

Ch. 49: Physiology of Bone

451

FIGURE 49-4. Resorbing apparatus of osteoclasts shown on electron micrograph. A section of an osteoclast with a highly infolded ruffled border is seen between two areas rel¬ atively devoid of subcellular particles, termed the clear or sealing zone. Large vacuoles are present in the osteoclast cy¬ toplasm, and there are abundant mitochondria. (Courtesy of Dr. Marijke E. Holtrop.)

Fibroblastic cells may also play a role by secreting local regu¬ lators. Somatomedin, or insulin-like growth factor 1 (IGF-I), which can be produced by fibroblasts, is a potent stimulator of bone growth. Mast cells are found adjacent to resorbing bone18 and can produce heparin, which enhances bone resorption in some culture systems (see Chap. 180). Finally, endothelial cells may play a role. These cells produce growth factors and are also a major source of prostacyclin (PCI2), which can stimulate bone resorption and may also affect bone blood flow.

EFFECTS OF HORMONES ON BONE CELLS Despite many studies of the direct effects of hormones on bone, the complex regulation of bone resorption and formation still is inadequately explained. The effects of systemic agents are probably modulated by interactions with local intercellular me¬ diators. For example, PTFf is clearly a potent stimulator of bone resorption both in vivo and in vitro but has not been shown to act on isolated osteoclasts in the absence of other bone cells. Pros¬ taglandins are also potent stimulators of bone resorption, but they decrease motility and resorptive activity of isolated osteo¬ clasts, as does calcitonin. The major factors that influence bone metabolism and their most important direct effects are listed in Table 49-1.

PARATHYROID HORMONE Although PTH was first shown to act directly on bone as a stimulator of resorption, much more is now known about its

effects on osteoblasts at the cellular and molecular levels.14,20 Some of this information has been derived from investigations of isolated bone cells or cloned osteosarcoma cells that have an osteoblastic phenotype; studies in vitro and in vivo generally have confirmed the findings in cell culture. The first effect of PTH on osteoblast-like cells is an activation of adenylate cyclase and cyclic adenosine monophosphate (cAMP)-dependent protein ki¬ nase. Other mediators may be involved; PTH can increase calcium entry and accelerate phosphatidylinositol turnover.-1 PTH also causes rapid changes in osteoblast cell shape associated with polymerization of actin. A subsequent decrease in collagen synthesis is associated with a diminution of procollagen messen¬ ger RNA (mRNA) levels in the cell. There also is an increased release of metalloproteinases from osteoblasts in response to PTH. Plasminogen activator activity is increased in part by de¬ creased production of an inhibitor, and this may result in the ac¬ tivation of latent collagenase. Alkaline phosphatase levels are usually decreased. PTH may also decrease BGP synthesis. PTH can increase prostaglandin synthesis and cell replication in bone cell and organ cultures.22 Most of these effects of PTH on bone can be considered cat¬ abolic; but the prolonged, intermittent administration of low doses of PTH can elicit an anabolic effect, with increased bone mass.23 This is the basis for the use of intermittent PTH admin¬ istration to treat osteoporosis. The anabolic response may be due to stimulation of precursor cell replication by PTH or release of growth factors from bone cells or matrix. Although the ability of PTH to stimulate bone resorption has

452

PART IV: CALCIUM AND BONE METABOLISM

been recognized for many years, the mechanism is poorly un¬ derstood. In vivo, PTH rapidly increases the number and activity of osteoclasts as measured by the extent of ruffled border area.24 Increased release of calcium and matrix constituents of bone can be measured within a few hours, but increases in hyaluronic acid synthesis and lysosomal enzyme release can be detected within minutes. PTH probably causes the fusion and activation of exist¬ ing osteoclast precursors because an increase in resorption and in osteoclast number is seen in organ cultures of bones treated with hydroxyurea, which prevents cell replication.25 PTH stimulation of bone resorption presumably is receptor mediated. The role of cAMP in mediating this response is contro¬ versial. Stimulators of adenylate cyclase activity and phosphodi¬ esterase inhibitors can enhance bone resorption, but their effect is generally smaller than that of PTH. Moreover, under certain conditions, these agents inhibit bone resorption, mimicking the action of calcitonin. Possibly, the stimulation of bone resorption is mediated by increased cell calcium. A role for intracellular calcium is also supported by the observation that the calcium ionophore A-23187 can stimulate bone resorption.26 The PTH re¬ ceptor has been cloned.27 It is present in osteoblasts and their precursors but has not been demonstrated on mammalian osteo¬ clasts. This single receptor can mediate increases in cAMP, phosphatidylinositol breakdown, and intracellular calcium. The receptor can be activated either by 1-34 PTH or by 1-34 PTHrelated protein.

1,25-DIHYDROXYVITAMlN D3 The major physiologic role of the hormonal form of vitamin D (l,25[OH]2D3, calcitriol) is to promote intestinal absorption of

TABLE 49-1 Systemic and Local Regulation of Bone Metabolism Direct Effects on Agent

Bone Resorption

Bone Formation

t t 4

4 4

CALCIUM-REGULATING HORMONES Parathyroid hormone 1,25-dihydroxyvitamin D Calcitonin

—

SYSTEMIC HORMONES Glucocorticoids Insulin Thyroxine Sex hormones Growth hormone

4

4

4 t t 4tt

—

t

—

t

GROWTH FACTORS Insulin-like growth factors

—

t

Epidermal growth factor + TGFa*

t

Fibroblast growth factor*

t

4 4 t t4

Platelet-derived growth factor*

t

TGF/3*

t4

LOCAL FACTORS Prostaglandin E2

t

Interleukin-1*

t

Tumor necrosis factor Bone-derived growth factors (BMP)

t —

t4t t4t 4t 4t

TGF, transforming growth factor; BMP, bone morphogenetic protein; direct effects are listed as increased (f), decreased (|), or unchanged (—) bone resorption or formation. * Increase may be mediated by endogenous prostaglandin synthesis, t Depends on concentration and presence of glucocorticoids. $ Effects depend on age and concentration.

calcium and phosphorus. It is also one of the most potent hor¬ mones acting on bone. Although the effects of l,25(OH)2D3 on the intestine promote skeletal growth and mineralization, the effects on bone appear to be catabolic, stimulating resorption and inhibiting formation. Like PTH, receptors for l,25(OH)2D3 have been demonstrated in osteoblastic cells. The hormone resembles PTH in inhibiting collagen synthesis but differs from PTH in its ability to increase BGP production.7 At high, toxic doses, l,25(OH)2D3 actually decreases mineralization.27 The mecha¬ nism of this impaired bone mineralization may be related to the effect on BGP production. l,25(OH)2D3 presumably acts by a classic steroid hormone pathway. There is a receptor in bone cells that binds to nuclear chromatin. This receptor has been demonstrated in isolated os¬ teoblasts and osteosarcoma cells and may mediate such tran¬ scriptional effects as the increase in mRNA for BGP and the de¬ crease in mRNA for collagen.28 Although l,25(OH)2D3 stimulates bone resorption, recep¬ tors have not been demonstrated in isolated osteoclasts, so the effect may be indirect. l,25(OH)2D3 also stimulates the produc¬ tion of multinucleated cells with an osteoclastic phenotype in bone marrow and spleen cell cultures.16,29 Resorption occurs at such low concentrations in organ culture that this effect can be used as a serum bioassay.30 However, this assay requires extrac¬ tion of the serum and, therefore, measures l,25(OH)2D3 that would normally circulate bound to vitamin D-binding protein. Hence, the concentrations that stimulate bone resorption in or¬ gan culture are probably 10-fold higher than the normal concen¬ tration of free hormone in the blood and extracellular fluid. Although there is substantial evidence that l,25(OH)2D3 is the bioactive form of vitamin D, there is evidence for effects of other metabolites on skeletal tissue. 25-Hydroxyvitamin D can stimulate bone resorption and inhibit bone formation at high concentrations, which may occur in vivo when toxic doses are given. 24,25-Dihydroxyvitamin D is formed by an alternative hydroxylation pathway in the kidney. This probably repre¬ sents an inactivation process, but there is evidence that 24,25dihydroxyvitamin D has anabolic effects, particularly on carti¬ lage. The importance of 24,25-dihydroxyvitamin D has been questioned because fluoridated analogues that cannot be hydroxylated at the 24 position can support normal skeletal growth and mineralization in rats.31 l,25(OH)2D3 not only has important direct effects on bone cells but also may act on bone indirectly through its function as an immunomodulator.32 l,25(OH)2D3 can stimulate macro¬ phage differentiation and IL-1 production. It also inhibits Tlymphocyte proliferation and decreases the production of IL-2. The physiologic importance of these actions remains uncertain (see Chap. 189).

CALCITONIN Calcitonin is a potent direct inhibitor of osteoclastic activity (see Chap. 52). In contrast to PTH and l,25(OH)2D3, receptors for calcitonin have been identified on osteoclasts. Moreover, isolated osteoclasts show a decrease in motility and resorptive activity when treated with this hormone. Calcitonin rapidly decreases the amount of active ruffled border of osteoclasts in organ cultures, although the cells may remain attached to the bone surfaces by their clear zones. In vivo, the number of osteoclasts decreases as the cells appear to migrate away from the bone surface. Calcito¬ nin increases cAMP content in cell populations enriched with os¬ teoclasts. Although it is unclear whether cAMP is the mediator of inhibition of bone resorption, this appears likely because agents that increase cAMP concentration can mimic the action of calci¬ tonin both in organ culture and in isolated osteoclasts. The direct inhibition of osteoclastic activity by calcitonin is transient in iso¬ lated cell systems, in organ cultures, and in patients with hyper¬ parathyroidism or hypercalcemia of malignancy. This "escape phenomenon" may be due to down-regulation of the calcitonin

Ch. 49: Physiology of Bone receptors (which have recently been cloned).4 33 The effects of calcitonin on osteoblastic function remain controversial.34 The fact that calcitonin is most effective clinically in osteoporotic pa¬ tients with high turnover and high rates of bone resorption sug¬ gests that its antiosteoclastic effect is most important.35

SYSTEMIC HORMONES THAT AFFECT BONE METABOLISM Many hormones that regulate somatic growth act directly or indirectly on the skeleton. These hormones not only modulate physiologic skeletal growth and development but also are impor¬ tant in the pathogenesis of metabolic bone disease. GLUCOCORTICOIDS

Glucocorticoids have complex direct and indirect effects on skeletal tissue. The major indirect effect is the inhibition of calcium absorption in the intestine. Presumably, this prompts secondary hyperparathyroidism and may explain the clinical ob¬ servation that bone resorption is increased in patients treated with glucocorticoids. The major direct effect on bone is a doserelated decrease in formation. This is probably mediated by a de¬ crease in the replication and differentiation of osteoblast precur¬ sors.36 However, glucocorticoids can also have a positive effect on osteoblast function. In some cell and organ cultures, physiologic concentrations of glucocorticoids can increase collagen synthesis, increase alkaline phosphatase levels, and enhance the response to other hormones. These anabolic effects may be due to an in¬ crease in osteoblast differentiation.3 Glucocorticoids can have both stimulatory and inhibitory effects on bone resorption.38 Stimulation may be due to enhanced osteoclast differentiation as well as secondary hyperparathyroid¬ ism. Inhibition of resorption may be due to decreased replication of osteoclast precursors or decreased production of boneresorbing factors, such as prostaglandins and interleukins. What¬ ever the mechanisms, hypercalcemia has been observed in adrenal insufficiency, and decreased bone mass is an important adverse effect of glucocorticoid excess (see Chaps. 58 and 63). OTHER SYSTEMIC HORMONES

Excesses and deficiencies of growth hormone are associated with increases and decreases in skeletal growth. This effect is probably not due to any direct action on skeletal tissue but rather is mediated by the somatomedins or IGFs (see Chaps. 14 and 169). In adults, the major source of IGF is the liver, but in fetal life, many other tissues can probably produce somatomedins, in¬ cluding skeletal tissue. Moreover, growth hormone can stimulate IGF-I production by bone cells.39 IGF-I has a pleiotropic effect, stimulating bone cell replication as well as collagen and noncol¬ lagen protein synthesis.40 IGF-II can also stimulate bone forma¬ tion. The relative importance of IGF-I and IGF-II in regulating bone growth and in metabolic bone disease is uncertain. Possi¬ bly, the decrease in bone mass seen in malnutrition and gastroin¬ testinal disorders is related to decreased production of these fac¬ tors. An age-related decrease in growth hormone and IGF-I secretion may play a role in bone loss.41 Bone tissue produces IGF-I and IGF-II as well as a number of IGF-binding proteins that can be both inhibitory and stimulatory.42 The regulation of these binding proteins may be as important as the regulation of IGFs themselves in the local control of bone formation. Insulin is an important regulator of somatic growth. At physiologic concentrations, insulin appears to stimulate osteo¬ blast function, selectively increasing collagen synthesis without affecting cell replication or protein synthesis in the periosteum.43 At higher concentrations, insulin can produce a pleiotropic effect, as does IGF-I. Insulin may be important in skeletal development. Bone mass may be increased by hyperinsulinism in the infants of diabetic mothers and decreased in diabetic children with insulin deficiency.

453

Thyroid hormones (thyroxine and triiodothyronine) are es¬ sential for maintaining skeletal growth and remodeling. They not only increase cartilage growth directly but also probably have a positive interaction with IGF-I. Thyroid hormones can increase bone turnover, an effect apparently due to direct stimulation of both bone resorption and formation.44,45 Decreased bone mass has been observed in hyperthyroid patients, particularly those who received large doses of exogenous thyroid hormones for long periods.44'46 Perhaps the greatest limitation in our understanding of skel¬ etal physiology is that we do not know how sex hormones act on bone. Androgens and estrogens are involved in the pubertal growth spurt and the maintenance of bone mass. Some of this may be due to changes in muscle mass, which then influence bone. The accelerated bone loss that occurs with estrogen with¬ drawal at menopause can be attributed to an increase in bone resorption. This has led to the concept that estrogens oppose the resorptive activity of PTH or other stimulators of osteoclastic ac¬ tivity. Both estrogen and androgen receptors have been identified in bone cells, particularly those of the osteoblastic lineage.47,48 The sex hormones change the production of cytokines, prosta¬ glandins, and growth factors by bone cells.49-53 However, the rel¬ ative importance of these effects in mediating the changes in bone turnover seen with sex hormone deficiency remains to be determined. In view of the many hormonal influences on the skeleton identified in the past few decades, it is likely that additional effects of systemic hormones on skeletal function will be discov¬ ered. Among the hormones that have been considered as possible skeletal regulators are prolactin, which may mobilize bone calcium; catecholamines, which increase cAMP in bone; and cer¬ tain growth factors, which may have a systemic role as well.

LOCAL REGULATORS

The ability of the skeleton to respond to local forces must depend on the existence of local regulators, for which there are a number of candidates.54 Prostaglandins. Prostaglandins are ubiquitous local modu¬ lators of cell function (see Chap. 170). Their role in skeletal phys¬ iology was first suggested by the observations that PGE2 can raise the cAMP concentration and stimulate bone resorption in vitro.55 Subsequently, it was shown that bone can produce large amounts of PGE2 and PGI2, which may act as vasodilators in bone, as they do elsewhere. Prostaglandin production in bone can be stimulated by mechanical stress; by factors associated with inflammation and injury, such as complement, thrombin, bradykinin, and IL-1; and by growth factors, such as epidermal growth factor, transforming growth factors, and platelet-derived growth factor. PTH can stimulate and glucocorticoids can inhibit prosta¬ glandin production in bone.22 5/ 58 The effects of PGE2 on bone metabolism are complex and biphasic. At concentrations of 10-4 to 10 7 M, particularly in the presence of cortisol, PGE2 can stimulate cell replication in cul¬ tured calvaria and increase bone formation 53 At higher concen¬ trations, there is inhibition of osteoblastic collagen synthesis. In vivo, large amounts of PGEj or PGE2 stimulate bone formation. The new bone formed often is woven and irregular and may be found in the periosteum or in the metaphysis.54 The ability of bone to respond to mechanical forces may be prostaglandin de¬ pendent.60 Impact loading of bone results in increased bone for¬ mation, which can be blocked by inhibitors of prostaglandin syn¬ thesis. PGE2 production by osteoblasts and osteocytes and PGI2 production by osteocytes have been implicated in this response to loading. Stimulation of bone resorption by PGE2 differs somewhat from the response to PTH; it is slower and may depend in part on stimulation of cell replication. Moreover, prostaglandins have an inhibitory effect on isolated osteoclasts similar to the response to calcitonin but of shorter duration. Stimulation of resorption by

454

PART IV: CALCIUM AND BONE METABOLISM

endogenous prostaglandins has been demonstrated in vivo in in¬ flammation and immobilization.61,62 Bone-Derived Growth Factors. Factors that stimulate bone growth have been identified in culture media in extracts of both mammalian and avian bone. Two major families of growth fac¬ tors are produced in bone and deposited in bone matrix: (1) the IGFs, including the IGF-binding proteins, and (2) the transform¬ ing growth factor-/? and bone morphogenetic protein family.63,64 The latter group contains at least 10 different proteins that are related to other regulatory peptides, including the activininhibins and invertebrate growth factors. Other Growth Factors. Epidermal, fibroblast, and plateletderived growth factors can all act on skeletal tissue (see Chap. 169). These factors can be derived from bone cells or from adja¬ cent hematopoietic or vascular tissue. They can stimulate bone resorption by either prostaglandin-dependent or prostaglandinindependent mechanisms. Their mitogenic effects are associated with decreased collagen synthesis in acute experiments in vitro, but the prolonged treatment may increase bone formation in vivo.65,66 Cytokines. Both bone cells and adjacent hematopoietic cells can produce cytokines, which profoundly influence bone metab¬ olism67 (see Chaps. 169 and 207). Cytokine-mediated bone re¬ sorption was first identified as osteoclast-activating factor, pro¬ duced by mitogen- or antigen-stimulated human leukocyte cultures. Subsequently, it was found that IL-1 was the major bone resorbing factor from macrophages. Tumor necrosis factors are also produced by leukocytes and are active bone resorbers. These cytokines can stimulate bone resorption by both prosta¬ glandin-dependent and prostaglandin-independent mecha¬ nisms.616/ IL-1 can inhibit collagen synthesis in osteoblasts but may stimulate bone turnover under some conditions.68 IL-6 is not a potent, direct stimulator of resorption but can enhance osteo¬ clastic formation in marrow cell cultures. Both IL-1 and IL-6 have been implicated as mediators of the increased bone resorption that occurs at menopause. Overproduction of IL-4 produced os¬ teoporosis in a transgenic mouse model.69 Cytokines may medi¬ ate inflammatory bone loss and the hypercalcemia of multiple myeloma and other lymphoproliferative disorders. Ions as Regulators. Calcium, phosphate, and other ions im¬ portant in bone metabolism not only are involved in feedback control by calcium-regulating hormones but also can act as regu¬ lators. In addition to the critical role of the supply of calcium and phosphorus in mineralization, organ culture studies suggest that both calcium and phosphate can influence the rate of matrix for¬ mation.14 The effect of calcium is nonspecific in that this ion is required for cell growth generally. Phosphate appears to be a more selective regulator; increasing phosphate concentrations are associated with increased formation of bone matrix, but not cartilage matrix, and may also stimulate bone formation in vivo. High serum phosphate concentrations are associated with rapid rates of bone growth. For example, in humans, phosphate con¬ centrations are higher in the first year of life and at puberty, when the relative rates of skeletal growth are fastest. Moreover, the serum phosphate concentration appears to be high in species that grow at a proportionally faster rate, such as the rat. Calcium and phosphate can regulate bone resorption indirectly through their effect on calcium-regulating hormones. PTH secretion is in¬ hibited and calcitonin secretion stimulated by calcium, while phosphate loading can lower ionized calcium and stimulate PTH secretion. Both calcium and phosphate have direct inhib¬ itory effects on la-hydroxylase in the kidney and decrease l,25(OH)2D3 levels. There are also direct effects. High local con¬ centrations of calcium, which develop during resorption in the ruffled border area, can cause loss of activity and detachment of osteoclasts.1. Phosphate can inhibit bone resorption directly by a physicochemical effect on mineral dissolution.70 • Magnesium has complex effects on skeletal metabolism (see Chap. 67). High concentrations can inhibit mineralization and PTH secretion, while severe magnesium depletion also is associ¬

ated with decreased PTH secretion and decreased hormone re¬ sponsiveness. The hydrogen ion concentration can certainly affect bone mineralization and demineralization. The increased hydrogen ion concentration in the ruffled border area is neces¬ sary not only for removal of mineral but also for maximal activity of the lysosomal enzymes that resorb matrix. Decreasing the hy¬ drogen ion supply by inhibiting the proton pump, blocking car¬ bonic anhydrase, or interfering with chloride-bicarbonate ex¬ change can all inhibit bone resorption.4 Many other ions can affect the skeleton. Fluoride can stimulate osteoblastic activity, which is the basis for its therapeutic use in osteoporosis (see Chaps. 7 and 63). Aluminum is being studied as a pathogenetic factor in renal osteodystrophy, where it appears to inhibit miner¬ alization and impair osteoblast growth and function (see Chaps. 7 and 60). However, aluminum may also have a direct stimula¬ tory effect on osteoblasts.71

REFERENCES 1. Hayes WC, Gerhart TN. Biomechanics of bone: applications for assess¬ ment of bone strength. In: Peck WA, ed. Bone and mineral research, annual 2, vol 3. Amsterdam: Elsevier 1983;259. 2. Martin B. A theory of fatigue damage accumulation and repair in cortical bone. J Orthop Res 1992; 10:818. 3. Eriksen EF. Normal and pathological remodeling of human trabecular bone: three dimensional reconstruction of the remodeling sequence in normals and in metabolic bone disease. Endocrinol Rev 1986; 7:379. 4. Raisz LG. Mechanisms and regulation of bone resorption by osteoclastic cells. In: Coe FL, Favus MJ, eds. Disorders of bone and mineral metabolism. New York: Raven Press, 1992:287. 5. Hui SL, Johnston CC Jr, Mazess RB. Bone mass in normal children and young adults. Growth 1985; 49:34. 6. Young MF, Kerr JM, Ibaraki K, et al. Structure, expression, and regulation of the major noncollagenous matrix proteins of bone. Clin Orthop 1992;281:275. 7. Johansen JS, Williamson MK, Rice JS, Price PA. Identification of proteins secreted by human osteoblastic cells in culture. J Bone Miner Res 1992; 7:501. 8. Anderson HC, ed. Fifth international conference on cell-mediated calcifi¬ cation and matrix vesicles. Bone Miner 1992; 17:107. 9. Underwood JL, DeLuca HF. Vitamin D is not directly necessary for bone growth and mineralization. Am J Physiol 1984;246:E493. 10. Friedenstein AJ, Latzinik NV, Gorskaya YF, et al. Bone marrow stromal colony formation requires stimulation by haemopoietic cells. Bone Miner 1992; 18: 199. 11. Reddi AH. Regulation of bone differentiation by local and systemic fac¬ tors. In: Peck WA, ed. Bone and mineral research, annual 2, vol 3. Amsterdam: Elsevier, 1983:27. 12. Delmas PD, Tracy RP, et al. Identification of the noncollagenous proteins of bovine bone by two-dimensional gel electrophoresis. Calcif Tissue Int 1984;36: 308. 13. Delmas PD. Biochemical markers of bone turnover for the clinical assess¬ ment of metabolic bone disease. Endocrinol Metab Clin North Am 1990; 19:1. 14. Raisz LG, Kream BE. Medical progress: regulation of bone formation. N Engl J Med 1983;309:29. 15. Allan EH, Zeheb R, Gelehrter TD, et al. Transforming growth factorbeta inhibits plasminogen activator (PA) activity and stimulates production of urokinase-type PA, PA inhibitor-1 messenger RNA, and protein in rat osteoblast¬ like cells. J Cell Physiol 1991; 149:34. 16. Suda T, Takahashi N, Martin TJ. Modulation of osteoclast differentiation. Endocr Rev 1992; 13:66. 17. Zaidi M, Alam ASMT, Shankar VS, et al. Cellular biology of bone resorp¬ tion. Biol Rev Cambridge Philosophic Soc 1993; 68:197. 18. Chatterjee D, Chakraborty M, Leit M, et al. The osteoclast proton pump differs in its pharmacology and catalytic subunits from other vacuolar H+-ATPase in neuronal and endocrine systems. J Exp Biol 1993; 172:193. 19. Helfrich MH, Nesbitt SA, Dorey EL, Horton MA. Rat osteoclasts adhere to a wide range of RGD (Arg-Gly-Asp) peptide-containing proteins, including the bone sialoproteins and fibronectin, via a B3 integrin. J Bone Miner Res 1992; 7:335. 20. Kream BE, Lafrancis D, Petersen DN, et al. Parathyroid hormone re¬ presses al(l) collagen promoter activity in cultured calvariae from neonatal transgenic mice. Mol Endocrinol 1993;7:399. 21. Bringhurst FR, Juppner H, Guo J, et al. Cloned, stably expressed parathy¬ roid hormone (PTH)/PTH-related peptide receptors activate multiple messenger signals and biological responses in LLC-PK1 kidney cells. Endocrinology 1993; 1322090. 22. Klein-Nulend J, Pilbeam CC, Harrison JR, et al. Mechanism of regulation of prostaglandin production by parathyroid hormone, interleukin-1, and cortisol in cultured mouse parietal bones. Endocrinology 1991; 128:2503. 23. Dempster DW, Cosman F, Parisien M, et al. Anabolic actions of parathy¬ roid hormone on bone. Endocr Rev 1993; 14:690. 24. Holtrop ME, King GJ, Cox KA, Reit B. Time-related changes in the ultra¬ structure of osteoclasts after injection of parathyroid hormone in young rats Calcif Tissue Int 1979;27:129.

Ch. 50: Parathyroid Hormone 25. Lorenzo JA, Raisz LG, Hock JM. DNA synthesis is not necessary for os¬ teoclastic responses to parathyroid hormone in cultured fetal rat long bones. J Clin Invest 1983; 72:1924. 26. Lorenzo JA, Raisz LG. Divalent cation ionophores stimulate resorption and inhibit DNA synthesis in cultured fetal rat bone. Science 1981:212:1157. 27. Schipani E, Karga H, Karaplis AC, et al. Identical complementary deoxy¬ ribonucleic acids encode a human renal and bone parathyroid hormone (PTH)/ PTH-related peptide receptor. Endocrinology 1993; 132:2157. 28. Harrison JR, Petersen DN, Lichtler AC, et al. 1,25-Dihydroxyvitamin D3 inhibits transcription of type I collagen genes in the rat osteosarcoma cell line ROS 17/2.8. Endocrinology 1989; 125:327. 29. Suda T, Takahashi N, Abe E. Role of vitamin-D in bone resorption. J Cell Biochem 1992; 49:53. 30 Stern PH, Hamstra AJ, DeLuca HF, Bell NH. Bioassay capable of measur¬ ing 1 picogram of 1,25-dihydroxyvitamin D3. J Clin Endocrinol Metab 1978;46:891. 31. Brommage R, DeLuca HF. Evidence that 1,25-dihydroxyvitamin D3 is the physiologically active metabolite of vitamin D3. Endocr Rev 1985; 6:491. 32. Manolagas SC, Provvedini DM, Tsoukas CD. Interactions of 1,25dihydroxyvitamin D3 and the immune system. Mol Cell Endocrinol 1985;43:113. 33. Lin HY, Harris TL, Flannery MS, et al. Expression cloning of an adenylate cyclase coupled calcitonin receptor. Science 1991;254:1022. 34. Wallach S, Farley JR, Baylink DJ, Brennergati L. Effects of calcitonin on bone quality and osteoblastic function. Calcif Tissue Int 1993;52:335. 35. Civitelli R, Gonnelli S, Zacchei F, et al. Bone turnover in postmenopausal osteoporosis: effect of calcitonin treatment. J Clin Invest 1988;82:1268. 36. Lukert B, Mador A, Raisz LG, Kream BE. The role of DNA synthesis in the responses of fetal rat calvariae to cortisol. J Bone Miner Res 1991; 6:453. 37. Shalhoub V, Conlon D, Tassinari M, et al. Glucocorticoids promote de¬ velopment of the osteoblast phenotype by selectively modulating expression of cell growth and differentiation of associated genes. J Cell Biochem 1993;50:425. 38. Lukert BP, Raisz LG. Glucocorticoid-induced osteoporosis: pathogenesis and management. Ann Intern Med 1990; 112:352. 39. McCarthy TL, Centrella M, Canalis E. Parathyroid hormone enhances the transcript and polypeptide levels of insulin-like growth factor I in osteoblastenriched cultures from fetal rat bone. Endocrinology 1989; 124:1247. 40. Hock JM, Centrella M, Canalis E. Insulin-like growth factor I has inde¬ pendent effects on bone matrix formation and cell replication. Endocrinology 1988;122:254. 41. Corpas E, Harman SM, Blackman MR. Human growth hormone and hu¬ man aging. Endocr Rev 1993; 14:20. 42. Okazaki R, Riggs BL, Conover CA. Glucocorticoid regulation of insulin¬ like growth factor-binding protein expression in normal human osteoblast-like cells. Endocrinology 1994,134:126. 43. Kream BE, Smith MD, Canalis E, Raisz LG. Characterization of the effect of insulin on collagen synthesis in fetal rat bone. Endocrinology 1985; 116:296. 44. Kawaguchi H, Yavari R, Stover ML, et al. Measurement of interleukin-1 stimulated constitutive prostaglandin G/H synthase (cyclooxygenase) mRNA lev¬ els in osteoblastic MC3T3-E1 cells using competitive reverse transcriptase polymer¬ ase chain reaction. Endocrine Res 1994; 20:219. 45. Kawaguchi H, Pilbeam CC, Voznesensky OS, et al. Regulation of the two prostaglandin G/H synthases by parathyroid hormone, interleukin-1, cortisol and prostaglandin E2 in cultured neonatal mouse calvariae. Endocrinology 1994; 135: 1157. 46. Rosen CJ, Adler RA. Longitudinal changes in lumbar bone density among thyrotoxic patients after attainment of euthyroidism. J Clin Endocrinol Metab 1993;75:1531. 47. Kornm BS, Terpening CM, Benz DJ, et al. Estrogen binding, receptor mRNA and biologic response in osteoblast-like osteosarcoma cells. Science 1988;241:81. 48. Colvard DS, Eriksen EF, Keeting PE, et al. Identification of androgen re¬ ceptors in normal human osteoblast-like cells. Proc Natl Acad Sci USA 1989; 86: 854. 49. Horowitz MC. Cytokines and estrogen in bone: anti-osteoporotic effects. Science 1993; 260:626. 50. Feyen JHM, Raisz LG. Prostaglandin production by calvariae from shamoperated and oophorectomized rats: effect of 17/3-estradiol in vivo. Endocrinology 1987;121:819. 51. Pilbeam CC, Klein-Nulend J, Raisz LG. Inhibition by 17/3-estradiol of PTH stimulated resorption and prostaglandin production in cultured neonatal mouse calvariae. Biochem Biophys Res Commun 1989; 163:1319. 52. Pilbeam CC, Raisz LG. Effects of androgens on parathyroid hormone and interleukin-1 stimulated prostaglandin production in neonatal mouse calvariae. J Bone Miner Res 1990;5:1183. 53. Ernst M, Rodan GA. Estradiol regulation of insulin-like growth factor-1 expression in osteoblastic cells: evidence for transcription control. Mol Endocrinol 1991;5:1081. 54. Raisz LG. Local and systemic factors in the pathogenesis of osteoporosis. N Engl J Med 1988:318:818. 55. Raisz LG, Martin TJ. Prostaglandins in bone and mineral metabolism. In: Peck WA, ed. Bone and mineral research, annual 2, vol 2. Amsterdam: Elsevier, 1983:286. 56. Raisz LG, Fall PM, Gabbitas BY, et al. Effects of prostaglandin E2 on bone formation in cultured fetal rat calvariae: role of insulin-like growth factor-I. Endo¬ crinology 1993; 133:1504. 57. Pilbeam CC, Kawaguchi H, Hakeda Y, et al. Differential regulation of inducible and constitutive prostaglandin endoperoxide synthase in osteoblastic MC3T3-E1 cells. J Biol Chem 1993;268:25643.

455

58. Tashjian AH, Voelkel EF, Lazzaro M, et al. a And d human transforming growth factors stimulate prostaglandin production and bone resorption in cultured mouse calvaria. Proc Natl Acad Sci USA 1985:82:4535. 59. Norrdin RW, Jee WSS, High WB. The role of prostaglandins in bone in vivo. Prostaglandins Leukotrienes Essent Fatty Acids 1990; 41:139. 60. Lanyon LE. Control of bone architecture by functional load bearing. J Bone Miner Res 1993;7:S369. 61. Boyce BF, Aufdemorte TB, Garrett IR, et al. Effects of interleukin-1 on bone turnover in normal mice. Endocrinology 1989; 125:1142. 62. Thompson DD, Rodan GA. Indomethacin inhibition of tenotomyinduced bone resorption in rats. J Bone Miner Res 1988; 3:409. 63. Centrella M, McCarthy TL, Canalis E. Transforming growth factor-beta and remodeling of bone. J Bone Joint Surg 1991;73A:1418. 64. Wozney JM. The bone morphogenetic protein family and osteogenesis. Mol Reprod Dev 1992;32:160. 65. Canalis E, Varghese S, McCarthy TL, Centrella M. Minireview: role of platelet derived growth factor in bone cell function. Growth Regul 1993; 2:151. 66. Hurley MM, Abreu C, Harrison JR, et al. Basic fibroblast growth factor inhibits type-1 collagen gene expression in osteoblastic MC3T3-E1 cells. J Biol Chem 1993;268:5588. 67. Lorenzo JA. The role of cytokines in the regulation of local bone resorp¬ tion. Crit Rev Immunol 1992; 11:195. 68. Marusic A, Raisz LG. Cortisol modulates the actions of interleukin-la on bone formation, resorption and prostaglandin production in cultured mouse pari¬ etal bone. Endocrinology 1991,129:2699. 69. Lewis DB, Liggitt HD, Effmann EL, et al. Osteoporosis induced in mice by overproduction of interleukin 4. Proc Natl Acad Sci USA 1993;90:11618. 70. Lorenzo JA, Holtrop ME, Raisz LG. Effects of phosphate on calcium re¬ lease, lysosomal enzyme activity in the medium, and osteoclast morphometry in cultured fetal rat bone. Metab Bone Dis Relat Res 1984;5:187. 71. Quarles LD, Wenstrup RJ, Castillo SA, Drezner MK. Aluminum-induced mitogenesis in MC3T3-E1 osteoblasts: potential mechanism underlying neoos¬ teogenesis. Endocrinology 1991; 128:3144.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. j.B. Lippincott Company, Philadelphia, © 1995

CHAPTER

50

PARATHYROID HORMONE DAVID GOLTZMAN AND GEOFFREY N. HENDY

Parathyroid hormone (PTH) is essential for the physiologic maintenance of calcium homeostasis, and a marked excess or de¬ ficiency can cause severe and potentially fatal illness. Because of its essential role in metabolism, skeletal function, and renal function, considerable effort has been expended and substantial advances have been made in understanding the biosynthesis, molecular biology, secretion, metabolism, and action of this hor¬ mone. Improved quantitation methods have enhanced our ap¬ preciation of its complex physiology and pathophysiology. The molecular biology approach has contributed valuable informa¬ tion about the structure and synthesis of this molecule and has led to the identification and characterization of a parathyroid hormone-like molecule, parathyroid hormone-related protein (PTHrP); a receptor that mediates the actions of PTH and PTHrP, the PTH/PTHrP receptor; and a parathyroid calcium-sensing receptor. This chapter examines the production, metabolism, func¬ tion, and measurement of PTH as a foundation for understand¬ ing the cause, pathogenesis, and diagnosis of disorders of the parathyroid glands.

BIOSYNTHESIS OF PARATHYROID HORMONE PTH follows a pattern of biosynthesis and of vectorial transport through organelles of the cell that now is well estab-

456

PART IV: CALCIUM AND BONE METABOLISM

lished for many peptide hormones (Fig. 50-1)1,2 The major glan¬ dular form of the hormone, an 84-amino acid, straight-chain peptide, PTH 1-84, is biosynthesized on the polyribosomes of the rough endoplasmic reticulum of the parathyroid gland. The gene for PTH encodes a large precursor, preproPTH, that is ex¬ tended at the amino-terminus of PTH 1—84 by 31 residues. The NH2-terminal 25-residue portion, characterized by its hydrophobicity, is called the signal, leader, or pre sequence, and it facilitates entry of the nascent hormone into the cisternae of the endoplas¬ mic reticulum. As the signal sequence of the synthesized hormone emerges from the ribosome, it binds to a signal recognition particle that stops further synthesis of the nascent protein. The signal recog¬ nition particle carrying the ribosome then binds to an integral membrane protein of the endoplasmic reticulum, called the dock¬ ing protein or signal recognition particle receptor.3 This protein re¬ leases the block in protein synthesis, and the nascent peptide is transported across the membrane into the cisternae of the endo¬ plasmic reticulum. The signal sequence is simultaneously re¬ moved at the inner surface of the endoplasmic reticulum, enzy¬ matically at a glycyl-lysyl bond. The resultant precursor molecule, proPTH, is extended at the NH2-terminus of PTH 184 by only six amino acids. The pro sequence is necessary for efficient translocation and cleavage of the signal peptide. Once formed, proPTH is transported to the Golgi apparatus. The prohormone hexapeptide has several basic resi 's that serve as a recognition sequence to yield the mature lone. Unlike many other prohormones, proPTH does not o i an¬ other sequence at the COOH-terminus and has not ber cted

within the circulation in states of parathyroid gland hyperfunc¬ tion. ProPTH has little intrinsic biologic activity until cleaved to create the hormonal form.1,4 The translocation of proPTH from the rough endoplasmic reticulum to the Golgi apparatus is an energy-requiring process.2 The conversion of proPTH to PTH appears to occur within the Golgi apparatus through the action of an endopeptidase with trypsin-like specificity.1,4 The enzyme involved is likely to be furin, one of the mammalian proprotein convertases that are re¬ lated to bacterial subtilisins.5 Little proPTH is stored within the gland. The resultant mature 84-amino acid form of the hormone is packaged in secretory granules and transported to the region of the plasma membrane. This appears to occur by a process involv¬ ing vesicular budding and fusion that is driven by lowmolecular-weight guanine nucleotide-binding proteins. The hormone is released by exocytosis in response to the principal stimulus to secretion, hypocalcemia. The calcium ion has not been shown to influence the enzymatic cleavages involved in the pro¬ cessing of preproPTH or proPTH. Little information is available concerning the posttranslational modification of the amino acid sequence of the hormone. Glycosylation does not appear to occur. Phosphorylation of proPTH and PTH occurs in vitro, where 10% to 20% of the hormone is phosphorylated at serine residues within the NH2terminal region of the molecule.6-8 However, the influence of this process on intraglandular processing of the molecule or on bio¬ activity remains undefined.

MOLECULAR BIOLOGY OF PARATHYROID HORMONE CHARACTERISTICS OF THE NORMAL PARATHYROID HORMONE GENE

FIGURE 50-1. Diagram of the biosynthesis of precursor and secretory forms of parathyroid hormone (PTH). Within the nucleus, transcription of the gene encoding PTH is followed by processing of the pre-mRNA through removal of intervening sequences. The mature mRNA leaves the nucleus and attaches to polyribosomes in the cytoplasm. The signal or pre- sequence of the hormone then binds to a signal recognition particle that interacts with a docking protein on the membrane of the endoplas¬ mic reticulum, facilitating entry of the nascent peptide into the cisternae. The signal sequence is removed, leaving the precursor proPTH. The NH2terminal hexapeptide of this molecule is then removed in the Golgi appa¬ ratus, and the mature hormone, PTH 1-84, is packaged into secretory granules.

The structural characterization of messenger RNAs (mRNAs) and genes encoding preproPTH from several mamma¬ lian species (i.e., human, bovine, porcine, rat, and mouse) and one avian species (i.e., chicken) has been accomplished using the techniques of molecular biology.7-11 In mammals, mature PTH has 84 amino acids, but the chicken form has 88 amino acids. The preproPTH gene is organized into three exons: exon I encoding the 5' untranslated region, exon II encoding the prepropeptide coding region and part of the prohormone cleavage site recogni¬ tion sequence, and exon III encoding the Lys-2-Arg-1 of the pro¬ hormone cleavage site, the 84 amino acids of the mature hor¬ mone, and the 3' untranslated region. Some of these organizational features are shared with the PTHrP gene, in which the same functional domains—the 5' un¬ translated region, prepro region of the precursor peptide, and the prohormone cleavage site and most or all of the mature pep¬ tide—are encoded by single exons12-15 (Fig. 50-2; see Chap. 51). For PTHrP, exons encoding alternative 5' untranslated regions, carboxyl-terminal peptides, and 3' untranslated regions may also exist, depending on the species. The PTH and PTHrP genes are both single-copy genes and have been mapped to the short arms of chromosomes 11 and 12, respectively.13-13 These two human chromosomes are thought to have been derived by an ancient duplication of a single chromo¬ some, and the PTH and PTHrP genes and their respective gene clusters have been maintained as syntenic groups in the human, rat, and mouse genomes.17 Overall, because of the similarity in NH2-terminal sequence of their mature peptides, their gene or¬ ganization, and chromosomal location, it is highly probable that the PTH and PTHrP genes evolved from a single ancestral gene and form part of a single gene family. Two common restriction fragment-length polymorphisms for the restriction enzymes Psfl and Taql have been detected at the human PTH gene locus, and a variable number of tandem

Ch. 50: Parathyroid Hormone

I hPTH

5’ nc

II

457

PTH gene regulatory region that normally silences gene tran¬ scription in nonparathyroid cells was replaced by a foreign se¬ quence that allowed inappropriate transcription to take place.26 Overall, molecular biology techniques have provided much useful information about the structures of PTH and PTHrP genes and their mRNAs and about the control of their expression. Re¬ combinant DNA techniques are being used to prepare PTH mol¬ ecules and analogues for structure-function analysis.27

III

prepro ■ lys-arg PTH

la 5’ nc 1

lb 5’ nc 1

hPTHRP

II 5’ nc 2

IV prepro 8 lys-ar

HORMONE SECRETION

33 3’nc 1

GENERAL FEATURES OF HORMONAL SECRETION

VI CTP1 3’nc 2

VII CTP2 3’nc 3 FIGURE 50-2. Comparison of the structural organization of the human parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) genes. Nc is the noncoding region, and CTP is the carboxylterminal peptide. Roman numerals denote exons.

repeat polymorphisms that occur with high frequency in the gen¬ eral population have been described within the human PTHrP gene.18 These DNA markers are useful for testing for linkage of inherited disease genes to these loci in family studies.

ALTERATIONS IN THE PARATHYROID HORMONE GENE STRUCTURE The tissue used for protein sequencing of human PTH and cDNA cloning was derived from tumors of the parathyroid gland.7,19 However, the sequence of human PTH deduced by analysis of cDNA clones was confirmed by analysis of cloned genomic DNA derived from normal tissue. The human PTH pro¬ duced by patients with hyperparathyroidism is structurally nor¬ mal. In a small number of parathyroid tumors examined, the PTH gene sequence is rearranged, and the 5' flanking region of the PTH gene is placed upstream of the cyclin D gene located on the long arm of chromosome 11.20 This is thought to lead to deregu¬ lated expression of the cyclin gene that contributes to tumor de¬ velopment. However, this type of gene rearrangement occurs in¬ frequently in parathyroid tumors. A more common event involves the loss of the multiple endocrine neoplasia type 1 locus, also on the long arm of chromosome 11, which probably encodes a tumor suppressor gene.21,22 Mutations have been identified in the PTH gene in some cases of familial isolated hypoparathyroidism. One patient with autosomal dominant hypoparathyroidism had a mutation within the protein coding region of the PTH gene in which there was a single base substitution (T > C) in exon II, resulting in the substi¬ tution of arginine (CGT) for cysteine (TGT) in the signal pep¬ tide.23 This places a charged amino acid in the hydrophobic core of the signal peptide, leading to inefficient processing of the mu¬ tant preproPTH to PTH. In a family with autosomal recessive isolated hypoparathyroidism, a donor splice mutation was iden¬ tified in the PTH gene of affected individuals at the exon IIintron II boundary that resulted in the loss of exon II, which en¬ codes the initiation codon and signal peptide.24 A search for evidence of ectopic PTH synthesis (i.e., synthe¬ sis outside of parathyroid tissue) indicates that it occurs only rarely in malignancies associated with hypercalcemia.25 How¬ ever, with the advent of highly specific PTH immunoassays and mRNA analysis, a few cases of true ectopic PTH production have been documented. In one case of an ovarian carcinoma, the 5'

Relatively little PTH is stored in secretory granules within the parathyroid glands. In the absence of a stimulus for release, intraglandular metabolism occurs, causing complete degradation of the hormone to its constituent amino acids or partial degrada¬ tion to fragments through a calcium-regulated enzymatic mech¬ anism.28 In cases of hypercalcemia, the predominant hormonal entities released from parathyroid glands appear to be fragments composed of midregion or COOH-terminal sequences, or both, containing little or no bioactivity.29,30 In cases of hypocalcemia, degradation of PTH within the parathyroid cell is minimized, and the major hormonal entity released appears similar to or identical with the bioactive PTH 1-84 molecule.31 Consequently, in the presence of hypocalcemia, increased amounts of bioactive PTH are secreted, even in the absence of additional synthesis of hor¬ mone. With a brief hypocalcemic stimulus, a biphasic secretory response often occurs. Hormone, presumably newly synthesized and derived from "immature” Golgi vesicles, is initially released in a large burst over a few minutes.2 This is followed by a lower response sustained for a longer period, presumably representing hormone stored in secretory granules. However, hormone stores are insufficient to maintain secretion for more than a few hours in the presence of a sustained severe hypocalcemic stimulus; ad¬ ditional PTH secretion depends on an increase in the number of parathyroid cells. Such an increase appears to be modulated by the reductions in circulating 1,25-dihydroxyvitamin D that often accompany hypocalcemia. A second protein, identical to chromogranin A from the adre¬ nal medulla, is cosecreted with PTH in most conditions leading to the release of PTH.32'33 This 50-kilodalton (kd) protein is synthe¬ sized within the parathyroid gland and stored with PTH within se¬ cretory granules. This molecule, which can be glycosylated and phosphorylated, is the major member of the chromograninsecretogranin (granin) family of proteins that occur in virtually all neuroendocrine cells.34,35 They play several roles in the process of regulated secretion, including targeting peptide hormones and neu¬ rotransmitters to secretory granules of the regulated secretory path¬ way. Chromogranin A also functions as a precursor of biologically active peptides that modulate neuroendocrine cell secretion in an autocrine or paracrine fashion (see Chap. 171).

MODULATORS OF PARATHYROID GLAND SECRETION The calcium ion is the main regulator of parathyroid gland activity, although several other agents influence the release of PTH from parathyroid glands. These include various ions, agents altering the activity of the parathyroid cell adenylate cyclase sys¬ tem (e.g., d-adrenergic catecholamines, histamine), peptides de¬ rived from chromogranin A, and vitamin D metabolites. A circadian rhythm has been reported for PTH secretion, with increased blood levels occurring at night.35 These studies may suggest neural or central nervous system influences on PTH secretion, or they could reflect circadian alterations in the levels of extracellular fluid calcium. Although intriguing, interpretation is difficult because of the heterogeneity of circulating PTH. Ra¬ dioimmunoassay (RIA) measurements may assess predomi¬ nantly bioinactive PTH fragments and could reflect diurnal alter¬ ations in metabolism rather than effects on secretion.

458

PART IV: CALCIUM AND BONE METABOLISM

IONS

Cations. The most potent of the cations modulating PTH release and the secretagogue that is most important in altering PTH release under physiologic and pathophysiologic circum¬ stances is the calcium ion (Fig. 50-3). Although there is an inverse relationship between ambient calcium levels and PTH release, this is a curvilinear, rather than proportional, relationship.3/ From in vivo studies of cattle, maximal rates of PTH secretion of about 16 ng/kg/minute appear to be rapidly achieved at calcium levels below 7.5 to 8.0 mg/dL (1.88-2.00 mM). When calcium levels are reduced from 10.0 to 9.5 mg/dL (2.50-2.38 mM), a small and gradual increase in PTH secretion occurs that does ex¬ hibit a proportional relationship to the ambient calcium. Halfmaximal secretion rates normally occur at calcium levels of about 8.5 mg/dL (2.12 mM), which is the set-point for PTH secretion. Basal secretion rates result after ambient calcium levels have risen above 11 mg/dL (2.75 mM) and appear to persist despite further increases in calcium concentration, even up to 16 to 18 mg/dL (4.00-4.50 mM). Similar results have been observed in studies with human parathyroid tissue in vitro. The nonsuppressible (more correctly, non-calcium suppressible) component of PTH secretion appears to comprise mainly bioinactive midre¬ gion and COOH-terminal fragments. However, direct determi¬ nation of the activity of hormonal material released when calcium levels are markedly elevated also demonstrates some bioactivity. This inverse relationship between PTH and extracellular calcium contrasts with the influence of the calcium ion as a secre¬ tagogue in most other secretory systems in which elevations in this ion enhance release of the secretory product. This distinction between the parathyroid cell and other secretory cells may be maintained intracellularly, where elevations rather than de-

Sites known to be influenced by calcium (*) include reversible reduction of preproPTH mRNA levels by elevated extracellular fluid calcium levels acting on preproPTH gene transcription, increase in the production and release of COOH-terminal fragments by elevated calcium levels, and in¬ crease in secretion of the mature form of PTH by reduction in extracellu¬ lar fluid calcium concentration. Whether calcium acts to alter the splicing of the pre-mRNA or the turnover of mature mRNA is unclear (?).

creases in cytosol calcium have been reported to correlate with decreased PTH release.38 Alterations in extracellular fluid calcium levels may be transmitted through a parathyroid plasma membrane calcium sensing receptor that couples through a Gprotein complex to phospholipase C. Increases in extracellular calcium lead to increases in inositol 1,4,5-trisphosphate (IP3) and mobilization of intracellular calcium stores. The manner in which this inhibits hormone secretion is not understood. Although it would be anticipated that increases in diacylglycerol would ac¬ company IP3 increases due to hydrolysis of phosphoinositides, activate protein kinase C, and result in reduced PTH secretion, this does not appear to occur in the parathyroid cell.39 Paradoxi¬ cally, agents that do stimulate protein kinase C, such as phorbol esters, stimulate rather than inhibit hormone secretion. The pre¬ cise steps in the pathway from changes in extracellular calcium levels to hormone release remain to be elucidated. A bovine parathyroid cell Ca2+-sensing receptor cDNA was identified by expression cloning in Xenopus laevis oocytes.40 The mRNA encodes a polypeptide of 1085 amino acids that is pre¬ dicted to contain a very large extracellular domain of 605 amino acids and a seven-unit membrane-spanning region characteristic of G-protein-coupled cell-surface receptors. Compared with the other known G-protein-coupled receptor family members, the Ca2+-sensing receptor shows some homology with the metabo¬ tropic glutamate receptors, sharing conserved cysteine residues and a hydrophobic sequence in the NH2-terminal region. The Ca2+-sensing receptor has a low affinity for Ca2+, and consistent with this, the receptor sequence does not contain any of the Ca2+ binding motifs found in high-affinity calcium-binding proteins. Highly acidic regions in the extracellular NH2-terminal domain and the second extracellular loop may bind calcium as they do in other known low-affinity Ca2+ binding proteins. Besides the parathyroid, the Ca2+-sensing receptor is also expressed in other cells having Ca2+-sensing functions, such as kidney cortex and outer medulla, thyroid, and some regions of the brain. Neomycin binds the receptor, which may account for the toxic renal effects of aminoglycoside antibiotics. The human Ca2+-sensing receptor gene has also been char¬ acterized and shown to consist of seven exons spanning more than 20 kb of genomic DNA.41 The long extracellular domain is encoded by the first two to six exons, and the remainder of the molecule is encoded by exon seven. Nonconservative missense mutations in the Ca2+-sensing receptor gene may result in the syndrome of familial hypocalciuric hypercalcemia when one al¬ lele is altered and in neonatal severe hyperparathyroidism when both copies of the gene are defective.4142 In vitro reductions in extracellular fluid calcium do not ap¬ pear capable of enhancing specific PTH biosynthesis, which seems to occur at a maximal or near-maximal rate per cell; how¬ ever, inconsistent results have been obtained in vivo. In vitro and in vivo studies employing hybridization assays for preproPTH mRNA have reported that elevated calcium levels reversibly and specifically reduce PTH mRNA.43 This occurs, at least in part, by a direct effect on transcription of the preproPTH gene. Although in vitro studies are conflicting, prolonged hypocalcemia in vivo may stimulate DNA replication, cell division, and the production of increased numbers of parathyroid cells or parathyroid hyper¬ plasia. This would increase the synthesis of proteins, including PTH, within the hypercellular parathyroid gland and ultimately would increase PTH release. In primary parathyroid gland hy¬ perfunction resulting in hyperparathyroidism, alterations in the calcium sensing mechanism may manifest as a set-point error, producing a shift to the right of the curve relating PTH secretion to extracellular calcium levels.44 Consequently, elevated concen¬ trations of extracellular fluid calcium may be required to reduce PTH secretion, resulting in an adenomatous or hyperplastic para¬ thyroid gland that is incompletely suppressed by calcium. Such a mechanism may underlie the observation that an increase in the mass of parathyroid tissue, such as that produced by transplan¬ tation, can be associated with hypercalcemia. If basal secretion

Ch. 50: Parathyroid Hormone per cell produces a significant amount of bioactive PTH, the cu¬ mulative increase in this basal or non-calcium-suppressible se¬ cretion arising from an increase in parathyroid cells also could be responsible for the hypercalcemia. The precise mechanistic rela¬ tionship of extracellular calcium to parathyroid cell growth re¬ mains to be determined. In in vitro studies, magnesium appears to parallel the effects of calcium on PTH release, although with reduced efficacy.45'46 This is consistent with the known affinity of the parathyroid calcium-sensing receptor for magnesium that is lower than that for calcium itself. Mild hypomagnesemia or hypermagnesemia stimulates or suppresses, respectively, PTH secretion.47 A special situation exists in clinical disorders associated with severe hypo¬ magnesemia in which PTH secretion is impaired47 (see Chap. 67). With the discovery of the syndrome of aluminum toxicity in ure¬ mia, characterized by osteomalacia, low circulating PTH levels, and a tendency toward hypercalcemia during treatment with vi¬ tamin D, the effects of aluminum on PTH secretion were assessed in vitro. Such studies, performed with rather high ambient alu¬ minum concentrations, have shown suppression of PTH release by this cation.48 A direct effect of aluminum to inhibit PTH secre¬ tion in vivo therefore could contribute to the low circulating PTH levels seen in the presence of aluminum intoxication. It is un¬ likely that aluminum plays any physiologic role in the normal regulation of PTH secretion (see Chaps. 7 and 60). Anions. The phosphate ion is of most interest clinically as a potential modulator of PTH release. Hyperphosphatemia in¬ duced by intravenous or oral administration of phosphate is as¬ sociated with increased circulating levels of PTH. However, the effects almost certainly are indirect and a result of the hypo¬ calcemia that accompanies the rise in serum phosphate.49 Phos¬ phate does not appear to modulate PTH secretion directly. The physiologic role of other anions, such as chloride, that have been associated with alterations of PTH levels in vitro remains unclear. MODULATORS OF ADENYLATE CYCLASE ACTIVITY IN THE PARATHYROID CELL

A group of adenylate cyclase-stimulating agonists, such as catecholamines, prostaglandins of the E series, calcitonin, gut hormones of the secretin family, and histamine influence PTH release in vitro.50-52 /?-Adrenergic agonists (e.g., epinephrine, iso¬ proterenol) also enhance PTH release in animals, and some de¬ creases in circulating PTH levels in humans have been reported with /3-blockers. Despite the ability of the ^-adrenergic catechol¬ amines and histamine to induce PTH secretion, it is uncertain what physiologic or pathophysiologic role these biogenic amines may have in humans.52,53 Agents that may lower cAMP levels within the parathyroid gland, such as a2-adrenergic agonists, prostaglandin F2, and so¬ matostatin, have been associated with decreased PTH secretion. CHROMOGRANIN A-DERIVED PEPTIDES

Peptides derived from chromogranin A (CgA), such as /3granin (i.e., CgA 1-113), synthetic bCgA 1-40, pancreastatin (i.e., porcine CgA 240-288), and parastatin (i.e., porcine CgA 347-419), have been reported to inhibit low-calcium-stimulated PTH release from parathyroid cells in culture.54 55 The physio¬ logic significance of these observations remains unclear. Within the parathyroid gland, processing of CgA to peptides occurs to a lesser extent than in some other endocrine tissues, such as the B cells of the pancreas, and the parathyroid cells could respond in a paracrine or endocrine fashion to CgA-derived peptides gener¬ ated elsewhere. STEROLS AND STEROIDS

Various studies have demonstrated a role for vitamin D me¬ tabolites in the modulation of PTH release. A feedback loop be¬ tween PTH-induced increase of vitamin D metabolite levels and

459

vitamin D metabolite-induced decrease of PTH levels has been postulated. With the demonstration that a high-affinity 1,25dihydroxy vitamin D receptor exists in parathyroid cells and with the localization of injected l,25-[3H]-dihydroxyvitamin D within the parathyroid cell, interest in this metabolite as a potential reg¬ ulator of PTH synthesis or secretion has arisen. Efforts that fo¬ cused on the role of 1,25-dihydroxyvitamin D in the biosynthesis of PTH provided evidence, in vitro and in vivo, that the sterol reversibly reduces levels of mRNA responsible for PTH synthe¬ sis.56,57 This is effected by the action of the sterol on preproPTH gene transcription. A vitamin D response element has been identified in the hu¬ man PTH gene promoter, although the binding of the vitamin D receptor to this element is weak, and the mechanism of the down-regulation of PTH gene transcription by 1,25-dihydroxyvitamin D must be elucidated.58 Although 1,25-dihydroxyvitamin D is of uncertain importance in influencing immediate hor¬ mone release, it plays a role in modulating hormone synthesis within the gland, altering the quantities of hormone available for immediate release by secretagogues. Moreover, an early in vivo effect of reduction in 1,25-dihydroxyvitamin D appears to be an increase in maximal releasable PTH due to stimulation of glandular proliferation.57 In vitro studies show that this effect of the sterol on cell proliferation is mediated by its action on early immediate response gene expression such as the MYC protooncogene.58 The role of other metabolites of vitamin D in modulating PTH biosynthesis or secretion remains unclear. However, "nonhypercalcemic" analogues of 1,25-dihydroxyvitamin D have been developed that do diminish PTH secretion in vitro and in vivo and that may serve in the future as therapeutics for hyperparathyroidism. Cortisol elevates extracellular levels of PTH in vivo and in vitro.59 It is unclear, however, whether this effect is a direct effect on synthesis, on alteration of hormonal release, or on an alter¬ ation of the levels of enzymes metabolizing PTH within the para¬ thyroid cell.60 Although these findings could help explain the mild secondary hyperparathyroidism reported with glucocorti¬ coid therapy, their overall significance remains unknown.

PERIPHERAL METABOLISM Besides metabolism within the parathyroid cell, PTH 1-84 undergoes extensive peripheral metabolism after release into the general circulation (Fig. 50-4). Although PTH 1-84 can be cleared from the circulation by the kidney and hormonal frag¬ ments may be generated in the kidney, such fragments probably do not reenter the circulation. Studies employing sequencespecific radioimmunoassays coupled with gel filtration of serum or plasma have shown that the major circulating forms of PTH are the midregion and COOH-terminal fragments.61 6' Such fragments may be released from the parathyroid gland in the presence of hypercalcemia. A major site of origin appears to be the liver. Studies em¬ ploying 125I-labeled PTH 1—84 injected intravenously into ani¬ mals have demonstrated that initial cleavage occurs between res¬ idues 33 and 34 and at sites COOH-terminal to this. These and other studies have indicated that the hepatic Kupffer cell is the most likely site of peripheral hormonal cleavage.6' The midre¬ gion and COOH-terminal fragments thus generated can enter the general circulation and subsequently be metabolized in the kidney. In view of structure-function studies that have localized the bioactivity of PTH 1-84 to the NH2-terminal third of the mole¬ cule, such midregion and COOH-terminal fragments should be biologically inert. Because of their long half-life in the circulation relative to intact PTH 1-84, such inert moieties generally com¬ prise most circulating PTH-related entities.68 Conversely, the cor¬ responding NH,-terminal fragments generated during hepatic

460

PART IV: CALCIUM AND BONE METABOLISM

NRF

CRF

FIGURE 50-4.

Model of parathyroid hormone (PTH) metabolism in the presence of normal renal function (NRF) and chronic renal failure (CRF). In the presence of NRF, PTH 1-84 released from the parathyroid gland is cleared by the kidney or metabolized in the liver, where amino (N; NH2) and carboxyl (C; COOH) fragments are generated. Carboxyl, but generally not NH2, fragments, are released into the circulation; these COOH fragments enter a pool, which also includes a contribution from the parathyroid gland, and are cleared by the kidney. In chronic renal failure, PTH secretion can be increased by a tendency toward hypocal¬ cemia, and fewer COOH fragments are released from the parathyroid glands. Failure of the nonfunctioning kidneys to clear PTH results in he¬ patic metabolism of this moiety, with increased production of NH2- and COOH fragments. Under these conditions, COOH-terminal fragments reach high circulating concentrations because of increased production and reduced renal clearance.

cleavage of PTH 1-84 would be expected to be bioactive, but such fragments seem to be completely degraded in the liver and do not reenter the circulation. The major circulating bioactive moiety is similar to or identical with the intact molecule PTH 184. Clearance of midregion and COOH-terminal fragments of PTH apparently depends almost solely on renal mechanisms. In cases of renal insufficiency, concentrations of midregion and COOH fragments may increase considerably (see Chaps. 57 and 60). By employing a sensitive renal cytochemical bioassay for PTH in association with gel filtration fractionation of plasma, it has been possible to confirm that the major circulating bioactive moiety in hyperparathyroidism is similar to or identical with PTH 1-84.69 These observations have been confirmed with the devel¬ opment of sensitive immunoradiometric assays that simulta¬ neously recognize NH2 and COOH epitopes on the PTH mole¬ cule and therefore detect only intact PTH 1-84. In secondary hyperparathyroidism associated with severe chronic renal fail¬ ure, additional low-molecular-weight bioactive forms may occa¬ sionally be detected.4 The finding of a half-life of disappearance of intact bioactive PTH in end-stage renal disease that cannot be differentiated from normal kinetics indicates that, with the gradual evolution of renal insufficiency, extrarenal sites of degradation assume increasing importance in the clearance of the hormone.4 This conclusion agrees with the finding that the clearance of NH2-terminal immunoreactivity is not decreased in patients with renal failure.68

ACTIONS OF PARATHYROID HORMONE PARATHYROID HORMONE FUNCTIONS ■The major function of PTH appears to be the maintenance of a normal level of extracellular fluid calcium. The hormone exerts important effects on bone and kidney and indirectly influences the gastrointestinal tract. In response to a fall in the extracellular

fluid ionized calcium concentration, PTH is released from the parathyroid cell and acts directly on the kidney to enhance re¬ nal calcium reabsorption and promote the conversion of 25hydroxyvitamin D to 1,25-dihydroxy vitamin D.70 This latter me¬ tabolite increases gastrointestinal absorption of calcium and, with PTH, induces skeletal resorption, causing the restoration of extracellular fluid calcium and the neutralization of the signal ini¬ tiating PTH release. The opposite series of homeostatic events occur in response to a rise in extracellular fluid calcium levels. Although this scheme outlines the overall events that occur after a fall in calcium, aspects of the response may vary with the extent of the fall in calcium concentration and the consequent rise in PTH. There is some evidence that the actions of PTH on target tissues may depend on its prevailing concentration.71 Con¬ sequently, certain actions of PTH, such as renal calcium retention and even skeletal anabolic actions, may predominate at relatively low circulating concentrations of PTH, but skeletal lysis may be¬ come evident only at higher levels of circulating PTH. Besides regulating calcium homeostasis, PTH elicits various other responses. Whether these other functions evolved inde¬ pendently or to complement the role of the hormone in main¬ taining calcium homeostasis is unclear. Among these other re¬ sponses are perturbations of other ions, the most marked of which are those involving phosphate. As a consequence of PTHenhanced 1,25-dihydroxyvitamin D production, the gastrointes¬ tinal absorption of phosphate is facilitated to some extent, and with PTH-induced skeletal lysis, phosphate and calcium are re¬ leased. These effects increase the extracellular fluid phosphate levels, but the predominant effect of PTH (i.e., inhibition of renal phosphate reabsorption) produces phosphaturia and a net de¬ crease in extracellular fluid phosphate concentration, which may be viewed as adjunctive to the role of PTH in raising calcium levels, although the effect on phosphate homeostasis is itself pro¬ found. The phosphaturic action of PTH is a classic manifestation of renal PTH responsiveness. In common with other peptide hormones, PTH is thought to interact through a receptor on the outer surface of the plasma membrane of target cells. In these target tissues, the result of this interaction of PTH with the membrane receptor has classically been appreciated to be the stimulation of the enzyme adenylate cyclase on the inner surface of the plasma membrane, although the same receptor can couple to phosphatidylinositol turnover as well. The product of this adenylate cyclase activity, cellular cAMP, and the products of phospholipase activity, IP3, diacylglycerol, and intracellular Ca , initiate a cascade of events lead¬ ing to the final cellular response to the hormone. Whether the PTH receptor activates both these intracellular signaling path¬ ways equivalently in all target tissues or acts preferentially by means of one or another pathway in different cells is unknown.

STRUCTURE OF PARATHYROID HORMONE CORRELATED WITH FUNCTION The amino acid sequences of the major glandular form of mammalian PTH, PTH 1-84, have now been determined in the human, bovine, porcine, and rat species (Fig. 50-5).10,19 The cor¬ responding amino acid sequence of the chicken peptide has also been determined and contains 88 rather than 84 amino acids. Studies correlating hormonal structure and function have em¬ phasized the importance of the NH2-terminal region to bioactiv¬ ity. Considerable deletion of the middle and COOH-terminal re¬ gion of the intact peptide can be tolerated without apparent loss of biologic activity. A peptide composed of the NH2-terminal 34 residues, PTH 1-34, appears to contain all of the conventional bioactivity of the intact hormone when tested in various bioassay systems/2 Synthetic NH2-terminal fragments of PTHrP, which share a high degree of homology with PTH within the NH2terminal 13 residues, have been shown to mimic PTH actions in many bioassay systems.73"75 Methionine residues, located within the NH2-terminal third

Ch. 50: Parathyroid Hormone

PARATHYROID HORMONE

HumanQ

Bovine

Porcine

Rat(^)

FIGURE 50-5. Amino acid sequence of mammalian parathyroid hor¬ mone 1-84. The backbone is that of the human sequence, and substitu¬ tions in each of the bovine, porcine, and rat hormones are shown at the specific sites.

of the PTH molecule, appear to be important for biologic func¬ tion; oxidation of these methionines to sulfoxides and sulfones, decreases bioactivity.76 The porcine hormone contains only a sin¬ gle methionine residue at position 8, but the human, bovine, rat, and chicken hormones each contain within their NH2-terminal regions additional methionine residues. All PTHs are equally sus¬ ceptible to oxidation. It is the methionine residue in position 8 that is uniquely important for inactivation by oxidation.77 Substi¬ tution of methionine residues by isosteric norleucine residues renders the molecule resistant to oxidation.78 However, the sub¬ stituted molecule does not retain full bioactivity. Enhanced bio¬ activity may be achieved when a carboxyamide is substituted for the carboxylic acid at the COOH-terminal end of the fragment. Only modest differences in biopotency exist between the hu¬ man, bovine, and porcine hormones in vivo, but in vitro, the syn¬ thetic bovine PTH 1-34 exhibits two to three times the potency of the other species of PTH 1-34 in renal adenylate cyclase assays, apparently from the substitution of alanine for serine in position 1 of the bovine molecule. A synthetic NH2-terminal analogue of the chicken peptide, which contains serine in position 1, is also less potent than bovine PTH 1-34 in various in vitro bioassays. However, a synthetic NH2-terminal fragment of the rat molecule appears more potent than comparable NH2-terminal fragments from the other species. Enhanced binding of the rat hormone to the renal and osseous receptor occurs, accounting for the ob¬ served increase in biopotency of rat PTH.7Q Stepwise deletion of the COOH end of the NH2-terminal 134 fragment causes progressive loss of adenylate cyclase medi¬ ated bioactivity; an inert molecule results with deletion of the middle and COOH ends of the molecule to position 26.72 A re¬ duction in biopotency correlates with a reduction in the capacity to bind to target tissue receptors. The contiguous sequence 25

461

to 34 is thought to be important for receptor binding.78-80 Never¬ theless, the NH2-terminal region of PTHrP, which interacts with the PTH receptor, exhibits little amino acid sequence homology with PTH in the 25-34 region. Simultaneous assay of the inactive 1-12 and 13-34 fragments of PTH fails to elicit bioactivity. Con¬ sequently, the major contribution of the 25-34 region may be to ensure the appropriate conformation of PTH 1-34 for receptor binding. Unlike the COOH region, relatively little deletion is toler¬ ated at the NH2-terminal end. The removal of the NH2-terminal residue of PTH 1-34 (position 1) elicits a sharp drop in bioactivity in adenylate cyclase assays in vitro but a smaller fall in bioactivity in vivo.71 These studies have highlighted the importance of posi¬ tion 1 in determining bioactivity. Synthetic analogues of the NH2-terminal peptide or recombinant analogues of the intact PTH 1-84 molecule in which position 1 has been extended or modified generally have lost substantial bioactivity. One excep¬ tion is the substitution of D-alanine at position 1, which reduces the activity of PTH 1-34 in vitro but increases it in vivo, presum¬ ably by enhancing resistance to aminopeptidase degradation. Deletion of the first two residues yields PTH 3-34, which is inert and functions as a weak antagonist in vitro.80 These findings em¬ phasize the importance of residues at positions 1 and 2 for ade¬ nylate cyclase stimulation. Similar results have been obtained with PTHrP. In vivo, analogues of PTH 3-34 and PTHrP 3-34 appear to retain partial agonist activity. Because of these results, attempts have been made to produce more potent antagonists that might also be useful in vivo. The further truncated peptide, PTH 7-34, lacks partial agonist activity and inhibits effects of PTH agonists on inducing phosphaturia and cAMP excretion in vivo.81 How¬ ever, the efficacy of PTH 7-34 analogues in antagonizing the os¬ seous and calcemic effects of PTH agonists remains relatively low. Although most in vitro studies correlating PTH structure and function have examined adenylate cyclase stimulating activity, several studies have been performed in which other in vitro ac¬ tivities have been assessed. Such studies have indicated that the NH2 residues of PTH 1-34 may not be essential to induce effects on phosphoinositide metabolism and on the augmentation of in¬ tracellular calcium levels. In vitro studies have described the mi¬ togenic effects of the 25-47 region of PTH in osseous cells (not dependent on cyclic AMP accumulation) and alkaline phospha¬ tase-stimulating activity of the 53-84 sequence of PTH in osse¬ ous cells. The clinical significance of these in vitro observations remains to be determined.

PARATHYROID HORMONE RECEPTOR AND INTRACELLULAR SIGNALING The PTH/PTHrP receptor is a member of the G-proteinlinked receptor superfamily. These glycoproteins have hy¬ drophobic sequences that are thought to span the plasma mem¬ brane seven times. These receptors couple to intracellular effectors through guanine nucleotide binding regulatory proteins or G proteins, which are heterotrimeric, consisting of a, /3, and y subunits. In the inactive state, the a subunit has GDP bound to it; however, when a ligand binds to the receptor, the G protein is activated by exchange of GTP for GDP and dissociates into a and fly subunits. The ot subunit, with GTP bound, can then stimulate (Gsa) or inhibit (Gi«), the activity of effector molecules such as adenylate cyclase or phospholipase C. The a subunit also has an intrinsic GTPase activity that hydrolyzes GTP to GDP, terminat¬ ing the effector activation. The PTH/PTHrP receptor belongs to a subgroup of the Gprotein receptor superfamily that, by virtue of their structural similarities, also includes the receptors binding secretin, calcito¬ nin, vasoactive intestinal peptide, glucagon, glucagon-like pep¬ tide I, and growth hormone-releasing hormone. These receptors show no significant sequence identity with other known G-

462

PART IV: CALCIUM AND BONE METABOLISM

protein-linked receptors. All of these receptors couple to the ade¬ nylate cyclase effector by means of Gsa. The activated PTH/ PTHrP receptor couples to at least two effectors: adenylate cy¬ clase and phospholipase C. Other members of this subgroup— including the receptors for calcitonin, glucagon, and glucagon¬ like peptide I—also couple to multiple signaling pathways. PTH/PTHrP receptor cDNAs have been cloned and charac¬ terized from several species and tissues, including opossum kid¬ ney, rat bone, and human kidney and bone.82“85 The amino acid sequences of the receptors are highly homologous, demonstrat¬ ing a marked conservation across species. The opossum and rat PTH/PTHrP receptors bind NH2-terminal analogues of PTH and PTHrP with similar affinity, while the human receptor appears to preferentially bind PTH. This is consistent with the study re¬ sults of relative biologic activities of PTH and PTHrP in vivo in humans, that showed PTHrP 1-34 to be less potent than PTH 1-34.86 The gene for the PTH/PTHrP receptor contains multiple introns (Fig. 50-6). For example, the mouse gene has at least 15 exons that span more than 32 kb of genomic DNA.8' There are eight exons containing predicted membrane-spanning domains. These exons are heterogeneous in length, and three of the exonintron boundaries fall within putative transmembrane se¬ quences, suggesting that these exons did not arise from duplica¬ tion events. The exon-intron organization of the PTH/PTHrP gene is similar to that of the growth hormone-releasing hormone gene, especially in the transmembrane regions, suggesting that the two genes evolved from a common precursor. The proximal promoter of the PTH/PTHrP gene is unusual because it does not contain a TATA box. However, it is GC rich, which would be consistent with the widespread expression of the receptor mRNA. Although the receptor mRNA is highly expressed in kid¬ ney and bone, the primary target tissues of PTH, it is also ex¬ pressed in nonclassic target tissues such as liver, brain, smooth muscle, spleen, testis, and skin.84'88 In most of these tissues, the receptor probably mediates the local action of PTHrP. Although the predominant transcript is 2.5 kb, some tissues also express smaller or larger transcripts that probably are the result of al¬ ternative splicing of the primary transcript. The functional sig¬ nificance of these different forms of the receptor is unknown. High circulating levels of PTH in hyperparathyroid states have been associated with hormonal desensitization in target tis¬ sues, apparently caused by diminished receptor capacity and a postreceptor reduction in functional levels of Gs.89,9(1 PTH recep¬ tors, similar to many peptide hormone receptors, appear to be subject to down-regulation. The renal resistance to PTH often seen in hyperparathyroid states may be partially the result of this kind of regulatory mechanism.91 More widespread reductions in Gs are associated with hormone resistance in the disorder, pseu¬ dohypoparathyroidism type la. The human PTH/PTHrP receptor gene has been localized to the short arm of chromosome 3.84 A search for receptor defects in patients with apparent resistance to endogenous PTH, such as in patients with pseudohypoparathyroidism type lb, has proved negative.92 These patients have end-organ resistance to PTH without typical features of Albright hereditary osteodystrophy and therefore are thought likely to manifest a defect in PTH/ PTHrP receptor expression or function. If no mutations are iden¬ tified in the receptor gene in such patients, it indicates that muta¬ tions in genes for other proteins involved in the PTH/PTHrP signaling pathway are most likely responsible for the defects. It may be that mutations within the PTH/PTHrP receptor are le¬ thal in humans.

ADENYLATE CYCLASE STIMULATION IN PARATHYROID HORMONE ACTION Adenylate cyclase stimulation and the subsequent genera¬ tion of cAMP are believed to be important events in the actions of PTH in the kidney and in the skeleton. Cyclic AMP mimics

phosphaturic and calcium-retaining effects of PTH in the kidney in vivo and in vitro and mediates PTH-stimulated renal lahydroxylase activity. Cyclic AMP has also been implicated in the hypercalcemic action of PTH and may simulate PTH-induced bone resorption in vitro. However, its role in mediating PTHinduced osteoclastic osteolysis is unclear. Details of the cascade of events that follow the generation of cellular cAMP have not been defined in target cells for PTH. Nevertheless, cAMP produced in such cells is believed to stimu¬ late cAMP-dependent protein kinase isoenzymes; types I and II have different biochemical characteristics and may serve differ¬ ent functions. The isoenzymes are tetramers consisting of two regulatory and two catalytic subunits that have similar catalytic but different regulatory components, termed RI and RII, respec¬ tively. With binding of cAMP to the regulatory component, the holoenzyme dissociates, releasing the catalytic component that facilitates the transfer of a terminal phosphate group from a nu¬ cleotide donor, usually ATP, to an amino acid residue (i.e., serine, threonine, or tyrosine) of the substrate protein. The substrate for this reaction or series of reactions in PTH-sensitive cells is un¬ characterized. However, PTH-induced stimulation of the two types of protein kinase has been demonstrated in normal osteo¬ blasts and in a malignant osteoblast line.93 Events that occur after this phosphorylation step and that ultimately lead to the physio¬ logic effects of the hormone are unknown. OTHER SECOND MESSENGERS OF PARATHYROID HORMONE ACTION

Besides cAMP, other second messengers, such as the calcium ion, have been implicated as potentially important in PTH action. In some species, transient hypocalcemia, presumably caused by calcium entry into bone cells, is the earliest event in the action of PTH on the skeleton in vivo. In vitro studies have shown that PTH promotes the uptake of calcium into isolated bone cells, that elevated calcium mimics or potentiates the effects of PTH on the enzymatic activities of isolated bone cells, and that calcium an¬ tagonists inhibit and calcium ionophores stimulate bone resorption. PTH stimulates phosphatidylinositol turnover in certain cell types and in renal membranes.94,95 In response to PTH, increased production of IP3 and diacylglycerol occurs, and increases in cy¬ toplasmic calcium, presumably induced by IP3, have been demonstrated. The cellular response to PTH may involve multiple mecha¬ nisms of cell signaling, and modulation of one message by an¬ other may affect the final response to the hormone.

EFFECTS OF PARATHYROID HORMONE IN TARGET TISSUES BONE

Consistent with its prime function of raising the extracellular fluid calcium concentration, the best-documented effect of PTH is a catabolic one in bone.96,y' The end result is the breakdown of mineral constituents and bone matrix, as manifested in vivo by the release of calcium and phosphate, by increases in plasma and urinary hydroxyproline, and by other indices of bone resorption. This process appears to be mediated by osteoclastic osteolysis, but the mechanism by which PTH causes osteoclastic stimulation is unclear. PTH, when administered in vivo, does not bind directly to multinucleated. osteoclasts, unlike calcitonin. In studies in which mononuclear cells, assumed to be osteo¬ clast related, have been prepared in vitro, PTH stimulation of adenylate cyclase and other enzyme activity has been reported.98 However, no direct effect of PTH has been demonstrated on mul¬ tinucleated osteoclasts in vitro.99 From in vivo studies employing autoradiography, PTH binding to a skeletal mononuclear cell in the intertrabecular region of the metaphysis but not to differen-

Ch. 50: Parathyroid Hormone dated osteoclasts has been reported.100 Consequently, PTH-mediated increases in osteoclast numbers and function appear to occur indirectly, possibly through effects on a mononuclear cell. PTH receptors have also been demonstrated on mature osteo¬ blasts in vivo and in osteosarcoma cells of osteoblast lineage in vitro.80 101 102 The results of these studies have been confirmed in experiments with the cloned PTH/PTHrP receptor. PTH stimulates second messenger accumulation in osteo¬ blast-enriched populations of cells from skeletal tissues and in osteosarcoma cells.103 104 This finding has prompted the sugges¬ tion that PTH-induced stimulation of multinucleated osteoclasts might proceed through the action of PTH-stimulated osteoblast activity.105 The capacity of PTH to enhance multinucleated os¬ teoclast formation in vitro appears to depend on the presence of mononucleated osteoblast-like cells. Early and late phases of calcium mobilization have been de¬ scribed after in vivo administration of PTH.106 The early hypercalcemic response occurs from 10 minutes to 3 hours after hor¬ mone exposure and does not appear to require new protein synthesis. This response may be a consequence of increased met¬ abolic activity of preexisting osteoclasts or of other cell types enhancing the transfer of calcium already in solution. A more sustained hypercalcemic response to PTH admin¬ istration, occurring over approximately 24 hours, appears to de¬ pend on new protein synthesis and to involve a quantitative in¬ crease in osteoclasts, a change in the structure of the osteoclasts (i.e., increased ruffled borders, a zone of the cell believed to be involved in skeletal resorption); an increase in the secretion of lysosomal enzymes, including collagenase and acid hydrolases such as acid phosphatase; and acidification of the extracellular milieu of the osteoclast. The consequences of the effects of PTH on osteoblast activ¬ ity are complex. Some in vitro studies have suggested that PTH may be mitogenic for bone cells.107 Evidence from in vivo studies after hormone administration and from direct studies in cell cul¬ ture of freshly isolated osteoblasts and osteosarcoma cells and in organ culture indicates that PTH may depress or increase the metabolic activity of osteoblasts. The inhibition of activity in¬ cludes the inhibition of collagen synthesis and a reduction of al¬ kaline phosphatase activity.108 Stimulatory activity may involve the mediation of growth factors released by osteoblastic cells in response to PTH. The examination of bone after in vivo PTH administration has also demonstrated an increase in osteoblasts and new bone formation, indicating that PTH may also play an anabolic role under some circumstances.109 Whether the anabolic

463

and catabolic effects of PTH on osteoblasts represent direct and indirect effects, effects of different domains of the PTH molecule, discrete functions in morphologically similar but functionally distinct osteoblasts, or differences in hormonal effects based on different times of exposure or different hormone concentrations remains to be determined. KIDNEY

One of the first-described effects of the administration of PTH intravenously was phosphaturia (see Chap. 201). Renal tu¬ bular reabsorption of phosphate is an active process, with a lim¬ ited transport capacity resulting in a maximum rate of tubular reabsorption (Tm PO4).n0 Because the absolute values of Tm P04 vary considerably among individuals and most of this variation can be explained by differences in glomerular filtration rate (GFR), the Tm P04/GFR ratio has been suggested as a more ac¬ curate index of phosphate reabsorption. This index, which repre¬ sents the sum of the heterogeneous maximum reabsorption rates of all individual nephrons, is reduced by increased concentra¬ tions of PTH and increased in its absence. Another relatively immediate effect of PTH that contributes to its role in calcium homeostasis is enhanced fractional reab¬ sorption of calcium from the glomerular fluid. However, exces¬ sive circulating concentrations of PTH ultimately are associated with a rise in urinary calcium because of increases in extracellular calcium levels and therefore in the filtered load of calcium. Aug¬ mentation of urinary cAMP excretion in response to PTH admin¬ istration is one of the earliest renal responses and is consistent with its postulated role as a second messenger for many or most renal responses. Nevertheless, evidence for an important role for inositol phosphates and intracellular calcium in the renal actions of PTH is increasing. The renal actions of PTH to increase urinary phosphate and cAMP excretion form the basis for the modified Ellsworth-Howard test that is used clinically to establish renal PTH responsiveness (see Chap. 59). PTH alters renal function because of its interactions with multiple regions of the nephron. Evidence for PTH binding to the primary foot processes of podocytes of renal corpuscles and for the stimulation of adenylate cyclase activity in rat glomeruli can be correlated with PTH's reduction of the GFR in rats as a result of decreasing the ultrafiltration coefficient.101 Evidence for the ex¬ pression of the cloned PTH/PTHrP receptor in renal glomeruli confirms the previous findings. PTH appears to reach the luminal surface of polar tubular

FIGURE 50-6.

Schematic representation of the parathyroid hormone (PTH) and parathyroid hormone-related protein re¬ ceptor. The gene contains at least 15 exons. Exon 1 encodes the 5' untranslated region of the mRNA. The portions of the receptor encoded by the remaining 14 exons are schematically depicted by the alternate blocks of unfilled and filled circles. Exons are depicted as follows: SS; putative signal sequence; E1-E4; extracellular sequences; T1-T7; transmembrane sequences; C; cyto¬ plasmic sequence. The mouse PTH/PTHrP receptor of 591 amino acids is shown.

464

PART IV: CALCIUM AND BONE METABOLISM

cells by glomerular filtration and the basolateral surface through the peritubular capillary plexus. High-capacity binding sites have been described on the periluminal portion of the earliest part of the proximal tubule, at which, related to the microvillar surface, PTH degradative events appear to occur. Saturable, specific, lowcapacity binding sites for PTH have been localized after injection in rats to the basolateral surface of the proximal convoluted tu¬ bule and pars recta, the thick ascending limb of the loop of Henle, and the distal convoluted tubule and pars arcuata of the collect¬ ing duct.101 This pattern of PTH binding and activity correlates well with the expression of the cloned PTH/PTHrP receptor and with the localization of PTH-stimulated adenylate cyclase activ¬ ity in the rat nephron, demonstrated in studies employing micro¬ dissection of tubules.111 These observations emphasize the diver¬ sity of PTH actions on the renal tubule, most of which can be mimicked by the infusion of cAMP onto the luminal aspect of tubular cells.112 The use of various techniques, including micropuncture and microperfusion, has localized PTH-induced inhibition of phos¬ phate reabsorption to the proximal convoluted tubule and to the pars recta.112 Inhibition of phosphate reabsorption in the proxi¬ mal convoluted tubule appears to be accompanied by inhibition of sodium and fluid reabsorption. However, sodium is also reab¬ sorbed more distally. Inhibition of phosphate reabsorption also may occur, although perhaps to a lesser extent, in the distal tu¬ bule. The proximal tubule appears to be the major site of action of PTH in stimulating the la-hydroxylase and increasing the pro¬ duction of 1,25-dihydroxyvitamin D. The PTH-induced inhibi¬ tion of bicarbonate transport occurs in the pars recta, and the effect of PTH in this nephron segment may explain the rise in urinary bicarbonate produced by PTH infusion and the proximal renal tubular acidosis that may occur.109 The important site of PTH action to increase calcium and probably magnesium transport appears to be in the thick ascending limb of the loop of Henle and in the distal convoluted tubule and earliest portion of the cortical collecting tubule. Despite the demonstration of the dual role of PTH in in¬ creasing extracellular fluid calcium concentrations through renal and skeletal routes, the relative importance of each is unclear.113 However, contributions of the kidney and skeleton to calcium homeostasis may depend on the concentration of circulating PTH and the duration of elevated hormonal levels. OTHER TARGET TISSUES

Although the administration of PTH in vivo can enhance intestinal calcium absorption, this effect appears to be indirect and mediated by the increased production of 1,25-dihydroxyvitamin D.70 Hepatocyte binding of PTH has been associated with adenylate cyclase stimulation and may reflect PTH-enhanced gluconeogenesis. Among other reported effects of PTH are direct effects on vascular tone, stimulation or inhibition of mitosis of various cells in vitro, increased concentrations of calcium in mammary and in salivary glands, and enhanced lipolysis in isolated fat cells. The demonstration of the widespread expression of the PTHrP gene and the equally disseminated ex¬ pression of the PTH/PTHrP receptor gene suggest that many of the noncalcemic actions of PTH may be carried out by PTHrP acting in an autocrine or paracrine manner.1133

MEASUREMENT RADIOIMMUNOASSAYS RIAs developed for human PTH generally do not employ human PTH (hPTH) 1-84 as a tracer because of its scarcity and because it lacks a tyrosine residue for convenient radioiodination. Instead, bovine PTH (bPTH) 1-84 is employed, possibly contrib¬ uting to the reduced sensitivity for hPTH. The antisera used in

PTH RIAs are generally polyclonal and have been raised against bPTH 1-84 or hPTH 1—84. Nevertheless, populations of anti¬ bodies within polyclonal antisera directed against specific epi¬ topes contained in the 1-84 molecule may predominate. Anti¬ body populations recognizing the COOH-terminal region of PTH 1-84 usually are readily obtained after immunization with bPTH 1-84; antibodies recognizing the midregion also occur with high frequency.114 Sufficiently sensitive antisera containing antibodies predominantly interacting with the NH2-terminal re¬ gion are more unusual but have been successfully raised.115 Attempts to direct antibody specificity have used several strategies. Although the development of monoclonal antibodies to PTH or PTH fragments would seem to be the most direct route to achieve specificity, this approach has not been successful for various technical and biochemical reasons. Instead, specificity has been achieved by employing polyclonal antisera with pre¬ dominant specificity for selected regions, as determined by their reactivity toward synthetic fragments of discrete regions of the molecule or by enhancing the specificity of such antisera by using synthetic fragments of the midregion or COOH-terminal end of PTH as tracers. An important advance in the measurement of PTH is the development of immunoradiometric assays (IRMAs) that employ antisera directed against the NH2-terminal and midregion or COOH region of the molecule. These assays (i.e., "intact” assays) detect mainly intact PTH 1-84 and appear to be the most sensi¬ tive and specific.116 Defining the specificity of an RIA is important because of the complex metabolism of PTH, which results in a multiplicity of circulating molecular forms. The most abundant circulating forms are midregion and COOH fragments because of their longer half-life in the circulation; these become even more pre¬ dominant in renal failure when clearance is further impaired.41 The presumed bioactive forms, intact PTH 1-84 and the NH2terminal fragment, are cleared more readily and circulate at lower levels. Midregion and COOH-directed RIAs detect long-lived fragments and intact bioactive hormone. These RIAs generally do not require the high sensitivity of NH2-directed assays to be useful, because they measure higher absolute levels of PTH. Most material measured by these RIAs is thought to be inac¬ tive, but this has not greatly restricted their clinical usefulness in the diagnosis of primary or secondary hyperparathyroidism. For primary hyperparathyroidism, the midregion and COOHdirected RIAs may be especially useful in providing an index of integrated secretory function of the parathyroid glands.63 How¬ ever, first it should be established that a given midregion or COOH-terminal RIA is clinically useful. Amino-terminal RIAs, which determine the level of short-lived PTH forms, can also be used to detect hypersecretion in primary hyperparathyroidism but may be especially useful in assessing acute changes in PTH secretion in physiologic studies. Two-site IRMAs, which also measure bioactive hormone, are generally more sensitive and can substitute for NH2-directed assays. For cases of hyperparathyroidism associated with renal fail¬ ure, NH2-directed assays have the theoretical advantage of pro¬ viding a better estimate of circulating bioactive PTH forms and differentiating decreased PTH clearance from hypersecretion. From a practical point of view, two-site IRMAs are preferred to NH2-directed assays. If PTH levels are determined serially during the progression of renal failure, COOH-directed assays also may provide useful estimates of the severity of the hyperparathyroid¬ ism, and hormone levels determined by COOH-directed assays in renal failure have correlated well with the extent of skeletal resorption.63 It has been suggested that midregion assays may detect intact PTH more readily than COOH-directed assays and may have a somewhat greater ability to measure a variety of PTH forms than the COOH-directed assays. However, midregion as¬ says are subject to restrictions and advantages similar to those of the COOH-directed assays. Few RIAs, no matter the degree of specificity, completely

Ch. 50: Parathyroid Hormone discriminate between concentrations of immunoreactive PTH found in normal persons and those detected in hyperparathy¬ roidism, although best results appear to be obtained with twosite IRMAs. It has been suggested that PTH levels should be in¬ terpreted in conjunction with prevailing levels of blood calcium. This assists in the assay analysis; if a given PTH level is measured in a normocalcemic individual and that same PTH level is found in a patient with hypercalcemia, the level in the latter case can be considered inappropriately elevated. Another limitation of most RIAs is the inability to measure values in all normal individuals. A lower limit of normality gen¬ erally cannot be established, which makes it difficult to ascertain reduced PTH levels. Sensitive two-site IRMAs often approach a lower limit of normality. PTH RIAs are useful in differentiating hypocalcemia resulting from PTH deficiency (i.e., hypoparathy¬ roidism) from hypocalcemia resulting from other causes. In the former situation, PTH is undetectable or very low, but in the lat¬ ter situation, the hypocalcemic stimulus is associated with in¬ creased PTH secretion and elevated levels of PTH (see Chaps. 57 and 60).

BIOASSAYS With the unraveling of the complex metabolism of PTH and the resulting heterogeneity of circulating hormone, the care that must be exercised in interpreting the results of PTH RIAs became apparent, and the possibility of employing PTH bioassays to sup¬ plement the information obtained from RIAs arose. Some PTH bioassays estimate the biologic effects of the hormone in vivo, and some estimate levels of the hormone based on biologic effects in vitro. It has been estimated that the normal circulating levels of bioactive PTH are about 1 pM. IN VIVO BIOASSAYS

Measurements of in vivo phosphaturic effects (e.g., determi¬ nation of Tm PO4/GFR) and renal calcium retention (e.g., frac¬ tional excretion of calcium) provide estimates of PTH effects in vivo and have been useful as adjunctive studies of PTH. Partly because of their lack of specificity, these assays have not achieved widespread popularity as indices of PTH concentrations in most clinical situations. Conversely, estimates of urinary cAMP excre¬ tion (measured by RIA) have been fairly widely used.117 Several hormones besides PTH (e.g., vasopressin) contribute to urinary cAMP levels, although the PTH-produced component is the major fraction. Greater specificity of urinary cAMP for PTH can be achieved by measuring the fraction of urinary cAMP that is of renal origin. This nephrogenous component can be deter¬ mined from the clearance of cAMP relative to the GFR, an esti¬ mate requiring plasma cAMP measurements, or it can be deter¬ mined by relating the urinary cAMP to 100 mL of glomerular filtrate. Nephrogenous cAMP is a specific and rather sensitive in vivo bioassay for PTH.n / Nephrogenous cAMP is often elevated in primary hyperparathyroidism and decreased in hypoparathy¬ roidism. There is, however, overlap with the normal range. Most nephrogenous cAMP determinations accurately reflect circulat¬ ing PTH levels as determined by RIA, but they do not have the sensitivity or specificity of the best two-site IRMAs. IN VITRO BIOASSAYS

Several attempts have been made to develop clinically use¬ ful in vitro bioassays for the measurement of active PTH. The capacity of PTH to stimulate adenylate cyclase, with the addition of guanyl nucleotides, in purified renal membrane preparations or tumor cell lines and the availability of synthetic antagonistic PTH fragments have imparted useful specificity to such renal membrane bioassay preparations.118,119 Unfortunately, the rela¬ tive insensitivity of this approach has precluded its use for any¬ thing other than experimental purposes. Another approach is the cytochemical PTH bioassay. The

465

most widely used has been a renal cytochemical bioassay (CBA) performed in guinea pig kidney segments maintained in nonpro¬ liferative organ culture.4,69,120 In response to graded doses of PTH, the increased glucose-6-phosphate dehydrogenase (G6PD) activity in renal tubules can be measured. The G6PD is quanti¬ tated by a color reaction using scanning and integrating micro¬ densitometry. The PTH stimulation of G6PD activity appears to be mediated by cAMP, but the physiologic role of the response is now unclear. The major advantage of CBAs in general and of the renal CBA for PTH in particular is its exquisite sensitivity. Hormone levels as low as 1 to 5 fg/mL have been detected. Un¬ der the assay conditions that are employed for PTH, the response appears to be specific for PTH or PTH-like substances. The major drawbacks of the method are its technical difficulty and low through-put, which have precluded its use for routine clinical assay purposes. Considerable progress has been made during the past sev¬ eral years in examining the biosynthesis of PTH, the regulation of PTH secretion, and the mechanism of PTH action. These ad¬ vances include elucidation of the molecular genetics of PTH, dis¬ covery of the parathyroid calcium "sensor," and determination of the structure of the PTH/PTHrP receptor. The identification of PTHrP has disclosed a new member of the PTH gene family and provided possibilities for understanding the biologic effects of both molecules. This improved comprehension of the bio¬ chemistry and physiology of PTH should translate into exciting insights into the pathophysiology of disease states in which PTH is implicated.

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466

PART IV: CALCIUM AND BONE METABOLISM

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Evidence for a role for protein kinase C in the control of PTH release FEBSLett 1984; 17:175. 40. Brown EM, Gambda G, Riccardi D, et al. Cloning and characterization of an extracellular Ca2+-sensing receptor from bovine parathyroid. Nature 1993; 366575. 41. Poliak MR, Brown EM, Chou Y-HW, et al. Mutations in the human Ca2+sensing receptor gene cause familial hypocalciuric hypercalcemia and neonatal se¬ vere hyperparathyroidism. Cell 1993:75:1297. 42. Poliak MR, Chou Y-HW, Marx SJ, et al. Familial hypocalciuric hypercal¬ cemia and neonatal severe hyperparathyroidism. Effects of mutant gene dosage on phenotype. J Clin Invest 1994;93:1108. 43. Russell J, Lettieri D, Sherwood LM. Direct regulation by calcium of cyto¬ plasmic messenger ribonucleic acid coding for pre-proparathyroid hormone in iso¬ lated bovine parathyroid cells. J Clin Invest 1983:72:1851. 44. Brown EM. 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hormone secretion: proportional control by calcium, lack of effect of phosphate. Endocrinology 1968:83:1043. 50. Abe M, Sherwood LM. Regulation of parathyroid hormone secretion by adenylate cyclase. Biochem Biophys Res Commun 1972;48:396. 51. Brown EM, Gardner DG, Windek RA, Aurbach GD. Relationship of intra¬ cellular 3',5'-adenosine monophosphate accumulation to parathyroid hormone re¬ lease from dispersed bovine parathyroid cells. Endocrinology 1978; 103:2323. 52. Heath H III. Biogenic amines and the secretion of parathyroid hormone and calcitonin. Endocr Rev 1980; 1:319. 53. Epstein S, Heath H III, Bell NH. Lack of influence of isoproterenol, pro¬ pranolol and dopamine on immunoreactive parathyroid hormone and calcitonin in normal man. Calcif Tissue Int 1983;35:32. 54. Fasciotto BH, Gorr S-U, De Franco DJ, et al. Pancreastatin, a presumed product of chromogranin-A (secretory protein-1) processing, inhibits secretion from porcine parathyroid cells in culture. Endocrinology 1989; 125:1617. 55. Drees BM, Rouse J, Johnson J, Hamilton JW. Bovine parathyroid glands secrete a 26-kDa N-terminal fragment of chromogranin-A which inhibits parathy¬ roid cell secretion. Endocrinology 1991; 129:3381. 56. Silver J, Russell J, Sherwood LM. Regulation by vitamin D metabolites of messenger ribonucleic acid for preproparathyroid hormone in isolated bovine parathyroid cells. Proc Natl Acad Sci USA 1985:82:4270. 57. Hendy GN, Stotland MS, Grunbaum D, et al. Characteristics of secondary hyperparathyroidism in vitamin D deficient dogs. Am J Physiol 1989;256:E765. 58. Demay MB, Kiernan MS, DeLuca HF, Kronenberg HM. Sequences in the human parathyroid hormone gene that bind the 1,25-dihydroxyvitamin D3 receptor and mediate transcriptional repression in response to 1,25-dihydroxy vitamin D3. Proc Natl Acad Sci USA 1992; 89:8097. 59. Kremer R, Bolivar 1, Goltzman D, Hendy GN. Influence of calcium and 1,25-dihdroxycholecalciferol on proliferation and proto-oncogene expression in primary cultures of bovine parathyroid cells. Endocrinology 1989; 125:935. 60. Fusik RF, Krukeja SC, Hargis GK, et al. Effect of glucocorticoids on func¬ tion of the parathyroid glands in man. J Clin Endocrinol Metab 1975; 40:152. 61. Silverman R, Yalow RS. Heterogeneity of parathyroid hormone: clinical and physiologic implications. J Clin Invest 1973:52:1958. 62. Segre GV, Niall HD, Habener JF, Potts JT Jr. Metabolism of parathyroid hormone: physiological and clinical significance. Am J Med 1974; 56:774. 63. Arnaud CD, Goldsmith RS, Bordier PJ, et al. Influence of immunohetero¬ geneity of circulating parathyroid hormone on radioimmunoassays of serum in man. Am J Med 1974;56:785. 64. Reiss E, Canterbury JM. Emerging concepts of the nature of circulating parathyroid hormones: implications for clinical research. Recent Prog Horm Res 1974;30:391. 65. Neuman WF, Neuman MW, Lane K, et al. The metabolism of labeled parathyroid hormone V. Collected biological studies. Calcif Tissue Res 1975; 18: 271. 66. Martin KJ, Hruska KA, Freitag JJ, et al. The peripheral metabolism of para¬ thyroid hormone. N Engl J Med 1979:301:1092. 67. Segre GV, D'Amour P, Hultman A, Potts JT Jr. Effects of hepatectomy, nephrectomy, and nephrectomy/uremia on the metabolism of parathyroid hor¬ mone in the rat. J Clin Invest 1981; 67:439. 68. Papapoulos SE, Hendy GN, Tomlinson S, et al. Clearance of exogenous parathyroid hormone in normal and uraemic man. Clin Endocrinol 1977; 7:211. 69. Goltzman D, Henderson B, Loveridge N. Cytochemical bioassay of para¬ thyroid hormone: characteristics of the assay and analysis of circulating hormonal forms. J Clin Invest 1980;65:1309. 70. DeLuca HF. Metabolism and molecular mechanism of action of vitamin D. Biochem Soc Trans 1981; 10:147. 71. Parsons JA, Rafferty B, Gray D, et al. Pharmacology of parathyroid hor¬ mone and some of its fragments and analogues. In: Talmage RV, Owen M, Parsons JA, eds. Calcium-regulating hormones. Amsterdam: Excerpta Medica, 1975:33. 72. Tregear GW, van Rietschoten J, Greene E, et al. Bovine parathyroid hor¬ mone: minimum chain length of synthetic peptide required for biological activity. Endocrinology 1973:93:1349. 73. Kemp BE, Moseley JM, Rodda CP, et al. Parathyroid hormone-related protein of malignancy: active synthetic fragments. Science 1987; 23:1568. 74. Horiuchi N, Caulfield MP, Fisher JE, et al. Similarity of synthetic peptide from human tumor to parathyroid hormone in vivo and in vitro. Science 1987; 23: 1566. 75. Rabbani SA, Mitchell J, Roy DR, et al. Influence of the amino-terminus on in vitro and in vivo biological activity of synthetic parathyroid hormone-like pep¬ tides of malignancy. Endocrinology 1988; 123:2709. 76. Tashjian AH Jr, Ontjes DA, Munson PL. Alkylation and oxidation of me¬ thionine in bovine parathyroid hormone: effects on hormonal activity and antige¬ nicity. Biochemistry 1964; 3:1175. 77. O'Riordan JLH, Woodhead JS, Hendy GN, et al. Effect of oxidation on biological and immunological activity of porcine parathyroid hormone. J Endocrinol 1974;63:117. 78. Nussbaum SR, Rosenblatt M, Potts JT Jr. Parathyroid hormone renal re¬ ceptor interactions: demonstration of two receptor binding domains. J Biol Chem 1980;255:10183. 79. Demay M, Mitchell J, Goltzman D. Comparison of renal and osseous bind¬ ing of parathyroid hormone and hormonal fragments. Am J Physiol 1985;249:E437. 80. Goltzman D, Peytremann A, Callahan E, et al. Analysis of the require¬ ments for parathyroid hormone action in renal membranes with the use of inhibit¬ ing analogues. J Biol Chem 1976;250:3199. 81. Horiuchi N, Holick MF, Potts JT Jr, Rosenblatt M. A parathyroid hormone

Ch. 51: Parathyroid Hormone-Related Protein inhibitor in vivo: design and biological evaluation of a hormone analog. Science 1983; 220:1053. 82. Juppner H, Abou-Samra AB, Freeman MW, et al. A G protein-linked re¬ ceptor for parathyroid hormone and parathyroid hormone-related peptide. Science 1991; 254:1024. 83. Abou-Samra AB, Juppner H, Force T, et al. Expression cloning of a para¬ thyroid hormone/parathyroid hormone-related peptide receptor from rat osteo¬ blast-like cells: a single receptor stimulates intracellular accumulation of both cAMP and inositol triphosphate and increases intracellular free calcium. Proc Natl Acad SciUSA 1992; 89:2732. 84. Pausova Z, Bourdon J, Clayton D, et al. Cloning of a parathyroid hor¬ mone/parathyroid hormone-related peptide receptor (PTHR) cDNA from a rat os¬ teosarcoma (UMR 106) cell line: chromosomal assignment of the gene in the human, mouse, and rat genomes. Genomics 1994;20:20. 85. Schipani E, Harga H, Karaplis AC, et al. Identical complementary deoxy¬ ribonucleic acids encode a human renal and bone parathyroid hormone (PTH)/ PTH-related peptide receptor. Endocrinology 1993; 132:2157. 86. Fraher LJ, Hodsman AB, Jonas K, et al. A comparison of the in vivo bio¬ chemical responses to exogenous parathyroid hormone-(l-34) [PTH-(1-34)J and PTH-related peptide-(l-34) in man. J Clin Endocrinol Metab 1992; 75:417. 87. McCuaig KA, Clarke JC, White JH. Molecular cloning of the gene encoding the mouse parathyroid hormone/parathyroid hormone related peptide receptor. Proc Natl Acad Sci USA 1994;91:5051. 88. Urena P, Kong X-F, Abou-Samra A-B, et al. Parathyroid hormone (PTH)/ PTH-related peptide receptor messenger ribonucleic acids are widely distributed in rat tissues. Endocrinology 1993; 133:617. 89. Mahoney CA, Nissenson RA. Canine renal receptors for parathyroid hor¬ mone: down-regulation in vivo by exogenous parathyroid hormone. J Clin Invest 1983; 72:411. 90. Forte LR, Langeluttig SG, Poelling RE, Thomas ML. Renal parathyroid hormone receptors in the chick: downregulation in secondary hyperparathyroid animal models. Am J Physiol 1982;242:E154. 91. Tomlinson S, Hendy GN, Pemberton DM, O'Riordan JLH. Reversible re¬ sistance to the renal action of parathyroid hormone in man. Clin Sci Mol Med 1976;51:59. 92. Schipani E, Weinstein LS, Bergwitz C, et al. Molecular heterogeneity of the PTH/PTHrP receptor in patients with pseudohypoparathyroidism (abstract 61). J Bone Min Res 1993;8(Suppl 1):S132. 93. Livesey SA, Kemp BE, Re CA, et al. Selective hormonal activation of cyclic AMP-dependent protein-kinase isoenzymes in normal and malignant osteoblasts. J Biol Chem 1982;257:14983. 94. Stern PH. Cationic agonists and antagonists of bone resorption. In: Cohn DV, Fujita T, Potts JT Jr, Talmage RV, eds. Endocrine control of bone and calcium metabolism. Amsterdam: Excerpta Medica, 1984:109. 95. Hruska KA, Moskowitz D, Esbrit P, et al. Stimulation of inositol triphos¬ phate and diacylglycerol production in renal tubular cells by parathyroid hormone. J Clin Invest 1987; 79:230. 96. Bingham P, Brazell I, Owen M. The effect of parathyroid extract on cellular activity and plasma calcium levels in vivo. J Endocrinol 1969; 45:387. 97. Holtrop ME, Raisz LG, Simmons HA. The effect of parathyroid hormone, colchicine and calcitonin on the ultrastructure and activity of osteoblasts in organ culture. J Cell Biol 1974; 60:346. 98. Luben RA, Wong GL, Cohn DV. Biochemical characterization with para¬ thormone and calcitonin of isolated bone cells: provisional identification of osteo¬ clasts and osteoblasts. Endocrinology 1976:99:526. 99. Chambers TJ, McSheehy PMJ, Thomson BM, Fuller K. The effect of calcium-regulating hormones and prostaglandins on bone resorption by osteoclasts disaggregated from neonatal rat bones. Endocrinology 1985; 116:234. 100. Rouleau MF, Mitchell J, Goltzman D. In vivo distribution of parathyroid hormone receptors in bone. Evidence that a predominant osseous target cell is not the mature osteoblast. Endocrinology 1988:123:187. 101. Rouleau MF, Warshawsky H, Goltzman D. Parathyroid hormone bind¬ ing in vivo to renal, hepatic and skeletal tissues of the rat using a radioautographic approach. Endocrinology 1986:118:919. 102. Rizzoli RE, Somerman M, Murray TM, Aurbach GD. Binding of radioiodinated parathyroid hormone to cloned bone cells. Endocrinology 1983; 113:1832. 103. Peck WA, Carpenter J, Messinger K, De Bra D. Cyclic 3',5'-adenosine monophosphate in isolated bone cells: response to low concentrations of parathy¬ roid hormone. Endocrinology 1973; 92:692. 104. Majeska RJ, Rodan SB, Rodan GA. Parathyroid hormone-responsive clonal cell lines from rat osteosarcoma. Endocrinology 1980; 107:1494. 105. Rodan GA, Martin TJ. Role of osteoblasts in hormonal control of bone resorption—a hypothesis. Calcif Tissue Int 1981:33:349. 106. Parsons JA, Potts JT Jr. Physiology and chemistry of parathyroid hor¬ mone. In: MacIntyre I, ed. Clinics in endocrinology and metabolism, vol 1. Calcium metabolism and bone disease. London: WB Saunders, 1972:33. 107. SchKiter K-D, Hellstern H, Wingender E, Mayer H. The central part of parathyroid hormone stimulates thymidine incorporation of chondrocytes. J Biol Chem 1989:264:11087. 108. Dietrich JW, Canalis E, Maina DM, Raisz LG. Hormonal control of bone collagen synthesis in vitro: effects of parathyroid hormone and calcitonin. Endocri¬ nology 1976;98:943. 109. Tam CS, Heersche JNM, Murray TM, Parsons JA. Parathyroid hormone stimulates the bone apposition rate independently of its resorptive action: differ¬ ential effects of intermittent and continual administration. Endocrinology 1982; 110:506.

467

110. Bijvoet OLM. Kidney function in calcium and phosphate metabolism. In: Avioli LV, Krane SM, eds. Metabolic bone disease, vol 1. New York: Academic Press, 1977:48. 111. Morel F. Regulation of kidney functions by hormones: a new approach. Recent Prog Horm Res 1983;39:271. 112. Agus ZS, Wasserstein A, Goldfarb S. PTH, calcitonin, cyclic nucleotides and the kidney. Annu Rev Physiol 1981; 43:583. 113. Nordin BEC, Peacock M. Role of the kidney in regulation of plasma calcium. Lancet 1969; 2:1280. 113a. Amizuka N, Warshawsky H, Golzman D, Karaplis A. Purathyroid hormone-related peptide-depleted mice show abnormal epiphyseal cartilage de¬ velopment and altered endochondral bone formation J Cell Biol 1994; 126:1611. 114. Marx SJ, Sharp ME, Krudy A, et al. Radioimmunoassay for the middle region of human parathyroid hormone: studies with a radioiodinated synthetic pep¬ tide. J Clin Endocrinol Metab 1981;53:76. 115. Papapoulos SE, Manning RM, Hendy GN, et al. Studies of circulating parathyroid hormone in man using a homologous amino-terminal specific immunoradiometric assay. Clin Endocrinol 1980; 13:57. 116. Nussbaum SR, Zahnadnik RJ, Labigne JR, et al. A highly sensitive twosite immunoradiometric assay of parathyrin (PTH) and its clinical utility in evaluat¬ ing patients with hypercalcemia. Clin Chem 1987;33:1364. 117. Broadus AE. Nephrogenous cyclic AMP. Recent Prog Horm Res 1981; 37: 667. 118. Nissenson RA, Abbott SR, Teitelbaum AP, et al. Endogenous biologically active human parathyroid hormone: measurement by a guanyl nucleotide-ampli¬ fied renal adenylate cyclase assay. J Clin Endocrinol Metab 1981;52:840. 119. Sato K, Han DC, Ozawa M, et al. A highly sensitive bioassay for PTH using ROS 17/2.8 subclonal cells. Acta Endocrinol (Copenh) 1987; 116:113. 120. Chambers DJ, Dunham J, Zanelli JM, et al. A sensitive bioassay of para¬ thyroid hormone in plasma. Clin Endocrinol 1978;9:375.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

51_

PARATHYROID HORMONERELATED PROTEIN EBERHARD BLIND, ROBERT A. NISSENSON, AND GORDON J. STREWLER

The parathyroid hormone (PTH) family of proteins has two members. The sister protein of PTH is a parathyroid hormonerelated protein (PTHrP), sometimes referred to as parathyroid hormone-like protein. Originally identified as the cause of hu¬ moral hypercalcemia in malignancy, PTHrP has a distinct set of physiologic functions that are mostly unrelated to the regulation of systemic calcium homeostasis but that rival the actions of PTH in their importance. It has been recognized since Fuller Albright's time that in some ways patients with malignant tumors causing hypercalce¬ mia resemble patients with primary hyperparathyroidism (pHPT). Malignancy-associated hypercalcemia is characterized not only by humorally mediated bone resorption but also by di¬ minished tubule resorption of phosphate with consequent phosphaturia and hypophosphatemia. When it was recognized that the disorder also produced an increase in nephrogenous cyclic adenosine monophosphate (cAMP), the component of urinary cAMP secreted into the urine from the renal tubule,1 it be¬ came clear that a humoral factor in patients with malignancyassociated hypercalcemia was mimicking PTH at the kidney. Increased nephrogenous cAMP was previously thought to be unique to hyperparathyroidism, reflecting increased secretion of cAMP from the renal tubule, where cAMP is the intracellular sec¬ ond messenger for PTH. Once it was recognized that increased cAMP in kidney or bone cells could be used as a bioassay to de¬ tect the humoral factor secreted by malignant tumors, the sub-

468

PART IV: CALCIUM AND BONE METABOLISM

stance was purified and shown to be a protein that was structur¬ ally related to PTH.2 4

nase. It is believed that chromosome 12, on which the PTHrP gene is located, and chromosome 11, where the PTH gene re¬ sides, arose by an ancient duplication in which the ancestral PTH/PTHrP gene was evidently copied along with its neighbors.

STRUCTURE AND BIOLOGIC PROPERTIES STRUCTURE AND PROCESSING OF PARATHYROID HORMONE-RELATED PROTEIN AND ITS GENE PTHrP is a protein of 139 to 173 amino acids.5"7 It resembles PTH in primary sequence only at the amino terminus, where 8 of the first 13 amino acids in the two peptides are identical (Fig. 51-1). Although this is a limited region of homology, it is a critical region of both peptides, not required for binding but necessary for receptors occupied by either hormone to activate adenylate cyclase and hence to produce cAMP as a second messenger. Thus, the homology of PTH and PTHrP at the amino terminal end is responsible for their shared biologic properties (see below). The gene for PTHrP is located on human chromosome 12. It is considerably more complex than the PTH gene, which is lo¬ cated on chromosome 11, with three promoters and four alterna¬ tively spliced exons upstream of the coding sequence.8 The com¬ plexity of the promoter region allows for considerable flexibility in the regulation of PTHrP gene transcription. There is evidence that the promoters are used differentially in different tissues8 and by the viral transactivating protein tax.9 Most of the prepro sequence of PTHrP is encoded on one exon, with the last two amino acids of the prepro sequence and 139 amino acids of the mature peptide encoded on a second exon. The splice junction between these two coding exons is precisely conserved between PTHrP and PTH. Downstream of the main coding sequence are two additional exons, which are alterna¬ tively spliced to contribute distinct carboxy terminal ends to the isoforms of PTHrP and distinct 3' noncoding sequences. The pro¬ tein isoforms encoded by these exons are identical through amino acid 139 but comprise 139, 141, or 173 amino acids in toto. This downstream complexity of the PTHrP gene may also be used for regulation. The three transcript families with different 3' un¬ translated sequences have markedly different half-lives, ranging from 20 minutes to about 7 hours. In addition, their stability is differentially regulated. Exposure of cells to transforming growth factor f3 specifically increases the half-life of the most unstable transcript, which encodes the 139 amino acid form of the protein.10 It is clear from conservation of sequence, gene structure, and chromosomal localization that PTHrP and PTH arose from a common ancestral gene. In addition to the striking resemblance of their amino terminal sequence and the conservation of the intron-exon boundaries between the two major coding exons, each gene is flanked by duplicated genes for lactate dehydroge¬

FIGURE 51-1.

Primary structures of the amino terminal part of parathyroid hormone-related protein and of para¬ thyroid hormone. Compared are the human sequences 1-34. Identical amino acids are highlighted.

SECRETED FORMS: PEPTIDE HETEROGENEITY The three mature PTHrP peptides predicted by cDNA are 139, 141, and 173 amino acids long. It is not clear whether some or all of these are secreted as full length proteins, although even the most carboxy terminal 141-173 immunoreactive peptide has been detected in tumor extracts.11 AMINO TERMINAL FRAGMENTS

The molecular size of PTHrP containing the bioactive amino terminal part found in plasma and in tumor extracts ranges any¬ where from 6 to 18 kilodaltons (kd),2"4 and, apparently, several different amino terminal fragments of PTHrP are secreted.12 Three different cell types (renal carcinoma cells, PTHrP transfected RIN-141 cells, and normal keratinocytes) cleave PTHrP after arginine-37 to produce an amino terminal fragment that is probably processed to PTHrP(l-36)13 (Fig. 51-2). This amino terminal PTHrP fragment contains the PTH-like region and could account completely for the PTH-like effects of PTHrP, as discussed later. MID-REGIONAL FRAGMENTS

This intracellular cleavage step also produces mid-regional PTHrP fragments of about 50 to 70 amino acids beginning with alanine-3813 (see Fig. 51-2). The carboxyl terminus of these frag¬ ments has not been identified, but it is likely that they terminate somewhere in the highly basic region PTHrP(88-106), which contains many possible cleavage sites. Mid-regional fragments of PTHrP generated intracellularly can apparently enter the regu¬ lated pathway of peptide secretion and become packaged in dense neurosecretory granules, suggesting that they may be un¬ der separate secretory control from amino terminal fragments.13 Mid-regional PTHrP fragments of similar or identical size are the predominant circulating forms in the plasma of patients with hu¬ moral hypercalcemia of malignancy.14 These mid-regional PTHrPs may play a physiologic role in transplacental calcium transport (see later), and synthetic mid-region peptides also ap¬ pear to have bioactivities in squamous carcinoma cells.15 CARBOXYL TERMINAL FRAGMENTS

The size of the mid-regional fragments suggests the exis¬ tence of additional carboxyl terminal PTHrP fragments, possibly resulting from cleavage at the multibasic amino acid clusters at

Ch. 51: Parathyroid Hormone-Related Protein

Predicted Gene Products

-36 1 ■■■■ -^6^1 ■■■■ -36 1

139 141

El

173

Intracellular

Secreted

FIGURE 51-2. Heterogeneity of parathyroid hormone-related protein (PTHrP) peptides. The common sequence of the predicted gene products is shown in black. The unique 140-141 and 140-173 sequences result from alternative RNA splicing. Multiple peptides are produced by intra¬ cellular processing and secreted. Peptide sequences whose termini are indeterminate are shown as dashed lines. Except for PTHrP(l-36), which has not yet been demonstrated in serum, all the secreted peptides are thought to circulate.

469

sera of patients with humoral hypercalcemia of malignancy. A peptide with PTHrP(109-138) circulates as a separate peptide that accumulates in patients with chronic renal failure, but not in those with cancer. A biologic function for this portion has not yet been defined.1819 PTHrP is posttranslationally modified in additional ways20; for example, PTHrP secreted by keratinocytes is glycosylated posttranslationally.21 Whether this is also the case with other cell types and with PTHrP forms circulating in plasma is unknown. The findings that cells process PTHrP to multiple peptide fragments, that some of these fragments may be under separate secretory control, and that one or more (besides its PTHlike amino terminus) may have its own bioactivity indicate that PTHrP could be, like the adrenocorticotropic hormonemelanocyte-stimulating hormone-endorphin precursor pro¬ opiomelanocortin, a polyprotein precursor for multiple bioactive peptides.22 The pattern of posttranslational modification may be tissue specific, and this would add another dimension of speci¬ ficity to the secreted forms of PTHrP.

IMMUNOASSAYS amino acids 88-91, 96-98, and 102-106. The high degree of con¬ servation between human, rat, and chicken PTHrP, not only in the amino terminal portion of PTHrP but also in the portion up to amino acid 111, suggests some biologic relevance of the region from amino acids 88-91. The very carboxyl terminal part of the conserved region, PTHrP(107-lll), was found in one study to potently inhibit osteoclastic bone resorption in vitro,16 but this was not confirmed in another model.12 PTHrP fragments even further carboxyl terminal do exist. Peptides with PTHrP(109138) but not PTHrP(l-36) immunoreactivity have been found in

FIGURE 51-3.

Because the known PTH-like bioactivity of PTHrP is located within the first 34 amino acids, most immunoassays have been directed against the amino terminal sequence 1-34 to 1-40 of PTHrP in radioimmunoassays (RIAs)23"26 or against larger frag¬ ments containing amino terminal PTHrP in immunoradiometric assays.19,27 Because the amounts of amino terminal PTHrP ex¬ tractable from normal serum are very low ( 25%) of surfaces covered with stainable aluminum and are considered to have aluminum-related bone disease. The major sources of this alumi¬ num are the aluminum-containing phosphate binders used to control hyperphosphatemia and dialysate solutions contami¬ nated with aluminum (see Chaps. 7 and 60). Aluminum accumu¬ lates at sites of bone formation (see Fig. 54-5C), where it may directly inhibit mineralization, leading to an increase in osteoid thickness and osteoid surface. However, aluminum also is toxic to osteoblasts and may impair their ability both to synthesize and to mineralize bone matrix. These two effects of aluminum reduce both the mineral apposition rate and the mineralizing surface. However, if matrix production also is inhibited, osteoid thickness is not increased. With greater recognition of the potential sources of aluminum and the substitution of phosphate binders contain¬

ing calcium for those containing aluminum, aluminum-related bone disease is becoming less of a clinical problem. Another form of low turnover bone disease has been de¬ scribed that is termed idiopathic aplastic or adynamic bone dis¬ ease and is not characterized by significant aluminum accumula¬ tion or staining. Its pathogenesis is unclear but may be related to various therapeutic maneuvers designed to prevent or treat hyperparathyroidism in patients undergoing dialysis, including the use of dialysates with higher calcium concentrations (3.0-3.5 mEq/L), large doses of calcium-containing phosphate binders, and calcitriol therapy. In general, these patients tend to have few or no symptoms of bone disease, and this "disease” ultimately may prove to be a histologic, rather than a clinically relevant, form of bone disorder. It is unknown whether patients with aplastic bone disease are at increased risk for the development of clinical problems in the future. The form of renal bone disease that is classified as mixed disease is characterized histologically by features of both osteitis fibrosa and osteomalacia. Such lesions are observed most com¬ monly in patients who are in transition between osteitis fibrosa and aluminum-related bone disease.

OSTEOPOROSIS36 44 The most striking feature of bone biopsy specimens from patients with osteoporosis is the reduction in cancellous bone vol¬ ume (see Chap. 63). About 80% of patients with vertebral crush fractures have lower than normal values. The reduction in can¬ cellous bone volume results primarily from progressive loss of en¬ tire trabeculae and, to a lesser degree, from thinning of those that remain (Fig. 54-7). Concerning the changes in the other static and dynamic pa¬ rameters in osteoporosis, there is still considerable debate over whether patients can be stratified into high, normal, or low turn¬ over groups. Even if they can, what is the pathogenetic and clin¬ ical significance of this so-called "histologic heterogeneity" in pa¬ tients with osteoporosis? In a study of 50 postmenopausal women with untreated osteoporosis, the investigators identified two subsets of patients, one with normal turnover and one with high turnover, the latter representing 30% of the cases.40 How¬ ever, this conclusion was based on the finding of a bimodal dis-

Ch. 54: Bone Quantification and Dynamics of Turnover

FIGURE 54-7. Iliac crest biopsy from a patient with postmenopausal osteoporosis. Note the marked reduction in cancellous bone volume and in the thickness of the cortices compared with the normal biopsy shown in Figure 54-2A. Goldner trichrome stain. Field width = 9.6 mm.

tribution in osteoid surface. The tetracycline-based bone formation rate, a more reliable measure of turnover rate, showed a normal distribution. Based on the interval between the 10th percentile and the 90th percentile for calculated bone resorption rate in a large group (n = 32) of normal postmenopausal women, another study classified 30% of women with untreated postmenopausal osteoporosis as having high turnover, whereas 64% and 6% had normal and low turnover, respectively.41 When bone formation rate was used as the discriminant variable, 19% were classified as having high turnover, 72% as having normal turnover, and 9% as having low turnover. Alternatively, in two studies of post¬ menopausal women with osteoporosis and their normal counter¬ parts, the same wide variation in turnover indices was found in both groups, leading to the conclusion that there were no impor¬ tant subsets of patients with osteoporosis.42,43 These studies, however, confirmed the earlier observations of others that, as a group, women with osteoporosis display a decrease in bone for¬ mation rate, and that some patients show profoundly depressed formation with little or no tetracycline uptake.38 From a clinical perspective, the impetus for classifying pa¬ tients with osteoporosis according to their turnover status stems from the notion that the turnover rate may influence the response to particular therapeutic agents. For example, patients with high turnover rates may respond better to antiresorptive treatments. There is evidence that this is true for calcitonin.44 However, in clinical practice, the biopsy is an impractical way to determine turnover status, and it is likely that biochemical markers of bone resorption and formation will be used increasingly for this pur¬ pose. In this regard, it is noteworthy that a high turnover group of patients also had elevated levels of bone Gla protein in serum.40 It is important to note that, in most cases, bone biopsy is performed when the disease is in an advanced stage, with multiple fractures already having occurred. It is probable that, in many cases, the disturbances in bone metabolism that led to the reduction in bone mass took place several years before the time of the biopsy and are no longer evident.443 Another confounding factor is that most patients who undergo biopsy for osteoporosis already have been treated with one or more pharmaceutical agents.

INDICATIONS FOR BIOPSY Because of the relatively recent availability of transiliac crest bone biopsy, the indications for this procedure are still evolving. Generally, biopsy of the iliac crest is useful only in diffuse dis¬

497

eases of the skeleton. A major use of the bone biopsy is as a diag¬ nostic tool in patients with skeletal disease manifested by bone pain, fractures, or osteopenia of unclear cause or pathogenesis. In such cases, a biopsy can provide important information about a pathologic process. There are only exceptional indications for performing this procedure in patients with localized skeletal dis¬ ease such as Paget disease of bone, primary bone tumors, or bone metastases involving the iliac crest. The indications for bone biopsy in women with postmeno¬ pausal osteoporosis are controversial. It would be difficult to per¬ form biopsies on the many women who have this disease. How¬ ever, bone biopsy can provide useful information in groups of patients less commonly affected by osteoporosis, such as young men and premenopausal women. Patients with osteopenia or women with postmenopausal osteoporosis should not undergo biopsy merely to measure cancellous bone volume to confirm the diagnosis of osteoporosis. The intraindividual and interindivid¬ ual variability in cancellous bone volume is too great, and there is too much overlap between cancellous bone volumes in patients with clinical osteoporosis and normal persons to make it useful. However, bone biopsy is useful to exclude subclinical osteoma¬ lacia. In one study, 5% of patients with typical crush fracture syndrome had clear-cut histologic evidence of osteomalacia de¬ spite normal biochemical and radiologic parameters.51 Moreover, the biopsy can be useful in defining, more precisely, the probable mechanisms of bone loss in individual patients with osteoporo¬ sis, and may aid in choosing the most appropriate course of ac¬ tion. For example, if the biopsy reveals a high bone turnover rate, it is important to carefully rule out endocrine disorders, such as hyperthyroidism and hyperparathyroidism. Finally, the biopsy is the best available way to evaluate the effect of various therapeu¬ tic maneuvers on bone cell function.52 Persons with renal osteodystrophy represent another group of patients in whom a transiliac crest bone biopsy may be ex¬ tremely helpful. Once again, however, the large number of pa¬ tients with renal disease precludes the use of this procedure in every case. Generally, if a symptomatic patient has biochemical evidence of secondary hyperparathyroidism (hyperphos¬ phatemia, hypocalcemia, and markedly elevated intact PTH lev¬ els), biopsy is unnecessary because it almost certainly will reveal osteitis fibrosa. However, patients with renal disease who have bone pain and fractures but who do not have the biochemical hallmarks typical of secondary hyperparathyroidism should un¬ dergo biopsy to determine whether they have osteomalacia or idiopathic aplastic bone disease, and whether aluminum accu¬ mulation appears to be the primary etiologic factor. Although bi¬ opsy can be useful in the clinical management of certain patients with bone disease, its primary use today is as a powerful research tool.

REFERENCES 1. Frost HM. Bone histomorphometry: choice of marking agent and labeling schedule. In: Recker RR, ed. Bone histomorphometry: techniques and interpreta¬ tion. Boca Raton, FL: CRC Press, 1983:37. 2. Parfitt AM. The physiological and clinical significance of bone histomorphometric data. In: Recker RR, ed. Bone histomorphometry: techniques and inter¬ pretation. Boca Raton, FL: CRC Press, 1983:143. 3. Rao DS. Practical approach to bone biopsy. In: Recker RR, ed. Bone histomorpbometry: techniques and interpretation. Boca Raton, FL: CRC Press, 1983:3. 4. Bordier P, Matrajt H, Miravet B, Hioco D. Mesure histologique de la masse et de la resorption des travees osseuse. Pathol Biol (Paris) 1964; 12:1238. 5. Dempster DW. The relationship between the iliac crest bone biopsy and other skeletal sites. In: Kleerekoper M, Krane S, eds. Clinical disorders of bone and mineral metabolism. New York: Mary Ann Liebert, Inc, 1988:247. 6. Baron R, Vignery A, Neff L, et al. Processing of undecalcified bone speci¬ mens for bone histomorphometry. In: Recker RR, ed. Bone histomorphometry: tech¬ niques and interpretation. Boca Raton, FL: CRC Press, 1983:13. 7. Villanueva AR. Bone. In: Sheehan DC, Hrapchak BB, eds. Theory and practice of histotechnology. St Louis: CV Mosby, 1980:89. 8. Parfitt AM. Stereological basis of bone histomorphometry; theory of quan¬ titative microscopy and reconstruction of the third dimension. In: Recker RR, ed. Bone histomorphometry: techniques and interpretation. Boca Raton, FL: CRC Press, 1983:53.

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PART IV: CALCIUM AND BONE METABOLISM

9. Malluche HH, Meyer WA, Sherman D, et al. A new semiautomatic method for quantitative static and dynamic bone histology. Calcif Tissue Int 1982; 34:439. 10. Malluche HH, Faugere M-C. Atlas of mineralized bone histology. Basel: Karger, 1987. 11. Frost HM. Bone histomorphometry: analysis of trabecular bone dynam¬ ics. In: Recker RR, ed. Bone histomorphometry: techniques and interpretation. Boca Raton, FL: CRC Press, 1983:109. 12. Eriksen EF. Normal and pathological remodeling of human trabecular bone: three dimensional reconstruction of the remodeling sequence in normals and in metabolic bone disease. Endocr Rev 1986; 7:379. 13. Parfitt AM, Drezner MK, Glorieux FH, et al. Bone histomorphometry: standardization of nomenclature, symbols, and units. J Bone Miner Res 1987; 2:595. 14. Frost HM. Bone remodeling and its relationship to metabolic bone dis¬ eases. Springfield, IL: CC Thomas, 1973. 15. Parfitt AM. Bone remodeling: relationship to the amount and structure of bone, and the pathogenesis and prevention of fractures. In: Riggs BL, Melton LJ III, eds. Osteoporosis: etiology, diagnosis, and management. New York: Raven Press, 1988:45. 16. Dempster DW. Bone remodeling. In: Coe FL, Favus M], eds. Disorders of bone and mineral metabolism. New York: Raven Press, 1992:355. 17. Melsen F, Mosekilde L, Kragstrup J. Metabolic bone diseases as evaluated by bone histomorphometry. In: Recker RR, ed. Bone histomorphometry: techniques and interpretation. Boca Raton, FL: CRC Press, 1983:265. 18. Parisien M, Silverberg SJ, Shane E, et al. The histomorphometry of bone in primary hyperparathyroidism: Preservation of cancellous bone structure. J Clin Endocrinol Metab 1990; 70:930. 19. Parisien MV, Mellish RWE, Silverberg SJ, et al. Maintenance of cancellous bone connectivity in primary hyperparathyroidism: trabecular strut analysis. J Bone Miner Res 1992; 7:913. 20. Teitelbaum SL. Pathological manifestations of osteomalacia and rickets. J Clin Endocrinol Metab 1980;9:43. 21. Jaworksi ZFG. Histomorphometric characteristics of metabolic bone dis¬ ease. In: Recker RR, ed. Bone histomorphometry: techniques and interpretation. Boca Raton, FL: CRC Press, 1983:241. 22. Sins ES, Clemens TL, Dempster DW, et al. Tumor-induced osteomalacia. Kinetics of calcium, phosphorus, and vitamin D metabolism and characteristics of bone histomorphometry. Am J Med 1987; 82:307. 23. Malluche HH, Ritz E, Lange HP, et al. Bone histology in incipient and advanced renal failure. Kidney Int 1976;9:355. 24. Hodsman AB, Sherrard DJ, Alfrey AC, et al. Bone aluminum and histo¬ morphometric features of renal osteodystrophy. J Clin Endocrinol Metab 1982;54: 539. 25. Boyce BF, Fell GS, Elder HY, et al. Hypercalcemic osteomalacia due to aluminum toxicity. Lancet 1982;2:1009. 26. Dunstan CR, Hills E, Norman AW, et al. The pathogenesis of renal osteo¬ dystrophy: role of vitamin D, aluminum, parathyroid hormone, calcium and phos¬ phorus. Q J Med 1985;55:127. 27. Parisien M, Charhon SA, Mainetti E, et al. Evidence for a toxic effect of aluminum on osteoblasts: a histomorphometric study in hemodialysis patients with aplastic bone disease. J Bone Miner Res 1988;3:259. 28. Charhon SA, Berland YF, Olmer MJ, et al. Effects of parathyroidectomy on bone formation and mineralization in hemodialized patients. Kidney Int 1985;27:426. 29. Sherrard DJ, Hercz G, Pei Y, et al. The spectrum of bone disease in endstage renal failure—an evolving disorder. Kidney Int 1993; 43:435. 30. Coburn JW, Salusky IB. Hyperparathyroidism in renal failure: clinical features, diagnosis, and management. In: Bilezikian JP, Levine MA, Marcuo R, eds. The parathyroids. New York: Raven Press, 1994:721. 31. Slatopolsky E, Delmaz J. Bone disease in chronic renal failure and after renal transplantation. In: Coe FL, Favus MF, eds. Disorders of bone and mineral metabolism. New York: Raven Press, 1992:905. 32. Felsenfeld AJ, Rodriguez M, Dunlay R, Llach F. A comparison of para¬ thyroid gland function in haemodialysis patients with different forms of renal os¬ teodystrophy. Nephrol Dial Transplant 1991;6:244. 33. Salusky IB, Coburn JW, Brill J, et al. Bone disease in pediatric patients undergoing dialysis with CAPD or CCPD. Kidney Int 1988;33:975. 34. Moriniere P, Cohen-Solal M, Belbrik S, et al. Disappearance of aluminic bone disease in a long term asymptomatic dialysis population restricting Al(OH)3 intake: emergence of an idiopathic adynamic bone disease not related to aluminum. Nephron 1989;53:93. 35. Hercz F, Pei Y, Greenwood C, et al. Low turnover osteodystrophy with¬ out aluminum: the role of "suppressed" parathyroid function. Kidney Int 1993; 44: 860. 36. Meunier PJ, Sellami S, Briancon D, Edouard C. Histological heterogeneity of apparently idiopathic osteoporosis. In: Deluca HF, Frost HM, Jee WSS, et al, eds. Osteoporosis, recent advances in pathogenesis and treatment. Baltimore: University Park Press, 1981:293. 37. Parfitt AM, Matthews CHE, Villanueva AR, et al. Relationships between surface, volume and thickness of iliac trabecular bone in aging and in osteoporosis. Implications for the microanatomic and cellular mechanisms of bone loss. J Clin Invest 1983; 72:1396. 38. Whyte MP, Bergfeld MA, Murphy WA, et al. Postmenopausal osteopo¬ rosis; a heterogeneous disorder as assessed by histomorphometric analysis of iliac crest bone from untreated patients. AmJ Med 1982; 72:193. 39. Meunier PJ. Assessment of bone turnover by histomorphometry in osteo¬ porosis. In: Riggs BL, Melton LJ III, eds. Osteoporosis: etiology, diagnosis, and man¬ agement. New York: Raven Press, 1988:317.

40. Arlot ME, Delmas PD, Chappard D, Meunier PJ. Trabecular and endocortical bone remodeling in postmenopausal osteoporosis: comparison with normal postmenopausal women. Osteoporos Int 1990; 1:41. 41. Eriksen EF, Hodgson SF, Eastell R, et al. Cancellous bone remodeling in type I (postmenopausal) osteoporosis: quantitative assessment of rates of formation, resorption, and bone loss at tissue and cellular levels. J Bone Miner Res 1990; 5:311. 42. Kimmel DB, Recker RR, Gallagher JC, et al. A comparison of iliac bone histomorphometric data in post-menopausal osteoporotic and normal subjects. Bone Miner 1990; 11:217. 43. Garcia Carasco M, de Vernejoul MC, Sterkers Y, et al. Decreased bone formation in osteoporotic patients compared with age-matched controls. Calcif Tis¬ sue Int.l989;44:173. 44. Civitelli R, Gonnelli S, Zacchei F, et al. Bone turnover in postmenopausal osteoporosis. Effect of calcitonin treatment. J Clin Invest 1988; 82:1268. 44a. Steiniche T. Christiansen P, Vesterby A, et al. Marked changes in iliac crest bone structure in postmenopausal women without any signs of disturbed bone remodeling or balance. Bone 1994;15:73. 45. Bressot C, Meunier PJ, Chapuy MC, et al. Histomorphometric profile, pathophysiology and reversibility of corticosteroid-induced osteoporosis. Metab Bone Dis Relat Res 1979; 1:303. 46. Dempster DW. Bone histomorphometry in glucocorticoid-induced osteo¬ porosis. J Bone Miner Res 1989; 4:137. 47. Meunier PJ, Coindre JM, Edouard CM, Arlot ME. Bone histomorphome¬ try in Paget's disease; quantitative and dynamic analysis of Pagetic and nonpagetic bone tissue. Arthritis Rheum 1980; 23:1095. 48. Valentin-Opran A, Charhon SA, Meunier PJ, et al. Quantitative histology of myeloma-induced bone changes. Br J Haematol 1982;52:601. 49. Baron R, Gertner JM, Lang R, Vignery A. Increased bone turnover with decreased bone formation by osteoblasts in children with osteogenesis imperfecta tarda. Pediatr Res 1983; 17:204. 50. Ste-Marie LG, Charhon SA, Edouard C, et al. Iliac bone histomorphome¬ try in adults and children with osteogenesis imperfecta. J Clin Pathol 1984;37:1081. 51. Meunier PJ. Bone biopsy in diagnosis of metabolic bone disease. In: Cohn DV, Talmage R, Matthews JL, eds. Hormonal control of calcium metabolism. Pro¬ ceedings of the Seventh International Conference on Calcium Regulating Hor¬ mones. Amsterdam: Excerpta Medica, 1981:109. 52. Holland EFN, Chow JWM, Studd JWW, et al. Histomorphometric changes in the skeleton of postmenopausal women with low bone mineral density treated with percutaneous estradiol implants. Obstet Gynecol 1994; 83:387.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

55_

MARKERS OF BONE METABOLISM MARKUS J. SEIBEL, SIMON P. ROBINS, AND JOHN P. BILEZIKIAN

Bone is a metabolically active tissue that throughout life un¬ dergoes constant remodeling. Skeletal turnover is maintained by two counteracting, usually balanced processes: bone formation and bone resorption. Bone formation is a function of osteoblast activity, and bone resorption is attributed to osteoclast activity. The underlying metabolic and cellular events responsible for bone remodeling are regulated by several systemic and local modulators, such as parathyroid hormone, vitamin D, sex hor¬ mones, glucocorticoids, calcitonin, prostaglandins, growth fac¬ tors (e.g., insulin-like growth factor), and numerous cytokines (see Chaps. 48, 49, 50, 53, 54, and 169). Under physiologic conditions, bone formation and bone re¬ sorption are coupled to each other. In adulthood, however, a slight inefficiency may develop such that bone formation does not quite match bone resorption, a situation believed to account in part for age-related bone loss in women and men. This slight imbalance is usually too subtle to be detected by parameters of bone metabolism, including calcium balance and measurement of bone markers. In metabolic bone diseases, a greater imbalance of bone turnover often occurs and is more readily detectable. For example, reduced bone formation, caused by decreased osteoblast

Ch. 55: Markers of Bone Metabolism

FORMATION

499

RESORPTION

AP BAP

TRAP

Osteocalcin OH - Proline Ca++ in Urine

CollagenPropeptides (PICP, PINP, PIIINP)

HydroxylysineGlycosides Pyridinium Crosslinks (PYD, DPD) Crosslinked Telopeptides (ICTP, INTP)

Osteopontin

Osteoblast

MATRIX

Osteoclast

activity, appears to be a predominant feature in corticosteroidinduced osteoporosis. Accelerated bone resorption, caused by in¬ creased osteoclast activity, is thought to be the initial event in postmenopausal bone loss. Hastened bone remodeling, caused by enhanced osteoblast and osteoclast activity, is a feature of ac¬ tive Paget disease of bone (see Chap. 64). These few examples illustrate that insight into the dynamics of bone turnover is often helpful in assessing clinical aspects of metabolic bone disease. Biochemical markers of bone turnover are noninvasive and extremely helpful tools in the assessment of metabolic bone dis¬ eases. In the clinical setting, these indices are mainly used for screening and diagnostic purposes, evaluating treatment regi¬ mens, and monitoring therapeutic effects. The various serum and urinary markers include enzymes released by osteoblasts or osteo¬ clasts and nonenzymatic peptides derived from the skeletal matrix during bone formation or bone resorption (Fig. 55-1). For clinical purposes, the markers of bone turnover are usually classified ac¬ cording to the metabolic process they are considered to reflect, either bone formation or bone resorption (Tables 55-1 and 55-2). Some bone markers, such as the serum amino-terminal procolla¬ gen type I propeptide and urinary hydroxyproline, are derived from anabolic and catabolic processes and are influenced by the rate of bone formation and bone resorption. Other markers, such as the bone isoenzyme of alkaline phosphatase or the urinary

FIGURE 55-1.

Schematic representation of the various bio¬ chemical markers of bone formation and bone resorption. AP, alkaline phosphatase; BAP, bone-specific alkaline phos¬ phatase; DPD, deoxypyridinoline; ICTP, carboxy terminal cross-linked telopeptide of type I collagen; INTP, aminoterminal cross-linked telopeptide of type I collagen; PICP, carboxy terminal propeptide of type I procollagen; PINP, amino-terminal propeptide of type I procollagen; PIIINP, amino-terminal propeptide of type III procollagen; PYD, pyridinoline; TRAP, tartrate-resistant acid phosphatase.

pyridinium cross-links of collagen, are more specific to the pro¬ cess of bone formation or bone resorption, respectively. Most of the compounds that are used as markers of skeletal metabolism are not unique to bone, and they occur in other tis¬ sues (see Tables 55-1 and 55-2). Few or perhaps none of the available markers is absolutely specific for bone. Moreover, most serum and urinary indices are influenced by nonskeletal diseases, such as inflammatory conditions, malignancies, and chronic re¬ nal or hepatic failure. Changes in biochemical markers of bone metabolism are not disease specific, and abnormal results should always be interpreted within the context of the clinical picture.

BIOCHEMISTRY OF BONE Bone is composed of approximately 70% mineral and 30% organic matter. The mineral, primarily in the form of hydroxyap¬ atite [Ca10(PO4)6(OH)2] crystals, is embedded in and aligned with the collagen fibrils, which play an important role in crystal for¬ mation. This calcium-collagen composite ensures the two main functions of bone: providing a structural framework and acting as a reservoir for mineral ions. The organic phase of bone is made of cells and a protein matrix, of which about 90% is collagen type I. Bone also contains a large number of different proteins, glycoproteins and proteo-

TABLE 55-1 Biomarkers of Bone Formation Marker (Abbreviation)

Tissue of Origin

Total alkaline phosphatase (AP, TAP)

Bone, liver, intestine, kidney, placenta

Bone-specific alkaline phosphatase (BAP)

Specimen

Method

Specificity

Serum

Colorimetric

In healthy adults 1:1 ratio between liver or biliary, and bonederived enzyme.

Bone

Serum

Colorimetric, electrophoretic, precipitation, IRMA

Specific product of osteoblasts; in some assays, cross-reactivity with liver isoenzyme.

Osteocalcin (OC, BGP)

Bone, platelets

Serum

RIA, ELISA

Specific product of osteoblasts; many immunoreactive forms in blood; some may be derived from bone resorption.

Carboxy terminal propeptide of type I procollagen (PICP)

Bone, soft tissue, skin

Serum

RIA, ELISA

Specific product of proliferating osteoblasts and fibroblasts.

Amino-terminal propeptide of type I procollagen (PINP)

Bone, soft tissue, skin

Serum

RIA, ELISA

Specific product of proliferating osteoblast and fibroblasts; partly incorporated into bone extracellular matrix.

500

PART IV: CALCIUM AND BONE METABOLISM

TABLE 55-2 Biomarkers of Bone Resorption Marker (Abbreviation)

Tissue of Origin

Specimen

Method

Specificity

Hydroxyproline, total and dialysable

Bone, cartilage, soft tissue, skin, blood

Urine

Colorimetric, HPLC

All fibrillar collagens and partly collagenous proteins, including Clq and elastin; present in newly synthezised and mature collagen.

Pyridinoline (PYD; Pyr)

Bone, cartilage, tendon, blood vessels

Urine

HPLC, ELISA

Collagens, with highest concentrations in cartilage and bone; absent from skin; present in mature collagen only.

Deoxypyridinoline (DPD, d-Pyr)

Bone, dentin

Urine

HPLC, ELISA

Collagens, with highest concentration in bone; absent from cartilage or skin; present in mature collagen only.

Carboxy terminal cross-linked telopeptide of type I collagen (ICTP)

Bone, skin

Serum

RIA

Collagen type I, with highest contribution probably from bone; may be derived from newly synthezised collagen.

Amino-terminal cross-linked telopeptide of type I collagen (1NTP, NTX)

Bone, skin

Urine

ELISA

Collagen type I, with highest contribution probably from bone.

Hydroxylysine glycosides

Bone, soft tissue, skin, serum—complement

Urine

HPLC

Collagens and collagenous proteins; glycosylgalactosyl-OHLys in high proportion in collagens of soft tissues, and Clq; Galyctosyl-OHLys in high proportion in skeletal collagens.

Tartrate-resistant acid phosphatase (TRAP)

Bone, blood

Plasma, serum

Colorimetric, RIA

Osteoclasts, platelets, erythrocytes.

Free 7-carboxyglutamic acid (GLA)

Bone, blood

Serum, urine

HPLC

Derived from bone proteins (e.g., osteocalcin, matrix Gla protein) and from blood clotting factors.

(OH-Pro, OHP)

glycans, many of which are negatively charged (Table 55-3). Al¬ though their precise functions are not established, these noncollagenous proteins are probably associated with the organization and mineralization of the skeletal matrix. Collagen is synthesized by osteoblasts as a larger precursor molecule. This "procollagen" molecule contains the triple helix portion, which bears several hydroxyproline residues, and glob¬ ular extensions at the N- and the C-terminal ends (i.e., N- and Cterminal propeptides). After secretion of the collagen molecule, these propeptides are removed en bloc by specific proteases at the cell surface. The C-terminal propeptide remains intact and appears as a 100-kilodalton (kd) protein in the blood. The helical collagen molecules spontaneously assemble into fibrils, which are then covalently cross-linked to impart the necessary tensile strength. This process is initiated extracellularly through the ac¬ tion of a single enzyme, lysyl oxidase. Thereafter, reactions of the

lysine-derived aldehydes occur spontaneously and culminate in the formation of trifunctional pyridinium cross-links (Fig. 55-2). Unlike hydroxyproline, which is already present in the newly synthesized protein, the pyridinium cross-links are found exclu¬ sively in mature collagens of the established extracellular matrix. Of the two cross-link analogues produced, deoxypyridinoline is located primarily in bone collagen, and pyridinoline occurs in cartilage and other soft tissues (see Chap. 183). Of the noncollagenous proteins in bone, osteocalcin or bone Gla protein is one of the most abundant (~ 15%). The protein contains 49 amino acid residues, three of which are -y-carboxyglutamic acid. The latter are formed in a posttranslational vitamin K-dependent process and are ultimately released into the circu¬ lation on the breakdown of osteocalcin. Transcription of the os¬ teocalcin gene itself is controlled by 1,25-dihydroxyvitamin D3. A small proportion of the newly synthesized protein is transported

TABLE 55-3 Biochemical Components of Bone Components

Origin

Collagen type I Osteocalcin Matrix gla protein Osteonectin Osteopontin (BSP I) Bone sialoprotein (BSP 11) Fibronectin Thrombospondin PG-I (biglycan) PG-II (decorin) Alkaline phosphatase Acid phosphatase Albumin a2-HS-glycoprotein

Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoblast Osteoclast Liver Liver

Percentage of NCP

*

6nA> *

*

*

*

*

9

4-3 90 >90 80 50 50 40§ 4§

6-25 25-300 4—12f 4-28J 10-35 150-1500 4-12 50% ft

ACTH, corticotropin; CRH, corticotropin-releasing hormone; f, increased or positive; change.

t

decreased or negative; -*■, no

674

PART V: THE ADRENAL GLANDS

pression test may be abnormal in 30% of hospitalized patients. In contrast, urinary free cortisol has a very great sensitivity and specificity (uncorrected or corrected for creatinine) and is the most efficient screening method for Cushing syndrome in hospi¬ talized patients. Several factors can lower the sensitivity and specificity of these tests. First, cortisol secretion is episodic or pulsatile and can result in widely variable levels. A normal diurnal variation is a pattern in which plasma cortisol levels from 16:00 hours to mid¬ night are less than 75% of the 08:00 hour values. Values at 16:00 hours can show considerable overlap in normal individuals and patients with Cushing syndrome. The plasma cortisol value at 23:00 hours is probably superior, because only about 3% of pa¬ tients with Cushing syndrome have been shown to have normal plasma cortisol levels at that time. Frequent sampling for serum cortisol is useful but requires hospitalization and may be rela¬ tively expensive. Second, 30% to 50% of obese people, particu¬ larly those with abdominal obesity and without Cushing syn¬ drome, have increased cortisol secretion rates and urinary 17-hydroxycorticosteroids, but urinary free cortisol values in pa¬ tients with Cushing syndrome are separated by at least 60 Mg/ day from those in obese individuals, even when urinary 17hydroxycorticosteroids show a significant overlap.38,39 Third, medications that interfere with cortisol metabolism can affect the determination of 17-hydroxycorticosteroids. Fourth, a variety of drugs that cause induction of hepatic microsomal hydroxylating enzymes may increase the metabolism of metyrapone and dexamethasone and result in lower levels of these compounds than expected for the dose administered.40 Under these circumstances, the response to these drugs may be abnormal without the pres¬ ence of Cushing syndrome. Patients with Cushing disease who suppress normally with the low-dose dexamethasone test usually reveal a decrease in the clearance of dexamethasone, producing plasma dexamethasone levels that are higher than expected.41 The measurement of plasma dexamethasone together with cortisol can help exclude abnormalities in dexamethasone clear¬ ance. Rarely, patients with factitious Cushing syndrome, who have been taking pharmacologic doses of synthetic glucocorti¬ coids, present with a paradoxical finding of the clinical manifes¬ tations of Cushing syndrome with suppressed ACTH and cortisol levels.

ANATOMIC LOCALIZATION DETECTION OF PITUITARY LESIONS After the diagnosis of Cushing disease has been established on clinical and biochemical grounds, the presence of pituitary lesions should be further determined by magnetic resonance im¬ aging (MRI) of the sella turcica. Because of the small size of most pituitary tumors associated with Cushing disease, the results of plain radiographic studies are often normal or misleading. Large microadenomas secreting ACTFf are extremely rare at the time the initial diagnosis of the disease is made. Flowever, small ( 1.6) verifies the pituitary source of ACTH. A right to left discrepancy may also help to lateralize ACTH secretion and aids in the pre¬ operative localization of the lesion. A lateralization of the source of ACTH by this procedure can help in cases in which a tumor is not found at the time of surgery. Partial resection of the side of the pituitary where the highest ACTH levels are recorded can be accompanied by remission of the disease. Failure to find the pituitary microadenoma or to induce cure after resection of the side of the pituitary with the highest concentration of ACTH may be due to failure to remove completely the involved part of the pituitary gland or to the possibility that confluent pituitary veins do not invariably drain into the ipsilateral inferior petrosal sinus, with a microadenoma in the opposite side of the pituitary gland.43 Another possibility is the presence of multiple microadeno¬ mas. The administration of CRH at the time of catheterization may enhance differences between the two sides; however, a si¬ multaneous response by the uninvolved gland may blur the differences. To correct for unequal dilution by nonpituitary venous blood, other pituitary hormones, including prolactin, thyroidstimulating hormone (TSH), human chorionic gonadotropin, and a subunit have been measured simultaneously. It was assumed that an ACTH-secreting microadenoma would not cause unequal delivery of these hormones into the two inferior petrosal sinuses, but correction of the ACTH gradients by these hormones did not improve the discriminating ability of the test.44

DETECTION OF ADRENAL LESIONS Techniques for the anatomic localization of adrenal lesions include abdominal CT scans and MRI, ultrasonography, and adre¬ nal scintigraphy with 6-/3-(131-I)-iodomethyl-19-norcholesterol.45 These techniques are noninvasive and provide good definition of structure and function of the adrenal glands. Adrenocortical masses can be anatomically defined by CT scanning, MRI, or ultrasonography (Fig. 73-7). CT can identify adrenal lesions as small as 1 cm in diameter. This level of resolu¬ tion can be important in patients with adrenal carcinoma to de¬ tect involved lymph nodes and hepatic and pulmonary metasta-

Ch. 73: Cushing Syndrome

675

FIGURE 73-7.

A 13-cm left adrenal mass (A) with areas of necrosis was detected by CT scanning in a 72-year-old woman with abdominal pain. She also had pulmonary nodules consistent with metastatic adrenal carcinoma.

ses. Hepatic metastases are found in about 42% of patients, and pulmonary metastases are found in in 45%. MRI is also helpful. Adrenal carcinomas are hypointense compared with liver in Tl-weighted images. They are hyperintense compared with liver in T2-weighted images. The superior blood vessel identification and the multiplanar capacity of MRI may make it the modality of choice in evaluating the extent of disease and in planning surgical excision.46 Ultrasonography can help define the benign or malignant character of a lesion. Malignant lesions are heterogeneous in appearance, with focal or scattered echopenic or echogenic zones representing areas of tumor necrosis, hemorrhage, or calcification.47 Scintigraphy with iodocholesterol provides an image reflec¬ tive of the structure of the adrenal gland and information about its function. Patients with bilateral adrenocortical hyperplasia demonstrate bilateral increased adrenal uptake of iodocholes¬ terol. Patients with cortisol-secreting adrenocortical adenomas, which suppress pituitary ACTH secretion and the function of the contralateral gland, demonstrate unilateral concentration of the tracer. Patients with Cushing syndrome secondary to an adreno¬ cortical carcinoma fail to show tracer uptake on either side. Car¬ cinomas have relatively low functional capacity per gram of tis¬ sue and fail to concentrate iodocholesterol in quantities sufficient to produce an image.48 Occasionally, actively secreting carcino¬ mas may image in a manner indistinguishable from a benign tumor. Patients with primary macronodular hyperplasia may show asymmetric uptake, with greater activity on the side of the pre¬ dominant nodules. This finding is important in determining the presence of bilateral adrenocortical disease, because a CT scan or MRI may show a mass on one side, but surgical resection of that mass may not result in remission if the contralateral gland is also abnormal. Radiographic differences between patients with mac¬ ronodular hyperplasia secondary to ACTH-secreting pituitary adenomas and primary micronodular hyperplasia of the adrenal glands have been described. In macronodular adrenocortical hy¬ perplasia, the nodules are visible on CT or MRI, and in micro¬ nodular disease, the micronodules are seen microscopically, but the adrenal glands do not demonstrate focal masses.4

LOCALIZATION OF ECTOPIC ACTH-SECRETING LESIONS The localization of ectopic sources of ACTH involves a variety of procedures, including CT of the chest, CT or MRI of the abdomen, thyroid scan, and selective venous catheterization and sampling in search of concentration gradients of ACTH (Fig. 73-8). Approximately 50% of these tumors are within the thorax

FIGURE 73-8. Selective venous catheterization and sampling in a 55year-old man with ectopic ACTH-dependent Cushing syndrome. ACTH levels (pg/mL) were measured in samples obtained throughout the ve¬ nous system. A peak level in the left innominate vein led to the discovery of a malignant, ACTH-secreting thymoma.

(e.g., small cell carcinomas, bronchial carcinoids, thymomas), and thoracic CT scans usually can localize the lesion. Other ACTH-secreting tumors are found in the pancreas (i.e., islet cell tumors), the thyroid (i.e., medullary carcinoma), and the adrenal medulla (i.e., pheochromocytoma). Ectopic ACTH-secreting carcinoids may be small and slow growing, and many years may elapse before they become radio¬ graphically apparent.50 Carcinoid tumors which possess somato¬ statin receptors may take up the somatostatin analogue octreo¬ tide. Using inIn-pentetreotide, it has been possible to detect these tumors as areas of increased uptake at the exact location of a suspected thoracic lesion seen on CT.51 Finding a pulmonary lesion may lead to a percutaneous bi¬ opsy for confirmation and eventual surgical excision of the lesion. The biopsy tissue can be analyzed by immunocytochemistry to demonstrate POMC-derived peptide secretory granules in the tu¬ mor cells or by extraction and analysis of the ACTH content in the tumor. The presence of POMC mRNA may also be a way of confirming that the tumor has the ability to produce ACTH.5‘

DIFFERENTIAL DIAGNOSIS OF CUSHING-TYPE HYPERCORTISOLISM AND PSEUDO CUSHING SYNDROME Hypercortisolism may exist in patients who do not have true Cushing syndrome. These patients suffer from obesity, depres-

676

PART V: THE ADRENAL GLANDS

sion, alcoholism, anorexia nervosa, bulimia, or acute stress. Be¬ cause their clinical presentation and biochemical findings overlap with those of patients with Cushing syndrome, the differential diagnosis can be challenging.

OBESITY Obese people, particularly those with abdominal or upper body segment obesity, share many of the metabolic, hormonal, and behavioral findings observed in Cushing syndrome. These include diabetes mellitus, hypertension, myocardial infarction, insomnia, and depression.25 Obesity is associated with increased cortisol production, as indicated by high cortisol secretion rates and urinary 17-hydroxycorticosteroids, but normal or slightly di¬ minished serum cortisol levels; these findings suggest an in¬ creased metabolic clearance rate for cortisol.39 Urinary free corti¬ sol is increased in proportion to the waist to hip ratio; these people also exhibit increased cortisol responsiveness to ACTH stimulation and to physical and mental stress.56 Unlike the well-defined causes of Cushing syndrome, the cause of the abnormality in adrenal function and its relationship to the complications of obesity have not been established. From the clinical standpoint, obese people do not usually exhibit signs of protein catabolism. Biochemically, they have a normal circa¬ dian rhythm of cortisol and ACTH secretion and suppress nor¬ mally with a low dose of dexamethasone.39

MAJOR DEPRESSIVE DISORDER Approximately 50% of patients with major depressive dis¬ order (MDD) hypersecrete cortisol and show early escape from the normal feedback inhibition by dexamethasone. Conversely, neuropsychiatric symptoms such as irritability, decreased libido, insomnia, and depressed mood also are frequently seen in pa¬ tients with Cushing syndrome. Deciding whether a patient with hypercortisolemia has primary depression or early Cushing syn¬ drome may be difficult. Some patients who eventually have a full-blown picture of Cushing syndrome begin with only in¬ termittent elevations of cortisol and symptoms of a major affec¬ tive disorder. Although similar in many respects to MDD, the depression seen in Cushing syndrome does have distinguishing clinical char¬ acteristics that may aid in the differential diagnosis. Irritability is a prominent and consistent feature, as are symptoms of auto¬ nomic activation such as shaking, palpitations, and sweating. De¬ pressed affect is often intermittent, and Cushing patients feel their best not their worst in the morning. Psychomotor retarda¬ tion is not so pronounced as to be clinically obvious, and most of these patients are not withdrawn, apathetic, or hopeless. Signifi¬ cant cognitive impairment, including disorder of memory, is a consistent and prominent clinical feature.57 Biochemically, pa¬ tients with Cushing syndrome exhibit higher cortisol levels than those with MDD, and these levels do not return to normal with antidepressants. The ACTH response to CRH may be helpful in the differential diagnosis. Although there is a substantial overlap between the two groups, patients with Cushing syndrome have a response, and those with MDD fail to respond to CRH.58

ALCOHOL-INDUCED PSEUDO CUSHING SYNDROME As originally described, patients with alcohol-induced pseudo Cushing syndrome present with moon facies, truncal obesity, easy bruising, and biochemical features consistent with hypercortisolism. They may fail to suppress normally with the 1.0 mg overnight dexamethasone test but recover normal suppressibility within 3 weeks of alcohol withdrawal. Similarly, the initially elevated 24-hour urinary free cortisol level returns to normal within a few days.59,60

CORTICOTROPIN-RELEASING HORMONE IN THE PATHOPHYSIOLOGY OF PSEUDO CUSHING SYNDROME CRH secretion may help to differentiate pseudo Cushing syndrome and true Cushing syndrome. Although CRH secretion may be increased in patients with pseudo Cushing syndrome, in most patients with ACTH-dependent or ACTH-independent Cushing syndrome, CRH secretion appears to be suppressed. When exogenous CRH is administered to patients with MDD, ambulatory alcoholics, and patients with anorexia nervosa, there is a diminished ACTH response compared with the increased re¬ sponse in patients with pituitary ACTH-dependent disease. Un¬ fortunately, there is a 25% overlap between the two groups.58

TREATMENT OF CUSHING DISEASE Optimal treatment of Cushing disease depends on an accu¬ rate diagnosis of the underlying pathology. Four approaches are used in the management of pituitary ACTH-dependent Cushing disease; pituitary surgery, pituitary irradiation, adrenal surgery, and drug therapy.7,61-63

PITUITARY SURGERY The treatment of choice is the microsurgical removal of mi¬ croadenomas or macroadenomas. If a pituitary adenoma or mi¬ croadenoma can be demonstrated by radiographic techniques, a transsphenoidal operation of the pituitary gland should be the preferred treatment. If a tumor is not detected by imaging tech¬ niques, a transsphenoidal exploration of the pituitary gland is still in order, because the tumor can be found in approximately 90% of patients.64^66 Even with considerable suprasellar extension, the tumor can be resected transsphenoidally. If a tumor invades the dura, total resection may be impossible, but good remission rates of 45% to 75% have been described for these cases. The microsurgical transsphenoidal selective resection of ACTH-secreting pituitary microadenomas is the most common treatment of Cush¬ ing syndrome and comes closest to the ideal form of treatment for this condition.67-69 Several reports have described a high cure rate with transsphenoidal surgical treatment of Cushing disease.64-66,70,71 The probability of finding pituitary pathology and of surgi¬ cally correcting the disease is highest among patients with a typ¬ ical endocrine testing pattern. 2 Typical diagnostic criteria for Cushing disease consist of elevated basal urinary 17-hydroxycorticosteroids and free cortisol, cortisol secretion rates, and mean basal serum cortisol levels; a positive response to metyrapone (i.e., elevated ACTH levels associated with a rise in urinary 17hydroxycorticosteroids); and abnormal suppression with lowdose dexamethasone but a greater than 50% suppression with high-dose dexamethasone. Patients with atypical diagnostic cri¬ teria have elevated basal levels but do not respond as described to metyrapone or to low or high doses of dexamethasone. Pituitary disease was found in 18 of 19 patients with typical preoperative endocrine test results but in only 6 of 11 patients with atypical test results. If a microadenoma can be identified and totally and dis¬ cretely resected, the remaining pituitary tissue remains func¬ tional, and patients can enjoy remission without loss of endocrine function.73 If a specific adenoma cannot be identified during sur¬ gery, the decision must be made about whether to perform a par¬ tial or total hypophysectomy. If preoperative inferior petrosal sinus sampling fias been carried out and is clearly lateralizing, an ap¬ propriate hemiresection of the hypophysis should be performed. If the endocrine studies strongly indicate a pituitary origin but the petrosal sinus sampling is not lateralizing and the patient does not wish to have children, a total hypophysectomy should be considered, but only after a lengthy preoperative discussion

Ch. 73: Cushing Syndrome with the patient regarding this possibility. If the patient wishes to have children, alternative forms of therapy including medical treatment or a total adrenalectomy must be considered. With transsphenoidal surgery, permanent anterior or posterior pitu¬ itary hormone deficiencies are rare. Transient diabetes insipidus may occur during the early weeks after surgery. Permanent dia¬ betes insipidus and cerebrospinal fluid rhinorrhea are uncom¬ mon complications with an initial procedure but may occur more commonly with repeated transsphenoidal surgery. Treatment failures are most common in patients with pituitary macroadeno¬ mas or in those in whom a distinct microadenoma has not been found. DELAYED RECURRENCE A delayed recurrence of Cushing disease after removal of a pituitary adenoma may be the result of regrowth of adenoma cells left behind in the peritumoral tissue during the first opera¬ tion. Attempts are usually made to prevent this cause of recur¬ rence by peritumoral edge resection after selective adenomec¬ tomy.65 The rates of disease recurrence vary among series, which may reflect the evaluation criteria and the technical ability of the pituitary neurosurgeons.74 After selective adenoma resection, it is common for patients to experience transient (6 months-2 years) secondary adrenal in¬ sufficiency requiring maintenance hydrocortisone replacement. During this period, the ACTH response to CRH is subnormal.75 If ACTH and cortisol do not fall to low levels, recurrence is more likely. Within 6 to 8 months after surgery, recovery of hypotha¬ lamic pituitary adrenal function and other tropic function usually takes place. The finding of transient deficiency of ACTH secre¬ tion after resection of a microadenoma favors the hypothesis of a pituitary origin of the disease. This contrasts with cases of CRH hypersecretion in which overstimulation of the residual corticotropes would be expected after the resection of the adenomatous tissue, leading to persistent or recurrent disease. SURGICAL RESULTS IN CHILDREN Transsphenoidal microadenomectomy is also successful in children and adolescents with Cushing disease.76 With successful treatment, growth retardation is replaced by catch-up growth or resumption of the growth rate; hypogonadism is followed by pu¬ bertal maturation and normal pubertal levels of gonadal steroids; and the blunted TSH response to thyroid-releasing hormone re¬ turns to normal. Effective treatment of Cushing disease must be instituted early to prevent early fusion of the epiphysis and per¬ manent stunting of growth.

PITUITARY IRRADIATION When transsphenoidal surgery has failed or alternative forms of treatment are desired, pituitary irradiation is an option. The most widely used type of pituitary irradiation is high voltage irradiation provided by cobalt-60 (60Co). The total recommended dose is 4000 to 5000 cGy, and favorable results can be effected in about 50% of patients.63 The best responses are observed in patients with the juvenile form of the disease or in adults younger than 40 years of age.7 When successful, 60Co irradiation has several advantages. Remission occurs with preservation of pituitary and adrenal function; panhypopituitarism seldom develops; normal repro¬ ductive function is restored when the patient is in remission; cor¬ ticosteroid replacement therapy is not needed; recurrence is rare; and normal cortisol secretion may be restored (i.e., circadian rhythm, normal suppressibility on dexamethasone).77 The major disadvantage is the slow therapeutic response to pituitary irradi¬ ation; 6 to 18 months may elapse before a clinical and biochemi¬ cal remission is achieved.

677

60Co irradiation alone is not adequate in patients who have severe Cushing syndrome. Symptoms may progress if the patient waits for remission, and severe, perhaps irreversible, complica¬ tions may result. Heavy particle beam irradiation and Bragg peak proton irradiation therapy, with a rate of improvement or re¬ mission as high as 80%, appears to be more effective than 60Co irradiation in the treatment of Cushing syndrome.78 79 However, the prevalence of postirradiation panhypopituitarism is high. Im¬ plants of gold-198 or yttrium-90 show complete or partial re¬ sponse in 77% of patients with Cushing disease, but the treat¬ ment is also complicated by hypopituitarism in 30% to 50% of the patients. Some reports suggest that significant disturbances of hypothalamic pituitary function follow megavoltage therapy; these may progress to overt hypopituitarism.80 The side effects and the efficacy of therapy may be related to the dosage regimen, with the greatest responses being observed when the highest dose of irradiation is administered. A higher incidence of postirradiation side effects, including radiation ne¬ crosis of the brain, occurs with higher dosage.81 Because this com¬ plication may occur from 2 to 20 years after completion of radia¬ tion therapy, its possibility should be entertained when local neurologic symptoms develop in patients with a history of radia¬ tion therapy for pituitary disease.

ADRENAL SURGERY In patients with advanced Cushing disease in whom trans¬ sphenoidal surgery has failed, bilateral total adrenalectomy is the preferred treatment. The major disadvantage of adrenalectomy is that it fails to attack the cause underlying the hypersecretion of ACTH. The complications may occur months or years later be¬ cause of the Nelson syndrome, with hyperpigmentation and an ACTH-secreting pituitary macroadenoma becoming clinically apparent.82 These ACTH-secreting tumors may become locally invasive and difficult to control by surgery or radiation therapy. Rarely, these tumors undergo distant metastases, and discrete he¬ patic metastatic nodules have been found. In a series of 79 con¬ secutive patients with Cushing disease treated with bilateral ad¬ renalectomy, there were three early postoperative deaths, but most patients did not fare worse than the general population.83 The most common cause of death among people who had un¬ dergone adrenalectomy for Cushing disease was cardiovascular in some cases, and in other cases, death was the result of the local effects of pituitary tumors.

DRUG THERAPY Various drugs have been used in the treatment of Cushing syndrome. They may act on neurotransmitters and decrease the secretion of ACTH, inhibit cortisol secretion, or compete with cortisol at the receptor level.

INHIBITORS OF ACTH SECRETION Cyproheptadine, bromocriptine, and sodium valproate have been used to suppress ACTH secretion and cause remission of Cushing syndrome. Cyproheptadine. Initially, it was reported that cyprohepta¬ dine in doses of up to 24 mg per day was able to suppress indices of cortisol secretion in patients with Cushing disease for a period of 3 to 6 months.84 This was associated with a prompt and sus¬ tained clinical remission. Urinary corticosteroid response to lowdose dexamethasone became normal during treatment, but the abnormal circadian periodicity of plasma cortisol persisted. The mechanism by which cyproheptadine caused this effect was thought to be an antiserotonin effect on the hypothalamus that inhibited ACTH secretion. Since then, there have been numerous positive and negative reports of the ability of cyproheptadine to suppress the biochemical and clinical manifestations of Cushing

678

PART V: THE ADRENAL GLANDS

disease. Sixty percent of 40 patients treated by various physicians with cyproheptadine had experienced satisfactory results.85 Un¬ desirable weight gain has been described as a consistent side effect of the drug. 4 Recurrence of the disease occurs in most pa¬ tients when therapy is interrupted, but there have been several isolated case reports of continued remission after the drug has been stopped.86 Cyproheptadine may be helpful in patients who need to be prepared for pituitary or adrenal surgery, because it may cause an amelioration of the metabolic abnormalities caused by Cushing syndrome. It has also been administered successfully to children in whom pituitary surgery is undesirable and during pregnancy complicated with Cushing syndrome.87 Although the response to cyproheptadine suggested that ACTH-producing tumors of the pituitary gland are responsive to hypothalamic regulation, other studies have shown a direct inhibitory effect of the drug in patients with macroadenomas as¬ sociated with Nelson syndrome.85 In these cases, cyproheptadine may act directly on the pituitary tumor and not by its antiseroto¬ nin effect.88 Bromocriptine. Bromocriptine, a dopamine receptor ago¬ nist, has not been consistently effective in the treatment of pa¬ tients with Cushing disease.89,90 In addition, those who respond require doses of bromocriptine larger than those that are used in the treatment of prolactinomas. Sodium Valproate. Several reports have shown that pro¬ longed treatment with sodium valproate is associated with im¬ provement in the clinical and biochemical manifestations of Cushing disease.91 The drug has been given in doses of 200 mg three times daily. Sodium valproate lowers plasma corticotropin levels and decreases urinary 17-hydroxycorticosteroids, 17ketosteroids, and free cortisol levels. It may also decrease the cor¬ ticotropin response to CRH. The mechanism by which sodium valproate inhibits corticotropin levels remains ill defined. It may suppress ACTH secretion through inhibition of 7-aminobutyric acid transaminase or by a direct effect on the pituitary microade¬ noma. It has been suggested that patients who respond to sodium valproate are those with intermediate lobe tumors, although it is not certain that such tumors occur in humans. Suppression of ACTH secretion by the drug has been observed in patients with pituitary adenomas associated with Nelson syndrome. Although sodium valproate remains an interesting drug from the research standpoint, it has not found a place in the standard pharmacologic treatment of patients with Cushing disease.

INHIBITORS OF ADRENAL FUNCTION Various inhibitors of adrenal function have been used to suppress cortisol secretion in patients with Cushing syndrome. They include aminoglutethimide, metyrapone, ketoconazole, trilostane, and mitotane. Aminoglutethimide. When initially used as an anticonvulsive drug, aminoglutethimide was observed to inhibit cortisol se¬ cretion. It was subsequently shown that aminoglutethimide effectively suppresses cortisol secretion in patients with adrenal cancer and ACTH-dependent Cushing disease.92,93 The mecha¬ nism of action of aminoglutethimide is the inhibition of choles¬ terol side chain cleavage and blocking of the conversion of cho¬ lesterol to As-pregnenolone in the adrenal cortex. As a result, the synthesis of cortisol, aldosterone, and androgens is inhibited. Histologically, the adrenocortical cells appear loaded with cho¬ lesterol droplets similar to the lipoidic form of congenital adrenal hyperplasia. Aminoglutethimide also inhibits the aromatization of androstenedione to estrone, an effect which has made it useful in the treatment of patients with carcinoma of the breast. The drug has been used in adults and in children in doses of 0.5 to 2 g daily.94,95 Cortisol levels fall gradually, and eventually, patients may need glucocorticoid replacement. In persons with cortisol-secreting adrenocortical carcinoma, the effect of amino¬ glutethimide can be maintained for many months with regres¬

sion of the clinical manifestations of Cushing syndrome.92 The drug is only transiently effective in patients with ACTHdependent Cushing syndrome. The inhibitory effect of the drug is overcome by the high levels of ACTH and cortisol levels, which return to pretreatment levels within days of instituting therapy.93 The effect of aminoglutethimide is promptly reversed by inter¬ ruption of therapy. Aminoglutethimide causes gastrointestinal (i.e., anorexia, nausea, vomiting) and neurologic (i.e., lethargy, sedation, blurred vision) side effects and can cause hypothyroidism in 5% of patients. A skin rash is frequently observed during the first 10 days of treatment, which usually subsides despite continuation of treatment. Headaches have also been observed when the larger doses are given. Metyrapone. Metyrapone is an 11-/3-hydroxylase inhibitor that is commonly used in the differential diagnosis of Cushing syndrome. It has also been used in the management of patients with Cushing disease. In doses of 250 mg twice daily to 1 g four times daily, patients experience biochemical and clinical re¬ mission. The total length of treatment has ranged from 2 to 66 months.96 Cortisol secretion is decreased, and production of 11deoxycortisol and DHEA, immediate and remote precursors of the blocked synthetic step, are increased. In ACTH-dependent Cushing syndrome, the production of 11-deoxycorticosterone, with its resultant mineralocorticoid effect, is also increased. Al¬ though plasma ACTH concentrations rise in these patients, the increase is insufficient to overcome the adrenal blockade induced by the drug. Metyrapone may cause hypertension and hypokalemic al¬ kalosis as the result of the accumulation of 11-deoxycorticoste¬ rone. In patients at risk for hypertensive crisis, such as pregnant women with preeclampsia, metyrapone may precipitate hyper¬ tensive emergencies. Metyrapone may also worsen hirsutism in these patients because of the increased production of adrenal an¬ drogens. Nausea, vomiting, and dizziness can result from treat¬ ment. Because of cost and side effects, it has been recommended that metyrapone only be used as an adjunct therapy in Cushing syndrome.9' Aminoglutethimide and metyrapone, with different effects on mitochondrial cytochrome P-450 enzymes, have been administered in combination with apparent additive effects.98 Ketoconazole. Ketoconazole is an imidazole derivative that inhibits the synthesis of ergosterol in fungi and cholesterol in t mammalian cells by blocking demethylation of lanosterol. In ad¬ dition to the effect on cholesterol synthesis, ketoconazole inhibits mitochondrial cytochrome P-450-dependent enzymes, such as 11-/3-hydroxylase and the enzymes needed for cholesterol side chain cleavage. The drug was also found to inhibit 3H-dexamethasone binding to glucocorticoid receptors in hepatoma tissue cul¬ ture cell cytosol and to block glucocorticoid action. Used in clinical practice as an antifungal medication, keto¬ conazole has been found to be a potent inhibitor of gonadal and adrenal steroidogenesis in vivo.99 In normal men, ketoconazole, administered in doses of 200 to 600 mg/day, is a potent inhibitor of testosterone production. Ketoconazole can also inhibit abnor¬ mal cortisol production in patients with adrenal adenoma and Cushing syndrome. These patients respond promptly, with dis¬ appearance of the clinical and metabolic manifestations of the disease within 4 to 6 weeks of treatment.99 The effect of ketoco¬ nazole appears to be persistent, because no escape from its sup¬ pressive effect has been reported for patients who receive the drug for prolonged periods. When patients are treated with keto¬ conazole, adrenal insufficiency is avoided by decreasing the dose sufficiently to maintain normal cortisol levels. The most frequent adverse reactions with this drug are nau¬ sea and vomiting, abdominal pain, and pruritus in 1% to 3% of patients. Hepatotoxicity, primarily of the hepatocellular type, has been associated with its use. This side effect should be monitored by liver function tests such as alkaline phosphatase, serum glutamic-oxaloacetic transaminase (SGOT), serum glutamicpyruvic transaminase (SGPT), and bilirubin, which should be

Ch. 73: Cushing Syndrome measured before starting treatment and at intervals during treat¬ ment. Transient minor elevations in liver enzymes have occurred during treatment, but the drug should be discontinued if even minor liver function test abnormalities persist, if the abnormali¬ ties worsen, or if they become accompanied by symptoms of pos¬ sible liver injury. Etomidate. Etomidate, an imidazole-containing anesthetic agent, can depress cortisol and aldosterone levels and severely impair the adrenal response to ACTH.100 This drug also inhibits 11-/3-hydroxylase and cholesterol side-chain cleavage enzymes in a manner similar to ketoconazole. Etomidate has not yet been used for treatment of patients with Cushing syndrome. Trilostane. Trilostane is an inhibitor of 3-/3-hydroxysteroid dehydrogenase and A5,4-isomerase, which results in a decreased conversion of pregnenolone to progesterone. Blocking of this en¬ zyme results in decreased synthesis of cortisol in the zona fasciculata, of aldosterone in the zona glomerulosa, and of androstenedione in the zona reticularis. Patients treated with trilostane in doses of 1000 to 1500 mg daily show improvement in the bio¬ chemical manifestations of the disease, with a 50% decrease in cortisol secretion, urinary free cortisol excretion, and plasma cor¬ tisol levels.101 However, trilostane has not been effective in a con¬ sistent enough manner for it to be recommended for the treat¬ ment of Cushing syndrome. Mitotane. Of all the pharmacologic agents described, mitotane is the only one that inhibits biosynthesis of corticosteroids and destroys adrenocortical cells secreting cortisol, producing a long-lasting effect. Mitotane acts on adrenocortical cell mito¬ chondria, where it inhibits 11-/3-hydroxylase and cholesterol side-chain cleavage enzymes. As a result of this inhibition, the production of cortisol, aldosterone, and DHEA is suppressed. Mi¬ totane appears to require metabolism for its action. Under the effect of mitochondrial P-450 monooxygenases, the drug is prob¬ ably transformed into an acyl-chloride, which covalently binds to important macromolecules in the cell mitochondria. The result is the destruction of the mitochondria with necrosis of the adre¬ nal cortex. The zona reticularis of the adrenal cortex appears to be most sensitive to the action of mitotane, and the glomerulosa is the least sensitive. A combination of 60Co irradiation of the pituitary gland with selective suppression of cortisol secretion with mitotane has been employed in the treatment of Cushing disease.102 Eighty percent of the patients treated with this drug plus pituitary irradiation

679

had clinical and biochemical remission of their disease (Fig. 73-9). One half of the patients treated by this combination of therapy had suppression of their elevated cortisol levels within 4 months of therapy. The initial decrease in cortisol secretion ap¬ peared to be a response to the administration of mitotane, be¬ cause plasma ACTH levels were still high when indices of cortisol secretion returned to normal. In addition to suppressing cortisol secretion, this drug appears to have a partial suppressive effect on ACTH. After suppression of cortisol secretion, there was minimal feedback increase in ACTH production, and in 70% of treated patients, an actual decrease in ACTH levels was observed. This response contrasts with the increase in ACTH levels in patients treated by adrenalectomy or with other adrenal inhibitors such as metyrapone. Mitotane is a selective inhibitor of the reticularis and fasciculata zones of the adrenal cortex. Aldosterone secretion is usu¬ ally spared, and the patients do not require mineralocorticoid re¬ placement when they develop adrenal insufficiency. The side effects of therapy include anorexia, nausea, diarrhea, somno¬ lence, pruritus, hypercholesterolemia, and hypouricemia. Ele¬ vated alkaline phosphatase levels can also occur as a result of the hepatotoxic effects of mitotane. Hypouricemia, a consistent finding, appears to be caused by increased renal clearance of uric acid. Low thyroxine levels found in patients treated with mito¬ tane are probably the result of interference with the competitive protein binding assay for this hormone. Mitotane competitively binds to thyroxine binding globulin in a manner similar to that of phenytoin, another diphenyl compound. Other indices of thy¬ roid function are in the normal range. All of the side effects de¬ scribed can be reversed by reducing the dose or by interrupting therapy. Mitotane also has well-known extraadrenal effects, derived from its effect as an inducer of microsomal hydroxylating en¬ zymes. As such, it can alter cortisol metabolism and the metabolic degradation of synthetic substituted steroids, which are predom¬ inantly inactivated by hydroxylation. A consequence of this effect is an early fall in the urinary excretion of 17-hydroxycorticosteroids, which occurs independently of its suppressive effects on cortisol secretion. Because of this effect, measuring urinary 17-hydroxycorticosteroid levels does not provide a reliable index of adrenal suppression by the drug. Changes in cortisol secretion rates, urinary free cortisol, and plasma cortisol levels are required to determine its biochemical response.

FIGURE 73-9. A, A 24-year-old man with severe Cushing disease failed to respond to 60Co pituitary irradiation. B, After mitotane therapy for 9 months, the features of Cushing syndrome disappeared.

680

PART V: THE ADRENAL GLANDS

Combined therapy with pituitary irradiation and mitotane chemotherapy can be given as primary medical treatment of Cushing syndrome when surgery is contraindicated or as the next modality of therapy when transsphenoidal pituitary surgery fails to bring about remission of the disease. The dose employed for the treatment of Cushing disease is 2 to 4 g daily. Therapy may be initiated with a dose of 500 mg twice daily and increased to 1 g four times daily, as needed to achieve adrenal suppressive effects. The urinary free cortisol excretion should be monitored, and the dose should be titrated to maintain the urinary free cortisol ex¬ cretion in the normal range. If adrenal insufficiency is suspected, hydrocortisone should be given orally. Because mitotane induces liver monooxygenases, which metabolize corticosteroids and other drugs, an adequate dose of fludrocortisone or hydrocorti¬ sone may be higher than expected. As the effect of radiation ther¬ apy becomes apparent with suppression of ACTH secretion, treatment with the drug can be gradually discontinued. RU-486. Mifepristone or RU-486 [17-/8-hydroxy-ll-/3-(4dimethyl amino)- 17-a-(l-propynyl)estra-4,9-dien-3-one] is a glucocorticoid antagonist which has been shown to effectively antagonize hypercortisolism causing Cushing syndrome.103 This compound is a 19-norsteroid with substitutions at positions Cu and C17; it antagonizes cortisol action competitively at the recep¬ tor level. With therapy, the somatic features of Cushing syn¬ drome ameliorate, mean arterial blood pressure is normalized, and suicidal depression can resolve. All biochemical glucocorti¬ coid sensitive parameters normalize, and ACTH and cortisol lev¬ els, as expected, remain unchanged. Although this drug may be effective in patients with autonomous cortisol production, the blocking effect of the compound on cortisol receptors may in¬ crease the secretion of ACTH in patients with pituitary ACTHdependent Cushing syndrome and cause a further increase in cortisol production. This additional cortisol production may be sufficient to overcome the antiglucorticoid effect of the drug. Mifepristone is well tolerated and nontoxic in doses ranging between 10 to 20 mg/kg/day. It is still an investigational drug, and its use is limited to investigational protocols.

TREATMENT OF ECTOPIC ADRENOCORTICOTROPIN SYNDROME Treatment of the ectopic ACTH syndrome involves the sur¬ gical resection of the primary tumor, followed by radiation ther¬ apy or chemotherapy, depending on the type of neoplasm pro¬ ducing the illness. In patients whose neoplasms cannot be resected, the use of adrenal inhibitors such as aminoglutethimide, metyrapone, and ketoconazole may ameliorate the clinical manifestations of the Cushing syndrome. However, the very high ACTH levels may overcome the suppressive effect of these drugs. Bilateral adrenalectomy is an alternative approach, but is not a practical one for patients who have rapidly progressive metastatic disease. However, because the underlying tumors may occasionally be slow growing (e.g., metastatic carcinoid, bron¬ chial carcinoids), an adrenalectomy followed by replacement therapy with normal amounts of hydrocortisone may improve considerably the metabolic consequence of the Cushing syndrome.

TREATMENT OF ACTH-INDEPENDENT CUSHING SYNDROME ADRENOCORTICAL ADENOMA Adrenocortical adenomas should be surgically removed.104 Because of suppression of the hypothalamic-pituitary-adrenal axis in these patients, adrenal insufficiency occurs postoperatively. These patients require replacement therapy with physio¬

logic doses of cortisol until recovery of the hypothalamic pitu¬ itary adrenal axis takes place. This may take 6 to 16 months.

ADRENAL CARCINOMA Adrenal carcinomas causing Cushing syndrome are highly malignant neoplasms resulting in a shortened life expectancy.1 5 Their treatment has not been well standardized, and the progno¬ sis has been poor regardless of therapy. Several approaches to therapy have been used. One method is surgical excision of the primary tumor and of large neoplastic abdominal masses. Although temporary remission of the disease frequently occurs with this approach, recurrence and eventual death from metastatic disease is the rule.106 Another approach is radiation therapy and nonspecific chemotherapy.107 These have been generally effective only for palliation of local disease, be¬ cause this neoplasm is generally resistant to these types of therapy. Agents that block corticosteroid hormone production by the tumor have also been used. Although effective in reversing the metabolic consequences of these tumors, these drugs do not alter the progression and eventual fatal outcome of the disease. Mito¬ tane has been the only drug which has proven effective in pa¬ tients with adrenocortical carcinoma.108 Most of the experience with mitotane comes from its use in patients with obvious metastases, but its effectiveness under those conditions has been dis¬ puted in the literature.106 109-111 Decreases in elevated urinary ste¬ roid levels, measurable disease response, and overall clinical response have been described.110 However, mean survival is short (8 months) when the drug is used after the appearance of metastatic disease. Isolated case reports have described impres¬ sive remissions and even cures of adrenocortical carcinoma after therapy with this drug.108'112,113 In general, survival appears to depend on the size of the primary lesion and the degree of local and distal extension of the neoplasm at the time of initial surgery. Criteria for staging adrenal cancer have been suggested. Patients with primary tumors smaller than 5 cm in diameter and without local or distal extension appear to have relatively good prognosis and longer survival. If mitotane therapy is to be effective, it should be instituted early, as adjuvant therapy, after the resection of the primary tu¬ mor and before local extension or distant metastasis has oc¬ curred.111114 Adverse effects of mitotane therapy are found to be dose dependent; they are intolerable with doses higher than 6 g daily. Treatment is usually begun with doses of 1 g twice daily and gradually increased up to tolerance. The drug should be ad¬ ministered with fat-containing food, because its absorption and transport appears to be coupled to lipoproteins. The prominent early side effects of larger doses are anorexia and nausea. The discomfort with these side effects can be minimized by adminis¬ tering the largest dose at bedtime so that patients will sleep through the most uncomfortable period. Side effects are usually reversed by interrupting therapy for several days and restarting the drug at a lower dose level. Because of possible teratogenic effects, patients on mitotane should be advised against pregnancy.

REFERENCES 1. Gold EM. The Cushing's syndromes: changing views of diagnosis and treatment. Ann Intern Med 1979;90:829. 2. Kathol RG, Delahunt JW, Hannah L. Transition from bipolar affective dis¬ order to intermittent Cushing's syndrome: case report. J Clin Psychiatry 1985;46: 194. 3. Kelly WF, Checkley SA, Bender BA. Cushing's syndrome and depression— a prospective study of 26 patients. Br J Psychiatry 1983; 142:16. 4. Reed K, Watkins M, Dobson H. Mania in Cushing's syndrome: case report. ] Clin Psychiatry 1983;44:416. 5. Saad MF, Adams F, Mackay B, et al. Occult Cushing's disease presenting with acute psychosis. Am J Med 1984; 76:759. 6. Starkman MN, Schteingart DE. Neuropsychiatric manifestations of pa¬ tients with Cushing's syndrome. Arch Intern Med 1981; 141:215.

Ch. 73: Cushing Syndrome 7. Schteingart DE. The diagnosis and medical management of Cushing's syn¬ drome. In: Thompson NW, Vinik AL, eds. Endocrine surgery update. New York: Grune & Stratton, 1983:87. 8. Daughaday, WH Cushing's disease and basophilic microadenomas—edi¬ torial retrospective. N Engl J Med 1984;310:919. 9. Lamberts SW], Delange SA, Stefanko SZ. Adrenocorticotropin-secreting pituitary adenomas originate from the anterior or intermediate lobe in Cushing's disease: differences in the regulation of hormone secretion. J Clin Endocrinol Metab 1982;54:286. 10. Lamberts SWJ, Stefanko SA, deLange SA, et al. Failure of clinical re¬ mission after transsphenoidal removal of a microadenoma in a patient with Cush¬ ing's disease: multiple hyperplastic and adenomatous cell nests in surrounding pi¬ tuitary tissue. ] Clin Endocrinol Metab 1980;50:793. 11. Young WF, Scheithauer BW, Gharib H, et al. Cushing's syndrome due to primary multinodular corticotrope hyperplasia. Mayo Clin Proc 1988; 63:256. 12. McKeever PE, Koppelman MCS, Metcalf D, et al. Refractory Cushing's disease caused by multinodular ACTH-cell hyperplasia. J Neuropathol Exp Neurol 1982:41:490. 13. VanCauter E, Refetoff S. Evidence for two subtypes of Cushing's disease based on the analysis of episodic cortisol secretion. N Engl J Med 1985:312:1343. 14. Glass AR, Zabadil AP, Halberg F, et al. Circadian rhythm of serum cortisol in Cushing's disease. ] Clin Endocrinol Metab 1984;59:161. 15. Schteingart DE, McKenzie AK. Twelve hour cycles of ACTH and cortisol secretion in Cushing's disease. J Clin Endocrinol Metab 1980;51:1195. 16. Liddle GW, Island DP, Ney RI. Cushing's syndrome caused by recurrent malignant bronchial carcinoid. Arch Intern Med 1963; 111:471. 17. Schteingart DE. Ectopic secretion of peptides of the proopiomelanocortin family. Endocrinol Metab Clin North Am 1991; 20:453. 18. Melmed S, Rushakoff RJ. Ectopic pituitary and hypothalamic hormone syndromes. Endocrinol Metab Clin North Am 1987; 16:805. 19. DeBold CR, Menefee JK, Nicholson WE, et al. Proopiomelanocortin gene is expressed in many normal tissues and in tumors not associated with ectopic adrenocorticotropin syndrome. Mol Endocrinol 1988;2:862. 20. White A, Clark AJ, Stewart MF. The synthesis of ACTH and related pep¬ tides by tumors. Baillieres Clin Endocrinol Metab 1990; 4:1. 21. Schteingart DE, Chandler WF, Lloyd RV, et al. Cushing's syndrome caused by an ectopic pituitary adenoma. Neurosurgery 1987;21:223. 22. Belsky JL, Cuello B, Swanson LW, et al. Cushing's syndrome due to ectopic production of corticotropin-releasing factor. ) Clin Endocrinol Metab 1985; 60:

496. 23. Schteingart DE, Lloyd RV, Akil H, et al. Cushing's syndrome secondary to ectopic CRH-ACTH secretion. J Clin Endocrinol Metab 1986; 63:770. 24. Marieb NJ, Spangler S, Kashgarian M, et al. Cushing's syndrome second¬ ary to ectopic cortisol production by ovarian carcinoma. J Clin Endocrinol Metab 1983:57:737. 25. Smalls AGH, Pieters GFFM, Van Haelst UJG, et al. Micronodular adreno¬ cortical hyperplasia in long standing Cushing's disease. ] Clin Endocrinol Metab 1983:58:25. 26. Lamberts SWJ, Bons EG, Bruining HA. Different sensitivity to adrenocorticotropin of dispersed adrenocortical cells from patients with Cushing's disease with macronodular and diffuse adrenal hyperplasia. J Clin Endocrinol Metab 1984:58:1106. 27. Shenoy BV, Carpenter PC, Carney JA. Bilateral primary pigmented nodu¬ lar adrenal cortical disease—rare cause of Cushing's syndrome. Am J Surg Pathol 1984;8:335. 28. Bohm N, Lippmann-Grob B, Petrykowski WV. Familial Cushing's syn¬ drome due to pigmented multinodular adrenocortical dysplasia. Acta Endocrinol 1983:102:428. 29. Wulffraat NM, Drexhaage HA, Wiersinga WM, et al. Immunoglobulins of patients with Cushing's syndrome due to pigmented adrenocortical micronodular dysplasia stimulate in vitro steroidogenesis. J Clin Endocrinol Metab 1988; 66:301. 30. Crapo L. Cushing's syndrome: a review of diagnostic tests. Metabolism 1971;28:955. 31. Kennedy L, Atkinson AB, Johnston H, et al. Serum cortisol concentrations during low dose dexamethasone suppression test to screen for Cushing's syndrome. BrMedJ 1984; 289:1188. 32. Sindler BH, Griffing GT, Melby JC. The superiority of the metyrapone test versus high dose dexamethasone test in the differential diagnosis of Cushing's syndrome. Am J Med 1983;74:657. 33. Abou-Samra AB, Fevre-Montange M, Pugeat M, et al. The value of betalipotropin measurement during the short metyrapone testing in patients with pitu¬ itary diseases and in Cushing's syndrome. Acta Endocrinol 1984; 105:441. 34. Bruno OD, Rossi MA, Contreras LN, et al. Nocturnal high dose dexameth¬ asone suppression test in the etiological diagnosis of Cushing's syndrome. Acta En¬ docrinol 1985; 109:158. 35. Abou Samra AB, Dechaud H, Estour B, et al. Beta-lipotropin and cortisol responses to intravenous infusion dexamethasone suppression test in Cushing's syndrome and obesity. J Clin Endocrinol Metab 1985; 61:116. 36. Chrousos GP, Schulte HM, Oldfield EH, et al. A corticotropin-releasing factor stimulation test—an aid in the evaluation of patients with Cushing's syn¬ drome. N Engl J Med 1984; 310:622. 37. Orth DN, DeBold CR, DeCherney GS, et al. Pituitary microadenomas causing Cushing's disease respond to corticotropin-releasing factor. J Clin Endocri¬ nol Metab 1982;55:1017. 38. Dunlap NE, Grizzle WE, Siegel AL. Cushing's—screening methods in hospitalized patients. Arch Pathol Lab Med 1985,-109:222. 39. Schteingart DE, Gregerman RI, Conn JW. A comparison of the character¬

681

istics of increased adrenocortical function in obesity and in Cushing's syndrome. Metabolism 1963; 12:484. 40. Werk EE, MacGee J, Sholiton LJ. Effect of diphenylhydantoin on cortisol metabolism in man. J Clin Invest 1964;43:1824. 41. Kapcala LP, Hamilton SM, Meikle AW. Cushing's disease with "normal suppression" due to decreased dexamethasone clearance. Arch Intern Med 1984; 144:636. 42. Oldfield EH, Chrousos GP, Schulte HM, et al. Preoperative lateralization of ACTH-secreting pituitary microadenomas by bilateral and simultaneous inferior petrosal venous sinus sampling. N Engl J Med 1985;312:100. 43. Snow RB, Patterson RH, Howith M, et al. Usefulness of preoperative in¬ ferior petrosal vein sampling in Cushing's disease. Surg Neurol 1988;29:17. 44. Zovickian J, Oldfield EH, Doppman JL, et al. Usefulness of inferior petro¬ sal sinus venous endocrine markers in Cushing's disease. J Neurosurg 1988;68:205. 45. Moses DC, Schteingart DE, Sturman MF, et al. Efficacy of radiocholesterol imaging of the adrenal glands in Cushing's syndrome. Surg Obstet Gynecol 1974; 139:1. 46. Smith SM, Patel SK, Turner DA, Matalon TA. Magnetic resonance im¬ aging of adrenal cortical carcinoma. Urol Radiol 1989; 11:1. 47. Hamper UM, Fishman EK, Hartman DS, et al. Primary adrenocortical car¬ cinoma: sonographic evaluation with clinical and pathological correlation in 26 pa¬ tients. AJR 1987;148:915. 48. Schteingart DE, Seabold JE, Gross MD, et al. lodocholesterol adrenal tis¬ sue uptake and imaging in adrenal neoplasms. J Clin Endocrinol Metab 1981;52: 1157. 49. Doppman JL, Miller DL, Dwyer AJ, et al. Macronodular adrenal hyperpla¬ sia in Cushing's disease. Radiology 1988; 166:347. 50. DeStefano D, Lloyd RV, Schteingart DE. Cushing's syndrome produced by a bronchial carcinoid tumor. Hum Pathol 1984; 15:890. 51. Philipponneau M, Nocaudie M, Epelbaum J, et al. Somatostatin analogs for the localization and preoperative treatment of adrenocorticotropin-secreting bronchial carcinoid tumor. J Clin Endocrinol Metab 1994; 78:20. 52. Barbareschi M, Mariscotti C, Frigo B, et al. Mediastinal malignant carci¬ noid with Cushing's syndrome: immunohistochemical and ultrastructural study. Appl Pathol 1989;7:161. 53. Coates PJ, Doniach I, Howlett TA, et al. Immunocytochemical study of 18 tumors causing ectopic Cushing's syndrome. J Clin Pathol 1986;39:955. 54. Doppman JL, Loughlin T, Miller DL, et al. Identification of ACTH produc¬ ing intrathoracic tumors by measuring ACTH levels in aspirated specimens. Radiol¬ ogy 1987;163:501. 55. Lapidus L, Bengtsson C, Hallstrom T, Bjomtorp P. Obesity, adipose tissue distribution and health in women. Results from a population study in Gothenburg, Sweden. Appetite 1989; 12:25. 56. Marin P, Darin N, Aneniva T, et al. Cortisol secretion in relationship to body fat distribution in premenopausal women. Metabolism 1992;41:882. 57. Starkman MN. The HPA axis and psychopathology. Cushing's syndrome. Psychiatr Ann 1993;23:691. 58. Gold PW, Loriaux DL, Roy A, et al. Responses to corticotropin-releasing hormone in the hypercortisolism of depression and Cushing's disease. N Engl J Med 1986:314:1329. 59. Rees LH, Besser GM, Jeffcoate WF, et al. Alcohol-induced pseudoCushing's syndrome. Lancet 1977; 1:726. 60. Lambert SW, KlijnJGM, deJongFH, Birkenhager JC. Hormone secretion in alcohol-induced pseudo-Cushing's syndrome: differential diagnosis with Cushing's disease. JAMA 1979;242:1640. 61. Aron DC. Cushing's syndrome: current concepts in diagnosis and treat¬ ment. Compr Ther 1987; 13:37. 62. Jeffcoate WJ. Treating Cushing's disease. Br Med J 1988; 296:227. 63. Orth D, Liddle GW. Results of treatment in 108 patients with Cushing's syndrome. N Engl J Med 1971;285:243. 64. Boggan JE, Tyrrell JB, Wilson CB. Transsphenoidal microsurgical manage¬ ment of Cushing's disease—report of 100 cases. J Neurosurg 1983; 59:195. 65. Nakane T, Kuwayama A, Watanabe M, et al. Long term results of trans¬ sphenoidal adenomectomy in patients with Cushing's disease. Neurosurgery 1987;21:218. 66. Pelkonen R, Eistola P, Grahme B, et al. Treatment of pituitary Cushing's disease: results of adrenal and pituitary surgery. Acta Endocrinol Suppl 1983; 251: 38. 67. Hardy J. Transsphenoidal surgery of hypersecreting pituitary tumors. In: Kohler PO, Ross GT, eds. Diagnosis and treatment of pituitary tumors. Amsterdam: Excerpta Medica, 1979:179. 68. Salassa RM, Laws ER Jr, Carpenter PC, et al. Transsphenoidal removal of pituitary microadenoma in Cushing's disease. Mayo Clin Proc 1978;53:24. 69. Tyrrell JB, Brooks RM, Fitzgerald PA, et al. Cushing's disease: selective transsphenoidal resection of pituitary microadenomas. N Engl J Med 1978; 289:753. 70. Kuwayama A, Kageyama N. Current management of Cushing's disease. Part I. Contemp Neurosurg 1985; 7:1. 71. Kuwayama A, Kageyama N. Current management of Cushing's disease. Part II. Contemp Neurosurg 1985; 7:1. 72. Chandler WF, Schteingart DE, Lloyd RV, et al. Surgical treatment of Cush¬ ing's disease. J Neurosurg 1987;66:204. 73. Schnall AM, Brodkey JS, Kaufman B, et al. Pituitary function after removal of pituitary microadenomas in Cushing's disease. J Clin Endocrinol Metab 1978; 47: 410. 74. Burch WM. Diagnosis and treatment of Cushing's disease at Duke Uni¬ versity (1977-1982). NC Med J 1983;44:293. 75. Avgerinos PC, Chrousos GP, Nieman LK, et al. The corticotropin-

682

PART V: THE ADRENAL GLANDS

releasing hormone test in the postoperative evaluation of patients with Cushing's syndrome. ] Clin Endocrinol Metab 1987;65:906. 76. Styne DM, Grumbach MM, Kaplan SL, et al. Treatment of Cushing's dis¬ ease in childhood and adolescents by transphenoidal microadenomectomy. N Engl J Med 1984;310:889. 77. Futterweit W, Krieger DT, Gabrilove JL. Adrenal cortical function studies in Cushing's syndrome due to nontumorous adrenocortical hyperfunction treated with pituitary irradiation. J Clin Endocrinol Metab 1962;22:364. 78. Kjellberg RN, Kliman B. A system for therapy of pituitary tumors. In: Kohler PO, Ross GT, eds. Diagnosis and treatment of pituitary tumors. Amsterdam: Excerpta Medica, 1973:234. 79. Lawrence JH, Okerlund MD, Linfoot JE, et al. Heavy particle treatment of Cushing's disease. N Engl J Med 1971;285:1263. 80. Sharpe GF, Kendall-Taylor P, Prescott RWG, et al. Pituitary function fol¬ lowing megavoltage therapy for Cushing's disease: long-term follow-up. Clin En¬ docrinol 1985; 22:169. 81. Aristizabal S, Caldwell WL, Avila J, et al. Relationship of time/dose fac¬ tors to tumor control and complications in the treatment of Cushing's disease by irradiation. Int J Radiat Oncol Biol Phys 1977;2:47. 82. Nelson DH, Meakin JW, Thorn GW. ACTH-producing pituitary tumors following adrenalectomy forCushing's syndrome. Ann Intern Med 1970;52:560. 83. Welbourn RB. Survival and cause of death after an adrenalectomy for Cushing's disease. Surgery 1985;97:16. 84. Krieger DT, Amorosa L, Linick F. Cyproheptadine-induced remission of Cushing's disease. NEnglJ Med 1975; 293:893. 85. Krieger DT. Cyproheptadine for pituitary disorders. N Engl J Med 1976;295:394. 86. Wiesen M, Ross F, Krieger DT. Prolonged remission of a case of Cushing's disease following cessation of cyproheptadine therapy. Acta Endocrinol (Copenh) 1983; 102:436. 87. Kasperlik-Zaluska A, Migdalska B, Hartwig W, et al. Two pregnancies in a woman with Cushing's syndrome treated with cyproheptadine—case report. Br J Obstet Gynecol 1980; 87:1171. 88. Ishibashi M, Yamaji T. Direct effects of thyrotropin-releasing hormone, cyproheptadine and dopamine on adrenocorticotropin secretion from human corticotroph adenoma cells in vitro. J Clin Invest 1981; 68:1018. 89. Kennedy AL, Sheridan B, Montgomery DAD. ACTH and cortisol response to bromocriptine: results of long-term therapy in Cushing's disease. Acta Endocri¬ nol 1978;89:461. 90. O'Mullane M, Walker B, Jefferson J, et al. Lack of effect of bromocriptine on ACTH levels in patients with bilateral adrenalectomy for pituitary-dependent Cushing's syndrome. J Endocrinol Invest 1978; 1:355. 91. Cavagnini F, Invitti C, Polly E. Sodium valproate in Cushing's disease. Lancet 1984;2:162. 92. Schteingart DE, Cash R, Conn JW. Aminoglutethimide and metastatic adrenal cancer. Maintained reversal (six months) of Cushing's syndrome. JAMA 1966; 198:1007. 93. Schteingart DE, Conn JW. Effects of aminoglutethimide upon adrenal function and cortisol metabolism in Cushing's syndrome. J Clin Endocrinol Metab 1967;27:1657. 94. Misbin Rl, Canary J, Willard D. Aminoglutethimide in the treatment of Cushing's syndrome. J Clin Pharmacol 1976; 16:645. 95. Zachman N, Gitzelmann RT, Zagalaka M, et al. Effect of aminoglutethi¬ mide on urinary cortisol and cortisol metabolites in adolescents with Cushing's syn¬ drome. Clin Endocrinol 1977;7:63. 96. Jeffcoate WJ, Rees LH, Tomlin S, et al. Metyrapone in long-term manage¬ ment of Cushing's disease. BrMedJ 1977;2:215. 97. Orth DN. Metyrapone is useful only as adjunctive therapy in Cushing's disease. Ann Intern Med 1978; 89:128. 98. Thoren M, Adamson U, Sjoberg HE. Aminoglutethimide and metyrapone in the management of Cushing's syndrome. Acta Endocrinol 1985; 109:451. 99. Sonino N, Boscaro M, Merola G, et al. Prolonged treatment of Cushing's disease by ketoconazole. J Clin Endocrinol Metab 1985; 61:718. 100. Feldman D. Ketoconazole and other imidazole derivatives as inhibitors of steroidogenesis. Endocrine Reviews 1986; 7:409. 101. Komanicky P, Spark RF, Melby JC. Treatment of Cushing's syndrome with trilostane (Win 24,540) an inhibitor of adrenal steroid biosynthesis. J Clin En¬ docrinol Metab 1978;47:1042. 102. Schteingart DE, Tsao HS, Taylor Cl, et al. Sustained remission of Cush¬ ing's disease with mitotane and pituitary irradiation. Ann Intern Med 1980;92:613. 103. Nieman LK, Chrousos GP, Kellner C, et al. Successful treatment of Cush¬ ing s syndrome with a glucocorticoid antagonist RU486. J Clin Endocrinol Metab 1985;71:536. 104. Scott HW, Abumrad NN, Orth DN. Tumors of the adrenal cortex in Cushing's syndrome. Ann Surg 1985; 201:586. 105. Huvos AJ, Hajdu SI, Brosfield RD, et al. Adrenal cortical carcinoma: clinicopathologic study of 34 cases. Cancer 1970; 25:354. 106. Hajjar RA, Hickey RC, Samaan NA. Adrenal cortical carcinoma: a study of 22 patients. Cancer 1975; 35:549. 107. Percarpio B, Knowlton AH. Radiation therapy of adrenal cortical carci¬ noma. Acta Radiol Oncol Radiat Phys Biol 1976; 15:288. 108. Becker D, Schumacher OP. o,p'-DDI) therapy in invasive adrenocortical carcinoma. Ann Intern Med 1977;82:677. 109. Hoffman DL, Mattox VL, Treatment of adrenocortical carcinoma with o,p'-DDD. Med Clin North Am 1972;50:999.

110. Hutter AM Jr, Kayhoe DE. Adrenal cortical carcinoma: results of treat¬ ment with o,p'-DDD in 138 patients. Am J Med 1966; 41:581. 111. Lubitz JA, Freeman L, Okun R. Mitotane use in inoperable adrenal corti¬ cal carcinoma. JAMA 1973; 223:1109. 112. Downing V, Eule J, Huseby RA. Regression of an adrenal cortical carci¬ noma and its neovascular bed, following mitotane therapy: a case report. Cancer 1974;34:1882. 113. Jarabak J, Rice K. Metastatic adrenocortical carcinoma: prolonged regres¬ sion with mitotane therapy. JAMA 1981;246:1706. 114. Schteingart DE, Motazedi A, Noonan RA, et al. The treatment of adrenal carcinoma. Arch Surg 1982; 117:1142.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

74

ADRENOCORTICAL INSUFFICIENCY D. LYNN LORIAUX

THE SYNDROMES OF ADRENAL INSUFFICIENCY The adrenal glands produce three classes of steroid hor¬ mone: glucocorticoid, mineralocorticoid, and adrenal androgen (ac¬ tually, androgen precursor). The primary glucocorticoid in hu¬ mans is hydrocortisone. This hormone is essential for life. The syndrome of adrenal insufficiency is the clinical manifestation of deficient production of this hormone. The central pathophysio¬ logic alteration is cardiovascular: reduced cardiac output and de¬ creased vascular tone with relative hypovolemia. This stimulates increased vasopressin secretion, resulting in water retention and hyponatremia. If salt balance is not maintained, which occurs if aldosterone also is deficient, hyponatremia is accompanied by hyperkalemia. Left untreated, this disorder leads to debility, prostration, coma, and death. The causes of adrenal insufficiency can be considered under two general headings: primary adrenal insufficiency (Addison disease), caused by destruction of the adre¬ nal glands themselves, and secondary adrenal insufficiency, caused by disordered hypothalamic-pituitary function leading to a rela¬ tive or complete deficiency of corticotropin (ACTH).

PRIMARY ADRENAL INSUFFICIENCY There are two main causes of primary adrenal disease: tu¬ berculosis and autoimmune adrenal destruction.1 The latter is a component of the polyendocrine deficiency syndrome2 (see Chap. 191). The causes of primary adrenal insufficiency are listed in Table 74-1. It is estimated that 70% of the cases of primary adrenal in¬ sufficiency in the industrialized world are associated with the polyendocrine deficiency syndrome. This disorder is autoim¬ mune. Findings that support this conclusion include a high prev¬ alence of suppressor T-cell abnormalities, the presence of anti¬ bodies against endocrine organs, and an association with other disorders of known autoimmune etiology such as vitiligo, alope¬ cia areata, celiac disease, autoimmune thyroiditis, and mucocu¬ taneous candidiasis.3,4 The histologic picture in the adrenal glands reveals lymphocytic infiltration, fibrosis, a loss of cortical cells, and an intact adrenal medulla. The disorder has two recognizable subtypes (Table 74-2). Type 1 is an illness of childhood, the mean age of onset being 12 years. Adrenal insufficiency, hypoparathyroidism, and mucocu¬ taneous candidiasis are the most common manifestations. Asso-

Ch. 74: Adrenocortical Insufficiency TABLE 74-1 Etiology of Adrenal Insufficiency Etiology

Occurrence (%)

PRIMARY ADRENAL INSUFFICIENCY Autoimmune (Polyendocrine deficiency syndrome)

70

Tuberculosis

20

Other

10

Fungal infections Adrenal hemorrhage Congential adrenal hypoplasia Sarcoidosis Amyloidosis Acquired immunodeficiency syndrome Adrenoleukodystrophy Adrenomyeloneuropathy Metastatic neoplasia Congential unresponsiveness to corticotropin

683

nosed by showing an increased plasma concentration of C-26 fatty acids and by demonstrating the pathognomonic, multilamellated inclusion bodies in the steroidogenic cells of the adrenal glands and testes. The two diseases differ in that adrenoleuko¬ dystrophy, a disorder of childhood, is dominated by a central neuropathy featuring cortical blindness and coma. Adrenomyelo¬ neuropathy, a disorder of young adults, is dominated by an ascend¬ ing mixed motor and sensory neuropathy culminating in spastic paraparesis. Metastatic cancer often is cited as a cause of adrenal insuffi¬ ciency. Although the adrenal glands are a common site of metas¬ tasis, these lesions uncommonly result in adrenal insufficiency.1. When adrenal insufficiency does occur in association with malig¬ nancy, it usually is an infiltrative neoplasm, such as lymphoma or leukemia, although metastatic carcinoma of the lung or breast are occasional offenders. Finally, the acquired immunodeficiency syndrome has an association with adrenal insufficiency (see Chap. 208). Whether this is the result of a direct effect of the virus on the adrenal glands or of a secondary superinfection (i.e., Cryptococcus, Myco¬ bacterium sp, or cytomegalovirus) remains unresolved.18-20

SECONDARY ADRENAL INSUFFICIENCY After exogenous glucocorticoids or corticotropin

Very common

SECONDARY ADRENAL INSUFFICIENCY

Common

Secondary adrenal insufficiency has three causes: adrenal suppression after exogenous glucocorticoid or ACTH administra¬ tion, adrenal suppression after the correction of endogenous glu¬ cocorticoid hypersecretion, and abnormalities of the hypothala¬ mus or pituitary gland leading to ACTH deficiency. The histologic appearance of the adrenal glands in second¬ ary adrenal insufficiency varies from normal-appearing glands to simple atrophy of the cortex with a normal medulla. Adrenal suppression by exogenous glucocorticoids is the most common cause of secondary adrenal insufficiency.21-23 The frequent use of glucocorticoids to treat inflammatory disorders, such as dermatitis, arthritis, and hepatitis, is the underlying rea¬ son. Supraphysiologic doses of glucocorticoids given long enough suppress hypothalamic corticotropin releasing hormone production and the ability of the anterior pituitary gland to re¬ spond to this hormone. The degree of adrenal suppression de¬ pends on three variables: dosage, schedule of administration, and duration of administration. Significant adrenal suppression is rarely seen with doses of hydrocortisone, or its equivalent, of less than 15 mg/m2/d. A divided dosage schedule is more sup¬ pressive than is a once-a-day or once-every-other-day schedule. Finally, the longer is the duration of administration, the greater is the likelihood of suppression. Treatment periods of less than 14 days, for example, rarely lead to clinically important adrenal suppression, whereas treatment periods long enough to allow the emergence of the signs of Cushing syndrome usually are usually associated with clinically significant suppression of adrenal func-

After the cure of Cushing syndrome (removing endogenous glucocorticoids) Hypothalamic and pituitary lesions

Uncommon

dated conditions include hypogonadism, pernicious anemia, chronic active hepatitis, and alopecia. The disorder has a reces¬ sive pattern of inheritance, clustering across sibships without ap¬ parent vertical transmission (see Chap. 181). Type 2 is a disorder of young adults. The mean age of onset is in the mid-20s. Adrenal insufficiency, autoimmune thyroid dis¬ ease, and diabetes mellitus are the most common manifestations. Associated immune disorders are rare. Susceptibility to this disorder seems to be inherited as a dominant trait in linkage disequilibrium with the HLA-B region of chromosome 6 (see Chap. 188). This form of the disease exhibits a vertical pattern of transmission.5 Worldwide, tuberculosis still is the most common cause of primary adrenal insufficiency6 (see Chap. 208). The adrenal glands can be replaced entirely by caseating granulomas. This phenomenon is virtually always accompanied by evidence of tu¬ berculosis in other organ systems, especially the lungs and kid¬ neys. Tuberculous adrenal glands are large and often contain calcium. This contrasts strikingly with the normal-sized or small, noncalcified glands found in patients with the polyendocrine de¬ ficiency syndrome. Also, fungi can colonize and destroy the adrenal cortex. All the commonly occurring fungi, except Candida, can cause adrenal insufficiency.7 10 Histoplasmosis is the most frequent. The adrenal glands are involved in more than one third of per¬ sons who die of histoplasmosis. This fungus is endemic in the Piedmont plateau of the Middle Atlantic states and in the Ohio and Tennessee valley regions of the Mississippi watershed. The gross and microscopic anatomic findings in adrenal glands in¬ fected with fungi are similar to those seen in tuberculosis. Rare causes of adrenal insufficiency include amyloidosis,11 adrenal hemorrhage12 (which is especially common during sepsis and anticoagulation), congenital adrenal hypoplasia, and two demyelinating disorders: adrenoleukodystrophy, or BrownSchilder disease, and adrenomyeloneuropathy, or sudanophilic leukodystrophy.14-16 The demyelinating diseases are similar in that they have an X-linked inheritance pattern (hence, are dis¬ eases of males) and markedly increased plasma C-26 fatty acid concentrations that are thought to reflect the biochemical abnor¬ mality responsible for the disorders. Both disorders can be diag¬

TABLE 74-2 Features of the Autoimmune Polyglandular Syndromes Characteristic Peak age of onset HLA association Hypoparathyroidism Mucocutaneous candidiasis Alopecia Chronic active hepatitis Pernicious anemia Hypogonadism Autoimmune thyroid disease Diabetes mellitus, type I

Type 1

Type 2

12 y

30 y B8 0 0 0 0 0 0 ++• +

None ++ ++ + + + + + 0

(From Neufeld M, MacLaren N, Blizzard R. Autoimmune polyglandular syndromes. Pediatr Ann 1980;9:154.)

684

PART V: THE ADRENAL GLANDS

tion. Secondary adrenal insufficiency can become manifest shortly after the cessation of corticosteroid therapy, or months later in a stressful setting such as an injury or a surgical proce¬ dure. The duration of impairment can be as long as 1 year after the correction of hypercortisolism.24 These findings have led to the conservative practice of replacing glucocorticoid before an anticipated stress in any patient who has received supraphysiologic dosages of glucocorticoids within the past year. An alterna¬ tive, and more satisfactory, practice is to test the functional ca¬ pacity of the adrenal glands directly with ACTH, basing the need for glucocorticoid supplementation on the results (see Chap. 76 for an extensive discussion of exogenous corticosteroid admin¬ istration and its complications).25 Any lesion of the hypothalamus or pituitary gland can lead to secondary adrenal insufficiency; examples include spaceoccupying lesions such as craniopharyngioma,26 pituitary ade¬ noma,27 metastases from distant malignancies,28 sarcoidosis,29 and infections with fungi (Nocardia, actinomycosis) or the tuber¬ cle bacillus.30 Trauma to the stalk or its blood supply also can lead to adrenal insufficiency.31 A deficiency of ACTH in the absence of any of these underlying causes is rare (see Chaps. 13 and 19).

SYMPTOMS AND SIGNS The symptoms and signs of primary and secondary adrenal insufficiency can be thought of in terms of chronic and acute syn¬ dromes.32 Symptoms of the chronic syndrome include weakness, fatigue, anorexia, nausea, abdominal pain, and diarrhea. An oc¬ casional patient, particularly with primary adrenal insufficiency, complains of orthostatic dizziness and, rarely, syncope. Signs in¬ clude weight loss and, particularly in primary insufficiency, or¬ thostatic hypotension. Symptoms and signs specific to primary adrenal insufficiency include salt craving and pigmentation of the skin and mucous membranes (Figs. 74-1 through 74-3). Vitiligo and alopecia also can occur in the autoimmune form of primary adrenal insufficiency.33 Radiologic findings include large, often calcified, glands in patients with an infectious cause.28 The symptoms of the acute syndrome include muscle, joint, and abdominal pain, and postural hypotension. Associated signs include fever, hypotension, and clouded sensorium. The patient may appear dehydrated. There is no hyperpigmentation in acute primary adrenal insufficiency, unless it is superimposed on a pa¬ tient with a prior chronic condition.

FIGURE 74-2. Patient with autoimmune adrenal insuffi¬ ciency. Note the darkening of sun-exposed areas of the face, neck, and arms; the dark nip¬ ples; and the darkened scars of the pretibial region. Other common sites of pigmentation in this disease are areas of pres¬ sure or irritation, such as the el¬ bows, knees, and knuckles.

LABORATORY FINDINGS The complete blood count can show a normocytic, normo¬ chromic anemia; neutropenia and eosinophilia (rarely greater than 10%); and a relative lymphocytosis. Common chemical ab¬ normalities include metabolic acidosis and prerenal azotemia. If the patient has not been eating, hypoglycemia can occur. Hypo¬ natremia is found in 90% of patients with chronic primary adre¬ nal insufficiency. Hyperkalemia occurs in 65%.34 Hypercalcemia occurs, but is rare35 (see Chap. 58). The electrolyte abnormalities differ in primary and second¬ ary adrenal insufficiency. The pattern of electrolyte alterations in primary adrenal insufficiency usually is dominated by deficient mineralocorticoid activity, leading to hyponatremia and hyper¬ kalemia. The electrolyte abnormalities in secondary adrenal in¬ sufficiency generally are dominated by water retention caused by increased vasopressin secretion, leading to a generalized hemodilution. Potassium concentrations are normal.36

DIAGNOSIS The diagnosis of adrenal insufficiency requires the presence of both clinical and chemical abnormalities compatible with the known manifestations of the disorder.

ACUTE ADRENAL INSUFFICIENCY Acute adrenal insufficiency should be suspected when hy¬ potension occurs in a patient with chronic adrenal insufficiency or in association with any of the known causes of adrenal in¬ sufficiency (see Table 74-1). When it is suspected, a blood sample should be drawn immediately for the measurement of plasma cortisol. Because plasma cortisol concentrations range between 20 and 120 jUg/dL during severe stress or shock in patients with normal adrenal function, a plasma cortisol concentration of less than 20 ug/dL favors a diagnosis of adrenal insufficiency. Treat¬ ment should not wait for the result but be initiated as soon as

Ch. 74: Adrenocortical Insufficiency

685

FIGURE 74-3. Patient with tuberculous Addison disease before (left) and 2 years after (right) com¬ mencement of cortisol therapy. The hyperpigmentation of the face and lips has disappeared. Note the lightening of the freckle (arrowhead).

the blood sample for cortisol has been obtained. Initial treatment should consist of the intravenous administration of 100 mg of hydrocortisone in association with steps to maintain blood pres¬ sure. Hydrocortisone, 100 mg every 6 hours, should be adminis¬ tered until the crisis is past or the diagnosis is excluded. Steps designed to establish a definitive diagnosis should be instituted immediately. CHRONIC ADRENAL INSUFFICIENCY When chronic adrenal insufficiency is suspected, or when the diagnosis of acute adrenal insufficiency is being confirmed, ACTH should be given as a screening test. Synthetic ACTH (Cortrosyn), 250 Mg, is given as an intravenous injection over 1 min¬ ute. Blood is drawn at 45 and 60 minutes for the measurement of cortisol.37 The lower limit of the normal response range is 20 Mg/ dL. (It should be noted that the results of this test may be normal in patients with adrenal insufficiency that immediately follows the removal of an exogenous or endogenous ACTH source38; see Chap. 72.) Two tests are useful for the differential diagnosis of chronic adrenal insufficiency: the measurement of plasma ACTH39 and computed tomography of the adrenal glands. High levels of plasma ACTH imply primary adrenal insufficiency; normal or low levels suggest secondary adrenal insufficiency.40 Finding large adrenal glands by computed tomography implies primary disease.41 Aldosterone deficiency also points to primary adrenal dis¬ ease. This can be diagnosed best by testing the ability of the pa¬ tient to retain salt.42 On a 10-mEq sodium diet, normal persons come into balance in 3 days. To the extent that a patient fails to do this, he or she requires salt supplementation or fludrocortisone treatment (see Chap. 76). An elevated resting plasma renin also is a rough guide to mineralocorticoid deficiency. Patients who appear to have secondary adrenal insufficiency without an obvi¬ ous cause, such as exogenous glucocorticoid or ACTH admin¬ istration, must undergo careful examination of the pituitary gland and hypothalamus by computed tomographic scanning or magnetic resonance imaging to exclude space-occupying lesions of these organs.

TREATMENT The treatment of adrenal insufficiency consists of replacing the missing hormones.43'44 The treatment of an adrenal crisis the¬

oretically would require about 200 mg of hydrocortisone daily. The standard regimen used in most centers provides 400 mg/d intravenously, about twice the amount calculated to be neces¬ sary. The basal production rate of cortisol has been thought to be about 12 to 15 mg/m2/d. Recent studies have challenged this, however, suggesting that the production rate of cortisol may be lower by as much as half. Nevertheless, replacement of cortisol at the rate of 12 to 15 mg/m2/d provides an adequate amount of bioactive cortisol at the cellular level. Although current practice favors a split dose of cortisol, the frequency of administration often can be reduced to once a day. In the author's experience, compliance is enhanced by a once-a-day regimen. The current standard of practice also recommends an in¬ crease in the rate of cortisol administration during stress. The definition of stress is vague, but conservative criteria include fe¬ ver above 38°C (100°F), surgical procedures or injuries, and gas¬ troenteritis with associated vomiting and diarrhea. Recent studies question the need for increased cortisol during such periods; until this is firmly demonstrated in humans, however, current guide¬ lines should be followed.45,46 The generally accepted guideline is that the daily dose of glucocorticoid should be doubled during periods of minor stress such as low-grade fever, vomiting, and diarrhea. In such circumstances, if the patient is not eating, the corticosteroid must be given parenterally. During periods of ma¬ jor stress, such as intraabdominal surgical procedures or major trauma, the dose of hydrocortisone should be increased to 200 mg/d. Once the stress has passed, usually by the second postop¬ erative day, the dose of glucocorticoid is reduced immediately and directly to the usual daily rate of 12 to 15 mg/m2 (see Chap. 76). The measurement of serum cortisol, serum ACTH, or urinary free cortisol, or of Porter-Silber chromogens is not a reliable guide to the appropriate maintenance dosage of glucocorticoid. Normal serum electrolyte levels, a good appetite, and a feeling of well¬ being are the best guides to adequate replacement. The appear¬ ance of the signs of Cushing syndrome, such as hypertension, weight gain, facial rounding, or supraclavicular puffiness, indi¬ cate overtreatment. Overtreatment also may result in diminished bone density.47 The production rate of aldosterone is about 100 Mg/d at all stages of life in salt-repleted humans.48 Fludrocortisone is roughly equipotent with aldosterone but is available only as an oral preparation. In normal persons, mineralocorticoid activity is supplied by both aldosterone and cortisol in roughly equal pro¬ portion. Thus, if cortisol is used for replacement, fludrocortisone, 100 Mg/d, will supply the remaining complement of mineralo¬ corticoid activity. If the glucocorticoid preparation used does not

686

PART V: THE ADRENAL GLANDS

have significant mineralocorticoid activity (i.e., prednisone or dexamethasone, which the author does not recommend for re¬ placement therapy), the dosage of fludrocortisone should be dou¬ bled. The serum potassium level is the best guide to the adequacy of mineralocorticoid replacement.

REFERENCES 1. O'Donnell WM. Changing pathogenesis of Addison's disease. Arch Intern Med 1950;86:266. 2. Loriaux DL. The polyendocrine deficiency syndromes. N Engl J Med 1985;312:1568. 3. Neufeld M, MacLaren N, Blizzard R. Autoimmune polyglandular syn¬ dromes. Pediatr Ann 1980; 9:154. 4. Vibo R, Aavik E, Peterson P, et al. Autoantibodies to cytochrome P450 enzymes P450 sec, P450 cl7, and P450 c21 in autoimmune polyglandular disease types 1 and II and in isolated Addison's disease. J. Clin Endocrinol Metab 1994; 78: 323. 5. Eisenbarth G, Wilson P, Ward F, Lebovitz HE. HLA type and occurrence of disease in familial polyglandular failure. N Engl J Med 1978; 298:92. 6. Irvine WJ, Barnes EW. Adrenocortical insufficiency. J Clin Endocrinol Metab 1972; 1:549. 7. Crispell KR, Parson W, Hamlin J. Addison's disease associated with histo¬ plasmosis. Am J Med 1956; 20:23. 8. Eberle DE, Evans RB, Johnson RH. Disseminated North American blasto¬ mycosis: occurrence with clinical manifestations of adrenal insufficiency JAMA 1977;238:2629. 9. Rawson AJ, Collins LH, Grant JL. Histoplasmosis and torulosis as causes of adrenal insufficiency. Am J Med Sci 1948;215:363. 10. Forbus WD, Beilerbreurtje AM. Coccidioidomycosis: a study of 95 cases of the disseminated type with special reference to the pathogenesis of the disease. Mil Surg 1946;99:653. 11. Irvine WJ, Toft AD, Feede CM. Addison's disease. In: James VHT, ed. The adrenal gland. New York: Raven Press, 1979:131. 12. O'Connell TX, Aston SJ. Acute adrenal hemorrhage complicating antico¬ agulant therapy. Surg Gynecol Obstet 1974,139:355. 13. Sperling MW, Wolfsen AR, Fisher DA. Congenital adrenal hypoplasia: an isolated defect of organogenesis. J Pediatr 1973; 82:444. 14. Schaumberg H, Powers JW, Raine CS. Adrenoleukodystrophy: a clinical and pathological study of 17 cases. Arch Neurol 1975;32:577. 15. Griffen JW, Goren E, Schaumberg H, et al. Adrenomyeloneuropathy: a probable variant of adrenoleucodystrophy. Neurology 1977;27:1107. 16. Blevins LS Jr, Shankroff J, Moser HW, Ladanson PW. Elevated plasma adrenocorticotropin concentration as evidence of limited adrenocortical reserve in patients with adrenomyeloneuropathy. J Clin Endocrinol Metab 1994; 78:261. 17. Sheeler LR, Myers JM, Eversham JJ, Taylor HC. Adrenal insufficiency secondary to carcinoma metastatic to the adrenal gland. Cancer 1983; 52:1312. 18. Tapper ML, Rotterdam HZ, Lerner CW, et al. Adrenal necrosis in the acquired immunodeficiency syndrome. Ann Intern Med 1984; 100:239. 19. Greene LW, Cole W, Green JB. Adrenal insufficiency as a complication of the acquired immunodeficiency syndrome. Ann Intern Med 1984; 101:497. 20. Aron DC. Endocrine complications of the acquired immunodeficiency syndrome. Arch Intern Med 1989; 149:330. 21. Danowski TS, Bonessi JV, Sabek G. Probabilities of pituitary-adrenal re¬ sponsiveness after steroid therapy. Ann Intern Med 1964; 101:11. 22. Plager JE, Cushman P. Suppression of the pituitary ACTH response in man by administration of ACTH or cortisol. J Clin Endocrinol Metab 1962; 22:147. 23. Jasani MK, Boyle TA, Dick WC, et al. Corticosteroid-induced hypothalamopituitary-adrenal axis suppression: prospective study using two regimens of cor¬ ticosteroid therapy. Ann Rheum Dis 1968; 27:352. 24. Graber AL, Ney RL, Nicholson WE. Natural history of pituitary-adrenal recovery following long term suppression with corticosteroids. J Clin Endocrinol Metab 1965;25:11. 25. Kehlet H, Binder C. Value of an ACTH test in assessing hypothalamicphuitary-adrenocortical function in glucocorticoid treated patients. BMJ 1973;2: 26. Banna M. Craniopharyngioma: a review article based on 160 cases Br I Radiol 1976;49:206. 27. Hankinson T, Banna M. Pituitary and parapituitary tumors. London: WB Saunders, 1976:51. 28. Vita JA, Silverberg SJ, Goland RS, et al. Clinical clues to the cause of Addison's disease. Am J Med 1985; 78:461. 29. Stuart CA, Neelon FA, Lebovitz HE. Hypothalamic insufficiency: the cause of hypopituitarism in sarcoidosis. Ann Intern Med 1978; 88:589. 30. Tandon PN, Pathak SN. Tuberculosis of the central nervous system. In: Tropical neurology. London: Oxford University Press, 1973:37. 335 ^ ®rteSa ^JV, Longridge NS. Fracture of the sella turcica. Injury 1975;6: 32. Thorn GW. Diagnosis and treatment of adrenal insufficiency. Springfield IL: Charles C Thomas, 1951. 6 33. Hertz KC, Gazze LA, Kirkpatrick CH, Katz SI. Autoimmune vitiligo: de¬ tection of antibodies to melanin producing cells. N Engl J Med 1977;297:634. 34. Lipsett MB, Pearson OH. Pathophysiology and treatment of adrenal cri¬ ses. N Engl J Med 1956; 254:511.

35. Jorgensen H. Hypercalcemia in adrenocortical insufficiency. Acta Med Scand 1973; 193:175. 36. Pearson OH, Whitmore WF, West CD. Clinical and metabolic studies of bilateral adrenalectomy for advanced cancer in man. Surgery 1953;34:543. 37. Lindholm J, Kehlet H, Blichert-Toft M. Reliability of the 30 minute ACTH test in assessing hypothalamic-pituitary-adrenal function. J Clin Endocrinol Metab 1978;47:272. 38. Kehlet H, Lindholm J, Bjerre P. Value of the 30 min ACTH test in assess¬ ing hypothalamic-pituitary-adrenocortical function after pituitary surgery in Cush¬ ing's disease. Clin Endocrinol (Oxf) 1984; 20:349. 39. Oelkers W, Diederich S, Bahr V. Diagnosis and therapy surveillance in Addison's disease: rapid adrenocortrotropin (ACTH) test and measurement of plasma ACTH, renin activity and aldosterone. J Clin Endocrinol Metab 1992;75: 259. 40. Schulte HM, Chrousos GP, Avgerinos P. The corticotropin-releasing hor¬ mone stimulation test: a possible aid in the evaluation of patients with adrenal in¬ sufficiency. J Clin Endocrinol Metab 1984;58:1064. 41. Schultz CL, Haaga JR, Fletcher BD. Magnetic resonance imaging of the adrenal glands: a comparison with computed tomography. Am J Radiol 1984-1431235. 42. Gill JR, Bell NH, Barrter FL. Impaired conservation of sodium and potas¬ sium in renal tubular acidosis. Clin Sci 1967;33:577. 43. Thorn GW, Lauler DP. Clinical therapeutics of adrenal disorders. Am J Med 1977;53:673. 44. Kehlet H, Binder C, Blichert-Toft M. Glucocorticoid maintenance therapy following adrenalectomy: assessment of dosage and preparation. Clin Endocrinol (Oxf) 1976;5:37. 45. Kehlet H. A rational approach to dosage and preparation of parenteral glucocorticoid substitution therapy during surgical procedures. Acta Anaesthesiol Scand 1975; 19:260. 46. Symreng T, Karlberg BE, Kagedal B, Schlidt B. Physiological cortisol sub¬ stitution of long term steroid-treated patients undergoing major surgery Br I Anaesth 1981;53:949. 47. Zelissen PM, Croughs RJ, van Rijk PP, Raymakers JA. Effect of glucocor¬ ticoid replacement therapy on bone mineral density in patients with Addison's dis¬ ease. Ann Intern Med 1994; 120:207. 48. New MI, Seaman MP, Peterson RE. A method for the simultaneous de¬ termination of the secretion rates of cortisol, 11-deoxycortisol, corticosterone, 11deoxycorticosterone, and aldosterone. J Clin Endocrinol Metab 1969;29:514.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

75_

CONGENITAL ADRENAL HYPERPLASIA PHYLLIS W. SPEISER

Congenital adrenal hyperplasia (CAH) is a group of inher¬ ited diseases caused by defective activity in one of five enzymes that contribute to the synthesis of cortisol from cholesterol in the adrenal cortex (Fig. 75-1). Details of normal adrenal steroidogen¬ esis are discussed in detail in Chapter 71. The term adrenal hyper¬ plasia derives from the tendency to glandular enlargement under the influence of adrenocorticotropin (ACTH) in an effort to com¬ pensate for inadequate cortisol synthesis. The alternate term ad¬ renogenital syndrome refers to the common associated finding of ambiguous external genitalia due to incidental deficiency or ex¬ cess production of adrenal androgens. Each particular enzyme deficiency produces characteristic alterations in the ratio of precursor hormone to product hormones. These hormonal imbalances are accompanied by clinically evident abnormalities, including abnormal development of the genitalia and pseudo¬ hermaphroditism, disturbances in sodium and potassium ho¬ meostasis, blood pressure dysregulation, and abnormal somatic growth1(Table 75-1). The molecular genetic basis for all but one of the enzymatic deficiencies is known; disease-causing muta¬ tions have been identified for the genes encoding the respective steroidogenic enzymes.

687

Ch. 75: Congenital Adrenal Hyperplasia Cholesterol

|

P450 see P450 cl7

P450 cl7

DHEA

17-OH-pregnenolone

Pregnenolone —

| 3/3-HSD

| 3P-HSD

| 3/3-HSD

|

P450C21

|

|

P450 cl 1

Estradiol*

Testosterone* —

P450 cl 1

| 11P-HSD

P450 ell

Cortisone*

18-OH-corticosterone

|

P450 arom

Cortisol

Corticosterone -

|

| 17P-HSD

| 17/3-HSD

P450C21

11-deoxycortisol

Deoxycorticosterone -

Estrone*

Androstenedione

17-OH-progesterone

Progesterone —

|

P450 arom

P450 cl7

P450 cl 7

P450 ell

Aldosterone

FIGURE 75-1.

The pathways of corticosteroid synthesis are diagrammed. Cholesterol is converted in several steps to aldosterone, cortisol, or sex steroids. Hormones marked by an asterisk (*) are produced largely outside the adrenal cortex. Deficiency of a given enzyme causes accumulation of hormonal precursors and a deficiency of products. DHEA, dehydroepiandrosterone; HSD, hydroxysteroid de¬ hydrogenase.

The most prevalent form of CAH is caused by deficiency of the cytochrome P450 enzyme, 21-hydroxylase (> 90% of cases), followed by a deficiency of 11-hydroxylase, 17-hydroxylase/ 17,20-lyase, and 3/3-hydroxysteroid dehydrogenase; deficiency of the side chain cleavage enzyme is rare. Deficiency of the en¬ zymes that do not impair cortisol synthesis do not come under the rubric of CAH and are therefore not discussed here. In addition to a classic form with onset in prenatal life, nonclassic forms of the enzyme deficiencies with onset in childhood or young adult life are also described.

EMBRYOLOGY The fetal gonads remain undifferentiated until about the seventh week of gestation (see Chap. 87). At that time, in normal 46,XY fetuses, the gene encoding the sex-determining factor of the Y chromosome (i.e., SRY and perhaps other autosomal genes) induce differentiation of Leydig cells within the testes. Testoster¬ one secretion begins by about 8 weeks of fetal life. In normal 46XX fetuses, the absence of high local concentrations of antimiil-

TABLE 75-1 • < . Clinical, Biochemical, and Genetic Characteristics of Congenital Adrenal Hyperplasia_ P450c21 \ P450c21 Characteristic_Enzyme_Enzyme_P450cll Enzyme Classic + in 46,XX

Nonclassic

3/3-HSD Enzyme

P450scc Enzyme

Classic + in 46,XY Mild in 46,XX +

Nonclassic

Classic +

P450cl7 Enzyme

3/3-HSP Enzyme

Classic + in 46,XY —Puberty in 2

Deficient phenotype Ambiguous genitalia

Classic + in 46,XX

Addisonian crisis Incidence (gen. pop.)

-1- in SW 1:14,000

1:100

Rare 1:100,000

~120 Cases

7

Common (?)

Hormones Glucocorticoids Mineralocorticoids Androgens

4 i in SW ff Prenatally

nl nl f postnatally

t ft Prenatally

i' t i

nl nl

Relative defi¬ ciency in 9

Relative defi¬ ciency in 2

Relative defi¬ ciency in 2

i

4 1 often 1 in 3 Weak androgens 1

1 Untreated 1 in SW f in SW + in SW

nl nl nl

t Often

f Often

t 1 ± Alkalosis

t

nl nl nl

± Alkalosis

\ 1 often f often -f if SW

++++ 170HP SW:del; nt 656 A —G SV: I172N

+ 170HP V281L

DOC, S R448H, frameshifts

DOC, B Term; frameshifts

DHEA, 17A5Preg Term, frameshifts

Estrogens Physiology Blood pressure Na balance K balance Acidosis Diagnosis Metabolite f Common mutations

+, present; ?, unknown; j, diminished quantity; waster; SV, simple virilizer; P450c, cytochrome P450; 11-deoxycortisol;

B, corticosterone;

nucleotide number; stitution;

DHEA,

f, increased quantity; 6, male; 9, female; nl, normal; SW, salt170HP, 17-hydroxyprogesterone; DOC, deoxycorticosterone; S,

dehydroepiandrosterone;

A-»G, transition of adenine to guanine;

17A5Preg, 17-A5-pregnenolone;

V281 L, mutation at valine 281 resulting in leucine substitution;

histidine substitution;

Term, termination mutation.

del, deletion;

nt,

1172N, mutation at isoleucine 172 resulting in asparagine sub¬ R448H, mutation at arginine 448 resulting in

f in 2 i

++ (lethal) Rare l \ 1 1

1 l t + None ?

688

PART V: THE ADRENAL GLANDS

lerian hormone allows differentiation of the ovaries, beginning at about 10 weeks' gestation (see Chap. 87). The internal genital duct structures are recognizable by 7 weeks. Mullerian ducts develop into the rostral third of the va¬ gina, the uterus, and fallopian tubes. Wolffian ducts develop into epididymis, vas deferens, seminal vesicles, and ejaculatory ducts under the influence of adequate local quantities of androgen. Embryonal development of the gonads and internal ducts are generally unaffected by vagaries in sex steroid hormone synthesis. In females, the external genitals' development is passive. The urogenital sinus differentiates into separate urethral and va¬ ginal orifices in normal females, and the labioscrotal folds remain separated by the labia minora, which hood the clitoris. In males, under the influence of high circulating levels of androgen, the urethral and genital orifices fuse to form an elongated penile ure¬ thra, and the labioscrotal folds fuse to form the scrotum. The latter changes may also occur in 46,XX fetuses exposed to high androgen levels from fetal adrenal or maternal sources. Con¬ versely, male external genitals may be hypoplastic if a defect ex¬ ists in testosterone synthesis or action. At about 7 weeks of gestation, the adrenal cortex differen¬ tiates from mesodermal tissues. Soon after, two adrenal zones form: a small peripheral adult cortex and a large inner fetal cor¬ tex. Steroid production by the fetal cortex begins in the latter half of the first trimester. Adrenal mass increases markedly during this time, and peaks at 15 weeks.3 General regulation of adrenal growth early in gestation is incompletely understood and is thought to be only partly attributable to adrenocorticotropic hor¬ mone (ACTH). Other likely trophic hormones include transform¬ ing growth factor-/? (TGF-/?), basic fibroblast growth factor (bFGF), and insulin-like growth factor-II (IGF-II).4 Beyond 20 weeks of gestation, adrenal growth and steroidogenesis are al¬ most exclusively responsive to ACTH. In utero administration of glucocorticoids should suppress fetal ACTH and, under most circumstances, inhibit adventitious adrenal steroid production in fetuses affected with a severe virilizing form of CAH (e.g., 21- or 11-hydroxylase deficiency).

CLINICAL FEATURES 21-HYDROXYLASE (P450c21) DEFICIENCY Patients with this commonly diagnosed enzyme deficiency cannot adequately synthesize cortisol. Insufficient cortisol syn¬ thesis results in overproduction of adrenal androgens, which are synthesized independently of 21-hydroxylase. Androgens in¬ duce somatic growth with inappropriately rapid advancement of

FIGURE 75-2.

External genitalia of a 2-month-old female infant with 21-hydroxylase deficiency.

linear growth, early epiphyseal fusion of the long bones, and short stature. Other features include precocious development of sexual hair, apocrine body odor, and penile or clitoral enlarge¬ ment. Reduced fertility may be observed in both sexes. Clinical features are outlined in Table 75-1. Females affected with the severe classic form of 21-hydrox¬ ylase deficiency are exposed to excess androgens prenatally and are born with masculinized external genitalia (Fig. 75-2). If the disease goes undiagnosed and the infant is untreated, further vir¬ ilization ensues (Fig. 75-3). About 75% of classic patients can¬ not synthesize aldosterone efficiently because of impaired 21hydroxylation of progesterone; these salt-wasting individuals fail to conserve sodium normally and usually come to medical atten¬ tion in the neonatal period with hyponatremia, hyperkalemia, and hypovolemic shock. The adrenal crises may prove fatal if proper medical care is not delivered. Patients with sufficient aldosterone production and no salt wasting who have signs of prenatal virilization and markedly increased production of hor¬ monal precursors of 21-hydroxylase (e.g., 17-hydroxyprogesterone) are referred to as simple virilizers. Earlier confusion regard¬ ing the origins of these two classic phenotypes has been resolved to a large extent by understanding the molecular genetics of the

Vagina

Urogenital sinus

FIGURE 75-3.

Variations in the differentiation of the external genitalia in congenital adrenal hyperplasia. In genetic females, adrenal androgen hypersecretion (enzymes 2, 4, and 5) is associated with various degrees of masculinization, leading to apparent male external genitalia. (From Grumbach MM, Ducharme ]. The effects of androgens on fetal development: androgen-induced female pseudohermaphroditism. Fertil Steril 1960,11:157.)

sinus

Ch. 75: Congenital Adrenal Hyperplasia disease, and it appears that allelic variation in the gene encoding active 21-hydroxylase (CYP21) is responsible for most pheno¬ typic variation, as is discussed later. Patients affected with the milder, nonclassic form of 21-hydroxylase deficiency may have signs of postnatal androgen excess.5 Except for rare cases with mild clitoromegaly, females with the nonclassic disorder are born with normal external geni¬ talia. The syndrome of polycystic ovarian disease has often been confused with nonclassic CAH 21-hydroxylase deficiency in young women with hirsutism, oligomenorrhea, and diminished fertility. Precise clinical distinction between the classic simple vir¬ ilizing disease and nonclassic disorder is sometimes difficult among males, because the hormonal reference standards for di¬ agnosis represent a continuum. Moreover, because males do not manifest ambiguous genitalia as a sign of in utero androgen ex¬ cess, the only other distinguishing clinical parameters are bone age and somatic growth pattern, which are nonpathognomonic. Phenotypic severity in nonclassic 21-hydroxylase deficiency var¬ ies greatly, and some individuals have been detected solely on the basis of hormonal or genetic testing in the course of family studies. Aldosterone synthesis is normal in patients with non¬ classic 21-hydroxylase deficiency. Table 75-2 describes features distinguishing salt-wasting, simple virilizing, and nonclassic forms of 21-hydroxylase deficiency. Table 75-3 describes specific mutations. Neonatal screening for 21-hydroxylase deficiency measur¬ ing heel-stick 17-hydroxyprogesterone levels has been effective in reducing neonatal morbidity and mortality.6 This has been particularly useful in males with salt-wasting disease in whom there is no obvious phenotypic clue to the diagnosis, such as am¬ biguous genitalia. The radioimmunoassay of heel-stick blood on filter paper was first employed on a wide scale among the Alas¬ kan Yup'ik Eskimos, who are one of two geographically isolated and genetically homogeneous groups at high risk for 21-hydrox¬ ylase deficiency CAH.7 Subsequently, many other newborn screening programs were developed for 21-hydroxylase defi¬ ciency CAH.8 The worldwide incidence of 21-hydroxylase defi¬ ciency CAH based on newborn screening is 1:14,554 live births; approximately 75% of infants detected in these programs manifest the salt-wasting phenotype.8 According to the HardyWeinberg law for populations at equilibrium, the heterozygote frequency for all classic 21-hydroxylase gene defects is 1:61 persons. A high frequency of nonclassic 21-hydroxylase deficiency has also been discerned.9 This disorder occurs most frequently among Ashkenazic Jews (1:27), but it is also common among other ethnic groups, such as Hispanics, residents of the former Yugoslavia, and Italians. Overall, in a mixed white population, the disease occurred in about 1 of 100 individuals. These esti¬ mates of disease frequency were derived indirectly based on re¬ sponse to ACTH stimulation combined with HLA typing. Con¬ firmation was obtained employing the statistical method of commingling distributions.111 Nonclassic 21-hydroxylase defi¬ ciency is among the most frequent autosomal recessive disorders in humans. Clinical investigation to diagnose nonclassic 21hydroxylase deficiency is warranted in any patient showing the

689

signs of androgen excess described previously; particularly high-risk groups include Ashkenazic Jews, children with preco¬ cious pubarche, and girls or women with hirsutism and oligomenorrhea.

11/3-HYDROXYLASE (P450c11) DEFICIENCY As in the case of 21-hydroxylase deficiency, patients with 11/3-hydroxylase deficiency channel accumulating precursor ste¬ roids into androgen pathways beginning in prenatal life, causing genital ambiguity in affected newborn females. Male infants show no abnormality of external genitalia. Later signs of andro¬ gen excess are observed in both sexes affected with 11/3-hydroxylase deficiency if the disease is not promptly recognized and treated.11 Patients with 11/3-hydroxylase deficiency account for approximately 5% of all CAH cases. Although in the general population this enzyme defect is found in about 1/100,000 live births, the disease frequency is approximately 1 in 5000 to 7000 Jews of Moroccan descent.12 There have been no systematic screening programs to detect forms of CAH other than 21hydroxylase deficiency. Nonclassic variants of 11 /3-hydroxylase deficiency have also been described.11 Hormonal imbalances differentiate 21- from 11/3-hydroxy¬ lase deficiency. In most cases, classic 21-hydroxylase deficiency is accompanied by deficient aldosterone synthesis and limited ability to conserve sodium. In patients with 11-hydroxylase de¬ ficiency, excessive production of the mineralocorticoid agonist deoxycorticosterone (DOC) or its metabolites results in sodium retention, hypokalemia, volume expansion, suppressed plasma renin activity (PRA), and hypertension. Hypertension, however, is not the sine qua non for diagnosis of 11/3-hydroxylase defi¬ ciency and is often absent in young children. Nonclassic cases may have variable elevations of DOC and 11/3-deoxycortisol (compound S) and have normal PRA levels.

17a-HYDROXYLASE/17,20-LYASE (P450c17) DEFICIENCY In 17a-hydroxylase/17,20-lyase deficiency, impaired pro¬ duction of glucocorticoids and sex steroids (C19/C18 compounds) causes failure to develop estrogenic sexual characteristics at puberty in genetic females and incomplete development of the external genitals in genetic males.13, 4 Shunting of P450cl7 precursor steroids into the 17-deoxy pathway produces mineral¬ ocorticoid excess,'with hypokalemic alkalosis and hypertension similar to the 11/3-hydroxylase deficiency. In rare cases, selective 17,20-lyase deficiency is detected. In such patients, cortisol and DOC levels are normal, but adrenal and gonadal C2i to C19 ste¬ roid conversion is impaired, preventing normal sex steroid production. More than 120 cases have been reported of severe or com¬ plete 17a-hydroxylase deficiency, mostly in combination with 17,20-lyase deficiency.15 There have been reports of patients from Canadian-Dutch Mennonite kindreds who share the same genotype.16 Relatively few genetic females have been detected. Partial deficiency of this enzymatic activity may be found in males with ambiguous genitalia.17

TABLE 75-2 Phenotype in 21-Hydroxylase Deficiency Characteristic

Salt Wasting

Simple Virilizing

Nonclassic Form

Age at diagnosis

Infancy

Childhood or adulthood

Aldosterone Virilization Mutation

Low Severe to moderate Severe

Infancy (females) or childhood (males) Normal Moderate to severe Moderate (severe + moderate)

Normal None to mild Mild (mild to moderate, mild + severe)

690

PART V: THE ADRENAL GLANDS

3/3-HYDROXYSTEROID DEHYDROGENASE DEFICIENCY 3/3-Hydroxysteroid dehydrogenase (3/3-HSD) is responsible for conversion of A5 to A4 steroids. Deficiency of this enzyme results in inefficient cortisol synthesis, oversecretion of dehydroepiandosterone (DHEA), which is only weakly androgenic, and oversecretion of pregnenolone, which is ineffective as a mineralocorticoid. Affected individuals typically have cortisol in¬ sufficiency and salt wasting. Genital ambiguity is also part of the syndrome. Although lack of potent androgens produces hypo¬ spadias in males, high levels of DHEA may cause clitoromegaly without urogenital sinus formation in females.18 In 3/3-HSD and 17a-hydroxylase/17,20-lyase deficiencies, potent androgens are deficient in prenatal life, predisposing males to gynecomastia. The precise frequency of severe defects in the adrenal 3/3-HSD gene is unknown. A nonclassic form of 3/3-HSD deficiency is diagnosed with variable frequency in children with precocious pubarche and fe¬ males with hirsutism and oligomenorrhea,19,20 but the hormonal profile with ACTH stimulation is less robust a diagnostic tool than that described for 21-hydroxylase deficiency. Some investi¬ gators have suggested that ovarian hyperandrogenism may be confused with 3/3-HSD deficiency.21 The physician must also ex¬ ercise caution in the interpretation of ACTH stimulation tests performed in infants younger than 1 year of age, because 3/3HSD is normally deficient in fetal life and relatively inactive in early infancy. Molecular genetic investigation will undoubtedly uncover cases of mild 3/3-HSD deficiency. No marked variations in the ethnic incidence of this defect are known; several classic cases have been identified in consanguineous families.

20,22-DESMOLASE (P450scc) DEFICIENCY This condition is also called lipoid adrenal hyperplasia or cholesterol desmolase deficiency. The enzyme defect blocks all steroid production, with buildup of cholesterol substrate. Defi¬ ciency of side-chain cleavage or cholesterol desmolase is ex¬ tremely rare, with only about 30 cases in the world's litera¬ ture.22^3 Complete 20,22-desmolase deficiency produces global adrenocortical insufficiency and is lethal because of marked cor¬ tisol deficiency and severe salt wasting. Partial defects result in pseudohermaphroditism in genetic males; lack of secondary sex¬ ual characteristics can be expected in genetic females. A single case report describes long-term follow-up of a patient diagnosed in the newborn period and successfully treated for 18 years.24 Cholesterol desmolase deficiency seems to occur with less sever¬ ity and somewhat more frequently among the Japanese.

OTHER STEROIDOGENIC DEFECTS Several other disorders involve adrenal steroid-synthesizing enzymes. Strictly speaking, the corticosterone methyloxidase de¬ ficiencies are not included among the adrenal hyperplasias, be¬ cause they do not affect cortisol synthesis and cause no distur¬ bance of the hypothalamic-pituitary-adrenal axis. A distal block in aldosterone synthesis results from defects in the CYP11B2 gene encoding 18-hydroxylase (CMO I) and 18-oxidase (CMO II) and causes salt wasting with hypotension and failure to thrive in in¬ fancy. Affected individuals are often clinically asymptomatic in later life. Defects in the CYP19 gene encoding cytochrome P450 aromatase (P450 arom) prevent the normal synthesis of estrogens and create a relative abundance of androgens. Such defects have recently been identified as a novel cause of ambiguous genitalia in 46,XX neonates and of virilism in the setting of polycystic ova¬ ries in young women.25,26 Classic deficiency of 17-ketosteroid reductase (i.e., 17/3hydroxysteroid dehydrogenase) is a cause of ambiguous genitalia in 46,XY neonates, who have a tendency to virilize at puberty, piobably by means of extragonadal 17/3-HSD activity and en¬

hanced 5a-reductase activity.27,28 Mild forms of this enzyme de¬ ficiency exist in young men with gynecomastia and in females with hirsutism and polycystic ovaries.29,30 Specific defects in the gene, E2DH17B2, encoding active 17/3-HSD have not been identified. Other rare inherited disorders of steroidogenesis, such as glucocorticoid-suppressible hyperaldosteronism (i.e., glucocorti¬ coid-remediable aldosteronism or dexamethasone-suppressible hyperaldosteronism), a regulatory defect of the CYP11B2 gene, and apparent mineralocorticoid excess, a putative defect in 11hydroxysteroid dehydrogenase, are discussed in Chapter 78.

DIAGNOSIS POSTNATAL DIAGNOSIS The diagnosis of 21-hydroxylase deficiency may be con¬ firmed by administering an intravenous bolus of ACTH and mea¬ suring the resultant elevation in blood levels of 17-hydroxyprogesterone.31 Usually, a panel of adrenal hormones is assayed before and after ACTH administration, but none is as specific a marker as 17-hydroxyprogesterone. Clinicians should be aware that cortisol stimulation is suboptimal after ACTH infusion in patients with severe defects in adrenal steroid synthesis. If for any reason blood testing cannot be employed or radioimmuno¬ assays for 17-hydroxyprogesterone are unavailable, the exam¬ iner can measure 17-ketosteroids or pregnanetriol in a 24-hour urine collection. The latter steroid is the principal direct urinary metabolite of 17-hydroxyprogesterone. Ancillary tests employed in the initial evaluation of infants with ambiguous genitalia include karyotype, pelvic and abdomi¬ nal ultrasound, and sinugram of the urogenital orifices using ra¬ diopaque dyes. Patients with nonclassic 21-hydroxylase deficiency have 17hydroxyprogesterone levels that exceed those seen in heterozy¬ gous carriers of an affected gene, but they are lower than those of patients with the classic form of the disorder.31 In the nonstimulated state, these patients may have near-normal serum hor¬ mone levels. The diagnosis of 11 /3-hydroxylase deficiency is made by the measurement of elevated basal or ACTH-stimulated DOC or 11deoxycortisol (i.e., compound S) in the serum or elevated levels of the tetrahydro-compounds (i.e., DOC or S) in a 24-hour urine collection.32 Another marker useful in pediatric diagnosis is 6ahydroxytetrahydro-11-deoxycortisol, which can be measured by gas chromatography and mass spectrometry of urine.33 As in 21hydroxylase deficiency, urinary 17-ketosteroids are usually ele¬ vated, reflecting increased shunting of 11/3-hydroxylase hor¬ monal precursors into the sex steroid pathway. Plasma renin ac¬ tivity is usually low in older children, accompanied by low levels of aldosterone. The diagnosis of 17n-hydroxylase/17,20-lyase is made by marked elevations of serum DOC and corticosterone (i.e., com¬ pound B) and the metabolites of these two steroids.13 Aldoste¬ rone is often ^w secondary to suppression of renin by excess DOC, as in the case of 11/3-hydroxylase deficiency. The 17ahydroxylase-deficient patients do not suffer from adrenal crisis despite inadequate cortisol synthesis. Overproduction of cortico¬ sterone provides adequate physiologic response to stress. Plasma ACTH levels are less elevated than in other conditions of im¬ paired cortisol production. Gonadotropin production is ex¬ tremely elevated in both sexes because of the absence of any sex steroid feedback; the gonads are atrophic. A high ratio of A5 to A4 steroids characterizes the 3/3-HSD deficiency.34 Serum levels of 17-hydroxypregnenolone and DHEA are elevated before and after ACTH stimulation. In¬ creased excretion of the A5 metabolites pregnanetriol and 16pregnanetriol in the urine is also diagnostic for this enzyme disorder.

Ch. 75: Congenital Adrenal Hyperplasia

PRENATAL DIAGNOSIS Prenatal diagnosis of 21-hydroxylase deficiency has been used for two decades in pregnancies known to be at risk.35,36 Hor¬ monal diagnosis is accomplished by finding elevated levels of amniotic fluid 17-hydroxyprogesterone or 21-deoxycortisol.37,38 Genetic diagnosis was first performed by identifying HLA mark¬ ers on fetal cells cultured from the amniotic fluid; the genes en¬ coding HLA antigens are closely linked to CYP21.39A0 Problems encountered with these diagnostic techniques included false¬ negative 17-hydroxyprogesterone levels in non-salt-losing cases and intra-HLA recombination.41 Early amniocentesis and chori¬ onic villus sampling have permitted diagnostic studies at the end of the first trimester.42,43 DNA obtained from such procedures may be analyzed by molecular genetic techniques, such as allelespecific hybridization with oligonucleotide probes for the normal and mutant alleles of CYP21.44,45 Pregnancies known to have a 25% risk for 21-hydroxylase deficiency may undergo “blind'' prenatal treatment of the fetus by administering dexamethasone to the mother beginning in the first trimester.46-48 Deferral of therapy until a molecular genetic diagnosis is known could hamper the ability to prevent genital ambiguity.49 Although prenatal treatment usually ameliorates virilization of affected females, results of prenatal treatment have not been completely successful in this regard.50,51 Failures to pro¬ duce normal female genitalia in affected girls with prenatal dexa¬ methasone therapy have been attributed to cessation of therapy in midgestation, to noncompliance, or to suboptimal dosing. Some treatment failures had no ready explanation.52 No fetus treated with low-dose dexamethasone has been born with a congenital malformation specifically attributable to dexamethasone therapy. The incidence of fetal deaths in treated pregnancies does not exceed that for the general population. Complications observed in a rodent model of in utero exposure to high-dose glucocorticoids included cleft palate, placental de¬ generation, intrauterine growth retardation, and unexplained fe¬ tal death.5j The incidence of maternal complications has varied among investigations. Serious side effects, such as overt Cushing syn¬ drome, massive weight gain, and hypertension, have been re¬ ported in about 1% of all treated pregnancies. Caution must be exercised in recommending prenatal ther¬ apy with dexamethasone, and women must be fully informed of these potential risks and nonuniformity of beneficial outcome to the affected female fetus. Despite these caveats, many parents of affected girls still choose prenatal medical treatment because of the severe psychological impact of ambiguous genitalia. In principle, a similar diagnostic and therapeutic approach should be effective in cases of 11/3-hydroxylase deficiency, in which affected female fetuses are also at risk for prenatal virilization.

TREATMENT Patients with simple virilizing or salt-wasting classic 21hydroxylase deficiency or those with 11/3-hydroxylase, 17ahydroxylase/17,20-desmolase, and 3/3-HSD deficiencies, as well as select symptomatic patients with nonclassic forms of these dis¬ eases, are treated with daily oral hydrocortisone or similar drugs. Treatment with glucocorticoids suppresses excessive secretion of ACTH, correcting the adrenal hormone imbalance. Patients with the salt-wasting form of CAH require additional supplementa¬ tion with mineralocorticoids (e.g., fludrocortisone, Florinef, 50200 jrg/day) and sodium chloride supplements (1 to 2 g/10 kg body weight). Older children and adults with simple virilizing disease who are treated adequately with glucocorticoids usually do not have a clinically apparent deficiency of aldosterone nor is renin markedly elevated. Many pediatric endocrinologists empir¬ ically treat all CAH patients with fludrocortisone and sodium

691

chloride despite the lack of signs of salt wasting. It is prudent to follow PRA in all patients as an index of the need for mineralocorticoid and salt supplements. Caution is advised to avoid de¬ velopment of hypertension consequent to excessive or unneces¬ sary treatment with the latter regimen. Glucocorticoid treatment also leads to reduction of mineralocorticoid hormones in 11/3- and 17a-hydroxylase deficiency, with amelioration of hypertension. In cases of long-standing hy¬ pertension, adjunctive antihypertensive drugs may be required to completely normalize blood pressure. The usual mode of treatment for CAH in childhood is with two to three divided daily doses of hydrocortisone totalling 10 to 20 mg/m2/day (average dose ~15 mg/m2/day). Even this relatively low dose may be supraphysiologic, because healthy children and adolescents secrete an average of approximately 7 /^g/m2 of cortisol daily.54,55 Experience indicates that once-daily hydrocortisone, because of its relatively rapid metabolism, is therapeutically suboptimal over the long term. Treatment efficacy should be monitored with frequent mea¬ surements of serum 17-hydroxyprogesterone (good control < 1000 ng/dL), androstenedione, and testosterone, in addition to PRA in young children,56 and assessment of growth, skeletal maturation, and pubertal status. If the response to maintenance hydrocortisone at the stan¬ dard dose is poor despite good medical compliance, a 2- to 4-day trial of dexamethasone (in a dose of ~20-30 /^g/kg/day to a maximum of 2 mg/day) may be more effective in suppressing the adrenal. Maintenance hydrocortisone may then be resumed, and adrenal hormone levels are monitored. If epiphyses are fused, the maintenance regimen may be changed to one of the longeracting glucocorticoids, prednisone or dexamethasone. The greater potency of these drugs means that slight dosing errors may result in iatrogenic Cushing syndrome and growth retarda¬ tion in children. Life-threatening stress, severe illness, or surgery demand parenteral therapy with high doses of hydrocortisone in any patient who is undergoing chronic treatment with exogenous glucocorticoids. Clinical trials are being initiated using androgen-receptor blockers and inhibitors of steroid synthesis in conjunction with glucocorticoids to ameliorate virilization ana to prevent iatro¬ genic glucocorticoid-induced growth retardation.5' Another po¬ tentially useful adjunct to standard therapy are the GnRH ana¬ logues, which serve to delay the onset of gonadarche. It has been suggested that androgen-receptor blockade may be preferable to glucocorticoids as primary treatment of mild 21hydroxylase deficiency.58 The latter therapeutic trials have been prompted by the observation that, although menses usually re¬ sume in regularity within 2 to 6 months after beginning gluco¬ corticoids in young women with nonclassic 21-hydroxylase de¬ ficiency, hirsutism is quite refractory to this mode of treatment. Surgical therapy is required in cases of ambiguous genitalia. Most often, this involves clitoroplasty and vaginoplasty in viril¬ ized females. Improved surgical techniques now permit these procedures to be performed in a single-stage operation by expe¬ rienced urologists.59 With the recognition of disturbed gender identity and role among young women with CAH, it is extremely important to provide early and continuing psychological counseling for them.60,61 With improved medical, surgical, and psychological treatments, an improved psychosexual outcome can be achieved.

GENETICS The autosomal recessive mode of inheritance of adrenal ste¬ roidogenic defects was recognized in the early 1950s.62-64 The linkage of 21-hydroxylase deficiency to the HLA complex on chromosome 6p was discovered in the late 1970s,65 and by the mid-1980s, further molecular genetic details had been unrav-

692

PART V: THE ADRENAL GLANDS

elled.66 Other human adrenal steroidogenic defects also have been subjected to molecular genetic analysis.

21-HYDROXYLASE DEFICIENCY The CYP21 (CYP21B) structural gene encoding steroid 21hydroxylase and a pseudogene (CYP21P or CYP21A) are located 30 kilobases (kb) apart in the HLA complex on chromosome 6p21.3.67,68 Although the two genes are 98% identical in nucleo¬ tide sequence, CYP21P has accumulated a number of mutations that render any gene product completely inactive. These include an 8 base pair (bp) deletion in exon 3, a frameshift in exon 7, and a nonsense mutation in exon 8. Most mutations causing 21-hydroxylase deficiency are caused by apparent recombinations between CYP21 and CYP21P. About 20% of these are unequal meiotic crossovers re¬ sulting in a deletion of a 30-kb DNA segment that includes the 3' end of the pseudogene and the greater portion of the active gene.69 This deleted haplotype is incapable of producing any ac¬ tive enzyme. About 80% of mutations result from apparent gene conversions that transfer small segments containing one or more deleterious mutations from CYP21P to CYP21. The most com¬ mon of these, accounting for an additional ~25% of mutant haplotypes, is a single A -► G transition at nucleotide 656 that causes abnormal pre-mRNA splicing. Less commonly found are seven missense mutations, which cause changes in the protein's amino acid sequence. Several large studies have examined the prevalence of indi¬ vidual mutations in an attempt to correlate specific mutations with particular clinical manifestations of the disease.70-73 These correlations are most reliably made in individuals who are homo¬ zygous or hemizygous (the other chromosome carries a deletion) for each mutation. Table 75-3 illustrates the mutations com¬ monly found in classic and nonclassic forms of 21-hydroxylase deficiency, grouped into three categories according to the pre¬ dicted level of enzymatic activity based on in vitro mutagenesis and expression.74- 7 Group A, with total ablation of enzyme ac¬ tivity, is most often associated with salt-wasting disease; group B, with 2% normal activity, consists predominantly of patients with simple virilizing disease; and group C, with 20% to 60% of normal activity, is most often associated with the nonclassic disorder. These studies suggest that mutant CYP21 enzymes carrying discrete amino acid substitutions identified in CAH patients ex¬ hibit in vivo activities that are generally consistent with in vitro predictions, and correlate with disease severity. Exceptions to this rule include patients with moderate or severe mutations and relTABLE 75-3 Disease-Causing Mutations in CYP21 Designation

Site

Percentage of Normal Enzyme Activity

GROUP A: NO ENZYME ACTIVITY Deletion Deletion of 8 basepairs Cluster: Ile-236 Asn Val-237 -► Glu Met-239 -*• Lys Insert T Phe-306 Gln-318 term Arg-356 -»• Trp nt 656 A -* G

Exons 1 to 8 Exon 3 Exon 6

0 0 0

Exon 7 Exon 8 Exon 8 Intron 2

0 0 0 ? amount residual activity

GROUP B: SEVERELY REDUCED ENZYME ACTIVITY Ile-172-► Asn

Exon 4

2

GROUP C: MODERATELY REDUCED ENZYME ACTIVITY Pro-30 -+ Leu Val-281 -»Leu

Exon 1 Exon 7

?, Indeterminate amount of residual activity.

30-60 20-50

atively mild disease. Because aldosterone is normally secreted at a rate 100 to 1000 times lower than that of cortisol, residual en¬ zyme activity as low as 0.6% of normal activity, as seen in the Ile172 -► Asn nonconservative substitution, allows enough aldo¬ sterone synthesis to prevent symptoms of salt wasting, resulting in the simple virilizing phenotype. Factors outside the CYP21 lo¬ cus may also influence development of the salt-wasting phenotype. Another point of interest in phenotype-genotype analysis is the wide range of clinical manifestations in patients carrying the group C nonclassic mutations (e.g., Val-281 -♦ Leu and Pro30 Leu). These mutations are expected to reduce enzyme ac¬ tivity to 20% to 60% of normal, with 17-hydroxyprogesterone being the preferred substrate. An individual heterozygous for a deletion of CYP21 (i.e., ablation of all enzyme activity derived from one chromosome) is also be expected to have about 50% of normal 21-hydroxylase activity, but such individuals have no signs of disease and have hormonal abnormalities detectable only with ACTH stimulation. This suggests that in vivo 21hydroxylase activity in patients with nonclassic 21-hydroxylase deficiency is often less than 50% of normal. One plausible expla¬ nation for such differences in clinical manifestations of disease is fluctuating intraadrenal concentrations of progesterone, which at physiologic levels (2-4 jiM)78 acts as a competitive inhibitor of the nonclassic mutant enzyme for its main substrate, 17-hydro¬ xyprogesterone. Individuals carrying two nonclassic alleles may have closer to 20% net 21-hydroxylase activity as intraadrenal progesterone concentration increases. Other factors contributing to phenotypic variability might include pseudosubstrate inhibi¬ tion of other steroidogenic enzymes by accumulated precursors of 21-hydroxylase.

11/3-HYDROXYLASE DEFICIENCY There are two human genes on chromosome 8q21-q22 that encode 11-hydroxylase (CYP11B) isozymes with predicted amino acid sequences that are 93% identical.79,80 Each has 9 ex¬ ons spaced over approximately 7 kb. CYP11B1, expressed at high levels in normal adrenal glands, is regulated by ACTH.79,81 CYP11B2, not readily detectable in Northern blots using normal adrenal RNA, is regulated primarily by angiotensin II, rather than by ACTH.79 Transcripts of CYP11B2 have been detected by hy¬ bridization to RNA from an aldosterone-secreting tumor or in normal adrenal mRNA by the more sensitive technique of reverse transcription coupled with the polymerase chain reaction.82,83 Defects in the CYP11B1 gene result in virilizing, hyperten¬ sive CAH, and defects in CYP11B2 cause a rare salt-wasting disease known as corticosterone methyloxidase II (CMO II) deficiency. A third disease, glucocorticoid suppressible aldoste¬ ronism, ensues when the regulatory region of CYP11B1 is transposed to a position, where it controls synthesis of CYP11B2, promoting glucocorticoid suppressible and ACTH-stimulable al¬ dosterone synthesis.84 Mutations in the CYP11B1 gene tend to cluster in exons 6, 7, and 8.85 The most common genetic alteration in Moroccan Jews with 11/3-hydroxylase deficiency is Arg-448 His.86 When in¬ troduced into CYP11B1 cDNA and expressed in cultured cells, this mutation abolishes normal enzymatic activity and is there¬ fore consistent with the classic, severe virilizing phenotype ob¬ served in these patients. Blood pressure was not uniformly ele¬ vated in all patients carrying this mutation, and as observed in 21-hydroxylase deficiency, there are apparently other factors that modify phenotype. Genetic defects in 11 /3-hydroxylase de¬ ficient patients from other ethnic backgrounds include a point mutation creating a termination codon in exon 2 and insertion of two basepairs in exon 9.87,88

17a-HYDROXYLASE/17,20-LYASE DEFICIENCY The P450cl7 structural gene (CYP17) spans 12.6 kb on chro¬ mosome 10,89 with an intron-exon organization similar to that of

Ch. 75: Congenital Adrenal Hyperplasia CYP21. The same gene is expressed in both the adrenal and the testis.90 Molecular characterization of specific mutations in CYP17 have been reported in a number of patients.15 In patients with classic, severe 17a-hydroxylase and 17,20-lyase deficien¬ cies, these have included a point mutation creating a stop codon in the first exon, a 7-bp duplication in exon 2 that produces a frameshift, and a four-base duplication in exon 8. Homozygous deletion of 3 bp in exon 1 was detected in a patient with apparent selective compromise of 17,20-lyase activity, a phenotypic fe¬ male with sexual infantilism. A genetic male with ambiguous genitalia was found to be a compound heterozygote with a stop codon introduced by a single base substitution in exon 4 on one chromosome and a nonconservative proline threonine substi¬ tution in exon 6 on the second chromosome.

3/3-HYDROXYSTEROID DEHYDROGENASE DEFICIENCY Two homologous genes encoding 3/3-HSD, type I, expressed in placenta and skin, and type II, expressed in adrenal and go¬ nads, have been identified on chromosome lpl3.91"94 This is the only enzyme discussed here that is not encoded by a gene in the cytochrome P450 superfamily. Type II gene mutations have been described in patients with classic 3/3-HSD deficiency. These in¬ clude two separate point mutations introducing termination co¬ dons in exon 4, insertion of a single base causing a frameshift, and two separate amino acid substitutions in highly conserved portions of the protein.95'97

CHOLESTEROL DESMOLASE DEFICIENCY The CYP1IA gene encoding this enzyme encompasses 20 kb on chromosome 15.98 Mutations in this gene have not yet been identified in patients with lipoid adrenal hyperplasia,99 although in vitro studies suggest that the 20a-hydroxylase function is de¬ ficient in at least one patient with the syndrome. Lesions affecting other cellular components fundamental to early steroidogenesis (e.g., cholesterol ester hydrolase, sterol carrier protein-2) could have similar effects.

CONCLUSION The adrenal hyperplasias have been extensively studied from the clinical and molecular genetic perspectives. The molec¬ ular basis of CAH resulting from deficiencies in all enzymes but cholesterol desmolase have been identified. Severe mutations, such as deletions, frameshifts, and nonsense codons, in the genes encoding steroidogenic enzymes result in gene products with no enzymatic activity. In contrast, milder mutations, such as conser¬ vative or nonconservative substitutions, may cause a lesser de¬ gree of enzyme impairment. The catalytic activity of such gene products may be differently affected for each of two different substrates.100 One practical result of molecular genetic characterization is the ability to perform accurate and early prenatal diagnosis. Cur¬ rent research efforts are focused on the regulation of these genes, understanding more about gene and enzyme structure-function relationships, further clinical-genetic correlations, and optimiz¬ ing treatment.

REFERENCES 1. New MI, White PC, Pang S, et al. The adrenal hyperplasias. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The metabolic basis of inherited disease, ed 6. New York: McGraw-Hill, 1989:1881. 2. White PC, New MI, Dupont B. Congenital adrenal hyperplasia. N Engl J Med 1987;316:1519. 3. Branchaud CL, Murphy BEP. Physiopathology of the fetal adrenal. In: Pasqualini JR, Scholler R, eds. Hormones and fetal pathophysiology. New York: Marcel Dekker, 1992:53. 4. Estivariz FE, Lowry PJ, Jackson S. Control of adrenal growth. In: James VHT, ed. The adrenal gland, ed 2. New York: Raven Press, 1992:43.

693

5. Kohn B, Levine LS, Pollack MS, et al. Late-onset steroid 21-hydroxylase deficiency: a variant of classical congenital adrenal hyperplasia. J Clin Endocrinol Metab 1982;55:817. 6. Pang S, Hotchkiss J, Drash AL, Levine LS, New MI. Microfilter paper method for 171.5 cm disparity in pole-to-pole diameter) and a unilateral delay in the appearance of contrast medium in the 1- to 5-minute exposures.3 False-negative results often occur in cases of RVH because of bilateral renal artery disease.3,19 The hypertensive urogram is used less frequently because it has low sensitivity and specificity (Table 80-2) and has the risk of neph¬ rotoxicity because of contrast agents. Radionuclide Renography. The renogram relies on a dispar¬ ity of renal function and of perfusion between the stenotic and nonstenotic kidneys. Newer isotopic compounds such as technetium-99m-DTPA accurately measure glomerular filtration rate, and compounds such as ["Tc]MAG measure both glomeru¬ lar filtration rate and tubular secretion.7 The addition of computer quantitation has improved its accuracy.7,8 Patients with RVH show decreased uptake, delayed peak values, and prolonged ex¬ cretion of these agents. Because of the low-risk and noninvasive nature of renography, it has many advantages. However, renog¬ raphy used alone has a high incidence of false-negative and false-positive results (see Table 80-2). Captopril administration during renography has improved its sensitivity and specificity5,7,8,13_16 ’8 (see Table 80-2). Captopril reduces angiotensin II-mediated vasoconstriction in the efferent arterioles, and lowers glomerular pressure and filtration rate. In the stenotic kidney, captopril reduces renal perfusion more than in the nonstenotic kidney, thereby revealing the asymmetric re¬ duction in renal function in RVH. Scintiphotographs and timeactivity curves are analyzed to assess renal perfusion, function, and size. The diagnostic criteria for the captopril renogram are not well standardized and vary between published reports. How-

Ch. 80: Endocrine Aspects of Hypertension ever, a general analysis of the procedure shows a 93% sensitivity and 95% specificity rate. Measurement of Plasma Renin Activity. Although hypoper¬ fusion in the stenotic kidney activates the RAS, renin secretion in the nonstenotic kidney is normal or low, so that circulating renin levels can vary from normal to high. Thus, when measured in peripheral venous samples, PRA is normal in 20% to 50% of cases of documented RVH.6,7 The interpretation is confounded by the fact that 16% to 20% of subjects with essential hyperten¬ sion have high PRA values. However, in RVH there are exagger¬ ated PRA responses to procedures that stimulate the RAS, such as upright posture, sodium restriction, and the administration of angiotensin converting enzyme (ACE) inhibitors.16 ACE inhibi¬ tors interrupt the conversion of angiotensin I to angiotensin II, so that the negative feedback effect of angiotensin II on renin re¬ lease is diminished, resulting in an increase in renin secretion. The captopril PRA test results in a marked increase in PRA in RVH versus other forms of hypertension.16 Captopril, 25 to 50 mg, is administered, and a blood sample for PRA is obtained after 1 hour. The test has relatively good sensitivity and specificity, is safe and inexpensive, and can be done as an outpatient or simul¬ taneously with captopril renography. Renal vein renin levels, sampled by percutaneous catheterization, will determine the functional significance of the stenotic lesion and will predict the blood pressure response to therapy.3,6 8 Renin production is in¬ creased in the stenotic kidney and suppressed in the contralateral kidney; asymmetry of renin production yields a renal vein renin ratio of 1.5:1 or greater in RVH. Although this procedure has a predictive value for surgical curability, it has declined in use be¬ cause it is an invasive procedure and because up to 60% of pa¬ tients who do not lateralize are, nevertheless, improved by surgery.20 Doppler Flow Studies. These procedures have been mark¬ edly improved using low-frequency tranducers for better visual¬ ization of the renal arteries and for the measurement of differ¬ ential blood flow velocities that determine the functional significance of a stenotic lesion.718 A renal-aortic flow velocity

737

ratio of >3.5 suggests RVH. The technique is highly operatordependent, accounting for the variable results, although data show a high sensitivity and specificity (see Table 80-2). Angiography. Renal angiography by the percutaneous, transfemoral route remains the “gold standard" for detecting re¬ nal artery stenosis, as well as its location and pathology. Athero¬ sclerotic lesions most often involve the proximal segment of the renal artery, and have a circular configuration. By contrast, fibromuscular disease is in the more distal portions of the renal artery, and is either localized or diffuse and bilateral (see Fig. 80-2). Angiography is costly, invasive, and has the risk of neph¬ rotoxicity. Because angiography does not always predict the functional significance of renal artery stenosis or its treatment outcome, many centers apply simultaneous angioplasty, with the blood pressure response serving as an indicator of functional sig¬ nificance. However, this approach has not been proven to be su¬ perior to the more conventional methods. Digital subtraction angiography avoids some of the compli¬ cations of percutaneous catheterization, because computer en¬ hancement of the renal area allows the injection of smaller amounts of contrast material. Injection has been in a peripheral vein, but an intraaortic injection site has been reported to provide better visualization.7 The procedure can be performed safely in azotemic patients, and it has been useful in hypertension after renal transplantation.4 A promising, noninvasive procedure for the diagnosis of renal artery stenosis is magnetic resonance angi¬ ography. In some cases of posttransplant stenosis, magnetic res¬ onance angiography has been the only effective noninvasive di¬ agnostic test.21 A proposed scheme for the diagnostic evaluation of suspected RVH is shown in Figure 80-3. TREATMENT OF RENOVASCULAR HYPERTENSION Surgery. The goals of therapy of RVH are the control of blood pressure and the preservation of renal function. The treat¬ ment options are surgery, angioplasty, and medical therapy. The optimal treatment for RVH remains uncertain, because few trials

FIGURE 80-3. Recommended diagnostic evaluation for renovascular hypertension. (From PrigentA, Froissart M. Kidney. Dunca G, Arruda ], eds. New York: Springer lnernational, 1994;3:138.)

738

PART V: THE ADRENAL GLANDS

have compared the three therapies. Often, surgery is reserved for patients for whom hypertension cannot be controlled and in whom renal function is deteriorating. Revascularization proce¬ dures include bypass using natural or synthetic arteries; natural arteries provide a better outcome.22 The surgical cure rate for uni¬ lateral atherosclerotic lesions is 50% to 75%; less favorable re¬ sults are seen in older subjects with long-standing hypertension. If possible, the surgical correction of bilateral renal artery stenosis should be pursued, because data show that blood pressure and renal function also improve after revascularization2' Percutaneous Transluminal Angioplasty. The technical suc¬ cess and cure rate for percutaneous transluminal angioplasty are improving, with an 87% success rate reported for fibromuscular disease and a 60% rate for unilateral atherosclerotic lesions.23 Os¬ tial stenoses are less likely to respond; the recurrence rate is high (47%) for atherosclerotic lesions.23 In transplant renal artery ste¬ nosis, angioplasty is first-line therapy with a cure rate of 70% at 5 years; surgery is less successful because of extensive scar tissue.3 Medical Therapy. In high-risk individuals with coexisting carotid or coronary artery disease, medical therapy is the choice. The natural course of RVH shows that many lesions progress over time; it remains uncertain if drug therapy affects the pro¬ gression of RVH. Because RVH is a renin-dependent form of hy¬ pertension, ACE inhibitors should be specific and effective. In unilateral RVH, ACE inhibitors are often effective as mono¬ therapy. However, ACE inhibitors can produce rapid loss of renal function in bilateral disease, or in RVH with a solitary kidney, owing to the almost complete dependency of renal function on angiotensin II.3 Calcium antagonists are effective antihyperten¬ sive agents in RVH and may induce less renal impairment than ACE inhibitors.3 However, in critical, high-grade stenoses, any agent that lowers blood pressure excessively can impair renal function.

RENIN-PRODUCING TUMORS Renin-producing tumors, a rare form of endocrine hyperten¬ sion that occurs in young persons, have the striking features of severe hypertension and hypokalemia.24,25 The levels of PRA in such patients are among the highest recorded in hypertensive syndromes; they can exceed 50 ng/mL/h.24 The hypokalemia, which often is at levels of less than 2.0 mEq/L, is attributable to intense secondary aldosteronism; the combined high PRA and aldosterone levels distinguish this disorder from primary aldo¬ steronism. Two categories of renin-producing tumors cause this syndrome: renal juxtaglomerular cell tumors; and a variety of extrarenal tumors, such as Wilms tumors and ovarian tumors.24,25 The biochemical and physiochemical properties of renin origi¬ nating from tumor production resemble those of the renin found in normal kidneys.24,26 Extrarenal renin-secreting tumors have higher concentrations of prorenin than do tumors of renal ori¬

gin.25,27 In a series of 15 cases of extrarenal renin-secreting tu¬ mors, 14 were in women, and 7 of these were located in the re¬ productive tract.27 In these patients, a high prorenin level served as a marker for this tumor. In renal renin-secreting tumors, renal vein PRA measure¬ ments can localize the tumor, but these tumors are small, so that radiologic visualization, including urography, computed tomog¬ raphy, and angiography may not detect the tumor.25 Even exploratory surgery can fail to find the tumor. In renal reninproducing tumors, nephrectomy or selective tumor resection is curative and ACE inhibitors are the medical treatment of choice.28

MINERALOCORTICOID HYPERTENSION Several mineralocorticoids, such as aldosterone and desoxycorticosterone (DOC), produce hypertensive syndromes if se¬ creted in excess (Table 80-3). Primary aldosteronism is the best example of mineralocorticoid hypertension (see Chap. 78). The mechanisms underlying hypertension include sodium retention, extracellular fluid expansion, high cardiac output, increased SNS activity, and structural changes in blood vessels.29 CONGENITAL ADRENAL HYPERPLASIA An excessive production of DOC occurs in several hyperten¬ sive syndromes (see Table 80-3). The hypertension accompany¬ ing the 11/3- and 17a-hydroxylation defects of congenital adrenal hyperplasia is secondary to excess DOC production (see Chap. 75). 0 In the 11/3-hydroxylase form of congenital adrenal hy¬ perplasia, hypertension, hypokalemia, and virilism occur. Re¬ duced cortisol activates corticotropin (ACTH), which, in turn, in¬ creases the synthesis of DOC and desoxycortisol. Aldosterone production is decreased, because 11/3-hydroxylation is required for its formation. Glucocorticoid therapy suppresses the ACTH, reduces the blood pressure, reverses the renin suppression, and corrects the hypokalemia. The 17a-hydroxylase deficiency syndrome also has hypoka¬ lemia and hypertension; however, it is accompanied by hypogo¬ nadism, because the enzyme deficiency also exists in the go¬ nads.29 Young adults are affected; in female individuals, there is primary amenorrhea. Steroidogenesis is shifted to the mineralo¬ corticoid pathway, with excess production of DOC, corticoste¬ rone, 18-hydroxydesoxycorticosterone, and 18-hydroxycorticosterone.30,31 The ensuing volume expansion suppresses renin, thereby reducing the production of aldosterone. Glucocorticoid administration corrects the hypertension and hypokalemia. APPARENT MINERALOCORTICOID EXCESS Another increasingly recognized form of mineralocorticoid hypertension is 11/3-hydroxysteroid dehydrogenase (11/3-HSD)

TABLE 80-3 Biochemical Features of Hypertensive Syndromes Involving Mineralocorticoid and Glucocorticoid Excess

Primary aldosteronism Cushing syndromes Pituitary or adrenal adenoma Paraneoplastic ACTH 11/3-Hydroxylase deficiency 17a-Hydroxylase deficiency Apparent mineralocorticoid excess Licorice ingestion Cortisol resistance

Blood Pressure

Serum Potassium

t

1

t t t t t t t

N

PRA

N/r

i i i

Aldosterone

Cortisol

DOC

ACTH

t

N

N

N

N 1 1

t t

N

t t t

t/N/| t t t

N N

N N

t

t

i

\ *

1

ACTH, corticotropin; DOC, desoxycorticosterone; PRA, plasma renin activity.

* Increased renin substrate. f Abnormal corticosteroid metabolism because of enzyme deficiency of 11/3-hydroxysteroid dehydrogenase in the kidneys.

1 Nf N| t

Ch. 80: Endocrine Aspects of Hypertension deficiency, also termed apparent mineralocorticoid excess (see Table 80-3). The disorder primarily affects juveniles and is char¬ acterized by hypertension, hypokalemia, and the suppression of renin and aldosterone.32"34 The 11/3-HSD enzyme deficiency is localized to the kidney and results in the failure to metabolize cortisol to cortisone, producing up to a 1000-fold excess of corti¬ sol in the kidneys (renal Cushing syndrome).34 Because the Type I mineralocorticoid receptor in the distal tubule is nonselective, it binds aldosterone and cortisol equally.35 In apparent mineralo¬ corticoid excess (AME), the excess renal cortisol binds to the min¬ eralocorticoid receptor, producing sodium retention, hyperten¬ sion, and hypokalemia; the sodium retention suppresses renin and aldosterone. In AME, the metabolites of cortisol, such as tetra hydrocortisol (THF), are high and those of cortisone (THE) are low; the abnormal elevation of the THF/THE ratio (>1.0) is di¬ agnostic.34 Treatment with dexamethasone and spironolactone corrects the hypertension and hypokalemia. An almost identical clinical picture is seen with the ingestion of large amounts of lic¬ orice, in which case, its metabolite, glycyrrhetinic acid, inhibits 11/3-HSD activity in the kidney36 (see Table 80-3). GLUCOCORTICOID REMEDIABLE ALDOSTERONISM Glucocorticoid remediable aldosteronism (GRA) was thought to be a rare form of hyperaldosteronism in which the hyperten¬ sion and hypokalemia responded to glucocorticoid administra¬ tion. The disorder is observed in individuals with a strong family history of hypertension and stroke, and is inherited as an autoso¬ mal dominant trait. Based on findings of a novel gene duplication in GRA subjects,37 the screening of kindred from index cases sug¬ gests that there is a higher incidence of GRA than had been pre¬ viously suspected. Gene duplication results in ectopic expression of the enzyme aldosterone synthase in the adrenal fasciculata zone rather than in its normal location in the zona glomerulosa. Thus, ACTH, rather than angiotensin II, controls aldosterone se¬ cretion in GRA; aldosteronism is rapidly corrected by the admin¬ istration of dexamethasone. Because of the ectopic location of aldosterone synthase, there is an overproduction of two hybrid metabolites of cortisol, 18-oxocortisol and 18-hydroxycortisol. These steroids can be used to screen for GRA, as well as perform¬ ing Southern blot analysis of DNA.38 A strong family history of hypertension and hemorrhagic stroke in young subjects should prompt an evaluation for this condition. Interestingly, normokalemia, rather than the expected hypokalemia, is found in many kindred with confirmed GRA.38 GLUCOCORTICOID RESISTANCE Glucocorticoid resistance is a hypertensive disorder accom¬ panied by hypokalemia with suppressed renin and aldosterone (see Table 80-3). High levels of plasma cortisol and a paucity of stigmata of Cushing syndrome suggest the diagnosis.39 The in¬ sensitivity to glucocorticoids is caused by inherited glucocorticoid receptor mutations.39 An insensitivity to cortisol at the hypotha¬ lamic-pituitary feedback for ACTH increases ACTH production, which, in turn, stimulates DOC and corticosterone formation; the

739

increased mineralocorticoid activity then causes volume expan¬ sion, hypertension, and the suppression of renin and aldoste¬ rone. An adrenal androgen excess can also be found, resulting in hirsutism in women, and precocious pseudopuberty in children. The demonstration of a functionally abnormal glucocorticoid re¬ ceptor in mononuclear cells confirms the diagnosis.39 Mutations occur in the glucocorticoid receptor-ligand binding domain and at a splice site.39 High doses of dexamethasone reduce the ACTH, and, thereby, correct the blood pressure and serum potassium abnormalities. A form of cortisol resistance has also been de¬ scribed in acquired immunodeficiency syndrome.40

HYPERTENSION ASSOCIATED WITH OTHER ENDOCRINOPATHIES CUSHING SYNDROME Hypertension is common in endogenous Cushing syndrome (up to 80%) and occurs less frequently with exogenous glucocor¬ ticoid therapy.41 The cardiovascular mortality and morbidity are much higher in Cushing syndrome, whether it be because of nat¬ ural or iatrogenic disease.42 This increased risk is attributed to the effects of cortisol on blood pressure, on atherosclerosis, and on the heart. The hypertension is thought to directly result from cor¬ tisol excess30 through at least three mechanisms (Fig. 80-4). Glu¬ cocorticoid excess increases the hepatic synthesis of angiotensinogen, the substrate for the production of the vasoconstrictor angiotensin II. This mechanism might suggest a renin-dependent form of hypertension, yet renin levels in Cushing syndrome often are normal to decreased. Glucocorticoid administration to normal subjects will enhance vascular reactivity to pressor hormones such as phenylephrine; indeed, many attribute its hypertensive action to this mechanism.43 Although cortisol in excess binds to mineralocorticoid receptors, most cases of Cushing disease or syndrome resulting from pituitary or adrenal adenoma do not have hypokalemia and suppressed renin.30 A more pronounced mineralocorticoid effect is seen in syndromes of paraneoplastic ACTH production in which high levels of cortisol and DOC, but not aldosterone, cause the hypokalemia and hypertension30 (see Chap. 213). High ACTH levels preferentially stimulate DOC se¬ cretion over aldosterone; the excess DOC causes volume expan¬ sion and the suppression of renin and aldosterone. A second mechanism of hypertension has been found in paraneoplastic ACTH syndromes; the renal enzyme 11/3-HSD is deficient, and there is a high urine THF/THE ratio similar to that seen in AME.33 In some cases of adrenal carcinoma, the partial enzyme block in 11 /3-hydroxylase leads to accumulation of its immediate substrate, DOC.30 DIABETES MELLITUS AND HYPERTENSION The frequency of hypertension in diabetes mellitus is high, reaching an incidence rate of about 50%.44 Hypertension in the diabetic greatly enhances the risk of macrovascular atheroscle¬ rotic complications and the microvascular complications of ne¬ phropathy and retinopathy. Also, lowering blood pressure

FIGURE 80-4.

Mechanisms of hyperten¬

sion in hypercortisolism.

740

PART V: THE ADRENAL GLANDS

successfully slows the rate of the progression of diabetic nephropathy.45 In insulin-dependent diabetes mellitus (IDDM), hyperten¬ sion appears after several years of diabetes and is mostly seen in the 40% of IDDM subjects who develop diabetic nephropathy. Thus, renal mechanisms explain most of the pathophysiology of hypertension in IDDM. In noninsulin-dependent diabetes melli¬ tus (NIDDM), hypertension has more complex origins, including the effects of aging, obesity, insulin resistance, atherosclerosis, and renal disease. Two characteristic features of hypertension in all diabetic patients are an increased vascular reactivity,46'47 and increased sodium retention.48 Administering norepinephrine or angiotensin II to diabetic subjects markedly elevates blood pres¬ sure compared with nondiabetics. Stressful events such as exer¬ cise and mental testing produce similar exaggerated responses.44 Exchangeable sodium is increased by about 10% over control lev¬ els in diabetic subjects and could lead to volume expansion and hypertension. A role for insulin in the hypertension of diabetes has been proposed because many studies show a positive corre¬ lation between insulin and blood pressure.44 In experimen¬ tal conditions, insulin has been shown to alter blood pressure¬ regulating mechanisms, such as SNS activity, sodium handling, and vascular tone.44'45 In normal persons, the infusion of insulin increases plasma norepinephrine levels and regional sympathetic neuronal burst activity.44,45 Also, insulin causes a prompt reduc¬ tion in sodium excretion.44 The effect of diabetes on the RAS is to reduce its activity, so that renin levels are low in many diabetic subjects.48 In IDDM, hyporeninemia develops while renal failure and hypertension progress; in some, this leads to the syndrome of hyporeninemic hypoaldosteronism. In NIDDM subjects, there is also a reduction in renin levels compared with nondiabetics; this occurs in pa¬ tients with normal renal function.48 The reduction of renin in di¬ abetes has been attributed to a defective conversion of prorenin to active renin, to chronic volume expansion, and to a decreased neural control of renin release.48 OBESITY AND HYPERTENSION A strong relationship exists between body weight and blood pressure, and weight loss has a powerful hypotensive effect.49,50 Obese hypertensive patients have a unique hemodynamic profile in that blood volume and cardiac output are increased; yet, pe¬ ripheral vascular resistance is normal to low. The hormone pro¬ file in obesity shows that norepinephrine and insulin levels are high,49 and, because insulin increases norepinephrine release, it is possible that the caloric excess causes hyperinsulinemia and stimulation of the SNS and blood pressure.51,52 During weight loss, the fall in blood pressure is highly correlated with reductions in plasma insulin and norepinephrine.53 HYPERCALCEMIA AND HYPERTENSION Estimates of hypertension in primary hyperparathyroidism have ranged from 50% to 70%. As much as 35% of patients with chronic hypercalcemia of other etiologies are hypertensive54,55 (see Chap. 58). Hypertension in primary hyperparathyroidism is sometimes associated with renal insufficiency, but other factors, such as hypercalcemia, parathyroid hormone (PTH) and its ana¬ logue, parathyroid hormone-related protein, and phosphorus and magnesium deficiency contribute to the hypertension. Calcium is a major mediator of vascular contractility; calcium in¬ fusion increases blood pressure56 and potentiates angiotensin II and norepinephrine. The positive relationship between serum calcium and blood pressure in hypertensive subjects suggests a cause-effect relationship.56 PTH may be involved, but it is con¬ sidered to be a vasodilator, because the acute administration of PTH induces a fall in blood pressure. However, more chronic exposure to PTH raises blood pressure. 1,25-dihydroxycholecalciferol is high in hyperparathyroidism and exerts effects on calcium mobilization in blood vessels. Renin activity is normal to

low in primary hyperparathyroidism.57 The results of parathy¬ roid surgery on hypertension are inconsistent. In some subjects, especially those with renal insufficiency, hypertension persists or is only partially corrected.58 Hypertension is not regarded as an indication for parathyroid surgery. In pseudohypoparathyroidism there is an increased preva¬ lence of hypertension59; this may be because of a more general¬ ized resistance to PTH, with a loss of its normal vasodilating effect on vascular PTH receptors. ACROMEGALY AND HYPERTENSION Hypertension is found in up to 50% of patients with acro¬ megaly60,61 (see Chap. 14). Human growth hormone promotes sodium reabsorption, and the extracellular fluid volume is in¬ creased in acromegaly; this is accompanied by suppressed renin levels.60,61 Also, there is evidence for overactivity of the SNS. The successful treatment of acromegaly often normalizes or improves blood pressure. THYROID DISEASE AND HYPERTENSION Thyroid hormone affects all regulatory aspects of the cardio¬ vascular system.62 Thyroid hormone excess increases heart rate, cardiac output, and stroke volume and decreases peripheral vas¬ cular resistance and diastolic blood pressure; however, systolic blood pressure increases. Cardiovascular changes with thyroid hormone are attributed to increased adrenergic nervous system activity through the /3-adrenergic receptor. 3 Because thyroid hormones are structurally related to catecholamines, they may be taken up and released at the neural synapse.63 Thyroid hormone stimulates the RAS mainly through increasing the hepatic pro¬ duction of angiotensinogen (renin substrate).61,64 Hypothyroidism and Hypertension. Hypertension, which is predominantly diastolic, has been reported in 15% to 30% of hy¬ pothyroid patients.61 Hypothyroidism is common in the elderly. Elderly persons often have unrelated hypertension; however, comparison studies have shown an increased prevalence of hy¬ pertension in the hypothyroid individuals.61 Contrary to the expected effects of low thyroid, SNS function is increased in hy¬ pothyroidism, with high plasma norepinephrine.61,64 This en¬ hanced a-adrenergic activity may raise total peripheral resistance and decrease cardiac output, as has been observed in hyperten¬ sive, hypothyroid patients. Renin levels are low in hypothyroid¬ ism.64 In about 30% of patients, thyroid hormone replacement reduces blood pressure. Hyperthyroidism and Hypertension. About 30% of subjects with Graves disease have systolic hypertension. The high systolic pressure and pulse pressure that are encountered are best ex¬ plained by increased cardiac output; this is thought to be medi¬ ated adrenergically, because /3-adrenergic blockade reduces cardiac output and pulse pressure.62,63 However, contrary to the known effects of thyroid hormone on sympathetic activity, cate¬ cholamine levels are normal to reduced in hyperthyroidism.62,63 In hyperthyroid rats, there is an increased density of /3-adrenergic receptors in the cardiovascular tissue, indicating that thyroid hor¬ mone may increase adrenergic activity through these receptors.63 Renin levels are elevated, but high PRA is thought not to contrib¬ ute to the hypertension.61 Successful treatment of hyperthyroid¬ ism usually corrects the hemodynamic abnormalities and reduces systolic blood pressure (see Chap. 41).

ENDOCRINE FUNCTION IN ESSENTIAL HYPERTENSION Essential hypertension is of unknown etiology; however, in this condition, there is evidence for the participation of several hormone systems that regulate cardiovascular function. The two systems most studied are the renin-angiotensin-aldosterone sys¬ tem and the SNS. Attention has also focused on circulating natri¬ uretic hormones, such as atrial natriuretic peptide (ANP); on ouabain-like factors; on endogenous vasodilator substances.

Ch. 80: Endocrine Aspects of Hypertension

741

such as the eicosanoids (prostaglandins, lipoxygenases, P450 ep¬ oxides); and on the kallikrein-kinin system. The use of clinical measurement of these hormones in the evaluation of hyperten¬ sive subjects is limited. RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM In essential hypertension, the activity of the renin-angioten¬ sin system varies widely; subjects can be classified as having low, normal, and high levels of PRA.65-67 Procedures to test for PRA include sodium restriction, upright posture, and diuretic admin¬ istration. Another method plots PRA against 24-hour sodium ex¬ cretion, a measurement that approximates steady-state dietary sodium intake67 (Fig. 80-5). From this approach, the concept of renin profiling in hypertension arose.67 In strong support of the renin profiling procedure is the marked increase in cardiovascular risk associated with high circulating levels of PRA.66 There also may be differences in blood pressure response in renin sub¬ groups; patients with low renin levels respond to diuretics and calcium channel blockers, whereas those with high renin levels respond to ACE inhibitors. The differential response to antihy¬ pertensive agents in renin subgroups reflects the degree of volume dependency (low renin) or of vasoconstrictor dependency (high renin).68 Low-Renin Essential Hypertension. About 30% of essential hypertensive subjects have low PRA levels, with a higher inci¬ dence in blacks and elderly hypertensive individuals.67 The best example of low-renin hypertension is primary aldosteronism with volume expansion, hypertension, hypokalemia, and sup¬ pressed PRA. Thus, initial studies of the mechanisms of lowrenin essential hypertension focused on mineralocorticoids. Several corticosteroids (18-hydroxycorticosterone, 18-hydroxydesoxycorticosterone, corticosterone, DOC, 19-nordesoxycorticosterone) have turned out not to be the candidate steroid in low-renin hypertension.69-71 In addition, hypokalemia and vol¬ ume expansion rarely occur in low-renin essential hypertension, and aldosterone levels are normal. A significant therapeutic find-

11 10 9 8 7 Plasma Renin Activity (ng/mL/hr)

5 4 3 2

Normotensives FIGURE 80-6.

Hypertensives

Changes in PAH clearance (renal blood flow) in normo-

tensive and essential hypertensive subjects on high sodium diet in re¬ sponse to angiotentensin

II.

Nonmodulators fail to change renal blood

II levels. (From Shoback, Williams GH, Moore Tf, et al. Defect in the sodium-modulated tissue responsiveness to an¬ giotensin 11 in essential hypertension. ] Clin Invest 1983;72:2115.) flow with high salt and angiotensin

ing in low-renin essential hypertension is the superior antihyper¬ tensive response to diuretics and calcium channel blockers.67 High-Renin Essential Hypertension. About 10% to 20% of patients with essential hypertension have elevated levels of PRA.65,67 It is uncertain whether these moderate increments in renin represent a distinct pathophysiologic abnormality, but these individuals may be at greater risk for cardiovascular dis¬ ease.66 One explanation for elevated PRA in the essential hyper¬ tensive is nephron heterogeneity with discordant renin secretion and sodium excretion; this causes a hypertensive vasoconstric¬ tion-volume relationship.68 The renin-dependency of the blood pressure is supported by showing a greater hypotensive response to inhibitors of the RAS (ACE inhibitors, angiotensin receptor inhibitors) in high-renin compared with normal- and low-renin subjects. Normal-Renin Essential Hypertension. Normal renin values are found in about 60% of subjects with essential hyperten¬ sion.65,67 An abnormal tissue response to angiotensin II has been reported in subjects with normal renin hypertension; "this is termed nonmodulating essential hypertension.72 Nonmodulation may be an intermediate phenotype in essential hypertension.73 In these subjects, the aldosterone response to angiotensin II infu¬ sion is subnormal on a low sodium diet, and the renal blood flow response to angiotensin II is subnormal on a high sodium intake (Fig. 80-6). Thus, sodium fails to normally modulate the tissue response to angiotensin II in both the adrenal glands and the kid¬ neys. Because administration of an ACE inhibitor completely cor¬ rects the abnormal responses, tissue angiotensin II defects may account for nonmodulation.72'73 Nonmodulation would explain the impaired renal sodium handling and salt sensitivity that is found in hypertension. The diagnosis of nonmodulation is difficult, requiring sodium balance and angiotensin II infusion. However, several new tests, such as angiotensinogen gene ex¬ pression and the red blood cell sodium, lithium (Na+, Li+) coun¬ tertransport assay hold promise as markers for nonmodulation/3

1 SYMPATHETIC NERVOUS SYSTEM IN ESSENTIAL HYPERTENSION 0

FIGURE 80-5.

100 200 24 Hr Urinary Sodium Excretion

300

Plasma renin activity as related to sodium excretion.

Shaded area represents normal range. High and low renin activity is de¬ fined as off the normal curve. (From Gavras 1. Hypertension primer. Dallas: American Heart Association, 1993:234.)

Increased SNS activity (see Chap. 82) occurs in a subset of ■ subjects with essential hypertension.74,73 In an analysis'6 of over 80 studies measuring plasma norepinephrine, younger hyperten¬ sive subjects had elevated values compared with normotensive controls. Hypertensive subjects also have increased renal norepi¬ nephrine spillover, indicating regional sympathetic excess/ In

742

PART V: THE ADRENAL GLANDS

studies75 using microneurography to measure regional sympa¬ thetic nerve activity, the recorded activity in skeletal muscle is high in essential hypertension. Inhibitors of sympathetic activity lower blood pressure proportionately to the baseline level of plasma norepinephrine.74'5 Stress, isometric exercise, and tilt ta¬ ble maneuvers all produce large norepinephrine responses in hy¬ pertension, and large blood pressure increases are seen with nor¬ epinephrine infusion. Thus, the combination of exaggerated blood pressure responses and high norepinephrine provides the neurogenic stimulus for hypertension. Groups most likely to have neurogenic hypertension are the young, the obese, and those with a hyperdynamic circulation.78 Elevated levels of epinephrine are also found in essential hy¬ pertension.79 Although epinephrine does not have intrinsic hy¬ pertensive properties, it is highly reactive to stress. Psychological stress increases epinephrine; this is associated with an increased sodium retention and augmented vascular reactivity.79 One hy¬ pothesis states that in essential hypertension, daily stress situa¬ tions lead to a cumulative increase in plasma epinephrine, caus¬ ing its uptake in prejunctional neurons that facilitate the release of the pressor catecholamine, norepinephrine/9 The third cate¬ cholamine product of SNS activity, dopamine, inhibits aldoste¬ rone secretion and enhances sodium excretion. Interestingly, re¬ duced urinary free dopamine response to salt-loading is observed in essential hypertension,80 indicating a deficiency of renal dopa¬ mine that could blunt normal natriuretic mechanisms. NATRIURETIC HORMONES AND HYPERTENSION The linear relationship between sodium intake and hyper¬ tension is documented in epidemiologic studies. Hormones that regulate sodium, such as aldosterone, dopamine, prostaglandins, bradykinin, ANP, and sodium pump inhibitors may play a role in this salt-blood pressure relationship. Sodium Pump Inhibitors. Evidence for a circulating natri¬ uretic substance that differs from ANP comes from volume ex¬ pansion studies showing that the enhanced sodium excretion in response to volume expansion is associated with increased blood levels of a factor that inhibits the Na+,K+-ATPase pump.81 De¬ fective sodium excretion in hypertension would produce volume expansion that would serve as a signal for release of a circulating pump inhibitor as a compensatory mechanism to block renal so¬ dium reabsorption and correct the volume overload. This pump inhibitor, however, acts on other tissue Na+,K+-ATPase pump sites; in the blood vessels, there would be an increase of intracel¬ lular sodium and calcium and a resetting of vascular tone.81 Im¬ portantly, increased intracellular sodium and calcium and re¬ duced Na+,K+-ATPase pump activity are found in experimental and human hypertension.87-84 Disturbances in several mem¬ brane cation transport pathways are also described in human hy¬ pertension, using peripheral cells (erythrocytes, leukocytes, platelets). The defects include a reduced Na+,K+ pump, an ele¬ vated Na+,K+ cotransport, a high Na+,Li+ countertransport, and a high Na+/H+ antiporter.82-84 The multiple membrane cation transport defects in hypertension suggest a more complex picture for sodium handling in hypertension than can be explained by a circulating pump inhibitor. The isolation and structural identification of a circulating compound that inhibits the Na+,K+-ATPase pump has been difficult. Because plasma from volume-expanded animals cross reacts with antibodies to the digoxin and ouabain molecules, these substances should have properties similar to those of cardiac glycosides, which inhibit Na+,K+-ATPase pump activity. One group has identified and characterized a ouabain-like com¬ pound from human plasma and adrenal glands that inhibits Na+,K+-ATPase pump activity.85 The physiologic effects of this endogenous ouabain include stimulation of vascular contraction and control of intracellular calcium stores.86 Atrial Natriuretic Peptides. There is a family of endogenous natriuretic peptides, including ANP, brain natriuretic peptide

(BNP) and C-type natriuretic peptide (CNP).87,88 The first to be isolated from the heart was ANP, which stimulates natriuresis, causes vasodilation, and inhibits several blood pressure control systems, including the renin-angiotensin-aldosterone system, the SNS, and the endothelin system.87 ANP is synthesized in atrial myocytes, thus documenting that the heart is an endocrine organ (see Chap. 173). ANP is released by increased intravascu¬ lar volume and atrial pressure overload through mechanisms of atrial stretch. BNP has properties similar to those of ANP, but is synthesized and stored in the central nervous system in addition to being present in atrial cells.88 In hypertension, the levels of BNP may be greater than the levels of ANP; thus, it is debated which peptide is more important in guarding against blood pres¬ sure elevations. CNP is produced in the endothelium and is a potent vasoactive peptide that dilates both veins and arteries, but it has no natriuretic properties. CNP is not a circulating peptide and acts in a paracrine fashion. Much of the function or these ANPs is determined by their receptors. Two of these receptors, ANPR-A and ANPR-B, are linked to guanyl cyclases. ANP and BNP bind to A receptors in the endothelium of blood vessels, whereas B receptors reside in vascular smooth muscle.88 The third is the ANPR-C receptor, which is a clearance receptor and plays an active role in deter¬ mining availability of the peptides by controlling their rate of re¬ moval from the circulation.88 89 In essential hypertension, the levels of ANP and BNP are elevated, but it has been argued that these values are actually relatively low for the level of blood pressure.87 The concept of a natriuretic peptide deficiency state in essential hypertension is appealing, but unproven. The most promising therapeutic ap¬ proach to raise natriuretic peptide levels and lower blood pres¬ sure is through the regulation of the ANPR-C clearance receptors and use of neutral endopeptidase inhibition to potentiate their biological action.89 Kallikrein-Kinin System. The products of the kallikrein-kinin system, the kinins, are natriuretic and diuretic. They have potent vasodilating properties, partly through stimulation of nitric oxide and prostaglandins.90,91 Kinins are produced from kininogens through cleavage by the enzyme kallikrein to form the two main kinins, bradykinin and lysyl-bradykinin (kallidin). Kinins act as paracrine and autocrine hormones through two receptors, the B1 and B2 receptors. It is the B2 receptors, belonging to the family linked to G proteins, that mediate most known regulating effects on blood flow to meet metabolic demands. Renal kinins play a role in the regulation of the microcirculation, and of water and sodium metabolism; the natriuretic effect is mediated in part by prostaglandins. Neutral endopeptidase inhibitors are natriuretic through the blocking of kinin hydrolysis leading to their accumu¬ lation. ACE inhibitors also prevent the breakdown of kinins; thus, kinin accumulation may potentiate the hypotensive action of ACE inhibitors. A reduction in the kallikrein-kinin system has been found in animal models of genetic hypertension; in children, it is a good marker of genetic hypertension.90,91 A restriction fragment length polymorphism for the kallikrein gene family is linked to blood pressure in tne spontaneously hypertensive rat.91 The admin¬ istration of kinin inhibitors raises blood pressure, whereas in an¬ imals, which are transgenic for kinin expression, there is a pro¬ longed hypotensive response.

REFERENCES 1. Hypertension Detection and Follow-Up Program Cooperative Group. The hypertension detection and follow-up program. Circ Res 1977;40(Suppl 1): 106. 2. The Fifth Report of the Joint National Committee on Detection, Evaluation and Treatment of High Blood Pressure (JNC V). Arch Intern Med 1993; 153:154. 3. Working Group on Renovascular Hypertension. Detection, evaluation and treatment. Arch Intern Med 1987; 147:820. 4. Mann SJ, Pickering TG. Detection of renovascular hypertension: state of the art. Ann Intern Med 1992; 117:845.

Ch. 80: Endocrine Aspects of Hypertension 5. Nally JV, Black HR. State of the art review: captopril renographypathophysiological considerations and clinical observations. Semin Nucl Med 1992;22:85. 6. Pauker SG, Kopelman RI. Screening for renaovascular hypertension: a witch hunt. Hypertension 1989; 14:258. 7. Prigent A, Froissart M. Current recommendations for diagnosis of renovas¬ cular hypertension. In: Kidney. 1994:138. 8. McGrath BP, Clarke K. Renal artery stenosis: current diagnosis and treat¬ ment. Med] Aust 1993; 158:343. 9. Martinez-Maldonado M. Pathophysiology of renovascular hypertension. Hypertension 1991; 17:707. 10. Mitchell KD, Braam B, Navar LG. Hypertensinogenic mechanisms medi¬ ated by renal actions of renin-angiotensin system. Hypertension 1992; 19(Suppl 1):

1-18-1. 11. Navar LG. Renovascular hypertension: pathophysiology. In: Izzo JL, Black HR, eds. Hypertension primer. Dallas: American Heart Association, 1993:99. 12. Mann SJ, Anderson WP, Woods RL. Intrarenal effects of angiotensin II in renal artery stenosis. Kidney Int 1987;31:S157. 13. Mann SJ, Pickering TG, Sos TA, et al. Captopril renography in the diag¬ nosis of renal artery stenosis: accuracy and limitations. Am J Med 1991;90:30. 14. Distler A, Spies KP. Diagnostic procedures in renovascular hypertension. Clin Nephrol 1991;36:174. 15. Elliot WJ, Martin WB, Murphy MB. Comparison of two noninvasive tests for renovascular hypertension. Arch Intern Med 1993; 153:755. 16. Wilcox CS. Use of angiotensin-converting-enzyme inhibitors for diagnos¬ ing renovascular hypertension. Kidney Int 1993;44:1379. 17. Erley CM, Duda SH, Wakat J, et al. Noninvasive procedures for the diag¬ nosis of renovascular hypertension in renal transplant recipients: a prospective analysis. Transplantation 1992; 54:863. 18. Postma CT, Van Der Steen PH, Hoefnagels WH, et al. The captopril test in the detection of renovascular disease in hypertensive patients. Arch Intern Med 1990; 150:625. 19. Thornbury JR, Stanley JC, Fryback DG. Hypertensive urogram: a nondiscriminatory test for renovascular hypertension. AJR 1982; 138:43. 20. Roubidoux MA, Dunnick NR, Klotman PE, et al. Renal vein renins: inabil¬ ity to predict response to revascularization in patients with hypertension. Radiology 1991; 178:819. 21. Debatin JF, Spritzer CE, Grist TM, et al. Imaging of the renal arteries: value of MR angiography. AJR 1991; 157:981. 22. Rieder CF, lliopoulos Jl, Thomas JH, et al. Trends in reconstruction for atherosclerotic renal vascular disease. Am J Surg 1984; 148:855. 23. Ramsey LE, Waller PC. Blood pressure response to percutaneous translu¬ minal angioplasty for renovascular hypertension: an overview of published series. Br Med J 1990;300:569. 24. Corvol P, Pinet F, Galen FX, et al. Seven lessons from seven reninsecreting tumors. Kidney Int 1988;34(Suppl 25):S38. 25. Mimran A. Renin-secreting tumors. In: Swales J, ed. Textbook of hyper¬ tension. Oxford, UK: Blackwell Scientific Publications, 1994:858. 26. Bruneval P, Fournier JG, Soubrier F, et al. Detection and localization of renin messenger mRNA in human pathologic tissues using in situ hybridization. Am J Pathol 1988; 131:320. 27. Anderson PW, Macaulay L, Do YS, et al. Extrarenal renin-secreting tu¬ mors: insights into hypertension and ovarian renin production. Medicine 1990;68: 257. 28. Aurell M, Rudin A, Tisell LE, et al. Captopril effect on hypertension in patients with renin-producing tumor. Lancet 1979;2:149. 29. Biglieri EG. Spectrum of mineralocorticoid hypertension. Hypertension 1991; 17:251. 30. Clore J, Schoolwerth A, Watlington CO. When is cortisol a mineralocorti¬ coid? Kidney Int 1992; 42:1297. 31. Melby JC. Clinical review: I. endocrine hypertension. J Clin Endocrinol Metab 1989; 69:697. 32. White PC, Speiser PW. Steroid 110-hydroxylase deficiency and related disorders. Endocrinol Metab Clin North Am 1994;23:325. 33. Seckl JR, Brown RW. 11-Beta-hydroxysteroid dehydrogenase: on several roads to hypertension. J Hypertens 1994; 12:105. 34. Stewart PM, Edwards CRW. The cortisol-cortisone shuttle and hyperten¬ sion. J Steroid Biochem Mol Biol 1991; 40:501. 35. Funder JW, Pearce PT, Smith R, Smith IA. Mineralocorticoid action: target tissue specificity is enzyme, not receptor mediated. Science 1988; 242:583. 36. Farese RV, Biglieri EG, Shackleton CHL, et al. Licorice-induced hypermineralocorticoidism. N Engl J Med 1991;325:1223. 37. Lifton RP, Dluhy RG, Powers M, et al. A chimeric 1 lbeta-hydroxylase/ aldosterone synthase gene causes glucocorticoid-remediable aldosteronism and hu¬ man hypertension. Nature 1992;355:262. 38. Rich GM, Ulick S, Cook S, et al. Glucocorticoid-remediable aldosteronism in a large kindred: clinical spectrum and diagnosis using a characteristic biochemical phenotype. Ann Intern Med 1992; 116:813. 39. Malchoff DM, Brufsky A, Reardon G, et al. A mutation of the glucocorti¬ coid receptor in primary cortisol resistance. J Clin Invest 1993; 91:1918. 40. Norbiato G, Bevilacqua M, Vago T, et al. Cortisol resistance in acquired immunodeficiency syndrome. J Clin Endocrinol Metab 1992; 74(3):608. 41. Gomez-Sanchez CE. Cushing's syndrome and hypertension. Hyperten¬ sion 1986; 8:256. 42. Whitworth JA. Studies on the mechanisms of glucocorticoid hypertension in humans. Blood Pressure 1994; 3:24. 43. Connell JMC, Whitworth JA, Davies DL, et al. Effects of ACTH and corti¬

743

sol administration on blood pressure, electrolyte metabolism, atrial natriuretic pep¬ tide and renal function in normal man. J Hypertens 1987; 5:425. 44. Tuck ML, Corry DB. Pathophysiology and management of hypertension in diabetes. Annu Rev Med 1991;42:533. 45. Corry DB, Tuck ML. Insulin-glucoregulatory hormones: implications for antihypertensive therapy. In: Epstein M, ed. Calcium antagonists in clinical medi¬ cine. Philadelphia: Hanley & Belfus, 1992:291. 46. Weidmann P, Beretta-Piccoli C, Trost BN. Pressor factors and responsive¬ ness in hypertension accompanying diabetes mellitus. Hypertension 1985;7(Suppl 2):II-33. 47. Tuck ML, Corry D, Trujillo A. Salt-sensitive blood pressure and exagger¬ ated vascular reactivity in the hypertension of diabetes mellitus. Am J Med 1990; 88: 210. 48. Trujillo A, Egenna P, Barrett J, Tuck M. Renin regulation in type II diabetes mellitus: influence of dietary sodium. Hypertension 1989; 13:200. 49. Tuck ML. Obesity, the sympathetic nervous system, and essential hyper¬ tension. Hypertension 1992; 19(Suppl l):I-67. 50. Reisin E. Sodium and obesity in the pathogenesis of hypertension. Am J Hypertens 1990; 3:164. 51. Landsberg L. Hyperinsulinemia: possible role in obesity-induced hyper¬ tension. Hypertension 1992; 19(Suppl 1):I-61. 52. Caro J. Insulin resistance in obese and nonobese man. J Clin Invest 1985; 75:809. 53. Maxwell MH, Heber D, Waks AU, Tuck ML. Role of insulin and norepi¬ nephrine in the hypertension of obesity. Am J Hypertens 1994; 7:402. 54. Brickman AS. Hyperparathyroidism, calcium disorders, and hyperten¬ sion. In: Izzo JL, Black HR, Eds. Hypertension primer. Dallas: American Heart As¬ sociation, 1993:110. 55. Lind L, Hvarfner A, Palmer M, et al. Hypertension in primary hyperpara¬ thyroidism in relation to histopathology. Eur J Surg 1991; 157:457. 56. Brickman AS, Nyby MD, vonHungen K, et al. Calciotropic hormones, platelet calcium and blood pressure in essential hypertension. Hypertension 1990; 16:515. 57. Zawada E Jr, Brickman AS, Maxwell MH, Tuck ML. Hypertension associ¬ ated with hyperparathyroidism is not responsive to angiotensin blockade. J Clin Endocrinol Metab 1980;50:912. 58. Sancho JJ, Rouco J, Riera-Vidal R, Sitges-Serra A. Long-term effects of parathyroidectomy for primary hyperparathyroidism on arterial hypertension. World J Surg 1992; 16:732. 59. Brickman AS, Stern N, Sowers JR. Hypertension in pseudohypoparathy¬ roidism. Am J Med 1988; 85:785. 60. Kratz C, Benker G, Weber F, et al. Acromegaly and hypertension: preva¬ lence and relationship to the renin-angiotensin-aldosterone system. Klin Wochenschr 1990; 68:583. 61. Connell JMC, Davies DL. Endocrine hypertension: thyroid disease and acromegaly. In: Swales JD, ed. Textbook of hypertension. Oxford, UK: Blackwell Scientific Publications. 1994:959. 62. Klein I, Ojama K. Cardiovascular manifestations of endocrine disease. J Clin Endocrinol Metab 1992; 75:339. 63. Levy GS, Klein I. Catecholamine-thyroid hormone interactions and car¬ diovascular manifestations of hyperthyroidism. AmJ Med 1990; 88:642. 64. Streeten DHP, Anderson GH, Howland T, et al. Effects of thyroid function on blood pressure: recognition of hypothyroid hypertension. Hypertension 1988; 11:78. 65. Laragh JH, Sealey JE. The renin-angiotensin-aldosterone system and the renal regulation of sodium and potassium and blood pressure homeostasis. In: Windhager EE, ed. Handbook of renal physiology. New York: Oxford University Press, 1992:1409. 66. Alderman MH, Madhavan S, Ooi WL, et al. Association of the reninsodium profile with risk of myocardial infarction in patients with hypertension. N EnglJ Med 1991;324:1098. 67. Laragh JH, Letcher RL, Pickering TG. Renin profiling for diagnosis and treatment of hypertension. JAMA 1979; 241:151. 68. Sealey JE, Blumenfeld JD, Bell GM, et al. On the renal basis for essential hypertension: nephron heterogeneity with discordant renin secretion and sodium excretion causing a hypertensive vasoconstriction-volume relationship. J Hypertens 1988;6:763. 69. Melby JC, Dale SL, Holbrook M, et al. 19-nor-corticosteroids in health, in hypertensive states in humans including 17-alpha-hydroxylase deficiency and in spontaneously hypertensive rats. Endocr Res Commun 1984-1985; 10:591. 70. Gomez-Sanchez CE, Holland OB, Upcavage R. Urinary-free 19-nordeoxycorticosterone and deoxycorticosterone in human hypertension. J Clin Endo¬ crinol Metab 1985; 60:234. 71. Buhler FR, Bolli P, Kiowski W, et al. Renin profiling to select antihyperten¬ sive baseline drugs: renin inhibitors for high renin and calcium entry blockers for low renin hypertension. Am J Med 1984; 77:36. 72. Shoback DM, Williams GH, Moore TJ, et al. Defect in the sodiummodulated tissue responsiveness to angiotensin II in essential hypertension. J Clin Invest 1983; 72:2115. 73. Williams GH, Dluhy RG, Lifton RP, et al. Non-modulation as an interme¬ diate phenotype in essential hypertension. Hypertension 1992;20:788. 74. Julius S. Changing role of the autonomic nervous system in human hy¬ pertension. J Hypertens 1990;9(Suppl 7):S59. 75. Mark AL. Regulation of sympathetic nerve activity in mild human hyper¬ tension. J Hypertens 1990;8(Suppl 7):S67. 76. Goldstein DS. Plasma catecholamines in essential hypertension: an ana¬ lytical review. Hypertension 1983;5:86.

744

PART V: THE ADRENAL GLANDS

77. Esler M, Jennings G, Lambert G, et al. Overflow of catecholamine neuro¬ transmitters to the circulation: source, fate, and function. Physiol Rev 1990;70:963. 78. Tuck ML, Stern N, Sowers JR. Enhanced 24-hour norepinephrine and renin secretion in young patients with essential hypertension: relation with circa¬ dian pattern of arterial blood pressure. Am J Cardiol 1985;55:112. 79. Rand MJ, Majewski H. Adrenaline mediates a positive feedback loop in noradrenergic transmission: its possible role in development of hypertension. Clin Exp Hypertens 1984;A6:347. 80. Gill JR, Grossman E, Goldstein DS. High urinary dopa excretion and low urinary dopamine: dopa ratio in salt-sensitive hypertension. Hypertension 1991; 18: 614. 81. Blaustein MP. Sodium ions, calcium ions, blood pressure regulation, and hypertension: a reassessment and a hypothesis. Am J Physiol 1977;232:C165. 82. Maxwell MH, Waks AU, Corry DB, Tuck ML. Altered sodium and potas¬ sium metabolism in the pathogenesis of hypertension. In: Maxwell MH, Kleeman C, Narrins R, eds. Disorders of fluid and electrolyte metabolism, ed 5. New York: McGraw-Hill, 1993:1245. 83. Hilton PJ. Na+ transport in hypertension. Diabetes Care 1991; 14:233. 84. Bobick A, Neylon CB, Little PJ. Disturbances of vascular smooth muscle cation transport and the pathogenesis of hypertension. In: Swales JD, ed. Textbook of hypertension. Oxford, UK: Blackwell Scientific Publications, 1994:175. 85. Hamlyn JM, Blaustein MP, Bova S, et al. Identification and characteriza¬ tion of a ouabain-like compound from human plasma. Proc Natl Acad Sci USA 1991;88(14):6259. 86. Blaustein MP. Physiologic effects of endogenous ouabain: control of in¬ tracellular calcium stores and cell responsiveness. Am J Physiol 1993; 264:0 367. 87. Brenner BM, Ballerman BJ, Gunning ME, Zeidel ML. Diverse biological actions of atrial natriuretic peptide. Physiol Rev 1990;70:665. 88. Roller KJ, Goeddel DV. Molecular biology of the natriuretic peptides and their receptors. Circulation 1992; 86:1081. 89. Margulies KB, Burnett JC. Neutral endopeptidase 24.11: a modulator of natriuretic peptides. Semin Nephrol 1993; 13:71. 90. Bhoola KD, Figueroa CD, Worthy K. Bioregulation of kinins: kallikreins, kininogens, and kinases. Pharmacol Rev 1992; 44:1. 91. Carretero OA, Scili AG. The kallikrein-kinin system. In: Fozzard HA, ed. The heart and cardiovascular system. New York: Scientific Foundations, Raven Press, 1991:1851.

kcal/m2/day). A nomogram for determining surface area is given in Figure 81-1. Normal daily sodium and potassium maintenance require¬ ments are 2 to 3 mEq/dL and 1 to 2 mEq/dL of water, respec¬ tively. When calculating electrolyte replacement, it must be re¬ membered that the exchangeable fluid compartment is relatively larger in children than in adults, ranging from 60% of body weight in small children to 40% in adults. Because of the rapid rate of turnover of children's body fluid, the electrolyte concen¬ trations of parenteral fluids should be distributed evenly throughout the day to prevent shifts in the tonicity of body fluids. Infants and children are intolerant of prolonged fasting be¬ cause of their high metabolic rate and functionally immature gluconeogenetic and glycogenolytic enzyme systems. When fasted, normal young children become hypoglycemic within as few as 20 hours. To prevent glycogenolysis, infants and young children need 6 to 8 mg/kg/min of glucose.1 The production of glucocorticoids and the excretion of their metabolites are essentially constant with respect to surface area and lean body mass throughout life. The daily secretion rate of cortisol approximates 6 to 8 mg/m2.2 Urinary cortisol excretion ranges from 15 to 70 Mg/m2 or Mg/g of creatinine. Urinary 17hydroxycorticoid excretion measured as Porter-Silber chromo¬ gens is a poor index of cortisol secretion in the neonate because of deficient glucuronyl transferase activity in the first month of life. Plasma cortisol concentrations vary from 4 to 25 Mg/dL, as in adults. The circadian rhythm of adrenocortical secretion is es¬ tablished by 3 months of age. However, the aldosterone secretion rate is constant throughout life at approximately 80 Mg/day.4 Thus, in infants, it is several times more than that of adults in terms of surface area.3 Plasma aldosterone levels and renin activ¬ ity are higher in infants than subsequently; the levels of these two constituents gradually decline during childhood (Table 81-1), but absolute levels vary among laboratories.5,6 Plasma dehydroepiandrosterone sulfate (DHEAS) levels are at adult levels at birth (as a consequence of the function of the fetal zone of the adrenal gland), fall during early infancy, and rise with adrenarche7,8 (Table 81-2).

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

WEIGHT (kg)

CHAPTER

81_

10

20

30

40

50

60

70

80

ADRENOCORTICAL DISORDERS IN INFANCY AND CHILDHOOD ROBERT L. ROSENFIELD AND ALBERT C. WATSON

GENERAL PRINCIPLES Along with the well-known perturbations of fluid, electro¬ lyte, and glucose homeostasis, adrenocortical diseases occurring in children also cause disturbed growth. The proper treatment of children with these disorders requires careful documentation of height and weight at regular intervals. Physicians who are relatively unfamiliar with pediatric pa¬ tients may assume that the fluid and electrolyte requirements of infants and children are similar to those of adults. Actually, in¬ fants are hypermetabolic, as compared with adults, because of the relatively large size of their high-energy-consuming organs (i.e., the brain, heart, liver, and kidneys) as compared to their somatic size. Water requirements change in proportion to caloric requirements. One milliliter of water is required for each kilocal¬ orie of energy expenditure. Water and calorie requirements are about constant throughout life relative to surface area (1500

FIGURE 81-1. Relationships of surface area to body weight. Individuals of normal size (5th to 95th percentile) vary less than 10% from the mean given here.

Ch. 81: Adrenocortical Disorders in Infancy and Childhood TABLE 81-1 Typical Normal Plasma Values in Infancy and Childhood for Renin-Aldosterone Axis PRA (ng/mL/hr)

Aldosterone (ng/mL)

Age

Range

Range

Term, 15 y, ambulatory >15 y, supine

3 WEEKS

Glycogen

Glycogen

Amino Acids

Amino Acids

Amino Acids

Fatty Acids

Glucose

Glucose

Glucose

+

♦

Fatty Acids

Glucose

Ketones

Glucose

Ketones

Protein

Fatty Acids + Ketones

Protein

Fatty Acids + Ketones

BRAIN

♦

Glucose

Fatty Acids

Energy

Energy

♦

♦

♦

♦

Amino Acids

Energy

♦

Triglycerides

Fatty Acids

Fatty Acids

Fatty Acids

♦

♦

Fatty Acids

Glutamine

Energy

Energy

Ammonia + Glucose

Glucose

Glucose

Glucose

Energy

Energy

Triglycerides

Glucose

♦

1 i

Amino Acids

Triglycerides

\

ADIPOSE TISSUE

KIDNEY

stores become depleted during the first 24 hours of fasting, plasma levels of glucose decrease modestly, gluconeogenesis be¬ comes a progressively more important source of glucose, and al¬ ternative substrates begin to replace glucose as a metabolic fuel.5 Free fatty acid release from adipose tissue triglyceride stores is augmented, resulting in increased plasma fatty acid levels, con¬ sumption of fatty acids by skeletal muscle and kidney, and spar¬ ing of glucose. The synthesis of ketone bodies by the liver is acti¬ vated by the increased availability of fatty acids and a rising glucagon/insulin ratio, elevating circulating levels of ketone bodies as starvation continues.6 Skeletal muscle, kidney, and brain begin to metabolize ketone bodies in proportion to their plasma concentrations, further reducing the requirement for glucose. The net breakdown of muscle protein during starvation re¬ flects the requirements of the liver and kidney for substrates for gluconeogenesis and ammoniagenesis, respectively. Alanine and other amino acids released from muscle are converted into glu¬ cose in the liver,7 whereas muscle-derived glutamine8 is utilized primarily in renal ammoniagenesis or as a fuel and precursor of gluconeogenic amino acids in the gastrointestinal tract.9 During early starvation, the increased urinary levels of metabolically generated anions in the form of ketone bodies requires an accom-

POSTABSORPTIVE

♦

i

Energy

Fatty Acids + Ketones

1 1

♦

Energy

Glutamine

Fatty Acids + Ketones

Energy

Ammonia + Glucose

Energy

Ketones

Glucose

Ketones

Energy

1165

i

Energy

i

Energy

FIGURE 126-2.

Principal pathways of metabolic fuel use and production by tissues during the different phases of starvation. The size of the ar¬ row reflects the relative importance of the pathway.

1166

PART IX: DISORDERS OF FUEL METABOLISM

panying excretion of sodium. This probably explains the natriuresis and diuresis, correlated with rapid weight loss, that occur during the first days of a fast.10 As total body sodium becomes depleted and ketone body production increases, ammonium de¬ rived primarily from glutamine replaces sodium as the primary urinary cation. As starvation progresses and the levels of ketone bodies and free fatty acids continue to rise, diminished requirements for en¬ dogenous glucose production enable an adaptive conservation of body protein.11 Thus, during long-term fasting, amino acid con¬ version to glucose is minimized, and the net breakdown of mus¬ cle protein is governed largely by the glutamine requirement for maintenance of acid-base balance through renal ammoniagenesis pathways.12 This series of metabolic adaptations during fasting assures adequate metabolic fuels for all tissues and the efficient utiliza¬ tion of nutrient stores. The net result is a remarkable capacity for survival in the absence of food intake. The maximal duration of fasting compatible with life in initially normal-weight persons is demonstrated by the unfortunate example of political protesters in Northern Ireland, who died after 45 to 76 days of essentially total fasting.13 Obese patients, who may have as much as four times the normal caloric reserve, have been treated clinically with total fasting for more than 200 days without serious complica¬ tions,14 although the apparent risk of sudden death from cardiac failure makes fasting of this duration inadvisable.15 Thus, the length of time a person can survive starvation differs with body composition. Generally, the loss of one third to one half of body nitrogen is incompatible with life in lean or obese patients, but the large fat stores in obesity allow longer-term sparing of body nitrogen. Patients with debilitating illnesses or malnourished, wasted persons may have a markedly decreased tolerance for nu¬ trient deprivation.

HORMONAL CONTROL AND ADAPTATION DURING STARVATION The most important factor controlling the metabolic adapta¬ tion to starvation is insulin: without a regulated decrease in the secretion and the circulating levels of insulin, endogenous glucose-generating pathways cannot be activated, and alterna¬ tive fuel stores cannot be mobilized. Superimposed on these do¬ minant actions of insulin are the effects of multiple other cata¬ bolic and anabolic hormones, including glucagon, growth hormone, growth factors, thyroid hormone, and glucocorticoids. Regulated change in the levels of each of these hormones is es¬ sential for effective metabolic adaptation during fasting.

INSULIN The changes in circulating hormone levels during starvation are illustrated in Figure 126-3. Plasma insulin levels decrease to about half the normal postabsorptive levels during the first 3 days of food withdrawal and then stabilize at low but physiolog¬ ically significant concentrations.16 This adaptation in insulin se¬ cretion develops gradually during fasting and, in turn, normal¬ izes only after several days of refeeding. Thus, when glucose or other food is ingested after a period of fasting, there is a subnor¬ mal insulin secretory response.17 In some nondiabetic persons, glucose intolerance may be observed after periods of inadequate food ingestion; therefore, the results of glucose tolerance tests can be difficult to interpret unless patients have had adequate carbohydrate and total caloric intake for several days before testing.

GLUCAGON During starvation, the blood glucose concentration is main¬ tained in part through the action of glucagon. Serum glucagon

A

B

FIGURE 126-3. Changes in hormone levels during fasting. A, Insulin. B, Glucagon. (Data in A and B from Marliss EB, Aoki TT, Unger RH, et al. Glucagon levels and metabolic effects in fasting man. J Clin Invest 1970;49: 2256.) C, Growth hormone and insulin-like growth factor I (IGF-I). (Data from Cahill GF Jr, Herrera MG, Morgan AP, et al. Hormone-fuel interrela¬ tionships during fasting. J Clin Invest 1966;45:1751; and Isley WL, Un¬ derwood LE, Clemmons DR. Dietary components that regulate serum somatomedin-C concentrations in humans. J Clin Invest 1983;71:175.) D, T3 and rT3. (Data from Merimee TJ, Fineberg ES. Starvation-induced alterations of circulating thyroid hormone concentrations in man. Metabolism 1976;25:79; and Gardner DF, Kaplan MM, Stanley CA, Utiger RD. Effect of triiodothyro¬ nine replacement on the metabolic and pituitary responses to starvation. N Engl] Med 1979; 300:579.)

levels increase within the first 48 hours and continue to rise throughout the first several days of fasting in normal humans.16 In obese persons undergoing prolonged fasting, plasma glucagon concentrations rise initially but return toward prefast levels after 3 to 4 weeks.18 Probably, in early starvation, hyperglucagonemia is attributable to decreased clearance of the hormone rather than to increased secretion.18 During prolonged starvation, glucagon levels return toward normal because of a decrease in secretion, with continued decreased clearance of the hormone. Pancreatic stores of glucagon do not appear to be diminished after short¬ term fasting, as evidenced by an exaggerated glucagon secretory response to arginine infusion.19 With low concentrations of insulin in the fasting state, glu¬ cagon contributes to the maintenance of glucose homeostasis by stimulating hepatic gluconeogenesis and glycogenolysis.6,20 An increase in the plasma glucagon/insulin ratio during early star¬ vation also promotes the generation of alternative fuels by in¬ creasing hepatic synthesis of ketone bodies and mobilizing free fatty acids from adipose tissue.21 In prolonged starvation, circu¬ lating glucagon returns to postabsorptive levels concurrent with the reduced demand for glucose (see Chap. 130).

GROWTH HORMONE AND INSULIN-LIKE GROWTH FACTOR I Serum growth hormone levels also become elevated early in starvation.22 The role of growth hormone as a metabolic regulator during fasting is unclear, however, because individual values are variable and do not correlate closely with metabolic adaptations. Because patients with growth hormone deficiency can become hypoglycemic during fasting,23 it seems reasonable to conclude

Ch. 126: Starvation that adequate levels of the hormone are important for the main¬ tenance of blood glucose in the fasting state but that elevated concentrations have an otherwise minor role in the metabolic ad¬ aptation to fasting. Possibly, elevated growth hormone secretion during fasting is a consequence, in part, of the normal feedback relation be¬ tween insulin-like growth factor I (IGF-I) and growth hormone.24 IGF-I, which is alternatively designated somatomedin C, is a pep¬ tide growth factor with a primary structure homologous to that of proinsulin; it is an important mediator of the anabolic actions of growth hormone25 (see Chaps. 14 and 169). Growth hormone stimulates IGF-I synthesis in the liver and some peripheral tis¬ sues, and there is evidence that IGF-I in turn exerts negative feed¬ back inhibition on growth hormone secretion.26 Although growth hormone appears to be the principal regulator of IGF-I, other factors, such as thyroid hormone, insulin, estrogens, and nutritional status, also influence IGF-I levels.27 As a consequence, circulating levels of IGF-I decrease during fasting in spite of ele¬ vated growth hormone levels,28'29 and feedback inhibitory effects of IGF-I on growth hormone secretion do not occur. During fast¬ ing, growth hormone binding in the liver is reduced in parallel with decreased IGF-I mRNA synthesis, suggesting growth hor¬ mone resistance as a mechanism contributing to decreased circu¬ lating IGF-I.30 Decreased IGF-I also occurs during protein restric¬ tion, however, even though liver growth hormone binding is not altered.31 Thus, protein restriction appears to affect growth hor¬ mone regulation of circulating IGF-I through a postreceptor mechanism. Fasting also reduces IGF-I mRNA levels in periph¬ eral tissues, including kidney, muscle, gut, and brain, while si¬ multaneously increasing IGF-I receptor mRNA.32 The combina¬ tion of low IGF-I and high growth hormone levels may have adaptive value by diminishing the energy expenditure necessary for growth-related processes and yet enabling growth hormone to promote the mobilization of alternative fuels through its lipo¬ lytic actions.29 The availability of IGF-I to tissues is directly in¬ fluenced by circulating IGF binding proteins (IGFBP). IGFBP-3 is thought to be the major carrier of IGFs in the circulation. Pro¬ longed fasting or protein depletion is correlated with decreased concentrations of IGFBP-3.33 IGFBP-2 and IGFBP-1 may mediate cellular transport of the IGFs. Both IGFBP-2 and IGFBP-1 tend to increase during prolonged fasting, likely as a consequence of decreased insulin concentrations.33 In malnourished patients given nutritional support, the di¬ rection of changes in serum IGF-I levels correlates closely with the direction of changes in nitrogen balance. Refeeding adequate energy but low protein only partially restores circulating IGFI concentrations. When total parenteral nutrition is provided to nutritionally deprived patients, serum IGF-I levels rise at a rate corresponding to the improvement in nitrogen balance.34 This does not appear to reflect simply increased synthesis of hepatic proteins secondary to improved nutrition, because the levels of other hepatic secretory proteins are not consistently raised during the time IGF-I increases. IGF-I may prove to be a sensitive indi¬ cator of the response to nutritional rehabilitation.35

THYROID HORMONE One of the energy-conserving adaptations during prolonged starvation is a decrease in the basal metabolic rate, which is me¬ diated at least in part by altered levels of triiodothyronine (T3). In normal humans undergoing a short-term fast, serum T3 levels decrease, whereas levels of thyroxine (T4), thyroid-stimulating hormone, and the response of thyroid-stimulating hormone to thyroid-releasing hormone are unchanged.36-38 Experimentally, starvation causes an increased sensitivity of pituitary thyrotrope cells to T3.39 The decrease in serum T3 coincides with an increase in less biologically potent reverse T3, suggesting that peripheral tissues convert a greater proportion of T4 into reverse T3 during fasting (see Chaps. 31 and 36). A similar hormonal pattern de¬ velops in adults with protein-energy malnutrition.40 If T3 levels

1167

are maintained by the administration of T3 during fasting, an in¬ crease in the catabolism of nutrient stores occurs, as demon¬ strated by elevated levels of glucose, free fatty acids, and ketone bodies,41 and by increased urinary urea excretion.37 Therefore, it is thought that diminished levels of T3 may explain the decreased oxygen consumption observed in prolonged starvation and may be protective in limiting muscle protein breakdown.

GLUCOCORTICOIDS In obese patients undergoing prolonged starvation, no change in cortisol production rate, plasma corticosteroid levels, or stimulation of cortisol production by corticotropin occurs.42 However, patients with glucocorticoid deficiency frequently have fasting hypoglycemia, because adequate glucocorticoid lev¬ els are necessary to maintain the activity of pyruvate carboxylase, a rate-limiting enzyme for gluconeogenesis, 3 and for the release of gluconeogenic amino acids from skeletal muscle.44 Although glucocorticoid levels do not change with fasting, it appears that normal levels are necessary for the adaptive response to starvation.

CATECHOLAMINES Increased sympathetic nervous system activity may contrib¬ ute to the elevation of plasma free fatty acids and glucagon con¬ centrations, and to the maintenance of blood glucose levels dur¬ ing fasting, but several lines of evidence suggest that this is not an important factor.45 For example, normal elevations in free fatty acid levels occur during fasting in patients who have un¬ dergone adrenalectomy, adrenergic blockade, or even complete disruption of the sympathetic efferent pathways at the level of the cervical cord.46-48 Similarly, catecholamine deficiency has not been associated with the development of fasting hypoglycemia. Therefore, it appears that sympathetic activity neither initiates nor maintains the metabolic adaptations to starvation.

IMPACT OF STARVATION ON ENDOCRINE AND NONENDOCRINE DISEASE The adaptive metabolic responses to starvation make it pos¬ sible for humans to survive long periods of inadequate nutrient intake.49 Because the metabolic adaptation to fasting is largely the result of endocrinologic regulation, the normal response can be markedly altered by endocrine disorders. For example, lack of a single hormone, such as cortisol50 or growth hormone,51 can cause severe hypoglycemia within a few hours of food depriva¬ tion. Fortunately, these primary endocrinologic diseases are rela¬ tively uncommon and generally recognized early. Much more commonly, patients with nonendocrine disease are nutritionally depleted but unable to generate a normal endo¬ crine response to partial or total fasting. Consequently, malnutri¬ tion can have a significant effect on morbidity and mortality rates. For example, after traumatic injuries, major operative proce¬ dures, burns, systemic infections, or other serious illnesses, a well-characterized catabolic stress response develops.5" An im¬ portant adaptive function of this response appears to be the ac¬ celerated mobilization of body nutrient stores, which are used in tissue repair, by inflammatory cells, and for processes such as acute-phase protein synthesis. The metabolic alterations of stress depend in large part on changes in hormone levels, which, as illustrated in Figure 126-4, are different from the endocrine re¬ sponse to fasting. Levels of sympathetic nervous system activity and circulating catecholamines rise early,53 followed somewhat later by more sustained elevations of glucocorticoids,54 gluca¬ gon,55 and growth hormone.56 Insulin levels may be decreased early but ultimately are normal or elevated.57 In addition, wounds, sepsis, or inflammation induce a variety of hormonal

1168

PART IX: DISORDERS OF FUEL METABOLISM INSULIN

CATECHOLAMINES

GLUCAGON

CORTISOL

FIGURE 126-4. Effects of burn injury on basal hormone levels. Plasma hormone concentrations were determined after 8 hours of fasting in 15 subjects with 25% to 90% burns. (Redrawn from Wolfe RR, Durkot MJ, Allsop JR, Burke JF. Glucose metabolism in severely burned patients. Metab¬ olism 1979;28:1031.)

mediators, or cytokines, such as tumor necrosis factor and the interleukins, which exacerbate skeletal muscle breakdown and debilitation.58 Attenuation of the metabolic effects of these stress mediators through nutritional intervention is limited, although specific nutrient formulas in combination with trophic hormones potentially may provide beneficial effects.59 When decreased nutrient intake or total fasting coincide with severe injury or illness, the normal metabolic adaptation to fasting does not develop. Instead of decreased energy require¬ ments and a lowered basal metabolic rate, energy requirements remain increased as a result of the demands for tissue repair pro¬ cesses, inflammatory cell formation and function, hyperdynamic circulation, and, sometimes, fever-associated shivering. In¬ creased concentrations of stress hormones, in particular gluco¬ corticoids, greater than the levels characteristic of fasting may lead to the net catabolism of tissue protein and may increase neg¬ ative nitrogen balance.60 Insulin levels remain normal or elevated in spite of fasting, reflecting a state of insulin resistance that pre¬ vents insulin from counteracting the catabolic effects of the stress hormones. In spite of this insulin resistance, there may be enough antilipolytic action of insulin in some patients to diminish free fatty acid mobilization and ketone body synthesis and, thus, in¬ terfere with the normal transition to lipid fuel consumption dur¬ ing fasting. Consequently, in some patients with multiple trau¬ matic injuries, levels of plasma ketone bodies remain low during fasting.61 This is associated with increased urinary nitrogen ex¬ cretion and, probably, less effective protein conservation. As in starvation, adaptation to a catabolic stress ultimately is characterized by a reduction of muscle protein catabolism and increased use of free fatty acids and ketone bodies.62 Depending on the demands for glucose consumption and overall energy use, and on the effectiveness of alternative fuel mobilization, how¬ ever, the adaptation may be delayed for many weeks. Thus, even modest degrees of undernutrition or short periods of total fasting can lead to significant nutritional depletion, such that the provi¬ sion of adequate nutritional support in the setting of catabolic diseases may be essential for optimal recovery or even survival. Parenteral feeding should be considered early in the course of critically ill patients if oral food intake is inadequate.

REFERENCES 1. Olsen RE. Protein-calorie malnutrition. New York: Academic Press, 1975. 2. Winick M. Long term effects of kwashiorkor. J Pediatr Gastroenterol Nutr 1987;6:833. 3. Wolstenholme GEW, O'Connor M. Nutrition and infection. Boston: Little, Brown, 1967. 3a. Adhikari M, Gita-Ramjee, Berjak P. Aflatoxin, kwashiorkor, and morbid¬ ity. Natural Toxins 1994;2:1. 4. Cahill GF, Owen OE, Morgan AP. The consumption of fuels during pro¬ longed starvation. Adv Enzyme Regul 1968;6:143. 5. Webber J, Macdonald IA. The cardiovascular, metabolic and hormonal changes accompanying acute starvation in men and women. Br J Nutr 1994; 71:437. 6. Gelfand RA, Sherwin RS. Glucagon and starvation. In: Lefebvre PJ, ed. Glucagon II. Handbook of experimental pharmacology, vol 66[II], Berlin: SpringerVerlag, 1983:223. 7. Felig P, Marliss E, Owen OE, Cahill GF Jr. Blood glucose and gluconeogenesis in fasting man. Arch Intern Med 1969; 123:293. 8. Marliss EB, Aoki TT, Pozefsky T, et al. Muscle and splanchnic glutamine and glutamate metabolism in postabsorptive and starved man. J Clin Invest 1971; 50:814. 9. Windmueller HG. Glutamine utilization by the small intestine. Adv Enzymol Relat Areas Mol Biol 1982;53:202. 10. Sigler MH. The mechanism of the natriuresis of fasting. J Clin Invest 1975;55:377. 11. How ketones spare protein in starvation. (Editorial) Nutr Rev 1989;3:80. 12. Aoki TT, Mueller WA, Brennan MF, Cahill GF Jr. Metabolic effects of glucose in brief and prolonged fasted man. Am J Clin Nutr 1975; 28:507. 13. Kerndt PR, Naughton JL, Driscoll CE, Loxterkamp DA. Fasting: the his¬ tory, pathophysiology and complications. West J Med 1982; 137:379. 14. Thomson TJ, Runcie J, Miller V. Treatment of obesity by total fasting for up to 249 days. Lancet 1966; 2:992. 15. Garnett ES, Barnard DL, Ford J, et al. Gross fragmentation of cardiac my¬ ofibrils after therapeutic starvation for obesity. Lancet 1969; 1:914. 16. Marliss EB, Aoki TT, Unger RH, et al. Glucagon levels and metabolic effects in fasting man. J Clin Invest 1970;49:2256. 17. Fink G, Gutman RA, Cresto JC, et al. Glucose-induced insulin release patterns: effect of starvation. Diabetologia 1974; 10:421. 18. Fisher M, Sherwin RS, Hendler R, Felig P. Kinetics of glucagon in man: effects of starvation. Proc Natl Acad Sci USA 1976;73:1735. 19. Aguilar-Parada E, Eisentraut AM, Unger RH. Effects of starvation on plasma pancreatic glucagon in normal man. Diabetes 1969; 18:717. 20. Ven de Werve G, Hue L, Hers HG. Hormonal and ionic control of the glycogenolytic cascade in rat liver. Biochem J 1977; 162:135. 21. McGarry JD, Foster DW. Regulation of hepatic fatty acid oxidation and ketone body production. Annu Rev Biochem 1980; 493:395. 22. Cahill GF Jr, Herrera MG, Morgan AP, et al. Hormone-fuel interrelation¬ ships during fasting. J Clin Invest 1966;45:1751. 23. Merimee TJ, Felig P, Marliss E, et al. Glucose and lipid homeostasis in the absence of human growth hormone. J Clin Invest 1971;50:574. 24. Abe H, Molitch ME, Van Wyk JJ, Underwood LE. Human growth hor¬ mone and somatomedin C suppress the spontaneous release of growth hormone in unanesthetized rats. Endocrinology 1983; 113:1319. 25. Chochinov RH, Daughaday WH. Current concepts of somatomedin and other biologically related growth factors. Diabetes 1976;25:994. 26. Clemmons DR, Underwood LE. Somatomedin-C/insulin-like growth factor I in acromegaly. J Clin Endocrinol Metab 1986; 15:629. 27. Phillips LS, Goldstein S, Gavin JR III. Nutrition and somatomedin XVI: somatomedins and somatomedin inhibitors in fasted and refed rats. Metabolism 1988;37:209. 28. Isley WL, Underwood LE, Clemmons DR. Dietary components that reg¬ ulate serum somatomedin-C concentrations in humans. J Clin Invest 1983;71:175. 29. Merimee TJ, Zapf J, Froesch ER. Insulin-like growth factors in the fed and fasted states. J Clin Endocrinol Metab 1982;55:999. 30. Straus DS, Takemoto CD. Effect of fasting on insulin-like growth factorI (IGF-I) and growth hormone receptor mRNA levels and IGF-I gene transcription in rat liver. Mol Endocrinol 1990; 4:91. 31. Maiter DM, Maes M, Underwood LE, et al. Early changes in serum con¬ centrations of somatomedin-C induced by dietary protein deprivation: contribu¬ tions of growth hormone receptor and post-receptor defects. J Endocrinol 1988; 118: 113. 32. Lowe WJ, Adamo M, Werner H, et al. Regulation by fasting of insulin¬ like growth factor-I and its receptor: effects on gene expression and binding. J Clin Invest 1989;84:619. 33. Clemmons DR, Underwood LE. Nutritional regulation of IGF-I and IGF binding proteins. Annu Rev Nutr 1991; 11:393. 34. Clemmons DR, Underwood LE, Dickerson RN, et al. Use of plasma somatomedin-C/insulin-like growth factor I measurements to monitor the response to nutritional repletion in malnourished patients. Am J Clin Nutr 1985; 41:191. 35. Unterman TG, Vazquez RM, Slas AJ, et al. Nutrition and somatomedin XIII: usefulness of somatomedin-C in nutritional assessment. Am J Med 1985; 78: 228. 36. Merimee TJ, Fineberg ES. Starvation-induced alterations of circulating thyroid hormone concentrations in man. Metabolism 1976;25:79. 37. Gardner DF, Kaplan MM, Stanley CA, Utiger RD. Effect of triiodothyro¬ nine replacement on the metabolic and pituitary responses to starvation. N Engl J Med 1979;300:579.

Ch. 127: Anorexia Nervosa and Other Eating Disorders 38. Vagenakis AG. Thyroid hormone metabolism in prolonged experimental starvation in man. In: Vigersky RA, ed. Anorexia nervosa. New York: Raven Press, 1977:243. 39. Hugues JN, Enjalbert A, Burger AG, et al. Sensitivity of thyrotropin (TSH) secretion to 3,5,3'-triiodothyronine and TSH-releasing hormone in rats during star¬ vation. Endocrinology 1986; 119:253. 40. Chopra I], Smith SR. Circulating thyroid hormones and thyrotropin in adult patients with protein-calorie malnutrition. J Clin Endocrinol Metab 1975; 40: 221. 41. Carter WJ, Shakir KM, Hodges S, et al. Effect of thyroid hormone on metabolic adaptation to fasting. Metabolism 1975; 24:1177. 42. Sabeh G, Alley RA, Robbins TJ, et al. Adrenocortical indices during fast¬ ing in obesity. J Clin Endocrinol Metab 1969; 29:373. 43. Baxter JD, Forsham PH. Tissue effects of glucocorticoids. Am J Med 1972;53:573. 44. Bondy PK, Ingle D], Meeks RC. Influence of adrenal cortical hormones upon the level of plasma amino acids in eviscerate rats. Endocrinology 1954;55: 354. 45. Jung RT, Shetty PS, James WPT. Nutritional effects on thyroid and cate¬ cholamine metabolism. Clin Sci 1980;58:183. 46. Levy AC, Ramey ER. Effect of autonomic blocking agents on depot fat mobilization in normal and adrenalectomized animals. Proc Soc Exp Biol Med 1958;99:637. 47. Misbin RI, Edgar PJ, Lockwood DH. Adrenergic regulation of insulin se¬ cretion during fasting in normal subjects. Diabetes 1970; 19:688. 48. Brodows RG, Campbell RG, Al-Aziz AJ, Pi-Sunyer FX. Lack of central autonomic regulation of substrate during early fasting in man. Metabolism 1976; 25: 803. 49. Joslin EP. Treatment of diabetes mellitus. Philadelphia: Lea & Febiger, 1916:243. 50. Bondy PK. Disorders of the adrenal cortex. In: Wilson JD, Foster DW, eds. Williams textbook of endocrinology, ed 7. Philadelphia: WB Saunders, 1985:816. 51. Goodman HG, Grumbach MM, Kaplan SJ. Growth and growth hormone 11: a comparison of isolated growth-hormone deficiency and multiple pituitary-hor¬ mone deficiencies in 35 patients with idiopathic hypopituitary dwarfism. N Engl J Med 1968; 278:57. 52. Wolfe RR, Durkot MJ, Allsop JR, Burke JF. Glucose metabolism in se¬ verely burned patients. Metabolism 1979,-28:1031. 53. Jaattela A, Alho A, Avikainen V, et al. Plasma catecholamines in severely injured patients: a prospective study on 45 patients with multiple injuries. Br J Surg 1975; 62:177. 54. Vaughan GM, Becker RA, Allen JP, et al. Cortisol and corticotrophin in burned patients. J Trauma 1982;22:263. 55. Wilmore DW, Lindsey CA, Moylan JA, et al. Hyperglucagonaemia after burns. Lancet 1974; 1:73. 56. Ross H, Johnston IDA, Welborn TA, Wright AD. Effect of abdominal op¬ eration on glucose tolerance and serum levels of insulin, growth hormone, and hy¬ drocortisone. Lancet 1966; 2:563. 57. Black PR, Brooks DC, Bessey PQ, et al. Mechanisms of insulin resistance following injury. Ann Surg 1982; 196:420. 58. Hardin TC. Cytokine mediators of malnutrition: clinical implications. Nutr Clin Pract 1993; 8:55. 59. Wilmore DW. Catabolic illness. N Engl J Med 1991:325:695. 60. Tishler ME, Leng E, Al-Kanhal M. Metabolic response of muscle to trauma: altered control of protein turnover. In: Dietze G, Kleinberger W, eds. Clini¬ cal nutrition and metabolic research proceedings, 7th congress. Munich: ESPEN, 1985:40. 61. Smith R, Fuller DJ, Wedge JH, et al. Initial effect of injury on ketone bod¬ ies and other blood metabolites. Lancet 1975; 1:1. 62. Krause MV, Mahan LK. The metabolic stress response and methods for providing nutritional care to stressed patients. In: Food, nutrition, and diet therapy, ed 6. Philadelphia: WB Saunders, 1979:694.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

127_

ANOREXIA NERVOSA AND OTHER EATING DISORDERS MICHELLE P. WARREN Starvation engenders various adaptive metabolic and endo¬ crine changes that decrease caloric demands and permit survival. The starvation associated with the syndrome of anorexia nervosa combines medical, endocrine, and psychological manifestations.

1169

The abnormality is partly hypothalamic in origin and represents an adaptation to the starvation state.1,2 Although not associated with starvation, bulimia (abnormal means of purging of calories or of weight) similarly involves endocrine and behavioral symptoms.

ANOREXIA NERVOSA Anorexia nervosa usually occurs during adolescence and in women younger than 25 years. Amenorrhea, weight loss, and behavioral changes constitute the classic triad, any one of which may precede the others. The incidence differs greatly among popula¬ tion groups, and there are high-risk populations.3 For example, 1 in 100 middle-class adolescent girls and 1 in 20 to 1 in 5 profes¬ sional ballet dancers have anorexia.4-6 The Diagnostic and Statis¬ tical Manual of Mental Disorders-lU-Revised estimates that the rate of anorexia in girls between the ages of 12 and 18 years ranges from 1 in 800 to 1 in 100.7 The high incidence of this disorder in dancers derives from the rigid standards for thinness as well as the many hours of exercise this profession entails.5 (Increased levels of activity and restricted eating can induce self¬ starvation in rats, providing an interesting animal model.8) On the other hand, the condition is rare among blacks, including black ballet dancers, despite their exposure to the rigid standards of competition and weight restriction.5,9 This difference may re¬ late to different social or cultural influences, or, perhaps, to more efficient metabolic mechanisms. The risk of a sister of a patient with anorexia nervosa acquiring the illness is 6%; this fact, plus studies on monozygous twins, suggests that inborn metabolic factors contribute to the syndrome.13 There is an increased inci¬ dence of anorexia nervosa in Turner syndrome, diabetes mellitus, and Cushing disease.6,11 The female/male ratio is 9/1.12 The con¬ dition has been reported in men who are training for competitive activity while restricting their weight.13 The age of onset shows a bimodal pattern, with a high inci¬ dence between 13 and 14 years, and again between 17 and 18 years. The dieting behavior is related to pubertal maturational development and may coincide with the rapid accumulation of fat that is normal at that time. Dieting in this age group also is related to negative feelings about body image independent of weight.14,15

THE CLINICAL SYNDROME Anorexia nervosa represents a prototype of "hypothalamic amenorrhea." The reproductive and physiologic adjustments ap¬ pear to be an adaptive phenomenon appropriate for the semistarved state. Generally, recovery from the amenorrhea and the psychiatric disturbance parallels the weight gain. The new criteria for the diagnosis of anorexia nervosa ap¬ pear in the Diagnostic and Statistical Manual of Mental DisordersIV.16 This new definition contains bulimic subgroups. The diag¬ nosis of anorexia nervosa depends on finding a symptom com¬ plex that includes severe weight loss (usually to less than 80% of ideal body weight; Fig. 127-1); behavioral changes such as hy¬ peractivity and preoccupation with food; and perceptual changes, in particular, a distorted view of the body accompanied by an unreasonable concern about being "too fat. The amenor¬ rhea may occur at any time, even preceding the syndrome, but often is related to the start of the food restriction, even if weight loss has been slight. If the weight is lost before menarche, pa¬ tients may have primary amenorrhea. The hyperactivity may begin in the guise of an athletic pur¬ suit. There may be an intense interest in low-calorie foods, with a large intake of diet sodas and raw vegetables, and avoidance of fried foods or other products high in calories. Hypercarotenemia may give a yellow cast to the skin, especially on the palms and soles; the sclerae remain clear. The high serum carotene level is only partly attributable to an increased intake of raw vegetables;

1170

PART IX: DISORDERS OF FUEL METABOLISM Osteoporosis and fractures occur as a result of long-term poor nutritional intake and prolonged estrogen deficiency.6'18-20 Brain computed tomographic scanning or magnetic resonance imaging occasionally demonstrates enlargement of the cortical sulci and subarachnoid spaces, as well as cerebral atrophy; sur¬ prisingly, in one patient, the atrophy was reversed with weight gain.6 The rare patients who die usually succumb to intercurrent infection.

ENDOCRINOPATHY HYPOTHALAMIC DYSFUNCTION

Low levels of serum luteinizing hormone (LH) and folliclestimulating hormone (FSH) are associated with a profound estro¬ gen deficiency.3 There may be low serum triiodothyronine (T3) and thyroxine (T4) levels. The serum cortisol concentration may be high, a finding that differentiates anorexia nervosa from pitu¬ itary insufficiency. Gonadotropin Abnormalities. In anorexia nervosa, there is a lack of the normal episodic, pulsatile variation in the secretion of LH, and there may be a pattern typical of early puberty21 (Fig. 127-2). These abnormalities normalize with weight gain. In ad¬ dition, the pattern of gonadotropin secretion can be normalized by the pulsatile administration of luteinizing hormone-releasing hormone (LHRH)22; if this hormone is injected every 2 hours, menstrual bleeding and ovulation also can be induced (Fig. 127-3). Interestingly, similar disturbances in LH secretion are noted in normal women who are exposed to a low-calorie diet.23 The amenorrhea probably is secondary to altered signals reaching the medial central hypothalamus from the arcuate nu¬ cleus or higher levels. (The arcuate nucleus probably is the center responsible for the episodic stimulation of LHRH). A subset of patients have pulsations of LH restored by naloxone, suggesting that increased opioid activity participates in the suppressed LHRH pulsations. Experiments with another opioid inhibitor, naltrexone, have shown variable effects on LH secretion.

FIGURE 127-1.

Young woman with severe anorexia nervosa.

there also is decreased metabolism of carotene, a precursor of vitamin A,6 The possible complaints and physical findings in¬ clude abdominal pain, intolerance to cold, vomiting, hypoten¬ sion, hypothermia, dry skin, lanugo-type hair, bradycardia, a systolic murmur, pedal edema, petechiae, and acrocyanosis. Despite the frequent leukopenia, which may be marked, there is no increase in the risk of infection, and cell-mediated immunity is intact. There may be anemia, thrombocytopenia, and hypoplastic bone marrow. Severe hypoalbuminemia is rare; nevertheless, pitting edema may occur, especially with refeeding. Dehydration may cause an elevated blood urea nitrogen level, which returns to normal after rehydration. Electrolyte abnormal¬ ities and hypophosphatemia may occur. Occasionally, hypogly¬ cemia has been severe enough to cause coma.11 Numerous medical problems occur in anorexia nervosa, in¬ cluding salivary gland enlargement, pericardial effusion, pancre¬ atitis, pancreatic insufficiency, delayed gastric emptying, poor in¬ testinal motility, liver dysfunction with increased hepatic enzyme levels, pneumomediastinum, kidney stones, coagulopathies, bi¬ lateral peroneal nerve palsies, and deficiencies of thiamine and zinc. As a heat-conserving mechanism, there may be marked va¬ soconstriction of the extremities. If the weight loss occurs at or before the growth spurt, there may be permanent growth defi¬ ciency. Duodenal ulcers may occur, and it is unwise to disregard complaints of abdominal pain.6 Electrocardiographic changes in¬ clude low-voltage, inverted T waves and, sometimes, arrhyth¬ mias. Hypoglycemia has been associated with coma and with low or absent insulin and C peptide levels, suggesting that this prob¬ lem results from malnutrition.17

FIGURE 127-2.

Plasma luteinizing hormone (LH) concentration every 20 minutes for 24 hours during acute exacerbation of anorexia nervosa (upper panel) and after clinical remission with return of body weight to normal (lower panel). The latter represents a normal adult pattern. (Boyar RN, Katz ], Finkelstein JW, et al. Anorexia nervosa: immaturity of the 24-hour luteinizing hormone secretory pattern. N Engl J Med 1974;291:861.)

Ch. 127: Anorexia Nervosa and Other Eating Disorders

1171

-i.v. injections every 2 hours — Saline

] I

GnRH 0.05 uglkg

FIGURE 127-3.

Plasma follicle-stimulating hor¬ mone (FSH; dotted line), luteinizing hormone (LH; solid line), and estradiol responses to luteinizing hormone releasing hormone (0.05 Mg/kg) every 2 hours in a patient with anorexia nervosa. Arrow indicates values below the sensitivity of estradiol assay. GnRH, gonadotropin-releasing hormone. (From Marshall JC, Kelch RP. Low dose pulsatile gonadotropin-releasing hormone in anorexia nervosa: a model of human pubertal development. J Clin En¬ docrinol Metab 1979;49:712.)

suggesting that the suppression of LH is not consistently opioidlinked.24 23 The pattern of response to injected LHRH is imma¬ ture, resembling that seen in prepubertal children—the FSH response is much greater than that of LH. The normalization of LH/FSH ratios with repeated injections of LHRH suggests that the pituitary gonadotropes have become sluggish because of the lack of endogenous stimulation, and that the episodic stimulation is important in determining the relative amounts of LH and FSH that are secreted. Moreover, patients who recover partially from anorexia nervosa tend to have exaggerated responses to injected LHRH.26 These changes are seen in normal children during early puberty. Thus, all of these changes indicate that the hypotha¬ lamic signals of the central nervous system revert to a prepubertal or pubertal state. Hypometabolic Manifestations. Despite their marked ca¬ chexia, patients with anorexia nervosa have clinical and meta¬ bolic signs suggestive of hypothyroidism: constipation, cold in¬ tolerance, bradycardia, hypotension, dry skin, prolonged ankle reflexes, low basal metabolic rate, and carotenemia.3 In addition, the altered metabolism of certain sex steroids, such as testoster¬ one, is analogous to that seen in hypothyroidism.3 Some of these changes suggest a compensatory hypometabolism. Studies on the circulatory system show that during maximal exercise, the attainable oxygen uptake and heart rate are low in children with anorexia nervosa; the maximal aerobic power (V02max) appears to be decreased disproportionately to the cir¬ culatory and body dimensions.3 An adaptation to caloric restric¬ tion, with metabolic rates reduced in proportion to the absolute reduction in body weight, has been documented in animals; this mechanism of energy conservation also may be operative in per¬ sons with anorexia. The hypometabolism that occurs in anorexia nervosa reverses with refeeding. There is a decrease in resting energy expenditure and thermic response to food.27 This hypo¬ metabolism appears to be an appropriate mechanism to conserve energy. The low serum T3 levels in anorexia nervosa may be ex¬ plained by an alteration in T4 conversion (see Chaps. 31 and 36). In anorexia nervosa, as in starvation, the peripheral deiodination of T4 is diverted from the formation of the active T3 to the pro¬ duction of the inactive reverse T3. Fasting decreases the hepatic uptake of T4, with a proportionate decrease in T3 production. (This "low T3 syndrome" rarely may mask hyperthyroidism.) The low serum T4 value in some patients with anorexia nervosa is somewhat more difficult to explain. Low T4 euthyroidism has been seen in seriously ill patients in whom there is a dysfunc¬ tional state of deficient T4 binding with a normal availability of peripheral tissue sites for free T4. Presumably, a similar mecha¬

nism may be operative in anorexia nervosa. The secretion of thyroid-stimulating hormone (TSH) is normal, but there is an augmented serum TSH response to thyrotropin-releasing hor¬ mone (TRH) stimulation, and the peak is delayed from 30 to be¬ tween 60 and 120 minutes.3 This change may reflect an altered setpoint for endogenous TRH regulation. One study shows a sub¬ normal response of T4 and T3 to TRH, with a normal TSH re¬ sponse, suggesting chronic understimulation of the thyroid as a consequence of hypothalamic hypothyroidism.28 In another study, the level of TRH in cerebrospinal fluid was found to be low.29 Hypothalamic-Adrenal Interrelations. Levels of serum corti¬ sol often are elevated in anorexia nervosa; 24-hour studies dem¬ onstrate normal episodic and circadian rhythms of serum corti¬ sol, but considerably higher levels30 (Fig. 127-4). This change, which also can be seen in malnutrition, is secondary to prolonga¬ tion of the half-life of cortisol because of reduced metabolic clear¬ ance. The urinary levels of corticosteroids, including 17-hydroxysteroids and 17-ketosteroids, usually are low. The production rate of cortisol may be elevated; suppression with dexamethasone is inadequate, and the cortisol concentrations may exceed the binding capacity of cortisol binding globulin.2 In addition, there is a decreased affinity of serum cortisol binding globulin for cortisol. Thus, unbound serum cortisol may be increased, becom¬ ing available to the tissues. Higher levels of cortisol might be ex¬ pected to suppress corticotropin. However, the circadian rhythm that is maintained at the higher serum cortisol levels suggests that a new setpoint has been determined by the hypothalamicpituitary-adrenal axis. Recent work on the hypothalamicpituitary-adrenal pathways suggests activation of this axis. Cor¬ tisol is elevated and responses to corticotropin-releasing hor¬ mone (CRH) are abnormal, CRH is increased in the cerebrospinal fluid of patients with anorexia.31 CRH is known to suppress LH pulses in both humans and animals, and may augment dopamin¬ ergic and opiodergic inhibition of gonadotropin releasing hormone. Miscellaneous hypothalamic abnormalities in anorexia ner¬ vosa include a deficiency in the handling of a water load (proba¬ bly as a result of a mild diabetes insipidus, characterized by an erratic serum vasopressin response to osmotic challenge); abnor¬ mal thermoregulatory responses with exposure to temperature extremes; and a lack of shivering. OTHER PITUITARY HORMONE ABNORMALITIES

Serum growth hormone levels are elevated in starvation or any other restriction of food beyond the normal 12- to 15- hour

1172

PART IX: DISORDERS OF FUEL METABOLISM

ANOREXIA NERVOSA (10)

CORTISOL

FIGURE 127-4. Hourly mean serum cortisol level derived from average of samples obtained 20 minutes before, on, and after the hour in 10 patients with anorexia nervosa, compared with 6 normal controls matched for age and sex. Circadian rhythm of cortisol remains intact in anorexia nervosa but at a higher level. (From Boyar RM, Heilman LD, Roffwang H, et al. Cortisol secretion and metabolism in anorexia nervosa. N Engl ] Med 1977;296:190.)

overnight fast. Generally, basal serum growth hormone levels are higher than normal in anorexia nervosa but respond normally to provocative stimuli. These high levels are associated with a decreased level of somatomedin C (i.e., insulin-like growth factor I), as also is found in starvation. Occasionally, low serum growth hormone levels are seen, with blunted responses to insulininduced hypoglycemia.6 Insulin-like growth factor is decreased, and both these abnormalities resolve with nutritional therapy. Nutritional deprivation may alter the growth hormone-insulin¬ like growth factor axis by down-regulation of growth hormone receptor or postreceptor. 2 Sleep in anorexia nervosa has been the subject of ongoing investigation.33 Growth hormone levels associated with deltawave sleep are normal.6 A paradoxic growth hormone secretory response to the infusion of TRH has been observed in un¬ derweight persons in both anorexia nervosa and starvation. The basal serum prolactin levels are normal, and TRH-stimulated prolactin levels also are normal, although the time of the peak prolactin level is delayed. With recovery (weight gain), all of these endocrine changes normalize. However, despite the nor¬ malization of serum gonadotropin secretory patterns, amenor¬ rhea persists in 30% of patients. ESTROGEN ABNORMALITIES

Sonographic imaging of the ovaries of patients with an¬ orexia nervosa demonstrates cystic involvement resembling that seen at adolescence.34,35 The low serum estradiol levels are partly attributable to the lack of ovarian stimulation. However, estrogen metabolism also is altered: the metabolism of estradiol, which normally proceeds with 16a-hydroxylation, is decreased in favor of 2-hydroxylation and the resulting formation of catechol estro¬ gen (2-hydroxyestrone).2 This latter compound has features of an antiestrogen because it has no intrinsic bioactivity. Thus, the extraordinarily low serum estrogen levels sometimes seen in an¬ orexia nervosa are compounded by an endogenously produced antiestrogen. Furthermore, the lack of adipose tissue may deny to patients extraovarian sources of estrogen: normally, fat converts androstenedione to estrone.

CLOCK TIME

tivity changes also may accompany hypothalamic tumors and other hypothalamic syndromes. Such changes also have been documented in rats with lesions of the ventromedial nucleus of the hypothalamus, leading investigators to conclude that the ventromedial nucleus inhibits food intake and promotes activity—similar to the pattern seen in anorexia nervosa.3 Some of the changes of anorexia nervosa, including the low¬ ered metabolic rate, a decrease in attainable oxygen uptake and V02max, an increase in serum cortisol (which stimulates gluconeogenesis and decreases peripheral glucose utilization), and the diminished serum gonadotropins (with a consequent loss of fer¬ tility), are appropriate adaptations to starvation.3 Because of these neuroendocrine changes, it has been speculated that ab¬ normalities of neurotransmission participate in the pathogenesis of the condition. In particular, excess dopamine and norepineph¬ rine have known effects on behavior and appetite. In addition, j3endorphin affects feeding behavior; this hormone is thought to modulate the secretion of LHRH from the hypothalamus, and its antagonist, naloxone, can restore LH pulsations in some persons with anorexia nervosa. Patients with anorexia nervosa and those with secondary amenorrhea on a hypothalamic basis commonly share a need for achievement and approval. On "fear of failure scales," patients with anorexia score the highest. Another early marker for anorexia nervosa is perceptual dis¬ tortion. These patients consider themselves to be too fat despite their low weights. They consistently overestimate body size; this overestimation tends to disappear with weight gain. The percep¬ tual distortion may reinforce dieting behavior, perpetuating the condition. "Anorexic behavior scales" have been said to aid in differ¬ entiating persons with anorexia nervosa from those with second¬ ary amenorrhea of other causes. Often, the scale consists of a psychological profile that is either self-administered or adminis¬ tered by a physician, nurse, or clinical psychologist. One study indicated that this scale is useful and accurate in distinguishing healthy persons from those with anorectic behavior.36 Thus, it may prove useful in the early diagnosis of anorexia nervosa, par¬ ticularly in patients with secondary amenorrhea only and little, if any, weight loss.

NEUROENDOCRINE AND PSYCHOLOGICAL CHARACTERISTICS AND INTERRELATIONS

OSTEOPOROSIS

The altered behavior patterns in anorexia nervosa are dis¬ tinctive. Sometimes, periods of gorging alternate with food avoidance and starvation. Altered food intake combined with ac¬

A leading complication of amenorrhea seen with anorexia and weight loss is osteopenia. This is present in spinal, radial, and femoral sites, and is associated with fractures.37-43 Longitudinal

Ch. 127: Anorexia Nervosa and Other Eating Disorders studies on bone density show little or no reversal with resolution of the amenorrhea.38 41 These observations are important because hypoestrogenism in young adulthood may predispose to prema¬ ture osteoporosis in later life. Increases in bone mass may occur in young persons before the return of normal menses, but bone mass remains below that of normal control subjects, possibly be¬ cause of prolonged hypoestrogenism in adolescence, and, thus, may have permanent effects on peak bone mass.42 Loss of bone mass also may occur. The effects of estrogen replacement on these changes need to be studied to determine whether the trend toward decreased bone mass can be reversed by therapy. In general, 25-hydroxyvitamin D, 1,25 dihydroxyvitamin D, and osteocalcin levels are normal, although osteocalcin levels may be depressed because of lower bone turnover.40 When re¬ versal of osteoporosis occurs, it is seen more often with recovery from anorexia and is associated more tightly with weight gain than with return of menses. Some studies suggest, however, that bone mass does not appear to recover even with weight gain, calcium supplementation, and exercise. The increased cortisol levels seen in anorexia have been suggested as a mechanism for the osteopenia.44

BULIMIA CHARACTERISTICS Bulimia usually is a condition of young women, often related to previous anorectic behavior. These persons gorge themselves and use unusual means to lose weight, such as vomiting, enemas, and abuse of laxatives or diuretics. Gorging episodes may al¬ ternate with periods of severe food restriction. Most commonly, this syndrome occurs in high school and college students. Among males, bulimia is more common than is anorexia nervosa. Ac¬ cording to the Diagnostic and Statistical Manual of Mental Disorders-Ill-Revised, 41/2% of girls and young women less than 20 years of age have bulimia, whereas other sources estimate that at least 20% of this population exhibits bulimic behaviors.45 This syndrome may occur in 3% to 15% of university students.46,47 The weight may fluctuate, but usually not to dangerously low levels. There often is a history of other impulsive behavior, such as alcohol or drug use. Depression is common. Stealing and shop¬ lifting, as well as unrestrained sexual promiscuity, may be part of the syndrome—unlike anorexia nervosa, in which patients generally are sexually inactive. Depression and obsessivecompulsive behavior often coexist with eating disorders, particu¬ larly when bulimia is also present. Other comorbid problems in¬ clude drug abuse and alcoholism.48 Patients with bulimia tend to be slightly older than those with anorexia, usually between 17 and 25 years. A separate condition, known as bulimia nervosa, has been described, in which bulimic behavior has evolved from the prior, more restrictive anorexia nervosa-type pattern.

CLINICAL MANIFESTATIONS Persons with bulimia have a wide variety of superimposed medical problems, including vomiting-related tooth decay, pa¬ rotid enlargement, stomach rupture, pancreatitis, metabolic alka¬ losis, and carpal-pedal spasm. Occasionally, persons with bulimia have menstrual irregu¬ larities despite normal weight.6 Some patients are anovulatory, yet have adequate estrogen secretion. There is evidence for hor¬ monal defects in CRH and cholecystokinin regulation.49,50 Bu¬ limic behavior often is secretive; many patients do not admit to these patterns even when questioned directly. The condition of¬ ten is chronic, and increased anxiety, irritability, depression, and poor social functioning are common.51 Eventually, protein and calorie malnutrition may supervene and contribute to the devel¬ opment of the reproductive disorder. Several neurologic problems are associated with bulimia, in¬

1173

cluding Huntington chorea and seizure disorders. Bulimia also may follow encephalitis and can be seen in association with the hypersomnia of the Kleine-Levin syndrome (periodic attacks of hypersomnia and bulimia, often secondary to encephalitis, head injury, or hypothalamic tumor) and with parkinsonism; the latter patients improve in their eating patterns with treatment.3

TREATMENT OF ANOREXIA NERVOSA AND BULIMIA The treatment of these syndromes is controversial. All treat¬ ment modalities are directed toward the reestablishment of normal weight and eating habits. Treatment has included combinations of psychotherapy, including family therapy, psy¬ choanalysis, and drugs.52 Tricyclic antidepressants, cyprohepta¬ dine, L-dopa, and metoclopramide have been used with variable success. Antidepressants may be the most successful, particularly for bulimia, in which drugs such as fluoxetine have a 30% success rate.53 Behavior modification has been attempted, again with variable efficacy. The early recognition of anorectic behavior is essential so that patients may be treated before the full-blown syndrome sets in. Because amenorrhea occurs early in the disease process, it of¬ ten is the first symptom that causes patients to seek help. Thus, physicians should be particularly attentive to a history of dieting and weight loss in their young patients with amenorrhea. Pa¬ tients who are 75% of ideal body weight or below need immedi¬ ate and aggressive intervention. Dietary therapy is important be¬ cause the response to psychotherapy is improved with nutritional rehabilitation. Usually, this is best done in a hospital setting by a team consisting of a psychiatrist or a psychologist, an internist or a pediatrician, and, if possible, a nutritionist with special interest and expertise in anorexia nervosa and related eating disorders. Mortality from anorexia nervosa ranges from 8% to 18%, with lower rates in pediatric and adolescent groups. Morbidity persists with eating disorders concomitant with depression, obsessivecompulsive behavior, and poor sexual adjustment. Eating prob¬ lems persist in more than half of all cases. Death results from starvation or its complications, including infection, renal or cardiac failure, arrhythmia, and complications of fluid imbal¬ ance.54 Suicide also occurs, with an incidence of 5% to 7%. In patients who do not have a return of menstrual function, fertility may be restored by the therapeutic induction of ovulation using clomiphene citrate or human menopausal gonadotropins. (Other causes of amenorrhea, such as pituitary tumors or prema¬ ture ovarian failure, must be ruled out.) Cyclic menstrual func¬ tion may be restored with LHRH administered intravenously or subcutaneously in a pulsatile manner through a pump. Despite a return to normal weight, some patients have permanent prob¬ lems. A continuing preoccupation with food and persistent diet¬ ing behavior are common.4 For those patients who have recovered from anorexia ner¬ vosa but who never menstruate again, cyclic estrogen and pro¬ gesterone replacement is indicated to prevent premature osteo¬ porosis. However, such patients may refuse estrogen therapy because of anxiety about gaining weight.

REFERENCES 1. Warren MP. Anorexia nervosa. In: Sciarra JJ, ed. Gynecology and obstet¬ rics, vol 5. Hagerstown, MD: Harper & Row, 1981:1. 2. Morley JE, Blundell JE. The neurological basis of eating disorders: some formulations. Biol Psychiatry 1988;23:53. 3. Warren MP. The effects of undernutrition on reproductive function in the human. Endocr Rev 1983;4:363. 4. Gamer DM, Garfinkel PE. Sociocultural factors in anorexia nervosa. Lan¬ cet 1978; 2:674. 5. Hamilton LH, Brooks-Gunn ], Warren MP. Sociocultural influences on eat¬ ing disorders in professional female ballet dancers. Int J Eating Disorders 1985; 4: 465.

1174

PART IX: DISORDERS OF FUEL METABOLISM

6. Warren MP. Anorexia nervosa. In: DeGroot L, ed. Endocrinology, ed 3. Philadelphia: WB Saunders, 1994. 7. American Psychiatric Association. Diagnostic and statistical manual of mental disorders, ed 3, revised. Washington, DC: American Psychiatric Association, 1987. 8. Epling WF, Pierce WD, Stephen L. A theory of activity-based anorexia. Int J Eating Disorders 1983; 3:27. 9. Aumariega AJ, Edwards P, Mitchell CB. Anorexia nervosa in black adoles¬ cents. J Am Acad Child Psychiatry 1984; 1:111. 10. Askevold F, Heiberg A. Anorexia nervosa: two cases in discordant MZ twins. Psychother Psychosom 1979; 32:223. 11. Zelin AM, Lant AF. Anorexia nervosa presenting as reversible hypogly¬ cemic coma. ] R Soc Med 1984; 77:193. 12. Warren MP, Vande Wiele RL. Clinical and metabolic features of anorexia nervosa. Am J Obstet Gynecol 1973; 117:435. 13. Smith NJ. Excessive weight loss and food aversion in athletes simulating anorexia nervosa. Pediatrics 1980;66:139. 14. Halmi KA, Casper RC, Eckert ED, et al. Unique features associated with age of onset of anorexia nervosa. Psychiatry Res 1979; 1:209. 15. Brooks-Gunn J, Warren MP. Biological and social contributions to nega¬ tive affect in young adolescent girls. Child Dev 1989; 60:40. 16. Wilson GT, Walsh BT. Eating disorders in the DSM-IV. J Abnorm Psychol 1991; 100:362. 17. Rich LM, Caine MR, Findling JW, Shaker JL. Hypoglycemic coma in an¬ orexia nervosa. Case report and review of the literature. Arch Intern Med 1990; 150: 894. 18. McAnamey ER, Greydanus DE, Campanella VA, Hoekelman RA. Rib fractures and anorexia nervosa. J Adolesc Health Care 1983; 4:40. 19. Ayers JW, Gidwani GP, Schmidt IM, Gross M. Osteopenia in hypoestrogenic young women with anorexia nervosa. Fertil Steril 1984;41:224. 20. Rigotti NA, Nussbaum SR, Herzog DB, Neer RM. Osteoporosis in women with anorexia nervosa. N Engl J Med 1984;311:1601. 21. Boyar RN, Katz J, Finkelstein JW, et al. Anorexia nervosa: immaturity of the 24-hour luteinizing hormone secretory pattern. N Engl J Med 1974;291:861. 22. Marshall JC, Kelch RP. Low dose pulsatile gonadotropin-releasing hor¬ mone in anorexia nervosa: a model of human pubertal development. J Clin Endo¬ crinol Metab 1979; 49:712. 23. Pirke KM, Schweiger U, Strowitzki T, et al. Dieting causes menstrual ir¬ regularities in normal weight young women through impairment of episodic lutein¬ izing hormone secretion. Fertil Steril 1989;51:263. 24. Grossman A, Moulte PJA, McIntyre H, et al. Opiate mediation of amen¬ orrhea in hyper-prolactinemia and in weight loss-related amenorrhea. Clin Endo¬ crinol (Oxf) 1983; 17:379. 25. Giusti M, Cavagnaro P, Torre R, et al. Endogenous opioid blockade and gonadotropin secretion: role of pulsatile luteinizing hormone-releasing hormone administration in anorexia nervosa and weight loss amenorrhea. Fertil Steril 1988;49:797. 26. Warren MP, Jewelewicz R, Dyrenfurth I, et al. The significance of weight loss in the evaluation of pituitary response to LH-RH in women with secondary amenorrhea. J Clin Endocrinol Metab 1975;40:601. 27. Vaisman N, Clarke R, Rossi M, et aUProtein turnover and resting energy expenditure in patients with undemutrition and chronic lung disease. Am J Clin Nutr 1992;55:63. 28. Kiyohara K, Tamai H, Takaichi Y, et al. Decreased thyroidal triiodothyro¬ nine secretion in patients with anorexia nervosa: influence of weight recovery. Am J Clin Nutr 1989;50:767. 29. Lesem MD, Kaye WH, Bissette G, et al. Cerebrospinal fluid TRH immunoreactivity in anorexia nervosa. Biol Psychiatry 1994;35:48. 30. Boyar RN, Heilman LD, Roffwarg H, et al. Cortisol secretion and metab¬ olism in anorexia nervosa. N Engl J Med 1977;296:190. 31. Gold P, Gwirtsman H, Avgerinos P, et al. Abnormal hypothalamicpituitary-adrenal function in anorexia nervosa. N Engl J Med 1986;314:1335. 32. Counts DR, Gwirtsman H, Carlsson LMS, et al. The effect of anorexia nervosa and refeeding on growth hormone-binding protein, the insulin-like growth factors (IGFs), and the IGF-binding proteins. J Clin Endocrinol Metab 1992; 75:762. 33. Levy AB, Dixon KN, Schmidt H. Sleep architecture in anorexia nervosa and bulimia. Biol Psychiatry 1988;23:99. 34. Adams J, Franks S, Poison DW, et al. Multifollicular ovaries: clinical and endocrine features and response to pulsatile gonadotropin-releasing hormone. Lan¬ cet 1985;2:1375. 35. Treasure JL, Gordon PAL, King EA, et al. Cystic ovaries: a phase of an¬ orexia nervosa. Lancet 1985; 2:1379. 36. Fries H. Studies on secondary amenorrhea, anorectic behavior and body image perception: Importance for the early recognition of anorexia nervosa. In: Vigersky R, ed. Anorexia nervosa. New York: Raven Press, 1977:163. 37. Bachrach LK, Guido D, Katzman D, et al. Decreased bone density in ado¬ lescent girls with anorexia nervosa. Pediatrics 1990; 86:440. 38. Rigotti NA, Neer RM, Skates SJ, et al. The clinical course of osteoporosis in anorexia nervosa: a longitudinal study of cortical bone mass. JAMA 1991;265: 1133. 39. Salsbury JJ, Mitchell JE. Bone mineral density and anorexia nervosa in women. Am J Psychiatry 1991; 148:768. 40. Davies KM, Pearson PH, Huseman CA, et al. Reduced bone mineral in patients with eating disorders. Bone 1990; 11:143. 41. Bachrach LK, Katzman DK, Litt IF, et al. Recovery from osteopenia in adolescent girls with anorexia nervosa. J Clin Endocrinol Metab 1991; 72:602. 42. Jonnavithula S, Warren MP, Fox RP, Lazaro ML Bone density compro¬

mised in amenorrheic women despite return of menses: a 2-year study. Obstet Gy¬ necol 1993; 81:669. 43. Fonseca VA, D'Souza V, Houlder S, et al. Vitamin D deficiency and low osteocalcin concentrations in anorexia nervosa. J Clin Pathol 1988; 41:195. 44. Biller BMK, Saxe V, Herzog DB, et al. Mechanisms of osteoporosis in adult and adolescent women with anorexia nervosa. J Clin Endocrinol Metab 1989; 68: 548. 45. Schwartz DM, Thompson MG, Johnson CL. Anorexia nervosa and bu¬ limia: the sociocultural context. In: Emmett SW, ed. Theory and treatment of an¬ orexia nervosa and bulimia. New York: Brunner/Mazel, 1985:95. 46. Stangler RS, Printz AM. DSM-II1: psychiatric diagnosis in a university population. Am J Psychiatry 1980; 137:937. 47. Halmi KA, Falk JR, Schwartz E. Binge-eating and vomiting: a survey of a college population. Psychol Med 1981; 11:697. 48. Holdemess CC, Brooks-Gunn J, Warren MP. The co-morbidity of eating disorders and substance abuse: a review of the literature. Int J Eating Disorders 1994; 16(1):1. 49. Mortola JF, Rassmussen DD, Yen SSC. Alterations of the adrenocorticotropin—cortisol axis in normal weight bulimic women: evidence for a central mech¬ anism. J Clin Endocrinol Metab 1989;68:517. 50. Geracioti TD Jr, Liddle RA. Impaired cholecystokinin secretion in bulimia nervosa. N Engl J Med 1988;319:689. 51. Herzog DB, Copeland PM. Medical progress: eating disorders. N Engl J Med 1986;313:295. 52. Freeman CPL, Barry F, Dunkeld-Tumbull J, Henderson A. Controlled trial of psychotherapy for bulimia nervosa. BMJ 1988; 296:521. 53. Walsh BT, Devlin MJ. The pharmacologic treatment of eating disorders. In: Shaffer D, ed. Pediatric psychopharmacology, psychiatric clinics of North Amer¬ ica, vol 15. Philadelphia: WB Saunders, 1992:149. 54. Comerci GD. Medical complications of anorexia nervosa and bulimia ner¬ vosa. Med Clin North Am 1990; 74:1293.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

128_

FUEL HOMEOSTASIS AND INTERMEDIARY METABOLISM OF CARBOHYDRATE, FAT, AND PROTEIN NEIL B. RUDERMAN, KEITH TORNHEIM, AND MICHAEL N. GOODMAN

FUEL HOMEOSTASIS ENERGY RESERVOIRS A basic problem in human fuel homeostasis is that the body requires a constant expenditure of energy to maintain cellular metabolism, yet intake of food (energy) is intermittent. To deal with this, humans, like all mammals, ingest more calories during a meal than they require for their immediate metabolic needs and store the excess in readily mobilized reservoirs of carbohydrate, fat, and protein1-3 (Table 128-1). The principal storage form of carbohydrate in humans is gly¬ cogen. About 80 g of carbohydrate is stored as glycogen in liver and 400 g is stored in muscle in the postabsorptive state. Hepatic glycogen can be used to generate free glucose for release into the circulation. In contrast, muscle does not possess the enzymatic machinery needed to generate free glucose; instead, its glycogen serves principally as a fuel for muscle itself and as a source of lactate, pyruvate, and alanine for gluconeogenesis during early starvation and exercise.4 The 6 kg of protein in a 70-kg man hypothetically could pro¬ vide an additional 24,000 kcal of fuel. However, unlike the glu¬ cose stored as glycogen and the lipid stored as triglyceride, the

1175

Ch. 128: Fuel Homeostasis and Intermediary Metabolism of Carbohydrate, Fat, and Protein amino acids in body protein do not constitute a true reservoir of expendable energy. Rather, each protein molecule appears to have a function, whether it be an enzyme, a structural compo¬ nent of a tissue such as collagen, or an element of a contractile system such as actin and myosin in skeletal muscle. Nevertheless, there is some breakdown of body protein during a fast, and many of the amino acids released are used by the liver for gluconeogenesis. By far the largest energy reservoir in humans is fat. A nonobese 70-kg man contains about 12 kg of adipose tissue triglyc¬ eride, the equivalent of roughly 110,000 kcal. In a totally starved person, this amount would be sufficient to supply fuel needs for about 60 days. Along with being more abundant, fat is a more efficient energy store than is either glycogen or protein: about 9.5 kcal is generated per gram of fat oxidized versus only 4 kcal/ g for protein and glycogen. Furthermore, fat exists in a nearly anhydrous environment in the adipocyte, whereas each gram of protein and glycogen is associated with about 3 g of water. Thus, the caloric density of adipose tissue is about 8.5 kcal/g, whereas a gram of glycogen or protein provides only 1 kcal. If we were to substitute an equicaloric amount of glycogen for the fat in the man described in Table 128-1, his weight would increase from 70 to 196 kg. Clearly, fat has evolved as the principal fuel reservoir in all mobile terrestrial organisms that carry out sustained activity.1,2

FUEL CONSUMPTION: BRAIN AND .MUSCLE Although all human tissues require energy, fuel homeostasis is understood most easily in terms of being regulated principally to serve the needs of brain and muscle, the major consumers of fuel. The brain uses glucose exclusively as its fuel except during prolonged starvation and during certain other ketotic states, when it also uses the lipid-derived fuels, acetoacetate and /?hydroxybutyrate (ketone bodies).1-3,5,6 In a 70-kg man, the brain oxidizes about 120 g of glucose per day, the equivalent of about 25% of the total caloric expenditure. Blood glucose levels must be carefully regulated to maintain brain energy metabolism. Muscle makes up 40% of the body's mass and accounts for 20% to 30% of its 02 consumption at rest and for as much as 90% during exercise. Unlike brain, muscle can use fatty acids as well as glucose as a fuel and, like brain, it can use ketone bodies.7-9 The relative use of these fuels depends on a person's nutritional and hormonal status, and, if exercise is being performed, on the duration and intensity of that exercise. Generally, glucose is the principal fuel of resting muscle after a carbohydrate meal, and fatty acids and ketone bodies are the principal fuel during periods of caloric deprivation.7-10 During exercise of mild to moderate intensity, fatty acids tend to be the principal fuel of muscle, espe¬ cially when the exercise is prolonged. In contrast, carbohydrate is used to a greater extent during the initial phases of exercise and when the exercise is intense.7-10

pear to differ from one tissue to another. Thus, hepatic glycogenolysis is stimulated by glucagon and epinephrine, muscle glycogenolysis by epinephrine and Ca2+ released during muscle contraction, and triglyceride lipolysis by a wide variety of endog¬ enous stimuli, one of the most important being norepinephrine released from sympathetic nerve endings.8,12

GLUCOSE HOMEOSTASIS IN NORMAL HUMANS The concentration of glucose is more closely regulated than that of any other fuel. In normal humans, the concentration in plasma generally is maintained between 70 and 120 mg/dL (3.86.7 mM), whereas variations in plasma free fatty acids (FFAs) and ketone bodies may be as great as 10- and 100-fold, respec¬ tively.3,6 Plasma glucose must be maintained above a certain level because it is the sole fuel of the central nervous system under most physiologic conditions. This presents no problem at normal plasma glucose concentrations because the metabolism of glucose by brain rather than its transport across the bloodbrain barrier is rate-limiting. However, as the plasma glucose concentration falls, brain glucose transport diminishes and, at hypoglycemic levels, it becomes limiting for brain glucose utili¬ zation.13 Thus, even moderate degrees of hypoglycemia can cause substantial cerebral dysfunction, and severe hypoglycemia can lead to seizures, coma, and even brain death. The precise glucose concentration at which central nervous system dysfunc¬ tion occurs may differ considerably; in patients with diabetes mellitus, symptoms tend to occur at higher concentrations, and in patients with chronic hypoglycemia, at lower concentrations of glucose.13 Recent studies in animals suggest this difference may be secondary to adaptations in glucose transport at the blood-brain barrier.14 Why the upper level of plasma glucose also is closely regu¬ lated in normal humans is unclear. Presumably, moderate eleva¬ tions in blood glucose are disadvantageous for survival. Concordantly, moderate degrees of hyperglycemia in pregnant women (i.e., gestational diabetes) are associated with an increased inci¬ dence of congenital malformations, morbidity, and mortality in the fetus. Furthermore, prevention of such hyperglycemia ap¬ pears to prevent these complications15 (see Chap. 150).

ROLE OF LIVER Maintenance of the plasma glucose concentration in the postabsorptive state is largely the responsibility of the liver. The liver can provide glucose for other tissues, either by breaking

TABLE 128-1 Fuel Reservoirs of Normal 70-kg Man After Overnight Fast Fuel (Organ)

REGULATORY CONTROLS The regulation of fuel homeostasis in humans is complex. Hormonal and neural factors, the levels of the fuels, and, in mus¬ cle, ongoing or prior contractions all play a role.8,9 Numerous fac¬ tors control the mobilization of fuels from their reservoirs; how¬ ever, one factor, insulin, is the principal regulator.11 Insulin stimulates glycogen synthesis and inhibits its breakdown in both muscle and liver. Moreover, it stimulates the synthesis and inhib¬ its the degradation of triglyceride and most proteins. Thus, insu¬ lin is the principal anabolic and anticatabolic hormone. Concordantly, insulin levels invariably are increased in the absorptive state when exogenous substrates are used for energy metabolism and fuel reservoirs are increased, and they are decreased in the postabsorptive state and during starvation, when fuel reservoirs are broken down to provide for the needs of vital organs. The catabolic factors that counter the effects of insulin ap¬

Mass (g)

Energy Content (kcal)

TISSUE Fat (adipose tissue) Protein (mainly muscle) Glycogen (muscle) Glycogen (liver)

12,000 6,000 400 80

110,000 24,000 1,600 320

CIRCULATING Glucose* Free fatty acids Triglycerides Ketone bodies Amino acids

20 0.3 3 0.2 6

80 3 30 0.8 24

* Circulating glucose, ketone bodies, and amino acids assume equal concentrations in plasma and interstitial fluid. During starvation, the amount of ketone bodies in the circulation may increase as much as 100-fold. (Data from Cahill GF: Starvation in man. N Engl J Med 1970;282:688; and Cahill GF, Aoki T, Rossini AA. Metabolism in obesity and anorexia nervosa. In: Wurtman R], Wurtman JJ, eds. Nutrition and the brain, vol 3. New York: Raven Press, 1979:1.)

1176

PART IX: DISORDERS OF FUEL METABOLISM

down its own glycogen stores or by synthesizing it from amino acids, lactate, pyruvate, and glycerol (gluconeogenesis). It occupies this unique role in metabolism because it contains the enzyme glucose-6-phosphatase, which catalyzes the conversion of glucose-6-phosphate to free glucose. Other tissues, including mus¬ cle, adipose tissue, and brain, also possess the enzymatic appara¬ tus to degrade glycogen and to synthesize glucose-6-phosphate from amino acids and lactate; however, they either lack glucose6-phosphatase, or they possess too little of it, and so do not re¬ lease free glucose into the circulation.8 Increases in glucagon and epinephrine appear to be the prin¬ cipal hormonal stimuli for glycogenolysis whenever blood glu¬ cose levels are falling. Insulin inhibits the stimulation of glycogenolysis by both glucagon and epinephrine, and substan¬ tial evidence suggests that the relative balance between insulin and these counter-insulin hormones determines the rate of glyco¬ genolysis under most physiologic conditions.16 Acting within this hormonal framework, hepatic glycogen metabolism also is mod¬ ulated by the concentration of glucose. High concentrations, such as occur after a meal, stimulate hepatic glycogen synthesis and inhibit its breakdown, whereas low glucose concentrations have the reverse effect.1718 Like glycogen breakdown, gluconeogenesis is stimulated by glucagon and catecholamines and inhibited by insulin, and its rate is largely determined by the balance between these hor¬ mones.18,1^ Glucocorticoids are permissive: when they are lack¬ ing, as in an adrenalectomized rat, the ability of glucagon and catecholamines to stimulate hepatic gluconeogenesis is lost, and the release of amino acids and other gluconeogenic precursors from the periphery is diminished. The principal gluconeogenic precursors are amino acids released from muscle and other tis¬ sues, lactate, and glycerol, which is derived principally from the hydrolysis of adipose tissue triglyceride.3,6'14,20 Lactate accounts for about 50% of gluconeogenic precursor in the postabsorptive state and an even higher percentage during exercise. It arises principally from red blood cells, platelets, and the renal medulla, which derive all of their energy from anaerobic glycolysis, and, more importantly, from tissues in which either glycolysis is ac¬ celerated beyond the capacity for pyruvate oxidation (e.g., exer¬ cising muscle) or pyruvate dehydrogenase is inhibited (e.g., mus¬ cle during starvation). Under all of these circumstances, glucose is metabolized only as far as lactate, which is reconverted to glu¬ cose in the liver. This sequence of events is referred to as the Cori cycle.3,8,12 Studies in rats suggest that the amino acids used for gluco¬ neogenesis are derived from protein breakdown in muscle, liver, and gut during early starvation, and almost exclusively from muscle during longer starvation.21 This protein breakdown is de¬ creased when plasma insulin levels are high, such as after a meal rich in carbohydrate and protein. Conversely, it is increased when plasma insulin levels are low, such as in early starvation and untreated type I diabetes, or when insulin is biologically in¬ effective, such as after trauma or during sepsis. The role of other hormonal factors is less clear. Glucagon can stimulate hepatic protein degradation directly, but it has no effect on muscle.3 Glu¬ cocorticoids in large amounts inhibit protein synthesis and prob¬ ably stimulate protein degradation in muscle and other tissues.22 However, the role of physiologic alterations in plasma glucocor¬ ticoids in the regulation of protein catabolism is not clear. Alanine is the principal amino acid used for gluconeogenesis in humans.23 Alanine and glutamine account for 50% of the amino acids released from muscle even though they make up less than 15% of muscle protein.3,23 The additional alanine arises from the amination of pyruvate generated principally by glycol¬ ysis; thus, alanine is a vehicle for the transfer of nitrogen from muscle to liver. Glutamine is formed primarily from the amidation of glutamate in muscle, a reaction catalyzed by glutamine synthetase.3 Glutamine is utilized primarily by the gut and kid¬ ney and is not a significant gluconeogenic substrate for the liver.6,24

ROLE OF KIDNEY Kidney, like liver, possesses the complete enzymatic appara¬ tus for gluconeogenesis. During brief periods of starvation, its contribution to gluconeogenesis is roughly 10% that of liver. During longer starvation and other states in which the kidney has to cope with a large acid load (e.g., metabolic acidosis), renal gluconeogenesis is accelerated. The principal gluconeogenic sub¬ strate for the kidney is glutamine, which also is its principal source of free NH3. During long-term starvation, when hepatic gluconeogenesis is diminished, the kidney may be responsible for as much as 50% of the glucose entering the circulation.3

THE FIVE PHASES OF GLUCOSE HOMEOSTASIS The roles of hepatic glycogen metabolism and gluconeogen¬ esis in the regulation of blood glucose are best illustrated by a description of glucose homeostasis in fed and fasted human be¬ ings. Glucose homeostasis can be divided into five phases on the basis of the origin of blood glucose, as depicted in Figure 128-1, in which glucose utilization is plotted against time in a theoretical person who ingests 100 g of glucose and then fasts for 40 days.3,6 ABSORPTIVE PHASE

For 3 to 4 hours after glucose ingestion {phase J, the absorp¬ tive period), blood glucose is derived principally from exogenous carbohydrate. The concentrations of insulin and glucose are in¬ creased, whereas that of glucagon is depressed. Glucose in excess of the fuel needs of the liver and peripheral tissues is stored as glycogen, predominantly in liver and muscle, or is converted to lipid. This is the only phase in which the liver is a net user of glucose. POSTABSORPTIVE PHASE AND EARLY STARVATION

By the end of the absorptive period, insulin, glucose, and glucagon return to basal (12 hours postabsorptive) levels (phase II) and the liver produces glucose, which is derived principally from stored glycogen. The major user of glucose now is the brain.

in

ORIGIN OF BLOOD GLUCOSE

:

TISSUES USING GLUCOSE

:

MAJOR FUEL OF BRAIN

:

in

rs

(HZ)

v

(E)

(I)

(H)

(IE)

Exogenous

Glycogen Hepatic gluco¬ neogenesis

Hepatic gluconeo¬ genesis Glycogen

Gluconeogenesis, hepatic ond renal

Gluconeogenesis, hepatic ond renal

All except liver. Muscle and adipose tissue at diminished rates

All except liver. Muscle and adipose tissue ot rates intermediate between II and GZ

Brom, rbcs, renal medulla. Small amount by muscle

Brain at a diminished rate, rbcs, renal medul la

Glucose

Glucose

Glucose, ketone bodies

Ketone bodies, glucose

All

Glucose

FIGURE 128-1.

Five phases of glucose homeostasis. Rbcs, red blood cells. (From Ruderman NB, Aoki TT, Cahill GF. Gluconeogenesis and its dis¬ orders in man. In: Hanson R, Mehlmar M, eds. Gluconeogenesis. New York: John Wiley & Sons, 1975:515.)

Ch. 128: Fuel Homeostasis and Intermediary Metabolism of Carbohydrate, Fat, and Protein Tissues that derive all or most of their energy from anaerobic glycolysis, such as red and white blood cells and the renal me¬ dulla, also use glucose. Muscle and adipose tissue use glucose at a decreased rate. Further, the oxidation of glucose is inhibited in these tissues at the pyruvate dehydrogenase step, causing in¬ creased release of lactate, pyruvate, and alanine, all of which can be used for gluconeogenesis. This decrease in glucose oxidation is the first of the body's adaptations to conserve protein while maintaining the brain's glucose supply during starvation. After an overnight fast, a substantial part of the glucose re¬ leased by liver is derived from glycogen.25 The approximately 80 g of glycogen in the liver are adequate to meet the fuel needs of peripheral tissues (about 180 g/day, of which 120 g is used by brain) for only 12 hours; therefore, gluconeogenesis must rapidly replace glycogen as the major provider of glucose. Concordantly, the ability of the liver to carry out gluconeogenesis is enhanced after 12 to 48 hours of starvation (phase III and early phase IV), apparently secondary to both a further decrease in insulin and an increase in glucagon. Likewise, the release of gluconeogenic precursors from peripheral tissues is increased because of insulin lack. Now that liver glycogen is depleted and the brain is not yet using significant amounts of ketone bodies, the demand for gluconeogenesis is at its peak. Thus, this also is the time of great¬ est susceptibility to hypoglycemia because of impaired gluconeo¬ genesis. Children26 and pregnant women15 are particularly sus¬ ceptible to hypoglycemia during this period: the child because of the disproportionate size of the brain relative to tissues that pro¬ vide gluconeogenic substrate (e.g., muscle) and the mother be¬ cause she has to supply glucose to the fetus as well as to herself.

1177

mal.13 Thus, in certain patients, glucagon secretion in response to a decreasing plasma glucose level is deficient. Epinephrine serves as a backup to glucagon in this circumstance; however, in some patients with type I diabetes, such as those with autonomic neur¬ opathy, its secretion also may be aberrant. Such patients are poor candidates for intensive insulin therapy. Patients with type I diabetes also may become hypoglycemic during and after exercise. Hypoglycemia occurs during exercise when plasma insulin levels are high as a result of previous injec¬ tions of insulin, because hepatic glucose production is suppressed in the face of increased glucose utilization by muscle.28 31 A sim¬ ilar mechanism probably accounts for the hypoglycemia that can occur in patients with type I diabetes many hours after exer¬ cise.28,32 To prevent hypoglycemia, many patients with type I di¬ abetes must ingest supplemental carbohydrate or diminish their insulin dose on days they exercise.32

TYPE II DIABETES The basis for impaired glucose homeostasis in patients with type II diabetes is less clear. Abnormalities in insulin secretion and peripheral resistance to the action of insulin may play a role, the latter particularly in patients with obesity (see Chaps. 133 through 135, and 140). Many studies suggest that fasting hyper¬ glycemia in these patients arises from increased hepatic glucose production and postprandial hyperglycemia arises from dimin¬ ished peripheral glucose utilization.33

INSULIN RESISTANCE SYNDROME (SYNDROME X) PROLONGED STARVATION

During the latter part of phase IV and in phase V, the rate of hepatic gluconeogenesis diminishes, and ketone bodies partially replace glucose as a fuel for the brain.1-3,5 The adaptations during this period conserve body protein. The mechanisms by which they occur are unclear; however, animal studies indicate that they require the presence of lipid fuels such as FFAs and ketone bodies.

EXERCISE The ability of normal humans to maintain glucose homeo¬ stasis is most severely tested during exercise. During intense ex¬ ercise, the glucose demand by muscle can increase 10-fold or more, yet plasma glucose levels must be maintained for the cen¬ tral nervous system. This increased demand for glucose is met by the liver.7 Liver provides glucose initially by breaking down its glycogen stores and later by rapid gluconeogenesis. In many re¬ spects, the response of the liver during exercise is a telescoped version of its response during starvation, with many of the same hormonal alterations, including diminished insulin and in¬ creased glucagon levels in plasma.28,29 There are significant differences, however, including the more important role of cate¬ cholamines in glucose homeostasis during exercise.28-30

GLUCOSE HOMEOSTASIS IN DIABETES TYPE I DIABETES The most common cause of glucose dysregulation in hu¬ mans is diabetes. Patients with type I diabetes, because of an ab¬ solute deficiency of insulin, have both an accelerated rate of he¬ patic glucose production and a decreased rate of glucose utilization by peripheral tissues. Insulin therapy corrects the hy¬ perglycemia; however, glycemic control equivalent to that of per¬ sons without diabetes rarely is achieved. An added therapeutic problem in patients with type I diabetes is that the counterregulatory response to insulin-induced hypoglycemia may be abnor¬

An increasing body of evidence suggests that type II diabetes in many persons is preceded by a period in which their peripheral tissues (mainly muscle) are resistant to the action of insulin.34,35 Thus, first-degree relatives of patients with type II diabetes36 and persons followed up longitudinally who later become diabetic37 both have been shown to be hyperinsulinemic and insulin resis¬ tant. A similar insulin-resistant state also may antedate essential hypertension, certain dyslipidemias, and premature coronary heart disease.34,38 It is often, although not invariably, associated with obesity,38 particularly obesity in which intra-abdominal fat is disproportionately increased.39 The metabolic defects causing this insulin resistance are still unclear; however, an impaired abil¬ ity of insulin to activate glycogen synthase in muscle has been described.35,36 An important and unresolved question is whether this insulin resistance is reversible with diet and exercise, and, if so, whether this will prevent the development of diabetes and the other disorders associated with this syndrome.40

INTERMEDIARY METABOLISM OF GLUCOSE AND GLYCOGEN GENERAL REMARKS The major pathways of glucose and glycogen metabolism are connected at glucose-6-phosphate (Fig. 128-2). Thus, glucose-6-phosphate is both the precursor for glycogen synthesis and glycolysis, and the product of glycogen breakdown and glu¬ coneogenesis. Moreover, it is the immediate substrate for the pentose phosphate pathway, which supplies nicotinamide ade¬ nine dinucleotide phosphate, reduced form, (NADPH) needed for fatty acid biosynthesis and other processes, and ribose-5phosphate, needed for nucleotide and nucleic acid biosynthesis. Glucose transport into the cell is important in the regulation of its metabolism in muscle and other nonhepatic tissues. Although the pathways are almost identical for muscle and liver (see Fig. 128-2), there are profound differences in the control and coordination of glycogen and glucose metabolism. For in¬ stance, in muscle, when glycogenolysis occurs during exercise.

PART IX: DISORDERS OF FUEL METABOLISM

1178

GLYCOGEN

GLUCOSE

r-UDP

Glucose-l-P—f ■^»yEF-glucose UTP

PP,

generally occur slowly, taking hours to days, and often are the result of increases or decreases of enzyme synthesis at the level of transcription. A more rapid change in enzyme concentration can be produced by proteolytic activation, such as occurs with digestive enzyme precursors (e.g., conversion of trypsinogen to trypsin) and blood clotting factors. REGULATION BY SUBSTRATE CONCENTRATION

Fructose-1,6-Pz * S-Dihydroxyacetone-P

i

I

KEY REGULATORY ENZYMES ©Hexokinase (glucokinase in liver) © Phosphofructokinase © Pyruvate kinase

Glycaraldehyde-3-P

© Pyruvate dehydrogenase

P, * NAD*©

©Pyruvate carboxylase

NADH^

© Phosphoenolpyruvate carboxykinase © Fructose 1.6-bisphosphatase

1.3-Pz-Glycerate

adp-^ k

© Glucose 6-phosphatase ® Glycogen synthase

ATP^

©Glycogen phosphorylose

3-P-Glycerate

I

2-P-Glycerate P jtno 1 pyruvate

^

0Vatp

Oxaloocetate ©$»GDP * P,

Changing the concentration of the substrate for an enzyme also can change the rate of a reaction, provided the concentration of substrate is not already saturating (i.e., [S] < KM or K0 5). This simple control is important in certain instances. For example, the sensitivity of the liver to changes in blood glucose concentrations, such as occur after a meal, is partly attributable to the presence of the high-KM (10 mM or 180 mg/dL) hexokinase, usually re¬ ferred to as glucokinase. Other hexokinases are saturated at submillimolar concentrations of glucose and, therefore, are insensi¬ tive to changes within the physiologic range. Another example of substrate regulation is the negative effect of ethanol on gluconeogenesis, a matter of great clinical importance in malnourished persons with alcoholism. Hypoglycemia in such persons is attrib¬ uted to a decrease in the hepatic concentration of the gluconeo¬ genic substrate, pyruvate.41 The latter occurs because of the shift of the lactate dehydrogenase equilibrium more strongly in favor of lactate as nicotinamide adenine dinucleotide, oxidized form, (NAD) is converted to nicotinamide adenine dinucleotide, re¬ duced form, (NADH) during ethanol oxidation.

Prwate^'^V-GTP ♦ CD, NAD * CoA

NADU©

NAD

Gluc-6-P

H £>

Pyruvate

Ch. 128: Fuel Homeostasis and Intermediary Metabolism of Carbohydrate, Fat, and Protein

1179

ISOENZYMES

IRS

IRS-PY

The metabolic differences between tissues are partly attrib¬ utable to differing amounts of specific enzymes or, in the extreme case, to their absence. For example, muscle cannot perform gluconeogenesis because of the absence of glucose-6-phosphatase. A more subtle difference is the presence of different isoenzymes, which are enzymes that catalyze the same reaction but have different amino acid sequences and, consequently, can have different kinetic or regulatory properties. The presence in liver of glucokinase, the high-KM isoenzyme of hexokinase, already has been noted. Another example is pyruvate kinase. In liver, for gluconeogenesis to proceed, pyruvate kinase must be strongly in¬ hibited, so that the phosphoenolpyruvate generated by the phosphoenolpyruvate carboxykinase reaction is not reconverted to pyruvate. This inhibition is made possible by the sensitivity of the liver isoenzyme to allosteric effectors and reversible phos¬ phorylation. The muscle isoenzyme lacks these regulatory properties.

REGULATION OF GLYCOGEN METABOLISM GLYCOGENOLYSIS

FIGURE 128-4. Hypothetical insulin signaling mechanisms.463'103 It has been suggested that insulin stimulates glucose transport and inhibits lipolysis by phosphatidylinositol 3-kinase (PI3K)46 and glycogen synthesis through the mitogen-activated protein kinase (MAPK)-S6 kinase signal¬ ing cascade.55 The roles of a p70 S6 kinase (not shown) that insulin acti¬ vates by an MAPK-independent mechanism104 and a newly discovered p32 S6 kinase (not shown) that appears to be the predominant insulinactivated S6 kinase in skeletal muscle105 are unclear. GSK-3, glycogen synthase kinase 3; PP1, protein phosphatase 1; PKC, protein kinase C.

Hormonal stimulation of glycogenolysis (e.g., by glucagon in liver and by epinephrine in muscle) occurs by a "cascade” mechanism (Fig. 128-5). Binding of the hormone to its receptor activates the membrane enzyme adenylate cyclase, which cata¬ lyzes the formation of cyclic adenosine monophosphate (cAMP) from adenosine triphosphate (ATP). cAMP activates the cAMPdependent protein kinase by binding to regulatory subunits and releasing active catalytic subunits. The active protein kinase then phosphorylates, and thereby activates, phosphorylase b kinase, which in turn phosphorylates glycogen phosphorylase b to yield the more active phosphorylase a, which then degrades glycogen. Such a cascade mechanism has the advantages of increased sensitivity to and amplification of the hormone signal, as well as coordinate regulation of opposing enzymes and related pathways.47 In reversing the cascade signal, the phosphorylated proteins are dephosphorylated by phosphoprotein phosphatases. In ad¬ dition, cAMP is hydrolyzed to adenosine monophosphate (AMP) by a cyclic nucleotide phosphodiesterase. The pharmacologic ac-

Hormone-Receptor

Hormone + Receptor

Adenyl cyclase

Cyclic AMP + PPi

ATP z

involved in cellular transformation and the expression of numer¬ ous oncogenes.44

/

RA

Protein kinase PROTEIN-PROTEIN INTERACTIONS

It has been increasingly appreciated that many events in metabolic regulation are mediated by protein-protein interac¬ tions. With respect to insulin, one example of this is the interac¬ tion of insulin with its receptor; another is the interaction of a protein substrate of the insulin receptor, IRS-1, with other pro¬ teins in the cell. After it is tyrosine phosphorylated at two or more sites, IRS-1 is able to interact with proteins that contain specific amino acid sequences referred to as SH-2 (src-homology 2) re¬ gions.45 These proteins include the 85-kilodalton (kd) subunit of the enzyme phosphatidylinositol 3-kinase and an adapter pro¬ tein, growth factor receptor bound protein 2 (GRB2). Phosphati¬ dylinositol 3-kinase has been implicated in the regulation of glu¬ cose transport and lipolysis.46 It and the GRB2-SOS complex may mediate many of the downstream effects of insulin, including mitogenesis, phospholipase A2 activation, and glycogen synthase activation (see later).463

z

2C + cAMP-R; ^Active ' catalytic subunits *. Phosphorylase b kinase

Phosphorylase b kinase (dependent on high Ca+ +

. (active)

ATP Phosphorylase b (dependent on high AMP)

z

z

ADP /' z y

/

ATP

^

Phosphorylase a

✓ (active)

\

ADP/'' z

Glycogen

~r

Glucose-1-P

p,

FIGURE 128-5.

"Cascade" mechanism for hormonally induced glyco¬ genolysis in muscle (by epinephrine) and liver (by glucagon). See text for discussion of the simultaneous effects on glycogen synthase and other enzymes through phosphorylation by the cyclic adenosine monophos¬ phate (cAMP)-dependent protein kinase. ATP, adenosine triphosphate; ADP, adenosine diphosphate.

1130

PART IX: DISORDERS OF FUEL METABOLISM

tion of the methylxanthines—caffeine, theophylline, and theo¬ bromine, found in coffee, tea, and cocoa—is attributable partly to their inhibition of this phosphodiesterase. Insulin action may involve stimulation of phosphoprotein phosphatase, the phos¬ phodiesterase, or both, possibly secondary to the signaling events depicted in Figure 128-4.48 A second means of triggering the phosphorylation, and hence the activation, of phosphorylase is by raising the intracel¬ lular Ca2+ concentration. Calmodulin, a calcium binding regula¬ tory protein, also is a subunit of phosphorylase b kinase. If the intracellular free calcium concentration is raised 10-fold or more to 10'6 M, as occurs in exercising muscle, calcium binding to cal¬ modulin is increased, and the nonphosphorylated phosphorylase b kinase is activated. The phosphorylated form of phosphorylase b kinase also is dependent on Ca +, but the low levels of free calcium (10 8—10"7 M) in resting muscle are sufficient to activate it. The phosphorylation of phosphorylase b kinase increases its affinity for the activator Ca2+. Under some conditions, calcium also may be an important modulator of glycogenolysis in the liver. Thus, in rat liver, epinephrine at physiologic concentrations binds to a-adrenergic receptors and stimulates glycogenolysis by increasing Ca2+.49 An increase in cAMP, such as occurs when epinephrine binds to /3-adrenergic receptors, is observed only at supraphysiologic concentrations of the hormone. The mechanism by which epinephrine raises cytoplasmic Ca2+ levels involves activation of phospholipase C to cleave inositol-containing phospholipids in the plasma membrane, thereby generating inositol trisphosphate, which releases Ca2+ from intracellular stores50 (see Chap. 3). Glycosylated inositol de¬ rivatives, similarly generated from glycosylated phosphoinositides, have been suggested as mediators of insulin action. Diacylglycerol, the residual moiety from the phospholipid cleavage, also can serve as a second messenger, most notably by activating protein kinase C. In concert with control by phosphorylation and dephos¬ phorylation, glycogen phosphorylase is modulated by allosteric regulators. Phosphorylase b is inhibited by ATP and glucose-6phosphate, and requires high concentrations of AMP or inosine monophosphate for activity. Phosphorylase a also is dependent on AMP under inhibitory conditions, but much lower concentra¬ tions suffice.51 Thus, phosphorylation increases the affinity of phosphorylase for this activator. Besides directly altering its ac¬ tivity, the allosteric regulators affect the phosphorylation and de¬ phosphorylation of phosphorylase. Thus, binding of AMP causes a change in conformation of phosphorylase a such that the phos¬ phate groups are “tucked in" and become resistant to removal by the phosphoprotein phosphatase.52 Conversely, binding of glu¬ cose displaces AMP and exposes the phosphate groups to attack. Glucose-6-phosphate both activates the phosphatase reaction and inhibits the phosphorylase b kinase reaction by binding to phosphorylase. The relative importance of allosteric effectors versus the phosphorylation cascade in the regulation of glycogenolysis probably is greatest in exercising muscle. There, increases in phosphorylase a levels are relatively small and transient in com¬ parison with the large stimulation of glycogenolysis.51 Likewise, I-strain mice, which lack muscle phosphorylase b kinase and therefore must depend on allosteric activation of phosphorylase b for glycogenolysis, are little affected by this defect during exer¬ cise. Their rate of glycogenolysis can exceed that of a normal mouse, and they exercise without difficulty; in fact, they have more endurance, presumably because of their larger reserves of glycogen.53 GLYCOGEN SYNTHESIS Glycogen synthase, the rate-limiting enzyme for glycogen synthesis, also is regulated by phosphorylation-dephosphorylation and by allosteric effectors. The classic view held that glyco¬ gen synthase was phosphorylated by cAMP-dependent protein

kinase, thus converting it from the active a (or I, for independent of the activator glucose-6-phosphate) form to the inactive or less active b (or D, for dependent) form of the enzyme. Thus, hor¬ monal stimulation would both activate glycogen breakdown and inhibit glycogen synthesis. In fact, the situation is somewhat more complex. Whereas phosphorylase has a single phosphory¬ lation site per subunit, glycogen synthase can be phosphorylated at more than 10 sites, and at least 9 protein kinases may be in¬ volved, including cAMP-dependent, calmodulin-dependent, phosphorylase b kinase, casein kinases I and II, and glycogen synthase kinase 3.54 Generally, a greater degree of phosphoryla¬ tion decreases the affinity of glycogen synthase for the activator glucose-6-phosphate and for its substrate uridine diphosphoglucose. However, the precise effects of phosphorylation and de¬ phosphorylation at specific sites remain unclear. Insulin-induced disposal of glucose involves stimulation of glycogen synthase activity, especially in muscle. Glycogen syn¬ thase kinase 3 action is decreased through insulin-induced phos¬ phorylation by S6 kinase (see Fig. 128-4). Insulin action also may involve S6 kinase activation of phosphoprotein phosphatase 1 (PP1), which dephosphorylates and, therefore, activates glyco¬ gen synthase. Epinephrine, operating through cAMP-dependent protein kinase, can counter the effect of insulin by causing phos¬ phorylation of a second site on the G-subunit that binds the phosphatase catalytic subunit to glycogen particles; this releases the catalytic subunit, rendering it ineffective. PP1 is further inac¬ tivated by binding to a cytosolic protein inhibitor on phosphory¬ lation of the inhibitor by cAMP-dependent protein kinase.55 De¬ rangements in these mechanisms of insulin signaling to activate glycogen synthase may be a cause of diabetes. Studies on insulinresistant Pima Indians have shown defects in PP1 activity.56 COORDINATE REGULATION OF GLYCOGEN SYNTHASE AND PHOSPHORYLASE Coordinate control of glycogen synthase and phosphorylase involves phosphoprotein phosphatase, as well as the protein ki¬ nases. In liver, phosphorylase a appears to inhibit dephosphory¬ lation (and hence activation) of glycogen synthase by binding preferentially to the phosphatase—even when its phosphate group is tucked in and cannot be hydrolyzed. Thus, only after a rise in glucose has exposed the phosphate group and most of the phosphorylase a has been converted to the b form is the phos¬ phatase free to act on glycogen synthase.17 This probably is a means of restricting operation of a futile cycle of simultaneous glycogen synthesis and breakdown. In this regard, it has been suggested that glucose could be a significant determinant of gly¬ cogen breakdown or synthesis in liver, with phosphorylase a functioning as an intracellular glucose receptor or sensor. Adding to this complexity is the finding that the regulation of the protein phosphatase(s) involves inhibitory proteins, which themselves are subject to phosphorylation and dephosphorylation, as indi¬ cated earlier.48'55'57'58

REGULATION OF GLYCOLYSIS PHOSPHOFRUCTOKINASE Control of glycolysis is discussed first in the context of a nongluconeogenic tissue such as muscle. Once glucose has been transported into the cell, the primary functional control point of glycolysis appears to be the phosphofructokinase reaction. This enzyme is affected by various metab¬ olites that reflect the fuel and energy status of the cell.59 ATP, a major product of glycolysis, serves as a classic feedback inhibitor of phosphofructokinase. (There should be no confusion over the second function of ATP, as a substrate: inhibition by ATP occurs when it binds to a regulatory site distinct from the catalytic site.) Conversely, AMP, adenosine diphosphate (ADP), and inorganic phosphate (Pi), which are products of ATP breakdown, all are activators of phosphofructokinase. They are present in lower

Ch. 128: Fuel Homeostasis and Intermediary Metabolism of Carbohydrate, Fat, and Protein concentrations than ATP and, during conditions of altered en¬ ergy demand, the percentage changes in their concentrations are much greater. (AMP is generated from ADP in the myokinase reaction: 2 ADP = AMP + ATP.) ATP inhibition of phosphofructokinase is potentiated by low pH; this may be a “safety switch" to turn off glycolysis and thereby prevent an excessive drop in pH from the continued generation of lactic acid. Inhibition of phosphofructokinase by a decrease in pH probably occurs in vivo in ischemic tissue. A second end product of glycolysis is acetylcoenzyme A (CoA), which can be used for fatty acid synthesis or as a substrate for the citric acid cycle. Citrate derived from the condensation of acetyl-CoA and oxaloacetate serves as a feed¬ back inhibitor of phosphofructokinase and probably mediates the inhibitory effects of fatty acids and ketone bodies on gly¬ colysis in the heart and other tissues.60 Other activators of phosphofructokinase include ammonia (from working muscle), fructose-1,6-bisphosphate (involved in the generation of glyco¬ lytic oscillations in muscle extracts that may be of advantage in maintaining a high-energy state61,62), and fructose-2,6-bisphosphate (of uncertain importance in muscle62,63 but of great impor¬ tance in liver63-67). Most of these activators and inhibitors affect the affinity of the enzyme for its substrate fructose-6-phosphate. The concentration of the latter, therefore, is an important deter¬ minant of enzyme activity. Sometimes, a rise in hexose mono¬ phosphate secondary to rapid glycogenolysis may be an impor¬ tant stimulator of glycolysis. HEXOKINASE AND GLUCOSE TRANSPORT

Phosphofructokinase is the logical control point of glycolysis because it is the first nonequilibrium reaction (“committed step") after the branch point at glucose-6-phosphate. However, it is preceded by nonequilibrium steps at hexokinase and (although not in liver) glucose transport. Hexokinase is inhibited noncompetitively by glucose-6-phosphate at a regulatory locus distinct from the catalytic site. Consequently, a block at phosphofructo¬ kinase (or excessive glycogenolysis) could secondarily inhibit hexokinase through a rise in the hexose monophosphates, and, conversely, activation of phosphofructokinase could release such inhibition. Glucose transport in muscle and adipose tissue is acti¬ vated by insulin, but the hormone appears to have no direct effect on muscle phosphofructokinase. Insulin may stimulate hexoki¬ nase activity by promoting binding of that enzyme to mitochon¬ dria for more efficient energy transfer.68 Anoxia also stimulates glucose transport, but it is unknown whether this is related to the concurrent increases in allosteric effectors of phosphofructoki¬ nase such as AMP and P;. Secondary regulation of the glycolytic pathway downstream from phosphofructokinase involves prod¬ uct inhibition of glyceraldehyde-3-phosphate dehydrogenase by 1,3-diphosphoglycerate and NADH, and of pyruvate kinase by ATP.

CONTROL OF GLUCONEOGENESIS AND GLYCOLYSIS IN LIVER SUBSTRATE CYCLES

The opposing glycolytic and gluconeogenic enzymes form ATP-consuming “substrate cycles" (see Fig. 128-2). These fre¬ quently were termed “futile cycles" when it was assumed such energy wastage would be prevented by tight regulation, so that only one opposing pathway would proceed at a given time. How¬ ever, in cellular metabolism, a greater premium seems to be placed on responsiveness and flexibility of control than on mini¬ mizing energy costs—witness, for example, the synthesis of mRNA precursor forms that are much larger than the final prod¬ uct, even though the addition of each extra nucleotide residue effectively costs twice as much as one turn of a metabolic "futile cycle." Coordinate regulation of simultaneously operating glyco¬ lytic and gluconeogenic pathways could have advantages in sen¬ sitivity to metabolic needs, and significant rates of recycling have

1181

been demonstrated under some conditions by sophisticated ra¬ diolabel experiments.8,18,69'70 REGULATORY PROPERTIES

The direction and magnitude of the flux between glucose and pyruvate are determined by the balance of regulatory effects on the key glycolytic and gluconeogenic enzymes. These en¬ zymes are adaptive in liver in response to alterations in the nutri¬ tional and hormonal state, and this is a key means by which they are chronically regulated. Pertinent allosteric effects on gluco¬ neogenic enzymes include the inhibition of fructose-1,6-bisphosphatase by AMP and fructose-2,6-bisphosphate, both of which activate the opposing glycolytic enzyme, phosphofructokinase; and the absolute dependence of the pyruvate carboxylase reaction on the activator acetyl-CoA. The latter property pro¬ vides a regulatory link between gluconeogenesis and fatty acid oxidation. Generally, the key glycolytic enzymes appear to be subject to more stringent control than are their gluconeogenic counterparts, and probably are the principal sites of regulation of net gluco¬ neogenic as well as glycolytic flux. Glucokinase, by virtue of its high Km, is sensitive to changes in glucose concentration in the physiologic range and has an adaptive response to insulin. In low-insulin states, such as starvation or diabetes, the amount of glucokinase is diminished greatly. Liver phosphofructokinase has the same wide range of allosteric effectors noted for muscle; nutritional and hormonal regulation of the enzyme in liver, in particular, involves fructose-2,6-bisphosphate. Liver pyruvate kinase has a requirement for the activator fructose-1,6-bisphos¬ phate: only in the presence of this metabolite does it have as great an affinity for its substrate, phosphoenolpyruvate, as the muscle isoenzyme has with or without fructose-1,6-bisphosphate. Thus, a decrease in phosphofructokinase activity would decrease fruc¬ tose-1,6-bisphosphate levels and, therefore, inhibit liver pyru¬ vate kinase. Liver pyruvate kinase also is strongly inhibited by ATP (feedback inhibition) and by alanine, a major gluconeogenic precursor released by muscle and gut. In addition, liver pyruvate kinase is subject to phosphorylation by the cAMP-dependent protein kinase. Phosphorylation inhibits the enzyme by decreas¬ ing its affinity for phosphoenolpyruvate and for the required ac¬ tivator, fructose-1,6-bisphosphate. FRUCTOSE-2,6-BISPHOSPHATE AND GLUCAGON ACTION

A prime example of the reciprocal regulation of glycolytic and gluconeogenic enzymes is the action on liver of glucagon, a hormone long known to stimulate gluconeogenesis. Activation of the cAMP-dependent protein kinase by glucagon inhibits the phosphofructokinase reaction by reducing the hepatic concen¬ tration of the potent activator fructose-2,6-bisphosphate.63-6' Fructose-2,6-bisphosphate is synthesized from fructose-6phosphate and ATP by 6-phosphofructo-2-kinase. The same protein also has the fructose-2,6-bisphosphatase activity (at a second site) that cleaves fructose-2,6-bisphosphate to fructose-6phosphate and P;. Phosphorylation of this multifunctional en¬ zyme by the cAMP-dependent protein kinase decreases the kinase activity and enhances the phosphatase activity, and this causes a decrease in fructose-2,6-bisphosphate. Because fructose-2,6-bisphosphate is an activator of phosphofructoki¬ nase, as well as an inhibitor of fructose-1,6-bisphosphatase, a fall in its concentration will decrease the conversion of fructose-6phosphate to fructose-1,6-bisphosphate and increase the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate, thus favoring net gluconeogenesis. Moreover, fructose1,6-bisphosphatase can be phosphorylated by the cAMP-dependent protein kinase, and the phosphorylated enzyme is more active by virtue of a reduced affinity for the inhibitors AMP and fructose-2,6-bisphosphate.71 Glucose opposes glucagon and raises fructose-2,6-bisphosphate levels partly by raising the con-

1

2

PART IX: DISORDERS OF FUEL METABOLISM tion of fructose-6-phosphate, hofructo-2-kinase.

C

the

substrate

for

6-

TDINATION WITH GLYCOGEN METABOLISM

The underlying mechanism for the multisite and coordinate control of glycogen and glucose metabolism in liver now can be seen: activation of cAMP-dependent protein kinase by glucagon leads to phosphorylation of phosphorylase kinase, phosphorylase, and glycogen synthase (thus promoting glycogenolysis), as well as pyruvate kinase, fructose-1,6-bisphosphatase, and 6phc 'phofructo-2-kinase/fructose-2,6-bisphosphatase (thus decre, ing fructose-2,6-bisphosphate and inhibiting glycolysis and promoting gluconeogenesis). Alternatively, glucose or insulin promotes the dephosphorylation of these enzymes and, hence, promotes glycogen synthesis and glycolysis. Thus, the balance between insulin and glucagon is perhaps the principal determi¬ nant of the setting of hepatic carbohydrate metabolism at a given time. Finally, it should be pointed out that there is some contro¬ versy over whether the immediate precursor for hepatic glycogen synthesis after carbohydrate administration is circulating glucose or gluconeogenic precursors, largely derived from the peripheral catabolism of the glucose.72,73

PYRUVATE DEHYDROGENASE Pyruvate dehydrogenase catalyzes the conversion of pyru¬ vate to acetyl-CoA, which, in turn, is oxidized to COz and H20 in the citric acid cycle or used for lipogenesis. Conversion of pyru¬ vate to acetyl-CoA by this multienzyme complex is under strin¬ gent control, because any carbon passing through no longer can be used for the resynthesis of glucose.74,75 The enzyme is inhib¬ ited by its products, acetyl-CoA and NADPf, and this inhibition is countered by CoA and NAD. Thus, the ratios acetyl-CoA/CoA and NADH/NAD are important determinants of its activity in situ. The enzyme is subject to inactivation and activation by phosphorylation and dephosphorylation reactions, respectively. The kinase that catalyzes the phosphorylation reaction is acti¬ vated by high ratios of ATP/ADP, acetyl-CoA/CoA, and NADH/NAD. The corresponding phosphatase is stimulated by high concentrations of calcium and pyruvate. Thus, pyruvate de¬ hydrogenase is sensitive to the relative need for acetyl-CoA for fatty acid synthesis, the generation of energy by the citric acid cycle, and the supply of pyruvate. Concordantly, pyruvate dehy¬ drogenase activity is increased in liver, muscle, and heart in the

FIGURE 128-6. Overview of free fatty acid and ketone body metabolism during brief and pro¬ longed starvation.

fed state and decreased in starvation and diabetes when abun¬ dant lipid fuels (increased acetyl-CoA/CoA and NADH/NAD) are available. Its activity also is markedly increased in muscle during exercise, presumably because of the activation of pyru¬ vate dehydrogenase phosphatase by Ca2+ and changes in intramitochondrial ATP, ADP, and redox state.76

SORBITOL PATHWAY Present in many tissues is the enzyme aldose reductase, which converts glucose to the sugar alcohol sorbitol. Aldose re¬ ductase has a very low affinity for glucose (KM about 20 mM); therefore, this reaction is of interest principally in patients with diabetes, in whom plasma and intracellular glucose concentra¬ tions are elevated. Increases in sorbitol have been linked to the pathogenesis of cataracts, neuropathy, and vascular disease in patients with diabetes.77,78 This may involve associated decreases in myoinositol, or nitric oxide,79 which in turn affect the plasma membrane sodium-potassium adenosine triphosphatase that is responsible for the ion gradients that are essential for nerve con¬ duction and certain transport processes.80 Galactose also is con¬ verted to its corresponding sugar alcohol (galactitol) by aldose reductase, and disease similar to that produced by diabetes has been noted in galactose-fed animals. Therefore, aldose reductase inhibitors are being tested for their ability to prevent or reverse long-term complications of diabetes.

LIPID METABOLISM The largest caloric reservoir in humans is triglyceride stored in adipose tissue. Triglycerides are degraded to FFAs and glycerol in all persons, and their degradation is increased during starva¬ tion and other situations (e.g., exercise) in which glucose cannot meet all the fuel needs of the body (Fig. 128-6). When FFAs enter the circulation, they are complexed to albumin, which facilitates their interorgan transport and diminishes their potential toxicity. In the liver, FFAs can be esterified to form triglyceride, oxidized to C02 and H20, or metabolized to ketone bodies (acetoacetate and (3-hydroxybutyrate), which can be used by the brain and muscle during brief starvation. During prolonged starvation, the brain continues to use ketone bodies, whereas muscle decreases its use of ketone bodies in favor of FFAs liberated from adipose tissue.

Ch. 128: Fuel Homeostasis and Intermediary Metabolism of Carbohydrate, Fat, and Protein

FREE FATTY ACID METABOLISM MOBILIZATION FROM ADIPOSE TISSUE AND TRANSPORT IN PLASMA

The fall of insulin levels in the plasma during starvation or diabetes orchestrates a series of events that lead ultimately to the breakdown of triglycerides stored in adipose tissue (i.e., lipolysis) and the elevation of FFA levels in the plasma. The breakdown of these triglyceride stores is regulated by a hormone-sensitive li¬ pase within the adipocyte. Several lipases interact to degrade the triglyceride molecule completely to form three molecules of fatty acid plus one of glycerol. The initial cleavage of the triglyceride molecule by triglyceride lipase appears to be the rate-limiting step, because the breakdown of diglyceride to free glycerol is about 10 times faster than the breakdown of triglyceride to di¬ glyceride. Thus, the release of the first fatty acid molecule from triglyceride is followed by rapid complete hydrolysis to FFAs and glycerol. The activity of triglyceride lipase in adipose tissue is regu¬ lated by the phosphorylation state of the enzyme and is subject to hormonal modulation in much the same manner as glycogen phosphorylase. Phosphorylation of the lipase is catalyzed by a cAMP-dependent protein kinase and is associated with activa¬ tion of the enzyme. Catecholamines, glucagon, and several other hormones that increase cAMP by activating adenylate cyclase, activate triglyceride lipase by this means.81 Dephosphorylation, catalyzed by a phosphoprotein phosphatase, inactivates the en¬ zyme. As with phosphorylase, insulin can facilitate inactivation of the lipase either by decreasing intracellular cAMP or by in¬ creasing the activity of a phosphoprotein phosphatase.82 It di¬ minishes cAMP by increasing the activity of a phosphodiesterase that converts cAMP to AMP, or it may decrease the activity of adenylate cyclase directly. Alternatively, the antilipolytic effect of insulin can occur when there is no change in cAMP levels within the adipocyte, suggesting that it can alter phosphatase ac¬ tivity by other mechanisms.83 Interestingly, the limiting enzyme for triglyceride formation, a-glycerophosphate acyltransferase, becomes inactive when phosphorylated by a cAMP-dependent protein kinase, and active when dephosphorylated by a phos¬ phoprotein phosphatase. Thus, the control is opposite to that of triglyceride lipase, permitting a tight control of triglyceride for¬ mation and breakdown. The principal long-chain fatty acids (at least 14 carbon atoms) found in human plasma are oleic (43%), palmitic (24%),

Acetoacetate

1i

p-hydroxybutyrate

1183

stearic (13%), linoleic (10%), and palmitoleic (5%). At least 10 fatty acid molecules may be bound by each albumin molecule, although this capacity is never reached under physiologic (0.2-2 mM) or even pathologic conditions (2-3 mM). Three of these 10 sites have a high affinity for fatty acids and, when they are fully occupied (at a fatty acid concentration of about 2 mM), the con¬ centration of fatty acids not bound to the albumin increases markedly.84 METABOLISM IN PERIPHERAL TISSUES

The concentration of FFAs in plasma is low (about 10 mg/L) compared with that of glucose. However, the half-life of FFAs in the circulation is less than 2 minutes, and their concentration increases several-fold during starvation and other situations in which triglyceride hydrolysis is accelerated. Consequently, FFA turnover in a normal human approximates 250 g/day, a value comparable to that for glucose.83 Fatty acids are oxidized by most tissues. Liver, kidney, heart, brown adipose tissue, and aerobic muscles (slow-twitch and fast-twitch oxidative fibers) have a high capacity for fatty acid oxidation, whereas fatty acid oxida¬ tion is low in brain (FFAs pass through the blood-brain barrier slowly), white adipose tissue, and fast-twitch white muscles with few mitochondria. Transport of FFAs from the plasma into cells is a passive process, occurring by simple diffusion across the membrane. Thus, a rise in plasma FFAs during starvation will increase their transport into cells such as muscle. Diffusion is de¬ pendent on the concentration gradient between the extracellular space and the cell interior. To ensure a favorable gradient, the concentration of free (unbound) fatty acids within the cell is kept low by binding to a specific fatty acid binding protein.86 This pro¬ tein also prevents an excessive build-up of unbound (free) fatty acids, which could act as detergents and damage cells by disrupt¬ ing the conformation of proteins and the organization of membranes. Long-chain fatty acids taken up by tissues ultimately may undergo /3-oxidation within the mitochondria (Fig. 128-7). Before entering the mitochondria, they first are activated to acyl-CoA derivatives by appropriate acyl-CoA synthetases. In contrast, medium- and short-chain fatty acids can be activated within the mitochondria. Because the mitochondrial inner membrane is im¬ permeable to CoA and its derivatives, a specific transport system is required to transfer long-chain fatty acyl-CoA across this mem¬ brane. This system has three components: (1) the enzyme carni-

Fatty acid-albumin

i

CELL MEMBRANE r Fatty acit2-protein ATP + CoA

\

r

pj-|

Triglyceride

Fatty ac yl-COA^=L ybutyrate

P-oxidation

NAD^-,

NADH- Aceto male diabetes More than eight other contributing loci

BB RAT MHC gene Recessive T-lymphopenia gene on chromosome 4 At least one other gene

HUMAN DR3- and DR4-associated MHC genes Insulin regulatory gene polymorphism Gene outside MHC? (concordance in HLA-identical siblings = 10%, concordance in monozygotic twins = 50%)

1206

PART IX: DISORDERS OF FUEL METABOLISM

of persons with type I diabetes have a histocompatibility-related gene contributing to the disease.23,24 The different alleles of the histocompatibility genes also are nonrandomly associated with each other (i.e., in linkage disequi¬ librium).22 Thus, many different histocompatibility genes are as¬ sociated with diabetes. For example, because DR3 is associated with type I diabetes, and alleles A1 and B8 are associated with DR3, alleles A1 and B8 also are associated with type I diabetes. One allele, DR2, appears to be protective. Persons heterozy¬ gous for both DR3 and DR4 are at highest risk for the develop¬ ment of type I diabetes. The excess risk of DR3 and DR4 hetero¬ zygotes extends even to identical twins. Almost 70% of monozygotic twins expressing both DR3 and DR4 alleles are con¬ cordant for type I diabetes, compared with 30% to 40% of twins not expressing both DR3 and DR4. This synergistic effect sug¬ gests that more than one gene within the MHC contributes to the development of type I diabetes. Independent of specific HLA-DR alleles, persons who have inherited the same HLA haplotypes as a sibling with type I dia¬ betes are at increased risk for the development of diabetes (Fig. 132-1). Thus, persons who are HLA-identical to a sibling with diabetes have about a 1:10 to 1:20 chance of developing diabetes, whereas siblings sharing neither HLA haplotype have less than a 1:100 chance of developing diabetes. The excess of persons who are HLA-identical to a diabetic sibling suggests that one diabeto¬ genic gene in the MHC functions in a recessive manner. Not all diabetic siblings express identical HLA haplotypes, however. This may be explained by a relatively large number of parents (e.g., 20%) who are potentially homozygous for diabetogenic MHC genes. Such a high percentage of homozygous parents is suggested by the observations that 5% of parents of children with type I diabetes develop overt type I diabetes, and that penetrance of even HLA-identical siblings is less than 1:4. Although DR alleles are associated with risk for type I dia¬ betes, DQ Ir molecules appear to be more important in determin¬ ing diabetes susceptibility,25 DR and DQ molecules are closely linked, and both function to bind peptides for presentation to CD4-positive T-lymphocytes. Each DQ molecule has two chains, a and /?. For DQ molecules, both chains are polymorphic. Each different amino acid sequence (polymorphism) of these chains is assigned a number. It is possible with DNA-based technology to rapidly (within hours) type small blood samples for DQ alleles. One hypothesis related the presence of aspartic acid at position 57 on the DQ-/? chain to diabetes risk (DQ alleles lacking aspartic acid at position 57 are frequently associated with diabetes26). There are, however, too many exceptions to this rule for it to be useful (e.g., DQB1*0402),27 given the ease of typing for specific alleles with current technology. Certain DQ molecules appear to provide almost complete protection from type I diabetes, such as DQA1*0102/ DQB1*0602.28 This molecule is usually associated with DR2, but

DM

1/5

1/20

1/100

DM

DM

DM

FIGURE 132-1.

HLA haplotype sharing versus approximate concor¬ dance for type I diabetes mellitus (DM) in a family where neither parent has type I diabetes. Letters refer to four MHC haplotypes in the family, with each parent passing on one of the two sixth chromosomes to each child (MHC region marked by HLA typing). Siblings HLA-identical to the proband have the highest risk of type I diabetes (1/10 to 1/5) and siblings sharing neither HLA haplotype have the lowest risk (1/100). (From Eisenbarth GS. Autoimmune beta cell insufficiency. Triangle 1984;24: 111.)

when DR2 is associated with other DQ molecules (e.g., DR2, DQB1*0502, which is found among patients with type I diabetes on the island of Sardinia), the haplotype is diabetogenic. Of more than 150 patients with type I diabetes, the author and his associ¬ ates have typed only one who had DQB1*0602, and this person had the polyendocrine autoimmune type I syndrome with its co¬ existent mucocutaneous candidiasis. The manner in which this DQ molecule protects against type I diabetes is unknown. The highest-risk DQ alleles associated with type I diabetes are DQA1*0501/DQB1*0201 associated with DR3, and DQA1*0301/DQB1*0302 associated with DR4. Persons hetero¬ zygous for these two alleles in the general population have a risk of diabetes similar to that of an offspring of a parent with type I diabetes (about 1:16). Such persons make up about 2% of the U.S. population, but account for 40% of patients with type I dia¬ betes. A research program to identify these persons at birth is under way. Subsequent studies will define the timing and se¬ quence of the appearance of autoantibodies, with the long-term goal of predicting type I diabetes in the general population. The fact that the incidence of diabetes developing in HLAidentical siblings (16%) is less than that in identical twins (40%50%) strongly suggests that another gene outside the MHC con¬ tributes to diabetes susceptibility. This is similar to the genetics of diabetes susceptibility of BB rats and NOD mice. When either of these animals is crossed with normal-strain animals, only off¬ spring inheriting a "diabetogenic” MHC gene and one other au¬ tosomal gene develop diabetes. Multiple other genes influence the susceptibility of NOD mice, and a gene on chromosome 4 influences a susceptibility associated with a T-cell immunodefi¬ ciency of BB rats (see Table 132-3). Too many false-positive results occur with HLA typing (30%-40% of the general population express DR3 and DR4) for this study to aid in clinical decision making. Moreover, HLA typ¬ ing is relatively expensive and can never indicate a risk for diabe¬ tes greater than do HLA-identical siblings (10%-20%). (Within a family, nondiabetic siblings who are HLA-identical, by serologic typing to a sibling with type I diabetes, are usually [> 99% of the time] identical at all HLA loci; nevertheless, their risk of develop¬ ing diabetes is only about 17%.) The imprecision of HLA typing for predicting diabetes even within families probably results in part from the inability to identify another genetic linkage group for type I diabetes. Even when such a linkage group is discovered, genetic prediction of the risk of type I diabetes cannot exceed the concordance rate of identical twins (50%). In addition to alleles within the MHC on chromosome 6, alleles of the insulin gene on chromosome 11 contribute to dia¬ betes susceptibility.29 About 90% of persons with type I diabetes are homozygous for an allele, termed A, that is defined by the FOK restriction enzyme, as compared to 60% of the general pop¬ ulation. There is some controversy regarding whether this insulin gene polymorphism shows "imprinting" (i.e., a differential in¬ fluence on diabetes susceptibility depending on whether it is in¬ herited from the father or the mother). The author's studies of U.S. patients confirm imprinting. If the B allele is inherited from a father, diabetes is usually "prevented," whereas maternal in¬ heritance does not alter diabetes risk. These insulin alleles do not differ in their coding sequence, but in the 3' and 5' regions of the genes. Thus, differential regulation of expression of insulin may have an important influence on diabetes risk. In addition to genes within the MHC and insulin alleles, it is likely that additional genes influence diabetes risk. With molecu¬ lar and computational tools provided by the Genome Project, and shared national repositories of cell lines and DNA from fam¬ ilies with multiple affected members, the search for these addi¬ tional genes is under way and has identified loci on chromosomes 2 and 15. It may be that environmental factors are not necessary for the triggering of type I diabetes. As in many cancers, somatic mutations may randomly trigger disease expression. Testing of this hypothesis will likely depend on the localization of major susceptibility genes.

Ch. 132: Classification, Diagnostic Testing, and Pathogenesis of Type I Diabetes Mellitus

1207

GENETIC AND ENVIRONMENTAL FACTORS

The lack of 100% concordance for type I diabetes in identical twins has been used to argue that environmental factors must contribute to the development of this disease.30,31 One environ¬ mental factor known to increase the incidence of type I diabetes is congenital rubella. After prenatal infection with this virus, as many as 20% of children later develop diabetes. As in spontane¬ ous type I diabetes, those who develop diabetes express HLA alleles DR3 and DR4.32 These children often also have thyroiditis and other immunologic disorders (e.g., agammaglobulinemia) in association with an abnormal T-lymphocyte phenotype that differs from that in both normal persons and usual patients with type 1 diabetes. No epidemiologically defined environmental factors other than congenital rubella have been associated with type I diabetes. It is known that viral infections, in particular those that occur close to the time of onset of overt diabetes, may precipitate hy¬ perglycemia (secondary to insulin resistance associated with in¬ fection), but they are unlikely to play a primary pathogenic role. Although Coxsackie virus B4 has been isolated from the pancreas of a child with recent-onset diabetes,33 the pancreas had multiple pseudoatrophic islets (islets with no B cells but abundant A and D cells) with no inflammation, indicating chronic B-cell destruction preceding the viral infection. Any search for environmental fac¬ tors that may trigger autoimmunity, such as drugs, unknown vi¬ ruses, or dietary components (e.g., milk proteins), must focus on factors that act months to years before the onset of diabetes rather than on acutely diabetogenic factors. ISLET CELL ANTIBODIES AND OTHER IMMUNOLOGIC MARKERS

About 5% of first-degree relatives of patients with type I di¬ abetes also develop diabetes. Immunologic and endocrinologic assays capable of identifying those relatives most likely to de¬ velop diabetes and predicting about when overt diabetes will oc¬ cur include the immunofluorescence assay for cytoplasmic islet cell antibody (Fig. 132-2), the results of which are positive in 70% to 80% of patients with new-onset type I diabetes. Some assays for islet cell antibodies34"36 and a few radioimmunoassays for antiinsulin autoantibodies37,38 have the requisite specificity to identify persons at high risk. Examples are the complementfixation tests for cytoplasmic islet cell antibodies, variants of the standard cytoplasmic islet cell antibody assays, fluid-phase antiinsulin autoantibody assays, and autoantibodies to a 64kilodalton (kd) islet protein (predominantly antibodies to glu-

FIGURE 132-2. Double immunofluorescent detection of islet cell anti¬ bodies reacting with frozen sections of human pancreas. Islets are identi¬ fied with monoclonal antibody (right) and binding of patients' sera with fluoresceinated protein A (left).

FIGURE 132-3.

Development of insulin autoantibodies and cyto¬ plasmic islet cell antibodies (ICA) in overt diabetes. (Adapted from Soeldner JS, Tuttleman M, Srikanta S, et al. Insulin dependent diabetes mellitus and initiation of autoimmunity: islet cell autoantibodies, insulin autoantibodies and beta cell failure. N Engl ] Med 1985;313:893.)

tamic acid decarboxylase [GAD]).39 Generally, these assays have remained research tools, partly because of the difficulty in stan¬ dardizing cytoplasmic islet cell antibody assays when the target antigen has not been isolated and the assay depends on obtaining frozen human pancreas at the time of cadaveric donation. Different assays vary widely in endpoint titers when applied to the same sera. Assays with the highest sensitivity have a high rate of false-positive results. Conversely, specific assays that give positive results in about 2% of normal first-degree relatives and less than 0.4% of the "normal” population identify patients at extremely high risk for the development of diabetes.40 Anti-islet cell antibodies can precede the development of overt diabetes by more than a decade35,39 (Fig. 132-3). HLA typ¬ ing of antibody-positive relatives and even antibody-positive "normal" persons indicates that they have the same HLA distri¬ bution as do patients with type I diabetes, and within 7 years, about 50% develop overt diabetes. Autoantibodies to human insulin also can precede by years the development of type I diabetes.38 Antiinsulin antibodies are present in both cytoplasmic antibody-positive and antibody¬ negative persons who develop diabetes, and are the first radio¬ immunoassay aid in predicting type I diabetes. Antiinsulin auto¬ antibodies are found in about 60% of persons who develop diabetes. When this test is combined with assays for cytoplasmic islet cell antibodies, 90% of patients with new-onset type I dia¬ betes have evidence of autoimmune disease. In addition to cytoplasmic islet cell antibodies and insulin autoantibodies, there are many immunologic abnormalities in patients with type I diabetes and their relatives.41 Many of these abnormalities (e.g., antithyroglobulin and microsomal antibod¬ ies, antibodies to single-stranded DNA, antibodies to the surface of rat islet cells and a rat insulinoma cell line) are inherited inde¬ pendently of the HLA susceptibility to type I diabetes and are present in as many as 30% of first-degree relatives. Such abnor¬ malities provide relatively little prognostic information but ap¬ pear to be related to the autoimmune background of type I diabetes. A major advance in the past several years has been the bio¬ chemical characterization of a series of islet autoantigens, includ¬ ing insulin, GAD (a major component of the 64-kd autoanti¬ gen),42 carboxypeptidase H,43 a milk-related islet protein

1208

PART IX: DISORDERS OF FUEL METABOLISM biochemical characterization of target antigens. Although the ex¬ act nature of these antigens is unknown, studies suggest that the target molecules of cytoplasmic islet cell antibodies are either membrane proteins45 or gangliosides and complex glycolipids,46 in which the carbohydrate sequence confers tissue and species specificity.

FIRST-PHASE INSULIN SECRETION AS AN INDEX OF EARLY INSULIN-DEPENDENT DIABETES MELLITUS

FIGURE 132-4.

Loss of first-phase insulin secretion in a prediabetic twin with islet cell antibody. The Y axis gives insulin concentrations at the times indicated after the intravenous injection of glucose. Initial phase of insulin release (1- and 3-minute) is progressively lost. DM, diabetes mellitus. (Adapted from Srikanta S, Ganda OP, Eisenbarth GS, Soeldner JS. Islet cell antibodies and beta cell function in monozygotic triplets and twins initially discordant for type I diabetes. N Engl ] Med 1983;308:322.)

(ICA69),44 ICA512, and ganglioside GM2-1. Biochemical assays are now available in several research laboratories that use recom¬ binant human proteins for antibodies to insulin, GAD, and ICA512. With just these three assays, more than 98% of patients with new-onset type I diabetes and prediabetes express at least one antibody, and more than 80% express two or more. Speci¬ ficity and sensitivity are much higher with these biochemical as¬ says than with cytoplasmic islet cell antibody testing. In contrast to cytoplasmic islet cell antibody testing, with its inherent prob¬ lems of reproducibility, biochemically determined autoanti¬ bodies are remarkably stable in the prediabetic phase. Interna¬ tional workshops to standardize insulin and GAD radioassays are under way. In both the diagnosis and prediction of type I diabetes, such assays should rapidly replace standard cyto¬ plasmic islet cell antibody testing. It is likely that commercial assays that aid in predicting the development of type I diabetes will be available soon. Neverthe¬ less, reliable assays probably will depend on the isolation and

FIGURE 132-5. Stages in development of type I diabetes begin¬ ning with genetic predisposition and ending with insulin-depen¬ dent diabetes with essentially complete B-cell destruction. (Adapted from Eisenbarth GS. Type I diabetes mellitus: a chronic au¬ toimmune disease. N Engl ] Med 1986;314:1360.)

About 2% of nondiabetic relatives of patients with type I diabetes have positive results on screening assays for islet cell and antiinsulin autoantibodies. When such antibodies are de¬ tected, intravenous glucose tolerance testing can be used to assess first-phase insulin release (Fig. 132-4) as a measure of subclinical B-cell dysfunction. The loss of first-phase insulin secretion, as well as its rate of fall, aids in predicting the time of onset of overt diabetes.46,47 At the initial detection of cytoplasmic islet cell anti¬ bodies and antiinsulin antibodies, one of four patients has firstphase insulin secretion below the first percentile of normal per¬ sons. All persons lose first-phase insulin secretion before the development of overt diabetes. For patients with initially normal insulin release, intravenous glucose tolerance testing is per¬ formed again in 3 to 6 months and, depending on its "stability," at subsequent 3- to 12-month intervals. Immunologically and endocrinologically, persons with abnormal results may be alerted to the risk of type I diabetes and advised concerning routine home monitoring for glucosuria or capillary blood glucose determination. To aid in predicting the time of onset of type I diabetes among antibody-positive relatives, a mathematic formula has been developed: Years to diabetes = 1.5 + 0.03 (insulin secretion) — 0.008 (insulin autoantibody concentration). This simple for¬ mula appears to account for 75% of the variance in the time of diabetes onset.48 Immunologic assays also are being used to aid in the classi¬ fication of patients with diabetes. Insulin dependence is a physi¬ ologic state that can evolve slowly, even in type I diabetes, from a stage in which hyperglycemia is controlled with diet or oral medication to a stage in which death occurs in the absence of insulin therapy (Fig. 132-5). Cytoplasmic islet cell antibodies are found in as many as 10% to 15% of patients with classic type II diabetes at the time of diagnosis, and over the ensuing 5 years, many of these patients become insulin dependent.35 Epidemiologic data from Japan, Pittsburgh, the Nether¬ lands, and Poland indicate that 1 in 200 children die of ketoaci-

Age (years)

Ch. 132: Classification, Diagnostic Testing, and Pathogenesis of Type I Diabetes Mellitus

1209

dosis at the time of diagnosis of their diabetes. It is likely that such deaths could be prevented by early detection and treatment of diabetes.

IMPLICATIONS FOR PREVENTIVE THERAPY The newer immunologic knowledge concerning type I dia¬ betes and the success of a wide variety of immunotherapies in preventing the diabetes of BB rats and NOD mice have led to trials of immunotherapy in patients with recent-onset type I dia¬ betes, and to a few trials in persons at high risk for the develop¬ ment of type I diabetes. These trials indicate that it will be possi¬ ble to limit B-cell destruction. Toxic side effects of the most powerful (and most effective) drugs are a serious problem, how¬ ever. For example, cyclosporine A is nephrotoxic at the dosages that appear to be required to induce remissions of type I diabe¬ tes,49'50 and azathioprine may be associated with epithelial ma¬ lignancies. Prednisone given after the onset of type I diabetes is ineffective, and a series of other therapies, such as plasmaphere¬ sis, antithymocyte globulin, and monoclonal antibody T12, pro¬ duce no long-term benefit. A series of new agents that are not significantly immunosup¬ pressive yet are able to limit B-cell destruction in animal models of type I diabetes are being studied. All immunologic attempts to limit B-cell destruction are considered investigational and should be used only under the oversight of human investigation committees.51 Trials investigating the prevention of type I diabetes and the amelioration of further B-cell loss after diabetes onset are con¬ centrating on nonimmunosuppressive therapies. Such trials in¬ clude administration of the vitamin nicotinamide,52 which mod¬ estly delays diabetes onset in NOD mice; vaccination with bacille Calmette-Guerin53; administration of oral insulin54; and therapy with parenteral insulin.55 Nicotinamide may have an effect by limiting free radical damage to B cells. In the NOD mouse model, a single injection of bacille Calmette-Guerin prevents diabetes but not insulitis. Such therapy may limit B-cell destruction by altering cytokines produced by infiltrating T cells. Oral insulin delays or prevents type I diabetes of NOD mice. Its effect is likely due to the generation (by peptides of insulin presented in the intestinal mucosa) of T cells that suppress inflammation. The most dramatic prevention of diabetes in both the NOD mouse and the BB rat has been obtained with parenteral administration of insulin. Such therapy prevents not only diabetes, but infiltra¬ tion of islets by T cells and destruction of B cells. A small pilot trial55 of intravenous insulin and low-dose subcutaneous insulin for the prevention of diabetes in high-risk relatives of patients with diabetes suggests that such therapy may delay and, for a subset, even prevent type I diabetes (Fig. 132-6).

AUTOIMMUNE POLYGLANDULAR FAILURE About 10% of patients with type I diabetes develop other organ-specific autoimmune diseases (see Chap. 191), such as Graves disease, hypothyroidism, Addison disease, and perni¬ cious anemia.56,57 Some patients develop multiple disorders as a part of two inherited polyendocrine autoimmune syndromes (type I and type II). The type I syndrome usually has its onset in infancy, with hypoparathyroidism, mucocutaneous candidiasis, and, somewhat later, Addison disease and other organ-specific disorders. Five percent of these children develop type I diabetes. This disorder is inherited in an autosomal recessive manner with no HLA association. The type II polyendocrine autoimmune syn¬ drome (Addison disease, type I diabetes [50% of patients], Graves disease, hypothyroidism, myasthenia gravis, and other organ-specific diseases) is strongly HLA-associated and has an onset from late childhood to middle age. In these families, there is a high prevalence of undiagnosed organ-specific autoimmune disease and, at a minimum, thyroid function tests should be per¬ formed in the first-degree relatives of these patients. Biochemical

FIGURE 132-6. Lifetable analysis of a pilot study of intravenous plus low-dose subcutaneous insulin in preventing diabetes in first-degree rel¬ atives of patients with type I diabetes. One of the five treated children and all seven islet cell autoantibody-positive untreated relatives developed clinical diabetes, the diagnosis being based on an abnormal glucose tol¬ erance test result or a high fasting plasma glucose level. (From Keller R], Eisenbarth GS, Jackson RA. Insulin prophylaxis in individuals at high risk of type I diabetes. Lancet 1993;341:928.)

evaluation for adrenal insufficiency and pernicious anemia should be performed if there is any suggestive symptom or sign (e.g., decreasing insulin requirements can herald the develop¬ ment of Addison disease in a patient with type I diabetes before electrolyte abnormalities or hyperpigmentation develop).

REFERENCES 1. National Diabetes Data Group. Classification and diagnosis of diabetes mellitus and other categories of glucose intolerance. Diabetes 1979; 28:1039. 2. WHO Expert Committee on Diabetes Mellitus. Second report. (Technical report series 1980.) Geneva: World Health Organization, 1980:646. 3. Marble A, Ferguson BD. Diagnosis and classification of diabetes mellitus and the non-diabetic melliturias. In: Marble A, Krall LP, Bradley RF, et al, eds. Joslin's diabetes mellitus, ed 12. Philadelphia: Lea & Febiger, 1985:332. 4. Tattersall RB, Fajans SS. A difference between the inheritance of classical juvenile-onset and maturity-onset diabetes of young people. Diabetes 1975; 24:44. 5. Nelson RL. Oral glucose tolerance test: indications and limitations. Mayo Clin Proc 1988; 63:263. 6. Ganda OP, Srikanta S, Brink SJ, et al. Differential sensitivity to beta cell secretagogues in "early" type I diabetes. Diabetes 1984;33:516. 7. Bergman RN, Finegood DJ, Ader M. Assessment of insulin sensitivity in vivo. EndocrRev 1985; 6:45. 8. Fajans SS, Conn JW. An approach to the prediction of diabetes mellitus by modification of the glucose tolerance test with cortisone. Diabetes 1954;3;296. 9. Koenig RJ, Cerami A. Hemoglobin Alc and diabetes mellitus. Annu Rev Med 1980;31:29. 10. Starkman HS, Soeldner JS, Gleason RE. Oral glucose tolerance—relation¬ ship with hemoglobin Alc. Diabetes Res Clin Pract 1987;6:343. 11. Fine J. Glucose content of normal urine. BM] 1965; 1:1209. 12. Agner E, Thorsteinssen B, Eriksen M. Impaired glucose tolerance and dia¬ betes mellitus in elderly subjects. Diabetes Care 1982;5:600. 13. Gepts W. The pathology of the pancreas in human diabetes. In: Adreani D, Federlin KF, DiMario U, Heding LG, eds. Immunology in diabetes. London: Kimpton Publishers, 1984:21. 14. Gepts W. Islet cell morphology in type I and type II diabetes. In: Irvine WJ, ed. Immunology in diabetes. Edinburgh: Teviot Scientific Publications, 1982:255. 15. Eisenbarth GS. Type I diabetes mellitus: a chronic autoimmune disease. N Engl] Med 1986;314:1360. 16. Makino S, Harada M, Kishimoto Y, Hayashi Y. Absence of insulitis and overt diabetes in athymic nude mice with NOD genetic background. Jikken Dobitsu Exp Anim 1986;35:495. 17. Blasi C, Pierelli F, Rispoli E, et al. Wolfram's syndrome: a clinical, diag¬ nostic and interpretative contribution. Diabetes Care 1986;9:521. 18. Rossini AA, Mordes JP, Like AA. Immunology of insulin-dependent dia¬ betes mellitus. Annu Rev Immunol 1985; 3:289. 19. Feingold KR, Lee TH, Chug MY, Siperstein MD. Muscle capillary base¬ ment membrane width in patients with Vacor-induced diabetes mellitus. J Clin In¬ vest 1986;78:102. 20. Jackson RA, Buse JB, Rifai R, et al. Two genes required for diabetes in BB rats. J Exp Med 1984; 159:1629.

1210

PART IX: DISORDERS OF FUEL METABOLISM

21. Rimoin DI, Rotter JI. The genetics of diabetes. In: Andreani D, DiMario U, Federlin KF, Heding LG, eds. Immunology in diabetes. London: Kimpton Publish¬ ing, 1984:45. 22. Stastny P, Ball E], Dry PJ, Hunez G. The human immune response region (HLA-D) and disease susceptibility. Immunol Rev 1983; 70:113. 23. Colrrtan PG, Eisenbarth GS. Immunology of type I diabetes. In: Alberti KGM, Krall LP, eds. The diabetes annual 4, vol 17. Amsterdam: Elsevier Science Publishers 1988:55. 24. Sheehy M], Schorf SJ, Rowe JR, et al. A diabetic susceptible HLA haplotype is best defined by a combination of HLA-DR and DQ alleles. J Clin Invest 1989;83:830. 25. Nepom GT. Immunogenetics and IDDM. Diabetes Rev 1993; 1:93. 26. Todd JA, Acha-Orbea H, Bell JI, et al. A molecular basis for MHC class II associated autoimmunity. Science 1988;240:1003. 27. Erlich HA, Griffith RL, Bugawan TL, et al. Implication of specific DQB1 alleles in genetic susceptibility and resistance by identification of IDDM siblings with novel HLA-DQB1 allele and unusual DR2 and DR1 haplotypes. Diabetes 1991;40:478. 28. Baisch JM, Weeks T, Giles R, et al. Analysis of HLA-DQ genotypes and susceptibility in insulin-dependent diabetes mellitus. N Engl J Med 1990;322:1836. 29. Lucassen AM, Julier C, Beressi J-P, et al. Susceptibility to insulin depen¬ dent diabetes mellitus maps to a 4.1 kb segment of DNA spanning the insulin gene and associated VNTR. Nature Genetics 1993;4:305. 30. Barnett AH, Eff C, Leslie RDG, Pyke DA. Diabetes in identical twins: a study of 200 pairs. Diabetologia 1981;20:87. 31. Blom L, Dahlquist G, Nystrom L, et al. The Swedish childhood diabetes study—social and perinatal determinants for diabetes in childhood. Diabetologia 1989;32:7. 32. Menser MA, Forrest JM, Brensby RD. Rubella infection and diabetes mel¬ litus. Lancet 1981; 1:57. 33. Yoon JW, London WT, Curfman BL, et al. Coxsackie virus B4 produces transient diabetes in non-human primates. Diabetes 1986;35:712. 34. Gale EAM, Bottazzo GF. Can we predict type I (insulin-dependent) diabe¬ tes? In: Krall L, ed. World book of diabetes in practice, vol 2. Amsterdam: Elsevier, 1985:25. 35. Irvine WJ, Gray RS, Steel JM. Islet cell antibody as a marker for early stage type I diabetes mellitus. In: Irvine WJ, ed. The immunology of diabetes. Edinburgh: Teviot Publishing, 1980:117. 36. Gorsuch AN, Spencer KM, Lister J, et al. Evidence for a long prediabetic period in type I (insulin-dependent) diabetes mellitus. Lancet 1981;2:1363. 37. Palmer JP, Asplin CM, Clemons P, et al. Insulin antibodies in insulindependent diabetics before insulin treatment. Science 1983; 222:1337. 38. Vardi P, Tuttleman M, Grinbergs M, et al. Consistency of anti-islet auto¬ immunity in "pre-type I diabetics" and genetically susceptible subjects: evidence from an ultrasensitive competitive insulin autoantibody (CIAA) radioimmunoas¬ say. Diabetes 1986;35(Suppl 1):86A. 39. Riley W, Maclaren N. Islet-cell antibodies are seldom transient. Lancet 1984; 1:1351. 40. Kuglin B, Bertrams J, Linke C, et al. Prevalence of cytoplasmic islet cell antibodies and insulin auto-antibodies is increased in subjects with genetically de¬ fined high risk for insulin-dependent diabetes mellitus. Klin Wochenschr 1989; 67: 66. 41. Buse JB, Eisenbarth GS. Autoimmune endocrine disease. Vitam Horm 1985;42:253. 42. Baekkeskov S, Aanstoot H, Christgau S, et al. Identification of the 64K autoantigen in insulin dependent diabetes as the GABA-synthesizing enzyme glu¬ tamic acid decarboxylase. Nature 1990;347:151. 43. Castano L, Russo E, Zhou L, et al. Identification and cloning of a granule autoantigen (carboxypeptidase H) associated with type I diabetes. J Clin Endocrinol Metab 1991; 73:1197. 44. Pietropaolo M, Castano L, Babu S, et al. Islet cell autoantigen 69 kDa (ICA69): molecular cloning and characterization of a novel diabetes associated au¬ toantigen. J Clin Invest 1993;92:359. 45. Baekkeskov S, Nielsen JH, Marner B, et al. Autoantibodies in newly diag¬ nosed diabetic children immunoprecipitate specific human islet cell proteins. Nature 1982;298:167. 46. Nayak RC, Omar MAK, Rabizadeh A, et al. "Cytoplasmic" islet cell anti¬ bodies: evidence that the target antigen is asialoglycoconjugate. Diabetes 1985; 34: 617. 47. Srikanta S, Ganda OP, Soeldner JS, Eisenbarth GS. First-degree relatives of patients with type I diabetes: islet cell antibodies and abnormal insulin secretion. N Engl J Med 1985;313:461. 48. Jackson R, Vardi P, Herskowitz R, et al. Dual parameter model for predic¬ tion of onset of type I diabetes in islet cell antibody positive relatives. Clin Res 1988;36:585A. 49. Stiller CR, Dupre J, Gent M, et al. Effect of cyclosporine immunosuppres¬ sion in insulin-dependent mellitus of recent onset. Science 1984; 223:1362. 50. Feutren G, Asson G, Karsenty G, et al. Cyclosporine increases the rate and length of remissions in insulin-dependent diabetes of recent onset: results of a multi-center trial. Lancet 1986; 2:119. 51. Colman PG, Eisenbarth GS. Immunological approaches to the treatment and prevention of childhood diabetes. Postgrad Med 1987;81:146. 52. Herskowitz RD, Jackson RA, Soeldner JS, Eisenbarth GS. Pilot trial to prevent type 1 diabetes: progression to overt IDDM despite oral nicotinamide. J Autoimmun 1989; 2:733. 53. Sadelain MWJ, Qin H-Y, Lauzon J, Singh B. Prevention of type I diabetes in NOD mice by adjuvant immunotherapy. Diabetes 1990; 39:583.

54. Zhang JZ, Davidson L, Eisenbarth GS, Weiner HL. Suppression of diabe¬ tes in nonobese diabetic mice by oral administration of porcine insulin. Proc Natl Acad Sci USA 1991; 88:10252. 55. Keller RJ, Eisenbarth GS, Jackson RA. Insulin prophylaxis in individuals at high risk of type I diabetes. Lancet 1993,-341:927. 56. Nuefeld M, Maclaren N, Blizzard RM. Two types of autoimmune Addi¬ son's disease associated with different polyglandular autoimmune (PGA) syn¬ dromes. Medicine (Baltimore) 1981;60:355. 57. Eisenbarth GS, Wilson P, Ward F, et al. The polyglandular failure syn¬ drome: disease inheritance, HLA-type and immune function: studies in patients and families. Ann Intern Med 1979;91:528.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

133_

ETIOLOGY AND PATHOGENESIS OF TYPE II DIABETES MELLITUS AND RELATED DISORDERS C. RONALD KAHN

NON-INSULIN-DEPENDENT DIABETES MELLITUS Type II diabetes is by far the most prevalent endocrine dis¬ ease. It is estimated to affect more than 12 million people in the United States, about half of whom are undiagnosed.1'2 The prev¬ alence increases with age and is greater than 9% of those older than 65 years of age. The prevalence is higher in Mexican Ameri¬ cans and Puerto Ricans and exceeds 35% in some Native Ameri¬ cans, especially Pima Indians. Development of type II diabetes is strongly influenced by genetic factors and by environmental factors, including obesity, decreased physical activity, and a low level of physical fitness. PATHOGENESIS Although type II or non-insulin-dependent diabetes melli¬ tus (NIDDM) is the more common form of the disease, the exact nature of its pathogenesis is even more controversial than that of IDDM. Because there are no specific diagnostic tests for type II diabetes, the diagnosis usually is based on clinical criteria only. NIDDM is influenced genetically, and it occurs in identical twins with almost total concordance.4,5 In contrast to insulindependent diabetes mellitus (IDDM), NIDDM is not associated with any specific HLA alloantigens. In NIDDM, insulin secretion and B-cell mass are relatively well preserved or only mildly ab¬ normal, and there is clear evidence for resistance to insulin action in the peripheral tissues.6-9 However, there is controversy over such basic issues as whether decreased insulin secretion or insu¬ lin resistance is the principal factor in the pathogenesis of type II diabetes. There is also uncertainty about how heterogeneous this syndrome is and about what the primary lesion may be. The ma¬ jor exceptions to this lack of knowledge are the rare patients with genetic syndromes of insulin resistance (see Chap. 140) and pa¬ tients with maturity-onset diabetes of youth (MODY), which is discussed later in this chapter. INSULIN SYNTHESIS AND SECRETION Even before the introduction of radioimmunoassays (RIA), morphologic studies suggested that the pancreas of a patient with

Ch. 133: Etiology and Pathogenesis of Type II Diabetes Mellitus and Related Disorders NIDDM has about 50% of the normal B-cell mass, whereas that of a patient with IDDM of more than a few years' duration has virtually no B cells.6 This finding is consistent with the data on extractable insulin as measured in bioassay and RIA. Immunoas¬ say of plasma insulin and of C-peptide has confirmed the pres¬ ence of functioning B cells in patients with NIDDM, but the ex¬ tent of function varies considerably depending on the type of stimulus used, the body weight of the patient, and the stage of disease.8-10 In most individuals with NIDDM, basal insulin levels are normal or elevated, and the degree of elevation correlates with the degree of obesity.11 Elevated insulin levels also occur in thin individuals with type II diabetes. Although a few patients have been identified with a defect in the conversion of proinsulin to insulin or mutant insulin molecules, in most patients with NIDDM, the proportion of proinsulin to insulin is normal, and the insulin and proinsulin have normal receptor binding and bioactivity. Although basal insulin levels usually are elevated in the type II diabetic, the insulin secretory responses to oral glucose differ considerably, depending on the extent of glucose intolerance. In patients with normal fasting glucose and 2-hour postprandial levels below 220 mg/dL, insulin secretion is increased in propor¬ tion to the degree of glycemia (Fig. 133-1). With more severe de¬ grees of glucose intolerance, the secretion of insulin in response to an oral glucose load is reduced. This bell-shaped curve is rem¬ iniscent of the Starling curve for cardiac function. Insulin re¬ sponse to mixed meals often is preserved in type II diabetics, even those with fasting glucose levels in excess of 200 mg/dL.10 In contrast to the relative preservation of insulin response to meals and oral glucose, there is a loss of acute (first)-phase insulin release in response to glucose given intravenously in virtually all patients with significant fasting hyperglycemia.9 Acute insulin release to /3-adrenergic stimuli, amino acids, and other insulin secretagogues in these same individuals often is normal, suggest¬ ing a specific defect in glucorecognition rather than a general de¬ fect in B-cell function. 13 This pattern of response resembles that seen in patients in the preclinical phase of type I diabetes. In stud¬ ies of perfused pancreases from animal models of type II diabe¬ tes, although first-phase secretion may be lost, glucose maintains its ability to potentiate arginine-induced insulin secretion.14 The

_i_i-1-1-

100

200

300

400

MEAN GLUCOSE ( mg/dL) 2 HOURS AFTER GLUCOSE LOAD

FIGURE 133-1. Relation between insulin secretion and glucose level 2 hours after a glucose load. Data were obtained for Pima Indians with various degrees of glucose intolerance; similar results have been observed in whites. (Data from Savage PJ, Dippe SE, Bennett PH, et al. Hyperinsulinemia and hypoinsulinemia: insulin responses to oral carbohydrate over a wide spectrum of glucose tolerance. Diabetes 1975; 24:262.)

1211

preservation of response to an oral glucose load probably is a reflection of the importance in this response of the potentiation of the glucose effect by gastrointestinal hormones. However, in humans with type II diabetes, the glucose potentiation is also blunted. A lost first-phase response to glucose can be restored at least partially by a-adrenergic blockade, opiate receptor block¬ ade, inhibitors of prostaglandin synthesis, lowering of the plasma glucose by dietary restriction, oral hypoglycemic agents, or even by insulin.1516 The fact that this lesion is functional and at least partially reversible makes it potentially amenable to therapeutic manipulation. Investigators have demonstrated that a fragment of glucagon-like peptide I (GLP-I) may potentiate glucoseinduced insulin secretion in the type II diabetic, offering a possi¬ ble new avenue for therapy.

INSULIN RESISTANCE Virtually all patients with NIDDM have some form of insu¬ lin resistance.1517 Conditions associated with the development of insulin resistance, especially obesity and advancing age, greatly increase the risk of NIDDM. Insulin resistance correlates with certain patterns of obesity and is greater in individuals with cen¬ tral obesity than those with more generalized obesity.18 At any given body weight, a high waist-to-hip ratio correlates with in¬ sulin resistance and increased risk of type II diabetes. Insulin resistance and hyperinsulinemia are also associated with hy¬ pertension and hypertriglyceridemia, deceased high-densitylipoprotein cholesterol, and increased risk of atherosclerosis and cardiovascular disease.19,20 The association of insulin resistance with these features in the absence of clinical type II diabetes has been referred to as syndrome X.19 In cases of NIDDM and syndrome X, insulin resistance is suggested by the elevated insulin levels and the fact that the pa¬ tient develops glucose intolerance with circulating insulin levels well above those seen in the type I diabetic. The simplest test of insulin sensitivity is the measurement of the fall in plasma glu¬ cose in response to a given dose of exogenous insulin. In normal individuals, glucose usually falls by more than 50% in response to a dose as small as 0.05 U/kg of body weight. In type II diabet¬ ics, this response may be markedly blunted, and as much as 0.3 U/kg may be required to produce a 50% fall in glucose. Because the variability of endogenous insulin secretion and the counterregulatory hormones released during hypoglycemia may modify the response to the insulin test, more sophisticated measures of insulin resistance have been developed in which these factors are minimized. These tests include the measurement of steady-state glucose during simultaneous insulin and glucose infusion in which pancreatic insulin is suppressed with propran¬ olol and epinephrine or somatostatin or the use of the euglycemic insulin clamp technique/1 In the latter, dose-response curves for the effect of insulin on glucose disposal in intact man can be con¬ structed (Fig. 133-2). Using this test, the nature of the insulin resistance can be dissected into changes in ED50 on dose-response curves (i.e., changes in insulin sensitivity) and changes in maxi¬ mal insulin effect (i.e., changes in insulin responsiveness).2122 In type II diabetes, there is decreased sensitivity in insulin action to decreased splanchnic glucose output (i.e., an effect primarily on the liver) and decreased sensitivity and decreased responsiveness of insulin action to increased glucose utilization (i.e., effects pri¬ marily on muscle and fat tissue).21,23 The resistance to insulin that occurs in the patient with NIDDM could result from defects at several levels of insulin ac¬ tion (see Chap. 131). To produce a signal at the target cell, insulin must bind to its receptor, generate a transmembrane signal by activation of the insulin receptor kinase, and initiate one or more intracellular signals leading to activation and inhibition of the different cellular processes. Defects at the insulin receptor (e.g., binding, signal generation) or at any of the postreceptor steps involved in insulin action could cause the alterations of type II diabetes.

1212

PART IX: DISORDERS OF FUEL METABOLISM

the major component of non-oxidative glucose metabolism.6,31 Which of these defects is primary and whether there are other defects in the intracellular steps of insulin action remains unknown. In animals and in cells in culture, prolonged exposure to high insulin levels produces postbinding desensitization and receptor down-regulation, suggesting a role for increased basal insulin levels in these defects.32,33 Like the defects in insulin secretion, the defects in insulin action are largely reversible when the dia¬ betes is treated and the metabolic abnormalities are corrected. This is true whether the treatment involves diet, oral hypoglyce¬ mic agents, or intensive insulin treatment.23,25"38 A schematic di¬ agram illustrating all of the various factors involved in the patho¬ genesis of type II diabetes is shown in Figure 133-5.

EVENTS IN THE DEVELOPMENT OF TYPE II DIABETES

INSULIN (fjU/mL) FIGURE 133-2. Glucose disposal during a euglycemic clamp in normal and type II diabetic patients, comparing predicted level of insulin resis¬ tance and assuming the only defect to be that of insulin binding, with the observed data, which indicate more severe insulin resistance, suggesting the presence of a postbinding defect as well. (Redrawn from data of Scarlett ]A, et al. Diabetes Care 1982;5:353.)

Decreased insulin receptor binding has been described in obese and thin individuals with type II diabetes21,24,25 (Fig. 133-3). This decrease in binding is attributable to a decrease in receptor number, with no changes in receptor affinity, and is thought to be secondary to down-regulation of the receptor by the elevated basal endogenous insulin level.25 Similar decreases in insulin binding are observed in patients with impaired glucose tolerance and in some obese individuals with normal glucose tol¬ erance, indicating that the decrease in insulin receptors alone probably does not entirely account for the insulin resistance. Be¬ cause there are "spare” receptors for insulin action in many tis¬ sues, a decrease in receptors would be expected to produce only a shift in the dose-response curve, with no changes in maximal response (i.e., decreased sensitivity).22 As noted previously, euglycemic clamp studies have indi¬ cated that there is decreased sensitivity and decreased respon¬ siveness, indicating postbinding defects in insulin action.21 Stud¬ ies suggest that one component of this postbinding defect is coupling to receptor kinase activation.26"28 Sequence variations in the major substrate of the insulin receptor, IRS-1, also occur in patients with NIDDM with increased frequency.29 Most studies have indicated that there is also a defect in glucose transport due to a defect in glucose transporter translocation30,31 (Fig. 133-4). Finally, there is also a defect in glycogen synthesis that forms

FIGURE 133-3. Defect in insulin receptor binding in dia¬ betes and obesity, illustrating the negative relation between receptor concentration and plasma insulin concentration. Data are plotted as insulin binding versus plasma insulin concentration. Shaded areas indicate the normal range. Data on the left are from thin and obese type II diabetics17,21 and on the right from obese individuals with and without diabetes.25

Like type I diabetes, type II diabetes is preceded by a long prediabetic phase in which glucose tolerance tests are normal, but insulin resistance is present39,40 (Fig. 133-6). Many patients also pass through a stage of impaired glucose tolerance in which basal and stimulated insulin levels are increased, further suggest¬ ing that insulin resistance precedes the functional insulin defi¬ ciency. At this stage, a decrease in insulin receptor binding and a decrease in insulin action in adipose tissue can be detected. The patient who has a diabetic glucose tolerance but still has normal fasting plasma glucose exhibits variable insulin secretion and some element of postbinding insulin resistance in muscle and fat. Fasting hyperglycemia suggests unsuppressed gluconeogenesis and indicates further resistance to insulin action at the liver. These patients also have a significant functional defect in insulin secretion, especially in glucose recognition.

GENETICS OF TYPE II DIABETES Although type II diabetes has a very strong genetic influ¬ ence, the genes leading to development of this disease are poorly understood, except for the patients with MODY diabetes that is described later. In a few individuals or families, genetic defects have been described in the insulin molecule leading to generation of a mutant insulin or a failure to process proinsulin and hyperproinsulinemia.41,42 Because all of these individuals are heterozy¬ gous and have one normal insulin allele, it is not completely clear why the patients develop diabetes or whether the diabetes is co¬ incidental with the mutant insulin. Genetic defects in the insulin receptor are somewhat more frequent, with about 50 different mutations having been de¬ scribed. Most of these patients have syndromes of severe insulin resistance such as leprechaunism, Rabson-Mendenhall syn¬ drome, or the type A syndrome of insulin resistance and acan¬ thosis nigricans.43 44 These patients are discussed in Chapter 140. A variant of type II diabetes has been described associated with a point mutation in the gene encoding the tRNA for leucine.

Ch. 133: Etiology and Pathogenesis of Type II Diabetes Mellitus and Related Disorders

does not progress. Researchers at the National Institutes of Health are about to undertake a major study to determine if the progression of IGT to NIDDM can be prevented by changes in life-style or pharmacologic intervention.

XI

c

1.00

=3

O GD C

0.75

3

GESTATIONAL DIABETES MELLITUS

V)

c Q) V)

1213

0.50

O C k

0.25

o "a. 200 units/day

Premixing with delay before injection may result in loss of regular insulin action

Peak

Duration

Special Considerations

SHORT-ACTING 6-8

4-6

For intravenous, intraperitoneal, and pump use Not available as human preparation

INTERMEDIATE-ACTING NPH (human)

Protamine zinc, phosphate buffer

1.5

5-8

18-24

Lente (human)

Amorphous, acetate buffer

2.5

6-12

18-28

LONG-ACTING Ultralente (human)

Amorphous and crystalline mix

3-4

9-15

22-26

Protamine zinc

Protamine, zinc, phosphate buffer

4-6

12-24

36-40

Must not be mixed with regular insulin (being discontinued)

3-8

18-24

Biphasic action, not suitable when frequent dose adjustments are required

MIXTURES NPH/regular

NPH 70%, regular 30%

0.5-1

* Onset, peak, and duration of action of insulins are approximations, because they vary according to injection technique, site, presence of insulin antibodies, and other variables that affect insulin pharmacokinetics.

Because of its peaking activity, when given as part of an intensive insulin regimen, it cannot be considered to provide basal insulin delivery and should be given twice a day.

INSULIN PURITY AND SOURCES The insulin market in industrialized nations is dominated by human insulin preparations, but pork and beef-pork mixtures are still widely available. Beef insulin is the most immunogenic of these, whereas pork insulin is only slightly more immunogenic than human insulin.2,4 This is consistent with the fact that beef insulin differs from human insulin by three amino acids, whereas pork insulin differs from human insulin by only one amino acid. Previously, insulin preparations contained trace amounts of proinsulin-like intermediates, desaminoinsulin, glucagon, pancre¬ atic polypeptide, somatostatin, and other contaminants of islet and exocrine tissue. Antibodies to many of these substances were found in the plasma of patients treated with these older insulin preparations. Modern purified insulins are significantly "cleaner" than those used 20 years ago, with the contaminants usually being less than 20 ppm.2

HUMAN INSULIN Biosynthetic human insulin was introduced commercially in 1982 and, since then, there have been several improvements in the manufacturing process. One approach is to use an Escherichia coli fermentation to produce proinsulin, which then is enzymati¬ cally cleaved to C-peptide and insulin, with subsequent pu¬ rification. The preparations are extremely pure, with proinsulin contamination being less than 1 ppm.5 Moreover, no immune responses to contaminating E coli proteins have been identified.5 The other major approach is to produce a nonhuman proinsulin precursor protein in yeast, which is then secreted into the media, cleaved to human insulin, and purified. Human regular insulin, perhaps by being slightly more hy¬ drophobic, is absorbed more rapidly than is pork insulin.3 In ad¬

dition, human NPH is absorbed slightly faster than is human Lente insulin.6 There was a widely publicized report suggesting that the use of human insulin was associated with more serious hypoglycemia than were animal insulins.7 This concern has been evaluated extensively in several thorough studies, which con¬ cluded that the risk of more dangerous hypoglycemia from hu¬ man insulin as compared to porcine insulin is either nonexistent or trivial.73 Although human insulin preparations are not appre¬ ciably superior to the purified porcine insulin, it is likely that they eventually will completely replace animal insulins. Biosynthetic proinsulin has a potency that is 5% to 10% of that of insulin, and at one point was thought to have therapeutic potential.8 Because of concerns about possible adverse effects on vascular disease, these plans have been abandoned.9

INSULIN CONCENTRATIONS Worldwide, insulin usually is provided in a concentration of 100 U/mL (U100). Concentrations of 40 U/mL (U40) still can be found, and clinicians should be alert to unexpected concentra¬ tions found in the formulations of some countries. Less concen¬ trated preparations, for lower-dose administration in children, can be made up using a commercially available dilution fluid. Regular insulin is available in a U500 strength for use in patients with high (> 200 U/day) requirements.

INSULIN PHARMACOKINETICS After intravenous injection, the half-life of circulating insu¬ lin appears to be 5 to 10 minutes in normal persons and patients with diabetes who do not have insulin antibodies.10,11 The disap¬ pearance curve is explained best by a multiexponential model.11 The distribution space has been estimated to approximate the in¬ sulin space (a measurement of the extracellular space), 16% of body weight.10 The apparent distribution space is increased in the presence of antibodies,11 but otherwise appears to be similar in normal persons and patients with insulin-treated diabetes.12

1240

PART IX: DISORDERS OF FUEL METABOLISM

A three-compartment model of the distribution space has been developed, consisting of the vascular compartment and two extravascular compartments, one of which equilibrates rapidly and one of which equilibrates slowly with the intravascular compart¬ ment. The metabolic clearance rate of insulin is 700 to 800 mL/ 2 / • 13 ' m /min. The liver is the major site of insulin clearance, accounting for about 50% of the total, whereas the kidney accounts for about 30% and skeletal muscle accounts for most of the rest.14 At supraphysiologic concentrations of insulin, hepatic clearance may become saturated, but this does not seem to be true with the kid¬ ney.15 Reduced insulin clearance has been found in obese per¬ sons.14 Biosynthetic and porcine insulins do not appear to differ appreciably in their splanchnic clearance.16 Renal function also is an important determinant of circulating insulin levels. Insulin pharmacokinetics are complicated further by the many factors that alter insulin absorption from the subcutaneous site.17 These may cause considerable variability in insulin action between individuals and from day to day in a given individual. Factors that tend to produce relatively increased insulin ab¬ sorption include low doses of insulin; dilute insulin solution; in¬ creased subcutaneous blood flow (exercise, massage, heat); local tissue injury; intramuscular injection; injection into the abdomen (at rest); and low antibody concentration. Factors that tend to produce relatively decreased insulin absorption include high doses of insulin; concentrated insulin solution; decreased subcutaneous blood flow (shock, cold, standing); lipohypertrophy; intradermal injection; injection into limbs (at rest); and high antibody concentration.

SITE OF INJECTION Insulin conventionally is injected into the subcutaneous tis¬ sues of the abdomen, buttock, anterior thigh, and dorsal arm. In unusual circumstances, insulin also may be injected intramuscu¬ larly to achieve more rapid uptake. Prolonged intramuscular in¬ sulin therapy, besides being painful, causes tissue scarring. Insu¬ lin is absorbed more rapidly from the abdominal wall than from the thigh or upper limb. If the limb is exercised, absorption is more rapid than expected because of increased blood flow. Tra¬ ditionally, rotation of insulin injection sites has been advocated to prevent lipohypertrophy or lipoatrophy. The increased purity of insulin preparations has greatly reduced the incidence of li¬ poatrophy, but hypertrophy still occurs, so site rotation still is advised. Nonetheless, there should be some consistency to the injection patterns; for example, it might be decided to use ab¬ dominal sites in the morning and the thighs at night.

SUBCUTANEOUS BLOOD FLOW With upright posture, subcutaneous blood flow diminishes considerably in the lower limbs (and to a lesser extent in the ab¬ dominal wall), decreasing the absorption rate of insulin.18 Con¬ versely, massage, increased ambient temperature (including hot baths), and exercise increase the rate of absorption.

VOLUME AND CONCENTRATION OF INSULIN The insulin absorption rate is inversely proportional to the volume and concentration of the injected insulin.17 Thus, NPH insulin action may be significantly longer when higher doses are given, and U500 regular insulin may have a duration of action similar to that of intermediate-acting insulins.

MIXING INSULINS Even though regular insulin and Lente insulin frequently are mixed in the same syringe before use, this practice raises concern, because much of the rapid-acting component is lost in the pro¬ cess. 4 The problem is even more severe if regular insulin is mixed

with Ultralente insulin.3'20 Less difficulty is found when regular insulin is mixed with NPH insulin.21 Premixed insulin prepara¬ tions are now available commercially; the most commonly used of these consists of 70% NPH and 30% regular insulin.

SUBCUTANEOUS INSULIN DEGRADATION The contribution of subcutaneous insulin degradation to variability in insulin absorption is controversial.17 There are re¬ ports of supposed massive subcutaneous insulin degradation.22,23 Although this phenomenon has been well documented in a few patients, it appears to be extraordinarily rare.

INSULIN ANTIBODIES Circulating insulin antibodies have important effects on in¬ sulin pharmacokinetics, delaying the onset of action of rapidly acting insulin and increasing the duration of action of both short and longer-acting insulins.24 Today, they rarely cause insulin resistance.

INDICATIONS AND MODE OF THERAPY Insulin treatment of type I diabetes usually is started in an outpatient setting, although an inpatient unit can be an excellent setting, especially for children. The initial requirements of pa¬ tients can be variable, and the inpatient setting provides both patients and physicians with a protected environment in which close monitoring permits insulin requirements to be determined efficiently. Patients' self-confidence also can be nurtured in this setting, which may be important when they experience their first episode of hypoglycemia. Further alterations can be made in an outpatient setting, with patients frequently monitoring their blood glucose levels and receiving advice over the telephone. It is important that dietary advice and insulin therapy be coordinated. Insulin treatment of many patients with type II diabetes and ges¬ tational diabetes almost always is initiated on an outpatient basis.2,25

INDICATIONS FOR INSULIN THERAPY The absolute indications for insulin therapy are diabetic ke¬ toacidosis, nonketotic hyperosmolar coma, postpancreatectomy diabetes, type I (juvenile onset) diabetes, and, probably, a fasting blood glucose level higher than 120 mg/dL in gestational diabe¬ tes. Insulin is indicated in patients with type II diabetes who fail to respond to an adequate trial of diet and oral hypoglycemic agents.2,25

DIABETES CONTROL AND COMPLICATIONS TRIAL The 9y2-year Diabetes Control and Complications Trial (DCCT) was carried out in 29 centers on 1441 patients with insu¬ lin-dependent diabetes mellitus (IDDM).2,26 There were two arms of the study, a group with no complications and a group with very mild to moderate” nonproliferative retinopathy. A mean hemoglobin AiC of about 7% was achieved in the intensive ther¬ apy group as compared to about 9% in the standard therapy group. The efficacy of intensive treatment was dramatic. In the primary prevention group, the risk of developing retinopathy was reduced by 76%, and in the secondary intervention cohort, the risk of progression was reduced by 54%. The risk of develop¬ ing microalbuminuria was reduced by 34% and 56%, respec¬ tively. The risk of developing neuropathy was reduced by 57% and 69%, respectively. There was a tendency for a reduction in the number of major cardiovascular and peripheral vascular events of borderline statistical significance. There are still ques¬ tions about whether there is a threshold for glycemic control that must be reached before benefits occur. The data suggest a contin-

Ch. 139: Insulin Therapy and Its Complications uum of beneficial effect such that any improvement in glycemic control should be expected to help. This is an important and prac¬ tical concept for those patients who are not able make a full com¬ mitment to a DCCT-style regimen. With regard to adverse effects, the incidence of severe hypo¬ glycemia (reactions needing assistance) was increased three-fold in the intensive therapy group. Intensive therapy also was asso¬ ciated with weight gain, which was 4.6 kg more than in the con¬ ventional group after 5 years. Although there is concern about how many patients will be able to follow this difficult regimen, the DCCT sets a new standard of care for persons with IDDM. Caution must be used in applying a DCCT level of care to chil¬ dren younger than 13 years, persons with hypoglycemic un¬ awareness, and patients with advanced complications. There is much debate about whether the DCCT results can be extrapolated to patients with non-insulin-dependent diabetes mellitus (NIDDM). Because of the similarity in the progression and character of the complications of NIDDM and IDDM,27 the authors take the position that near-normoglycemia should be a goal of therapy for those with NIDDM, who can expect to benefit from reduced risk of microvascular and neuropathic complica¬ tions. Concerns about weight gain probably are overstated. Ar¬ guments have been raised about whether insulin treatment might worsen macrovascular disease.28 Although this question de¬ serves more study, the hypothesis seems circumstantial and unconvincing.

1241

Nonobese patients who remain poorly controlled on more than 1.0 U/kg/day should be evaluated carefully for compliance fail¬ ure or for occult causes of insulin resistance. INITIATING TREATMENT

Once initial instability is controlled with regular insulin, treatment can be started with a single injection of intermediate¬ acting insulin given before breakfast at a dosage of 0.2 to 0.3 U/ kg/day. This is increased gradually while observing the blood glucose profile. If the fasting blood glucose concentration contin¬ ues to be high (> 200 mg/dL) when normal or low values are found in the afternoon and evening, it is advisable to introduce a second injection of intermediate-acting insulin either before sup¬ per or before bedtime to control fasting hyperglycemia. Regular insulin may be added before breakfast and before dinner as indi¬ cated by the blood glucose patterns. In patients with type II diabetes, an intermediate-acting in¬ sulin or, less commonly, Ultralente can be given in the morning. Usually, a second injection of intermediate-acting insulin (often best given at bedtime) is required. When the fasting blood glu¬ cose concentration is controlled and the postbreakfast levels are too high, an additional dose of regular insulin may be introduced. Some patients with type II diabetes have a less stable pattern and may require a more complex regimen similar to that used in type I diabetes. THE “DAWN PHENOMENON”

SETTING GOALS OF THERAPY Although normalization of all aspects of metabolism is the ideal in the treatment of type I and type II diabetes, this goal rarely is attainable with current forms of therapy. Nevertheless, near-normoglycemia can be achieved in selected patients and, ideally, should be the goal of therapy in most cases. In these se¬ lected patients, with appropriate insulin adjustment26 and coor¬ dination of diet and exercise, the goals should be a fasting blood glucose value between 90 and 120 mg/dL and a 2-hour post¬ prandial blood glucose value of less than 150 mg/dL. In patients who are less willing to follow demanding regimens, or in those who have defective counterregulatory hormone responses that place them at risk for the development of hypoglycemia, treat¬ ment goals should be modified. In patients with type II diabetes who follow diet therapy and who have some preservation of en¬ dogenous insulin secretion, it is possible to safely achieve fasting blood glucose levels of less than 100 mg/dL and postprandial levels of 160 mg/dL or less in many cases.29 DAILY REQUIREMENTS

Daily insulin production in normal persons usually is 24 to 36 U; however, this is secreted into the portal circulation.1 Pa¬ tients with IDDM who have no endogenous insulin secretion, as evidenced by the absence of circulating C-peptide, generally require between 0.5 and 1.0 U/kg/day. Requirements may be divided into basal and prandial needs. The basal requirement is necessary for suppression of hepatic glucose output, and usually constitutes 40% to 60% of the daily dose. The remaining amount is necessary for nutrient disposal after meals.2,29 These consider¬ ations are applied most easily using the approach of combined Ultralente and regular insulin or the technique of continuous subcutaneous insulin treatment. Insulin requirements in thin patients with type II diabetes usually are similar to those of patients with type I diabetes. Obese patients generally require more, with insulin requirements some¬ times being as high as 2.0 U/kg/day. Patients requiring less than 0.5 U/kg/day may have some endogenous insulin production or may be insulin sensitive be¬ cause of vigorous physical conditioning or diminished food in¬ take. Renal failure or a counterregulatory hormone defect, such as adrenocortical or pituitary failure, also should be considered.

The term dawn phenomenon describes the increase in hepatic glucose output that occurs in persons with and without diabetes in the early morning hours.30,31 It is thought to be mediated by nocturnal surges of growth hormone, and may cause difficulties with control. In patients with diabetes (both type I and type II), intermediate-acting insulin taken in the morning, or even at din¬ ner time, frequently fails to control this problem. The strategy of giving intermediate-acting insulin at bedtime has been particu¬ larly successful. Patients treated by continuous subcutaneous in¬ sulin therapy often maintain good control of their early morning glucose levels.

SIDE EFFECTS OF INSULIN TREATMENT HYPOGLYCEMIA Hypoglycemia is the most frequently occurring side effect of insulin treatment. The common causes of hypoglycemia include missed meals or erratic meal timing, excessive insulin dosage, and unplanned exercise (Table 139-2). Other causes include failure to reduce insulin dosage after temporary periods of increased re¬ quirements during illness and pregnancy. Renal failure, alcohol excess, and remission from diabetes also must be considered. Rare causes include Addison disease, hypopituitarism, hypothy¬ roidism, and intentional overdosage, which may be factitious or suicidal. Although these causes should be considered, occasional hypoglycemia may occur with no demonstrable etiology. With the increased emphasis on "tight” metabolic control, the inci¬ dence of hypoglycemia increases, as has been well demonstrated by the DCCT.26

POSTHYPOGLYCEMIC HYPERGLYCEMIA Many years ago, Somogyi32 postulated that overtreatment with insulin produces hypoglycemia, which is followed by hy¬ perglycemia caused by activation of counterregulatory hor¬ mones. As the relative contributions of glucagon, epinephrine, cortisol, and growth hormone to the counteraction of hypoglyce¬ mia became better understood, there seemed to be a solid patho¬ physiologic basis for this putative Somogyi phenomenon. Studies in persons without diabetes showed that when glucose levels fell

1242

PART IX: DISORDERS OF FUEL METABOLISM TABLE 139-2 Causes of Hypoglycemia in Diabetic Patients Receiving Insulin Treatment Causes of Hypoglycemia_Circumstances ERRATIC NUTRIENT INTAKE

Missed meals and snacks; gastroparesis; malabsorption

ERRATIC INSULIN ABSORPTION

Changes in subcutaneous blood flow (e.g., exercise)

PROLONGED INSULIN ACTION

Circulating insulin antibodies Renal failure (creatinine clearance < 20 mL/min)

EXERCISE

Facilitates glucose disposal, may increase insulin absorption

COUNTERREGULATORY HORMONE FAILURE

Addison disease, hypopituitarism

Adrenomedullary failure of long-standing diabetes

ALTERED GLUCONEOGENESIS

Alcohol excess, ^-adrenergic blockade, advanced liver disease

BEHAVIORAL DISORDER

Factitious: malingering, psychiatric illness, learning disorder

OVERINSULINIZATION

Remission from type I diabetes Recovery from period of insulin resistance Marked reduction in caloric intake

to about 55 mg/dL or less, increased plasma glucagon and epi¬ nephrine levels had important stimulatory effects on hepatic glu¬ cose output.33-35 Cortisol and growth hormone secretion also are stimulated by hypoglycemia, but do not contribute as much to the glucose rise that occurs after hypoglycemia. Persons with normal B-cell function do not become hyperglycemic after exper¬ imental insulin-induced hypoglycemia because the glucose rise is limited by increased insulin secretion. The situation is different in IDDM. For unclear reasons, glucagon responses are lost once B-cell function is markedly reduced; then epinephrine assumes the dominant protective role against hypoglycemia. Because in¬ creasing glucose levels after hypoglycemia cannot be restrained by compensatory insulin secretion in IDDM, it was reasonable to expect extremely high glucose responses, a so-called rebound. However, serious questions have been raised about how often such rebounds actually occur. The assumption that high glucose levels, particularly in the morning, resulted from the Somogyi phenomenon (rebound) had become a convenient and popular explanation for part of the in¬ stability commonly seen in IDDM. Finally, careful studies were performed to determine how often this phenomenon occurs, and it was found that nocturnal hypoglycemia was followed only in¬ frequently by morning hyperglycemia. These studies examined persons with documented low blood glucose levels in the middle of the night and found that, if anything, this hypoglycemia was followed by low glucose values before breakfast and even later in the day.35-37 The best explanation is that when there is enough insulin to cause hypoglycemia at night, there usually also is enough persisting insulin effect from the subcutaneous insulin to limit whatever rebound might have occurred.

UNEXPLAINED MORNING HYPERGLYCEMIA Patients with IDDM often have high glucose levels in the morning that are difficult to explain. Although rebound can oc¬ cur, it appears to be infrequent, and alternative explanations should be considered. The dawn phenomenon, described earlier, occurs in persons with and without diabetes. In the early morn¬ ing hours, there is a transient state of insulin resistance that ap¬ pears to be caused by nocturnal secretion of growth hor¬ mone.35'38”40 Although cortisol secretion also increases early in the morning, this seems to play a minor role in the dawn phe¬ nomenon. In persons without diabetes, this early morning insulin resistance is limited by compensatory insulin secretion, but in pa¬ tients with IDDM, troublesome hyperglycemia can occur. Pa¬ tients with IDDM who use insulin pumps often set their pumps to provide increased basal insulin secretion in the early morning hours to counter this dawn phenomenon. The consistency of the

dawn phenomenon in diabetes has not been well defined, but variability in growth hormone secretion may contribute to difficult-to-understand differences in morning glucose levels. Another major cause of hyperglycemia in the morning is a waning insulin effect. For example, intermediate-acting insulin taken the previous morning should have largely worn off, and even that taken before supper can be losing its effect. Sometimes, improvement can result from moving the injection of intermedi¬ ate-acting insulin from before supper to bedtime. Other factors also frequently are responsible for morning hyperglycemia, such as large evening meals or late snacks.

INSULIN EDEMA Frank edema occurs in some patients with diabetes after treatment of uncontrolled diabetes is instituted, and mild sodium and fluid retention is a common occurrence even without edema.41-43 Patients can be frustrated to find that improved dia¬ betes control often is associated with transient weight gain from fluid retention in spite of decreased caloric intake. For patients with troublesome edema, the judicious use of diuretics can be helpful. Insulin has a sodium-retaining effect on the kidney, which could be the best explanation for the phenomenon. An¬ other contributor could be glucagon, which is known to have a natriuretic effect. Plasma glucagon levels are increased in uncon¬ trolled diabetes, and a fall in glucagon with insulin treatment could contribute to the sodium retention. An inverse phenome¬ non probably accounts for the natriuresis and fluid loss that ac¬ companies caloric restriction, which is associated with decreased plasma insulin and increased glucagon levels. Another contribu¬ tor to the edema of insulin treatment may be the increased capil¬ lary permeability that is associated with poor metabolic control.44'45

LIPOATROPHY Lipoatrophy is characterized by a loss of subcutaneous fat at insulin injection sites, which can be severe enough to be disfig¬ uring.4'46 Now that purified insulin is used, this phenomenon is seen infrequently. The cause of this complication is unknown, but is suspected to be immunologic. Biopsies of affected areas reveal the presence of immunologic mediators such as IgM, IgE, and C3.47 Perhaps a lipolytic cytokine is released during an im¬ mune reaction. When unpurified insulins were the culprit, the atrophy could be reversed by injecting the affected area with pu¬ rified insulin, with restoration of the subcutaneous fat in a few months.

Ch. 139: Insulin Therapy and Its Complications

LIPOHYPERTROPHY Lipohypertrophy is a nonimmune phenomenon, consisting of a localized hypertrophy of subcutaneous fat that develops from repeated injections of insulin into a highly circumscribed area. The skin over the area tends to become less sensitive; pa¬ tients, particularly children, use these sites repeatedly to avoid the discomfort of using new injection sites. Insulin absorption may be delayed at these sites,48 which can lead to problems with glycemic control. The hypertrophy is assumed to be the result of repeated local stimulation of adipocyte lipogenesis by insulin. Lipohypertrophy resolves spontaneously with the use of other insulin injection sites.

ORTHOSTATIC HYPOTENSION Normally, insulin stimulates the cardiovascular sympathetic nervous system.49 However, in the presence of autonomic neu¬ ropathy, insulin has a direct vasodilator effect on the vascular bed that can lead to hypotension.50 These episodes sometimes are manifest as atypical "hypoglycemia," because the patient may experience sweating, tremor, and excitement as a result of the cardiovascular activation of adrenomedullary catecholamines. Neuroglycopenia may be mimicked by the fall in cerebral perfu¬ sion from the orthostatic hypotension.50

INSULIN ALLERGY Shortly after the introduction of insulin treatment in the 1920s, it was noted that allergic reactions frequently occurred. In retrospect, this is not surprising, because the preparations were impure and contained insulin fragments, insulin multimers, pro¬ insulin, proinsulin intermediates, and whole or fragmented Cpeptide. In addition, many other peptides were included in the preparations. For example, patients could be found to have cir¬ culating antibodies against glucagon, somatostatin, and pancre¬ atic polypeptide.51 The problem of insulin allergy has been greatly reduced by the purification of animal insulins, and by the introduction and widespread use of human insulin.4,46

1243

beef-pork insulin may have some increase in insulin require¬ ments as a result of insulin binding by antibodies in plasma. These antibodies could be less reactive with human insulin, so that switching to a human preparation might lead to insulin re¬ actions and a need for a reduction in dosage. On the other hand, the difference in reactivity could be minimal and necessitate no meaningful change in dosage. Discontinuing insulin therapy used to be feared because of the justified concern that an amnes¬ tic antibody response might occur when therapy was restarted.4 There still should be concern about restarting therapy with hu¬ man insulin in patients who previously have been treated with impure animal insulin preparations. However, there probably is little risk of discontinuous insulin administration if a patient was started on pure human insulin therapy. Therefore, patients with IDDM who are having a remission (honeymoon), and who origi¬ nally were given human insulin, can be taken off such therapy until it is again required. The effect of insulin antibodies on insulin pharmacokinetics may be important, but has been difficult to study. The presence of binding IgG antibodies in serum can delay the time needed to reach peak levels of free insulin and also can cause a prolongation of insulin effect.58-60 This binding theoretically should alter the peak actions of rapid-, intermediate-, and long-acting insulins. The effects on regular insulin should be adverse, because the de¬ sired fast action for meals would be altered. Some prolongation of the peak effects of NPH or Lente insulins could be either ben¬ eficial or detrimental for particular patients. Unfortunately, there is no convenient way to measure the influence of these antibodies in individual patients so that therapy can be altered meaning¬ fully. Even if a single test were available, there probably would be variability that would be hard to sort out. The experience with the DCCT suggests that good to excellent control can be achieved with similar approaches in most patients with IDDM, indicating that differences in insulin antibodies usually are not clinically im¬ portant. Nonetheless, clinicians should be aware of the potential influence of insulin antibodies in certain situations, such as the common patient who has problems with insulin reactions 22 to 24 hours or more after the administration of NPH or Lente insulin.

IMMUNOGENICITY OF INSULIN

IMMUNE INSULIN RESISTANCE

The immunogenicity of insulin has undergone extensive study, and is receiving renewed attention because it may serve as an important B-cell antigen in the pathogenesis of autoimmune diabetes.52 A genetic predisposition to insulin allergy has been found, such that insulin antibodies are more likely to develop in persons with the human leukocyte antigen haplotypes B15 and DR4 than in those with the haplotypes B8 and DR3.53-55 More¬ over, the combination of BW44 and DR7 makes a person partic¬ ularly susceptible to antibody formation.54 The species of insulin used also makes a difference; bovine insulin, which differs from human insulin by three amino acid residues, is more immuno¬ genic than is porcine insulin, which has only one amino acid difference. Interestingly, human insulin also is immunogenic, with low titers of antibodies developing in most patients. The tertiary structure of human insulin probably is slightly altered in the manufacturing process or in subcutaneous sites so that new antigenic epitopes can be presented. The immunogenicity of in¬ sulin preparations is not limited to insulin itself; both protamine and zinc occasionally can elicit allergic reactions.56,57

Immune insulin resistance is a rare problem today. When impure insulin was used, it was more common and usually de¬ fined as high titers of antibodies and insulin requirements of more than 200 U/day.46,61 The plasma of patients with immune insulin resistance can bind more than 50 U of insulin per liter, which means that the amount introduced by subcutaneous injec¬ tions is a small proportion of the total amount of bound insulin. Sometimes these patients were extremely difficult to treat be¬ cause they had poor control even when given thousands of units of insulin per day. Such patients have no meaningful peak of whatever insulin they are given, and sometimes are best treated with U500 regular insulin administered twice a day. A species switch to human insulin sometimes leads to a reduction in the dosage requirement. Another strategy has been to give cortico¬ steroids to reduce antibody production. Some success also has been obtained with sulfated insulin (obtained from Connaught Laboratories in Canada), which is not as well bound by antibod¬ ies because epitopes are hidden by the added sulfate groups.

THE INFLUENCE OF INSULIN ANTIBODIES ON INSULIN REQUIREMENTS AND PHARMACOKINETICS

When antibodies develop in a person against a particular species of insulin, such as beef, there almost always is cross reactivity with other insulins, such as pig and human, even though this reactivity usually is weaker. 46 This has impor¬ tant clinical ramifications, because a typical patient treated with

LOCALIZED REACTIONS TO INSULIN

Localized reactions to insulin used to be seen commonly with the initiation of insulin treatment, but with the introduction of purified insulin, they hardly ever are significant today. Reac¬ tions used to be seen in as many as 50% of patients, but now are found in less than 2%.4,46,62 They usually occur after 10 days of treatment and within the first few months of therapy. They can

1244

PART IX: DISORDERS OF FUEL METABOLISM

subside spontaneously within a few days, but often persist for weeks. These reactions can be characterized by biopsy, but this step rarely is warranted. Several types of immune reactions have been defined.4'46 Immediate hypersensitivity reactions (type I, IgEmediated reactions) have been the most common. These occur minutes after injection and consist of local swelling, itching, ery¬ thema, and even wheal and flare responses, with dissipation usu¬ ally occurring in a few hours. Less commonly seen are delayed reactions (type IV, T-cell-mediated). Inflammation can start 8 to 12 hours after the injection, with a peak at 24 to 48 hours. These reactions typically consist of swelling, erythema, and induration. The least commonly seen reaction is the intermediate reaction (type III or Arthus reaction caused by immune complexes). These begin 4 to 8 hours after injection and peak at about 12 hours. The reaction consists of induration, itching, and pain. These different reactions can overlap, so that clinical identification of the specific type often is not possible. Because the reactions often are self¬ limited and cause little discomfort, treatment rarely is needed. Oral antihistamines can be helpful for those having a significant IgE component. Cell-mediated reactions can be helped by inject¬ ing a small amount of glucocorticoid along with the insulin (0.1 mg or less of dexamethasone should suffice). SYSTEMIC REACTIONS TO INSULIN

Systemic reactions to insulin occur infrequently, particularly now that purified insulins are so widely used.46,55 Nonetheless, they are frightening and often difficult to treat. The most typical generalized reactions are said to occur most often after in¬ terrupted treatment with unpurified insulin. The reactions usu¬ ally are IgE-mediated, with generalized urticaria, pruritus, flush¬ ing, and wheezing. Anaphylactic shock with circulatory collapse occurs rarely. These patients have high circulating levels of IgE, which reacts with bovine, porcine, and human insulin, revealing similar cross reactivity to that seen with IgG. Skin testing usually elicits wheal and flare reactions to all three of these insulins, and can be useful to identify the least antigenic insulin. Skin testing is important for making sure that the reactions can be linked with insulin allergy and not some other immunogen. Testing also should be carried out with zinc and protamine, which can cause allergic responses; these can be obtained from Eli Lilly Company. Intradermal skin testing should be initiated with an insulin dose of 0.001 U in a volume of 0.02 mL. If there is no reaction, 0.1 U should be used, and then 1.0 U should be tried; a negative reac¬ tion to this larger dose makes it unlikely that insulin allergy is responsible. Other systemic reactions that have been attributed to insulin allergy include thrombocytopenic purpura, serum sick¬ ness, and Coombs-positive hemolytic anemia. High levels of IgG sometimes are seen in these patients.

TABLE 139-3 Insulin Allergy Desensitization Schedule Time (h)

Dose (U/0.1 mL)

0 0.5

0.001 id 0.002 id 0.004 sc 0.01 sc 0.02 sc 0.04 sc 0.1 sc 0.2 sc 0.4 sc 1 sc 2 sc 4 sc 8 sc

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

id; intradermal; sc, subcutaneous. From VanHaeften TW, Gerich JE. Complications of insulin therapy. In: Becker, ed. Principles and practice of endocrinology and metabolism, ed 1. 1990:112.

If a patient with generalized insulin allergy is taking animal insulin, a switch to human insulin should be made. If the sys¬ temic reactions continue, the patient should be desensitized in a hospital setting. Desensitization kits can be obtained from the Eli Lilly Company. Human insulin should be used for the process, and the starting dose should be 0.001 U given intradermally. The dose then should be increased at 30-minute intervals, as shown in Table 139-3. If a reaction occurs, the next injection should be dropped back by two dilutions. During the procedure, epineph¬ rine, oxygen, antihistamines, and corticosteroids should be avail¬ able, and medical personnel should be ready to perform cardio¬ pulmonary resuscitation. Most patients can be desensitized within 10 hours, and the procedure was found to be successful in 94% of one large series.46 Pork insulin was used in this series, but human insulin can be expected to do as well. To maintain the desensitization, it probably is best to administer insulin at least twice a day. The small number of patients who continue to have some allergic manifestations often are treated with antihista¬ mines and, sometimes, corticosteroids. The mechanism for the desensitization still is not well un¬ derstood. Perhaps the most attractive explanation is that the con¬ tinuing administration of antigen keeps mast cells and basophils depleted of mediators such as histamine. Another hypothesis is that antigen stimulates IgG formation, which can block the abil¬ ity of antigen to reach IgE sites. In addition, for unclear reasons, IgE levels seem to fall during desensitization.

SPECIAL ASPECTS OF INSULIN TREATMENT CHILDHOOD AND ADOLESCENCE The general principles of insulin treatment already outlined also are applicable to children.63 In young children, unpredict¬ able food intake and activity increase the likelihood of hypogly¬ cemia and marked glucose excursion. Low-dose insulin syringes should be used. Sometimes, insulin doses of 2 U and less may be required, making it necessary to dilute the insulin. Insulin admin¬ istration should be performed by parents until children are 5 or 6 years old. After that, injections may be given by children under supervision until the age of 10 to 12 years. Nocturnal hypoglyce¬ mia is a common occurrence with conventional insulin therapy, and may present as seizures. These patients, who may have a low seizure threshold, should have their nocturnal blood glucose measured periodically, receive a bedtime snack routinely, and be given intermediate-acting insulin before supper cautiously. Adolescents face many temptations to reject the disciplines necessary for adequate diabetes management,64 and "brittle" di¬ abetes is commonly seen in this age group. During the growth spurt, insulin requirements generally increase substantially, and should be reviewed regularly (see Chap. 151).

PREGNANCY The benefits of good diabetes control have been demon¬ strated most impressively for pregnant patients with diabetes65 (see Chap. 150). These patients generally are highly motivated to carry out the disciplines of intensive insulin therapy. Insulin requirements may drop slightly in the first trimester, then grad¬ ually increase in the second trimester, and finally peak in the third trimester. Immediately after delivery, requirements drop precipitously and return to prepregnancy levels.

OLD AGE The primary goals of therapy in elderly patients are to pro¬ vide symptomatic relief, prevent diabetic ketoacidosis, halt un¬ wanted weight loss, and prevent hypoglycemia.66 The last is an important consideration in socially isolated patients, and a visit¬ ing nurse may provide valuable assistance. Premixed insulins are

Ch. 139: Insulin Therapy and Its Complications helpful for patients in whom the adjustment of regular and inter¬ mediate insulin is not necessary. Although most older patients have stable diabetes, some may have labile diabetes that is difficult to manage.

REMISSION FROM TYPE I DIABETES A few weeks or sometimes months after the onset of type I diabetes, a remission frequently is observed that is manifested as a rapidly diminishing insulin requirement (the "honeymoon period").2 67 Sometimes, it may be possible to discontinue insulin therapy for a few weeks or even months. This may confuse pa¬ tients and their families; thus, it may be advisable to continue a token dose of insulin until the requirements rise again. The need to continue monitoring must be emphasized, because there may be an abrupt decompensation with the development of an in¬ tercurrent illness. Unfortunately, meticulous control does not seem to preserve residual function in the long term.68

COMBINED USE OF INSULIN AND SULFONYLUREAS There has been long-standing interest in the possibility that the combination of insulin and oral agents would provide better control than does insulin alone. There is general agreement that adding sulfonylureas to a regimen for type I diabetes is not help¬ ful. Considerable experience has been gained with the use of combined therapy in type II diabetes, and the addition of sulfo¬ nylurea agents usually leads to only a modest reduction of insulin requirements.69 The use of intermediate-acting insulin at bed¬ time in early oral agent failure has been shown to be a useful strategy70-72 but, with time, a more intensive insulin regimen usu¬ ally is required.

SURGERY AND ACUTE ILLNESS Patients with diabetes are likely to undergo surgery at some time in their lives,73 and they often are at increased risk because of heart disease, sepsis, impaired wound healing, negative nitro¬ gen balance, electrolyte disturbances, and renal failure. Meticu¬ lous anesthetic and metabolic care should be provided. Diabetes may present for the first time during an acute illness; thus, if pos¬ sible, the metabolic state should be stabilized before embarking on surgery. General anesthesia, surgery, and even the expectation of an operation may greatly increase the secretion of counterregulatory hormones, such as cortisol, catecholamines, glucagon, and growth hormone, and this has an adverse effect on blood glucose levels. Fewer problems are seen with spinal or local anesthesia. During general anesthesia, the patient is fasting and uncon¬ scious; therefore, particular care must be taken to prevent hypoglycemia. The specific metabolic aims in the surgical patient with dia¬ betes are prevention of hypoglycemia and excess hyperglycemia (> 250 mg/dL). Both excess ketosis and lactic acidosis must be prevented. The regimen should be easily understood and exe¬ cuted, remembering that the surgical and nursing teams may have many other critical concerns during and after the operation. Operations should be elective whenever possible, so that good preoperative diabetic control can be achieved. For major proce¬ dures, the patient ideally should be hospitalized for a few days before surgery. The patient's operation should be scheduled at an early hour to facilitate the careful monitoring that is necessary after surgery. Many insulin regimens have been advocated for manage¬ ment of the perioperative period.73 An easy and generally reliable regimen is to give half the total dosage as intermediate-acting insulin subcutaneously on the morning before the operation.74 It is advisable to infuse 5% dextrose at the rate of 100 mL/h during the procedure. The major alternative is to give regular insulin by continuous infusion at a rate of 0.5 to 2.0 U/h, with adjustments

1245

as needed. A disadvantage of insulin infusion is that if the intra¬ venous line is turned off inadvertently, ketosis may develop rap¬ idly because of the short half-life of intravenous insulin. Insulin may stick to tubing, reducing its bioavailability; this problem may be overcome by running 50 mL of the infusate through the line before starting the infusion. Intravenous insulin therapy often is necessary with surgery that entails cardiopulmonary bypass, because requirements may increase suddenly during hypother¬ mia and again during rewarming, rising to as much as 10 to 20 U/h. In the postoperative period, the patient's ability to eat is a major determinant of the subsequent insulin requirement.

RENAL FAILURE Normally, the kidney is responsible for about 30% of insulin clearance.43 In patients with diabetes, advanced nephropathy (creatinine clearance < 20 mL/min) is accompanied by a reduc¬ tion in insulin requirements resulting from reduced insulin clear¬ ance.76 Insulin requirements may fall by 50% or more and, occa¬ sionally, patients can discontinue insulin therapy because residual insulin production is sufficient to achieve acceptable glycemic control. Insulin requirements also fall with acute renal fail¬ ure in patients with diabetes, and the institution of dialysis often leads to an increase in insulin requirements, suggesting that there is some circulating substance that facilitates insulin action or di¬ minishes clearance.75 In patients undergoing peritoneal dialysis, insulin can be given intraperitoneally, which yields satisfactory control, although substantial dosages (60-200 U/day) may be needed.77

“BRITTLE” DIABETES Brittle diabetes has been variously defined.78 Some reserve the term for describing patients with IDDM in whom diabetic ketoacidosis frequently develops. Others include a broader group of patients with diabetes who have severe glycemic excursions that may not actually require hospitalization. Brittle diabetes is a heterogeneous entity. In certain patients, the metabolic instabil¬ ity has its origins in manipulation of diabetes treatment; fre¬ quently, psychological and social problems need to be resolved before control can be achieved. Conversely, there are patients who cannot be found to have such an explanation for their insta¬ bility, and their apparent intrinsic "brittleness" remains poorly understood. Occasionally, patients may be labeled as having a subcutaneous insulin degradation syndrome or insulin resistance of unknown origin, but these are rare conditions. The management of brittle diabetes begins with the taking of a detailed history, preferably by a physician experienced with diabetes.79 The circumstances and details of previous hospital¬ izations must be examined carefully. The patient's family should be interviewed. Sometimes, hospitalization is helpful so that fre¬ quent blood glucose sampling can be performed (on at least six occasions over 24 hours, preferably with two samples at night [e.g., 2:00 AM and 6:00 am] to detect possible nocturnal hypogly¬ cemia and the dawn phenomenon). The patient's activities should be supervised carefully, particularly the dietary intake and level of activity, and the patient should not be allowed to leave the ward unsupervised. All insulin injections should be ad¬ ministered by the nursing staff, and the patient should not have access to needles or syringes. If the patient is suspected of diluting the insulin, the insulin concentration in the suspect vial can be measured. If metabolic control becomes reasonably stable when manipulation by the patient has been eliminated, special investi¬ gations may not be necessary. However, if the patient has had frequent episodes of diabetic ketoacidosis and sustained poor control, insulin requirements may be high (1-3 U/kg/day) but may fall with the institution of better control. It is important to identify patients having frequent hypoglycemia and rebound hy¬ perglycemia (the Somogyi effect), because improvement will oc¬ cur with a reduction of the insulin dose. With psychological test-

1246

PART IX: DISORDERS OF FUEL METABOLISM

ing, some patients may be found to have a learning disorder; in these cases, special teaching may be required.80 Special tests, such as gastric emptying, may identify patients with chaotic blood glucose patterns caused by the gastroparesis of diabetic autonomic neuropathy (see Chap. 143). Psychological and social support for both the patient and the family is necessary in most cases of brittle diabetes. Special modes of insulin delivery have been advocated, including intraperitoneal and continuous intravenous insulin infusion. How¬ ever, these approaches predictably fail in patients whose condi¬ tions are caused mainly by manipulative behavior.

INTENSIVE INSULIN THERAPY Now that the DCCT results have shown conclusively that good glycemic control with near-normoglycemia can prevent or slow the development of complications, an increasing number of patients with IDDM will use intensive therapy.26 This approach to diabetes care demands intensive monitoring of blood glucose, careful attention to diet, an insulin regimen that mimics the nor¬ mal diurnal and postprandial insulin excursions, and frequent adjustment of the insulin dosage to match changing circum¬ stances.81 There are two approaches: multiple injections (inten¬ sive conventional therapy) or CSII ("pump" therapy). Provided the guidelines are followed, both approaches can provide sus¬ tained improvements in metabolic control.

achieved with CSII.85 If the physician's experience and support team for CSII management is limited, then intensive conven¬ tional therapy is preferable. Some patients prefer the pump be¬ cause of the greater flexibility it provides with meal timing and because it reduces the need for snacks, which is an important consideration for patients with demanding occupations. More¬ over, the pump may help to prevent the adverse effect of unpre¬ dictable peaking of intermediate-acting insulin that is seen in some patients with conventional therapy. Before starting CSII, it is useful to test the patient's response to intensive conventional therapy, because this provides the physician with an idea of pa¬ tient compliance and psychological adaptability. Despite inten¬ sive encouragement, many patients are not motivated to perform the necessary monitoring 4 to 6 times each day, to ensure regular meal timing, and to take additional snacks. With pump therapy, additional care is necessary; for example, batteries and infusion lines must be changed regularly and the pump must be protected from water and undergo periodic maintenance. If the patient can achieve excellent control with conventional therapy, a change to a pump is unlikely to provide additional benefits. Patients who fail to perform the necessary amount of monitoring and insulin dose adjustment, or who develop serious hypoglycemia, proba¬ bly should not continue intensive conventional therapy. Patients who can adhere to the disciplines and who have preserved glu¬ cose counterregulation, but who fail to have a satisfactory re¬ sponse to intensive conventional therapy, may then try CSII.

BENEFITS

INTENSIVE CONVENTIONAL THERAPY

When optimal results are obtained with intensive conven¬ tional therapy, one can expect to achieve near-normalization of plasma glucose values, lipid levels, and circulating amino acid concentrations, and glucagon and growth hormone diurnal pro¬ files also may approach a more normal pattern.82 The main rea¬ son to use intensive therapy is to prevent or slow the progression of the complications of diabetes. The DCCT provides unequivo¬ cal evidence that improved glycemic control reduces microvascular and neuropathic complications. Moreover, there also may be a beneficial influence on macrovascular disease.

There are four commonly used regimens of intensive con¬ ventional therapy86 (Fig. 139-1). Regimen A, commonly called a split-mix, is a frequently used approach in patients who are not undergoing intensive therapy. However, in conjunction with careful caloric control, exercise, and more frequent monitoring, it can yield a blood glucose profile and glycohemoglobin that are nearly as good as those obtained with more complex regimens. Regimens B, C, and D involve three or more injections per day. These regimens may have a greater potential for suppressing fasting hepatic glucose output before breakfast. Postprandial glu¬ cose excursions can be controlled by regular insulin injections given 30 minutes before each of the three meals according to a sliding scale. Although regimen A (split-mix) is the simplest regimen, it has the greatest potential for causing nocturnal hypoglycemia be¬ cause of the peaking of intermediate-acting insulin during the early hours of the morning. Regimens B and C may reduce the chance of nocturnal hypoglycemia and also are more likely to suppress the dawn rise in blood glucose. Regimen D, an Ultralente program, attempts to mimic the continuous basal insulin delivery achieved with a pump. The basal Ultralente insulin dose is given as 40% to 60% of total daily requirements. In all four regimens, ihe fasting blood glucose guides the choice of dosage for the intermediate- and long-acting insulins. Blood glucose should be checked intermittently at 3:00 am to document possi¬ ble nocturnal hypoglycemia. Generally, with intensive conven¬ tional therapy, the insulin dose exceeds that required for CSII by 20%. The goal of therapy (Table 139-4) should be a fasting blood glucose generally between 90 and 120 mg/dL, and a 1- to 2-hour postprandial peak of less than 140 mg/dL. Total daily dosage requirements usually are between 0.7 and 0.9 U/kg. The premeal insulin dose is based on a sliding scale, devised by trial and error, by which the dose is determined from the premeal blood glucose level.26 The prebreakfast insulin dose often is greater than that needed for the evening meal. Regular insulin delivery may be facilitated by the insulin "pen" in regimens C and D.

RISKS The potential benefits of intensive therapy must be weighed carefully against the risks. Any intensive therapy regimen in¬ creases the risk of hypoglycemia, and this danger must not be underestimated.83 Patients who have hypoglycemic reactions without warning should not undertake intensive therapy with an objective of achieving normoglycemia. The incidence of ketoaci¬ dosis may be increased in patients receiving CSII. This probably occurs because interruption of the infusion rapidly leads to virtu¬ ally complete insulin deficiency. There are many potential causes of interruption, including pump failure, accidental kinking of the infusion catheter, dislodgment of the needle, and insulin aggre¬ gation in the infusion line. These mishaps may be compounded by failure of the patient to take appropriate corrective action, such as restarting conventional therapy promptly. The risk of di¬ abetic ketoacidosis appears to be falling as experience with CSII grows. The use of CSII may cause subcutaneous abscesses and cellulitis. Staphylococcal infections of the skin are a contraindi¬ cation to CSII because of the danger of septicemia and endocar¬ ditis. Patients with psychiatric disturbances, alcoholism, limited intelligence, and multiple advanced complications generally are not suitable candidates for intensive therapy. Intensive therapy is a demanding and expensive undertaking, especially with the "pump," and many patients who start these programs are unable to continue for a prolonged period.84

SELECTING THE REGIMEN About the same level of metabolic control can be achieved with either intensive conventional therapy or CSII, although there have been claims that marginally better results may be

CONTINUOUS SUBCUTANEOUS INSULIN INFUSION REGIMENS Various pumps for CSII delivery are available, providing more flexibility in delivery rates, additional safety features, and

Ch. 139: Insulin Therapy and Its Complications

Morn¬ ing

Afternoon

Evening

1247

Night

bO UJ U. U. UJ

2 REG

REG NPH/LENTE

oo

MEALS

MEALS

KCJ LU

uu LL LU

2 Lj oo 2:

MEALS FIGURE 139-1.

A to D, Regimens commonly used for intensive conventional insulin therapy (see text for discussion). B, L, S, and HS, refer to breakfast, lunch, supper, and bedtime, respectively. D shows idealized profile of bovine Ultralente. Human Ultralente has broad peaks at about 9 to 15 hours after injection. (From Schade DS, Santiago JV, Skyler JS, Rizza RA. Insulin secretion in non-diabetics and insulindependent subjects. In: Schade DS, Santiago JV, Skyler JS, Rizza RA, eds. In: Intensive insulin therapy. Amster¬ dam: Excerpta Medica, 1983:129.)

greater portability than earlier models. The basal dose usually is 40% to 60% of the total daily dose,2'87 and also is derived from the fasting and 3:00 am blood glucose values. If a marked dawn phenomenon is observed, a higher rate of infusion can be pro¬ grammed by using pumps with variable basal rates 2 to 3 hours before dawn. The fasting and postprandial blood glucose goals are the same as for conventional insulin therapy, and the premeal dose also is based on a sliding scale determined from a trial-anderror approach.87 The premeal bolus should be delivered 30 min¬ utes before meals, as with conventional therapy.

EXPERIMENTAL FORMS OF INSULIN THERAPY Experimental approaches to insulin therapy include new in¬ sulin analogues, nasal insulin, implantable insulin pumps,

“closed-loop" insulin delivery systems, and pancreas and islet transplantation. Various insulin analogues made by recombinant DNA tech¬ nology are now undergoing clinical trials. The association of in¬ sulin to form dimers and oligomers can slow its absorption; there¬ fore, the strategy has been to create insulins designed to minimize these interactions.88,89 Early studies have shown these analogues to have faster absorption and shorter duration of action than reg¬ ular human insulin, a characteristic that more closely mimics nor¬ mal insulin secretion with meals. These analogues may be useful for covering meals in both type I and type II diabetes. Nasal insulin administration appeared to be feasible in pre¬ liminary studies.90 As with the insulin analogues, absorption is rapid and duration of action is short, making it particularly useful for covering meals. Clinical trials are continuing, but it remains to be seen whether this approach will prove practical.

TABLE 139-4 Goals of Intensive Insulin Therapy and Guide for Adjusting Conventional or Pump Therapy* Blood Glucose Goal

Therapy Requiring Adjustment Conventional

Pump Basal rate

Time

(mg/dl)

(mmol/L)

Fasting (prebreakfast)

80-120

4.4-6.6

Ultralente or intermediate

Before meals

70-120

3.8-6.6

Check meal and snack timing and profile of intermediate-acting

< 140

< 7.7

70-120

3.8-6.6

insulin

2 h after meals 2

AM

to 4

AM

Premeal injection

Bolus dose

Intermediate or Ultralente

Basal rate

* Home monitoring of blood glucose should be performed four to five times a day and two or three snacks are taken in addition to regularly timed meals for patients on intensive conventional therapy.

1248

PART IX: DISORDERS OF FUEL METABOLISM

Implantable variable-rate insulin pumps have received con¬ siderable attention in the past few years as potential insulin de¬ livery systems for both type I and type II diabetes.91 They are placed within the peritoneum. Some patients have been treated successfully with these devices for more than 5 years. Intraperitoneal insulin delivery is attractive because of the theoretic ad¬ vantages of portal insulin delivery, including the possibility of reducing systemic hyperinsulinemia and better regulation of in¬ termediary metabolism. These pumps are being compared to other forms of insulin therapy.91 The devices are "open-loop" systems that rely on self-monitoring of the glucose level. A closed-loop system, in which a monitor capable of continuous glucose sensing is linked to an intraperitoneal pump, would be a major advance. A large and complex closed-loop artificial pan¬ creas has been available for hospitalized patients for some time, but is impractical for home use and rarely is used now, even in hospitals. Progress in developing glucose sensors has been slow, but there are encouraging results with a noninvasive approach in which absorbance spectra are measured using light spectroscopy in the near infrared range.92 Whole pancreas transplantation is a therapy now being offered by many medical centers.93'94 It is largely restricted to pa¬ tients who also are receiving kidney transplants with immuno¬ suppression. The number of transplants performed is small, mainly because of the limited supply of cadaver organs. Segmen¬ tal pancreas transplants are not feasible because of the risk of diabetes developing in donors. The most common approach is for recipients simultaneously to receive a kidney and a pancreas from the same cadaver donor. The pancreas is placed in the pelvis with drainage into the bladder. The surgery is accompanied by a small risk of death and considerable morbidity, but in experi¬ enced centers, about 80% of the grafts are functioning well at 1 year and about 50% at 5 years. A successful result provides nor¬ mal glucose levels and the patients have no dietary ^restrictions. There continue to be arguments about the balance among the benefits, risks, and expense of this approach. Most of the recipi¬ ents already have advanced complications, so it is not surprising that meaningful improvements are not observed. However, many clinicians believe that the quality of patients' lives is im¬ proved by the procedure, and that is its main justification. The field of islet cell transplantation has made important progress in the past 20 years, but faces difficult obstacles before it can be offered as routine therapy.94 96 There already is experience with more than 200 islet transplants in which human islets have been transplanted into the portal vein of patients with IDDM, who usually are immunosuppressed. Most of these have failed within a few weeks, but an increasing number of patients are enjoying longer periods of normoglycemia without insulin; a few have lasted for more than a year. Obstacles include the need for a more plentiful source of islet tissue, because the amount available from cadaver pancreases is insufficient. The possibility of using porcine or bovine islets as xenografts is being actively explored. In addition, bioengineering is being used to develop insulinproducing cell lines, but progress is still at an early stage. There are difficult immunologic barriers, which include either allograft or xenograft rejection, as well as autoimmune attack. Immunolo¬ gists are making great strides in developing safer drugs, which can target more specific parts of the immune system, and in learn¬ ing more about the induction of tolerance. Other approaches to islet transplantation include immunoisolation of islets in diffu¬ sion chambers or microcapsules.

4. Schernthaner G. Immunogenicity and allergenic potential of animal and human insulins. Diabetes Care 1993; 16(Suppl 3):155. 5. Chance RE, Frank BH. Research, development, production, and safety of biosynthetic human insulin. Diabetes Care 1993; 16(SuppI 3):133. 6. Houtzagers CMGJ, Berntzen PA, van der Stap H, et al. Absorption kinetics of short- and intermediate-acting insulins after jet injection with Medi-Jector II. Diabetes Care 1988; 11:739. 7. Berger W, Keller U, Honegger B, Jaeggi E. Warning symptoms of hypogly¬ cemia during treatment with human and porcine insulin in diabetes mellitus Lancet 1989; 1:1041. 7a. Cryer PE. 1993; 16(Suppl 3):40.

Hypoglycemia

unawareness

in

IDDM.

Diabetes

Care

8. Robbins DC, Tager H, Rubenstein A. Biological and clinical importance of proinsulin. N Engl J Med 1984;310:1165. 9. Galloway JA, Kooper SA, Spradlin CT, et al. Biosynthetic human proinsu¬ lin: review of chemistry, in vitro and in vivo receptor binding, animal and human pharmacology studies, and clinical experience. Diabetes Care 1992; 14:666. 10. Rasio EA, Hampers CL, Soeldner JS, Cahill GF. Diffusion of glucose, in¬ sulin, inulin and Evans blue protein into thoracic duct lymph of man J Clin Invest 1967; 46:903. 11. Sherwin RS, Kramer KJ, Tobin JD, et al. A model of the kinetics of insulin. J Clin Invest 1974;53:1481. 12. Stimmler L. Disappearance of immunoreactive insulin in normal and adult onset subjects. Diabetes 1967; 16:652. 13. Navelesi R, Pilo A, Ferrannini E. Kinetic analysis of plasma disappearance in non-ketotic diabetic patients and in normal subjects. J Clin Invest 1978;61:197. 14. Polonsky KS, Given BD, Hirsch L, et al. Quantitative study of insulin secretion and clearance in normal and obese subjects. J Clin Invest 1988;81:435. 15. Ferrannini E, Wahren J, Faber OK, et al. Splanchnic and renal metabolism of insulin in human subjects: a dose response study. Am J Physiol 1983; 244:E517. 16. Sacca L, Orofino G, Petrone A, Vigorito C. Direct assessment of splanchnic uptake and metabolic effects of human and porcine insulin. J Clin Endocrinol Metab 1984; 59:191. 17. Binder C, Lauritzen T, Faber O, Prammer S. Insulin pharmacokinetics. Diabetes Care 1984; 7:188. 18. Hildebrant P, Birch K, Sestoft O, Nielson ST. Orthostatic changes in sub¬ cutaneous blood flow and insulin absorption. Diabetes Res 1985;2:187. 19. Heine RJ, Bilo HJG, Fonk T, et al. Absorption kinetics and action profiles of mixtures of short- and intermediate-acting insulins. Diabetologia 1984; 27:558. 20. Colagiuri S, Villalobos S. Assessing effect of mixing insulins by glucoseclamp technique in subjects with diabetes mellitus. Diabetes Care 1986;9:579. 21. Galloway JA, Spradlon T, Jackson RL, et al. Mixtures of intermediate act¬ ing insulin: an update. In: Skyler JS, ed. Insulin update: 1982. Amsterdam- Excerpta Medica, 1982:111. r 22. Paulsen EP, Courtney GW, Duckworth WC. Insulin resistance caused by massive degradation of subcutaneous insulin. Diabetes 1979;28:640. 23. Home PD, Massi-Benedetti M, Gill GV, et al. Impaired subcutaneous ab¬ sorption of insulin in "brittle" diabetes. Acta Endocrinol (Copenh) 1982; 101:414. 24. Kurtz AB, Nabarro JDN. Circulating insulin-binding antibodies. Diabeto¬ logia 1980; 19:329. 25. Kovisto VA. 1993; 16(Suppl 3):29.

Insulin therapy in type II diabetes.

Diabetes Care

26. The DCCT Research Group. The effects of intensive treatment of diabetes on the development and progression of long-term complications in insulin-depen¬ dent diabetes mellitus. N Engl J Med 1993;329:977. 27. Nathan DM. Long-term complications of diabetes mellitus. N Enel J Med 1993;328:1676. 28. Stout RW. Insulin and atheroma, 20-yr perspective 1990; 13:631.

Diabetes Care

29. Holman RR, Turner R. Diabetes: the quest for basal normoglycemia Lan¬ cet 1977; 1:469. 30. Gerich JE. Glucose counterregulation and its impact on diabetes mellitus Diabetes 1988; 37:1608. 31. Bolli G, Fanelli CG, Perriello G, De Feo P. Nocturnal blood glucose control in type I diabetes mellitus. Diabetes Care 1993; 16(Suppl 3):71. 32. Somogyi M. Insulin as a cause of extreme hyperglycemia and instability. Bull St Louis Med Soc 1938;32:498. 33. Gerich JE, Campbell PJ. Overview of counterregulation and its abnormal¬ ities in diabetes mellitus and other conditions. Diabetes Metab Rev 1988;4:93. 34. Clutter WE, Rizza RA, Gerich JE, Cryer PE. Regulation of glucose metab¬ olism by sympathochromaffin catecholamines. Diabetes Metab Rev 1988; 4:1. 35. Widom B, Simonson DC. Iatrogenic hypoglycemia. In: Kahn CR, Weir GC, eds. Joslin's diabetes mellitus, ed 13. Philadelphia: Lea & Febiger, 1994:489. 36. Lerman IG, Wolfsdorf JI. Relationship of nocturnal hypoglycemia to day¬ time glycemia in IDDM. Diabetes Care 1988; 11:636. 37. Hirsch IB, Smith LJ, Havlin CE, et al. Failure of nocturnal hypoglycemia 133aUSe dayt'me hyPerg'ycemia in patients with IDDM, Diabetes Care 1990; 13:

REFERENCES 1. Schade DS, Santiago JV, Skyler JS, Rizza RA. Insulin secretion in non-diabetics and insulin dependent subjects. In: Schade DS, Santiago JV, Skyler JS, Rizza RA, eds. Intensive insulin therapy. Princeton, NJ: Excerpta Medica, 1983:23. 2. Rosenzweig JL. Principles of insulin therapy. In: Kahn CR, Weir GC, eds Joslin's diabetes mellitus, ed 13. Philadelphia: Lea & Febiger, 1994:460. 3. Heinemann L, Richter B. Clinical pharmacology of human insulin. Diabetes Care 1993; 16(Suppl 3):90.

38. Bolli G, Gerich J. The dawn phenomenon—a common occurrence in both noninsulin-dependent and insulin-dependent diabetes mellitus N Enel I Med 1984;310:746. 6 1 39. Bolli G, De Feo P, De Cosmo S, et al. Demonstration of a dawn phenome¬ non in normal human volunteers. Diabetes 1984;33:1150, 40. Campbell P, Bolli G, Cryer P, Gerich J. Pathogenesis of the dawn phe¬ nomenon in patients with insulin-dependent diabetes mellitus N Engl 1 Med 1985;312:1473. B 41.0 Hare JA, Ferriss JB, Twomey BM, et al. Changes in blood pressure, body

Ch.14Q: Syndromes of Insulin Resistance fluids, circulating angiotensin II and aldosterone, with improved diabetic control. Clin Sci 1982;63:415s. 42. Evans DJ, Pritchard-Jones K, Trotman-Dickenson B. Insulin oedema. Post¬ grad Med J 1986;62:665. 43. Rabkin R, Ryan MP, Duckworth WC. The renal metabolism of insulin. Diabetologia 1984;27:351. 44. O'Hare JA, Ferriss JB, Twomey B, O'Sullivan DJ. Poor metabolic control, hypertension and microangiopathy independently increase the transcapillary es¬ cape rate of albumin in diabetes. Diabetologia 1983;25:260. 45. Wheatly T, Edwards OM. Insulin edema and its clinical significance: met¬ abolic studies in three cases. Diabet Med 1985; 2:400. 46. Galloway JA, de Shazo RD. Insulin chemistry, pharmacology, dosage al¬ gorithms and the complications of insulin treatment. In: Rifkin H, Porte D Jr, eds. Ellenberg and Rifkin's diabetes mellitus theory and practice, ed 4. New York: Else¬ vier, 1990:497. 47. Reeves W, Allen B, Tattersell R. Insulin-induced lipoatrophy: evidence for an immune pathogenesis. Br Med J 1980; 280:1500. 48. Young RJ, Hannan W, Frier B, et al. Diabetic lipohypertrophy delays insu¬ lin absorption. Diabetes Care 1984; 7:479. 49. Rowe JW, Young JB, Minaker KM, et al. Effect of insulin and glucose infu¬ sions on sympathetic nervous system activity in normal man. Diabetes 1981;30: 219. 50. Page M McB, Watkins PJ. Provocation of postural hypotension by insulin in diabetic autonomic neuropathy. Diabetes 1976; 25:90. 51. Chance R, Root M, Galloway J. The immunogenicity of insulin prepara¬ tions. Acta Endocrinol (Copenh) 1976;83(Suppl 205): 185. 52. Keller RJ, Eisenbarth GS, Jackson RA. Insulin prophylaxis in individuals at high risk of type 1 diabetes. Lancet 1993; 341:92. 53. Mann D, Mendell N, Kahn C, et al. In vitro lymphocyte proliferation re¬ sponse to therapeutic insulin components: evidence for genetic control by the major histocompatibility complex. J Clin Invest 1983;72:1130. 54. Kahn C, Mann D, Rosenthal A, et al. The immune response to insulin in man: interaction of HLA alloantigens and the development of the immune re¬ sponse. Diabetes 1982; 31:716. 55. Kahn C, Rosenthal A. Immunologic reactions to insulin: insulin allergy, insulin resistance and the autoimmune insulin syndrome. Diabetes Care 1979; 2: 283. 56. Feinglos M, Jegasothy B. "Insulin" allergy due to zinc. Lancet 1979; 1:122. 57. Stewart W, McSweeney S, Kellett M, et al Increased risk of severe prot¬ amine reactions in NPH-insulin-dependent diabetics undergoing cardiac catheter¬ ization. Circulation 1984; 70:788. 58. Kurtz A, Nabarro J. Circulating insulin-binding antibodies. Diabetologia 1980; 19:329. 59. Waldhausl W, Bratusch-Marrain P, Kruse V, et al. Effect of insulin anti¬ bodies on insulin pharmacokinetics and glucose utilization in insulin-dependent diabetic patients. Diabetes 1985; 34:166. 60. Van Haeften T, Bolli G, Dimitriadis G, et al. Effect of insulin antibodies and their kinetic characteristics on plasma free insulin dynamics in patients with diabetes mellitus. Metabolism 1986;35:1649. 61. Davidson J, DeBra D. Immunologic insulin resistance. Diabetes 1978; 27: 307. 62. Arkins JA, Engbring NH, Lennon EJ. The incidence of skin reactivity to insulin in diabetic patients. J Allergy 1962;33:69. 63. Wolfsdorf JI, Anderson Bj, Pasquarello C. Treatment of the child with diabetes. In: Kahn CR, Weir GC, eds. Joslin's diabetes mellitus, ed 13. Philadelphia: Lea & Febiger, 1994:530. 64. Tattersall RB, Lowe J. Diabetes and adolescence. Diabetologia 1981;20: 517. 65. Kitzmiller JL. Sweet success with diabetes: the development of insulin therapy and glycemic control for pregnancy. Diabetes Care 1993; 16(Suppl 3): 107. 66. Tattersall RB. Diabetes in the elderly—a neglected area? Diabetologia 1984;27:167. 67. Agner T, Damm P, Binder C. Remission in IDDM: prospective study of basal C-peptide and insulin dose in 265 consecutive patients. Diabetes Care 1987;10:164. 68. Perlman K, Erlich RM, Filler RM, Albisser AM. Sustained normoglycemia in newly diagnosed type I diabetic subjects: short term effects and one year fol¬ lowup. Diabetes 1984;33:995. 69. Peters AL, Davidson MB. Insulin plus a sulfonylurea agent for treating type 2 diabetes. Ann Intern Med 1991; 115:45. 70. Riddle MC. New tactics for type II diabetes: regimens based on interme¬ diate-acting insulin taken at bedtime. Lancet 1985; 1:192. 71. Taskinen MR, Sane T, Helve E, et al. Bedtime insulin for suppression of overnight free-fatty acid, blood glucose, and glucose production in NIDDM. Diabe¬ tes 1989;38:580. 72. Yki-Jarvinen H, et al. Comparison of insulin regimens in patients with NIDDM. N Engl J Med 1992;327:1426. 73. Alberti KGMM, Gill GV, Elliott MJ. Insulin delivery during surgery in the diabetic patient. Diabetes Care 1982;5(Suppl 1):65. 74. Hare J, Rossini AA. How to control the blood sugar level in the surgical diabetic patient. Arch Surg 1976;111:945. 75. Rabkin R, Ryan MP, Duckworth WC. The renal metabolism of insulin. Diabetologia 1984;27:351. 76. Rabkin R, Simon NM, Steiner S, Colwell JA. Effect of renal disease on renal uptake and excretion of insulin in man. N Engl J Med 1970; 282:182. 77. Amair P, Khanna R, Leibel B, et al. Continuous ambulatory dialysis in diabetics with end-stage renal disease. N Engl J Med 1982,-306:625.

1249

78. Gill GV, Walford S, Alberti KGMM. Brittle diabetes. Present concepts. Diabetologia 1985,-28:579. 79. Gale EAM. Basic principles in the management of unstable diabetic con¬ trol. In: Pickup J, ed. Brittle diabetes. Oxford: Blackwell Scientific, 1984:83. 80. Schade DS, Eaton PR, Drumm DA, Duckworth WC. A clinical algorithm to determine the etiology of brittle diabetes. Diabetes Care 1985; 8:5. 81. Schade DS, Santiago JV, Skyler JS. Implementation of and application of intensive therapy. In: Shade DS, Santiago JV, Skyler JS, Rizza RA, eds. Intensive insulin therapy. Amsterdam: Excerpta Medica, 1983:175. 82. Schade DS, Santiago JV. Effect of intensive treatment on substrate and hormonal abnormalities. In: Schade DS, Santiago JV, Skyler JS, Rizza RA, eds. In¬ tensive insulin therapy. Amsterdam: Excerpta Medica, 1983:71. 83. Anonymous. Acute mishaps during insulin pump treatment. (Editorial) Lancet 1985;1:911. 84. Bell DSH, Ackerson C, Cutter G, Clements RS Jr. Factors associated with discontinuation of continuous subcutaneous insulin infusion. Am J Med Sci 1988;295:23. 85. Skyler JS. Lessons from studies of insulin pharmacokinetics. Diabetes Care 1986;9:666. 86. Schade DS, Santiago JV, Skyler JS, Rizza RA. Intensive conventional ther¬ apy. In: Schade DS, Santiago JV, Skyler JS, Rizza RA, eds. Intensive insulin therapy. Amsterdam: Excerpta Medica, 1983:129. 87. Skyler JS, Seigler DE, Reeves ML. Optimised pumped insulin delivery. Diabetes Care 1982;5:135. 88. Brange J, Owens DR, Kang S, Volund A. Monomeric insulins and their experimental and clinical implications. Diabetes Care 1990; 13:923. 89. Galloway JA. New directions in drug development: mixtures, analogues, and modeling. Diabetes Care 1993; 16(Suppl 3): 16. 90. Salzman R, Manson JE, Griffing GT, et al. Intranasal aerosolized insulin; mixed meal studies and long-term use in type I diabetes. N Engl J Med 1985; 312: 1078. 91. Saudek CD. Future developments in insulin delivery systems. Diabetes Care 1993; 16(Suppl 3):122. 92. Robinson MR, Eaton RP, Haaland DM, Koepp GW. Noninvasive glucose monitoring in diabetic patients: a preliminary evaluation. Clin Chem 1992; 38:1618. 93. Sutherland DE. Pancreatic transplantation: state of the art. Transplant Proc 1991;24:762. 94. Shaffer D, Monaco AP. Whole-pancreas and islet-cell transplantation. In: Kahn CR, Weir GC, eds. Joslin's diabetes mellitus, ed 13. Philadelphia: Lea & Feb¬ iger, 1994:560. 95. Lacey PE. Status of islet cell transplantation. Diabetes Rev 1993; 1:76. 96. Weir GC. Current status of pancreas and islet cell transplantation. In: Kohler PO, ed. Current opinion in endocrinology and diabetes. Philadelphia: Cur¬ rent Science, 1994:226.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

140_

SYNDROMES OF INSULIN RESISTANCE JEFFREY S. FLIER

This chapter considers a group of syndromes that have in common severe tissue resistance to the actions of insulin (Table 140-1). Over the past 20 years, an increasing number of patients with these clinical syndromes have been described, although the research interest in these diseases has been discordant with their prevalence. Intense studies have yielded important insights, into both the molecular basis for these diseases and the molecular mechanism of insulin action. Although typically a part of the differential diagnosis of insulin resistance, the insulin resistance that is due to antiinsulin antibodies, as occurs in patients receiv¬ ing insulin therapy for diabetes, is considered in Chapter 139.

INSULIN RECEPTORS AND INSULIN ACTION Although insulin is best known for its ability to promote glu¬ cose metabolism, this hormone exerts a wide variety of effects at the cellular level. In addition to stimulating glucose and amino

1250

PART IX: DISORDERS OF FUEL METABOLISM

acid transport, insulin also can activate or inactivate cytoplasmic and membrane enzymes, alter the rate of synthesis and degrada¬ tion of various proteins and specific mRNAs, and influence the processes of cell growth and differentiation.1 These multiple effects vary widely from tissue to tissue and in dose-response and time course. Some effects, such as the stimulation of glucose transport activity, occur within seconds at very low insulin con¬ centrations. At the other extreme, actions to promote cell growth in certain cells require hours and generally involve higher con¬ centrations of the hormone. Further complicating the study of insulin action is the relationship between insulin and the socalled insulin-like growth factors(IGFs)2(seeChaps. Hand 169). These peptides (IGF-I and IGF-II) have major structural homolo¬ gies with insulin, but they have little or no immunologic cross reactivity with the hormone. Both IGF-I and IGF-II have distinct receptors to which insulin also can bind, but with reduced affin¬ ity.3 The IGF-I receptor can mediate many of the same acute met¬ abolic events that are regulated by the insulin receptor. Gener¬ ally, however, the IGFs, acting through the IGF-I receptor, have more potent effects on cell growth than does insulin, acting through the insulin receptor. Some of the actions of insulin that are seen at very high concentrations appear to be exerted through binding to and activation of IGF receptors (rather than insulin receptors).

INSULIN RECEPTORS The plasma membrane receptors for insulin initially were defined by their insulin binding characteristics, which typically include high affinity for insulin, rapid and saturable binding, and specificity for insulin and related molecules in proportion to their bioactivity.4 The functional binding characteristics of insulin have been highly conserved throughout evolution. Much has been learned about the structure of the receptor molecule, which has been cloned5 6 and studied extensively by mutational analy¬ sis. The insulin receptor is a glycoprotein composed of at least two distinct subunits, referred to as a and /3, with molecular masses of 135,000 and 95,000 daltons, respectively.7 These two subunits arise from a common precursor proreceptor molecule that is encoded by a single gene. These subunits are held together by disulfide bonds; the receptor resides most often in the mem¬ brane in a form with two a and two /3 subunits. Alternative mRNA splicing results in two receptor isoforms that differ slightly in binding affinity for insulin and are expressed at differ¬ ent ratios in different tissues.8,9 The potential significance of this is unknown. The number of receptors expressed per cell varies considerably, from several hundred per mature erythrocyte to several hundred thousand per adipocyte. The functional heterogeneity of the insulin receptor mole-

cule has now become apparent. Thus, the a subunit sits external to the plasma membrane and is the receptor subunit that contains the insulin binding site. The a subunit is linked through disulfide bonds to the transmembrane /? subunit, which is the subunit re¬ sponsible for transmembrane signal transduction. As an intact a-/3 unit, the insulin receptor functions as an insulin-stimulated tyrosine kinase.10 Protein kinases are enzymes that participate in the transfer of phosphate groups from high-energy phosphate compounds, such as adenosine triphosphate, to amino acid resi¬ dues of proteins. For the insulin receptor, this leads to an auto¬ phosphorylation reaction with the incorporation of phosphate groups into tyrosine residues on the /? subunit of the receptor, as well as the phosphorylation of exogenous substrates (Fig 140-1). The fact that the kinase activity is intrinsic to the receptor and is stimulated by insulin binding has led to the speculation that this activity is the transmembrane signal leading to a cascade of phosphorylation events culminating in insulin's pleiotropic effects at the cellular level. Flowever, the precise mechanism of signal transduction is uncertain. The most obvious mechanism would involve phosphorylation of one or more endogenous sub¬ strates, leading to a cascade of phosphorylation-dephosphoryla¬ tion reactions. Several proteins that are rapidly phosphorylated on tyrosine residues in response to insulin have been identified. The best defined of these is a protein referred to as insulin recep¬ tor substrate-1.11 Much has been learned about the mechanism by which tyrosine phosphorylation of insulin receptor substrate1 permits this molecule to associate with several signal transduc¬ tion molecules that facilitate the propagation of the insulin signal (see Chap. 131).11 The complexity of this downstream cascade is far greater than was previously anticipated. Given the diverse nature of insulin's effects on cellular function, it may be that no single early biochemical event will emerge as central to all the actions of insulin. RECEPTOR REGULATION

Insulin receptors are not static components of the cellular ma¬ chinery; rather, they have a half-life measured in hours. In addi0

0

TABLE 140-1 Clinical Syndromes of Extreme Insulin Resistance INHERITED (PRIMARY) CELLULAR DEFECTS IN INSULIN ACTION Classic Type A Syndrome of Insulin Resistance With Acanthosis Nigricans Variants of Type A Syndrome With

Muscle cramps Acral hypertrophy, pseudoacromegaly Lipodystrophy Pediatric Syndromes With Severe Insulin Resistance

Leprechaunism (abnormal facies, growth retardation) Rabson-Mendenhall syndrome (dental dysplasia, dystrophic nails, precocious puberty ACQUIRED INSULIN RESISTANCE Autoantibodies to the Insulin Receptor (Type B) Accelerated Insulin Degradation

FIGURE 140-1. Schematic representation of the insulin receptor and insulin signal transduction. The binding of insulin to the a subunit acti¬ vates autophosphorylation of tyrosine residues on the 0 subunit, which leads to activation of the intrinsic tyrosine kinase of the receptor. The major known substrate of the insulin receptor tyrosine kinase is IRS-1. Tyrosine phosphorylation of specific tyrosines on IRS-1 causes interac¬ tion with molecules such as syp, nek, PI-3 kinase, and grb through spe¬ cific domains on these molecules. The best characterized pathway for downstream signaling involves the sequential involvement of the pro¬ teins sos, ras, raf, MEKK, and, eventually, an array of other serine kinases and phosphatases that bring about the actions characteristic of the hor¬ mone. The downstream actions of syp, nek, and PI-3 kinase remain un¬ certain. PI-3, phosphatidyl inositol-3; MEKK, MAP kinase/ERK kinase.

Ch.140: Syndromes of Insulin Resistance tion to this rapid turnover under basal conditions, the affinity and number of insulin receptors are subject to dynamic regulation by many signals emanating from inside and outside of the cell. A major factor regulating the concentration of insulin receptors is insulin itself. Thus, when cells are cultured in a medium contain¬ ing insulin, they exhibit a time- and temperature-dependent de¬ crease in the concentration of insulin receptors, a phenomenon termed down-regulation.12 The mechanism for this may be com¬ plex, but typically appears to involve an insulin-induced acceler¬ ation of receptor degradation. In addition to this in vitro phe¬ nomenon of down-regulation, the number of insulin receptors on cells immediately removed from patients with various dis¬ eases has correlated inversely with the concentration of insulin to which the cells are tonically exposed in vivo. This phenomenon, whereby the concentration of insulin receptors is regulated by ambient insulin levels, is believed to play a major role in the pathogenesis of insulin resistance in several disease states, most notably obesity.13 Many other modulators of receptor concentration or affinity have been described through in vivo or in vitro studies. These include various physiologic states (e.g., age, diurnal variation, diet, exercise, menstrual cycle, and pregnancy) and drugs (e.g., oral hypoglycemic agents, such as sulfonylureas and the biguanides; and corticosteroids). Other modulators are dietary maneu¬ vers such as fasting or high-carbohydrate feeding, exercise, and the level of specific molecules that can influence receptor expres¬ sion, such as hormones (cortisol, growth hormone), nucleotides, ketones, and autoantibodies against the receptor.14 In many dis¬ eases, one or more of these receptor modulators may be respon¬ sible for insulin receptor alterations and partially responsible for the clinical resistance to insulin (Table 140-2).

INSULIN RESISTANCE: GENERAL CONSIDERATIONS Insulin resistance is defined as a state in which a given con¬ centration of insulin produces less than the expected bioeffect. Usually, this brings to mind the image of an insulin-treated dia¬ betic patient who remains hyperglycemic despite large doses of exogenous insulin. Although such a patient certainly qualifies as insulin-resistant, this clinical situation represents only one of many clinical presentations of the insulin-resistant disorders. Other presentations include hypoglycemia, acanthosis nigricans, hyperandrogenism, autoimmunity, abnormal growth (growth failure or accelerated linear growth), lipodystrophy, and muscle cramps. It also is apparent now that insulin resistance often ac¬ companies such common disorders as hypertension and coro¬ nary artery disease associated with an atherogenic lipid profile, in a syndrome referred to as syndrome X.15 Patients with insulin resistance thus span a broad spectrum of glucose homeostasis: at one end, these patients may be grossly diabetic despite large doses of insulin; at the other end, they may be normoglycemic despite severe insulin resistance, which is overcome by the compensatory hypersecretion of endogenous insulin. Regardless of whether a patient is diabetic, resistance to insulin can be demonstrated by various means. A commonly used indirect approach relates the degree of insulin resistance to the level of radioimmunoassayable insulin in blood. In some sit¬ uations, the fasting insulin level is related directly to the degree of insulin resistance, but this approach is subject to error if the insulin measured by radioimmunoassay is not fully bioactive, as in those patients who have certain point mutations in the struc¬ tural gene encoding the insulin molecule.16 Insulin sensitivity also can be assessed by measuring the re¬ sponse to the direct intravenous infusion of insulin. Although useful information can be obtained by measuring this response, the variable secretion of counterinsulin hormones in response to hypoglycemia makes a mechanistic interpretation of data ob¬ tained with this method difficult. To circumvent this problem,

1251

the euglycemic insulin clamp technique may be used.1' With this technique, the biochemical response (i.e., glucose disposal, antilipolysis) is assessed at different steady-state insulin levels, while the plasma glucose levels are held constant with a computerassisted variable glucose infusion.

THE CLINICAL SPECTRUM OF INSULINRESISTANT DISORDERS The syndromes of extreme insulin resistance span a broad clinical spectrum. Glucose homeostasis ranges from normal to severely impaired, with hyperglycemia that may be extremely refractory to insulin therapy. The disorder may appear in patients of any age and of either sex. In patients with severe diabetes, it typically serves as the indicative feature of their disease. How¬ ever, because diabetes often is absent in patients with insulin re¬ sistance, various associated clinical features may be the sole basis for clinical diagnosis. Unless the clinician is aware of the associa¬ tion of these features (e.g., acanthosis nigricans, ovarian hyper¬ androgenism, abnormality of growth, and lipodystrophy) with insulin resistance, the latter may go undetected.

BIOCHEMICAL BASIS FOR CLINICAL HETEROGENEITY IN INSULIN-RESISTANT STATES The diverse cellular actions of insulin result from at least two factors: the generation of multiple distinct effects on postreceptor signaling pathways within target cells; and the ability of insulin to bind to and act through the IGF-I receptor as well as through the classic insulin receptor. As one consequence of these complex signaling mechanisms, resistance to one action of insulin (e.g., its glucose-lowering effect) need not necessarily be associated with equally severe resistance to other important actions of insulin (e.g., antilipolysis, amino acid uptake, or growth stimulation). It is likely that heterogeneity in the degree to which insulin action on various cellular pathways is impaired plays a central role in determining the clinical specificity of these heterogeneous disorders.

PATHOGENETIC MECHANISMS RESPONSIBLE FOR SEVERE INSULIN RESISTANCE Several different classifications for the pathogenesis of insu¬ lin resistance have been proposed. One useful classification di-

TABLE 140-2 Diseases and Clinical States With Insulin Resistance in Which Insulin Receptor Function May Be Altered INSULIN-RESISTANT STATES Obesity Type II diabetes Diabetic ketoacidosis Acromegaly Glucocorticoid excess Uremia Cirrhosis of liver Viral infection Genetic syndromes Type A syndrome of insulin resistance with acanthosis nigricans, leprechaunism, ataxia telangiectasia, myotonic dystrophy Antiinsulin receptor antibodies

INSULIN-SENSITIVE STATES Growth hormone deficiency Glucocorticoid deficiency Anorexia nervosa

1252

PART IX: DISORDERS OF FUEL METABOLISM

vides these disorders into those in which there is "primary" target cell resistance to insulin and those in which insulin resis¬ tance is caused by factors apart from the target cell. PRIMARY TARGET CELL DEFECTS

Primary target cell defects can be due to defects in the insulin receptor itself, or to defects in signaling components apart from the insulin receptor (Table 140-3). Disorders at the level of the insulin receptor gene have been defined over the past few years.18'20 These may present as a marked reduction in the num¬ ber of (functionally normal) insulin receptors, due to multiple biochemical defects, including mutations in the receptor gene or its promoter, causing reduced ability to synthesize receptor mRNA; or to mutations in the receptor gene, causing impaired ability of the mature receptor protein to insert into or remain within the membrane. Alternatively, qualitative abnormalities of receptor function have been seen, also resulting from multiple gene defects. These have included receptor structural mutations causing reduced affinity of hormone binding, altered function of the receptor as a hormone-activated kinase, and impaired in¬ teraction of an activated receptor with other signaling compo¬ nents. With a clearer molecular understanding of the postrecep¬ tor events by which insulin elicits its various metabolic actions within the cell, the genes encoding some of these signaling com¬ ponents will likely be found to be responsible for extreme tissue resistance to insulin in some cases. It also has been reported that some patients have high levels of an unidentified inhibitor of re¬ ceptor kinase activity.21 AUTOANTIBODIES

Severe insulin resistance also can be caused by several mechanisms apart from primary defects in cellular responsive¬ ness. One well-described mechanism involves the spontaneous development of circulating autoantibodies that recognize deter¬ minants in the insulin receptor molecule. Such antibodies affect insulin action through a direct inhibition of access to the insulin binding site, a desensitization of one or more steps subsequent to insulin binding, an acceleration of receptor degradation, or a combination thereof.

TABLE 140-3 Mechanisms for Extreme Target Cell Resistance to Insulin I. PRIMARY (GENETIC) TARGET CELL RESISTANCE TO INSULIN A. Defect intrinsic to the insulin receptor 1. Receptor gene mutations causing decreased number of membrane receptors a. Decreased receptor synthesis b. Increased receptor degradation 2. Receptor gene mutations causing qualitatively abnormal membrane receptors a. Decreased affinity of insulin binding b. Decreased signal transduction (i.e., autophosphorylation, coupling to other postreceptor components) B. Mutation in gene encoding signaling component other than insulin receptor C. Inhibition of insulin receptor function II. AUTOANTIBODIES TO INSULIN RECEPTOR A. Inhibition of insulin binding B. Postreceptor densensitization C. Accelerated receptor desensitization III. ACCELERATED INSULIN DEGRADATION IV. THEORETIC MECHANISMS NOT YET DEMONSTRATED TO CAUSE EXTREME INSULIN RESISTANCE A. Mutant insulin acting as competitive antagonist B. Nonantibody circulating antagonist (apart from known counterinsulin hormones)

ACCELERATED DEGRADATION

The biochemical basis for insulin degradation in vivo is im¬ perfectly understood. It is known that the in vivo clearance and subsequent degradation of circulating insulin is, to a large degree, a process that is mediated through the insulin receptor.22,23 Sev¬ eral proteolytic enzymes that may be responsible for hormonal degradation subsequent to receptor binding have been identified. Whether subcutaneously administered insulin is excessively de¬ graded by extracellular enzymes in some patients is uncertain, and the enzymes responsible for such an activity have not been identified. OTHER POTENTIAL MECHANISMS

Theoretically, a mutation in the insulin molecule might pro¬ duce a molecule that would have characteristics of a competitive antagonist. Mutant insulins have been described,16 but these have been weak agonists that have reduced receptor affinity, without the properties of a competitive antagonist (i.e., they have full bioactivity for any amount of receptor occupancy). However, because these species bind to receptors with low affinity and are poorly cleared from the circulation, these mutant insulins circu¬ late at high concentrations, and an insulin-resistant state can be mistakenly diagnosed. Unlike patients with true insulin-resistant states, patients with such mutant insulins are normally sensitive to exogenous insulin. The second potential mechanism would be a heretofore undescribed circulating factor (hormonal, metabolic) that might induce a state of insulin resistance. The observation that tumor necrosis factor a may be overproduced by adipocytes in obesity and may be capable of inducing insulin resistance is an example of such a mechanism.24,25

NATURE AND PATHOGENETIC BASIS FOR CLINICAL FEATURES COMMONLY ASSOCIATED WITH SEVERE INSULIN RESISTANCE Many patients with extreme target tissue resistance to insu¬ lin do not have overt diabetes. However, nearly all such patients do manifest one or more of a group of characteristic clinical fea¬ tures that suggest the existence of severe insulin resistance. These features include the skin lesion acanthosis nigricans, ovarian hyperandrogenism, accelerated or impaired linear growth, lipoatrophy/lipohypertrophy, and a variety of others (see Table 140-1). The molecular basis for the association of these features with se¬ vere tissue resistance to insulin is only partially understood, but the clinical importance of these associations is clear.

ACANTHOSIS NIGRICANS THE LESION

Acanthosis nigricans is a skin lesion characterized by brown, velvety, hyperkeratotic plaques, most often found in the axillae, the back of the neck, and other flexural areas26 (Fig. 140-2A). The condition ranges in severity from minimal cases with mild discol¬ oration of limited areas to extreme cases in which the entire sur¬ face of the skin may be heavily involved. The pathologic changes are found primarily in the epidermis. There is a complex folding (papillomatosis) of an overgrown epidermis that, although only slightly thickened, has an increased number of cells per unit sur¬ face area (see Fig. 140-2B). Other changes noted are hyperkera¬ tosis and an increase in the number of melanocytes, the lat¬ ter contributing to the darkened appearance (see Chaps 147 and 212). F CLINICAL ASSOCIATIONS

The clinical associations of acanthosis nigricans fall into two main groups: malignant neoplasms and insulin-resistant states.

Ch.140: Syndromes of Insulin Resistance

1253

FIGURE 140-2. A, Clinical appearance of acanthosis nigricans on the back of the neck. B, Photomicro¬ graph of acanthotic skin, revealing papillomatosis, increased keratin, and thickening of epidermis.

No feature of the skin lesion itself (i.e., the site or histologic ap¬ pearance) differentiates between these two groups. Acanthosis nigricans associated with insulin resistance appears to be more common than the form associated with internal malignancy. The lesion is found in all clinical conditions that are characterized by markedly reduced insulin action at the cellular level. These in¬ clude genetic defects in insulin action, antireceptor antibodyinduced insulin resistance, and the more common, and pathogenetically less well-defined, insulin-resistant states, such as those associated with obesity. The acanthosis that occasionally is pres¬ ent in various endocrinopathies (e.g., Cushing syndrome, acro¬ megaly) also may reflect the insulin resistance that is commonly present in these disorders.27 CELLULAR MECHANISMS

The precise mechanism responsible for the association be¬ tween tissue insulin resistance and acanthosis nigricans is un¬ known. Perhaps the skin lesions are caused by high levels of cir¬ culating insulin acting through receptors for IGF in the skin.26 Given the fact that various growth factors are produced by tumors,28 this hypothesis also could account for malignancyassociated acanthosis, if tumor oncogene products were able to activate IGF receptors in the skin. CLINICAL IMPLICATIONS

Because of an increased awareness of the association be¬ tween acanthosis and insulin resistance, this skin condition is be¬ ing recognized more often by internists, endocrinologists, and gynecologists; it is not as uncommon as previously thought. For example, it has been detected in as many as 10% of women being evaluated for polycystic ovary disease, none of whom had overt diabetes.29 Because multiple molecular defects, ranging from au¬ toimmune receptor antibodies to genetic abnormalities of recep¬ tor molecules and obesity, may be responsible for this lesion, the referral of patients with acanthosis nigricans for metabolic eval¬ uation should be considered. The possibility of a malignant tu¬ mor always should be raised, especially when the condition de¬ velops rapidly in an adult, although experience suggests that it is much less often a sign of a malignant neoplasm (see Chap. 213) than of an insulin-resistant state. The extent of a metabolic eval¬ uation should depend on the clinical context, including the pres¬ ence or absence of other clinical features of insulin resistance. The measurement of plasma glucose and insulin levels consti¬ tutes the minimum evaluation to determine the presence of insu¬ lin resistance in patients with acanthosis nigricans; if the glucose

and insulin levels are normal, an insulin-resistant state can be ruled out. Hyperinsulinemia, with or without hyperglycemia, is consistent with insulin resistance, and this finding should prompt further studies, such as attempts to detect circulating antiinsulin receptor antibodies or studies of insulin receptor expression and function using receptors expressed on circulating blood cells or cultured skin fibroblasts.

OVARIAN DYSFUNCTION Evidence from various sources suggests that insulin and IGFs are important regulators of ovarian function. Clinically, there is an association between hyperinsulinemic states of tis¬ sue insulin resistance and ovarian hyperandrogenism. Ovarian hyperandrogenism has been seen in a wide range of insulinresistant states, including genetic disorders of tissue resistance to insulin,30 autoimmune insulin receptor deficiency,30 a subset of patients with obesity and polycystic ovary disease in whom insu¬ lin resistance may have both genetic and nutritional compo¬ nents,29,31 and a much larger group of patients with typical poly¬ cystic ovary disease in whom a correlation between ambient insulin levels and the degree of hyperandrogenism has been de¬ fined.32'33 The breadth of this clinical association suggests that insulin may play a surprisingly pervasive role in the pathogenesis of these ovarian disorders.34,35 In further support of this notion, in vitro studies demonstrate that insulin and IGF both have spe¬ cific receptors in human ovarian cells36 37 and exert multiple effects on ovarian growth and steroidogenesis38 40 (see Chaps. 93 and 98). MECHANISM FOR THE ASSOCIATION

There are two major hypotheses for the association of ovar¬ ian hyperandrogenism and insulin resistance in these patient groups. The first views insulin as exerting its actions through IGF receptors in the ovary, a result of the extremely high levels of insulin that typically circulate in these patients. This explanation requires that IGF receptor pathways are normal, or at least less impaired than insulin receptor pathways, and this appears so in some patients. Alternatively, as has been observed for other met¬ abolic pathways (e.g., persistent antilipolysis, and the absence of ketosis despite marked hyperglycemia in patients with both genetic and immune-mediated insulin resistance), the action of insulin to promote events in the ovary through insulin receptors may be maintained despite the loss of action on pathways related to glucose homeostasis.

1254

PART IX: DISORDERS OF FUEL METABOLISM

PATHOLOGIC FINDINGS AND TREATMENT

Pathologic findings in the ovary are nonspecific, and range from typical findings of polycystic ovary disease to extreme cases of ovarian hyperthecosis. The latter is more prevalent in those patients with the greatest degrees of androgen overproduction. Testosterone levels in some of these patients are sufficiently high (> 200 ng/mL) to strongly suggest the existence of an androgenproducing tumor. In such situations, the documentation of insu¬ lin resistance should serve to markedly diminish this possibility. The treatment of ovarian hyperandrogenism in patients with insulin-resistant disorders is difficult. Women with clearly genetic syndromes of insulin resistance, in whom ovarian hyper¬ androgenism is often the most severe clinical complaint, have not responded to the usual therapies for polycystic ovary disease, including wedge resection. In a few patients, complete ovariec¬ tomy has been required, with consequent marked reduction in androgen levels and, as expected, no change in the insulin action defect. In patients with obesity and polycystic ovary disease, in whom the insulin resistance probably is multifactorial and less severe than in the foregoing group, it is prudent to recommend long-term caloric restriction. In several cases, this has caused im¬ provement in the insulin resistance as well as the acanthosis nigricans and hyperandrogenism.29 Finally, in patients with ovarian hyperandrogenism and insulin resistance caused by anti¬ insulin receptor antibodies, the ovarian lesion should remit when antireceptor antibodies disappear, whether spontaneously or be¬ cause of immunosuppressive therapy.

SPECIFIC SYNDROMES OF EXTREME INSULIN RESISTANCE THE SYNDROME OF INSULIN RESISTANCE CAUSED BY AUTOANTIBODIES TO THE INSULIN RECEPTOR (TYPE B INSULIN RESISTANCE) CLINICAL FEATURES

The existence of insulin receptor autoantibodies was first documented during the evaluation of three patients who exhib¬ ited extremely insulin-resistant diabetes and acanthosis nigri¬ cans. 0 At least 30 additional patients have been described since. As is often found in autoimmune disease, the condition is more common in women. Cases have been recorded in various ethnic groups, including Japanese and Mexican, but most cases have been among blacks. The mean age of first diagnosis is between 30 and 40 years, but the diagnosis has been made as early as 12 years and as late as 78 years. Acanthosis nigricans is a character¬ istic feature, but the skin lesion occasionally has been absent. The most common clinical presentation is symptomatic dia¬ betes, marked by symptoms of polyuria, polydipsia, and weight loss. Although plasma glucose values have varied, levels higher than 300 mg/dL have been common. However, ketoacidosis is generally absent or mild. Resistance to exogenous insulin therapy is the hallmark of the disease, and this typically is noted to be present at the time of initial insulin use (unlike the insulin resis¬ tance caused by autoantibodies to insulin). The extent of the in¬ sulin resistance is indicated by the marked endogenous hyperinsulinemia, and by the fact that individual patients have failed to respond to insulin in dosages as high as 100,000 U/d. In these circumstances, patients may hot derive any benefit from contin¬ ued insulin therapy. A few patients have only mild glucose intol¬ erance and, in a small subgroup, preexisting insulin-resistant di¬ abetes may be followed by a phase of severe hypoglycemia.41 In other patients, in whom diabetes or glucose intolerance never developed, autoantibodies to the insulin receptor have caused hypoglycemia.42 CLINICAL COURSE AND THERAPY

Over several years of follow-up, patients with this syndrome have had various outcomes. The spontaneous remission of insu¬

lin resistance with disappearance of receptor antibodies has been documented in a few patients.41 In another group, diabetes and severe insulin resistance have persisted for several years, and in¬ sulin therapy apparently has been of little or no benefit. Patients with marked hyperglycemia and refractory severe insulin resis¬ tance have been treated with various experimental regimens. These have included glucocorticoids,41 antimetabolites, and plasma exchange.43 Given the fluctuating course in the absence of therapy, and the few patients studied, it has been difficult to obtain a strong indication of the degree to which these therapies have been effective. At least 3 of 30 reported cases have died while suffering from spontaneous hypoglycemia after a prior di¬ abetic phase, and although the pathogenetic basis for this transi¬ tion has not been elucidated, there appears to be a significant risk for the development of hypoglycemia among those who have this condition. AUTOIMMUNE FEATURES

Patients with autoantibodies to the insulin receptor charac¬ teristically also have symptoms or laboratory test results indica¬ tive of more widespread autoimmune disease (e.g., leukopenia [> 80%], antinuclear antibodies [> 80%], elevated sedimentation rate [> 80%], elevated serum IgG [> 80%], proteinuria [50%], alopecia [36%], nephritis [30%], hypocomplementemia [29%], arthritis [20%], and vitiligo [14%]).44 Prominent among these are alopecia, vitiligo, arthralgias and arthritis, Raynaud phenomena, enlarged salivary glands, elevated sedimentation rate, leukope¬ nia, hypergammaglobulinemia, and a positive antinuclear anti¬ body test result. About one third of patients meet the established criteria for systemic lupus erythematosus, Sjogren's syndrome, or some other distinct autoimmune entity. Among those patients with systemic lupus, lupus nephritis has been seen. Premeno¬ pausal women with insulin receptor autoantibodies may have ovarian hyperandrogenism of a type similar to that observed in patients with other syndromes of extreme tissue resistance to insulin. CHARACTERISTICS OF ANTIBODIES TO THE INSULIN RECEPTOR

The extent of insulin binding to receptors on circulating monocytes of these individuals is markedly reduced and of low affinity, and sera from affected patients can reproduce these findings when exposed to normal insulin receptors in vitro.45 The inhibitory capacity of these sera is due to antibodies, predomi¬ nantly IgG,46 that bind to the insulin receptor molecule and sterically hinder insulin binding. The antibodies also can precipitate insulin receptors from solution. Titers vary over a wide range and have been extremely high in some individuals, typically those with the greatest insulin resistance. Antibodies from these pa¬ tients inhibit insulin binding to insulin receptors from a wide va¬ riety of target tissues and a broad range of animal species, sug¬ gesting interaction with a highly conserved region of the receptor molecule. Indeed, a conserved epitope in the insulin receptor a subunit has been identified as the site of antibody binding in most cases.47 The antibodies have been polyclonal, and individual populations of antibodies in some sera may show some degree of specificity for receptors on a given target tissue. Essentially, all sera from affected patients have proved capable of inhibiting in¬ sulin binding to the insulin receptor, although sensitive assays based on the ability to precipitate receptors from solution have been designed. The existence of precipitating antibodies that do not inhibit binding is reported to occur,48 as seen in myasthenia gravis, in which antibodies to acetylcholine receptors of this type are the predominant antibody species. Antibodies from some pa¬ tients also can inhibit IGF-I binding to its closely related receptor, although the functional significance of these antibodies is unknown. The ability of antibodies to bind to the insulin receptor and inhibit insulin binding provides an explanation for the reduced

Ch.140: Syndromes of Insulin Resistance

1255

insulin binding and the observed insulin resistance. However, studies of the bioactivity of these antibodies in vitro are more complex. Sudden exposure of cells to antireceptor immunoglob¬ ulins elicits a wide range of insulin-like effects.49 This finding raises a potential paradox between in vitro and in vivo observa¬ tions. A partial resolution of this paradox has come from in vitro studies in which the insulin-mimetic effects are seen to be tran¬ sient, followed by insulin resistance. The latter is due to postre¬ ceptor desensitization of some step that is subsequent to insulin binding, as well as to an enhanced rate of receptor degradation.50 A persistent insulin-like action of these antibodies may account for the hypoglycemia that occurs during the course of the illness in some of these patients, but so far, in vitro examination of the antibodies from hyperglycemic or hypoglycemic patients has not provided an explanation for these differences. The passive transfer of antibodies obtained from one patient to rabbits has caused an insulin-resistant phenotype with postprandial hyper¬ glycemia.51 However, animals so treated also have a tendency to fasting hypoglycemia, and this probably is a reflection of persis¬ tent insulin-like properties of the antibodies.

cular. Excessive muscular development may be due in part to hy¬ perandrogenism, but it also may be due to the effects of nigh plasma concentrations of insulin, possibly acting through IGF-I receptors in muscle. Some patients have had acral enlargement, most notably involving the hands, as well as coarsening of the facial features (Fig. 140-3). A role for insulin, acting through both insulin and IGF-I receptors that are unable to signal increased glucose uptake, but are capable of stimulating other pathways, has been suggested as a cause of this "pseudoacromegaly" in one well studied patient.53 The acanthosis nigricans has ranged from mild to moderately severe, and usually does not develop before the age of 7 to 10 years. Ovarian hyperandrogenism ranges from moderate to severe, and has tended to be refractory to all the usual therapeutic modalities. Pathologic examination of ovarian tissue in a few individuals has shown ovarian hyperthecosis and stromal hyperplasia.54 In one patient, complete ovariectomy with a resultant fall in androgen levels did not yield any change in insulin sensitivity or insulin receptor status. The relationship of this disorder to the more common clinical group with obesity and hyperandrogenism was discussed earlier.

THE TYPE A SYNDROME OF INSULIN RESISTANCE AND ITS VARIANTS

CLINICAL PHYSIOLOGY

CLINICAL FEATURES

The initial description of the type A syndrome of insulin re¬ sistance involved three peripubertal, thin women with carbohy¬ drate intolerance or overt diabetes, hyperandrogenism, acantho¬ sis nigricans, and severe target cell resistance to insulin.30 Subsequent patients have had insulin-resistant diabetes, but usu¬ ally were first seen for evaluation of signs and symptoms of marked hyperandrogenism, acanthosis nigricans, or both. Typi¬ cally, glucose tolerance in these patients is mildly impaired or even normal. Although patients typically are first seen at about the age of expected puberty, some cases have been discovered much later in life, and when younger siblings of affected patients have been evaluated, insulin resistance has been found at sub¬ stantially younger ages. Insulin resistance has been observed in a brother of an affected female proband, indicating that the disor¬ der can occur in men, and that androgen excess is not required for the development of insulin resistance.52 However, the apparent absence of hyperandrogenism in affected men removes one of the major presenting complaints in this disorder, and an accurate prevalence in both men and women is unknown. Body Habitus. The body habitus of these patients is note¬ worthy. Some patients are thin and others are remarkably mus¬

Relatively little information is available on the clinical phys¬ iologic function of these patients. The use of euglycemic insulin clamps in several patients has disclosed a severely impaired abil¬ ity of insulin to promote glucose utilization as well as a marked defect in insulin clearance.23 The latter probably arises because receptor-mediated pathways play an important role in the clear¬ ance of insulin. INSULIN ACTION AT THE CELLULAR LEVEL

Insulin action at the cellular level has been studied inten¬ sively in a few patients with these syndromes. Although it was anticipated that the clinical phenotypes seen in individual pa¬ tients with distinct insulin-resistant syndromes each would be associated with a unique abnormality at the level of the target cell, our current molecular understanding of these syndromes has not yet provided such a correlation. Three patients with distinct insulin-resistant syndromes have been shown to have different mutations in the insulin receptor gene.55-57 Studies of insulin action have involved insulin receptor binding on various cell types, studies of the insulin receptor ki¬ nase, and studies of insulin action on classic biochemical path¬ ways. Insulin binding studies can be divided into two types: those performed with freshly obtained cells (most commonly

1256

PART IX: DISORDERS OF FUEL METABOLISM

monocytes58 and red cells,59 but occasionally adipocytes), and those performed with cultured cells. Studies with fresh cells most closely reflect the in vivo milieu, and studies with cultured skin fibroblasts60,61 or Epstein-Barr virus-transformed lymphoblasts62 permit an assessment of the genetic component of the defect. At the level of insulin receptor binding, three categories of abnor¬ malities have been observed: a markedly reduced number of in¬ sulin receptors that are otherwise normal in affinity; receptors that bind insulin with altered affinity; and receptors that are nor¬ mal in both number and affinity of insulin binding. The latter group may be the most common variety. With the discovery that the insulin receptor is a tyrosine pro¬ tein kinase that is autophosphorylated when insulin binds, the kinase function of the insulin receptor in these patients became the subject of intense scrutiny. Studies have been performed in circulating monocytes and erythrocytes,59 as well as in cultured fibroblasts61 and Epstein-Barr virus-transformed lymphoblasts.63 As expected, patients with markedly decreased binding have de¬ creased kinase activity. More interesting is that several patients with normal binding have reduced kinase activity, suggesting a role for this biochemical function in transduction of the insulin signal.61,64 The normalcy of insulin binding and kinase activity in other patients is consistent with a defect that is truly beyond the level of the insulin receptor. Genetic studies have revealed that many patients with the type A syndrome have mutations at the insulin receptor gene locus that typically alter the expression or function of one al¬ lele.1819 These disorders often are inherited in a genetically dominant fashion. In other phenotypically similar patients, per¬ haps most of those with the type A syndrome, receptor mutations have not been identified, and the genetic cause remains unknown.65 Studies of insulin action in freshly isolated adipocytes or cul¬ tured fibroblasts of these patients are limited. Defects in insulinstimulated glucose transport or utilization have been demon-

strated,66 but limited data are available on other pathways of insulin or of IGF action.

LEPRECHAUNISM Leprechaunism is a rare inherited disease characterized by an unusual facial appearance (Fig. 140-4), intrauterine and post¬ natal growth retardation, sparse subcutaneous fat, hirsutism, clitoromegaly, and early death.67 Patients have various abnormali¬ ties of glucose homeostasis, most commonly displaying fasting hypoglycemia associated with B-cell hypertrophy and marked endogenous hyperinsulinemia. Cultured cells from several pa¬ tients have shown heterogeneous abnormalities of insulin ac¬ tion,68 insulin receptor binding,69 and insulin receptor function, as well as defects in IGF-I receptor pathways.68 All patients stud¬ ied to date have had mutations affecting the expression or func¬ tion of both alleles of the insulin receptor gene,19 and patients with no functional insulin receptors have been described.

LIPODYSTROPHIC STATES The lipodystrophic states are a phenotypically diverse group of syndromes characterized by either complete or partial lack of adipose tissue, often severe abnormalities of carbohydrate and lipid metabolism, and various associated somatic features. The disorders are considered here because of their frequent coexis¬ tence with severe tissue resistance to insulin, as well as a spec¬ trum of clinical features that overlap with those seen in other syndromes of severe insulin resistance. CLINICAL FEATURES

Classically, the lipodystrophic disorders have been divided into those that are congenital and those that are acquired, both of which are rare70 (Table 140-4). Congenital Forms. In its congenital form, the lipoatrophy may be generalized (transmitted as an autosomal recessive trait) or partial (transmitted as an autosomal dominant trait). The con¬ genital partial lipodystrophies include a form with lipoatrophy that spares the face, as well as a form with truncal and proximal extremity lipoatrophy but distal extremity and facial lipohypertrophy (Fig. 140-5). More than 40 cases of the congenital total lipoatrophy syndrome (also known as the Berardinelli-Seip syn¬ drome) have been described.71 Parental consanguinity is high in these patients, in whom the disease occurs equally in males and females; it usually is diagnosed at birth or within the first 2 years. Patients have accelerated linear growth, accelerated genital mat¬ uration, muscle hypertrophy, and cerebral pathology, as well as various other congenital defects (Table 140-5). Insulin resistance, as assessed by elevated fasting insulin levels, develops or be¬ comes manifest between the ages of 6 and 9 years, and this pre¬ cedes the development of diabetes by several years. Hepatic cir¬ rhosis, which develops in the context of fatty liver, is a major cause of morbidity and mortality.

TABLE 140-4 Classification of Lipodystrophic Disorders CONGENITAL LIPODYSTROPHY Total lipoatrophy Partial lipoatrophy Face sparing Distal sparing ACQUIRED LIPODYSTROPHY Total lipoatrophy Partial lipoatrophy FIGURE 140-4. A neonate with leprechaunism, displaying characteris¬ tic facies and muscle wasting.

Upper atrophy-lower hypertrophy Dermatome pattern

Ch.140: Syndromes of Insulin Resistance

FIGURE 140-5. Posterior view of a patient with distal extremity lipohypertrophy and proximal extremity and truncal lipodystrophy.

Acquired Forms. Lipoatrophy also can be either total or par¬ tial. Acquired total lipoatrophy is not known to be inherited, and can first develop in childhood or adulthood (Fig. 140-6). Typi¬ cally, lipoatrophy develops rapidly over days or weeks, and may be noted to be preceded by an acute infectious illness. Although alterations in linear growth rate usually are not found in this dis¬ order, the other associated features typical of congenital lipoatro¬ phy are commonly seen, including insulin-resistant diabetes, ac¬ anthosis nigricans, muscle hypertrophy, hepatic cirrhosis, and increased metabolic rate. The acquired syndrome of upper body lipoatrophy with lower body lipohypertrophy, seen almost ex-

1257

FIGURE 140-6. A patient with acquired total lipoatrophy, accompanied by muscular hypertrophy, cirrhosis, and characteristic curly hair.

clusively in women, is associated with recurrent infections and glomerulonephritis (Fig. 140-7). Several of these patients have a distinct alteration in complement metabolism, with accelerated catabolism of C3.72 The mechanistic link between this defect and the lipoatrophy remains an enigma.

TABLE 140-5 Clinical Features of Patients With Lipodystrophic Disorders Lipodystrophy Metabolic dysfunction Altered glucose homeostasis: hyperglycemia, no ketosis Insulin resistance: endogenous, exogenous Hypertriglyceridemia Hypermetabolism: increased metabolic rate Acanthosis nigricans Accelerated linear growth, acromegaloid features Muscle hypertrophy, phlebomegaly, genital hypertrophy Hepatomegaly: fatty liver, cirrhosis Hypertrichosis, hirsutism Cardiomegaly: idiopathic hypertrophic subaortic stenosis (IHSS), also termed asymmetric septal hypertrophy (ASH) Miscellaneous Mental retardation, central nervous system dysfunction Cystic angiomatosis of bone

FIGURE 140-7. A patient with acquired partial (face and upper extrem¬ ity) lipoatrophy with hypocomplementemic nephritis.

1258

PART IX: DISORDERS OF FUEL METABOLISM

INSULIN RESISTANCE IN LIPODYSTROPHIC STATES

The pathogenesis of the insulin resistance in lipoatrophic di¬ abetes is poorly understood, and efforts to define it are compli¬ cated by the marked heterogeneity within this group of disorders. As in the type A and B syndromes of insulin resistance, initial efforts to understand the lipodystrophic states have focused on the insulin receptor. These studies have yielded mixed results and no clear insight into either the mechanisms responsible for the insulin-resistant state or its association with lipoatrophy. Studies of cultured fibroblasts obtained from patients with con¬ genital total lipoatrophy have shown either a modest reduction in insulin binding or normal insulin binding characteristics.73,74 Likewise, studies of insulin receptors on circulating monocytes and erythrocytes have yielded heterogeneous results, including normal binding, decreased binding associated with a reduced number of receptors, and reductions in receptor affinity.75 To fur¬ ther complicate our understanding, affected persons within the same family have shown different patterns of insulin binding, suggesting that the observed receptor abnormalities may be sec¬ ondary to other unknown abnormalities. Patients studied to date have not had mutations affecting the insulin receptor gene.65

SUBCUTANEOUS INSULIN DEGRADATION SYNDROME Among insulin-treated diabetics, a subgroup has been de¬ scribed in whom the subcutaneous administration of insulin in high doses is ineffective, whereas insulin administered by the in¬ travenous route produces a normal response.76 A role for subcu¬ taneous insulin degrading activity in the etiology of this syn¬ drome is suggested both by direct assay of such activity in subcutaneous tissue and by the therapeutic response observed when insulin is coinjected with the protease inhibitor aprotinin (Trasylol). Other causes for insulin resistance have been excluded in such patients, some of whom apparently have required pro¬ longed administration of insulin by the intravenous route. The course is one of spontaneous exacerbations and remissions. The initial patient with this syndrome was extremely well docu¬ mented. However, in a follow-up study of 20 patients referred for evaluation of this entity, subcutaneous insulin degradation could not be documented.77 Instead, these patients had problems with compliance or other emotional problems responsible for their problem with insulin therapy. Thus, such problems should be evaluated carefully in patients referred for evaluation of resis¬ tance to subcutaneous insulin with sensitivity to intravenous insulin.

REFERENCES 1. Kahn CR, Baird KL, Flier JS, et al. Insulin receptors, receptor antibodies, and the mechanism of insulin action. Recent Prog Horm Res 1981; 37:477 2. Froesch ER, Schmid C, Schwander J, Zapf J. Actions of insulin-like growth factors. Annu Rev Physiol 1985;47:443. 3. Rechler MM, Nissley SP. The nature and regulation of the receptors for insulin-like growth factors. Annu Rev Med 1985;47:425. 4 F^ychet P, Roth J, Neville DM Jr. Insulin receptors in the liver: specific binding of I-insulin to the plasma membrane and its relation to insulin bioactivitv Proc Natl Acad Sci USA 1971; 68:11833. 5. Ullrich A, Bell JR, Chen EY, et al. Human insulin receptor and its relation¬ ship to the tyrosine kinase family of oncogenes. Nature 1985,-313:756. 6. Goldfine ID. The insulin receptor: molecular biology and transmembrane signalling. Endocr Rev 1987;8:235. 7. Czech M. The nature and regulation of the insulin receptor: structure and function. Annu Rev Physiol 1985;57:357. 8. Moller DE, Caro JF, Flier JS. Tissue specific expression of two alternatively spliced insulin receptor mRNA's in man. Mol Endocrinol 1989; 3:1263.

9 Yamaguchi Y, Flier JS, Benecke H, et al. Ligand binding properties of the two isoforms of the human insulin receptor. Endocrinology 1993; 132:1132 10. Kasuga M, Fujita-Yamaguchi Y, Blithe DL, et al. Tyrosine specific protein

receptor concentrations: a direct demonstration in cell culture. Proc Natl Acad Sci USA 1974;71:84. 13. Bar RS, Gorden P, Roth J, Kahn CR. Fluctuations in the affinity and con¬ centration of insulin receptors on circulating monocytes of obese patients I Clin Invest 1977;58:1123. 14. Grunberger G, Taylor SI, Doris RF, Gorden P. Insulin receptors in normal and disease states. J Clin Endocrinol Metab 1983; 12:191. 15. Reaven GM. Role of insulin resistance in human disease Diabetes 1988;37:1495. 16. Haneda M, Polonsky KS, Tager HS, et al. Familial hyperinsulinemia due to a structurally abnormal insulin: definition of an emerging new clinical syndrome N Engl J Med 1984; 310:1288. 17. DeFronzo RA, Tobin JD, Andres R. Glucose clamp technique: a method for quantifying insulin secretion and resistance. Am J Physiol 1979;237:E214. 18. Flier JS. Syndromes of insulin resistance: mechanisms, syndromes and implications. N Engl J Med 1991; 325:935. 19. Taylor SI. Lilly Lecture: molecular mechanisms of insulin resistance. Les¬ sons from patients with mutations in the insulin-receptor gene Diabetes 1992-411473. 20. O Brien TD, Rizza RA, Carney JA, Butler PC. Islet amyloidosis in a patient with chronic massive insulin resistance due to antiinsulin receptor antibodies, f Clin Endocrinol Metab 1994;79:290. 21. Maddux BA, Sbraccia P, Reaven GM, et al. Inhibitors of insulin receptor tyrosine kinase in fibroblasts from diverse patients with impaired insulin action: evidence for a novel mechanism of postreceptor insulin resistance. J Clin Endocrinol Metab 1993; 77:73. 22. Zeleznik AJ, Roth J. Demonstration of the insulin receptor in vivo in rab¬ bits and its possible role as a reservoir for plasma hormone. J Clin Invest 1978; 61: 1363. 23. Flier JS, Minaker KL, Landsberg L, et al. Impaired in vivo insulin clearance in patients with target cell resistance to insulin. Diabetes 1982;31:132. 24. Spiegelman BM, Hotamisligil GS. Through thick and thin: wasting obe¬ sity, and TNF alpha. Cell 1993; 73:625. 25. Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of tu¬ mor necrosis factor-alpha: direct role in obesity-linked insulin resistance Science 1993;259:87. zt>. t-uer jb. the metabolic importance of acanthosis nigricans. Arch Dermatol 1985; 121:193. 27. Ober KP. Acanthosis nigricans and insulin resistance associated with hy¬ pothyroidism. Arch Dermatol 1985,121:229. 28. Bishop JM. The molecular genetics of cancer. Science 1987,-235:305. 29. Flier JS, Eastman RC, Minaker KL, et al. Acanthosis nigricans in obese women with hyperandrogenism: characterization of an insulin-resistant state dis¬ tinct from the type A and type B syndromes. Diabetes 1985;34:101. 30. Kahn CR, Flier JS, Bar RS, et al. The syndromes of insulin resistance and acanthosis nigricans: insulin receptor disorders in man. N Engl J Med 1976; 294:739. 31. Peters EJ, Stuart CA, Prince MJ. Acanthosis nigricans and obesity: ac¬ quired and intrinsic defects in insulin action. Metabolism 1986;35:807. 32. Chang RJ, Nakamura RM, Judd HI, Kaplan SA. Insulin resistance in nonobese patients with polycystic ovarian disease. J Clin Endocrinol Metab 1983;57: 33. Poretsky L, Kalin MF. The gonadotropic function of insulin. Endocr Rev 1987;8:132. 34. Poretsky L. On the paradox of insulin-induced hyperandrogenism in in¬ sulin resistant states. Endocr Rev 1991; 12:3. 35. Dunaif A. Insulin resistance and ovarian dysfunction in insulin resistance. In: Moller D, ed. Insulin resistance. New York, John Wiley & Sons, 1993:301. 36. Poretsky L, Grigorescu F, Seibel M, et al. Distribution and characterization of insulin and insulin-like growth factor I (IGF-I) receptors in normal human ovary J Clin Endocrinol Metab 1985;61:728. 37. Adashi EY, Resnick CE, Hernandez ER, et al. Characterization and regu¬ lation of a specific cell membrane receptor for somatomedin-C insulin-like growth factor I in cultured rat granulosa cells. Endocrinology 1988; 122:194. 38. Veldhuis JD, Kolp LA, Toaff ME, et al. Mechanisms subserving the trophic actions of insulin on ovarian cells. J Clin Invest 1983; 72:1046. 39. Veldhuis JD, Nestler JE, Strauss JF III. The insulin-like growth factor somatomedin-C, modulates low density lipoprotein metabolism by swine granulosa cells. J Endocrinol 1987; 113:21. 40. Veldhuis JD, Rodgers RJ. Mechanisms subserving the steroidogenic syn¬ ergism between follicle-stimulating hormone and insulin-like growth factor I (so¬ matomedin C). Alterations in cellular sterol metabolism in swine granulosa cells I BioIChem 1987;262:7658. 41. Flier JS, Bar RS, Muggeo M, et al. The evolving clinical course of patients with insulin receptor antibodies: spontaneous remission or receptor proliferation with hypoglycemia. J Clin Endocrinol Metab 1978; 47:985. „ 42:Ja/lor SI' Grunberger G, Marcus-Samuels B. Hypoglycemia associated with antibodies to the insulin receptor. N Engl J Med 1982; 307:1422 43. Muggeo M, Flier JS, Abrams RA, et al. Treatment by plasma exchange of a patient with autoantibodies to the insulin receptor. N Engl J Med 1979; 300:477 44. Tsokos GC, Gorden P, Antonovych T, et al. Lupus nephritis and other autoimmune features in patients with diabetes mellitus due to autoantibody to in¬ sulin receptors. Ann Intern Med 1985; 102:176. 4'i, Pber H Kahn CR, Roth J, Bar RS. Antibodies that impair insulin receptor

USA 19a8C3V80y21lS37SSOClated ^ ^ pUrified insulin recePtor- Proc Natl Acad Sci

1975ni90n63n UnUSUal diabetic Wndrome with severe insulin resistance. Science

11. Myers MG, White MF. The new element of insulin signalling: insulin re¬ ceptor substrate-1 and proteins with SH2 domains. Diabetes 1993;42:643. 12. Gavin JR III, Roth J, Neville DM Jr. Insulin dependent regulation of insulin

46. Flier JS, Kahn CR, Jarrett DB, Roth J. Characterization of antibodies to the insulin receptor: a cause of insulin resistant diabetes in man. J Clin Invest 1976;58:

Ch. 141: Cardiovascular Complications of Diabetes 47. Zhang B, Roth RA. A region of the insulin receptor important for ligand binding (residues 450-601) is recognized by patients' autoimmune antibodies and inhibitory monoclonal antibodies. Proc Natl Acad Sci USA 1991;88:9858. 48. Bloise W, Wajchenberg BL, Moncada VY, et al. Atypical antiinsulin anti¬ bodies in a patient with type B insulin resistance and scleroderma. J Clin Endocrinol Metab 1989; 68:227. 49. Kahn CR, Baird KL, Flier JS, Jarrett DB. Effect of anti-insulin receptor an¬ tibodies on isolated adipocytes. J Clin Invest 1977;60:1094. 50. Taylor SI, Marcus-Samuels B. Anti-receptor antibodies mimic the effect of insulin to down regulate insulin receptors in cultured human lymphoblastoid cells. J Clin Endocrinol Metab 1984;58:182. 51. Dons RF, Havlik R, Taylor SI, et al. Clinical disorders associated with autoantibodies to the insulin receptor. Stimulation by passive transfer of immuno¬ globulins to rats. J Clin Invest 1983; 72:1072. 52. Flier JS, Young JB, Landsberg L. Familial insulin resistance with acanthosis nigricans, acral hypertrophy and muscle cramps: a new syndrome. N Engl J Med 1980; 390:970. 53. Flier JS, Moller DE, Moses AC, et al. Insulin-mediated pseudoacromegaly: clinical and biochemical characterization of a syndrome of selective insulin resis¬ tance. J Clin Endocrinol Metab 1993; 76:1533. 54. Flier JS. Virilization and hyperpigmentation in a 15 year old girl. N Engl J Med 1982;306:1537. 55. Kadowski T, Bevins CL, Cama A, et al. Two mutant alleles of the insulin receptor gene in a patient with extreme insulin resistance. Science 1988; 240:787. 56. Yoshimasa Y, Seino S, Whittaker J, et al. Insulin-resistant diabetes due to a point mutation that prevents proreceptor processing. Science 1988; 240:784. 57. Moller DE, Flier JS. Detection of an alteration in the insulin-receptor gene in a patient with insulin resistance, acanthosis nigricans, and the polycystic ovary syndrome. N Engl J Med 1988;319:1526. 58. Bar RS, Muggeo M, Kahn CR, et al. Characterization of the insulin receptor in patients with syndromes of insulin resistance and acanthosis nigricans. Diabetologia 1980; 18:209. 59. Grigorescu F, Flier JS, Kahn CR. Characterization of binding and phos¬ phorylation defects of insulin receptors in the type A syndrome of insulin resistance. Diabetes 1986;35:127. 60. Podskalny JM, Kahn CR. Cell culture studies on patients with extreme insulin resistance. I. Receptor defects on cultured fibroblasts. J Clin Endocrinol Metab 1982;54:261. 61. Grigorescu F, Flier JS, Kahn CR. Defect in insulin receptor phosphoryla¬ tion in erythrocytes and fibroblasts associated with severe insulin resistance. J Biol Chem 1984;259:15003. 62. Taylor SI, Samuels B, Roth J. Decreased insulin binding in cultured lym¬ phocytes from two patients with extreme insulin resistance. J Clin Endocrinol Metab 1982; 54:919. 63. Whittaker J, Zick Y, Roth J, Taylor SI. Insulin-stimulated receptor phos¬ phorylation appears normal in cultured Epstein-Barr virus-transformed lymphocyte cell lines derived from patients with extreme insulin resistance. J Clin Endocrinol Metab 1985;60:381. 64. Grunberger G, Zick Y, Gorden P. Defect in phosphorylation of insulin receptors in cells from an insulin-resistant patient with normal insulin binding. Sci¬ ence 1984;223:932. 65. Moller DE, Cohen O, Yamaguchi Y, et al. Prevalence of mutations, in the insulin receptor gene in subjects with features of the type A syndrome of insulin resistance. Diabetes 1994; 43:247. 66. Podskalny JM, Kahn CR. Cell culture studies on patients with extreme insulin resistance. II. Abnormal biological responses in cultured fibroblasts. J Clin Endocrinol Metab 1982;54:269. 67. Donohue WL, Uchida I. Leprechaunism: a euphemism for a rare familial disorder. J Pediatr 1954; 45:505. 68. Knight AB, Rechler MM, Romanus JA, et al. Stimulation of glucose incor¬ poration and amino acid transport by insulin and an insulin-like growth factor in fibroblasts with defective insulin receptors cultured from a patient with lepre¬ chaunism. Proc Natl Acad Sci USA 1981; 78:2554. 69. Taylor SI, Roth J, Blizzard RM, Elders MJ. Qualitative abnormalities in insulin binding in a patient with extreme insulin resistance: decreased sensitivity to alterations in temperature and pH. Proc Natl Acad Sci USA 1981;76:7157. 70. Senior B, Gellis SS. The syndromes of total and partial lipodystrophy. Pediatrics 1964; 33:593. 71. Seip M, Trygstad O. Generalized lipodystrophy. Arch Dis Child 1963; 38: 447. 72. Sisson JG. The complement abnormalities of lipodystrophy. N Engl J Med 1976:294:461. 73. Oseid S. Decreased binding of insulin to its receptor in patients with con¬ genital generalized lipodystrophy. N Engl J Med 1977;296:245. 74. Rosenbloom AL. Normal insulin binding to cultured fibroblasts from pa¬ tients with lipoatrophic diabetes. J Clin Endocrinol Metab 1977; 44:803. 75. Wachslicht-Rodbard H, Muggeo M, Kahn CR, et al. Heterogeneity of the insulin-receptor interaction in lipoatrophic diabetes. J Clin Endocrinol Metab 1981; 52:416. 76. Freidenberg GR, White N, Cataland S, et al. Diabetes response to intrave¬ nous but not subcutaneous effectiveness of aprotinin. N Engl J Med 1981; 305:363. 77. Schade DS, Duckworth WC. In search of the subcutaneous-insulinresistance syndrome. N Engl J Med 1986;315:147.

1259

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

141_

CARDIOVASCULAR COMPLICATIONS OF DIABETES GEORGE L. KING AND EDWARD J. KOSINSKI

Diabetic macrovascular complications include both cardiac and peripheral vascular disease. The major pathogenic process underlying these disease categories is atherosclerosis,1-5 which accounts for most of the mortality in the diabetic popula¬ tion; in addition, a cardiomyopathy has also been ascribed to diabetes.6-8 When matched for other variables, atherosclerosis tends to occur at an earlier age and with greater severity in diabetic pa¬ tients than in the nondiabetic population. There is at least a two¬ fold increase in the incidence of myocardial infarction and a four¬ fold increase of intermittent claudication and gangrene of the lower extremities1,2,9 (Table 141-1). Being a diabetic patient sub¬ stantially eliminates the relative protection from atherosclerosis possessed by the premenopausal woman (Fig. 141-1). There is also an increased tendency toward cerebral thrombosis and in¬ farction in diabetics, but not of cerebral hemorrhage (see Table 141-1). The reasons for the accelerated atherosclerosis and for the cardiomyopathy in diabetic patients are unclear, although nu¬ merous mechanisms have been proposed. In this chapter the au¬ thors review the abnormal metabolic factors that may contribute to these cardiovascular processes in diabetes and discuss the clin¬ ical aspects of cardiovascular disease.

PATHOLOGY AND ETIOLOGY OF DIABETIC MACROANGIOPATHY The principal pathologic process encountered in diabetic macroangiopathy is atherosclerosis, which is similar to that found in nondiabetic populations (i.e., fatty streaks, fibrocellular plaques and ulcerations, thrombosis, and calcifications).1-3 9 In diabetic patients there is a particular predisposition for involve¬ ment of the arteries below the knee: the tibial and peroneal ves¬ sels.10-12 Not uncommonly, this pattern of pathology leads to a fairly specific finding on physical examination: normal popliteal but absent pedal pulses. Distinctive differences in the pathology of the vascular lesions between type I and type II diabetes are not found. An occasional finding in some diabetic patients is the occurrence of linear calcifications in the media of arteries of the lower limbs13'14; this is distinct from the spotty distribution com¬ monly seen in atherosclerosis. The risk factors for atherosclerosis in diabetic patients are multiple, and most are similar to those in the nondiabetic popu¬ lation. A detailed summary of this and other aspects of athero¬ sclerosis are reviewed elsewhere.5'15-20 A well-known hypothesis for the development of atherosclerosis is the "response-toinjury" theory. To summarize briefly, in diabetes, the endothe¬ lial cells lining the arterial intima are exposed to many different physical and chemical injuries, such as hypertension,21 hyper¬ cholesterolemia,22'23 and, possibly, hyperglycemia.24-2” Repeated or chronic injury to the endothelium leads to complex interac¬ tions between the endothelial cells and the circulatory elements, such as platelets, macrophages, and growth factors, resulting in the gradual accumulation of smooth-muscle cells, connective tis-

1260

PART IX: DISORDERS OF FUEL METABOLISM TABLE 141-1 Predisposition to Cardiovascular Events* in Diabetes Mellitus Men

Women

Diabetic

Nondiabetic

Diabetic

Nondiabetic

Cardiovascular disease

39.1

19.1

27.2

10.2

Cardiovascular disease death

17.4

8.5

17.0

3.6

Congestive heart failure

7.6

3.5

11.4

2.2

Intermittent claudication

12.6

3.3

8.4

1.3

4.7

1.9

6.2

1.7

24.8

14.9

17.8

6.9

Atherothrombotic brain infarction Coronary heart disease

* Average annual age-adjusted incidence per 1000. ( ata from Kannel WB, McGee DL. Diabetes and cardiovascular disease: the Framingham study. JAMA 1979;241:2035 )

sue matrix, and lipid in both the intima and media; this contri¬ butes to the narrowing of the vessel lumen and rheologic abnor¬ malities that eventually can lead to the complete occlusion of the lumen. The earliest lesions seen are fatty streaks in focal areas of the intima, characterized microscopically by the presence of macro¬ phages, lipid, and smooth-muscle cells. 15-20,27,28 These fatty streaks usually cause little obstruction or few symptoms. There are some observations suggesting a precursor-product relation¬ ship between fatty streaks and the more advanced fibrous plaque lesions; the latter consist mainly of a central core of lipid and of necrotic cell debris covered by a fibromuscular cap containing smooth muscle cells, macrophages, and collagen. Besides being susceptible to many of the pathogenic factors operative in nondiabetics, diabetic patients are at a particular dis¬ advantage because of their metabolic disorder and the associated diabetic microangiopathy. The main metabolic factors implicated in the development of neuronal and macrovascular complications of diabetics are hy¬ perglycemia and insulin resistance.5'24-26'29-33 There are now three main theories to explain the effects of hyperglycemia on the vascular and hematogenous cells that may become involved in the process of atherosclerosis. One theory is based on the finding that intracellular levels of sorbitol are increased because of an augmented conversion by the enzyme aldose reductase of the high levels of glucose within the cells.29'30 These large sorbitol concentrations may alter cellular functions directly by osmotic changes or, indirectly, by altering levels of myoinositol and ino¬ sitol phosphates29-30 (see Chap. 142). However, whether these cellular changes lead to the acceleration of the atherosclerotic

FIGURE 141-1. Comparison of the cumu¬ lative mortality of patients with insulin-depen¬ dent diabetes mellitus to that of the general pop¬ ulation from the Framingham study. (From Krolewski AS, et al. Magnitude and determinants of coronary artery disease in juvenile-onset, insulindependent diabetes mellitus. Am J Cardiol 1987-59750.)

process is unclear. Another theory suggests that hyperglycemia may increase the levels of nonenzymatic glycosylation of cellular and matrix proteins in patients with poorly controlled diabetes.31 These glycosylated proteins, such as albumin or low-density li¬ poprotein (LDL), may interact differently with vascular cells to promote injury to endothelial cells and proliferation of smooth muscle. In addition, the cross-linked protein products may in¬ teract with specific receptors on macrophages that then release vasoactive substances, such as platelet-derived growth factor (PDGF) or tumor necrosis factor (TNF), that would affect vascu¬ lar cells. Another theory suggests that hyperglycemia may di¬ rectly affect the genome and, thereby, alter vascular cellular func¬ tion. This is based on the findings that elevated glucose levels may influence the expression of many cellular genes affecting basement matrix, growth factors, and cytokine receptors.32,33 The mechanism of this effect of hyperglycemia is probably mediated through the activation of the protein kinase C pathway, which is known to regulate the expression of many cellular genes.34 ENDOTHELIAL CELLS Noncellular elements, such as large peptide hormones and LDL, have specific receptors on the endothelial cells and appear to be transported across the cells in a receptor-mediated transcytosis pathway.20'35 Cellular elements can cross the endothelial barrier by penetrating between the cells. Besides regulating he¬ matologic and coagulation factors, endothelial cells can produce vasoactive agents such as PDGF, which are heparin-like com¬ pounds, that have profound effects on the metabolism and pro¬ liferation of smooth-muscle cells and also can attract leukocytes

ATTAINED AGE (years)

Ch. 141: Cardiovascular Complications of Diabetes to areas of injuries.15,36-39 For example, PDGF can stimulate smooth-muscle cells to proliferate and migrate, whereas heparin¬ like components will inhibit their growth (see Chap. 169). Injury to the endothelium may result in desquamation or alteration of its function, which could decrease its nonthrombogenic surfaces and release vasoactive factors affecting the smooth-muscle cells.15,36-39 In the diabetic milieu, multiple fac¬ tors can increase the frequency of endothelial cell injury. Factors such as hyperglycemia,2 26 29 3,3 increased plasma LDL,*4,40-42 de¬ creased high-density lipoproteins (HDL),43,44 abnormal rheologic factors,45,46 and abnormalities of platelet aggregation and coagu¬ lation47 all have been implicated as being injurious to the endo¬ thelial cells. In addition, the altered endothelial cells caused by hyperglycemia or other factors in the diabetic plasma milieu can alter the nonthrombogenic properties of the endothelial cells by decreasing the production of prostacyclin and increasing produc¬ tion of growth factors such as PDGF. Some studies that used aor¬ tic preparations from diabetic animals report elevation of sorbitol levels, with changes in phosphoinositols as well. Phosphoinositol metabolism can have a regulatory function on the prostaglan¬ din production and growth factor action, which could be a mech¬ anism by which hyperglycemia produces the various metabolic changes.29,30 Interestingly, hyperglycemia has been shown to cause activation of protein kinase C, an enzyme system that may affect vascular permeability and cellular growth. Thus, the effect of hyperglycemia could be responsible for some of the diabetic complications.

SMOOTH-MUSCLE CELLS Smooth-muscle cells are the preponderant cells in fibrous plaques, although they can also be found in fatty streaks. In the latter, macrophages or monocytes are the major components.15 In response to specific chemoattractants such as PDGF, smoothmuscle cells migrate from the media of the vascular wall into the intima, where they proliferate.15 39,48 This is one of the key events in the development of atherosclerosis. The proliferation of smooth-muscle cells may be stimulated by several growth fac¬ tors, such as PDGF15 and fibroblast growth factor (FGF),49 insulin-like growth factors (IGF-I and IGF-II),50 and even in¬ sulin itself.5152 In diabetic patients, epidemiologic studies have suggested an association between hyperinsulinemia and athero¬ sclerosis.12-14 Studies using cultured aortic smooth-muscle cells from humans and animals indicate that both insulin and IGF-I are mitogenic, although at physiologic concentrations, insulin is active only in combination with other mitogenic substances that may be secreted from endothelial cells.50,5 Possibly, there are other, as yet unidentified, growth factors that may be found in the plasma of diabetic patients; this is supported by reports that diabetic plasma stimulates the proliferation of arterial smoothmuscle cells more than does nondiabetic plasma.53

1261

in diabetic patients also contains many atherogenic substances. The major elements are the lipids and the lipoproteins (see Chap. 159). Flypercholesterolemia, decrease of HDL cholesterol, and hypertriglyceridemia have been reported in up to 50% of dia¬ betic patients, more frequently in type II than in type I dia¬ betes.5-24,40_44 The various reported abnormalities of lipopro¬ teins are summarized in Table 141-2. Low-density lipoproteins are the main carrier of cholesterol to tissues. Elevation of LDL levels is associated with early onset of atherosclerosis; these levels are reported to be elevated in pa¬ tients with type II diabetes and in those with poorly controlled type I diabetes. One reason for this is the increased glycosylation of LDL caused by hyperglycemia.59,60 The modified LDL is inter¬ nalized less and, hence, less degraded. However, the question remains of whether the extent of glycosylation found in the plasma of diabetic patients is high enough to alter its metabolism. Besides glycosylation, LDL from the diabetic patients may have an altered composition (such as being enriched in triglycerides); this may also alter its uptake by fibroblasts.61 The modified LDL can be further modified by the arterial vascular cells. These al¬ tered LDL molecules can be internalized to a greater extent by circulating macrophages, which then can interact with the vas¬ cular cell wall by releasing vasoactive factors or by becoming foam cells. The most common lipid abnormality in diabetic patients is hypertriglyceridemia.2,5,20 This is probably due to decreased lipoprotein lipase activity necessary for the breakdown of chylomicrons and triglycerides.70 Thus, the plasma levels of chylomicrons and very low-density lipoproteins (VLDLs) are el¬ evated.20,41,50 Overproduction of triglycerides has also been found mainly in type II diabetic patients.5,70 The increase of VLDLs could accelerate the atherosclerotic process in several ways; one is that VLDL may be toxic for the metabolism and growth of endothelial cells.62 Another possibility is that VLDLs from diabetic animals deposit more lipids in macrophages, which can be precursors of foam cells in the arterial walls.65 Plasma HDL levels are decreased in diabetic patients.65 Be¬ cause the role of HDL is to remove cholesterol from peripheral tissue, a lower level is associated with the premature onset of atherosclerosis. In diabetic patients, HDL levels are often de-

TABLE 141-2 Predisposition to Lipoprotein Abnormalities in Type I and Type II Diabetes Lipoprotein

Changes

LDL

Elevated in plasma40 Increase in glycosylation59,60 Modification by arterial wall that leads to increased uptake by smooth-muscle cells61

HEMATOGENOUS FACTORS

Toxicity to arterial endothelial cells62

Cellular elements from the blood, specifically platelets and macrophages, also play an important role in the atherosclerotic process.54 These cellular components contain vasoactive and va¬ sotrophic factors, such as PDGF,55 FGF,49 TNF,56 transforming growth factor (TGF), and other lymphokines. Some of these peptides, such as TNF, can cause endothelial cells to secrete mitogenic factors (e.g., PDGF) besides being a trophic and chemoattractant agent to smooth-muscle cells.56,5' In addition, macrophages also have a functional role in the ingestion and deg¬ radation of cholesterol-carrying lipoproteins. Abnormalities in platelet function have been demonstrated in diabetic patients,47 including an increased sensitivity to aggregation and augmented synthesis of thromboxane A2.58 Each of these abnormalities can, in turn, increase the release of growth factors, such as PDGF and the vasoactive factors. In addition to the cellular components, the plasma fraction

T riglyceride-enriched63 VLDL

Elevated in plasma20,41,42 Increase uptake by macrophages64 Altered in composition Endothelial cell cytotoxicity62,64 Impaired degradation with increased amount of remnant (LDL)66

HDL

Decreased in plasma65 Glycosylated67 Triglyceride-enriched68

Chylomicra

Impaired degradation69 Lipoprotein lipase decreased70

Remnant (IDL)

Increased due to abnormalities in degradation in chylomicron and VLDL5,66

1262

PART IX: DISORDERS OF FUEL METABOLISM

creased and can be elevated by improved plasma glucose control using either insulin or sulfonylureas.71 The decreased level is probably due to the diminution of insulin-sensitive lipoprotein lipase activities, which indirectly causes a decrease in the transfer of phospholipids and proteins from VLDL and chylomicrons to HDL3, resulting in a decrease of HDL2A, which is important for transferring cholesterol.65 It has also been suggested that HDL catabolism may be accelerated because of the increased nonenzymatic glycosylation of HDL.67

HYPERGLYCEMIA Hyperglycemia has been postulated to have a major role in causing complications in diabetic patients. Probably, hyperglyce¬ mia is not the major initiator9 of macrovascular atherosclerotic disease because diabetes does not greatly increase the prevalence of macrovascular disease in ethnic populations in whom athero¬ sclerotic disease is low.72 However, it is possible that hyperglyce¬ mia may enhance the effect of other risk factors such as by the glycosylation of lipoproteins. In addition, basement membrane matrix protein could also be involved and become cross-linked. The consequence of this chemical reaction could be multiple, such as in reduced degradation of the basement membrane; the production of cross-linked protein products might bind to monocytes, leading to the release of vasoactive substances such as PDGF or TNF. Nonenzymatic glycosylation of proteins will lead to the increased formation of oxidative products that can react with lipids and proteins to cause vascular changes and damage.73 Hyperglycemia may also cause dysfunction of vascular cel¬ lular elements. Some studies have reported that elevated plasma glucose levels affect the proliferation of cultured endothelial cells. In addition, in large arteries, an intracellular elevation of sorbitol has also been reported, raising the possibility that this may affect endothelial cell metabolism and functions as well.29 As previously stated, hyperglycemic-induced changes in protein kinase C can affect many vascular cellular functions.

HORMONES The levels of several hormones are altered in the plasma of diabetic patients; some of these substances have been reported to be vasoactive or trophic. It is possible that they have a role in the development of vascular complications in diabetes. Elevated plasma insulin levels (either at fasting states as may occur in type II diabetes or in patients treated with insulin) may enhance the proliferation of the arterial smooth-muscle cells, es¬ pecially in the presence of other growth factors.50'51 Hyperinsulinemia and insulin resistance have been associated with the de¬ velopment of hypertension and increased risk of macrovascular disease in the diabetic patient. IGF-I, IGF-II, and growth hor¬ mone have also been reported to increase the synthesis of DNA and to induce cellular proliferation of smooth muscle cells.52'74 However, these growth factors probably do not have a major role in initiating atherosclerosis because in conditions in which growth hormone and IGF-I levels are elevated, such as acromeg¬ aly, the prevalence of atherosclerosis is not significantly in¬ creased. Levels of counterregulatory hormones such as cortisol and catecholamines are also elevated; there is some suggestive evidence that coronary artery disease is increased in Cushing syndrome and in patients treated with prednisone.75

CARDIOLOGIC DISEASES IN DIABETES Diabetes causes both microangiopathic and macroangiopathic abnormalities in the cardiovascular system. In addition, cardiomyopathy without coronary artery disease has been de¬ scribed in diabetic patients—who can represent up to 22% of all patients with idiopathic cardiomyopathy.8 The major macroangiopathic abnormalities are due to atherosclerosis in the large cor¬

onary arteries, which will lead to the development of ischemic heart disease.1-5 In the Framingham Heart Study, the frequency of congestive heart failure was two and five times greater in dia¬ betic men and women, respectively, in comparison with their nondiabetic cohorts, even factoring out known risk factors.2 Even in patients suffering from myocardial infarction, the severity of congestive heart failure is much greater than expected as esti¬ mated from the size of the infarction, again suggesting myocar¬ dial dysfunction existing in parallel with cardiac ischemia.76 In the microvessels, basement membrane thickening and microan¬ eurysms have also been described in the cardiac capillaries from diabetic patients, similar to other capillary beds.7;f Often, both microangiopathic and macroangiopathic abnormalities are pres¬ ent in the diabetic patient; and, thus, it is difficult to distinguish the relative impact of each disorder in the patient's clinical presentation.

CARDIOMYOPATHY Although the exact cause of diabetic cardiomyopathy re¬ mains unknown, it is clear that acute metabolic derangements found in diabetes produce alterations in cardiac myofibrillar per¬ formance. Numerous studies examining the myocardium of ex¬ perimental animals and also of diabetic patients have demon¬ strated that altered glucose metabolism results in a derangement of myofibrillar performance.78 Tissue culture studies have shown a decrease in the velocity of contraction of myocardial cells when exposed to a high glucose environment.78 In addition, in the pres¬ ence of high glucose concentrations, alterations are often found in the relaxation pattern of myocardial cells. Normalization of the glucose concentrations results in restoration of normal contractile relaxation indices. Diabetic cardiomyopathy was first reported in 1972 for both insulin-dependent and non-insulin-dependent patients.79 Sub¬ sequently, many reports have confirmed that this is a specific clinical entity. With the use of gated blood pool studies after vig¬ orous exercise, both type I and type II diabetics have been shown to demonstrate an abnormal ejection fraction response. From catheterization studies, consistent abnormalities of cardiac func¬ tion have been demonstrated in diabetic patients, even with no or minimal evidence of coronary artery disease. These abnormal¬ ities have included elevated left ventricular and diastolic pres¬ sures, decreased ejection fractions, and increased ventricular wall stiffness. Hemodynamic functional abnormalities, including lower cardiac output and lower left ventricular compliance,80 have also been found in newly diagnosed diabetic patients under the stress of exercise. Studies of systolic time intervals and M-mode echocardiog¬ raphy in asymptomatic diabetics have revealed an increase of the preejection period (PEP)/left ventricular ejection time (LVET), which is an index of decreased left ventricular contractility and compliance. These studies allow for repetitive observation; pro¬ spective follow-up investigations have shown an association be¬ tween the presence of microangiopathy and cardiac dysfunction. In one study, 3 months of insulin therapy reversed the previously noted abnormalities, suggesting that the cardiac abnormality is related to metabolic alterations.mi The pathologic basis for the abnormal systolic and diastolic function remains uncertain. Major histologic abnormalities are found in the diabetic heart; this encompasses virtually all levels of the myocardium, extending from the basement membrane to major intramural arteries.8'77'85 Specifically, the thickness of the capillary basement membranes is increased in the diabetic heart, much as it is in other organs affected by microangiopathy. In ad¬ dition, small capillaries and venules exhibit aneurysmal forma¬ tion and, occasionally, intense vasospasm; this might lead to an alteration in the diffusion characteristics of the interstitium. Marked myocardial fibrosis is also a frequent finding, and abso¬ lute measurements of fibrous tissue in diabetic hearts are greater than those of nondiabetics. The arterial vasculature also exhibits

Ch. 141: Cardiovascular Complications of Diabetes changes, consisting of medial hypertrophy, endothelial thicken¬ ing, and a thickened extracellular matrix of the intramural arteri¬ oles. Of these changes, it appears that the extensive fibrous tis¬ sue, which forms in the interstitium as a result of abnormalities in the interactions between the vascular cell walls and hematog¬ enous elements, or perhaps because of alterations of interstitial proteins, may be one of the major factors responsible for the ab¬ normality of both systolic and diastolic function. Changes in cardiac function and histology have also been reported in animal models of diabetes. There is an impairment in

FIGURE 141-2.

1263

the development of left ventricular pressure and a delay in the rate of muscle relaxation (Fig. 141 -2). 3 However, two differences have been reported between the models of type I and type II diabetes in animals. The heart of the insulin-dependent animal clearly has a greater impairment to generate tension against an elevated preload. Second, the hearts of non-insulin-dependent animals exhibit a greater decrease in cardiac compliance than those of insulin-dependent diabetic animals, findings that occur in diabetic patients as well.81 Increased fatty acid and triglycerides have been noted in the

Comparison of the mechanical functions of the hearts from diabetic (O—O) and non¬

diabetic (•—•) rats in response to insulin. (From Schaffer SW, et al. Development of a cardiomyopathy in a

model of non-insulin-dependent diabetic. Am J Physiol 1985;248:H179.)

1264

PART IX: DISORDERS OF FUEL METABOLISM

cardiac tissue of diabetic animals as a result of elevated levels of their plasma free fatty acids. The stimulation of fatty acid metab¬ olism influences glycerides by means of the accumulation of citric acid cycle intermediates, which are potent inhibitors of phosphofructokinase, a rate-limiting enzyme of glycerin. Glycolysis and glucose oxidation are hindered further by decreases in glucose uptake and activities of pyruvate dehydrogenase, which are reg¬ ulated by insulin.81,84 These changes in carbohydrate metabolism may be responsible for the dysfunction of the diabetic heart un¬ der stress. Besides abnormal glucose metabolism, calcium transport between the sarcolemma and the sarcoplasmic reticu¬ lum have also been reported.85 Because Ca2+ fluxes are important in cardiac contractility, the decrease in the Ca2+ pool may be re¬ sponsible for the reduction of contractility found in cardiac mus¬ cle from diabetic animals and humans. The decrease of contrac¬ tility in the diabetic heart might be due to a change of the predominant active form of myosin adenosine triphosphatase (ATPase) of the normal heart to a less active type.86 Biochemical parameters in the cardiac muscle have also been reported to be altered. The a 1-adrenoceptor is decreased in diabetic rats, and this change is due to activation of protein kinase C.87 Further¬ more, other changes such as cardiac lipoprotein lipase, G-protein actions, increased NADPH/NADP ratio, type IV collagen, and decreased a-2-(Na+)-K+-ATPase activities have also been reported.88 At the molecular level, the expression of several genes in the heart has been reported to be altered by diabetes. Glucose transporter, GLUT4, which is expressed mostly in insulin sensi¬ tive tissue (e.g., muscle, fat, and the heart), is reduced in diabetic rats, leading some investigators to postulate that the decrease in glucose transport could be partially responsible for the decrease in cardiac work. The expression of cardiac myosin heavy chain shifts from predominantly a to predominantly (3, with the onset of diabetes, and this effect is reversed by insulin administration. The expression of Ca ATPase mRNA is reduced in diabetic as well as in insulin-resistant obese mice, suggesting an explanation for the delay in diastolic relaxation.89,90 Thus, the cardiac dysfunction of diabetic patients can be due to atherosclerotic changes in the coronary macrovessels or to metabolic alterations of the myocardium resulting from exposure to the abnormal metabolic milieu in diabetic patients. Although control of the hyperglycemia appears to be capable of reversing the latter changes, the data are not clear concerning any benefi¬ cial effects on macrovascular atherosclerotic developments. Despite the dramatic changes in diabetic heart disease, it is often difficult to diagnose diabetic cardiomyopathy because other potential cardiomyopathic etiologies are frequently present in di¬ abetics, obscuring an exact causation. Because of the high preva¬ lence of coronary artery disease in the diabetic patient, there may be a history of known or suspected myocardial infarction, which could be the explanation for systolic or diastolic cardiac impair¬ ment. In addition, the diabetic patient often has a history of hy¬ pertension, which, by itself, can lead to the development of such

abnormalities. The presence of renal failure with resultant ane¬ mia, hypertension, and volume overload can impose additional stress on the myocardium, unmasking an underlying diabetic myopathic state. Thus, diabetic cardiomyopathy is frequently the silent partner of a more clinically obvious form of diabetic heart disease; its effect may influence both the presenting clinical symptoms and the response to therapy.

AUTONOMIC NEUROPATHY OF THE HEART Various abnormalities in heart rate have been described in the diabetic population. These include persistent tachycardia, ab¬ sence of a rate variation with the Valsalva maneuver, and a blunting of the normal variation of the heart rate that occurs dur¬ ing deep breathing91 (Fig. 141-3). These abnormalities are mainly due to dysfunction of the vagus nerve, although sympathetic ac¬ tivity to the heart may also be altered in patients with severe au¬ tonomic neuropathy. Such an inability of sympathetic modula¬ tion may become a factor during exercise, in which case, maximizing the heart rate may be functionally important.92 An evaluation of the parasympathetic regulation of the heart rate can be clinically useful. Several methods have been used to evaluate cardiac parasympathetic function, including (1) heart rate or RR interval variation during deep breathing, (2) heart rate response to Valsalva maneuver, and (3) heart rate response to standing. The sensitivity of detecting a clinically relevant abnor¬ mality is increased if two of these simple tests are used together. The principle behind these assays is to measure the vagal regulation of the heart rate, which is reflected in the RR intervals. The variation in the heart rate change depends on the blood flow back to the heart. The tachycardia normally observed during the Valsalva maneuver is induced by the lack of vagal tone, whereas the bradycardia that occurs after the maneuver is due mainly to an increase of vagal tone.92,93 Thus, a deficiency of vagal activity will lead to a decrease in the variation of heart rate during these maneuvers. In one study, the variation in heart rate during one deep breath was reduced significantly in 62 of 64 diabetic pa¬ tients with other autonomic symptoms and in 30% of diabetic patients who had peripheral neuropathy but no autonomic symptomatology.919 Prolonged follow-up of up to 5 years did not show any improvement and, in some patients, demonstrated deterioration.92 Indeed, the mortality differed remarkably be¬ tween diabetic patients with and without abnormal cardiovascu¬ lar reflex tests. In a study of 73 diabetic patients, the mortality in those with abnormal cardioreflex testing was threefold to four¬ fold higher; in 20% the death was sudden, suggesting cardiac arrhythmia as a possible cause94 (Fig. 141-4). Similar findings of a decrease in respiratory variations of the RR interval in diabetics have been reported. However, these differences from those of the nondiabetic population are not as marked as the heart rate variation just described. However, the high mortality is mostly due to other serious illnesses. Nevertheless, diabetics with severe autonomic dysfunction should be carefully followed.

Normal response

minutes

Ch. 141: Cardiovascular Complications of Diabetes

1265

FIGURE 141 -4. Comparison of 5-year survival curves (age- and sexmatched) of a general population and various types of diabetic popu¬ lations classified according to the presence of autonomic neuropathy ANS, autonomic neuropathic stimulation testing. (From Clark BF, Ew¬ ing DJ. Cardiovascular reflex test in the natural history of diabetic auto¬ nomic neuropathy. NY State ] Med 1982; 82:903.)

MACROANGIOPATHIC DIABETIC HEART DISEASE The major clinical complication of long-standing diabetes is atherosclerotic cardiovascular disease.1-5 The Framingham study demonstrated the marked prevalence of coronary artery disease in both men and women with diabetes.2 Diabetic men have a twofold greater risk of dying of ischemic heart disease than do nondiabetic controls. Female diabetic patients are particularly vulnerable to the effects of atherosclerotic heart disease; their in¬ cidence of ischemic heart disease is fivefold that of the nondia¬ betic female population.2 9 A review of the coronary angiograms of cardiac patients re¬ vealed that the involvement in diabetics was more severe and had a more diffuse pattern than in nondiabetic patients.9r,“97 Sim¬ ilar findings were found in an angiographic study of juvenileonset insulin-dependent diabetics. In addition, the female juve¬ nile diabetic patients were particularly prone to have a diffuse pattern of coronary artery involvement. Although classic manifestations of coronary artery disease are often found in the diabetic patient, there may be a discrep¬ ancy between the clinical symptoms and the severity of underly¬ ing heart disease. Not uncommonly, rather mild symptoms are associated with marked, and potentially life-threatening, coro¬ nary artery lesions. Although this phenomenon occurs in many nondiabetic patients with ischemic heart disease, it appears to be more prevalent in those with diabetes. Not uncommonly, dia¬ betic patients with ischemic heart disease may not experience chest pain and may complain of subtle findings such as exertional dyspnea, mild diaphoresis, nausea and vomiting, or generalized weakness. Thus, in assessing the diabetic patient with coronary artery disease, it is important to have a high index of suspicion of underlying atherosclerotic cardiovascular disease and not be misled by what appear to be mild or stable clinical symptoms. Because of the subtlety of presentation and the difficulty in relying on symptomatology to assess the clinical severity of coro¬ nary atherosclerosis, it is wise to obtain an objective evaluation using some modality of exercise testing to assess both the pres¬ ence and the severity of coronary artery disease. The indications for coronary angiography are the same for diabetic as for nondi¬ abetic patients. The outcome of coronary bypass graft surgery in diabetics is excellent for survival and symptomatic relief.93-9' The

hazards of angiography per se in diabetic patients are increased only in those patients with abnormal renal function. There is, in general, an increased risk of compromising renal function when using radiographic dyes in diabetic patients. This risk can be nor¬ malized by reducing the dose of the dye, by hydrating the pa¬ tients, and by the possible use of mannitol to augment urine out¬ put and avoid hypotension. On the day of the procedure, good glucose control should be maintained—either by continuous in¬ sulin pump or by splitting the morning dose of insulin (half be¬ fore the procedure and the remaining half afterward). The blood glucose value should be checked frequently during the proce¬ dure. A cautionary note should be raised in the care of insulin¬ taking diabetics who are scheduled to undergo cardiac surgery after angiography. There is an increased danger of anaphylaxis after the injection of protamine, which is employed to neutralize the actions of administered heparin. The increased rate of reac¬ tion is probably due to previous exposure to protamine in the NPH insulin used by diabetic patients.98

MYOCARDIAL INFARCTION In an early review of morbidity and mortality in diabetics after a myocardial infarction,93 an overall mortality of 30% was found; there was a high frequency of congestive heart failure. In addition, 30% of all of the diabetic patients presenting to the coronary care unit had no pain, compared with fewer than 10% in the nondiabetic population. The 1-year mortality was mark¬ edly increased (40%) compared with the generally expected mor¬ tality of 15% to 20% in the nondiabetic population. A more re¬ cent review of the Joslin Clinic experience has confirmed the continuing high mortality in diabetic patients having either an initial or subsequent myocardial infarction.9 Interestingly, female diabetic patients had a particularly bad prognosis, both for their initial infarct and during the 1-year follow-up.2 9 In a large, multicenter study that examined the 1-year mor¬ tality after a myocardial infarction, diabetic patients emerged as a subgroup with a particularly poor prognosis. Although the non¬ diabetic counterparts experienced only a 10% mortality, the dia¬ betic population had over 20% mortality within 2 years.9 ’ Close analysis of multiple cardiovascular parameters did not elucidate

1266

PART IX: DISORDERS OF FUEL METABOLISM

the increased mortality in the diabetic group. Specifically, the ex¬ tent of myocardial infarction as assessed by global left ventricular function (quantitated by radionuclide ventriculogram) failed to explain the marked discrepancy found between diabetic and nondiabetic patients. In addition, the results of baseline Holter monitoring and low-grade exercise tolerance tests before dis¬ charge from the hospital were not statistically different between the two groups. The mode of death in the diabetic group usually consisted of progressive congestive heart failure or sudden death. Although the underlying cause for the increased mortality is not definitely known, the unique characteristics of diabetic heart disease may be important factors. For example, there is an in¬ creased propensity for lethal ventricular arrhythmias, pre¬ sumably caused by more extensive fibrosis and, hence, less responsiveness to antiarrhythmic agents. In addition, the cardiomyopathic changes unique to diabetes may result in more dra¬ matic abnormalities because of the altered diastolic compliance of the left ventricle. Although indices of systolic performance may be comparable in both diabetic and nondiabetic groups, in¬ creased stiffness of the diabetic ventricle may aggravate hemo¬ dynamic changes and, thereby, lead to more severe and pro¬ gressive congestive heart failure.8 Autonomic neuropathy, particularly the loss of parasympathetic innervation, may predis¬ pose to a more vulnerable ventricular myocardium in terms of arrhythmia potential.94 There is a greater propensity for coronary vasoconstriction to occur in diabetic patients with parasympa¬ thetic denervation. Although speculative, some or all of these unique characteristics of diabetic heart disease may be responsi¬ ble for the increased initial and 1-year mortality found in diabet¬ ics with acute myocardial infarction.

MANAGEMENT OF DIABETIC ISCHEMIC HEART DISEASE MEDICAL MANAGEMENT The medical therapy for cardiovascular disease for diabetic patients is very similar to that for the nondiabetic population. However, a few aspects of therapy that are particularly pertinent to diabetic patients are discussed. DIET PLAN The diet plan is an important aspect of therapy. This is be¬ cause with proper diet and weight loss (depending on the type of diabetes), the peripheral sensitivity or insulin secretion, or both, will normalize, thus improving the blood glucose control and re¬ ducing some of the risk factors such as elevation of LDL and low¬ ering of HDL levels. The initial goal is to construct a diet that will enable the diabetic patient, if obese, to lose weight. Without unusual physical activity, patients who are taking in 35 kcal/kg will, in general, maintain their weight. Because a deficit of 3500 kcal is needed to lose 1 lb, in patients with normal physical activ¬ ity, a diet program allowing 1200 kcal/d will result in a loss of 1 to 2 lb/wk. Although this may not appear to be particularly significant, many obese diabetic patients have a clear improve¬ ment in insulin action after losing only a few pounds. The second goal of the diet is to aid the body in maintaining plasma glucose control and a normal metabolic milieu to avoid acute complica¬ tions. An increase in fiber content of the diet also may be helpful for this, owing to its effect in delaying enteric absorption (see Chaps. 124 and 137). The second goal of the diet plan is to attempt to decrease risk factors such as hyperlipidemia, hypertension, and nephropathy—a11 which accelerate the rate of atherosclerosis. For multiple reasons, hyperlipidemia is especially common in female diabetic patients, thus, a diet low in saturated fat should be strictly followed. Other factors that can accentuate the lipid ab¬ normalities, such as alcoholic beverages, should be avoided. In

addition, familial hyperlipidemia may be found, which will greatly accentuate the lipid abnormalities, especially an elevation of plasma triglyceride levels.20'22-24 Drug treatment with triglyc¬ eride- and cholesterol-lowering agents may be required (see Chap. 158). However, plasma glucose control should be tried first because this can significantly lower both plasma VLDL and LDL levels. The frequency of hypertension is increased in the diabetic population even before the development of clinical renal disease. Hypertension has been demonstrated to be a strong risk factor for the development and progression of diabetic cardiac, retinal, and peripheral vascular complications99; thus, it should be treated vigorously. A low salt diet in combination with drug ther¬ apy is often required. Also, animal studies suggest that a low pro¬ tein diet along with plasma glucose control in diabetic patients may improve or stabilize deteriorating renal function; longer hu¬ man trials are in progress to determine the efficacy and safety of these low protein diets. It should also be emphasized that ciga¬ rette smoking in diabetic patients must be strongly discouraged because the increase of risk for cardiovascular morbidity and mortality is enhanced in a multiple fashion (see Chap. 221). EXERCISE Exercise in diabetic patients can be helpful in several ways. First, moderate exercise has been demonstrated to improve insu¬ lin sensitivity and glucose tolerance, even in the absence of weight loss. Second, in combination with a proper diet program, exercise can be helpful in promoting weight loss and thereby lead to reduced cardiovascular mortality. Improvement in glucose sensitivity caused by exercise and weight loss can lead to a dosage reduction of oral hypoglycemic agents or insulin. Exercise may also reduce the risk of vascular complications, not only by im¬ proving plasma glucose control but also by increasing plasma HDL, which can lessen the risk of cardiovascular disease. In ad¬ dition, risk factors for macrovascular disease in diabetic patients, such as the levels of LDL, VLDL, and endogenous insulin (or insulin dose), may also be lowered. Although the advantages of an exercise program can be sub¬ stantial for diabetic patients, it should not be initiated without proper planning because there are some potential risks. There may be an increased occurrence of hypoglycemia in patients tak¬ ing oral hypoglycemia agents caused by an augmented sensitivity to insulin or an increased absorption of exogenously adminis¬ tered insulin. Exercise that might increase retinal intravascular pressure, such as exercise associated with straining, should also be limited. Patients who suffer from severe sensory neuropathy have an increased risk of injuring their lower extremities. For type II diabetic patients, who are generally older than type I diabetics, care should be taken to avoid precipitating ar¬ rhythmia and myocardial infarction. Also, the high prevalence of peripheral vascular involvement in diabetic patients may result in easily bruised skin, which could lead to abscess formation and osteomyelitis. Nevertheless, a supervised and planned exercise program can usually avoid these potential hazards (see Chaps 8 and 137). K Exercise Regimen. In the initial medical evaluation, a de¬ tailed examination of the cardiac and vascular systems, in addi¬ tion to ophthalmoscopic studies, is necessary to rule out cardiac lesions or proliferative retinopathy, which may be exacerbated by strenuous exercise programs. Laboratory evaluations are nec¬ essary to evaluate the control of plasma glucose levels and to determine the patient's working capacity. The evaluation of cardiac and working capacities should include resting and exer¬ cise electrocardiograms in the patient older than 40 years old or with a history of cardiac symptoms. Endurance-type exercise such as walking, cycling, jogging, and aerobic workouts are generally recommended over those of strength building (e.g„ weight lifting) because of the increased potential of the latter to transiently increase blood pressure. The exercise plan usually begins with a short warm-up period with

Ch. 141: Cardiovascular Complications of Diabetes stretching routines, followed by 10 to 30 minutes of endurance¬ building activities. These exercises should stimulate the heart rate to increase up to 50% to 75% of the maximal rate, depending on the persistence in the exercise program. These exercise plans need to be performed at least thrice weekly to achieve beneficial effects; also this exercise frequency is the best tolerated by patients. DRUG THERAPY

The specific pharmacologic therapy for cardiac dysfunction among the diabetic and the nondiabetic population does not differ greatly. However, several general points should be stressed. Obviously, in patients with type I disease, insulin treat¬ ment is required; whether normalized glucose excursions will prevent the development of cardiovascular complications has not been established. For type II diabetes, one must decide whether to use insulin or oral hypoglycemic agents. Questions also have been raised concerning the safety of the sulfonylureas in diabetic patients with a history of cardiac dis¬ ease. These concerns were a result of the findings of the Univer¬ sity Group Diabetes Program (UGDP), which concluded that there was an increase of cardiovascular deaths in the tolbuta¬ mide-treated group compared with the insulin-treated group.100 These differences became significant after 3 j years. However, the validity of these conclusions has been contested (see also Chap. 138). Several subsequent smaller studies have been inconclusive. The authors recommend that sulfonylureas be used cautiously, and only after diet treatment has been exhaustively attempted. Even after starting oral hypoglycemic agents, diet and weight control programs should be continued. In addition, these drugs should be discontinued if further weight reduction alone can re¬ sult in satisfactory control of plasma glucose. The drug therapy of angina pectoris in diabetic patients differs slightly from the nondiabetic population. This primarily pertains to the use of /3-adrenergic blocking agents. Long¬ standing diabetic patients with impaired autonomic function of¬ ten have a poor sympathetic response to hypoglycemia, and some of its warning signs may be blunted. In addition, nonselective /3-adrenergic blockers inhibit gluconeogenesis and, there¬ fore, prolong the recovery phase from hypoglycemia because this requires mobilization of glucose from the liver. Clinically, these problems are dealt with best by warning diabetic patients that their symptoms of hypoglycemia may be more subtle. When the symptoms are finally perceived, the patients will have a shorter time to respond and to remedy their hypoglycemia before uncon¬ sciousness may occur. The complete absence of symptoms when hypoglycemia occurs usually constitutes a contraindication to the use of /3-adrenergic blocking drugs. The advantage of a selective /3-blocker is limited to a faster recovery phase from hypoglyce¬ mia; it would appear that this minor advantage may be clinically worthwhile. Another problem encountered with the use of /3-adrenergic blocking drugs in diabetic patients is their lack of efficacy among those patients with significant autonomic neuropathy. A major benefit of /3-adrenergic blockers is the slowing of heart rate and a subsequent decrease of myocardial oxygen requirements, thereby minimizing the possibility of myocardial ischemia. How¬ ever, in autonomic neuropathy, the parasympathetic control of heart rate is often lost. Consequently, the resting heart rate is higher than in those persons with a normally functioning vagus nerve. Patients with parasympathetic denervation do not experi¬ ence the same magnitude of decrease in heart rate after full /3adrenergic blocking doses. This is due to the relatively greater importance of the parasympathetic tone, which results in only minor changes in heart rate response and, therefore, only minor improvement of myocardial oxygen requirements. Combined with the propensity of /3-adrenergic blockers to aggravate hypo¬ glycemic episodes, this narrows the therapeutic/toxic ratio of these agents. In individuals with autonomic dysfunction, it is sometimes best to select a calcium channel antagonist as a pri¬

1267

mary mode of therapy, since these drugs cause a decrease in heart rate by a direct nonadrenergic-mediated depression of sinus mode function. Frequently, calcium channel antagonists can re¬ sult in a more impressive negative chronotropic response than do /3-adrenergic blockers, especially when there is substantial auto¬ nomic dysfunction. Lastly, the promising findings that angioten¬ sin converting enzyme inhibitors are able to delay the onset of diabetic nephropathy and exert cardiac protective effects have provided a strong impetus for their use in diabetic patients with symptoms of nephropathy and hypertension.101

SURGICAL APPROACHES BALLOON ANGIOPLASTY

Coronary artery balloon angioplasty has been used exten¬ sively in both diabetic and nondiabetic populations. The results have shown hospital death to be about 0.2% in some cen¬ ters102,103; restenosis rates are 30% to 40% in 6 months. Diabetes, along with male sex, unstable angina, and pathologic findings of long or near-total lesions are risk factors that result in higher mortality and higher rates of restenosis. CORONARY ARTERY BYPASS SURGERY

Numerous studies have demonstrated the effectiveness of coronary artery bypass surgery, when feasible, in both type I and type II diabetes.9-97 However, patients with type I diabetes rep¬ resent a unique population in whom coronary artery disease is more extensive and diffuse; hence, they have been considered to be less suitable candidates for bypass surgery.95-97 A small group of type I diabetics were followed after having coronary artery bypass surgery.97 At the time of the operation, the patients had a mean age of 44 years and a mean duration of diabetes of 30 years. Retinopathy and neuropathy occurred in 11 of 15 and 8 of 15 patients, respectively; 5 of 13 and 2 of 15 had peripheral vasculopathy and neuropathy, respectively. All pa¬ tients, except one, were classified as functional class IV by the criteria of the New York Heart Association. Because of the fre¬ quent occurrence of angina, in spite of maximal medical therapy, the patients were subjected to coronary angiography and sur¬ gery. Angiographic findings showed that 8 patients had more than one vessel involved by 70% or greater narrowing. Two of 13 patients had left main coronary artery stenosis. More than 70% of the patients had focal narrowing. Left ventricle function studies revealed an ejection fraction greater than 50 in all of the patients. All the nondiffuse vessels were bypassed and no perioperative mortality was reported. Clinical evaluation for up to 8 years showed an initial symptomatic improvement in all of the patients after 1 year, and 60% of the treated patients remained minimally symptomatic after 5 years. Repeat angiograms found progression of disease occurred mainly in previously nongrafted vessels. Thus, in this study, type I diabetic patients with coronary artery disease were able to be treated with coronary artery bypass grafts with good results. With type II diabetics, the results of coronary artery bypass grafting have been quite favorable, both for symptomatic relief and survival. Compared with the nondiabetic patients, as a group, the adult-onset diabetics included a higher percentage of females, a higher prevalence of hypertension, and an increased prevalence of ventricular hypertrophy. Angiographic studies have suggested that coronary arteries from diabetic patients have more diffuse disease, resulting in a greater number of grafts per¬ formed.95,96 Perioperative morbidity, involving infection, wound healing, and renal failure, was also greater in the diabetic group.95,96 Long-term survival appears to be lower as well. In spite of increased perioperative complications, a better survival rate in diabetic patients with bypass grafts when com¬ pared with medical management has been reported. The periop¬ erative morbidity can be minimized by regulating precisely the patient's glucose levels within strict euglycemic control with an

1268

PART IX: DISORDERS OF FUEL METABOLISM

insulin pump or with multiple insulin injections and frequent blood glucose monitoring (see Chap. 139).

DIABETIC PERIPHERAL VASCULAR DISEASE The increased incidence of peripheral vascular disease, gan¬ grene, and subsequent amputation in diabetic patients has been documented in many studies.2'5'9-12 In one report, 5% of patients had symptoms of peripheral vascular disease within 1 year of diagnosis of their diabetes; after 12 years of follow-up, this in¬ creased to 23%. In the Framingham study, 12.6% of the male diabetic patients had claudication, as opposed to only 3.3% of the control group.2 Although peripheral vascular disease is more common in nondiabetic males than in nondiabetic females, the incidence in diabetic patients between the sexes is almost equal. Also, periph¬ eral vascular disease occurs more commonly below the knees in diabetics, whereas in the nondiabetic it is more likely to be situ¬ ated in the aortic, iliac, and femoral vessels. Because atheroscle¬ rosis of large vessels, small vessels, or arterioles does not progress at the same rate, it is possible to have more severe disease in small vessels than in large vessels, leading to small patchy areas of gan¬ grene of the foot or the toes in the presence of a palpable dorsal pedal or posterior tibial pulse.2'8-12104 In addition, collateral cir¬ culation may develop poorly in diabetic patients. Not to be confused with the atherosclerosis process is focal calcification of the media, particularly in the medium-sized mus¬ cular arteries (Monckeberg sclerosis); this is also increased in diabetic patients. This process involves degeneration of smoothmuscle cells, followed by calcium deposition. Its characteristic radiographic appearance consists of regular, concentric calcifi¬ cations that are seen especially in the pelvic and femoral vessels. These medial changes, alone, do not cause narrowing of the lu¬ men and have little clinical significance, unless they are associ¬ ated with atherosclerosis, in which case an arterial occlusion may occur.

SIGNS AND SYMPTOMS The earliest symptom of peripheral vascular disease is in¬ termittent claudication, which is characterized by pain on walk¬ ing and is relieved by stopping. This usually begins in the calf and may involve various muscle groups, depending on the location of the occlusion.2'912104 A more serious symptom is rest pain, which is usually worse at night and may require narcotics for relief. Be¬ cause rest pain is often relieved by sitting with the feet depen¬ dent, edema of the legs may occur in those patients who sleep in a chair. r Cold feet is a common complaint in patients with peripheral arterial insufficiency. The cold feet are what prompt the diabetic patients to use heating pads, often resulting in burns to their rel¬ atively insensitive feet. The presence of diabetic neuropathy is the main and primary cause of foot lesions. Because of sensory deficiency, diabetic patients may repeatedly injure their feet, which then may heal poorly because of the compromised vascu¬ lature. The poor blood supply results in malnutrition of the foot, leading to thickened nails, diminished subcutaneous fat, and loss of hair. Frequently, there is associated fungal infection (see Chaps. 142, 147, and 148). Examination of the patient with peripheral vascular disease reveals diminished or absent pulses, depending on the areas of involvement. Similarly to nondiabetic patients, there is a high occurrence of atherosclerotic occlusion of the femoral and popli¬ teal arteries. However, there is a strikingly increased involvement of the tibial and peroneal arteries. Therefore, it is common to find the presence of a popliteal pulse in the presence of an ischemic foot. Pallor of the foot on elevation is an important sign of isch¬ emia. If the patient then sits with the legs dependent, venous and capillary filling times are usually less than 20 seconds if collateral

circulation to the foot is satisfactory; this may be prolonged to minutes if the extremity is ischemic. Also, a bright or dusky red color may develop on dependency if the circulation is quite poor.

LABORATORY TESTS Two of the most widely used noninvasive tests include seg¬ mental blood pressures in the leg and pulse volume recordings (with the Doppler flowmeter). Segmental systolic pressures are used to identify the area or level of the obstruction. By consecu¬ tively inflating the cuffs, which are placed below the knee and above the ankle, segmental pressures can be obtained. All pres¬ sure gradients should demonstrate a drop of less than 30 mm Hg. Diabetic patients frequently have elevated systolic pressures at all levels; this is thought to be due to medial calcification of the peripheral vessels. Pulse volume recordings are used to measure the instantan¬ eous variations of arterial volume in a specific limb segment dur¬ ing each cardiac cycle. Specially designed cuffs are used for digi¬ tal tracing; this is particularly important in diabetic patients, who are prone to develop disease of the small arteries. An exercise test or reactive hyperemia test may also be valu¬ able when patients suffer from claudication, even though the resting pressure and volume index may be normal. These pa¬ tients may have small-vessel disease. However, clinical judgment is often more valuable than noninvasive tests in determining the level of occlusion and the likelihood of success.

THERAPY FOR PERIPHERAL VASCULAR DISEASE The treatment of peripheral vascular disease requires multiple approaches, including meticulous control of the plasma glucose level, weight reduction, cessation of smoking, and avoid¬ ance of injury. None of the vasodilator drugs available can help this condition; indeed, they may be contraindicated because of their effect in lowering systemic pressure, leading to decreased collateral blood flow. The main objective of medical treatment is to educate the patients to take good care of their feet; this can markedly reduce the rate of amputation. Such measures involve a daily inspection of the feet and the use of correctly fitted shoes. Nails and calluses should be regularly examined by a podiatrist. The feet should be kept warm, dry, and clean. If any infection or lesion is found, hospitalization and antibiotics are indicated. Besides good foot care, the cessation of cigarette smoking is also extremely impor¬ tant and effective in decreasing symptoms and amputation rates. Exercise programs, such as walking, can improve the symptoms in most patients. Various drug treatments have been tried with inconclusive results. Pentoxifylline, a drug that appears to increase the flexi¬ bility of red blood cells, is being used for improving the symp¬ toms of intermittent claudication.105 106 However, the reported results have not been encouraging. Aspirin has also been used because of its possible beneficial effect in diminishing the ability of platelets to adhere to one another. However, no prospective trials of its effect on peripheral vessels have been reported, al¬ though it may be helpful in preventing coronary and cerebral events. Vasodilators are not effective for intermittent claudica¬ tion, probably because of such factors as sclerosis of the vessel, abnormalities of autonomic control, and vessels that may already be dilated. Vascular surgery is the definitive procedure for improving blood flow in peripheral vascular disease. Indications for arterial surgery include rest pain, claudication that interferes with work, or an area of gangrene. Before surgery, the location and extent of involvement, as well as the feasibility of improvement, must first be ascertained by cautious angiography. Operations to restore blood flow to the ischemic limb include angioplasty and bypass surgery. In angioplasty, a small balloon catheter, carefully put into place and distended under fluoros-

Ch. 141: Cardiovascular Complications of Diabetes copy, may push the diseased areas into the arterial wall, relieving the obstruction. Unfortunately, in the diabetic patient, multisegmental artery disease is often present and involvement of small vessels may render this method less useful. Saphenous vein grafts or other graft materials such as Da¬ cron tubes or glutaraldehyde-treated umbilical veins can be used to bypass the obstructing arterial lesions. The results of the by¬ pass surgery have been very good. Because the vessels frequently involved are tibial and peroneal arteries,12 vein graft from the popliteal to either the dorsalis pedis or posterior tibial artery can be performed successfully.12 Long-term results in arterial recon¬ struction are almost identical when comparing diabetic and non¬ diabetic patients.107

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29. Simmons DA, Kern EFO, Winegrad Al, Martin DB. Basal phosphatidylinositol turnover controls aortic Na+/K+ATPase activity. J Clin Invest 1986; 77:503. 30. Greene DG, Lattimer SA, Sima AAF. Sorbitol, phosphoinositides and sodium-potassium-ATPase in the pathogenesis of diabetic complications. N Engl J Med 1987;316:599. 31. Brownlee M, Vlassara H, Cerami A. Nonenzymatic glycosylation and the pathogenesis of diabetic complications. Ann Intern Med 1984; 101:527. 32. Bucala R, Model P, Cerami A. Modification of DNA by reducing sugars: a possible mechanism for nucleic acid aging and age-related dysfunctions in gene expression. Proc Natl Acad Sci USA 1984; 81:105. 33. Lorenzi M, Mortisano DF, Toledo S, Barrieux A. High glucose induces DNA damage in cultured human endothelial cells. J Clin Invest 1986; 77:322. 34. Inoguchi T, Battan R, Handler E, et al. Preferential elevation of protein kinase C isoform /3II and diacylglycerol levels in the aorta and the heart of diabetic rats: differential reversibility to glycemic control by islet cell transplantation. Proc Natl Acad Sci USA 1992; 89:11059. 35. Navab M, Hough GD, Berliner JA, et al. Rabbit beta-migrating very low density lipoprotein increases endothelial macromolecular transport without altering electrical resistance. J Clin Invest 1986; 78:389. 36. Moncada S, Herman AG, Higgs EA, Vane JR. Differential formation of prostacyclin (PGX or PGI2) by layers of the arterial wall: an explanation for the anti¬ thrombotic properties of the vascular endothelium. Thromb Res 1977; 11:323. 37. Gajdusk CM, Dicorleto P, Ross R, Schwartz SM. An endothelial cellderived growth factor. J Cell Biol 1980; 85:467. 38. Castellot JJ Jr, Favreau LV, Karnovsky MJ, Rosenberg RD. Inhibition of vascular smooth muscle cell growth by endothelial cell-derived heparin: possible role of a platelet endoglycosidases. J Biol Chem 1982;257:11256. 39. Senior RM, Huang JS, Griffin GL, Deul TF. Dissociation of the chemotactic and mitogenic activities of platelet-derived growth factor by human neutrophil elastase. J Cell Biol 1985; 100:351. 40. Goldberg RB. Lipid disorders in diabetes. Diabetes Care 1981;4:561. 41. Ginsberg H, Grundy SM. Very low density lipoprotein metabolism in non-ketotic diabetes mellitus: effect of dietary restrictions. Diabetologia 1982; 23: 421. 42. Taskinen MR, Beltz WF, Harper I, et al. Effect of NIDDM on very low density lipoprotein triglyceride and apolipoprotein B metabolism: studies before and after sulfonylurea therapy. Diabetes 1986; 35:1268. 43. Miller GJ. High density lipoprotein and atherosclerosis. Ann Rev Med 1980; 31:97. 44. Kaplan RM, Wilson DK, Hartwell SC, et al. Prospective evaluation of HDL cholesterol changes after diet and physical conditioning programs for patients with type II diabetes mellitus. Diabetes Care 1985;8:343. 45. Davies PF, Dewey CF, Bussolari SR, et al. Influence of hemodynamic forces on vascular endothelial function in vitro studies of shear stress and pinocytosis in bovine aortic cells. J Clin Invest 1984; 73:1121. 46. McMillan DE. Effects of insulin on physical factors: atherosclerosis in di¬ abetes mellitus. Metabolism 1985;34(Suppl):70. 47. Colwell JA, Lopes-Virella M, Haluska PV. Pathogenesis of atherosclerosis in diabetes. Diabetes Care 1981; 4:121. 48. Grotendorst GR, Chang T, Seppa HEJ, et al. Platelet derived growth fac¬ tor is a chemoattractant for vascular smooth muscle cells. J Cell Physiol 1982; 113: 261. 49. Thomas KA. Fibroblast growth factors. FASEB J 1987,1:434. 50. King GL, Goodman AD, Buzney S, et al. Receptors and growth-promot¬ ing effects of insulin and insulin-like growth factors on cells from bovine retinal capillaries and aorta. J Clin Invest 1985;75:1028. 51. Stout RW. The role of insulin in atherosclerosis in diabetics and non¬ diabetics, a review. Diabetes 1981;30(Suppl 2):54. 52. King GL. Cell biology as an approach to the study of the vascular compli¬ cations of diabetes. Metabolism 1985;34(Suppl 1): 17. 53. Hamet P, Sugimoto H, Umeda F, et al. Abnormalities of platelet-derived growth factors in insulin-dependent diabetes mellitus. Metabolism 1985;34(Suppl 1):25. 54. Rabbani LE, Loscalzo J. Recent observations on the role of hemostatic determinants in the development of the atheromatous plaque. Atherosclerosis 1994; 105:1. 55. Deul TF, Huang JS. Platelet-derived growth factor structure, function and roles in normal transformed cells. J Clin Invest 1984; 74:669. 56. Beutler B, Cerami A. Cachectin: more than a tumor necrosis factor. N Engl J Med 1987;316:379. 57. Assoian RK, Grotendorst GR, Miller DM, et al. Cellular transformation by coordinated action of three peptide growth factors from human platelets. Nature 1984,-309:804. 58. Prisco D, Rogasi PG, Paniccia R, et al. Altered membrane fatty acid com¬ position and increased thromboxane A2 generation in platelets from patients with diabetes. Prostaglandins Leukot Essent Fatty Acids 1989;35:15. 59. Gomen B, Baenziger J, Schonfeld G, et al. Non-enzymatic glycosylation of low density lipoprotein in vitro: effects on cell interactive properties. Diabetes 1981; 30:871. 60. Schonfeld G. Diabetes, lipoprotein and atherosclerosis. Metabolism 1985;34(Suppl 1):41. 61. Brown MS, Goldstein JL. Lipoprotein metabolism in the macrophage: im¬ plications for cholesterol deposition in atherosclerosis. Annu Rev Biochem 1983; 52: 223. 62. Tauber JP, Cheng J, Gaspodarowicz D Effect of high and low density lipoproteins in proliferation of cultured bovine vascular endothelial cells. J Clin In¬ vest 1980; 66:696.

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PART IX: DISORDERS OF FUEL METABOLISM

63. Lopes-Virella MF, Sherer GK, Lees AM, et al. Surface binding internal¬ ization and degradation by cultured human fibroblasts of low density lipoprotein isolated from type 1 (insulin dependent) diabetic patients: changes with metabolic control. Diabetologia 1982; 22:430. 64. Kraemer FB, Lopez RD. Effects of diabetes on very low density lipid ac¬ cumulation in mouse peritoneal macrophages. Diabetes 1983;32(Suppl 1):14A. 65. Nikkila EA. High density lipoproteins in diabetes. Diabetes 1981; 30(Suppl 2):82. 66. Weisweiler P, Dransner M, Schwandt P. Dietary effects on very low den¬ sity lipoproteins in type II diabetes mellitus. Diabetologia 1982; 23:101. 67. Witzum JL, Fisher M, Tiziana P, et al. Non-enzymatic glycosylation of high density lipoproteins accelerates its catabolism in guinea pigs Diabetes 1982;31:1023. 68. Biesbroeck RC, Albers JJ, Wahl PW, et al. Abnormal composition of high density lipoproteins in non-insulin-dependent diabetics. Diabetes 1982;31:126. 69. Regrave JG, Snibson DA. Clearance of chylomicron triacylglycerol and cholesterol ester from the plasma of streptozotocin-induced diabetic and hypercholesterolemic hypothyroid rats. Metabolism 1977;26:493. 70. Brunzell JD, Porte D Jr, Bierman EL. Abnormal lipoprotein lipase medi¬ ated plasma triglyceride removal in untreated diabetes mellitus associated with hy¬ pertriglyceridemia. Metabolism 1979; 28:901. 71. Nathan DM, Roussell A, Godine JE. Glyburide or insulin for metabolic control in non-insulin-dependent diabetes mellitus. Ann Intern Med 1988; 108:334. 72. Kawata R, Yamakido M, Nishimoto Y, et al. Diabetes and its vascular complications in Japanese migrants on the island of Hawaii. Diabetes Care 1979-2161. 73. Baynces JW. Role of oxidative stress in development of complications in diabetes. Diabetes 1991;40:405.

9' ■ Batist G, Blaker M, Kosinski EJ, et al. Coronary bypass surgery in juvenile onset diabetes. Am Heart J 1983; 106:51. 98. Stewart WJ, McSweeney SM, Kellett MA, et al. Increased risk of severe protamine reactions in NPH insulin-dependent diabetics undergoing cardiac cath¬ eterization. Circulation 1984; 70:788. 99. Christlieb AR. Hypertension in the diabetic patient. In: Marble A, Krall LP, Bradley RF, et al, eds. Joslin's diabetes mellitus, 12th ed. Philadelphia: Lea & Febiger, 1985:583. 100. Goldner MG, Knatteruch GL, Prout TE. Effect of hypoglycemic agents on vascular complications in patients with adult-onset diabetes: III. Clinical implica¬ tions of UGDP results. JAMA 1971; 218:1400. 101. Lewis EJ, Hunsicker LG, Bain RP, Rohde RO. The effect of angiotensin¬ converting enzyme inhibition on diabetic nephropathy. N Engl J Med 1993; 329: 1456. 102. Blackshear JL, O'Callaghan WG, Califf RM. Medical approaches to the prevention of restenosis after coronary angioplasty. J Am Coll Cardiol 1987; 9:834. 103. Ellis SG, Roubin GS, King SB III, et al. In-hospital cardiac mortality after acute closure after coronary angioplasty: analysis of risk factors from 8,207 proce¬ dures. J Am Coll Cardiol 1988; 11:211. 104. LoGerfo FW. Vascular disease, matrix abnormalities and neuropathy: implications for limb salvage in diabetes mellitus. J Vase Surg 1987;5:793. 105. Green R, McNamara J. The effect of pentoxifylline on patients with in¬ termittent claudication. J Vase Surg 1988; 7:356. 106. Baumann JC. New prospects for the conservative management of pe¬ ripheral arterial disease: clinical investigations with pentoxifylline (Trental 430). Pharmatherapeutics 1983;l(Suppl 3):30. 107. Auer AJ, Hurley JJ, Bennington HB, et al. Distal tibial vein grafts for limb salvage. Arch Surg 1983; 118:587.

74. Ververis J, Ku L, Delafontaine P. Fibroblast growth factor regulates insulin-like growth factor-binding protein production by vascular smooth muscle cells. Am J Med Sci 1994;307:77. 75. Soffer LJ, lannaune A, Gabriloue L. Cushing's syndrome: a study of 50 patients. Am J Med 1961; 30:129. 76. Kerciakes DJ. Myocardial infarction in the diabetic patient. Clin Cardiol 1985;8:466.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

77. Factor SM, Okun EM, Minase T. Capillary microaneurysms in the human diabetic heart. N EnglJ Med 1980;302:384.

J.B. Lippincott Company, Philadelphia, © 1995.

78. Vadlamudi RVSV, Rogers RL, McNeill JH. The effect of chronic alloxanand streptozotocin-induced diabetes on isolated rat heart performance. Can J Phys¬ iol Pharmacol 1982; 60:902. 79. Rubier S, Dlugash J, Yuceoglu YZ, et al. New type of cardiomyopathy associated with diabetic glomerulosclerosis. Am J Cardiol 1972;30:599. 80. Carlstrom S, Karlefors T. Haemodynamic studies on newly diagnosed diabetics before and after adequate insulin treatment. Br Heart J 1970; 32:355. 81. Schaffer SW, Artman MF, Wilson GL. Properties of insulin-dependent and non-insulin-dependent diabetic cardiomyopathies. In: Kawai C, Abelmann WH, eds. Pathogenesis of myocarditis and cardiomyopathy. Tokyo: University of Tokyo Press, 1987:149. 82. Leland OS, Makie PC. Heart disease and diabetes. In: Marble A, Krall LP, Bradley RF, et al, eds. Joslin's diabetes mellitus. Philadelphia: Lea & Febiger, 1985: 83. Schaffer SW, Tan BH, Wilson GL. Development of a cardiomyopathy in a model of non-insulin-dependent diabetic. Am J Physiol 1985;248:H179. 84. Kerby AL, Radcliffe PM, Rundle JR. Diabetes and the control of pyruvate dehydrogenase in rat heart mitochondria by concentration ratios of adenosine tri¬ phosphate/adenosine diphosphate of reduced/oxidized nicotinamide-adenine di¬ nucleotide and of acetyl-coenzyme Al coenzyme A. Biochem J 1977; 164:504. 85. Pierce GN, Kutrsyk MJB, Dhalla NS. Alteration in Ca+2-binding by and composition of the cardiac sacrolemmal membrane in chronic diabetes Proc Natl Acad Sci USA 1983; 80:5412. 86. Dillmann WH. Methyl-palmoxirate increases Ca+2-myosin ATPase activ¬ ity and changes myosin isoenzyme distribution in the diabetic rat heart Am I Phvsiol 1985;248:E602. 1 87. Tanaka Y, Kashiwagi A, Saeki Y, Takagi Y. Effects of verapamil on the cardiac alpha 1-adrenoceptor signalling system in diabetic rats. Eur I Pharmacol 1993;244:105. 88. Aronstam RS. Insulin prevention of altered muscarinic receptor-G pro¬ tein coupling in diabetic rat atria. Diabetes 1989; 38:1611. 89. Garvey WT, Hardin D, Juhaszova M, Doninguez JH. Effects of diabetes on myocardial glucose transport system in rats: implications for diabetic cardiomy¬ opathy. Am J Physiol 1993;264:H387. 90. Dillmann WH, Barrieux A, Shanker R. Influence of thyroid hormone on myosin heavy chain mRNA and other messenger RNAs in the rat heart Endocrine Res 1989; 15:565. 91. MacKay JD, Page MMcB, Cambridge J, Watkins PJ. Diabetic autonomic neuropathy. Diabetologia 1980; 18:471. 92. Watkins PJ, MacKay JD. Cardiac denervation in diabetic neuropathy. Ann Intern Med 1980; 92:304. 93. T age MM, Watkins PJ. The heart in diabetes: autonomic neuropathy and cardiomyopathy. Clin Endocrinol Metab 1977;6:377. 94. Clark BF, Ewing DJ. Cardiovascular reflex test in the natural history of diabetic autonomic neuropathy. NY State J Med 1982;82:903. 95. Salomon NW, Page US, Okies JE, et al. Diabetes mellitus and coronary artery bypass. J Thorac Cardiovasc Surg 1983;85:264. 96. Johnson WD, Pedraza PM, Kayser KL. Coronary artery surgery in diabe¬ tes: 261 consecutive patients followed four to seven years. Am Heart I 1982-104-

CHAPTER

142

DIABETIC NEUROPATHY DOUGLAS A. GREENE, DAVID A. GELBER, MICHAEL A. PFEIFER, AND PATRICIA B. CARROLL

Peripheral neuropathy is probably the most common, and certainly one of the most troubling, of the chronic complications of diabetes.1 Although first described as a clinical entity almost 200 years ago, diabetic neuropathy was recognized relatively re¬ cently as a sequela rather than a cause of diabetes,2 and its patho¬ genesis and therapy remain controversial. Advances in our un¬ derstanding of nerve metabolism have provided a rationale for definitive therapeutic approaches that now are undergoing clini¬ cal trials.3

DEFINITION AND PREVALENCE Diabetic neuropathy is characterized as clinical or subclinical based on clinical signs and symptoms, and as distal symmetrical polyneuropathy, focal or multifocal neuropathy, and autonomic neu¬ ropathy, depending on its distribution (Table 142-1). In both insulin-dependent (type I) and non-insulin-dependent (type II) diabetes mellitus, the prevalence of neuropathy varies with the duration and severity of hyperglycemia.4 Clinical neuropathy is rarely reported within the first 5 years of diabetes, except in pa¬ tients with type II disease, in whom preexisting asymptomatic hyperglycemia is difficult to exclude.2. In a 25-year prospective study of 4400 unselected diabetics, neuropathy, defined clini¬ cally as the loss of Achilles or patellar reflexes, or both, plus di¬ minished vibratory sensation, with or without other clinical signs and symptoms of peripheral neuropathy, was detected in 12% of patients at diagnosis, primarily older, presumably type II diabet¬ ics.4 Thereafter, prevalence increased linearly with the duration of diabetes, reaching 50% after 25 years. The duration-corrected prevalence and incidence rates of neuropathy did not differ sub¬ stantially with age, suggesting that neuropathy occurs similarly

Ch. 142: Diabetic Neuropathy TABLE 142-1 Ciassification of Diabetic Neuropathy I. Distal symmetric polyneuropathy A. Sensory-motor and autonomic ("mixed") neuropathy B. Sensory neuropathy 1. Predominantly large-fiber involvement 2. Predominantly small-fiber involvement 3. Diffuse (large- and small-) fiber involvement C. Motor neuropathy

II. Focal and multifocal neuropathies A. Cranial neuropathy B. Mononeuropathy/mononeuropathy multiplex 1. Entrapment mononeuropathy 2. Other mononeuropathies C. Radiculopathy (intercostal neuropathy) D. Plexopathy (asymmetric motor neuropathy)

III. Autonomic neuropathy (Reprinted with permission from Greene DA, Pfeifer MA. In: Olefsky JM, Sherwin RS, eds. Diabetes mellitus, management and complications. New York: Churchill Living¬ stone 1985:223.)

in type I and type II diabetes. Neuropathy also complicates sec¬ ondary forms of diabetes (pancreatectomy, nonalcoholic pancre¬ atitis, and hemochromatosis)2 and, therefore, reflects the dura¬ tion and severity, rather than the underlying pathogenesis, of diabetes. Because the frequency of neuropathy, retinopathy, and ne¬ phropathy increases during the first 10 to 15 years of diabetes, patients with one complication are also more likely to have an¬ other, based on chance alone;4 furthermore, end-stage renal fail¬ ure may accelerate retinopathy and neuropathy.5 Discordance for renal, retinal, and neurologic complications is common, par¬ tially because of the markedly different independent variables operative on each (e.g., hypertension for nephropathy and reti¬ nopathy, but not for neuropathy5; alcohol for neuropathy, but not for nephropathy or retinopathy).2

1271

hemoglobin in response to metabolic therapy, indicating a per¬ sisting metabolic component to conduction slowing.2,7 Conduc¬ tion is further slowed with the development of clinically overt neuropathy; however, the predictive value of conduction slow¬ ing in subclinical neuropathy for the subsequent clinical devel¬ opment or the course of neuropathy is uncertain. Because maxi¬ mum conduction velocity primarily reflects large rapidly conducting fibers, small-fiber neuropathy may not reveal itself in standard electrodiagnostic studies. In clinically overt neuropathy, most slowing of nerve con¬ duction is attributable to the loss of large-diameter nerve fibers, with a small, additional component for which there is no struc¬ tural explanation and which possibly reflects persistent direct metabolic effects (Fig. 142-1).8 Conversely, in acutely diabetic an¬ imals, the marked but reversible conduction slowing is unaccom¬ panied by any segmental demyelination or axonal degeneration.2 Studies in more chronically diabetic BB-rats have identified a novel lesion: loss of specialized paranodal junctional complexes between terminal loops of myelin and the axolemma. This lesion appears to account for the less rapidly reversible conduction slowing in this animal model.9 Thus, conduction slowing in dia¬ betes reflects a dynamic combination of altered structure and me¬ tabolism in a diabetic nerve that cannot be easily differentiated electrophysiologically.

CLINICAL SYNDROMES OF DIABETIC NEUROPATHY Clinical diabetic neuropathy is categorized into distinct syn¬ dromes according to the distribution of the neurologic deficit, each syndrome having a characteristic presentation and course (see Table 142-1). ITowever, in many cases, the occurrence of overlap syndromes precludes a straightforward classification.

DISTAL SYMMETRIC POLYNEUROPATHY Distal symmetric polyneuropathy is the most commonly rec¬ ognized peripheral neurologic complication of diabetes.2 The

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PATHOLOGY OF DIABETIC NEUROPATHY Distal neurogenic atrophy, detectable within the first few weeks of diabetes, precedes the more generalized structural al¬ terations involving all major peripheral nerve components.6 The numbers of larger nerve fibers are reduced and smaller fibers in¬ creased, suggesting either sprouting of smaller, or shrinkage of larger, fibers. Demyelination and remyelination are mild except in rare cases with associated, prominent proliferation of Schwann cells.2,6 Axonal loss and atrophy account for most clin¬ ical and functional impairment in diabetic polyneuropathy. Endoneurial fibrosis, connective tissue proliferation and thickening, and reduplication of endoneurial capillary and perineurial base¬ ment membranes, all parallel the nerve fiber damage; however, none are pathognomonic for diabetes. Similar, but slightly more advanced, lesions accompany overt clinical neuropathy; thus, a nerve biopsy is rarely helpful, either for diagnosis or for staging.

ELECTROPHYSIOLOGY A slightly delayed nerve conduction at the onset of type I diabetes is rapidly normalized with the institution of insulin ther¬ apy, implying an early reversible metabolic component to nerve conduction slowing.2 Thereafter, nerve conduction varies in¬ versely with the duration and severity of hyperglycemia; it im¬ proves proportionately with the decrease of serum glycosylated

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300 mg/day of albumin) or a diminished GFR within a period of 10 years. Patients with highgrade microalbuminuria (>100 mg/day) are at particularly high risk of developing renal impairment.57 Microalbuminuria also predicts the development of diabetic nephropathy in type II dia¬ betics,57-60 although it is not as good a predictor as in type I dia¬ betics. Because of the high predictive value of microalbuminuria for the development of renal disease, it is generally accepted that microalbuminuria represents the earliest phase of diabetic ne¬ phropathy, especially in patients with IDDM. Some caution must be exercised concerning the clinical in¬ terpretation of microalbuminuria.61 The upper limit of normal should not be considered as absolute, and common sense must be used in judging borderline cases. A number of factors (e.g., exercise, high blood pressure, urinary tract infection, and poor diabetic control) elevate the urinary albumin excretion rate.62 Ob¬ viously, if such confounding factors are present, the finding of microalbuminuria does not necessarily imply incipient diabetic nephropathy. Although several authors have suggested that exercise-induced microalbuminuria is a harbinger of diabetic re¬ nal disease, there is little experimental data to support this. An¬ other concern about the clinical interpretation of microalbumin¬ uria centers on its development during the first 5 years in IDDM patients. In these patients, microalbuminuria is unlikely to have the same ominous prognostic significance as microalbuminuria that occurs 10 to 15 years after the onset of diabetes. This state¬ ment is not applicable to type II diabetics, who may have had their disease for many years before the diagnosis of diabetes was established. The interpretation of microalbuminuria in white type II diabetics is further complicated by the observation that about 25% of such patients have microalbuminuria, yet the inci¬ dence of renal disease in this population is only 5% to 10%.3,58,63,64 Although microalbuminuria predicts the develop¬ ment of renal disease in type II diabetics, it is not as good a pre¬ dictor as in type I diabetic patients. Thus, NIDDM patients with microalbuminuria have a 5-fold (as opposed to 20-fold in IDDM) increased risk of developing proteinuria over a 10-year period. However, in type II diabetics, microalbuminuria is highly predic¬ tive of cardiovascular (myocardial infarction, stroke) morbidity and mortality.58,63,64,65 From the routine laboratory standpoint, the earliest detect¬ able manifestation of diabetic glomerulosclerosis is Albustixpositive proteinuria (see Fig. 144-2), which begins about 15 to 18 years after the diagnosis of diabetes.50,54-57,66 At this time, the GFR may still be normal or even elevated, but within a mean of 5 years after the onset of proteinuria, the GFR begins to decline, and the serum urea nitrogen and creatinine concentrations in¬ crease. Within 3 years after the first elevation of serum creatinine concentration, about half of the patients have progressed to endstage renal insufficiency. Heavy proteinuria (>3 g/day) and the nephrotic syndrome are common, occurring in over half of those who progress to end-stage renal failure. This course may be different in type II diabetics. NIDDM patients often have signifi-

1288

PART IX: DISORDERS OF FUEL METABOLISM

cant but low-grade proteinuria (250-500 mg/day), yet renal function remains stable and serial kidney biopsies fail to demon¬ strate progressive renal disease.3'67

LABORATORY ABNORMALITIES

ilar observations have been made in recent-onset, type II diabet¬ ics.71 However, in long-term diabetics with reduced GFR and diabetic glomerulosclerosis, the TmG is raised, and glucose in the urine becomes an unreliable means of monitoring the adequacy of diabetic control. Even in diabetic patients without renal dis¬ ease, glucosuria correlates poorly with the plasma glucose concentration.

PROTEINURIA Proteinuria is the earliest laboratory manifestation of dia¬ betic renal disease. Using fractional dextran clearances and uri¬ nary albumin and IgG excretion, the increased transglomerular flux of proteins in IDDM patients has been shown to result from an augmented transglomerular ultrafiltration pressure gradient and an alteration in the molecular charge of the glomerular bar¬ rier that results from the loss of anionic charges (heparin sulfate and sialic acid residues) from the GBM.44-47,68 Neither the num¬ ber of pores in the GBM nor the pore size is altered by the diabetic condition.68 Early in the course of diabetic nephropathy, loss of barrier charge selectivity, without alteration of pore size diameter, appears to be the primary factor that allows the es¬ cape of albumin without change in the clearance of other macromolecules.13

GLOMERULAR FILTRATION RATE The GFR often remains elevated, although marked renal his¬ tologic changes are present. Thus, a decline in GFR from elevated to normal values without an improvement in metabolic control represents an ominous finding. The most widely employed labo¬ ratory tests for GFR are the serum creatinine and the serum urea nitrogen concentrations. However, both are influenced by prerenal (i.e., extracellular fluid volume depletion) and postrenal (i.e., urinary tract obstruction) factors. More importantly, the GFR may decline by 40% to 50% before either test increases into the abnormal range. Therefore, many authors have advocated serial determinations of the creatinine clearance. In patients with renal failure of diverse causes, a plot of the reciprocal of the serum creatinine concentration as a function of time is useful in follow¬ ing the progression of renal disease. Pragmatically, the author advocates following the creatinine clearance in diabetic patients with normal serum creatinine levels. Once the serum creatinine concentration becomes elevated, either the reciprocal of the se¬ rum creatinine or the creatinine clearance can be followed. The GFR is determined by two factors: the net transmem¬ brane ultrafiltration pressure and the glomerular ultrafiltration coefficient. The ultrafiltration pressure is governed by the balance between the transmembrane hydraulic pressure, which increases GFR, and the intraglomerular oncotic pressure, which decreases GFR. In the rat, experimental diabetes elevates the transmem¬ brane ultrafiltration pressure.69 Because the glomerular capillary oncotic pressure is normal or reduced in patients with diabetic nephropathy, this factor cannot explain the decrease in GFR. By exclusion, therefore, it has been concluded that the glomerular ultrafiltration coefficient must be reduced. The ultrafiltration co¬ efficient is determined by the surface area available for filtration and the hydraulic permeability. Changes in the latter term have not been evaluated. Early in the course of IDDM, the total glo¬ merular capillary surface area is increased70 and, most likely, con¬ tributes to the glomerular hyperfiltration. However, in diabetic patients with clinically manifest renal disease, the mesangial ma¬ trix is greatly expanded, with obliteration of many capillary lumina.5 ,5“ Anatomically, it is likely that a reduction in surface area for filtration plays a significant role in the decline in GFR in pa¬ tients with advanced diabetic nephropathy.

GLUCOSURIA In normal persons, the maximum tubular reabsorptive ca¬ pacity for glucose (Tmc) varies inversely with the GFR, and sim¬

HYPERKALEMIA Normally, potassium homeostasis depends on both renal and extrarenal mechanisms.72,73 Many factors predispose the di¬ abetic to the development of hyperkalemia. The primary hor¬ mones that regulate the distribution of potassium between intra¬ cellular and extracellular compartments are insulin, epinephrine, and aldosterone.72 73 Because all of these hormones may be defi¬ cient, it is not surprising that hyperkalemia is so prevalent in the diabetic population.72 Furthermore, as the plasma glucose con¬ centration rises, the increased tonicity causes an osmotic shift of fluid and electrolytes, primarily potassium, out of cells. Metabolic acidemia, common in diabetic patients, also predisposes to hy¬ perkalemia. During the development of metabolic acidemia, about half of a hydrogen ion load is buffered within cells; this occurs in exchange for potassium ions.72,73 Renal mechanisms also contribute to the development of hy¬ perkalemia in the diabetic patient. When the GFR falls to less than 15 to 20 mL/min, the ability of the kidney to excrete potas¬ sium may become impaired.72 Many type I diabetic patients dem¬ onstrate a marked interstitial nephritis with prominent tubular atrophy. Because most urinary potassium is derived from distal and collecting tubular cell secretion, renal potassium excretion becomes impaired. Hypoaldosteronism is common in diabetics, particularly in those with evidence of impaired renal function.72,74Most patients have no clinical symptoms and are diagnosed on routine labora¬ tory screening or during evaluation for some other, unassociated illness. The baseline plasma aldosterone concentration is low and fails to increase normally after volume contraction. In most pa¬ tients, the plasma renin level also is reduced and accounts for the hypoaldosteronism. However, in about 20% of patients with hypoaldosteronism, normal basal renin values have been re¬ ported.72'75 Moreover, all patients with the syndrome of hyporeninemic hypoaldosteronism have clinically significant hyperka¬ lemia, which is the most potent stimulus to aldosterone secretion. This suggests that, along with hyporeninemia, there may be a primary adrenal defect in aldosterone secretion. This hypothesis is supported by the observation that the aldosterone response to angiotensin II and adrenocorticotropic hormone, agents which directly stimulate aldosterone secretion by the zona glomerulosa, is markedly impaired in persons with hypoaldosteronism.72,74 The cause of the defect in aldosterone secretion is unknown. A number of mechanisms have been suggested. Hyporeninemia could result from damage to the juxtaglomerulosa apparatus, im¬ paired conversion of the biologically inactive renin precursor (“big renin") to renin, decreased circulating catecholamine levels or autonomic neuropathy, diminished circulating prostaglandin levels, or chronic extracellular fluid volume expansion secondary to hyperglycemia and sodium retention. However, none of these explanations can satisfactorily account for the development of hyporeninemia in most diabetics. Impaired aldosterone secretion may be caused by intracellular potassium depletion within the zona glomerulosa of the adrenal gland secondary to insulin de¬ ficiency or insulin resistance.68,71 Several enzymatic steps in¬ volved in aldosterone biosynthesis are potassium dependent.72 A disruption of normal tubuloglomerular feedback mechanisms may also suppress aldosterone secretion.72,76,77 In diabetic pa¬ tients with fasting plasma glucose levels in excess of 180 mg/dL, there is a large increase in the filtered load of glucose. The resul¬ tant osmotic diuresis could impair sodium and chloride reabsorp¬ tion by all segments of the nephron, disrupting the normal tubu-

Ch. 144: Diabetic Nephropathy loglomerular feedback control mechanism and leading to suppression of renin and aldosterone secretion. The complexity of the alterations in the renin-aldosterone axis in the diabetic is underscored by a report in which the aldo¬ sterone axis was characterized in 59 normokalemic diabetics with normal GFR.78 In half of the patients, both the renin and aldoste¬ rone responses were normal; 10% demonstrated diminished al¬ dosterone secretion despite a normal renin response; 20% had impaired renin release with a normal aldosterone response; and 20% manifested impaired secretion of both renin and aldoste¬ rone. These results suggest that there are multiple defects in the renin-aldosterone axis and that the origin of hyperkalemia is multifactorial. Many drugs impair aldosterone secretion and, if used in the diabetic, the plasma potassium concentration should be closely monitored. Of these, the /3-blockers are the most widely known. Captopril, a converting enzyme inhibitor, has been advocated for the treatment of diabetic nephropathy.79 This agent frequently causes hyperkalemia, and this complication should be monitored closely. Another widely used class of drugs, the nonsteroidal antiinflammatory prostaglandin inhibitors, causes hyporeninemic hypoaldosteronism and hyperkalemia.72 The diuretic agents (e.g., spironolactone, triamterene, and amiloride) block potassium secretion by the renal tubular cell.72

METABOLIC ACIDOSIS Metabolic acidosis commonly is observed in type I diabetic patients.72,74,80 Metabolic acidosis can be divided into two broad categories: anion gap and nonanion gap or hyperchloremic. The anion gap is calculated by subtracting the concentrations of the major anions (chloride plus bicarbonate) from the major cation (sodium). The difference should not exceed 12 ± 2 mEq/L. If the value is greater than 14 mEq/L, an anion gap acidosis is present. In the diabetic, there are three causes of an anion gap acidosis: renal insufficiency, ketoacidosis, and lactic acidosis. The latter two are discussed in Chapter 149. In diabetic nephropathy, as in other causes of chronic renal disease, when the GFR declines to 20 to 25 mL/min, the ability of the kidney to excrete titratable acid becomes impaired, and the laboratory manifestation is an anion gap acidosis. The causes of an anion gap acidosis are well known to the clinician. Less well recognized is the frequent occurrence of a hy¬ perchloremic (or nonanion gap) metabolic acidosis. The syndrome of hypoaldosteronism is commonly observed in diabetic patients, particularly those with renal impairment.72,74 75 Aldosterone is an important regulator of ammonia production and hydrogen ion secretion by the distal nephron, and over half of the reported cases of hyporeninemic hypoaldosteronism present with a hy¬ perchloremic metabolic acidosis.72,74,75 Because aldosterone does not affect urinary acidification, urine pH remains acidic (pH < 5.4). Some diabetic patients have a primary renal tubular defect in hydrogen secretion and present with true distal renal tubular acidosis, that is, an inability to acidify the urine (pH >5.4) despite systemic acidosis. This defect may be related to the prominent interstitial nephritis, to the tubular basement membrane thicken¬ ing, or to an intracellular abnormality in any of the steps involved in hydrogen ion secretion. Other diabetics may present with a hyperchloremic metabolic acidosis due to widespread chronic in¬ terstitial nephritis with decreased ammonia production. Their urine pH is maximally acidic, indicating that the ability of the distal tubule and collecting duct to generate a steep pH gradient is intact. In these patients, the primary problem is impaired am¬ monia production, leading to a decrease in the total amount of hydrogen ion that can be excreted. In the absence of ammonia, which is one of the major urinary buffers, the urine pH is maxi¬ mally acidic. Hyperkalemia may also cause a hyperchloremic metabolic acidosis by inhibiting ammonia synthesis by the renal tubular cell.

1289

CLINICAL CORRELATIONS It often is stated that diabetic nephropathy is unusual in the absence of retinopathy, neuropathy, and hypertension. These as¬ sociations were first popularized by Root and colleagues,81 who referred to the triopathy of diabetes: nephropathy, retinopathy, and neuropathy. The occurrence of this triad was supported by other studies.82 However, the validity of this association has also been challenged.83

DIABETIC RETINOPATHY Diabetic retinopathy (e.g., hemorrhages, exudates, prolifer¬ ative retinopathy) is present in most diabetic patients with endstage renal failure who are admitted into dialysis or transplanta¬ tion programs.84 However, when diabetic nephropathy is first diagnosed (i.e., documentation of persistent proteinuria or eleva¬ tion of the serum creatinine concentration), 30% to 40% of pa¬ tients do not have evidence of diabetic retinopathy by routine ophthalmologic examination,66,82,85 even though fluorescein an¬ giography will demonstrate typical diabetic abnormalities in es¬ sentially 100% of patients. As the renal disease progresses, how¬ ever, diabetic retinopathy appears to accelerate. 83 In one study, evidence of retinopathy was noted in only 61 of 150 diabetic pa¬ tients when nephropathy was first diagnosed, but retinal in¬ volvement developed in another 42 during the follow-up.66 In diabetic patients placed on hemodialysis, a rapid progression of diabetic retinopathy often ensues. A dissociation between reti¬ nopathy and nephropathy is evident if one examines diabetic pa¬ tients with established retinopathy. After 15 to 20 years, over 80% of diabetic patients have evidence of retinopathy, but as many as 30% to 50% have no laboratory evidence of renal dis-

DIABETIC NEUROPATHY The association between diabetic nephropathy and neurop¬ athy is much less impressive than between diabetic nephropathy and retinopathy. In patients who have had diabetes for 20 years, about half have some evidence of neuropathic involvement.89 In diabetics with end-stage renal failure, the incidence of neuropa¬ thy varies from 60% to 90%.56,86 However, the specificity of these neuropathologic abnormalities must be questioned because dial¬ ysis often leads to their reversal.90 As with retinopathy, uremia appears to exacerbate the progression of diabetic neuropathy. When diabetic nephropathy is first diagnosed, less than half of patients have clinically evident diabetic neuropathy.

HYPERTENSION Increased blood pressure is uncommon (10%-20%) when diabetic nephropathy (i.e., persistent proteinuria) is first diag¬ nosed.66,91 However, once the serum creatinine concentration be¬ comes elevated, there is a progressive increase in the incidence of hypertension, which correlates closely with the severity of the renal disease.91 When end-stage renal failure ensues, 70% to 80% of diabetic patients are hypertensive.6*191 Patients with heavy proteinuria are particularly prone to develop hypertension. In most patients, the hypertension appears to be volume dependent and becomes relatively easy to control after patients are started on dialysis and dry weight is attained.92,93 There is little evidence to suggest that renin plays any role in the genesis of the hypertension.91

EDEMA The full-blown Kimmelstiel-Wilson syndrome includes edema, hypertension, proteinuria, and azotemia. In patients without renal disease or in those with early proteinuria (1 g/day) and renal insuffi¬ ciency (serum creatinine > 2 mg/dL) exceeds 50%, and the inci¬ dence of end-stage renal disease is about 50%.39,40,154,155 Renal histologic changes closely resemble those in IDDM patients with renal insufficiency. Thus, in this well-defined genetic population, the course of diabetic nephropathy is similar to that in IDDM. It is likely, therefore, that the natural history of renal disease in whites with NIDDM resembles that in Pima Indians and IDDM patients.

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74. DeFronzo RA. Hyperkalemia and hyporeninemic hypoaldosteronism. Kidney Int 1980; 17:118. 75. Schambelan M, Sebastian A, Biglieri E. Prevalence, pathogenesis, and functional significance of aldosterone deficiency in hyperkalemic patients with chronic renal insufficiency. Kidney Int 1980; 17:89. 76. Hostetter JH, Rennke HG, Brenner BM. The case for intrarenal hyperten¬ sion in the initiation and progression of diabetic and other glomerulopathies. Am J Med 1982; 72:375. 77. Brenner BM, Meyer TW, Hostetter TH. Dietary protein intake and the progressive nature of kidney disease. N Engl J Med 1982; 307:652. 78. deChatel R, Weidmann P, Flammer J, et al. Sodium, renin, aldosterone, catecholamines and blood pressure in diabetes mellitus. Kidney Int 1977; 12:412. 79. Taguma Y, Kitamoto Y, Futaki G, et al. Effect of captopril on heavy pro¬ teinuria in azotemic diabetics. N Engl J Med 1985; 313:1617. 80. Halperin ML, Bear RA, Hannaford MC, Goldstein MB. Selected aspects of the pathophysiology of metabolic acidosis in diabetes mellitus. Diabetes 1981; 30: 781. 81. Root HF, Porte WH, Frehner H. Triopathy of diabetes: sequence of neu¬ ropathy, retinopathy, and nephropathy. Arch Intern Med 1984; 94:931. 82. Pirart J. Diabetes mellitus and its degenerative complications: a pros¬ pective study of 4,400 patients observed between 1944 and 1973. Diabetes Care 1978; 1:168. 83. Bilous RW, Viberti GC, Christiansen JS, et al. Dissociation of diabetic complications in insulin-dependent diabetics: a clinical report. Diabetic Nephropa¬ thy 1985;4:73. 84. Comty CM, Kjellstrand D, Shapiro FL. Results of treating diabetic pa¬ tients by chronic hemodialysis. Dialysis Transplantation 1976; 5:20. 85. Deckert T, Paulsen JE. Prognosis for juvenile diabetics with late diabetic manifestations. Acta Med Scand 1968; 183:351. 86. Kahn HA, Bradley FR. Prevalence of diabetic retinopathy: age, sex, and duration of diabetes. Br] Ophthalmol 1975; 59:345. 87. Feldman JN, Kirsch SR, Beyer MM, et al. Prevalence of diabetic nephrop¬ athy at the time of treatment for diabetic retinopathy. In: Friedman EA, L'Esperance FA, eds. Diabetic renal-retinal syndrome. New York: Grune & Stratton, 1982:9. 88. Chahal PS, Kohner EM. The relationship between diabetic retinopathy and diabetic nephropathy. Diabetic Nephropathy 1983;2:4. 89. McCrary RF, Pitts TO, Puschett JB. Diabetic nephropathy: natural course, survivorship, and therapy. Am J Nephrol 1981; 1:206. 90. Najarian JS, Sutherland DER, Simmons RL, et al. Kidney transplantation for the uremic diabetic patient. Surg Gynecol Obstet 1977; 144:682. 91. Ritz E, Hasslacher C. Genesis and treatment of hypertension in diabetes mellitus. Diabetic Nephropathy 1984; 3:2. 92. Kjellstrand CM, Whitley K, Comty CM, Shapiro FL. Dialysis in patients with diabetes mellitus. Diabetic Nephropathy 1983; 2:5. 93. Massry SG, Feinstein El, Goldstein DA. Early dialysis in diabetic patients with chronic renal failure. Nephron 1979; 23:2. 94. Strate M, Thygesen K, Hansen L, Harvald B. Survival in diabetic hyper¬ tensives. Diabetic Nephropathy 1985;4:7. 95. Parving H-H, Smidt UM, Friisberg B, et al. A prospective study of glo¬ merular filtration rate and arterial blood pressure in insulin-dependent diabetics with diabetic nephropathy. Diabetologia 1981;20:457. 96. Christensen CK, Mogensen CE. Correlations between blood pressure and kidney function in insulin-dependent diabetics: with emphasis on incipient ne¬ phropathy. Diabetic Nephropathy 1985;4:34. 97. Mogensen CE. Long-term antihypertensive treatment inhibiting progres¬ sion of diabetic nephropathy. Br Med J 1982;285:685. 98. Lewis EJ, Hunsicker LG, Bain RP, Rohde RD. The effect of angiotensinconverting-enzyme inhibition on diabetic nephropathy. N Engl J Med 1993; 3291456. 99. Berkman J, Rifkin H. Unilateral nodular diabetic glomerulosclerosis (Kimmelsteil-Wilson): report of a case. Metabolism 1973;22:175. 100. Krolewski AS, Canessa M, Warram JH, et al. Predisposition to hyper¬ tension and susceptibility to renal disease in insulin-dependent diabetes mellitus N Engl J Med 1988;318:140. 101. Mauer SM, Steffes MW, Connett J, et al. The development of lesions in the glomerular basement membrane and mesangium after transplantation of nor¬ mal kidneys to diabetic patients. Diabetes 1983;32:948. 102. Steffes MW, Buchwald H, Wigness BD, et al. Diabetic nephropathy in the uninephrectomized dog: microscopic lesions after one year. Kidney Int 1982- 21 • 721. 103. Parving H-H, Viberti GC, Keen H, et al. Hemodynamic factors in the genesis of diabetic microangiopathy. Metabolism 1983;32:943. 104. Bressler P, DeFronzo RA. Drugs and diabetes. Diabetes Rev 1994;2:53. 105. Tuttle KR, DeFronzo RA, Stein JH. Treatment of diabetic nephropathy: a rational approach based on its pathophysiology. Semin Nephrol 1991; 11:220. 106. Ravid M, Savin H, Jutrin I, et al. Long-term stabilizing effect of angio¬ tensin-converting enzyme inhibition on plasma proteinuria in normotensive type II diabetic patients. Ann Intern Med 1993; 188:577. 107. Jerums G, Allen FJ, Tsalamandris C, Cooper ME. Angiotensin convert¬ ing enzyme inhibition and calcium channel blockade in incipient diabetic nephrop¬ athy. Kidney Int 1992;41:904. 108. Marre M, Chatellier G, Leblanc H, et al. Prevention of diabetic nephrop¬ athy with enalapril in normotensive diabetics with microalbuminuria Br Med J 1988;297:1092. 109. Mathiesen ER, Hommel E, Giese J, Parving H-H. Captopril postpones and may even prevent development of diabetic nephropathy. Diabetes 1990;39(Suppl 1):72A.

110. Rudberg S, Aperia P, Freyschuss U, Persson B. Enalapril reduces mi¬ croalbuminuria in young normotensive type 1 (insulin-dependent) diabetic patients irrespective of its hypotensive effect. Diabetologia 1990; 33:470. 111. Lithell HOL. Effect of antihypertensive drugs on insulin, glucose, and lipid metabolism. Diabetes Care 1991; 14:203. 112. Ellenberg M. Diabetic neuropathy. In: Ellenberg M, Rifkin H, eds. Dia¬ betes mellitus: theory and practice. New Hyde Park, NY: Medical Examination Pub¬ lishers, 1983:777. 113. Bryd L, Sherman RL. Radio-contrast-induced renal failure: a clinical and pathophysiologic review. Medicine (Baltimore) 1979;58:270. 114. Ballard DJ, Humphrey LL, Melton LJ, et al. Epidemiology of persistent proteinuria in type II diabetes mellitus: population-based study in Rochester, Min¬ nesota. Diabetes 1988;37:405. 115. Mogensen CE. Microalbuminuria predicts clinical proteinuria and early mortality in maturity-onset diabetes. N Engl J Med 1984;310:356. 116. Watts GF, Harris R, Shaw KM. The determinants of early nephropathy in insulin-dependent diabetes mellitus: a prospective study based on the urinary excretion of albumin. Q J Med 1991;288:365. 117. Norgaard K, Storm B, Graae M, Feldt-Rasmussen B. Elevated albumin excretion and retinal changes in children with type 1 diabetes are related to long¬ term poor blood glucose control. Diabetic Med 1989; 6:325. 118. Torffvit O, Agardh E, Agardh CD. Albuminuria and associated medical risk factors: a cross-sectional study in 476 type 1 (insulin-dependent) diabetic pa¬ tients. Part 1. J Diab Compl 1991;5:23. 119. Tuttle KR, Stein JH, DeFronzo RA. The natural history of diabetic ne¬ phropathy. Semin Nephrol 1990; 10:184. 120. Microalbuminuria Collaborative Study Group. Microalbuminuria in type I diabetic patients. Diabetes Care 1992; 15:495. 121. Rasch R. Prevention of diabetic glomerulopathy in streptozotocin dia¬ betic rats by insulin treatment: kidney size and glomerular volume. Diabetologia 1979; 16:125. 122. Mauer SM, Steffes MW, Sutherland DER, et al. Studies of the rate of regression of the glomerular lesions in diabetic rats treated with pancreatic islet transplantation. Diabetes 1975;24:280. 123. Bilous RW, Mauer SM, Sutherland DER, et al. The effects of pancreas transplantation on the glomerular structure of renal allografts in patients with insulin-dependent diabetes. N Engl J Med 1989;321:80. 124. Feldt-Rasmussen B. Microalbuminuria and clinical nephropathy in type 1 (insulin-dependent) diabetes mellitus: pathophysiological mechanisms and inter¬ vention studies. Danish Med Bull 1989;36:405. 125. Viberti GC, Walker JD. Diabetic nephropathy: etiology and prevention. Diabetes Metab Rev 1988;4:147. 126. Mogensen CE. Prevention and treatment of renal disease in insulindependent diabetes mellitus. Semin Nephrol 1990; 10:260. 127. Feldt-Rasmussen B, Mathiesen E, Deckert T. Effect of two years of strict metabolic cotnrol on the progression of incipient nephropathy in insulin-dependent diabetes. Lancet 1986; 2:1300. 128. Dahl-Jorgensen K, Hanssen KF, Kierulf P, et al. Reduction of urinary albumin excretion after 4 years of continuous subcutaneous insulin infusion in insulin-dependent diabetes mellitus. Acta Endocrinol 1988; 117:19. 129. The Kroc Collaborative Study Group. Blood glucose control and the evolution of diabetic retinopathy and albuminuria: a preliminary multicenter trial. N Engl J Med 1984;311:365. 130. DeFronzo RA, Alvestrand A, Smith D, et al. Insulin resistance in uremia. J Clin Invest 1981; 67:563. 131. DeFronzo RA, Tobin JD, Rowe JW, Andres R. Glucose intolerance in uremia: quantification of pancreatic beta cell sensitivity to glucose and tissue sensi¬ tivity to insulin. J Clin Invest 1978;62:425. 132. Garber AJ, Bier D, Cryer PE, Pagliara AS. Hypoglycemia in compen¬ sated chronic renal insufficiency: substrate limitation of gluconeogenesis. Diabetes 1974;23:982. 133. Grajower M, Walter L, Albin J. Hypoglycemia in chronic hemodialysis patients: association with propranolol use. Nephron 1980; 26:126. 134. Ama-r P, Knanna R, Leibel B, et al. Continuous ambulatory peritoneal dialysis in diabetics with end stage renal disease. N Engl J Med 1982;306:625. 135. Crossley K, Kjellstrand GM. Intraperitoneal insulin for control of blood sugar in diabetic patients during peritoneal dialysis. Br Med J 1971; 1:269. 136. Nolph KD. Chronic peritoneal dialysis in a patient with diabetes melli¬ tus and heart disease. Kidney Int 1979; 15:698. 137. Mitchell JC, Frohnert PP, Kurtz SB, Anderson CF. Chronic peritoneal dialysis in juvenile-onset diabetes mellitus: a comparison with hemodialysis. Mayo Clin Proc 1978; 53:775. 138. Comty CM, Leonard A, Shapiro FL. Nutritional and metabolic problems in dialyzed patients with diabetes mellitus. Kidney Int 1974;6:S51. 139. Jacobs C, Broyer M, Brunner FP, et al. Combined report on regular dial¬ ysis and transplantation in Europe, XI, 1980. Proc Eur Dial Transplant Assoc 1981; 18:2. 140. Bryan FA. National Dialysis Registry seventh annual progress report AK-CUP. NIAMD Report No. AK-7-7-1387. Research Triangle Park, NC. 141. Sutherland DER, Fryd DS, Morrow CE, et al. Kidney transplantation in diabetics at the University of Minnesota: an analysis of results by era. Transplant Proc 1983; 15:1110. 142. Fryd DS, Kruse LV, Simmons RL, et al. Donor source, number of transplants, age at transplant, and diabetes: risk factors in the cyclosporine era. Transplant Proc 1989;21:1655. 143. Hostetter TH, Rennke HG, Brenner BM. Compensatory renal hemody-

Ch. 145: Diabetes and the Eye namic injury: a final common pathway of residual nephron destruction. Am J Kid¬ ney Dis 1982; 1:310. 144. Barsotti G, Guiducei A, Ciardella F, Giovannetti S. Effects on renal func¬ tion of a low nitrogen diet supplemented with essential amino acids and ketoanalogues and of hemodialysis and free protein supply in patients with chronic renal failure. Nephron 1981; 27:113. 145. Mitch WE, Bras E, Walser M. Long-term effects of a new ketoacid-amino acid supplement in patients with chronic renal failure. Kidney Int 1982; 22:371. 146. Giordano C. Protein restriction in chronic renal failure. Kidney Int 1982;22:401. 147. Editorial. Diet and nephropathy. Lab Invest 1989;60:165. 148. Klahr S, Levey AS, Beck GJ, et al. The effects of dietary protein restric¬ tion and blood-pressure control on the progression of chronic renal disease. N Engl J Med 1990;330:877. 149. Zeller KR, Whittaker E, Sullivan L, et al. Effect of restricting dietary pro¬ tein on the progression of renal failure in patients with insulin-dependent diabetes mellitus. N Engl J Med 1991;324:78. 150. Mauer SM, Sutherland DER, Steffes MW, et al. Pancreatic islet trans¬ plantation: effects on the glomerular lesions of experimental diabetes in the rat. Diabetes 1974; 23:748. 151. Viberti GC, Walker JD. Diabetic nephropathy: etiology and prevention. Diabetes Metab Rev 1988;4:147. 152. Yoshida Y, Fogo A, Shirago H, et al. Serial micropuncture analysis of single nephron function in subtotal renal ablation. Kidney Int 1988; 33:855. 153. Hatch FE, Watt MF, Kramer NC, et al. Diabetic glomerulosclerosis: a long-term follow-up study based on renal biopsies. Am J Med 1961; 31:216. 154. Teutsch SM. Risk factors for diabetic nephropathy among the Utes on the Uintah and Ouray Reservations. US Public Health Service Report, 1981. 155. Bahr AA. Current status of dialysis as a method of treatment in kidney failure in the Gila River Indian Community. US Public Health Service Report, 1981.

1297

tes mellitus (IDDM), new studies indicate that over 50% of pa¬ tients develop retinopathy within that time. A large population study showed over 60% of patients with retinopathy by 10 years, and the prevalence approached 100% after 15 years.5 This inves¬ tigation also showed proliferative diabetic retinopathy (PDR), the most sight-threatening type, in 40% to 60% of patients with dia¬ betes for 20 or more years. This high prevalence had been sug¬ gested 20 years earlier, but it was at variance with other studies of the time.6 In a study of patients with type I diabetes followed from the onset of their diabetes, a 60% cumulative incidence of PDR was found by 40 years.7 In type I disease, background diabetic retinopathy (BDR) commonly develops after 5 years of diabetes and is ubiquitous by 15 to 20 years. PDR is uncommon before 10 years, develops dur¬ ing the second decade, and becomes very common after 20 years. Very young patients are relatively immune from developing sig¬ nificant eye disease until after puberty. Data on older patients (mostly type II or non-insulindependent diabetes mellitus [NIDDM]) show two major differ¬ ences: retinopathy is present in about 20% at the onset of diabe¬ tes, probably reflecting the uncertainty in dating the actual onset, and the percentage of patients developing any retinopathy or PDR is lower (i.e., 60%-80% develop retinopathy; 10%-20% de¬ velop PDR).8 Older patients at onset who do develop PDR do so after shorter durations of diabetes than their younger cohorts.9 DETERMINANTS

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

145

DIABETES AND THE EYE LAWRENCE I. RAND Diabetes is a leading cause of blindness and visual disability in the nations in which nutritional and infectious diseases have, for the most part, been controlled.1,2 The improved quality of medical care in these countries has allowed diabetic individuals to survive the 20 to 40 years necessary for severe eye complica¬ tions to develop. During the past 15 years, our knowledge of the natural history of diabetic eye disease has greatly increased, and equally impressive advances have been made in its treatment. Our knowledge about the determinants of this disease has in¬ creased but is still rudimentary. However, it now is possible to establish clinical management guidelines that should reduce dra¬ matically the occurrence of severe visual disability and blindness.

DIABETIC RETINOPATHY The principal cause of blindness among diabetics is disease of the retina. Those who are particularly interested in the cause and treatment of diabetic retinopathy commonly use several ab¬ breviations, which are listed in Table 145-1.

EPIDEMIOLOGY DISTRIBUTION Epidemiology is the study of the distribution and determi¬ nants of disease. Our knowledge of when and how often diabetic eye disease develops has been advanced by studies using stan¬ dardized photographic evaluations of the fundus to detect early retinopathy.3,4 Although older studies had suggested that retinopathy was uncommon before 10 years of type I or insulin-dependent diabe¬

There are many risk factors for diabetic retinopathy, but the evidence for most of these is inconclusive. The duration of diabe¬ tes has been uniformly accepted as an important factor, but it may be a surrogate variable, representing increasing exposure to one or more components of the diabetic syndrome. The most thoroughly investigated of these is the level of plasma glucose, and most studies have supported an association between lower plasma glucose levels and a lower incidence of retinopathy.10-14 The largest and most definitive of these studies was the Dia¬ betes Control and Complications Trial (DCCT), which random¬ ized 1441 IDDM patients, who were 13 to 39 years of age, be¬ tween standard diabetes therapy and an intensive therapy aimed at keeping blood sugars as close to normal as possible. After an average of more than 6 years of follow-up, intensively treated

TABLE 145-1 Abbreviations Used in Studying Diabetic Retinopathy OPHTHALMOLOGIC TERMS BDR

Background diabetic retinopathy

DR

Diabetic retinopathy

HMA

Hemorrhages and microaneurysms

HRC

High-risk characteristics

IDDM

Insulin-dependent diabetes mellitus

ILM

Internal limiting membrane

IRMA

Intraretinal microvascular abnormalities

NIDDM

Non-insulin-dependent diabetes mellitus

NPDR

Nonproliferative diabetic retinopathy

NVD

New blood vessels on the optic disc

NVE

New blood vessels elsewhere

PDR

Proliferative diabetic retinopathy

PPDR

Preproliferative diabetic retinopathy

TDR

Transitional diabetic retinopathy

EPIDEMIOLOGIC AND PATHOPHYSIOLOGIC STUDIES DCCT

Diabetes control and complications trial

DRS

Diabetic retinopathy study

DRVS

Diabetic retinopathy vitrectomy study

ETDRS

Early treatment diabetic retinopathy study

1298

PART IX: DISORDERS OF FUEL METABOLISM

TABLE 145-2 Diabetic Retinopathy Nonproliferative Background

Transitional

Preproliferative

Proliferative

Microaneurysm only or with occasional blotch hemorrhage or fleck of hard exudate

Significant blotch hemorrhages (STD2A) or intraretinal microvascular abnormalities (IRMA) or soft exudates or venous abnormalities

Three or more of the transitional lesions present in multiple fields or large amounts of any one lesion in the presence of others

New blood vessels on the optic disc (NVD); new blood vessels elsewhere (NVE); fibrous proliferation; preretinal hemorrhage; vitreous hemorrhage

patients without retinopathy at baseline showed a 27% reduction in the development of first microaneurysms and a 76% reduction in a sustained three-step change in retinopathy level from base¬ line. Among those already having some retinopathy, intensively treated patients showed a 54% reduction in the sustained threestep endpoint and a 47% reduction in the development of PDR. The risks of worsening albuminuria and of neuropathy were also reduced.15 This study established the value of intensive therapy aimed at near normoglycemia as the treatment of choice in IDDM. Whether NIDDM would benefit similarly was not ad¬ dressed by the DCCT, but many physicians in the diabetes com¬ munity have drawn that conclusion.153 The major adverse effects of intensive therapy were a threefold increase in severe hypogly¬ cemia and weight gain. Other factors in addition to hyperglycemia probably influ¬ ence retinopathy, the balance of which determines an individu¬ al's risk of developing severe retinopathy. Some factors are met¬ abolic and related to plasma glucose levels; others may be systemic but not necessarily diabetes specific; and others may be localized within the eye.16 Evidence exists that HLA-associated factors may influence retinopathy risk (see Chap. 188). Hypertension has been suggested as an important predictor of retinopathy.17 18 Because hypertension in these patients most often is associated with renal disease, it may be part of the dia¬ betic syndrome.19 Only about 50% of patients developing PDR have or ultimately develop nephropathy. This group has hyper¬ tension and a high mortality (i.e., 60% 5-year survival). The other 50% are nonhypertensive and have almost normal long-term survival.2" Hypertension may increase extravasation of intravas¬ cular fluid and large molecules, and an association with lipid de¬ posits in the retina has been found. It may, however, be the bal¬ ance between intravascular and extravascular (i.e., intraocular) pressure that has the greatest influence on this process. Although cigarette smoking is not a major risk factor for retinopathy, it should be avoided21 (see Chap. 221). After significant retinopathy develops, local factors within the eye related to the type and severity of retinopathy are the best predictors of long-term visual outcome.22 The most important of these is the presence of neovascularization on the optic disc (NVD), along with vitreous or preretinal hemorrhage, severe intraretinal hemorrhages and microaneurysms (HMA), and venous beading. Among systemic factors, only proteinuria is an important predic¬ tor of severe visual loss.

cludes the first microaneurysms, along with an occasional dot or blot hemorrhage or a hard exudate. Most diabetics develop this degree of retinopathy, and it is of limited prognostic importance unless it develops before puberty or after a very short duration of diabetes. It is the “noise" or “background" in the system. Patients who develop these changes may not progress any further, at least not for many years. The lesions may come and go, probably accounting for the small group of patients with no apparent retinopathy despite long-duration diabetes. It is unu¬ sual for an eye to have more than 10 microaneurysms without having at least one small intraretinal hemorrhage or fleck of exu¬ date. However, an eye may have several dozen microaneurysms without having any other lesions and still be considered BDR. This early stage of retinopathy is characterized pathophysiologically by predominantly intravascular and perivascular abnormal¬ ities: basement membrane thickening, pericyte loss, capillary di¬ lation, and microaneurysm formation.23,24 These processes antecede the first visibly detectable lesions and may be caused directly by the metabolic abnormalities of diabetes or secondarily by retinal hyperperfusion.25 Transitional Diabetic Retinopathy. The development of soft exudates (i.e., cotton wool spots), venous-caliber abnormalities, intraretinal microvascular abnormalities (IRMAs), or more exten¬ sive amounts of HMA moves an eye to a "transitional" stage of retinopathy26 (Fig. 145-2). In these conditions, the pathologic

CLASSIFICATION Pathologists have divided diabetic retinopathy into two groups, nonproliferative diabetic retinopathy (NPDR) and PDR, based on the absence or presence of preretinal new blood vessels or other fibroproliferative tissue. Previously, the term BDR had been used synonymously with NPDR. A clinically useful classi¬ fication scheme is shown in Table 145-2. NPDR is divided into three stages: BDR, now used in a more restricted way; transitional diabetic retinopathy; and preproliferative diabetic retinopathy. NONPROLIFERATIVE DIABETIC RETINOPATHY

Background Diabetic Retinopathy. BDR is the earliest ophthalmoscopically visible stage of retinopathy (Fig. 145-1) and in¬

FIGURE 145-1.

Scattered microaneurysms (arrows) or occasional blotch

hemorrhages in background diabetic retinopathy. These are more appar¬ ent on this black and white photograph than they would be in the fundus (i.e., red against an orange background). (Courtesy of Fundus Photo Read¬

ing Center, Madison, Wl.)

Ch. 145: Diabetes and the Eye

FIGURE 145-2.

Diabetic Retinopathy Study Standard Photo 2A shows

moderate hemorrhages (thin arrow) and microaneurysms (thick arrow).

(Courtesy of Fundus Photo Reading Center, Madison, WI.)

processes extend from the capillary and its wall to involve larger blood vessels and areas of nonvascular neural retina. Soft exu¬ dates are infarcts in the nerve fiber layer of the retina; microscop¬ ically, they show swollen areas of axonal debris. These are the lesions that were reported to progress early in the course, after the rapid normalization of plasma glucose levels. Hemorrhages are predominantly extravasated blood in the retinal substance; the various shapes are determined by the loca¬ tion of the blood: dot and blot, deep, flame-shaped, superficial lesions. IRMAs and venous abnormalities are caused by different responses to intraretinal vascular occlusive phenomena. IRMAs probably are dilated capillaries remaining in areas where parts of the capillary bed have closed down. The early-occurring venous abnormalities are localized irregularities in vessel caliber related to local hemodynamic factors. Some eyes may remain stable for many years and may even appear to revert to BDR as soft exu¬ dates resolve and blood resorbs. Other eyes rapidly progress to more advanced stages. Only regular follow-up, at 6-month in¬ tervals, can differentiate these groups. Preproliferative Diabetic Retinopathy. Large numbers and combinations of lesions advance the status of an eye to the pre¬ proliferative stage. Retinal ischemia progresses from being focal and limited to being the dominant process. Most of these eyes advance to PDR after several years and should be closely fol¬ lowed at 4-month intervals. Severely affected eyes in this group show large areas of avascular retina along with severe venous beading and can develop severe NVD and hemorrhage and loss of vision in a few months. They are probably at greater risk for severe visual loss than eyes with mild PDR having only small, nonelevated patches of new vessels elsewhere.

1299

ter of the eye. Tension is exerted along the attachments of these vessels to the retina and vitreous, and these fragile vessels bleed, causing various degrees of visual loss. Not all PDR rapidly leads to blindness. Patches of new blood vessels greater than 1 disc diameter from the optic disc, which are less than 0.5 disc area in size and not associated with vitreous or preretinal hemorrhage, do not place the eye at great risk of severe visual loss (7% 2-year risk). These eyes may remain stable for many years without treatment, and more than 10% actually may regress. When the patches become large and grow densely along an elevated posterior vitreous face, they can bleed and lead to retinal detachment and severe visual loss (25% 2-year risk). NVD are associated with the worst visual prognosis. New blood vessels frequently are located near the optic disc, partly because the internal limiting membrane is absent in this area, but also because it is the natural path of egress of substances from the eye, including a putative neovascular factor.27,273 Hemodynamic factors may also contribute to the location of blood vessels on or near the optic disc. Small amounts of NVD are associated with a 10% 2-year risk of severe visual loss, unless vitreous or preretinal hemorrhage is present, in which case the risk increases to 26%. When NVD alone cover one third or more of the surface of the disc (Fig. 145-3), they are also associated with a 26% 2-year risk of severe visual loss. NVD of this extent associated with vitreous or preretinal hemorrhages carry a 37% 2-year risk of severe vi¬ sual loss. Those characteristics of PDR carrying a 25% or greater 2year risk of severe visual loss have been designated as high-risk characteristics and mandate immediate consideration of panretinal photocoagulation.28'29 Eyes with high-risk characteristics and eyes having significant areas of retinal ischemia are at risk of de¬ veloping rubeosis iridis and neovascular glaucoma. In rubeosis, new blood vessels develop on the surface of the iris, frequently starting at the pupillary margin. These must be differentiated from dilated capillaries on the sphincter, referred to as microrubeosis, which are less ominous. Rubeosis can progress rapidly to cover large areas of the iris surface and, more importantly, to cover the filtration angle responsible for the egress of fluid from the eye. When this occurs, the eye is considered to have impend-

PROLIFERATIVE DIABETIC RETINOPATHY PDR is considered to be the most ominous stage of retinop¬ athy; in the past, it was associated with visual loss. It is charac¬ terized by the growth of abnormal new blood vessels through the internal limiting membrane of the retina and onto the retinal surface. These vessels frequently attach to the posterior surface of the vitreous. When this gel liquefies and contracts, as it is prone to do in diabetics, the vessels are pulled forward toward the cen¬

FIGURE 145-3.

Diabetic Retinopathy Study Standard

Photo

10A

shows moderate neovascularization of the optic disc (arrow). The extent of new vessel formation often causes severe visual loss. (Courtesy of Fun¬

dus Photo Reading Center, Madison, Wl.)

1300

PART IX: DISORDERS OF FUEL METABOLISM

ing neovascular glaucoma. Immediate panretinal photocoagula¬ tion is indicated for these eyes, along with goniophotocoagulation (i.e., direct photocoagulation of blood vessels on the surface of the angle) as a stop-gap measure in some instances. After the filtration angle is closed, neovascular glaucoma develops, and the eye has an extremely poor visual prognosis. DIABETIC MACULOPATHY Diabetic maculopathy, which encompasses the lesions of di¬ abetic retinopathy (e.g., hemorrhages, microaneurysms, hard ex¬ udates, IRMAs) and is associated with retinal edema and its se¬ quelae, is located in the macular region of the retina. It is the major vision-threatening component of diabetic retinopathy. It may occur in any stage. It is most common and is the primary problem in older-onset patients. In these patients, most of the retina may be spared, aside from a thickening of the retina with edema and deposition of lipid rings and plaques in the outer ret¬ inal layers near the center of vision. In younger patients, the edema is associated more with areas of nonperfusion and diffuse capillary leakage and less with deposition of exudates. In these eyes, maculopathy is associated with proliferative disease. The 3year risk of visual loss (i.e., doubling of visual angle from 20/20 to 20/40) in a large, heterogeneous group of maculopathy pa¬ tients with good vision was 24%.30 Optic disc edema is accumulation of fluid around the optic nerve head, which frequently is asymptomatic. It is usually uni¬ lateral and may be detected on a routine ophthalmoscopic exam¬ ination. It appears as a congested and swollen nerve head and must be differentiated from papilledema, NVD, and ischemic op¬ tic neuropathy. Visual acuity is normal or only slightly decreased. The blind spot is enlarged without characteristic visual field de¬ fects. Laboratory workup and neurologic evaluation to rule out other causes of a congested optic nerve are negative. The edema resolves spontaneously over several months, but these eyes must be watched closely for the development of NVD.

FIGURE 145-4.

Cumulative event rates of severe visual loss

less than 5/200 at two consecutive visits 4 months apart. Data are shown for panretinal argon laser treatment.

Most eyes with diabetic retinopathy go into remission. In patients who never develop severe changes, it may appear as if no retinopathy were ever present. Macular edema dries up, leav¬ ing a mottled pigment epithelium, and new blood vessels shrink and are replaced by fibrous tissue. This fibrous tissue can lead to further visual problems if it exerts traction on the retina: antero¬ posterior traction leading to traction retinal detachment or tan¬ gential traction leading to retinal wrinkling. Unfortunately, re¬ mission often came too late, and many eyes were left quiescent but with poor visual function. The condition of these eyes, with pale optic nerve heads, wispy fibrous strands, and attenuated ret¬ inal vessels, has been called involutional diabetic retinopathy. With panretinal photocoagulation and vitrectomy, visual func¬ tion can be preserved or restored in many cases.

MANAGEMENT PHOTOCOAGULATION Photocoagulation refers to the use of light to destroy tissue. In diabetes, the tissue being destroyed is the retina, and the mo¬ dalities used are xenon arc white light and argon or krypton la¬ sers. Both xenon arc and argon laser panretinal photocoagulation were proven effective in treating PDR by the Diabetic Retinopa¬ thy Study (DRS; Fig. 145-4). A 60% reduction in severe visual loss (i.e., vision less than 5/200 at two consecutive visits) in treated eyes was documented at 2 years and was maintained at 5 years. In most modern treatments, an argon laser is used, primar¬ ily because of its ease of application and fewer side effects. The krypton laser, a new red laser that penetrates blood, has been used to treat eyes when adequate argon photocoagulation is not possible because of vitreous hemorrhage or other opacities. It should not be substituted routinely for argon in clear media cases, because it is more painful. Photocoagulation is routinely applied to eyes with high-risk characteristics. In these eyes, the DRS study showed a reduction

Ch. 145: Diabetes and the Eye

1301

on a fluorescein angiogram or delivered in a grid-like pattern to areas of diffuse leakage or capillary nonperfusion.32 The treatable lesions are those which the ETDRS has decided warrant photo¬ coagulation if clinically significant macular edema is present. They include discrete points of retinal hyperfluorescence or leak¬ age (most are microaneurysms), areas of diffuse leakage within the retina (e.g., microaneurysms, intraretinal microvascular ab¬ normalities, diffusely leaking retinal capillary bed), and retinal avascular zones. VITRECTOMY

FIGURE 145-5.

Retina, 24 hours after argon laser panretinal photoco¬

agulation in the Diabetic Retinopathy Study. (Courtesy of Fundus Photo

Reading Center, Madison, WI.)

in 2-year risk of severe visual loss from 26% to 12%. Treatment consists of 1200 to 2000 or more 500-/am burns placed 0.5 burn diameters apart, avoiding the macula, papillomacular bundle, optic disc, or major vessels and extending out to the equator (Fig. 145-5). The application of only 100 to 200 burns is not panretinal photocoagulation; it probably is not effective and should not be considered acceptable therapy unless there are extenuating cir¬ cumstances. Treatment is usually applied in two to four sessions and may require retrobulbar anesthesia. The treatment of eyes with less severe proliferative retinopathy than high-risk charac¬ teristics frequently is done, but the 5-year risk of severe visual loss is 3.7% in these eyes. Early treatment reduces the risk to 2.6%.29 Focal treatment of macular edema has been proven effective by the Early Treatment Diabetic Retinopathy Study (ETDRS; Fig. 145-6). The 3-year rate of doubling of the visual angle was re¬ duced from 24% to 12%.31 Treatment involves considerably fewer applications than panretinal photocoagulation, perhaps only 5 or 10, most commonly 50 to 200, and rarely as many as 500. Burns are smaller (50-100 /um), more focused, and confined to the macular region. They are aimed at focal leakage points seen

When photocoagulation fails to stem the course of retinopa¬ thy, and recurrent vitreous hemorrhage or a traction detachment of the macula develops, vitrectomy surgery may become neces¬ sary. Surgery is rarely performed unless hemorrhage has been present for several months or detachment involves or immi¬ nently threatens the fovea. The goals of vitrectomy surgery are to clear an opaque vitreous and to release any anteroposterior or tangential traction being exerted on the retina and causing retinal detachment or distortion. It is often necessary to remove the lens during surgery, but this increases the risk of postoperative neovascular glaucoma and is done only when lens opacities interfere with the surgeon's ability to do an adequate vitrectomy.33 The Diabetic Retinopathy Vitrectomy Study group has shown that early vitrectomy for nonclearing vitreous hemor¬ rhage is preferable to waiting a year or more, particularly in juve¬ nile-onset patients.34 The study group also reported benefit from vitrectomy in some eyes before hemorrhage or detachment occurs.35 Numerous instruments are available to perform surgery, each with its own advantage. It is difficult surgery, and results are not uniformly good. Fortunately, with the increasing use of timely photocoagulation, fewer diabetic eyes are undergoing vi¬ trectomy than 5 years ago.

GUIDELINES FOR FOLLOW-UP Diabetic patients should have regular eye examinations for diabetic retinopathy. Yearly examinations should begin after 5 years in juvenile-onset type 1 diabetes and at the onset of diabe¬ tes in older-onset patients. Examinations should be through a di¬ lated pupil or use a nonmydriatic fundus camera for screening people without known disease. After significant retinopathy de¬ velops, an ophthalmologist should examine the eyes every 4 to 6 months.36 Following these simple guidelines enables timely treat-

No. of Eyes Group Immediate Deferral

Baseline 754 1,490

12 mo 614 1,178

36 mo 268 526

24 mo 416 812

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o

♦ 2.58 < Z< 3.29

c o C/5

> £

20

-

I C/5

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0-

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36

FIGURE 145-6.

Early Treatment Diabetic Reti¬

nopathy Study results show a 50% reduction

Months of Follow-up

(from 24% to 12%) in visual loss at 3 years.

1302

PART IX: DISORDERS OF FUEL METABOLISM

merit of patients with retinopathy and markedly reduces the de¬ velopment of visual loss in diabetic patients.

OTHER EYE DISORDERS IN DIABETES DIABETIC CATARACT Opacification of the crystalline lens or cataract is an impor¬ tant ocular manifestation of diabetes.37 Three types of cataracts have been documented: the metabolic or "snowflake" cataract, the senile cataract, and secondary cataract or cataract "complicata."38 Metabolic cataracts are seen primarily in young diabetic pa¬ tients with uncontrolled diabetes.39 The snowflake appellation derives from their flocculent appearance, which starts in the subcapsular regions of the lens. They may progress rapidly, and rarely, total opacification of the lens can occur over a period of days, resulting in a mature cataract. The institution of adequate diabetic control stops or reverses these lens opacities if discov¬ ered in their incipient stages. Metabolic cataract develops in most animal models of diabetes. Investigation of this cataract led to the discovery of the sor¬ bitol pathway, an alternative route for glucose metabolism re¬ quiring the enzyme aldose reductase, in which sorbitol, a sugar alcohol, is the by-product (see Chap. 142). Inhibition of sorbitol production by the use of an aldose reductase inhibitor prevents the development of cataract in experimental animals with diabe¬ tes or with galactosemia. The possible role of sugar alcohol accu¬ mulation as an underlying factor in other diabetic complications, such as neuropathy and retinopathy, has received much atten¬ tion. Aldose reductase inhibitors are under investigation, but their clinical efficacy is still uncertain. Senile cataract is the most common form of cataract seen in diabetics, and it cannot be differentiated from the senile cataract seen in nondiabetics. In diabetics, however, the senile changes of nuclear sclerosis and cortical and subcapsular opacification de¬ velop at an earlier age than in nondiabetics: 59% of older-onset diabetics who are between 35 and 54 years of age, compared with 12% of similar nondiabetics.37 They may progress to a vision¬ impairing level more rapidly, necessitating cataract extraction. Cataract complicata, which is associated with other ocular diseases such as iridocyclitis, chorioretinitis, high myopia, or ret¬ inal detachment, was seen in 6% of a large group of diabetics, not significantly different from the rate among nondiabetics.38 The indications for cataract surgery and intraocular lens (IOL) insertion have changed over time. Initially, the insertion of IOLs was not recommended in diabetics, particularly in cases complicated by retinopathy. This was because of poor visibility of the fundus, with iris clip and anterior chamber lenses precluding good laser treatment. However, with the development of poste¬ rior chamber lenses and YAG laser capsulotomy, these problems were overcome, and diabetics, even those with significant reti¬ nopathy, can benefit from this revolutionary advance in visual rehabilitation after cataract surgery. Nevertheless, it appears that the visual outcome in diabetics is not as good as in nondiabetics, primarily because of worsening maculopathy after surgery, par¬ ticularly after YAG laser capsulotomy. Although the visual acu¬ ities usually improve postoperatively, the criteria for surgery probably should be more stringent in diabetics than in nondia¬ betics. Laser treatment of all leaking microaneurysms in or near .the macula should be performed before surgery, if possible. The incidence of rubeosis iridis and neovascular glaucoma in these eyes after cataract extraction is significant.39

DIABETIC OPHTHALMOPLEGIA Paralysis of ocular movement due to cranial nerve palsies is an uncommon (0.4%) but dramatic complication of diabetes.40 The third nerve is most commonly affected, followed by the sixth

nerve. Infrequently, the fourth nerve may be involved alone or in combination with one of the other nerves. Usually, the pres¬ enting complaint is diplopia, which may be associated with ipsilateral headache or eye pain, which can precede the onset of dip¬ lopia. Bilateral nerve palsies are not rare. Complete recovery of function usually occurs in 1 to 9 months. Recurrence may develop, but aberrant regeneration of the nerve is not seen. Particularly important in third-nerve pal¬ sies of diabetic origin is the sparing of the pupillary fibers, which differentiate these from palsies due to intracranial aneurysms and tumors, which affect the pupil in 80% to 90% of patients. Nevertheless, ocular palsies in a diabetic should prompt a thor¬ ough medical and neurologic evaluation, because 42% of palsies seen in diabetics in one series were of nondiabetic origin.40 Other diagnoses to consider include myasthenia gravis, Graves disease, herpes zoster, demyelinating disease, primary and metastatic brain tumors, and hypoglycemia. The treatment of ophthalmoplegia is symptomatic, aiming to relieve the diplopia, and it usually consists of temporary occlu¬ sion of one eye with a mild analgesic, if needed. Severe pain is not characteristic, and the need for strong analgesics may indicate an intracranial aneurysm.

GLAUCOMA Primary open angle glaucoma is more common among indi¬ viduals with diabetes (4.0%) than it is among those without this disease (1.8%). Moreover, diabetes is more common among glau¬ coma patients (4%—18%) than the general population (2%).41 Glaucoma (i.e., elevated intraocular pressure) has been proposed as protecting an eye from developing severe diabetic retinopathy, based on studies of patients with diabetes and unilateral glau¬ coma. Because the intraocular pressure is the main component of tissue pressure in the eye and retinal venous pressure usually just barely exceeds intraocular pressure, alterations in the regulation of intraocular pressure and its relationship with vascular resis¬ tance may play roles in the pathogenesis of diabetic retinopathy. The treatment of open angle glaucoma in diabetics must be influenced by their general medical conditions. This includes some caution with the use of topical /3-blockers in masking hypo¬ glycemic symptoms or affecting frequently coexistent cardiovas¬ cular disease. After instilling drops, punctal pressure can reduce the systemic effects of these medications. Acetazolamide (Diamox) or other carbonic anhydrase inhibitors may be used if needed, but because they can cause a metabolic acidosis, more frequent electrolyte monitoring is required. Renal disease may influence how these and other pressure-lowering drugs may be used, and close cooperation between the ophthalmologist and internist is important.

REFERENCES 1. Kahn HA, Hiller R. Blindness caused by diabetic retinopathy. Am ] Oph¬ thalmol 1974; 78:58. 2. Caird FI, Pirie A, Ramsell TG. Diabetes and the eye. Oxford: Blackwell Scientific Publications, 1969. 3. Rand LI. Recent advances in diabetic retinopathy. Am J Med 1981; 70:595. 4. Krolewski AS, Warram JH, Rand LI, Kahn CR. Epidemiologic approach to the etiology of type I diabetes mellitus and its complications. N Engl J Med 1987;317:22. 5. Klein R, Klein BEK, Moss SE, et al. The Wisconsin epidemiologic study of diabetic retinopathy. II. Prevalence and risk of diabetic retinopathy when age at diagnosis is less than 30 years. Arch Ophthalmol 1984; 102:520. 6. White P. Childhood diabetes. Diabetes 1960;9:345. 7. Krolewski AS, Warram JH, Rand LI, et al. Risk of proliferative diabetic retinopathy in juvenile-onset type I diabetes—a 40-year follow-up study. Diabetes Care 1986; 9:443. 8. Klein R, Klein BEK, Moss SE, et al. The Wisconsin epidemiologic study of diabetic retinopathy. III. Prevalence and risk of diabetic retinopathy when age at diagnosis is 30 or more years. Arch Ophthalmol 1984; 102:527. 9. Aiello LM, Rand LI, Briones JC, et al. Diabetic retinopathy in Joslin Clinic patients with adult-onset diabetes. Ophthalmology 1981; 88:619. 10. Knowles HC Jr. The control of diabetes mellitus and the progression of retinopathy. In: Goldberg MF, Fine SL, eds. Treatment of diabetic retinopathy. Warrenton, VA: Airlie House, 1968:115.

Ch. 146: Diabetes and Infection 11. Canny CLB, Kohner EM, Trautman J, et al. Comparison of stereo fundus photographs for patients with insulin-dependent diabetes during conventional in¬ sulin treatment or continuous subcutaneous insulin infusion. Diabetes 1985; 34(Suppl):50. 12. Lauritzen T, Frost-Larsen K, Laresen HW, et al. Effect of 1 year of near¬ normal blood glucose levels on retinopathy in insulin-dependent diabetics. Lancet 1983; 1:200. 13. Dahl-Jorgensen K, Hanssen KF, Brinchmann-Hansen O, et al. Near-normoglycemia retards the progression of early retinopathy and neuropathy in IDDM. Three year results from the Oslo Study. Diabetes 1986;35:41A. 14. Ramsay RC, Goetz FC, Sutherland DER, et al. Progression of diabetic retinopathy after pancreas transplantation for insulin-dependent diabetes mellitus. N Engl J Med 1988; 318:208. 15. The Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl ] Med 1993; 329:977. 15a. The Diabetes Control Complications Trial. Effects of intensive diabetes treatment on development and progression of long-term complication in adoles¬ cents with insulin dependent diabetes mellitus: Diabetes Control and Complica¬ tions Trial. J Pediatr 1994; 125:177. 16. Rand LI, Krolewski AS, Aiello LM, et al. Multiple factors in the prediction of risk of proliferative diabetic retinopathy. N Engl J Med 1985;313:1433. 17. Knowler WC, Bennett PH, Ballintine EJ. Increased incidence of diabetic retinopathy with elevated blood pressure. N Engl J Med 1980;302:645. 18. Janka HU, Warram JH, Rand LI, Krolewski AS. Risk factors for progression of background retinopathy in long-standing IDDM. Diabetes 1989; 38:460. 19. Krolewski AS, Canessa M, Warram JH, et al. Predisposition to hyperten¬ sion and susceptibility to renal disease in insulin-dependent diabetes mellitus. N Engl J Med 1988;318:140. 20. Rand LI, Krolewski AS, Warram JH. Late complications: the critical period. In: Friedman EA, L'Esperance FA Jr, eds. Diabetes renal-retinal syndrome. Preven¬ tion and management. New York: Grune & Stratton, 1985:297. 21. Christiansen JS. Cigarette smoking and prevalence of microangiopathy in juvenile-onset insulin-dependent diabetes mellitus. Diabetes Care 1978; 1:146. 22. Rand LI, Prud'homme JG, Ederer F, et al. Factors influencing the develop¬ ment of visual loss in advanced diabetic retinopathy. Diabetic Retinopathy Study report no. 10. Invest Ophthalmol 1985;26:983. 23. Cogan DG, Kuwabara T. The Mural cell in perspective. Arch Ophthalmol 1967; 78:133. 24. Ashton N. Vascular basement membrane changes in diabetic retinopathy. BrJ Ophthalmol 1974;58:344. 25. Soeldner JS, Christacopoulos PD, Gleason RE. Mean retinal circulation time as determined by fluorescein angiography in normal, prediabetic, and chemical diabetic subjects. Diabetes 1976; 25:903. 26. The Diabetic Retinopathy Study Research Group. A modification of the Airlie House Classification of Diabetic Retinopathy. Diabetic Retinopathy Study (DRS) report no. 7. Invest Ophthalmol 1981;21:210. 27. D'Amore P, Thompson RW. Mechanisms of angiogenesis. Annu Rev Physiol 1987;49:453. 27a. Aiello LP, Avery RL, Arrigg PG, et al. Vascular Endothelial Growth Fac¬ tors in ocular fluid of patients with diabetic retinopathy and other retinal disorders. N Engl J Med 1994;331:1480. 28. The Diabetic Retinopathy Study Research Group. Four risk factors for severe visual loss in diabetic retinopathy. The third report from the Diabetic Reti¬ nopathy Group. Arch Ophthalmol 1979; 97:654. 29. The Diabetic Retinopathy Study Research Group. Preliminary report on effects of photocoagulation therapy. Am J Ophthalmol 1976; 81:1. 30. Early Treatment Diabetic Retinopathy Study Research Group. Photoco¬ agulation for diabetic macular edema. Early Treatment Diabetic Retinopathy Study report no. 1. Arch Ophthalmol 1985,103:1796. 31. Early Treatment Diabetic Retinopathy Study Research Group. Early Pho¬ tocoagulation for Diabetic Retinopathy. ETDRS report number 9. Ophthalmol 1991;98(Suppl):766. 32. Rand LI, Davis MD, Hubbard LD, et al. Color photography vs. fluorescein angiography in the detection of diabetic retinopathy in the Diabetes Control and Complications Trial. Arch Ophthalmol 1987; 105:1344. 33. Rice TA, Michels RG, Maguire MG, Rice EF. The effect of lensectomy on the incidence of iris neovascularization and neovascular glaucoma after vitrectomy for diabetic retinopathy. AmJ Ophthalmol 1983; 95:1. 34. The Diabetic Retinopathy Vitrectomy Study Research Group. Early vitrec¬ tomy for severe vitreous hemorrhage in diabetic retinopathy. Two-year results of a randomized trial. Diabetic Retinopathy Vitrectomy Study report no. 2. Arch Oph¬ thalmol 1985; 103:1644. 35. The Diabetic Retinopathy Vitrectomy Study Research Group. Early vitrec¬ tomy for severe proliferative diabetic retinopathy in eyes with useful vision. Clinical application of results of a randomized trial. Diabetic Retinopathy Vitrectomy Study report no. 4. Ophthalmology 1988; 95:1321. 36. Grunwald JE, Riva CE, Sinclair SH, et al. Laser Doppler velocimetry study of the retinal circulation in diabetes mellitus. Arch Ophthalmol 1986; 104:991. 37. Klein BEK, Klein R, Moss S. Prevalence of cataracts in a population based study of persons with diabetes mellitus. Ophthalmology 1985;92:1191. 38. Waite JH, Beetham WP. Visual mechanism in diabetes mellitus. Compar¬ ative study of 2002 diabetics and 457 non-diabetics for control. N Engl J Med 1935;212:367. 39. Aiello LM, Rand LI, Weiss JN, et al. The eyes and diabetes. In: Marble A, Krall L, Bradley RF, et al., eds. Joslin's diabetes mellitus, ed 12. Philadelphia: Lea & Febiger, 1985:600.

1303

40. Zorrilla C, Kozak GP. Ophthalmoplegia in diabetes mellitus. Ann Intern Med 1967;67:968. 41. Armstrong JR, Daily RK, Dobson HL, Gerard LJ. The incidence of glau¬ coma in diabetes mellitus. A comparison with the incidence in the general popula¬ tion. AmJ Ophthalmol 1960;50:55.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

146

DIABETES AND INFECTION GEORGE M. ELIOPOULOS Previously, infection was a major cause of death of patients with diabetes mellitus. Thus, considerable attention has been fo¬ cused on the apparently increased risk of various infections in diabetic patients.l la With the development of effective antibiotics and the recognition of the importance of glucose regulation, un¬ controlled sepsis has become an uncommon primary cause of mortality in diabetes.2 Nevertheless, infection is still responsible for serious morbidity in this disease. Diabetics do appear to be predisposed to certain infections; some are extremely character¬ istic (e.g., malignant external otitis, rhinocerebral mucormycosis); some occur predominantly in patients with diabetes mellitus (e.g., emphysematous cystitis, emphysematous pyelonephritis, emphysematous cholecystitis, acute necrotizing fasciitis); and some are increased in incidence in diabetics (e.g., tuberculosis, urinary tract infection [females], gram-negative pneumonia). Once established, many infections are tolerated poorly in this population, and the stress of infection often complicates man¬ agement of the diabetes, which should initiate a search for infec¬ tion in any patient with unexplained loss of glucose control. Although medical advances have greatly reduced diseases such as tuberculosis, which had affected diabetic patients dispro¬ portionately, medical progress actually has broadened the spectrum of infections encountered. For example, treatment of end-stage diabetic nephropathy with hemodialysis, chronic peri¬ toneal dialysis, or renal transplantation subjects many diabetics to the infectious complications associated with these therapeutic modalities. Usually, infections encountered in diabetic patients are not unique to this group. Although it is important to be aware of the unusual disorders to which the diabetic is subject, it is perhaps more important to be familiar with measures for the aggressive diagnosis and treatment of more common infections that may manifest in an unusual manner or with greater severity in the patient with diabetes mellitus.

HOST FACTORS PREDISPOSING TO INFECTION PRIMARY BARRIERS TO INFECTION The integrity of the skin and mucosal defenses is the primary barrier to local or systemic infection. Breaks in the skin, whether they are minor fissures arising in dystrophic areas or frank ulcer¬ ations due to ischemia or neuropathic trauma, provide an oppor¬ tunity for bacterial invasion. Most common in the diabetic foot (see Chap. 148), such infections also arise in the hand, the peri¬ neum, or elsewhere. Vascular punctures for hemodialysis and in¬ dwelling catheters for peritoneal dialysis obviously disrupt these natural barriers. Factors that determine microbial colonization of skin and

1304

PART IX: DISORDERS OF FUEL METABOLISM

mucosal surfaces are poorly understood. Carriage rates of Staph¬ ylococcus aureus and pharyngeal colonization with gram-nega¬ tive bacilli may be increased in diabetics.3,4 In one study, among individuals colonized with S. aureus, type I diabetics were more likely to be colonized with methicillin-resistant isolates than were patients from control groups.5 Because colonization with a mi¬ croorganism frequently precedes infection, these observa¬ tions may explain the frequent occurrence of staphylococcal in¬ fections and the increased risk of gram-negative pneumonia in diabetics.1,2

and to staphylococcal lysate are not correlated with glucose lev¬ els.1819 Release of the lymphokine “migration inhibition factor" was abnormal in cells obtained from maturity-onset diabetics and nonhyperglycemic obese individuals but not from well-controlled ketosis-prone diabetics.20 Defective responses correlated inversely with fasting insulin levels but not with levels of plasma glucose.

DEFENSES AGAINST MICROBIAL INVASION

STAPHYLOCOCCAL INFECTIONS

PHAGOCYTES Evidence suggests that abnormalities in phagocytic cell func¬ tion contribute to the susceptibility of diabetics to infection or to the increased severity of some infections. Reported defects in¬ clude decrease of mobilization, chemotaxis, adherence, phagocy¬ tosis, and killing by polymorphonuclear leukocytes; also noted have been reductions in levels of leukotriene B4, prostaglandin E, and thromboxane B2.6"12 In monocytes, there is decreased phago¬ cytosis.13 Expression of monocyte carbohydrate-binding recep¬ tors (which would be expected to recognize components of bac¬ terial cell walls) was reduced in patients recovering from ketoacidosis.14 Abnormal leukocyte mobilization into Rebuck skin windows has been noted, although there is considerable overlap with control values.6 Impaired leukocyte chemotaxis to Escherichia coli extracts occurs in some diabetic patients; this effect does not correlate with plasma glucose levels.7 On the other hand, the diminished adherence to nylon fibers by leukocytes from poorly controlled diabetics is partially corrected by treating the hyperglycemia.8 Studies of phagocytosis of microbes by polymorphonuclear leukocytes give conflicting results, which may be due to methodologic factors or the particular organism examined. Phagocyto¬ sis of Candida guilliermondii by leukocytes obtained from diabetic patients is abnormal.9 Both diabetic leukocytes and plasma con¬ tribute to this defect, but neither blood glucose concentration nor levels of glycosylated hemoglobin correlate with functional ab¬ normalities. Defects in phagocytosis of staphylococci by poly¬ morphonuclear leukocytes have also been reported in diabetes. Impairment of microbial killing by diabetic leukocytes has been documented more consistently. A detailed study of bacteri¬ cidal activity against S. aureus found defective killing in patients with poorly controlled diabetes but not in well-controlled type I diabetics.111 However, increased levels of bactericidal activity oc¬ curred in leukocytes from nondiabetic patients with acute infec¬ tions but not in leukocytes from well-controlled acutely infected diabetics. Controlled insulin withdrawal, causing mild ketoaci¬ dosis, induced defective leukocyte killing, which was reversed by in vitro incubation of cells with insulin. Experimental evidence suggests that inhibition of aldose reductase mitigates reductions of superoxide production and intracellular killing by leukocytes from diabetic subjects when these cells are incubated in glucose in vitro.1516 Diminished killing of bacteria by polymorphonuclear leukocytes from diabetic patients correlated with impairment of oxygen-dependent microbicidal systems; however, the direct rel¬ evance of these findings to the risk of infection in diabetes is not clear.17 Evidence for defective control of fungi by monocytes from diabetic patients is supported by animal studies.13 LYMPHOCYTES Defects in cell-mediated immunity have been described in diabetics, but malnutrition and chronic debilitation probably contribute to clinically significant abnormalities.2 Impaired mito¬ genic response to phytohemagglutinin has been demonstrated inconsistently.1819 Abnormal responses to phytohemagglutinin

BACTERIAL INFECTIONS

Infections due to S. aureus are common in patients with dia¬ betes, but there is little evidence of increased risk. Early experi¬ ence suggested a higher mortality rate in diabetics with staphylo¬ coccal bacteremia, particularly in patients with cardiovascular disease or ketoacidosis. However, a study in which diabetic and nondiabetic patients with bacteremia were stratified by severity of underlying illness found no increase in mortality in the dia¬ betic group.21 Nevertheless, among patients with an identifiable source of infection, significantly more diabetics developed endocarditis.

PNEUMONIA Diabetic patients are not at significantly increased risk of de¬ veloping pneumococcal pneumonia in the absence of complicat¬ ing illness, but mortality in bacteremic pneumococcal disease may be greater. Antibody response to pneumococcal polysaccha¬ ride vaccine is not impaired by diabetes. Providing partial protec¬ tion against this common cause of community-acquired pneumo¬ nia by immunization should be seriously considered, especially in the elderly diabetic patient. Pharyngeal colonization with gram-negative bacteria is more common in diabetic patients, and diabetes is a risk factor for the development of gram-negative pneumonia.1

TUBERCULOSIS Before the availability of effective antimycobacterial chemo¬ therapy, tuberculosis was up to 16 times more common in dia¬ betics than in nondiabetics.2 Today, tuberculosis is so uncommon in the United States that any increased risk of infection in patients with diabetes would be difficult to detect. In other parts of the world, however, diabetics are still disproportionately represented among patients with tuberculosis.22

MALIGNANT EXTERNAL OTITIS Malignant external otitis is an aggressive, locally invasive (hence "malignant") infection due to Pseudomonas aeruginosa, which occurs almost exclusively in diabetics.23 Infection begins in the external ear canal, where pain, purulent drainage, and granulations are characteristically present. Tenderness and swelling may extend to the pinna and periauricular tissues. Fever and leukocytosis are uncommon. Spread to deeper tissues causes osteomyelitis of the temporal bone and cranial neuropathies. Neurologic complications other than isolated facial nerve palsy adversely affect prognosis. Treatment traditionally has consisted of an antipseudomonal penicillin plus an aminoglycoside for a minimum of 4 weeks. The availability of newer antimicrobial agents has extended therapeutic options. Both ceftazidime and ciprofloxacin have been used as single agents with high success rates in the treatment of this entity.24-26 Radiologic demon¬ stration of osteomyelitis may necessitate surgical debridement and an extended course of antibiotics in some patients (see Chap. 210).

Ch. 146: Diabetes and Infection

1305

grene), necrotizing fasciitis may also arise as a synergistic process involving streptococci, gram-negative bacilli, and anaerobes. Twenty percent or more of cases occur in diabetics. Commonly involving the leg or perineum, these infections develop after sur¬ gery or minor trauma, or they may spread from perianal infec¬ tions. Systemic toxicity and pain are usually prominent and gas may be present. The term necrotizing cellulitis is applied if the process extends to involve muscle. Fournier's gangrene is a form of necrotizing fasciitis or cellulitis affecting the male genitalia and perineum; an analogous situation is seen in females with involve¬ ment of the vulva and perineum. Treatment requires wide surgi¬ cal debridement and antibiotics. In mixed infections, empiric therapy is directed against streptococci, Enterobacteriaceae, and anaerobes, including Bacteroides fragilis.

URINARY TRACT INFECTION

FIGURE 146-1.

A middle-aged diabetic woman presented with fever

and gross pyuria. A coned-down anteroposterior radiograph of the right kidney shows gas within the parenchyma of the kidney (K) and subcapsular gas (arrows). A nephrectomy was performed within 24 hours. The kidney was diffusely involved with multiple, small, gas-filled microab¬ scesses. (Courtesy of Dr. Michael Hill.)

NECROTIZING SOFT TISSUE INFECTION Necrotizing infections of the skin and soft tissues are fortu¬ nately rare, but when they occur, they frequently progress rap¬ idly to cause death or serious morbidity. Necrotizing fasciitis primarily involves the fascia and subcutaneous tissues. Origi¬ nally described with group A streptococci (i.e., streptococcal gan¬

Several studies have reported an increased incidence of bacteriuria in diabetic women.1,28 The frequency of asymptomatic bacteriuria in diabetic schoolgirls is not significantly increased, nor is urinary tract infection in males.29,30 Emphysematous cysti¬ tis is an uncommon manifestation of bladder infection seen largely (>50% of cases) in diabetics. Gas in the bladder wall is produced by bacterial fermentation. Gross hematuria occurs in about half of the cases. In most patients the infection responds to appropriate antibiotics.31 Autopsy studies from the 1930s indicated that pyelonephri¬ tis was more common in diabetics. Pyelonephritis may be com¬ plicated in rare cases by renal papillary necrosis, and the sloughed papillae may subsequently obstruct urine outflow. A rare, severe form of renal parenchymal infection, emphysema¬ tous pyelonephritis, occurs more frequently in diabetic patients (Fig. 146-1).32 Gas is seen in the renal tissue, and the kidney may be completely destroyed. Infection is most often caused by E. coli or Klebsiella. Failure to respond to appropriate antibiotic therapy may necessitate nephrectomy. Even so, mortality in these se¬ verely ill patients is approximately 33%.33 At least a third of pa¬ tients with perinephric abscesses have diabetes. The advent of computed tomography has facilitated delineation of such pro¬ cesses (Fig. 146-2). Although the development of a neurogenic bladder is a fre¬ quent complication of diabetes, it has been difficult to ascribe any increased tendency toward urinary infections to this condition except as related to the need for instrumentation.34 Additional factors such as nonneurogenic bladder outlet disorders probably contribute to the risk of infection. Animal studies suggest that

FIGURE 146-2.

Computed tomographic demonstration

of a perinephric abscess (A) arising from a transplanted kid¬ ney (K). P, psoas muscles.

1306

PART IX: DISORDERS OF FUEL METABOLISM

FIGURE 146-3.

Broad, nonseptate hyphae with right-an¬

gle branching seen in mucormycosis.

osmotic diuresis, as seen in uncontrolled diabetes, predisposes to ascending infections, possibly because of vesicoureteral reflux or dilution of urinary bacteriostatic activity.35

EMPHYSEMATOUS CHOLECYSTITIS Diabetes is present in about a third of cases of emphysema¬ tous cholecystitis, in which gas is found within the gallbladder lumen, gallbladder wall, or pericholecystic tissues.36 Organisms recovered at surgery include streptococci, Clostridia, and gram¬ negative bacilli. In contrast to the more common form of chole¬ cystitis, this type of cholecystitis occurs more often in males and gangrene of the gallbladder is more frequent.

FUNGAL INFECTIONS RHINOCEREBRAL MUCORMYCOSIS Diabetic ketoacidosis is a major predisposing factor in this rare infection caused by fungi of the order Mucorales (e.g., Mucor, Rhizopus, and Absidia).363 The process begins on the palate or in the nasal passages, where a black eschar may be seen. Infec¬ tion spreads to the paranasal sinuses, orbits, or brain. Necrosis is prominent because of blood vessel invasion. Fever, lethargy, headache, and facial swelling are often present. Orbital invasion causes proptosis, decreased ocular motion, and vision loss. Thrombosis of the venous sinuses or carotid system may occur. Diagnosis is made by biopsy of affected tissues. Broad, nonsep¬ tate hyphae that tend to branch at right angles are characteristic (Fig. 146-3). Treatment requires prompt control of diabetes and correc¬ tion of acidosis, aggressive surgical debridement of infected tis¬ sues, and the systemic administration of amphotericin B aggres¬ sively. Studies suggest that diabetic ketoacidosis induces a defect in the ability of macrophages to inhibit spore germination and impairs both leukocyte chemotaxis to fungal products and leuko¬ cyte-mediated hyphal injury.

FUNGAL URINARY TRACT INFECTION Funguria with Candida species or Torulopsis glabrata is com¬ mon in diabetics, particularly with urethral catheterization, with the prior use of antibiotics, and in the presence of glucosuria. Yeast infections may be asymptomatic or may produce symp¬ toms that are indistinguishable from those of bacterial infection. Occasionally, such infections ascend to the renal parenchyma.

cause ureteral obstruction, or disseminate hematogenously. Sys¬ temic therapy is required with upper tract disease. Infections lim¬ ited to the bladder may be treated with amphotericin B instilla¬ tions.3613 Oral 5-flucytosine has been used in the treatment of infection caused by susceptible yeasts, but infection is difficult to eradicate when continued use of indwelling catheters is required and the drug has important side effects.37 Preliminary informa¬ tion suggests that fluconazole, which can be given parenterally or orally, may be as effective as amphotericin B irrigations in treating candidal bladder infections,38 but this is an area that mer¬ its further study.

REFERENCES 1. Wheat LJ. Infection and diabetes. Diabetes Care 1980;3:187. la. Sentochnik DE, Eliopoulos GM. Infection and diabetes. In: Kahn CR, Weir GC, eds. Joslin's diabetes mellitus. Malvern, PA: Lea & Febiger, 1994:867. 2. Coopan R. Infection and diabetes. In: Marble A, Krall LP, Bradley RF, et al, eds. Joslin's diabetes mellitus. Philadelphia: Lea & Febiger, 1985:737. 3. Chandler PI, Chandler SD. Pathogenic carrier rate in diabetes mellitus. Am J Med Sci 1977;273:259. 4. Mackowiak PA, Martin RM, Jones SR, Smith JW. Pharyngeal colonization by gram-negative bacilli in aspiration-prone persons. Arch Intern Med 1978,138: 1224. 5. Berman DS, Schaefler S, Simberkoff MS, Rahal JJ. Staphylococcus aureus colonization in intravenous drug abusers, dialysis patients, and diabetics. J Infect Dis 1987;155:829. 6. Brayton RG, Stokes PE, Schwartz MS, Louria DB. Effect of alcohol and various diseases on leukocyte mobilization, phagocytosis, and intracellular bacterial killing. N Engl J Med 1970; 282:123. 7. Molenaar DM, Palumbo PJ, Wilson WR, Ritts RE Jr. Leukocyte chemotaxis in diabetic patients and their non-diabetic first-degree relatives. Diabetes 1976; 25: 880. 8. Bagdade JD, Stewart M, Walters E. Impaired granulocyte adherence: a re¬ versible defect in host defense in patients with poorly controlled diabetes. Diabetes 1978,-27:677. 9. Davidson NJ, Sowden JM, Fletcher J. Defective phagocytosis in insulin controlled diabetics: evidence for a reaction between glucose and opsonising pro¬ teins. J Clin Pathol 1984; 37:783. 10. Repine JE, Clawson CC, Goetz FC. Bactericidal function of neutrophils from patients with acute bacterial infections and from diabetics. J Infect Dis 1980; 142:869. 11. Jubiz W, Draper RE, Gale J, Nolan G. Decreased leukotriene B4 synthesis by polymorphonuclear leukocytes from male patients with diabetes mellitus. Pros¬ taglandins Leukot Med 1984; 14:305. 12. Qvist R, Larkins RG. Diminished production of thromboxane B2 and prostaglandin E by stimulated polymorphonuclear leukocytes from insulin-treated subjects. Diabetes 1983; 32:622. 13. Geisler C, Almdal T, Bennedsen J, et al. Monocyte functions in diabetes mellitus. Acta Pathol Microbiol Immunol Scand 1982; 90:33. 14. Stewart J, Collier A, Patrick AW, et al. Alterations in monocyte receptor function in type 1 diabetic patients with ketoacidosis. Diabetic Med 1991; 8:213. 15. Tebbs SE, Lumbwe CM, Tesfaye S, et al. The influence of aldose reduc¬ tase on the oxidative burst in diabetic neutrophils. Diabetes Res Clin Pract 1992; 15: 121.

Ch. 147: Diabetes and the Skin 16. Tebbs SE, Gonzales AM, Wilson RM, et al. The role of aldose reductase inhibition in diabetic neutrophil phagocytosis and killing. Clin Exp Immunol 1991;84:482. 17. Wykretowicz A, Wierusz-Wysocka B, Wysocki J, et al. Impairment of the oxygen-dependent microbicidal mechanisms of polymorphonuclear neutrophils in patients with type 2 diabetes is not associated with increased susceptibility to infec¬ tion. Diabetes Res Clin Pract 1993; 19:195. 18. Speert DP, Silva J Jr. Abnormalities of in vitro lymphocyte response to mitogens in diabetic children during acute ketoacidosis. Am J Dis Child 1978; 132: 1014. 19. Casey J, Strum C Jr. Impaired response of lymphocytes from non-insulindependent diabetics to staphage lysate and tetanus antigen. J Clin Microbiol 1982; 15:109. 20. Kolterman OG, Olefsky JM, Kurahara C, Taylor K. A defect in cell-medi¬ ated immune function in insulin-resistant diabetic and obese subjects. J Lab Clin Med 1980;96:535. 21. Cooper G, Platt R. Staphylococcus aureus bacteremia in diabetic patients: endocarditis and mortality. Am J Med 1982; 73:658. 22. Olmos P, Donoso J, Rojas N, et al. Tuberculosis and diabetes mellitus: a longitudinal retrospective study in a teaching hospital. Rev Med Chile 1989; 117: 979. 23. Doroghazi RM, Nadol JB Jr, Hyslop NE Jr, et al. Invasive external otitis: report of 21 cases and review of the literature. Am J Med 1981; 71:603. 24. Johnson MP, Ramphal R. Malignant external otitis: report on therapy with ceftazidime and review of therapy and prognosis. Rev Infect Dis 1990; 12:173. 25. Lang R, Goshen S, Kitzes-Cohen R, et al. Successful treatment of malig¬ nant external otitis with ciprofloxacin: report of experience with 23 patients. J Infect Dis 1990; 161:537. 26. Giamarellou H. Malignant otitis externa: the therapeutic evolution of a lethal infection. J Antimicrob Chemother 1992;30:745. 27. LeFrock JL, Mulavi A. Necrotizing skin and subcutaneous infections. J Antimicrob Chemother 1982;9:183. 28. Zhanel GG, Harding GK, Nicolle LE. Asymptomatic bacteriuria in pa¬ tients with diabetes mellitus. Rev Infect Dis 1991; 13:150. 29. Pometta D, Rees SB, Younger D, Kass EH. Asymptomatic bacteriuria in diabetes mellitus. N Engl J Med 1967;276:1118. 30. Lindberg U, Bergstrom AL, Carlsson E, et al. Urinary tract infection in children with type I diabetes. Acta Paediatr Scand 1985; 74:85. 31. Lee JB. Cystitis emphysematosa. Arch Intern Med 1960; 105:150. 32. Evanoff GV, Thompson CS, Foley R, Weinman EJ. Spectrum of gas within the kidney: emphysematous pyelonephritis and emphysematous pyelitis. Am J Med 1987; 83:149. 33. Zabbo A, Montie JE, Popowniak KL, Weinstein AJ. Bilateral emphysema¬ tous pyelonephritis. Urology 1985;25:293. 34. Sobel JD. Pathogenesis of urinary tract infections. Infect Dis Clin North Am 1987; 1:751. 35. Levison ME, Pitsakis PG. Effect of insulin treatment on the susceptibility of the diabetic rat to Escherichia co/i-induced pyelonephritis. J Infect Dis 1984; 150: 554. 36. Sarmiento RV. Emphysematous cholecystitis. Arch Surg 1966;93:1009. 36a. Nussbaum ES, Hall WA. Rhinocerebral mucormycosis: changing pat¬ terns of disease. Surg Neurol 1994;41:152. 36b. Jacobs LG, Skidmore EA, Cardoso LA, Ziv F. Bladder irrigation with amphotericin B for treatment of fungal urinary tract infections. Clin Infect Dis 1994; 18:313. 37. Drutz DJ. Newer antifungal agents and their use, including an update on amphotericin B and flucytosine. In: Remington JS, Swartz MN, eds. Current clinical topics in infectious diseases, vol 3. New York: McGraw-Hill, 1982:97. 38. Fan-Harvard P, Oh J, O'Donovan, et al. Amphotericin B bladder irriga¬ tion vs fluconazole in the treatment of candidal cystitis. In: Abstracts of the 32nd Interscience Conference on Antimicrobial Agents and Chemotherapy, 1992, ab¬ stract 631.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

147

DIABETES AND THE SKIN RICHARD C. EASTMAN AND ROBERT J. TANENBERG The skin of the patient with diabetes may manifest various abnormalities and is prone to the development of certain infec¬ tions.1,2 Additionally, the injection or infusion of insulin and the administration of oral hypoglycemic agents may lead to cutane¬ ous reactions. Occasionally, skin and soft tissue changes may alert the clinician to the presence of diabetes.

1307

NONINFECTIOUS COMPLICATIONS OF DIABETES Various noninfectious skin diseases may occur in the patient with diabetes. Some conditions, such as xanthomas in patients with hypertriglyceridemia, carotenoderma, and reduced skin elasticity, are directly related to metabolic abnormalities, while other conditions, such as diabetic dermopathy, necrobiosis lipo¬ idica diabeticorum, granuloma annulare, and bullosis diabet¬ icorum, are of uncertain etiology and may occur in nondiabetics, in patients with impaired glucose tolerance, and in patients with overt diabetes. In these conditions, subtle metabolic factors, en¬ vironmental factors, or genetic factors probably influence the de¬ velopment of the skin abnormality. The relationship between metabolic control and these cutaneous manifestations is not clear.1,3

XANTHOMAS Xanthomas due to hypertriglyceridemia may occur in the uncontrolled diabetic. Triglyceride levels are usually greater than 1000 mg/dL when xanthomas are present. Eruptive xanthomas characteristic of hypertriglyceridemia occur primarily on the ex¬ tensor surfaces of the extremities and over the buttocks, and they manifest as red-yellow, 2- to 5-mm maculopapular lesions (Fig. 147-1). A red inflammatory border is characteristic. Eruptive xanthomas secondary to uncontrolled diabetes usually clear with improved metabolic control. Patients with fa¬ milial dyslipidemias may require therapy with drugs to reduce triglyceride levels to a satisfactory range (see Chap. 158).

SCLEREDEMA Scleredema is asymmetric nonpitting induration of the skin on the posterolateral aspects of the neck, shoulders, and upper back.1,3-5 Although the condition is often preceded by a strepto¬ coccal infection in the nondiabetic, this is rarely the case in the patient with diabetes.1,3,4 Patients are frequently obese and have microvascular and macrovascular complications of diabetes. The disease affects men more commonly than women, and it may occur in children. Spontaneous resolution in 6 months to 2 years, common in the nondiabetic, rarely occurs in patients with diabetes.4

WAXY SKIN AND REDUCED JOINT MOBILITY Reduced skin elasticity in diabetics has long been recog¬ nized; it has a “hidebound" quality, resembling the skin of pa¬ tients with scleroderma.4 The condition is associated with limited joint mobility and with poor metabolic control. The correlation of these abnormalities with concentrations of glycosylated hemo¬ globin suggests that metabolic factors influence the development of the skin and joint changes. Improvement may occur with im¬ proved metabolic control (see Chap. 206).4 This condition is dis¬ tinct from Dupuytren contracture of the palmar fascia, which, although increased in incidence in diabetics, is extremely com¬ mon in the nondiabetic population.

PERFORATING DERMATOSES Kyrle disease, perforating folliculitis, and reactive perforat¬ ing collagenosis are disorders that may be more common in the diabetic, particularly in patients with chronic renal failure.1 These disorders are characterized by papules with a central keratotic plug, which is gradually extruded. The lesions are often refrac¬ tory to therapy, although topical tretinoin and ultraviolet light may improve some cases.4

CAROTENODERMA The elastic tissue of patients with diabetes may demonstrate yellow discoloration due to deposition of carotenoids, which are

1308

PART IX: DISORDERS OF FUEL METABOLISM

pigments present in green and yellow vegetables. The frequency may be as high as 10% in patients with diabetes.1,3 Blood caro¬ tene levels are usually elevated. Hypothyroidism, hypogo¬ nadism, hypopituitarism, bulimia, and anorexia nervosa are also associated with carotenoderma and should be considered in the differential diagnosis. Brown discoloration of the nail fold due to advanced glycosylation end-products may occur in diabetics.3

DIABETIC DERMOPATHY Dermopathy is a complication of diabetes and is twice as common in males.1,3 The occurrence of the lesions in patients without diabetes is evidence that factors other than hyperglyce¬ mia are causative. The high frequency of other complications of diabetes in affected patients suggests that microangiopathy is an important factor in the pathogenesis. Half of the patients have concurrent retinopathy, neuropathy, and nephropathy. Base¬ ment membrane thickening is found in areas of dermopathy, yet adjacent areas of unaffected skin also show similar changes. The predominant occurrence of the lesions on the lower extremities implicates trauma, neuropathy, and basement membrane thick¬ ening. However, the lesions are not reliably reproduced by

FIGURE 147-2.

Diabetic dermopathy. Note the predominant oc¬

currence on the anterior tibial surfaces. The lesions are pigmented and slightly depressed below the surrounding skin.

trauma.6 Heat or cold traumatization of the extremities in diabet¬ ics of more than 10 years' duration may induce lesions that re¬ semble those of dermopathy.7 Although the lesions occur mostly on the lower extremities ("shin spots"), they also may occur on the arms, thighs, trunk, and scalp; they begin as dull red macules or papules, which are 5 to 12 mm in diameter.3 Crops of four to five lesions may appear over a period of a week and then persist or slowly resolve (Fig. 147-2). As the lesions evolve, they become shallow, depressed, hyperpigmented scars. The lesions are asymptomatic and require no treatment.

NECROBIOSIS LIPOIDICA DIABETICORUM Necrobiosis (degeneration of collagen) is an uncommon complication of diabetes that occurs predominantly in female pa¬ tients. Occasionally, typical lesions may develop in persons with¬ out any identifiable abnormality in carbohydrate metabolism. One fourth of the patients have impaired glucose tolerance rather than overt diabetes at the time of the development of the lesions, indicating that severe or long-standing diabetes is not a prerequi¬ site.3,8 The lesions show degeneration of collagen, granuloma-

Ch. 147: Diabetes and the Skin tous inflammation of subcutaneous tissues and of blood vessels, capillary basement membrane thickening, and obliteration of vessel lumina.4 The lesions of necrobiosis occur most commonly in the pretibial areas and are bilateral in 75% of the cases. They begin as red-brown papules that enlarge and coalesce to form irregular lesions, which may be several centimeters in diameter (Fig. 147-3). The lesions ulcerate in 35% of the cases; although usually painless, they may be painful if ulcerated. As the lesions evolve, they appear as atrophic plaques with a thin, translucent surface manifesting a “porcelain-like sheen.” Various therapies have been used: fluorinated corticoste¬ roids (applied topically, under occlusive dressings, or injected into the lesion), salicylates with dipyridamole, pentoxifylline, systemic corticosteroids, nicotinamide, and clofazimine.3 Topical benzoyl peroxide, seaweed-based alginate dressings, and hydro¬ colloid occlusive dressings may be helpful.3 Grafting of ulcerated areas may occasionally be necessary, although recurrences are common.4

GRANULOMA ANNULARE Granuloma annulare is a dermatitis with histologic similari¬ ties to necrobiosis lipoidicq diabeticorum.4 Patients with general¬ ized lesions are more likely to demonstrate impaired glucose tol¬ erance or overt diabetes.2,4 The lesions occur predominantly on the upper extremities and manifest as flesh-colored plaques with a raised border. The lesions do not ulcerate and are asymptom¬ atic. In the diabetic, resolution occurs spontaneously over several 1 4 years.

BULLOSIS DIABETICORUM Tense bullae of the feet and hands are rare but distinctive manifestations of diabetes. The lesions are of uncertain cause,

1309

although trauma, microangiopathy, and vasculitis have been im¬ plicated.1,3 The blisters may develop in patients during bed rest, indicating that factors other than trauma are involved. The plan¬ tar surfaces and margins of the feet are the most common sites of occurrence. The lesions develop acutely, are asymptomatic, and manifest as tense, 0.5- to 3.0-cm bullae without surrounding in¬ flammation. Healing without scarring occurs over a period of 2 to 4 weeks. Rupture of the lesions should be avoided to prevent superinfection. Drainage and topical antibiotics may be required for large lesions.1

OTHER ASSOCIATED DERMATOSES Other conditions in which an association with diabetes has been reported are lichen planus, lichen sclerosus et atrophicus, psoriasis, bullous pemphigoid, and Kaposi sarcoma.9-11 Vitiligo may be present in patients with autoimmune diseases associated with diabetes.3 The diabetic may also manifest changes of the fingernails due to infections (with Pseudomonas aeruginosa, Staph¬ ylococcus aureus, Proteus mirabilis, or Candida albicans) or to vas¬ cular insufficiency (hypertrophic changes, pterygium, yellow dis¬ coloration).12 Controlled studies have not shown an increased prevalence of epidermophytosis or of generalized pruritus in diabetics.8

INFECTIONS OF THE SKIN AND SOFT TISSUES Various factors have been identified that may predispose the diabetic to infectious diseases (see Chap. 146).13 Persons with un¬ controlled diabetes may be immunocompromised and suscepti¬ ble to the development of certain infections of the skin and soft tissues.14-17 Diabetics, even those whose disease is well con¬ trolled, may have an increased rate of colonization as well as in¬ fections of the skin with C. albicans, Staphylococcus, and Strepto¬ coccus.13,18 Intertrigo in obese diabetics, as in the nondiabetic, may become superinfected with these organisms (Fig. 147-4). Glucosuria predisposes to recurrent candidal vulvovaginitis in fe¬ males. Deterioration of metabolic control in susceptible individ¬ uals may be accompanied by recurrent infection. Surgical wounds or minor abrasions are more likely to become infected. Certain cutaneous infections are particularly likely to appear in the diabetic and deserve special consideration. Prompt diagnosis and appropriate treatment of some infections at an early stage are essential to avoid serious, even life-threatening, complications.

NECROTIZING FASCIITIS

FIGURE 147-3.

Necrobiosis lipoidica diabeticorum. In the large lesion

on the lower extremity, note the irregular border and the silvery overlying skin.

Necrotizing fasciitis is due to mixed aerobic and anaerobic skin and soft tissue infection.19,20 Decubitus ulcers, the skin of the perineum, and the extremities are often the sites of initiation of the infection. Infections beginning in the perineum are associated with a higher mortality rate. At the time of diagnosis, the infec¬ tion has usually spread laterally, dissecting along tissue planes. The infection is limited to the subcutaneous tissues, sparing the underlying muscle.19 Early in the course of the infection, the patient may complain of myalgia in the infected area. The early symptoms may be mis¬ leadingly benign, suggesting musculoskeletal pain. Careful phys¬ ical examination and a high index of suspicion are necessary to make the diagnosis. On examination, there is tenderness in re¬ sponse to palpation over the infected area. Subcutaneous gas oc¬ casionally may be noted by palpation but is detected more reli¬ ably by radiographs. Hypalgesia or anesthesia may be present, owing to involvement of cutaneous nerves. A thin, gray-brown exudate with a feculent odor is characteristic. Systemic toxicity is manifested by fever, tachycardia, and elevated white blood cell count out of proportion to the local manifestations; ketoacidosis and coma have also been reported.1319 21

1310

PART IX: DISORDERS OF FUEL METABOLISM

FIGURE 147-4. Candidal infection of the inframammary fold in a diabetic. "Satellite" lesions that are separated from the area of principal involvement are characteristic. (Cour¬ tesy of Dr. George Kozak.)

Debridement, at times radical, of necrotic tissue is necessary for the patient to survive. Antibiotics should be started empiri¬ cally after appropriate cultures of tissue and blood are obtained. A combination of clindamycin and an aminoglycoside will pro¬ vide the necessary coverage for Staphylococcus, anaerobes, and gram-negative rods and should be continued until the patient is out of danger. Even with treatment, the reported mortality in patients older than age 50 is 50%.16

The ear canal should be irrigated, drained, and debrided, if indicated. Consultation with an otolaryngologist is advisable. Systemic antibiotic therapy with an aminoglycoside and a semi¬ synthetic penicillin, such as ticarcillin, piperacillin, or carbenicillin, is the treatment of choice. Appropriate monotherapy com¬ pares successfully with combination therapy in moderate infections.25

RHINOCEREBRAL MUCORMYCOSIS MALIGNANT EXTERNAL OTITIS Malignant external otitis occurs in patients who are immu¬ nocompromised and may complicate diabetes.22”24 Microangi¬ opathy of the ear canal resulting in poor local perfusion has been implicated in the pathogenesis of the infection.22 The infection may begin indolently with ear pain and drainage and, if un¬ treated, may extend to the periaural soft tissues, to the cells of the mastoid process, and to the meninges, brain substance, and sinuses. Thrombosis of the intracranial veins may occur. On ex¬ amination, the tympanic membrane is normal when visualized.23 Granulation tissue can be visualized at the juncture of the carti¬ laginous and bony portions of the canal in most cases.22 Culture of the drainage typically yields Pseudomonas aeruginosa.2,1

FIGURE 147-5. Erythrasma in a type I diabetic with nephrotic syndrome. Note the swollen genitalia. The borders of the lesions are sharply defined and irregular.

Mucormycosis is a rare, but life-threatening, complication of diabetes.13,16,26 It may be a presenting manifestation of diabetes in elderly patients, may occur with or without the presence of ketoacidosis, and may occur in patients with well-controlled dia¬ betes.2' The infection begins with invasion through the nasal mu¬ cosa by fungi of the genus Mucor, Rhizopus, or Absidia. There is early spread to the soft tissues of the face, orbit, and sinuses. Thrombosis of the vascular supply may produce necrosis of the palate and septum. The patient characteristically presents with facial cellulitis and orbital swelling and may manifest an orbital apex syndrome with oculomotor palsies and loss of vision. There is a black nasal discharge and black eschar of the nasal mucosa. Gram stain of

Ch. 147: Diabetes and the Skin

1311

FIGURE 147-7. Lipohypertrophy of the thigh in a patient repeatedly injecting purified insulin into the same site. The striae are not character¬ istic and were associated with the use of corticosteroids in this case. FIGURE 147-6. Extensive urticarial reaction to insulin. The lesions on the back of the leg are raised and pink with surrounding pallor. Other areas of the body showed similar lesions.

the discharge will show broad, nonseptate hyphae, and culture usually yields the organism. Amphotericin B is the treatment of choice. Surgical debride¬ ment is essential, because the organism may persist in devitalized tissue.

illae or groin (Fig. 147-5). Involvement may be extensive. The lesions manifest a characteristic coral-red fluorescence under a Wood light. Gram stain shows a small, gram-positive bacillus, and aerobic culture of the material will grow Cory neb act erium minutissimum. Treatment with erythromycin is effective.

DERMATOLOGIC COMPLICATIONS OF THE TREATMENT OF DIABETES

ERYTHRASMA

IMMUNOLOGIC REACTIONS TO INSULIN

Erythrasma is a common, if not always recognized, infection in diabetics.3,13 It begins as a pruritic, red-brown patch in the ax-

Hypersensitivity reactions to insulin preparations occurred commonly in the past, before the application of improved puri-

FIGURE147-8. Multiple abdominal abscesses at the sites of needle insertions in a patient on chronic sub¬ cutaneous insulin infusion. (Courtesy of Dr. Julio Santiago.)

1312

PART IX: DISORDERS OF FUEL METABOLISM TABLE 147-1 Dermatologic Findings in Syndromes or Diseases Associated With Diabetes Polyglandular failure

Vitiligo; premature graying; addisonian hyperpigmentation; chronic mucocutaneous candidiasis

Hemochromatosis

Gray, brown, or intermediate shades of hyperpigmentation; alopecia

Porphyria cutanea tarda

Bullous eruption in sun-exposed areas; hypertrichosis; milia

Syndromes of insulin resistance and acanthosis nigricans Type A

Acanthosis nigricans; hirsutism; accelerated growth; clitoromegaly

Type B

Acanthosis nigricans; alopecia

Polycystic ovary syndrome

Hirsutism; acne; alopecia; acanthosis nigricans

Total lipoatrophy (Lawrence-Seip Syndrome)

Absent subcutaneous fat; acanthosis nigricans; hyperhidrosis; masculinization

Leprechaunism

Acanthosis nigricans; premature aging of the skin

Ataxia-telangiectasia

Telangiectasia

Progressive lipodystrophy

Hyperhidrosis; absent subcutaneous fat

fkation techniques for commercial insulins and before the avail¬ ability of monospecies pork and human insulins (Fig. 147-6).8 Although less common, hypersensitivity reactions may occur in patients on the new insulins and may pose difficult management problems (see Chap. 139). Focal lipoatrophy, or loss of subcutaneous fat in areas of in¬ sulin injection, most likely represents an immunologic reaction to impurities in the insulin preparation and is less common in pa¬ tients using the purer forms of insulin. In contrast, focal lipohypertrophy at areas of insulin injections is most likely due to inhi¬ bition of lipolysis by high local concentrations of insulin (Fig. 147-7) (see Chap. 139).

COMPLICATIONS OF CHRONIC SUBCUTANEOUS INSULIN ADMINISTRATION Local infection, allergy to tape and tubing materials, and hard subcutaneous nodules are complications of chronic subcu¬ taneous insulin injection.24 Localized areas of cellulitis and ab¬ scess formation occur in 40% of patients treated by insulin infu¬ sion (Fig. 147-8). Leaving the catheter or needle in place for more than 48 hours is associated with a high risk of infection. Deterio¬ ration in the degree of glycemic control may be the first sign of problems at the infusion site, before overt signs of infection or inflammation are present. When there is an unexplained deterio¬ ration in plasma glucose control, the needle and catheter should be changed. Local abscesses are treated with warm compresses, incision and drainage if necessary, and antibiotic therapy. Some patients on chronic subcutaneous insulin injection de¬ velop tender nodules with a rock-hard consistency at the sites of needle insertion.28 Local trauma from prolonged contact of nee¬ dles left under the skin, multiple injections into the same site, or local hematoma formation from the movement of needles under the skin may explain the development of these nodules. Interac¬ tions of the insulin with tubing materials may play a role, and changing the type of insulin infused may lead to improvement. The lesions may take months to resolve.28

REACTIONS TO ORAL ANTIDIABETIC AGENTS Oral hypoglycemic agents are structurally related to the sul¬ fonamides. Three percent of patients develop allergic skin reac¬ tions, which may include pruritus, urticaria, photosensitivity, ex¬ foliative dermatitis, and toxic epidermal necrolysis.6 Jaundice has been reported with the use of chloropropamide. The secondgeneration sulfonylurea agents glipizide and glyburide must be

used with caution in patients who have reacted in the past to sulfonylureas or other oral hypoglycemic drugs. Chloropropamide-induced alcohol flushing was initially re¬ ported in 5% of patients taking the drug.6 Fortunately, the second-generation oral hypoglycemic agents do not cause this troublesome reaction (see Chap. 138).

DERMATOLOGIC FINDINGS IN SECONDARY DIABETES Skin problems, such as excessive sweating in patients with acromegaly, plethora or hirsutism in the patient with Cushing syndrome, or pallor and sweating due to pheochromocytoma, may initially bring the patient to medical attention. Patients with glucagonoma have a characteristic dermatitis—necrolytic migra¬ tory erythema—that involves the perioral area, intertriginous re¬ gions, and lower extremities (see Chap. 176).29 The diabetes re¬ solves with successful treatment of the neoplasm. Glucose intolerance or diabetes also occurs in several rare syndromes, such as hemochromatosis and porphyria. Many of these patients also have characteristic dermatologic manifesta¬ tions, which are summarized in Table 147-1. Acanthosis nigricans is a verrucous, hyperplastic, hyperpigmented skin manifestation relatively common in obesity, poly¬ cystic ovary syndrome, and other rarer defects in insulin action due to various abnormalities.30-32 This finding suggests an underlying disorder of insulin resistance (see Chaps. 140, 212, and 213).

REFERENCES 1. Jelinek JE. The skin and diabetes. Philadelphia: Lea & Febiger, 1986. 2. Perez MI, Kohn SR. Cutaneous manifestations of diabetes. J Am Acad Der¬ matol 1994; 30:519. 3. Jelinek JE. The skin in diabetes. Diabet Med 1993; 10:201. 4. Brik R, Berant M, Vardi P. The scleroderma-like syndrome of insulin-dependent diabetes mellitus. Diabetes Metab Rev 1991; 7:121. 5. Inasaki T, Kohama T, Houjou S, et al. Diabetic scleredema-like changes in a patient with maturity onset type diabetes of young people. Dermatology 1994,188:228. 6. Boyd AG, Annes AM, Campbell IW. Skin manifestations of diabetes mel¬ litus. Practitioner 1982,-226:253. 7. Lithner F. Cutaneous reactions of the extremities of diabetics to local ther¬ mal trauma. Acta Med Scand 1975,-198:319. 8. Feingold KR, Elias PM. Endocrine-skin interactions: cutaneous manifesta¬ tions of pituitary disease, thyroid disease, calcium disorders, and diabetes. J Am Acad Dermatol 1987; 17:921. 9. Garcia-Bravo B, Sanchez-Pedreno P, Rodriguez-Pichardo A, Camacho F. Lichen sclerosus et atrophicus: a study of 76 cases and their relation to diabetes. J Am Acad Dermatol 1988; 19:482.

Ch. 148: The Diabetic Foot 10. Goodfield M], Millard LC. The skin in diabetes mellitus. Diabetologia 1989; 31:567. 11. Dahl MV. Bullous pemphigoid: associated diseases. Clin Dermatol 1987;5:64. 12. Greene RA, Scher RK. Nail changes associated with diabetes mellitus. ] Am Acad Dermatol 1987; 16:1015. 13. Murphy DP, Tan JS, File TM. Infectious complications in diabetic pa¬ tients. Primary Care 1981;8:695. 14. Repine JE, Clauson CC, Goetz FC. Leucocytes and host defense: Bacteri¬ cidal functions of neutrophils from patients with acute bacterial infections and from diabetes. J Infect Dis 1980; 142:869. 15. Rayfield E], Ault M], Keusch GT, et al. Infection and diabetes: the case for glucose control. Am J Med 1982; 72:439. 16. Edwards JE Jr, Tillman DB, Miller ME, Pitchon HE. Infection and diabetes mellitus. West J Med 1979; 130:515. 17. Wilson RM. Neutrophil function in diabetes. Diabetic Med 1986;3:509. 18. Bartholomew G, Roden B, Bell DAH. Oral candidiasis in IDDM. Diabetes 1985;34:103A. 19. Addison WA, Livengood CH, Hill GB, et al. Necrotizing fasciitis of vulvar origin in diabetic patients. Obstet Gynecol 1984; 63:473. 20. Farrell LD, Karl SR, Davis PK, et al. Postoperative necrotizing fasciitis in children. Pediatrics 1988;82:874. 21. Hautekeefe ML, Nagler JM, Mertens AH, et al. Necrotizing fasciitis pre¬ cipitating diabetic ketoacidotic coma. Intensive Care Med 1986; 12:383. 22. Doroghazi RM, Nadol JB, Hyslop NE, et al. Invasive external otitis. Am J Med 1981; 71:603. 23. Cohen D, Friedman P. The diagnostic criteria of malignant external otitis. J Laryngol Otol 1987; 101:216. 24. Scherbeuske JM, Winton GB, James WD. Acute Pseudomonas infection of the external ear (malignant external otitis). J Dermatol Surg Oncol 1988; 14:165. 25. Myers BR, Mendelson MH, Parisier SC, Hirschman SF. Malignant exter¬ nal otitis: comparison of monotherapy vs. combination therapy. Arch Otolaryngol Head Neck Surg 1987; 113:974. 26. Kilpatrick CJ, Speer AG, Tress BM, King JO. Rhinocerebral mucor¬ mycosis. Med J Aust 1983; 1:308. 27. Sandler R, Tallman CB, Kearny DG, Irving WR. Successfully treated rhi¬ nocerebral phycomycosis in well-controlled diabetes. N Engl J Med 1971; 285:1180. 28. Levandoski LA, White NH, Santiago JV. Localized skin reactions to insu¬ lin: insulin lipodystrophies and skin reactions to pumped subcutaneous insulin therapy. Diabetes Care 1982;5:6. 29. Kalian A, Rafael M, Perez-Gigaredo A, Neimanis A. Necrolytic migratory erythema. Arch Dermatol 1977; 113:792. 30. Kahn CR, Flier JS, Var RS, et al. The syndromes of insulin resistance and acanthosis nigracans. N Engl J Med 1976; 294:739. 31. Flier JS, Eastman RC, Minaker KA, et al. Acanthosis nigricans in obese women with hyperandrorganism: characterization of an insulin-resistant state dis¬ tinct from the type A and B syndromes. Diabetes 1985;34:101. 32. Carroll PB, Eastman RC. Insulin resistance: diagnosis and treatment. En¬ docrinologist 1991; 1:89.

1313

of many health care professionals regarding the treatment of di¬ abetic foot problems.

PATHOPHYSIOLOGY Although careful control of diabetes and avoidance of smok¬ ing may postpone the development of foot problems, it will not prevent them. Three primary pathologic situations occur in the diabetic, which singly or in combination are responsible for the development of foot problems: neuropathy, arterial insuffi¬ ciency, and infection.

NEUROPATHY The diabetic neuropathic foot may look healthy, but it has altered proprioception, making the patient less aware of the po¬ sition of his or her foot, and diminished touch and pain, causing an insensitive foot. Moreover, peripheral neuropathy affects the intrinsic and skeletal muscles of the foot and leg, causing atrophy and deformity. The result of this motor neuropathy is a musclewasted foot with prominent metatarsal heads, clawed toes, and limited joint mobility. The resulting deformities create high foot pressures with subsequent callus formation and ulceration if re¬ petitive moderate stress (as in walking) continues. The patient is unaware of these stresses because of an insensitive foot. The autonomic system is adversely affected by neuropathy, often causing autosympathectomy in the lower extremities; the feet be¬ come anhidrotic and the skin is dried and cracks easily. The over¬ all result is a limb that is highly susceptible to minor trauma and a patient who is unaware of an existing problem until it has be¬ come a serious limb-threatening infection (Figs. 148-1 and 148-2; see Chap. 142).

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

148

THE DIABETIC FOOT GARY W. GIBBONS

PREVALENCE Foot problems and diabetes are almost synonymous. About 25% of diabetics will eventually consult a clinician, surgeon, or podiatrist for diabetes-related problems of the lower extremities. Because diabetics are 17 times more likely to develop gangrene (a word to avoid using in front of the patient), it is not surprising that 66% of the major amputations performed in the United States are performed on diabetics. The American Diabetes Asso¬ ciation and Healthy People 2000 (the health objectives of the US Public Health Service) have a goal to reduce this major amputa¬ tion rate.1 Despite the tremendous advances that have been made in the knowledge, technology, and treatment of diabetes, diabetic foot problems continue to be a major health concern, causing serious morbidity, mortality, and economic consequences. Many of these tragic consequences could be avoided by better patient education and understanding and by eliminating misconceptions

FIGURE 148-1.

Plantar neuropathic ulcer in a diabetic patient. There is a nonhealing, painless, circular, punched-out ulceration surrounded by a callus (arrows) overlying the metatarsal head. These ulcers, which are due to the combined effects of neuropathy and ischemia, occur at sites of greatest pressure. The anesthesia and anhidrosis predispose to their for¬ mation. If improperly treated, these ulcers progress to osteomyelitis and gangrene. Therapy includes debridement, trimming of the callus, rest, redistribution of weight with custom-molded inserts, and appropriate ed¬ ucation in foot care. Note the onychomycosis of the toenails (arrowheads), a condition to which diabetics are predisposed.

1314

PART IX: DISORDERS OF FUEL METABOLISM teries that precludes revascularization, and this myth must be eliminated to reduce the frequency of major amputation.2,3 Dia¬ betics also tend to have poor collateral circulation, with much more atherosclerotic involvement of the distal zones of the pro¬ funda femoral artery and the infragenicular arteries.4 Further, the atherosclerotic plaque and media of diabetic arteries frequently contain extensive calcium (medial calcinosis), making the artery rigid and noncompressible. These peculiarities may explain the interpretive results of standard noninvasive tests, which are of¬ ten incorrect or misleading when applied to the diabetic lower extremity.5 Ischemia may complicate up to 60% of nonhealing diabetic foot ulcers.

INFECTION

FIGURE 148-2.

Severe ulceration and gangrene of the foot of a diabetic

patient, requiring amputation. Many of these tragic complications can be avoided by education of patients and of health care professionals.

ISCHEMIA Although the severity of diabetes is not crucial to the devel¬ opment of vascular disease, peripheral vascular disease is esti¬ mated to be 20 times more common in the diabetic population (see Chap. 141). It appears at a younger age; there is an almost equal affinity for men and women; and bilateral involvement is usual. The pathology of atherosclerosis resembles that of the nondiabetic, with three main distinctions. There is a predilection for the more distal tibial/peroneal vessels of the lower leg, as demonstrated by the fact that 40% of diabetics presenting with gangrene will have a palpable popliteal pulse. The foot arteries, especially the dorsalis pedis and its branches, are usually spared. There is no occlusive microvascular lesion affecting the foot ar-

TABLE 148-1 Patient Education and Responsibility

Diabetic patients tolerate infection poorly. Infection pre¬ vents diabetic control, and uncontrolled diabetes affects infec¬ tion. Defects in the host defense mechanism of many diabetics predisposes them to infection and certainly alters their response to infections. Chemotaxis, phagocytosis, and the bactericidal function of diabetic neutrophils are diminished, particularly in patients with hyperglycemia or ketoacidosis (see Chap. 146). Systemic signs and symptoms (such as fever or elevation of the white blood cell count) of a septic process often occur late, mak¬ ing unexplained and uncontrolled hyperglycemia the only reli¬ able sign of a potentially limb-threatening infection.6,7 Patients with a foot ulcer should not be sent home just because they are afebrile or have a normal white blood cell count. More commonly, it is a combination of the three primary pathologic situations that interact to cause the problem.8 The un¬ protected neuropathic foot is particularly prone to breakdown and ulcerations. Vascular compromise in the traumatized area delays an already compromised host response to infection, the delivery of antimicrobial agents to the area, and proper wound healing.

MANAGEMENT IMPORTANCE OF PREVENTION

1. DAILY FOOT INSPECTION BY PATIENT AND FAMILY Red or ecchymotic areas Calluses Blisters Open sores or dry fissures Fungus infections

2. GOOD HYGIENE No heat or soaks in any form Wash and dry carefully No astringents Antifungal medication as needed Lanolin preparation or petroleum jelly as needed No bathroom surgery Proper nail, corn, and callus treatment

3. FITTED FOOTWEAR No barefoot walking No crowding from the toes to the heel Podiatric appliances, such as molded insoles Keep feet and shoes dry Break in new shoes slowly Inspect footwear for foreign bodies or wear

4. AVOID POTENTIALLY INJURIOUS OBJECTS AND SITUATIONS; KEEP NIGHTLIGFIT IN BATHROOM AND BEDROOM 5. EARLY AND PROMPT REPORTING OF ANY CHANGES OR CONCERNS

The most successful management of diabetic foot problems begins with prevention. The level of patient education and un¬ derstanding correlates inversely with the development of foot problems. The same must be said for the physician who elects to care for these patients. Both must realize that any traumatic le¬ sion or ulcer on the lower extremity is important and must be attended to immediately. The patient should be educated to understand his or her re¬ sponsibilities as outlined in Table 148-1. Patients and their fami¬ lies need to establish a routine that begins with daily inspection of the feet and legs. Because the loss of visual acuity is common in many diabetic patients, a family member or friend may help look for calluses, fissures, red or ecchymotic areas, fungal infec¬ tions, and open sores or blisters. Proper hygiene includes wash¬ ing and drying the feet carefully and avoiding the use of all as¬ tringents. Heat or soaks in any form are to be avoided. Lanolin preparations or petroleum jelly must be used on dry areas, and antifungal medication should be used as needed. “Bathroom sur¬ gery" must be avoided, especially for the nails, corns, or calluses. When nails are trimmed, a slight rounding of the edges is preferred. Proper footwear is essential because the diabetic will not tol¬ erate crowding in any area of the foot. Podiatric appliances such as inserts and spacers are often needed to protect sensitive, highrisk areas. Extra-depth shoes may be helpful, but simply chang¬ ing shoes periodically during the day suffices for most patients. The diabetic should never go barefoot and should avoid situa¬ tions likely to cause problems. There should be a nightlight in the bedroom. All footwear must be inspected daily for foreign bodies

Ch. 148: The Diabetic Foot or wear, and new shoes must be broken in slowly. Although these principles sound simple, it must be remembered that it is patient understanding and adherence to proper care that play a primary role in avoidance of foot problems.8

THERAPY FOR A FOOT ULCER The course of treatment for a foot ulcer depends on its se¬ verity (Table 148-2).9,10 The first major decision is whether the patient needs to be admitted to the hospital or treated at home. The severity of tissue destruction may not be totally apparent to the patient from just looking at the ulcer or infected callus, especially in those who continue to bear weight on a painless area or do not have the visual acuity to recognize a problem. It is imperative for the physician to unroof all encrusted areas and inspect the wound to determine the extent of any deep tissue destruction and the presence of any possible bone and/or joint involvement. The physician must emphasize to the patient and family the importance of debridement and inspection so that the patient understands that the debridement did not cause the problem. Early superficial ulcers may be treated at home provided that cellulitis, if present, is only minimal, that there is no evidence of any systemic toxicity, and that the patient is compliant, reliable, and has a vigilant support system. The injured foot must be put to complete rest; neuropathy includes sensory and proprioceptor loss, so that partial weight-bearing as perceived by the patient actually may be full weight-bearing. If infection is present, cul¬ tures are taken and initially a broad-spectrum oral antibiotic is started and changed, pending subsequent sensitivity reports and the response of the wound. Staphylococcus aureus and Streptococ¬ cus species are most often cultured, and antibiotic therapy should at least effectively cover these organisms. Dressings must be kept simple, such as plain gauze sponges moistened with diluted iso¬ tonic antiseptic solutions applied to the open areas one to two times daily. Quarter-strength povidone-iodine (Betadine) or plain saline are frequently used. Dry cracks or fissures respond to antibiotic ointments or lanolin-based creams. Dressings can eas¬ ily be done by the patient, a family member or friend; this will become even more important with increasing cost constraints on all treatment programs. Whirlpools, heat, or soaks in any form are to be avoided, as is the use of enzymatic debriding agents or astringents. If an ulcer is infected and if there is no significant improvement within 48 hours, hospitalization is advised. Once healing is achieved under careful surveillance, gradu¬ ated weight-bearing is begun, with podiatric appliances and modifications of footwear a prerequisite for sensitive, high-risk areas of the foot. A Charcot joint may develop if weight-bearing progresses too rapidly. Its presentation may be strikingly similar to that of an acute infection, with warmth, redness, and swell¬ ing.11 With an early Charcot joint, there is usually no open area and an antecedent history of some minor trauma initiating the process. The radiographic picture may be misinterpreted as os¬ teomyelitis, but the experienced clinician can usually make the diagnosis, especially if it is included early in the differential diagnosis.

1315

treat deeply infected wounds and osteomyelitis frequently result in failure and a higher amputation level. The choice of an initial antibiotic regimen is influenced by several variables, including likely pathogens. Gram staining of the purulent material, local bacterial resistance patterns, prior an¬ tibiotic therapy, preexisting renal or hepatic dysfunction, and the severity of the infection. A review of diabetic patients with seri¬ ous limb-threatening infections has emphasized the importance of mixed and multiple organisms (3.2 isolates per ulcer).1’ Aero¬ bic gram-positive cocci (93%) and gram-negative bacilli (50%) are prevalent in a similar manner, whether systemic toxicity is present or not. Anaerobic cultures are positive in 69% of patients. Certainly, any wound that has crepitance, a foul, fetid odor, or gas evident on radiography is harboring anaerobes. As soon as deep cultures are obtained, broad-spectrum intravenous antibi¬ otics are administered to ensure adequate serum levels. Later, changes are made depending on sensitivity reports and the re¬ sponse of the infection, provided that proper wound care has been achieved. Proper surgical wound care is essential to the successful management of any limb-threatening infection/ 9 This requires immediate surgical debridement of all necrotic tissue and drain¬ age of pus. This must be done even in a patient with compro¬ mised circulation. Vascular reconstruction in a patient with an ongoing limb-threatening infection is contraindicated. The sever¬ ity of tissue destruction and sepsis may not be totally apparent from looking at the ulcer or infected callus. Diabetics do not tol¬ erate undrained infection; adequate debridement cannot be achieved in a deep necrotic diabetic wound using small stab wounds or drains. The debridement and drainage must be such that all necrotic material is removed and dependent drainage is adequate to prevent any pooling of pus. Dressings are initiated with the initial surgical procedure. The most effective dressings are plain gauze sponges moistened with isotonic antiseptic solu¬ tions or saline and applied to the open wound two to three times daily. Whirlpools, soaks, or hot compresses are avoided because they may lead to more complications. Enzymatic debriding oint¬ ments and other astringents, especially full-strength solutions.

TABLE 148-2 Diabetic Foot Ulcer Mild

Limb Threatening

Superficial

Deep ulcer

Minimal or no cellulitis

± Bone involvement

No bone involvement

>2-cm cellulitis

No systemic toxicity

Threatened limb loss ± Systemic toxicity

R,

Rx

Rest injured part

Immediate admission

Culture and sensitivities

Control blood glucose

Initial broad-spectrum oral antibiotic (change based on sensitivities and reponse)

Culture and sensitivities

LIMB-THREATENING INFECTIONS

Careful debridement

Limb-threatening infections (see Table 148-2) require imme¬ diate admission to the hospital, with the patient placed on com¬ plete bed rest. Because hyperglycemia must be brought under control rapidly, insulin (not oral agents) is most often required. Although the patient's condition must be stabilized medically, this should not delay necessary surgical intervention. The essen¬ tials for limb salvage include proper surgical wound care and an¬ tibiotic therapy. Frequently, systemic toxicity or shock will not be reversed until the septic process is debrided and drained. It is a fallacy to think that antibiotics alone will solve the problem. In the author's experience, 6-week courses of antibiotics alone to

Local dressings Podiatric appliances and special shoes Careful follow-up

Initial broad-spectrum intravenous antibiotics; specific antibiotics based on sensitivities and response Early surgical debridement, dependent drainage and open amputation Local dressings Later selected revascularization and conservative amputations or revisions Podiatric applicances and special shoes Careful follow-up

1316

PART IX: DISORDERS OF FUEL METABOLISM

are also to be avoided, because they are injurious to already com¬ promised tissues. Topical growth factors may hold promise for the future, but they are expensive for routine use and further clinical trials are needed. There is no indication for hyperbaric oxygen limb cham¬ bers and little evidence supporting immersion chambers for rou¬ tine treatment of infected diabetic ulcers. OSTEOMYELITIS

Inadequate diagnosis and treatment of osteomyelitis in¬ creases the risk of major amputation. All of the reports recom¬ mending one or more combinations of any of the current radiologic imaging techniques are flawed, and these tests are expensive. A sterile probe hitting the bone or joint is equal in sensitivity and specificity to any of these tests. A plain radiograph is recommended on admission, but special scans are reserved for complicated cases where probing is equivocal. Prolonged courses of antibiotics rarely cure osteomyelitis, especially cases with as¬ sociated deep infection, gangrene, ischemia, and bacteremia. Dead necrotic infected bone should be removed for the reasons mentioned previously. ROLE OF VASCULAR RECONSTRUCTION

Once the situation is fully stabilized, vascular reconstruction can be undertaken in selected patients with vascular insufficiency who are suitable candidates, d The results of inflow and outflow procedures in diabetics compare favorably with those dealing primarily with nondiabetic patients, in whom most of the proce¬ dures are done for claudication and not for limb salvage.1415 The major difference is that about 33% of the diabetics are dead at 5 years from other complications. Advances in arteriography, mi¬ croscopic loops, fine arterial sutures, needles, and instruments now allow for routine successful revascularization of the pedal arteries of ischemic diabetic feet.16 If successful revascularization is accomplished, more conser¬ vative distal amputations or revisions can be carried out to achieve healing and limb salvage.17 Gradual and progressive weight-bearing under careful surveillance is mandatory and of¬ ten requires special orthotics and/or shoes to keep these highrisk areas healed and pressure free.

2. LoGerfo FW, Coffman JD. Vascular and microvascular disease in the dia¬ betic foot: implications for foot care. N Engl JMed 1984; 311:1615. 3. Pomposelli FB, Marcaccio EJ, Gibbons GW, et al. Dorsalis pedis arterial bypass: durable limb salvage for foot ischemia in patients with diabetes mellitus. J Vase Surg (in press). 4. King TA, DePalma RG, Rhodes RS. Diabetes mellitus and atherosclerosis involvement of the profunda femoris artery. Surg Gynecol Obstet 1984; 159:553. 5. Gibbons GW, Wheelock FC Jr. Problems in the noninvasive evaluation of the peripheral circulation in the diabetic. Prac Cardiol 1982; 8:115. 6. Gibbons GW, Freeman DV. Diabetic foot infections. In: Howard RJ, Sim¬ mons RL, eds. Surgical infectious diseases. Norwalk, CT: Appleton & Lange, 1988: 585. 7. Gibbons GW. Diabetic foot sepsis. In: Brewster D, ed. Common problems in vascular surgery. Chicago: Year Book Medical Publishers, 1989:412. 8. Delbridge L, Appleberg M, Reeve TS. Factors associated with development of foot lesions in the diabetic. Surgery 1983;93:78. 9. Gibbons GW, Wheelock FC Jr. Cutaneous ulcers of the diabetic foot. In: Ernest CB, Stanley JC, eds. Current therapy in vascular surgery. Philadelphia: BC Decker, 1987:233. 10. Gibbons GW. Diabetic foot sepsis. Semin Vase Surg 1992;5(4): 1. 11. Sinha S, Frykberg RG, Kozak GP. Neuroarthropathy in the diabetic foot. In: Kozak G, ed. Clinical diabetes mellitus. Philadelphia: WB Saunders, 1983:415. 12. Gibbons GW, Eliopoulos GM. Infection of the diabetic foot. In: Kozak GP, Hoar CS, Rowbotham JL, et al, eds. Management of the diabetic foot problem. Joslin Clinic and New England Deaconess Hospital. Philadelphia: WB Saunders, 1984:97. 13. Gibbons GW, Freeman DV. Vascular evaluation and treatment of the di¬ abetic. Clin Podiatr Med Surg 1987;4:337. 14. Hoar CS, Campbell DR. Aorto-iliac reconstruction. In: Kozak GP, Hoar CS, Rowbotham JL, et al, eds. Management of the diabetic foot problem. Joslin Clinic and New England Deaconess Hospital. Philadelphia: WB Saunders, 1984: 159. 15. Wheelock FC, Gibbons GW. Arterial reconstruction: femoral, popliteal, tibial. In: Kozak GP, Hoar CS, Rowbotham JL, et al., eds. Management of the Dia¬ betic Foot Problem. Joslin Clinic and New England Deaconess Hospital. Philadel¬ phia: WB Saunders, 1984:173. 16. Pomposelli FB, Jepson SJ, Gibbons GW, et al. A flexible approach to infrapopliteal vein grafts in patients with diabetes mellitus. Arch Surg 1991; 126:724. 17. LoGerfo FW, Gibbons GW, Pomposelli FB, et al. Trends in the care of the diabetic foot. Arch Surg 1992; 127:617. 18. Caputo GM, Cavanagh PR, Ulbrecht JS, Gibbons GW, Karchmer AW. Current concepts: Assessment and management of foot disease in patients with diabetes. N Engl J Med 1994; 13:854. 19. Gibbons GW, Maracaccio EJ, Burgess AM RN, et al. Improved quality of diabetic foot care, 1984 vs. 1990: Reduced length of stay and costs, insufficient reimbursement. Arch Surg 1993; 1283:576.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CONCLUSION The fear of gangrene or amputation is one of the over¬ whelming concerns of diabetic patients who suffer the many complications of their disease. Neuropathy, ischemia, and an al¬ tered host defense mechanism make these patients particularly prone to developing foot ulcers, which often become infected. Occasionally, it is only the complications of odor, hyperglycemia, or systemic symptoms that bring the patient to the hospital with a septic foot. Preventing limb-threatening ulcers or infections begins with patient education and understanding. Early recognition of any foot problem and its prompt treatment are essential. Treating se¬ rious limb-threatening conditions requires considerable experi¬ ence. Diabetics generally have greater risk factors (usually cardiac), and diabetic arteries require the maximum skill and ex¬ perience of the operating surgeon. A team approach is the most cost-effective method to salvage the diabetic foot.18 In the past decade, the amputation rate at all levels of the diabetic lower extremity has been reduced by utilizing the concepts outlined in this chapter. An aggressive approach to limb salvage is less ex¬ pensive than resorting to major amputation, and the benefits to the patient and society are unquestionably superior.19

REFERENCES 1. U.S. Department of Health and Human Services. Healthy people 2000— national health promotion and disease prevention objectives. Washington, DC: US Government Printing Office, 1991:73.

CHAPTER

149_

DIABETIC ACIDOSIS, HYPEROSMOLAR COMA, AND LACTIC ACIDOSIS K. GEORGE M.M. ALBERTI

The diabetic acidoses and comas remain a significant cause of mortality and morbidity, much of it unnecessary. Many of the problems encountered could be avoided by the education of pa¬ tients, health care professionals, and physicians in appropriate preventive measures and by the use of systematic, logical ther¬ apy. Several reviews are recommended for further reading.1'9

DIABETIC KETOACIDOSIS Diabetic ketoacidosis (DKA) may be defined as a state of un¬ controlled diabetes mellitus in which there is hyperglycemia (usually >300 mg/dL or 16.7 mmol/L) with a significant lower¬ ing of arterial blood pH (5 mmol/L). The cut-off between DKA and hyperosmolar hyperglycemic nonketotic coma (HONK) is somewhat arbitrary, although hyperglycemia tends to be much more severe in the latter, with ketone body levels lower.

EPIDEMIOLOGY There are few good data available on the incidence of DKA. In a survey in Rhode Island, DKA accounted for 1.6% of all ad¬ missions to the hospital, with previously undiagnosed diabetes accounting for 20% of these. The annual incidence was 14 per 100,000 people.10 In Denmark, rates of 8.5 per 100,000 people were reported for 1975 to 1979, with the highest rates coming from the lowest socioeconomic groups.11 An update from Den¬ mark showed an annual incidence of 4.5%, with highest risk in female adolescents.12 The best data have been compiled by the National Diabetes Group in the United States, who report an an¬ nual incidence of 3 to 8 episodes per 1000 diabetic patients, with 20% to 30% occurring in new diabetics.13 Higher figures have been reported by the Centers for Disease Control and Preven¬ tion14 at 26 to 38 per 100,000 population and an annual incidence of 1.0 to 1.5% of all diabetics in the period 1980 to 1987. Rates were three-fold higher in black men than in white men. Mortality rates for established DKA are relatively high, ac¬ counting for 10% of all diabetes-related deaths in the United States between 1970 and 1978.15 Rates were highest in non¬ whites and in the over 65-year-old age group (59% of all DKA deaths). In most published series, mortality rates lie between 4% and 10%. A report from Birmingham, United Kingdom showed a rate of 3.9% in 929 episodes over a 21-year period, with less than 2% in those younger than 70 years of age.16 In nonspecialized centers, rates increase to 20% or 25%, with even higher rates in the elderly. Poor prognostic factors include age, low pH, hypo¬ tension, high plasma urea and glucose, and severe associated dis¬ ease. Many of the deaths, particularly metabolic deaths in youn¬ ger patients, are avoidable.17

PATHOPHYSIOLOGY Diabetic ketoacidosis results from absolute or relative insulin deficiency.1 4 In the former, there is a total lack of insulin, as found in a newly presenting, young patient with insulindependent diabetes mellitus (IDDM). In relative insulin defi¬ ciency, circulating insulin is present, but there is excessive secretion of the counterregulatory hormones (e.g., glucagon, cat¬ echolamines, cortisol, growth hormone), and insulin secretion cannot increase sufficiently to counter their actions. Normally, metabolic homeostasis is maintained by a fine

1317

balance between the actions of insulin and the actions of the counterregulatory hormones. Insulin has anabolic and anticatabolic actions; the other hormones are primarily catabolic, with the exception of growth hormone, which has both anabolic (i.e., protein metabolism) and catabolic (i.e., carbohydrate and lipid metabolism) effects. The normal control of metabolism by insulin and the catabolic hormones is reviewed in Chapters 128 and 130 and is outlined here only briefly. FAT METABOLISM

In the fed state in normal persons, the high circulating insu¬ lin levels inhibit adipose tissue lipolysis and stimulate reesterifi¬ cation through the provision of glycerol-3-phosphate from glu¬ cose, which is actively transported into the cell. Endothelial cell lipoprotein lipase activity in adipose tissue is also stimulated, re¬ leasing fatty acids from triglycerides, which diffuse into the adi¬ pocyte and are esterified to form triglyceride (Fig. 149-1). In the fasted state, the lower insulin levels are adequate to reduce but not prevent lipolysis; reesterification is low; and fatty acids (and glycerol) diffuse into the circulation. Lipolysis is maintained through the actions of the catecholamines and cortisol. The increased circulating fatty acids are taken up by the liver and activated to fatty acyl-coenzyme A (CoA). In the fed state, these would be mainly esterified to triglyceride. At the same time, insulin stimulates de novo synthesis of fatty acids from glucose, which follows the same route. In the fasted state, the actions of glucagon predominate, with fatty acyl-CoA entering the mito¬ chondria via the carnitine shuttle (Fig. 149-2). This is the key reg¬ ulatory step through modulation of the enzyme carnitine acyl transferase I situated on the outer membrane of the mitochon¬ drion. Lack of insulin causes direct stimulation of enzyme activ¬ ity, and a decrease in the levels of malonyl-CoA has the same effect. Malonyl-CoA is a key intermediate early in the fatty acid synthetic pathway. This pathway is stimulated by insulin and inhibited by glucagon by direct actions on acetyl-CoA carboxyl¬ ase; in the fasted state, the high glucagon and low insulin levels result in low activity and low malonyl-CoA levels. Glucagon also increases the amount of carnitine available for the shuttle, prob¬ ably by enhancing hepatic uptake of carnitine, with activation of the shuttle through a mass action effect. The net result is an increase in fatty acid oxidation, with the formation of increased quantities of acetyl-CoA and the forma¬ tion of acetoacetyl-CoA through 3-hydroxy-3-methylglutarylCoA. Some acetyl-CoA condenses with oxaloacetate to form ci¬ trate, which enters the tricarboxylic acid cycle, but the capacity for this is limited and oxaloacetate levels are decreased in severe insulin deficiency. Acetoacetyl-CoA is converted to acetoacetate

FIGURE 149-1.

Adipose tissue fatty acid metabolism. HSLipase, hormone-sensitive lipase; LPL-ase, lipoprotein lipase; Insulin+, stimulated by insulin; Insulininhibited by insulin.

1318

PART IX: DISORDERS OF FUEL METABOLISM The excess hydrogen ions have pathophysiologic conse¬ quences. They have a negative inotropic effect and cause periph¬ eral vasodilatation, resulting in lower blood pressure. The pe¬ ripheral vasodilatation also explains both the warm periphery displayed by most patients, even when they are hypotensive and dehydrated, and the low or normal body temperature during in¬ fection. If pH levels fall below 7.0, there may be inhibition of the central nervous system. One reflection of this is inhibition of the respiratory center, causing a paradoxically normal respiratory rate. Insulin resistance also occurs, exacerbating the ketoacidotic state. This is not, however, a major problem during therapy. Hy¬ drogen ion excess also displaces potassium from within cells. There is some dispute about whether this occurs with organic acidemias, but plasma K+ levels rise with acute ketoacidosis in humans.18

Fatty Acid

CARBOHYDRATE METABOLISM

FIGURE 149-2. Ketone body formation in liver cells in insulin defi¬ ciency. CAT I and CAT II, carnitine acyl transferases I and II.

and 3-hydroxybutyrate, with some spontaneous decarboxylation of the former to yield acetone (Fig. 149-3). Acetone levels may approach those of acetoacetate in insulin deficiency. The ketone bodies cannot be used in the liver because the enzyme thiolase is lacking. They diffuse into the circulation and are used as fuels by many tissues after being converted to acetoacetyl-CoA and acetyl-CoA. In starvation, there is controlled release of ketone bodies into the circulation, with levels reaching a plateau at 4 to 6 mmol/L after several days, as utilization matches production, although there are some urinary losses. There is sufficient insulin available to balance the effects of glucagon and the other catabolic hor¬ mones. In severe insulin deficiency, absolute or relative, the key factors are a large increase in fatty acid supply to the liver and unrestrained ^-oxidation and ketone body production. Indeed, the former may be sufficient to saturate the mitochondrial uptake mechanisms, and there is spillover into triglyceride production, with resultant fatty liver and hypertriglyceridemia. There is di¬ minished extrahepatic ketone body use because insulin is lacking. Ketone bodies accumulate in the circulation and levels may reach concentrations of 30 mmol/L. The two major ketone bod¬ ies are weak acids, and they dissociate completely at normal pH. This creates a major hydrogen ion load that soon exceeds normal buffering mechanisms. Hyperventilation eliminates some of the acid, and there is a loss of hydrogen ions in the urine buffered by phosphate and ammonia. Some ketone bodies are lost in the urine, with sodium as the accompanying cation.

CH3.CHOH-CH2.COOH 3-hydroxybutyric acid

„ — » CH3.CO-CH2-COOH acetoac^etic acid

CH3*CO-CH3 acetone

FIGURE 149-3. The ketone bodies. Note that 3-hydroxybutyric acid is not chemically a ketone, but it is referred to as a ketone body.

In normal persons in the fasted state, there is a controlled supply of glucose from the liver, maintaining blood glucose levels between about 54 and 90 mg/dL (3-5 mmol/L) (see Chap. 200). Gluconeogenesis is promoted by glucagon, cortisol, and cate¬ cholamines, and glycogenolysis is fostered by glucagon and cat¬ echolamines. Insulin exerts an anticatabolic effect by decreasing these processes. In extrahepatic tissues, there is insufficient insu¬ lin to enhance glucose uptake, particularly in muscle and adipose tissue. Catecholamines, cortisol, and growth hormone also in¬ hibit glucose uptake. Fatty acids and ketone bodies become major oxidative fuels. There is an increase in the flow of the gluconeo¬ genic substrates, lactate, pyruvate, glycerol, and alanine to the liver, with increased hepatic extraction. Glucagon enhances ala¬ nine uptake, and cortisol induces several transaminases, increas¬ ing the carbon skeletons available for gluconeogenesis. In the liver, the key regulatory step for glycogenolysis and for gluconeogenesis is as follows: phosphofructokinase FRUCTOSE 6-PHOSPHATE

^

FRUCTOSE 1,6-BISPHOSPHATE

fructose 1,6- bisphosphatase

This step is finely regulated by fructose 2,6-bisphosphate, which stimulates phosphofructokinase and inhibits fructose 1,6bisphosphatase, increasing flux down the glycolytic pathway.19 Glucagon, and to a lesser extent epinephrine, inhibits fructose 2,6-bisphosphate formation. Thus, in the fasted state, there is an increased flow of carbon toward gluconeogenesis. The effects of glucagon on this process are sustained, but glucagon has shorter effects on glycogenolysis. This makes teleologic sense in that sup¬ plies of glycogen are limited. In the fed state, glycogenolysis and gluconeogenesis are in¬ hibited. Insulin levels are high, and glycogen synthesis from glu¬ cose 6-phosphate is stimulated through activation of glycogen synthase. The amount of dietary glucose passing directly to gly¬ cogen is small. Instead, glucose is broken down to lactate and pyruvate in the intestinal mucosa, and these intermediates pass directly to the liver by the portal vein for incorporation into gly¬ cogen. Similarly, some lactate and pyruvate from peripheral tis¬ sues follow the same route (Fig. 149-4). At the same time, hepatic glycolysis is stimulated by insulin. These two processes (gluco¬ neogenesis and glycolysis) probably occur in different cell types in the liver. At first, this looks like a catabolic process, but it is the route for de novo fatty acid synthesis from glucose and allows for the storage of excess dietary carbohydrate as fat. Insulin stimu¬ lates pyruvate dehydrogenase, yielding acetyl-CoA and then malonyl-CoA through the action of acetyl-CoA carboxylase at the beginning of the fatty acid synthetic pathway. The fatty acids are then esterified and transported to adipose tissue as very low density lipoproteins. There is a paradox in that both glycolysis and upward flow of three-carbon units must be happening sim¬ ultaneously. This probably is achieved by heterogeneity of func¬ tion within the hepatocyte population. In extrahepatic tissues.

Ch. 149: Diabetic Acidosis, Hyperosmolar Coma, and Lactic Acidosis

FIGURE 149-4. state.

primarily muscle and adipose tissue, insulin enhances glucose uptake through mobilization of glucose transporters. In muscle, glycogen reserves are replenished, and glucose is used as an oxi¬ dative fuel, with lipid metabolism decreased. In adipose tissue, there is increased glycerol-3-phosphate (a-glycerophosphate) formation and reesterification of fatty acids from lipolysis and from circulating very low density lipoproteins. In insulin deficiency, absolute or relative, there is accentua¬ tion of the processes seen in the fasted state. Thus, hepatic glu¬ cose production rapidly increases, doubling within 2 hours of in¬ sulin deprivation of insulin-treated diabetic patients.20 There is a small mass action effect of glucose tending to inhibit glucose production, but this is insufficient to make a significant impact. In the fed state, hepatic glucose production remains unabated, peripheral glucose uptake and metabolism are diminished, and hyperglycemia is greatly accentuated. Experimentally, insulin deficiency is associated with a failure to mobilize and synthesize GLUT4, the insulin-sensitive glucose transporter.21 For more se¬ vere hyperglycemia to occur, the catabolic hormones are critical. Glucagon levels increase early in insulin deprivation, with corti¬ sol levels increasing later. In pancreatectomized patients, insulin deprivation results in a much diminished and sluggish rise in plasma glucose levels and very little increase in ketogenesis. In pure insulin deficiency, there is a long prodromal period before very high glucose levels are found. This may be related to the developing acidemia, with the stimulating effects of the increased production of reducing equivalents from (8-oxidation. In most cases of DKA, precipitating factors cause a rapid rise in catabolic hormone secretion, which will cause rapidly accelerated glucose production. In established DKA, secretion of all the counterregulatory hormones is markedly increased, leading to a vicious met¬ abolic circle. The hyperglycemia is associated with glycosuria as the renal threshold for glucose is exceeded. If sustained, this causes an os¬ motic diuresis, with considerable loss of fluid and electrolytes. In severe DKA, the following deficits, expressed per kilogram of body weight, are encountered: water, 50 to 100 mL; sodium, 7

1319

Hepatic glucose metabolism in the fed

to 10 mmol; potassium, 3 to 12 mmol; chloride, 4 to 7 mmol; phosphate, 0.5 to 1.5 mmol; magnesium, 0.25 to 0.75 mmol; and calcium, 0.25 to 0.75 mmol. The loss is hypotonic with respect to saline, which has implications for replacement therapy. There is progressive dehydration, with loss of intracellular fluids and electrolytes into the extracellular fluid, with the water and potas¬ sium lost into the urine. Eventually, there is hypovolemia with hypotension and tachycardia, which are worsened by the acidemia. PROTEIN METABOLISM

In the fed state, insulin stimulates amino acid uptake by tis¬ sues such as muscle and increases protein synthesis. This effect is balanced by cortisol, which promotes protein degradation. In the fasted state, if insulin levels are low, there is controlled degrada¬ tion of protein, enabling amino acids to be used for gluconeogenesis. The plasma levels of branched chain amino acids are in¬ creased, and alanine levels tend to fall. There is a clear reciprocal relationship between alanine and ketone body levels, which tends to conserve amino acids when ketone body levels are high. Insulin deficiency leads to increased protein degradation and decreased protein synthesis, with the increase in amino acid availability providing the substrate for gluconeogenesis. Clini¬ cally, this protein catabolism is reflected as muscle wasting, with visceral proteins tending to be spared. Wasting is apparent, how¬ ever, only if there has been a prolonged prodromal period.

PRECIPITATING FACTORS Infection is by far the most common of the precipitating fac¬ tors for DKA, causing more than 50% of identified causes in nearly all series. This may occur in established IDDM patients or in previously undiagnosed patients. Infections may be minor, such as urinary tract infection, skin lesions, or bacterial throat infections, or more severe. In developing countries, pulmonary tuberculosis and malaria may present as DKA, leading to diag¬ nostic uncertainty, particularly with respect to malaria. Infec-

1320

PART IX: DISORDERS OF FUEL METABOLISM

TABLE 149-1 Signs and Symptoms of Diabetic Ketoacidosis Symptoms, Signs

cently. Often, the breath smells of acetone, and there may be oliguria in the later stages. Preceding symptoms include nausea and vomiting, thirst and polyuria in nearly all cases, and, less commonly, leg cramps and abdominal pain. There may also be no bowel sounds, with gastric stasis and pooling of fluid. Occasionally, the patient may present with an acute abdomen (pain and rigidity). If this occurs in young pa¬ tients, virtually all cases resolve with conservative treatment; in older patients, there may be intraabdominal disease.26 It is sensi¬ ble to treat the metabolic disturbance first. If there is no resolution or there is worsening of the abdominal state during the first 3 to 4 hours of treatment, diagnostic reevaluation should be considered. Nearly all the signs and symptoms of DKA can be ascribed to different aspects of the metabolic disturbance (Table 149-1). Thus, the dehydration, polyuria, and thirst are secondary to the osmotic diuresis. The hypotension and tachycardia are caused by the fluid loss and the acidemia. Acidemia also causes the hyper¬ ventilation. The inappropriately low body temperature and warm skin are the result of the vasodilatation caused by the aci¬ demia. The vomiting and nausea are probably the consequence of hyperketonemia, and the leg cramps and gastric stasis may be secondary to intracellular potassium depletion. The impaired consciousness correlates only with plasma osmolality, which im¬ plies that intracellular fluid loss from cerebral cells is involved, although impaired cerebral circulation caused by hypotension may also contribute. Hypovolemia and hypotension cause prerenal failure with consequent oliguria.

Cause

Polyuria, polydipsia

Osmotic diuresis

Anorexia, fatigue

?

Nausea, vomiting

? Ketosis

Weight loss

Protein, fat catabolism

Abdominal pain

? K+ depletion, fluid pooling

Leg cramps

? K+ depletion

Dehydration

Osmotic diuresis

Hypotension

Dehydration, acidemia

Tachycardia

Dehydration, acidemia

Hyperventilation

Acidemia

Gastric stasis

? K+ depletion

Hypothermia

Peripheral vasodilation, acidemia

Impaired consciousness

Hyperosmolality

tion causes a marked increase in secretion of cortisol and gluca¬ gon. Established IDDM patients with infections often diminish their food intake and may mistakenly decrease their insulin doses, whereas these should be increased based on the results of home blood glucose monitoring. Urine ketones should also be checked routinely in ill IDDM patients with increased insulin doses if ketones are more than trace positive. Other precipitating factors include omission of insulin doses in known IDDM patients, a well known phenomenon in many "brittle" diabetics and in any young IDDM patient with recurrent episodes of DKA. There is still argument about whether manipu¬ lative behavior alone is responsible for all such episodes of DKA or whether emotional disturbances themselves can directly pre¬ cipitate ketoacidosis.23 Neuroses are more common in patients with recurrent DKA, but this does not indicate cause and effect. Another cause of "pure" insulin deficiency in more recent times is the malfunction of insulin infusion devices, with very high oc¬ currence rates in some centers, in particular because of catheter failure,24 with a rate of 0.14 per patient year in one large series.25 Other established precipitating factors include cerebrovas¬ cular accidents, acute myocardial infarction, and trauma. Each of these is accompanied by increased secretion of catecholamines, glucagon, and cortisol, with predictable metabolic consequences if insulin doses are not increased. Rarer causes include Fourier gangrene (sudden, severe gangrene of the scrotum), infusion of ^-sympathomimetic agents, and pheochromocytoma.

DIAGNOSIS In most cases, the rapid diagnosis of DKA should be possible at the bedside (Table 149-2). The clinical history usually is help¬ ful. Clinical examination and bedside measurement of blood glu¬ cose and plasma ketones (using a test strip) should complete the diagnosis. Some caution should be exercised with regard to teststrip glucose measurement: if the strips are not stored properly or used by untrained personnel, erroneous results can be obtained. Emergency room staff should be instructed in test-strip glu¬ cose measurement. The condition of "euglycemic" ketoacidosis should also be noted, in which blood glucose levels are not very elevated despite severe ketoacidosis,27 although if this is defined as a blood glucose level of 180 mg/dL or less, it is rare, occurring in only 1% of cases.28 This has been found in patients who have been on insulin pump therapy and in those who have fasted for long periods before admission. One study has confirmed that in¬ sulin deficiency in the fasted state is associated with a more rapid rise in hydrogen ion concentration but a slower rise in blood glu¬ cose than in the fed state, although glucose levels still were not strictly "euglycemic."29 Ketone bodies in plasma are tested for, using either test strips or tablets. For tablets, plasma should be diluted and a positive result at a dilution of 1 in 8 or above is significant. For the test strips, 1-plus or more is significant. These nitroprusside-based

SIGNS AND SYMPTOMS The classic clinical presentation of severe DKA includes Kussmaul respiration (i.e., deep, sighing hyperventilation), dehy¬ dration, hypotension, tachycardia, warm skin, normal or low temperature, and altered state of consciousness. Only about 10% are totally unconscious, and even this figure has diminished re¬

TABLE 149-2 Bedside Differential Diagnosis of Coma Blood Glucose* (mg/dL)

Plasma Ketones*

Hyperventilation

Dehydration

Diabetic ketoacidosis

>300

+ to +++

++

++

Low to normal

Warm

Hyperosmolar, hyperglycemic, nonketotic coma

>500

0 to -1-

0

+++

Low to normal

Normal

0

0

0

Normal

Cold, clammy

20-200

Tr to +

+++

0

Low

Warm

Normal or raised

0 to Tr

0 to -1-

0 to +

Variable

Normal

Diagnosis

Hypoglycemic coma Lactic acidosis Nonmetabolic comas Tr, trace; +, mild; ++, moderate; +++, severe. * Using test strips.

12), but patients can present with a normal anion gap and a hyperchloremic acidosis.30 There are other causes of an acidosis with an increased anion gap, including lactic acidosis, uremia, and ingestion of agents such as methanol and salicylates; there¬ fore, plasma ketones must be checked as well.6 Plasma sodium levels usually are low despite the total body deficit of hypotonic saline. This is because the hyperglycemia draws fluid from the intracellular space, diluting the plasma. It can be calculated that for every 50 mg/dL elevation in plasma glucose, plasma sodium is decreased by 1 mmol/L; a plasma glucose of 750 mg/dL with a plasma sodium of 128 mmol/L implies a "true” sodium of 142 mmol/L.31 Pseudohyponatremia occasionally is found in DKA patients with severe hyperlipidemia.32 All plasma constituents give artifactually low readings. The laboratory often informs the clinician of the problem, because the blood sample may have caused blockage of the laboratory autoanalyzers. Plasma potassium levels can be high, normal, or low. High levels usually are indicative of very acute onset of DKA, with urinary excretion not having kept pace with intracellular losses. They also may be found in the "sick cell syndrome" (a severe toxic state with general cell leakage) or in acute anuria occurring simultaneously with DKA. Normal plasma levels generally are associated with a significant total body potassium deficit. Low plasma potassium levels are an indication of a very large total body deficit. They occur either in an insidious onset of DKA or in patients presenting with DKA who have been taking diuretics, particularly thiazides, without adequate oral replacement. Serum bicarbonate levels are less helpful. In any significant metabolic acidosis, bicarbonate levels are very low, and the pH and pC02 give more useful information. Chloride levels do not help, except in occasional cases of hyperchloremic acidosis. Plasma osmolality is a useful guide to the severity of the metabolic state. It can be calculated easily using the following equation:

2(plasma Na* + K*Xmmol/L) + BUN (mg/dL)

2.8

1321

glucose (mg/dL)

= plasma osmolality in mOsm/L

In those centers using SI units the equation becomes: 2(Na+ + K+)(mmol/L) + glucose (mmol/L) + plasma urea (mmol/L) = osmolality in mOsm/L This gives results that agree closely with measured osmolality, except in occasional situations, such as alcohol overdose, in which there is a major osmolal contribution from an unsuspected plasma constituent. Other tests or analyses that should be carried out routinely include sending urine and blood samples for culture and sensi¬ tivity and a throat swab, if indicated. Because infection is a com¬ mon precipitating factor, antibiotics frequently will be used. Samples for culture should be sent before antibiotic therapy be¬ gins. Blood for hemoglobin, hematocrit, and white blood cell count tends to be sent routinely as well. These tests are less help¬ ful. The hematocrit indicates hemoconcentration, but so does cre¬ atinine. The white blood cell count is singularly unhelpful and can be misleading for the unwary. There is almost always a leu¬ kocytosis in severe DKA, but this correlates with blood ketone body levels and not with the presence of infection.33 The two main signs of infection—pyrexia and leukocytosis—are either absent or misleading in DKA. Thus, a differential white cell count is of little help. An electrocardiogram should be performed in the emer¬ gency room. This may give information on ischemic heart disease or myocardial infarction. More important, it provides a yardstick for subsequent acute changes in plasma potassium levels, which should be followed by electrocardiographic monitoring. The baseline electrocardiogram is necessary because acidemia can of itself produce changes, some of which can mimic ischemia.34 A chest radiograph is often done routinely. This is probably reason¬ able, in case of subsequent iatrogenic disorders, such as the adult respiratory distress syndrome or infection.

TREATMENT There are five main elements of treatment: fluid, insulin, po¬ tassium, alkali, and "other" measures. These are discussed in turn (see Appendix 1, p 1327). FLUID

The first priority of treatment is fluid replacement. Insulin therapy is effective only if fluid is given rapidly in the early stages. The total water deficit ranges from 50 to 100 mL/kg of

TABLE 149-3 Initial Investigation for the Diagnosis and Management of Diabetic Ketoacidosis Bedside

Laboratory

1. Blood glucose (using test strips)

1. Blood glucose

2. Plasma ketones (test strips or

2. Plasma urea and electrolytes

tablets) 3. Plasma potassium*

3. Arterial blood pH, pC02, p02|

4. Plasma creatinine*

4. Microscopy and culture of urine

5. Plasma urea*

5. Blood culture

6. Electrocardiogram

6. Throat swab culture

7. Chest radiograph

7. Hemoglobin

* These are available in certain centers as "dry chemistry" bedside methods using machines such as the Reflotron, Seralyser, or Ektachem. 1 Capillary pH and blood gases may be measured instead.

1322

PART IX: DISORDERS OF FUEL METABOLISM

body weight, with a sodium deficit of 7 to 10 mmol/kg. Several tailored replacement fluids that were relatively hypotonic were previously recommended. Now, it is agreed that isotonic saline (0.154 mol/L; 0.9%) is the appropriate initial replacement fluid. Concerns have been expressed about overzealous rates of fluid replacement. The author's current practice is to give 1 L in the first hour, then 1 L in 2 hours, and then 1 L every 4 hours until the patient is well hydrated (see Appendix 1, p 1328). This rou¬ tine should be varied according to the fluid status of the patient. In patients with cardiovascular disease or in elderly or shocked patients, who are at increased risk for development of heart failure,35 a central venous pressure (CVP) line should be in¬ serted and the rate of fluid administration guided by CVP measurement. The exception to the use of isotonic saline is the presence or development of hypernatremia (measured plasma sodium >150-155 mmol/L). In this case, half-normal (0.45%) saline should be used, but infused more slowly. When saline is used, plasma sodium levels inevitably rise, partly because the infused fluid has a higher sodium content than the extracellular fluid in DKA patients, partly because water without sodium will be mov¬ ing into cells, and partly because glucose levels will be falling. This rise in sodium levels is helpful, however, in that it prevents plasma osmolality from falling too quickly while blood glucose levels are decreasing. This may be beneficial in preventing the development of cerebral edema. Hyperchloremia almost invari¬ ably develops late in treatment. This is occasionally associated with acidosis, but there is little evidence to suggest that it is harmful. Most DKA patients who are hypotensive on presentation re¬ spond with a rise in blood pressure to the first 1 to 2 L of saline. If systolic blood pressure remains below 90 mm Hg, one to two units of blood or plasma expanders should be given, often with dramatic effect. If this fails, 100 mg of hydrocortisone sodium succinate may be given IV, with an appropriate increase in sub¬ sequent insulin therapy. Once blood glucose levels have fallen to 250 mg/dL (13.8 mmol/L), 10% glucose is substituted for saline. If this occurs be¬ fore the patient is adequately rehydrated, saline should be con¬ tinued simultaneously. The importance of adequate early rehydration cannot be ov¬ eremphasized. Simple rehydration alone lowers blood glucose levels by improving the renal excretion of glucose, with hemodilution accounting for as much as a 23% fall in blood glucose.36 Tissue perfusion is also improved, allowing the small amounts of insulin present to begin to act. Rehydration, even without insulin, decreases counterregulatory hormone secretion.37 INSULIN

During the 1970s and 1980s, there was a major change in the use of insulin in the treatment of DKA. Before 1973, large doses of insulin (i.e., hundreds of units) were routinely used. Then it was shown that relatively small amounts of insulin given intramuscularly (IM) or as a continuous IV infusion were just as effective in lowering blood glucose, and had several advan¬ tages.38,39 Subsequently, this was confirmed by many groups.1-3 Among the advantages of the low-dose regimens are decreased problems with hypokalemia during therapy, a lower occurrence of late hypoglycemia, and a more predictable response to ther¬ apy. There is also an adequate but somewhat slower rate of fall of blood glucose levels, which is less likely to cause osmotic disequilibrium. Insulin Resistance. The major concern in the use of low doses of insulin has been insulin resistance. It has been shown that fractional glucose turnover and the rate of fall of blood glu¬ cose levels in DKA patients are decreased up to 10-fold compared with nonketotic, well controlled diabetics.40 Similarly, in animals and humans, insulin binding by adipocytes is decreased, as is postreceptor insulin action. This is accompanied, in ketoacidotic

rats, by a marked diminution in total body insulin responsive¬ ness. These changes correlate with the degree of acidemia, which is most severe when the pH is less than 7.0, and can be repro¬ duced by NH4C1 administration, suggesting that it is the acidemia per se that is responsible. Despite these experimental findings, major insulin resistance only rarely is a clinical problem. There is a somewhat slower rate of fall of glucose in patients with infections, but the response usually is adequate. There are several reasons for this. First, the initial response to therapy is primarily the result of rehydration. Second, the circulating insulin levels produced with low-dose regimens are high physiologically. An infusion of 10 units of in¬ sulin per hour produces peripheral insulin levels of more than 150 |dJ/mL, well above those found in normal persons. Sim¬ ilarly, with standard IM regimens, levels of more than 80 /uU/mL are engendered. These levels are sufficient, even in the face of insulin resistance, to inhibit lipolysis, thereby cutting off the sup¬ ply of substrate for ketogenesis, restraining hepatic gluconeogenesis and helping to decrease glucagon levels; this diminishes the drive to ketone body and glucose production. There is little im¬ pact on peripheral glucose uptake initially, but there are adequate circulating fuels, and ketone body use steadily increases; the in¬ sulin influence on potassium transport into cells is also submaximal, which may be an advantage. Intravenous Insulin Regimens. Several insulin regimens have been proposed, with doses ranging from 2 to 10 U/hour as a continuous infusion, or 10 U/hour as an hourly bolus. It seems more logical to give the insulin as a continuous infusion. The au¬ thor's routine is to give 6 U/hour in saline, using an infusion pump and a separate line (see Appendix 1, p 1327). In children, a dose of 0.1 U/kg/hour is used. Because insulin has a circulating half-life of 4 to 5 minutes and a biologic half-life of no more than 30 minutes, it is critical that the insulin be given continuously, because there are no depots. If the infusion stops for any reason, the effects will rapidly disappear. Insulin adsorbs to plastic and glass; therefore, some physicians recommend making the insulin solution in polygeline or albumin or drawing back 1 mL of the patient's blood into the syringe. In practice, adsorption is not a problem, particularly if the first 5 mL of the insulin in saline so¬ lution (1 U/mL) is flushed through the administration apparatus. Blood glucose levels should be checked after the first 2 hours. If there has not been a significant fall (50-100 mg/dL or 2.8-5.7 mmol/L), then the infusion pump and line, the rehydra¬ tion scheme, and the blood pressure should be checked, and the insulin infusion rate should be doubled if these are satisfactory. This should be repeated every 2 hours until blood glucose levels are falling satisfactorily. When blood glucose levels have fallen to 250 mg/dL and 10% dextrose has been substituted for saline (100 mL/hour), the insulin dose should be decreased to 4 U/ hour, and subsequently modified according to hourly bedside blood glucose readings. Intramuscular Regimen. Hourly IM insulin provides an al¬ ternative to continuous IV insulin and is particularly useful in centers where reliable infusion pumps are not available or where nursing care is inadequate. In this case, a loading dose of insulin should be given as either 20 units insulin IM or 10 units IM plus 10 units IV in hypotensive or very dehydrated patients. Thereaf¬ ter, 5 to 6 units should be given hourly as deep IM injections. In children, a loading dose of 0.25 U/kg is given, followed by 0.1 U/kg hourly. Adequate rehydration is critical for IM insulin to be effective. If, after 2 hours, there is not a significant response, substitute the IM regimen with continuous IV insulin, having first checked that rehydration is progressing satisfactorily. When blood glucose reaches 250 mg/dL and IV glucose is commenced, the insulin dose should be decreased to 5 to 6 units every 2 hours (see Appendix 1, p 1328). POTASSIUM

More iatrogenic deaths during the treatment of DKA have been caused by changes in plasma potassium than by any other

Ch. 149: Diabetic Acidosis, Hyperosmolar Coma, and Lactic Acidosis factor. There is usually a large deficit of intracellular total body potassium (3-12 mmol/kg body weight). Despite this, as many as 33% of DKA patients may have elevated plasma K+ levels ini¬ tially.42 This loss of intracellular potassium into the extracellular space, which occurs in all cases, has been attributed to the acide¬ mia, intracellular volume depletion, and lack of insulin. The role of acidemia has been questioned, however. Additional factors include a direct effect of hyperglycemia and hyperglucagonemia.43 In a careful analysis, glucose, pH (negatively), and the anion gap were independent, significant determinants of plasma K+ on presentation. Once treatment commences, plasma K+ levels inevitably fall, except in those presenting with the sick-cell syndrome. The fall is the result of intracellular volume repletion, hemodilution, reversal of the acidemia, loss of K+ in the urine as urine flow is reestablished, and a direct effect of insulin on intracellular K+ transport. Thus, hypokalemia is inevitable unless potassium is replaced. There are arguments about when potassium replacement should begin. Some physicians recommend waiting until plasma potassium levels are known, levels are low normal or low, and urine flow has been reestablished; probably, this is too late. The author's practice is to start cautious replacement at 20 mmol KC1/ hour in the saline infusion from the time of the first dose of insu¬ lin, then to modify the amount infused according to subsequent plasma values (see Appendix 1, p 1328). It has been suggested that potassium should be given as phosphate or half as phos¬ phate and half as chloride. However, phosphate requirements are very different from those for potassium, so it is probably sen¬ sible to replace them separately, if at all, and to use KC1. Electrocardiographic monitoring is an invaluable guide to rapid changes in plasma potassium, and all patients should be monitored at least in the early stages of therapy. In the future, rapid chemistry analyzers, which can be used nearby, will prove invaluable for frequent monitoring of potassium. IV potassium replacement should be continued for as long as IV therapy is con¬ tinued. Thereafter, oral potassium replacement should be contin¬ ued for several days, because much of the potassium adminis¬ tered IV will be lost in the urine, and the total body deficit will be only partly replenished. If alkali is given, additional potassium should be given (20 mmol/100 mmol sodium bicarbonate). OTHER ELECTROLYTES

There is a deficiency of magnesium, calcium, and phosphate, as well as of sodium and potassium in DKA patients. It is argu¬ able, however, whether these need to be replaced immediately. Most debate has concerned phosphate. During treatment of DKA, plasma phosphate levels fall, sometimes to undetectable levels. Red cell 2,3-diphosphoglycerate levels are also very low and take 4 to 48 hours to return to normal. This may cause impaired oxygen delivery to tissues when the acidemia is corrected. It has been argued that the low phosphate levels impede recovery of 2,3-diphosphoglycerate. Several trials of phosphate replacement have been carried out. In one, published in 19 4 8,44a mortality was less in the treated group. However, none of the more recent trials have shown benefit, and in all cases, biochemical hypocalcemia was found in the treated group.45 It is possible that phosphate changes are less with the use of low-dose insulin than they were previously. It is not the author's practice to replace phosphate. Similarly, although mag¬ nesium levels are low during therapy, no convincing evidence shows that replacement is beneficial.

1323

brospinal fluid pH, impaired oxyhemoglobin dissociation, and rebound alkalosis.46 In animals and in humans, it has been shown that anaerobic glycolysis is increased and oxidative glu¬ cose metabolism is not improved, and blood glucose falls no faster.47,48 Despite this, it is usually considered advisable to give mod¬ erate amounts of bicarbonate when the pH is less than 6.95; 100 mmol containing 20 mmol KC1 should be given over 45 minutes. This should be repeated until the pH is above 7.0. It also may be helpful to give 50 mmol bicarbonate containing 10 mmol KC1 to those patients distressed by hyperventilation. This can have a dramatic beneficial effect. OTHER MEASURES

Clinical therapy for DKA patients should not be forgotten (Table 149-4). On admission, an assiduous search should be made for precipitating factors. This is most likely to be infection, but careful clinical examination is required, and appropriate ther¬ apy should be instituted. If there is any hint of infection or if major invasive measures are used, broad-spectrum antibiotics should be given once appropriate cultures have been taken. Be¬ cause signs of infection may be missing or misleading and phago¬ cyte function is impaired in uncontrolled diabetes, antibiotics should be used less cautiously than is usual. In many patients, there is considerable pooling of fluid in the gastrointestinal tract; often, there is vomiting. Because aspiration of vomit is a known cause of morbidity and mortality in DKA patients, nasogastric suction should be instituted early in the semiconscious or unconscious patient. The use of CVP and electrocardiographic monitoring has been discussed. Urine output is another guide to progress. If no urine has been passed in the first 4 hours, the bladder should be catheterized (with simultaneous antibiotics). If there is oliguria or anuria, 40 mg furosemide given IV may reinstitute adequate urine flow. If oliguria or anuria persist, potassium replacement should be stopped. Fluid should be replaced less aggressively un¬ less the patient is still very dehydrated with a low CVP and blood pressure. There is an increased risk of thromboembolic episodes, par¬ ticularly in the elderly, the unconscious, and those with very hy¬ perosmolar conditions. In these patients, heparin (500 units ev¬ ery 4-6 hours given subcutaneously) should be used. Some patients become extremely agitated and may harm valuable IV lines. A small dose of IV diazepam can help, and it does not have any deleterious metabolic effects. MONITORING OF THERAPY

A guide to the monitoring of therapy is given in Table 149-5. This includes both biochemical and clinical monitoring essential to the successful outcome of treatment. The guidelines will require modification according to the individual needs of pa¬ tients. Temperature measurement may be helpful because an infection-induced pyrexia may be revealed after 4 to 6 hours of treatment. Charts should be prepared for standard use to prevent

TABLE 149-4 General Therapy for Diabetic Ketoacidosis Search for and treat any precipitating factors Nasogastric suction Catheterization

ALKALI

IV furosemide for oliguria

There is still no universal agreement about correcting the aci¬ demia of severe DKA. The acidemia has certain pathophysiologic consequences, including negative inotropism, peripheral vasodi¬ latation, central nervous system depression, and insulin resis¬ tance. On the other hand, vigorous alkalinization has deleterious consequences, including hypokalemia, a paradoxical fall in cere¬

Whole blood or plasma expanders for hypotension Central venous pressure monitoring Electrocardiographic monitoring Antibiotics Low-dose heparinization

1324

PART IX: DISORDERS OF FUEL METABOLISM

omissions. Caution should be exercised in interpreting urine or plasma ketones. These will diminish but may remain positive for as long as 48 hours; however, this is not caused by continued ketogenesis. Rather, because acetone is extremely lipid soluble, it will continue to diffuse out of structural lipid for many hours. In contrast, blood 3-hydroxybutyrate will fall rapidly, although this is not measured by the usual tablet or test-strip procedures.

SECONDARY PHASE OF TREATMENT Even if blood glucose levels have fallen toward normal, con¬ tinued vigilance and care are required. Ketoacidosis may recur. Saline should be replaced with 10% dextrose containing 20 mmol KC1/500 mL, given at 100 mL/hour. This is used in preference to 5% dextrose because it provides more calories in the catabolic patients, and it has been shown that the ketosis and acidemia clear more rapidly with the higher carbohydrate load.49 Insulin doses should be modified as described earlier. IV therapy should be continued until the first meal, when subcutaneous short¬ acting insulin should be given. If IV insulin has been used, the insulin infusion should be continued until at least 1 hour after the subcutaneous insulin is given to allow time for absorption of the latter.

COMPLICATIONS OF THERAPY There are several well recognized complications that can oc¬ cur during the treatment of DKA. HYPOGLYCEMIA

Hypoglycemia was common as a late sequel to the treatment of DKA when larger doses of insulin were used, particularly with IM or subcutaneous regimens. It is less common now but still occurs if monitoring is not adequate or if the results of monitoring are not acted on. An alarmingly high rate has been reported from three private hospitals.50 HYPERKALEMIA AND HYPOKALEMIA

These were discussed in detail elsewhere44 and earlier. Hy¬ pokalemia is more common. It is unnecessary and does not occur

TABLE 149-5 Monitoring Therapy for Diabetic Ketoacidosis Parameter

Action

CLINICAL Pulse, BP

Every half hour for 4 hours, every hour for 4 hours, then every 2 to 4 hours

Temperature

At 0, 2, 4, 6 hours, then every 6 hours

Urine flow

Hourly for 6 hours, then every 4 hours with fluid balance chart

Conscious state

Every hour

CVP

Every hour in those with CVP line

BIOCHEMICAL Plasma glucose

Hourly by test strip until BG 7.0: obtain at 0 and 4 to 6 hours. If pH 7.0, then 4 hours later.

Plasma ketones

At 0, 6 and 12 hours

THROMBOEMBOLIC EPISODES

Urine glucose

Every 4 hours

Careful examination shows that most DKA patients have platelet hyperaggregability, elevation of clotting factors, in¬ creases in circulating fibrin degradation products, or combina-

BG, blood glucose; CVP, central venous pressure.

Ch. 149: Diabetic Acidosis, Hyperosmolar Coma, and Lactic Acidosis tions of all these. Disseminated intravascular coagulopathy oc¬ curs in DKA patients during therapy, and there is an increase in late thromboembolic phenomena in those who are elderly or very hyperosmolar. These increased risks certainly warrant the use of routine anticoagulation in the more severely affected patients. OTHER COMPLICATIONS

Inhalation pneumonia and shock have been described. Mu¬ cormycosis and rhabdomyolysis are rare complications (see Chap. 146). MORTALITY

Deaths in DKA can be subdivided into avoidable and un¬ avoidable. In the unavoidable category are overwhelming infec¬ tion, massive myocardial infarction, or terminal carcinoma, in which DKA is a secondary event. The avoidable category in¬ cludes the many different iatrogenic causes. In a survey of deaths in DKA in patients younger than 50 years of age, most were deemed avoidable; hypokalemia, uncontrolled sepsis, inhalation pneumonia, cerebral edema, and clotting disorders comprise the bulk of such causes. In another study, thromboembolic events, bronchopneumonia, and cardiac failure were the main causes.16

1325

patients are elderly and are taking diuretics, which accelerate de¬ hydration. At the same time, thirst mechanisms are defective in the elderly, which also increases the rate at which dehydration occurs. Patients sometimes consume large volumes of soft drinks with high sugar content in response to thirst, which worsens the hyperglycemia. None of these theories explain the lack of ketoacidosis. Usu¬ ally, ketone body levels are elevated, but less than in DKA pa¬ tients, suggesting a continuum rather than two totally separate conditions. Levels of counterregulatory hormones and of insulin do not clearly separate DKA from HONK patients.2 The hyperosmolality is caused partly by glucose, the levels of which are higher on average in HONK than in DKA patients. HONK patients also tend to have higher plasma urea levels, al¬ though the latter diffuses freely into most cells and does not con¬ tribute substantially to altered osmotic gradients. At least half of HONK patients, however, also have high-normal or high plasma sodium levels. If glucose levels are allowed for, then, there is marked, "real" hypernatremia in most cases.59 The cause of this is unknown, except for the dehydration being more severe, but plasma sodium often makes a major contribution to the hyper osmolality.

PRECIPITATING FACTORS PREVENTION Because the mortality rates of severe DKA range from 5% to 20%, prevention is extremely important. This implies proper education of the patient and primary health care personnel. The patient should have clear information on how to respond to ill¬ ness and to periods of poor control. All patients should be given "sick-day rules" (see Appendix 2, p 1328). The primary health care physician or nurse should be quick to respond to impending ketosis with, for example, one to two insulin injections every hour and with instructions to increase fluid intake. This should be combined with the instruction that, as soon as vomiting com¬ mences, medical help should be sought because it indicates the need for IV fluids. Such guidance should decrease the incidence of severe DKA.

HYPEROSMOLAR HYPERGLYCEMIC NONKETOTIC COMA Hyperosmolar hyperglycemic nonketotic coma occurs at about a tenth of the frequency of classic DKA; however, it carries a much higher mortality.58 This is consistent with the finding that most patients are older than 50 years of age. It usually occurs in patients with non-insulin-dependent diabetes mellitus and often is the first indication that the patient has diabetes.

PATHOPHYSIOLOGY The cause of HONK is unclear.2 There is undoubtedly insu¬ lin deficiency, albeit relative, with marked hypersecretion of the counterregulatory hormones. However, presumably there is enough insulin to suppress lipolysis or ketogenesis. Perhaps the following occurs: Patients with non-insulin-dependent diabetes mellitus have insulin insensitivity. Hepatic glucose production is accelerated and hyperglycemia occurs. If there is an increase in counterregulatory hormone secretion, it further increases hepatic glucose output and decreases extrahepatic glucose use. There is then increasing hyperglycemia, which is exacerbated by oral car¬ bohydrate ingestion, because the extra glucose load cannot be metabolized. There is still sufficient insulin, however, to prevent accelerated lipolysis. The hyperglycemia leads to intracellular fluid loss and osmotic diuresis with dehydration, hemoconcentration, and further worsening of the hyperglycemia. Potassium is lost from cells and excreted in the urine. The loss of potassium conceivably may further inhibit insulin secretion. Many of the

The precipitating factors for HONK are multiple and many case reports have appeared of rare causes.9 Infection is the single most important factor, with presumed counterregulatory hor¬ mone hypersecretion as the cause of the metabolic disturbance. Cardiovascular emergencies, such as a cerebrovascular accident and myocardial infarction, are the other major factors. The cereb¬ rovascular accident is particularly important because it can cause severe hyperglycemia, or “piqure" diabetes. This may be associ¬ ated with an inability to drink, and hyperosmolality can ensue. Drugs such as corticosteroids and thiazides also precipitate HONK.

PRESENTATION Usually, patients with HONK are older than those with DKA, although HONK can occur in youth, and the history of poorly controlled diabetes (e.g., polyuria, polydipsia, anorexia, some weight loss, fatigue) may extend back for several weeks.60 There is often recent infection. Focal neurologic signs may be present, and there almost always is impaired consciousness, with 20% or more being in coma.60'61 On examination, there is severe dehydration and hypotension, with or without shock.

DIAGNOSIS The history and initial clinical examination often suggest the diagnosis; there is an obvious lack of hyperventilation. However, in the comatose patient not previously known to be diabetic, se¬ vere dehydration may be the only clue. Bedside diagnosis with glucose test strips will give a firmer guide, together with plasma ketones, which are negative or only trace positive (see Table 149-2). Initial therapy can be commenced while waiting for lab¬ oratory results. Laboratory investigations are the same as for DKA (see Table 149-3). These reveal a very high blood glucose (600-2500 mg/dL; 33.3-138 mmol/L), often hypernatremia, a normal or low potassium, and a grossly elevated blood urea. Cal¬ culated osmolality exceeds 350 mOsm/L and often is greater than 400 mOsm/L. Arterial pH is greater than 7.2; p02 is often decreased, but the anion gap paradoxically tends to be increased. A review of the literature9 has shown a mean glucose of 1166 mg/dL compared with 475 mg/dL in DKA, Na+ higher at 143 compared to 131 mEq/L, and free fatty acids lower at 0.73 to 0.96 mM compared to more than 2 mM. Glucagon levels, how¬ ever, were higher. Osmolality also was much higher, 384 versus 309 mOsm/kg.

1326

PART IX: DISORDERS OF FUEL METABOLISM

TREATMENT The general principles of treatment are similar to those out¬ lined for DKA. FLUIDS

The priority in treatment is rehydration. The average fluid deficit is about 9 L. Until laboratory results are available, isotonic saline may be given, giving 1 L in 15 to 30 minutes, and a second liter during 1 to 2 hours. If the patient is normonatremic or hypernatremic (>145 mmol/L), half-normal saline should be used, giving 1 L every 2 hours for 6 hours, then 1 L every 4 hours. CVP monitoring should be used routinely to provide rapid rehydra¬ tion. If sodium levels remain very high, 5% dextrose can be used for rehydration. HONK patients usually are insulin sensitive, and the extra glucose load can be coped with easily. Shock or hypo¬ tension are often problems on admission or during therapy, and the use of 1 to 2 L of a plasma expander or of albumin can be invaluable. Although plasma osmolality tends to fall rapidly, ce¬ rebral edema is less of a problem in patients with HONK than with DKA. When blood glucose levels approach 250 mg/dL (13.8 mmol/L), 10% dextrose should be commenced. It may be neces¬ sary to continue hypotonic saline infusion simultaneously.

ria are more likely to be present because of both prerenal failure and preexisting renal disease. Equally important are thromboem¬ bolic phenomena, which are common in HONK, in which hyper¬ osmolality, age, hyperglycemia, and unconsciousness contrib¬ ute.62 Thromboembolic complications, circulatory collapse, and preexisting severe disease are often causes of death in these pa¬ tients, and anticoagulation is indicated. HONK is a serious, often lethal, form of diabetic coma. As with DKA, it is often preventable by early diagnosis of noninsulin-dependent diabetes mellitus and by careful attention to education of patients about infections. Many HONK patients do not require insulin after the acute episode, and a trial without insulin should be carried out before the patient leaves the hospital.

LACTIC ACIDOSIS Lactic acidosis occurs when the metabolism of pyruvate and lactate are blocked.60'63 It is a condition in which blood lactate levels are greater than 5 mmol/L, and there is a significant de¬ crease in arterial blood pH ( 6 mmol/L. Maintain K+ between 4 and 5 mmol/L. If K+ < 3 mmol/L, increase to 40 mmol/hour; if K+ is 3 to 4 mmol/L, increase to 30 mmol/hour; if K+ is 5 to 6 mmol/L, decrease to 10 mmol/hour. Monitor with electrocardiogram. 4. Sodium bicarbonate. If pH < 6.95, give 100 mmol with 20 mmol KC1 over 45 minutes as isotonic solution. Check pH 15 to 30 minutes later. Repeat until pH > 7.0. For distressing hyperventilation with pH >7.0, give 50 mmol containing 10 mmol KC1. 5. Continued treatment. A. Monitor glucose with test strip at bedside hourly and in laboratory at hours 2 and 6, then every 4 hours. B. Monitor K+ in laboratory at hours 2 and 6, then every 6 hours. C. Laboratory measurements of creatinine and electrolytes at hours 3, 6, and 24. D. Frequent monitoring of pulse, BP, temperature (see Ta¬ ble 149-5). E. When blood glucose < 250 mg/dL, change to 10% dex¬ trose, 500 mL every 4 hours. Continue saline if patient still dehydrated. Change insulin to 3 to 4 U/hour IV or 6 units IM every 2 hours. Modify according to bedside glucose estimations. Maintain blood glucose between 150 and 250 mg/dL. F. When patient is ready to eat, reinstitute short-acting, subcutaneous insulin therapy. If on IV insulin regimen, continue for 1 hour after subcutaneous insulin is given. G. Continue oral K+ replacement for 1 week. 6. Other measures. A. If no urine passed by hour 4, catheterize. B. Give 40 mg furosemide if oliguric. C. Give antibiotics if infection suspected or invasive pro¬ cedures used. D. Institute nasogastric suction if patient is comatose or semiconscious. E. Give oxygen if pOz < 80 mm Hg. F. Heparinize (5000 units subcutaneously every 4 hours) if patient is comatose or very hyperosmolar (>360 mOsm/L). G. Give blood or plasma expander (2 units) if systolic BP < 80 mm Hg at hour 2.

APPENDIX 2. SICK-DAY RULES FOR TYPE I PATIENTS 1. Insulin should never be omitted. 2. If food is not taken, the carbohydrate equivalent should be taken as milk or sugar-containing fluids.

3. Blood glucose levels should be self-monitored before each meal and at bedtime. 4. If blood glucose < 234 mg/dL (13 mmol/L), continue usual insulin. If blood glucose > 234 mg/dL (13 mmol/L) but < 400 mg/dL (22.2 mmol/L), take 4 units extra of regular insulin. If blood glucose > 400 mg/dL (22.2 mmol/L); take 8 units extra of regular insulin. 5. Test urine for ketones two to three times each day. 6. If vomiting occurs or blood glucose > 400 mg/dL for 24 hours, or if urine ketones are 2 plus, call a physician or go to the nearest emergency room.

REFERENCES 1. Marshall SM, Alberti KGMM. Hyperglycaemic emergencies: a further look. In: Alberti KGMM, Krall LP, eds. The diabetes annual/6. Amsterdam: Else¬ vier, 1990:390. 2. Schade DS, Eaton RP, Alberti KGMM, Johnston DG. Diabetic coma, ketoacidotic and hyperosmolar. Albuquerque, NM: New Mexico Press, 1981:250. 3. Keller U. Diabetic ketoacidosis: current views on pathogenesis and treat¬ ment. Diabetologia 1986,-29:71. 4. Foster DW, McGarry JD. The metabolic derangements and treatment of diabetic ketoacidosis. N Engl J Med 1983,-309:159. 5. Schreiber M, Kamel KS, Cheema-Dhadli S, Halperin ML. Ketoacidosis: emphasis on acid-base aspects. Diabetes Reviews 1994;2:98. 6. Fleckman AM. Diabetic ketoacidosis. Endocrinol Metab Clin North Am 1993; 22:181. 7. Marshall SM, Walker M, Alberti KGMM. Diabetic ketoacidosis and hyper¬ glycaemic non-ketotic coma. In: Alberti KGMM, DeFronza RA, Keen H, Zimmet P, eds. International textbook of diabetes mellitus. London: Wiley, 1992:1151. 8. Cohen RD. Lactic acidosis: new perspectives on origins and treatment. Di¬ abetes Reviews 1994; 2:86. 9. Ennis ED, Srahl EJvB, Kreisberg RA. The hyperosmolar hyperglycemic syndrome. Diabetes Reviews 1994;2:115. 10. Faich GA, Fishbein HA, Ellis SE. The epidemiology of diabetic acidosis: a population-based study. AmJ Epidemiol 1983; 117:551. 11. Ellemann K, Soerensen JN, Pedersen L, et al. Epidemiology and treatment of diabetic ketoacidosis in a community population. Diabetes Care 1984; 7:528. 12. Snorgaard O, Eskildsen PC, Vadstrup S, Nerup J. Diabetic ketoacidosis in Denmark: epidemiology, incidence rates, precipitating factors and mortality rates. J IntMed 1989;226:223. 13. Fishbein HA. Diabetic ketoacidosis, hyperosmolar nonketotic coma, lac¬ tic acidosis and hypoglycemia. In: Harris MI, Hamman RF, eds. Diabetes in Amer¬ ica. Washington, DC: U.S. Department of Health and Human Services, 1985:XII. 14. Division of Diabetes Translation In: Diabetes Surveillance 1980-1987. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control, 1990:27. 15. Holman RC, Herron CA, Sinnock P. Epidemiologic characteristics of mortality from diabetes with acidosis or coma. United States 1970-78. Am J Public Health 1983; 73:1169. 16. Basu A, Close CF, Jenkins D, et al. Persisting mortality in diabetic ketoac¬ idosis. Diabetic Med 1993; 10:282. 17. Tunbridge WMG. Deaths due to diabetic ketoacidosis. Q J Med 1981;50:

502. 18. Oster JR, Perez GO, Vaamonde CA. Relationship between blood pH and potassium and phosphorus during acute metabolic acidosis. Am J Physiol 1978; 235: F345. 19. Hers HG, Van Schaflingen E. Fructose 2,6-bisphosphate two years after its discovery. BiochemJ 1982; 206:1. 20. Miles JM, Gerich JE. Glucose and ketone body kinetics in diabetic ketoac¬ idosis. Clin Endocrinol Metab 1983; 12:303. 21. Sivitz WI, DeSautel SL, Kayano T, et al. Regulation of glucose transporter messenger RNA in insulin-deficient states. Nature 1989;340:72. 22. Rwiza HJ, Swai ABM, McLarty D. Failure to diagnose diabetic ketoacido¬ sis in Tanzania. Diabetic Med 1986;3:181. 23. Tattersall R. Brittle diabetes. BrMedJ 1985;291:555. 24. Peden NR, Braaten JT, McKendry JBR. Diabetic ketoacidosis during long¬ term treatment with continuous subcutaneous insulin infusion. Diabetes Care 1984; 7:1. 25. Chantelau E, Spraul M, Muhlhauser I, et al. Longterm safety, efficacy and side-effects of continuous subcutaneous insulin infusion treatment for type 1 (insulin-dependent) diabetes mellitus: a one centre experience. Diabetologia 1989; 32:421. 26. Campbell IW, Duncan LJP, Innes JA, et al. Abdominal pain in diabetic metabolic decompensation: clinical significance. JAMA 1975;233:166. 27. Munro JF, Campbell IW, McCuish AC, Duncan LJP. Euglycemic diabetic ketoacidosis. Br MedJ 1973,-2:578. 28. Jenkins D, Close CF, Krentz AJ, et al. Euglycaemic diabetic ketoacidosis: does it exist. Acta Diabetol 1993; 30:251. 29. Burge MR, Hardy KJ, Schade DS. Short term fasting is a mechanism for the development of euglycemic ketoacidosis during periods of insulin deficiency. J Clin Endocrinol Metab 1993; 76:1192. 30. Adrogue HJ, Wilson H, Boyd AE, et al. Plasma acid-base patterns in dia¬ betic ketoacidosis. N Engl J Med 1982;307:1603.

Ch. 150: Diabetes Mellitus and Pregnancy 31. Katz MA. Hyperglycemia-induced hyponatremia: calculation of expected serum sodium depression. N Engl ] Med 1973; 289:843. 32. Kaminska ES, Pourmotabbed G. Spurious laboratory values in diabetic ketoacidosis and hyperlipidemia. Am J Emerg Med 1993; 11:77. 33. Alberti KGMM, Hockaday TDR. Diabetic coma: a reappraisal after five years. Clin Endocrinol Metab 1977;6:421. 34. Kamimura M, Hancock EW. Acute MI pattern in diabetic ketoacidosis. Hosp Pract 1992;Dec. 15:28. 35. Horrocks PM, Wright AD, Nattrass M, Fitzgerald MG. Intravenous fluid therapy and heart failure in uncontrolled diabetes in the elderly. Practical Diabetes 1987;4:219. 36. West ML, Marsden PA, Singer GG, Halperin ML. Quantitative analysis of glucose loss during acute therapy for hyperglycemic, hyperosmolar syndrome. Diabetes Care 1986;9:465. 37. Owen OE, Licht JH, Sapir DG. Renal function and effects of partial rehy¬ dration during diabetic ketoacidosis. Diabetes 1981;30:510. 38. Alberti KGMM, Hockaday TDR, Turner RC. Small doses of intramuscular insulin in the treatment of diabetic coma. Lancet 1973;2:515. 39. Page MM, Alberti KGMM, Greenwood R, et al. Treatment of diabetic coma with continuous low-dose intravenous insulin. Br MedJ 1974;2:687. 40. Fisher JN, Shahshahani MN, Kitabchi AE. Diabetic ketoacidosis low-dose insulin therapy by various routes. N Engl J Med 1977;297:238. 41. Barrett EJ, DeFronzo RA, Bevilacqua S, Ferannini E. Insulin resistance in diabetic ketoacidosis. Diabetes 1982;31:923. 42. Van Gaal L, De Leeuw I, Bakaert J. Serum potassium levels in untreated diabetic ketoacidosis. Diabetologia 1981;21:338A. 43. Viberti GC. Glucose-induced hyperkalaemia: a hazard for diabetics. Lan¬ cet 1978;2:690. 44. Adrogue HJ, Lederer ED, Suki WN, Eknoyan G. Determinants of plasma potassium levels in diabetic ketoacidosis. Medicine (Baltimore) 1986; 65:163. 44a. Franks M, Berris RF, Kaplan NO, Myers GB. Metabolic studies in dia¬ betic acidosis II. The effect of the administration of sodium phosphate. Arch Intern Med 1948;81:42. 45. Wilson HK, Keuer SP, Lea AS, et al. Phosphate therapy in diabetic keto¬ acidosis. Arch Intern Med 1982; 142:517. 46. Oster JR, Alpert HC, Rodriguez GR, Vaamonde CA. Effect of acute rever¬ sal of experimentally induced ketoacidosis with sodium bicarbonate on the plasma concentrations of phosphorus and potassium. Life Sci 1988; 42:811. 47. Hale P], Crase ], Nattrass M. Metabolic effects of bicarbonate in the treat¬ ment of diabetic ketoacidosis. Br Med J 1984; 289:1035. 48. Gamba G, Oseguera J, Castrejon M et al. Bicarbonate therapy in severe diabetic ketoacidosis: a double blind, randomised placebo controlled trial. Rev In¬ vest Clin 1991,'43:234. 49. Mincu I, Ionescu-Tiigoviste C, Cheta D, Babes E. Le role de Tapport de glucose dans le traitement de la cetoacidose diabetique severe. Gazette Med France 1979;86:1665. 50. Malone NL, Klos SE, Gennis VM, Goodwin jS. Frequent hypoglycemic episodes in the treatment of patients with diabetic ketoacidosis. Arch Intern Med 1992; 152:2472. 51. Hillman K. Resuscitation in diabetic ketoacidosis. Crit Care Med 1983; 2: 53. 52. Fein IA, Rackow EC, Sprung CL, Grodman R. Relation of colloid osmotic pressure to arterial hypoxemia and cerebral edema during crystalloid volume load¬ ing of patients with diabetic ketoacidosis. Ann Intern Med 1982;96:570. 53. Krane EJ, Rockoff MA, Wallman JK, Wolfsdorf JI. Subclinical brain swell¬ ing in children during treatment of diabetic ketoacidosis. N Engl J Med 1985;312: 1147. 54. Arieff Al, Kleeman CR. Studies of mechanisms of cerebral edema in dia¬ betic comas: effects of hyperglycemia and rapid lowering of plasma glucose in nor¬ mal rabbits. J Clin Invest 1973;52:571. 55. Van der Meulen JA, Klip A, Grinstein S. Possible mechanism for cerebral oedema in diabetic ketoacidosis. Lancet 1987; 2:306. 56. Carroll P, Matz R. Adult respiratory distress syndrome complicating se¬ vere uncontrolled diabetes mellitus: report of 9 cases and a review of the literature. Diabetes Care 1982;5:574. 57. Breidbart S, Saenger P. Adult respiratory distress syndrome in an adoles¬ cent with diabetic ketoacidosis. J Pediatr 1987; 3:736. 58. Khardori R, Soler NG. Hyperosmolar hyperglycemic nonketotic syn¬ drome: report of 22 cases and a brief review. Am J Med 1984; 77:899. 59. Daugirdas JT, Kronfol NO, Tzamalovkas AH, Ing TS. Hyperosmolar coma: cellular dehydration and the serum sodium concentration. Ann Intern Med 1989:110:855. 60. Wachtel TJ, Silliman RA, Lamberton P. Predisposing factors for the dia¬ betic hyperosmolar state. Arch Intern Med 1988; 147:499. 61. Press GA, Barshop BA, Haas RH, et al. Abnormalities of the brain in nonketotic hyperglycemia: MR manifestations. AJNR 1989; 10:315. 62. Whelton MJ, Walde D, Havard CWH. Hyperosmolar nonketotic diabetic coma: with particular reference to vascular complications. Br Med J 1971; 1:85. 63. Johnson SF, Loge RV. Palinopsia due to nonketotic hyperglycemia. West J Med 1988; 148:331. 64. Cohen RD, Woods HF. Lactic acidosis revisited. Diabetes 1984;32:181. 65. Luft D, Schmulling RM, Eggstein M. Lactic acidosis in biguanide treat¬ ment of diabetics. Diabetologia 1978; 14:75. 66. Cohen RD, Woods HF. Clinical and biochemical aspects of lactic acidosis. Oxford: Blackwell, 1976. 67. Stacpoole PW, Lorenz AC, Thomas RG, Harman EM. Dichoroacetate in the treatment of lactic acidosis. Ann Intern Med 1988; 108:58.

1329

68. Fulop M, Hoberman HD. Alcoholic ketosis. Diabetes 1975; 24:785. 69. Fulop M. Alcoholism, ketoacidosis, and lactic acidosis. Diabetes Metab Rev 1989;5:365. 70. Johnston DG, Alberti KGMM. Diabetic emergencies: practical aspects of the management of diabetic ketoacidosis and diabetes during surgery. Clin Endo¬ crinol Metab 1980;9:437. 71. Marshall SM, Hyperglycaemic emergencies. J R Coll Phys Edinb 1995;25: 105-117.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

150_

DIABETES MELLITUS AND PREGNANCY LOIS JOVANOVIC-PETERSON AND CHARLES M. PETERSON

Before the advent of insulin, few young diabetic women lived to childbearing age. Before 1922, fewer than 100 pregnan¬ cies were reported, with a greater than 90% infant mortality rate and a 30% maternal mortality rate.1 In the mid-1970s, physicians were still counseling diabetic women to avoid pregnancy.2 This philosophy was justified because of the poor obstetric history in 30% to 50% of diabetic women. Improved infant mortality rates finally occurred when treatment strategies stressed better control of maternal plasma glucose levels. As the pathophysiology of pregnancy complicated by diabetes has been elucidated and as management programs have achieved and maintained normoglycemia throughout pregnancy, perinatal mortality rates have decreased to levels seen in the general population (Fig. 150-1).3

THE DIABETOGENIC FACTORS OF PREGNANCY PLASMA GLUCOSE DURING PREGNANCY The fetal demise associated with pregnancy complicated by diabetes seems to arise from glucose.4 Elevated maternal plasma glucose levels should always be avoided. To achieve normoglycemia, a clear understanding of "normal” carbohydrate metabo¬ lism in pregnancy is paramount. Glucose is transported to the fetus by facilitated diffusion, whereas amino acids are actively transported across the placenta. Moreover, alanine is siphoned selectively to the fetus.5 The ma¬ ternal serum glucose concentration drops below nonpregnant values to between 55 and 65 mg/dL in the fasting state.6 Simul¬ taneously, plasma ketone concentrations are several times higher and free fatty acids are elevated after an overnight fast/ 8 Thus, pregnancy simulates a state of "accelerated starvation," leading to the use of alternative fuels for maternal metabolism, while glu¬ cose is spared for fetal consumption (Fig. 150-2).9

DIABETOGENIC HORMONES OF THE PLACENTA The second half of pregnancy is characterized by a further lowering of plasma glucose levels. Although maternal glucose levels remain below nonpregnant levels, insulin levels increase markedly, partly because of increasing anti-insulin hormonal ac¬ tivity. The major diabetogenic hormones of the placenta are hu¬ man placental lactogen (hPL), estrogen, and progesterone. Also, serum maternal cortisol levels (both bound and free) are in¬ creased; at the elevated levels seen during gestation, prolactin has a diabetogenic effect.10

1330

PART IX: DISORDERS OF FUEL METABOLISM

Mean maternal blood glucose (mg/dL) FIGURE 150-1. The relationship between mean maternal glucose levels and the drop in infant mortal¬ ity over the years.

HPL

CORTISOL

The strongest insulin antagonist of pregnancy is hPL or hu¬ man chorionic somatomammotropin (hCS). This placental hor¬ mone appears in increasing concentration beginning at 10 weeks of gestation (see Chap. 106). By 20 weeks of gestation, plasma hPL levels are increased 300-fold, and by term, the turnover rate is about 1000 mg/d.11 The mechanism of action whereby hPL raises plasma glucose levels is unclear, but probably originates from its growth hormone-like properties. The hPL also promotes free fatty acid production by stimulating lipolysis, which pro¬ motes peripheral resistance to insulin.

Most of the marked rise of serum cortisol during pregnancy can be attributed to the increase of cortisol-binding globulin in¬ duced by estrogen. However, free cortisol levels are also increased.12 Thus, the rising cortisol levels may unmask diabetes in a predisposed individual.

PROGESTERONE

When progesterone is administered to normal nonpregnant fasting women, the serum insulin concentration rises and the glu-

MATERNAL

FETAL

PLACENTAL Decreased

FIGURE 150-2.

Schematic representation of nutrient fluxes across the placenta.

Hyperplasia

Ch. 150: Diabetes Mellitus and Pregnancy cose concentration remains unchanged. In monkeys, progester¬ one increases both early and total insulin responses to glucose.

PROLACTIN

The rise in pituitary prolactin early in pregnancy is triggered by the rising estrogen levels. Prolactin's structure is similar to growth hormone, and at concentrations reached by the second trimester (>200 ng/mL) prolactin can affect glucose metabolism. Although there are no studies that examine prolactin alone as an insulin antagonist, there is indirect evidence that suppressing prolactin in gestational diabetic women with large doses of pyridoxine improves glucose tolerance.

INSULIN DEGRADATION DURING PREGNANCY There is increased degradation of insulin in pregnancy. This degradation is caused by placental enzymes comparable to liver insulinases. The placenta also has membrane-associated insulin¬ degrading activity.13 Concomitant with the hormonally induced insulin resis¬ tance and increased insulin degradation, the rate of disposal of insulin slows. The normal pancreas can adapt to these factors by potentiation of insulin secretion. If the pancreas fails to respond adequately to these alterations, or if the clearance of glucose is defective, then gestational diabetes results.

1331

SCREENING TIMING

The optimal time to screen in pregnancy is between 24 and 28 weeks of gestation.16 The diabetogenic stimuli in pregnancy are sufficient then to manifest diabetes in at least 75% of gesta¬ tional diabetic women. If the screening is delayed until the 32nd week of gestation, 100% of gestational diabetic women will be detected, but by then, after 4 to 6 weeks of sustained hyperglyce¬ mia, 75% of the infants may already have developed fetopathy. If there is suspicion that a first-trimester pregnant woman may have preexisting, undiagnosed diabetes, then the screening should be performed at the first visit. If the testing is negative in the first trimester and at the usual examination between 24 and 28 weeks, the woman may be a part of the 25% of the gestational diabetic population who develop diabetes in the third trimester. They tend to be older than 33 years of age and are greater than 120% of ideal body weight.16 PROCEDURE

The screening test consists of 50 g of oral glucose and a plasma glucose determination at 1 hour, and it may be given re-

TABLE 150-1 Flow Chart for Management of Diabetes and Pregnancy (IDDM) Week of Gestation

EFFECT OF HYPERGLYCEMIA ON THE PREGNANCY AND THE FETUS

-6

If the mother has hyperglycemia, the fetus will be exposed to either sustained hyperglycemia or intermittent pulses of hy¬ perglycemia. Both situations prematurely stimulate fetal insulin secretion. The Pederson hypothesis links maternal hyperglyce¬ mia-induced fetal hyperinsulinemia to morbidity of the infant.4 Fetal hyperinsulinemia may cause increased fetal body fat (macrosomia) and, therefore, a difficult delivery, or cause inhibition of pulmonary maturation of surfactant and, therefore, respiratory distress of the neonate. The fetus may also have decreased serum potassium levels caused by the elevated insulin and glucose lev¬ els and may therefore have cardiac arrhythmias. Neonatal hypo¬ glycemia may cause permanent neurologic damage. Hyperglyce¬ mia in the mother may lead to maternal complications, such as polyhydramnios, hypertension, urinary tract infections, candidal vaginitis, recurrent spontaneous abortions, and infertility. Thus, a vigorous effort should be made to diagnose diabetes early and to achieve and maintain normoglycemia throughout pregnancy. As mentioned earlier, improved treatment protocols have low¬ ered maternal plasma glucose levels and the infant mortality rate has dropped (see Fig. 150-1). Treatment protocols should be de¬ signed to establish normoglycemia before conception (Table 150-1).

-2

Test

Treatment

Glycoslyated hemoglobin (GHb)

Normalization of GHb levels

Self blood glucose monitoring (SBGM) daily* GHb SBGM daily*

+2

GHb SBGM daily* Thyroid function Kidney function

Recheck GHb to assure normality before conception. Teach basal temperature checking. Reinforce insulin and diet plan. Insulin: 0.7 unit/kg/24 hours Diet: 25 kcal/kg/24 hours

Eye examination Physical examination Routine prenatal care

+8-18

GHb every 2 weeks SBGM daily*

Increase diet up to 30 kcal/ kg/24 hours and insulin as needed.

Sonogram at 8 and 12 weeks

+18-20

GHb every 2 weeks

Increase diet as needed.

SBGM daily*

Increase insulin to 0.8 unit/ kg/24 hours

Kidney function at 22 weeks Eye examination at 22 weeks Thyroid function at 22 weeks Physical examination at 22 weeks Sonogram at 22 weeks

DIAGNOSIS OF GESTATIONAL DIABETES

+30-36

GHb every 2 weeks SBGM daily*

Gestational diabetes is diabetes first recognized during preg¬ nancy; it generally disappears as soon as the pregnancy is termi¬ nated. The prevalence of gestational diabetes in the United States is 2% to 13%, depending on the genetics of the population under study.14 Classic risk factors identify a population of women at risk for gestational diabetes (e.g., obesity, family history of dia¬ betes, family history of macrosomia, or previous poor obstetric history); however, these risk factors identify only 50% of women diagnosed as having gestational diabetes.15 Therefore, it is neces¬ sary to screen all pregnant women, regardless of history, for ges¬ tational diabetes.

Increase insulin and diet as needed. Admit for bed rest if blood pressure is rising.

Repeat kidney, eye, and physical examination at 32-34 weeks +36-41

Obstetric surveillance protocol established to assess uterine growth, fetal well-being, GHb every 2 weeks

Increase diet as needed. Increase insulin to 0.9-1.0 unit/kg/24 hours. Deliver if fetal distress.

SBGM daily* * For IDDM, perform 6-8 times daily and check the reflectance meter weekly for accuracy.

1332

PART IX: DISORDERS OF FUEL METABOLISM TRIAGE PROCEDURE FOR GESTATIONAL DIABETES

gardless of the time of the last meal. If the plasma glucose con¬ centration 1 hour after the oral load is less than 140 mg/dL (7.8 mmol/L), the woman does not have gestational diabetes. If her plasma glucose level is more than 140 mg/dL (>7.8 mmol/L), a glucose tolerance test is indicated, consisting of a 100-g glucose drink after a minimum of 8 hours of fasting. A fasting plasma glucose blood sample should be drawn no later than 9:00 AM, and then a plasma glucose level should be obtained 1, 2, and 3 hours after the glucose load. Glucose should be determined on venous plasma, using the hexokinase method, and not capillary blood measurements, which use glucose oxidase-impregnated test strips and are less accurate for this purpose. Once the diagnosis of gestational dia¬ betes is made, these strips become the mainstay of treatment strategies. DIAGNOSTIC CRITERIA

Diagnostic criteria for gestational diabetes is based on the 100-g glucose load and the plasma result of the fasting values at 1, 2, and 3 hours (Table 150-2).15 These criteria correctly identify the woman at risk for a stillbirth. They do not identify women at risk of delivering a macrocosmic infant. Other tests and cutoffs need to be employed in order to identify the macrocosmic fe¬ tus.163 There is no diagnostic significance to values at 4 and 5 hours. Unfortunately, glycosylated hemoglobin, which is a test of long-term plasma glucose control in type I and type II diabetes mellitus, is not sensitive enough to diagnose gestational diabe¬ tes.16 The flow diagram (Fig. 150-3) outlines the steps in the triage of a gestational diabetic woman toward her optimal management.

PG: Plasma glucose GTT: glucose tolerance test PC: after a meal

FIGURE 150-3. THERAPY FOR GESTATIONAL DIABETES

The goal of management of the gestational diabetic woman is to maintain normoglycemia. Most pregnant women never ex¬ ceed 120 mg/dL of plasma glucose, even at 1 hour after a meal, despite the ingestion of large quantities of carbohydrate. It has been shown that if the peak postprandial glucose value is greater than 120 mg/dL, the risk of macrosomia rises exponentially.17 Because a nutritious meal for the mother and her unborn child necessitates at least a 40 mg/dL increase of plasma glucose, if the woman's fasting glucose is much greater than 90 mg/dL she will be unable to maintain her postprandial levels below 120 mg/ dL. Therefore, any woman whose fasting plasma glucose level is elevated above 90 mg/dL requires insulin to allow for the post¬ prandial excursions resulting from the minimal nutritional re¬ quirements of pregnancy. The woman should measure plasma glucose fasting and 1 hour after each meal. Diet. If the woman's fasting plasma glucose level is less than 90 mg/dL, then a trial of dietary therapy is possible. The diet in pregnancy of the diabetic woman who is 80% to 120% of ideal body weight is the same as for the nondiabetic pregnant woman, or 30 kcal/kg/24 h. Less than 40% of the calories should TABLE 150-2 Glucose Tolerance Test Criteria for Diagnosis and Classification DIET-CONTROLLED GESTATIONAL DIABETES

Flow chart for the screening and diagnostic triage pro¬ cedure for gestational diabetes.

be consumed in the form of carbohydrate, because carbohydrate is the main contribution to the peak postprandial glucose level.1819 The breakfast meal must be small, and the carbohydrate por¬ tion of this meal minimal. The dietary plan of frequent, small feedings is designed to avoid postprandial hyperglycemia and preprandial starvation ketosis (Table 150-3). In the obese diabetic woman (>120% of ideal body weight), fewer calories per kilo¬ gram of total pregnant weight need be given, because these women have a larger percentage of their body weight in the form of adipose tissue; 24 kcal/kg/24 h or less will often allow the patient to maintain euglycemia and remain ketosis free.20 Insulin. If a woman does need insulin because her plasma glucose levels exceed the criteria for normoglycemia or her blood glucose level can only be normalized by starvation,21 a fourinjections-a-day regimen is prescribed, similar to the one out¬ lined later for the type I insulin-dependent diabetic woman (Ta¬ ble 150-4) In a massively obese woman, the initial doses of insu¬ lin may need to be increased to 1.5 to 2.0 units/kg to overcome the combined insulin resistance of pregnancy and obesity.21 Exercise. Arm exercises performed in a seated position are safe and facilitate the maintenance of normoglycemia.22,23

Two or more of values given below: Fasting 105 mg/dL 1 h 190 mg/dL 2 h 165 mg/dL 3 h 145 mg/dL

TABLE 150-3 Diet Calculation for Women 80% to 120% of Ideal Body Weight

After 100 g of oral glucose TREATMENT

Trial of diet. Initiate insulin if normoglycemia* is not maintained on diet alone.

INSULIN REQUIREMENT

If the fasting plasma glucose level is greater than 90 mg/dL (in addition to the elevation of two or more of the post-drink values [see above]), then insulin should be prescribed immediately.

* Normoglycemia = fasting 10 minutes) suggests inadequate treatment or another cause of the symptoms. Prolonged or repeated hypogly¬ cemia can cause permanent neurologic injury.17

FASTING HYPOGLYCEMIA EVALUATION

The evaluation of fasting hypoglycemia (Fig. 152-3) is es¬ sentially the workup for possible insulinoma.18 The investigation of insulinoma entails invasive testing, and the treatment is pri¬ marily surgical. Fasting hypoglycemia and an inappropriate hyperinsulinemia at the time of hypoglycemia must be documented before any further tests are performed. The single, most useful test is the in-hospital monitored fast for up to 48 hours. The in¬ sulin that is released by insulinomas usually is not suppressed by declining plasma glucose; fasting individuals with insulinomas become hypoglycemic because the fasting plasma glucose level depends on the hepatic output of glucose. Conversely, during a 48-hour fast, normal individuals rarely develop plasma glucose concentrations below 40 mg/dL and almost never develop neuroglycopenic symptoms in this setting.3,4 The observed fast is the most important test in evaluating fasting hypoglycemia, and it should be carefully performed, with attention to the collection of appropriate data. The intent is to demonstrate pathologic hypoglycemia, and this is best accom-

EVALUATION OF HYPOGLYCEMIA Clinical Suspicion

I MEDICATIONS/TOXINS Insulin Sulfonylureas Ethanol Salicylates Hypoglycemia Other

FASTING HYPOGLYCEMIA

POSTPRANDIAL HYPOGLYCEMIA

Y Adults (Rule out insulinoma) ___I_ Observed Fast 48-72 hours

Unobserved overnight fast to rule out fasting

Y

Meal tolerance test

(glucose < 40 mg/dL) Insulin/C-peptide Increased

Decreased

I

I

RULE OUT SURREPTITIOUS HYPOGLYCEMIA

Presumed Insulinoma Localization angiography transhepatic sampling Surgery

FIGURE 152-3.

1345

Consider: Congestive heart failure Uremia Sepsis Tumor Autoimmune

Algorithm for the evaluation of hypoglycemia.

Trial of frequent meals with few simple carbohydrates

1346

PART IX: DISORDERS OF FUEL METABOLISM

plished by demonstrating spontaneous hypoglycemia with neuroglycopenic symptoms. The fast must be conducted in the hos¬ pital and with provision for careful observation. The patient must not be allowed to leave the room, and frequent assessment by medical staff is essential. A secure intravenous line, preferably with a running infusion without glucose, must be present, and an ampule of 50% glucose solution for rapid administration should be available. Access to glucagon usually is unnecessary. Before initiation of the fast, a simple neurologic examination stressing coordination, recent memory, and calculations should be performed to provide a baseline. The time of initiating the fast is determined by a careful his¬ tory to elicit a reasonable estimate of the patient's tolerance for fasting; it is best that the hypoglycemia occurs midday with ade¬ quate staffing present. Fasts often are begun at midnight or after breakfast, depending on whether there are symptoms only after skipping meals or usually before breakfast and depending on the severity of the symptoms. During the fast, patients may ingest noncaloric foods such as black coffee or artificially sweetened noncaloric beverages. Simultaneous insulin and glucose samples are obtained at the beginning and every 4 hours thereafter; glu¬ cose should be determined by the glucose oxidase method in the clinical laboratory and not solely by a bedside glucose meter, be¬ cause the latter often is inaccurate at glucose levels less than 60 mg/dL. When the blood sugar has fallen below 50 mg/dL, insu¬ lin and glucose samples should be obtained every hour and bed¬ side glucose meter determinations made every 30 minutes or with changes in clinical status (e.g., sweating). These procedures are continued until the blood sugar falls below 40 mg/dL; this is significant hypoglycemia, and the pa¬ tient should be assessed for neuroglycopenia frequently thereaf¬ ter. Specimens for insulin and glucose values usually are drawn every 15 minutes; at the termination of the fast, a C-peptide level is also obtained to independently verify endogenous inappropri¬ ate insulin secretion. The fast should be terminated only for true neuroglycopenia and not because of signs of catecholamine ex¬ cess, such as sweating or tremor. At the least, to rule out labora¬ tory error, two or more blood glucose levels below 40 mg/dL should be obtained before concluding the fast. A failure to observe hypoglycemia by 48 hours of fasting may occur in cases of insulinoma; 90% of patients have true hy¬ poglycemia within this time frame, but another 5% require fast¬ ing to 72 hours.2 Rarely should the fast be carried out beyond 72 hours, even if hypoglycemia has not occurred. An analysis of the pattern of insulin and glucose levels during the fast is helpful in such circumstances; insulin levels should fall progressively with prolonged fasting; failure to suppress insulin and C-peptide lev¬ els despite prolonged fasting still indicates inappropriate insulin secretion and warrants further investigation. For a blood glucose value less than 40 mg/dL (2.2 mM), the appropriate concentration of insulin in the serum is less than 6 /uU/mL (36 pM). Insulin levels above the limits of detectability in such well-supervised insulin assays suggest an insulinoma, espe¬ cially if confirmed by detectable levels of C-peptide. The combi¬ nation of fasting hypoglycemia values of less than 40 mg/dL, neuroglycopenia, and the failure to suppress insulin secretion are diagnostic of an insulinoma. The plot of all the insulin and glu¬ cose values obtained during the fast also is useful. Ketonuria after 12 or more hours of fasting indicates normal suppression of in¬ sulin during a fast and is not observed in patients with insulinomas. In some centers, the ratio of insulin (in /mL) to glucose (in mg/dL) is used to analyze data from a fast; in cases of insu¬ linoma, the insulin to glucose ratio exceeds 0.3 during the fast. The authors think this analysis usually is unnecessary, and false¬ positive results are observed in obese individuals with moderate insulin resistance. The authors prefer to use absolute endpoints to avoid these false-positive results. There are several important caveats of the observed fast. First, women have lower plasma concentrations of glucose dur¬

ing a fast than men, and normal women occasionally have values below 40 mg/dL in the second 24 hours.4 These women, how¬ ever, are asymptomatic and have insulin concentrations that are normally suppressed. Second, some insulinomas suppress their insulin release in response to hypoglycemia. Third, false eleva¬ tions can occur in serum insulin measurements because of the presence of anti-insulin antibodies. To avoid these pitfalls, it is important to continue the fast under close supervision until mild but definite neuroglycopenic symptoms are documented. The ap¬ pearance of symptomatic hypoglycemia is pathologic and, in the presence of inappropriate hyperinsulinemia, is diagnostic for insulinoma. The diagnosis of insulinoma is further supported by finding that a high percentage (> 25%) of circulating fasting immunoreactive insulin in these patients is actually proinsulin, suggesting poor processing of the peptide by these tumors (Fig. 152-4). The determination of the percentage of insulin that is the proinsulin¬ like component is based on measurements using an insulin stan¬ dard for the insulin and PLC. The PLC is elevated in type II diabetes and familial hyperproinsulinemia, but these are hyper¬ glycemic, not hypoglycemic, conditions. In a review of of 25 pa¬ tients with documented insulinoma, an analysis of samples drawn at the termination of a fast and in the presence of hypo¬ glycemia showed that an elevated percent proinsulin had a sen¬ sitivity of 84%. An assay that measures only proinsulin and gives similar sensitivity and specificity in insulinoma has not been val¬ idated.18-20 Other tests to detect insulinomas can be divided in two types. One type relies on the demonstration of increased insulin secretory capacity. The best standardized example is the tolbuta¬ mide test, although calcium and glucagon challenges have been used.21 These tests rely on a well-characterized normal range, es-

* Lymph node metastasis only f Liver metastasis

FIGURE 152-4. Proinsulin-like component in insulinoma patients. The normal amount of immunoreactive insulin that migrates with proinsulin on gel filtration is less than 25%, as indicated by the dotted line. In more than 90% of the patients with benign or malignant insulinomas, the plasma contains much more proinsulin than normal. Although the aver¬ age percentage of proinsulin (horizontal bars) is higher for patients with malignant insulinoma than for those with benign tumors, because of an overlap of values, this difference cannot discriminate benign from malig¬ nant tumors.

Ch. 152: Hypoglycemic Disorders in the Adult tablished at the test center. The second type demonstrates the inability to suppress insulin secretion. These tests are less time consuming than the observed fast. The C-peptide test is a prom¬ ising new approach of this type. The C-peptide level in plasma is measured before and after an infusion of exogenous insulin; the response is blunted or absent in insulinoma patients. Because it does not rely on external controls, it may be very useful and is appealing in its simplicity.22 It is too early to determine if it will supplant the observed fast. Both types of tests can be useful in difficult cases for which the routine fasting results are equivocal. MANAGEMENT

The only effective treatment of insulinoma is surgical extir¬ pation. Insulinomas usually are discrete, single nodules, less than 2 cm in diameter, which are evenly distributed in frequency of occurrence throughout the pancreas. Pancreatic surgery is fraught with morbidity, particularly if the pancreatic duct is in¬ jured. The preoperative localization of insulinomas is extremely important and should be pursued aggressively (see Chap. 153). For the localization of insulinomas, abdominal ultrasound and computerized tomography (CT) with or without bolus-con¬ trast enhancement have sensitivities of 30% to 50%.18 CT scans may be useful to document metastatic disease and are commonly performed in the evaluation of insulinoma. Although the experi¬ ence is limited, magnetic resonance scanning is more sensitive for identifying metastases and may be more sensitive for identifying the primary pancreatic tumor. When available, the best test for insulinoma localization is angiography with subselective injections to visualize the entire pancreatic vascular bed. The success rate with this technique is 30% to 50% for primary tumors and more than 90% for meta¬ static disease.18 In cases not identified by subselective arteriogra¬ phy, localization is accomplished by demonstrating excessive in¬ sulin secretion from a region of the pancreas. One of two techniques is calcium infusion in the arterial branches of the ce¬ liac plexus, with immediate sampling for stimulation of insulin release into the hepatic vein. This technique can identify vascular beds that harbor insulinomas by demonstrating exaggerated re¬ sponsiveness to calcium. Recent experience suggests that this may be the method of choice because of a high sensitivity (e.g., positive results for 10 of 11 patients studied) and low risk of com¬ plications.18 Percutaneous transhepatic venous sampling of the pancreatic venous drainage is also successful in identifying 70% of occult insulinomas by demonstrating a "step up" in insulin secretion from a region of the pancreas. However, this technique is attended by greater morbidity. Multiple insulinomas occur in about 10% of cases, particu¬ larly in the setting of familial type 1 multiple endocrine neoplasia (MEN-1), and excessive secretion by one of several nodules may impede demonstration of the multiplicity of the tumors. Patients with MEN-1 may have several tumors, only some of which se¬ crete insulin. These patients may present with symptoms refera¬ ble to another hormone secreted in excess and incidentally be found to have an insulinoma (see Chap. 182). For example, pa¬ tients with the MEN-1 syndrome may present with symptoms referable to hyperparathyroidism or the Zollinger-Ellison syn¬ drome, but an incidental insulinoma is found by careful history, screening tests, or surgery. Levels of insulin and determination of the percentage of proinsulin may be used to screen for insu¬ linoma. Preoperative localization does not obviate careful palpa¬ tion of the entire pancreas, especially in cases that are localized by venous sampling alone. Intraoperative ultrasound may facili¬ tate the exploration of the pancreas, particularly by identifying the depth of the nodule within the substance of the pancreas. Rarely, excessive insulin secretion is caused by diffuse le¬ sions of the pancreas, such as multiple adenomatosis or nesidi¬ oblastosis. Nesidioblastosis probably is a congenital lesion of the pancreas and is a common cause of hypoglycemia in infants; it is extremely rare and should be carefully verified before bein|5 accepted as a cause of hypoglycemia in adults (see Chap. 155).23

1347

Surgical removal (see Chap. 154) of an insulinoma is cura¬ tive in more than 80% of the cases.24 Distal tail lesions may re¬ quire concomitant splenectomy, and preoperative pneumococcal vaccination is advisable. The exploration of lymph nodes in the region is important in assessing the nature of the tumor. Insu¬ linoma histology does not correlate well with tumor behavior. Ten percent of all insulinomas are malignant, and these are rec¬ ognized solely by the presence of hepatic metastases.18 Occasion¬ ally, only local lymph node spread is found at surgery. In the absence of hepatic disease, the resection of involved nodes is of¬ ten curative, and surgical debulking of malignant tissue can be of great benefit. Islet cell tumor metastases may be nonsecretory or may secrete a hormone different from that of the primary tumor. Isolated metastases to tissues outside the abdomen have not been reported. Medicinal therapy to diminish insulin release from the tu¬ mor is limited (Table 152-3). Diazoxide suppresses insulin release in about 50% of all insulinoma lesions, and the response to this agent may be inversely correlated with the elevation of the per¬ centage of proinsulin. In responsive cases, diazoxide, in doses of 400 to 600 mg/day, can be extremely useful in preoperative or chronic management. Side effects include salt retention and gastrointestinal intolerance; these can be minimized by gradual escalation from small doses to effective amounts. A promising agent is the long-acting somatostatin analogue, octreotide acetate (see Chap. 166).26 Other agents of occasional use are calcium channel-blocking agents and phenytoin sodium (Dilantin), which can reduce insulin release in a few cases. In difficult cases of severe hypoglycemia with nonresectable metastatic tumors, some success has been reported with alterna¬ tive therapies, such as catheterization and occlusion of the vas¬ cular supply to the tumor.27 However, these approaches have limited applicability because of situations of multiple bloodsupplying vessels to the tumor and the difficulty in selectively damaging the tumor without affecting normal tissue. Metastatic insulinoma requires careful evaluation for proper management. Large, rapidly expanding liver metastases or hyperinsulinism and hypoglycemia are clear indications for chemo¬ therapeutic intervention. The progression of metastases may be slow, and small amounts of nonfunctional metastatic disease may not require intervention, particularly in elderly patients. In cases requiring therapy, the most effective regimen is a combina¬ tion of streptozocin and 5-fluorouracil, which achieves partial or complete response in 60% (see Table 152-3). The main side effect of this therapy is the nephrotoxicity of the streptozocin, which can cause permanent renal damage and necessitates the cessation of therapy. Doxorubicin (Adriamycin) has been added to the combination regimen in some trials. Tumor markers are particu¬ larly helpful in following the course of metastatic insulinomas; these include insulin, the percentage of PLC, and a-human cho¬ rionic gonadotropin (a-hCG). Elevation of these markers can precede the detection of increased tumor burden, and an increase in serum hCG or its a subunit occurs in about 50% of malignant insulinomas. Chemotherapy is not curative; the goal of therapy is the relief of symptoms.

NONINSULINOMA TUMOR-ASSOCIATED HYPOGLYCEMIA Certain tumors have been associated with profound fasting hypoglycemia (see Table 152-3 and Chap. 213).28 The hypogly¬ cemic syndrome caused by these noninsulinoma tumors is indis¬ tinguishable from that resulting from insulinoma, but the lesions are easily differentiated by the absence of inappropriate hyperinsulinemia. Hypoglycemia is most commonly a late manifestation of these tumors, appearing when they are quite large (400 g-1 kg). Mesenchymal tumors, particularly those composed of spin¬ dle cells, are the most common types associated with hypoglyce¬ mia. Other tumors that may cause hypoglycemia include sarco¬ mas, hepatocellular tumors, and carcinoid-like tumors/1 Mesenchymal tumors associated with hypoglycemia can be be-

1348

PART IX: DISORDERS OF FUEL METABOLISM

TABLE 152-3 Insulinoma: Insulin-Suppressing Agents and Chemotherapy for Metastatic Disease

Agent

Trade Name

Dosage

Complete or Partial Response

Excretion

Toxicity

Renal

Gastrointestinal intolerance; edema; hirsutism

INSULIN-SUPPRESSING AGENTS IN INSULINOMA THERAPY Diazoxide

Proglycem

200-600 mg PO daily

50%

Somatostatin analogue

Octreotide acetate Sandostatin

Experimental, SC

Anecdotal

Verapamil

Isoptin, Calan

Experimental, IV

Anecdotal

Liver

Heart block; hypotension

Phenytoin

Dilantin

300-400 mg PO daily

Anecdotal

Liver

CNS; hepatotoxic; skin rash; thrombocytopenia, leukopenia

Abdominal cramps, possible gallstones

CHEMOTHERAPEUTIC AGENTS IN METASTATIC INSULINOMA Streptozocin

Same

500 mg/m2 IV daily for 5 days of Rx; cycled every 6 wk

35-50%

Liver > renal

Nephrotoxic; bone marrow; liver

Streptozocin plus 5-FU

Same + fluorouracil

Same as above plus 5-FU, 400 mg/m2 IV, both daily for 5 days of Rx; cycled every 6 wk

60%

See above, plus liver for 5-FU

Above toxicity; diarrhea; mucositis; hepatotoxicity (5-FU)

Doxorubicin

Adriamycin

60 mg/m2 IV; cycled every 23 wk; limit: 500 mg/m2

Under study

Liver

Myelosuppression; cardiotoxicity; alopecia

Dacarbazine

DTIC-Dome

250 mg/m2 IV daily for 5 days; cycled monthly

Anecdotal

Renal > liver

Myelosuppression; thrombocytopenia

(From Comi, RJ, Gorden, P, Doppman, JL. Insulinoma. In: Go VL, Di Magno E, Gardner J, et al, eds. The pancreas: biology, pathobiology and diseases. New York: Raven Press, 1993:979.)

nign or malignant. Ectopic production of insulin remains to be documented; the absence of inappropriate circulating insulin is a hallmark of patients with these tumors. Many of these patients have increased concentrations of cir¬ culating insulin-like growth factor-II (IGF-II) or a subtle increase of IGF-II activity relative to IGF-I activity in plasma. Abnormali¬ ties in the amounts of the binding proteins for these growth fac¬ tors have been described, suggesting that the hypoglycemia may be the result of an increase in the fraction of IGF-II available to bind to IGF-II or insulin receptors to induce hypoglycemia.29 Tumor consumption of circulating glucose in excess of he¬ patic capability to produce glucose and a loss of hepatic cells from metastatic disease are two nonhormonal mechanisms that have been proposed, but the enormous capacity of the liver for gener¬ ating glucose renders them unlikely as general mechanisms. These tumors, because of their large size, are usually easily detected by radiologic investigations of the thoracic, abdominal, or retroperitoneal cavities. Treatment is primarily surgical, al¬ though radiation therapy sometimes has been effective. Gener¬ ally, they are unresponsive to antitumor agents. Table 152-4 summarizes typical tumor types and features observed in nonin¬ sulinoma tumor-associated hypoglycemia.

FACTITIOUS HYPOGLYCEMIA Surreptitious, self-induced (i.e., factitious) hypoglycemia is difficult to document, even when suspected, and it is extremely difficult to discover if unsuspected. It is not rare; factitious hypo¬ glycemia should be an early and seriously considered diagnosis for all patients with hypoglycemia.18 Individuals with access to insulin, such as medical personnel or relatives of diabetics, are especially suspect. These persons rigorously deny self-induced hypoglycemia and may permit invasive testing and even unnec¬ essary surgery (Table 152-5). A search of the patient's possessions or room usually is un¬ rewarding. The single most important diagnostic maneuver is the

measurement of anti-insulin antibodies in blood.30 These anti¬ bodies are indicative of prior exogenous insulin administration, particularly for bovine and porcine insulins. Because the titers of this antibody may be low, a concentrating technique or gel fil¬ tration may be necessary for their detection. Although insulin antibodies may be present in rare, autoimmune forms of hypo¬ glycemia, factitious disease must be specifically excluded in these patients. The C-peptide is released into the circulation from the same granules as endogenous insulin; circulating C-peptide con¬ centrations are suppressed during the hypoglycemia that is in¬ duced by the hyperinsulinemia of exogenous insulin administra¬ tion. Along with anti-insulin antibody titers and C-peptide measurements, high-performance liquid chromatography (HPLC) methods can separate human from beef and pork insu¬ lins.31 However, the increased use of human insulins from re¬ combinant sources makes detection of surreptitious insulin injec¬ tion more difficult.

AUTOIMMUNE CAUSES OF HYPOGLYCEMIA The first and best characterized autoimmune disease associ¬ ated with hypoglycemia is the syndrome of type B extreme insulin resistance, in which circulating antibodies to the insulin receptor are present3- (see Chap. 140). These persons usually demonstrate the skin lesion acanthosis nigricans and various nonspecific au¬ toimmune features, including anemia, thrombocytopenia, ne¬ phritis, and an elevated sedimentation rate. Typically, these per¬ sons are insulin resistant and hyperglycemic; rarely, they manifest severe fasting hypoglycemia from an insulinomimetic effect. In some of these patients, alternating episodes of hyper¬ glycemia and hypoglycemia may occur. Because the degradation of insulin normally is mediated by the receptor, circulating insu¬ lin levels may be paradoxically elevated at times of hypoglyce¬ mia, mimicking the features of insulinoma. Plasma PLC levels and insulin response to secretagogues are normal, and the dem¬ onstration of anti-insulin receptor antibodies confirms the diagnosis.

Ch. 152: Hypoglycemic Disorders in the Adult

1349

TABLE 152-4 Noninsulinoma Tumor Hypoglycemia TUMOR TYPE (IN ORDER OF FREQUENCY) Mesenchymal

Benign tumor or sarcoma of muscle, mesothelial cell and neurofibroma, hemangiopericytoma, fibrosarcoma

Hepatoma Adrenocortical tumor

Usually carcinoma, often left sided

Gastrointestinal tumors

Epithelial tumors from all regions of gastrointestinal tract

Lymphoma Other

Teratoma, genitourinary epithelial tumors

COMMON FEATURES OF HYPOGLYCEMIA-ASSOCIATED NONINSULINOMA TUMORS Large size

Greater than 500 g, 5 cm in diameter

Localization

Abdominal > thoracic (50% retroperitoneal)

Age of presentation

Usually over 30 years of age

Locally invasive

Occasionally metastatic or multicentric

The spontaneous, autoimmune anti-insulin antibody syndrome is also associated with hypoglycemic episodes. This syndrome is extremely rare, with most reported cases occurring in Japan and in association with treatment with propylthiouracil for autoim¬ mune thyroid disease.33,34 The disease is difficult to document in sporadic cases, and prior insulin use must be carefully excluded. The mechanism of hypoglycemia in this disorder is not un¬ derstood, but it is postulated to involve the production of antiidiotypic antibodies to the anti-insulin antibodies, which interact with the insulin receptor to mimic insulin at its receptor.

ALCOHOL-INDUCED HYPOGLYCEMIA The liver is the central organ in normal glucose homeostasis (see Fig. 152-1). Hepatic disease or other disorders can impair the ability of the liver to store or to produce glucose.35 The glycogen storage diseases and other enzymatic deficiencies that impair he¬ patic glucose metabolism are usually discovered early in life.36 Rarely, a mild form of these disorders occurs in adolescence, but ordinarily, genetic enzymatic deficiencies are not a consideration in adult hypoglycemia (see Chap. 155). Diffuse acquired liver dis¬ ease, such as cirrhosis, fulminant hepatitis, and even hepatic con¬ gestion caused by congestive heart failure can result in impaired hepatic gluconeogenesis, although very late in the course of these diseases. Focal liver diseases, including extensive hepatic metastases, rarely cause hypoglycemia (see Chap. 200). Most commonly, fasting hypoglycemia of hepatic origin de¬ rives from acute, acquired impairment of hepatic glucose output, primarily by hepatic toxins. The most common circumstance is hypoglycemic coma in chronic alcoholics. There usually is a his¬ tory of extremely poor nutrition for several days, followed by acute alcohol ingestion. The metabolism of alcohol and the pro¬ duction of glucose from precursors require oxidative steps using nicotinamide-adenine dinucleotide (NAD) as a proton receptor.

Acute alcohol administration depletes the liver of NAD, and glu¬ coneogenesis ceases.38 This causes profound hypoglycemia and neuroglycopenia, manifested as coma. The treatment of these in¬ dividuals requires glucose and thiamine. The latter is required for CNS glucose metabolism, and glucose alone may precipitate another deficiency state with neurologic sequelae. Hypoglycemia in sepsis probably is of hepatic origin; hepatic gluconeogenesis is presumably impaired by a toxin.

HORMONAL DEFICIENCY SYNDROMES AND HYPOGLYCEMIA Endocrinopathies can affect circulating glucose levels by im¬ pairing gluconeogenesis.39,40 Deficiencies of corticotropin, corti¬ sol, growth hormone, or thyroxine can diminish the amounts and activities of the enzymes involved in gluconeogenesis and dimin¬ ish the hepatic capacity for glucose output. These hormonal de¬ ficiencies alone rarely produce hypoglycemia, but they can com¬ pound other hypoglycemic stresses, such as medications. Combined deficiencies, such as cortisol and growth hormone, may be more prominent causes of spontaneous hypoglycemia. Deficiencies of other hormones, such as glucagon, catechol¬ amines, or other pituitary hormones are not associated with hy¬ poglycemic syndromes.

POSTPRANDIAL HYPOGLYCEMIA Postprandial hypoglycemia (see Fig. 152-2) or reactive hypo¬ glycemia is better designated as a postprandial syndrome. This di¬ agnosis is controversial. There are a few patients who suffer symptomatic hypoglycemia 2 to 4 hours after a meal. In one study of 116 patients referred for evaluation of reactive hypogly¬ cemia, 16 developed symptoms at the time of their lowest glucose during oral glucose tolerance testing, but 14 of these developed

TABLE 152-5 Features That Differentiate Insulinomas From Factitious Hypoglycemia Surreptitious Administration or Ingestion Test

Insulinoma

Insulin

Sulfonylurea

Antibodies to insulin

Not present

Present

Not present

Sulfonylurea levels (blood or urine)

Not present

Not present

Present

Immunoreactive insulin

Normal or elevated

Normal or elevated

Normal or elevated

C-peptide

Normal or elevated

Decreased

Normal or elevated

Proinsulin

Usually increased*

Normal or decreased

Normal

* The italicized statements represent the most diagnostic tests in each situation.

1350

PART IX: DISORDERS OF FUEL METABOLISM

the same symptoms after receiving a placebo without caloric value in a blinded fashion.41 There was an absence of a consistent relationship between blood glucose concentrations and symp¬ toms in a study using well-standardized home glucose monitor¬ ing in a large number of patients with postprandial syndromes.42 Only 8 of 132 measurements obtained at the time of symptoms showed a glucose less than 50 mg/dL (2 8 mM). Patients complaining of neuroglycopenic symptoms 1.5 to 5 hours after meals should be investigated by means of a mixed meal tolerance test, in which a standardized meal of normal com¬ position is ingested, and then the plasma glucose concentration is monitored every 30 minutes for 5 hours while under observa¬ tion for symptoms. Patients who develop symptoms simulta¬ neously with true hypoglycemia may be considered to have post¬ prandial hypoglycemia. The treatment is a trial of a lowcarbohydrate diet, which is effective in many cases; more fre¬ quent, but smaller, meals also may be effective. The diagnosis should not be evaluated by means of an oral glucose tolerance test, because careful studies have shown an incidence of hypo¬ glycemia in as many as 16% of normal persons after the ingestion of large amounts of simple carbohydrates, and the low blood sugar levels in such instances are an artifact. An important subgroup of patients with a postprandial syn¬ drome are patients who have undergone gastric outlet surgery, particularly for peptic ulcer.42a In these patients, postprandial hy¬ poglycemia does occur, probably because of rapid transit of large amounts of nutrients, especially carbohydrates, from the gastric remnant to the small bowel. Although not well understood, this is thought to cause the elaboration of large amounts of local gut factors that cause a hypersecretion of insulin from the pancreas. This phenomenon is distinct from the dumping syndrome, in which the rapid transit of a large osmotic load through the gut causes a rapid fluid shift and a marked autonomic response with¬ out an associated hypoglycemia. The treatment of postsurgical postprandial hypoglycemia usually consists of a trial of small meals; if this fails, surgical intervention may be required. Figure 152-2 summarizes the approach to the postprandial syndrome.

OTHER CAUSES OF HYPOGLYCEMIA There are several pharmacologic agents that cause hypogly¬ cemia as a side effect.37 The most common offenders after the insulins are the sulfonylureas. These include pentamidine, which is used in the treatment of Pneumocystis carinii infections,42b antiarrhythmic agents such as disopyramide, and some antimalarial drugs. The acute ingestion of hepatic toxins, such as large doses of acetaminophen, also cause hypoglycemia as a result of fulmi¬ nant liver failure. Ingestion of the Caribbean fruit, ackee, causes hypoglycemia because of a substance that has been isolated and called hypoglycin (see Chap. 2 2 2).43 In any evaluation of hypo¬ glycemia, a careful drug and ingestion history is required. Plasma glucose levels less than 50 mg/dL (2.8 mM) may oc¬ cur after prolonged strenuous exercise, such as running a mara¬ thon. Although seizures attributed to hypoglycemia have occa¬ sionally been reported, symptomatic hypoglycemia is unusual in these individuals, and symptoms of exhaustion have not been shown to be caused by hypoglycemia.44 Uremia also has been associated with hypoglycemia. The fasting hypoglycemia occurring in this condition is attributed to failure to produce substrate from the peripheral tissues (notably a nine) for hepatic glyconeogenesis. However, this complication of c "emia is rare.45

REFERENCES

4. Merimee T, Tyson JE. Hypoglycemia in man, Diabetes 1977;26:161. 5. Katz LD, Glickman MG, Rapoport S, et al. Splanchnic and peripheral dis¬ posal of oral glucose in man. Diabetes 1983;32:675. 6. Cahill GF Jr. Starvation in man. N Engl J Med 1970; 282:668. 7. Felig P, Marliss E, Owen E, Cahill GF Jr. Role of substrate in the regulation of hepatic gluconeogenesis in man. Adv Enzyme Regul 1969; 7:41. 8. Felig P, Wahrin J, Sherwin R, Hendler R. Insulin and glucose in normal physiology and diabetes. Diabetes 1976;25:1091. 9. Mitrakou A, Ryan C, Veneman T, et al. Hierarchy of glycemic thresholds for counterregulatory hormone secretion, symptoms and cerebral dysfunction Am J Physiol 1991;260:E67. 10. Rizza RA, Cryer PE, Gerich JE. Role of glucagon, catecholamines, and growth hormone in human glucose counterregulation: effects of somatostatin and combined a- and ^-adrenergic blockade on plasma glucose recovery and glucose flux rates following insulin-induced hypoglycemia. J Clin Invest 1978; 64:62. 11. Field JB. Hypoglycemia. Endocrinol Metab Clin North Am 1989; 18:27. 12. Blackman JD, Towle VL, Lewis GF, et al. Hypoglycemic threshold for cognitive dysfunction in humans. Diabetes 1990;39:828. 13. DCCT Research Group. The effect of intensive treatment of diabetes on the development and progression of long term complications in insulin dependent diabetes mellitus. N Engl J Med 1993; 329:977. 14. Cryer P, Gerich J,. Glucose counterregulation, hypoglycemia and inten¬ sive insulin therapy in diabetes mellitus. N Engl J Med 1985; 313:232. 15. Gerich JE, Mokaw M, Veneman T, et al. Hypoglycemia unawareness. Endocr Rev 1991; 12:356. 16. Comi RJ. Approach to adult hypoglycemia. Endocrinol Metab Clinics North Am 1993; 22:247. 17. Malouf R, Brust JCM. Hypoglycemia: causes, neurological manifestations and outcome. Ann Neurol 1985; 17:421. 18. Comi RJ, Gorden P, Doppman JL. Insulinoma. In: Go VL, Di Magno E, Gardner J, et al, eds. The pancreas: biology, pathobiology and diseases. New York: Raven Press, 1993:979. 19. Hampton SM, Beyzavi K, Teale D, Marks V. A direct assay for proinsulin in plasma and its applications in hypoglycemia. Clin Endocrinol 1988;29:9. 20. Doherty GM, Doppman JL, Shawker TH, et al. Results of a prospective strategy to diagnose, localize and resect insulinoma. Surgery 1991; 110:989. 21. McMahon MM, O'Brien PC, Service FJ. Diagnostic interpretation of the intravenous tolbutamide test for insulinoma. Mayo Clin Proc 1989; 64:1481. 22. Service FJ, O Brien PC, Yao OP, Young WF. C peptide stimulation test: effects of gender, age, and body mass index; implications for the diagnosis of insu¬ linoma. J Clin Endocrinol Metab 1992; 74:204. 23. Fong T-L, Warner NE, Kumar D. Pancreatic nesidioblastosis in adults. Diabetes Care 1989; 12:108. 24. Norton JA, Doherty GM, Fraker DL. Surgery for endocrine tumors of the pancreas. In: Go VL, Di Magno E, Gardner J, et al, eds. The pancreas: biology, pathobiology and diseases. New York: Raven Press, 1993:997. 25. Berger M, Bordi C, Cuppers HJ, et al. Functional and morphological char¬ acterization of human insulinomas. Diabetes 1983; 32:921. 26. Kvols LK, Buck M, Moertel CG, et al. Treatment of metastatic islet cell carcinoma with a somatostatin analogue SMS-201-995. Ann Intern Med 1987-107162. 27. Moore TJ, Peterson LM, Harrington DP, Smith RJ. Successful arterial em¬ bolization of an insulinoma. JAMA 1982;248:1353. 28. Ron D, Powers AC, Pandian MR, et al. Increased insulin-like growth fac¬ tor II production and consequent suppression of growth hormone secretion: a dual mechanism for tumor-induced hypoglycemia. J Clin Endocrinol Metab 1989 68701. 29. Zapf J, Schmid C, Guler WP, et al. Regulation of binding proteins for insulin like growth factors in humans. Increased expression of IGF binding proteins during IGF-1 treatment of healthy adults and in patients with extrapancreatic tumor hypoglycemia. J Clin Invest 1990; 86:952. 30. Grunberger G, Weiner JL, Silverman R, et al. Factitious hypoglycemia due to surreptitious administration of insulin: diagnosis, treatment, and long-term follow-up. Ann Intern Med 1988; 108:252. 31 Klein RF, Seino S, Sanz N, et al. High performance liquid chromatography used to distinguish the autoimmune hypoglycemia syndrome from factitious hypo¬ glycemia. J Clin Endocrinol Metab 1985;61:571. 32. Taylor SI, Barbetti F, Accili D, et al. Syndromes of autoimmunity and hypoglycemia. Autoantibodies directed against insulin and its receptor. Endocrinol Metab Clin North Am 1989; 18:123. 33. Ichihara K, Shima K, Sarto Y, et al. Mechanism of hypoglycemia observed in a patient with insulin autoimmune syndrome. Diabetes 1977;26:500. 34. Benson EA, Ho P, Wang C, et al. Insulin autoimmunity as a source of hypoglycemia. Arch Intern Med 1984; 144:2351. 35. Felig P, Brown WV, Levine RA, Klatskin G. Glucose homeostasis in viral hepatitis. N Engl J Med 1970;283:1436. 36. Greene HL, Ghishan FK, Brown B, et al. Hypoglycemia in type IV glycogenesis: hepatic improvement in two patients with nutritional management J Pediatr 1988; 112:55. 37. Seltzer H. Drug induced hypoglycemia. Endocrinol Metab Clin North Am 1989,18:163.

1. Wfnpple AO. The surgical therapy of hyperinsulinism. J Int Chir 1938'3‘

38. Kreisberg RA, Siegel AM, Owen CW. Glucose-lactate interrelationship: effect of ethanol. J Clin Invest 1971; 50:175.

2. Service FJ. Hypoglycemic disorders. Boston: GK Hall Medical Publishers,

39. Wajchenberg BL, Pereira VG, Pupo AA, et al. On the mechanism of insulin hypersensitivity in adrenocortical deficiency. Diabetes 1964; 13:169.

237. 1983. 3. Marks V. Recognition and differential diagnosis of spontaneous hypoglycaemia. Clin Endocrinol 1992; 37:309.

40. Hochberg Z, Hardoff D, Atias D, Spindel A. Isolated ACTH deficiency with transitory GH deficiency. J Endocrinol Invest 1985;8:67.

Ch. 153: Localization of Islet Cell Tumors 41. Lev Ran A, Anderson RW. The diagnosis of postprandial hypoglycemia. Diabetes 1981;30:996. 42. Palardy J, Havrankova J, Lepage R, et al. Blood glucose measurements during symptomatic episodes in patients with suspected postprandial hypoglyce¬ mia. N Engl J Med 1989; 321:1421. 42a. Andreasen JJ, Orskov C, Holet JJ. Secretion of glucagon-like peptide-1 and reactive hypoglycemia after partial gastrectomy. Digestion 1994;55:221. 42b. Sweeney BJ, Edgecombe J, Churchill DR, et al. Choreo-athethosis/bullismus associated with pentamidine-induced hypoglycemia in a patient with the acquired immunodeficiency syndrome. Arch Neurol 1994;51:723. 43. McTague JA, Forney R Jr. Jamaican vomiting sickness in Toledo, Ohio. Ann Emerg Med 1994:23:116. 44. Felig P, Cherif A, Minagawa A, et al. Hypoglycemia during prolonged exercise in normal men. N Engl J Med 1982; 306:895. 45. Garber AJ, Bier DM, Cryer PE, Pagliara AS. Hypoglycemia in compen¬ sated chronic renal insufficiency: substrate limitation of gJuconeogenesis. Diabetes 1974;23:982.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

153_

LOCALIZATION OF ISLET CELL TUMORS DONALD L. MILLER AND JOHN L. DOPPMAN

About one third of all islet cell tumors are clinically silent (nonfunctioning) and of little interest to the endocrinologist. Lo¬ calization of these tumors is trivial because they are virtually al¬ ways large at presentation. In general, this is also true of the less common functioning islet cell tumors, including glucagonomas, VIPomas, and the rarer functioning tumors.1 Unfortunately for the clinician, insulinomas and gastrinomas, which are much more common than all other functioning islet cell tumors com¬ bined, are also much smaller at presentation. Patients with these lesions present the endocrinologist, radiologist, and surgeon with the challenging problem of tumor localization, an essential pre¬ requisite to effective surgical therapy.2,3 It is essential to distinguish between the diagnosis and the localization of islet cell tumors.4 The diagnosis of an insulinoma or gastrinoma does not depend on the radiologic demonstration of a tumor. Islet cell tumors are named according to the predom¬ inant hormone they elaborate, but they are indistinguishable in appearance on all available imaging studies. For this reason, demonstration of a tumor on an imaging study cannot confirm the diagnosis. Localization efforts should not begin until an endocrine di¬ agnosis has been established. Attempts at localization in the ab¬ sence of a firm diagnosis may confuse matters if imaging proce¬ dures yield false-positive or equivocal results. Furthermore, the failure to locate a tumor does not mean that the diagnosis is in¬ correct. The tumor may be too small to image. The cardinal rule of endocrine radiology is diagnosis first; localization second.

1351

Broadly speaking, the available imaging modalities may be classified as noninvasive or invasive. Individual modalities are dis¬ cussed in the following sections.

NONINVASIVE STUDIES ULTRASOUND AND ENDOSCOPIC ULTRASOUND

The standard abdominal ultrasound is most helpful when the patient is thin and the tumor is large. Anatomic factors and the presence of gas in overlying bowel usually prevent examina¬ tion of the entire pancreas. The sensitivity is only 25% to 30% in most series.1,2,5,6 Endoscopic ultrasound, performed with a spe¬ cial endoscope containing an ultrasound transducer at its tip, al¬ lows the placement of the transducer closer to the pancreas. In turn, this permits the use of higher frequency transducers, typi¬ cally 7.5 or 12 MFIz, resulting in greater spatial resolution and improved sensitivity compared with standard abdominal ultra¬ sound.7 In a series of 37 patients with 39 islet cell tumors, none of which had been detected with standard ultrasound or computed tomography (CT), endoscopic ultrasound enabled the localiza¬ tion of 32 tumors (82% sensitivity) with no incorrect localiza¬ tions.8 However, this technique seems to be most sensitive for the detection of tumors in the pancreatic head and body, and less sensitive for the detection of tumors in the pancreatic tail, the duodenum, and other extrapancreatic locations.9 On ultrasound examinations, islet cell tumors are well de¬ fined, smoothly marginated, round or oval lesions that are usu¬ ally hypoechoic compared with the surrounding pancreas. They may have a thin hyperechoic rim. The appearance is the same on all types of ultrasound examinations, including standard abdom¬ inal ultrasound, endoscopic ultrasound, and intraoperative ultra¬ sound (discussed later)1-7 (Fig. 153-1). COMPUTED TOMOGRAPHY

Small islet cell tumors are difficult to identify on CT. These tumors are seen as well defined, round or oval, enhancing masses (Fig. 153-2A). The degree of enhancement is variable. The tumor may be 10 Hounsfield units (HU) to 30 HU more dense than the surrounding pancreas, but it may also be nearly isodense, and a contour abnormality may be the only CT indication of the tu¬ mor.1 Rare cases of nonenhancing small islet cell tumors have been reported.1 According to published series, CT has a sensitivity of 30% to 60% for the detection of primary gastrinomas, 11% to 73% for the detection of primary insulinomas, and approximately 50%

IMAGING MODALITIES FOR ISLET CELL TUMOR LOCALIZATION A number of imaging studies are available to the endocrine radiologist for localizing an islet cell tumor. The number of stud¬ ies in use clearly indicates that no one imaging modality is suffi¬ ciently sensitive or specific to be relied on by itself. It is almost always necessary to use a combination of these techniques in a patient with an insulinoma or gastrinoma.

FIGURE 153-1.

Intraoperative ultrasound of the pancreatic head in the transverse plane. The insulinoma is a 10 X 16 mm sonolucent mass (ar¬ rows) adjacent to the superior mesenteric vein. The tumor was success¬ fully enucleated.

1352

PART IX: DISORDERS OF FUEL METABOLISM

FIGURE 153-2. A, This 45-year-old man has a 12-mm in¬ sulinoma (large arrow) adjacent to the tail of the pancreas. The pseudocyst (small arrows) along the anterior margin of the pancreatic body resulted from a previous unsuccessful operation. B, Magnetic resonance imaging, using the STIR sequence, shows the insulinoma as a nodule of high signal intensity in the pancreatic tail (large arrow). The pseudocyst is also seen as a very bright collection of fluid along the anterior margin of the pancreatic body (small arrows).

for the localization of all small islet cell tumors.1 However, as endocrine diagnostic methods improve, patients present with ever smaller tumors, and CT sensitivity has decreased. The Na¬ tional Institutes of Health (NIH) experience is that less than 30% of these tumors are detected by CT.610 Similar results have been reported by others.7 MAGNETIC RESONANCE IMAGING

Magnetic resonance imaging (MRI) is not ideal for the exam¬ ination of the pancreas because long scanning times, peristalsis, and respiratory and cardiac motion induce significant noise in images of the upper abdomen, and fluid-filled loops of bowel create difficulties in interpretation. MRI of the pancreas is a sub¬ ject of active investigation; there is no consensus as to the best pulse sequences or the value of intravenous contrast material ad¬ ministration. There is evidence that fat-suppression pulsesequences aid in evaluation of the pancreas.611-12 The NIH expe¬ rience is that gadolinium paramagnetic contrast agents have not been helpful for the detection of pancreatic islet cell tumors,6 but other centers have found otherwise.11 Islet cell tumors demon¬ strate high signal intensity on T2-weighted images and short ^ inversion recovery (STIR) fat suppression images613 (see Fig. 153-2B).

SOMATOSTATIN RECEPTOR IMAGING

Many endocrine tumors, including most islet cell tumors, contain somatostatin receptors.14 Administration of a radiola¬ beled form of a somatostatin analogue permits scintigraphic de¬ tection of some of these tumors.1415 Scintigraphy with these agents is also potentially useful for predicting the likelihood of response to octreotide therapy, and the radiolabeled analogues may prove to be useful for directed internal radiation therapy for these tumors.16 Unfortunately, gastrinomas and insulinomas may be so small and located so deep within the abdomen that they may not be detectable in this manner with any reasonable degree of sensitivity. Furthermore, the spatial resolution of scin¬ tigraphy is so low that exact anatomic localization is difficult to achieve with this modality alone.

INVASIVE PROCEDURES ANGIOGRAPHY

Despite the proliferation of high-technology noninvasive lo¬ calization procedures, angiography remains a mainstay in the search for islet cell tumors.1'2,4,6 Pancreatic arteriography for islet cell tumor localization should include selective arteriography of the proper or common hepatic artery (and any accessory hepatic

Ch. 153: Localization of Islet Cell Tumors arteries), the gastroduodenal artery, the splenic artery, the supe¬ rior mesenteric artery, and, if possible, the dorsal pancreatic artery.1,4 On arteriograms, small islet cell tumors appear as rounded or oval, well-marginated lesions with smooth borders and homo¬ geneous intense staining that persists into the late arterial and capillary phases (Fig. 153-3). The stain results from the filling of vessels that are too small to be individually resolved, so neovas¬ cularity and discrete vessels are not seen within the tumor.1 Hy¬ po vascular islet cell tumors exist but are rare.4 Angiography permits the detection of primary islet cell tu¬ mors as small as 5 mm, versus at least 7 mm for CT and ultra¬ sound.17 Overall, in published studies,1 angiography has a sensi¬ tivity of about 65% for the detection of primary islet cell tumors, with false-positive rates of 3% to 9%. At the NIH, angiography has had a sensitivity rate of about 50%.6,10

1353

ultrasound, intraoperative ultrasound permits the transducer to be placed close to the area of interest. There is no intervening gas or bone to impede sound transmission, and the spatial resolution is much higher than that achievable with conventional ultra¬ sound (see Fig. 153-1 and Chap. 154). For insulinomas, which are almost always within the pan¬ creas, the reported sensitivity rate of intraoperative ultrasound ranges from 75% to 100%, and is probably about 90%, with false-positive results being relatively uncommon.1,23 In studies in which intraoperative ultrasound has been compared with other modalities, it is invariably superior to all of them.1 Because of the difficulty of detecting extrapancreatic primary lesions, intraoper¬ ative ultrasound is less effective for the localization of gastrino¬ mas, and has a lower sensitivity and a higher false-positive rate for the localization of these lesions.23

SCREENING FOR METASTASES ARTERIAL STIMULATION AND VENOUS SAMPLING

A relatively new technique, arterial stimulation and venous sampling, was introduced for the localization of gastrinomas18 and refined for the localization of both gastrinomas and insulino¬ mas.19,20 During angiography, a secretagogue is injected into one of the arteries that supplies the pancreas and liver (secretin is used to stimulate gastrinomas, and calcium is used to stimulate insulinomas). Venous blood samples are obtained from a catheter placed in a hepatic vein. These samples reflect the hormone con¬ centration in portal venous blood, and can be obtained without the need for portal vein puncture and catheterization. The pro¬ cess is then repeated for each of the other arteries supplying the pancreas and liver. The hepatic vein samples are assayed for either gastrin or insulin, as appropriate. An increase of 100% in hormone concen¬ tration over baseline levels permits a localization to the arterial territory supplied by the injected artery.4 In this manner, the tu¬ mor can be localized to the head or tail of the pancreas, and liver metastases may be demonstrated.21,22 In the authors' practice, ar¬ terial stimulation and venous sampling has completely replaced portal venous sampling for the localization of gastrinomas and insulinomas4,21,22 (Fig. 153-4). INTRAOPERATIVE ULTRASOUND

Intraoperative ultrasound has shown the most promise of any modality introduced in the last 10 years. As with endoscopic

Malignant islet cell tumors metastasize to peripancreatic lymph nodes and to the liver. The spread to local-regional nodes is not considered a contraindication to attempts at curative sur¬ gery.16 All of the cross-sectional imaging techniques (ultrasound, CT, MRI) are effective for evaluation of the liver.1613 MRI has challenged the preeminence of angiography, which had been considered the most sensitive technique for the detection of he¬ patic metastases for these tumors.1,4,6,10 Contrary to previous teaching, it seems that hypervascular hepatic metastases, such as those from islet cell tumors, can be adequately visualized on CT scans with the bolus intravenous administration of iodinated contrast material. Unenhanced CT scans probably are not neces¬ sary.24,25 Somatostatin-receptor imaging has been advocated for screening the entire body for metastatic disease but requires fur¬ ther study.16

THE RADIOLOGIC APPROACH TO ISLET CELL TUMOR LOCALIZATION The localization of an insulinoma or gastrinoma commonly requires a number of procedures. The most invasive, expensive, and technically demanding studies are used last. The choice and sequence of procedures is dependent, in part, on the particular areas of expertise of the radiologists performing and interpreting the studies. For most modalities, and, particularly for ultrasound and invasive vascular procedures, the adequate performance of

FIGURE 153-3. A, The selective injection of the gastroduodenal artery demonstrates a 1-cm area of staining (arrows) in the head of the pancreas. B, A MRI, using the STIR sequence, shows the same 1-cm insulinoma as a focus of high signal intensity in the posterior portion of the pancreatic head (arrows).

1354

PART IX: DISORDERS OF FUEL METABOLISM

INSULIN (uU/mL)

cation of variant arterial anatomy in the area of the pancreas and liver.4,6,10 Angiography should be combined with arterial stimu¬ lation and venous sampling. Although it does not image lesions and can only indicate in which arterial territory a primary lesion may be found, it is not dependent on tumor size for detection. It is, therefore, potentially more sensitive for tiny lesions than any other modality, with the possible exception of octreotide receptor imaging. Finally, intraoperative ultrasound must be available during surgical exploration. It is more helpful for the localization of in¬ sulinomas than for gastrinomas, but in either situation it is a valu¬ able adjunct to the surgeon's palpating finger.

REFERENCES INSULIN (yU/ml)

FIGURE 153-4.

Two typical examples of the results of arterial stimula¬ tion and venous sampling for the localization of insulinomas. A, There is a brisk rise in insulin from right hepatic vein samples after the injection of calcium into the gastroduodenal artery. The insulin levels were not affected by similar calcium injection into the superior mesenteric and splenic arteries. This result localizes the tumor in the pancreatic head. The arteriography result was negative, and an 8-mm tumor was resected using intraoperative ultrasound from deep within the head of the pan¬ creas. B, The elevation of insulin levels follows the injection of calcium into the splenic vein. In this patient, the arteriography result also was negative. A 13-mm tumor was removed from the distal pancreas.

the procedure is highly operator dependent. Unless a skilled ra¬ diologist is available, a recommended procedure may not be worth doing. Regardless of the specific islet cell tumor being sought, the sequence of possible studies is often the same, although the effectiveness of each technique may vary with tumor type. Insu¬ linomas, which are solitary (92%), intrapancreatic (99.5%), and tend to be distributed uniformly throughout the pancreas, are more easily located than are gastrinomas, 80% of which are multifocal and 30% of which are located outside the pan¬ creas.1,10 26,27 The localization of insulinomas is of greater impor¬ tance clinically because there is no effective medical therapy for hyperinsulinism. Among the cross-sectional imaging methods, there is little to recommend ultrasound, CT, or MRI as the best choice for initial imaging. At least one should be done to evaluate the liver and to search for an obvious pancreatic lesion, and a case can easily be made for performing two, or even all three studies, on the grounds that they are complementary. In experienced hands, en¬ doscopic ultrasound also may be extremely helpful for the detec¬ tion of a small pancreatic primary. The authors believe that arteriography should always be performed. It is capable of imaging small pancreatic and extrapancreatic primary lesions; it is an extremely sensitive test for the detection of hepatic metastases, and it also permits the identifi¬

1. Miller DL. Islet cell tumors of the pancreas: diagnosis and localization. In: Freeny PC, Stevenson GW, eds. Margulis and Burhenne's alimentary tract radiol¬ ogy, ed 5. Hanover: CV Mosby, 1994:1167. 2. Fedorak I], Ko TC, Gordon D, et al. Localization of islet cell tumors of the pancreas: a review of current techniques. Surgery 1993; 113:242. 3. Thompson GB, Service F], van Heerden JA, et al. Reoperative insulinomas, 1927 to 1992: an institutional experience. Surgery 1993;114:1196. 4. Miller DL. Endocrine angiography and venous sampling. Radiol Clin North Am 1993; 31:1051. 5. Doherty GM, Doppman JL, Shawker TH, et al. Results of a prospective strategy to diagnose, localize, and resect insulinomas. Surgery 1991; 110:989. 6. Pisegna JR, Doppman JL, Norton JA, et al. Prospective comparative study of ability of MR imaging and other imaging modalities to localize tumors in patients with Zollinger-Ellison syndrome. Digest Dis Sci 1993; 38:1318. 7. Palazzo L, Roseau G, Salmeron M. Endoscopic ultrasonography in the pre¬ operative localization of pancreatic endocrine tumors. Endoscopy 1992;24(Suppl 1):350. 8. Riisch T, Lightdale OJ, Botet JF, et al. Localization of pancreatic endocrine tumors by endoscopic ultrasonography. N Engl J Med 1992;326:1721. 9. Doppman JL. Pancreatic endocrine tumors: the search goes on. (Editorial) N Engl J Med 1992;326:1770. 10. Doppman JL, Shawker TH, Miller DL. Localization of islet cell tumors. Gastroenterol Clin North Am 1989; 18:793. 11. Semelka RC, Cumming MJ, Shoenut JP, et al. Islet cell tumors: comparison of dynamic contrast-enhanced CT and MR imaging with dynamic gadolinium en¬ hancement and fat suppression. Radiology 1993; 186:799. 12. Semelka RC, Simm FC, Recht MP, et al. MR imaging of the pancreas at high field strength: comparison of six sequences. J Comput Assist Tomogr 1991; 15: 966. 13. Carson BC, Johnson CD, Stephens DH, et al. MRI of pancreatic islet cell carcinoma. J Comput Assist Tomogr 1993; 17:735. 14. Krenning EP, Kwekkeboom DJ, Bakker WAP, et al. Somatostatin receptor imaging with ["’In-DTPA-D-Phe1]- and [I23I-Tyr3]-octreotide: the Rotterdam expe¬ rience with more than 1000 patients. EurJ Nucl Med 1993;20:716. 15. Ur E, Bomanji J, Mather SJ, et al. Localization of neuroendocrine tumours and insulinomas using radiolabelled somatostatin analogues, 123]-Tyr3-octreotide and ulln-pentatreotide. Clin Endocrinol (Oxf) 1993;38:501. 16. Kvols LK. Somatostatin-receptor imaging of human malignancies: a new era in the localization, staging, and treatment of tumors. Gastroenterology 1993,105:1909. 17. Gunther RW, Klose KJ, Riickert K, et al. Localization of small islet cell tumors: preoperative and intraoperative ultrasound, computed tomography, arteri¬ ography, digital subtraction angiography, and pancreatic venous sampling. Gastrointest Radiol 1985,10:145. 18. Imamura M, Takahashi K, Adachi H, et al. Usefulness of selective arterial secretin injection test for localization of gastrinoma in the Zollinger-Ellison syn¬ drome. Ann Surg 1987;205:230. 19. Doppman JL, Miller DL, Chang R, et al. Gastrinomas: localization by means of selective intraarterial injection of secretin. Radiology 1990; 174:25. 20. Doppman JL, Miller DL, Chang R, et al. Insulinomas: localization with selective intraarterial injection of calcium. Radiology 1991; 178:237. 21. Thom AK, Norton JA, Doppman JL, et al. Prospective study of the use of intraarterial secretin injection and portal venous sampling to localize duodenal gastrinomas. Surgery 1992; 112:1002. 22. Doppman JL, Miller DL, Chang R, et al. Intraarterial calcium stimulation test for detection of insulinomas. World J Surg 1993; 17:439. 23. Norton JA, Cromack DT, Shawker TH, et al. Intraoperative ultrasono¬ graphic localization of islet cell tumors: a prospective comparison to palpation. Ann Surg 1988;207:160. 24. Chomyn JJ, Stamm ER, Thickman D. CT of melanoma liver metastases: is the examination without contrast media superfluous? J Comput Assist Tomogr 1992; 16:568. 25. Patten RM, Byun J-Y, Freeny PC. CT of hypervascular hepatic tumors: are unenhanced scans necessary for diagnosis? AJR 1993; 161:979. 26. Rothmund M, Angelini L, Brunt LM, et al. Surgery for benign insulinoma: an international review. World J Surg 1990; 14:393. 27. Pipeleers-Marichal M, Somers G, Willems G, et al. Gastrinomas in the duodenum of patients with multiple endocrine neoplasia type 1 and the ZollingerEllison syndrome. N Engl J Med 1990; 322:723.

Ch. 154: Surgery of the Endocrine Pancreas Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

154_

SURGERY OF THE ENDOCRINE PANCREAS

[CRH], parathyroid hormone-related protein [PTHrP], growth hormone releasing hormone [GHRH]). Others are not associated with any known syndromes, but may have important roles as markers of the presence or the clinical progress of the tumors (e.g., pancreatic polypeptide, neurotensin, calcitonin, a-human chorionic gonadotropin3"8). The neoplasms associated with the most clinically relevant hormones are considered in the next section.

JON C. WHITE AND JOHN W. HARMON

FUNCTIONAL ISLET CELL TUMORS

Surgery for tumors of the pancreas often is considered futile because of the predominance of exocrine tumors of this organ, which usually are malignant, often are unresectable, and rarely are curable.1 However, endocrine tumors of the pancreas are en¬ countered less commonly than are exocrine tumors, and are more amenable to surgical treatment. About 50% of pancreatic endo¬ crine tumors are reported to be benign;2 this figure varies be¬ tween series, however, because there are no histologic features that distinguish benign from malignant lesions. Malignancy is determined by the presence of distant metastases or local tumor invasion.3 Benign tumors can be resected and cured, and even malignant endocrine tumors that induce clinical syndromes can be detected early, allowing for timely surgical intervention that can result in significant palliation or even curative resection. The first successful resection of an insulinoma took place in 1929, although the insulinoma syndrome was not described by Whipple until 1935. Since then, many different islet cell tumors and syndromes have been recognized, including gastrinomas, vi¬ pomas, glucagonomas, somatostatinomas, and other lesions that produce a variety of humoral products, such as pancreatic poly¬ peptide, adrenocorticotropic hormone (ACTH), parathyroid hormone-related protein, and serotonin. Clinically, these tumors are differentiated by the syndromes they induce or the biochem¬ ical profiles they produce. The surgical approach to each of these pancreatic endocrine neoplasms varies according to the end-organs it affects, its ma¬ lignant potential, its solitary or multiple nature, and the ease with which it can be localized (Tables 154-1 and 154-2). The surgical procedures used to cure or palliate pancreatic endocrine tumors are more varied than are those used for pancreatic exocrine tumors. As many as 19 different gastroenteropancreatic neuroendo¬ crine cells have been identified that elaborate up to 40 different humoral products.4 Some of these humoral products are associ¬ ated with clinical endocrine manifestations (e.g., insulin, gastrin, glucagon, somatostatin, ACTH, corticotropin releasing hormone

INSULINOMA Insulinomas are the most common functional islet cell tu¬ mors. Most are solitary and benign (75%), but a few are malig¬ nant (10% to 15%) or multifocal (10% to 15%).9 These tumors may be extremely small or they may present as hyperplasia. Be¬ cause of variability in their size and appearance, they can be difficult to localize. Despite the fact that most of these lesions are benign, the hyperinsulinemia they cause can be dangerous and complete resection or maximal cytoreduction usually is necessary (see Chap. 152). Localization of insulinomas, which can be accomplished with computed tomography (CT), magnetic resonance imaging (MRI), mesenteric angiography, or portal venous sampling, should be attempted before operation. CT and angiography usu¬ ally are done first and are most useful in detecting larger lesions (see Chap. 153).10,11 Although these techniques are relatively specific, they are not very sensitive. Their accuracy generally is reported to be about 80%. If a tumor cannot be identified with CT or angiography, either sampling of the mesenteric vein or in¬ jection of the mesenteric artery with calcium to stimulate insulin secretion may localize the neoplasm to a particular region. Radiolabeled octreotide12 and provocative angiographic studies using calcium stimulation13 also have been used to improve the accu¬ racy of preoperative localization. Some surgeons believe that extensive preoperative localiza¬ tion is neither indicated nor cost-effective.14 They contend that intraoperative localization has a greater sensitivity,15 and they report that intraoperative ultrasound, endoscopic transillumina¬ tion, and palpation are more sensitive than preoperative tech¬ niques and can differentiate between benign and malignant le¬ sions.16 When all attempts to localize a tumor at surgery are unsuccessful, some surgeons perform a blind distal pancreatec¬ tomy in the hope of excising an occult tumor. If the hyperinsulin¬ emia is responsive to diazoxide, another approach is to perform a biopsy of the pancreas to rule out hyperplasia and then to insti-

TABLE 154-1 Characteristics of Functional Pancreatic Endocrine Tumors Tumors

Rate of Malignancy (%)

Incidence

Associated Clinical Syndrome Hypoglycemia and hyperinsulinemia Zollinger-Ellison syndrome Dermatitis, diabetes, anemia, deep venous thrombosis Watery diarrhea, hypokalemia, achlorhydria Cholelithiasis, diabetes, steatorrhea ACTH, CRH; Cushing syndrome; GHRH: acromegaly; PTHrP: hypercalcemia

Insulinoma Gastrinoma Glucagonoma

1079 60-7079 60-7079

1.0 MPY23 0.1-0.4 MPY23 0.06 MPY80

Vipoma

60-7079

0.13 MPY80

Somatostatinoma Miscellaneous ACTH CRH GHRH PTHrP

9079 Insufficient data

1355

< 0.06 MPY80 Rare

MPY, per million population per year; ACTH, adrenocorticotropic hormone; CRH, corticotropin releasing hormone; GHRH, growth hormone releasing hormone; PTHrP, parathyroid hormone-related protein.

1356

PART IX: DISORDERS OF FUEL METABOLISM

TABLE 154-2 Surgical Aspects of Pancreatic Endocrine Tumors Type

Size

Location

Surgical Approach

Insulinoma

Often small, but can be large11

Distributed throughout pancreas11

Preoperative and intraoperative localization can be challenging. Resection of benign or malignant disease should be aggressive. When hyperplasia or occult tumors cause significant symptoms, a subtotal pancreatectomy may be required. The objective of surgery should be to extirpate the neoplasm completely or to control the hyperinsulinemia.

Gastrinoma

Often small, but can be large

Pancreatic head, duodenum28

Tumors usually are found in the "gastrinoma triangle" but can be difficult to locate. Symptoms can be controlled with medical or surgical treatment of the end-organ (stomach), but resection of tumor can improve long-term survival and sometimes is curative.

Glucagonoma

Large11

Pancreatic body and tail47

Glucagonomas usually are found in the body and tail of the pancreas, making distal pancreatectomy the most commonly performed resection. Most tumors are large when first seen and are not amenable to curative resection, but may be debulked.

Vipoma

Large50

75% pancreatic body and tail,50 retroperitoneum, adrenal, lung

Vipomas usually are found in the body and tail of the pancreas but may be found in other pancreatic and extrapancreatic locations, making localization important. Pancreatic tumors in the body and tail may be resected by distal pancreatectomy.

Somatostatinoma

Small to large

Pancreatic head and tail, duodenum

Somatostatinomas produce a mild and nonspecific clinical syndrome and often are found incidentally during routine surgical exploration. Tumors are distributed throughout the pancreas and duodenum. Despite the mild symptomatology of the syndrome, an aggressive surgical approach to pancreatic and extrapancreatic tumors is warranted.

Often small, but can be large

Variable

Surgical ablation of these tumors results in regression of the associated humoral syndromes and should be considered the primary treatment modality.

Large71

Pancreatic head71

Nonfunctional tumors are detected late, when mass effects from large tumors cause symptoms. When they can be extirpated completely, resection is indicated. Debulking is controversial.

FUNCTIONAL TUMORS

MISCELLANEOUS TUMORS ACTH, CRH, GHRH, PTHrP

NONFUNCTIONAL TUMORS

ACTH, adrenocorticotropic hormone; CRH, corticotropin releasing hormone; GHRH, growth hormone releasing hor¬ mone; PTHrP, parathyroid hormone-related protein.

tute medical therapy.17 On occasion, patients can be maintained on diazoxide until their tumors grow to a detectable size and can be localized and resected. Tumors can be excised at a second or third exploration, although operative complications are more common in subsequent procedures.18 In such cases, if diazoxide was ineffective before surgery, an 80% pancreatectomy may be required to control the hyperinsulinemia.17 If the insulinoma has been localized and is small and benign, enucleation or local excision is the preferred approach. If the tu¬ mor is large or malignant, a formal pancreatic resection, including pancreaticoduodenectomy,19 or tumor debulking may be needed to resect the tumor completely and control the hyperinsulinemia. Although enucleation is appealing because of the greater conser¬ vation of pancreatic tissue, the incidence of pancreatic fistula is higher than after pancreatectomy.20 The results of surgery with all procedures tend to be excellent, with 70% to 90% of patients experiencing relief of symptoms or complete cure. When the surgical localization or extirpation of an insu¬ linoma is not possible, streptozocin, especially in combination with 5-fluorouracil, can be administered to destroy the B cells.9 There also is evidence that the somatostatin analogue, octreotide, may effectively suppress insulin release and reduce the morbidity and mortality of the persistent hyperinsulinemia (see Chap. 166).21 Although this drug has been less effective for treating in¬ sulinomas than for treating other pancreatic tumors, a therapeu¬ tic trial is warranted.22 Most cases of insulinoma are nonfamilial and sporadic, but 10% are associated with the multiple endocrine neoplasia type I

(MEN-I) syndrome (see Chap. 182). Patients with insulinoma and MEN-1 often have multiple pancreatic tumors. Conse¬ quently, surgical extirpation is not as effective in these patients as it is in patients with sporadic tumors. The primary objective of surgery in patients with hyperinsulinemia and MEN-I is to resect the primary tumor, which is likely to be secreting most of the insulin.23 Hyperinsulinemia can be controlled using this ap¬ proach, but these patients must be observed carefully for recur¬ rent disease.

GASTRINOMA Gastrinomas are a type of ectopic islet cell tumor,24 and are the most common malignant functional endocrine tumors of the pancreas (see Chap. 176). Although 60% of gastrinomas are ma¬ lignant, long-term survival can be achieved by resection or by appropriate treatment of the end-organ symptomatology. Islet cell tumors are present in 65% to 80% of patients with the MENI syndrome, and gastrinoma is the most common type.25 When gastrinomas occur in MEN-I, the pancreatic tumors always are multiple and are not amenable to surgical resection. There has never been a case report of MEN-I in which the local resection of a tumor has normalized serum gastrin levels, although there have been reports of aggressive subtotal resection providing symp¬ tomatic relief.26 Gastrinoma is most noted for its endocrine effects. It was in 1955 that Zollinger and Ellison27 described two patients with ul¬ cers in the jejunum and outlined a syndrome in which pancreatic

Ch. 154: Surgery of the Endocrine Pancreas tumors were associated with aggressive peptic ulcer disease. Be¬ cause Zollinger-Ellison syndrome is being recognized and diag¬ nosed earlier, the associated ulcers often are less virulent, and tend to be routine ulcers of the duodenum. The presence of gas¬ trinoma is suggested by a serum gastrin level greater than 500 pg/mL, and a secretin test is used to confirm the diagnosis. Both gastrinomas and insulinomas differ from other pancre¬ atic endocrine tumors in that they often are small and difficult to localize. Insulinomas are distributed equally throughout the pancreas, but most gastrinomas are found in the gastrinoma tri¬ angle, which is bordered by the cystic and common bile ducts superiorly, the junction of the second and third portions of the duodenum inferiorly, and the junction of the neck and body of the pancreas medially.28 Most intraabdominal gastrinomas also are found in the right side of the abdomen.29 A smaller number are found to the left of the superior mesenteric artery. Tumors in different locations do not exhibit the same biologic behavior, suggesting that they may have different etiologies.30 CT, MRI, sonography, arteriography, and percutaneous transhepatic ve¬ nous sampling are used for preoperative localization of gas¬ trinoma in the same manner as for insulinoma. Secretin is the agent used to stimulate gastrin secretion during provocative angiography.31 Although most gastrinomas can be localized before surgery using these techniques, intraoperative exploration may be the most direct and sensitive means of detecting occult tumors.2 These neoplasms are being found increasingly often in the duo¬ denum, and occasionally can be located by preoperative duode¬ nal endoscopy, intraoperative endoscopy with transillumination, or intraoperative duodenotomy with exploration.32 Duodenal tu¬ mors are located most often in the proximal duodenum just distal to the pylorus.23 Small duodenal tumors also can be located with the help of intraarterial methylene blue after preoperative angio¬ graphic regional localization with secretin.33 Despite the variety of preoperative and intraoperative techniques available for local¬ izing these tumors, many are never located or successfully re¬ sected. Often, metastases are discovered in lymph nodes but the primary tumor cannot be found. If preoperative localization is successful and resection is fea¬ sible, as much of the gastrinoma should be removed as possi¬ ble.34,35 This can involve enucleation, formal resection, or tumor debulking. Pancreaticoduodenectomy may be required for both duodenal and pancreatic tumors.36 If the tumor cannot be local¬ ized or resected, significant palliation can be achieved by treating the ulcer disease medically with H2-receptor blockers or H+-K+ proton pump inhibitors. Gastrectomy has been performed for Zollinger-Ellison syndrome to control ulcer symptoms, and va¬ gotomy has been used to reduce medication requirements, with mixed results.37 These procedures have played a smaller role since effective medications to inhibit acid secretion have become available. Patients with malignant tumors treated either medi¬ cally or with ulcer operations ultimately succumb to metastatic disease. The complete resection of all grossly evident tumor seems to provide the greatest long-term survival38 and should be the primary surgical goal in all patients without metastatic dis¬ ease or with the MEN-I syndrome. Surgical exploration not only provides the only chance for cure, but also is helpful in iden¬ tifying prognostic features associated with long-term survival, such as small tumor size, an extrapancreatic primary tumor, and the absence of tumor metastases.39 Formerly, it was believed that the removal of metastatic lymph nodes in addition to gastrectomy resulted in regression of the primary tumor in some patients with gastrinoma. It now seems more likely that most of these apparent "regressions” re¬ sulted from the serendipitous removal of small duodenal tumors during gastrectomy,40 and there is little support for the concept of gastrinoma regression. All patients should receive long-term postoperative follow¬ up because recurrent disease can present many years after appar¬ ently curative resection. Calcium or secretin provocative tests

1357

may be helpful for detecting recurrent disease early or for pre¬ dicting whether a patient will remain free of symptoms.41 Even after apparently curative resection, some patients with gas¬ trinoma retain a slightly hypersecretory state and require low doses of antisecretory drugs.*2 When resection of a gastrinoma is not possible or the tumor cannot be found at surgical exploration, streptozocin and 5fluorouracil can be used for palliation, as they are in insulinoma. H2-receptors or H+-K+ proton pump blockers can be used to con¬ trol the ulcer disease. Octreotide reduces symptoms of ZollingerEllison syndrome and occasionally controls tumor growth,43 but is not effective in shrinking tumors.44 Tumors that cannot be lo¬ cated initially and are treated with chemotherapy may enlarge and can be resected at a future operation.

GLUCAGONOMA Glucagonomas are rare tumors of the A cells of the pancre¬ atic islets, with about 100 cases reported in the world literature.23 The first glucagon-producing tumor associated with a cutaneous rash was reported in 1942,45 but the glucagonoma syndrome was not fully described until 1966.46 Although 60% of these tumors are malignant, most are solitary; hence, surgical resection can be curative.47 The most characteristic and debilitating clinical find¬ ing in patients with glucagonoma is a necrolytic migratory rash. This skin lesion, in association with diabetes and weight loss, should suggest the diagnosis; elevated serum immunoreactive glucagon levels then should instigate a search for the tumor (see Chap. 176). These tumors tend to be large and located in the body and tail of the pancreas, and usually are not difficult to detect. If a glucagonoma cannot be seen on routine imaging studies, mes¬ enteric arteriography or selective venous sampling with radioim¬ munoassay for glucagon may be required.48 If the diagnosis is made early and the tumor is localized to the body or tail of the pancreas, a distal pancreatectomy can be curative. This operation, which does not require concomitant duodenectomy with reanastomosis of the pancreatic duct, common bile duct, and gastrointestinal tract, is performed easily with min¬ imal morbidity. Tumors in the head of the pancreas require pan¬ creaticoduodenectomy for complete excision. Aggressive cytoreduction of large, unresectable tumors is indicated before the use of chemotherapy. Unfortunately, chemotherapy for glucagonoma has been disappointing. Streptozocin has been used in combination with 5-fluorouracil and octreotide to alleviate symptoms in patients with unresectable disease, but has met with limited success.49 Be¬ cause the tumor grows slowly, patients who are not candidates for curative resection still can enjoy prolonged symptom-free survival.47

VIPOMA Vipomas are extremely rare tumors that elaborate vasoactive intestinal peptide (VIP), producing a syndrome characterized by watery diarrhea, hypokalemia, and achlorhydria (WDHA syndrome) or pancreatic cholera (see Chap. 176). Vipomas typically secrete a range of peptides, of which VIP is the most clinically relevant.6 Diagnosing these neoplasms on the basis of basal serum VIP lev¬ els can be difficult; the use of pentagastrin as a provocative agent has been helpful.6 Similar to glucagonomas, vipomas usually are large and easy to locate. Although 80% of vipomas are located in the pancreas, others can be found in the retroperitoneum, the adrenal gland, or the lung,50 making preoperative localization helpful. These tumors are located predominantly in the body and tail of the pancreas. CT and angiography are the primary radiographic techniques used when localization is required. Vipomas have been localized by technetium-99m sestamibi scanning.51 Because the vipoma syndrome can be caused by a malignant tumor (50%) or by hyperplasia (20%), the surgical approach var-

1358

PART IX: DISORDERS OF FUEL METABOLISM

ies widely, depending on the results of the preoperative evalua¬ tion. As in all tumors of the endocrine pancreas, complete resec¬ tion is desirable, but aggressive cytoreduction helps to control the clinical syndrome when total extirpation is not possible. Tumors located in the body and tail of the pancreas usually can be re¬ sected by distal pancreatectomy. When tumors are not found in the pancreas, an extensive exploration may be necessary. When the lesions still cannot be located after careful abdominal explo¬ ration, including the retroperitoneum, some surgeons advocate distal pancreatectomy. Patients whose disease is not controlled with distal pancreatectomy may require total pancreatectomy to alleviate their symptoms.50 The resolution of symptoms has been reported even with resection of recurrent metastatic disease.52 When surgery fails to control the WDHA syndrome, octreo¬ tide has been shown to inhibit the release of VIP from human vipoma cells and, rarely, to shrink metastases.53

SOMATOSTATINOMA Somatostatinomas are among the more recently described pancreatic endocrine tumors. The few tumors reported have been solitary, malignant, and virulent.50,54-56 Overproduction of so¬ matostatin, an inhibitory hormone acting on the endocrine sys¬ tem and digestive organs, leads to vague clinical symptoms (see Chap. 176). The true incidence of somatostatinoma may not be known because the symptom complex of diabetes, cholelithiasis, and steatorrhea is nonspecific and usually not very severe.57 So¬ matostatin inhibits the release of glucagon as well as insulin, so the diabetes produced is mild, and often is not insulindependent. Increased serum levels of somatostatin and de¬ pressed plasma concentrations of both immunoreactive insulin and glucagon can be used to establish the diagnosis of somato¬ statinoma.24 These tumors have been discovered in the head and tail of the pancreas and in the duodenum.58 Most somatostatino¬ mas located in the duodenum cause only symptoms related to local disease, such as obstructive jaundice.59,60 Because humoral manifestations of the somatostatinoma syndrome are relatively vague, these tumors often present with local symptoms. Many somatostatinomas are detected as an inci¬ dental finding on surgical exploration or abdominal radiography, so the need to localize occult somatostatinomas is unusual. When localization is required, CT and arteriography are useful. When the results of hormonal studies raise suspicion for somato¬ statinoma, the frequent occurrence of duodenal neoplasms makes endoscopy or contrast radiography helpful in localizing the tumor. Intraarterial methylene blue also can be used to find small duodenal tumors.60 As with other functional pancreatic endocrine tumors, sur¬ gical excision of somatostatinomas should be attempted when possible. Somatostatinomas in the head of the pancreas usually require pancreaticoduodenectomy. In addition, distal pancre¬ atectomy and enucleation have been reported for pancreatic dis¬ ease.24 Tumors in the periampullary region that cause jaundice require pancreaticoduodenectomy, whereas other duodenal tu¬ mors can be excised by segmental duodenal resection. When metastatic disease is encountered, an aggressive approach to the primary disease as well as tumor debulking is warranted.

MISCELLANEOUS FUNCTIONAL ISLET CELL TUMORS Parathyroid Hormone-Related Protein. PTHrP-producing tu¬ mors of the pancreas are of particular interest because this hor¬ mone can cause hypercalcemia (see Chaps. 51 and 213). Al¬ though not all PTHrP-secreting tumors produce elevated levels of calcium,61 some are associated with life-threatening hypercal¬ cemia.62 These lesions can be mistaken for a MEN-I syndrome with associated parathyroid hyperplasia, but the two entities can be differentiated by measuring PTH and PTHrP levels.63 Tumor resection results in resolution of the hypercalcemia. Growth Hormone Releasing Hormone. GHRH, which usually

is secreted by the hypothalamus, can be produced and secreted by a pancreatic islet cell tumor. The resulting acromegaly can be treated by resection of the pancreatic tumor, which corrects the biochemical abnormalities (see Chap. 213).64 Recurrent tumor causes a relapse of the endocrine disorder, demonstrating that the optimal therapy is complete extirpation of the neoplasm. Adrenocorticotropic Hormone and Corticotropin Releasing Hor¬ mone. ACTH or CRH can be secreted by pancreatic tumors.65,66 CRH is commonly produced by pancreatic endocrine tumors, but is only rarely associated with elevated levels of ACTH or with the manifestations of Cushing syndrome.66 However, when large pancreatic tumors secrete ACTH, they can cause severe hypercortisolism, with asthenia, muscle weakness, hypertension, hypokalemic alkalosis, and carbohydrate intolerance.67 Small pancreatic tumors that secrete ACTH usually produce milder symptoms. Tumors that produce predominantly the pro¬ opiomelanocortin precursor of ACTH generally do not manifest Cushing syndrome. When tumors producing ACTH or CRH can be located, they should be resected (see Chaps. 73 and 213).

NONFUNCTIONAL ISLET CELL TUMORS Once thought to be rare, nonfunctioning islet cell tumors account for about half the endocrine tumors of the pancreas re¬ ported in recent series.2,68 This increased incidence is due to the widespread use of abdominal CT and MRI, which can detect small and previously occult lesions. Although some of these masses may represent functional tumors that are discovered be¬ fore they become clinically significant, most nonfunctional tu¬ mors grow large and do not produce any recognized hormonal syndromes. Clinically, these silent tumors usually demonstrate neurosecretory granules that contain immunoreactive peptides on immunohistochemical staining.69 This suggests that these socalled nonfunctional tumors secrete peptide products that are physiologically silent, are inactive in the amounts secreted, or possess chemical conformations that are not bioactive. The pres¬ ence in the serum of clinically silent secretory products can be useful to detect recurrence of these nonfunctional tumors after resection. Pancreatic polypeptide, neurotensin, calcitonin, and oihuman chorionic gonadotropin can be used as markers for some nonfunctional pancreatic endocrine tumors.5-8 Because nonfunctioning tumors do not induce any charac¬ teristic clinical syndromes, their presentation is similar to that of adenocarcinoma of the pancreas. Nonfunctional islet cell and ductal tumors usually cause symptoms from their mass effects, leading to biliary and gastrointestinal obstruction, back pain, and weight loss. Because small tumors cause no symptoms, they are not discovered except as an incidental finding during abdominal exploration or imaging. Localization of occult nonfunctional tu¬ mors usually is not required. In one large series investigating nonfunctioning pancreatic masses, nonductal neoplasms represented more than 8% of all the pancreatic tumors evaluated.70 Because the prognosis and treatment of nonductal tumors is different from that of the more commonly encountered ductal neoplasms, a histopathologic di¬ agnosis should be established for all pancreatic masses before a treatment plan is formulated. Nonfunctional tumors are predominantly malignant (90%),71 and are found most often in the head of the pancreas. Despite their size and location, 40% are resectable at the time of discov¬ ery.9 Because they do not produce debilitating syndromes related to the elaboration of humoral products, the risks and benefits of resective surgery should be weighed carefully. If a formal pan¬ creatic resection can extirpate the entire tumor, most surgeons would agree that this is the preferred approach.72 In addition, although some surgeons advocate tumor debulking,73 others question the advisability of resective surgery short of curative extirpation in patients without humorally related disease unless the symptoms caused by the local disease are severe. Biliary by-

Ch. 154: Surgery of the Endocrine Pancreas pass, gastrointestinal bypass, and chemical splanchnicectomy are used to relieve symptoms created by the mass effects of the tumor in patients with adenocarcinoma of the pancreas. These also are appropriate operations in patients with nonfunctional endocrine tumors of the pancreas, who often have symptoms related to lo¬ cal disease. Nonoperative percutaneous or endoscopic biliary by¬ pass also can be helpful in selected cases when the risks of sur¬ gery are prohibitive. Unlike patients with adenocarcinoma of the pancreas, pa¬ tients with nonfunctional endocrine tumors can have long-term survival, and this should be taken into account when considering palliative operations. Specifically, if an operation is performed for biliary obstruction, a concomitant gastrointestinal bypass should be considered because enteric obstruction becomes more likely with prolonged survival. Long-term survival after gastro¬ jejunostomy also makes peristomal jejunal ulceration more likely. For this reason, vagotomy should be performed or appro¬ priate H2-receptor blocker prophylaxis initiated.

SURGICAL ASPECTS OF PANCREATIC ENDOCRINE TUMORS Endocrine Pancreatic Tumors Versus Endocrine Tumors. Adenocarcinoma of the pancreas is the fourth leading cause of cancer death in the United States. About 20,000 new cases are diagnosed each year, and 5-year survival is about 2% regardless of therapy.74 By comparison, 200 to 1000 endocrine tumors of the pancreas are found in the United States each year,23,75 and 5year survival after surgery is nearly 100% for benign tumors and more than 40% for malignant tumors.76 Another advantage of operating on endocrine tumors is the significant symptomatic re¬ lief from hormonal syndromes that can be obtained by curative resection or tumor cytoreduction. Endocrine Pancreatic Tumors: Surgical Procedures. Like duc¬ tal tumors, islet cell tumors of the pancreas can be solid or cys¬ tic.77 The treatment of cystic endocrine tumors, which can be be¬ nign, malignant, functional, or nonfunctional, is similar to that of solid endocrine tumors. Operations performed for endocrine tumors of the pancreas include enucleation, segmental resection, distal pancreatectomy, pancreaticoduodenectomy, total and near-total pancreatectomy, tumor cytoreduction, bypass proce¬ dures, and operations on other involved organs such as the stom¬ ach, duodenum, and liver (see Table 154-2). One unusual feature of endocrine tumors of the pancreas not shared by nonendocrine tumors is the response to tumor debulking. It has been demon¬ strated, in some of these tumors, that surgical reduction of the size of the lesion alone can significantly improve long-term sur¬ vival.78 In contrast, surgery for adenocarcinoma of the pancreas is limited mainly to pancreaticoduodenectomy or bypass. Intraoperative Localization. Tumor localization is important and sometimes difficult for endocrine neoplasms of the pancreas, which can be small but clinically symptomatic. On occasion, tu¬ mors cannot be localized before surgery and must be found at surgery. Surgeons performing these operations should be famil¬ iar with intraoperative ultrasound, duodenotomy, and other in¬ traoperative localizing techniques, as well as with the indications for biopsy or blind resection. Finally, laparoscopic surgery may change the approach to the diagnosis, localization, and treatment of these unusual neoplasms as it is changing the approach to so many other surgical diseases. It is important for any physician evaluating patients with pancreatic masses to understand the possibility and significance of finding an endocrine tumor. It also is important for any surgeon operating on patients with pancreatic endocrine tumors to be thoroughly familiar with the evaluation and localization of these lesions, with the intraoperative decision-making process, and with the wide range of ablative procedures used for these unusual neoplasms.

1359

REFERENCES 1. Warshaw AL, Swanson RS. What's new in general surgery: pancreatic can¬ cer in 1988. Ann Surg 1988:208:541. 2. Yeo C], Wang BH, Anthone GJ, Cameron JL. Surgical experience with pan¬ creatic islet-cell tumors. Arch Surg 1993; 128:1143. 3. Grant CS. Surgical management of malignant islet cell tumors. World J Surg 1993:17:498. 4. Delcore R, Friesen SR. Gastrointestinal neuroendocrine tumors. J Am Coll Surg 1994:178:187. 5. Strodel WE, Vinik AI, Lloyd RV, et al. Pancreatic polypeptide-producing tumors. Silent lesions of the pancreas? Arch Surg 1984; 119:508. 6. Brunt LM, Mazoujian G, O'Dorisio TM, Wells SA. Stimulation of vasoactive intestinal peptide and neurotensin secretion by pentagastrin in a patient with VIPoma syndrome. Surgery 1994; 115:362. 7. McCleod MK, Vinik AI. Calcitonin immunoreactivity and hypercalcitoninemia in two patients with sporadic, nonfamilial, gastroenteropancreatic neuro¬ endocrine tumors. Surgery 1992; 111:484. 8. Perkins PL, Mcleod MK, Jin L, et al. Analysis of gastrinomas by immunohistochemistry and in situ hybridization histochemistry. Diagn Mol Pathol 1992; 1: 155. 9. Modlin IM, Lewis JJ, Ahlman H, et al. Management of unresectable malig¬ nant endocrine tumors of the pancreas. Surg Gynecol Obstet 1993; 176:507. 10. Aspestrand F, Kolmannskog F. CT compared to angiography for staging tumors of the pancreatic head. Acta Radiol 1992; 33:556. 11. Hammond PJ, Jackson JA, Bloom SR. Localization of pancreatic endocrine tumors. Clin Endocrinol (Oxf) 1994;40:3. 12. VanEyck CHJ, Brunning HA, Reubi JC, et al. Use of isotope-labelled somatostatin analogs for visualization of islet-cell tumors. World J Surg 1993; 17: 444. 13. Doppman JL, Miller DL, Chang R, et al. Intraarterial calcium stimulation test for detection of insulinomas. World J Surg 1993; 17:439. 14. Van Heerden JA, Grant CS, Czako P, et al. Occult functioning insulino¬ mas: which localizing studies are indicated? Surgery 1992; 112:1010. 15. Bottger TC, Junginger T. Is preoperative radiographic localization of islet cell tumors in patients with insulinomas necessary? World J Surg 1993; 17:427. 16. Norton JA, Cromack DT, Shawker TH, et al. Intraoperative ultrasono¬ graphic localization of islet cell tumors. Ann Surg 1988;207:160. 17. Joffe SN. Pancreatic islet cell tumor. In: Cameron JL, ed. Current surgical therapy, ed 2. St Louis: CV Mosby, 1986:285. 18. Thompson GB, Service FJ, van Heerden JA, etal. Reoperative insulinomas, 1927 to 1992: an institutional experience. Surgery 1993; 114:1196. 19. Udelsman R, Yeo CJ, Hruban RH, et al. Pancreaticoduodenectomy for selected pancreatic endocrine tumors. Surg Gynecol Obstet 1993; 177:269. 20. Menegaux F, Schmitt G, Mercadier M, Chigot JP. Pancreatic insulinomas. Am J Surg 1993; 165:243. 21. Von Eyben FE, Grodum E, Gjessing HJ, et al. Metabolic remission with octreotide in patients with insulinoma. J Intern Med 1994; 235:245. 22. Buchanan KD. Effects of somatostatin on neuroendocrine tumors of the gastrointestinal system. Recent Results Cancer Res 1993; 129:45. 23. Norton JA. Neuroendocrine tumors of the pancreas and duodenum. Curr Probl Surg 1994;31:82. 24. Friesen SR. Tumors of the endocrine pancreas. N Engl J Med 1982; 306: 580. 25. Shepard JJ, Challis DR, Davies PF, et al. Multiple endocrine neoplasia, type 1. Arch Surg 1993; 128:1133. 26. Cherner JA, Sawyers JL. Benefit of resection of metastatic gastrinoma in multiple endocrine neoplasia type 1. Gastroenterology 1992; 102:109. 27. Zollinger RM, Ellison EH. Primary peptic ulcerations of the jejunum asso¬ ciated with islet cell tumors of the pancreas. Ann Surg 1955; 142:709. 28. Stabile BE, Morrow DJ, Passaro E. The gastrinoma triangle: operative im¬ plications. Am J Surg 1984; 147:25. 29. Sawicki MP, Howard TJ, Dalton M, et al. The dichotomous distribution of gastrinomas. Arch Surg 1990; 125:1584. 30. Howard TJ, Sawicki MP, Stabile BE, et al. Biologic behavior of sporadic gastrinoma located to the right and left of the superior mesenteric artery. Am J Surg 1993; 165:101. 31. Imamura M, Takahashi K. Use of selective arterial secretin injection test to guide surgery in patients with Zollinger Ellison syndrome. World J Surg 1993; 17: 433. 32. Thompson NW, Pasieka J, Fukuuchi A. Duodenal gastrinomas, duode¬ notomy, and duodenal exploration in the surgical management of Zollinger-Ellison syndrome. World J Surg 1993; 17:455. 33. Ko TC, Flisak M, Prinz RA. Selective intra-arterial methylene blue injec¬ tion: a novel method of localizing gastrinoma. Gastroenterology 1992; 102:1062. 34. Harmon JW, Norton JA, Collin MJ, et al. Removal of gastrinomas for con¬ trol of Zollinger-Ellison syndrome. Ann Surg 1984; 200:396. 35. Norton JA, Doppman JL, Jensen RT. Curative resection in ZollingerEllison syndrome: results of a 10-year prospective study. Ann Surg 1992; 215:8. 36. Delcore R, Friesen SR. Role of pancreatoduodenectomy in the manage¬ ment of primary duodenal wall gastrinomas in patients with Zollinger-Ellison syn¬ drome. Surgery 1992; 112:1016. 37. Richardson CT, Feldman M, McClelland RN, et al. Effect of vagotomy in Zollinger-Ellison syndrome. Gastroenterology 1979; 77:682. 38. Zollinger RM, Ellison EC, Fabri PJ, et al. Primary peptic ulcerations of the jejunum associated with islet cell tumors: twenty five year evaluation. Ann Surg 1980;192:422.

1360

PART IX: DISORDERS OF FUEL METABOLISM

39. Farley DR, van Heerden JA, Grant CS. The Zollinger-Ellison syndrome: a collective surgical experience. Ann Surg 1992;215:561. 40. Delcore R, Friesen SR. Zollinger-Ellison syndrome. Arch Surg 1991; 126:556. 41. Fishbeyn VA, Norton JA, Benya RV, et al. Assessment and prediction of long-term cure in patients with the Zollinger-Ellison syndrome: the best approach. Ann Intern Med 1993; 119:199. 42. Pisegna JR, Norton JA, Slimak GG, et al. Effects of curative gastrinoma resection on gastric secretory function and antisecretory drug requirement in the Zollinger-Ellison syndrome. Gastroenterology 1992; 102:767. 43. Arnold R, Neuhaus C, Benning R, et al. Somatostatin analog sandostatin and inhibition of tumor growth in patients with metastatic endocrine gastroenteropancreatic tumors. WorldJ Surg 1993; 17:511. 44. Geelhoed GW, Bass BL, Mertz SL, Becker KL. Somatostatin analog: effects on hypergastrinemia and hypercalcitoninemia. Surgery 1986; 100:962. 45. Becker SW, Kahn D, Rothman S. Cutaneous manifestations of internal malignant tumors. Arch Dermatol Syph 1942;45:1069. 46. McGavran MH, Unger RH, Recant L, et al. A glucagon-secreting alpha¬ cell carcinoma of the pancreas. N Engl J Med 1966;274:1408. 47. Higgins GA, Recant L, Fischman AB. The glucagonoma syndrome: surgi¬ cally curable diabetes. Am J Surg 1979; 137:142. 48. Ingemansson S, Holst J, Larsson LI, Lunderquist A. Localization of glucagonomas by catherization of the pancreatic veins and with glucagon assay. Surg Gynecol Obstet 1977; 145:509. 49. Boden G. Insulinoma and glucagonoma. Semin Oncol 1987; 14:253. 50. Jaffe BM. Surgery for gut hormone-producing tumors. Am J Med 1987; 82:68. 51. Cesani F, Ernst R, Walser E, Villanueva-Meyer J. Tc-99m sestamibi im¬ aging of a pancreatic VIPoma and parathyroid adenoma in a patient with multiple type I endocrine neoplasia. Clin Nucl Med 1994; 19:532. 52. Nagorney DM, Bloom SR, Polak JM, Blumgart LH. Resolution of recurrent Verner-Morrison syndrome by resection of metastatic vipoma. Surgery 1983;93: 348. 53. Kraenzlin ME, Ch'ng JLC, Wood SM, et al. Long-term treatment of a VIPoma with somatostatin analogue resulting in remission of symptoms and possi¬ ble shrinkage of metastases. Gastroenterology 1985;88:185. 54. Larsson LI, Holst JJ, Kuhl C, et al. Pancreatic somatostatinoma: clinical features and physiologic implications. Lancet 1977;1:666. 55. Sakazaki S, Umeyama K, Nakagawa H, et al. Pancreatic somatostatinoma. Am J Surg 1983; 146:674. 56. Kelly TR. Pancreatic somatostatinoma. Am J Surg 1983; 146:671. 57. Krejs GJ, Orci L, Conlon JM, et al. Somatostatinoma syndrome: biochem¬ ical, morphologic and clinical features. N Engl J Med 1979;301:2&5. 58. Kaneko H, Yanaihara N, Ito S, et al. Somatostatinoma of the duodenum. Cancer 1979; 44:2273. 59. Malone MJ, Silverman ML, Braasch JW, et al. Early somatostatinoma of the papilla of the duct of Santorini. Arch Surg 1985; 120:1381. 60. O'Brien TD, Chejfec G, Prinz RA. Clinical features of duodenal somatostatinomas. Surgery 1993,114:1144. 61. Miraliakbari BA, Asa L, Boudreau SF. Parathyroid hormone-like peptide in pancreatic endocrine carcinoma and adenocarcinoma associated with hypercal¬ cemia. Hum Pathol 1992;23:884. 62. Tarver DS, Birch SJ. Case report: life-threatening hypercalcemia second¬ ary to pancreatic tumor secreting parathyroid hormone-related protein—successful control by hepatic arterial embolization. Clin Radiol 1992; 46:204. 63. Mitlak BH, Hutchinson JS, Kaufman SD, Nussbaum SR. Parathyroid hormone-related peptide mediates hypercalcemia in an islet cell tumor of the pan¬ creas. Horm Metab Res 1991;23:344. 64. Price DE, Absalom SR, Davidson K, et al. A case of multiple endocrine neoplasia: hyperparathyroidism, insulinoma, GRF-oma, hypercalcitoninemia and intractable peptic ulceration. Clin Endocrinol (Oxf) 1992;37:187. 65. Gullo L, De Giorgio R, D'Errico A, et al. Pancreatic exocrine carcinoma producing adrenocorticotropic hormone. Pancreas 1992; 7:172. 66. Tsuchihashi T, Yamaguchi K, Abe K, et al. Production of immunoreactive corticotropin-releasing hormone in various neuroendocrine tumors. Jpn J Clin On¬ col 1992;22:232. 67. Howlett TA, Drury PL, Perry L, et al. Diagnosis and management of ACTH-dependent Cushing's syndrome: comparison of the features in ectopic and pituitary ACTH production. Clin Endocrinol (Oxf) 1986; 24:699. 68. Venkatesh S, Ordonez NG, Ajani J, et al. Islet cell carcinoma of the pan¬ creas. Cancer 1990; 65:354. 69. Heitz PU, Kasper M, Polak JM, et al. Pancreatic endocrine tumors. Hum Pathol 1982; 13:263. 70. Dejong SA, Pickleman J, Rainsford K. Nonductal tumors of the pancreas. The importance of laparotomy. Arch Surg 1993; 128:730. 71. Kent RB, van Heerden JA, Weiland LH. Nonfunctioning islet cell tumors. Ann Surg 1981; 193:185. 72. Evans DB, Skibber JM, Lee JE, et al. Nonfunctioning islet cell carcinoma of the pancreas. Surgery 1993; 114:1175. 73. Eckhauser FE, Cheung PS, Vinik Al, et al. Nonfunctioning malignant neu¬ roendocrine tumors of the pancreas. Surgery 1986; 100:978. 74. Gordis L, Gold EB. Epidemiology of pancreatic cancer. World J Surg 1984; 8:808. 75. Brennan MF, MacDonald JS. The endocrine pancreas. In: Devita V, Hellman S, Rosenberg SA, eds. Principles and practice of oncology, ed 2. Philadelphia: JB Lippincott, 1985:1206.

76. Thompson GB, van Heerden JA, Grant CS, et al. Islet cell carcinoma of the pancreas: a twenty-year experience. Surgery 1988; 104:1011. 77. Schwartz RW, Munfakh NA, Zweng T, et al. Nonfunctioning cystic neu¬ roendocrine neoplasms of the pancreas. Surgery 1994; 115:645. 78. Danforth DN, Gorden P, Brennan MF. Metastatic insulin-secreting carci¬ noma of the pancreas: clinical course and the role of surgery. Surgery 1984;96:1027. 79. Debas HT, Mulvihill SJ. Neuroendocrine gut neoplasms: important les¬ sons from uncommon tumors. Arch Surg 1994; 129:965. 80. Buchanan KD, Johnston CF, O'Hare MMT, et al. Neuroendocrine tumors: a European view. Am J Surg 1986; 81:14.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

155

HYPOGLYCEMIA OF INFANCY AND CHILDHOOD ALLEN M. GLASGOW

DEFINITION Hypoglycemia is difficult to explicitly define; there is no clear agreed-on blood glucose value. A reasonable lower limit of nor¬ mal for blood glucose is 40 mg/dL for all pediatric age groups.1 The corresponding plasma value would be 46 mg/dL, assuming an average 15% higher plasma value. In infants, the diagnosis of hypoglycemia must often be based strictly on the blood glucose level. There is concern that a low blood glucose level may ad¬ versely affect brain development in infants, even in those who are asymptomatic.2 In older children, a diagnosis of hypoglyce¬ mia should be limited to patients with symptoms associated with a relatively low blood glucose level. Unless the situation is unu¬ sually complicated (prolonged severe hypoglycemia, Reye syn¬ drome, or maple syrup urine disease), the symptoms should rap¬ idly improve as the hypoglycemia is corrected. Normal children are more susceptible to hypoglycemia and less tolerant to fasting than adults. Fasting tolerance is low in infancy, gradually increases during childhood, and approaches adult tolerance at about 10 to 12 years of age. The increased sus¬ ceptibility to hypoglycemia in infancy and childhood is thought to arise from the increased brain/muscle mass ratio.

CLASSIFICATION OF HYPOGLYCEMIA Table 155-1 presents a classification of the different causes of hypoglycemia based on age of onset, pathogenesis, and some of the most important hormonal and biochemical findings. Note that many of the causes of hypoglycemia usually occur under circumstances in which the cause is readily apparent (e.g., children with diabetes mellitus, fulminant hepatitis) or as only one part of a complete clinical picture (e.g., Reye syndrome, ga¬ lactosemia, maple syrup urine disease). It is the child who is oth¬ erwise healthy and who has hypoglycemia as an isolated finding who usually presents a diagnostic problem. It is useful to consider five broad categories: (1) ketotic hypoglycemia, (2) hyperinsulinism, (3) defects in fatty acid oxidation, (4) hormonal deficiency, and (5) defects in glycogen metabolism or gluconeogenesis. Al¬ most all children with isolated hypoglycemia have a disorder re¬ lated to one of these categories.

Ch. 155: Hypoglycemia of Infancy and Childhood

DIAGNOSTIC STUDIES The first step for diagnosing the cause of hypoglycemia in children is to try to determine which of the five major categories is the most likely. The category typically can be determined from the presence or absence of hepatomegaly and from some biochemical and hor¬ monal tests obtained while the child is hypoglycemic. These tests can be obtained during a spontaneous attack or after fasting the child to induce hypoglycemia. The following tests are obtained during an episode of hypoglycemia: plasma glucose, insulin, growth hormone, cortisol, glucagon, epinephrine and norepi¬ nephrine, lactate, and /3-hydroxybutyrate (Fig. 155-1). The plasma glucose concentration is measured to confirm hypoglycemia. An elevated insulin level (above 10-12 ^U/mL) indicates that hyperinsulinemia is likely; a low insulin level does not completely exclude hyperinsulinemia. The normal hormonal response to hypoglycemia is a rise in growth hormone (more than 8 ng/mL), cortisol (more than 20 ng/mL), epinephrine, and glu¬ cagon (not well defined but probably well above 100 pg/mL). A low level of one of the hormones suggests that the hypoglycemia may be due to deficiency of that hormone. Most patients with defects in glycogenolysis have marked hepatomegaly. If the de¬ fect involves gluconeogenesis, as in glucose-6-phosphate defi¬ ciency, gluconeogenic substrates, notably lactate, accumulate. /?Hydroxybutyrate is measured to assess fatty acid mobilization and oxidation. Hyperinsulinemia (which inhibits fatty acid mo¬ bilization) and defects in fatty acid oxidation are typically associ¬ ated with hypoketonemic hypoglycemia, but some patients with these disorders may have a ketogenic response. The length of fast necessary to exclude an underlying disor¬ der causing hypoglycemia in children suspected to have hypo¬ glycemia is uncertain. A child older than 1 year of age who does

not become hypoglycemic during 24 hours of fasting is unlikely to have more than mild ketotic hypoglycemia. A fast of 18 hours should exclude severe hypoglycemia in those younger than 1 year of age.

GLYCOGENOLYSIS AND GLUCONEOGENESIS The level of plasma glucose is maintained by the balance between glucose use, on the one hand, and glucose intake and production, on the other. Glucose use in the brain and other neu¬ ral tissues is largely unregulated and nearly constant, except dur¬ ing prolonged fasting when ketone bodies contribute signifi¬ cantly. Glucose oxidation in most other tissues (especially muscle and adipose tissue) varies considerably. In the fed state when the blood insulin level is high, glucose is readily oxidized; in the fasting state, little glucose is oxidized. In the fasting state, glucose is produced in the liver by glyco¬ genolysis and gluconeogenesis. During prolonged fasting, gluco¬ neogenesis also occurs in the kidneys. Glucose production is in¬ hibited by insulin and stimulated by the counterregulatory hormones (glucagon, catecholamines, cortisol, and growth hormone).

GLYCOGEN SYNTHESIS AND BREAKDOWN The metabolic steps of glycogen synthesis and breakdown are shown in Figure 155-2.3 Glucose is stored in the liver as gly¬ cogen. Glucose (and other sugars) absorbed from foods enter the liver and are converted to glucose-6-phosphate. Evidence indi¬ cates that much of the glucose is converted to three-carbon inter¬ mediates before being converted to glucose-6-phosphate in the liver. Glucose-6-phosphate is converted to glucose-1-phosphate

FAST 12 HOURS IF 12 MO

BLOOD GLUCOSE NORMAL NO FURTHER TESTING

BLOOD GLUCOSE LOW

WITH HEPATOMEGALY (Also usually Hyperuricemia and Hyperlipidemia)

WITHOUT HEPATOMEGALY Measure: Insulin Growth Hormone Cortisol Lactate

DEFECT IN GLYCOGEN METABOLISM OR GLUCONEOGENESIS

d-Hydroxybutyrate Glucagon Epinephrine-Norepinephrine NORMAL RESPONSE ♦ KETOTIC HYPOGLYCEMIA INSULIN HIGH

NO RISE IN 0HYDROXYBUTYRATE

HYPERINSULINEMIA

DEFECT IN FATTY ACID OXIDATION

HORMONE RESPONSE LOW

HORMONE DEFICIENCY

LACTATE HIGH

LACTATE NORMAL

DEFICIENCY OF GLYCOGEN SYNTHETASE PHOSPHORYLASE DEBRANCHER ETC. DEFICIENCY OF GLUCOSE - 6 - PHOSPHATASE FRUCTOSE -1,6- DIPHOSPHATASE

FIGURE 155-1.

1361

Flow diagram for diagnosis of hypoglycemia (see text).

1362

PART IX: DISORDERS OF FUEL METABOLISM

TABLE 155-1 Hypoglycemia in Infancy and in Childhood: Classification by Age, Pathophysiology, and Major Findings Age

Major Categories

Primary Diagnosis

NEONATAL (TRANSIENT) 0-7 d

Exact cause unknown

More common in small-for-date, fetal distress, and sick newborns

Hyperinsulinism

Infant of diabetic mother Erythroblastosis Discontinuation of IV glucose

NEONATAL (PERSISTENT) INFANCY AND EARLY CHILDHOOD 0-2 yr

Hyperinsulinism

Islet cell hyperplasia Nesidioblastosis Islet cell adenoma Leucine sensitivity Beckwith syndrome

Glycogen storage disease

Glycogen synthetase def Debrancher def Phosphorylase def Phosphorylase kinase def Glucose-6-phosphatase def

Defect in gluconeogenesis

Fructose-1 -6-diphosphatase def Phosphoenolpyruvate carboxykinase def

Hormone deficiency

Growth hormone def Cortisol def Glucagon def Thyroid hormone def

Defect in fatty acid oxidation

Carnitine def Medium-chain acyl CoA dehydrogenase def Long-chain acyl CoA dehydrogenase def Long-chain acyl CoA carnitine transferase def Long chain 3-OH acyl CoA dehydrogenase def Short chain 3-OH acyl CoA dehydrogenase def

Miscellaneous

Galactosemia

Salicylate intoxication

Fructose intolerance

Alcohol intoxication

Maple syrup urine disease

Reye syndrome

Propionic acidemia

Jamaican vomiting sickness

Methylmalonic acidemia

Hepatitis

Other organic acidemias

Massive nonpancreatic tumors

Malnutrition

OLDER CHILDREN 1-18 yr NOTE: SOME OVERLAP WITH ABOVE AGE GROUP

Hyperinsulinism

Secondary to therapy of diabetes Islet cell adenoma Malicious insulin or oral hypoglycemic administration

Ketotic

Due to insufficient substrate (alanine) Due to epinephrine def

Miscellaneous

See above

Nonfasting hypoglycemia

Postgastrectomy Pyloroplasty etc. Functional, reactive ?

—*■, appropriate level; 1, decreased level; f, increased level; def, deficiency; CoA, coenzyme A.

by phosphoglucomutase. Glucose-1-phosphate and uridine tri¬ phosphate are then converted to uridine diphosphate-glucose. The glucose residue from uridine diphosphate-glucose is added to a glycogen molecule by glycogen synthetase. Glycogen syn¬ thetase adds glucose residues in a 1,4 linkage, yielding a straight chain of glucose molecules. When the length of the chain is be¬ tween 7 and 21 glucose units, a second enzyme, amylo-a-1,4—►«1,6-transglucosylase (brancher), transfers a number of linked glucose units to another section of the glycogen molecule in a 1,6

linkage. This yields the tree-like structure of glycogen. Glycogen synthesis is regulated by changes in the activity of glycogen syn¬ thetase. Glycogen synthetase exists in two forms: a less active phosphorylated form and an active dephosphorylated form. Phosphorylation of glycogen synthetase is catalyzed by a protein kinase. Increased levels of cyclic adenosine monophosphate (cAMP) activate this kinase, which increases the phosphorylation of glycogen synthetase, thereby decreasing glycogen synthesis. The concentration of cAMP is increased by glucagon and cate-

Ch. 155: Hypoglycemia of Infancy and Childhood

1363

TABLE 155-1 Hypoglycemia in Infancy and in Childhood: Classification by Age, Pathophysiology, and Major Findings Pathophysiology

Insulin

Hormones

Lactate

/8-Hydroxybutyrate

No

—►

-

-

-

No

t

-

-

fUtilization

No (usually)

t

-

—►

fUtilization

Yes (marked)

-

-

Depends on disorder

Yes (marked)

—

-*

t

No

-

Yes (mild—moderate)

-

Hepatomegaly

-t

Affected hormone

—►

—►

(Production fUtilization

(Production

(Production

-

—►

t

1

(Production fUtilization

(

fUtilization

Uncertain

Variable Note: Hypoglycemia in these patients is usually only part of a complex disorder

No

t May include nonhuman insulin

—

No

-

-

-

-

(Production

No

-

( Epinephrine

-

—

(Production

No

t

|

f Utilization

appropriate level; (, decreased level; f, increased level; def, deficiency; CoA, coenzyme A.

cholamines and, under certain conditions, is decreased by insulin. The intracellular concentration of cAMP also regulates the breakdown of glycogen. High levels of cAMP increase the activ¬ ity of phosphorylase kinase kinase which phosphorylates and ac¬ tivates phosphorylase kinase; activated phosphorylase kinase, in turn, phosphorylates and activates phosphorylase, which cata¬ lyzes the removal of glucose in the form of glucose-1-phosphate from the segments of glycogen in 1,4 linkage. Glucose-1-

phosphate is converted successively to glucose-6-phosphate and glucose by the action of phosphoglucomutase and glucose-6phosphatase. Another enzyme, debrancher, which has both transferase and glucosidase activity, moves a trisaccharide from a 1,6 to a 1,4 linkage, simultaneously releasing a free glucose. Phosphorylase then removes glucose residues down to within four units of another branch point. About 60 g of glucose are found in the liver of an adult man, which can maintain the blood glucose for only a few hours. Dur-

1364

PART IX: DISORDERS OF FUEL METABOLISM Glycogen Synthetase (b)

GLYCOGEN METABOLISM FIGURE 155-2.

Schematic presentation of glycogen metabolism. G, a glucose unit.

ing long periods of fasting, glucose is formed from noncarbohy¬ drate precursors by gluconeogenesis.

SUBSTRATES FOR GLUCONEOGENESIS The substrates for gluconeogenesis are lactate, glycerol, and amino acids. The major source of lactate is anaerobic glycolysis. Glucose is oxidized to lactate in peripheral tissues, and the lactate is reconverted to glucose in the liver with the consumption of noncarbohydrate energy sources. In this overall process, the pe¬ ripheral tissues that can only oxidize glucose are supported by noncarbohydrate energy sources, and there is no net consump¬ tion of glucose. Glycerol is released from triglycerides and may account for as much as one third of glucose production. The other major sub¬ strates for gluconeogenesis are amino acids that are released pri¬ marily from muscle. Many amino acids in muscle are partially metabolized before they are released. Alanine is the predominant amino acid released from muscle during fasting. Frequently, glu¬ coneogenesis is limited by the amount of available substrate. The major enzymatic control point for gluconeogenesis and glycolysis occurs at the interconversion of fructose-6-phosphate and fructose-1,6-diphosphate. During glucose oxidation, phosphofructokinase catalyzes the conversion of fructose-6-phosphate to fructose-1,6-diphosphate, and fructose-1,6-diphosphatase catalyzes the reverse reaction in the gluconeogenic direction. The activity of these two enzymes and, thus, the balance between glycolysis and gluconeogenesis is controlled by the intracellular level of fructose-2,6-diphosphate.4 Fructose-2,6-diphosphate is pro¬ duced from, or converted to, fructose-6-phosphate by fructose2,6-diphosphatase. The direction in which this enzyme is active depends on its own phosphorylation. High insulin levels cause dephosphorylation of this enzyme, increasing fructose-2,6-

diphosphate levels, activating phosphofructokinase, and pro¬ ducing glycolysis. High glucagon levels lead to phosphorylation of the enzyme, decreasing fructose-2,6-diphosphate levels and, in turn, activating fructose-1,6-diphosphatase and producing gluconeogenesis. Two other steps in glycolysis are physiologically irreversible. The glycolytic step for conversion of phosphoenolpyruvate to pyruvate is reversed in the gluconeogenic direction by two en¬ zymes: pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Glucose-6-phosphatase catalyzes the conversion of glucose-6-phosphate to glucose. This step is common to both glycogenolysis and gluconeogenesis.

DISEASES OF GLYCOLYSIS AND GLUCONEOGENESIS GLUCOSE-6-PHOSPHATASE DEFICIENCY Glucose-6-phosphatase deficiency (type I) generally is the most severe of the hepatic glycogen storage diseases.5 Some pa¬ tients with similar clinical manifestations have normal in vitro enzymatic activity (type IB). This variety arises from failure of glucose-6-phosphate to be transported into the microsome. The clinical manifestations of glucose-6-phosphatase defi¬ ciency include short stature, cherubic features, hepatomegaly, hypoglycemia, lactic acidosis, hyperlipidemia, hyperuricemia, platelet dysfunction (leading to nose bleeds), and, in some pa¬ tients, a renal Fanconi syndrome or recurrent episodes of fever. The hypoglycemia results from the absence of an enzyme involved in both glycogenolysis and gluconeogenesis. Many pa¬ tients have a low blood glucose level of 10 to 20 mg/dL after a relatively short fast of 6 to 8 hours. The lactic acidosis results

Ch. 155: Hypoglycemia of Infancy and Childhood

1365

from the shunting of glucose units from glycogenolysis through the glycolytic pathway to lactate, which cannot be converted to glucose because of the block in gluconeogenesis. The hyperlipid¬ emia and hyperuricemia result from excessive fatty acid, choles¬ terol, and urate synthesis owing to the excessive accumulation of precursors during periods of fasting. Many of the clinical manifestations of glucose-6-phosphatase deficiency—including the short stature, lactic acidosis, hy¬ perlipidemia, and hyperuricemia—appear to result from abnor¬ mal diversions of substrates during periods of fasting and hypoglycemia. Therefore, the major goal of treatment is to main¬ tain a fed state. In the fed state, glucose-6-phosphatase normally is inactive. Feeding can be achieved at night by giving a slow intragastric infusion of nutrients or by giving cornstarch at bed¬ time.6 The cornstarch is slowly digested, releasing glucose over 6 to 8 hours. During the day, patients are given frequent (every 2 to 3 hours) small feedings of a high-starch diet. In the teenaged years, patients may develop hepatic adenomas and, in a few cases, adenocarcinoma. It is unknown if newer methods of main¬ taining the blood glucose decrease the incidence of adenoma. Re¬ nal failure is a recently recognized manifestation of type I glyco¬ gen storage disease.7.

OTHER ENZYME DEFECTS Debrancher deficiency (type III) is usually of intermediate se¬ verity. Patients with this disorder often have short stature, hypo¬ glycemia, and hyperlipidemia, but they do not have lactic acido¬ sis, hyperuricemia, Fanconi syndrome, or liver tumors. These patients may have muscle weakness, including cardiomyopathy, and a greater likelihood of developing hepatic fibrosis and cir¬ rhosis (Fig. 155-3). Treatment has the same rationale as that for type I, except that in debrancher deficiency, the patients are placed on a high protein diet. These patients can convert amino acids to glucose. Because this disorder is usually milder, treat¬ ment need not be as aggressive as for type I disease. Deficiencies of phosphorylase (type VI), phosphorylase kinase (type IX), or phosphorylase kinase kinase (type XI) usually cause moderate hepatomegaly and mild to moderate hypoglycemia. These patients usually do not have the other problems seen in type I disease. Usually, all that is needed for treatment is a frequent-feeding diet and avoidance of prolonged fasting. With the exception of phosphorylase kinase deficiency, which is X-linked recessive, the disorders of glycogen storage are inherited in an autosomal recessive manner. Glycogen synthetase deficiency is associated with severe neo¬ natal hypoglycemia and fatty hepatomegaly. The clinical features of fructose-1,6-diphosphatase deficiency8 and fructose intolerance (fructose aldolase deficiency) include he¬ patomegaly caused by fatty infiltration, lactic acidosis, hypogly¬ cemia, hyperlipidemia, and hyperuricemia. Many patients fail to thrive, and some may develop liver failure, including hyperbili¬ rubinemia and a prolonged prothrombin time. Fructose ingestion causes lactic acidosis and hypoglycemia, not the normal glycemic response. Treatment consists of avoiding fructose and, in fruc¬ tose-1,6-diphosphatase deficiency, frequent feedings. A few patients with severe hypoglycemia and a deficiency of phosphoenolpyruvate carboxykinase have been reported.9 The glycogen storage diseases that are not associated with hypoglyce¬ mia include types II (Pompe), IV (Andersen), V (McArdle), VII, and X.

MOBILIZATION AND OXIDATION OF FATTY ACIDS During fasting, fat becomes the major source of energy; free fatty acids are released from adipose tissue and oxidized to ke¬ tones in the liver. The release of fatty acids is increased by the counterregulatory hormones and decreased by insulin.

FIGURE 155-3.

One-year-old girl with glycogen storage disease type III. She presented with asymptomatic hepatomegaly and became hypo¬ glycemic when fasted. Note the cherubic features.

The initial step in long-chain fatty acid oxidation is the for¬ mation of the coenzyme A (CoA) derivative (Fig. 155-4). This derivative is then converted to the fatty acid carnitine derivative by the enzyme carnitine palmitoyl transferase. Only the fatty acid carnitine can enter the mitochondria. The fatty acid carnitine then is reconverted to fatty acid CoA inside the mitochondria. The rate-limiting enzyme in fatty acid oxidation is carnitine pal¬ mitoyl transferase. The activity of this enzyme is sensitive to the intracellular level of malonyl CoA. Further intramitochondrial oxidation of fatty acid CoA be¬ gins with dehydrogenation by one of three relatively chain length-specific acyl-CoA-dehydrogenases (long-chain, mediumchain, and short-chain acyl CoA dehydrogenase). Subsequent steps involve hydrogenation by enol-CoA-hydratase, dehydro¬ genation by /3-hydroxyacyl-CoA-dehydrogenase, and the split¬ ting off of an acetyl-CoA by a thiolase. When fatty acid oxidation is blocked, there is an increase in co-oxidation, leading to increased production of the dicarboxylic acids (adipic, suberic, sebacic). In addition, many of these disor¬ ders lead to the accumulation of the acyl-carnitine derivatives that are the substrate for the missing enzyme, that is, octanoylcarnitine in medium-chain acyl-CoA-dehydrogenase deficiency.

1366

PART IX: DISORDERS OF FUEL METABOLISM

R

- O' Several Steps

CH2 - CHj

O R

- CoA Carnitine Palmitoyl Transferase

R - CHj - CH

C

.O

-Carnitine Carnitine Palmitoyl Translocase Mitochondria

R - CH2 - CH2 - C

*0

- Carnitine

Carnitine Palmitoyl Transferase ▼ *0 R-CH2-CH2-C - CoA

FIGURE 155-4. acid oxidation.

Schematic presentation of fatty

DISORDERS OF FATTY ACID OXIDATION Several disorders of fatty acid oxidation recently have been described that are associated with hypoglycemia. These disorders often share the features of: (1) hypoglycemia, (2) hypoketonemia, (3) dicarboxylic aciduria or excretion of other fatty acid oxidation intermediates, (4) muscle weakness, (5) cardiomyopa¬ thy, (6) hepatic dysfunction, and (7) low serum and tissue carni¬ tine levels. Medium-chain acyl-CoA-dehydrogenase deficiency ap¬ pears to be one of the most common of these disorders.1010* Patients with this defect usually have episodic hypoglycemia as¬ sociated with mild to moderate hepatic dysfunction (a Reye syndrome-like presentation with elevated transaminase levels, mild hyperammonemia, and prolongation of the prothrombin time, but without hyperbilirubinemia). The episodes may be in¬ duced by fasting. The intravenous infusion of glucose usually rapidly corrects the hypoglycemia and mild acidosis. During acute episodes, and inconsistently when well, patients excrete in¬ creased urinary levels of dicarboxylic acids and medium-chain acyl-carnitines. Urine and serum ketone bodies are low. Patients also tend to have low levels of serum and tissue carnitine, proba¬ bly secondary to increased urinary carnitine losses. Mild muscle weakness and abnormal electromyographic readings are also common findings. Treatment consists of avoiding fasting. A high carbohydrate diet and carnitine replacement may also be of some benefit. One specific nucleotide substitution, A to G at nucleotide 985, accounts for about 90% of the mutations causing this disorder. Long-chain acyl-CoA-dehydrogenase deficiency has a similar but more severe clinical presentation. The nonketotic hypoglyce¬

mia associated with hepatic dysfunction tends to occur at an ear¬ lier age. The skeletal muscle weakness is more severe, and a cardiac involvement can lead to a cardiomyopathy and cardiac arrest during fasting. Primary carnitine deficiency presents with muscle weakness combined with nonketotic hypoglycemia and episodic hepatic dysfunction.11,12 The primary defect is in the renal and cellular transport of carnitine. The carnitine transport defect can be di¬ rectly demonstrated in cultured fibroblasts or by measurement of renal carnitine reabsorption. Several patients reported to have primary carnitine deficiency and a renal carnitine transport defect subsequently were found to have carnitine deficiency sec¬ ondary to another disorder (e.g., medium-chain acyl-CoAdehydrogenase deficiency.) Many patients with primary carni¬ tine deficiency improve symptomatically with L-carnitine therapy, although the change in the low tissue levels of carnitine is often minimal. Muscle carnitine palmitoyl transferase deficiency causes rhabdomyolysis, usually after prolonged exercise. Two patients have been reported with a deficiency of carnitine palmitoyl transferase that apparently was confined to the liver.13 These patients had hypoketonemic hypoglycemia in the first year of life. Therapy with oral medium-chain triglycerides corrected the hypoglyce¬ mia, but long-term results with this treatment have not been reported. Long-chain 3-hydroxy acyl-CoA-dehydrogenase deficiency is associated with severe hypoglycemia, liver dysfunction, muscle weakness, and cardiomyopathy. Single patients with defects in short-chain 3-hydroxy acyl-CoA-dehydrogenase and acyl-carnitine translocase,14 which translocates long-chain acyl-carnitine across the mitochondrial membrane, have been described. Both

Ch. 155: Hypoglycemia of Infancy and Childhood disorders cause hypoglycemia, encephalopathy, and muscle weakness. A deficiency of electron transfer flavoprotein or electron transfer flavoprotein dehydrogenase, which are involved in the transfer of electrons from the acyl-CoA-dehydrogenases to ubi¬ quinone oxidoreductase, causes hypoglycemia as part of a com¬ plex disorder. The clinical presentation of these disorders can vary from severe overwhelming acidosis and multiple defects (often referred to as glutaric aciduria type II) to hypoglycemia, less severe acidosis, and developmental delay (often referred to as ethylmalonic-adipic aciduria.) The avoidance of prolonged fasting appears to be very im¬ portant in patients with fatty acid oxidation disorders. If the de¬ fect is confined to long-chain fatty acid oxidation, a high medium-chain triglyceride diet may be beneficial.15 L-Carnitine therapy also may help, although the carnitine deficiency in these patients probably is not the primary problem, except in primary carnitine deficiency. It can be expected that patients with defects in all of the en¬ zymes of fatty acid oxidation will be found, as has been the case for enzymes involved in glycogen storage.

HYPERINSULINEMIA In older children and adults, hyperinsulinemia almost al¬ ways is due to an islet cell adenoma or carcinoma (assuming the exclusion of malicious or accidental insulin or oral hypoglycemic administration). An islet cell adenoma is rare in children younger than 1 year of age.16 In infants up to about 1 year of age, hyper¬ insulinemia may be due to diffuse B-cell hyperplasia or nesidi¬ oblastosis}7'19 Normally, the endocrine tissue of an infant is less well organized into islets than in older children and adults; insu¬ lin, glucagon, and somatostatin-producing cells may be seen scattered singly or in small clumps among the acinar cells. Some infants with clinical hyperinsulinemia appear to have an in¬ creased mass of insulin-producing cells (i.e., nesidioblastosis); however, others cannot be clearly differentiated from normal on the basis of pathologic examination of the pancreas.20 Islet cell hyperplasia/nesidioblastosis can be inherited as an autosomal recessive trait.

MANIFESTATIONS The hypoglycemia in patients with hyperinsulinemia, par¬ ticularly infants, may be particularly severe. Many patients be¬ come hypoglycemic after only a few hours of fasting; others be¬ come hypoglycemic even when receiving routine intravenous glucose therapy. Conversely, in older children, the symptoms of hyperinsulinemia may not be as dramatic. Some infants with hyperinsulinemia develop hypoglycemia when given leucine or a high protein meal. Leucine-sensitive hy¬ poglycemia was once thought to be a separate disorder; however, most patients probably have hyperinsulinemia. In most of those patients, a low protein diet is not sufficient therapy. Nevertheless, such a diet can be helpful when combined with other therapy for hyperinsulinemia. The general course of hyperinsulinemia due to a diffuse ab¬ normality is one of improvement. Some infants may improve sig¬ nificantly by 2 to 6 months of age; others may require years be¬ fore therapy can be successfully withdrawn.

DIAGNOSIS The diagnosis of hyperinsulinemia is dependent on the dem¬ onstration of an abnormally high serum insulin concentration and coexistent hypoglycemia (see Chap. 152). In the presence of hypoglycemia, a serum insulin level of less than 6 /uU/mL is expected. Hyperinsulinemia is suggested by a basal glucose con¬ sumption of over 5 mg/kg/h, determined by gradually reducing

1367

an intravenous glucose infusion until the serum glucose falls to hypoglycemic levels. Patients with hyperinsulinemia have unex¬ pectedly low levels of serum /3-hydroxybutyrate if they are fasted until they become hypoglycemic.16 This has been attributed to the inhibition of fatty acid mobilization by the elevated insulin, but partly it may reflect the short fast tolerated by these patients. Patients with hyperinsulinemia are also reported to have abnormally low levels of branch-chain amino acids during hypoglycemia.

THERAPY Because most older children with hyperinsulinemia have an adenoma, surgical exploration is indicated (see Chap. 154). In infants, the possibility of an adenoma is much lower. Infants usu¬ ally are treated first medically. Great care is often needed to grad¬ ually decrease therapy. The overall goal is to aggressively avoid hypoglycemia, but to procrastinate, if possible, to await sponta¬ neous improvement. Treatment consists of a combination of medication: diazoxide, 8-12 mg/kg; subcutaneous administra¬ tion of somatostatin (octreotide);203 and for short-term control, glucagon infusions. In addition, avoidance of fasting may further include intravenous glucose, continuous feedings, frequent low protein and high carbohydrate feedings, and oral cornstarch. The aim is to develop a therapy that can be maintained long-term while still giving a good margin for avoiding hypoglycemia (low¬ est blood glucose, about 60 mg/dL). If normoglycemia cannot be maintained with medical therapy, surgical exploration and a 70% pancreatectomy is indicated if no adenoma is found. Patients with severe hypoglycemia may continue to need medical ther¬ apy, and a few patients may require a total pancreatectomy to control the hypoglycemia. Recurrent hypoglycemia can cause permanent neurologic damage. Thus, it is important to give enough intravenous glucose to avoid hypoglycemia and to pro¬ ceed with definitive therapy without undue delay. It is also es¬ sential to make sure that the hyperinsulinemia in an infant is not in part due to the intravenous infusion of large amounts of glu¬ cose. Because some infants may have transient hyperinsulin¬ emia, it is important to wait a reasonable length of time to deter¬ mine whether intravenous glucose support can be slowly withdrawn. Hypoglycemia caused by hyperinsulinemia also can occur in association with omphalocele, macroglossia, and gigantism (Beckwith syndrome) or in the cerebrohepatorenal syndrome (Bowen-Zellweger syndrome). Hypoglycemia due to malicious insulin administration in children should be suspected if there is severe but temporary hy¬ poglycemia and very high serum insulin levels. It can be con¬ firmed if the serum C-peptide is low or if the presence of circu¬ lating nonhuman insulin can be demonstrated.

KETOTIC HYPOGLYCEMIA Ketotic hypoglycemia probably accounts for 90% of the chil¬ dren who have hypoglycemia beyond infancy.2' Typically, hy¬ poglycemia first occurs at about l1/2 to 5 years of age. After 8 or 9 years of age, hypoglycemia in children with this disorder is uncommon. Many children with ketotic hypoglycemia are small and thin for their age, and many were small for their gestational age at birth. Attacks often include neurologic symptoms, ranging from lethargy to seizures and coma, and they most commonly occur in the morning. An early-morning seizure in any child should suggest ketotic hypoglycemia.

ETIOLOGY The cause of ketotic hypoglycemia is unclear. One theory is that it is due to deficient release of substrate from muscle for gluconeogenesis, particularly alanine. Children with this disor-

1368

PART IX: DISORDERS OF FUEL METABOLISM

der have low serum alanine levels. They also have an appropriate rise in serum glucose if given an infusion of alanine during hypo¬ glycemia. The cause of the proposed decrease in muscle alanine release may be a specific defect or simply the relative decrease in muscle mass in these children. Another possibility is that many of these children may have a deficient catecholamine response to hypoglycemia.22 Adrenal medullary unresponsiveness to hypoglycemia, or Zetterstrom syndrome, a common diagnosis in the 1960s, was diagnosed on the basis of failure of urinary epinephrine to increase in the 3 hours after insulin-induced hypoglycemia. The clinical features of this disorder are identical to what is now known as ketotic hy¬ poglycemia. Studies suggest that about half of the patients who would otherwise fulfill the criteria for ketotic hypoglycemia have a reduced plasma epinephrine response to hypoglycemia.23 Because almost any child will become hypoglycemic after a 24- to 36-hour fast, ketotic hypoglycemia may be simply one end of the normal spectrum rather than a distinct disorder. Often the distinction between ketotic hypoglycemia and normalcy is not clear.

DIAGNOSIS AND TREATMENT The diagnosis of ketotic hypoglycemia is usually based on the response to fasting. Typically, children with ketotic hypogly¬ cemia become hypoglycemic in 12 to 24 hours and have a normal hormonal and metabolic response to fasting. Normal children be¬ come hypoglycemic in 24 to 36 hours. Children who have had clinical episodes of hypoglycemia, but who do not become hypo¬ glycemic during a 24-hour fast, probably have a mild form of ketotic hypoglycemia. The treatment consists of assuring that prolonged periods of fasting do not occur. Most important is the provision of a bedtime snack every night. During intercurrent illnesses, the child should be given carbohydrate-rich liquids. Parents should be taught to test for urine ketones so that they can tell when hypoglycemia is likely to occur.

GLUCAGON DEFICIENCY Glucagon deficiency rarely has been reported to cause recur¬ rent hypoglycemia in infants. This disorder also is associated with failure to thrive, and in some patients, it may be familial.24

REACTIVE OR FUNCTIONAL HYPOGLYCEMIA Reactive or functional hypoglycemia often is diagnosed in children, but there are no clear criteria for making this diagnosis. It has been suggested that it is greatly overdiagnosed. Indeed, some investigators question if this syndrome actually does occur in otherwise normal children. Hypoglycemia and a dumping

syndrome occur in some children after gastric or pyloric surgery.25

REFERENCES 1. Pagliara AS, Karl IE, Haymond M, Kipnis DM. Hypoglycemia in infancy and childhood. Part I. J Pediatr 1973; 82:365. 2. Cornblath M, Schwartz R, Aynsley-reen A, Lloyd JK. Hypoglycemia in infancy: the need for rational definition. Pediatrics 1990;85:834. 3. Hems DA, Whitton PD. Control of hepatic glycogenolysis. Physiol Rev 1980;60:1. 4. Foster DW. From glycogen to ketones and back. Diabetes 1984; 33:1188. 5. Greene HL. Glycogen storage disease. Semin Liver Dis 1982;2:291. 6. Chen YT, Cornblath M, Sidbury JB. Cornstarch therapy in type 1 glycogenstorage disease. N Engl J Med 1984; 310:171. 7. Chen YT, Coleman RA, Scheinman J, et al. Renal disease in type I glycogen storage disease. N Engl J Med 1988; 318:7. 8. Pagliara AS, Karl El, Keating JP, et al. Hepatic fructose in 1,6-diphospha¬ tase deficiency, a cause of lactic acidosis and hypoglycemia in infancy. J Clin Invest 1972; 51:2115. 9. Hommes FA, Bendien K, Elema JD, et al. Two cases of phosphoenolpyruvate carboxykinase deficiency. Acta Pediatr Scand 1976; 65:233. 10. Stanley CA, Hale DE, Coates PM, et al. Medium-chain acyl-CoA dehy¬ drogenase deficiency in children with non-ketotic hypoglycemia and low carnitine levels. Pediatr Res 1983; 17:877. 10a. Iafolla AK, Thompson RJ, Roe CR. Medium-chain acylcoenzyme A de¬ hydrogenase deficiency: clinical course in 120 affected children. ] Pediatr 1994; 124: 409. 11. Stanley CA, Treem WR, Hale DE, et al. A genetic defect in carnitine transport causing primary carnitine deficiency. In: Tanaka K, Coates PM, eds. Fatty acid oxidation: clinical biochemical and molecular aspects. New York: Alan R Liss, 1990;457. 12. Treem WR, Stanley CA, Finegold DN, et al. Primary carnitive deficiency due to a failure of carnitine transport in kidney, muscle and fibroblast. N Engl J Med 1988,-319:1331. 13. Bougneres PF, Saudubray J, Marsac C, et al. Fasting hypoglycemia result¬ ing from hepatic carnitine palmitoyl transferase deficiency. ] Pediatr 1981;98:742. 14. Stanley CA, Hale DE, Berry GT, et al. A deficiency of acyl carnitine translocase in the inner mitochondrial membrane. N Engl J Med 1992;327:19. 15. Glasgow AM, Engle AG, Bier DM, et al. Hypoglycemia, hepatic dysfunc¬ tion, muscle weakness, cardiomyopathy, free carnitine deficiency and long-chain acylcarnitine excess responsive to medium chain triglyceride diet. Pediatr Res 1983; 17:319. 16. Stanley CA, Baker L. Hyperinsulinism in infants: diagnosis by demon¬ stration of abnormal response to fasting. Pediatrics 1976;56:702. 17. Rosenberg L, Duguid WP, Brown RA, Vinik AT Induction of nesidi¬ oblastosis will reverse diabetes in Syrian golden hamster. Diabetes 1988;37:344. 18. Mathew PM, Young JM, Abu-Osba YK, et al. Persistent neonatal hyper¬ insulinism. Clin Pediatr 1988; 27:148. 19. Daneman D, Ehrlich RM. The enigma of persistent hyperinsulinemic hy¬ poglycemia of infancy. J Pediatr 1993; 123:573. 20. Rahier ]. Relevance of endocrine pancreas nesidioblastosis to hyperinsul¬ inemic hypoglycemia. Diabetes Care 1989; 12:164. 20a. Glaser B, Hirsch H], Landau H. Persistent hyperinsulinemic hypoglyce¬ mia of infancy: long-term octreotide treatment without pancreatectomy, j Pediatr 1993;123:644. 21. Haymond MW, Pagliara AS. Ketotic hypoglycemia. Clin Endocrinol Metab 1983; 12:447. 22. Broberger O, Zetterstrom R. Hypoglycemia with an inability to increase the epinephrine secretion in insulin-induced hypoglycemia. J Pediatr 1961;59:215. 23. Hansen IL, Levy MM, Kerr DS. The 2-deoxyglucose test as a supplement to fasting for detection of childhood hypoglycemia. Pediatr Res 1984; 18:227. 24. Vidnes J, Oyasaeter S. Glucagon deficiency causing severe neonatal hy¬ poglycemia in a patient with normal insulin secretion. Pediatr Res 1977; 11:943. 25. Rivkees SA, Crawford JD. Hypoglycemia pathogenesis in children with dumping syndrome. Pediatrics 1987; 80:937.

Ch. 156: Biochemistry and Physiology of Lipid and Lipoprotein Metabolism

SECTION

1369

D

LIPID METABOLISM 20 carbons long. Linoleic acid, for example, has two double bonds and 18 carbons; linolenic acid has three double bonds and 18 carbons. Fatty acids are free (i.e., nonesterified) or esterified to other organic molecules. Free fatty acids are transported in the plasma bound to albumin and serve as a readily available form of energy or as a substrate for complex lipid biosynthesis. There are three major classes of complex lipids: triglycerides, cholesterol, and phospholipids. The most abundant complex lipid is triglyceride (i.e., triacylglycerol), which serves as a storage form of fatty acids. Triglycerides consist of three fatty acid molecules esterified to one glycerol molecule (see Fig. 156-1). Glycerol es¬ ters containing one or two fatty acid molecules are called mono¬ glycerides and diglycerides, respectively. Cholesterol, composed of a four-ring hydrocarbon and an eight-carbon side chain (see Fig. 156-1), is an important class of lipids that serves in mem¬ brane structure and as a precursor to steroid hormones and bile acids. In the blood, about two thirds of the cholesterol is esterified to a fatty acid through the hydroxyl group at residue 3 of the cholesterol molecule to form cholesteryl ester. Phospholipids contain two fatty acids esterified to two of the three hydroxyl groups on glycerol (see Fig. 156-1). The third hydroxyl group is esterified to phosphate; this complex lipid is referred to as phosphatidic acid. Typically, in mammalian tissue, the phosphatidic acid is esterified to the hydroxyl group of a hydrophilic molecule, such as choline, serine, or ethanolamine, forming phosphatidyl¬ choline, phosphatidylserine, and phosphatidylethanolamine, re¬ spectively (see Fig. 156-1). The combination of hydrophobic and hydrophilic molecules in phospholipids allows them to function at water-lipid interfaces, making them ideal components of membranes and of surface coats of plasma lipoproteins. Disorders in lipid transport, often reflected in changes in the quantity and structure of plasma lipoproteins, cause metabolic derangements that lead to several diseases. An understanding of the cause and treatment of these disorders requires a knowledge of the metabolism of the various plasma lipoproteins. The principal sites of synthesis of plasma lipoproteins are

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

156_

BIOCHEMISTRY AND PHYSIOLOGY OF LIPID AND LIPOPROTEIN METABOLISM ROBERT W. MAHLEY

LIPIDS, LIPOPROTEINS, AND LIPID TRANSPORT An efficient system for lipid transport is a prerequisite for normal metabolism in vertebrates. Most lipids are found in mem¬ branes, which maintain the integrity of cells and allow compart mentalization of the cytoplasm into specific organelles. Lipids also function as a major form of stored nutrients (e.g., triglycer¬ ides), as precursors for steroid hormones and bile acids (e.g., cho¬ lesterol), and as intracellular and intercellular messengers (e.g., prostaglandins, phosphatidylinositol). Lipids are organic molecules that are insoluble or minimally soluble in water because of their hydrophobic nature. One class of lipids is fatty acids. There are numerous types of fatty acids, which differ in length and in the number and position of their double bonds. Fatty acids that lack double bonds are called satu¬ rated, and those with one or more double bonds are unsaturated or polyunsaturated (Fig. 156-1). The most abundant saturated fatty acids are 16 and 18 carbons long and are referred to as pal¬ mitic and stearic acids, respectively. The common unsaturated fatty acids have one to three double bonds and are typically 16 to

A. Fatty Acids Stearic Acid: Oleic Acid: Linoleic Acid:

CH3 - (CH2)i6 - COOH CH3 - (CH2)7 - CH = CH - (CH2)7 - COOH CH3 - (CH2)4 - CH = CH - CH2 - CH = CH - (CH2)7 - COOH

C. Phospholipids

B. Triglycerides

o

o

II

HoC — O - C - Fatty Acid

H2C-0- C -(CH2)16-CH3 I o HC-O - C -(CH2)16-CH3

1

l 1 h2c -

9

H2C-0- C -(CH2)16-CH3 I_II_I Glycerol

0 II

HC — O — C — Fatty Acid

O o- p-

q^j

I 3

o - ch2 - ch2 - n+ - ch3 I

CHo

Fatty Acid

Choline

Phosphatidylcholine

Tristearin

D. Cholesterol

ch3

i

7ch3

CH - CH2 - CH2 - CH2 - CH xch3

OH

FIGURE 156-1.

Structure of common lipids.

1370

PART IX: DISORDERS OF FUEL METABOLISM

TABLE 156-1 Characterization of Plasma Lipoproteins

Class

Density of Flotation (g/mL)

Major Lipids

Major Apoproteins

Origins

Functions

MAJOR CLASSES OF PLASMA LIPOPROTEINS Chylomicrons

d < 0.95

Triglyceride

B-48, A-I, A-IV (E and Cs by transfer from HDL)

Synthesized by small intestine

Transport of dietary triglyceride and cholesterol from the intestine to other tissues

Chylomicron remnants

d < 0.95

Triglyceride,

B-48, E

Derived from chylomicrons by lipase hydrolysis of triglyceride

Delivery of cholesterol to the liver; represent atherogenic lipoproteins

Very low density lipoproteins (VLDL)

d < 1.006

B-100, E, Cs

Synthesized by liver

Transport of triglyceride to peripheral tissues; free fatty acids liberated by

Intermediatedensity lipoproteins (IDL)

d= 1.006-1.019

Triglyceride, cholesterol

B-100, E

Derived from VLDL by lipase hydrolysis of triglyceride

Precursor of LDL; a fraction is taken up by the liver

Low-density lipoproteins (LDL)

d = 1.019-1.063

Cholesterol

B-100

Derived from VLDL and IDL by lipase hydrolysis of triglyceride

Major carrier of cholesterol, which is utilized by peripheral tissue via LDL receptor-medicated uptake; correlates directly with accelerated coronary artery disease

High-density lipoproteins (HDL)

d= 1.063-1.21

Phospholipid, cholesterol

A-I, A-II, Cs

Synthesized by liver and intestine; also derived from surface of chylomicrons and VLDL during lipolysis

Facilitate removal of cholesterol from peripheral tissues; redistribute cholesterol to other tissues and to the liver; HDL-cholesterol correlate inversely with coronary artery disease

cholesterol

Triglyceride

lipase hydrolysis

SPECIALIZED CLASSES OF PLASMA LIPOPROTEINS Lipoprotein (a) [Lp(a)J

d= 1.05-1.12

Cholesterol

B-100, apo(a)

Apo(a) from the liver complexes with LDL

Concentration correlates directly with accelerated coronary artery disease

Fraction I

d< 1.006

Triglyceride, cholesterol

B-48, E

Intestine

Chylomicron remnants; atherogenic lipoproteins

Fraction II

d < 1.006

Triglyceride, cholesterol

B-100, E

Liver

VLDL remnants; atherogenic lipoproteins

/3-Very low density lipoproteins CS-VLDL)

the liver and the intestine. The plasma lipoproteins are watersoluble macromolecular complexes (i.e., pseudomicellar parti¬ cles) of lipids (e.g., triglycerides, cholesterol, phospholipids) and one or more specific proteins, referred to as apolipoproteins or apo¬ proteins. The apoprotein component of these complexes deter¬ mines the fate of the various lipoproteins by targeting their de¬ livery of lipid to specific cells. Generally, the nonpolar lipids (i.e., triglycerides and cholesteryl esters) are found in the center of the particles, surrounded by the more polar lipids (i.e., phospholipids and free cholesterol) and apoproteins. Human plasma lipoproteins are commonly divided into six major classes, differentiated primarily by the density at which they float during ultracentrifugation. They are defined further on the basis of particle size, electrophoretic mobility, and apoprotein content. The major classes of lipoproteins and their roles in metabolism are listed in Table 156-1.1-5

PLASMA LIPOPROTEINS: AN OVERVIEW CHYLOMICRONS AND CHYLOMICRON REMNANTS Chylomicrons (density < 0.95 g/mL) are synthesized by the small intestine to transport dietary triglyceride and cholesterol from the site of absorption by the intestinal epithelium to various cells of the body (Fig. 156-2). They are normally absent from the

plasma after fasting overnight (12 hours). The triglycerides of these particles are hydrolyzed within the plasma compartment by the action of lipoprotein lipase (LPL), which is attached to the endothelial surfaces of capillaries, especially in adipose tissue, the heart, and skeletal muscle. The lipoprotein particles gener¬ ated by the action of LPL on chylomicrons are referred to as chy¬ lomicron remnants. They are enriched in cholesterol (by virtue of the loss of triglyceride) and, under normal conditions, are rapidly cleared by the liver. Chylomicron remnants, which accumulate in the plasma of animals whose diets are high in fat and cholesterol and in the plasma of patients with type III hyperlipoproteinemia, have been linked to the development of accelerated atherosclerosis.5,6

VERY LOW DENSITY LIPOPROTEINS Very low density lipoproteins (VLDL; density < 1.006 g/ mL) are synthesized by the liver to transport triglycerides and cholesterol from the hepatocytes to various tissues of the body (see Fig. 156-2). Within the plasma compartment, the triglycer¬ ides of VLDL are hydrolyzed by LPL and hepatic LPL, gen¬ erating a series of smaller, cholesterol-enriched lipoproteins: intermediate-density lipoproteins (IDL; density = 1.006-1.019 g/ mL) and low-density lipoproteins (LDL; density = 1.019-1.063 g/ mL). Smaller VLDL and IDL, referred to as VLDL remnants, ap¬ pear to be atherogenic lipoproteins.5,6

Ch. 156: Biochemistry and Physiology of Lipid and Lipoprotein Metabolism

1371

FIGURE 156-2.

Summary of the metabolism of chylomicrons, very low density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and chylomicron remnants. FFA, free fatty acids.

LOW-DENSITY LIPOPROTEINS LDL represent the end product of VLDL catabolism and are the major cholesterol-transporting lipoproteins in the plasma. Because of defective or absent LDL receptors in patients with fa¬ milial hypercholesterolemia or defective apolipoprotein (apo) B-100 in patients with familial defective apoB-100, LDL accumu¬ late in the plasma at levels that correlate directly with the exis¬ tence of accelerated coronary artery disease.5-8

HIGH-DENSITY LIPOPROTEINS High-density lipoproteins (HDL; density = 1.063-1.21 g/ mL) originate from several sources: the liver, the intestine, and within the plasma compartment during lipolytic processing of chylomicrons and VLDL. The HDL participate in a process re¬ ferred to as reverse cholesterol transport, a postulated pathway whereby HDL acquire cholesterol from peripheral tissues and transport the cholesterol, directly or indirectly, to the liver for excretion5,6 (Fig. 156-3). Observations suggesting an inverse cor¬ relation between HDL levels and atherosclerotic vascular disease in humans (i.e., low HDL levels associated with increased coro¬ nary artery disease) have focused attention on this lipoprotein class and its role in cholesterol metabolism. In humans, much of the cholesteryl ester present in the lipoproteins appears to be formed in plasma in association with HDL by the enzyme lecithinxholesterol acyltransferase (LCAT).9 This enzyme catalyzes the transfer of a fatty acid from phospholipid (i.e., lecithin) to the 3|8-hydroxy position of cholesterol, forming a cholesteryl ester. The cholesteryl esters formed by this reaction are transferred to other lipoproteins by the cholesteryl ester transfer protein

156-2. To understand lipoprotein metabolism and the disease states associated with lipid abnormalities, it is necessary to con¬ sider functions that have been ascribed to specific apoproteins.

TRANSPORT AND REDISTRIBUTION OF LIPIDS AMONG CELLS APOPROTEINS B AND E Apoproteins B-100 and E are the major proteins responsible for recognition of lipoproteins by specific cell-surface receptors that mediate uptake of lipoprotein cholesterol by cells.311-13 Apo¬ protein B-48 lacks the receptor binding domain and does not bind to the LDL receptor. There appear to be two major lipoprotein receptors: the LDL receptor and the chylomicron (apoE) remnant

(CETP).

APOPROTEINS The metabolism of the various plasma lipoproteins is regu¬ lated and directed by the presence of specific apoproteins that characterize each of the major lipoprotein classes. The apopro¬ tein constituents of the major lipoproteins can be visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE; Fig. 156-4); their properties are listed in Table

FIGURE 156-3.

Summary of the metabolism of high-density lipopro¬ teins (HDL). The HDL are formed by the intestine and liver and by the transfer of free cholesterol (FC), phospholipid (PL), and apoproteins from chylomicrons and very low density lipoproteins (VLDL) during lipolysis. The HDL can acquire cholesterol from various tissues possessing excess cholesterol (HDL-C). The E apoprotein produced by various cells in pe¬ ripheral tissues is added to the HDL-C to form HDL with apo E. IDL, intermediate-density lipoproteins; LDL, low-density lipoproteins.

1372

PART IX: DISORDERS OF FUEL METABOLISM

B

46K —— A-IV 35K —~ E

28KDH■V A-l

Chylomicrons FIGURE 156-4.

VLDL

LDL

— HDL —

Sodium dodecyl sulfate-polyacrylamide gels of human

plasma lipoprotein classes, demonstrating the major apoproteins associ¬

VLDL, very low density lipoproteins; LDL, low-density lipoproteins; HDL, high-density lipoproteins. (From Mahley RW, lnnerarity TL. Lipoprotein receptors and cholesterol homeosta¬ sis. Biochim Biophys Acta 1983;737:197.) ated with each lipoprotein class.

receptor (apparently equivalent to the LDL receptor-related protein [LRP]).14-16 Low-Density-Lipoprotein Receptor. The LDL receptor, some¬ times referred to as the apoB-100,E receptor, is on the surface of most extrahepatic cells and hepatic parenchymal cells.7 This receptor participates in the delivery of cholesterol to various cells, where it is used in membrane biosynthesis, or to steroidproducing cells, where it acts as a precursor for hormone produc¬ tion. In the liver, the LDL receptor functions in the removal and catabolism of LDL and a fraction (about one half) of the VLDL and IDL. The LDL receptors bind apoB-100-containing and apoEcontaining lipoproteins; once bound, the lipoproteins are inter¬ nalized by endocytosis of the receptors in coated pits and are

degraded within the lysosomes of the cells. Before the complex enters the lysosome, the receptors dissociate from the lipoprotein in an endosomal compartment of the cell and recycle to the sur¬ face of the cell, where they can again participate in lipoprotein binding and uptake. The receptors have a half-life (t,/2) of about 20 hours. The cholesterol liberated from the degraded lipoproteins participates in three ways in the regulation of intracellular cho¬ lesterol metabolism. First, the delivery of lipoprotein cholesterol to the cell suppresses cholesterol synthesis by regulating the ac¬ tivity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCoA reductase), the rate-limiting enzyme involved in intracellular cholesterol biosynthesis from mevalonate. Second, intracellular lipoprotein cholesterol stimulates the activity of acyl-CoA:cholesterol acyltransferase (ACAT). This causes the reesterification of excess cholesterol so that it can be stored, usually in small quan¬ tities, within the cell as cholesteryl ester. Third, the delivery of lipoprotein cholesterol by receptor-mediated uptake in quantities exceeding cellular needs causes down-regulation of the expres¬ sion of the LDL receptor on the cell surface. Conversely, a defi¬ ciency of cholesterol causes an increase in the number of recep¬ tors. This regulation of expression also appears to function in vivo, in that dietary fat and cholesterol consumption decrease the expression of hepatic LDL receptors, but treatment with the bile acid sequestrant cholestyramine increases the expression of he¬ patic LDL receptors. Delivery of lipoprotein cholesterol to the cell follows a tightly regulated pathway that functions in the mainte¬ nance of intracellular cholesterol homeostasis.1-4,11,12 The LDL receptor pathway is regulated similarly by apoBcontaining or apoE-containing lipoproteins.3,11,12 However, there is one major difference between these two ligands: apoE-containing lipoproteins bind to the receptor with a much higher affinity (20-25-fold) than do apoB-containing LDL. The higher affinity of apoE binding results from the ability of apoE-containing par¬ ticles to form multiple interactions with the LDL receptor. Anal¬ ysis of the structure of the LDL receptor reveals several cysteinerich repeats that also possess critical negatively charged glutamic and aspartic acid residues involved in the binding of apoB-100or apoE-containing lipoproteins.7 The physiologic importance of the high binding affinity of apoE-containing lipoproteins lies in the very rapid rate of plasma clearance of these lipoproteins (in minutes), compared with the much slower clearance of apoB-

TABLE 156-2 Characterization of the Major Apoproteins Apoprotein B-100

Plasma Concentration (mg/dL) 80-100

Molecular Mass (daltons)

Major Sites of Synthesis

Functions

-513,000

Liver

Intracellular formation of VLDL; ligand for the LDL receptor; structural protein for VLDL, IDL, and LDL

-246,000

Intestine

Intracellular formation of chylomicrons; structural protein for chylomicrons and their remnants Ligand for the LDL and apoE receptors; mediates uptake of chylomicron remnants, certain VLDL, IDL, and HDL with apoE (HDL,, HDLC)

B-48

100 nm in diameter) and readily float by ultracentrifugation (density < 0.95 g/mL). They are composed of about 98% to 99% lipid (~90% of the lipid is triglyceride) and 1% to 2% protein. Chylomicrons are present in postprandial plasma (but absent af¬ ter an overnight fast) and possess several apoproteins (i.e., B-48, A-I, A-IV, E, and Cs) as they circulate in the plasma (see Fig. 156-4). The distinctive apoprotein is apoB-48, a form of apoB that has an apparent molecular mass about one half of that of apoB100. It is the form of apoB synthesized by the intestine and is a marker for lipoproteins produced by the intestinal epithe¬ lium.33,34 ApoB-48 is formed in the intestine by a unique process

The VLDL are particles 30 to 70 nm in diameter that float by ultracentrifugation at a density less than 1.006 g/mL. They are composed of 85% to 90% lipid (~55% triglyceride, ~20% cho¬ lesterol, ~15% phospholipid) and 10% to 15% protein. Their distinctive apoprotein constituent is apoB-100, the hepatic form of apoB. Moreover, the VLDL contain apoE and apoCs. The VLDL have pre-/3- or a2-electrophoretic mobility and were once referred to as pre-/3-lipoproteins. ORIGIN

The VLDL are synthesized by the liver, and their production can be stimulated by an increased availability of free fatty acid

1376

PART IX: DISORDERS OF FUEL METABOLISM

delivered to the hepatocytes. Synthesis of triglyceride and phos¬ pholipid to be used in the formation of VLDL occurs in the rough and smooth endoplasmic reticulum. The VLDL cholesterol may be synthesized de novo or reused from cholesterol acquired by the liver during lipoprotein catabolism (e.g., from LDL choles¬ terol). Electron microscopy has shown that the VLDL particles first appear in the cell at the rough endoplasmic reticulumsmooth endoplasmic reticulum junction (i.e., transitional ele¬ ments) before they enter the Golgi apparatus. Within the Golgi apparatus, the carbohydrate processing of several of the apoprot¬ eins occurs. Large Golgi apparatus secretory vesicles appear to fuse with the luminal surface of hepatocytes and to release the VLDL particles into the space of Disse, from which they enter the plasma. The major protein constituents of the newly synthesized VLDL are apoB-100, apoE, and small amounts of the apoCs. Within the plasma, the VLDL acquire additional C apoproteins, primarily from EIDL.

the total plasma cholesterol is in LDL. They are about 20 nm in diameter and are composed of approximately 75% lipid (~35% cholesteryl ester, ~10% free cholesterol, ~10% triglyceride, ~20% phospholipid) and 25% protein. The apoB-100 is essen¬ tially the only protein present in these particles. The LDL have /3-electrophoretic mobility and were once referred to as /3-lipoproteins. ORIGIN

The LDL represent the end products of lipase-mediated hy¬ drolysis of VLDL. Moreover, as the triglyceride-rich core of the larger VLDL particles is removed, the surface lipids and proteins are remodeled with the transfer of excess surface constituents to HDL. The result is the formation of a cholesterol-rich small par¬ ticle devoid of almost all apoproteins, except apoB-100. METABOLIC FATE

METABOLIC FATE

The VLDL triglycerides are hydrolyzed by the action of LPL and, to a lesser extent, by hepatic lipase (see Fig. 156-2). The VLDL are progressively converted to smaller and smaller parti¬ cles that become increasingly cholesterol rich. The products of VLDL catabolism are referred to as IDL (density = 1.006-1.019 g/mL) and LDL (density = 1.019-1.063 g/mL). About 50% of the VLDL is removed directly from the plasma by the liver before the VLDL molecules are converted to either IDL or LDL. The per¬ centage of VLDL converted to LDL appears to depend partially on the number of LDL receptors expressed by the liver. For ex¬ ample, in Watanabe heritable hyperlipidemic (WHHL) rabbits, which have defective receptors, there is a marked increase in the conversion of VLDL to LDL, compared with normal rabbits (i.e., a decreased hepatic uptake of VLDL secondary to decreased numbers of LDL receptors and an increased conversion of VLDL to LDL).35 The receptor-mediated uptake of VLDL (and partially lipolyzed VLDL) depends primarily on the presence of apoE on these particles, and the receptor responsible for their uptake appears to be the LDL receptor. In cholesterol-fed animals, in which the LDL receptors are markedly down-regulated, the partially lipolyzed VLDL are not readily cleared, but are largely converted to LDL in a much higher percentage than is observed in normal animals.

The LDL are removed from the plasma at a relatively slow rate (T1/2 of 2-3 days) through interaction with LDL receptors in the liver hepatocytes and extrahepatic tissues (see Fig. 156-2). ApoB-100 is the protein moiety that mediates their uptake by the receptors. It appears that more than two thirds of LDL are actu¬ ally cleared from the plasma by receptors in the liver. The LDL are degraded in the hepatocytes, and the cholesterol is reused for lipoprotein (VLDL) biosynthesis and membrane synthesis or becomes a precursor for the biosynthesis of bile acids. The bile acids and free cholesterol are delivered to the bile. It is through this latter mechanism that cholesterol is eliminated from the body. The LDL are recognized as major atherogenic lipoproteins. This is demonstrated most clearly in patients with familial hyper¬ cholesterolemia.14 These individuals lack LDL receptors or have defective receptors, incapable of mediating normal binding or uptake of LDL. Individuals homozygous for such defects have markedly elevated LDL concentrations (>500 mg/dL) and usu¬ ally die of coronary artery disease as teenagers. The LDL also accumulate in the plasma of patients with familial defective apoB-100.8,36 This disorder is caused by a single amino acid sub¬ stitution of glutamine for arginine at residue 3500 in the apoB100, which prevents the interaction of the LDL with the LDL receptor.

INTERMEDIATE-DENSITY LIPOPROTEINS

HIGH-DENSITY LIPOPROTEINS

CHARACTERISTICS

CHARACTERISTICS

The IDL (density = 1.006-1.019 g/mL) are normally present in very low concentrations in the plasma and are intermediate in size and composition between VLDL and LDL. Their primary protein constituents are apoB-100 and apoE.

The HDL are smaller particles (8-13 nm) and float by ultra¬ centrifugation at a density of 1.063 to 1.21 g/mL. They contain about 50% lipid (~25% phospholipid, ~15% cholesteryl esters, ~5% free cholesterol, ~5% triglyceride) and 50% protein. Their major apoproteins are apoA-I, apoA-II, and apoCs. The HDL mi¬ grate in the apposition on electrophoresis and were once referred to as a-lipoproteins. The HDL can be further subdivided into HDL2 (density = 1.063-1.125 g/mL) and HDL3 (density = 1.125-1.21 g/mL). They can also be subdivided on the basis of their apoprotein content: apoA-I alone or apoA-I/A-II particles.

ORIGIN

The IDL are metabolic products of VLDL catabolism and precursors of LDL generated in the plasma by the action of lipases. METABOLIC FATE

As shown in Figure 156-2, the IDL may be further processed by the action of LPL and hepatic lipase or removed from the plasma by the LDL receptor. These lipoproteins are considered to be atherogenic and constitute a component of VLDL remnant particles that float at a density of 1.006 to 1.019 g/mL.

LOW-DENSITY LIPOPROTEINS CHARACTERISTICS

The LDL (density = 1.019-1.063 g/mL) are the major cholesterol-carrying lipoproteins in the plasma; about 70% of

ORIGIN

The different forms of HDL are synthesized by the liver and intestine (see Fig. 156-3); however, little is known about the in¬ tracellular sites of synthesis and secretion of these particles. ApoA-I-containing disks are produced by the intestine and liver and generated from the surface of remnant lipoproteins during lipolysis. It appears that these precursors of HDL are converted to spherical particles by the action of LCAT on the cholesterol acquired by the HDL. Cholesteryl ester formation catalyzed by LCAT enriches the core of the disk with cholesteryl esters, caus¬ ing conversion of the disks to spherical particles.

Ch. 156: Biochemistry and Physiology of Lipid and Lipoprotein Metabolism By ultracentrifugation, HDL are subdivided commonly into HDL2 (i.e., larger, more lipid-rich HDL) and HDL3 (i.e., smaller HDL particles). Metabolic interconversions between HDL2 and HDL3 have also been described. For example, the smaller HDL3 acquire phospholipid and cholesterol during chylomicron and VLDL lipolysis or acquire cholesterol from cells, converting them to the larger HDL2. The CETP transfers cholesterol from the HDL2 to lower-density lipoproteins (e.g., VLDL, IDL), and the HDL2 become enriched in triglycerides. Hepatic lipase catalyzes the hydrolysis of the triglycerides and surface phospholipids from the HDL2, regenerating the HDL3 from the HDL2 particles. The HDL have received considerable attention because it is the change in their concentration that correlates inversely with coro¬ nary artery disease. The HDL2 and HDL3 have been further fractionated into nu¬ merous subfractions; there are distinct subclasses within HDL2 and HDL3 that differ biochemically and metabolically. For exam¬ ple, within the HDL2 subclass, there are HDL that contain apoE along with apoA-I. The presence of the apoE has significant met¬ abolic consequences; these particles can be recognized by the LDL receptor, but HDL that lack apoE cannot. This subclass, characterized by being more enriched in cholesterol and contain¬ ing apoE, is referred to as HDL3 or HDLC.3,5 The HDL3 (HDL with apoE) are present in the plasma of humans, but they are more abundant in the plasma of many animals. The concentration of HDL with apoE in the plasma correlates indirectly with CETP activity; i.e., animals like rats, mice, and dogs that are deficient in CETP have high levels of HDL with apoE, but humans and rab¬ bits have CETP and low levels of HDL with apoE. The HDL participate in a process of redistribution of choles¬ terol among cells, a process referred to as reverse cholesterol transport. Cholesterol from peripheral cells is transferred to the liver for excretion from the body5,6 (see Fig. 156-3). The HDL (primarily HDL3, but also HDL2) can acquire cholesterol from cells possessing excess cholesterol. The cholesterol can be esterified by the action of LCAT, increasing the cholesteryl ester content of the particles. In humans, most cholesteryl esters are transferred by CETP to VLDL, IDL, or LDL, and the cholesteryl esters of HDL are indirectly delivered to the liver for excretion from the body through the LDL pathway. During the process of cholesterol loading of the HDL, some of the cholesterol-enriched HDL also acquire apoE. By virtue of the presence of apoE, these HDL are then recognized by the lipoprotein receptors on various cells. Cholesterol transport to the liver may occur directly by the interaction between HDL with apoE and the hepatic lipoprotein receptors and by the subsequent uptake of the cholesterol. These mechanisms involving HDL may represent the process whereby HDL exert their protective effect in retarding or reversing coro¬ nary artery disease. METABOLIC FATE

In addition to the complex series of interconversions of which they are a part, HDL appear to be catabolized primarily in the liver. The mechanism for their uptake remains undefined. It appears that the cholesterol may be removed from the particles, particularly in the liver, without the whole particle being taken up and degraded. The whole particle can also be cleared from the plasma.

OTHER SPECIALIZED LIPOPROTEINS LIPOPROTEIN(a)

Characteristics. The density of flotation of lipoprotein(a) [Lp(a); density = 1.05-1.12 g/mL) is between that of LDL and HDL. The Lp(a) particles closely resemble LDL in lipid composi¬ tion and represent apoB-100-containing LDL that acquire apo(a).37-39 The Lp(a) particles migrate with a2-mobility on electrophoresis. ApoB-100 is a major protein constituent of Lp(a); however, unlike the apoB-100 of LDL, the apoB-100 of Lp(a) is disulfide-

1377

linked to another protein referred to as the Lp(a) antigen, or apo(a).37-39 The apoB-100 and apo(a) are present in the Lp(a) at a ratio of 1:1. The apo(a) is highly glycosylated and exists in multiple forms. There may be more than 30 allelic forms of apo(a) in the human population, with molecular weights from about 400,000 to 800,000.39 The concentration of Lp(a) in the plasma varies indirectly with the molecular size, ranging from barely de¬ tectable to as much as 100 mg of lipoprotein per deciliter. Most consider values of less than 30 mg/dL for Lp(a) to be desirable, and high levels appear to be correlated with an increased risk of coronary artery disease. The sequence of apo(a) has been determined, and it has a remarkable homology to plasminogen. Apo(a) has numerous re¬ peats of a sequence homologous to kringle 4 of plasminogen.37-39 Apo(a) has been shown to bind to plasminogen receptors; it may interfere with fibrinolysis by disrupting the conversion of plas¬ minogen to plasmin. Apo(a), although homologous to plasmino¬ gen, possesses no enzymatic activity. Origin. The origin of Lp(a) is poorly understood. Although apo(a) is synthesized by the liver, it is unclear whether it associ¬ ates with LDL-like particles within the liver and is secreted into the plasma as a complex. It is possible to assemble the complex in vitro, and it has been established that apo(a) secreted from the liver of transgenic mice forms the Lp(a) complex in the plasma when human LDL are injected into transgenic mice expressing apo(a)40 or when human apoB-producing mice are crossed with those expressing apo(a).41 Metabolic Fate. Little is known about the metabolism of Lp(a).42 Plasma levels of this lipoprotein do not correlate with age, sex, total cholesterol, triglyceride, or apoB.43 With some ex¬ ceptions, Lp(a) levels are rather refractory to pharmacologic and dietary manipulation.43,44 There is a correlation between high levels of Lp(a) and accelerated coronary artery disease in some studies, but not others.43,45'46 Apo(a) has been detected immunochemically within atherosclerotic lesions.42 /3-VERY-LOW-DENSITY (REMNANT) LIPOPROTEINS

Characteristics and Origin. The /3-VLDL are ^-migrating, cholesterol-enriched plasma lipoproteins that float at a density less than 1.006 g/mL. They are induced by fat and cholesterol feeding and are present in the plasma of patients with type III hyperlipoproteinemia.5,6,17,18 There are two major subclasses of /3-VLDL. Fraction I, which is of intestinal origin, consists of chy¬ lomicron remnants that accumulate in the plasma and contains predominantly apoB-48 and apoE. Fraction II, which is of hepatic origin, consists of VLDL remnants that contain predominantly apoB-100 and apoE. Both fractions are composed primarily of triglyceride and cholesterol and are more cholesterol rich than chylomicrons or VLDL. The fraction I and fraction II /3-VLDL accumulate in the plasma in response to diets high in fat and cholesterol. It appears that their accumulation is secondary to excessive consumption of dietary fat and cholesterol and to a decrease in the expression of hepatic LDL receptors that are down-regulated by the increased delivery of dietary cholesterol to the liver.5 6 Fraction I and fraction II /3-VLDL accumulate in type III hy¬ perlipoproteinemia and are responsible for the hypertriglyceri¬ demia and hypercholesterolemia seen in patients with this disor¬ der. Their accumulation is partially a result of the occurrence of genetic variants of apoE (usually apoE-2) that are defective in their ability to bind to the lipoprotein receptors5 61/18 (see Table 156-3). Metabolic Fate. The normal metabolic fates of chylomicron remnants and VLDL were described earlier. In both conditions in which /3-VLDL accumulate, the normal processes are im¬ paired.5,6,17,18 The accumulation of fraction I /3-VLDL (i.e., cho¬ lesterol-enriched chylomicron remnants) is secondary to im¬ paired hepatic clearance and overproduction of these particles. Fraction II /3-VLDL (i.e., VLDL remnants) accumulate because of impaired hepatic uptake and retarded conversion to LDL.

1378

PART IX: DISORDERS OF FUEL METABOLISM

Under the abnormal condition of /3-VLDL accumulation, it appears that these lipoproteins are cleared by alternative mecha¬ nisms, which may account for their apparent atherogenicity. Ac¬ celerated atherosclerosis in many animals fed diets high in fat and cholesterol and in patients with type III hyperlipoproteine¬ mia correlates with the occurrence of /3-VLDL in the plasma. These /3-VLDL are unique in their ability to cause marked cholesteryl ester accumulation in macrophages, which they can convert in vitro to foam cells.5,61718 Macrophages are one of the major cell types responsible for cholesterol accumulation in atherosclerosis.

REFERENCES 1. Assmann G. Lipid metabolism and atherosclerosis. Stuttgart: FK Schattauer Verlag, 1982. 2. Grundy SM. Cholesterol and atherosclerosis. Diagnosis and treatment. Philadelphia: JB Lippincott, 1990. 3. Mahley RW, Innerarity TL, Rail SC Jr, Weisgraber KH. Plasma lipoproteins: apolipoprotein structure and function. J Lipid Res 1984; 25:1277. 4. Myant NB. Cholesterol metabolism, LDL, and the LDL receptor. San Diego: Academic Press, 1990. 5. Mahley RW. Atherogenic lipoproteins and coronary artery disease: con¬ cepts derived from recent advances in cellular and molecular biology. Circulation 1985; 72:943. 6. Mahley RW, Weisgraber KH, Innerarity TL, Rail SC Jr. Genetic defects in lipoprotein metabolism: elevation of atherogenic lipoproteins caused by impaired catabolism. J Am Med Assoc 1991;265:78. 7. Hobbs HH, Russell DW, Brown MS, Goldstein JL. The LDL receptor locus in familial hypercholesterolemia: mutational analysis of a membrane protein. Annu Rev Genet 1990;24:133. 8. Innerarity TL, Mahley RW, Weisgraber KH, et al. Familial defective apoli¬ poprotein B100: mutation of apolipoprotein B that causes hypercholesterolemia. J Lipid Res 1990;31:1337. 9. Assmann G, von Eckardstein A, Funke H. Lecithin:cholesterol acyltransferase deficiency and fish-eye disease. CurrOpin Lipidol 1991; 2:110. 10. Swenson TL. Transfer proteins in reverse cholesterol transport. Curr Opin Lipidol 1992; 3:67. 11. Brown MS, Goldstein JL. A receptor-mediated pathway for cholesterol homeostasis. Science 1986; 232:34. 12. Mahley RW. Apolipoprotein E: cholesterol transport protein with expand¬ ing role in cell biology. Science 1988; 240:622. 13. Davignon J, Gregg RE, Sing CF. Apolipoprotein E polymorphism and ath¬ erosclerosis. Arteriosclerosis 1988; 8:1. 14. Goldstein JL, Brown MS. Familial hypercholesterolemia. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The metabolic basis of inherited disease, ed 6. New York: McGraw-Hill, 1989:1215. 15. Brown MS, Herz J, Kowal RC, Goldstein JL. The low-density lipoprotein receptor-related protein: double agent or decoy? Curr Opin Lipidol 1991; 2:65. 16. Mahley RW, Hussain MM. Chylomicron and chylomicron remnant catab¬ olism. Curr Opin Lipidol 1991; 2:170. 17. Mahley RW, Rail SC Jr. Type III hyperlipoproteinemia (dysbetalipoproteinemia): the role of apolipoprotein E in normal and abnormal lipoprotein metab¬ olism. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The metabolic and molec¬ ular base of inherited disease, ed. 7. New York: McGraw-Hill, 1995:1953. 18. Rail SC Jr., Mahley RW. The role of apolipoprotein E genetic variants in lipoprotein disorders. J Intern Med 1992; 231:653. 19. Wilson C, Wardell MR, Weisgraber KH, et al. Three-dimensional structure of the LDL receptor-binding domain of human apolipoprotein E. Science 1991; 252: 1817. 20. Knott TJ, Rail SC Jr, Innerarity TL, et al. Human apolipoprotein B: struc¬ ture of carboxyl-terminal domains, sites of gene expression, and chromosomal lo¬ calization. Science 1985;230:37. 21. Ji Z-S, Fazio S, Lee Y-L, Mahley RW. Secretion-capture role for apolipo¬ protein E in remnant lipoprotein metabolism involving cell surface heparan sulfate proteoglycans. J Biol Chem 1994;269:2764. 22. Assmann G, Schmitz G, Funke H, von Eckardstein A. Apolipoprotein A-l and HDL deficiency. Curr Opin Lipidol 1990; 1:110. 23. Schmitz G, Williamson E. High-density lipoprotein metabolism, reverse cholesterol transport and membrane protection. Curr Opin Lipidol 1991;2:177. 24. Fielding CJ. Reverse cholesterol transport. Curr Opin Lipidol 1991; 2:376. 25. Barter PJ. Enzymes involved in lipid and lipoprotein metabolism. Curr Opin Lipidol 1990; 1:518. 26. Brown ML, Hesler C, Tall AR. Plasma enzymes and transfer proteins in cholesterol metabolism. Curr Opin Lipidol 1990; 1:122. 27. Hayden MR, Ma Y, Brunzell J, Henderson HE. Genetic variants affecting human lipoprotein and hepatic lipases. Curr Opin Lipidol 1991; 2:104. 28. Kern PA. Lipoprotein lipase and hepatic lipase. Curr Opin Lipidol 1991; 2: 162. 29. Olivecrona T, Bengtsson-Olivecrona G. Lipases involved in lipoprotein metabolism. Curr Opin Lipidol 1990; 1:116. 30. Thuren T, Wilcox RW, Sisson P, Waite M. Hepatic lipase hydrolysis of lipid monolayers. Regulation by apolipoproteins. J Biol Chem 1991;266:4853.

31. Segrest JP, Jackson RL, Morrisett JD, Gotto AM Jr. A molecular theory of lipid-protein interactions in the plasma lipoproteins. FEBS Lett 1974; 38:247. 32. Breslow JL. Genetic basis of lipoprotein disorders. J Clin Invest 1989; 84: 373. 33. Young SG. Recent progress in understanding apolipoprotein B. Circula¬ tion 1990; 82:1574. 34. Scott J. Regulation of the biosynthesis of apolipoprotein Bjoo and apolipo¬ protein B48. Curr Opin Lipidol 1990; 1:96. 35. Bilheimer DW, Watanabe Y, Kita T. Impaired receptor-mediated catabo¬ lism of low density lipoprotein in the WHHL rabbit, an animal model of familial hypercholesterolemia. Proc Natl Acad Sci USA 1982; 79:3305. 36. Innerarity TL. Familial hypobetalipoproteinemia and familial defective apolipoprotein B100. Genetic disorders associated with apolipoprotein B. Curr Opin Lipidol 1990; 1:104. 37. UtermannG. The mysteries of lipoprotein(a). Science 1989;246:904. 38. Utermann G. Lipoprotein(a): a genetic risk factor for premature coronary heart disease. Curr Opin Lipidol 1990; 1:404. 39. Lackner C, Boerwinkle E, Leffert CC, et al. Molecular basis of apolipopro¬ tein (a) isoform size heterogeneity as revealed by pulsed-field gel electrophoresis. J Clin Invest 1991;87:2153. 40. Chiesa G, Hobbs HH, Koschinsky ML, et al. Reconstitution of lipoprotein(a) by infusion of human low density lipoprotein into transgenic mice expressing human apolipoprotein(a). J Biol Chem 1992; 267:24369. 41. Linton MF, Farese RV Jr, Chiesa G, et al. Transgenic mice expressing high plasma concentrations of human apolipoprotein B100 and lipoprotein(a). J Clin In¬ vest 1993; 92:3029. 42. Rader DJ, Cain W, Ikewaki K, et al. The inverse association of plasma lipoprotein(a) concentrations with apolipoprotein(a) isoform size is not due to differences in Lp(a) catabolism but to differences in production rate. J Clin Invest 1994; 93:2758. 43. Spinier SA, Cziraky MJ. Lipoprotein(a): physiologic function, association with atherosclerosis, and effects of lipid-lowering drug therapy. Ann Pharmacother 1994;28:343. 44. Mendoza S, Velazquez E, Osona A, et al. Postmenopausal cyclic estrogenprogestin therapy lowers lipoprotein(a). J Lab Clin Med 1994; 123:837. 45. Daida H, Lee YJ, Yokoi H, et al. Prevention of restenosis after percutane¬ ous transluminal coronary angioplasty by reducing lipoprotein(a) levels with lowdensity lipoprotein apheresis. AmJ Cardiol 1994;73:1037. 46. Kario K, Matsuo T, Imiya M, et al. Close relation between lipoprotein(a) levels and atherothrombotic disease in Japanese subjects >75 years of age. Am J Cardiol 1994; 73:1187. 47. Beisiegel U. Lipoprotein(a) in the arterial wall. Curr Opin Lipidol 1991; 2: 317.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

157

LIPOPROTEIN DISORDERS ERNST J. SCHAEFER

HYPERLIPIDEMIA AND CORONARY ARTERY DISEASE Coronary heart disease (CHD) is a major cause of death in the United States.1 Although the CHD mortality rate is declining, this illness nevertheless kills about 500,000 Americans annually.1 It is estimated that almost 70% of all Americans have some de¬ gree of atherosclerotic narrowing of their coronary arteries.1 Ap¬ proximately 6 million Americans suffer from CHD, and one third of these have limited activity as a result.1 Each year, about 1.5 million Americans have a myocardial infarction, about 1 million undergo cardiac catheterization, 400,000 receive coronary artery bypass grafts, and another 350,000 have an angioplasty proce¬ dure performed.1 A primary contributing factor to CHD is an elevated blood cholesterol level due to an increased level of low-densitylipoprotein (LDL) cholesterol.1-4 About 50% of all U.S. adults

Ch. 157: Lipoprotein Disorders (i.e., 95 million persons) have cholesterol levels higher than 200 mg/dL, and about 37 million adults have values higher than 240 mg/dL. Approximately 60 million are candidates for medical ad¬ vice and intervention.4 Elevated LDL cholesterol is a significant risk factor for CHD, and lowering LDL cholesterol decreases this risk.1'6 Severely ele¬ vated triglycerides (> 1000 mg/dL or 11.3 mmol/L) are associ¬ ated with an increased risk of pancreatitis, and lowering these levels reduces this risk.5,6 Serum or plasma LDL cholesterol levels are increased by diets high in saturated fat and cholesterol, mainly because of de¬ creased LDL receptor-mediated catabolism.7,8 Human popula¬ tions on high-saturated-fat and high-cholesterol diets have ele¬ vated LDL cholesterol levels and a significantly higher rate of CHD due to atherosclerosis than populations on low-saturatedfat and low-cholesterol diets.3,4,9 Elevated LDL cholesterol levels and decreased high-density-lipoprotein (HDL) cholesterol levels are independent risk factors for premature CHD in Western society 3,4,9,io vyomen have higher HDL cholesterol levels than men and a lower age-adjusted risk of CHD.9'11 Prospective studies indicate that dietary treatment or diet and drug therapy that lowers LDL cholesterol can reduce subse¬ quent CHD morbidity and mortality.12'24 Some studies also indi¬ cate a benefit in CHD risk reduction from lowering LDL choles¬ terol and increasing HDL cholesterol.21,22,25 Moreover, studies indicate that aggressive lipid modification can result in stabiliza¬ tion of existing coronary atherosclerosis and some regression of this process.18,26'35 One of the largest trials, the Coronary Primary Prevention Trial, which compared the cholesterol-lowering drug cholestyramine with a placebo, produced statistically significant reductions in LDL cholesterol levels and in the incidence of CHD.12,13 An aggregate analysis that pooled the results of serum cholesterol-lowering trials confirmed an effect on CHD inci¬ dence.4 The 1984 Consensus Development Conference on Low¬ ering Blood Cholesterol to Prevent Heart Disease concluded: "It has been established beyond a reasonable doubt that lowering definitively elevated blood cholesterol levels, specifically blood levels of LDL cholesterol, will reduce their risk of heart attacks caused by coronary artery disease."36

EPIDEMIOLOGIC EVIDENCE A large body of epidemiologic evidence supports a direct re¬ lationship between the serum levels of total and LDL cholesterol and the risk of CHD. This association is continuous throughout the range of cholesterol levels in the population.2'4,9'11 According to results from the third National Health and Nutrition Examina¬ tion Survey, the average LDL cholesterol level of U.S. adults is 130 mg/dL.4 At higher levels of total and LDL cholesterol, the direct relationship between CHD risk and cholesterol levels be¬ comes particularly strong; for persons with cholesterol values in the top 10% of the population distribution, the risk of CHD mor¬ tality is four times as high as the risk in the bottom 10% of the population.9

GENETIC AND PHYSIOLOGIC EVIDENCE Premature CHD can result from high LDL cholesterol levels even in the absence of other risk factors. This is most clearly dem¬ onstrated in children with the rare homozygous familial hyper¬ cholesterolemia, characterized by the absence of specific cellsurface receptors that normally remove LDL cholesterol from the circulatory system. LDL cholesterol levels can be as high as 1000 mg/dL (26 mmol/L), and severe atherosclerosis and CHD often develop before 20 years of age.5,7,37 Patients with the more com¬ mon heterozygous form of familial hypercholesterolemia and partial deficiencies of LDL-receptor function generally develop premature CHD in the middle decades of life.5'7 38

1379

ANIMAL MODEL EVIDENCE Animal models have demonstrated a direct relationship be¬ tween LDL cholesterol and atherosclerosis. Animals consuming diets high in saturated fat and cholesterol develop LDL choles¬ terol elevation and atherosclerosis.39 Such diets also increase HDL cholesterol, an effect that may be compensatory. These hypercholesterolemic animals develop intimal lesions that progress from fatty streaks to ulcerated plaques, resembling those of hu¬ man atherosclerosis. In laboratory trials, severe atherosclerosis in monkeys regresses when blood cholesterol is lowered through diet or drug therapy. Such studies support a causal relationship between LDL cholesterol and atherosclerosis and suggest revers¬ ibility of the process with the reduction of the serum LDL choles¬ terol level.39 The combined findings of these studies support the concept that lowering total and LDL cholesterol levels can reduce the in¬ cidence of CHD events and the death rate due to myocardial in¬ farction.12'35 Moreover, the pooled analysis of clinical trial find¬ ings suggests that intervention is as effective in preventing recurrent myocardial infarction and mortality in patients experi¬ encing a recurrent attack as it is in primary prevention. The com¬ plete set of evidence strongly supports the concept that reducing total and LDL cholesterol levels can reduce CHD risk in younger and older men, in women, and in individuals with moderate ele¬ vations of cholesterol.4 It is important to recognize the magnitude of CHD reduction associated with lowering serum cholesterol levels. For persons with serum cholesterol levels initially in the range of 250 to 300 mg/dL (6.5-7.8 mmol/L), each 1% reduction in serum choles¬ terol level yields approximately a 2% reduction in CHD rates.9 It is reasonable to estimate that a 30% reduction in the serum cholesterol level would reduce CHD risk by as much as 60%. Moreover, studies indicate that aggressive lipid modification can result in stabilization of existing coronary atherosclerosis and some degree of regression.18 28'3 5

PATIENT EVALUATION The Adult Treatment Panel of the National Cholesterol Ed¬ ucation Program (NCEP) has recommended that individuals at risk for CHD should be identified by total serum cholesterol and HDL cholesterol levels, and that, if indicated, they should be fur¬ ther classified for treatment based on LDL cholesterol levels.3 4 40 The NCEP's continuing mandate is to develop guidelines for the detection of hypercholesterolemia and therapeutic guidelines that affect its treatment. The NCEP also enlists participation by and contributions from interested national, state, and local orga¬ nizations. Its purpose is to educate physicians, other health pro¬ fessionals, and the general public about the significance of ele¬ vated blood cholesterol levels and the importance of treatment.

TOTAL CHOLESTEROL AND HIGH-DENSITYLIPROTEIN CHOLESTEROL The classification system begins with the measurement of total cholesterol and HDL cholesterol levels for screening the general population in the fasting or nonfasting state. In the au¬ thor's view, it is not unreasonable to get a screening triglyceride value at that time. Accurate fingerstick methods are available for cholesterol and HDL cholesterol screening in the office setting.41 An accurate home cholesterol test that can be selfadministered by the patient has become available.42 Total choles¬ terol levels below 200 mg/dL (5.2 mmol/L) have been classified as desirable, those between 200 and 239 mg/dL (5.2-6.2 mmol/ L) have been classified as borderline-high, and those greater than or equal to 240 mg/dL (>6.2 mmol/L) have been classified as high risk. Levels of HDL cholesterol below 35 mg/dL (0.9 mmol/ L) have been classified as low.3,4 Fasting triglyceride levels above

1380

PART IX: DISORDERS OF FUEL METABOLISM

or equal to 400 mg/dL (>4.5 mmol/L) have been classified as elevated.3,4 Approximately 25% of the adult population (> 40 million persons) in the United States who are 20 years of age or older falls into the high-risk blood cholesterol classification, and another 54 million people have borderline-high blood cholesterol levels.4 About 20% of males and 5% of females have low HDL choles¬ terol levels, and fewer than 5% of men and women have elevated triglyceride levels. All patients who are screened should receive information about an NCEP or American Heart Association step 1 diet and CHD risk factors. According to the NCEP Adult Treatment Panel guidelines, patients who have desirable total cholesterol and nor¬ mal HDL cholesterol values should have their values checked again within 5 years.3,4 If the patient has a borderline-high value, information about other CHD risk factors should be obtained3,4 (Table 157-1). If the patient has a cholesterol value in the borderline-risk category and a normal HDL cholesterol level, in the absence of CHD (i.e., prior myocardial infarction or angina) or two or more CHD risk factors (see Table 157-1), dietary information should be provided and the cholesterol value checked within the next year. If the patient has a borderline-high value and a history of CHD or two or more CHD risk factors, or the patient has a highrisk total cholesterol value or has a low HDL cholesterol value, LDL cholesterol levels should be assessed so that an appropriate treatment regimen can be determined.3,4 LDL cholesterol is rou¬ tinely calculated after measuring serum total cholesterol, triglyc¬ eride, and HDL cholesterol after an overnight fast. The normal ranges for total cholesterol, triglyceride, very low density lipo¬ protein (VLDL) cholesterol, LDL cholesterol, and HDL choles¬ terol are provided in Table 157-1, and options for measuring LDL cholesterol are discussed later. Another issue is whether apolipoprotein (apo) A-I, apoB, Li¬ poprotein^) [Lp(a)], or LDL size should be measured for assess¬ ing CHD risk. In prospective studies, only Lp(a) among these pa¬ rameters was shown to be an independent risk factor after smoking, blood pressure, diabetes, LDL cholesterol, and HDL cholesterol were taken into account.43-56 In the author's view, Lp(a) or Lp(a)-cholesterol should be part of CHD risk assessment in patients with established CHD.43-48,57 However, measurement of the other parameters cannot be recommended at this time.

NATIONAL CHOLESTEROL EDUCATION PROGRAM GUIDELINES The NCEP Adult Treatment Panel has developed guidelines for the diagnosis and treatment of individuals older than 20 years of age with elevated blood cholesterol levels associated with an increase in LDL cholesterol levels.3-4 The goals of therapy and the particular level of LDL cholesterol requiring the initiation of diet and drug therapy depend on the presence or absence of CHD or two or more CHD risk factors (Table 157-2). The presence of secondary causes of elevated LDL cholesterol levels (>160 mg/ dL or 4.1 mmol/L) must be ruled out. These include hypothy¬ roidism, obstructive liver disease, and nephrotic syndrome. LDL cholesterol decision points for initiating diet and drug therapy are given in Table 157-3. The NCEP guidelines have been accepted by all major U.S. medical organizations, including the American College of Physicians, the American Heart Association, and the American Medical Association.4 Guidelines for the general population and children and adolescents have also been developed.58,59 The recommendation that LDL cholesterol values be used as the primary criterion for treatment decisions for patients with elevated cholesterol levels makes accurate measurement a na¬ tional public health imperative as reviewed by the NCEP Labo¬ ratory Standardization Panel.60

If a patient has an LDL cholesterol level of 160 mg/dL (4.1 mmol/L), it represents approximately the 75th percentile for middle-aged Americans (see Table 157-1). It is important to con¬ firm any abnormalities by repeat determinations. Hospitalization or acute illness can affect lipid values, and lipid determinations should generally be carried out in the free-living state. An ele¬ vated or borderline-high triglyceride level (>200 mg/dL or 2.3 mmol/L) has not clearly been shown to be an independent risk factor for premature heart disease. However, an elevated triglyc¬ eride level is inversely associated with a low level of HDL choles¬ terol, which has been shown to be a significant risk factor for CHD. Common secondary causes of elevated LDL cholesterol and triglyceride values and of decreased HDL cholesterol include hypothyroidism, obstructive liver disease, kidney disease, excess alcohol intake, and the use of corticosteroids, estrogens, idblocking agents, and thiazide diuretics.4 If possible, these factors should be screened for and treated before initiating diet or drug therapy for lipid disorders. Screening should include an evalua¬ tion of glucose, albumin, liver transaminases, alkaline phospha¬ tase, creatinine, and thyrotropin, and the patient should be asked about alcohol intake and the use of ^-blockers, estrogens, corticosteroids, anabolic steroids, thiazides, and hormone preparations.

LOW-DENSITY-LIPOPROTEIN CHOLESTEROL MEASUREMENT Unlike total cholesterol quantitation, there is no consensusapproved and validated reference method for the direct measure¬ ment of LDL cholesterol. The accurate measurement of LDL cho¬ lesterol depends on the separation of LDL particles in serum from other lipoproteins: chylomicrons, VLDL, and HDL. Traditionally, LDL has been defined as all lipoproteins within the density range of 1.019 to 1.063 g/mL. However, in common practice, the defi¬ nition has been broadened to include intermediate-density lipo¬ protein (IDL, 1.006-1.019 g/mL). Using this definition, LDL is composed of LDL + IDL + Lp(a). This definition serves as the basis for the cut-points defined by the NCEP Adult Treatment Paqel. The options for measuring LDL cholesterol include ultracenfrifugation, the Friedewald calculation for estimating LDL cholesterol levels, and a direct method for measuring LDL cho¬ lesterol that uses immunoseparation of lipoproteins by their re¬ spective apolipoprotein content. Ultracentrifugation involves the separation of lipoproteins based on their density differences after an 18-hour spin at 109,000 X g.59 The VLDL and chylomicrons float to the top and are separated using a tube slicing technique from the 1.006 g/ mL infranatant (i.e., “1.006 bottom"). This infranatant fraction contains LDL and HDL. A heparin-manganese precipitation rea¬ gent is added to the 1.006 bottom to precipitate LDL, leaving HDL in the supernatant. The cholesterol concentrations of the 1.006 g/mL of infranatant and the HDL cholesterol supernatant are measured using the Abell-Kendall cholesterol reference method: LDL cholesterol = infranatant cholesterol — HDL cholesterol. This procedure has been adopted by the Centers for Disease Control and the Reference Network Laboratories for Standard¬ izations as a means of directly measuring LDL cholesterol in the research setting and serves as the standard.60 However, ultra cen¬ trifugation is poorly suited to the routine, clinical laboratory for several reasons. It requires cumbersome procedures; it is ex¬ tremely labor intensive and technique dependent; it requires ex¬ pensive instrumentation; and although it is the accepted refer¬ ence method, it is an indirect measurement. Most clinical laboratories use the equation known as the Friedewald formula61 to estimate a patient's LDL cholesterol con¬ centration: estimation of LDL cholesterol = total cholesterol — HDL cholesterol — VLDL cholesterol. The estimation of VLDL cholesterol equals the triglyceride level divided by five.

Ch. 157: Lipoprotein Disorders ^COHO'N^OOO'QO^m^^ ^^•60 mg/DL (1.6 mmol/L)

The Friedewald formula estimates the LDL cholesterol con¬ centration by subtracting the cholesterol associated with the other classes of lipoproteins from total cholesterol. This involves three independent lipid analyses, each contributing a potential source of error. It also involves a potentially inaccurate estimate of VLDL cholesterol. Because no direct VLDL cholesterol assay is available, it is calculated from the triglyceride value divided by a factor of five. This divisor can also add error to all LDL cholesterol estimates, but it is especially inappropriate for individuals with elevated triglyceride levels. Clinical laboratories Use automated enzymatic analyses for cholesterol and triglyceride within serum or plasma, and HDL cholesterol is measured after precipitation of other lipoproteins in serum or plasma with heparin manganese chloride, dextran magnesium sulfate, or phosphotungstic acid.60 The drawbacks of using the Friedewald formula for determining levels of LDL cholesterol are that it is estimated by calculation; it requires multiple assays and multiple steps each adding a poten¬ tial source of error; it is increasingly inaccurate as triglyceride lev¬ els increase; it requires that patients fast for 12 to 14 hours before specimen collection to avoid a triglyceride bias; and it is not stan¬ dardized.60,61 Moreover, LDL cholesterol concentrations cannot be reported for individuals with elevated triglyceride levels (> 400 mg/dL or 4.5 mmol/L).61 It has been reported that the formula becomes increasingly inaccurate in calculating true LDL cholesterol levels at borderline triglyceride levels (200-400 mg/ dL or 2.3-4.5 mmol/L).62,63 The inadequacies of the methods for measuring LDL choles¬ terol necessitated the development of a direct method by which clinical laboratories may accurately and practically assess LDL cholesterol concentrations in patient samples. In 1990, the Labo¬ ratory Standardization Panel of the NCEP recommended the de¬ velopment of a direct LDL cholesterol measurement method.60 The direct method for measuring serum or plasma LDL choles¬ terol concentration that was introduced was suitable for routine use in the clinical laboratory. This immunoseparation technology uses affinity-purified goat polyclonal antisera to human apolipo-

TABLE 157-3 National Cholesterol Education Program Adult Treatment Panel II Treatment Guidelines Low-Density-Lipoprotein Cholesterol Values [mg/dL (mmol/L)] Therapy_>230(3.4)

>160(4.2)

DIET*

Yes, if CHD is present

DRUGS (AFTER DIET*)

Yes, if CHD is present

Yes, if 2 or more CHD risk factors are present Yes, if 2 or more CHD risk factors are present

>190(5.0) Yes

Yes

* The goal of diet therapy is reading the initiation value, and the goal of drug ther¬ apy is 30 mg/dL or 0.8 mmol/L below the initiation value. CHD risk factors are listed in Table 157-1. All CHD patients should be placed on an NCEP step 2 diet.

proteins A-I and E, which are coated on latex particles; this facil¬ itates the removal of chylomicrons, VLDL, and HDL in nonfast¬ ing or fasting specimens. After incubation and centrifugation, LDL cholesterol remains in the filtrate solution. The LDL choles¬ terol concentration is obtained by performing an enzymatic cho¬ lesterol assay on the filtrate solution. This direct LDL cholesterol immunoseparation method allows direct quantitation of LDL cholesterol from one measurement, the use of fasting and nonfasting samples, and an LDL choles¬ terol measurement regardless of elevated triglyceride levels. When the direct LDL cholesterol assay was carried out on serum obtained from 115 subjects, who were fasting or nonfasting and were normal or hyperlipidemic, and was compared with those obtained by ultracentrifugation analysis, the correlation was 0.97, with a small negative bias of 2.9%. Subjects with LDL cho¬ lesterol levels greater than or equal to 160 mg/dL, as obtained by ultracentrifugation, were correctly classified 93.8% of the time.64 In a similar study carried out on serum obtained from 177 sub¬ jects with normal or elevated lipid levels, the correlation between the direct LDL cholesterol and the value obtained by ultracentrif¬ ugation was 0.98, with between-run and within-run coefficients of variation of less than 3%.65 The direct LDL cholesterol assay was found to be accurate using nonfasting and hypertriglyceridemic samples in the author's laboratory. This direct LDL cho¬ lesterol assay has been approved by the Food and Drug Admin¬ istration and is commercially available to laboratories.

TREATMENT TREATMENT GUIDELINES FOR ELEVATED LOW-DENSITY-LIPOPROTEIN CHOLESTEROL DIET THERAPY

LDL cholesterol levels requiring dietary intervention are shown in Table 157-3. The cornerstone of the treatment of lipid disorders is diet therapy requiring the restriction of total fat to 30% or less of calories, saturated fat to 10% (step 1 diet) or less than 7% (step 2 diet); and restriction of cholesterol to less than 300 mg/ day (step 1 diet) or less than 200 mg/day (step 2 diet).2-4 Approx¬ imately 50% of saturated fat and 70% of cholesterol in the U.S. diet comes from hamburgers, cheeseburgers, meat loaf beef steaks, and roasts; eggs; whole milk, cheese, and other dairy products, including ice cream; hot dogs, ham, and lunch meat; doughnuts, cookies, and cake. These foods should be restricted, and they should be substituted with poultry (white meat) without skin, fish, skimmed or low-fat milk, nonfat or low-fat yogurt, and low-fat cheeses. The use of fruits, vegetables, and grains is en¬ couraged. Oils that can be used are unsaturated vegetable oils containing polyunsaturated fat and monounsaturated fatty acids, such as canola, soybean, olive, or corn oil. However, such oils should only be used in moderation. The consumption of hydro¬ genated vegetable oils rich in trans-fatty acids, such as stick mar¬ garine, should be kept to a minimum. Excellent patient dietary pamphlets are available from the American Heart Association as well as the NCEP on the step 1 and step 2 diets. The step 1 diet is recommended for the entire U.S. population, and for patients with elevated LDL cholesterol, the step 2 diet is used if an inadequate response to the step 1 diet is achieved. Patients who are unable to achieve an adequate response with diet after receiving pamphlets and counseling by the physician and office nurse should be referred to a registered dietitian for instruction on following the step 2 diet. In most cases, diet therapy should be tried for at least 6 months before initiating drug therapy, and a regular exercise program and con¬ trol of other risk factors should be encouraged. Dietary fat restric¬ tion (< 20% of calories) along with exercise appears to essential in preventing the age-related weight gain and obesity that often is associated with hyperlipidemia in our society. Such restriction

Ch. 157: Lipoprotein Disorders is important in hypertriglyceridemic subjects to promote weight loss (see Chap. 158). Responsiveness to dietary therapy is related to compliance and specific genetic factors (e.g., apoE and apoA-IV isoforms), and compliance and success should be monitored using LDL cho¬ lesterol levels.2-4'66"69 DRUG THERAPY

Levels of LDL cholesterol requiring drug therapy after diet treatment are shown in Table 157-1. Lipid-lowering medications can be divided into two general classes: drugs effective in lower¬ ing LDL cholesterol (> 15% reduction) and drugs effective in lowering triglyceride levels (> 15% reduction). There are three classes of agents that meet the LDL cholesterol-lowering criteria: anion exchange resins (e.g., cholestyramine, colestipol), niacin, and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) re¬ ductase inhibitors (e.g., lovastatin, pravastatin simvastatin, fluvastatin). Of these three types of drugs, patient compliance with resins and niacin is often poor, but with the HMG-CoA reductase inhibitors, it is generally excellent, as is their efficacy (30% reduc¬ tion).12'13'23,28'31'70"74 However, long-term safety and efficacy in CHD risk reduction in large-scale, long-term, placebo-controlled trials has not been documented with the “statins," although these agents appear to be safe.28,31,70-74 Shorter-term, small-scale and angiographic studies indicate safety, efficacy, and significant benefit with respect to coronary atherosclerosis and CHD risk reduction; larger studies are underway.28 31,70"74 The resins and niacin remain the drugs of choice for lowering LDL cholesterol in younger, asymptomatic patients. HMG-CoA reductase inhibitors are the drugs of choice for CHD patients and for middle-aged and elderly patients because of efficacy and tolerability, and they soon will probably become the drugs of choice for all hypercholesterolemic patients. There are three agents that lower triglyceride levels by more than 15%: niacin, gemfibrozil, and the HMG-CoA reductase in¬ hibitors. All of these agents generally also lower LDL cholesterol levels and raise HDL cholesterol levels. Niacin and gemfibrozil have been shown to lower CHD risk prospectively20 "3 (see Chap. 158).

1383

latter combination is generally well tolerated, but patients should be monitored for the possible development of myositis. PATIENTS WITH HYPERTRIGLYCERIDEMIA AND NORMAL LOW-DENSITY-LIPOPROTEIN CHOLESTEROL

For patients with hypertriglyceridemia only (> 200 mg/dL or 2.3 mm/L) and normal LDL cholesterol levels, there are no clear medication guidelines.3,4 However, diet and exercise are en¬ couraged, as well as the elimination of secondary causes of ele¬ vated triglycerides, such as lack of exercise, obesity, diabetes, al¬ cohol, estrogens, and /3-blockers. If the patient has a fasting triglyceride level in excess of 1000 mg/dL (11.3 mmol/L) while on a restricted diet, medication to reduce the risk of pancreatitis is recommended. However, before taking this step, the physician should make sure that these patients are not taking estrogens, thiazides, or /3-blockers; are using alcohol; or have uncontrolled diabetes mellitus. Caloric and fat restriction is also important in these patients. The drug of choice in such patients is generally gemfibrozil because most have glucose intolerance. In the ab¬ sence of glucose intolerance, niacin can be tried. In patients in whom these agents are not effective or if additional triglyceride reduction is needed, fish oil capsules (1 g) at a dose of three to five capsules twice daily are effective in lowering triglycerides. PATIENTS WITH MODERATE HYPERTRIGLYCERIDEMIA OR LOW HIGH-DENSITY-LIPOPROTEIN CHOLESTEROL

In patients with moderate hypertriglyceridemia, especially in those with HDL cholesterol deficiency, lifestyle changes in¬ cluding weight reduction and an exercise program are very help¬ ful, as are the cessation of smoking and /3-blockers. If patients have established heart disease, the use of niacin, gemfibrozil, or reductase inhibitors should be considered to normalize their lipid levels. The goal of therapy in CHD patients is to achieve an LDL cholesterol less than 100 mg/dL (2.6 mmol/L).3 4 Some experts also recommend reduction of triglycerides to less than 200 mg/ dL (2.3 mmol/L), efforts to increase the HDL cholesterol to over 40 mg/dL (1.0 mmol/L) if possible, and attempts to decrease the total cholesterol/HDL cholesterol ratio to less than 5.0. In the absence of heart disease, only lifestyle modification (i.e., diet and exercise) can be recommended to patients with moderate hyper¬ triglyceridemia or HDL cholesterol deficiency.

TREATMENT OF VARIOUS LIPID ABNORMALITIES PATIENTS WITH ONLY ELEVATED LOW-DENSITYLIPOPROTEIN CHOLESTEROL

For younger, asymptomatic patients with increased LDL cholesterol only, the drugs of choice are cholestyramine or coles¬ tipol (i.e., resins). If patients cannot tolerate resins, even at low doses, niacin or a combination of resins and niacin should be used. For patients with CHD, the elderly, or those who cannot tolerate these agents, HMG-CoA reductase inhibitors should be used. The combinations of niacin or an HMG-CoA reductase in¬ hibitor with an anion exchange resin are also effective.75 76 For postmenopausal women who have had a hysterectomy, estrogen replacement is effective in lowering LDL cholesterol and raising HDL cholesterol, but estrogens should not be used in patients with hypertriglyceridemia.77 In some cases, the estrogen patch can be used and the hypertriglyceridemia treated with other medications. Estrogen use has been associated with a significant reduction in CHD mortality in postmenopausal women. ' PATIENTS WITH ELEVATED LOW-DENSITY-LIPOPROTEIN CHOLESTEROL AND ELEVATED TRIGLYCERIDES

For asymptomatic younger patients with elevations in LDL cholesterol and triglycerides (> 200 mg/dL or 2.3 mmol/L), the drug of choice is niacin.80 For patients who cannot tolerate this agent or for older persons, an HMG-CoA reductase inhibitor should be used. A combination of resins and niacin, gemfibrozil and resins, or gemfibrozil and pravastatin can also be used.81 The

LIPID-LOWERING DRUGS ANION EXCHANGE RESINS

Cholestyramine and colestipol are anion exchange resins that bind bile acids, increase conversion of liver cholesterol to bile acids, and upregulate LDL receptors in liver.2-6 These processes result in an increase in LDL catabolism and a decrease in plasma LDL cholesterol by about 20%. Side effects include bloating and constipation, elevation of triglycerides, and interference with the absorption of digoxin, tetracycline, thyroxine, phenylbutazone, and Coumadin; these drugs should be given 1 hour earlier or 4 hours after the resin. Cholestyramine (4-g packets or scoops) or colestipol (5-g scoops) can be started at 1 scoop or packet twice daily and gradually increased to 2 scoops twice daily or 2 scoops three times daily; the scoops are half the price of the packets. Cholestyramine tablets (1 g) were taken off the market because of difficulties with swallowing. The constipation caused by the anion exchange resins may require treatment. Cholestyramine (6 scoops/day) has been shown to lower LDL cholesterol by 12% and reduce CHD risk prospectively by 19% over 7 years in middle-aged, asymptomatic, hypercholesterolemic men.12,13 NIACIN

Niacin decreases triglycerides and VLDL cholesterol by 40%, decreases LDL cholesterol by 20%, and raises HDL choles¬ terol values by 20%. Niacin should be started at a dosage of 100

1384

PART IX: DISORDERS OF FUEL METABOLISM

mg, taken orally twice daily with meals, and gradually increased to 1 g, taken orally twice or three times daily with meals (some authorities recommend higher doses up to 9 g/day). Side effects include flushing, gastric irritation, and elevations of uric acid, glucose, and liver enzymes in some patients. Niacin should not be used in patients with liver disease or a history of an ulcer or used by diabetic patients not on insulin. Long-acting niacin causes less flushing and can be used initially, but it causes excess gastrointestinal toxicity. Niacin should be discontinued if liver enzymes increase to over three times the upper normal limit. This drug was shown to lower total cholesterol levels by 10% and to reduce the recurrence of myocardial infarction by 20% after a 5year period of administration in men with CHD.80 The use of niacin was also associated with an 11% reduction in all-cause mortality rates 10 years after the cessation of niacin.23 Niacin in combination with clofibrate has been shown to reduce mortality in CHD patients compared with usual care.19

most potent, with a 40% reduction achieved at a dosage of 40 mg/day, and with lovastatin and pravastatin, reductions of 30% to 33% have been reported at this dose. The drugs inhibit HMGCoA reductase, the rate-limiting enzyme in cholesterol biosyn¬ thesis, causing upregulation of LDL receptors, enhancing LDL catabolism. At maximal dosages, the four agents decrease plasma LDL cholesterol by 25% to 40%.28'31'70-74 They may also decrease VLDL and LDL cholesterol production. These agents decrease plasma triglycerides and cholesterol and increase HDL choles¬ terol levels moderately. Long-term safety and efficacy in CHD risk reduction have not been established, although angiographic and short-term study data are quite promising. These agents are likely to become the drugs of choice after the large-scale studies are completed if the results are positive. The first of many of these studies will be reported in 1995. PROBUCOL

GEMFIBROZIL

Gemfibrozil is given at a dose of 600 mg, taken orally twice daily, and it is generally well tolerated. The drug is effective in lowering triglycerides and VLDL cholesterol by 35% by decreas¬ ing the production and enhancing breakdown of VLDL. The drug usually lowers LDL cholesterol by 5% to 15% and increases HDL cholesterol by 5% to 15%. Rarely, patients may get gastrointesti¬ nal symptoms, muscle cramps or intermittent indigestion. The drug should not be used by patients with renal insufficiency, and it is also known to potentiate the action of warfarin sodium. The drug may raise LDL cholesterol levels in hypertriglyceridemic pa¬ tients. Gemfibrozil has been found to reduce CHD prospectively by 34% over 5 years in middle-aged, asymptomatic, hypercholesterolemic men.20-22

3-HYDROXY-3-METHYLGLUTARYL-COENZYME A REDUCTASE INHIBITORS

Lovastatin. Lovastatin is a fungal metabolite and is pro¬ duced by fermentation. The drug is usually started at a dose of 10 to 20 mg, taken orally every day at supper, and it can be in¬ creased to 40 mg, taken orally every day; 20 mg, taken orally twice daily; or even 40 mg, taken orally twice daily. Pravastatin. Pravastatin is usually started at 10 or 20 mg, taken orally each day bedtime, and it can be increased to 40 mg, taken orally each day at bedtime. Its structure is similar to lova¬ statin, except that it is an open acid form and has a hydroxyl group attached to it, making it a more polar compound; conse¬ quently, this drug has greater liver selectivity and less penetration into other tissues. Simvastatin. Simvastatin is usually started at a dose of 10 mg, taken orally each day at supper, and it can be increased to 20 or 40 mg, taken orally daily. Its structure is similar to lovastatin, except that it has an additional methyl group. Fluvastatin. Fluvastatin is structurally different from the other agents and is the first synthetic HMG-CoA reductase inhib¬ itor. It is usually started at a dose of 20 mg, taken orally each day, and it can be increased to 40 mg, taken orally once daily. Guidelines for Use. The HMG-CoA reductase inhibitors should be started at a low dose and gradually titrated upward, because the effect may be maximal at 20 mg/day with any of these agents instead of 40 mg/day. These drugs are generally well toler¬ ated but occasionally may cause liver enzyme elevation (l%-2%); significant creatine phosphokinase elevation with myaglias and myositis (0.1%); especially in combination with gemfibrozil or cy¬ closporine, and gastrointestinal side effects.28'31^70"74'82 Carefully controlled studies indicate that these agents do not cause cata¬ racts, sleep problems, or daytime performance disturbances. Pra¬ vastatin use may be associated with less myositis and should be considered in patients who have developed this problem with other statins. Fluvastatin is the least expensive of these com¬ pounds, but only 25% reductions in LDL cholesterol have been reported at a dose of 40 mg/day. Simvastatin appears to be the

Probucol is an antioxidant, given at a dose of 500 mg that is taken orally twice daily. It is a second-line drug that lowers LDL cholesterol 10% to 15%. It can be used in treating familial hyper¬ cholesterolemia for increasing nonreceptor LDL catabolism; it may cause gastrointestinal side effects. The drug also lowers HDL cholesterol by 15% to 25% by decreasing its production. The long-term safety and efficacy in CHD risk reduction have not been established. One angiographic study did not demonstrate a significant benefit with probucol. COMBINATION DRUG THERAPIES

Niacin and resins together are very effective, as are reductase inhibitors and resins, in lowering LDL cholesterol (50%-60% re¬ duction).73 7h The combination of gemfibrozil and reductase in¬ hibitors is not recommended, because the myositis incidence is approximately 5% with the lovastatin-gemfibrozil combina¬ tion.82 If this combination is used, it should be used with caution, and the creatine phosphokinase levels should be monitored. However, pravastatin and gemfibrozil in combination have been found to be efficacious in lipid lowering and are well tolerated.81 Niacin and reductase inhibitors are also effective, but because the incidence of significant liver enzyme elevation is about 10%, this combination should be used with caution. Gemfibrozil with fish oil capsules or with niacin can be used to lower triglycerides. The response to drug therapy should be monitored using LDL choles¬ terol levels.

FAMILIAL LIPOPROTEIN DISORDERS FAMILIAL HYPERCHOLESTEROLEMIA WITH XANTHOMAS Familial hypercholesterolemia with xanthomas was origi¬ nally recognized in the 1930s, and its autosomal codominant mode of inheritance was subsequently documented.83-86 With the advent of the classification of lipoprotein disorders in the 1960s, it was recognized that this condition was associated with marked elevations in LDL, with other lipoprotein fractions being reasonably normal (i.e., type IIA hyperlipoproteinemia).5 It was later documented that approximately 30% of 500 male survivors of myocardial infarction younger than 60 years of age had serum cholesterol or triglyceride levels above the 95th percentile.87 Moreover, it was shown that of 176 families of these hyperlipidemic myocardial infarction survivors, 15 families or 3% of the total group of 500 subjects had familial hypercholes¬ terolemia and that 5 kindreds or 1% had familial hypercholester¬ olemia that was associated with tendinous xanthomas.88 Pheno¬ type analysis revealed increased LDL or /Mipoproteins in these kindreds. 1 In the author's studies of 102 kindreds in whom the proband had documented coronary atherosclerosis by angiogra¬ phy before 60 years of age, 3% of the kindreds had isolated LDL cholesterol levels above the 90th percentile, with 1 % of the kin-

Ch. 157: Lipoprotein Disorders dreds having familial hypercholesterolemia with tendinous xan¬ thomas and an LDL receptor mutation.90 A few patients have tendinous xanthomas and normal cholesterol levels. These pa¬ tients are discussed in the sections on cerebrotendinous xantho¬ matosis or /3-sitosterolemia. Patients with heterozygous familial hypercholesterolemia have been documented to have delayed clearance of LDL apoB.91 Patients with familial hypercholesterolemia were shown to have various mutations at the LDL receptor gene locus, resulting in a lack of expression or expression of defective LDL receptors.7,92-94 More than 30 different mutations at this locus have been de¬ scribed.92-94 The estimated prevalence of this disorder in the het¬ erozygous state is 1 of 500 persons in the general population, although large-scale population studies have not been per¬ formed. Some patients with phenotypic familial hypercholester¬ olemia have a defect within apoB-100, resulting in defective binding of LDL to the LDL receptor.95,96 In adults with heterozygous familial hypercholesterolemia, LDL cholesterol levels are usually higher than 250 mg/dL, but triglyceride and HDL cholesterol levels are generally normal.38 Clinically, these patients usually develop arcus senilis and tendi¬ nous xanthomas. The clinical diagnosis, in the author's view, is established by an LDL cholesterol level above the 90th percentile in two or more family members and the presence of tendinous xanthomas within the kindred (Fig. 157-1). The average age of onset of CHD is approximately 45 years for men and 55 years for women with untreated heterozygous familial hypercholesterol¬ emia.38 These patients may also have a higher than normal prev¬ alence of calcific aortic stenosis. Treatment consists of a NCEP step 2 diet low in saturated fat (< 7% of calories) and cholesterol (< 200 mg/day) and, in most cases, combined drug therapy. Dietary treatment alone usually results in only small reductions in LDL cholesterol in these pa¬ tients, and the initial drug of choice is an anion exchange resin, which can be combined with niacin or an HMG-CoA reductase inhibitor.3,4,75,76,97,98 The most effective therapy for heterozygotes is the combination of a resin, even at low doses, depending on tolerability, and maximal doses of an HMG-CoA reductase inhibitor.98 Some homozygotes may respond modestly to medications, but these patients generally require selective pheresis to remove

1385

LDL every 1 to 2 weeks for effective control and CHD preven¬ tion.99-101 Portacaval shunting, liver transplantation, and gene therapy remain experimental.102 Familial hypercholesterolemia homozygotes often have LDL cholesterol levels higher than 500 mg/dL, and they frequently have decreased HDL cholesterol levels. In addition to having tendinous xanthomas, these patients often develop tuberous xanthomas and aortic stenosis secondary to cholesterol deposits on the valve leaflets (see Fig. 157-1). The average onset of CHD is about 10 years of age for receptor¬ negative homozygotes and 20 years for receptor-defective homo¬ zygotes.37 LDL-lowering therapy is mandatory for CHD preven¬ tion in these patients.

POLYGENIC FAMILIAL HYPERCHOLESTEROLEMIA WITHOUT XANTHOMAS Among the 3% of CHD patients who have familial hyper¬ cholesterolemia only one third have tendinous xanthomas and are truly heterozygous for familial hypercholesterolemia with potential LDL receptor defects.88,90 Other CHD kindreds with fa¬ milial hypercholesterolemia have more modest LDL cholesterol elevations (> 190 mg/dL) without xanthomas. These kindreds have been classified as polygenic familial hypercholesterolemia; no clear defect has been found. Having the apoE4 allele is known to be associated with elevations in LDL cholesterol levels, and these patients may be more likely to be heterozygous or homozygous for apoE4.66,103,104 The clinical diagnosis of this disorder is estab¬ lished by the presence of LDL cholesterol values greater than the 90th percentile in two or more family members and a lack of xanthomas in the family. The treatment of these patients in¬ cludes implementation of an NCEP step 2 diet and the use of cholesterol-lowering medications, such as resins, niacin, or HMG-CoA reductase inhibitors. For patients with established CHD, these latter agents are the drugs of choice because of their efficacy and tolerability.

FAMILIAL COMBINED HYPERLIPIDEMIA Familial combined hyperlipidemia (FCH) was initially char¬ acterized by the finding of hypercholesterolemia and hypertri¬ glyceridemia within the same kindred and by relatives having

FIGURE 157-1.

A and B, Tuber¬ ous xanthomas in a patient with homozygous familial hypercholes¬ terolemia (i.e., low-density lipo¬ protein receptor negative) and ten¬ dinous xanthomas (arrows). C and D, Circus cornease (arrow) and se¬ vere coronary atherosclerosis in patients with heterozygous famil¬ ial hypercholesterolemia.

1386

PART IX: DISORDERS OF FUEL METABOLISM

one or both of these abnormalities.87-89,105 This disorder was found in approximately 10% of myocardial infarction survivors younger than 60 years of age. Using 95th percentile criteria for serum cholesterol and triglyceride levels, affected subjects were shown to have elevations in VLDL, LDL, or both on phenotyping analysis.88,89 In the author's series, about 14% of kindreds with premature CHD had FCH.90 The clinical diagnosis of FCH is established by the finding of serum or plasma LDL cholesterol or triglyceride levels above the 90th percentile (usually LDL cholesterol >190 mg/dL or triglyc¬ eride >250 mg/dL) within the family and in at least two family members, with both abnormalities occurring within the kin¬ dred.90 Most patients with FCH also had HDL cholesterol values above the 10th percentile.90 It has been reported that patients with FCH have overproduction of apoB-100, but the precise de¬ fect is unknown.106- 08 Data indicate that hepatic apoB-100 se¬ cretion is largely substrate driven.109 Patients with FCH often are overweight and hypertensive, and they may also be diabetic and have gout. Treatment with diet, an exercise program, and if nec¬ essary, the use of niacin or HMG-CoA reductase inhibitors are important for CHD prevention.

Familial hypoalphalipoproteinemia is relatively common. It is characterized by FIDL cholesterol levels that are less than the 10th percentile of normal in two or more kindred members, and it is observed in approximately 4% of kindreds with premature CHD.90 136,137 These patients have decreased HDL apoA-I pro¬ duction or enhanced HDL apoA-I fractional catabolism.114-116,138 The precise molecular defect is unknown. FCH, familial hyper¬ apobetalipoproteinemia, familial dyslipidemia, and familial hy¬ poalphalipoproteinemia may be variants of the same disorder, characterized by a genetic predisposition in populations on ath¬ erogenic diets, especially in those with male-pattern obesity; the condition is associated with oversecretion of apoB-containing li¬ poproteins and enhanced catabolism of apoA-I-containing lipo¬ proteins. These derangements are common, are clearly not mo¬ nogenic, and result in an accumulation of LpB:E and LpB and in decreases in LpA-I and LpA-I/A-II particles.139,140 Treatment consists of a step 2 diet and efforts to optimize triglyceride and LDL cholesterol levels with niacin, gemfibrozil, or a statin.

FAMILIAL HYPERAPOBETALIPOPROTEINEMIA

Familial dysbetalipoproteinemia was originally named type III hyperlipoproteinemia.5 These patients accumulate VLDL

FAMILIAL DYSBETALIPOPROTEINEMIA

Familial hyperapobetalipoproteinemia is characterized by apoB values above the 90th percentile in the absence of other lipid abnormalities in the kindred with at least two affected fam¬ ily members, using age and gender adjusted norms.109-112 This disorder occurred in 5% of CHD kindreds in the author's series; it is thought to be a variant of FCH. It also is associated with overproduction of apoB-100.90

FAMILIAL DYSLIPIDEMIA Familial hypertriglyceridemia is a common familial lipid dis¬ order in which at least two kindred members have fasting triglyc¬ eride levels greater than the 90th percentile of normal. Approxi¬ mately 5% of myocardial infarction survivors younger than 60 years of age were found to have this disorder, using the 95th percentile as the standard. In the author's studies, using the 90th percentile, approximately 15% of CHD kindreds had this disor¬ der.87 90 In the a the author's series, all kindreds except one had HDL cholesterol deficiency within the family as well. The author and colleagues have named this disorder familial dyslipidemia. Hypertriglyceridemia and HDL cholesterol levels must be less than the 10th percentile in the kindred for the family to have this condition.90 These patients are frequently overweight and may have male-pattern obesity, insulin resistance, type II diabetes, and hypertension. The precise defect is unknown, but the pa¬ tients have increased hepatic triglyceride secretion and enhanced HDL apoA-I fractional catabolism.106-108,113-116 No clear therapeutic guidelines have been formulated, other than treatment of other CHD risk factors, a diet and exercise pro¬ gram, and optimization of LDL cholesterol levels.

FAMILIAL HYPOALPHALIPOPROTEINEMIA Severe HDL deficiency (HDL cholesterol 40 mg/dL, using assays that assess the level of the entire particle).157 158 Elevated levels of Lp(a) are associated with premature CHD.159 Approximately 15% of patients with premature CHD have familial Lp(a) ex¬ cess.90,157 These patients do not have xanthomas. Lp(a) appears

1387

to promote atherosclerosis and atherothrombosis by two mecha¬ nisms: deposition in the arterial wall and inhibition of fibrinolysis. Assays for the measurement of Lp(a) are commercially avail¬ able, and an Lp(a) cholesterol assay has been developed as well.157,158 Isoproteins of apo(a) differ in their molecular weights. Decreased apo(a) molecular weight is associated with increased Lp(a) levels.155-162 Apo(a) has been shown to contain multiple repeats of a protein domain that is highly homologous to the kringle 4 domain of plasminogen and one repeat of a protein domain highly homologous to the kringle 5 domain of plasmino¬ gen.163 The variability in apo(a) molecular weight appears to be related to a decreased number of kringle 4-like repeats.162 Ele¬ vated levels of Lp(a) are also observed in patients with heterozy¬ gous familial hypercholesterolemia.47,164 Diets and medications (e.g., resin, HMG-CoA reductase in¬ hibitors) that lower LDL levels have no effect on Lp(a), but niacin administration has been reported to decrease Lp(a) levels.165 No guidelines for the treatment of Lp(a) excess have been formu¬ lated, but treatment with niacin of such patients is warranted if they have established CHD, because such therapy has been shown to decrease morbidity and mortality in unselected CHD patients.23

SEVERE HYPERTRIGLYCERIDEMIA Severe hypertriglyceridemia (triglyceride values > 1000 mg/dL or 11.3 mmol/L) occasionally is observed in middle-aged or elderly individuals who are obese and have glucose intoler¬ ance and hyperuricemia.5,6 They usually have familial hypertri¬ glyceridemia or FCH that is exacerbated by other factors such as obesity and diabetes mellitus. These patients usually have HDL cholesterol deficiency and may develop lipemia retinalis and eruptive xanthomas (Figs. 157-4 through 157-6). They are at in¬ creased risk for developing pancreatitis due to triglyceride depo¬ sition in the pancreas and in the liver (Figs. 157-7 and 157-8) and

FIGURE 157-3. Cross sections of cor¬ onary artery (low-power microscopy), showing atherosclerosis (A), aortic and iliac atherosclerosis (B), and palmar xanthomas (C), compared with normal palm (D), in patients with dysbetali¬ poproteinemia or type III hyperlipo¬ proteinemia associated with apoE2 homozygosity.

1388

PART IX: DISORDERS OF FUEL METABOLISM

yj

may have paresthesias and emotional lability. They often have delayed chylomicron and VLDL cholesterol clearance and excess VLDL production. Treatment consists of a calorie-restricted step 2 diet. For pa¬ tients with diabetes mellitus, it is crucial to control the blood glu¬ cose as well as possible. Medications that are effective in lowering the triglycerides to less than 1000 mg/dL (11.3 mmol/L) to re¬ duce the risk of pancreatitis include gemfibrozil and fish oil cap¬ sules (6-10 capsules/day).166 Patients who have severe hypertriglyceridemia in childhood or early adulthood and who are not obese often have a deficiency of the enzyme lipoprotein lipase or its activator protein (apoCII), resulting in markedly impaired removal of triglyceride. They have a defect in chylomicron and VLDL catabolism. These pa¬ tients are at increased risk for recurrent pancreatitis; it is impor¬ tant to restrict their dietary fat to less than 20% of calories. Niacin or gemfibrozil are generally ineffective. However, fish oil cap¬ sules (6/day) may be help certain patients to keep their triglycer¬ ide levels below 1000 mg/dL (11.3 mmol/L) and to minimize the risk of pancreatitis.112

SEVERE HIGH-DENSITY-LIPOPROTEIN DEFICIENCIES Severe HDL deficiencies are rare disorders that are charac¬ terized by HDL cholesterol levels below 10 mg/dL in the absence of liver disease or severe hypertriglyceridemia, and some have been associated with premature CHD. APOLIPOPROTEIN A-l, C-lll, AND A-IV DEFICIENCY

FIGURE 157-4. Eruptive xanthomas on the buttocks of a patient with severe hypertriglyceridemia and diabetes mellitus.

The proband in the kindred with apoA-I, apoC-III, and apoA-IV deficiencies died of severe diffuse coronary atheroscle¬ rosis at 45 years of age. She had marked HDL deficiency, de¬ creased triglyceride levels, and normal LDL cholesterol val¬ ues.120-122 She had mild corneal opacification but no planar xanthomas. There also has been evidence of fat malabsorption (i.e., vitamin E, vitamin K, and essential fatty acid deficiency).

FIGURE 157-5. Eruptive xanthomas in a patient with severe hypertriglyceridemia associated with li¬ poprotein lipase deficiency. The xanthomas are filled with lipid-laden macrophages.

Ch. 157: Lipoprotein Disorders

1389

I and apoC-IJI genes.126 Heterozygotes in this kindred had HDL cholesterol, apoA-I, and apoC-III values that were approximately 50% of normal. Treatment is to optimize other CHD risk factors. APOLIPOPROTEIN A-l DEFICIENCY

Several kindreds have been reported in which the homozy¬ gous proband had HDL deficiency, planar xanthomas, and un¬ detectable plasma levels of apoA-I.127 128 The defect has been shown to be due to various point mutations, resulting in lack of apoA-I gene expression. No evidence of fat malabsorption was noted. Treatment is to optimize other CHD risk factors. APOLIPOPROTEIN A-l VARIANTS

FIGURE 157-6.

Lipemia retinalis in the veins of the retina in a patient with severe hypertriglyceridemia associated with lipoprotein lipase de¬ ficiency. The patient had marked hypertriglyceridemia (>2000 mg/dL). There is a nonuniform, white, mottled appearance of the veins (arrows).

Plasma apoA-I and apoC-III were undetectable.121 Heterozy¬ gotes had levels of HDL cholesterol, apoA-I, apoC-III, and apoAIV that were 50% of normal.123 The defect is a deletion of the entire apoA-I/C-III/A-IV gene complex.123 Treatment should consist of optimization of other risk factors, including LDL cho¬ lesterol levels. APOLIPOPROTEIN A-l AND C-lll DEFICIENCY

A kindred has been reported in which two sisters presented in their late twenties with CHD, planar xanthomas, and mild cor¬ neal opacification with marked HDL deficiency, normal LDL cholesterol values, and decreased triglycerides. No evidence of fat malabsorption was found.124 125 Plasma apoA-I and apoC-III were not detectable in these homozygotes, and the defect was shown to be a DNA rearrangement affecting the adjacent apoA-

Studies examining apoA-I isoforms by isoelectric focusing have led to the discovery of 18 different mutations within the apoA-I sequence. The mutations are at residues 3 (Pro, 2 muta¬ tions), 4 (Pro), 89 (Asp), 103 (Asp), 107 (Lys, 2 mutations), 136 (Glu), 139 (Glu), 143 (Pro), 147 (Glu), 158 (Ala), 165 (Pro), 169 (Glu), 173 (Arg), 177 (Arg), 198 (Glu), and 213 (Asp) within the 243 residue apoA-I sequence.129-132 All diagnosed persons have been heterozygotes. The residue 173 mutation (Arg-Cys) is known as apoA-I Milano and is associated with mild hypertriglyc¬ eridemia and markedly decreased HDL cholesterol levels and no evidence of premature CHD.130 The residue 165 mutation (ProArg) has also been associated with decreased HDL cholesterol and apoA-I levels, as has the 143 mutation (Pro-Arg).131 The lat¬ ter mutation results in decreased ability of apoA-I to activate the enzyme LCAT. Other mutations have not been associated with decreased HDL cholesterol, but the mutations at residue 3 (ProHis or Pro-Arg) result in an increased pro-apoA-I to apoA-I ratio in plasma, suggesting reduced conversion of pro-apoA-I to ma¬ ture apoA-I in these persons.131 The incidence of apoA-I variants is rare, occurring in 1 of 1000 normal persons as well as in myo¬ cardial infarction survivors.131 TANGIER DISEASE

Tangier disease was named after the Chesapeake Bay island home of the original kindred. Homozygotes with this disorder have marked HDL deficiency, mild hypertriglyceridemia, and decreased LDL cholesterol values.117-119 ApoA-I levels are 1% of normal, but apoC-III and apoA-IV values are within normal lim¬ its. These patients have lipid-laden macrophages resulting in en¬ larged orange tonsils, hepatosplenomegaly, and lymphadenopathy119 (Fig. 157-9). The defect is not known. These patients have hypercatabolism of HDL constituents, but the primary structures

FIGURE 157-7.

Section of pancreatic tissue from a patient with chronic recurrent pancreati¬ tis secondary to severe hypertriglyceridemia as¬ sociated with lipoprotein lipase deficiency. No¬ tice the replacement of acinar cells with fat (F) and the presence of intact islets of Langerhans (dark-staining cells; I), and nerve fibers (NF;

lighter-staining cells in round cluster within sheath).

1390

PART IX: DISORDERS OF FUEL METABOLISM

FIGURE 157-8. Diffuse triglyceride deposition in the liver parenchyma of a patient with severe hypertriglyceridemia associated with lipoprotein lipase deficiency.

of apoA-I and apoA-II are normal.119 Tangier patients appear to have altered processing of HDL by macrophages. Heterozygotes have HDL cholesterol and apoAI-I values that are 50% of nor¬ mal. Homozygotes may develop premature CHD and peripheral neuropathy.119 Treatment consists of optimization of CHD risk factors. LECITHIN:CHOLESTEROL ACYLTRANSFERASE DEFICIENCY

The enzyme LCAT is responsible for cholesterol esterifica¬ tion in plasma. Patients with LCAT deficiency have a very high proportion of plasma cholesterol in the unesterified form, marked HDL cholesterol deficiency, hypertriglyceridemia, and increased amounts of free cholesterol-rich VLDL and LDL. They develop marked corneal opacification, anemia, proteinuria, renal insufficiency, and atherosclerosis. Treatment consists of dietary saturated fat and cholesterol restriction and renal dialysis and transplantation if necessary.133

FISH EYE DISEASE

Fish eye disease is associated with mild hypertriglyceridemia and significant HDL deficiency. Patients with fish eye disease de¬ velop striking corneal opacification, but they have not been re¬ ported to develop premature CHD. These patients have a defi¬ ciency of a-LCAT, which differs from /?-LCAT in that it acts only on HDL; /3-LCAT acts on VLDL and LDL. This disorder appears to be a milder variant of LCAT deficiency.134'135

DEFICIENCIES OF VERY LOW DENSITY LIPOPROTEIN AND LOW-DENSITY LIPOPROTEIN ABETALIPOPROTEINEMIA

Abetalipoproteinemic patients often present in childhood with diarrhea, fat malabsorption, and failure to gain weight nor¬ mally. Intestinal biopsy reveals lipid-laden epithelial cells (Fig.

FIGURE 157-9. Enlarged orange tonsils (T) (A), omental lipid deposition (arrows), at the base of the mesentery (B), and stippled liver with lipid deposition (arrows) (C), in a patient with homozygous Tangier disease undergoing surgical exploration. The lipid deposition is characterized by cholesterol ester-laden macrophages. The patient also had mild corneal opacification. (Schaefer E], Triche TJ, Zech LA, et al. Massive omental reticuloendothelial cell lipid uptake in Tangier disease after splenectomy. Am ]Med 1983;75:

Ch. 157: Lipoprotein Disorders 157-10). Untreated, these patients develop spinocerebellar ataxia and retinitis pigmentosa in their teens and twenties. Laboratory analysis reveals plasma cholesterol values of approximately 40 mg/dL, triglyceride levels of 20 mg/dL, and HDL cholesterol of approximately 40 mg/dL.167 168 The diagnosis is confirmed by undetectable plasma apoB. The defect is an inability to secrete apoB-containing lipoproteins (e.g., chylomicrons, VLDL, LDL).168 Intestinal apoB mRNA levels are increased. Patients also have acanthocytosis and deficiencies of fat-soluble vitamins and essential fatty acids168 (see Fig. 157-10). Supplementation with vitamin A and E is recommended.169'172 Vitamin E replacement appears to prevent the onset of neuropa¬ thy.169'172 Obligate heterozygotes (parents) have normal lipopro¬ tein profiles. Restriction of dietary fat may be necessary to mini¬ mize diarrhea. It is not known whether these patients should be supplemented with the essential fatty acids linoleic acid and alinolenic acid.173 HYPOBETALIPOPROTEINEMIA

The clinical and laboratory picture is the same for hypobetalipoproteinemic patients as for those with abetalipoproteinemia.174-177 However, obligate heterozygotes in these kindreds have LDL cholesterol and apoB values that are 50% of normal. The defect is an inability to synthesize normal amounts of apoB protein, and intestinal apoB mRNA levels are decreased.177 The treatment is the same as in abetalipoproteinemia and is only in¬ dicated for homozygotes. NORMOTRIGLYCERIDEMIC ABETALIPOPROTEINEMIA

Some persons have normal chylomicron formation but lack plasma apoB-100 and LDL in plasma. One patient had serum cholesterol levels of 25 mg/dL and a triglyceride level that in¬ creased from 30 mg/dL to 250 mg/dL with fat feeding. She had mental retardation, marked vitamin E deficiency, and ataxia, which improved with vitamin E supplementation. These patients have apoB-48 in their plasma and have been classified as having normotriglyceridemic abetalipoproteinemia.178

FIGURE 157-10. Light microscopy and scanning elec¬ tron microscopy of acanthocytes (A and B) and lipid¬ laden intestinal epithelial cells (arrows in C) in a patient with abetalipoproteinemia.

1391

HYPOBETALIPOPROTEINEMIA WITH ABNORMAL APOLIPOPROTEIN B MOLECULAR WEIGHT

Another variant of these disorders, hypobetalipoproteinemia with abnormal apoB molecular weight, is associated with ab¬ normal apoB molecular weight. These subjects have marked de¬ ficiencies of VLDL and LDL and very low plasma apoB levels. The apoB is of abnormal molecular weight as assessed by poly¬ acrylamide gels.179-182 This disorder has been called hypobetalipoproteinemia with truncated apoB. Cholesterol levels are approxi¬ mately 40 mg/dL, but triglyceride levels can be as high as 100 mg/dL. CHYLOMICRON RETENTION DISEASE

Another group of patients with fat malabsorption, diarrhea, and deficiency of fat-soluble vitamins, and lipid-laden intestine epithelial cells has been described. LDL cholesterol and apoB lev¬ els are about 50% of normal, and after fat feeding, no significant increase in triglyceride levels occur.183 184 The defect is an inabil¬ ity to secrete apoB-48-containing lipoprotein from the intes¬ tine. Only apoB-100 is present in plasma; no apoB-48 is found. Treatment is similar to abetalipoproteinemia. This disorder has been designated as chylomicron retention disease or Anderson disease.184

XANTHOMAS WITH NORMAL LIPOPROTEIN LEVELS CEREBROTENDINOUS XANTHOMATOSIS

Cerebrotendinous xanthomatosis (CTX) is a rare familial ste¬ rol storage disorder with accumulations of cholestanol and cho¬ lesterol in most tissues, particularly in xanthomas and the brain. Clinically, this disorder is characterized by dementia, spinocere¬ bellar ataxia, tuberous and tendinous xanthomas, early athero¬ sclerosis, and cataracts. The defect in CTX is a lack of the hepatic mitochondrial 26-hydroxylase enzyme involved in the normal biosynthesis in bile lipids and bile acids. Patients with CTX have normal plasma lipoprotein levels, except for reduced plasma HDL cholesterol. The diagnosis should be suspected in a patient

1392

PART IX: DISORDERS OF FUEL METABOLISM

with tendinous xanthomas and a normal cholesterol level. It can be established by documentation of elevated plasma cholestanol levels by gas chromatography. If the diagnosis is made reason¬ ably early, treatment with chenoxeoxycholate at a dose of 250 mg three times daily reduces cholestanol levels to normal and apparently halts the progression of the disease.185

(enzymes B and C are present), which can be demonstrated by Cellogel electrophoresis of the enzyme obtained from circulating lymphocytes or fibroblasts. The condition is usually fatal by 6 months of age.

PHYTOSTEROLEMIA

Patients with cholesterol ester storage disease are first seen in the first or second decade of life with hepatomegaly. The liver disease may progress to hepatic fibrosis, causing esophageal var¬ ices. Malabsorption is not a feature. Lysosomal cholesterol ester deposition in macrophages in liver, intestine, spleen, lymph nodes, and aorta has been documented. Usually, these patients have type Ila or type lib hyperlipoproteinemia, and occasionally also have HDL deficiency. They have a marked deficiency of iso¬ enzyme A of lysosomal acid lipase, as assessed in fibroblasts or circulating lymphocytes. The disease differs from Wolman dis¬ ease in its severity, its lack of intestinal malabsorption, the lipo¬ protein abnormalities, and the predominantly lysosomal choles¬ terol ester deposition instead of cholesterol ester and triglyceride accumulation. Patients with cholesterol ester storage disease may develop strikingly premature coronary artery atherosclerosis. Heterozygotes exist for acid lipase deficiency (i.e., Wolman dis¬ ease or cholesterol ester storage disease), and they appear to be at increased risk for premature CHD.

Phytosterolemia is a rare, inherited sterol storage disorder characterized by tendinous and tuberous xanthomas and by a strong predisposition to premature coronary atherosclerosis.185 Increased amounts of phytosterols such as sitosterol and campesterol are found in plasma and in various tissues. Increased se¬ rum cholesterol and cholestanol levels have also been found in some patients. The basic biochemical defect has not been eluci¬ dated. Unlike normal persons, these patients absorb plant sterols from the intestine. Phytosterolemia should be suspected in pa¬ tients who develop xanthomas in early childhood despite normal or only moderately elevated serum cholesterol levels. The diag¬ nosis can easily be established by an analysis of plasma sterols. Treatment consists of a diet containing the lowest possible amount of plant sterols, with the elimination of all sources of vegetable fats and all plant foods with a high fat content. Such a diet should not contain vegetable oil, shortening, or margarine, nor should it contain nuts, seeds, chocolate, olives, or avocados. Cholestyramine should be used in addition to restricted diets, be¬ cause it causes significant reductions in serum phytosterols, cho¬ lesterol, and cholestanol. Such treatment presumably can reduce the risk of subsequent atherosclerosis in these patients.185

HYPOBETALIPOPROTEINEMIA Hypobetalipoproteinemia is similar to abetalipoproteinemia in its clinical and laboratory manifestations for homozygotes, ex¬ cept that heterozygotes have VLDL and LDL levels that are about 50% of normal. A similar molecular defect exists for the B apolipoproteins. Clinically, homozygous hypobetalipoproteinemia may be a somewhat less severe condition in terms of neurologic and visual impairment than abetalipoproteinemia. Heterozy¬ gotes have decreased levels of LDL synthesis. They usually have no clinical sequelae and may have enhanced longevity.

CHOLESTEROL ESTER STORAGE DISEASE

CONCLUSION The routine measurement of apolipoproteins is not recom¬ mended because of a lack of standardization in available assays and the lack of prospective data documenting that the assays are superior to standard lipid measurements in CHD risk assessment. Lp(a) may be the exception. A direct method for assessing LDL cholesterol levels will be an important contribution for the diag¬ nosis and management of lipid disorders. The availability of the HMG-CoA reductase inhibitors has had a profound effect on the management of lipid disorders, and in the future, they may achieve decreased age-adjusted CHD rates. More emphasis should be placed on diet and exercise programs.

REFERENCES NORMOTRIGLYCERIDEMIC ABETALIPOPROTEINEMIA One female subject with normotriglyceridemic abetalipo¬ proteinemia has been reported. She had mild mental retardation and vitamin E deficiency. In the fasting state, her plasma lipid and lipoprotein cholesterol levels were similar to patients with abetalipoproteinemia, but after a fat load, her plasma triglyceride levels rose to as high as 200 mg/dL, and chylomicrons and apoB48 were present. Apolipoprotein B-100 was not detectable in her plasma. The molecular defect in this disease appears to be an inability to secrete apoB-100, although apoB-48 production is un¬ impaired (see step 2 in Fig. 157-3).

WOLMAN DISEASE Wolman disease appears in the first few weeks of life, with persistent vomiting and diarrhea, hepatosplenomegaly, xantho¬ matosis, and adrenal calcification. Usually, anemia is evident by the sixth week of life. These patients have fat malabsorption and steatorrhea, and they develop liver enzyme abnormalities. They have decreased adrenal responsiveness to ACTH stimulation. Plasma lipid levels are generally normal or decreased. Choles¬ terol ester and triglyceride deposition occurs in the lysosomes of liver parenchymal and Kupffer cells and in macrophages of the adrenal gland, lymph nodes, intestinal mucosa, spleen, testes, thyroid, ovaries, and other tissues. Patients with Wolman disease have a complete absence of enzyme A of lysosome acid lipase

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106. Chait A, Albers JJ, Brunzell JD. Very low density lipoprotein overproduc¬ tion in genetic forms of hypertriglyceridaemia. EurJ Clin Invest 1980; 10:17. 107. Kissebah AH, Alfarsi S, Adams PW. Integrated regulation of very low density lipoprotein triglyceride and apolipoprotein-B kinetics in man: normolipemic subjects, familial hypertriglyceridemia and familial combined hyperlipidemia. Metab Clin Exp 1981;30:856. 108. Janus ED, Nicoll AM, Turner PR, et al. Kinetic bases of the primary hyperlipidaemias: studies of apolipoprotein B turnover in genetically defined subjects. EurJ Clin Invest 1980; 10:161. 109. Sniderman A, Cianftone K. Substrate delivery as a determinant of he¬ patic apoB secretion. Arterioscler Thromb 1993; 13:629. 110. Sniderman A, Teng B, Genest J, et al. Familial aggregation and early expression of hyperapobetalipoproteinemia. AmJCardiol 1985;55:291. 111. Sniderman AD, Wolfson C, Teng B, et al. Association of hyperapobeta¬ lipoproteinemia with endogenous Hypertriglyceridemia and Atherosclerosis. Ann Intern Med 1982;97:833. 112. Teng B, Thompson GR, Sniderman AD, et al. Composition and distribu¬ tion of low density lipoprotein fractions in hyperapobetalipoproteinemia, normolipidemia, and familial hypercholesterolemia. Proc Natl Acad Sci USA 1983; 80:6662. 113. Genest J, Sniderman A, Cianflone K, et al. Hyperapobetalipoproteine¬ mia: plasma lipoprotein responses to oral fat load. Arteriosclerosis 1986;6:297. 114. Schaefer EJ, Zech LA, Jenkins LJ, et al. Human apolipoprotein A-I and A-II metabolism. J Lipid Res 1982;23:850. 115. Schaefer EJ, Ordovas, JM. Metabolism of the apolipoproteins A-I, A-II, and A-IV. In: Segrest J, Albers J, eds. Methods in enzymology, plasma lipoproteins, part B: characterization, cell biology and metabolism. New York: Academic Press, 1986:420. 116. Brinton EA, Eisenberg S, Breslow JL. Increased apo A-I and apoA-II frac¬ tional catabolic rate in patients with low high density lipoprotein cholesterol levels with or without hypertriglyceridemia. J Clin Invest 1991; 87:536. 117. Fredrickson DS, Altrocchi PH, Avioli LC. Tangier disease: combined clin¬ ical staff conference at the National Institutes of Health. Ann Intern Med 1961;55: 1016. 118. Schaefer EJ, Blum CB, Levy RI, et al. Metabolism of high density lipopro¬ teins apolipoproteins in tangier disease. N Engl J Med 1978; 299:905. 119. Serfaty-Lacrosniere C, Lanzberg A, Civeira F, et al. Homozygous tangier disease and cardiovascular disease. Atherosclerosis 1994; 107:85. 120. Schaefer EJ, Heaton WH, Wetzel MG, Brewer HB Jr. Plasma apolipopro¬ tein A-I absence associated with a marked reduction of high density lipoproteins and premature coronary artery disease. Arteriosclerosis 1982; 2:16. 121. Schaefer EJ. Clinical, biochemical, and genetic features in familial disor¬ ders of high density lipoproteins. Arteriosclerosis 1984; 4:303. 122. Schaefer EJ, Ordovas JM, Law S, et al. Familial apolipoprotein A-I and C-III deficiency, variant II. J Lipid Res 1985;26:1089. 123. Ordovas JM, Cassidy DK, Civeira F, et al. Familial apolipoprotein A-I, C-III and A-IV deficiency and premature atherosclerosis due to deletion of a gene complex on chromosome 11. J Biol Chem 1989;264:16339. 124. Norum RA, Lakier JB, Goldstein S, et al. Familial deficiency of apolipo¬ protein A-I and C-III and precocious coronary artery disease. N Engl J Med 1982;306:1513. 125. Norum RA, Forte TM, Alaupovic P, Ginsberg HN. Clinical syndrome and lipid metabolism in hereditary deficiency of apolipoproteins A-I and C-III, vari¬ ant I. Adv Exp Med Biol 1986; 201:137. 126. Karathanasis SK, Ferris E, Haddad IA. DNA inversion within the apoli¬ poproteins AI/CIIl/AIV-encoding gene cluster of certain patients with premature atherosclerosis. Proc Natl Acad Sci USA 1987; 84:7198. 127. Matsunaga T, Hiasa Y, Yanagi H, et al. Apolipoprotein A-I deficiency due to a codon 84 nonsense mutation of the apolipoprotein A-I gene Proc Natl Acad Sci USA 1991;88:2793. 128. Deeb SS, Cheung MC, Peng R, et al. A mutation in the human apolipo¬ protein A-I gene, dominant effect on the level and characteristics of plasma high density lipoproteins. J Biol Chem 1991;266:13654. 129. Funke H, Von Eckardstein A, Pritchard PH, et al. A frameshift mutation in the human apolipoprotein A-I gene causes high density lipoprotein deficiency, partial lecithimcholesterol acyltransferase deficiency, and corneal opacities. J Clin Invest 1991:87:371. 130. Weisgraber KH, Bersot TP, Mahley RW, et al. A-I Milano apoprotein: isolation and characterization of a cysteine-containing variant of the A-I apoprotein from human high density lipoproteins. J Clin Invest 1980;66:901. 131. Von Eckardstein A, Funke H, Walter M, et al. Structural analysis of hu¬ man apolipoprotein A-I variants. J Biol Chem 1990;265:8610. 132. Von Eckardstein A, Holz H, Sandkamp M, et al. Apolipoprotein C-III (Lys58-Glu). J Clin Invest 1991; 87:1724. 133. Glomset JA, Norum KR, Gjone E. Familial lecithin: cholesterol acyltrans¬ ferase deficiency. In: Stanbury JB, Wyngaarden JB, Fredrickson DS, et al, eds. The metabolic basis of inherited disease. New York: McGraw-Hill, 1983:643. 134. Carlson LA. Fish-eye disease: a new familial condition with massive cor¬ neal opacities and dyslipoproteinemia. Eur J Clin Invest 1982; 12:41. 135. Carlson LA, Holmquist L. Evidence for deficiency of high density lipo¬ protein lecithimcholesterol acyltransferase activity (LCAT) in fish-eye disease Acta Med Scand 1985;218:189. 136. Vergani C, Bettale A. Familial hypoalphalipoproteinemia. Clin Chim Acta 1981; 114:45. 137. Third JLHC, Montag J, Flynn M, et al. Primary and familial hypoalphali¬ poproteinemia. Metabolism 1984; 33:136. 138. Le AN, Ginsberg HN. Heterogeneity of apolipoprotein A-I turnover with

Ch. 158: Therapy of the Hyperlipoproteinemias reduced concentrations of plasma high density lipoprotein cholesterol. Metabolism 1988;37:614. 139. Genest JJ, Bard JM, Fruchart JC, et al. Plasma apolipoproteins (a), A-l, A-II, B, E, and C-III containing particles in men with premature coronary artery disease. Atherosclerosis 1991;90:149. 140. Genest JJ Jr, Bard JM, Fruchart JC, et al. Familial hypoalphalipoproteinemia in premature coronary disease. Arterioscler Thromb 1993:13:1728. 141. Hazzard WR, O'Donnell TF, Lee YL. Broad-beta disease (type III hyper¬ lipoproteinemia) in a large kindred. Evidence for a monogenic mechanism. Ann Intern Med 1975;92:141. 142. Morganroth J, Levy RI, Fredrickson DS. The biochemical, clinical and genetic features of type III hyperlipoproteinemia. Ann Intern Med 1975;82:158. 143. Utermann G, Hees M, Steinmetz A. Polymorphism of apolipoprotein E and occurrence of dysbetalipoproteinaemia in man. Nature 1977;269:604. 144. Zannis VI, Breslow JL. Human very low density lipoprotein apolipopro¬ tein E isoprotein polymorphism is explained by genetic variation and posttranslational modification. Biochemistry 1981; 20:1033. 145. Weisgraber KH, Rail SC Jr, Mahley RW. Human apolipoprotein E iso¬ protein subclasses are genetically determined. Am J Hum Genet 1981; 33:11. 146. Rail SC Jr, Weisgraber KH, Innerarity TL, et al. Identical structural and receptor binding defects in apolipoprotein E2 in hypo-, normo- and hypercholesterolemic dysbetalipoproteinemia. J Clin Invest 1983;71:1023. 147. Ghiselli G, Schaefer EJ, Gascon P, Brewer HB Jr. Type III hyperlipopro¬ teinemia associated with apolipoprotein E deficiency. Science 1981;214:1239. 148. Schaefer EJ, Gregg RE, Ghiselli G, et al. Familial apolipoprotein E defi¬ ciency. J Clin Invest 1986;78:1206. 149. Cladaras C, Hadzopoulou-Cladaras M, Felber B, et al. The molecular basis of a familial apo E deficiency: an acceptor splice site mutation in the third intron of the deficient apo E gene. J Biol Chem 1987;262:2310. 150. Schaefer EJ. Dietary and drug treatment. In: Brewer HB Jr, ed. Moderator, type III hyperlipoproteinemia: diagnosis, molecular defects, pathology and treat¬ ment. Ann Intern Med 1983; 93:623. 151. Berg K. A new serum type system in man—the Lp system. Acta Pathol Microbiol Scand 1963;59:369. 152. Berg K, Dahlen G, Borreson AL. Lp(a) phenotypes, other lipoprotein pa¬ rameters and a family history of coronary heart disease in middle-aged males. Clin Genet 1979; 16:347. 153. Dahlen GH, Guyton JR, Attar M. Association of levels of lipoprotein Lp(a), plasma lipids, and other lipoproteins with coronary artery disease docu¬ mented by angiography. Circulation 1986; 74:758. 154. Dahlen GH, Guyton JR, Attar M, et al. Association of levels of Lp(a), plasma lipids, and other lipoproteins with coronary artery disease documented by angiography. Circulation 1986;74:758. 155. Fless GM, Rolih CA, Scanu AM. Heterogeneity of human plasma lipo¬ protein (a): isolation and characterization of the lipoprotein subspecies and their apoproteins. J Biol Chem 1984;259:11470. 156. Utermann G, Menzel HJ, Kraft HG, et al. Lp(a) glycoprotein phenotypes. Inheritance and relation to Lp(a)-lipoprotein concentrations in plasma. J Clin Invest 1987; 80:458. 157. Genest J, Jenner JL, McNamara JR, et al. Prevalence of lipoprotein (a) [Lp(a)] excess in coronary artery disease. Am J Cardiol 1991; 67:1039. 158. Jenner JL, Ordovas JM, Lamon-Fava S, et al. Effects of age, sex, and menopausal status on plasma lipoprotein (a) levels: the Framingham Offspring Study. Circulation 1993;87:1135. 159. Genest JJ, McNamara JR, Ordovas JM, etal. Lipoprotein cholesterol, apo¬ lipoprotein A-I, B and Lp(a) abnormalities in men with premature coronary artery disease. J Am Coll Cardiol 1992; 19:792. 160. Genest JJ, McNamara JR, Salem DN, Schaefer EJ. Prevalence of risk fac¬ tors in men with premature coronary artery disease. Am J Cardiol 1991;67:1185. 161. Loscalzo J, Weinfeld M, Fless GM, Scanu AM. Lipoprotein (a), fibrin binding, and plasminogen activation. Arteriosclerosis 1990; 10:240. 162. Gavish D, Azrolan N, Breslow JL. Plasma Lp(a) concentration is inversely correlated with the ratio of kringle IV/kringle V encoding domains in the apo(a) gene. J Clin Invest 1989; 84:2021. 163. McLean JW, Tomlinson JE, Kuang WJ, et al. cDNA sequence of human apolipoprotein (a) is homologous to plasminogene. Nature 1987;330:132. 164. Seed M, Hoppichler F, Reaveley D, et al. Relation of serum lipoprotein (a) concentration and apolipoprotein (a) phenotype to coronary heart disease in patients with familial hypercholesterolemia. N Engl J Med 1990; 322:1494. 165. Carlson LA, Hamsten A, Asplund A. Pronounced lowering of serum levels of lipoprotein (a) in hyperlipidaemic subjects treated with nicotinic acid. J Intern Med 1989;226:271. 166. Schaefer EJ. Hyperlipoproteinemia. In: Rakel RE, ed. Conn's current therapy. Philadelphia: WB Saunders, 1991:515. 167. Bassen FA, Kornzweig AL. Malformation of the erythrocytes in a case of atypical retinitis pigmentosa. Blood 1950;5:381. 168. Gotto AM, Levy RI, John K, Fredrickson DS. On the nature of the protein defect in abetalipoproteinemia. N Engl J Med 1971; 284:813. 169. Muller DPR, Lloyd JK, Bird AC. Long-term management of abetalipo¬ proteinemia. Arch Dis Child 1977;52:209. 170. Muller DPR, Lloyd JK, Wolff OH. Vitamin E and neurological function. Lancet 1983; 1:225. 171. Hegele RA, Angel A. Arrest of neuropathy and myopathy in abetalipo¬ proteinemia with high dose vitamin E therapy. Can Med Assoc J 1985; 12:41. 172. Kayden HJ, Traber MG. Clinical, nutritional, and biochemical conse¬ quences of apolipoprotein B deficiency. Adv Exp Med Biol 1986; 201:67.

1395

173. Wetterau JR, Aggerbeck LP, Bouma ME, et al. Absence of microsomal triglyceride transfer protein in individuals with abetalipoproteinemia. Science 1992;258:999. 174. Levy RI, Langer T, Gotto AM, Fredrickson DS. Familial hypobetalipoproteinemia, a defect in lipoprotein synthesis. Clin Res 1970; 18:539. 175. Cottrill C, Glueck CJ, Leuba V, et al. Familial homozygous hypobetalipoproteinemia. Metabolism 1974;23:779. 176. Berger GMB, Brown G, Henderson HE, Bonnici F. Apolipoprotein B de¬ tected in the plasma of a patient with homozygous hypobetalipoproteinemia: im¬ plications for aetiology. J Med Genet 1983;20:189. 177. Ross RS, Gregg RE, Law SW, et al. Homozygous hypobetalipoproteine¬ mia: a disease distinct from abetalipoproteinemia at the molecular level. J Clin In¬ vest 1988;81:590. 178. Malloy MJ, Kane JP, Hardman DA, et al. Normotriglyceridemia abetali¬ poproteinemia: absence of the B-100 apoprotein. J Clin Invest 1981;677:1441. 179. Steinberg D, Grundy SM, Mok HI, et al. Metabolic studies in an unusual case of asymptomatic familial hypobetalipoproteinemia and fasting chylomicroemia. J Clin Invest 1979; 64:292. 180. Young SG, Northey ST, McCarthy BJ. Low plasma cholesterol levels caused by a short deletion in the apoB gene. Science 1988;241:591. 181. Witzum JL. Lipoprotein B37, a naturally occurring lipoprotein containing the amino-terminal portion of apolipoprotein B-100, does not bind to the apolipo¬ protein B, E (low-density lipoprotein) receptor. J Biol Chem 1987b;262:16604. 182. Collins DR, Knott TJ, Pease RJ, et al. Truncated variants of apolipoprotein B cause hypobetalipoproteinemia. Nucleic Acids Res 1988; 16:8361. 183. Anderson CM, Townley RRW, Freeman JP. Unusual causes of steator¬ rhea in infancy and childhood. Med J Aust 1961; 11:617. 184. Levy E, Marcel Y, Deckelbaum RJ, et al. Intestinal apo B synthesis, lipids, and lipoproteins in chylomicron retention disease. J Lipid Res 1987; 28:1263. 185. Bjorkem I, Skrede S. Familial diseases with storage of sterols other than cholesterol: cerebrotendinous xanthomatosis and phytosterolemia. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. Metabolic basis of inherited disease. New York: McGraw-Hill, 1989:1283.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

158_

THERAPY OF THE HYPERLIPOPROTEINEMIAS JOHN C. LAROSA

RATIONALE FOR THERAPY The treatment of hyperlipoproteinemia involves both diet and drug therapy and, in selected patients for whom these are inadequate, more invasive interventions. Clinical trials with both mortal and morbid coronary heart disease (CHD) endpoints as well as trials using serial angiogra¬ phy1,2 have demonstrated that the lowering of plasma lowdensity lipoprotein (LDL) cholesterol levels slows the progression of coronary atherosclerosis and lowers the risk of coronary events. High-density lipoprotein (HDL) cholesterol is a powerful, negative predictor of coronary risk. Clinical trials have not yet demonstrated clearly the independent value of raising HDL levels.3 The value of plasma triglyceride as an independent predictor of atherosclerosis is poor at best. Elevated triglycerides are often associated with elevated cholesterol, however, and frequently are a marker for familial disorders in which atherogenic lipopro¬ teins, such as intermediate-density lipoprotein (IDL) and chy¬ lomicron remnants, accumulate. Plasma triglyceride levels greater than 200 mg/dL (2.3 mmol/L), moreover, are associated with the appearance of a triglyceride-rich, small, dense form of LDL, which is thought to be particularly atherogenic. In addition, triglyceride levels greater than 1000 mg/dL (11.4 mmol/L) indi-

1396

PART IX: DISORDERS OF FUEL METABOLISM

cate chylomicronemia, a condition that, if left untreated, may cause pancreatitis.3

that older patients may be more susceptible to the side effects of drugs.6

TRIGLYCERIDE

GOALS OF THERAPY CHOLESTEROL The goal of therapy in hyperlipoproteinemia is the preven¬ tion of its complications; for most patients, these are vascular. The National Cholesterol Education Program (NCEP), coordi¬ nated by the National Institutes of Health (NIH), has issued guidelines for detection and treatment of hypercholesterolemia (Table 158-1).4 A detailed description of these guidelines is be¬ yond the scope of this chapter. In general, however, patients with cholesterol levels in excess of 240 mg/dL (6.2 mmol/L) are can¬ didates for diet and perhaps drug therapy if their LDL levels are 160 mg/dL (4.1 mmol/L) or greater. Therapeutic targets are to lower LDL cholesterol levels below 130 mg/dL (3.4 mmol/L) and even below 100 mg/dL (2.6 mmol/L) if the patient already hasCHD. Support for actively treating cholesterol elevations is most extensive in adulthood, but less well supported at the extremes of age.4a,4b Dyslipoproteinemia is less common in children than in adults; when it does occur, it is more likely to be related to a genetic abnormality. As with adults, diet therapy should always be attempted first. In children, drugs should be used more spar¬ ingly and only in the most resistant cases. Guidelines for detec¬ tion and treatment of hypercholesterolemia in children have also been developed by the NCEP.5 The value of therapy in elderly patients is less certain. Epi¬ demiologic evidence indicates that total cholesterol levels con¬ tinue to predict coronary risk in elderly patients. Older patients, moreover, are more likely to have advanced atherosclerosis. Nev¬ ertheless, prudence dictates that particular attention be paid to the overall nutritional adequacy of the diet and the possibility

Triglyceride levels higher than 1000 mg/dL (11.4 mmol/L) are associated with high levels of circulating chylomicrons and may lead to pancreatitis. In such cases, severe restriction of all dietary fat is necessary. Chylomicronemia is affected only mar¬ ginally and unpredictably by drugs. Elevated triglyceride levels are often associated with low HDL levels.7 In addition, elevated triglyceride may also be a marker for dyslipoproteinemias, which are associated with in¬ creased cardiovascular risk. Some patients with high triglyceride levels have “familial combined hyperlipidemia.” A few patients with hypertriglyceridemia have type III dyslipoproteinemia, that is, accumulation of IDL and chylomicron remnants. Both of these groups are at increased risk for development of atherosclerosis and should be treated. An NIH consensus panel recommended that persons with triglyceride levels greater than 200 mg/dL (2.3 mmol/L) be con¬ sidered candidates for therapy if they had a concomitant increase in LDL cholesterol levels, a low HDL cholesterol level, or a family history of CHD that might be indicative of a genetic abnormality of lipoprotein metabolism.3

HIGH-DENSITY LIPOPROTEIN There is no definitive evidence that changing HDL levels re¬ tards atherogenesis or lowers coronary risk in either animals or humans. Data, however, from the National Health, Lung, and Blood Institute Type II Intervention Study,8 the Lipid Research Clinic Coronary Primary Prevention Trial,9 and the Helsinki Study10 suggest an independent benefit. Although dietary factors can affect HDL levels, diet does not seem to be a prominent determinant of HDL cholesterol, which is more closely related to body weight, exercise status, and gender.

TABLE 158-1 Summary of National Cholesterol Education Program (NCEP) Guidelines For Screening, Use Total Cholesterol

For Therapeutic Decisions, Use LDL

High

5240 mg/dL (6.2 mmol/L)

Borderline-high

200-239 mg/dL (5.2-6.2 mmol/L)

130-159 mg/dL (3.4-4.1 mmol/L)

Desirable

130 mg/dL (3.4 mmol/L)

LDL if CHD is present

>100 (2.6 mmol/L)

Threshold for Drug Intervention (After Diet Trial)

Targets for Therapy

LDL if no other risk factors*

>190 mg/dL (4.9 mmol/L)

LDL if no CHD is present

5160 mg/dL (4.1 mmol/L)

IGF-II > insulin

IGF-II receptor

IGF-II >> IGF-I >> insulin

Insulin receptor

Insulin >> IGF-I > IGF-II

plasmic tail.17 The extracellular domain contains binding sites for IGF-II and mannose-6-phosphate, and ligand binding at one site influences ligand binding at the other. The IGF-II/mannose-6phosphate receptor is important in the uptake and intracellular trafficking of mannose-6-phosphate-containing lysosomal en¬ zymes and may play a role in clearance of IGF-II from the circu¬ lation, because it does display many characteristics of a typical clearance receptor. The cytoplasmic tail of the IGF-II/mannose6-phosphate receptor lacks any obvious catalytic activity, but it does have sequences that exhibit some similarity to regions found in G-protein-linked receptors.18 Flowever, convincing evidence for a role of the IGF-II/mannose-6-phosphate receptor in IGF signal transduction remains elusive. Studies of mice in which the IGF-I or IGF-II genes had been inactivated by gene targeting sug¬ gests that this molecule does not play an obligate role in IGF-II action.11"13 A significant fraction of the IGF-II/mannose-6phosphate receptor occurs in a soluble form in the circulation as a result of a proteolytic cleavage that produces a truncated receptor protein that lacks a transmembrane domain. Given the extremely high affinity of the IGF-II/mannose-6phosphate receptor for IGF-II, the soluble form of the receptor could be considered to be a form of IGF-II binding protein. This possibility is discussed in more detail in the following section, and the remainder of this section will focus on the IGF-I receptor, which, based on the phenotype of IGF-I receptor-deficient mice, appears to be responsible for all of the biologic actions of IGF-I and most or all of those of IGF-II.

INSULIN-LIKE GROWTH FACTOR-1 RECEPTOR

The IGF-I receptor is encoded by a large gene that contains 21 exons and is widely expressed throughout development.14

IGF-I receptor gene expression varies from tissue to tissue, with levels generally decreasing at later developmental stages.20 IGF-I receptor gene expression is also modulated by nutritional sta¬ tus.21 In addition to developmental, tissue-specific, and nutri¬ tional factors predicted to be involved in IGF-I receptor gene expression, specific molecules that appear to function in the reg¬ ulation of IGF-I receptor gene expression are fibroblast growth factor (FGF), progestins, and transcription factors such as SP1 and the WT1 tumor-suppressor gene product; the latter may also regulate IGF-II gene expression.22-25 The sequence of events initiated by ligand binding to recep¬ tor tyrosine kinases, such as the IGF-I receptor, has been eluci¬ dated.26 In the case of the IGF-I and insulin receptors, ligand binding to the a subunit alters the conformation of the extracel¬ lular portion of the receptor, and a conformational change occurs in the intracellular domain of the receptor. As a result, the kinase domains of the receptor are activated and phosphorylate, in a fra ns mechanism, a cluster of three tyrosine residues in the kinase domain itself. Subsequently, tyrosines in the juxtamembrane and C-terminal domains are phosphorylated along with other sub¬ strates, the most important of which is insulin receptor substrate 1 (IRS-1 or ppl 85). IRS-1 phosphorylation requires autophosphorylation of a specific tyrosine in the juxtamembrane region of the receptor /3 subunit. IRS-1 phosphorylation occurs on several tyrosine resi¬ dues found in specific motifs that, when their tyrosine residues are phosphorylated, are recognized by the SH2 domains of sev¬ eral components of the signal transduction pathway. One of these is the p85 regulatory domain of P13 kinase which, on bind¬ ing to IRS-1, activates the pi 10 catalytic subunit, which then phosphorylates several phosphoinositide derivatives at their 3' position. Another major factor interacting with IRS-1 is the adapter protein Grb-2. This protein occurs as a complex with the p21ras guanine nucleotide exchange factor mSOS; this complex involves the SH3 domain of Grb-2 and a proline-rich region in mSOS. The net effect of receptor phosphorylation of IRS-1 and the recruitment of the Grb-2/mSOS complex is to position the latter close to the plasma membrane, where it can activate p21ras

Ch. 169: Growth Factors and Cytokines by facilitating the displacement of GDP in the guanine nucleotide binding site of p21ras and its replacement with GTP. The active form of p21ras interacts with and activates the pro¬ tein kinase RAF1, which then interacts with and activates iso¬ forms of MAP kinase kinase (also known as MEK). MAP kinase activates isoforms of MAP kinase (also known as ERK). MAP ki¬ nase or other kinase substrates of MAP kinase, such as S6 kinase, may then phosphorylate and activate specific transcription fac¬ tors such as FOS and JUN. In this fashion, a signal transduction cascade involving the IGF-I receptor, IRS-1, Grb-2, mSOS, p21ras, the RAF1, MEK, and ERK protein kinases, and specific transcription factors links extracellular ligand-receptor interac¬ tion with changes in gene expression in the nucleus. Such cas¬ cades, usually involving tyrosine and serine or threonine kinases, are characteristic of signal transduction by receptor tyrosine ki¬ nases. Some of the features of this pathway are used by other types of growth factor receptors, including those used Dy some cytokines. The contribution of the insulin receptor itself to IGF signal¬ ing is probably minimal because of the relatively poor binding of the IGFs to this receptor. There is evidence, however, that hybrid insulin/IGF-I receptors can form in cells expressing both recep¬ tors.27 These hybrids, consisting of an insulin receptor a and (3 subunit and an IGF-I receptor a and (3 subunit, appear to act more like IGF-I receptors in terms of binding affinities, but they may exert a different range of biologic actions than those elicited by activation of "pure” receptor. A potential role for the insulin re¬ ceptor in IGF actions may result from its ability to form hybrid receptors under certain circumstances.

INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS A third and major component of the IGF system is the family of IGFBPs. IGFBPs 1 through 6 are encoded by a gene family and are characterized by cysteine-rich N- and C-termini and lessconserved central regions.28 The IGFBPs bind IGFs with affinities similar to or greater than those of the IGF-I receptor, but they do not bind insulin. The IGFBPs are found in biologic fluids, in the extracellular matrix, and in the conditioned media of many cell lines. Although initially considered to be carrier proteins, it is now clear that the IGFBPs play active and important roles in modulating IGF action. REGULATION

The production of IGFBPs is itself regulated by several fac¬ tors. For example, IGFBP-1 gene expression is regulated by nu¬ tritional status, insulin, and glucocorticoids; IGFBP-2 gene ex¬ pression is regulated by insulin, and IGFBP-5 gene expression is regulated by IGF-I and by retinoic acid.29'31 Several IGFBPs are subject to glycosylation or phosphorylation, and most occur in soluble or cell-associated forms, IGFBP-1 and -2 through ArgGly-Asp (RGD) motifs that may interact with integrins. Several IGFBPs are susceptible to inactivating proteases, whose activities may be subject to regulation.32,33 The production and activity of the IGFBPs can be controlled at many levels, including synthesis, degradation, modification, and cell association. FUNCTIONS

The means by which the IGFBPs may influence IGF action are also varied. The half-lives of IGFs (particularly IGF-I) in the circulation are affected by their association with IGFBP-3 in a 150-kilodalton (kd) complex resulting from the sequential asso¬ ciation of IGF-I or IGF-II, IGFBP-3, and an acid-labile subunit (ALS). The presence of IGFs in such a complex serves, among other purposes, to prevent the hypoglycemia that would occur if the excess of circulating IGF were in a free form and able to bind, albeit with a low affinity, to insulin receptors in adipose and mus¬ cle tissue. The 150-kd complex also prolongs the half-lives of cir¬ culating IGFs and serves as a reservoir from which IGFs can be

1455

dissociated in free form or more directly transferred to other IGFBPs found in the circulation. Complexes of IGF with other IGFBPs are smaller (lacking ALS-like components) and can leave the circulation to deliver IGFs directly to tissues. Locally pro¬ duced IGFs probably associate with IGFBPs in the extracellular fluid, so that IGFs derived from hemocrine and paracrine or au¬ tocrine sources are bound to IGFBPs. The effects of these IGFBPs on IGF action in a given situation depends on the specific IGFBPs, because some of them vary in their affinity for IGF-I and IGF-II, as well as their occurrence in a soluble or cell-associated form; this influences IGF binding in some cases. Positive effects of IGFBPs on IGF action may result from an effective increase in the local concentration of IGF, presentation to the receptor in a form that facilitates receptor activation, or possibly by triggering IGFindependent events that contribute to IGF action at a postrecep¬ tor level. The inhibitory effects of IGFBPs may result from se¬ questration of free IGF or from activation of IGF-independent processes that attenuate receptor-activated pathways. INDEPENDENT ACTION

IGFBPs may function in an IGF-independent manner, and the secreted IGF-II/mannose-6-phosphate receptor may func¬ tion as an IGFBP. The first of these is pertinent because it may form the basis for some of the effects of IGFBPs on IGF action, raising the possibility of biologic effects elicited by IGFBPs in the absence of IGFs. IGFBP-1 and IGFBP-2 contain RGD sequences that, in the case of IGFBP-1, have been shown to enable its bind¬ ing to a specific integrin receptor, and IGFBP-3 has been demon¬ strated to bind to specific cell-surface proteins.34,35 Intracellular processes triggered by such interactions could interact with and enhance or inhibit cellular signaling by the IGF-I receptor, or such processes could have biologic consequences in and of them¬ selves. Studies under way should elucidate the contribution of these interactions to overall IGF action. The potential functioning of the secreted form of the IGFII/mannose-6-phosphate receptor as an IGFBP is based on its extremely high affinity for IGF-II and its high concentration in the circulation. It is possible that this molecule serves the same purpose for IGF-II that the IGFBP-3/ALS complex serves for IGF-I.

INSULIN-LIKE GROWTH FACTORS IN HEALTH AND DISEASE NORMAL GROWTH AND DEVELOPMENT

The IGFs are essential for normal growth and development. Prenatally, IGF-I and IGF-II are differentially expressed in a tissue-specific manner, whereas the IGF-I receptor and the IGFII/mannose-6-phosphate receptors are ubiquitously expressed.36 IGFBP-1 and -2 are also expressed in fetal tissues, although to a lesser extent.37 When individual genes encoding certain members of the IGF system are inactivated by mutation or by homologous recombinant gene-targeting techniques, the consequences for fe¬ tal development are extremely serious. Loss of the IGF-II/ mannose-6-phosphate receptor due to the Tme-deletion mutant results in fetal death, but homologous deletion of IGF-I, IGF-II, or the IGF-I receptor genes results in overall growth retardation of the fetus, generalized retardation in organ development, and in the case of IGF-I and the IGF-I receptor gene deletion, in peri¬ natal lethality.11-13 Postnatal growth also depends on IGF. During the pubertal growth spurt, the levels of circulating IGF-I and the expression of the IGF-I gene in the liver rise in parallel with those of GH; hepatic-derived IGF-I is the primary mediator of GH-dependent longitudinal bone growth.5 GROWTH DISORDERS

In GH-deficient dwarfs, circulating IGF-I levels fall. Larontype dwarfs are small, despite normal or even elevated circulat¬ ing GH levels. These patients have reduced circulating IGF-I lev-

1456

PART X: DIFFUSE HORMONAL SECRETION

els due to GH resistance as a result of a genetic GH receptor de¬ fect. Malnutrition and poorly controlled type I diabetes similarly result in poor growth spurts during puberty. In these latter con¬ ditions, a reversible GH receptor or postreceptor defect have been implicated in the cause of the growth retardation and the associated reduction in circulating IGF-I levels. NERVOUS SYSTEM

IGFs, their receptors, and certain binding proteins are ex¬ pressed widely throughout the nervous system prenatally and postnatally.39,40 The IGFs affect the growth, differentiation, and neuromodulation of neurons and glial cells. They can stimulate neurite outgrowth in neurons and synaptogenesis at the neuro¬ muscular junction, and they induce the catecholaminergic phe¬ notype in sympathetic neuronal precursors and commitment of progenitor cells to the oligodendrocyte lineage. IGF-I stimulates the evoked release of acetylcholine from cortical slices and cate¬ cholamine release from chromaffin cells. IGFs are expressed in denervated muscle after sciatic nerve injury, which correlates with reinnervation, and when added exogenously, they stimulate regeneration of damaged nerves. In addition to their role in prenatal growth and development of the nervous system, the IGFs play important roles in the nor¬ mal functioning of the adult nervous system. The apparent neu¬ rotrophic effects of the IGFs suggest a potential role for them in certain diseases as an etiologic agent in Alzheimer disease or as a therapeutic agent in neurodegenerative disorders.41,42

I receptors) at the growing end of bone.51 In contrast, osteoblasts express IGF-I, and this expression is enhanced by parathyroid hormone, PGE2, and estrogen.6,52 In cooperation with other growth factors, the IGFs affect proliferation and differentiation of bone cells, and they may be extremely important in callus for¬ mation after a fracture and therapeutically relevant in cases of osteoporosis (see Chap. 49). IGFBPs are also expressed in these cells, and the level of IGFBP-4, which inhibits IGF-I action on proliferation and differentiation, is increased by l,25(OH)2 vita¬ min D3.53 IGFBP-5 enhances IGF-I effects on bone cells. IGF-I enhances formation of multinucleated osteoclastic cells, thereby coupling bone formation and resorption. DIABETES

The IGF system has been implicated in many of the side effects of diabetes. The delayed pubertal growth spurt in poorly controlled type I diabetes is associated with reduced circulating IGF-I levels associated with insulinopenia, which results in the GH resistance at the level of the liver. Diabetic microangiopathy and macroangiopathy may be partially the result of the mitogenic effects of IGFs on vascular smooth muscle cells. Early hemody¬ namic kidney changes associated with enlarged kidneys and the increased glomerular filtration rate and renal plasma flow char¬ acteristic of poorly controlled type I diabetics can be reproduced by IGF-I infusion.54 Whether this leads to chronic renal disease in diabetics is unknown. Alternatively, recombinant human IGFI has been shown to reduce insulin resistance temporarily in type I and type II diabetics and may be useful during crises.55

IMMUNE SYSTEM

Differentiation of T cells, induction of granulocytic differ¬ entiation by granulocyte-macrophage colony-stimulating factor (GM-CSF), and differentiation of hemopoietic progenitors by erythropoietin (EPO) are associated with local production of IGFI, which acts through IGF-I receptors that are widely expressed on all myeloid and lymphoid cells. In addition to stimulating pro¬ liferation and differentiation of these cells, IGF-I exerts chemoat¬ tractant effects on T-cell progenitors migrating from hemopoietic tissues to the thymus, where they are further differentiated by cytokines. At sites of inflammation, macrophage-derived IGF-I, together with interleukin-1 (IL-1), enhances migration of T lym¬ phocytes to the site. These cytokine-activated T cells undergo clonal expansion in response to IGF-I.43 In addition to hemocrine IGF-I, local (paracrine or autocrine) IGF-I exerts a significant effect in concert with the cytokines on the immune and hemopoietic systems.44,45 The possibility of us¬ ing recombinant human IGF-I to enhance the immune response in such diseases as acquired immunodeficiency syndrome (AIDS) remains an important potential use and deserves further investigation.

CANCER

The IGF-I receptor has intrinsic tyrosine kinase activity and mediates cell proliferation, and the IGF system may be involved in malignancy. Numerous tumors of various types express high levels of IGF-I or IGF-II, IGF receptors, and certain IGFBPs.5 57 Modulation of tumor growth by retinoic acid and other tumor inhibitors is associated with alterations in expression of compo¬ nents of the IGF system.58 Non-islet cell tumors overexpress IGF-II. Lack of normal proteolytic processing of the prohormone results in increased lev¬ els of pro-IGF-II (i.e., ''big IGF-I''). Pro-IGF-II is incompletely neutralized by the 150-kd IGFBP-3 complex and is associated primarily with the smaller 50-kd IGFBP-2 complex, which rap¬ idly transfers the ligand out of the circulation and delivers it to target tissues, inducing hypoglycemia.59 Wilms tumors are asso¬ ciated with overexpression of IGF-II and the IGF-I receptor be¬ cause of a lack of inhibition of the promoters of those genes.9,25 The overexpression of the IGF system in tumors is a therapeutic avenue that needs to be explored. POTENTIAL CLINICAL USES

REPRODUCTIVE SYSTEM

Delayed puberty is commonly associated with GH defi¬ ciency and is assumed to be the result of reduced IGF-I levels, which play an important role in ovarian, uterine, and testicular physiology. Gonadotropins and sex steroids enhance local IGF-I production and IGF-I receptor expression.46,47 Conversely, IGF-I modulates follicle-stimulating hormone (FSH) action in the ovary and enhances steroidogenesis in ovary and testes.48 Patients un¬ dergoing hormonal manipulation for in vitro fertilization show an improved response when GH is administered systemically, presumably enhancing hemocrine and local IGF-I production.49 Estrogen enhances uterine IGF-I expression, which affects endo¬ metrial physiology, and IGF-I may also be important for embryo implantation in the uterus.50

Clinically, recombinant human IGF-I has been extremely useful in reversing negative N2 balance in several catabolic states and reducing insulin resistance in common forms of diabe¬ tes.55,60-63 It also induces growth in Laron-type dwarfism.64 Other potential uses include nerve regeneration; healing of wounds, fractures, and osteoporosis; and recovery from acute renal fail¬ ure.60,65,66 It may also be useful in treating AIDS by activating the immune response. Potential side effects after prolonged use include tumor formation and angiopathy.

OTHER GROWTH FACTORS PLATELET-DERIVED GROWTH FACTORS

BONE

STRUCTURE

The pubertal growth spurt is mediated by circulating IGF-I on chondrocytes (which do not express IGF-I but do express IGF-

PDGFs are a family of proteins consisting of disulfidebonded dimers of A and B chains.67 The A and B chains are en-

Ch. 169: Growth Factors and Cytokines coded by separate genes that apparently arose by gene duplica¬ tion and divergence. They have retained about 60% similarity in their amino acid sequences, and their eight cysteine residues are perfectly conserved. The major form of PDGF in humans is the AB heterodimer. The BB homodimer (homologous to the viral sis oncogene) is found in other species, and the AA homodimer is expressed by certain tissues and a glioma cell line. The expression of PDGF is surprisingly high in many regions of the brain, but expression by most nonneural tissues is quite low. Plowever, after activation or injury, PDGF expression is markedly enhanced. PDGF receptors are expressed by vascular smooth muscle cells, fibroblasts, and glial cells, but the receptors are not ex¬ pressed by most hemopoietic, epithelial, or endothelial cells. Two subtypes have been identified. The a receptor binds all three PDGF isoforms (i.e., AA, AB, BB), and the (8 receptor only binds PDGF-BB with high affinity.68,69 Both receptor subtypes contain five immunoglobulin-like domains, a single transmembrane se¬ quence, and an intracellular protein tyrosine kinase region that is split by a kinase insert region. Ligand binding leads to receptor dimerization, activation of the kinase, and subsequent associa¬ tion and activation of numerous endogenous substrates. These include phospholipase A2/ phospholipase Cy, phosphatidylinositol 3'-kinase, and RAS-GAP. These substrates interact directly with phosphotyrosine residues on the PDGF receptor by means of their SH2 domains.

FUNCTIONS

PDGF induces cell proliferation in mesenchymal cells, in¬ cluding fibroblasts, osteoblasts, arterial smooth muscle cells, and brain glial cells.69 PDGF is a competence factor, allowing cells to enter the G0/G! phase of the cell cycle, but further progression is the function of other growth factors.70 Wound Healing. PDGF is synthesized and released at the site of injury by platelets, vascular cells, monocyte-macrophages, fibroblasts, and skin epithelial cells. PDGF, by means of a para¬ crine mechanism, induces proliferation and chemotaxis of con¬ nective tissue cells and production of extracellular matrix, thereby enhancing healing.71-72 Osteogenesis. PDGF plays an important role in bone for¬ mation and metabolism by stimulating DNA synthesis and colla¬ gen synthesis by osteoblasts. In addition to normal bone devel¬ opment, PDGF is potentially capable of enhancing new bone formation after fractures.73 Atherosclerosis. Characteristic of this atherosclerosis is an abnormal proliferation of arterial smooth muscle cells, increased number of macrophages, and excessive deposition of connective tissue. In addition to platelet-derived PDGF, vascular endothelial cells and activated macrophages also express PDGF. PDGF re¬ ceptor expression is increased in the cells in proximity to the mac¬ rophages, the intimal smooth muscle cells. PDGF is one of the most important growth factors involved in atherogenesis.74 The restenosis that follows balloon angioplasty is also asso¬ ciated with increased PDGF and receptor expression, particularly by neointimal smooth muscle cells. Fibrosis. PDGF and receptors play a role in many fibrotic diseases, including myelofibrosis, scleroderma, and pulmonary fibrosis, by stimulating connective tissue cell proliferation, che¬ motaxis, and collagen synthesis, which are all pathognomonic features of these diseases.75,76 Neoplasia. The acutely transforming Simian sarcoma virus genome contains a retroviral homologue of the cellular gene en¬ coding PDGF-B. This led to speculation that the cell-cycle com¬ petence factor PDGF may be involved in tumor cell growth. Tu¬ mors such as gliomas, sarcomas, melanomas, mesotheliomas, carcinomas, and hemopoietic cell-derived tumors overexpress PDGF. Many tumors are associated with increased connective tissue formation and fibrosis, which may be the result of tumorderived PDGF effects.77 78 Although PDGF may be involved in pathologic states, its

1457

value therapeutically in treating wounds and bone fractures, to name a few examples, remains to be explored.

EPIDERMAL GROWTH FACTOR FAMILY The epidermal growth factor family of growth factors in¬ clude EGF, transforming growth factor-a (TGF-a), amphiregulin, and heparin-binding EGF.79'82 They are each synthesized as a much larger membrane-bound glycosylated precursor before processing into a smaller mature peptide. EPIDERMAL GROWTH FACTOR

The 1217-amino acid, membrane-bound EGF precursor and the 53-amino acid mature peptide are capable of interacting with cell-surface EGF receptors. This interaction causes dimerization of the single-chain EGF receptors, activation of the cytoplasmic tyrosine kinase domain, and subsequent biologic responses.82 EGF is a potent stimulator of cell multiplication, and it mod¬ ulates the differentiation and specialized functions of various cells. EGF's effects on development include eyelid opening, teeth eruption, lung maturation, and skin development.83 In keeping with its initial isolation from salivary glands, EGF has been shown to protect the gastric mucosa by inhibiting gastric acid secretion.84-85 The overexpression of EGF and the EGF receptor occurs in certain carcinomas. The EGF receptor (c-erb-1) is homologous to the avian viral oncogene v-erb B, strongly supporting the notion that overexpression may be involved in tumorigenesis.79 A corre¬ lation has been demonstrated between amplification of the EGF receptor gene and poor prognosis in breast, lung, and bladder cancers.77'86,87 TRANSFORMING GROWTH FACTOR-a

TGF-a resembles EGF structurally and functionally. It is synthesized as part of a 160-amino acid cell-surface precursor, and the mature 50-amino acid TGFa is proteolytically cleaved and released from the extracellular domain.86 It is a potent mito¬ gen, acting through the EGF receptor.88 It is expressed in preim¬ plantation embryos and the fetus and is essential in normal de¬ velopment. In adults, it is expressed by the anterior pituitary, brain, decidual cells, skin keratinocytes, bronchus, kidney, and genital tract and has been implicated in wound healing and in¬ flammation, angiogenesis, and bone resorption.89,90 TGF-a is overexpressed in many cancers, in which it is implicated, along with the EGF receptor, as being tumorigenic.

TRANSFORMING GROWTH FACTOR-0 FAMILY TGF-01 is a disulfide-linked dimer of two identical chains of 112 amino acids. The chains are synthesized as 390-amino acid precursor molecules. The cleaved proregion remains associated with the mature TGF-01 dimer forming a biologically latent com¬ plex, which becomes active on disassembly of this complex.91 This family of growth factors in humans includes TGF-0, the activin-inhibin family, and miillerian inhibitory hormone.1 3,9“ BIOSYNTHESIS

The TGF-0 peptides represent three separate gene products expressed by many normal cells and tissues. Expression is active throughout embryonic development and into adulthood. Gene expression is regulated by multiple factors at the level of tran¬ scription, and except in the case of platelets, in which TGF-0 is stored in a-granules, the IGF-0S are released from cells through a constitutive pathway. TGF-01 released from cells is in the 'la¬ tent” form and the proregion contains mannose-6-phosphate, which binds to IGF-II/mannose-6-phosphate receptors, and an RGD sequence, which may be important for its interaction with integrin receptors.93,94 The role of these residues in regulating the

1458

PART X: DIFFUSE HORMONAL SECRETION

release of active TGF-/? remains undefined; however, proteases play a definitive role in conversion from the latent to the active form. RECEPTORS

There are two distinct receptors that mediate the effects of TGF-/3. The type I receptor is expressed only by hemopoietic cells that are growth-inhibited by TGF-/3 and is expressed with the type II receptor by many different cells and tissues in which growth inhibition, extracellular matrix protein synthesis, and differentiation are the major responses. In addition to these two classic receptors, betaglycan, an abundant membrane proteogly¬ can, also binds TGF-/3. A soluble form of betaglycan is found in the extracellular matrix. Betaglycan binding of TGF-d has been invoked as important in the storage of TGF-/3 in the matrix, pre¬ sentation of the ligand to the receptor, and even clearance of TGF-/3, whereby the membrane form internalizes with the ligand.94 ACTIONS

The bioactions of TGF-/3 are extensive and varied. TGF-/3 can inhibit or stimulate proliferation, depending on the culture conditions. In the presence of mitogen-rich medium, TGF-/3 in¬ hibits; in the presence of mitogen-free medium, TGF-/3 can en¬ hance proliferation by inducing PDGF. TGF-/3 causes enhanced cell-cell adhesion in mesenchymal and epithelial cells and various cell lines. This process is accom¬ panied by increased extracellular matrix production and expres¬ sion of cell-adhesion receptors. These effects explain, at least in part, the role of TGF-/3 in wound healing, tissue repair, and angi¬ ogenesis. TGF-/3 is expressed by activated macrocytes and mac¬ rophages at sites of wound healing or inflammation and is a che¬ moattractant for these cells. Bone remodeling is enhanced by locally produced TGF-/3.95'96 TGF-/3 has also been invoked as a causative mediator in dis¬ eases, including acute mesangial proliferative glomerulosclerosis, fibrotic diseases such as lung fibrosis, liver cirrhosis, arterial re¬ stenosis after angioplasty, and myelofibrosis.97,98 Because TGF-/3 forms have antiproliferative effects on T and B lymphocytes, they have potent immunosuppressive effects in vivo.99,100 The ele¬ vated TGF-d expression in lymphocytes may be one explanation for the general immunosuppressive effects of the AIDS virus de¬ spite the limited number of lymphocytes that are actually in¬ fected. The potential benefits of the antiinflammatory and immu¬ nosuppressive effects of TGF-/3 in systemic disease, such as rheumatoid arthritis, await further experimentation. As a sup¬ pressor of cell proliferation, the absence of TGF-/3 or its receptor may result in oncogenesis.101 Only retinoblastoma cells have been reported to be devoid of TGF-/3 receptors, which may en¬ able increased oncogenic potential.

INHIBIN AND ACTIVIN Inhibins and activins are dimeric polypeptides composed of similar subunits (see Chaps. 18, 111, and 113). Inhibins (i.e., 7/3A, 7/3B) inhibit production of FSH in pituitary cells, sex steroid in the gonads, and many placental hormones. The activins (i.e., /3A/3A, (8A|8B) stimulate the production of all these hormones. Ac¬ tivins also induce differentiation of erythroleukemia cells. NERVE GROWTH FACTOR FAMILY Nerve growth factor (NGF) is part of a family of neurotrophins that includes brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and NT-4 or NT-5. NGF is a highly con¬ served, 118-amino acid protein exhibiting more than 70% homology with all vertebrate species' forms. The various mem¬ bers of the family (i.e., NGF, BDNF, NTs) are also conserved in certain regions and also have similar predicted tertiary structures.102

RECEPTORS

Initial studies demonstrated the existence of low-affinity re¬ ceptors that bound NGF, BDNF, and NT-3, and high-affinity re¬ ceptors were found that were specific for NGF or BDNF. “105 The low-affinity receptor was initially shown to be a 75-kd in¬ trinsic membrane protein (p75). A 140-kd tyrosine kinase recep¬ tor encoded by the protooncogene TRK has been found to bind NGF with high affinity and to mediate NGF effects. TRK-B is a TRK-related gene product that binds BDNF and NT-3, and TRKC binds NT-3 with high affinity. TRK and TRK-B contain tyrosine kinase activity, but p75 does not. A model for the functional in¬ teraction of the NGF-related peptides and functional receptors suggests that p75, TRK, and TRK-B individually are low-affinity receptors, and the association of p75 with TRK or TRK-B gener¬ ates a high-affinity, functional receptor. FUNCTIONS

NGF-related peptides stimulate survival and differentiation of a range of target neurons. TRK B expression is widespread throughout the central nervous system, serving more general functions, and TRK and p75 are co-localized to the medial septal nucleus and nucleus of the Broca diagonal band, which contains the NGF-responsive magnocellular cholinergic neurons project¬ ing to the hippocampus and cerebral cortex. NGF is the prototypic growth factor that controls cell sur¬ vival. Neurons that project to an inappropriate target are auto¬ matically eliminated, because they fail to be stimulated by neurotrophic factors, but neurons projecting to the appropriate target cell are innervated accordingly. The other members of the family have similar functions but act on different subsets of neurons.106,107 Selective degeneration of magnocellular cholinergic neurons in nucleus basalis of Meynert is seen in patients with senile de¬ mentia of the Alzheimer type. Clinical trials have begun using NGF directly intraventricularly in patients with Alzheimer's de¬ mentia or to support transplanted adrenal medullary tissue in Parkinson disease.

FIBROBLAST GROWTH FACTOR FAMILY Seven members of the FGF family are known. Acidic FGF (FGF-a) and basic FGF (FGF-/3) have different tissue preferences for expression and function. The family includes a new member: keratinocyte growth factor (KGF).io8-m The FGFs support the survival of neural cells and stimulate proliferation of many types of cells, including fibroblasts, endothelial cells, smooth muscle cells, hepatocytes, and skeletal myoblasts. Moreover, mesoderm induction is FGF dependent. Two classes of FGF binding sites have been characterized. The low-affinity, high-capacity receptors are cell-surface proteo¬ glycans containing heparan sulfate side chains. The high-affinity tyrosine kinase receptors are important for transducing the sig¬ nals. These high-affinity receptors represent a family of gene products. The extracellular domains have three immunoglobulin-like loops, which are involved in ligand binding and are highly conserved.112 The high- and low-affinity receptors collaborate in FGF binding. The low-affinity, heparan sulfate-containing receptors bind the FGF molecule, allowing it to dimerize so that it can bind to the high-affinity receptors. This results in activation of tyrosine kinase activity and activation of phospholipase C7I, one of the major receptor substrates in the signal transduction pathway.

VASCULAR ENDOTHELIAL GROWTH FACTOR Angiogenesis, the proliferation of capillary networks, re¬ quires degradation of the extracellular matrix of a local venule and the chemotaxis and proliferation of endothelial cells. The process normally occurs during embryonic development, wound healing, and cyclically in the endometrium and ovary. It may

1459

Ch. 169: Growth Factors and Cytokines play an important role in the pathogenesis of several diseases, especially cancer. aFGF, bFGF, EGF, TGF-a, TGF-/3, PGE2/ TNFa, and IL-8 are all candidate angiogenic factors. Ffowever, the newly identified vascular endothelial growth factor (VEGF) seems to be the best candidate. VEGF is a potent mitogen specific for endothelial cells and promotes angiogenesis.113114 VEGF is a basic, heparin-binding homodimeric glycoprotein that exists as several isoforms derived from alternative splicing of RNA from multiple exons. VEGF receptors are expressed exclu¬ sively by endothelial cells and exhibit tyrosine kinase activity. VEGF is expressed by a variety of tumors and the degree of vas¬ cularization of the malignancy correlates with the level of VEGF mRNA. Antibodies to VEGF can inhibit tumor growth, strongly supporting the hypothesis of its involvement in tumor progres¬ sion. Potential therapeutic uses for a VEGF antagonist include malignancies and restenosis after angioplasty.

CYTOKINES The cytokine family contains a diverse collection of proteins that, by activation of specific cell-surface receptors, regulate many cellular processes, including the immune and inflamma¬ tory systems, and differentiation processes such as hemopoiesis (Table 169-3). This family includes the interleukins (IL), of which there are now more than 14; the tumor necrosis factors (TNF-a, -|3), the interferons (IFN-a, -j3, -y), the macrophage and granulo¬ cyte colony-stimulating factors (M-CSF/CSF-1, G-CSF, GMCSF), and several other molecules, including leukemia inhibitory factor (LIF), stem cell factor (SCF), B-cell growth factor (BCGF), erythropoietin (EPO), and the SIS protein family (of which IL-

8 is a member), which also includes macrophage inflammatory proteins (MIPla, MIP1/3) and the RANTES chemokine (regu¬ lated upon activation, normal T expressed, and presumably se¬ creted). In this section, the major subgroups of this family are discussed, including the ILs, TNFs, IFNs, CSFs, and miscella¬ neous other members in terms of their contributions to the vari¬ ous cellular processes described previously. Cytokines are closely allied with growth factors because they are often synthesized by multiple cell types. Exceptions to this are IL-2 through IL-5 and IFN-7, which are produced spe¬ cifically by lymphoid cells. IL-3, for example, is predominantly produced by activated T cells. Although typical hormones often have unique actions in specific types of target cells, cytokines, like several growth factors, may have an array of actions in many target cell types, and a given action may be produced by multiple, distinct cytokines. This would predict that many cytokines are redundant in their effects; such a conclusion is supported by the results of the gene-targeting experiments described in subse¬ quent sections (see Table 169-3).

INTERLEUKINS There are 14 characterized species of IL: IL-la, IL-1/3, and IL-2 through IL-13. The existence of additional IL-8-related pep¬ tides suggests that this subfamily of cytokines will continue to expand. INTERLEUKIN-1

IL-la and IL-1/3 are encoded by similar but distinct, closely linked genes on human chromosome 2.115 Both proteins are ini¬ tially synthesized as part of larger precursor peptides. Although

TABLE 169-3 Sources and Potential Clinical Applications of Selected Cytokines Cytokine

Sources_Applications

IL-1

Many cell types, including monocytes, keratinocytes, B cells,

Stimulation of hemopoiesis alone or in conjunction with CSFs

astrocytes, endothelial cells IL-2

Activated T cells, NK cells, LAK cells

Treatment of metastatic melanoma and renal cell cancer, often in conjunction with IFN-a, LAK cells or TILs

IL-3

Activated T cells

Stimulation of hemopoiesis in combination with CSFs or EPO

IL-4

T cell and thymocytes

Potential inhibition of solid tumors and B-cell lymphomas

IL-6

Lymphoid and nonlymphoid cells

Potent stimulator of the of

TNF-a

Many cell types, primarily monocytes and activated macrophages

hypothalamic-pituitary-adrenal axis

and secretion

vasopressin

Many potential applications, including reduction of ascites in ovarian cancer; anti-TNF-a antibodies may be useful in treatment of septicemia

TNF-/3

Activated lymphocytes

Similar to those of TNF-a

M-CSF

Many lymphoid and nonlymphoid cells

Circulating marker for ovarian and endometrial cancer and lymphohemopoietic malignancies, stimulation of hemopoiesis in conjunction with other CSFs

G-CSF

Stromal cells, macrophages, fibroblasts, endothelial cells

Modulation of neutrophil production and function; relevant to treatment of cancer neutropenia, thionamide-induced neutropenia, and infectious diseases

GM-CSF

Activated T cells, macrophages, fibroblasts, endothelial cells

Similar to those of G-CSF

IFN-a

Some tissues such as spleen and liver; lymphocytes

Used for treatment of hairy cell leukemia and Kaposi sarcoma; somewhat

IFN-/3

Fibroblasts, some endothelial cells

Potential antiviral agent and treatment for cancers also treated with IFN-a

IFN-y

T cells, NK cells

Potential wide-spectrum antiviral and anticancer agent; effective in

Adult kidney and liver

Treatment of anemia in numerous clinical settings, orthostatic

T cells, monocytes, bone marrow stromal cells, thymic epithelial

Potential use in combination with G-CSF or GM-CSF in myeloid

effective with hepatitis C

treatment of chronic granulomatous disease EPO

hypotension LIF

cells SCF

Bone marrow, fibroblasts, placenta

leukemia and for stimulating platelet production Potential treatment of HIV and aplastic anemia

CSF, colony-stimulating factor; EPO, erythropoietin; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulo¬ cyte-macrophage colony-stimulating factor; HIV, human immunodeficiency virus; IFN, interferon; IL, interleukin; LAK, lymphokine-activated killer cells; LIF, leukemia inhibitory factor; M-CSF, macrophage colony-stimulating factor; NK, natural killer cells; SCF, stem cell factor; TNF, tumor necrosis factor.

1460

PART X: DIFFUSE HORMONAL SECRETION

they, like all cytokines, are secreted, they do not contain typical signal peptides; the mechanism of secretion of the mature pep¬ tide is unknown. IL-1 is produced by many cell types, including monocytes and macrophages, neutrophils, astrocytes and mi¬ croglia, endothelial cells, fibroblasts, T and B lymphocytes, and platelets. IL-1 is one of the most pleiotrophic members of the IL family in that it induces the widest range of responses, including co-stimulation of lymphocytes, PGE release, fever induction, IL2 and IFN-/3 and -y release, and bone resorption.116 IL-1 is involved in immune and inflammatory responses and in hema¬ topoiesis. IL-1/3 has been shown to be cytotoxic for isolated pan¬ creatic B cells and may play a causative role in autoimmune as¬ pects of diabetes. Almost all of the effects of IL-1 are also seen with TNF, and synergy with TNF can be demonstrated in many cases. INTERLEUKIN-2 IL-2 is an important component in the immune response. It is produced by antigen-induced T cells, and its subsequent in¬ teraction with IL-2 receptors, which are also antigen induced, leads to the clonal expansion of effector T-cell populations. In addition to proliferative effects, IL-2 stimulates differentiation, inducing the production of IFN-7 and IL-4 by T cells. IL-2 also has effects on B cells (which themselves can produce IL-2 after antigen or IL-2 stimulation), natural killer (NK) cells, lymphokine-activated killer (LAK) cells, monocytes, macrophages, and oligodendrocytes. The T-cell-activating capacity of IL-2 has fa¬ cilitated the study of lymphocyte function in vitro and has pro¬ moted its consideration as a form of immune replacement ther¬ apy in immunodeficient or immunocompromised patients.117 Its effect on LAK cell function has led to the development and test¬ ing of IL-2/LAK therapy in clinical trials, in which it has been effective in treating renal carcinomas and malignant melano¬ mas.118 IL-2 therapy also reduces the number of opportunistic infections in AIDS patients. INTERLEUKIN-3 IL-3 is produced primarily by activated T lymphocytes, al¬ though there is some evidence that most cells may synthesize IL3 under certain conditions. IL-3's major function is in hemopoie¬ sis, in which it stimulates the growth of bone marrow stem cells and the differentiation of myeloid stem cells into macrophages, neutrophils, basophils, eosinophils, basophils, mast cells, mega¬ karyocytes, and erythroid cells.119 IL-3 does not appear to act on lymphocytes or their immediate precursors, but it nonetheless has the widest target range of action of any of the hemopoietic growth factors. At early stages in the differentiation of erythroid cells, neutrophils, monocytes, and eosinophils, IL-3 appears to work in concert with the CSFs. By virtue of its being produced by activated T cells and stimulating the growth and differentiation of several myeloid lineages, IL-3 links the immune system to hemopoiesis.120

nonlymphoid cells and is involved in acute-phase reactions to infection and the regulation of immune responses in addition to B-cell development.126 It is similar to IL-1 in its involvement in all three of the major areas of biologic function characteristic of the cytokines. INTERLEUKIN-8 IL-8 is a member of the RANTES/SIS family of cytokines that are characterized by specific arrangements of cysteine resi¬ dues that function as chemoattractants for inflammatory cells. The members of this family that contain conserved C-X-C motifs include platelet binding protein (PBP), connective tissue¬ activating peptide III (CTAP-III), /3-thromboglobulin (/3-TG), and neutrophil-activating protein-2 (NAP-2). NAP-2, /3-TG, and CTAP-III are derived from PBP by progressive N-terminal trun¬ cation. Different forms of IL-8 itself, which was initially called neutrophil-activating protein 1 (NAP-1), are generated by N-terminal cleavages. The particular form of IL-8 produced appears to be cell type specific. IL-8 is produced by a wide variety of cells, including leukocytes, monocytes, neutrophils, fibroblasts, endo¬ thelial cells, and possibly, lymphocytes. IL-8 appears to function primarily in the inflammatory response, regulating neutrophil ac¬ tivation and chemotaxis. The members of the RANTES/SIS fam¬ ily that are characterized by a C-C motif include RANTES itself and MIP; these are more specific chemoattractants for macro¬ phages and lymphocytes.127 INTERLEUKIN-9 IL-9 has been shown to function as a growth factor for helper T cells and as an erythroid colony-stimulating factor. Its lymphocytic activity appears to be rather specific in that it is ac¬ tive with CD4+ T cells but not cytotoxic CD8+ T cells. INTERLEUKIN-10 IL-10 is an "anticytokine" produced by T helper-2 lympho¬ cytes and by B cells, macrophages, and keratinocytes. Although it has several stimulatory activities, such as co-stimulation of stem cell growth and the growth of thymocytes and mast cell and megakaryocyte progenitors, it can inhibit the production of other cytokines by T helper-1 lymphocytes, macrophages, and NK cells.128 IL-10 has been shown to function in B-cell growth and differentiation into Ig-secreting cells.129 INTERLEUKIN-11, INTERLEUKIN-12, AND INTERLEUKIN-13 IL-11, IL-12, and IL-13, because of their more recent discov¬ ery or identification as interleukins, are significantly less well characterized than the factors described previously. IL-11 is in¬ volved in megakaryocytopoeisis, and IL-12 can synergize with IL-2 in the activation of NK on LAK cells and can function as a Tcell growth factor.

INTERLEUKIN-4, INTERLEUKIN-5, AND INTERLEUKIN-7

IN VIVO INTERLEUKIN FUNCTIONS

IL-4, IL-5, and IL-7 are involved in B-cell growth and differentiation. IL-4 and IL-5 are primarily produced by helper T cells, and IL-7 is produced by bone marrow stromal cells.121 ~123 In addition to their contribution to B-cell development, these molecules also influence other cell types. IL-5, for example, is important in eosinophil development, and IL-7 is active with Bcell and T-cell precursors.124 As is the case with IL-3, these he¬ mopoietic agents also link immune and hematopoietic responses.

Gene-targeting experiments have contributed to our under¬ standing of the roles of IL-2, IL-4, and IL-10 in vivo. Somewhat surprisingly, IL-2-deficient mice do not exhibit any major defect in T-cell development in the thymus, but in vitro responses of T cells to mitogens and the generation of cytotoxic T cells are diminished.130 The lack of more pronounced defects in these an¬ imals illustrates the level of redundancy seen in the cytokine sys¬ tem in general.131 IL-4-deficient mice exhibit extremely low lev¬ els of serum IgGl and no detectable IgE, as would be expected from the role of IL-4 in B-cell proliferation and IgGl and IgE secretion.13" Although the postnatal treatment of mice with a monoclonal anti-IL-10 antibody results in the overproduction of IFN-y by T cells, in accord with its "anticytokine" properties, genetically IL-10-deficient mice do not exhibit the same pheno¬ type as the antibody-treated animals.133 134 This may reflect the

INTERLEUKIN-6 IL-6 is also important in B-cell development, but it appears to work at a later stage, promoting the differentiation of B cells into plasma cells. IL-6 can function as a competence factor for hemopoietic stem cells.12’’ IL-6 is produced by lymphoid and

Ch. 169: Growth Factors and Cytokines existence of compensatory mechanisms operative in the genetargeted mice.

TUMOR NECROSIS FACTORS TNF-a (i.e., cachectin) and TNF-/? (i.e., lymphotoxin) are po¬ tent cytokines encoded by two tightly linked genes (i.e., within 1 kb of one another) on human chromosome 6 and on mouse chromosome 17 (in the middle of the major histocompatibility complex) that exhibit a wide spectrum of actions.135 The bio¬ effects induced by the TNFs include the hemorrhagic inflamma¬ tion of transplanted tumors (hence “tumor necrosis factor"), cy¬ totoxicity, and the modulation of inflammatory, immune, proliferative, and antiviral responses. Direct comparisons have shown that TNF-a and TNF-/? are qualitatively equivalent with respect to their activities. TNF-a can stimulate angiogenesis in vivo.136 The active form of the TNFs is a trimer.137 Although TNF/? has a conventional signal peptide and is secreted from the cells that synthesize it in a typical fashion, TNF-a can be expressed as a plasma membrane-anchored protein because of its long signal sequence and can activate TNF receptors on adjacent cells in a juxtacrine mode of action138 (see Chap. 1). The principal sources of TNF-a are monocytes and activated macrophages, and TNF-/? is synthesized by mitogen-activated lymphocytes. The therapeutic use of the TNFs has been hampered by del¬ eterious side effects such as angiogenic activity.139 Some of these difficulties may be overcome though the synthesis of mutant TNFs that exhibit anticancer properties but are less toxic.140

COLONY-STIMULATING FACTORS Initially, the CSFs were described as a single factor in the conditioned media of embryonic fibroblasts that could stimulate mouse bone marrow cells to form colonies in soft agar. Further purification and characterization resulted in the identification of four distinct components responsible for colony-stimulating ac¬ tivity that differed with respect to the specific cell types involved in colony formation. 1L-3 (described in a previous section), ini¬ tially called multi-CSF, stimulated the growth of colonies con¬ taining mixtures of granulocytes, macrophages, megakaryocytes, and erythrocytes. Macrophage CSF (M-CSF/CSF-1), granulo¬ cyte CSF (G-CSF), and granulocyte-macrophage CSF (GM-CSF) stimulated the growth of macrophages, granulocytes, or mixed populations of neutrophilic granulocytes and macrophages, re¬ spectively. Subsequent studies have clarified the role of the vari¬ ous CSFs. MACROPHAGE COLONY-STIMULATING FACTORS

M-CSF is an important regulator of myeloid lineage devel¬ opment and is produced in vivo by several types of bone marrow stromal cells including fibroblasts, adipocytes, and reticular and endothelial cells. Monocytes and macrophages also produce MCSF when stimulated by GM-CSF, TNF-a, or IFN-7. M-CSF is also produced by uterine glandular epithelial cells during preg¬ nancy, and M-CSF appears to function in placental development in addition to hemopoiesis.141 In humans, the single M-CSF gene is transcribed into two differentially spliced mRNAs that encode two M-CSF precursor peptides.142 These each dimerize to pro¬ duce two forms of mature M-CSF. M-CSF stimulates the prolif¬ eration of monocytes and synergizes with other cytokines, such as IL-3, IL-la, IL-6, G-CSF, and GM-CSF, in eliciting the differ¬ entiation of earlier myeloid progenitors. M-CSF produced by fi¬ broblasts and endothelial cells after tissue damage recruits monocytes and stimulates macrophages.143 M-CSF can be syn¬ thesized by uterine glandular endothelial cells; this M-CSF then can activate M-CSF receptors on placental trophoblasts. M-CSF appears to play a role in several biologically important processes, including hemopoiesis, inflammation, and placental development.

1461

GRANULOCYTE COLONY-STIMULATING FACTORS

G-CSF is encoded by a single-copy gene on human chromo¬ some 17 that gives rise to two G-CSF mRNAs as a result of differential splicing.144'145 These encode mature proteins of 174 and 177 amino acids that function as monomers. Although many cell types produce G-CSF in vitro, its synthesis in vivo is much more restricted. Normal serum levels of G-CSF are extremely low, but they are increased in response to infection.146 After the infection is controlled, G-CSF levels return to normal. Local bone marrow production is apparently sufficient for maintenance of neutrophil levels, but cell types such as monocytes, endothelial cells, fibroblasts, chondrocytes, and astroglia require stimulation by IL-1 or TNF-a to produce G-CSF in response to infection. GCSF is necessary for the maintenance of normal neutrophil pro¬ duction and modulation of neutrophil production and respon¬ siveness in disease.14' GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTORS

GM-CSF is related to certain other hemopoietic growth fac¬ tors, specifically IL-3 and IL-5, in terms of gene structure and location, bioactivity, and receptor binding. The GM-CSF gene is on human chromosome 5, linked closely to the IL-3 gene and less closely to the IL-5 gene.148 The murine and human GM-CSF amino acid sequences are only 54% conserved, and their activi¬ ties also appear to be species specific.149 GM-CSF is produced by activated T cells and by several other cell types, including keratinocytes and TNF-a- and IL-1-stimulated endothelial cells.150151 GM-CSF, along with IL-3, is involved in the maturation of sev¬ eral hematopoietic lineages, including granulocytes, macro¬ phages, megakaryocytes, erythrocytes, and eosinophils. In addi¬ tion to these effects on progenitor cells, GM-CSF, like IL-3, can enhance basophil histamine release and eosinophil function. GM-CSF functions in hemopoiesis and in the inflammatory re¬ sponse and, like G-CSF, on progenitor and mature cell types. In general terms, the CSFs are characterized by their ability to in¬ fluence progenitor development and the differentiated functions of the mature cell types produced.

INTERFERONS IFNs were initially characterized as a substance that pro¬ tected cells from viral infection.152 Based on their physical prop¬ erties and source, the IFNS were subsequently divided into type I or type II. Type I IFNs included the acid-resistant form produced by virally infected leukocytes and fibroblasts, and type II IFN corresponded to the acid-stable form produced by antigen- or mitogen-stimulated lymphocytes. In the current nomenclature, fibroblast IFN is called IFN-a, leukocyte IFN is IFN-/?, and type II or "immune" IFN is IFN-7. However, even this classification is proving too simple for the IFN family of proteins.153 There are at least 15 distinct genes encoding different forms of human IFN-a and 9 IFN-a pseudogenes. These IFN-a genes and the single IFN-/? gene are clustered on human chromosome 9.154 A similar arrangement occurs in the mouse genome, with multiple IFN-a genes and pseudogenes and the single murine IFN-/? gene clustered on mouse chromosome 4. A relatively unique feature of the IFN-a and IFN-0 genes is that they lack introns. IFN-a and IFN-/? can be produced by many cell types after viral stimulation, and the IFN-a gene is constitutively transcribed in spleen, liver, kidney, and peripheral lymphocytes.155 Coupled with the fact that the primary effects of IFN-a and IFN-/? (through activation of widely expressed IFN receptors in target cells) are concerned with interference with viral replication, this raises the question of a cytokine-like action of these particular IFNs in addition to their obvious role as mediators of an immedi¬ ate response to viral infection. However, IFN-a and IFN-/? do exhibit antiproliferative effects, in some cases mediated through

1462

PART X: DIFFUSE HORMONAL SECRETION

down-regulation of growth factor receptors, and stimulation of the synthesis of IFN-a and IFN-/3 by IL-2 can be seen in mouse bone marrow cells.156 IFN-7 is encoded by a single-copy gene on human chromo¬ some 12, and unlike the various IFN-a and IFN-/3 genes, it does contain introns.157 IFN-7 is produced specifically by T cells, in¬ cluding NK cells, CD4 T helper-1 cells, and CD8 cytotoxic sup¬ pressor cells. IFN-7 produced by these cells influences several cell types in the immune system. IFN-7 stimulates proliferation and pro¬ duction of IL-4 and IL-5 by CD4 T helper-2 cells, cytotoxic activ¬ ity by NK cells (a potential example of an IFN-7 autocrine loop), antibody production by B cells, and microbicidal and tumoricidal activity and major histocompatibility complex class II gene ex¬ pression by macrophages. Such observations have led to the feel¬ ing that IFN-a and IFN-/3 were of paramount importance in viral resistance, but that IFN-7 was primarily an immune modulator. However, studies of mice in which the IFN-7 gene or the gene encoding a required component of the IFN-7 receptor had been inactivated by homologous recombination have forced a reeval¬ uation of this issue.158, 59 The response to certain viral infections requires IFN-7 function, but IFN-7 was not required for the pro¬ duction of NK cells. These data emphasize the antiviral proper¬ ties of IFN-7 and put its immune functions in a new perspective. These studies also confirmed the necessary role of IFN-7 in mac¬ rophage activation, particularly nitric oxide production by mac¬ rophages, the basis of their antiparasitic action.

ERYTHROPOIETIN EPO is produced by the proximal tubule cells of the kidney, where its production is controlled by the number and oxygen¬ carrying capacity of circulating erythrocytes (see Chap. 177). EPO is secreted into the circulation, where it interacts with recep¬ tors in fetal liver and in adult spleen and bone marrow.160 EPO appears to function as a classic hormone, but it is considered to be a member of the cytokine family because it is similar to other cytokines in terms of structure and function. For example, EPO is a glycoprotein whose size is in the range of those of other cyto¬ kines, and it functions in hemopoiesis, being mitogenic for erythroid precursors. Unlike the situation with most other cytokines, the glycosylation of EPO appears to be essential for biologic activity. EPO does not affect the differentiation of pluripotent stem cells, but in concert with IL-3 or GM-CSF, it stimulates the devel¬ opment of a more mature progenitor population, erythroid burst¬ forming cells, into erythroid colony-forming units (CFU-E). CFU-E cells can then be directly stimulated by EPO alone to form mature red blood cells. By virtue of its effects on red cell produc¬ tion, recombinant human EPO is in clinical use in the treatment of disorders such as renal failure-associated anemia and or¬ thostatic hypotension.161

LEUKEMIA INHIBITORY FACTOR LIF is an archetypal cytokine that exhibits a bewildering ar¬ ray of effects in vitro, only one of which is its ability to inhibit the proliferation of certain leukemia cell lines.162 According to strictly in vivo data, LIF is produced by a wide range of cells, including activated T cells and monocytes, bone marrow stromal cells, and thymic epithelial cells in humans and extraembryonic tissues and embryonic stem (ES) cells in mice. The in vivo actions of LIF include the stimulation of acutephase protein synthesis in hepatocytes and modulation of ery¬ throid, megakaryocyte, and lymphocyte numbers in mice. A primary role for L.IF in embryogenesis had been suggested by several studies, but definitive evidence was obtained in studies of mice in which the LIF gene had been inactivated by gene targeting.103 Female LIF-deficient mice exhibit a defect in uterine function that prevents embryo implantation, rendering them in¬

fertile. The lack of other obvious detrimental consequences again demonstrates the redundancy of the cytokine system, at least with respect to the myriad of other actions ascribed to LIF. Inter¬ estingly, a major current use of LIF is in maintaining the un¬ differentiated state of murine ES cells in short-term culture, ob¬ viating the need for co-culture of ES cells with fibroblast feeder layers in gene-targeting procedures.164

STEM CELL FACTOR SCF also known as mast cell growth factor, is the ligand for the KIT receptor.165 SCF is synthesized as a 248-amino acid pre¬ cursor and can exist in a cell-associated and a mature, 164-amino acid, soluble form. SCF is produced by BRL cells, marrow stromal cell lines, and human fibroblasts. SCF is a potent stimulator of mast cells but also exhibits synergisms with the CSFs and is active on lymphoid progenitors.

GROWTH FACTOR AND CYTOKINE RECEPTORS CATEGORIES Growth factor receptors are divided into four major catego¬ ries based on structural features in their intracellular domains or in the extracellular domains of one of the components of the re¬ ceptor complex. The tyrosine kinase receptor family includes the EGF receptor, a transmembrane protein that contains a tyrosine kinase domain in its intracellular domain and an extracellular ligand binding do¬ main that includes cysteine-rich regions. Other members of this family include the insulin and IGF-I receptors and the insulin receptor-related receptor, all of which exist as heterotetramers consisting of two transmembrane /3 subunits that contain tyro¬ sine kinase domains in their intracellular regions and two extra¬ cellular ligand binding a subunits that are linked to each other and to the /? subunits by disulfide bonds and which contain a single cysteine-rich region.166 This family does not include any known cytokine receptors. A second receptor family is known as the immunoglobulin superfamily, whose distinguishing feature is the existence of re¬ peated immunoglobulin-like domains in the extracellular domain of the receptor. This family includes the PDGF-A, PDGF-B, MCSF, and SCF receptors, which contain five immunoglobulin-like domains and a split tyrosine kinase domain, and the IL-1 recep¬ tor, which contains these immunoglobulin-like domains and lacks intrinsic tyrosine kinase activity. The largest of these receptor families is the hemopoietic re¬ ceptor family, which is characterized by conserved pairs of cys¬ teine residues and a WSXWS motif that occurs in the proximal extracellul ir region of the receptor. Included in this group are the receptors for IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-12, G-CSF, GM-CSF, EPO, IFN-a, IFN-/3, IFN-7, LIF, oncostatin M (OSM), ciliary neurotrophic factor (CNTF), GH, and prolactin.167 In some cases, the active receptor complex involves an additional compo¬ nent that determines ligand binding specificity and contributes to signal transduction. The WSXWS motif-containing components of the IL-2 and EPO receptors contain proline-rich regions in their intracellular juxtamembrane regions, which may interact with SH3 domain-containing cytoplasmic proteins. The fourth receptor family is characterized by the presence of 40-amino acid repeats in the extracellular domain and includes the receptors for the TNFs and NGF.

LIGAND BINDING AND SIGNALING The various types of growth factor receptors also differ in their binding and signal transduction mechanisms. In the case of tyrosine kinase receptors such as the EGF, insulin, and PDGF

Ch. 169: Growth Factors and Cytokines receptors, ligand binding to the extracellular domain results in receptor dimerization (except in the case of the heterotetrameric receptors) and activation of the receptor tyrosine kinase. Subse¬ quently, autophosphorylation of the receptor and phosphoryla¬ tion of endogenous substrates occurs, initiating signal transduc¬ tion cascades such as that involving SH2 and SH3 domaincontaining adapter molecules, RAS modulators and RAS itself, and a series of tyrosine and serine-threonine kinases such as RAF1, MAP kinase kinase (MEK), MAP kinases (i.e., ERK-1, -2, -3), S6 (RSK) kinase isoforms, and transcription factors such as FOS and JUN. In this fashion, ligand binding eventually results in changes in cellular metabolism and gene expression.168 The binding and signaling mechanisms employed by the other three groups of growth factor receptors have been less well characterized than those of receptor tyrosine kinases, but some of the mechanisms by which several cytokines exert their effects have begun to be elucidated. With respect to ligand binding and its immediate consequences, it is likely that most non-tyrosine kinase receptors also dimerize to initiate signal transduction. In the case of the TNF receptor, studies suggest that the p75 TNF receptor molecule is not actively involved in signal transduction but binds TNF and, in a sense, passes the TNF to the p55 TNF receptor, which then initiates the biologic actions characteristic of TNF. The role of the p75 moiety is to increase the effective local concentration of TNF, facilitating binding to the p55 recep¬ tor moiety.169 It has been proposed that such a ligand passing mechanism may also be employed by the IL-1 and TGF-/3 receptors. In the case of the hemopoietic receptor family, the WSXWS motif-containing component (/3 subunit) of the receptor is in some cases shared by several cytokines, with binding specificity determined by a separate a subunit. GM-CSF, IL-3, and IL-5, which exert similar bioeffects, use receptors that share a common /3 subunit, but the assembly of an activated receptor complex is initiated by ligand binding to specific a subunits.170 The liganda subunit complex then binds to and dimerizes the appropriate 8 subunit. The IL-2 receptor also appears to consist of a and 8 subunits. The situation described for the GM-CSF, IL-3, and IL-5 re¬ ceptors is found in a more complex form in the case of the IL-6, LIF, CNTF, and OSM receptor group.171 Several lines of evidence suggested that these cytokines represent a functionally related subfamily. This hypothesis was supported by the discovery that each of these ligands requires the 8 subunit of the IL-6 receptor (i.e., gpl30) as a component of the receptor signaling complex. The situation differs from that of the GM-CSF, IL-3, and IL-5 receptor group in that IL-6 binds an a subunit and this then binds to and dimerizes the IL-6 receptor 8 subunit, but CNTF (and pos¬ sibly OSM) bind to specific a subunits that then bind to gpl30 and result in its dimerizing with the LIF receptor 8 subunit (that is related to gpl30). LIF itself binds directly to the LIF receptor 8 subunit, which then recruits gpl30 into a heterodimeric complex. The IL-6/LIF/CNTF/OSM receptor family consists of various combinations of 8 subunit homodimers or heterodimers whose function is (except in the case of LIF) initiated by ligand binding to a specific a subunit. The IL-2, IL-4, and IL-7 receptors consist of ligand-specific 8 subunits whose binding affinity is increased by and signal trans¬ duction made possible by association with a common y sub¬ unit.172-174 Previously, IL-4 and IL-7 receptor 8 subunits had been identified, as had a and 8 IL-2 receptor subunits. Preliminary ev¬ idence now suggests that this y subunit may also constitute part of the IL-3 receptor, which would then consist of a, 8, and y components, like the IL-2 receptor.

POSTRECEPTOR EVENTS The postreceptor events involved in cytokine signal trans¬ duction are not as fully elucidated as those initiated by activation of the receptor tyrosine kinases, but studies have identified some

1463

of the components of the relevant pathways. An immediate post¬ receptor component appears to be the JAK family of cytoplasmic tyrosine kinases, which includes JAK1, JAK2, and Tyk2. Several cytokines have been shown to induce the tyrosine phosphoryla¬ tion and kinase activity of JAK2, which also associates with spe¬ cific cytoplasmic juxtamembrane regions of cytokine receptor 8 subunits.175 Genetic studies have demonstrated that Tyk2 and JAK1 are required for IFN-a signaling, but IFN-7 signaling re¬ quires JAK1 and JAK2. In the case of the IFNs, JAK kinase activa¬ tion results in the phosphorylation and nuclear localization of components of specific transcription factor complexes.176 The available data suggest that cytokines interact with different combinations of transmembrane receptor components, resulting in dimerization of some of these components. These di¬ mers then activate cytoplasmic tyrosine kinases, such as those of the JAK family, to alter the phosphorylation state and subcellular localization of specific transcription factors. It appears that the signaling mechanisms employed by various growth factors may differ in detail, but the general processes and types of cellular factors employed are qualitatively conserved.

GROWTH FACTORS AND ONCOGENES Oncogenes were originally described as regions of tumor vi¬ ruses that were necessary for transformation of infected cells. It was subsequently found that many viral oncogenes had normal cellular counterparts, called protooncogenes. Given that growth factors regulate normal growth and that oncogenes elicit abnor¬ mal growth, certain relationships would be expected to exist be¬ tween these two groups of molecules. The role of protooncogenes in normal growth would be expected to be elucidated by studies of these relationships. Some oncogenes have been shown to be related to growth factors and growth factor receptors. Other oncogenes have been shown to be related to downstream targets of growth factor re¬ ceptors, such as FOS and JUN. The v-szf oncogene product was found to be identical to the PDGFB chain, and the k-fgf oncogene product is similarly related to FGF. The v-ros product is related to the insulin receptor, and this may explain the tumorigenicity of the overexpressed IGF-I receptor. The FMS oncogene product corresponds to the M-CSF receptor, and the EGF, HER-2/NEU, and KIT receptors are oncogenic if appropriately activated. A corollary of the connection between growth factors and oncogenes is the regulation of growth factor activity by antion¬ cogenes, now known more commonly as tumor-suppressor genes. This is exemplified by the ability of the Wilms tumorsuppressor gene product, WT1, to repress the transcription of the IGF-II, IGF-I receptor, PDGFA, and M-CSF genes. The products of the p53, RBI (retinoblastoma), and APC (adenomatosis polyp¬ osis coli) tumor-suppressor genes may also exert this effect, in part, through modulation of growth factor action.

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1464

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the brain. In: Loughlin SE, Fallon JH, eds. Neurotrophic factors. San Diego: Aca¬ demic Press, 1992:391. 41. Torres-Aleman I, Pons S, Santos-Benito FF. Survival of Purkinje cells in cerebellar cultures is increased by insulin-like growth factor I. Eur J Neurosci 1992;4:864. 42. Ishii DN, Recio-Pinto E. Role of insulin, insulin-like growth factors and nerve growth factors in neurite formation. In: Raizada MK, Phillips ML, LeRoith D, eds. Insulin, insulin-like growth factors and their receptors in the CNS. New York: Plenum Press, 1987:315. 43. Landreth KS, Narayanan R, Dorshkind K. Insulin-like growth factor-I reg¬ ulates pro-B cell differentiation. Blood 1992;5:1207. 44. Fu Y-K, Arkins S, Wang BS, et al. A novel role of growth hormone and insulin-like growth factor-1. J Immunology 1991; 146:1602. 45. Gelato MC. Growth hormone-insulin-like growth factor I and immune function. Trends Endocrinol Metab 1993;4:106. 46. Levy MJ, Hernandez ER, Adashi EY, et al. 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TGF-beta 1 is an autocrine¬ negative growth regulator of human colon carcinoma FET cells in vivo as revealed by transfection of an antisense expression vector. J Cell Biol 1992; 116:187. 102. Levi-Montalcini R. The nerve growth factor 35 years later. Science 1987;237:1154. 103. Ebendal T. Function and evolution in the NGF family and its receptors. J Neuroscience Res 1992;32:461. 104. Ross AH. Identification of tyrosine kinase Trk as a nerve growth factor receptor. Cell Regul 1991;2:685. 105. Bothwell M. Keeping track of neurotrophin receptors. Cell 1991; 65:915. 106. Raff MC, Barres BA, Bume JF, et al. Programmed cell death and the control of cell survival: lessons from the nervous system. Science 1993;262:695. 107. Rabizadeh S, Oh J, Zhong L-T, et al. Induction of apoptosis by the lowaffinity NGF receptor. Science 1993;261:345. 108. Klagsbrun M, Edelman ER. Biological and biochemical properties of fi¬ broblast growth factors: implications for the pathogenesis of atherosclerosis. Arte¬ riosclerosis 1989; 9:269. 109. Hearn MTW. Structure and function of the herapin-binding (fibroblast) growth factor family. Clin Endocrinol Metab 1991; 5:321. 110. Finch PW, Rubin JS, Miki T, et al. Human KGF is FGF-related with prop¬ erties of a paracrine effector of epithelial cell growth. Science 1989;245:752. 111. Goldfarb M. The fibroblast growth factor family. Cell Growth Differ 1990; 1:439. 112. Yayon A, Klagsbrun M, Esko JD, et al. Cell surface, heparin-like mole¬ cules are required for binding of basic fibroblast growth factor to its high affinity receptor. Cell 1991; 64:841. 113. Leung DW, Cachianes G, Kuano W-J, et al. Vascular endothelial growth factor is a secreted angiogenic mitogen. Science 1989;240:1306.

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114. Ferrara N. Vascular endothelial growth factor. Trends Cardiovasc Med 1993;3:244. 115. Clark BD, Collins KL, Gandy MS, et al. Genomic sequence for human prointerleukin-1 beta: possible evolution from a reverse transcribed interleukin-1 alpha gene. Nucleic Acids Res 1986; 14:7897. 116. Dinarello CA. Interleukin-1. Rev Infect Dis 1984; 6:51. 117. Lutze MT, Strausser JL, Rosenberg SA. In vitro growth of cytochrome human lymphocytes. II: use of T-cell growth factor (TCGF) to clone human T-cells. J Immunol 1980; 124:2972. 118. Rosenberg SA, Lutz MT, Muul LM, et al. A progress report on the treat¬ ment of 157 patients with advanced cancer using lymphokine-activated killer cells and interleukin-2 or high-dose interleukin-2 clone. N Engl J Med 1987;316:889. 119. Ihle JN, Keller J, Henderson L, et al. Biological properties of interleukin-3. I: demonstration of WEHI-3 growth factor activity, P cell stimulatory factor activity, colony stimulating factor activity and histamine producing cell stimulating factor activity. J Immunol 1982; 129:2431. 120. Schrader JW, Clark-Lewis I, Crapper RM, et al. The physiology and pa¬ thology of pan-specific hemopoietin (IL-3). Interleukin-3, the pan-specific hemopoietin. In: Schrader JW, ed. Lymphokines, vol 15. New York: Academic Press 1988: 849. 121. Palliard X, de Waal-Malefyt R, Yssel H, et al. Simultaneous production of IL-2, IFN-7 and IL-4 by human lymphocyte clones. J Immunol 1988; 141:849. 122. Yokota T, Arai N, deVries J, et al. Molecular biology of interleukin 4 and interleukin 5 genes and biology of their products that stimulate B cells, T cells and hemopoietic cells. Immunol Rev 1988; 102:137. 123. Welch PA, Namen AE, Goodwin RG, et al. Human IL-7: a novel T cell growth factor. J Immunol 1989; 143:3562. 124. Cosman D, Namen AE, Lupton S, et al. Interleukin 7: a lymphoid growth factor active on T and B cell progenitors. Lymphokine Recept Interact 1989; 179: 229. 125. Van Snick J. Interleukin-6: an overview. Annu Rev Immunol 1990;8: 253. 126. KishimotoT. The biology of interleukin-6. Blood 1990; 74:1. 127. Taub DD, Conlon K, Lloyd AR, et al. Preferential migration of activated CD8+ T cells in response to MIP-la and MIP-l/L Science 1993;260:355. 128. Rennick D, Berg D, Holland G. Interleukin 10: An overview. Prog Growth Factor Res 1992;4:207. 129. Fluckiger A-C, Garrone P, Durand I, et al. Interleukin 10 (IL-10) upregulates functional high-affinity IL-2 receptors on normal and leukemic B cells. J Exp Med 1993; 178:1473. 130. Schorle H, Holtschke T, Hiinig T, et al. Development and function of T cells in mice rendered interleukin-2 deficient by gene targeting. Nature 1991; 352: 621. 131. Paul WE. Pleiotropy and redundancy: T cell-derived lymphokines in the immune response. Cell 1991;57:521. 132. Kuhn R, Rajewsky K, Muller W. Generation and analysis of interleukin4 deficient mice. Science 1991;254:707. 133. Ishida H, Hastings R, Kearny J, Howard M. Continuous anti-interleukin 10 antibody administration depletes mice of Ly-1 B cells but not conventional B cells. J Exp Med 1992; 175:1213. 134. Paul WE. Poking holes in the network. Nature 1992;357:16. 135. Vilcek J, Lee TH. Tumor necrosis factor. J Biol Chem 1991;266:7315. 136. Frater-Schroder M, Risau W, Hallman R, et al. Tumor necrosis factor type a, a potent inhibitor of endothelial cell growth in vitro, is angiogenic in vivo. Proc Natl Acad Sci USA 1987; 84:5277. 137. Jones EY, Stuart DI, Walker NPC. Structure of tumor necrosis factor. Nature 1989; 338:225. 138. Kreigler M, Perez C, DeFay K, et al. A novel form of TNF/cachectin is a cell-surface cytotoxic transmembrane protein: ramifications for the complex physi¬ ology of TNF. Cell 1988;53:45. 139. Balkwill FR. Tumor necrosis factor and cancer. Prog Growth Res 1992; 4: 121. 140. Van Ostade X, Vandenabeele P, Everaedt B, et al. Human TNF mutants with selective activity on the p55 receptor. Nature 1993;361:266. 141. Arceci RJ, Shanahan F, Stanley ER, et al. The temporal expression and location of colony-stimulating factor-1 (CSF-1) and its receptor in the female repro¬ ductive tract are consistent with CSF-1 regulated placental development. Proc Natl Acad Sci USA 1989;86:8818. 142. Ladner MB, Martin GA, Noble JA, et al. Human CSF-1: gene structure and alternative splicing of mRNA precursors. EMBO J 1987;6:2693. 143. Wang JM, Griffin JD, Rambaldi A, et al. Induction of monocyte migration by recombinant macrophage colony-stimulating factor. J Immunol 1988; 141:575. 144. Tweardy DJ, Cannizzaro LA, Palumbo AP, et al. Molecular cloning and characterization of a cDNA for human granulocyte colony-stimulating factor (GCSF) from a glioblastoma multiforme cell line and localization of the G-CSF gene to chromosome band 17q21. Oncogene Res 1987; 1:209. 145. Nagata S, Tsuchiya M, Asano S, et al. The chromosomal gene structure and two mRNAs for human granulocyte colony-stimulating factor. EMBO J 1986; 5:

575. 146. Kawakami M, Tsutsumi H, Kumakawa T, et al. Levels of serum granulo¬ cyte colony-stimulating factors in patients with infections. Blood 1990; 76:1962. 147. Layton JE. Granulocyte colony-stimulating factor: structure, function and physiology. Growth Factors 1992;6:179. 148. Heubner K, Osobe M, Croce CM, et al. The human gene encoding GMCSF is at 5q21-q32, the chromosome region deleted in the 5q abnormality. Science 1985;230:1282. 149. Migatake S, Otsuka T, Yokota T, et al. Structure of the chromosomal gene

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for granulocyte-macrophage colony-stimulating factor: comparison of the mouse and human genes. EMBO J 1985; 4:2561. 150. Chodakewitz JA, Kupper TS, Coleman DL. Keratinocyte-derived granu¬ locyte /macrophage colony-stimulating factor induces DNA synthesis by peritoneal macrophages. ] Immunol 1988,140:832. 151. Seiff CA, Tsai S, Faller DV. Interleukin 1 induces cultured human endo¬ thelial cell production of granulocyte-macrophage colony-stimulating factor. ] Clin Invest 1987;79:48. 152. Issacs A, Lindenmann J. Virus interference. I: the interferon. Proc Roy Soc 1957;B147:258. 153. Pestka S, LangerJA, Zoon KC, Samuel CE. Interferons and their actions. Annu Rev Biochem 1987;56:727. 154. Slate DL, D'Eustachio P, Pravtcheva D, et al. Chromosomal location of a human a interferon gene family. ] Exp Med 1982; 155:1019. 155. Tovey MG, Streuli M, Gresser I, et al. Interferon messenger RNA is pro¬ duced constitutively in the organs of normal individuals. Proc Natl Acad Sci USA 1987; 79:7809. 156. Reis LFL, Lee TF1, Vilcek ]. Tumor necrosis factor acts synergistically with autocrine interferon-/} and increases interferon-/} mRNA levels in human fibro¬ blasts. J Biol Chem 1989;264:16351. 157. Gray PW, Geoddel DV. Structure of the human immune interferon gene. Nature 1982;298:859. 158. Dalton DK, Pitts-Meek S, Keshav S, et al. Multiple defects of immune cell function in mice with disrupted interferon--)' genes. Science 1993;259:1739. 159. Huang S, Hendriks W, Althage A, et al. Immune response in mice that lack the interferon-7 receptor. Science 1993; 259:1742. 160. Krantz SB. Erythropoietin. Blood 1991;77:419. 161. Graber SE, Krantz SB. Erythropoietin: biology and clinical use. Hematol Oncol Clin North Am 1989;3:369. 162. Kurzrock R, Estrov Z, Wetzler B, et al. LIF: not just a leukemia inhibitory factor. Endocr Rev 1991,-12:208. 163. Stewart DL, Kaspar P, Brunet LF, et al. Blastocyst implantation depends on maternal expression of leukemia inhibitory factor. Nature 1992;359:76. 164. Williams RL, Hilton D], Pease S, et al. Myeloid leukemia inhibitory factor (LIF) maintains the developmental potential of embryonic stem cells. Nature 1988,-336:684. 165. Copeland NG, Gilbert D], Cho BC, et al. Mast cell growth factor maps to near the steel locus on mouse chromosome 10 and is deleted in a number of steel alleles. Cell 1990;63:175. 166. Yarden Y, Ullrich A. Growth factor receptor tyrosine kinases. Annu Rev Biochem 1988;57:443. 167. Kishimoto T, Taga T, Akira S. Cytokine signal transduction. Cell 1994; 76:253. 168. White MF, Kahn CR. The insulin signaling system. J Biol Chem 1994; 269:1. 169. Tartaglia LA, Pennica D, Goeddel DV. Ligand passing: the 75-kDa tumor necrosis factor (TNF) receptor recruits TNF for signaling by the 55-kDa TNF recep¬ tor. Proc Natl Acad Sci USA 1993; 268:18542. 170. Goodall GJ, Bagley CJ, Vadas MA, Lopez AF. A model for the interaction of the GM-CSF, IL-3 and IL-5 receptors with their ligands. Growth Factors 1993; 8: 87. 171. Stahl N, Yancopoulos GD. The alphas, betas, and kinases of cytokine receptor complexes. Cell 1993; 74:587. 172. Kondo M, Takeshita T, Ishii N, et al. Sharing of the interleukin-2 (IL-2) receptor 7 chain between receptors for IL-2 and IL-4. Science 1993; 262:1874. 173. Noguchi M, Nakamura Y, Russell SM, et al. Interleukin-2 receptor 7 chain: a functional component of the interleukin-7 receptor. Science 1993; 262: 1877. 174. Russell SM, Keegan AD, Harada N, et al. Interleukin-2 receptor 7 chain: a functional component of the interleukin-4 receptor. Science 1993; 262:1880. 175. Witthuhn BA, Quelle FW, Silvennoinen O, et al. JAK2 associates with the erythropoietin receptor and is tyrosine phosphorylated and activated following stimulation with erythropoietin. Cell 1993;74:227. 176. Hunter T. Cytokine connections. Nature 1993;366:114.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

170_

PROSTAGLANDINS AND OTHER ARACHIDONIC ACID METABOLITES R. PAUL ROBERTSON

Few scientific areas have surpassed the field of arachidonic acid metabolism in the accumulation of new biologic information over the past two decades. Arachidonic acid and one or more of its products—prostaglandins, thromboxanes, and leukotrienes—

have been investigated as regulators or counterregulators of vir¬ tually every organ and tissue in the mammalian body. Moreover, roles for these fatty acids have emerged and continue to be dis¬ covered for many endocrine organs and their target tissues. Prostaglandins, thromboxanes, and leukotrienes are not blood-borne hormones in the classic sense. Although it is true that they have many hormonal effects, there is no evidence that they have hemocrine characteristics. Rather, they are paracrine hormones, or autacoids, that are synthesized by the tissue in which they act and primarily provide fine modulation of ongoing cellular activity.

ARACHIDONIC ACID METABOLISM Arachidonic acid is stored in the membranes of cells as part of phospholipids. Phospholipase A2 activation is the mechanism for cleavage of arachidonic acid from phosphotidylcholine arachidonate and the initiation of the arachidonic acid cascade. A phospholipase-activating protein termed PLAP has been identi¬ fied in some cells. An alternate mechanism involves phosphatidylinositol arachidonate and three enzymes: phospholipase C, a diacylglycerol lipase, and a monoglyceride lipase.1 The cyclooxygenase and the lipoxygenase pathways are two major routes by which arachidonic acid is oxygenated. Products of the cyclooxygenase pathway include all of the prostaglandins (PG) and thromboxanes (TX). The lipoxygenase pathway gener¬ ates the leukotrienes (LT) and other substances such as hydroxyeicosatetraenoic acids (HETE) (Fig. 170-1). Several lipoxygenase pathways, including 5-lipoxygenase and 12-lipoxygenase, are important to human physiology. All metabolites of arachidonic acid, collectively, are called eicosanoids. Arachidonic acid metabolites in the cyclooxygenase pathway carry the subscript 2; LT derivatives in the lipoxygenase pathway carry the subscript 4. These subscripts designate the number of double bonds between carbon atoms in the side chains. Eicosanoids are not stored within cells; they are synthe¬ sized rapidly according to the needs of the tissue in which they originate. Fish oils contain omega-3 fatty acids, which can de¬ crease production of some arachidonate metabolites and increase levels of prostanoids with the subscript 3.

INFLUENCE OF DRUGS Several groups of drugs in clinical practice, including corti¬ costeroids and nonsteroidal antiinflammatory drugs (NSAIDs), in¬ hibit the arachidonic acid cascade (Fig. 170-2). Although these drugs have important clinical uses and have been helpful in un¬ derstanding the relevance of arachidonic acid metabolism to mammalian physiology, none of them specifically inhibits the synthesis of single eicosanoids. The sites of action of these drugs occur early in the arachidonic acid cascade; consequently, they influence the production of many eicosanoids simultaneously. Therefore, it is difficult to ascribe the clinical effect of any of these drugs to the absence of a particular eicosanoid. Another major limitation to full elucidation of the roles of arachidonic acid me¬ tabolites is the paucity of drugs available to serve as specific eico¬ sanoid receptor antagonists.

CATABOLISM Eicosanoids are catabolized rapidly in vivo. Prostaglandin E (PGE) and PGF are degraded almost completely during a single passage through the liver and the lung. Nonmetabolized PGE2 in the urine reflects renal and seminal vesicle production, whereas urinary PGE2 metabolites represent total body synthesis. Both PGI2 and TXA2 are also rapidly catabolized in vivo, as are the LTs. However, most of the eicosanoids have much longer chem¬ ical half-lives when stored under proper laboratory conditions.

Ch. 170: Prostaglandins and Other Arachidonic Acid Metabolites

1467

PGFjoc FIGURE 170-1. Representative arachidonic acid metabolites and their structures that are relevant to hu¬ man physiology and pathophysiology. LT, leukotriene; PG, prostaglandin; TX, thromboxane.

ASSAY Six methods are available to measure eicosanoids in physio¬ logic fluids; bioassay, radioimmunoassay, chromatography, re¬ ceptor assay, enzyme-linked immunoassay, and mass spectrom¬ etry. Special precautions should be taken in handling samples because eicosanoid synthesis may be stimulated during the col¬ lection procedure. For example, PGE2 and TXA2 may be gener¬ ated if blood is allowed to clot or if platelets are not carefully separated from plasma. This problem can be minimized by using an inhibitor of eicosanoid synthesis in the collection tube. Mea¬

surements of inactive metabolites of PGE2, PGI2, and TXA2 (e.g., 13,14-dihydro-15-keto-PGE2, 6-keto-PGFla, and TXB2, respec¬ tively) are commonly used for physiologic fluids because the par¬ ent substances are so short-lived in vivo. Native eicosanoids can be reliably measured in studies using in vitro experiments, such as organ incubations or cell culture.

MECHANISM OF ACTION Tissues and cells with receptors for eicosanoids include adi¬ pocytes, hepatocytes, pancreatic B cells, adrenal cortex and me-

PHOSPHOLIPID

CORTICOSTEROIDS PHOSPHOLIPASE A2

LIPOXYGENASE

CYCLOOXYGENASE Cyclic Endoperoxides PGG2. PGH2

MEPACRINE

-T-

ARACHIDONIC ACID

SALICYLATES INDOMETHACIN

-

Hydroperoxyeicosatetraenoic Acid HPETE

EPOXYGENASE

II— METYRAPONE pgd2 pge2

TxA2

PGF2ot

Hydroxyeicosatetraenoic Acid HETE

pgi2 Epoxyeicosatrienoic Acid EET

Dihydroxyeicosatrienoic Acid DHET FIGURE 170-2. Arachidonic acid metabolism. In this scheme, arachidonic acid is cleaved from phos¬ pholipid by phospholipase A2 and subsequently oxygenated predominantly by cyclooxygenase or lipox¬ ygenase. Active metabolites of the former pathway include the prostaglandins and thromboxane A2, whereas active metabolites of the latter pathway include the leukotrienes and HETE. Phospholipase¬ acting protein (PAP) and 5-lipoxygenase-activating protein (FLAP) are found in some cells and activate, respectively, cyclooxygenase and 5-lipoxygenase.

Leukotrienes LTA4 LTB4 ltc4 ltd4 lte4

1468

PART X: DIFFUSE HORMONAL SECRETION

dulla, corpus luteum, uterus, kidney, stomach, ileum, thymus, skin, brain (including pineal gland), lung, platelets, red blood cells, neutrophils, macrophages, and monocytes. These receptors usually are found in plasma membranes and are specific for a given type of eicosanoid. In several instances, the eicosanoid re¬ ceptor density can decrease or increase in response to local in¬ creases or decreases, respectively, of the ligand for that recep¬ tor.23 Moreover, down-regulation of the PGE receptor causes postreceptor effects. For PGE2, there is evidence of interactions with adenylate cyclase as an important postreceptor mechanism. Both the stimulatory (Gs) and inhibitory (Gj) regulatory subunits of adenylate cyclase may mediate certain actions of PGE2.4'6 However, our knowledge of the immediate postreceptor effects of eicosanoids is meager. There appear to be several subtypes of receptors recognizing PGE2 that are being cloned.7

PHYSIOLOGY AND PATHOPHYSIOLOGY RELEVANT TO THE ENDOCRINE SYSTEM The areas of endocrinology and metabolism in which eico¬ sanoids have been investigated most intensely include carbohy¬ drate metabolism, lipolysis, bone resorption, and reproductive physiology. However, effects of eicosanoids and drugs that pre¬ vent their synthesis have also been investigated in several other endocrine and metabolic tissues.

170-3).13,14 Type II diabetics characteristically lack first-phase in¬ sulin responses to intravenous glucose, but not responsiveness to other secretagogues. Exogenous PGE2 inhibits first-phase insu¬ lin responses to glucose stimulation. In addition, virtually all NSAIDs (except indomethacin) consistently enhance glucoseinduced insulin secretion. Intravenous sodium salicylate infusion doubles the basal insulin level, partially restores defective firstand second-phase insulin responses to intravenous glucose, and accelerates glucose disappearance rates after intravenous glucose challenges. Exogenous PGE2 reverses the augmentation of glucose-induced insulin secretion by NSAIDs.15 Conflicting reports fall into two categories. The first involves studies of the effects of PGE2 itself, rather than effects of PGE2 on glucose stimulation of insulin secretion. Sometimes, PGE2 be¬ haves as a weak stimulator of insulin secretion if glucose concen¬ trations are held constant. This effect appears to depend on acti¬ vation of islet adenylate cyclase.16 The second category involves the use of indomethacin as an inhibitor of islet cyclooxygenase. Indomethacin not only fails to augment insulin secretion, but usually inhibits it. Although indomethacin inhibits islet cycloox¬ ygenase, it also affects other enzyme systems and calcium flux across membranes.17 This multiplicity of indomethacin's effects may explain why it is discordant with other structurally unrelated inhibitors of cyclooxygenase that augment glucose-induced insu¬ lin secretion. LIPOXYGENASE PRODUCTS

CARBOHYDRATE METABOLISM AND DIABETES MELLITUS CYCLOOXYGENASE PRODUCTS

Reports of the involvement of PGs in carbohydrate metabo¬ lism appeared as early as the later nineteenth century. Sodium salicylate was used in the late 1800s to decrease glycosuria in diabetic patients; very little significance was attributed to this therapy, especially because insulin was discovered in the 1920s. However, the situation changed with the discovery that NSAIDs inhibit cyclooxygenase.8 Concomitantly, it was found that PGs of the E series inhibit glucose-induced insulin secretion,9'11 an effect now known to be mediated by G-proteins. Consequently, the hypothesis was formulated that PGs of the E series may con¬ tribute to abnormal glucose-induced insulin secretion in diabetes mellitus.12 Although initially conflicting conclusions were pub¬ lished, a relatively clear picture seems to have emerged (Fig.

There has been much work done that examines the effect of lipoxygenase products on insulin secretion.1819 Generally, drugs that inhibit lipoxygenase inhibit glucose-induced insulin secre¬ tion. 12-HETE appears to be the major lipoxygenase product in the pancreatic islet. 12-Hydroperoxyeicosatetraenoic acid, the precursor to 12-HETE, augments glucose-induced insulin secre¬ tion, whereas many other lipoxygenase products, including 12HETE, do not. No clinical studies that assess the effects of lipox¬ ygenase products or inhibitors on human insulin secretion are yet available. DUAL ACTION OF ARACHIDONIC ACID METABOLITES

The prevailing hypothesis is that arachidonic acid pathways can exert both negative and positive modulatory effects on glucose-induced insulin secretion.12 The negative modulatory effect appears to be mediated by PGE2, whereas the positive

PANCREATIC ISLET

t [GLUCOSE]

FIGURE 170-3. Hypothetical relationship between arachi¬ donic acid metabolites and glucose-induced insulin secretion in the pancreatic islet. The cyclooxygenase pathway is shown to have a PGE2-mediated negative modulatory effect on insu¬ lin secretion, whereas the lipoxygenase pathway has a 12hydroxyperoxyeicosatetraenoic acid (HPETE)-mediated posi¬ tive modulatory effect on insulin secretion. Which physiologic and pathophysiologic conditions regulate the cyclooxygenase and lipoxygenase pathways, respectively, to yield net negative and net positive modulation of glucose-induced insulin secre¬ tion are unknown.

Ch. 170: Prostaglandins and Other Arachidonic Acid Metabolites modulatory effect appears to be mediated by 12-hydroperoxyeicosatetraenoic acid. It is not yet established under what physio¬ logic or pathophysiologic conditions one or the other of these two pathways dominate to cause net negative or net positive modu¬ latory effects. EFFECTS ON HEPATIC GLUCOSE PRODUCTION

Eicosanoids also have been implicated in the regulation of glucose production by the liver, a major component of carbohy¬ drate homeostasis. Hepatocytes contain receptors that are spe¬ cific for PGE, and down-regulation of these receptors is associ¬ ated with heterologous desensitization of hepatocyte adenylate cyclase.4 Exogenous PGE2 inhibits glucagon-induced glucose production,20 although it also has been suggested that PGE exerts a positive modulatory role on glycogenolysis.21 Virtually no in¬ formation is available about the effects of lipoxygenase products on hepatic glucose production.

LIPOLYSIS The ability of PGE2 to inhibit hormone-stimulated lipolysis was one of the first physiologic actions of PGs to be discovered22: PGE2 is as potent as insulin. Also, PGE receptors were first dem¬ onstrated in fat cells.23 An early hypothesis,24-25 still being evalu¬ ated, is that fat cells synthesize PGE2 intracellularly in response to incoming hormonal signals to provide local counterregulation of hormone-induced lipolysis (Fig. 170-4). Although the inhibi¬ tory effect of PGE2 on lipolysis is easily reproduced, inconsistent effects of NSAIDs on lipolysis have raised doubts about this hy¬ pothesis. These drugs are not specific inhibitors of PGE2 synthe¬ sis, and how effectively many of these agents inhibit cyclooxy¬ genase in fat cells has not been assessed. Evidence now suggests that during catecholamine-induced lipolysis, coordinate regula¬ tion is provided by the antilipolytic action of PGE2 and the lipo¬ lytic action of PGI2. It has been observed that a circulating me¬ tabolite of PGE2 (13,14-dihydro-15-keto-PGE2) is elevated in rats that have been made diabetic by streptozocin26 and in type I hu¬ man diabetic patients who are temporarily deprived of insulin.27 These data suggest that, during accelerated lipolysis, PGE2 plays a host defense role in which it is synthesized by fat cells to coun¬ teract increased lipolytic hormone levels.

BONE RESORPTION AND THE HYPERCALCEMIA OF MALIGNANCY Prostaglandin E2 is equipotent to parathyroid hormone (PTH) as a stimulator of bone resorption.28 After this boneresorptive effect of PGE2 had been demonstrated, two extensive series of experiments in two different animal models29 30 were conducted. They convincingly demonstrated that tumor-bearing animals had increased synthesis of PGE2, and that treatment of the animals with corticosteroids and NSAIDs decreased both PGE2 synthesis and circulating levels of calcium. These experi¬ ments led to the hypothesis that hypercalcemia associated with certain malignancies in humans might be explained by increased levels of PGE2. Initially, it was thought that ectopic (paraneoplas-

1469

tic) production of PTH explained most of these cases. It has be¬ come apparent, however, that ectopic PTH production is a rare phenomenon (see Chap. 58). Even greater interest in PGE2 arose when it was observed that urinary levels of PGE metabolites were elevated in hypercalcemic patients who had solid malig¬ nancies, a finding not observed in normocalcemic patients with malignancies or in hypercalcemic patients with parathyroid ade¬ nomas.31 The suggestion that tumor-associated increased synthe¬ sis of PGE2 might account for the hypercalcemia was strength¬ ened by observations that NSAIDs could lower elevated calcium levels in patients with malignancies.31 Subsequently, it has be¬ come evident that most subjects with hypercalcemia and malig¬ nancies do not respond to these drugs.32 Nevertheless, it appears that the responders were the patients with independent evidence for elevated PGE2 levels.33 Evidence suggests that parathyroid hormone-related protein is the most common mediator of hyper¬ calcemia in malignancy (see Chap. 51). The source of the excess PGE2 levels is not clear. Perhaps the most reasonable explanation is metastatic seeding of bone. That tumor cells can synthesize PGE2 in culture suggests that meta¬ static tumor cells in bone could synthesize PGE2, which could act locally to resorb bone. Although hypercalcemia in malignancy can occur in the absence of demonstrable bone metastases, radio¬ isotope scans may not be sensitive enough to detect multiple, small metastases. Another possibility is that in the presence of lung metastases, venous drainage from the tumor containing PGE2 arrives at bone through the arterial circulation without first passing through lung and liver tissue, where PGE would be degraded.

REPRODUCTIVE PHYSIOLOGY LUTEOLYSIS

Hysterectomy in sheep during the luteal phase is associated with luteal maintenance, suggesting that the uterus produces a luteolytic substance. PGF2a can cause luteal regression. Conse¬ quently, experiments were designed34 to assess whether PGF2a in uterine venous drainage might reach the ovary without passing through the systemic and pulmonary circulations, where it would be degraded. After the infusion of radiolabeled PGF2a into the uterine vein of sheep, the amount of radioactivity was many times higher in the ovarian arterial plasma than in the iliac arte¬ rial plasma. Consequently, a countercurrent phenomenon be¬ tween the uterine vein and ovarian artery may allow PGF2a from the uterus to reach the ovary and induce luteolysis. UTERINE EFFECTS: DYSMENORRHEA

Prostaglandins of the E and F series are synthesized by hu¬ man endometrium. These PGs stimulate uterine contractions; therefore, their administration by intravenous infusion or tablet form has been used to initiate labor.35 The hypothesis that PGE or PGF, or both, may participate in dysmenorrhea follows from the clinical observation that women have successfully used NSAIDs to treat the discomfort associated with this syndrome. Moreover, it has been observed that PGF and PGE levels in men¬ strual blood are decreased in patients taking drugs that inhibit PG synthesis. In controlled trials comparing PG synthesis inhibitors with placebo in women with dysmenorrhea, symptomatic im¬ provement has been greater after therapy with these drugs.36

t CAMP

t CATECHOLAMINE

OTHER ENDOCRINE GLANDS AA

t pge2

FFA

FIGURE 170-4. Hypothetical sequence of events in fat cells in which a hormone stimulates the formation of cAMP and lipolysis but, at the same time, stimulates synthesis of PGE2, which then produces negative feed¬ back on adenylate cyclase to counterregulate the generation of cAMP and lipolysis. AA, arachidonic acid; FFA, free fatty acid; TG, triglyceride.

Eicosanoids have been implicated in the control of hormone secretion by several other endocrine glands (Table 170-1). For example, a number of eicosanoids stimulate hormone re¬ lease37-41 from the pituitary gland (see Table 170-1). Other stud¬ ies assessing the effects of NSAIDs on the secretion of these hormones have been performed. Research in these areas is in¬ sufficient to determine to what extent eicosanoids might be im-

1470

PART X: DIFFUSE HORMONAL SECRETION

portant modulators of pituitary gland function or might be pathophysiologic agents in pituitary disease states. The observations that PGE2 decreases42 and PGF2o in¬ creases43 PTH secretion remain uncontested. Somewhat more work has been done on the potential roles of eicosanoids as reg¬ ulators of adrenal cortex function.44,45 However, this area also needs substantially more work before many of the conflicting re¬ ports can be satisfactorily resolved.

LTE4 are vasoconstrictors in most vascular beds. PGE2 has been postulated to be a primary factor in the maintenance of physio¬ logic patency of the ductus arteriosus in the fetus. Trials with NSAIDs have been undertaken in newborn human infants with patent ductus arteriosus that caused closure of this vessel.49 In¬ fants younger than 35 weeks of age are most likely to respond, and some individuals require a second course of therapy.

RENAL EFFECTS

PHYSIOLOGY AND PATHOPHYSIOLOGY RELEVANT TO OTHER BODY SYSTEMS4647 PLATELETS It has been proposed that a balance between PGI2 and TXA2 levels modulates platelet aggregation.48 Platelets synthesize TXA2, which is a potent stimulator of aggregation. PGI2 is syn¬ thesized by endothelial cells of blood vessels, and it potently an¬ tagonizes platelet aggregation. It is thought that TXA2 and PGI2 exert their opposing effects by decreasing and increasing, respec¬ tively, platelet generation of cyclic adenosine monophosphate. It follows that endothelial damage, and a concomitant decrease in PGI2 synthesis, may allow unbridled platelet aggregation at the site of vessel wall damage. It has been hypothesized that this situation would favor the eventual development of atherosclerosis.

INFLUENCE ON DUCTUS ARTERIOSUS Many eicosanoids are vasoactive substances. PGE2 and PGI2 are vasodilators, whereas PGF2a, TXA2, and LTC4, LTD4, and TABLE 170-1 Stimulatory and Inhibitory Actions of Eicosanoids on Endocrine Organ Function* Organ/Function

Stimulator

Inhibitor

Glucose-stimulated insulin secretion

12-HPETE

pge2

Glucagon secretion

pgd2, pge2

PANCREAS

GENERAL EFFECTS

Arachidonic acid metabolites influence both the reninangiotensin-aldosterone system and the vasopressin system50,51 (see Chaps. 26 and 177). Both PGE2 and PGI2 stimulate renin secretion. They also decrease renal vascular resistance and in¬ crease blood flow. The NSAIDs decrease total renal blood flow and can lead to acute renal vasoconstriction and decreased renal function in some circumstances, such as in volume depletion, in edematous states, and in older patients. Indomethacin increases sensitivity to exogenous vasopres¬ sin, and, conversely, PGE2 decreases vasopressin-stimulated wa¬ ter transport. BARTTER SYNDROME

Bartter syndrome is characterized by increased levels of plasma renin, aldosterone, and bradykinin; resistance to the pres¬ sor effect of angiotensin infusion; hypokalemic alkalosis; and re¬ nal potassium wasting in the presence of normal blood pressure (see Chap. 78). It has been postulated that excessive PGE2 or PGI2 synthesis plays a role in this syndrome 52 Both PGE2 and PGI2 stimulate the release of renin and blunt the pressor effects of an¬ giotensin. Elevated levels of PGE2 and PGI2 metabolites have been found in the urine of patients with this syndrome. Thera¬ peutic trials with NSAIDs have reversed virtually all of these clin¬ ical abnormalities except hypokalemia. Consequently, it has been concluded that a PG, presumably PGE2 or PGI2, may be respon¬ sible for mediating many of the manifestations of Bartter syn¬ drome, although excessive PG levels themselves are not the pri¬ mary defect.

GASTROINTESTINAL EFFECTS LIVER Glucagon-stimulated glucose production

pge2

FAT Hormone-stimulated lipolysis

pge2

BONE Resorption

PGE2, PGE-m, 6-K-PGE, PGF,„, PGI2

Prostaglandin E, taken orally, protects the gastrointestinal mucosa from several forms of injury by a direct, cytoprotective effect.53 It also inhibits gastric acid secretion. Because gastric acid secretion is excessive in patients with peptic ulcer disease, ana¬ logues of PGE2 have been used as therapeutic agents.54 These agents are more effective than placebo in relieving pain and de¬ creasing gastric acid secretion in patients with peptic ulcer dis¬ ease. The healing of ulcer craters is accelerated in patients treated with these analogues compared with placebo-treated patients.54

UTERUS Contraction

pge2, pgf2„

PULMONARY EFFECTS

OVARIES Progesterone

pgf2o

PITUITARY Prolactin

PGE,

LH

PGE,, PGE2, 5-HETE

TSH

PGA„ PGB], PGE,, PGE,a

GH

PGE,

PARATHYROID PTH

pge2

pgf2o

GH, growth hormone; HETE, hydroxyeicosatetraenoic acid; HPETE, hydroperoxyeicosatetraenoic acid; LH, luteinizing hormone; PG, prostaglandin; PTH, parathyroid hor¬ mone; TSH, thyroid-stimulating hormone. * General trends of literature reports; based on experiments in which exogenous eicosanoids have been studied directly.

Arachidonic acid metabolites may play a role in the clinical manifestations of allergic and drug-associated asthma.55 Many arachidonic acid metabolites can be formed by lung tissue. PGF2a, TXA2, and LTC4, LTD4, and LTE4 are potent bronchoconstrictors, whereas PGE2 is a potent bronchodilator. The effect of PGF2a is antagonized by PGE2 and by catecholamines, but not by atropine, antihistamines, serotonin antagonists, or a-adrenergic antagonists. An interesting subset of asthmatic patients have symptoms precipitated by drugs such as aspirin and indomethacin—the syndrome of aspirin-sensitive asthma. If arachidonic acid metab¬ olites play a role in this particular syndrome, it might involve the inhibition of cyclooxygenase and shunting of substrate to the LT pathway, thereby inducing formation of large amounts of bronchoconstrictor substances (see Chap. 180).

Ch. 170: Prostaglandins and Other Arachidonic Acid Metabolites

IMMUNOREGULATION AND INFLAMMATION INFLAMMATORY RESPONSE

Much information about potential roles of eicosanoids in the immune response continues to accumulate.5*1 It has been recog¬ nized that small amounts of PGE2 suppress stimulation of human lymphocytes by mitogens. Moreover, the inflammatory response usually is associated with the local release of arachidonic acid metabolites. This has led to the hypothesis that eicosanoids act as negative modulators of lymphocyte function. Release of PGE by mitogen-stimulated lymphocytes is envisioned as a negativefeedback control mechanism by which lymphocyte activity is regulated. Indomethacin augments lymphocyte responsiveness to mitogens. Several lines of evidence support a relationship between in¬ flammation and the generation of arachidonic acid metabolites. Inflammatory stimuli, such as histamine and bradykinin, release PGs. LTC4, LTD4/ and LTE4 are more potent than histamine as bronchoconstrictors. PGE2 and LTD4 are commonly present in areas of inflammation. During phagocytosis, polymorphonuclear cells release eicosanoids that are chemotactic for leukocytes. Va¬ sodilatation induced by PGE is not abolished by antagonists of known mediators of the inflammatory response such as atropine, propranolol, methysergide, or antihistamines. Thus, it has been postulated that PGE and other eicosanoids may have direct in¬ flammatory effects, and other mediators of inflammation may act by influencing eicosanoid release. RHEUMATOID ARTHRITIS

The inflammatory response and bone resorption that accom¬ pany rheumatoid arthritis may depend, to some degree, on the local generation of eicosanoids. Moreover, rheumatoid synovia synthesize PGE2 in tissue culture, and media from these cultures promote bone resorption. The inclusion of indomethacin in the culture medium blocks this bone-resorptive capacity, but does not prevent bone resorption caused by exogenous PGE2. Hence, it has been postulated that PGE2 produced by the synovia may be responsible for the bone resorption seen in patients with rheu¬ matoid arthritis.57

PLATELET-ACTIVATING FACTOR A related compound to arachidonic acid is platelet-activat¬ ing factor (PAF). PAF is a phospholipid synthesized by the hy¬ drolysis of arachidonic acid, the release of which is coupled to the synthesis of PAF. This phospholipid autacoid has a wide range of physiologic actions, including platelet activation, increased vas¬ cular permeability, uterine contraction, and several effects on re¬ productive function.58

CONCLUSION Arachidonic acid metabolites are important modulators of physiologic activity in many tissues. These metabolites and their inhibitors may have important therapeutic applications (e.g., me¬ tabolites [peptic ulcer disease, ductus-dependent congenital heart disease, hypertension, induction of labor, excessive lipolysis] and inhibitors [rheumatoid arthritis, hypercalcemia of cancer, in¬ flammation, fever, dysmenorrhea, Bartter syndrome, type II dia¬ betes mellitus, anticoagulation, patent ductus arteriosus]). In ad¬ dition, eicosanoids may play a role in the pathogenesis of human disease. The development of drugs that specifically and selec¬ tively inhibit the synthesis of single eicosanoids and that selec¬ tively antagonize receptors for specific eicosanoids will yield ad¬ ditional clinical information.

REFERENCES 1. Majerus PW. Arachidonate metabolism in vascular disorders. ] Clin Invest 1983;72:1521.

1471

2. Robertson RP, Westcott KR, Storm DR, Rice MG. Down-regulation in vivo of prostaglandin E receptors and adenylate cyclase stimulation in rat liver plasma membranes. Am J Physiol 1980;239:E75. 3. Robertson RP, Little SA. Down-regulation of prostaglandin E receptors and homologous desensitization of isolated adipocytes. Endocrinology 1983; 113: 1732. 4. Garrity MJ, Andreason T], Storm DR, Robertson RP. PGE-induced heter¬ ologous desensitization of hepatic adenylate cyclase: consequences on the guanyl nucleotide regulatory complex. J Biol Chem 1983; 258:8692. 5. Robertson RP, Tsai P, Little SA, et al. A receptor-mediated, adenylate cyclase-coupled mechanism for PGE2-inhibition of insulin secretion in HIT cells. Diabetes 1986; 35:1016. 6. Kowluru A, Metz SA. Stimulation of prostaglandin E2 of a high-affinity GTPase in the secretory granules of normal rat and human pancreatic islets. Biochemj 1994; 297:399. 7. Yang J, Xia M, Goetzl E], An S. Cloning and expression of the EP3-subtype of human receptors for prostaglandin E2. Biochem Biophys Res Commun 1994; 198: 999. 8. Vane JR. Inhibition of prostaglandin synthesis as a mechanism of action for aspirin-like drugs. Nature 1971; 231:232. 9. Robertson RP, Gavareski DJ, Porte D Jr, Bierman EL. Inhibition of in vivo insulin secretion by prostaglandin Ej. J Clin Invest 1974;54:310. 10. Robertson RP, Chen M. A role for prostaglandin E (PGE) in defective insulin secretion and carbohydrate intolerance in diabetes mellitus. J Clin Invest 1977;60:747. 11. Burr IM, Sharp R. Effects of prostaglandin Ej and of epinephrine on the dynamics of insulin release in vitro. Endocrinology 1974;94:835. 12. Robertson RP. Eicosanoids as pluripotential modulators of pancreatic is¬ let function. Diabetes 1988; 37:367. 13. Robertson RP. PGE, carbohydrate homeostasis and insulin secretion: a suggested resolution of the controversy. Diabetes 1983;32:231. 14. Robertson RP. Arachidonic acid metabolite regulation of insulin secre¬ tion. Diabetes Metab Rev 1986;2:261. 15. Metz SA, Robertson RP, Fujimoto WF. Inhibition of prostaglandin E syn¬ thesis augments glucose-induced insulin secretion in cultured pancreas. Diabetes 1981; 30:551. 16. Johnson DG, Fujimoto WY, Williams RH. Enhanced release of insulin by prostaglandins in isolated pancreatic islets. Diabetes 1973;22:658. 17. Metz SA. Anti-inflammatory agents as inhibitors of prostaglandin syn¬ thesis in man. Med Clin North Am 1981; 65:713. 18. Metz S, VanRollins M, Strife R, et al. Lipoxygenase pathway in islet en¬ docrine cells. J Clin Invest 1983; 71:1191. 19. Yamamoto S, Nakadate T, Nakaki T, et al. Prevention of glucose-induced insulin secretion by lipoxygenase inhibitor. Eur J Pharmacol 1982; 78:225. 20. Brass EP, Garrity MJ, Robertson RP. Inhibition of glucagon-stimulated hepatic glycogenolysis by E-series prostaglandins. FEBS Lett 1984; 169:293. 21. Ganguli S, Sperling MA, Frame E, Christensen R. Inhibition of glucagoninduced hepatic glucose production by indomethacin. AmJ Physiol 1979;236:E58. 22. Steinberg D, Vaughn M, Nestel PJ, et al. Effects of the prostaglandins on hormone-induced mobilization of free fatty acids. J Clin Invest 1964; 43:1533. 23. Kuehl FA, Humes JL. Direct evidence for a prostaglandin receptor and its application to prostaglandin measurements. Proc Natl Acad Sci USA 1972; 69:480. 24. Shaw JE, Ramwell PW. Release of prostaglandin from rat epididymal fat pad on nervous and hormonal stimulation. J Biol Chem 1968; 243:1498. 25. Christ EJ, Nugteren DH. The biosynthesis and possible function of pros¬ taglandins in adipose tissue. Biochim Biophys Acta 1970;218:296. 26. Axelrod L, Levine T. Plasma prostaglandin levels in rats with diabetes mellitus and diabetic ketoacidosis. Diabetes 1982;31:994. 27. McRae JR, Day RP, Metz SA, et al. Prostaglandin E2 metabolite levels during diabetic ketoacidosis. Diabetes 1985;34:761. 28. Klein DC, Raisz LG. Prostaglandins: stimulation of bone resorption in tissue culture. Endocrinology 1970;86:1436. 29. Tashjian AH Jr, Voelkel EF, Levine L, Goldhaber P. Evidence that the bone resorption-stimulating factor produced by mouse fibrosarcoma cells is prosta¬ glandin E2: a new model for the hypercalcemia of cancer. J Exp Med 1972; 136:1329. 30. Voelkel EF, Tashjian AH Jr, Franklin R, et al. Hypercalcemia and tumor prostaglandins: the VX2 carcinoma model in the rabbit. Metabolism 1975; 24:973. 31. Seyberth HW, Segre GV, Morgan JL, et al. Prostaglandins as mediators of hypercalcemia associated with certain types of cancer. N Engl J Med 1975;293: 1278. 32. Robertson RP, Baylink DJ, Metz SA, Cummings KB. Plasma prostaglan¬ din E in patients with cancer with and without hypercalcemia. J Clin Endocrinol Metab 1976; 43:1330. 33. Metz SA, McRae JR, Robertson RP. Prostaglandins as mediators of para¬ neoplastic syndromes: review and up-date. Metabolism 1981; 30:299. 34. McCracken JA, Baird DT, Goding JR. Factors affecting the secretion of steroids from the transplanted ovary in the sheep. Recent Prog Horm Res 1971; 27: 537. 35. Casey C, Kehoe J, Mylotte MJ. Vaginal prostaglandins for the ripe cervix. IntJ Gynaecol Obstet 1994;44:21. 36. Budoff PW. Zomspirac sodium in the treatment of primary dysmenorrhea syndrome. N Engl J Med 1982; 307:714. 37. Ojeda SR, Harms PG, McCann SM. Central effect of prostaglandin E, (PGEi) on prolactin release. Endocrinology 1974;95:613. 38. Naor Z, Vanderhoek JY, Lindner HR, Catt KJ. Arachidonic acid products as possible mediators of the action of gonadotropin-releasing hormone. Adv Pros¬ taglandin Thromboxane Leukotriene Res 1983; 12:259.

1472

PART X: DIFFUSE HORMONAL SECRETION

39. Brown MR, Hedge GA. In vivo effects of prostaglandins on TRH-induced TSH secretion. Endocrinology 1974;95:1392. 40. Drouin J, Labrie F. Specificity of the stimulatory effect of prostaglandins on hormone release in rat anterior pituitary cells in culture. Prostaglandins 1976; 11: 355. 41. Hedge GA. Hypothalamic and pituitary effects of prostaglandins on ACTH secretion. Prostaglandins 1976; 11:293. 42. Gardner DG, Brown EM, Windeck R, Aurbach GD. Prostaglandin E2 stimulation of adenosine 3',5'-monophosphate accumulation and parathyroid hor¬ mone release in dispersed bovine parathyroid cells. Endocrinology 1978; 103:577. 43. Gardner DG, Brown EM, Windeck R, Aurbach GD. Prostaglandin F2a inhibits 3',5'-adenosine monophosphate accumulation and parathyroid hormone release from dispersed bovine parathyroid cells. Endocrinology 1979; 104:1. 44. Matsuoka H, Tan SY, Mulrow PJ. Effects of prostaglandins on adrenal steroidogenesis in the rat. Prostaglandins 1980; 19:291. 45. Carchman RA, Shen JC, Bilgin S, Rubin RP. Diverse effects of Ca2+ on the prostacyclin and corticotropin modulation of adenosine 3':5'-monophosphate and steroid production in normal cat and mouse tumor cells of the adrenal cortex. Biochem Pharmacol 1980;29:2213. 46. Robertson RP, ed. Symposium on prostaglandins in health and disease. Med Clin North Am 1981;65:711. 47. Zipser RD, Laffi G. Prostaglandins, thromboxanes and leukotrienes in clinical medicine. West J Med 1985; 143:485. 48. Moncada S, Vane JR. Arachidonic acid metabolites and the interactions between platelets and blood vessel walls. N Engl J Med 1979;300:1142.

SECTION

49. Heyman MA, Rudolph AM, Silverman NH. Closure of the ductus arteri¬ osus in premature infants by inhibition of prostaglandin synthesis. N Engl J Med 1976;295:530. 50. Ferris TF. Prostaglandins and the kidney. Am J Nephrol 1983; 13:139. 51. Orloff J, Handler JS, Bergstrom S. Effect of prostaglandin (PGE]) on the permeability response of the toad bladder to vasopressin, theophylline and adeno¬ sine 3',5'-monophosphate. Nature 1965;205:397. 52. Gill JR, Frolich JC, Bowden RE, et al. Bartter's syndrome: a disorder char¬ acterized by high urinary prostaglandins and a dependence of hyperreninemia on prostaglandin synthesis. Am J Med 1976;61:43. 53. Redfern JS, Feldman M. Role of endogenous prostaglandins in preventing gastrointestinal ulceration: induction of ulcers by antibodies to prostaglandins. Gas¬ troenterology 1989; 96:596. 54. Vantrappen G, Janssens J, Popiela T, et al. Effect of 15 (R)-15-methylprostaglandin E2 (arbaprostil) on the healing of duodenal ulcer. Gastroenterology 1982; 83:357. 55. Hyman AL, Mathe AA, Lippton HL, Kadowitz PJ. Prostaglandins and the lung. Med Clin North Am 1981;65:789. 56. Goetz E, Scott WA, eds. Regulation of cellular activities by leukotrienes. J Allergy Clin Immunol 1984; 74:309. 57. Robinson DR, Tashjian AH, Levine L. Prostaglandin-stimulated bone re¬ sorption by rheumatoid synovia. J Clin Invest 1975;56:1181. 58. Venable ME, Zimmerman GA, MacIntyre TM, Prescott SM. Platelet-acti¬ vating factor: a phospholipid autocoid with diverse actions. J Lipid Res 1993;34: 691.

B_

SEVERAL SITES OF DIFFUSE HORMONAL SECRETION Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

171_

THE DIFFUSE NEUROENDOCRINE SYSTEM ERIC S. NYLEN AND KENNETH L. BECKER

The diffuse neuroendocrine system (DNES) comprises a widespread system of endocrine cells that are scattered through¬ out many organs and tissues (Table 171-1). Many of these cells constitute an important part of several large “classic" glands, such as the hypothalamus, pituitary, thyroid, parathyroid, pan¬ creas, and adrenal medulla. As in the glandular-based cells, the dispersed cells also contain characteristic secretion granules and produce and secrete certain bioactive peptide hormones that have local and distal functions. Frequently, there is independent secretion of the same peptide hormones in different regions of the body, where these substances may have different functions. These endocrine cells and their peptide hormones combine many aspects of the “traditional" nervous and endocrine systems.

different cells that release hormones into the blood to control dis¬ tal sites. Furthermore, it was postulated that the evolutionary de¬ velopment of nervous and endocrine cells occurred at different times. This concept of distinct nervous and endocrine systems has been shown to be oversimplified and, more importantly, inaccu¬ rate. These two major regulatory systems are known to share fea¬ tures of genetic programming, messenger transduction, and physiologic function that derive from ancient unicellular devel¬ opment. Even in specialized multicellular organisms, these shared features render any facile distinction between neurons and endocrine cells difficult to impossible. The adrenal chromaffin cell was one of the first noted excep¬ tions to the traditional dichotomy between neurons and endo¬ crine cells. These medullary cells release large amounts of cate¬ cholamines into the circulation, acting on distal tissues; however, embryologically, they originate from the neural crest, and histo¬ logically, they have the appearance of nerve cells (see Chaps. 70 and 82). Another inconsistency is the hypothalamus: a “gland" that consists of neurons that produce oxytocin and vasopressin; after storage in the posterior pituitary, these hormones are re¬ leased systemically (see Chaps. 10 and 26). Additionally, cells of the gastrointestinal tract were described as early as 1870 and, thereafter, were considered to constitute part of a diffuse endo¬ crine system possessing a paracrine function. Subsequently, re¬ markable similarities have been demonstrated between these lat¬ ter epithelial cells and the nervous system.

THE NERVOUS-ENDOCRINE OVERLAP HISTORICAL BACKGROUND Previously, although involved in homeostatic regulation, nervous and endocrine cells were regarded as distinct anatomic and functional entities. Conceptually, neurons were considered to be ectodermal, often possessing a characteristically elongated shape, and controlling other cells by synaptic neurocrine release. Conversely, endocrine cells previously were thought to be quite

The existence of a diffuse system of endocrine cells was first suggested by work on the intestinal mucosa by Heidenhain.1 Subsequently, this concept was extended by several investiga¬ tors, including Pearse and co-workers,2-4 who pointed out that although these cells occur in different anatomic sites, they share

Ch. 171: The Diffuse Neuroendocrine System certain similar morphologic and functional properties. Because of their cytochemical characteristics, these cells were grouped under the acronym of APUD (amine precursor uptake and subsequent decarboxylation). This system of classification, which also in¬ cluded the gastrointestinal endocrine cells, was considered to cor¬ respond to the diffuse endocrine system that had been proposed previously in 1938 by Feyrter.5 On the basis of the observation that the autonomic neurons, the thyroidal C cells, and the adrenal chromaffin cells are derived from the neural crest, Pearse and co-workers2-4 further suggested that the APUD cells share a common embryologic origin; partly based on this presumed common embryogenesis, they used the categorical term neuroendocrine. Subsequently, several studies have shown that neural-like APUD characteristics do not neces¬ sitate either a neural crest or ectodermal origin. Although some of these cells are, indeed, derived from the neural crest, a series of allograft experiments have shown, for example, that the socalled gastroenteropancreatic axis of endocrine cells is derived from endoderm.6 As new information has evolved, it appears best to reserve the term APUD to indicate the aforementioned histochemical characteristics. The term neuroendocrine cell refers to shared phe¬ notypic expression involving established neuronal and endocrine features such as morphology and genetic programming.

DISTRIBUTION OF THE DIFFUSE NEUROENDOCRINE SYSTEM CELLS

1473

toradiography or peroxidase staining.12 This method, in contrast with immunocytochemistry, reveals the genetic expression. Morphologically, most of the epithelial DNES cells reach the luminal aspect of the epithelium; often, there is a striking polarity of orientation into a pyramidally shaped structure, with a narrow apical portion (see Fig. 171-1) that often possesses microvillus extensions. In the gut, where most anatomic studies have been performed, those cells reaching the lumen are termed open, whereas those without luminal contact are termed closed (Fig. 171-2). The DNES cells may form organoid clusters, such as in the lung (neuroepithelial bodies), or in the carotid body.

ULTRASTRUCTURE The DNES cell possesses all of the ultrastructural character¬ istics of an actively secreting cell, with well-developed endoplas¬ mic reticulum and Golgi apparatus, and an abundant microfil¬ ament and microtubular system. Electron microscopic and immunohistochemical analyses have revealed that certain DNES

TABLE 171-1 Distribution and Classification of Some of the Peptide- and AmineContaining Cells of the Diffuse Neuroendocrine System* Tissue

Cell types

Peptides

Biogenic Amines

The DNES consists of specialized endocrine cells that mostly are intraepithelial and typically are scattered in several luminal tissues. All are characterized by the presence of hormonal pep¬ tides and amines stored within cytoplasmic secretory granules. Pearse and co-workers3 have included at least 40 individual cell types in the DNES. Accordingly, the system has a central division, which comprises the neuroendocrine cells of the hypothalamicpituitary axis and the pineal gland, and a peripheral division (see Table 171-1), which includes the neuroendocrine cells of the gas¬ troenteropancreatic axis, lung, parathyroid, adrenal medulla, sympathetic ganglia, skin, and thyroid C cells. Additional neuro¬ endocrine cells of the breast, endometrium, prostate, urethra, and the testicular Leydig cells also have been included.7 10 Be¬ cause of the diminishing distinctions between neurons and en¬ docrine cells and the absence of a strict definition of a DNES cell, it is not surprising that this classification is controversial and that it is modified as new peptides and related marker proteins are discovered. Nevertheless, despite such incertitudes of classifica¬ tion, the concept of the DNES is both creative and practical.

Thyroid

C cell

CT, PDN-21

5-HT

C cell PNE or K cell PNE or K cell PNE or K cell

CGRP, BLP, SN CT, BLP Leu-enk CGRP, CCK, Endo

G D EC ECL

Gastrin, Enk SN

D S EC, EC2(M) I(CCK) G K(GIP) L N

SN Secretin SP, SK Motilin CCK Gastrin GIP GFP, PYY NT

Pancreas

A B D G PP

Glucagon, CRH Insulin SN Gastrin PP, CRH

5-HT 5-HT DA

HISTOLOGY AND MORPHOLOGY

Adrenal

A NA

Enk, NPY Dynorphin, BLP

E NE

Historically, the silver stains, which demonstrate either ar¬ gentaffin staining (uptake and deposition of silver on secretion granules) or argyrophilic staining (positive silver staining after the addition of a mild reducing agent), were the commonly used stains for identifying many of the DNES cells (Fig. 171-1). Because of the APUD properties of the DNES cells, they of¬ ten show a characteristic fluorescence of their biogenic amines when exposed to formaldehyde vapor (see Fig. 171-1). Addition¬ ally, the DNES cells stain avidly for certain enzymes, including glycerophosphate dehydrogenase, nonspecific esterases, and cholinesterase. The most recently developed techniques for the localization of DNES cells involve immunohistochemistry; these methods rely on a specific antigen-antibody reaction linked to a wellvisualized probe such as a fluorochrome or enzyme11 (see Fig. 171-1). In hybridization histochemistry, a labeled, cloned com¬ plementary DNA (or RNA) probe is hybridized to the intracellu¬ lar DNA or RNA of a peptide and subsequently localized by au¬

Sympathetic Ganglia

SIF

Enk

DA, 5-H'

Paraganglia

Main

Enk

NE, DA

Carotid

I cell

SP Met- and leu-enk

NE, DA

Skin Genitourinary

Merkel

CT, BLP, Met-enk, VIP CT, BLP, SN

H 5-HT

Lung

Stomach

Intestine

5-HT

5-HT H

5-HT

BLP, bombesin-like peptides; CCK, cholecystokinin; CGRP, calcitonin gene-related peptide; CRH, corticotropin releasing hormone; CT, calcitonin; DA, dopamine; E, epineph¬ rine; EC, enterochromaffin; ECL, enterochromaffin-like; Endo, endothelin; Enk, enkephalin; GPP, glucagon family peptides (including enteroglucagon); GIP, gastric inhibitory peptide (glucose-dependent insulinotropic peptide); 5-HT, serotonin; H, histamine; Leu-enk, leuenkephalin; Met-enk, met-enkephalin; NE, norepinephrine; NPY, neuropeptide Y; NT, neurotensin; PDN-21, katacalcin; PP, pancreatic polypeptide; PYY, peptide YY; S/E, small intensely fluorescent cells; SK, substance K; SN, somatostatin; SP, substance P; VIP, vaso¬ active intestinal peptide. * This listing is a composite of several classifications. It is undergoing continuous modifications and updating, and is shown for illustrative purposes only. (Data from Pearse AGE, Takor-Takor T. Fed Proc 1979;38;2288; di SanfAgnese PA, deMesy Jense KL. J Urol 1987;7:1250; Solicia E, et al. Experientia 1987;43:839.)

1474

PART X: DIFFUSE HORMONAL SECRETION with an electron-dense core of variable density and appearance, and a single, limiting outer membrane. The size of these secretion granules varies from 50 to 400 nm in diameter. Often, there is a relative homogeneity of size or appearance for granules of a given peptide population. These secretion granules are highly complex structures14 that store hormonal peptides and their pre¬ cursors, as well as biogenic amines, high-energy phosphate com¬ pounds, ions, polyamines,15 and chromogranins. Studies with colloidal gold conjugated to immunoglobulins16 have disclosed that secretion granules in some cells contain more than one pep¬ tide.17 Generally, the secretion of the intragranular peptide hor¬ mones of the DNES occurs by exocytosis and is discontinuous: there is a preliminary accumulation and storage of the hormone, which is discharged in response to specific local stimuli. Brain neurons contain, along with secretion granules, an abundance of small synaptic vesicles (40-60 nm diameter) that are thought to be the storage sites of “classic" neurotransmitters. These small synaptic vesicles, in contrast with the dense-core se¬ cretion granules, undergo local regeneration and contain certain characteristic intrinsic membrane proteins including synaptophysin (p38).18 Interestingly, this acidic glycosylated protein (approx¬ imately 38,000 daltons) also has been localized to many DNES cells (e.g., adrenal medulla, carotid body, pituitary gland, pancre¬ atic islets, gastric mucosa, thyroid, skin, and lung) and DNES tu¬ mors.19 This finding emphasizes that small synaptic vesicles and dense-core granules constitute different secretory organelles and that there are common and distinctive endomembranous systems that are shared by both neurons and many endocrine cells (Figs. 171-3 and 171-4).

PAN-NEUROENDOCRINE MARKERS

9

h

FIGURE 171-1. The pulmonary neuroendocrine cells (PNECs) and neu¬ roepithelial bodies (NEBs). The photomicrographs on the left (a,c,e,g) il¬ lustrate NEBs in adult hamster lungs after exposure to a systemic carcin¬ ogen, diethylnitrosamine, whereas the right-hand panel shows DNES cells of human bronchial epithelium. In these photomicrographs, the cells have been visualized by using special staining techniques, a, A small bronchus with two NEBs (Grimelius silver impregnation, magnification X130). b. Two PNECs with chromogranin A immunoreactivity. Notice the overlying ciliated epithelium (Nomarski optics, X570). c. Strongly argyrophilic, large NEB (Grimelius silver impregnation, X330). d. Classic, flask-shaped PNEC reaching the bronchial lumen (Leu-7 immunoreac¬ tivity, X840). e. Formaldehyde-induced fluorescence of serotonin in a NEB. Notice the surrounding bronchial epithelium and alveoli which are negatively stained (X260). f, A solitary PNEC with characteristic cell pro¬ cesses that extend from the basal membrane to the bronchial lumen. The adjacent PNEC demonstrates an unstained nucleus (serotonin immuno¬ reactivity, X660). g, A NEB with basally located calcitonin immunoreac¬ tivity (X340). h. Hyperplastic PNECs along the bronchial epithelium demonstrating bombesin immunoreactivity (X410). The general tech¬ niques and markers such as silver impregnation, formaldehyde-induced fluorescence, chromogranin A, and Leu-7 allow a universal identification of dispersed endocrine cells in various organs, whereas the specific hor¬ monal products such as serotonin, calcitonin, and bombesin characterize selected subpopulations of cells. (Courtesy of Dr. R. Ilona Linnoila, NCI, Bethesda, Maryland.) cells and their malignant counterparts contain cytoskeletal inter¬ mediate filaments, termed neurofilaments, which previously were thought to be associated exclusively with neurons.13 The most distinctive feature shared both by neurons and DNES cells is the presence of cytoplasmic secretory granules.

The DNES cells display certain distinctive features that serve as useful markers, such as the presence of large concentrations of a highly acidic glycolytic enolase isoenzyme (2-phospho-Dglycerate hydroxylase) called neuron-specific enolase. This eno¬ lase enzyme (EC 4.2.1.11) consists of two subunits giving rise to three isoenzymes: a, /3, and y. Immunostaining of the 78,000dalton y subunit of this cytoplasmic enzyme has shown that it is not exclusive to mature neurons, but that it is also present in DNES cells as either the 77 or ay isomers, thus providing a vehi¬ cle for mapping the distribution of the DNES. This "neuronal'' glycolytic enzyme is also found within the derivative neoplasms of the DNES and can be detected in the circulation.21 Another marker is the leu-7 (HNK-1) antigen, which initially was shown to react with natural killer cells. This 110,000-dalton glycoprotein is associated with myelinated nerves in the central nervous system (CNS) and peripheral nervous system (PNS), as well as endocrine cells in the gut, pancreas, and lung.22 Addition¬ ally, certain neuroendocrine tumors such as neuroblastoma, mel¬ anoma, and small-cell lung cancer also react with leu-7 antisera. Interestingly, this antigen also is found in macrophages, and it has been suggested that these two different cell types (small-cell lung cancer and macrophages) share a common hematopoietic origin.23 However, it has been argued that the presence of shared antigens does not prove a common ancestral lineage.22 Chromogranin originally was found to be stored within the cells of the adrenal medulla and to be secreted along with cate¬ cholamines during the exocytosis of their secretion granules.24 The chromogranins have been separated into three classes: A, B, and C. They all have similar properties and tissue distribution and are cosecreted with bioactive peptides. They are acidic pro¬ teins, with a high glutamic acid content. Chromogranin A (ap¬ proximately 48,000 daltons) is a structural protein often present in neurons (CNS and PNS), neuroendocrine cells, and tumors of the neuroendocrine cells; it is not found in secretion granules of exocrine glands.25 Staining for chromogranin A has suggested additional cellular DNES candidates, including cells within the lobular ductules of the breast and cells in lymphoid tissues such

Ch. 171: The Diffuse Neuroendocrine System

1475

FIGURE 171-2.

Schematic representation of flask-shaped neuroendocrine cells of the “open" (left) and “closed” (right) types. Both cell types can release hormonal substances into the circu¬ lation (hemocrine) and to neighboring cells (par¬ acrine). The open-cell type can, in addition, release its content into the luminal aspect (solinocrine). (Modified with permission from Track NS, et al. In: Glass BJ, ed. Gastrointestinal hormones. New York: Raven Press, 1980:75.)

as the spleen, the lymph nodes, lamina propria, and the human fetal liver.26 A portion of the chromogranin A structure gives rise to the peptide pancreastatin, which exerts inhibitory influences on insulin, gastric acid, and exocrine secretion.26 "7 Another por¬ tion of chromogranin A gives rise to an additional peptide: chro¬ mostatin (Table 171-2). Several other features are characteristic of the DNES. Be¬ cause of its APUD nature, these cells and their related tumors commonly express the biogenic amine enzyme L-dopa decarbox¬ ylase.28 Other characteristics include the presence of the brain creatine kinase BB enzymes and aldolase C.29-30 Protein gene product 9.5, with a molecular mass of 25 kilodaltons, is present in the CNS and the PNS. It has been demonstrated in the DNES,

FIGURE 171-3.

except for the gastrointestinal tract. It is a cytoplasmic protein with a more wide distribution than neuron-specific enolase. Its name derives from its 9.5-cm mobility on polyacrylamide gel electrophoresis.31"33 Additional markers include neural-adhesion molecule (N-CAM), and 7B2. The latter is a secretory protein that is found in multiple DNES sites.34-35

PEPTIDE CONTENT More than 35 physiologically active peptides have been identified as DNES products (see Table 171-1). Occasionally, the same peptide hormone has been found in different constituent

By use of Nomarski optics, synaptophysin (p38) immunoreactivity is seen localized to the mucosa of the rat fundus. Endocrine cells staining positive for p38 (arrow) are scattered among glands. The exocrine cells of the gastric glands do not stain for p38. v, blood vessels surrounded by immunoreactive en passant varicose terminals. (Courtesy of Drs. F. Navone, R. ]ahn, P. Greengard, P. DeCamilli, University of Milano, Italy.)

1476

PART X: DIFFUSE HORMONAL SECRETION

FIGURE 171-4. Electron micro¬ graphs using immunogold label¬ ing. A, Anterior pituitary: ultrathin frozen sections showing most of the gold particles associated with small vesicular profiles with clear content (arrows). These are inter¬ spersed among secretory granules (G) and, sometimes, in close proximity to them (calibration bar = 150 nm). B, Adrenal medulla: agarose-embedded subcellular particles of the adrenal medulla showing a small, round vesicle immunoreactive for p38 (arrows). Membranes of secretory granules (G) are unlabeled (calibration bar = 100 nm). C, immunogold parti¬ cles are selectively localized on the cytoplasmic surface of small synap¬ tic vesicles (pairs of small arrows). Large dense-core vesicles (large ar¬ rows) are unlabeled (calibration bar = 100 nm). (From Navone F, ]ahn R, DiGioia G, et al. Protein p38: an inte¬ gral membrane protein specific for small vesicles of neurons and neuro¬ endocrine cells. J Cell Biol 1986; 103: 2511.)

DNES cells: calcitonin is found in the hypothalamus, in the pitu¬ itary gland, in C cells of the thyroid, and in the pulmonary neu¬ roendocrine cell; oxytocin is found in the hypothalamus and in the ovary; and somatostatin is found in the hypothalamus, the D cells of the stomach, intestine, pancreas, and in thyroid C cells. Many of the cells of the DNES, as well as many neurons, produce more than one peptide; for example, the pulmonary neuroendo¬ crine cells produce bombesin, calcitonin, calcitonin gene-related peptide, leu-enkephalin, endothelin, cholecystokinin, and per¬ haps somatostatin36 (see Chap. 172). Many of these coexpressed peptides also can be costored in the same secretion granule.17 Most of the peptides of the DNES are shared with the so¬ matic and autonomic nervous system (e.g., endorphins, somato¬ statin, calcitonin, vasoactive intestinal peptide, gastrin, cholecys¬ tokinin, and insulin). Importantly, the synthetic steps in the neurons and in the DNES cells that lead to the production and

TABLE 171-2 Potential Physiologic Roles of Chromogranin A Calcium binding Catecholamine binding Modulation of intravascular hormone processing Glucocorticoid-responsive autocrine inhibition of proopiomelanocortin secretion Production of bioactive peptides such as pancreastatin and chromostatin

eventual secretion of these peptides and amines are similar (Fig. 171-5). Neurons of the CNS and PNS containing peptides have been termed peptidergic. These peptides typically are involved in neurocrine transmission or neuromodulation, or both. This mul¬ tifaceted function has led to the use of the term regulatory peptides.

BIOGENIC AMINES At some time during their development, all DNES cells syn¬ thesize biogenic amines. However, at any one time, only a few mature DNES cells store these amines. Typically, biogenic amine synthesis is demonstrated by preincubation with the amine pre¬ cursors L-dopa or 5-hydroxytryptophan. The synthesis of dopa¬ mine and serotonin from their respective amino acid precursors requires L-dopa decarboxylase (see Fig. 171-5). The endogenous amines of the DNES include dopamine, serotonin, norepineph¬ rine, epinephrine, and histamine (see Table 171-1). Although amines are present along with peptides within the secretory gran¬ ules, little is known about the role of amines in the synthesis or secretion of the coexistent peptides. The relative proportions of these different substances vary considerably, depending on the particular cell type. For example, the adrenal medullary cells pre¬ dominantly produce and secrete biogenic amines, whereas the pancreatic islet cells principally produce and secrete peptides.

Ch. 171: The Diffuse Neuroendocrine System

1477

CELL BODY

A

5-Hydroxytryptophan

5-Hydroxytryptamine

(Serotonin)

DOPA Decarboxylase

DOPA

(DDC)

Dopamine

FIGURE 171-5.

A, The localization of the process of peptide and amine synthesis in a neuroendocrine cell is depicted. Peptide production is initiated with mRNA transcription followed by accumulation and processing in the rough endoplasmic reticulum (RER) and Golgi apparatus. Dense-core vesicles produced from the latter site further process and store the peptide, followed by transport to terminal sites and subsequent release by exocytosis. Small synaptic vesicles are found in the terminals where they undergo local regeneration. (From Hakanson R, Sundler F. The design of the neuroendocrine system: a unifying concept and its consequences. Trends Pharmacol Sci 1983;4:41). B, The enzyme L-dopa decarboxylase (DDC) plays a key role in the production of serotonin and catecholamines in neuroendocrine cells.

CLINICAL RELEVANCE OF THE DIFFUSE NEUROENDOCRINE SYSTEM PHYSIOLOGY PARACRINE SECRETION

The aforementioned presence of several features that classi¬ cally had been associated with only neurons has validated the concept of a DNES. Unfortunately, it is difficult to obtain experi¬ mental physiologic information from a system of scattered cells; diffuse surgical extirpation is impossible, and studies of the re¬ lease of small amounts of hormone by one or several cells are difficult. As initially suggested by Feyrter5 these cells exert local regulatory influences through paracrine secretion. This form of secretory transport represents one of the first means of cell-tocell regulation; it occurs early in the evolutionary record within coelenterates, organisms that lack a circulatory system. Paracrine secretion has been retained in mammals, for which an important role for this form of communication and control is gradually be¬ ing uncovered. With the recognition of the ubiquitous distribu¬ tion of peptide-containing cells, the existence of a paracrine cellto-cell transfer of information is seen to provide a means by which such communication can be regulated locally, precisely, and with relevance to local needs. The paracrine response to local stimulation may be highly specific, similar to the initiation of fol¬

licular maturation by ovarian androgens,37 or more generalized, as in epithelial growth.38 Paracrine secretion can occur through discrete anatomic delivery systems, which involve long cyto¬ plasmic processes (Fig. 171-6A) that also include terminal swell¬ ings adjacent to target cells—a structuring that is reminiscent of neurons. Furthermore, the message is delivered in a highly con¬ centrated form. Interestingly, DNES cells in culture can display neuron-like processes (see Fig. 171-6B). In keeping with their neuroendocrine characteristics, these cultured cells generate de¬ polarizing currents that reach a threshold and produce an allor-nothing action potential—a phenomenon that previously had been seen only in nerve and muscle.39 40 These properties are ob¬ served in normal as well as in tumor cells and can be enhanced by nerve growth factor. The copresence of several amines and peptides, and the highly structural cellular specialization of DNES cells, provide an increased plasticity to the possible informational content of the paracrine messages from any single cell.

THE DIFFUSE NEUROENDOCRINE SYSTEM AND THE GUT

The gut exemplifies an extraordinary functional con¬ vergence of the nervous and endocrine systems. Subsequent to substance P being detected in the gut and in the brain,41 many endocrine peptides found within the gut also have been found in

1478

PART X: DIFFUSE HORMONAL SECRETION

FIGURE 171-6. A, Dendritic morphology of thyroidal neu¬ roendocrine C cells. Calcitonin-containing C cell in 1-day human neonatal thyroid (X400), immunostained with anti¬ calcitonin antiserum and the avidin-biotin immunoperoxidase technique. A prominent dendritic process is evident in this pyramidally shaped cell, suggesting a possible paracrine role. B, Phase-contrast micrograph of a neoplastic C cell in tissue culture (X400), derived from a human medullary car¬ cinoma of the thyroid (cells courtesy ofRoos BA. Endocrinology 1988:122:1551). Multiple dendritic processes are evident in many of the cells in culture. (Photographs courtesy of Dr. Mary E. Sunday, Brigham and Women's Hospital, Boston.)

the CNS and vice versa; this has prompted the concept of a "brain-gut" axis. Also, functionally, portions of the autonomic nervous system (including, in particular, the gastrointestinal tract, as well as the urogenital, respiratory, and cardiovascular systems) are regarded as components of a nonadrenergic noncholinergic effector system.42 In many of these tissues, the DNES cells, and these local peptide-containing neuronal cells and gan¬ glia, together coordinate local neuroendocrine regulatory func¬ tions.43 This is particularly prominent in the gut, which possesses an autonomous "enteric nervous system"44 (see Chap. 175). CHEMORECEPTION

Many of the DNES cells of the gut (open type; see Fig. 171-2), and DNES cells elsewhere, have morphologic and func¬ tional characteristics of specialized chemoreceptive cells. These cells maintain the basic architecture of primitive neurons, with an apical receptive site containing microvilli or cilia and a basal secretory portion; the cells appear to perform sensory stimulus reception and conduction tasks. Their receptive sites are activated by various stimuli, which include dissolved (or ambient) oxygen tension and other undefined chemicals in the different luminal milieux. Many of the DNES cells that have this configuration are primary sensory cells, such as taste buds, hair cells of the inner ear, and olfactory cells; in an expanded concept, these latter sen¬ sory cells, as well as DNES cells, have been grouped by some investigators into a system of paraneurons,45 The chemoreceptive neuroendocrine cells, such as the type 1 glomus cell of the carotid body, the pulmonary neuroendocrine cell, and the gastric and pancreatic islet cells, often are associated with, and influenced by, the presence of autonomic nerves. Re¬ garding the carotid body and pulmonary neuroendocrine cells, there is evidence for a complex synaptic interaction.46,47 The type 1 glomus cell, which is involved in the sensing of oxygen dis¬ solved in the blood, can directly modulate the firing rate of the local afferents by the release of its dopamine content. Thus, the DNES and the local "enteric nervous system" represent addi¬ tional functional arms of the autonomic nervous system. In this context, the abnormally elevated procalcitonin level (a DNESderived peptide) often associated with severe illnesses, such as burns and sepsis, may be viewed as a marker of the regulatory systemic activity of the DNES48 (see Chap. 53).

CONTROL OF CELLULAR GROWTH Several of the peptides produced and secreted by the DNES possess a trophic growth activity that is exerted via autocrine or paracrine means. Thus, bombesin-like peptide has an important regulatory role on the maturation and proliferation of cells in the lung and gut (see Chap. 161). Bombesin-like peptides and other DNES peptides, such as calcitonin gene-related peptide, calci¬ tonin, and endothelin have a broad repertoire of growthstimulatory and inhibitory activity on a variety of cells. Refine¬ ments in the preparation and cell culture of the DNES should

provide further insights into this physiology.49

important area

of cell

DYSREGULATED GROWTH AND CANCER Hyperplasia, dysplasia, and neoplasia (neuroendocrinomas or neuroendocrine tumors) involving the DNES are well-estab¬ lished phenomena. Indeed, often there is a gradual progression from the hyperplastic phase to overt neoplasia (e.g., familial medullary thyroid cancer), and the tumor growth is characteris¬ tically slow. Many of the features of the normal DNES cells are either maintained or frankly overexpressed in these abnormal cells; this has significant clinical impact on diagnosis and therapy. Thus, a wide range of DNES hyperplasias and tumors produce and secrete constituents that give rise to hormonal syndromes of paraneoplastic nature (e.g., lung cancer and the ACTH-induced Cushing syndrome). Furthermore, the measurement of the par¬ ticular hormone can be used as an aid in the diagnosis and in following the therapeutic impact of treatment. An advance in the area of neuroendocrine oncology has been the introduction of diagnostic ligands to receptors on DNES cells. Thus, a wide vari¬ ety of tumors can be visualized by means of octreotide scintigra¬ phy that can visualize somatostatin binding sites.50 Many of these tumors that have somatostatin receptors also respond to admin¬ istration of this somatostatin analogue by decreased peptide se¬ cretion and diminished growth (see Chap. 166). Another radio¬ active ligand being similarly investigated is vasoactive intestinal peptide (VIP), which appears to selectively bind to a different class of DNES tumor receptors from those occupied by octreo¬ tide.51 In view of the abundance of peptide receptors on DNES tumors, various synthetic receptor ligands should prove to be ex¬ tremely useful in both the diagnostic exploration for tumors and the therapeutic delivery of tumoricidal substances to receptor¬ bearing tumors.

CONCLUSION The DNES is a vast entity that comprises cells that are dis¬ persed throughout many organs and tissues. These cells possess distinctive "neuronal" characteristics, including the presence of dense-core secretion granules that contain regulatory peptides and biogenic amines. They also possess several enzymatic and physicochemical features found in neurons. Some DNES cells display chemoreceptive features. By means of locally released peptides and amines, the DNES cells, in parallel with local neu¬ rons and ganglia, constitute a functional homeostatic system that is concerned with precise regulatory adjustments that reflect local tissue requirements, but that also may respond to nervous or hu¬ moral stimulation from distant regions of the body. The increase of knowledge concerning the DNES and its peptide hormones has broadened our understanding of endocrine physiology and pathophysiology; eventually, this knowledge should facilitate the diagnosis of disease and provide new strategies for interven¬ tional and therapeutic modalities.

Ch. 172: The Endocrine Lung

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1479

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Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

172

THE ENDOCRINE LUNG KENNETH L. BECKER

ANATOMY AND PHYSIOLOGY The lungs have unique topographic, anatomic, and meta¬ bolic characteristics.1,2 They possess a huge interface between the outside environment and the body, facilitating their function as organs of gaseous exchange that are responsible for the oxy¬ genation of all body tissues. The enormous, distensible, lowresistance vasculature of the lungs receives the entire systemic venous output of the body by the pulmonary artery and bears the responsibility for its arterialization. The hepatic venous blood joins the inferior vena cava near the right side of the heart, bring¬ ing hepatic metabolic products directly to the lungs. The thoracic duct carries gastrointestinal chylomicrons to the superior vena cava, to the heart, and to the lungs. Innumerable changes in pleu¬ ral pressure subject the lungs to expansion and relaxation to draw air into the bronchial tree and to facilitate the systemic inflow of venous blood into the heart. A great diversity of cell types accomplishes these physiologic functions. Finally, the left side of the heart pumps the oxygenated blood from the lungs to all tis¬ sues throughout the body.

METABOLIC ACTIVITIES The lungs are enormous endocrine organs.3 Metabolically, the lungs degrade, modify, or activate many substances that ar¬ rive from the systemic venous circulation. The vast surface area of the pulmonary endothelium provides the enzymatic ma-

1480

PART X: DIFFUSE HORMONAL SECRETION

chinery required to inactivate some of the prostaglandins and other arachidonic acid metabolites. Other bioactive hormonal substances, such as serotonin, norepinephrine, and bradykinin, are metabolized intracellularly by the lungs. Moreover, the rela¬ tively inactive substance, angiotensin I, which is formed within the blood by the action of renin on angiotensinogen, is hy¬ drolyzed within the pulmonary endothelium to form the active angiotensin II. Other metabolic functions of the lung include ste¬ roid transformations and lipolysis.

H H

H H HC=

C-C-NH2 H H

=C-C-C-NH2 l

I H-N>

N

H H

OH DOPAMINE

HISTAMINE

OH H

o

ch3

II

I

ch3-c-o-ch2-n-ch 3

ENDOCRINE ACTIVITIES

ch3 The lungs generate many hormones that act on cells and tis¬ sues within the lung and that also influence other tissues.3,4 These pulmonary hormones, none of which is unique to the lungs, in¬ clude the biogenic amines, the arachidonic acid and other cell mem¬ brane phospholipid metabolites, and peptides. Depending on the hormone and its site, the stimuli that induce the release of these various chemical messengers may be intraluminal (e.g., inspired air), mechanical (e.g., inhaled dusts), neural (e.g., vagal or sym¬ pathetic nerves), chemical perturbation of adjacent tissues (e.g., acidosis), or blood-borne hormonal stimuli from distant tissues (e.g., catecholamines). These released hormones may stimulate, inhibit, modulate, or integrate their effector cells. Within the lungs, they may alter regional blood flow, dilate or contract bron¬ chial smooth muscle, influence mucous gland activity, change vascular permeability, modify the metabolism of adjacent pulmonary cells, or influence cellular secretion or cellular proliferation.

BIOGENIC AMINES Biogenic amines include serotonin, dopamine, norepineph¬ rine, epinephrine, and histamine. Two related substances are acetylcholine and 7-aminobutyric acid (Fig. 172-1). Most of these substances can act as neurotransmitters (Fig. 172-2), and some also are contained within the synaptosomes of neurons and within the secretion granules of endocrine cells. The biogenic amines may be detectable in the peripheral blood of normal per¬ sons and are increased in various pathologic conditions. Within the lung, the biogenic amines function as potent paracrine or hemocrine hormones. The principal pulmonary source of histamine is the pulmo¬ nary mast cell (see Chap. 180). These cells, which are numerous near pulmonary blood vessels, in the respiratory epithelium, and also free within the bronchial lumen, produce histamine and many other hormonal mediators, including prostaglandins. Im¬ portant intrapulmonary sources of several biogenic amines (e.g., serotonin, norepinephrine, and perhaps dopamine) are the pul¬ monary neuroendocrine (PNE) cells.

PULMONARY NEUROENDOCRINE CELLS The PNE cells (also called Feyrter cells or Kulchitsky cells) are distinctive, scattered cells found within the bronchial epithe¬ lium of humans, other mammals, birds, amphibians, and rep¬ tiles.5 These cells, which stain with silver, may form intramucosal clusters called neuroepithelial bodies (see Fig. 171-1 in Chap. 171). PNE cells are situated near the basement membrane of the epithelium of the entire respiratory airway; they occur in the lar¬ ynx, trachea, bronchi, bronchioles, the alveoli, and the ducts of the peribronchial glands. In particular, they are found at bifur¬ cations of the bronchial tree. In humans, they are seen as early as the eighth week of gestation.6 The PNE cells are far more numer¬ ous in the developing fetus and newborn than in the adult, in whom they are sparse. The neuroepithelial bodies are rare in the adult. In common with the widespread diffuse neuroendocrine system of peptide-secreting cells of the anterior pituitary gland,

NOREPINEPHRINE

ACETYLCHOLINE

0 H H H 11

1

1

1

ho-c-c-c-c-nh2 III

H H H GAMMA-AMINO BUTYRIC ACID (GABA) EPINEPHRINE

NH 2

FIGURE 172-1. Structure of several of the nonpeptide neurotransmit¬ ters and bioactive derivatives (From Becker KL. The endocrine lung. In: Becker KL, GazdorAF, eds. The endocrine lung in health and disease. Phila¬ delphia: WB Saunders, 1984:5.)

thyroid C cells, pancreatic islets, and gastrointestinal tract, the PNE cells fluoresce when exposed to formaldehyde vapor, either spontaneously or after exposure to 5-hydroxytryptophan or dihydroxyphenylalanine (L-dopa): this indicates the intracellular enzyme L-dopa decarboxylase (see Chap. 171). Further, this broad group of cells contains an enzyme of the brain and periph¬ eral nervous system, neuron-specific enolase7 (see Chap. 171). By electron microscopy, the PNE cells, which often have pseudopod-like cytoplasmic processes that interdigitate with other cells, contain rounded or ovoid membrane-bound secretion granules, which are situated principally at the basal pole of the cell and are extruded by exocytosis. The PNE cells may abut on the airway lumen; the neuroepithelial bodies protrude into the lumen in a spherical fashion. There is no consistent, immediately adjacent vascular supply to either the PNE cells or the neuroepi¬ thelial bodies. Although the PNE cells are seldom individually and directly associated with nerve endings, the neuroepithelial bodies often are innervated and respond to neurocrine stimuli.8 The intraluminal protrusion of the neuroepithelial bodies and their nervous connections suggest that these organoid structures might function as sensing elements, responding to local airway changes, such as humidity, temperature, pIT, inspired air content, particulate matter, or various irritants.9 There are several peptide hormones occurring within the se¬ cretion granules of the PNE cells. Presumably, along with acting on adjacent cells in a paracrine manner, the biogenic amines play a role in the synthesis, storage, or secretion of these peptide hor¬ mones with which they coexist. The large number of PNE cells in the fetus and newborn suggests a role in pulmonary development and in postnatal cir¬ culatory adjustments. Experimentally, the PNE cells discharge their granules when exposed to acute or chronic hypoxia, hypercapnea, irritant gases like nitrous oxide, and various drugs like

Ch. 172: The Endocrine Lung Cholinergic neuron

Noradrenergic

1481

Serotonergic ■ Tyrosine

Deaminated derivatives

NE

5-HT

COMT

X

X

-► Normetanephrine

X

Postsynaptic tissue

1 XX

X:

Postsynaptic tissue

FIGURE 172-2.

Biochemical events that occur at synapses that involve some of the biogenic amines. A, Cholinergic neuron. B, Noradrenergic neuron. C, Serotonergic neuron. ACh, acetylcholine; ACE, acetylcho¬ linesterase; x, receptor; NE, norepinephrine; MAO, monoamine oxidase; COMT, catechol-O-methyltransferase; 5-HTP, 5-hydroxytryptophan; 5-HT, 5-hydroxytryptamine [serotonin]; 5-HIAA, 5-hydroxyindoleacetic acid. (From Ganong WF. Review of medical physiology. Norwalk, CN: Appleton b Lang, 1987.)

nicotine, reserpine, or calcium ionophores. Some of these agents also may exert prenatal influences on the PNE cells.10 The PNE cells also probably exert important effects in disease states. Hy¬ perplasia of the PNE cells occurs in laboratory animals after the chronic inhalation of asbestos and after the administration of the pulmonary carcinogen, diethylnitrosamine.11'12 Also, the antena¬ tal exposure of maternal monkeys to dexamethasone increases the number of neuroepithelial bodies in the newborn.13 A marked PNE cell hyperplasia occurs in patients with acute pneu¬ monitis; chronic obstructive lung disease; heavy smokers; in pa¬ tients with intrinsic, nonimmunologic bronchial asthma; and in infants with chronic bronchopulmonary dysplasia. Often, chronic PNE cell hyperplasia is associated with the appearance of increased peripheral blood levels of one or more of their hormonal products. Additionally, acute pulmonary stim¬ ulation, such as occurs in hamsters exposed to cigarette smoke, in humans with acute pneumonitis, or in those who inhale noxious fumes in a fire, releases PNE cell hormones into the blood.1415

PULMONARY PROSTAGLANDINS AND OTHER ARACHIDONIC ACID AND CELL MEMBRANE PHOSPHOLIPID METABOLITES The physiologically active prostaglandins and other arachidonic acid metabolites produced within the lungs include platelet-activating factor (PAF), the prostaglandins (PG) (e.g., PGE2/ PGF2a, PGD2, and PGI2 [prostacyclin]), thromboxane (Tx), and the leukotrienes (LT) (e.g., LTB4, LTC4, LTD4, and LTE4).16 18 These hormones are not stored in the lungs, but are newly syn¬ thesized by various pulmonary cellular constituents, such as the mast cells, smooth muscle, fibroblasts, endothelium (prostacyclin in particular), alveolar macrophages, type II alveolar epithelial cells, polymorphonucleocytes, basophils, and platelets. Most of the active arachidonic acid metabolites are biosynthesized by the cyclooxygenase pathway; the lipoxygenase pathway leads to the formation of the leukotrienes (see Chap. 170). PAF is a metabo¬ lite of cell membrane phospholipid, which plays an important role in inflammatory pulmonary conditions and other lung disorders.19

These pulmonary metabolites produce effects that differ ac¬ cording to the site of the pulmonary effector cells or tissues, the prior functional state of the cells or tissues, and the presence or absence of other pulmonary hormones. Pharmacologically, the pulmonary action often differs according to the route of admin¬ istration, the species studied, and the experimental design. Their release can be induced by several other pulmonary hormones (e.g., serotonin, histamine, angiotensin II, endothelin-1, and bradykinin). These potent, evanescent compounds are also released in various pathologic pulmonary conditions, such as asthma, pul¬ monary edema, or asbestosis. Arachidonic acid and other cell membrane phospholipid metabolites are important in both nor¬ mal pulmonary physiology and in disease processes involving the lungs. Some of their pharmacologic and physiologic pulmo¬ nary effects are summarized in Table 172-1.

PEPTIDE HORMONES The pulmonary peptide hormones originate mostly from four sources: the PNE cell (e.g., calcitonin, calcitonin generelated peptide [CGRP], bombesin-like peptide, cholecystokinin, somatostatin, and leu-enkephalin),20 peptidergic nerves (e.g., CGRP, vasoactive intestinal peptide [VIP], and substance P), the pulmonary endothelial cell (e.g., angiotensin II, and endothelin1), and the blood of the pulmonary vasculature (e.g., bradykinin, which is produced in the blood from kininogen by the action of the enzyme kallikrein) (see Chaps. 77 and 163). Undoubtedly, several other pulmonary cells produce peptide hormonal prod¬ ucts. Some of the pharmacologic and physiologic effects of the pulmonary peptides and biogenic amines are shown in Table 172-2. Sometimes, a hormone is produced by more than one cell type; potentially functions as a neurocrine, an autocrine, a para¬ crine, a solinocrine, or a hemocrine messenger (see Chap. 1); and exerts effects that vary according to its site of production.

GROWTH FACTORS AND CYTOKINES Although they are peptides, the many humoral growth fac¬ tors and cytokines often are discussed under a category separate

1482

PART X: DIFFUSE HORMONAL SECRETION

TABLE 172-1 Pharmacologic and Physiologic Actions of Pulmonary Arachidonic Acid Metabolites and Other Derivatives of Membrane Phospholipids That are Synthesized in the Lung*

Metabolite

Effect on Bronchi

Effect on Pulmonary Vessels

PAF

Constriction

Constriction

1. A proinflammatory peptide 2. Induces leukocyte recruitment 3. Releases mediators from inflammatory and epithelial cells 4. Increases thromboxane and histamine release

Plays an important role in pathogenesis of several pulmonary inflammatory diseases. Increased mRNA expression in asthmatic patients. Participates in the development of allergic reactions. Induces bronchial hyperreactivity. Induces airway microvascular leakage and may cause lung edema. Induces aggregation of platelets. Stimulates neutrophil adhesion to endothelial cells. Plays a role in neonatal respiratory disease syndrome.

pge2

Dilation

Variable (often vasodilation but can constrict)

1. Systemic vasodilation 2. Decreases mucus secretion

Rapidly inactivated by lung endothelium.

Other Pertinent Effects

Comments

3. Inhibits platelet aggregation 4. Maintains patency of ductus arteriosus in fetus 5. Potentiates vasoconstriction by histamine 6. Decreases postinjury leak from vasculature 7. Decreases postinjury neutrophil recruitment

8. Regulates fetal lung fluid transport 9. Ameliorates the hypoxia of ischemic lung injury 10. Inhibits production of tumor necrosis factor-alpha

pgf2„

Constriction

Constriction (potent)

1. Variable systemic vasoconstriction 2. Increases mucus secretion

Rapidly inactivated by lung endothelium.

3. Antagonizes TxA2-induced platelet aggregation 4. Stimulates rapidly adapting receptors, which may play a role in reflex bronchoconstriction of anaphylaxis 5. Regulates fetal lung fluid transport

pgd2

Constriction

Constriction

pgi2

Dilation

Dilation (potent)

1. Slight systemic vasodilation 2. Increases mucus secretion

Pulmonary vasodilation in fetal goats.

3. Inhibits platelet aggregation 1. Systemic vasodilation (potent) 2. Inhibits platelet aggregation (potent) 3. Disaggregates platelets 4. Antithrombotic effect may protect against atherosclerosis 5. Membrane stabilizing effect 6. Maintains patency of ductus arteriosus in fetus 7. Inhibits release of leukotrienes

TxA2

Constriction

Constriction (potent)

1. Potent stimulation of platelet aggregation 2. Enhances leukocyte adhesiveness 3. Inhibits release of leukotrienes

Leukotrienes

Constriction

Variable

1. Increases capillary permeability 2. Increases mucus release 3. Chemotactic for polymorphonuclear cells (LTB4) 4. Decreases tracheal mucus velocity 5. Releases TxA2 and prostaglandins from lung

Synthesized by endothelial cells. Short-lived, but not appreciably metabolized by lungs. Degraded to 6-ketoPGFla. Pulmonary vasodilating effects may facilitate newborn adaptation to extrauterine life. Reverses physiologic dead space and shunting associated with pulmonary embolism. Inhibits leukocyte aggregation. Protects lungs against the pulmonary hypertension and increased permeability caused by endotoxin injury. Protects pulmonary circulation from excess vasoconstriction. Active and short lived. Contained within platelets. An ingredient of RCS. Inhibits adenylate cyclase activity ir platelets. Degraded to the inactive TxB2. Mediator of hypoxic vasoconstriction. LTB4 attracts alveolar macrophages. LTC4 and LTD4 are ingredients of SRS-A. Pulmonary vasoconstriction of LTD4 is mediated by cyclooxygenase metabolites. Pulmonary vasodilation of LTE4 is mediated by prostaglandins. Direct effect of LTE4 may be pulmonary vasoconstriction. Leukotrienes mediate allergen-induced bronchoconstriction.

IT, leukotriene; PAF, platelet-activating factor; PG, prostaglandin; RCS, rabbit aorta contracting substances; SRS-A, slowreacting substance of anaphylaxis; Tx, thromboxane. * Some of these effects vary with the species studied, the dosage, route of administration, and the experimental design. (Modified from Becker KL. The endocrine lung. In: Becker KL, Gazdar AF, eds. The endocrine lung in health and disease. Philadelphia: WB Saunders, 1984.)

from that of the other peptide hormones. Many cells of the lung give rise to various forms of these substances, which may be se¬ creted in physiologic circumstances (e.g., alveolar macrophages, leukocytes, mast cells, smooth muscle cells, bronchial epithelium, and type II cells). In pathologic circumstances, the growth factors

and cytokines exert important effects. These actions, which may be helpful or harmful, depend on the circumstances, the presence of other humoral substances, and the amount of the agents that are secreted. Some of their pharmacologic and physiologic effects are shown in Table 172-3.

1483

Ch. 172: The Endocrine Lung TABLE 172-2 Some Pharmacologic and Physiologic Effects of Pulmonary Pertinence

Hormone

Location Within Lung

Effects

Angiotensin II

Endothelium

Causes pulmonary vasoconstriction; releases pulmonary prostaglandins, including prostacyclin; might play a role in hypoxic vasoconstriction.

Atrial natriuretic hormone

Alveolar cells, muscle of pulmonary veins, PNE

Causes vasodilation, bronchodilation, and decrease in pulmonary artery pressure; stimulates surfactant production; increases blood flow perfusing poorly ventilated regions.

Bombesin-like peptides

PNE cells, alveolar macrophages

Causes constriction of pulmonary artery; causes bronchoconstriction that cannot be inhibited by antagonists of acetylcholine, histamine, or serotonin; releases serotonin and histamine from mast cells; enhances growth of bronchial epithelial cells; induces mitosis in PNE cells; stimulates surfactant biosynthesis; induces mucus secretion. Centrally, it can increase pulmonary tidal volume and can cause apneusis-like alterations in the breathing pattern. The high levels during the fetal-neonatal period suggest a role in intrauterine life or in neonatal

Bradykinin

From plasma of lung vasculature

adaptation; increases lung branching in embryogenesis. Causes pulmonary vasodilation or contraction; causes bronchoconstriction, either directly or through prostaglandin release; stimulates pulmonary release of prostaglandins, prostacyclin, and thromboxane; releases histamine from mast cells; competitively inhibits enzymic conversion of angiotensin I to II; may play a role in the physiologic pulmonary vasodilation at birth; may contract the ductus arteriosus; increases permeability of pulmonary endothelium.

Calcitonin

PNE cells

Promotes growth of cartilage; increases endothelial prostacyclin synthesis; inhibits synthesis of prostaglandins and thromboxane within the lungs; centrally, can increase tidal volume; antagonizes the bronchoconstrictor effects of bombesin-like peptide and of substance P; may control local immune reactions by influencing multinuclear alveolar macrophages. Precursor peptides (e.g., procalcitonin) are produced as a result of the inflammatory cytokine cascade and may play a role in the pulmonary response to injury or sepsis.

Calcitonin gene-related

PNE cells, nerves

Causes vasodilation and bronchodilation; blocks the bombesin-related peptide-induced and substance P-induced increase in airway tone; increases ciliary beat frequency; induces eosinophilic chemotaxis; induces proliferation of bronchial epithelium; inhibits degradation of tachykinin. Its peptidergic neurotransmitter role may mediate receptor functions of the

Nerves? PNE cells

Possibly has a peptidergic function in the lung; may cause bronchoconstriction; increases

peptide

respiratory epithelium. Cholecystokinin

pulmonary blood flow. CRH

Unknown

Unknown

Endothelin

Endothelium of vasculature, bronchiolar epithelium, submucosal glands, PNE

Causes bronchoconstriction and vasoconstriction; can be vasodilatory, depending on K+ channel; influences airway mucosal blood flow; enhances vascular permeability; stimulates pulmonary arachidonate 15-lipoxygenase activity; induces release of thromboxane, histamine, and prostacyclin in the lung; may be involved in airway differentiation during embryogenesis; stimulates surfactant secretion from alveolar type II cells; stimulates surfactant secretion from alveolar type II cells; influences neuronal transmission; may function as a proinflammatory peptide, being locally produced at sites of pulmonary injury, may play a role in causation of the adult respiratory distress syndrome. Increased levels in

cells, type II alveolar pneumocytes

congestive heart failure may protect the lung from pulmonary edema. Galanin

Nerves

Possibly has peptidergic effects; possibly is antagonist of substance P.

Histamine

Mast cells, PNE cells?

Causes vasoconstriction of pulmonary arteries; may cause vasodilation; may play a role in the local regulation of pulmonary blood flow and in hypoxic vasoconstriction; increases vascular permeability; usually causes bronchoconstriction but may cause bronchodilation; releases prostaglandins, thromboxane, and leukotrienes from lung; stimulates bronchial glandular

Nerves?

Causes vasodilation and possibly bronchoconstriction; increases mucus secretion; increases

Neuropeptide K (NPK)

Nerves?

Possibly causes bronchoconstriction.

Neuropeptide Y (NPY)

Nerves

Possibly has peptidergic function; potentiates catecholamine-induced vasoconstriction.

Neurotensin

Nerves? PNE cells?

Possibly has peptidergic function; causes bronchoconstriction; degranulates mast cells and releases histamine; increases vascular permeability; induces leukocyte chemotaxis; enhances

PNE cells, nerves

d-Endorphin and met- and leu-enkephalins competitively inhibit angiotensin converting enzyme. Intravenously, leu-enkephalin increases respiratory rate and can affect pulmonary

secretion. Neurokinin A (NKA)

pulmonary vascular permeability.

phagocytosis; inhibits cholinergic and noncholinergic neurotransmission. Opioid peptides

artery pressure; intraarterially, it causes pulmonary vasoconstriction. Enkephalin may stimulate pulmonary ] receptors, with consequent apnea, bradycardia, and hypotension. Endogenous opiates may minimize the stress of chronic airway obstruction. Opioids may function as neurotransmitters in PNE cell-sensory nerve interaction. They inhibit release of endogenous acetylcholine from postganglionic parasympathetic pulmonary neurons, depress the contractile response of tracheal smooth muscle, which is induced by field stimulation and hence may have a role in bronchodilation; and may play a role in immune—inflammatory reactions. Peptide histidine isoleucine (PHI)

Nerves

Possibly has a peptidergic function in the lung.

Peptide histidine methionine (PHM)

Nerves

Possibly causes bronchodilation.

Serotonin

Platelets, PNE cells

Causes pulmonary vasoconstriction and, in some species, pulmonary venodilation; causes bronchoconstriction; stimulates synthesis of prostaglandins within the lungs; promotes platelet aggregation.

(continued)

1484

PART X: DIFFUSE HORMONAL SECRETION

TABLE 172-2 Some Pharmacologic and Physiologic Effects of Pulmonary Pertinence Caused by Known or Suspected Hormones Within the Lung (continued) Hormone

Location Within Lung

Effects

Somatostatin

Nerves, PNE cells

Possibly has peptidergic function in the lung; intravenously, increases pulmonary artery pressure; releases serotonin and histamine from mast cells; down-regulates /3-adrenergic function of airway smooth muscle.

Substance P

Nerves

Possibly has peptidergic function in the lung; causes tracheobronchoconstriction, increased pulmonary vascular permeability, and possibly vasodilation; stimulates synthesis and release of tracheobronchial mucus; releases histamine from mast cells.

Vasoactive intestinal peptide (VIP)

Nerves

Possibly has peptidergic function in the lung; suppresses acetylcholine release from vagus nerve terminals; enhances ventilation and causes bronchoconstriction; decreases thromboxane release; protects against histamine and PGF2o and leukotriene D4-induced bronchoconstriction; dilates pulmonary vessels that have previously been constricted by prostaglandin or leukotriene; inhibits basal bronchial mucus production; increases ciliary beat frequency.

CRH, corticotropin releasing hormone; PGF2„, prostaglandin F2a; PNE, pulmonary neuroendocrine. (Modified from Becker KL. The endocrine lung. In: Becker KL, Gazadar AF, eds. The endocrine lung in health and disease. Philadelphia: WB Saunders, 1984.)

FUNCTIONS OF PULMONARY HORMONES Both the secretion and the action of most of the pulmonary hormones depend on or are modulated by the presence or ab¬ sence of other hormones: ACTH noncompetitively inhibits the pulmonary synthesis of angiotensin II; bradykinin competitively inhibits the synthesis of angiotensin II; angiotensin II releases prostacyclin; substance P releases mast cell histamine; histamine releases pulmonary arachidonic acid metabolites; endothelin-1 induces the release of PAF; calcitonin and CGRP block

bombesin- and substance P-induced increases in airway tone20; and VIP counteracts the vasoconstrictor and bronchoconstrictor effects of LTD4.

PHYSIOLOGIC ROLE AT BIRTH Pulmonary hormones play an important role in pulmonary adaptations that occur at birth. After aeration of the lungs, the pulmonary vasoconstriction of the fetus reverts to dilatation.21 This change is essential. It permits gas exchange and allows the

TABLE 172-3 Pharmacologic and Physiologic Actions of Some of the Growth Factors and Cytokines Within the Lung* Growth Factor/Cytokine_Pharmacologic and Physiologic Effects Basic fibroblast growth factor

Decreases elastin production by neonatal lung fibroblasts; stimulates growth of fibroblasts and endothelial cells; may play a role in fibroproliferation following acute lung injury.

Epidermal growth factor

Plays a role in the differentiation of pulmonary epithelium; increases synthesis and secretion of surfactant; enhances pulmonary functional maturation in utero.

Fibroblast growth factor

Has mitogenic effect for fibroblasts and possibly for vascular smooth muscle.

Granulocyte/macrophage colony-stimulating factor

Increases proliferation of neutrophil precursors; prolongs the survival of neutrophils and increases their bactericidal activity; facilitates IgA-mediated phagocytosis.

Interferon gamma

Activates alveolar macrophages and increases their ability to express IgG fc receptors and class II histocompatibility antigens; augments neutrophil recruitment and enhances their microbial activity; stimulates release of tumor necrosis factor a; increases release of oxygen radicals; induces synthesis of phospholipase A2 and third component of complement; inhibits growth of fibroblasts and collagen synthesis.

Interleukins

Exert a vast number of effects on the lung. For example: 1L-1 is proinflammatory. It induces leakage of proteins from the vasculature, increases accumulation of neutrophils, increases cellular antimicrobial activity, and augments antibody formation. It activates fibroblasts and induces their production of IL-6 and also induces granulocyte/macrophage colonystimulating factor release from the bronchial epithelium. It interacts with tumor necrosis factor a in mediating septic shock. IL-3 damages vascular endothelium and predisposes to pulmonary edema. It augments production of IL-6. IL-6 is a proinflammatory cytokine that is involved in the tissue immune response. It also may serve as a marker for lung injury. It is an important mediator of the sepsis syndrome. IL-12 enhances the cytologic activity of lymphocytes and induces production of tumor necrosis factor a. It inhibits the development of pulmonary fibrosis via suppression of the synthesis of collagen. In some models, interferon gamma inhibits the inflammatory response and diminishes protective immunity in the host.

Keratinocyte growth factor

Stimulates growth of type II pneumocytes.

Platelet-derived growth factor

Increases growth of lung fibroblasts and may play a role in maintaining normal lung structure and repairing injury.

Tumor necrosis factor a

Potent mediator of the inflammatory cascade; produced in response to many pathogens; stimulates macrophages and polymorphonuclear chemotaxis and activates their antimicrobial activity; stimulates neutrophil adhesion to endothelial cells; induces vascular proliferation and collagen synthesis; inhibits the synthesis of protein and, at higher levels, causes breakdown of protein; stimulates production of other cytokines.

IL, interleukin. * This is a partial list of the growth factors and cytokines that are secreted in the lungs. These substances are multifunctional and have important roles in both normal homeostasis and in the pathogenesis of lung disease. Their effects vary according to their level of secretion, the presence of other humoral agents, and the overall clinical setting.

Ch. 172: The Endocrine Lung right ventricle to perfuse the pulmonary circulation with little effort. It seems likely that this vasodilation results from the diffuse intrapulmonary release of prostacyclin.22 The therapeutic administration of prostacyclin into the pulmonary artery of a hu¬ man neonate has successfully ameliorated the refractory hypox¬ emia resulting from the syndrome of persistent fetal circulation. The initial oxygenation of the newborn releases bradykinin, which causes pulmonary vasodilation and assists in constricting the ductus arteriosus. This blood vessel, which connects the pul¬ monary artery and aorta, allows blood to bypass the vasoconstricted fetal pulmonary bed and decreases the workload of the heart. During fetal development, it is the secretion of PGE2 and, perhaps, the local endothelial production of prostacyclin that maintains the patency of the ductus arteriosus. This effect wanes just before birth, possibly because of an increased degradation of PGE2. At birth, exposure to atmospheric oxygen probably pro¬ motes the synthesis of PGF2a, which may effect the closure of the ductus arteriosus. Pulmonary hormones also appear to play a role in postnatal lung development.23

PULMONARY HORMONES IN LUNG DISEASE In addition to the normal physiologic effects of pulmonary hormones, the increased levels in lung disease influence the symptomatology, course, and outcome of the illness. For exam¬ ple, asthma, a condition characterized by paroxysmal wheezing resulting from narrowing of the bronchial airways, is associated with the release of several bronchoconstrictive hormones: hista¬ mine, PAF, PGF2a, the leukotrienes, thromboxane A2, substance P, serotonin, and endothelin. A similar panoply of bronchocon¬ strictive hormonal agents is released during systemic anaphylaxis (i.e., extreme hypersensitivity to a substance manifested by a diffuse bronchoconstriction and perivascular congestion that can cause fatal respiratory failure).24 In this condition, the secretion of PGF2a probably facilitates the release of histamine and leukotrienes. The release of prostacyclin may blunt this bronchoconstriction. In localized hypoxia within the lung, pulmonary blood must be diverted away from the hypoxic alveoli to improve the perfusion-ventilation balance (i.e., hypoxic vasoconstrictor re¬ sponse).25 This local pulmonary vasoconstriction probably is me¬ diated by one or more of the hormones released in hypoxia (e.g., angiotensin II, endothelin-1, serotonin, and histamine). Alterna¬ tively, an excessive secretion of these hormones during hypoxia can be harmful (e.g., angiotensin II can cause ultrastructural le¬ sions of the alveolar epithelium). It is thought that bradykinin, which is released in local lung hypoxia, can modulate the vaso¬ constrictor reflex. In severe acute hypoxia, VIP and prostacyclin are secreted, both of which may cause a protective pulmonary vasodilation in nonhypoxic areas of the lungs and which may enhance the vascular perfusion of the myocardium and the brain. The excess oxygenation of the lungs (i.e., hyperoxia) can be harmful, leading to pulmonary congestion, endothelial necrosis, and edema.26 In this condition, pulmonary serotonin is increased, partly because of poor degradation. This leads to obstruction of the vasculature by platelet aggregation. Also, the potent vaso¬ constrictor thromboxane A2 is increased in hyperoxia because of inhibition of its inactivating enzyme, 15-hydroxyprostaglandin dehydrogenase. Chronic hyperoxia also causes significant PNE cell hyperplasia. In pulmonary embolism, the local acute obstruction of blood supply leads to physiologic shunting, perhaps mediated by re¬ lease of serotonin, PGF2a, and PGD2, but the vasodilatory effect of the secreted prostacyclin ameliorates the severity of the acute pulmonary hypertension, decreases obstruction by diminishing platelet aggregation, and facilitates the eventual reversal of the vascular shunting.3,27 Excess levels of bradykinin and subsequent pulmonary endothelial permeability can lead to the pulmonary edema seen in the acute respiratory failure of pulmonary embolism.

1485

Various pulmonary hormones are increased locally or pe¬ ripherally in other conditions involving the lung, such as hyp¬ oxia, mechanical ventilation, environmental injury from irritant gases or inorganic dusts, and acute or chronic cigarette smok¬ ing.28 Increased production of fibroblast-promoting growth fac¬ tors by the alveolar macrophage may play a role in the abnormal type III procollagen metabolism in patients with idiopathic pul¬ monary fibrosis.29 In asthma, there is an absence of VIP from nerve fibers of the lung, increased lung levels of endothelin-1,30,31 as well as increased secretion of tumor necrosis factor a, granu¬ locyte/macrophage colony-stimulating factor, and the interleu¬ kins (IL) (e.g., IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, and IL-8).32,33

PULMONARY HORMONES IN PERIPHERAL BLOOD To what extent is the local increase of a pulmonary hormone accompanied by an increased level in the peripheral blood? Ex¬ perimentally, when PNE cell hyperplasia is induced in hamsters by the administration of nitrosamines, a progressive increase in pulmonary calcitonin is parallelled by an increase in blood levels of this hormone.34 In patients with acute bacterial or viral pneu¬ monitis and in burn patients with acute lung injury from irritant gases, serum levels of calcitonin (especially calcitonin precursors) are increased.35-37 Serum calcitonin precursor levels often are high in pulmonary tuberculosis and in patients with chronic lung disease from cystic fibrosis.38,39 Chronic smokers have increased levels of bombesin-like peptides in their bronchial tree and urine.40 Serum calcitonin precursors and ACTH precursors, as well as atrial natriuretic peptide, are increased in chronic obstruc¬ tive pulmonary disease.38,41 It is mostly the procalcitonin compo¬ nent of the CALC-1 gene that is increased in many of these con¬ ditions (see Chap. 52). Interestingly, in this regard, serum procalcitonin levels are high in the systemic inflammatory re¬ sponse syndrome (SIRS), because of either infectious or noninfectious injury.42,43 Indeed, such levels may be used as a parame¬ ter of the severity of the condition. Although the source of the procalcitonin in this condition is uncertain, much of it it may be from the lung, because the adult respiratory distress syndrome (ARDS) is commonly a component of SIRS.44 Serum angiotensin II levels are increased in rodents with thiourea or paraquatinduced lung damage after an increase in angiotensin converting enzyme activity; similar increases occur in patients with pulmo¬ nary sarcoidosis, pulmonary embolism, or anaphylaxis and in ox¬ ygenation of the fetus.45 Blood bradykinin levels are increased in the respiratory distress syndrome of the neonate and in endotoxic shock. Blood endorphins, perhaps of pulmonary origin, are in¬ creased in hypoxic sheep and also in men with high-altitude pul¬ monary edema, as well as in response to the pulmonary changes accompanying endotoxic shock.46 Blood VIP levels are increased in animals with anaphylaxis, acute hypoxia, or acute respiratory acidosis.

PULMONARY HORMONES IN LUNG CANCER Peripheral blood levels of some of the pulmonary hormones are increased in some varieties of lung cancer. The hormones that are commonly increased in patients with the relatively benign pulmonary carcinoid or the malignant small-cell lung cancer (SCLC) often are the hormones known or suspected to be pro¬ duced by the normal or the dysplastic PNE cell (e.g., calcitonin, CGRP, mammalian bombesin, ACTH, and somatostatin). In¬ creased blood levels of VIP, a hormone found in pulmonary nerves and ganglia, usually are associated with types of lung ma¬ lignancy other than SCLC.4, The study of the carcinoid tumor and SCLC (see Chap. 214) offers important insights into the na¬ ture of their putative cells of origin, the PNE cells.48 Some of the peptide hormones that commonly are increased in the blood of SCLC patients frequently are increased in patients with other varieties of lung cancer. Perhaps this is because of a heterogeneity of cell types within the tumor. Alternatively, the

1486

PART X: DIFFUSE HORMONAL SECRETION

high levels of some of the hormones encountered in the blood of patients with cancer of the lung other than SCLC may reflect their smoking-related PNE cell hyperplasia.49 In this respect, some studies of long-term cell cultures of lung cancer demon¬ strate that bombesin-like peptides and calcitonin occur almost exclusively in SCLC cultures; somatostatin and ACTH are found frequently, but not exclusively, in these cell lines.50 Of course, one or more of the PNE cell-associated peptides are found in the endocrine cells of many other tissues (e.g., ante¬ rior pituitary gland, thyroid C cells, gastrointestinal endocrine cells, and pancreatic islets), and tumors involving nonendocrine tissues are commonly associated with increased hormonal pep¬ tide blood levels. In health and in disease, the lung is a complex endocrine organ that produces a host of hormones that act locally or diffusely within the lung and that affect extrapulmonary tissues. The pulmonary effects of most of these hormones vary according to the concurrent physiobiochemical status of their environment. Some of these effects are beneficial and some are not. There must be other hormones that are pathophysiologically important within the lung. Some of them may be peptide por¬ tions of the larger precursors from which most active peptides are synthesized, and some may be products of alternative posttranslational processing steps. As is the case with the known pul¬ monary hormones, they also will be found within other tissues and will act on different effectors.

REFERENCES 1. Fishman AP. The diverse functions of the lung. In: Becker KL, Gazdar AF, eds. The endocrine lung in health and disease. Philadelphia: WB Saunders, 1984: 47. 2. Said SI. Metabolic functions of the pulmonary circulation. Circ Res 1982; 50:325. 3. Becker KL. The endocrine lung. In: Becker KL, Gazdar AF, eds. The endo¬ crine lung in health and disease. Philadelphia: WB Saunders, 1984:3. 4. Becker KL. The coming of age of a bronchial epithelial cell. Am J Respir Crit Care Med 1994; 149:183. 5. Becker KL, Gazdar A. The pulmonary endocrine cell and the tumors to which it gives rise. In: Reznick-Schuller HM, ed. Comparative respiratory tract car¬ cinogenesis, vol 2. Boca Raton: CRC Press, 1984:161. 6. Cutz E, Conen PE. Endocrine-like cells in human fetal lungs: an electron microscopic study. Anat Rec 1972; 173:115. 7. Schmechel DE, Marangos PJ, Brightman MW. Neuron-specific enolase is a marker for peripheral and central neuroendocrine cells. Nature 1979; 276:834. 8. Nylen ES, Becker KL, Snider RH, et al. Cholinergic-nicotinic control of growth and secretion of cultured pulmonary neuroendocrine cells. Anat Rec 1993;236:129. 9. Lauweryns JM, Goddeeris P. Neuroepithelial bodies in the human child and adult lung. Am Rev Resp Dis 1975; 111:469. 10. Nylen ES, Linnoila RI, Becker KL. Prenatal cholinergic stimulation of pul¬ monary neuroendocrine cells by nicotine. Acta Physiol Scand 1988; 132:117. 11. Johnson NF, Wagner JC, Wills HA. Endocrine cell proliferation in the rat lung following asbestos inhalation. Lung 1980; 158:221. 12. Reznick-Schuller H. Proliferation of endocrine (APUD-type) cells during early DEN-induced lung carcinogenesis in hamsters. Cancer Lett 1971; 1:255. 13. Dayer AM, Kapanci Y, Rademakers A, et al. Increased numbers of neuro¬ epithelial bodies (NEB) in lungs of fetal Rhesus monkeys following maternal dexamethasone treatment. Cell Tissue Res 1985; 239:703. 14. Tabassian AR, Nylen ES, Giron AE, et al. Evidence for cigarette smokeinduced calcitonin secretion from lungs of man and hamster. Life Sci 1988; 42:2323. 15. Tabassian AR, Snider RH Jr, Nylen ES, et al. Heterogeneity studies of hamster calcitonin following acute exposure to cigarette smoke: evidence for mono¬ meric secretion. Anat Rec 1993; 236:253. 16. Greally P, Cook AJ, Sampson AP, et al. Atopic children with cystic fibrosis have increased urinary leukotriene E4 concentrations and more severe pulmonary disease. J Allergy Clin Immunol 1994;93:100. 17. Trochtenberg DS, Lefferts PL, King GA, et al. Effects of thromboxane syn¬ thase and cyclooxygenase inhibition on PAF-induced changes in lung function and arachidonic acid metabolism. Prostaglandins 1992;44:555. 18. Boichot E, Lagente V, Mencia-Huerta M, Braquet P. Bronchopulmonary responses to endothelin-1 in sensitized and challenged guinea pigs: role of cycloox¬ ygenase metabolites and platelet-activating factor. Fundam Clin Pharmacol 1993; 7: 281. 19. Chung KF. Platelet-activating factor in inflammation and pulmonary dis¬ orders. Clin Sci 1992;83:127. 20. Polak JM, Becker KL, Cutz E, et al. Lung endocrine cell markers, peptides and amines. Anat Rec 1993;236:169.

21. Assali NS, Morris JA. Circulatory and metabolic adjustments of the fetus at birth. Biol Neonate 1964; 7:141. 22. Leffler CW, Hessler JR. Perinatal pulmonary prostaglandin production. Am J Physiol 1981;241:H756. 23. Motoyama EK, Brody JS, Colten HR, Warshaw JB. Postnatal lung devel¬ opment in health and disease. Am Rev Respir Dis 1988; 137:742. 24. Schulman ES, Newball HH, Demers LM, et al. Anaphylactic release of thromboxane A2, prostaglandin D2, and prostacyclin from human lung paren¬ chyma. Am Rev Respir Dis 1981; 124:402. 25. Fishman AP. Vasomotor regulation of the pulmonary circulation. Annu Rev Physiol 1980;42:211. 26. Clark JM, Lambertsen CJ. Pulmonary oxygen toxicity: a review. Pharma¬ col Rev 1971;23:37. 27. Malik AB, Johnson A, Tahamont MV. Mechanisms of lung vascular injury after intravascular coagulation. Ann NY Acad Sci 1982;384:213. 28. Tabassian AR, Nylen ES, Linnoila RI, et al. Stimulation of pulmonary neuroendocrine cells and associated peptides following repeated exposure to ciga¬ rette smoke in hamsters. Am Rev Resp Dis 1989; 140:436. 29. Cantin AM, Boilcau R, Begin R. Increased procollagen III, aminoterminal peptide-related antigens and fibroblast growth signals in the lungs of patients with idiopathic pulmonary fibrosis. Am Rev Resp Dis 1988; 137:572. 30. Ollerenshaw S, Jarvis D, Woolcock A, et al. Absence of immunoreactive vasoactive intestinal polypeptide in tissue from the lungs of patients with asthma. N Engl J Med 1989;320:1244. 31. Springall DR, Howarth PH, Counihan H, et al. Endothelin immunoactivity of airway epithelium in asthmatic patients. Lancet 1991; 1:697. 32. Marini M, Vittori E, Hollenberg J, Mattoli S. Expression of the potent in¬ flammatory cytokines, granulocyte-macrophage-colony-stimulating factor and interleukin-6 and interleukin-8, in bronchial epithelial cells of patients with asthma. J Allergy Clin Immunol 1992;89:1001. 33. Bradding P, Roberto JA, Montefort S, et al. Interleukin-4, -5, and -6 and tumor necrosis factor-alpha in normal and asthmatic airways: evidence for the hu¬ man mast cell as a source of these cytokines. Am J Respir Cell Molecular Biol 1994; 10:471. 34. Linnoila RI, Becker KL, Silva OL, et al. Calcitonin as a marker for diethylnitrosamine-induced pulmonary endocrine cell hyperplasia in hamsters. Lab Invest 1984; 51:39. 35. Becker KL, O'Neil WJ, Shider RH Jr, et al. Hypercalcitonemia in inhalation burn injury: a response of the pulmonary neuroendocrine cell? Anat Rec 1993; 236: 136. 36. Nylen ES, Jeng J, Jordan MH, et al. Late pulmonary sequela following burns: persistence of hyperprocalcitonemia using a 1-57 amino acid N-terminal flaking peptide assay. Respir Med 1995; 89:41. 37. Nylen ES, Snider RJ Jr, O'Neil W, et al. Pneumonitis-associated hyperpro¬ calcitonemia. (Submitted for publication) 1995. 38. Becker KL, Nash DR, Silva OL, et al. Increased serum and urinary calcito¬ nin levels in patients with pulmonary disease. Chest 1981; 79:211. 39. Becker KL, Silva OL, Snider RH, et al. The pathophysiology of pulmonary calcitonin. In: Becker KL, Gazdar AF, eds. The endocrine lung in health and disease. Philadelphia: WB Saunders, 1984:277. 40. Aguayo SM, Kane MA, King T, et al. Increased level of bombesin-like peptides in the lower respiratory tract of asymptomatic cigarette smokers. J Clin Invest 1989;84:1105. 41. Ayvazian LF, Schneider B, Gewirtz G, Yalow RS. Ectopic production of big ACTH in carcinoma of the lung. Am Rev Respir Dis 1975; 3:279. 42. Assicot M, Gendrel D, Carsin H, et al. High serum procalcitonin concen¬ trations in patients with sepsis and infection. Lancet 1993; 1:515. 43. Bone RC, Balk RA, Cerra FB, et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Chest 1992; 101:164. 44. Bone RC, Balk RA, Cerra FB, et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Chest 1992; 101:1644. 45. Lieberman J, Nosal A, Schlessner LA, Sastre-Foken A. Serum angiotensin¬ converting enzyme for diagnosis and therapeutic evaluation of sarcoidosis. Am Rev Respir Dis 1979; 120:329. 46. Bar-or D, Marx JA, Good JT Jr. Naloxone, beta endorphins, and highaltitude pulmonary edema. Ann Intern Med 1982; 96:684. 47. Said SI, Faloona GR. Elevated plasma and tissue levels of vasoactive in¬ testinal polypeptide in the watery-diarrhea syndrome due to pancreatic, broncho¬ genic and other tumors. N Engl J Med 1975;293:155. 48. Becker KL, Nylen ES, Cassidy MM, Tabassian AR. The normal and abnor¬ mal pulmonary endocrine cell. In: Kaiser HE, ed. Progressive stages of malignant neoplastic growth. Netherlands: Martinus Nijhoff, 1988. 49. Kelley MJ, Becker KL, Rushin JM, et al. Calcitonin elevation in small cell lung cancer without ectopic production. Am J Respir Crit Care Med 1994; 149:183. 50. Gazdar AF, Carney DN, Becker KL, et al. Expression of peptide and other markers in lung cancer cell lines. Recent Results Cancer Res 1985;99:167.

Ch. 173: The Endocrine Heart Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

173_

THE ENDOCRINE HEART ELLEN W. SEELY AND GORDON H. WILLIAMS The effects of the endocrine system on the heart have been appreciated for many years. More recently, it has been discov¬ ered that the heart functions as an endocrine organ. In 1956, it was observed that expansion of the left atrium of the dog led to increased urine flow. Within the wall of the right auricle, myoendocrine cells have been demonstrated in various mammals, including humans.2 These cells contain secretory granules typical of neuroendocrine cells (Fig. 173-1); fewer of them occur in the left auricle. It was noticed that they increased in number with volume loading.3 It then was postulated that these cells might secrete a factor promoting natriuresis and diuresis in response to increased volume. In the rat, extracts from these cells increased urinary sodium excretion, offering further support for the hy¬ pothesis that they played a role in volume homeostasis.4 Several peptides have been isolated from the heart, brain, and urine and collectively named atrial natriuretic factor (ANF), atrial natri¬ uretic peptide (ANP), or atrial natriuretic hormone (ANH).5 Some of these peptides are not even synthesized in the heart, but in other organs (e.g., brain, kidney).

ATRIAL NATRIURETIC HORMONE BIOCHEMISTRY AND MOLECULAR BIOLOGY Purified ANH possesses natriuretic and diuretic properties demonstrable in several species, including humans.6 The amino acid sequences of several of these peptides and their precursors have been determined in the rat, mouse, and human (Fig. 173-2).7,8 The COOH-terminal is highly conserved among these three species, suggesting that it is critical to biologic function. A disulfide bridge between Cys129 and Cys145 also is crucial for ANH's biologic effect.8 Human ANH differs from rat ANH at the COOH-terminal by a substitution of methionine for isoleucine at position 17. Whether all of the currently characterized peptides

1487

are of physiologic significance is unclear. Some may result from proteolysis during and after extraction, with only one or two pep¬ tides being the naturally occurring circulating forms.8 Peptides of nearly identical structure and at least some similar properties have been isolated from brain tissue (brain natriuretic peptide [BNP]) and urine (urodilatin).9 Several groups of investigators have cloned the rat and human cDNA, and the ANH gene has been localized to the distal short arm of the human chromosome 1, and, in the mouse, to chromosome 4. The rat peptide synthe¬ sized from its cDNA consists of 152 amino acids, with the signal peptide comprising 24 amino acids. The human peptide con¬ tains one less amino acid, but its signal peptide contains one more. Specifically, the human peptide does not contain the COOH-terminal Arg-Arg amino acid sequence characteristic of the rat.10,11

STRUCTURE-ACTIVITY RELATIONSHIPS Atrial natriuretic hormone has been extensively studied on both a molecular and physiologic level.12"15 Several investiga¬ tions have assessed the importance of different structural charac¬ teristics of this peptide to its bioeffect. The bioassays included relaxation of the chick rectum and rabbit aorta, diuresis or natri¬ uresis in the intact rat, and in vitro inhibition of aldosterone se¬ cretion. In general, the removal of any of the COOH-terminal peptides markedly reduces the bioactivity of the hormone, re¬ gardless of which assay is used. Terminal cleavage does not mod¬ ify bioactivity until its length is reduced to less than 23 amino acids. Increasing the peptide's length by adding to the NH2terminal gradually reduces its biologic efficacy. From these stud¬ ies, the active ANH is a 28-amino-acid fragment. In urine, the active compound is a 32-amino-acid peptide. In addition, a brain peptide and a so-called c-type natriuretic peptide have been described.

LOCALIZATION OF ANH RECEPTORS AND BIOCHEMICAL ACTION DISTRIBUTION Atrial natriuretic hormone receptors are distributed widely. The highest concentration of receptors is in the glomerulus of the kidney. ANH receptors have been solubilized from the renal glomerulus and are a single class with high affinity (Kd about 27 pM). The zona glomerulosa also has a high concentration of

FIGURE 173-1. Myoendocrine cell from the human right atrium. Secretory granules (SG) nucleus (N), mitochondria (Mi), myofibrils (My), glycogen (G/), and golgi apparatus (G) are demonstrated; X20,000. (From Forssmann WG, Hock D, Lottspeich F, et al. The right auricle of the heart is an endocrine organ. Anat Histol Embryol 1983;168:307.)

1488

PART X: DIFFUSE HORMONAL SECRETION 99

FIGURE 173-2. Amino acid sequences of human and rat atrial natriuretic hormone. The circulating molecule is derived from a much larger prohor¬ mone. The sequence in these two species is similar, with the disulfide bond critical for biologic activity. (From Cantin M, Genest J. The heart as an endocrine gland. SciAm 1986; 254:76)

ANH binding sites. Binding sites occur in the brain, particularly the circumventricular organs and the median eminence, the en¬ dothelial lining of all four cardiac chambers, arteries, veins, arte¬ rioles, venules, lung, small intestine, colon, and eye. Most of the ANH receptors in the kidney are located on the podocytes of the visceral epithelium of the glomerulus. Fewer binding sites are found on capillaries and mesangial cells. Although ANH binding sites have been observed in the renal medulla, they are less plen¬ tiful than in the glomerulus and are heavily concentrated in the vascular endothelial cells, with smaller amounts in the proximal tubule, collecting duct, and the ascending limb of the loop of Henle. Three different receptor subtypes have been reported: ANH-receptor A, ANH-receptor B, and ANH-receptor C. The first two contain guanylate cyclase and are important for biologic effects of ANH, whereas the last one appears to be a clearance receptor. ANH-receptor A preferentially binds ANH, whereas ANH-receptor B binds c-type natriuretic peptide. How these two systems interact is unclear. 6

chymal cells of the salivary glands, in nerve fibers, and in cell bodies of the hypothalamus and pons. Both the anterior and pos¬ terior pituitary and the superior cervical ganglion appear to con¬ tain immunoreactive ANH. It is now clear that BNP is a structur¬ ally distinct peptide from ANH. A third distinct peptide

MECHANISM OF ACTION

Atrial natriuretic hormone appears to exert its action by one of two mechanisms: inhibition of adenylate cyclase activity or stimulation of particulate guanylate cyclase activity. When syn¬ thetic ANH is infused into normal persons or animals, an increase in the circulating levels and urinary excretion of cyclic guanosine monophosphate results. Little, if any, effect on circulating or uri¬ nary cyclic adenosine monophosphate has been demonstrated (Fig. 173-3). In vitro, ANH inhibits adenylate cyclase activity in a dose-dependent fashion, with an apparent between 5 X 10-11 and 1CT10 M, although activation of particulate guanylate cyclase is its most consistent effect. This has been documented in zona glomerulosa cells, vascular smooth muscle cells, renal tubular cells, and renal glomeruli. ANH does not activate soluble guanyl¬ ate cyclase, at least in the kidney and the adrenal, although in the latter gland this is controversial.

PRODUCTION SITES FOR ANH Atrial natriuretic hormone is produced primarily in the right atrium, but it may be produced in the left atrium and in the ven¬ tricles.17 Immunoreactive ANH has been detected in the paren¬

FIGURE 173-3. Plasma cyclic GMP and AMP response to bolus intra¬ venous injection of atrial natriuretic hormone (ANH; 50 /rg) in eight nor¬ mal men. ANF, atrial natriuretic factor. (From Gerzer R, Witzgall H, Trem¬ blay J, et al. Rapid increase in plasma and urinary cyclic GMP factor bolus injection of atrial natriuretic factor in man. J Clin Endocrinol Metab 1985;61: 1217.)

Ch. 173: The Endocrine Heart (urodilatin) is made in the kidney.9 Neuroendocrine tumors may produce ANH.18

1489 1200 > —

03

800

BIOLOGIC EFFECTS OF ANH Atrial natriuretic hormone primarily affects the functions of the kidney, the peripheral vascular system, and the adrenal gland. It (or a related peptide) also may have effects, albeit less convincingly, on the brain, particularly the pituitary.19 It has been proposed to be a major regulator of sodium and volume regulation in humans, although the data are inconsistent and controversial.20

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RENAL EFFECTS

Atrial natriuretic hormone decreases renovascular resistance in rats and dogs and increases renal blood flow. Other vascular beds do not manifest these changes. ANH produces marked natriuresis, which appears to be partly independent of the changes observed in renal blood flow and the glomerular filtration rate. In the steady state, during continuing ANH infusion, the increase in renal blood flow is not sustained, and the glomerular filtration rate becomes constant; however, there is a persistent increase in sodium excretion.21 The mechanisms whereby ANH increases natriuresis may involve intrarenal shunting of blood flow to the more salt-losing nephrons or an increase in inner medullary blood flow leading to an inner medullary washout.22 In support of the inner medullary washout theory is the observation that ANH produces a decrease in urine osmolality without a change in free water clearance. Because there are ANH receptors on renal tubules, and, at least in some cases, changes in particulate guanylate cyclase activity have been reported, ANH also may have a direct effect on the renal tubule. A physiologic function accom¬ panying these biochemical changes, however, has not been reported. VASCULAR EFFECTS

Atrial natriuretic hormone causes vasodilatation. The exact mechanisms are unclear and may depend partly on the state of sodium and volume balance before the administration of the hor¬ mone. In normotensive dogs, the fall of blood pressure seems to be caused primarily by a decrease in cardiac output, because systemic vascular resistance is not reduced.21 However, in studies using hypertensive models, such as the two-kidney Goldblatt rat in which angiotensin II is the modulator of the hypertension, a decrease in systemic vascular resistance is seen with low-dose infusion of ANH. In vitro studies supporting this observation in¬ clude the finding that ANH can antagonize the vasoconstrictive effect of angiotensin II on the rabbit aorta.21 EFFECTS ON THE RENIN-ALDOSTERONE SYSTEM

Atrial natriuretic hormone suppresses both renin release and aldosterone secretion (Fig. 173-4). In many studies, the inhibitory effect of ANH on aldosterone secretion is used as a bioassay for the hormone. The infusion of ANH causes a decrease in renin secretion in the isolated perfused rat kidney and in normal dogs.6,21 If the renin-angiotensin system is activated, ANH ap¬ pears to be less effective in suppressing renin release. The inhibition of aldosterone secretion is profound and in¬ dependent of the effect of ANH on renin release. Suppression has been observed basally, in vivo, in vitro, and when aldoste¬ rone secretion has been stimulated by angiotensin II, adrenocor¬ ticotropic hormone, or potassium.6,21,23 However, some data in normal subjects suggest that the physiologic effect of ANH on aldosterone secretion in vivo may be only marginal.24 The mech¬ anism for modifying aldosterone secretion may be related to the activation of particulate guanylate cyclase or to the inhibition of adenylate cyclase, both of which are modified by ANH in vitro in

120

140

160

Time (min)

FIGURE 173-4. Effect of synthetic atrial natriuretic hormone (ANH) on renin and aldosterone secretion in the anesthetized dog. The solid bars represent an infusion of ANH at a rate of 0.1 ^g/min/kg. (From Maack T, Marion DN, Camargo MJ, et al. Effects of auriculin (atrial natriuretic factor) on blood pressure, renal function, and the renin-aldosterone system in dogs. Am J Med 1984; 77:1069.)

glomerulosa cells.5 Moreover, perhaps by one of these two mech¬ anisms, ANH inhibits the conversion of cholesterol to pregneno¬ lone and of corticosterone to aldosterone. Thus, ANH can inhibit both the early and late pathways of aldosterone biosynthesis. BRAIN AND PITUITARY EFFECTS

Besides its major effects on vascular, renal, and adrenal function, ANH probably modifies the action of a number of other systems. The ones most extensively studied have been the brain and the pituitary. It is uncertain whether the relevant peptide in this tissue is ANH, BNP, or both. ANH receptors have been demonstrated in brain, with a high concentration of these recep¬ tors located in the anterior ventral periventricular preoptic nu¬ cleus adjacent to the wall of the third ventricle. Experimental le¬ sions in this area in rats affect fluid and electrolyte balance. Although this may be the result of interference with other sys¬ tems, it also may be caused by the reduction of an ANH effect. Also, fibers from the preoptic nucleus that stain heavily for immunoreactive ANH lead to the parabrachial nucleus, which is involved in cardiovascular regulation.19 This observation sug¬ gests that ANH may be a central nervous system (CNS) neuro¬ transmitter involved in the regulation of peripheral volume status.25 Effects of ANH on arginine vasopressin (AVP) release also have been demonstrated, although the results are conflicting. In vitro, ANH increases AVP release. On the other hand, in vivo, right atrial distention increases ANH release and reduces AVP

1490

PART X: DIFFUSE HORMONAL SECRETION

secretion.6 This maneuver causes an appropriate coordinated in¬ crease in the excretion of both sodium, by an increase in ANH, and water, by a decrease in AVP.

REGULATION OF ANH RELEASE Most data suggest that the release of ANH is regulated pri¬ marily by the degree of stretch of the right atrium.26 Although secondary regulators also may modify its response, these proba¬ bly effect changes by atrial stretch. Normal manipulations of vol¬ ume change ANH levels. Volume expansion in Sprague-Dawley rats induces a rapid diuresis accompanied by a rise in the level of plasma immunoreactive ANH. In this animal model, the diuresis and natriuresis can be inhibited if ANH antisera are injected in¬ travenously at the beginning of the volume expansion. Adrena¬ lectomy abolishes the acute natriuretic effects of ANH, which are restored partially by combined glucocorticoid and mineralocorticoid therapy. Water deprivation for 5 days leads to a significant decrease in the plasma and atrial levels of ANH, and a high so¬ dium intake produces an increase in ANH.

CIRCULATING LEVELS In normal persons, the circulating level of ANH usually is less than 15 pg/mL, using ANH!_26 as a standard. Circulating levels of pro-ANH have also been detected. Initial studies in which immunoreactive ANH was measured without extraction of plasma yielded levels 6-fold to 10-fold higher. Most assays use an extraction process before assay. The levels of ANH are not different in women and men, during the menstrual cycle, or with supine or upright posture. However, the bolus injection of so¬ dium chloride, a high-salt diet, and pregnancy (a physiologic volume-expanded state) cause an increase in the circulating lev¬ els of ANH. Thus, ANH appears to be regulated by changes in sodium and volume status. It also seems to be more responsive to acute than chronic manipulation of sodium intake. Finally, it appears less sensitive than the renin-angiotensin-aldosterone system to changes in volume manipulation. Whether this is

70

50

IR-ANH (P9/mL)

30

••

10

£

i-

NT (24)

HT (28)

-tt-

FIGURE 173-5. Plasma levels of immunoreactive atrial natriuretic hor¬ mone (IR-ANH) in 24 normotensive (NT) and 28 hypertensive (HT) pa¬ tients. (From Sagnella GA, Mnrkandu ND, Shore AC, MacGregor GA. Raised circulating levels of atrial natriuretic peptides in essential hypertension. Lan¬ cet 1986; 1:179.)

FIGURE 173-6. Immunoreactive atrial natriuretic hormone (IR-ANH) levels in normal persons on a regular diet, patients with cirrhosis, and patients with heart failure. (From Shenker Y, Sider RS, Ostafin EA, Grekin RJ. Plasma levels of immunoreactive atrial natriuretic factor in healthy sub¬ jects and in patients with edema. JClin Invest 1985;76:1684.)

caused by an inherent difference in the sensitivity of the two sys¬ tems or by differences in the reliability of the assay systems is unclear.

PATHOPHYSIOLOGY OF ANH HYPERTENSION In rats with two-kidney, one-clip hypertension (reninangiotensin Il-dependent), the infusion of ANH causes a signifi¬ cant decrease in blood pressure. A decrease in blood pressure is seen in the one-kidney, one-clip model, but to a lesser extent. The hypotensive effect of ANH in these pathologic states is greater than that seen in normotensive animals.6 Further, ANH de¬ creases blood pressure in the spontaneously hypertensive rat, but in the Dahl salt-sensitive rat, salt loading induces a greater eleva¬ tion of ANH than in control animals. Discrepancies have been reported in the levels of immuno¬ reactive ANH in patients with essential hypertension. Some studies have suggested that there is no difference; others have reported that patients with essential hypertension have signifi¬ cantly higher levels of ANH than age-, sex-, and race-matched controls.22-29 Even in these studies, however, there is consider¬ able overlap between the two groups (Fig. 173-5). A third pro¬ posed involvement of ANH in hypertension is a genetically de¬ termined deficiency in its production or effect.30 There are three hypotheses to explain the increased levels of circulating ANH in some patients with essential hypertension: a decrease in sensitivity of peripheral tissue to ANH; a compensa¬ tory increase to counteract a primary decreased ability of the kid¬ ney to excrete sodium; or a decrease in metabolic clearance. There are no convincing data to prove any of these hypotheses.

HEART FAILURE Atrial natriuretic hormone levels also have been assessed in heart failure. In hamsters with inherited cardiomyopathy and congestive heart failure, a decrease in bioassayable atrial ANH and increased ventricular ANH have been reported.31 This de¬ crease in ANH may reflect the depletion of ANH caused by an increased release in response to heart failure or a primary reduc¬ tion in ANH synthesis. The second possibility would implicate

Ch. 173: The Endocrine Heart ANH as a culprit in the pathogenesis of the heart failure. Several studies have reported increased levels of ANH in patients with heart failure, although there is considerable overlap with normal control subjects (Fig. 173 - 6).32,33 Although it is uncertain whether the degree of ANH elevation is appropriate for the degree of vol¬ ume overload, there are no consistent data suggesting that pa¬ tients with heart failure have a deficiency of ANH as a com¬ pounding factor in their abnormal sodium and volume status. Several case reports have documented that paroxysmal atrial tachycardia induces substantial increases in plasma immunoreactive ANH.34 An elevated plasma ANH level has been suggested to be a useful predictor of cardiac recovery after right ventricular in¬ farction.35 In patients with cardiac arrest, high ANP levels blunted pressor response during cardiopulmonary resuscitation.

CONCLUSION Atrial natriuretic hormone has acute effects on the kidney, causing natriuresis and diuresis; chronic effects on the reninaldosterone system, which also could produce natriuresis; effects on the vasculature leading to decreased blood pressure; and pos¬ sible CNS effects, which would provide for CNS modulation of cardiovascular function. The widespread systemic effects of ANH make it an excellent candidate for a multisystem regulator of volume status. However, several lines of evidence cast doubt on its relative importance in this complex process in humans. Further studies will be necessary to resolve this question.

22. Raine AEG, Ledingham JGG. Renal actions of atrial natriuretic factor. Clin Sci 1989; 76:1. 23. Atarashi K, Mulrow PJ, Franco-Saenz R. Effect of atrial peptides on aldo¬ sterone production. J Clin Invest 1985; 76:1807. 24. Bahr V, Sander-Bahr C, Ardevol R, et al. Effects of atrial natriuretic factor on the renin aldosterone system: in vivo and in vitro studies. J Steroid Biochem Mol Biol 1993; 45:173. 25. Sakamoto M, Tanaka I, Oki Y, et al. Atrial natriuretic peptide and vaso¬ pressin in human plasma. Peptides 1988;9:187. 26. Christensen G. Release of atrial natriuretic factor. Scand J Clin Lab Invest 1993;53:91. 27. Goetz KL. Physiology and pathophysiology of atrial peptides. Am J Phys¬ iol 1988;254:E1. 28. Sagnella GA, Markandu ND, Shore AC, MacGregor GA. Raised circulat¬ ing levels of atrial natriuretic peptides in essential hypertension. Lancet 1986; 1:179. 29. Nicholls MG, Espiner EA, Ikram H, et al. Atrial natriuretic peptide in human hypertension. Eur Heart J 1987;8:123S. 30. Weldmann P, Ferrari P, Allemann Y, et al. Development of essential hy¬ pertension: a syndrome involving ANF deficiency? Can J Physiol Pharmacol 1991;69:1582. 31. Franch HA, Dixon RAF, Blaine EH, Siegl PKS. Ventricular atrial natri¬ uretic factor in the cardiomyopathic hamster model of congestive heart failure. Circ Res 1988; 62:31. 32. Shenker Y, Sider RS, Ostafin EA, Grekin RJ. Plasma levels of immunore¬ active atrial natriuretic factor in healthy subjects and in patients with edema. J Clin Invest 1985; 76:1684. 33. Brandt RR, Wright RS, Redfield MM, Burnett JC Jr. Atrial natriuretic pep¬ tide in heart failure. J Am Coll Cardiol 1993;22:86A. 34. Zullo MA. Atrial regulation of intravascular volume: observations on the tachycardia-polyuria syndrome. Am Heart J1991; 122:188. 35. Yasuda S, Nonogi H, Miyazaki S, et al. Coronary reperfusion enhances recovery of atrial natriuretic peptide secretion. Circulation 1994; 89:558.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

REFERENCES 1. Henry JD, Gauer OH, Reeves JL. Evidence of the atrial location of receptors influencing urine flow. Circ Res 1956;4:85. 2. Forssmann WG, Hock D, Lottspeich F, et al. The right auricle of the heart is an endocrine organ. Anat Histol Embryol 1983; 168:307. 3. DeBold AJ. Heart atria granularity: effects of changes in water-electrolyte balance. Proc Soc Exp Biol Med 1979; 161:508. 4. DeBold AJ, Borenstein HB, Veress AT, Sonnenberg H. A rapid and potent natriuretic response to intravenous injection of atrial myocardial extract in rats. Life Sci 1981; 28:89. 5. Rosenblatt M, Jacobs JW, eds. Atrial natriuretic factor. Endocrinol Metab Clin North Am 1987; 16:63. 6. Trippolo NC, MacPhee AA, Cole FE. Partially purified human and rat atrial natriuretic factor. Hypertension 1983;5:81. 7. Cantin M, Genest J. The heart and the atrial natriuretic factor. Endocr Rev 1985;6:107. 8. Maack T, Camargo MJF, Kleinert HD, et al. Atrial natriuretic factor: struc¬ ture and functional properties. Kidney Int 1985;27:607. 9. Goetz KL. Renal natriuretic peptide (urodilatin?) and atriopeptin: evolving concepts. Am J Physiol 1991; 261 :F921. 10. Nemer M, Chamberland M, Sirois D, et al. Gene structure of human cardiac hormone precursor, pronatriodilatin. Nature 1984; 312:654. 11. Greenberg BD, Bencen GH, Seilhamer JJ, et al. Nucleotide sequence of the gene encoding human atrial natriuretic factor precursor. Nature 1984; 312:656. 12. Lang RE, Tholken H, Ganten D, et al. Atrial natriuretic factor: a circulat¬ ing hormone stimulated by volume loading. Nature 1985;314:264. 13. Yamaji TY, Ishibashi M, Takaku F. Atrial natriuretic factor in human blood. J Clin Invest 1985;76:1705. 14. Sagnella GA, Makandu ND, Shore AC, MacGregor GA. Effects of changes in dietary sodium intake and saline infusion on immunoreactive atrial na¬ triuretic peptide in human plasma. Lancet 1985;2:1208. 15. Christensen G. Cardiovascular and renal effects of atrial natriuretic fac¬ tor. Scand J Clin Lab Invest 1993;53:203. 16. Jamison RL, Canaan-Kuhl S, Pratt R. The natriuretic peptides and their receptors. Am J Kidney Dis 1992; 20:519. 17. Edwards BS, Ackermann DM, Lee ME, et al. Identification of atrial natri¬ uretic factor within ventricular tissue in hamsters and humans with congestive heart failure. J Clin Invest 1988;81:82. 18. Yoshinaga K, Yamaguchi K, Abe K, et al. Production of immunoreactive atrial natriuretic polypeptide in neuroendocrine tumors. Cancer 1994; 73:1292. 19. Morel G, Chabot J-G, Belles-Isles M, Heisler S. Synthesis and internaliza¬ tion of atrial natriuretic factor in anterior pituitary cells. Mol Cell Endocrinol 1988; 55:219. 20. Goetz KL. Evidence that atriopeptin is not a physiological regulator of sodium excretion. Hypertension 1990; 15:9. 21. Cole BR, Needleman P. Atriopeptins: volume regulatory hormones. Clin Res 1985;33:389.

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CHAPTER

174_

THE ENDOCRINE ENDOTHELIUM THOMAS F. LUSCHER, RAGHVENDRA K. DUBEY, AND GEORG NOLL Apart from hormones generated from “classic” endocrine glands, several other cells, such as the vascular endothelium, are capable of generating substances that can circulate and affect neighboring smooth-muscle cells and blood cells. Hence, the en¬ dothelium acts as an important regulatory organ within the cir¬ culation by generating several vasoactive substances that act in a paracrine, autocrine, solinocrine, and, under certain conditions, hemocrine fashion (see Chap. 1). Critically located as a barrier between smooth-muscle cells and the blood, the endothelium plays a pivotal functional role in maintaining the homeostasis of the normal vessel by generating substances that modulate vascular tone, as well as growth, coag¬ ulation, platelet function, and the release of circulating hor¬ mones.1 Furthermore, the endothelium is a target organ in car¬ diovascular disease (Tables 174-1 and 174-2).

TABLE 174-1 Cardiovascular Diseases Associated With Abnormal Nitric Oxide Levels Atherosclerosis Microvascular angina Essential hypertension Diabetes mellitus Endotoxic shock Impotence

1492

PART X: DIFFUSE HORMONAL SECRETION

TABLE 174-2 Cardiovascular Diseases Associated With Elevated Endothelin Levels Acute myocardial infarction Atherosclerosis Cardiogenic shock Cerebral/myocardial vasospasm Congestive heart failure Endotoxic shock Hypertension Pulmonary hypertension Raynaud phenomenon

Endothelial cells can produce and release a variety of vaso¬ active substances1 (Fig. 174-1): (1) endothelium-derived relaxing factors (EDRFs), such as nitric oxide (NO), endothelium-derived hyperpolarizing factor, and prostacyclin, as well as other prosta¬ glandins; and (2) endothelium-derived contracting factors, in¬ cluding cyclooxygenase-derived contracting factors, endothelins, and, possibly, angiotensin II, either produced locally or taken up from the circulation.

ENDOTHELIUM-DERIVED RELAXING FACTORS Endothelium-Derived Nitric Oxide. In the presence of endo¬ thelium, acetylcholine induces relaxation, which cannot be pre¬ vented by the use of inhibitors of cyclooxygenase which blocks prostacyclin production, suggesting that a new EDRF must be

FIGURE 174-1.

involved.2 Endothelium-dependent relaxations have been dem¬ onstrated in large (conduit) arteries and in resistance vessels of most mammalian species, including humans.1,3'4 The release of EDRF can be demonstrated under basal conditions: in response to mechanical forces such as shear stress (exerted by the circulating blood)5,6 and after activation of receptor-operated mechanisms by acetylcholine, neurotransmitters, various local and circulating hormones, and substances derived from platelets and the coagu¬ lation system3,4 (see Fig. 174-1). EDRF is a diffusible substance with a half-life of a few seconds that has been identified as NO.7,8 Relaxation of smooth-muscle cells by endothelium-derived NO (EDNO) is associated with activation of soluble guanylyl cy¬ clase and an increase in intracellular cyclic 3'5'-guanosine mono¬ phosphate (cGMP) in vascular smooth muscle9 (see Fig. 174-1). The inhibitor of soluble guanylate cyclase, methylene blue, pre¬ vents the production of cGMP and inhibits endotheliumdependent relaxations. Soluble guanylate cyclase is also present in platelets and activated by EDNO1" (see Fig. 174-1). Increased levels of cGMP in platelets are associated with reduced adhesion and aggregation. Therefore, EDNO causes both vasodilatation and platelet deactivation and, thereby, represents an important antispastic and antithrombotic feature of the endothelium. EDNO is formed from L-arginine by oxidation of the guanidino-nitrogen terminal of L-arginine11 (see Fig. 174-1). NO synthase has been cloned12; it is primarily a cytosolic enzyme re¬ quiring calmodulin, Ca2+, and /3-nicotinamide adenine dinucleo¬ tide hydrogen phosphate, reduced form (NADPH), and has sim¬ ilarities with cytochrome P-450 enzymes. Several isoforms of the enzyme occur in endothelial cells, as well as in platelets, macro¬ phages, vascular smooth-muscle cells, and the brain.

Endothelium-derived vasoactive substances. The endothelium releases relaxing factors (right) and contracting factors (left). The relaxing factors include nitric oxide (NO), prostacyclin (PG12), and endothelium-derived hyperpolarizing factor (EDHF). NO and PGI2 cause not only relaxation, but also inhi¬ bition (©) of platelet function. The contracting factors include the local vascular renin-angiotensin (AT) system, endothelin (ET), and cyclooxygenase-derived contracting factors such as thromboxane A2 (TXA2) and prostaglandin H2 (PGH2). In addition, the cyclooxygenase pathway is a source of oxygen-derived free radicals (02). Circles represent receptors. A, angiotensin receptor; AA, arachidonic acid; ADP, adenosine diphosphate; ATP, adenosine triphosphate; ATG, angiotensinogen; ACE, angiotensin converting enzyme; Ach, acetylcholine; BK, bradykinin; B2, bradykinin receptor; cAMP, cyclic adenosine monophosphate; cGMP, cyclic guanosine monophosphate; ECE, endothelin converting enzyme; 5-HT, serotonin; T, thrombin recep¬ tor; TGFp transforming growth factor /31; Thr, thrombin. (From Liischer TF, Boulanger CM, Dohi Y, Yang Z. Endothelium-derived contracting factors. Hypertension 1992;19:117.)

i,

Ch. 174: The Endocrine Endothelium Analogues of L-arginine, such as L-NG-monomethyl argi¬ nine (l-NMMA), or L-nitroarginine methylester (L-NAME) in¬ hibit endothelium-dependent relaxations to serotonin in porcine coronary arteries, an effect that is restored by L-arginine but not by D-arginine.13 In quiescent arteries, L-NMMA causes endothe¬ lium-dependent contractions.14 In intact organs, L-NAME mark¬ edly decreases local blood flow.15 When infused in rabbits, larginine methylester induces long-lasting increases in blood pressure that are reversed by L-arginine.16 This demonstrates that the vasculature is in a constant state of vasodilation because of the continuous basal release of NO from the endothelium. Of particular pathophysiologic interest is the discovery of an endog¬ enous inhibitor of the L-arginine NO pathway known as asym¬ metric dimethyl-arginine,17 which is also produced by cultured endothelial cells. This indicates that endogenously produced substances can regulate the activity of this pathway both locally and systemically (it is also detected in plasma). Hence, increased production or elimination of this endogenous inhibitor can pro¬ foundly affect the function of the cardiovascular system (e.g., in patients with renal failure). Endothelium-Derived Hyperpolarizing Factors. In the porcine coronary circulation, L-NMMA inhibits relaxations to serotonin but only slightly inhibits those to bradykinin.12,13 Other inhibi¬ tors of the action of EDNO, such as hemoglobin and methylene blue, as well as inhibitors of cyclooxygenase, also are ineffective. Thus, endothelial cells appear to release a relaxing factor distinct from NO and prostacyclin. Acetylcholine causes not only endo¬ thelium-dependent relaxation, but also endothelium-dependent hyperpolarization of vascular smooth muscle.18 An endotheliumdependent hyperpolarizing factor (see Fig. 174-1) distinct from NO could explain these responses, although NO also has been shown to have hyperpolarizing properties under certain condi¬ tions. The endothelium-derived hyperpolarizing factor appears to activate adenosine triphosphate-sensitive K+ channels,19 but its chemical nature remains elusive. Prostacyclin. Endothelial cells are an important source of prostacyclin, which is synthesized within the vasculature in re¬ sponse to shear stress, hypoxia, and several mediators also lead¬ ing to the formation of EDNCh0 (see Fig. 174-1 and Chap. 170). Prostacyclin causes relaxation by increasing cyclic 3',5'-adenosine monophosphate (cAMP) in smooth muscle and platelets,21 where it also inhibits platelet aggregation, particularly together with NO.

ENDOTHELIUM-DERIVED CONTRACTING FACTORS Cyclooxygenase-Dependent Endothelium-Derived Contracting Factor. Exogenous arachidonic acid can evoke endotheliumdependent contractions prevented by indomethacin (an inhibi¬ tor of cyclooxygenase).122 In the human saphenous vein, acetylcholine and histamine evoke endothelium-dependent contractions; in the presence of indomethacin, however, endothelium-dependent relaxations are unmasked.23 The prod¬ ucts of cyclooxygenase-mediated contractions are thromboxane A2, in the case of acetylcholine, and endoperoxides (prostaglan¬ din H2), in the case of histamine.23 Thromboxane A2 and endoperoxide activate both vascular smooth muscle and platelets, thereby counteracting the protective effects of NO and prostacy¬ clin in the blood vessel wall (see Fig. 174-1). The cyclooxygenase pathway is a source of superoxide an¬ ions that can mediate endothelium-dependent contractions ei¬ ther by the breakdown of NO or by a direct effect on vascular smooth muscle.1,24 Thus, the cyclooxygenase pathway produces a variety of endothelium-derived contracting factors; their re¬ lease appears particularly prominent in veins and in the cerebral and ophthalmic circulation (see Chap. 170).

1493

Endothelin. Endothelial cells produce the 21-amino acid peptide endothelin25 (Fig. 174-2). Among the three peptides— endothelin-1, endothelin-2, and endothelin-3—endothelial cells appear to produce exclusively endothelin-1. The translation of mRNA generates preproendothelin, which is converted to big endothelin; its conversion to endothelin1 by the endothelin converting enzyme is necessary for the de¬ velopment of full vascular activity.25 The expression of mRNA and the release of the peptide is stimulated by thrombin, transforming growth factor-/?, interleukin-1, epinephrine, angio¬ tensin II, arginine vasopressin, calcium ionophore, and phorbol ester.25-28 In addition, hypoxia stimulates the release of endo¬ thelin in isolated vessels.29 Endothelin-1 is a potent vasoconstrictor both in vitro and in vivo.25,30 In the human heart, eye, and forearm, endothelin causes vasodilation at lower concentrations and marked contrac¬ tions at higher concentrations.1,15,31 In the heart, this may lead to ischemia, arrhythmias, and death. Circulating levels of endothelin-1 are low,25 suggesting that little of the peptide is formed under physiologic conditions be¬ cause of the absence of stimuli or the presence of potent inhibi¬ tory mechanisms. Alternatively, it may be released preferentially toward smooth-muscle cells.2125 Possible pathways involved in regulating the mechanism of endothelin production are (1) cGMP-dependent27,32; (2) cAMP-dependent33; and (3) an inhibi¬ tory factor produced by vascular smooth-muscle cells.34 Further¬ more, endothelin can release NO and prostacyclin from endothe¬ lial cells, which may represent a negative feedback mechanism.35 EDNO also modulates the actions of endothelin at the level of vascular smooth muscle. The contractions in response to endo¬ thelin are enhanced after endothelial removal, indicating that basal production of EDNO reduces its response.30 Stimulation of the formation of EDNO by acetylcholine reverses endothelin induced contractions in most blood vessels, although this mech¬ anism appears to be less potent in veins.30 Three distinct endothelin receptors have been cloned, the ETa-, ETb-, and ETc-receptors.36-38 Endothelial cells express ETBreceptors linked to the formation of NO and prostacyclin, which may explain the transient vasodilator effects of endothelin when it is infused in intact organs or organisms. In vascular smooth muscle, ETa- and, partly, ETB-receptors mediate contraction and proliferation. ETB-receptors equally bind endothelin-1 and endo¬ thelin-3, whereas ETA-receptors preferentially bind endothelin1. Several endothelin antagonists lower blood pressure, suggesting that endothelin may contribute to blood pressure regulation.39 Angiotensins. Angiotensin II is a vasoactive octapeptide formed from its inactive decapeptide precursor, angiotensin I, by the action of a dipeptidyl carboxypeptidase, angiotensin convert¬ ing enzyme, which also is present on endothelial cells40 (see Fig. 174-1 and Chap. 77). Possible local angiotensin II synthesis in the vascular wall is of special interest in view of the multiple vascular actions of angiotensin II. Angiotensin II not only exerts a direct vasoconstrictor effect, but also enhances sympathetic noradrenergic transmission,41 exhibits mitogenic and trophic ac¬ tions in the vasculature,42 and induces endothelin synthesis.28 Hence, vascular or endothelial angiotensin converting enzyme activity may play an important role in regulating normal vascular function.

Endothelin-1:

CSCSSLMDKECVYFCHLDIIW

Endothelin-2:

CSCSSWLDKECVYFCHLDIIW

Endothelin-3:

CTCFTYKDKECVYYCHLDIiW

FIGURE 174-2.

The structures of the three 21-amino acid human endothelins. Complete sequence homologies between the three peptides are underlined. Amino acids are designated by standard one-letter ab¬ breviations (see Chap. 161, Table 161-2 for the key for these amino acid abbreviations).

1494

PART X: DIFFUSE HORMONAL SECRETION

AUTOCRINE AND PARACRINE REGULATION OF VASCULAR STRUCTURE The endothelium produces several factors that regulate the proliferation and migration of underlying smooth-muscle cells43'44 (Fig. 174-3). Denudation of endothelial cells is followed by platelet adhesion and aggregation, resulting in the release of platelet-derived growth factor and other mitogens. These events result in the migration and proliferation of vascular smoothmuscle cells and strongly suggest that the endothelium normally has a net inhibitory influence on these responses (see Fig. 174-3, left panel). The endothelium synthesizes substances, in¬ cluding heparan sulfate, NO, and prostaglandins, that inhibit the growth of smooth-muscle cells, which may explain why vascular structure normally remains stable43-46 (see Fig. 174-3, left panel). Under certain conditions, the endothelium can generate sub¬ stances such as platelet-derived growth factor, basic fibroblast growth factor, insulin-like growth factor I, colony-stimulating factor I, endothelin-1, transforming growth factor-/?, interleukin1, and tumor necrosis factor-a that can either induce proliferation by themselves or stimulate growth factor gene expression in smooth-muscle cells43'44'47 (see Fig. 174-3, right panel). In addi¬ tion, endothelial dysfunction is associated with adhesion of cir¬ culating blood cells, such as platelets and monocytes, which also are an important source of growth factors. Endothelial dysfunction in certain disease states could mark¬ edly alter the effects of endothelial cells on the behavior of smooth-muscle cells and contribute to changes in vascular struc¬ ture. Structural abnormalities of the media of large conduit and resistance arteries are involved in the pathophysiology of hyper¬

tension. In large conduit arteries, intimal thickening and athero¬ sclerosis are important consequences of hypertension and other cardiovascular risk factors, which are responsible for cardiovas¬ cular complications such as myocardial infarction and stroke (see later). Hypertensive resistance arteries exhibit an increased media-lumen ratio, which primarily involves the migration and rearrangement of vascular smooth- muscle cells within the media (i.e., remodeling), contributing to the increase in peripheral vas¬ cular resistance in hypertension. Although unknown, an imbal¬ ance in the production of endogenous inhibitors of migration and proliferation, and of promoters of these responses by endothelial cells could partially explain these structural vascular changes oc¬ curring in hypertension.

HEMOCRINE EFFECTS OF ENDOTHELIAL MEDIATORS The endothelium-derived mediators can affect the produc¬ tion of circulating hormones and, at least in certain disease states, increased production of these substances allows them to act as humoral factors (Fig. 174-4). Renin-Angiotensin System. In isolated renal tissue, NO, re¬ leased either from isolated canine blood vessels or from cultured porcine endothelial cells, inhibits renin production.48 Together with the NO that is released in response to shear stress, this mechanism could regulate renin secretion in response to changes in local hemodynamics and, hence, may act as an intrarenal baroreceptor.1 Endothelin inhibits renin production in vitro49 in iso¬ lated glomeruli of the rat,49 but augments renin production mark-

’cGMPc£Mp ©ft Gf)

ED5> PGh

(inactive) Thr. A

rTGFR

Platelets

Endothelium

TTJ bFGF PDGF ET HS/HP

Smooth muscle cells

EDNO TGFI3

PDGF ET EDNO ^*(TGFf3) ®

©

®

HS/HP

PDGF

Smooth muscle cells

FIGURE 174-3. Endothelium-derived vasoactive factors and vascular growth. The endothelium produces growth inhibitors such as heparin (HP), heparan sulfate (HS), transforming growth factor-/3 (TGF/1), and nitric oxide {EDNO). It releases endothelium-derived growth promoters such as platelet-derived growth factor {PDGF), thrombospondin (TS), and endothelin (ET). At sites of damaged endothelium, the production of EDNO and prostacyclin (PGJ2) is diminished, favoring platelet adhesion and aggregation. PDGF is re¬ leased by aggregating platelets and leads to proliferation as well as migration of vascular smooth muscle cells into the intima. The endothelium most probably takes part in these structural changes of the vascular wall, at least indirectly, by inhibiting platelet aggregation and, with that, the release of growth-stimulating factors. bFGF, basic fibroblast growth factor; cAMP, cyclic adenosine monophosphate; cGMP, cyclic guanosine monophosphate. {From Liischer TF, Tanner FC. Endothelial regulation of vascular tone and growth. Am J Hypertens 1993;6:283S.)

Ch. 174: The Endocrine Endothelium ET

FIGURE 174-4.

Endocrine actions of endothelium-derived mediators. Nitric oxide (NO) and endothelin (ET) can affect various endocrine regu¬ lators of the cardiovascular system, such as the renin-angiotensin (A) sys¬ tem, atrial natriuretic factor (ANF), the hypophysis, and the adrenal glands. ACE, angiotensin converting enzyme; ACTH, adrenocorticotropic hormone; AVP, arginine vasopressin; E, epinephrine; NE, norepineph¬ rine; PGH2, prostaglandin H2; PG12, prostacyclin.

edly in vivo because of the pronounced renal vasoconstriction.50 However, angiotensin II, which is the final product of the reninangiotensin system, stimulates endothelin production in endo¬ thelial cells in culture,26 as well as in intact blood vessels.28 Atrial Natriuretic Peptide. In the atrium of the rat, removal of the endocardium augments the basal release of atrial natriuretic peptide51 (ANP; see chap 173). A similar effect can be obtained with inhibitors of EDNO, suggesting that the endothelium acts as an inhibitor of the myocardial production of ANP. Endothelin1, however, is a potent secretagogue for ANP in cultured rat atrial myocytes.52 ANP released from myocytes can increase cGMP in the endothelium and, in turn, inhibit the release of endothelin-1 and, possibly, NO.32 Pituitary Hormones. Endothelin is produced by neuronal cells and also is found in human cerebrospinal fluid, suggesting that it acts as an important mediator in the central nervous sys¬ tem. In humans, intravenous administration of endothelin-1 in¬ creases basal plasma concentrations of corticotropin, whereas those of prolactin, thyrotropin, luteinizing hormone, folliclestimulating hormone, and growth hormone remain unchanged.53 However, stimulated serum concentrations of luteinizing hor¬ mone and follicle-stimulating hormone tend to be higher in the presence of endothelin infusion, whereas the peptide exerts a suppressive action on stimulated plasma concentrations of pro¬ lactin and growth hormone. In addition, endothelin-1 reduces the antidiuretic effects of arginine vasopressin in vivo. Catecholamines. The addition of endothelin-1 to primary cultures of bovine adrenal chromaffin cells augments the efflux of norepinephrine and epinephrine.54 In contrast, endothelin in¬ hibits adrenergic neurotransmission in the guinea pig femoral ar¬ tery.55 In adrenocortical glomerulosa cells, endothelin-1 stimu¬ lates aldosterone release.56

ENDOTHELIUM DYSFUNCTION IN HYPERTENSION Abnormal vascular tone and growth are important in the pathophysiology of hypertension and atherosclerosis.1 The en¬

1495

dothelium is critically involved in this process because several vasoactive factors generated by the endothelium influence these characteristics in an autocrine or paracrine fashion. In hyperten¬ sion, certain morphologic and functional alterations of the endo¬ thelium occur.1 Endothelial cells of hypertensive vessels have an increased volume and bulge into the lumen, and the subintimal space exhibits structural changes, with increased fibrin and cell deposition. Furthermore, the interaction of platelets and mono¬ cytes with the endothelium is increased as compared to normotensive control subjects. Endothelium-Dependent Relaxations. Endothelium-depen¬ dent relaxations to acetylcholine are reduced in the aortic, cere¬ bral, and peripheral microcirculations of most experimental models of hypertension.57-59 Similarly, the vasodilator effects of acetylcholine in the human forearm of hypertensive subjects have been found to be blunted in most studies.60-65 In the coro¬ nary circulation of the spontaneously hypertensive rat (SHR), lit¬ tle endothelial dysfunction occurs.66 In the human coronary circulation, however, endothelium-dependent responses are impaired in epicardial and microvessels in patients with hy¬ pertension, particularly in the presence of left ventricular hyper¬ trophy.67 As it does under most circumstances, the response to the direct vasodilator sodium nitroprusside remains preserved, and the impaired responses to acetylcholine must be related to alterations in endothelial function. In experimental animals, the degree of impairment of endothelium-dependent responses is positively correlated with the level of blood pressure and seems to increase as a function of the severity and duration of hypertension.68 This suggests that most of the endothelial dysfunction in hypertension is a conse¬ quence rather than a cause of the high blood pressure. As in perfused mesenteric resistance arteries of the SHR, endotheliumdependent relaxations are reduced on intraluminal but not extra¬ luminal application of acetylcholine.69 Thus, the intraluminal surface of the endothelium, which is most exposed to blood pres¬ sure, is particularly susceptible to endothelial dysfunction. The mechanisms that may be responsible for impaired endothelium-dependent responses in hypertension include1 (Fig. 174-5) (1) decreased release of EDNO; (2) decreased release of other endothelium-derived vasodilator substances, such as endothelium-dependent hyperpolarizing factor or prostacyclin; (3) impaired diffusion of these substances from the endothelium to the vascular smooth-muscle cells; (4) decreased responsive¬ ness of the vascular smooth-muscle cells to vasodilator sub¬ stances; or (5) augmented release of endothelium-derived con¬ tracting factors. Formation of Nitric Oxide. The basal formation of NO is re¬ duced in established, but not in early, hypertension of SHRs,69 renovascular hypertensive rats,70 and ren-2 transgenic rats70 71 (see Fig. 174-5). In patients with essential hypertension, infusion of l-NMMA into the brachial artery causes less vasoconstriction (or decreases in forearm blood flow) in those who are hyperten¬ sive as compared to those who are normotensive, although the response to phenylephrine is comparable.72 73 This suggests that there is reduced basal formation of NO in human essential hypertension. In patients with hypertension, the endothelium-dependent vasodilation to acetylcholine is improved after treatment with a cyclooxygenase inhibitor.63 However, because inhibition of cyclooxygenase-derived contracting factors does not fully nor¬ malize endothelium-dependent vasodilation in hypertensive subjects, an additional defect that involves the L-arginine-NO pathway is implicated. In patients with essential hypertension, treatment with L-arginine does not affect the response to acetyl¬ choline,73 suggesting that the defect involves either the uptake of the precursor of NO or another pathway (i.e., endotheliumdependent hyperpolarizing factor; see earlier). Endothelium-Dependent Contractions. Although it is com¬ monly assumed that impaired endothelium-dependent relax-

1496

PART X: DIFFUSE HORMONAL SECRETION thelin production. In mesenteric resistance arteries of DOC A (desoxycorticosterone acetate)-salt hypertensive rats, but not in SHRs, increased production of endothelin occurs in the presence of normal circulating levels of the peptide. In contrast to the direct contractile responses to endothelin, the potentiating properties of low and threshold concentrations of endothelin are increased with aging and hypertension,25'28 in¬ dicating that this indirect amplifying effect of endothelin could contribute to increased vascular contractility as pressure rises and the blood vessel wall ages. In addition, the expression of ETAand ETB-receptors appears to be tissue-specific in hypertensive rats.74

ENDOTHELIUM-DEPENDENT RESPONSES IN ATHEROSCLEROSIS

FIGURE 174-5. Endothelial dysfunction in hypertension. In hyperten¬ sion, the basal formation of nitric oxide (NO) appears to be reduced, whereas the stimulated formation of NO appears to be impaired in more advanced hypertension. In addition, the hypertensive endothelium can form cyclooxygenase-derived contracting factor (prostaglandin H2 [PGH2]). The effects of endothelin (ET-I) in hypertension are controver¬ sial. Normal circulating levels have been most commonly reported. The vascular responsiveness to ET-1 can be reduced, normal, or increased. The concomitant reduced formation and responsiveness of vascular smooth muscle to endothelium-derived NO leads to an imbalance be¬ tween NO and endothelium-derived contracting factors, which may con¬ tribute to the increased peripheral vascular resistance and complications of hypertension. 5-HT, serotonin; Ach, acetylcholine; L-arg, L-arginine; AA, arachidonic acid; cGMP, cyclic guanosine monophosphate; ATP, adenosine monophosphate; ADP, adenosine diphosphate. Circles repre¬ sent receptors. ETA, ETA receptor; ETB, ETB receptor; M, muscarinic re¬ ceptor; P2, purinergic receptor; S,, serotonergic receptor; Tx, thromboxane receptor. (Prom Liischer TF, Boulanger CM, Dohi Y, Yang Z. Endotheliumderived contracting factors. Hypertension 2992; 29:2 2 7.)

ations are primarily related to reduced release of NO, they may also be caused by increased production of endothelium-derived contracting factors57 (Fig. 174-6). In the SHR, the reduced re¬ sponse to acetylcholine in the aorta is related to the production of prostaglandin H2. In the circulation of the human forearm, impaired vasodilation to acetylcholine is improved (although not normalized) by pretreatment with indomethacin (a cyclooxygen¬ ase inhibitor) in patients with essential hypertension,73 suggest¬ ing that increased production of prostaglandin H2 or another cyclooxygenase-derived contracting factor contributes to im¬ paired endothelium-dependent vascular regulation in human hypertension. The fact that platelets and platelet-derived prod¬ ucts (i.e., adenosine diphosphate-adenosine triphosphate, sero¬ tonin) are able to stimulate the formation of this contracting fac¬ tor58 strongly suggests that this form of endothelial dysfunction may also contribute to complications of hypertension (i.e., stroke, myocardial infarction). Endothelin. Circulating levels of endothelin typically are not increased in experimental or human hypertension25 (see Fig. 174-5). This suggests that at least the luminal release of the pep¬ tide into the circulation is unaltered except in the presence of vascular disease (i.e., atherosclerosis) or renal failure. However, because more than twice as much endothelin is released abluminally as into the lumen,21 measurement of circulating endothelin levels may not be appropriate to determine local vascular endo¬

Hyperlipidemia. Morphologically, the endothelium remains intact in the prestage of atherogenesis.75 Functional alterations occur in the early human atherosclerotic lesions associated with the presence of oxidized low-density lipoproteins (OX-LDLs).76 In isolated porcine coronary arteries, endothelium-depen¬ dent relaxations to platelets, serotonin, and thrombin are inhib¬ ited by OX-LDLs.77 78 In contrast, relaxations to the NO-donor linsidomine are maintained, excluding reduced responsiveness of smooth muscle to EDNO. This inhibition is specific for OXLDLs because it is not induced by comparable concentrations of native low-density lipoproteins. 7 The inhibitor of NO produc¬ tion, l-NMMA, exerts a similar inhibitory effect on endotheliumdependent relaxations as do the modified lipoproteins, suggest¬ ing that OX-LDLs interfere with the L-arginine pathway. The activity of NO synthase appears to remain unaffected, however, because L-arginine evokes full relaxation in vessels treated with OX-LDLs. Pretreatment of isolated vessels with L-arginine im¬ proves the reduced endothelium-dependent responses to seroto¬ nin.79 Thus, OX-LDLs may interact with the intracellular signal transduction mechanisms (e.g., the function of Grproteins)80 or the availability of L-arginine77 (see Fig. 174-6). Similarly, in hypercholesterolemic pigs, in vivo inhibition of endotheliumdependent relaxation to serotonin occurs in coronary arteries ex¬ posed to OX-LDLs.81 Furthermore, in humans with hypercholes¬ terolemia, L-arginine infusion augments the blunted increase in local blood flow in response to acetylcholine.82 In addition to their effect on the L-arginine pathway, both native lowdensity lipoproteins and OX-LDLs inactivate NO and cause endothelium-dependent,79 as well as endothelium-independent, contraction. OX-LDLs induce mRNA expression and endothelin release84 (see Fig. 174-6). Threshold and low concentrations of endothelin potentiate contractions induced by serotonin in the human coro¬ nary artery. Similarly, endothelin-1 potentiates norepinephrine and serotonin induced contractions in the human internal mam¬ mary artery. Thus, even small increases in local endothelin levels may be important.85 Atherosclerosis. Atherosclerosis is associated with severe morphologic changes of the intima of large arteries (i.e., intimal thickening, proliferation of smooth-muscle cells, accumulation of lipid-containing macrophages).75 However, endothelial denuda¬ tion does not occur, except at late stages. In porcine coronary arteries, established atherosclerosis se¬ verely impairs endothelium-dependent relaxations to serotonin and also reduces endothelium-dependent relaxations to bradykinin in the presence of hypercholesterolemia.81 However, endothelium-independent relaxations to nitrovasodilators re¬ main preserved, except in severely atherosclerotic arteries. Sim¬ ilarly, in atherosclerotic human coronary arteries, endotheliumdependent relaxations to substance P, bradykinin, aggregating platelets, and calcium ionophores are attenuated,86 and in vivo acetylcholine causes paradoxic vasoconstriction.

Ch. 174: The Endocrine Endothelium 5-HT

ox LDL

native LDL

BK

SIN-1

5-HT

1497

Tx A2

FIGURE 174-6. Schematic representation of the effects of low-density lipoproteins (LDL) in the blood vessel wall. Most likely, oxidation of LDL is an important step in the dysfunction of the endothelium in hyperlipidemia and atherosclerosis. Oxidized low-density lipoproteins (ox LDL) may interact with the intracellular availability of L-arginine (L-ARG) and the G-protein (G,) of the serotonergic receptor (Si), and they may also inactivate nitric oxide (NO). In addition, ox LDL can increase the endothelial produc¬ tion of endothelin-1 by protein kinase C. 5-HT, serotonin; TxA2, thromboxane A2; EDRF, endotheliumderived relaxing factor; cGMP, cyclic guanosine monophosphate; BK, bradykinin; SIN-1, molsidomine (nitric acid donor).

Controversy exists regarding the mechanism responsible for the marked impairment or loss of endothelium-dependent relax¬ ations in atherosclerosis. EDRF release as measured by bioassay in porcine coronary arteries with hypercholesterolemia and ath¬ erosclerosis is reduced.81 Direct measurements of NO in the rab¬ bit aorta, however, suggest increased formation of NO with con¬ comitant massive breakdown of the endogenous nitrovasodilator (to the biologically inactive nitrite and nitrate).87 This observation suggests that increased formation of superoxide radicals and other products in the endothelium inactivates NO, possibly as a result of decreased activity of superoxide dismutase in the ath¬ erosclerotic blood vessel wall. Increased circulating levels of endothelin are associated with human atherosclerosis,88 and the circulating in endothelin levels correlate positively with the degree of atherosclerotic disease and the number of vascular beds involved. The increased endothelin production is derived not only from endothelial cells of athero¬ sclerotic blood vessels, but also from vascular smooth-muscle cells migrating into the intima. Increased local levels of endo¬ thelin may contribute to the known increased vasoconstrictor re¬ sponses of atherosclerotic blood vessels and, because of the pro¬ liferative properties of endothelin,47 to the atherosclerotic process itself.

Acknowledgment The work of the investigators reported herein was supported by the Swiss National Research Foundation (No. 32-32541.91), the Karl Meyer Stiftung, Vaduz/Liechtenstein, and a grant-in-aid by Patria Insurances.

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endothelium-dependent relaxations in arterial and in venous coronary bypass grafts. N Engl J Med 1991; 319:462. 5. Rubanyi GM, Romero JC, Vanhoutte PM. Flow-induced release of endothelium-derived relaxing factor. Am J Physiol 1986; 250:H 1145. 6. Pohl U, Holtz ], Busse R, Bassenge E. Crucial role of endothelium in the vasodilator response to increased flow in vivo. Hypertension 1986; 8:37. 7. Palmer RM], Ferrige AG, Moncada S. Nitric oxide release accounts for the biological activity of endothelium-derived relaxing factor. Nature 1987;327:524. 8. Feelisch M, te Poel M, Zamora R, et al. Understanding the controversy over the identity of EDRF. Nature 1994;368:62. 9. Rapoport RM, Draznin MB, Murad F. Endothelium-dependent relaxation in rat aorta may be mediated through cyclic GMP-dependent protein phosphoryla¬ tion. Nature 1983; 306:174. 10. Radomski MW, Palmer RM], Moncada S. Comparative pharmacology of endothelium-derived relaxing factor, nitric oxide and prostacyclin in platelets. Br J Pharmacol 1987; 92:181. 11. Palmer RMJ, Ashton DS, Moncada S. Vascular endothelial cells synthesize nitric oxide from L-arginine. Nature 1988;333:664. 12. Bredt DS, Hwang PM, Glatt CE, et al. Cloned and expressed nitric oxide synthase structurally resembles cytochrome P-450 reductase. Nature 1991; 351:714. 13. Richard V, Tschudi MR, Liischer TF. Differential activation of the endo¬ thelial L-arginine pathway by bradykinin, serotonin and clonidine in porcine coro¬ nary arteries. AmJ Physiol 1990;259:H-1433. 14. Tschudi M, Richard V, Biihler FR, Liischer TF. Importance of endothe¬ lium-derived nitric oxide in intramyocardial porcine coronary arteries. Am J Physiol 1990;260:H13. 15. Meyer P, Flammer ], Liischer TF. Endothelium-dependent regulation of the ophthalmic microcirculation in the perfused porcine eye. Role of nitric oxide and endothelins. Invest Ophthalmol Vis Sci 1993;34:3614. 16. Rees DD, Palmer RMJ, Moncada S. The role of endothelium-derived nitric oxide in the regulation of blood pressure. Proc Natl Acad Sci USA 1989; 86:3375. 17. Vallance P, Leone A, Colver A, et al. Accumulation of an endogenous inhibitor of nitric acid synthesis in chronic renal failure. Lancet 1992;339:572. 18. Feletou M, Vanhoutte PM. Endothelium-dependent hyperpolarization of canine coronary smooth muscle. Br J Pharmacol 1988;93:515. 19. Standen NB, Quayle JM, Davies NW, et al. Hyperpolarizing vasodilators activate ATP-sensitive K+-channels in arterial smooth muscle. Science 1989; 245: 177. 20. Moncada S, Vane JR. Pharmacology and endogenous roles of prostaglan¬ din endoperoxides, thromboxane A2 and prostacyclin. Pharmacol Rev 1979; 30:293. 21. Wagner O, Christ G, Wojta J, et al. Polar secretion of endothelin-1 by cultured endothelial cells. J Biomed Chem 1992;267:16066. 22. De Mey JG, Claeys M, Vanhoutte PM. Endothelium-dependent inhibitory effects of acetylcholine, adenosine diphosphate, thrombin and arachidonic acid in the canine femoral artery. J Pharmacol Exp Ther 1982; 222:166. 23. Yang Z, von Segesser L, Bauer E, et al. Differential activation of the endo-

1498

PART X: DIFFUSE HORMONAL SECRETION

thelial L-arginine and cyclooxygenase pathway in the human internal mammary artery and saphenous vein. Circ Res 1991; 68:52. 24. Katusic ZS, Vanhoutte PM. Superoxide anion is an endothelium-derived contracting factor. Am J Physiol 1989; 257:H33. 25. Liischer TF, Boulanger CM, Dohi Y, Yang Z. Endothelium-derived con¬ tracting factors. (Brief review) Hypertension 1992; 19:117. 26. Kohno M, Yasunari K, Yokokawa K, et al. Inhibition by atrial and brain natriuretic peptide of endothelin. A secretion after stimulation with angiotensin II and thrombin of cultured human endothelial cells. J Clin Invest 1991;87:1999. 27. Boulanger C, Liischer TF. Release of endothelin from the porcine aorta: inhibition by endothelium-derived nitric oxide. J Clin Invest 1990; 85:587. 28. Dohi Y, Hahn AWA, Boulanger CM, et al. Endothelin stimulated by an¬ giotensin II augments vascular contractility of hypertensive resistance arteries. Hy¬ pertension 1992; 19:131. 29. Kourembanas S, Marsden PA, McQullan LP, Faller DV. Hypoxia induces endothelin gene expression and secretion in cultured human endothelium. J Clin Invest 1991; 88:1054. 30. Liischer TF, Yang Z, Tschudi M, et al. Interaction between endothelin1 and endothelium-derived relaxing factor in human arteries and veins. Circ Res 1990;66:1088. 31. Kiowski W, Liischer TF, Linder L, Biihler FR. Endothelin-1-induced vaso¬ constriction in man: reversal by calcium channel blockade but not by nitrovasodilators or endothelium-derived relaxing factor. Circulation 1991; 83:469. 32. Saijonmaa O, Ristimaki A, Fyhrquist F. Atrial natriuretic peptide, nitro¬ glycerine, and nitroprusside reduce basal and stimulated endothelin production from cultured endothelial cells. Biochem Biophys Res Commun 1990; 173:514. 33. Yokokawa K, Kohno M, Yasunari K, et al. Endothelin-3 regulates endothelin-1 production in cultured human endothelial cells. Hypertension 1991; 18:304. 34. Stewart DJ, Langleben D, Cemacek P, Cianflone K. Endothelin release is inhibited by coculture of endothelial cells with cells of vascular media. Am J Physiol 1990;259:H1928. 35. Warner TD, Mitchell JA, de Nucci G, Vane JR. Endothelin-1 and endothelin-3 release EDRF from isolated perfused arterial vessels of the rat and rabbit. J Cardiovasc Pharmacol 1989; 13(Suppl 5):85. 36. Arai H, Hori S, Aramori I, et al. Cloning and expression of a cDNA encod¬ ing an endothelin receptor. Nature 1990;348:730. 37. Sakurai T, Yanagisawa M, Takuwa Y. Cloning of a cDNA encoding a non¬ isopeptide-selective subtype of the endothelin receptor. Nature 1990; 348:732. 38. Emori T, Hirata Y, Marumo F. Specific receptors for endothelin-3 in cul¬ tured bovine endothelial cells and its cellular mechanism of action. FEBS Lett 1990;263:261. 39. Liischer TF. Do we need endothelin antagonists? Cardiovasc Res 1993; 27: 2089. 40. Shai S-Y, Fishel RS, Martin BM, et al. Bovine angiotensin converting en¬ zyme cDNA cloning and regulation. Increased expression during endothelial cell growth arrest. Circ Res 1992;70:1274. 41. Severs WB, Daniels-Severs AE. Effects of angiotensin on the central ner¬ vous system. Pharmacol Rev 1973; 25:415. 42. Dubey RK, Roy A, Overbeck HW. Culture of renal arteriolar smooth mus¬ cle cells: mitogenic responses to Ang II. Circ Res 1992; 71:1143. 43. Liischer TF, Tanner FC. Endothelial regulation of vascular tone and growth. Am J Hypertens 1993;6:283S. 44. Dzau VJ, Gibbons GH. Vascular remodelling: mechanisms and implica¬ tions. J Cardiovasc Pharmacol 1993;21(Suppl I):S1. 45. Garg UC, Hassid A. Nitric-oxide generating vasodilators and 8bromo-cyclic guanosine monophosphate inhibit mitogenesis and proliferation of cultured rat vascular SMCs. J Clin Invest 1989;83:1774. 46. Dubey RK, Ganten D, Liischer TF. Enhanced migration of smooth muscle cells from Ren-2 transgenic rats in response to angiotensin II: inhibition by nitric oxide. Hypertension 1993; 22:412. 47. Hirata Y, Takagi Y, Fukuda Y, Marumo F. Endothelin is a potent mitogen for rat vascular smooth muscle cells. Atherosclerosis 1989; 78:225. 48. Vidal-Ragout MJ, Romero JC, Vanhoutte PM. Endothelium-derived relax¬ ing factor inhibits renin release. Eur J Pharmacol 1988; 149:401. 49. Matsumura Y, Nakase K, Ikegawa R, et al. The endothelium-derived va¬ soconstrictor peptide endothelin inhibits renin release in vitro. Life Sci 1989; 44:149. 50. Miller WL, Redfield MM, Burnett JC Jr. Integrated cardiac, renal, and en¬ docrine actions of endothelin. J Clin Invest 1989;83:317. 51. Lorenz RR, Sanchez-Ferrer CF, Burnett JC, Vanhoutte PM. Influence of endocardial derived factor(s) on the release of atrial natriuretic factor. (Abstract) FASEBJ 1988:2:1293. 52. Fukuda Y, Hirata Y, Yoshimi H, et al. Endothelin is a potent secretagogue for atrial natriuretic peptide in cultured rat atrial myocytes. Biochem Biophys Res Commun 1988,155:167. 53. Vierhapper H, Wagner O, Nowotny P, Waldhausl W. Effect of endothelin1 in man. Circulation 1990; 81:1415. 54. Boarder MR, Marriott DB. Characterization of endothelin-1 stimulation of catecholamine release from adrenal chromaffin cells. J Cardiovasc Pharmacol 1989; 13(Suppl 5):223. 55. Wiklundin NP, Oehlen A, Cederqvist B. Inhibition of adrenergic neu¬ roeffector transmission by endothelin in the guinea-pig femoral artery. Acta Physiol Scand 1988; 134:311. 56. Gomez-Sanchez CE, Foecking MF, Chiou S. Endothelin binding to cul¬ tured calf adrenal zona glomerulosa cells and stimulation of aldosterone secretion. J Clin Invest 1989;84:1032. 57. Liischer TF, Vanhoutte PM. Endothelium-dependent contractions to ace¬ tylcholine in the aorta of the spontaneously hypertensive rat. Hypertension 1986; 8: 344.

58. Liischer TF, Vanhoutte PM. Endothelium-dependent responses to aggre¬ gating platelets and serotonin in spontaneously hypertensive rats. Hypertension 1986;8(Suppl 1I):55. 59. Mayhan WG, Faraci FM, Heistad DD. Impairment of endotheliumdependent responses of cerebral arterioles in chronic hypertension. Am J Physiol 1987;253:H1435. 60. Linder L, Kiowski W, Biihler FR, Liischer TF. Indirect evidence for release of endothelium-derived relaxing factor in human forearm circulation in vivo: blunted response in essential hypertension. Circulation 1990:81:1762. 61. Panza JA, Quyyumi AA, Brush JE Jr, Epstein SE. Abnormal vascular endothelium-dependent vascular relaxation in patients with essential hypertension. N Engl J Med 1990;323:22. 62. Creager MA, Roddy M-A, Coleman SM, Dzau VJ. The effect of ACE inhi¬ bition on endothelium-dependent vasodilation in hypertension. J Vase Res 1992; 29: 97. 63. Taddei S, Virdis A, Mattei P, Salvetti A. Vasodilation to acetylcholine in primary and secondary forms of human hypertension. Hypertension 1993;21:929. 64. Liischer TF. The endothelium and cardiovascular disease—a complex re¬ lation. N Engl J Med 1994; 330:1081. 65. Cockcroft J, Chowienczyk PJ, Benjamin N, Ritter JM. Preserved endotheliumdependent vasodilation in patients with essential hypertension. N Engl J Med 1994; 330:1036. 66. Tschudi MR, Criscione L, Liischer TF. Effect of aging and hypertension on endothelial function of rat coronary arteries. J Hypertens 1991;9(Suppl 6):164. 67. Treasure CB, Manoukian SV, Klein JL, et al. Epicardial coronary artery responses to acetylcholine are impaired in hypertensive patients. Circ Res 1992; 71: 776. 68. Liischer TF, Vanhoutte PM, Raij L. Antihypertensive therapy normalizes endothelium-dependent relaxations in salt-induced hypertension of the rat. Hyper¬ tension 1987;9(Suppl III): 193. 69. Dohi Y, Thiel M, Biihler FR, Liischer TF. Activation of the endothelial Larginine pathway in pressurized mesenteric resistance arteries: effect of age and hypertension. Hypertension 1990; 15:170. 70. Dohi Y, Criscione L, Liischer TF. Renovascular hypertension impairs for¬ mation of endothelium-derived relaxing factors and sensitivity to endothelin-1 in resistance arteries. Br J Pharmacol 1991; 104:349. 71. Tschudi MR, Noll G, Arnet U, et al. Alteration in coronary artery vascular reactivity of hypertensive Ren-2 transgenic rats. Circulation 1994;89:2780. 72. Calver A, Collier J, Moncada S, Vallance P. Effect of local intra-arterial NG-monomethyl-L-arginine in patients with hypertension: the nitric oxide dilator mechanism appears abnormal. J Hypertens 1992; 10:1025. 73. Panza JA, Casino PR, Badar DM, Quyyumi AA. Effect of increased avail¬ ability of endothelium-derived nitric oxide on endothelium-dependent vascular re¬ laxation in normals and in patients with essential hypertension. Circulation 1993;87:1475. 74. Hayzer PJ, Cicila G, Cockerham C, et al. Endothelin A and B receptors are downregulated in the hearts of hypertensive rats. Am J Med Sci 1994;307:222. 75. Ross R. The pathogenesis of atherosclerosis—an update. N Engl J Med 1986:314:488. 76. Yla-Herttuala S, Palinski W, Rosenfeld ME, et al. Evidence for the pres¬ ence of oxidatively modified low-density lipoproteins in atherosclerotic lesions of rabbit and man. J Clin Invest 1989:84:1086. 77. Tanner FC, Noll G, Boulanger CM, Liischer TF. Oxidized low-density li¬ poproteins inhibit relaxations of porcine coronary arteries: role of scavenger recep¬ tor and endothelium-derived nitric oxide. Circulation 1991; 83:2012. 78. Kugiyama K, Kerns SA, Morrisett JD, et al. Impairment of endotheliumdependent arterial relaxation by lysolecithin in modified low-density lipoproteins. Nature 1990;344:160. 79. Simon BC, Cunningham LD, Cohen RA. Oxidized low density lipopro¬ teins cause contraction and inhibit endothelium-dependent relaxation in the pig coronary artery. J Clin Invest 1990;86:75. 80. Flavahan NA. Atherosclerosis or lipoprotein-induced endothelial dys¬ function: potential mechanisms underlying reduction in dysfunction in EDRF/nitric oxide activity Circulation 1992;85:1927. 81. Shimokawa H, Vanhoutte PM. Impaired endothelium-dependent relax¬ ation to aggregating platelets and related vasoactive substances in porcine coronary arteries in hypercholesterolemia and atherosclerosis. Circ Res 1989; 64:900. 82. Creager MA, Gallagher SH, Girerd XJ, et al. L-arginine improves endothelium-dependent vasodilation in hypercholesterolemic humans. J Clin In¬ vest 1992;90:1248. 83. Galle J, Bassenge E, Busse R. Oxidized low-density lipoproteins potentiate vasoconstrictions to various agonists by direct interaction with vascular smooth muscle. Circ Res 1990;66:1287. 84. Boulanger CM, Tanner FC, Hahn AWA, et al. Oxidized low-density lipo¬ proteins induce mRNA expression and release of endothelin from human and por¬ cine endothelium. Circ Res 1992;70:1191. 85. Yang Z, Richard V, von Segesser L, et al. Threshold concentrations of endothelin-1 potentiate contractions to norepinephrine and serotonin in human arteries: a new mechanism of vasospasm? Circulation 1990; 82:188. 86. Forstermann U, Miigge A, Alheid U, et al. Selective attenuation of endothelium-mediated vasodilation in atherosclerotic human coronary arteries. Circ Res 1988; 62:185. 87. Minor RL, Myers RR Jr, Guerra R Jr, et al. Diet-induced atherosclerosis increases the release of nitrogen oxides from rabbit aorta. J Clin Invest 1990; 86: 2109. 88. Lerman A, Edwards BS, Hallett JW, et al. Circulating and tissue endothelin immunoreactivity in advanced atherosclerosis. N Engl J Med 1991; 325:997.

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

175_

THE ENDOCRINE GASTROINTESTINAL TRACT: PATHOPHYSIOLOGY STEPHEN R. BLOOM AND JULIA M. POLAK

The first substance to be named a hormone was secretin. It was isolated from the gastrointestinal tract in 1902. The under¬ standing of this endocrine system developed slowly because the endocrine cells are scattered throughout the gastrointestinal mu¬ cosa rather than gathered together as glands. This complicates

1499

the traditional approach to studying endocrinology. Endocrine cells of any one type cannot be completely removed to observe a deficiency syndrome or to make an extract containing only one active hormone. Progress awaited the powerful modern methods of protein and peptide isolation, capable of extracting undam¬ aged active hormones at concentrations of one part in a hundred thousand million. Once isolated and sequenced, there is little difficulty in obtaining large quantities of the pure synthetic pep¬ tide for testing. The story of gut hormones is by no means complete; more hormones await discovery. For example, enterochromaffin-like cells are visible in the mucosa of the gastric fundus (Fig. 1751). These cells are stimulated to multiply when acid secretion is deficient (see Fig. 175-1). In achlorhydria, they even become tu¬ morous. Although they clearly contain granules of a secretory product, investigators are uncertain what this is. The rate of dis¬ covery of new gastrointestinal regulatory peptides has acceler¬ ated as techniques of isolation have improved, and this exposi¬ tion of current knowledge of gut endocrine pathophysiology necessarily is an interim one.

FIGURE 175-1. A, Enterochromaffin-like cells ly¬ ing against the basement membrane of human fundic mucosa. Bouin's fixed tissue, Servier and Munger silver impregnation technique, X500. B, Hyperpla¬ sia of enterochromaffin-like cells in fundic mucosa of a patient with pernicious anemia and atrophic gastritis; X200.

1500

PART X: DIFFUSE HORMONAL SECRETION

FIGURE 175-2. Electron micrograph of endocrine cell from human ileum. Pleomorphic electron-dense secre¬ tory granules are located in the distal cytoplasm close to the basement membrane. Microvilli are located at the apical pole, protruding into the gut lumen. Glutaraldehyde-fixed tissue was used, which was postosmicated and araldite-embedded, with uranyl acetate and lead citrate counterstains; X9500.

METHODS IN GASTROINTESTINAL ENDOCRINOLOGY

INDIVIDUAL PEPTIDES GASTRIN

As with much of the rest of endocrinology, there is extensive use of and heavy reliance on specific reactions with antibodies. The most practical method of measuring gut hormones in plasma is by radioimmunoassay. Unfortunately, different groups of re¬ searchers use antisera of different specificity and sensitivity. Rarely is precise comparability of numerical results possible be¬ tween laboratories, and no international quality control system has been developed. Thus, although there is now broad agreement on the order of magnitude of the concentrations of circulating gut hormones, each laboratory has its own individual normal reference range. For most hormones, we are still in the "pioneering stage," in which basic facts, such as the best means of preventing the degradation of peptides after plasma collection and the biologic importance of the many alternative hormonal forms, are unclear. Techniques for the visualization of the neuroendocrine sys¬ tem have advanced considerably, at both light microscopy and electron microscopy levels (Fig. 175-2). The. old histologic mark¬ ers of secretory granules in the cytoplasm of endocrine cells—for example, the uptake of silver salts to produce a silver deposit with (argyrophilia) or without (argentaffinia) the addition of a reducing agent—have been supplemented by staining enzymes (e.g., neu¬ ron-specific enolase); specific granular proteins (e.g., chromogranin; Fig. 175-3); or intermediate filaments (e.g., neurofilaments). Greater specificity is obtained by employing immunocytochemistry using antibodies against specific peptides to identify their cells of production and the type of posttranslational en¬ zymic processing that has occurred. By electron microscopy, dense-core secretory granules distinguish neuroendocrine tissue, and the analysis of the size, electron density, halo, and other characteristics of the granule membrane can differentiate the storage granules of different peptides (Table 175-1). Antibodies to specific peptides can be labeled with tiny gold particles of a particular size, and the intracellular storage granule producing a particular peptide can be identified (Fig. 175-4). Probes of the complementary nucleic acid sequence to mRNA, when tagged with a suitable marker, allow the identification of the particular cell containing this message (i.e., hybridization histochemistry). Particular hormone binding sites on the outside of the cell can be identified using antibodies to the receptor or a specifically labeled ligand, which often is radioactive and visualized by autoradiography.

The hormone gastrin is cleaved from its prohormone such that the bioactive sequence resides in the last four amino acids of the COOH-terminal. The NH2-terminal is variable; the main

FIGURE 175-3. Electron micrograph of chromogranin immunoreactivity in a human enterochromaffin cell. Glutaraldehyde fixation, immunogold staining procedure with 20-nm gold particles, and uranyl acetate and lead citrate counterstains were used; X25,000.

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology

1501

TABLE 175-1 Ultrastructural Classification and Distribution of Human Gastroentero-Pancreatic Endocrine Cells Small Intestine

Stomach Cell

Main Product

P

Peptides? Peptides? 5-HT peptides Somatostatin Insulin Pancreatic polypeptide Glucagon Unknown Unknown (b, histamine) Gastrin Gastrin COOH-terminal gastrin/cholecystokinin (CCK) Cholecystokinin (CCK)

D,

EC D

B

PP(F) A X ECL G IG TG I S K Mo N L

Pancreas a f r,b + + + +

Oxyntic Antral Upper Lower Intestine + + + +

+ f + +

+

+ b b

f +

a,

fetus

+•

{ + (

f + +

a,b +

Secretin Glucose-dependent insulinotropic peptide (GIP) Motilin Neurotensin Enteroglucagon (GLI)

f +

+ + + + +

b f f f f

4 f

+

+

+

or newborn; b, animals;/, few; r, rare.

(From Solria E, Capella C, Buffa R, et al. The diffuse endocrine-paracrine system of the gut in health and disease: ultrastructural features. Scand J Gastroenterol Suppl 1981; 70:25.)

molecular forms are 14, 17, and 34 amino acids long. The clear¬ ance of the larger form (G-34) from the circulation is slow, with a half-life of about 40 minutes in humans, but the smaller G-17 has a half-life of only 5 minutes.1 Gastrin is synthesized almost entirely in endocrine cells of the mucosa of the gastric antrum and the upper small intestine. The major product of the antral G cell is G-17; the smaller-granule intestinal G cell produces G-34 and larger gastrin forms. Pharmacologically, gastrin stimulates the secretion of acid by the parietal cells of the gastric fundus and body, and the longer-term growth of this mucosa. It also increases the contractility of the smooth muscle of the lower esophagus and the stomach, but this effect is seen only at higher doses and may not be important.2 Gastrin is released by amino acids and the breakdown prod¬ ucts of proteins, as well as by local distention and central stimuli conducted through the vagus. Its release is directly inhibited by

low gastric luminal pH. Thus, there is a feedback mechanism whereby gastrin stimulates the secretion of acid, which, in turn, inhibits the release of further gastrin. Much of the control of gas¬ trin release is mediated by a paracrine control system, with local release of the inhibitory hormone, somatostatin (see later), from neighboring D cells.3 In atrophic gastritis, acid secretion falls and very high gastrin levels result. There is a marked hyperplasia of the gastrin-producing G cells (Fig. 175-5). Rarely, during surgery, a part of the antrum may be cut off from the lumen and, there¬ fore, not be acidified by the acid secreted by the main body of the stomach. Under these circumstances, the G cells secrete large amounts of gastrin, stimulating ever more acid secretion, which, in turn, results in severe peptic ulceration of the tissues still in contact with the acid. After vagotomy, the vagal stimulus to gas¬ trin is removed, but directly stimulated acid secretion also is greatly reduced; thus, overall gastrin levels are considerably higher than before vagotomy. Two types of cholecystokinin (CCK) receptors (see later) have been identified, A and B.4 The B type is found throughout the brain and in the gastric fundus. Gastrin binds to this B type receptor (i.e., it is the gastrin recep¬ tor). Specific receptor antagonists have been developed that effectively inhibit acid secretion.4

PANCREATIC POLYPEPTIDE

FIGURE 175-4. Electron micrograph of human pancreatic islet A cell granules double immunostained to reveal the topographic segregation of glicentin (5-nm gold) to the halo and GLP-2 (40-nm gold) to the core. Glutaraldehyde fixation and a double immunogold staining procedure were used. (Primary antisera are raised in different species. Species-spe¬ cific second-layer antibodies adsorbed to gold particles are applied to complete the detection.) Uranyl acetate and lead citrate were counter¬ stains; X52,100.

Pancreatic polypeptide (PP) is secreted as a 36-amino-acid peptide. Evolutionarily, it is related in its sequence to two other peptides, the gut hormone peptide tyrosine tyrosine (PYY) and the neuropeptide tyrosine (NPY; Table 175-2). PP is produced by small-granule endocrine cells found in the islets of Langerhans and scattered through the exocrine pancreas. PP inhibits gall¬ bladder contraction, pancreatic enzyme secretion, and gastric acid secretion.5 However, these actions are weak and may be un¬ important physiologically; its principal role is unknown. PP is released by its cholinergic innervation; therefore, levels are very low after administration of atropine or after vagotomy. Any stimulus to pancreatic exocrine secretion (e.g., CCK) also stimulates the release of PP. After a meal, the rise of PP is ex¬ tremely rapid, and high plasma concentrations are achieved.6 Unlike insulin, it appears to have no effect on circulating nutri¬ ments. There is no consequence of PP deficiency after total pan¬ createctomy or of massive excess due to PP-producing tumors. In

1502

PART X: DIFFUSE HORMONAL SECRETION the fasting state, the basal concentrations of PP fluctuate with the interdigestive myoelectric complex in a way similar to motilin.

SECRETIN Secretin, a 27-amino-acid peptide (see Table 175-2), has many sequence similarities to pancreatic glucagon, glucosedependent insulinotropic peptide (GIP), vasoactive intestinal peptide (VIP), growth hormone releasing hormone, and peptide histidine isoleucine. Together they form a family that, early in its evolution, presumably derived from a single precursor peptide. Secretin is produced by sparse endocrine cells in the duodenal and jejunal mucosa. It shares several pharmacologic actions with other members of this peptide family (e.g., inhibiting gastric acid and stimulating insulin release). Its most potent action, however, is to stimulate the secretion of a watery alkaline juice from the ducts of the pancreas; this is probably its only physiologic role.7-9 Secretin is released into the bloodstream whenever the duodenal pH falls below 4, but this does not occur very often. After a meal, ingested food initially neutralizes gastric acid and plasma secretin levels fall.10 The highest levels occur in the fast¬ ing state, in which secretin may be important in protecting the duodenal mucosa from acid and, thus, in preventing peptic ulceration.

CHOLECYSTOKININ

FIGURE 175-5.

A, Normal human antrum immunostained for gastrin. Numerous G cells can be seen in the mucosa; XI25. B, Hyperplasia of G cells in antral mucosa from a patient with pernicious anemia and atrophic gastritis; XI25.

Cholecystokinin is identical in the last five COOH-terminal amino acids to gastrin (see Chap. 162). In both hormones, this sequence is the bioactive site, but the relative specificity of CCK for the pancreas and gallbladder is achieved by the three amino acids adjacent to the terminal pentapeptide, which differ from those in gastrin. As previously mentioned, there are two types of CCK receptor: A, which is specific for CCK and is responsible for gallbladder contraction and pancreatic enzyme secretion, and B, which also is the gastrin receptor. The main CCK brain receptor

TABLE 175-2 Amino Acid Sequences of Peptides Found in the Gut Peptide

Sequence

NPY;

19 20 18 14 15 17 12 16 11 13 9 10 6 7 8 1 2 4 '5 3 Tyr-—Pro —Ser —Lys ■—Pro --Asp--Asn —Pro ■—Gly--Glu-—Asp —Ala -—Pro —Ala —Glu--Asp-—Met-—Ala --Arg--Tyr-

PYY (porcine); PP;

Tyr —Pro -—Ala —Lys ■—Pro --Glu--Ala —Pro ■—Gly--Glu —Asp —Ala --Ser —Pro —Glu--Glu-—Leu--Ser --Arg--TyrAla —Pro —Leu —Glu-—Pro --Val --Tyr —Pro ■—Gly--Asp-—Asn —Ala --Thr —Pro —Glu-—Gln-—Met-—Ala -—Gln--Tyr-

Secretin;

19 20 14 16 17 18 12 13 15 11 10 1 4 5 6 8 9 2 3 7 His —Ser —Asp —Gly —Thr--Phe--Thr —Ser —Glu--Leu —Ser —Arg -—Leu —Arg —Glu-—Gly -—Ala --Arg-—Leu —Gin—

Glucagon: GIP:

His —Ser —Gin —Gly —Thr--Phe--Tyr —Ser —Asp--Tyr —Ser —Lys -—Tyr —Leu —Asp-—Ser --Arg- -Arg- —Ala -—Gin— Tyr —Ala —Glu —Gly —Thr--Phe--lie —Ser —Asp--Tyr —Ser —lie -—Ala —Met —Asp-—Lys -—lie -—His --Gin —Gin —

VIP:

20 17 18 19 14 16 11 12 13 15 10 4 5 6 7 8 9 1 3 2 His —Ser —Asp —Ala —Val --Phe--Thr —Asp —Asn--Tyr —Thr —Arg -—Leu —Arg —Lys -—Gln-—Met-—Ala --Val-—Lys —

PHI:

His —Ala —Asp —Gly —Val --Phe--Thr —Ser —Asp--Phe —Ser —Lys -—Leu —Leu —Gly-—Gln-—Leu--Ser -—Ala —Lys —

Motilin (porcine):

19 20 17 18 12 13 14 15 16 10 11 7 8 9 1 2 4 5 6 3 Phe —Val —Pro —He —Phe--Thr-—Tyr —Gly —Glu-—Leu —Gin —Arg -—Met —Gin —Glu-—Lys -—Glu--Arg-—Asn —Lys —

Neurokinin alpha: Neurokinin beta: Substance P:

Galanin (porcine):

10 1 2 6 7 8 9 3 4 5 His —Lys —Thr —Asp —Ser -—Phe--Val —Gly —Leu -—Met —NH2 Asp —Met —His —Asp —Phe-—Phe--Val —Gly —Leu-—Met —nh2 Arg —Pro —Lys —Pro —Gln-—Gln--Phe —Phe —Gly-—Leu —Met —nh2 17 18 19 20 14 15 16 11 12 13 8 9 10 1 2 4 5 6 7 3 Gly —Trp —Thr —Leu —Asn--Ser --Ala —Gly —Tyr -—Leu —Leu —Gly -—Pro —His —Ala --lie -—Asp-—Asn —His —Arg—

GIP, glucose-dependent insulinotropic peptide; NPY, neuropeptide tyrosine; PHI, XX; PP, pancreatic polypeptide; PYY, peptide tyrosine tyrosine; VIP, vasoactive intestinal peptide.

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology is the B type. Its role is unknown. Although the octapeptide of CCK is the main form in the brain, several larger NH2-terminally extended forms are synthesized in the gut (e.g., CCK-33, -39, or -58).11 In the gut, CCK occurs mainly in endocrine cells of the upper intestinal mucosa, but extremely small amounts also are in nerves throughout the gut.12 CCK stimulates gallbladder contrac¬ tion, pancreatic enzyme secretion, and pancreatic growth. It also may stimulate the secretion of succus entericus from the mucosa of the small intestine. Plasma levels of the larger forms of CCK (but not CCK-8) rise after luminal stimulation by long-chain fatty acids and certain amino acids (e.g., tryptophan and tyrosine). There is controversy about what proportion of the normal post¬ prandial pancreatic enzyme secretion is controlled by circulating CCK, by the local pancreatic innervation, and by unknown fac¬ tors. It also is unclear whether there is any feedback control in humans whereby a lack of enzyme secretion (as in chronic pan¬ creatitis) increases the level of CCK, although this feedback does occur in the rat. The isolation of the mRNAs of gastrin and CCK demon¬ strated a small peptide beyond the main sequence (a COOHflanking peptide) that showed considerable sequence conserva¬ tion; in CCK, it appears to be sulfated. Although the sulfate is necessary for bioactivity in CCK, it is unclear whether the same applies to its flanking peptide.

the gastrointestinal tract. It is highest just before or coincidental with the initiation of a new interdigestive myoelectric complex, the contraction wave that sweeps down the intestine about every hour and a half in the fasting state and removes debris from the lumen, thus preventing bacterial overgrowth.15 Although the in¬ fusion of motilin in fasting volunteers can induce the formation of a premature complex, it is unclear whether motilin is the con¬ trolling agent or, more likely, is merely one of the agents setting the background contractility of digestive tract smooth muscle. Erythromycin has been found to bind to the motilin receptor. Al¬ though this is independent of its antibiotic activity, it explains the gastrointestinal side effects. A more specific motilin receptor agonist is being developed as a prokinetic agent.16

GLUCOSE-DEPENDENT INSULINOTROPIC PEPTIDE The peptide first discovered as a gastric inhibitory peptide (GIP) later was found to be more potent in stimulating the B cell to release insulin and was renamed glucose-dependent insulinotropic peptide (still GIP).17 It is a member of the glucagon and secretin family and is 42 amino acids long (see Table 175-2). It is found only in the mucosa of the upper intestine, where it is pro¬ duced by an endocrine cell given the designation K by its electron microscopic appearance. Because GIP was a potent stimulant of insulin release, it was suggested as a possible mediator of the enteroinsular axis, the mechanism that gives a much greater insu¬ lin release when nutriments are taken through the alimentary tract than when they are given intravenously.1® It is released into the bloodstream after food ingestion, particularly carbohydrates and long-chain fatty acids, which appear to be the main stimuli.1Q When intravenous infusions of GIP and glucose are given to mimic the normal postprandial rise, the release of insulin is not as great as that seen after a meal, suggesting that there may be other components of the enteroinsular axis, such as activation of the direct innervation of the B cell. No definite abnormality of GIP has been found in diabetes mellitus.20,21 Interestingly, cases of nodular adrenal hyperplasia and Cushing syndrome induced

MOTILIN Motilin, a 22-amino-acid peptide, does not have sequence similarities to any other family of regulatory peptides13 (see Table 175-2). It is produced by mucosal endocrine cells of the duode¬ num and jejunum but is absent from the stomach and colon.14 Motilin increases the contractility of the gastrointestinal smooth muscle. It can accelerate gastric emptying and colonic motor ac¬ tivity. Considerable amounts are released in the fasting state, but the relatively high plasma concentrations achieved are little affected by eating a meal. Continual measurements during fast¬ ing have shown that motilin varies with the contractility state of

34 35 36 31 32 33 29 30 24 25 26 27 28 21 22 23 Tyr--Ser--Ala -—Leu--Arg--His--Tyr --lie --Asn--Leu--He --Thr --Arg--Gin —Arg--Tyr--nh2 Tyr--Ala--Ser —Leu--Arg--His--Tyr-—Leu--Asn--Leu--Val--Thr --Arg--Gin —Arg--Tyr--nh2 Ala -—Ala --Asp-—Leu--Arg--Arg--Tyr--He --Asn--Met--Leu--Thr --Arg -—Pro —Arg--Tyr--nh2 27 28 21 22 23 24 25 26 Arg-—Leu--Leu--Gin--Gly--Leu--Val--nh2

29

30

31

32

33

34

35

36

37 38 39 40 41 Lys —-His-—Asn--He --Thr

42

Asp--Phe--Val ■—Gin--Trp-—Leu-—Met-—Asn--Thr Asp-—Phe-—Val —Asn--Trp-—Leu-—Leu-—Ala --Gin--Lys --Gly-—Lys -—Lys -—Asn —Asp--Trp-—Lys —-His-—Asn--lie --Thr--Gin 27 28 22 24 25 26 21 23 Lys -—Tyr-—Leu —Asn-—Ser --lie -—Leu-—Asn--nh2 Lys -—Tyr--Leu —Glu--Ser-—Leu-—Met-—nh2 21 22 Gly--Gin

29 27 28 25 26 24 21 22 23 Ser —Phe--His —Asp-—Lys --Tyr--Gly —Leu-—Ala --nh2

1503

—Gin

1504

PART X: DIFFUSE HORMONAL SECRETION

by an abnormal described.22,23

adrenal

response

to

GIP

have

been

NEUROTENSIN Neurotensin is a 13-amino-acid peptide that is produced by endocrine cells of the ileal mucosa and is released by a mixed meal and long-chain fatty acids (see Chap. 164).24,25 Neurotensin inhibits gastric acid and gastric emptying, stimulates pancreatic bicarbonate juice and intestinal secretions, and increases intesti¬ nal motor activity.26 The rise in plasma concentrations of neurotensinl-13 after a normal meal are two-fold to four-fold above basal levels, not enough to instigate the actions mentioned ear¬ lier. Initial assays suggested that the rise was much greater, but this was the result of a cross-reaction of an inactive breakdown fragment, neurotensin 1-8, which built up in the blood because it is cleared more slowly.27 Whether neurotensin has a more impor¬ tant role as a local (paracrine) hormone, acting in the adjacent mucosa itself, is unknown.

ENTEROGLUCAGON AND GLUCAGON-LIKE PEPTIDES Enteroglucagon (also called glicentin, gut glucagon, and gas¬ trointestinal glucagon-like immunoreactivity or GLI) was de¬ tected as a cross-reactant in early pancreatic glucagon radioim¬ munoassays. It was later found that antisera reacting with the COOH-terminal of pancreatic glucagon did not detect the intes¬ tinal material, which also had a higher molecular weight.28 En¬ teroglucagon was found to have the complete amino acid se¬ quence of pancreatic glucagon within it; it was speculated that tertiary folding of the molecule sterically hindered the COOHterminal antigenic site normally exposed in pancreatic glucagon. Isolation of the mRNA for pancreatic glucagon demonstrated that the sequence of this enteroglucagon from the gut was pres¬ ent in its entirety in the preproglucagon molecule29 (Fig. 175-6). Thus, the main differences between the A cell of the pancreas and the enteroglucagon cell of the intestinal mucosa lie in the posttranslational enzymatic processing of an identical pre¬ propolypeptide. A further twist to the story was that, in the preprohormone, the COOH-flanking sequence beyond glucagon contained the se¬ quences of two further glucagon-like peptides (GLP-1 and GLP-2).29,30 GLP-1 was found in piscine proglucagon and the conservation of the sequence was as good as that of pancreatic glucagon. The forces of natural selection have operated to pre¬ vent alteration of the amino acid sequence, which would have occurred by random mutation. It appears that GLP-1 is essential for survival. However, in the A cell of the pancreas, it was found that, although the 29-amino-acid glucagon was cleaved and se¬ creted as such, GLP-1 and GLP-2 were secreted as a single large

molecule, containing both sequences. Conversely, the enteroglu¬ cagon cell in the intestinal mucosa does not cleave the glucagon sequence, but secretes the entire enteroglucagon peptide, con¬ taining within it the pancreatic glucagon sequence. However, it does cleave out and split apart the two GLPs, which are then secreted separately.31 GLP-1 and GLP-2 may have roles in the process of digestion other than in carbohydrate metabolism, but no pharmacologic action at low doses has yet been shown for either molecule. It has been shown that GLP-1 is not secreted as such but is cleaved to form a shorter molecule, GLP-17_36 NH2. The latter is biologically active and inhibits gastric acid secretion and stimulates insulin secretion at physiologic blood concentra¬ tions. Thus, it appears to be an important new gut hormone in humans. It may be the main “incretin/' and appears to be effective in lowering blood glucose levels in patients with maturity-onset (type II) diabetes.32 Although the role of the GLPs produced by the enterogluca¬ gon cell is unknown, the role of enteroglucagon can be surmised. A tumor that produced enteroglucagon was associated with marked gut hyperplasia, which completely disappeared when the tumor was removed.33 In animals, resection of part of the gut causes the remainder to hypertrophy greatly. The enteroglucagon-producing cells are most numerous in the colonic mucosa, although they occur throughout the intestine. After small gut re¬ section, the entry of malabsorbed food into the colon produces very high enteroglucagon levels. Therefore, the hypothesis was advanced that enteroglucagon was "growth hormone to the gut." Furthermore, animals that had isolated gut loops opening onto the abdominal wall showed a hyperplasia of the mucosa in these loops that was proportional to the plasma enteroglucagon concentrations.34 A crude isolate of enteroglucagon caused hy¬ perplasia in cultured enterocytes.35 A partial sequence of entero¬ glucagon, constituting the entire COOH-terminal sequence that contains pancreatic glucagon, was found to inhibit gastric acid secretion and, therefore, was named oxyntomodulin.28 This smaller form of enteroglucagon is produced by the enterogluca¬ gon cells and released into the circulation, albeit in smaller amounts than enteroglucagon itself. The enteroglucagon system probably inhibits gastric acid secretion late after a meal and maintains mucosal growth in proportion to the amount of unab¬ sorbed food reaching the colon.36 High levels of plasma entero¬ glucagon are recorded in several common gastrointestinal condi¬ tions in which this action is appropriate.

PEPTIDE TYROSINE TYROSINE Peptide tyrosine tyrosine (PYY, using the IUPAC notation for tyrosine of Y to distinguish it from tryptophan) is a 36-aminoacid peptide in the PP and NPY family (see Table 175-2). PYY is found in a similar distribution to that of enteroglucagon, in the

Enteroglucagon (69aa)

FIGURE 175-6.

Diagram of the active peptides found in human preproglucagon. In the bowel, there is no cleavage on either side of glucagon and the 69 amino acid entity, enteroglucagon, is released. GLP-1 and GLP-2, glucagon-like peptide 1 and 2, respectively. (Also see Chap. 130.) (From Bell Gl, Santerre RF, Mullenbach GT. Hamster pre-pro-glucagon contains the sequence of glucagon and two related peptides. Nature 1983; 302; 716.)

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology mucosal endocrine cells of the lower half of the small intestine and throughout the large bowel.37 Highest concentrations are present in the rectal mucosa. Immunocytochemical localization suggests that some of the endocrine cells produce both PYY and enteroglucagon. However, they clearly are under separate con¬ trol, because the distribution concentrations of PYY and entero¬ glucagon do not correlate. PYY inhibits pancreatic exocrine and intestinal secretion.38 Human studies have demonstrated an inhibition of gastric acid secretion, a delay in gastric emptying, and a decrease in intestinal motility. It seems likely that these effects are important physio¬ logically, because there is a steep rise in plasma concentrations of PYY after a meal.39 Because PYY, like enteroglucagon, is released by carbohydrates and long-chain fatty acids, it may act in concert in preventing escape of these foodstuffs into the colon by inhib¬ iting intestinal motility to allow more time for absorption, which is aided by the proposed enteroglucagon stimulus to mucosal growth.

GROWTH HORMONE RELEASING HORMONE AND OTHER ENDOCRINE PEPTIDES Growth hormone releasing hormone, the 44-amino-acid peptide released from the hypothalamus into the pituitary portal circulation to stimulate growth hormone release, is found in sig¬ nificant concentrations in the mucosa of the small intestine.40 Several putative hormonal peptides also have been reported in small concentrations in the gut.

SOMATOSTATIN Although most gut hormones, such as gastrin, secretin, motilin, and GIP, are confined to the gut, CCK and somatostatin also are major neural peptides.41,42 Somatostatin (see Chap. 166) occurs in two main forms with identical COOH-terminal active sequences S-14 and S-28. It is produced by many specific endo¬ crine cells in the mucosa of the stomach and intestine, as well as by the islets of Langerhans. It is a powerful inhibitor of hormone release (i.e., of all the gastrointestinal and pancreatic hormones) and directly inhibits the response of effector tissues. For example, somatostatin completely inhibits the release of gastrin and, dur¬ ing an exogenous gastrin infusion, completely inhibits the action of gastrin on the parietal cell, producing achlorhydria. Somatostatin is present in the enteric neural system, where it presumably acts as a neurotransmitter or neuromodulator. It has a broad spectrum of action, which is difficult to correlate with any physiologic role as a circulating hormone. Therefore, it has been proposed that its main physiologic action is entirely local, as a paracrine substance. This would allow gastric somatostatin to inhibit the stomach but not affect insulin release, and somato¬ statin in the islets of Langerhans could affect insulin release but not influence acid secretion. There is, however, a rise of plasma somatostatin after a meal, and when this rise is mimicked by an exogenous infusion of somatostatin, it does produce a partial but significant inhibition of insulin release.43 Thus, it may be that so¬ matostatin acts simultaneously as a hemocrine agent, a paracrine substance, and a neurotransmitter in the gut. Work in animals with high concentrations of somatostatin antibodies suggests that it does have a wide-ranging physiologic inhibitory role, but the exact definition of its importance in humans awaits the de¬ velopment of specific non-toxic inhibitors. The powerful inhibi¬ tory actions of somatostatin are used to block the hormone secre¬ tion and protect the tissue affected in endocrine tumor syndromes (see Chap. 176). Five somatostatin receptors have been cloned. They have differential affinity for particular syn¬ thetic somatostatin analogues as well as a differential tissue dis¬ tribution44-46 (see Chap. 166). For example, somatostatin receptor 5 binds preferentially to S-28 and is found in the anterior pitu¬ itary but not in islets.

1505

VASOACTIVE INTESTINAL PEPTIDE AND PEPTIDE HISTIDINE ISOLEUCINE (METHIONINE) Vasoactive intestinal peptide and peptide histidine isoleu¬ cine are 28- and 27-amino-acid peptides, respectively, with con¬ siderable sequence homologies.47,48 They are cosynthesized in the same prohormone (see Chap. 168). In humans, the last amino acid of the equivalent peptide to peptide histidine isoleucine is methionine; therefore, the human form is called PHM. Posttranslational enzymatic processing of the prohormone is vari¬ able; the nasal mucosa, stomach, and genitalia produce consider¬ able amounts of big PHM, a COOH-terminally extended PHM.49 This peptide system is synthesized entirely in neurons that form a considerable proportion of the myenteric and submucous neu¬ ronal population of the gastrointestinal tract. VIP, which is a member of the glucagon and secretin family of peptides, inhibits gastric acid and stimulates pancreatic bicar¬ bonate secretion and insulin release from the B cell. It also is a relaxant of vascular smooth muscle and the muscle of the alimen¬ tary tract. A very potent action is the stimulation of enterocyte secretion, and the major feature of VIP-producing tumors is se¬ vere watery diarrhea. These actions are mimicked by PHM, which appears to act at the same receptor. PHM, however, is slightly less potent, particularly as a vasodilator. The biologic re¬ lationship between these two peptides and the physiologic ad¬ vantages of having two coreleased and similar neurotransmitters is unclear. Occasionally, the local release of VIP is so great that it can be detected in the peripheral circulation (e.g., after bowel ischemia) and, therefore, may play a hemocrine role. As with the other alimentary neural peptides, both VIP and PHM are present in fasting plasma from healthy persons in detectable concentra¬ tions, but these do not appear to show physiologically meaning¬ ful changes postprandially, and the levels are presumably too low to be important. Another low-abundance family member, termed pituitary adenylate cyclase-activating polypeptide, has been identified with its own mRNA.50 It acts at the VIP receptor, but is more potent.

ENDOGENOUS OPIOIDS There are three precursor molecules, proenkephalin, prodynorphin, and proopiomelanocortin, that generate a wide variety of peptides with opioid properties (see Chap. 165).51-53 In the gut, the main representatives are enkephalin and dynorphin. Both are present in high concentrations and are produced by a significant population of myenteric and submucous neurons. One of the ear¬ liest known actions of the opioid peptides was the prevention of diarrhea. Thus, important actions of these agents are inhibiting gastrointestinal secretions, probably indirectly by the submucous neural plexus, and increasing smooth-muscle contractility, partly by the myenteric plexus and perhaps by a cholinergic mechanism.54

SUBSTANCE P AND THE TACHYKININS Substance P is one of the best characterized neuropeptides in mammalian tissue (see Chap. 167). It is thought to have an important role as a neurotransmitter or neuromodulator in pri¬ mary sensory neurons. It is an 11-amino-acid peptide produced by one of two distinct mRNAs, the result of alternate RNA splic¬ ing of a single genomic sequence.55,56 One of these mRNAs en¬ codes substance P alone; the other encodes both substance P and a closely related decapeptide, substance K (or neurokinin alpha). Another related peptide, presumably produced by a separate mRNA, also has been isolated from the pig spinal cord and is called neurokinin beta (see Table 175-2).57 Together, they form the mammalian tachykinin family. In the gut, substance P and substance K are produced in nearly equimolar concentrations by neurons of the intrinsic enteric nervous system. In contrast, the amounts of neurokinin beta are extremely low. Work on tachy-

1506

PART X: DIFFUSE HORMONAL SECRETION

kinin receptors has demonstrated that there are three different types, known as NK1, NK2, and NK3,58 with different relative affinities for the different tachykinins.59 Substance P produces contraction of alimentary smooth muscle and vasodilation. The COOH-terminal sequence of the peptide contains the active site.

CALCITONIN GENE-RELATED PEPTIDE Calcitonin gene-related peptide (CGRP) was discovered during work on the calcitonin gene (see Chap. 52). Alternative intranuclear RNA splicing yielded either mRNA for calcitonin or mRNA for a novel peptide of then-unknown function (see Chap. 2).60,61 CGRP is a 37-amino-acid peptide with a disulfide link in its amino-terminal region and without any sequence sim¬ ilarity to calcitonin. Its distribution in the body is similar to that of substance P; it is found in high concentrations in lamina 2 of the spinal cord and in the dorsal root ganglia. It is presumed, like substance P, to play a role in the sensory nervous system.62 In the dorsal root ganglia, for example, it occurs in greater amounts than does substance P, and it appears that all substance P-producing neurons also produce CGRP. The concentrations in the gut, where it is found particularly in blood vessels, are distinctly lower than those of substance P, and unlike substance P, it is signifi¬ cantly depleted from the gut in animals treated with the sensory toxin capsaicin. It is likely that a much higher proportion of ali¬ mentary CGRP-containing nerves come from neurons extrinsic to the gut itself. CGRP is a powerful vasodilator that inhibits gas¬ tric acid secretion and relaxes smooth muscle. It probably is im¬ portant in alimentary vasodilation, but ascertaining its true phys¬ iologic importance is difficult. Progress has been assisted by the observation that CGRP 8-37 is a powerful antagonist. Another gene has been identified, producing another CGRP that differs in only a few amino acids and is termed CGRP/3- It is synthesized in gut neurons specifically and presumably plays a part in local gut physiology. Its pharmacology is similar to that of the original CGRP.

GALANIN Galanin is a 29-amino-acid peptide whose name derives from the fact that it has a glycine at one end and an alanine at the other (see Table 175-2). It has no sequence similarities with any other known peptide. It is produced by the enteric nervous sys¬ tem, mainly ganglion cells of the submucosal plexus.63 Many of these cells also synthesize VIP. Galanin is a powerful contractor of alimentary smooth muscle and may have a physiologic role as a natural antagonist of muscle-relaxing peptides like substance P and CGRP.64

NEUROPEPTIDE TYROSINE Neuropeptide tyrosine is a 36-amino-acid peptide in the PP and PYY family (see Table 175-2).65 It is found in significant con¬ centrations in the gut. In animals, treatment with the neurotoxic agent 6-hydroxydopamine, which destroys catecholaminecontaining neurons, completely depletes the gut of NPY. Thus, alimentary NPY is present in the extrinsic adrenergic innervation and is stored with catecholamines.66 NPY has a similar spectrum of action to circulating PYY, and the two may act at the same receptor. When administered into the paraventricular nucleus of the hypothalamus, both stimulate food ingestion dramatically.67 NPY is a powerful vasoconstrictor, and it can relax stimulated smooth muscle. It inhibits stimulated intestinal juice production. Pharmacologic studies have been complicated by the easy degra¬ dation of NPY; many laboratory preparations turn out to be bioinactive.

BOMBESIN-LIKE PEPTIDE Bombesin-like peptide (BLP, or gastrin-releasing peptide) occurs in two major forms, a 27-ammo-acid peptide and its COOH-terminal decapeptide.68 The entire bioactivity resides in

the last seven amino acids, which are completely conserved from amphibian bombesin.69 The amounts present in the human gut are small; it is synthesized by the intrinsic neurons of the myen¬ teric and submucous plexus. BLP is a potent stimulant of the re¬ lease of many other gastrointestinal and pancreatic regulatory peptides and, thus, acts in an opposite sense to the inhibitor so¬ matostatin. It also directly stimulates pancreatic enzyme secre¬ tion and gastric acid secretion. The high circulating concentra¬ tions of BLP immunoreactivity, which may be associated with medullary carcinoma of the thyroid and small-cell carcinoma of the bronchus, have not been associated with major changes in gastrointestinal physiology (see Chap. 161).70

OTHER NEUROPEPTIDES Several other peptides have been tentatively identified in the neural system and appear to be present in the gut, but firmer information is lacking. For example, neuromedin B is a peptide similar to BLP in its actions and sequence, although it is produced by different neurons.71 It occurs in the gut of some mammals but has not been investigated in humans. A peptide isolated from porcine spinal cord with uterine-contracting activities, known as neuromedin U, also is present in the gut neural system. A peptide originally isolated from the pituitary and given its chromato¬ graphic position name, 7B2, occurs widely in the neural system, including the gut.72 Because it has no identified pharmacologic activity, it is uncertain whether it acts as a regulatory or structural peptide.

PATHOPHYSIOLOGY OF THE GUT ENDOCRINE SYSTEM CHANGES AT BIRTH In the human fetus, gastrin, secretin, motilin, GIP, VIP, enteroglucagon, and somatostatin have been detected in the intes¬ tine as early as 8 weeks, and neurotensin was found at 12 weeks. The adult pattern of distribution is established by 20 weeks. In¬ testinal concentrations of regulatory peptides increase steadily until term, when they are close to adult levels.73 After birth, dramatic physiologic changes occur in the gas¬ trointestinal tract. The newborn infant switches from intrave¬ nous nutrition from the placenta to intermittent enteral feeding. Milk must be propelled through the gut, digested, and absorbed, and the infant must achieve metabolic homeostasis unaided. Gut hormones may play a key role in this process. Thus, infants who are fed intravenously (e.g., while awaiting surgery for intestinal atresia) show low levels of gut hormones, similar to the levels found in plasma from cord blood at birth. Conversely, basal hor¬ mone values rise between 3-fold and 13-fold in infants fed orally. Furthermore, a normal postprandial pattern slowly develops, with no change in gastrin, enteroglucagon, neurotensin, secretin, or GIP, after a feeding in 6-day-old infants; a highly significant postprandial elevation of these hormones, similar to the adult pattern, is seen by day 24. At this stage, plasma concentrations of gut hormones are several-fold higher than those usually seen in adults.74 Interestingly, the hormone pattern in bottle-fed infants is different from that in breast-fed infants; for example, basal lev¬ els of GIP, motilin, neurotensin, and VIP are significantly higher for breast feeding.75 What influence, if any, this has on the devel¬ opment of the gastrointestinal tract and metabolic responses to nutriments is unknown.

OBESITY AND OLD AGE Although it would seem likely that obesity and the associ¬ ated high food input might change either basal or postprandial gut hormone concentrations, the pattern of response to a meal of each of the hormones is not different from that in age- and sexmatched healthy control subjects.76 There has been speculation

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology about the possibility that the various hormones whose levels rise greatly after food ingestion (e.g., CCK) could be responsible for the phenomenon of satiety, but there is no evidence that periph¬ eral circulating concentrations of the hormones can affect food intake in humans. There is no evidence that obesity results from the lack of such a peripheral circulating signal. With developing age, the propensity of the stomach to secrete acid is diminished, presumably because of an autoimmune gastritis or previous at¬ tacks by infectious or toxic agents. This is associated with the operation of a feedback loop, because gastrin is normally sup¬ pressed by acid secretion. In old age, although the mean plasma gastrin concentration is significantly higher, the feedback mech¬ anism does not differ greatly from that in younger persons. PP and motilin are elevated with age, although the reason for and consequences of this increase, which is particularly marked in the case of PP, are unknown.77

GASTRIC PATHOLOGY A reduction in acid secretion, a common phenomenon with age, elevates gastrin. The achlorhydria associated with autoim¬ mune gastritis (pernicious anemia) is caused by massively ele¬ vated gastrin levels.9 Rarely, the antrum itself is destroyed in the autoimmune process, and hypergastrinemia is not seen. Gastrin stimulates the growth of the fundic enterochromaffin-like cells (see Figs. 175-1 and 175-2), and malignant gastric carcinoid may be a rare complication of hypergastrinemia of achlorhydria. It is uncertain whether the long-term administration of the acidinhibitory H2-receptor-blocking agents or the newer gastric proton pump inhibitory agents, by further suppressing acid se¬ cretion, may cause sufficient hypergastrinemia to develop a ma¬ lignant carcinoid syndrome. This phenomenon has been re¬ ported in animals dosed with these agents.78 Considerable interest has been shown in the question of whether duodenal ulcer (or peptic ulcer) results from abnormal gut hormones, excessive acid stimulation, or a failure of acid in¬ hibition or neutralization.79 A high percentage of patients with duodenal ulcer have been found to be infected with Helicobacter pylori. This bacterium lives in the mucous layer and secretes a urease, which destroys the protection the mucus offers the duo¬ denal mucosa. Some patients with duodenal ulcer have mildly elevated gastrin levels, and they are more sensitive to the effects of exogenous gastrin. Therapeutically, reduction of acid allowed ulcer healing and prevented recurrence. The frequent use of antacids is moderately effective but causes troublesome diarrhea or constipation. The first successful surgical treatment was antrectomy, which worked by removing the main source of gastrin. Almost 10% of men have duodenal ulcers, and this major surgical approach, which has a high mortality and morbidity, clearly was unsatisfactory; subse¬ quently, it was found that vagal denervation of the body and fundus of the stomach, a much quicker procedure, was nearly as effective. This was superseded by the H2-receptor-blocking agents; these, in turn, may be superseded by the more powerful proton pump inhibitors. The approach to acid inhibition first in¬ volved removal of a circulating hormone (hemocrine), then of the innervation (neural), and currently of a local stimulant (para¬ crine), neatly illustrating three ways in which the body's regula¬ tors work. Duodenal ulcer is permanently cured by elimination of the Helicobacter through the administration of antibiotics com¬ bined with complete gastric acid suppression.79'80 The consequences of the more severe types of gastric surgery (e.g., antrectomy or truncal vagotomy and pyloroplasty) are loss of normal gastric retention of food. In some patients, the dumping syndrome occurs. Tachycardia, hypotension, and abdominal dis¬ comfort develop shortly after a meal. The normal postprandial rises of intestinal hormone levels are grossly exaggerated, with very high plasma levels of, for example, VIP, neurotensin, enteroglucagon, and PYY.81 It is uncertain whether these elevated hormonal concentrations play any role in causing the syndrome.

1507

Similar symptoms, although of lesser magnitude, occur in the normal population and frequently are mistaken for reactive hy¬ poglycemia. Reactive hypoglycemia does occur after upper gas¬ trointestinal surgery and may be precipitated partly by excessive stimulation of insulin due to the very high levels of gut hor¬ mones; however, this is unproven.

INTESTINAL SURGERY In a healthy man, a considerable length of the small intestine can be resected without consequence, if the first 30 cm and the last 15 cm are left intact. This is partly because of compensatory functional change, which is the result of hormonal influences. In patients with partial ileal resection, a two-fold rise in gastrin and enteroglucagon concentrations was seen; moreover, there was a three-fold rise of PP and a four-fold rise of motilin82 (Fig. 175-7). In these patients, PYY also is elevated; it acts in concert with the presumed growth-enhancing activity of enteroglucagon by delaying gastric emptying and intestinal transit rate. Con¬ versely, colonic resection does not elevate enteroglucagon or PYY, hormones present in highest concentration in the colonic mucosa, but does produce small but significant elevations of PP and gastrin. Other hormones, such as GIP and neurotensin, are unaffected by these procedures. The tendency for peptic ulcer formation after massive small-bowel resection may relate partly

FIGURE 175-7.

Plasma motilin concentrations in a group of patients who had previously undergone partial small intestinal resection, a group who had undergone partial large intestinal resection, and an agematched and sex-matched normal control group after a 530-kcal test breakfast. (From Besterman HS, Adrian TE, Mallinson CN, et al. Gut hor¬ mone release after intestinal resection. Gut 1982;23:854.)

1508

PART X: DIFFUSE HORMONAL SECRETION

FIGURE 175-8.

Plasma glucose-depen¬ dent insulinotropic peptide (GIP) concen¬ trations in 19 patients who had undergone a 7-inch jejunum to 7-inch terminal ileum intestinal bypass for treatment of obesity are compared with those of age-matched and sex-matched groups of normal-weight controls and patients with morbid obesity. (From Bloom SR, Polak JM. The hormonal pat¬ tern of adaptation—a major role for entero¬ glucagon. Scand J Gastroenterol 1982;17:93.)

to the elevation of gastrin levels, but other factors also are important.83 Ileal bypass is an operation carried out in patients with famil¬ ial hypercholesterolemia to reduce serum cholesterol levels by causing bile salt malabsorption. A study undertaken a year after a biopsy of the distal third of the ileum showed virtually no change in the pattern of release of gastrointestinal hormones, al¬ though postprandial CCK concentrations were elevated.84 The operation of jejunoileal bypass was once popular for obe¬ sity. The first 7 inches of jejunum were anastomosed to the last 7 inches of ileum, leaving a large blind loop. In a study in which patients were followed up for 1 year after this procedure, the average weight of the patients had fallen from 225% of ideal body weight to 181%, but then had stabilized. Glucose tolerance was greatly improved, but the postprandial insulin release was less than that of age-matched normal-weight control subjects and greatly less than that of obese subjects. The postprandial re¬ lease of GIP was almost completely obliterated (Fig. 175-8), and that of enteroglucagon was elevated 16-fold (Fig. 175-9); neuro¬ tensin was elevated 8-fold and gastrin was elevated 2-fold.76 These changes can be explained anatomically. The area of bowel with GIP cells is bypassed, and the hormones produced beyond the bypass are elevated in compensation. The result of the very high enteroglucagon levels may be that the bowel left in continu¬ ity hypertrophies, and indeed, this is observed. When the pa¬ tients are examined 10 years later, they have regained their orig¬ inal weight, and their absorption is virtually back to normal. Therefore, the operation has been abandoned. An alternative procedure, in which the bypass loop of intestine starts higher up and contains both biliary and pancreatic secretions, is more effective at maintaining weight loss. A similar pattern of hor¬ mone change is seen, with decreased GIP and increased enteroglucagon.85

MALABSORPTION Chronic pancreatitis, especially if associated with steatorrhea, causes several changes in gut hormone secretion, Within the gland itself, endocrine cells participate in the pathologic process, and PP release is reduced greatly. In cystic fibrosis, for example, there is virtually no postprandial release of PP.86 Plasma neuro¬ tensin also is particularly elevated. Not surprisingly, such malab¬ sorption, with nutriments appearing in the colon, causes an in¬ creased release of enteroglucagon and PYY87,88 (Fig. 175-10).

FIGURE 175-9.

Plasma enteroglucagon concentrations in 19 patients who had undergone a 7-inch jejunum to 7-inch terminal ileum intestinal bypass for treatment of obesity are compared with those of age-matched and sex-matched groups of normal-weight controls and patients with morbid obesity. (From Bloom SR, Polak JM. The hormonal pattern of adap¬ tation—a major role for enteroglucagon. Scand J Gastroenterol 1982; 17:93.)

1509

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology 70 i

PYY

Chronic Pancreatitis with Steatorrhea n=l2

120 -plasma PYY pmol /L

tropical sprue

n=9

60100

-

5080o E

40Chronic Pancreatitis without Steatorrhea n = 21

Q.

30-

20-

Healthy Controls n = 16

60 -

40 -

----♦ 10-

0J

20 i-1-1-1

0

60

120

-

healthy controls •—»—•-—»—*---*

i

180

Minutes

0 -

r~

-i-

0

60

"l

180

minutes

FIGURE 175-10.

Plasma PYY concentrations in 12 patients with chronic pancreatitis and exocrine pancreatic failure, in 21 patients with chronic pancreatitis without steatorrhea, and in 16 age-matched and sexmatched healthy controls after eating a 530-kcal test breakfast at time zero. (From Adrian TE, Savage AP, Bacarese-Hamilton A], et al. Peptide YY abnormalities in gastrointestinal diseases. Gastroenterology 1986;90:379.)

120

n=12

FIGURE 175-12. Plasma PYY concentrations in nine patients with se¬ vere tropical sprue and 12 age-matched and sex-matched healthy con¬ trols after eating a 530-kcal test breakfast at time zero. (From Adrian TE, Savage AP, Bacarese-Hamilton A], et al. Peptide YY abnormalities in gastro¬ intestinal diseases. Gastroenterology 1986;90:374.)

MOTILIN

TIME (minutes) Time (minutes) FIGURE 175-11.

Plasma enteroglucagon concentrations in 11 patients with active malabsorption due to untreated celiac disease, in 13 patients who have been on a gluten-free diet and are now symptom-free, and in 13 age-matched and sex-matched normal controls after eating a 530-kcal test breakfast at time zero. (From Besterman HS, Bloom SR, Sarson DL, et al. Gut-hormone profile in coeliac disease. Lancet 1978;1:785.)

FIGURE 175-13. Plasma motilin concentrations in patients with acute infective diarrhea (origin unknown) and in age-matched and sexmatched healthy controls after eating a 530-kcal test breakfast at time zero. (From Besterman HS, Christofides ND, Welsby PD, et al. Gut hormones in acute diarrhoea. Gut 1983; 24:665.)

1510

PART X: DIFFUSE HORMONAL SECRETION is deficient in response to a test meal, but normal when secretin and CCK are administered exogenously. Conversely, the hor¬ mones released from the mucosa beyond the diseased area (e.g., neurotensin and enteroglucagon) are grossly elevated89 (Fig. 175-11). It was known that, despite the appearance of atrophy in the mucosa of the upper small intestine, enterocyte turnover was greatly increased, but the cells were being destroyed. One potent influence increasing the rate of cell turnover may be the high circulating concentrations of enteroglucagon. Westerners who work in the tropics often develop a chronic malabsorptive syndrome known as tropical sprue. This is thought to result partly from bacterial overgrowth of the small intestine after long-term consumption of heavily infected food. It yields high concentrations of motilin, enteroglucagon, and PYY88-90 (Fig. 175-12). These gut hormone changes disappear completely when the condition is treated with tetracycline and folic acid, as do the changes of celiac disease when patients are put on a gluten-free diet.

INFLAMMATION

Time (minutes) FIGURE 175-14.

Plasma enteroglucagon concentrations in patients with acute infective diarrhea (origin unknown) and in age-matched and sex-matched healthy controls after eating a 530-kcal test breakfast at time zero. (From Besterman HS, Christofides ND, Welsby PD, et al. Gut hormones in acute diarrhoea. Gut 1983;24:665.)

In celiac disease, a condition in which sensitivity to wheat gluten causes immune destruction of the upper intestinal mu¬ cosa, gastric and pancreatic hormones are unaffected, but intesti¬ nal hormones (e.g., secretin, CCK, and GIP) are reduced greatly. This explains the observation that pancreatic exocrine secretion

FIGURE 175-15. A, Submucosa of normal human colon showing bundles of vasoactive intestinal pep¬ tide immunoreactive fibers; X350. B, Submucosa and base of mucosa of colon from a patient with Crohn colitis. There is a hyperplastic reaction of the benzoquinone solution-fixed tissue and indirect im¬ munofluorescence technique; X350.

Acute diarrhea consequent to infection with bacteria or vi¬ ruses, which frequently are of unknown type and origin, dramat¬ ically elevates plasma motilin (Fig. 175-13), enteroglucagon (Fig. 175-14), and PYY.91 These changes disappear with recovery and are presumably important in encouraging reparative cell growth and readjusting gastrointestinal motility. Acute gastric infections are associated with dramatic elevations of plasma gastrin, pre¬ sumably important in stimulating reparative gastric cell growth and acid. The pattern of change in inflammatory bowel disease is less specific. In Crohn disease, the most significant abnormality in circulating hormones is the increased PP release, with smaller increases of GIP, motilin, and enteroglucagon.92 Histologic ex¬ amination of the bowel shows a remarkable change in the ap¬ pearance of the VIP innervation, with the nerves appearing di¬ lated and tortuous92 (Fig. 175-15). In ulcerative colitis, no marked local abnormality of the neuroendocrine system has been noted, but plasma PP, gastrin, GIP, and motilin are moderately elevated.93

NEURAL ABNORMALITIES Hirschsprung disease is a condition in which a part of the bowel, usually the large bowel, is narrowed secondary to an aganglionic segment. The condition is congenital, but in less se-

Ch.175: The Endocrine Gastrointestinal Tract: Pathophysiology vere cases, it may occur in adult life. Not surprisingly, the affected segments show strikingly reduced concentrations of plasma VIP and substance P.94 Chronic gastrointestinal Chagas disease is man¬ ifested many years after infection with the flagellate protozoan, Trypanosoma cruzi. Periganglionitis and degeneration of intrinsic¬ cell bodies are the main histologic features; there is severe dener¬ vation, with megaesophagus, megacolon, and megaduodenum, and consequent functional obstruction. The concentrations of VIP, enteroglucagon, substance P, and somatostatin in the bowel wall are dramatically reduced.95 Conversely, idiopathic chronic autonomic atrophy (Shy-Drager syndrome), which produces marked gut dysfunction secondary to cord degeneration of auto¬ nomic neurons without local gut disease, is associated with com¬ pletely normal bowel concentrations of all regulatory peptides.95 Dysfunctional bowel syndromes are common (e.g., “irritable bowel syndrome," "spastic bowel").96 Patients who had abdom¬ inal pain and constipation, abdominal pain alone, or abdominal pain and diarrhea without any detectable pathologic changes were studied to see whether they had matching functional ab¬ normalities of gut hormone release. No important changes from the normal pattern were detectable, and there is no evidence that changes in the gut hormone system cause these conditions.97

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1511

syndrome mediated by abberrant adrenal sensitivity to gastric inhibitory polypep¬ tide. N Engl] Med 1992;327:981. 24. Polak JM, Sullivan SN, Bloom SR, et al. Neurotensin in human intestine: radioimmunoassay and specific localisation to the N cell. Nature 1977;270:183. 25. Go VLW, Demol P. Role of nutrients in the gastrointestinal release of immunoreactive neurotensin. Peptides 1981;2:267. 26. Thor K, Rokaeus A, Kager L, Rosell S. (Gln4)-neurotensin and gastrointes¬ tinal motility in man. Acta Physiol Scand 1980; 110:327. 27. Lee YC, Allen JM, Uttenthal LO, et al. The metabolism of intravenously infused neurotensin in man and its chromatographic characterization in human plasma. ] Clin Endocrinol Metab 1984;59:45. 28. Holst ]]. Gut glucagon, enteroglucagon, gut glucagon-like immunoreac¬ tivity, glicentin—current status. Gastroenterology 1983,-84:1602. 29. Bell GI, Santerre RF, Mullenbach GT. Hamster pre-pro-glucagon contains the sequence of glucagon and two related peptides. 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Human distribution and release of a putative new gut hormone, peptide YY. Gastroenterology 1985; 89: 1070. 38. Guo Y-S, Singh P, Draviam E, et al. Peptide YY inhibits the insulinotropic action of gastric inhibitory polypeptide. Gastroenterology 1989;96:690. 39. Aponte GW, Fink AS, Meyer JH, et al. Regional distribution and release of peptide YY with fatty acids of different chain length. Am J Physiol 1985; 249:G745. 40. Arimura A, Culler MD, Matsumoto K, et al. Growth hormone releasing factors in the brain and the gut: chemistry, actions, and localization. Peptides 1984;5:41. 41. Reichlin S. Somatostatin (first of two parts). N Engl J Med 1983;309:1495. 42. Bloom SR, Polak JM. Somatostatin. BMJ 1987;295:288. 43. Gyr K, Beglinger C, Kohler E, et al. Circulating somatostatin. Physiological regulator of pancreatic function. J Clin Invest 1987; 79:1595. 44. Panetta R, Greenwood MT, Warszynska A, et al. Molecular cloning, func¬ tional characterization, and chromosomal localization of a human somatostatin re¬ ceptor (somatostatin receptor type 5) with preferential affinity for somatostatin-28. Mol Pharmacol 1994;45:417. 45. Hou C, Gilbert RL, Barber DL. Subtype-specific signaling mechanisms of somatostatin receptors SSTR1 and SSTR2. J Biol Chem 1994;269:10357. 46. Kubota A, Yamada Y, Kagimot S, et al. Identification of somatostatin re¬ ceptor subtypes and an implication for the efficacy of somatostatin analogue SMS 201-995 in treatment of human endocrine tumors. J Clin Invest 1994; 93:1321. 47. Said SI. Vasoactive intestinal polypeptide (VIP): current status. Peptides 1984;5:143. 48. Tatemoto K. PHI—a new brain-gut peptide. Peptides 1984;5:151. 49. Yiangou Y, Christofides ND, Blank MA, et al. Molecular forms of peptide histidine isoleucine-like immunoreactivity in the gastrointestinal tract. Non-equimolar levels of peptide histidine isoleucine and vasoactive intestinal peptide in the stomach explained by the presence of a big peptide histidine isoleucine-like mole¬ cule. Gastroenterology 1985;89:516. 50. Inagaki N, Yosluda H, Mizuta M, et al. Cloning and functional character¬ ization of a third pituitary adenylate cyclase-activating polypeptide receptor subtype expressed in insulin-secreting cells. Proc Natl Acad Sci USA 1994;91:2679. 51. Thompson JW. Opioid peptides. BMJ 1984;288:259. 52. Miller R. How do opiates act? Trends in Neurological Sciences 1984; 7: 184. 53. North RA. Opioid receptor types and membrane ion channels. TINS 1986; 8:114. 54. Miller RJ, Brown DR. Opiates and the gut. Dig Dis Sci 1984; 16:5. 55. Nawa H, Kotani H, Nakinishi S. Tissue specific generation of two pre-pro¬ tachykinin mRNAs from one gene by alternative RNA splicing. Nature 1984;312: 729. 56. Nakanishi S. Structure and regulation of the pre-pro-tachykinin gene. TINS 1986;8:41. 57. Kimura S, Okada M, Sugita Y, et al. Novel neuropeptides, neurokinin alpha and beta, isolated from porcine spinal cord. Proc Jpn Acad 1983; 59:101. 58. McCarson FE, Krause JE. NK-1 and NK-3 type tachykinin receptor mRNA expression in the rat spinal cord dorsal horn is increased during adjuvant or formalin-induced nociception. J Neurosci 1994; 14:712. 59. Quirion R. Multiple tachykinin receptors. TINS 1985;6:183. 60. Jonas V, Lin CR, Kawashima E, et al. Alternative RNA processing events in human calcitonin/calcitonin-gene-related peptide gene expression. Proc Natl Acad Sci USA 1985; 82:1994. 61. Editorial. Calcitonin gene-related peptide. Lancet 1985;2:25. 62. Gibbins IL, Furness JB, Costa M, et al. Co-localization of calcitonin generelated peptide-like immunoreactivity with substance P in cutaneous vascular and visceral sensory neurons of guinea pigs. Neurosci Lett 1985;57:125.

1512

PART X: DIFFUSE HORMONAL SECRETION

63. Ekblad E, Rokaeus A, Hakanson R, Sundler F. Galanin nerve fibers in the rat gut: distribution, origin and projections. Neuroscience 1985; 16:355. 64. Ekblad E, Hakanson R, Sundler F, Wahlestedt C. Galanin: neuromodulatory and direct contractile effects on smooth muscle preparations. Br ] Pharmacol 1985;86:241. 65. Emson PC, De Quidt ME. NPY—a new member of the pancreatic poly¬ peptide family. TINS 1984; 7:31. 66. Ferri G-L, Ali-Rachedi A, Tatemoto K, et al. Immunocytochemical local¬ ization of neuropeptide Y-like immunoreactivity in extrinsic noradrenergic and in¬ trinsic gut neurons. In: Ratzenhofer M, Hofler H, Walter GF, eds. Frontiers of hor¬ mone research interdisciplinary neuroendocrinology, vol 12. Basel: S Karger, 1984: 81. 67. Lambert PD, Wilding W, al-Dokhayel AA, et al. The effect of central blockade of kappa-opioid receptors on neuropeptide Y-induced feeding in the rat. Brain Res 1993:629:146. 68. Spindel E. Mammalian bombesin-like peptides. TINS 1986; 7:130. 69. Erspamer V. Half a century of comparative research on biogenic amines and active peptides in amphibian skin and molluscan tissues. Comp Biochem Phys¬ iol [B] 1984; 79:1. 70. Bostwick DG, Bensch KG. Gastrin releasing peptide in human neuroen¬ docrine tumours. J Pathol 1986; 146:237. 71. Namba M, Ghatei MA, Anand P, Bloom SR. Distribution and chromato¬ graphic characterization of neuromedin B-like immunoreactivity in the human spi¬ nal cord. Brain Res 1985;342:183. 72. Suzuki H, Christofides ND, Adrian TE, et al. Ontogeny of a novel pituitary protein (7B2) in the human fetal intestine. Regul Pept 1985; 12:289. 73. Bryant MG, Buchan AMJ, Gregor M, et al. Development of intestinal reg¬ ulatory peptides in the human fetus. Gastroenterology 1982;83:47. 74. Lucas A, Aynsley-Green A, Bloom SR. Gut hormones and the first meals. Clin Sci 1981; 60:349. 75. Lucas A, Sarson DL, Blackburn AM, et al. Breast vs bottle: endocrine re¬ sponses are different with formula feeding. Lancet 1980; 1:1267. 76. Bloom SR. Hormonal changes after jejuno-ileal bypass and their physio¬ logical significance. In: Maxwell JD, Gazet J-C, Pilkington TR, eds. Surgical man¬ agement of obesity. London: Academic Press, 1980:115. 77. Adrian TE, Bloom SR. Gut and pancreatic hormones in the elderly. In: Hodkinson M, ed. Clinical biochemistry of the elderly. New York: Churchill Living¬ stone, 1984:273. 78. Larsson H, Carlsson E, Mattsson H, et al. Plasma gastrin and gastric enterochromaffinlike cell activation and proliferation. Studies with omeprazole and ranitidine in intact and antrectomized rats. Gastroenterology 1986;90:391. 79. Adamek RJ, Wegener M, Labenz J, et al. Medium-term results of oral and intravenous omeprazole/amoxicillin Helicobacter pylori eradication therapy. Am J Gastroenterol 1994; 89:39. 80. Forbes GM, Glaser ME, Cullen D], et al. Duodenal ulcer treated with Hel¬ icobacter pylori eradication: seven-year follow-up. Lancet 1994;343:258. 81. Adrian TE, Long RG, Fuessl HS, Bloom SR. Plasma peptide YY (PYY) in dumping syndrome. Dig Dis Sci 1985;30:1145. 82. Besterman HS, Adrian TE, Mallinson CN, et al. Gut hormone release after intestinal resection. Gut 1982; 23:854. 83. Buxton B. Small bowel resection in gastric acid hypersecretion. Gut 1974;15:229. 84. Allen JM, Sarson DL, Adrian TE, et al. Effect of partial ileal bypass on the gut hormone responses to food in man. Digestion 1983;28:191. 85. Sarson DL, Scopinaro N, Bloom SR. Gut hormone changes after jeju¬ noileal (JIB) or biliopancreatic (BPB) bypass surgery for morbid obesity. Int J Obes 1981;5:471. 86. Allen JM, Penketh ARL, Adrian TE, et al. Adult cystic fibrosis: postpran¬ dial response of gut regulatory peptides. Gastroenterology 1983;85:1379. 87. Besterman HS, Adrian TE, Bloom SR, et al. Pancreatic and gastrointestinal hormones in chronic pancreatitis. Digestion 1982; 24:195. 88. Adrian TE, Savage AP, Bacarese-Hamilton AJ, et al. Peptide YY abnor¬ malities in gastrointestinal diseases. Gastroenterology 1986;90:379. 89. Besterman HS, Bloom SR, Sarson DL, et al. Gut-hormone profile in coeliac disease. Lancet 1978; 1:785. 90. Besterman HS, Cook GC, Sarson DL, et al. Gut hormones in tropical mal¬ absorption. BMJ 1979;1:1252. 91. Besterman HS, Christofides ND, Welsby PD, et al. Gut hormones in acute diarrhoea. Gut 1983; 24:665. 92. Bishop AG, Polak JM, Bryant MG, et al. Abnormalities of vasoactive in¬ testinal polypeptide-containing nerves in Crohn's disease. Gastroenterology 1980;79:853. 93. Besterman HS, Mallinson CN, Modigliani R, et al. Gut hormones in in¬ flammatory bowel disease. ScandJ Gastroenterol 1983; 18:1845. 94. Taguchi T, Tanaka K, Ikeda K, et al. Peptidergic innervation irregularities in Hirschsprung's disease. Virchows Arch [A] 1983;401:223. 95. Long RG, Bishop AE, Barnes AJ, et al. Neural and hormonal peptides in rectal biopsy specimens from patients with Chagas' disease and chronic autonomic failure. Lancet 1980; 1:559. 96. Waxman D. The irritable bowel: a pathological or a psychological syn¬ drome?! R Soc Med 1988;81:718. 97. Besterman HS, Sarson DL, Rambaud JC, et al. Gut hormone responses in the irritable bowel syndrome. Digestion 1981; 21:219.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

176_

ENDOCRINE TUMORS OF THE GASTROINTESTINAL TRACT STEPHEN R. BLOOM, PETER J. HAMMOND, AND JULIA M. POLAK

Peptide endocrine tumors of the gastrointestinal tract arise mostly in the pancreas (Fig. 176-1). They are usually slow grow¬ ing; most often, their clinical manifestations are entirely due to excess hormone. They have provided useful information on the long-term action of hormones—an experiment of nature. Be¬ cause they are slow growing, palliation is useful even when they have metastasized; usually, this involves suppressing the release or blocking the actions of the particular hormonal peptide. The tumor bulk produces problems only late in the clinical course. There is a striking variation in the malignancy of these tu¬ mors. At one extreme are insulinomas, about 80% of which are benign (see Chaps. 152 and 155). Even if they occur in a small child, once resected, they may not recur during the next 60 years. Conversely, virtually all gastrinomas may be malignant, as is sug¬ gested by long-term follow-up of gastrinoma patients who, after apparently successful resection of the primary pancreatic tumor, show a steady rate of recurrence, with a predicted 100% inci¬ dence after about 30 years. Although each of the endocrine tumors produces a single major peptide product, they frequently produce other peptides, and the cell population often is mixed. Sometimes the clinical picture changes over time, particularly after therapeutic interven¬ tion, such as tumor debulking, when the initial excess hormone may be superseded by a new principal hormone producing a different clinical picture. Thus, tumor types are in some way re¬ lated and can be thought of as "islet cell tumors." This is particu¬ larly true in the multiple endocrine neoplasia syndrome type I with the features of parathyroid disease (usually hyperplasia), pituitary tumor, and pancreatic tumors of any type. This familial condition can present with an insulinoma in one member of the family and a gastrinoma in another. It is important to screen other family members for abnormalities of calcium metabolism, for ab¬ normal pituitary function, and for pancreatic tumors (see Chap. 182).

ENDOCRINE TUMORS OF THE GASTROINTESTINAL TRACT GASTRINOMA Zollinger and Ellison first described the triad of fulminating and recurrent peptic ulceration, with failure of response to stan¬ dard medical and surgical therapy, in association with an islet cell tumor of the pancreas in 1955.1 Subsequently, there have been many reports of this uncommon tumor. Previously, it was diag¬ nosed late; often, there was massive gastric acid secretion and gastric mucosal hypertrophy, associated with recurrent peptic ul¬ cer with perforation or hemorrhage. With improved clinical awareness of the syndrome, gastrinomas often are diagnosed early, when the clinical picture differs little from that of the com¬ mon duodenal ulcer. However, because peptic ulcers are com¬ mon and gastrinomas rare, it is not usually economical to screen all ulcer cases. The annual incidence of gastrinoma is about one patient per million people.3 Thus, only those patients with persistently re-

Ch. 176: Endocrine Tumors of the Gastrointestinal Tract

1513

FIGURE 176-1.

Hematoxylin and eosin stain of a pancreatic endocrine tumor. The lesion shows a solid growth pattern of regular cells with regular nu¬ clei. Nucleoli can be seen in some cells, but mitotic figures are absent. Bouin's fixation; X400.

curring ulcer after treatment, with a particularly virulent course, with peptic ulceration in atypical sites, or who are unusually young are screened. Patients often suffer from diarrhea, some¬ times predating the ulceration by many months. This is the result of the high acid output blocking the action of pancreatic enzymes and irritating the upper small intestine, resulting in a high secre¬ tory rate. A barium meal study that shows hyperrugosity of the stomach (multiple ulcers), or jejunal ulcers, indicates the need to exclude a gastrinoma. Because gastrinomas are the most common pancreatic tumors associated with multiple endocrine neoplasia syndrome type I, a high plasma gastrin in this condition is sus¬ pect. Gastrin does not produce any effects other than on the stomach, so that a patient who previously has undergone a total gastrectomy can have gastrin concentrations elevated 1000-fold without any clinical consequences. The confirmation of the diagnosis of a gastrinoma depends on the finding of high gastrin in the face of high acid secretion. High gastrin per se is not associated with peptic ulcer except con¬ comitantly with a gastrinoma. It is the authors' experience that less than 1% of the samples sent to a laboratory for radioimmu¬ noassay of plasma gastrin that bear the label "gastrinoma?" and that have elevated gastrin will actually have a gastrin-producing tumor. By far the most common cause of raised gastrin is reduced acid secretion. This can occur even with an active peptic ulcer and, although uncommon, is far more frequent than the very rare gastrinoma. Thus, it is only the first step in the diagnosis of a gastrinoma to demonstrate a high gastrin level. Of course, if the patient has a proven pancreatic endocrine tumor and aggressive peptic ulceration, the high gastrin may clinch the diagnosis. In almost every other circumstance, it is necessary to demonstrate high acid secretion. Because this involves the unpleasant in¬ sertion of a gastric tube and an expensive, prolonged, and un¬ comfortable test, it is deservedly unpopular, but necessary nonetheless. Each laboratory has its own normal range, and local results must be judged against it. In the authors' laboratory, a gastrin level above 40 pmol/L is considered necessary before the diag¬ nosis of gastrinoma can be considered; a basal acid output of greater than 15 mEq/hour would confirm the diagnosis. Tests of stimulated acid production do not appear to contribute to the diagnostic accuracy. Unfortunately, equivocal results may be ob¬ tained, particularly if gastrinomas are diligently sought and de¬ tected early. Thus, a number of provocative tests have been de¬ vised. Perhaps the most common is the infusion of pure secretin

(2 units/kg intravenously), which normally suppresses gastrin output, but which in gastrinomas yields a greater than 50% rise within half an hour. Unfortunately, a significant number of false¬ positive results occur; therefore, this test should be reserved for equivocal cases. Other tests, such as the gastrin response to calcium infusion or meal provocation, are even less useful.1 Also, there are some circumstances in which plasma gastrin elevation can be expected to occur, for example in renal failure, after va¬ gotomy, and with ingestion of acid inhibitory agents. These should be considered when making the diagnosis of gastrinoma. If the suspicion of a gastrinoma is sufficiently high, it is rea¬ sonable to attempt to localize the lesion (see Chap. 153). If, using the best techniques, a tumor cannot be localized, surgical explo¬ ration is not warranted. This is not because the exploration is dangerous but because it leads the surgeon into the temptation of having to do "something." Commonly, the something is partial pancreatectomy, which usually is not helpful and often is dan¬ gerous. This is a contentious area with many different opinions. Nevertheless, with the availability of powerful pharmacologic agents that completely inhibit acid secretion ("medical gastrec¬ tomy"), such as the proton pump inhibitor omeprazole, it seems reasonable to wait until the diagnosis becomes clearer and a tu¬ mor can be localized.33 Careful follow-up with routine monitor¬ ing of plasma gastrin levels is advisable, but results are made more difficult to interpret by the necessary ingestion of agents to inhibit acid secretion. A condition of antral G-cell hyperplasia has been described, with high plasma gastrin and high acid output. The cause of this has been postulated to be a relative loss of acid inhibition of the G cell. It is difficult to know, however, whether it is a definite entity or merely one end of a normal range. It is diagnosed by counting G cells in an antral biopsy and showing hyperplasia (there is atrophy with a gastrinoma). Unfortunately, the distribu¬ tion of the G cells in the antral mucosa is very uneven, and small patches of apparent hyperplasia occur, even in normal persons. The condition may be similar to the very rare excluded antrum syndrome after upper gastrointestinal surgery. The accidental sur¬ gical isolation of normal gastrin-producing stomach tissue pre¬ vents the tissue from being bathed by acid; therefore, the normal feedback inhibition of the G cell by acid is lost. Most gastrinomas originate in the pancreas, but as many as 40% are located in the duodenum, where they are frequently multiple and may have greater malignant potential; therefore, initial curative resection should be attempted if possible.4 The cell

1514

PART X: DIFFUSE HORMONAL SECRETION

of origin of the gastrinoma in the pancreas remains controversial, because gastrin normally is not present in the adult pancreas. However, gastrin has been found in the human fetal pancreas. Gastrin easily is demonstrated by immunocytochemistry. At the ultrastructural level, gastrinomas frequently exhibit either large, electron-lucent or small, electron-dense granules.

GLUCAGONOMA The glucagonoma syndrome was first characterized with the publication of a series of case reports of nine patients, but several individual case reports had been published previously.5-6 There are now over 100 case reports in the literature. The average age of onset is about 55 years, and women predominate by about two to one.7-8 The most characteristic but unexpected feature of the syndrome is the presence of a necrolytic migratory erythematous rash. This first affects the groin, and this area is usually the last to heal on therapy. There are superficial skin blisters, but unless there is secondary infection, there is no inflammatory infiltrate. The rash tends to migrate, leaving behind a healing center, which often has permanent brown pigmentation. The appearance is sufficiently characteristic for dermatologists who have never seen the condition before to be able to diagnose it from the text¬ book description. The patients are frequently anemic, with a normochromic-normocytic pattern. Weight loss is a major fea¬ ture, and the patients' cachectic appearance can be confused with pancreatic acinar cell carcinoma, although in the latter, the clini¬ cal course is far more aggressive. Patients also have frequent, painful glossitis and angular stomatitis. Plasma glucose is often elevated, although the diabetes is usually mild. Once glucagon was thought to be important in the pathogenesis of diabetes and its complications, but the finding that glucagonoma patients with very high plasma pancreatic glu¬ cagon concentrations had only mild diabetes, with no evidence of increased diabetic complications or ketoacidosis, led to the down¬ grading of its possible importance in the common, idiopathic form of diabetes. Often, patients are mildly depressed, although this may not be a specific consequence of glucagon elevation but rather the result of a chronic illness. There is a tendency to ve¬ nous thrombosis, which is often the cause of death. The diagnosis of the glucagonoma syndrome, once consid¬ ered, is very straightforward. Plasma glucagon values are grossly elevated (in the authors' laboratory, above 50 pmol/L). There are very few confusing circumstances. Patients with renal failure undoubtedly have high glucagon-like reactivity in their plasma, but the cause is usually obvious. Glucagon is slightly elevated with chronic starvation or hypoglycemia and is slightly ele¬ vated in diabetes mellitus. The plasma concentrations found in glucagonomas usually grossly exceed those seen in the other circumstances. The sequence of preproglucagon is known (see Chaps. 130 and 175), and a specific pattern of posttranslational enzymatic processing is particular to the A cell. In tumors, the enzyme pro¬ cessing is often deficient. For example, with glucagonomas, large molecular forms are released systemically (Fig. 176-2). Moreover, the tumors produce glucagon-like peptides in considerable quan¬ tities, but their possible physiologic effects are unknown.9 Rarely, patients without glucagonoma have familial hyperglucagonemia, and this can be diagnosed because several members of the family can be affected.10 Certain types of progestogenic andro¬ gens can specifically elevate glucagon.11 An interesting biochem¬ ical feature of the glucagonoma syndrome is that the plasma con¬ centration of amino acids is usually low, particularly alanine and glutamine. This is expected because of the stimulation of hepatic gluconeogenesis by glucagon. The glucagonoma tumor is usually single and, by the time of diagnosis, large. This directly contrasts with insulinomas and gastrinomas, which may present early, perhaps because their product is so potent. About half of the glucagonomas have me¬ tastasized by the time of diagnosis, usually to the liver. Histolog-

FIGURE 176-2. Gel chromatographic pattern of plasma pancreatic glu¬ cagon from three patients with a glucagonoma. The first arrow marks the position of large-molecular-weight plasma proteins (V0), and the second arrow indicates the position of pancreatic glucagon PG(h). The plasma profile of the patient in the lowest panel is almost entirely composed of large-molecular-weight glucagon. (From Bloom SR, Adrian TE, Mallinson CN, et al. The glucagonoma syndrome and the effect of a new long-acting subcutaneous somatostatin. In: Andreani D, Lefebvre P, Marks V, eds. Current views on hypoglycaemia and glucagon. New York: Academic Press, 1980:127.)

ically, the tumors have the classic appearance of an endocrine neoplasm, and immunocytochemical methods allow the specific diagnosis. At the ultrastructural level, there often are several populations of secretory granules, some of which may display the classic appearance of the A-cell granule with an eccentric core.

VIPOMA Many types of tumors are associated with diarrhea, but in 1958, Verner and Morrison described two cases in which a pan¬ creatic tumor appeared to be responsible.12 Because gastrinomas may also be associated with diarrhea, emphasis was placed on the low acid secretion, and the term WDHA (watery diarrhea, hypokalemia, and achlorhydria) was applied. In 1973, these tu¬ mors were found to produce vasoactive intestinal peptide (VIP) and were renamed VlPomas.13-14 They were subsequently found to produce another peptide capable of inducing watery secretions from the small intestine, peptide histidine methionine (PHM), and these two peptides were produced by a single preprohor¬ mone15 (see Chap. 168). The term VIPoma will be used here, but it is conceivable that PHM is the more important mediator of the watery diarrhea syndrome. The most striking clinical feature of the VIPoma syndrome is severe watery diarrhea with stool volumes of up to 20 L/day and potassium losses of greater than 300 mEq/day. In the early stages, this is usually intermittent, but with continued tumor growth, it becomes continuous and life threatening. The stool is otherwise normal and does not contain mucus or blood; steator-

Ch. 176: Endocrine Tumors of the Gastrointestinal Tract rhea is not a feature. The severe diarrhea is accompanied by hy¬ pokalemia, and this can be severe enough to cause temporary quadriplegia. It is frequently accompanied by a metabolic acido¬ sis, as a result of bicarbonate loss in the stool. Small bowel biopsy is normal. The average duration of symptoms before diagnosis is about 3 years; other features are weight loss, hypercalcemia, and mild glucose intolerance. Occasionally, abdominal colic or flush¬ ing attacks are described.16 The diagnosis depends on finding an elevated VIP concen¬ tration in plasma. When infused in humans, VIP has a half-life of less than a minute, and is thus cleared very rapidly. This probably explains why, despite a body-wide VIPergic nervous system, basal plasma VIP levels usually are low ( 10,000 pmol/L). Nevertheless, there was no obvious clin¬ ical syndrome associated with the high plasma PP concentra¬ tions. As mentioned in Chapter 175, the pharmacologic effects of PP are weak and, presumably, escape from its action readily oc¬ curs. However, the measurement of plasma PP offers another aid to the diagnosis of a pancreatic tumor because, on the average, it is elevated in more than 50% of the patients. The high levels of PP are not suppressed by atropine, which causes a highly sig¬ nificant reduction of PP release from the normal PP cell under tonic vagal drive. VIPomas most frequently secrete PP (about 75%), and insulinomas least frequently (about 25%). Rare tumors produce only PP, but are associated with no clinical endocrine syndrome. In one interesting case, a skin rash was reported.2" Histologically, the tumors are usually composed of mixed cell types, one of which can be immunocytochemically identified as producing PP.

o E Cl

SOMATOSTATINOMAS

$•». i-i

Normal WDHA

PHM FIGURE 176-3.

Normal

WDHA

VIP

Plasma peptide histidine methionine (PHM) and vaso¬ active intestinal peptide (VIP) concentrations in normal controls and in patients with the watery diarrhea syndrome (VIPoma). Because of the slower clearance from the plasma of PHM, concentrations are much higher than those of the cosynthesized VIP. WDHA, watery diarrhea, hy¬ pokalemia, and achlorhydria. (From Yiangou Y, Williams SJ, Bishop AE, et al. Peptide histidine-methionine immunoreactivity in plasma and tissue from patients with vasoactive intestinal peptide-secreting tumors and watery diar¬ rhoea syndrome. ] Clin Endocrinol Metab 1987;64:131.)

These are relatively rare tumors and are frequently not asso¬ ciated with any clinical syndrome.18,23 Earlier reports described gallstones, steatorrhea, diabetes, and weight loss; subsequently, hypoglycemia was noted in some cases."1 The tumors usually present when they are of considerable size, and the clinical fea¬ tures may partly reflect the presence of a large pancreatic mass. A history of up to a decade of mild diabetes is often obtained. In as many as 50% of cases, the somatostatinoma is duodenal in origin, usually periampullary. These tumors often occur in asso¬ ciation with neurofibromatosis type 1 (von Recklinghausen syn¬ drome) and rarely cause the clinical syndrome.25 Various molec¬ ular forms of the hormonal peptide are produced.26 7 These tumors provide an interesting example of long-continued gross elevation of somatostatin, a topic of some relevance now that the long-acting somatostatin analogue, octreotide acetate, is being used therapeutically28 (see Chap. 166).

1516

PART X: DIFFUSE HORMONAL SECRETION

FIGURE 176-4. Indium- 111 —la¬ beled pentetreotide scan (A) show¬ ing a primary nonfunctioning pan¬ creatic neuroendocrine tumor with metastases to liver, lymph nodes, and bone, confirmed on bone scan

A

(B).

FIGURE 176-5. A, Hepatic arteriogram showing three large he¬ patic metastases in the right lobe. B, Hepatic arteriogram of the same patient after hepatic artery embolization, which completely oc¬ cluded the arterial supply to the secondaries seen in A.

Ch. 176: Endocrine Tumors of the Gastrointestinal Tract

OTHER ENDOCRINE TUMORS OF THE GUT Several other peptides are produced by pancreatic endocrine tumors, including neuropeptide Y, calcitonin gene-related pep¬ tide, and bombesin-like peptide.28,29 No particular clinical features are associated with these rare lesions. Production of corticotropin-releasing hormone, however, is associated with Cushing syndrome, and growth hormone-releasing hormone is associated with acromegaly. The latter situation prompted the initial purification of growth hormone-releasing hormone from a pancreatic tumor.30 Many tumors produce small amounts of such peptides without necessarily causing any clinical syndrome.31 A protein originally isolated from the pituitary and given the chromatographically trivial name of 7B2 was found to be present in the pancreas and to be produced by many pancreatic tumors.32 Plasma 7B2 concentrations were considerably elevated in this cir¬ cumstance and offered the prospect of a further diagnostic test. No clinical features were associated with the elevation of 7B2.

TUMOR LOCALIZATION The most effective mechanism for localizing pancreatic tu¬ mors remains classic arteriography with selective contrast injec¬ tion into particular arteries and the use of background subtrac¬ tion. Digital subtractive arteriography is valuable. Hepatic metastases also show up well on arteriography. Computed tomo¬ graphic scans of the pancreas are less valuable than elsewhere in the body, but have the advantage of being non-invasive. Not all hepatic metastases show up, owing to an occasional lack of den¬ sity contrast. Often, small lesions cannot be detected. Magnetic resonance imaging may now be the best method for detecting hepatic metastases if the correct protocol is used, but it is less effective with pancreatic primaries. Both computed tomography and magnetic resonance imaging are useful for following the progress of tumor growth.33 Ultrasound is of lower resolution and rarely helpful. The technique of transhepatic portal venous sampling with measurement of plasma concentrations of hor¬ mone unfortunately has a fairly high morbidity. It requires highly experienced personnel and the procedure takes a long time if, as is necessary, all the venous tributaries are cannulated. Simulta¬ neous hepatic vein sampling is required, because tumor hormone production can vary spontaneously with time and give false lo¬ calization. An alternative technique is arterial stimulated (he¬ patic) venous sampling, which can be performed at the same time as angiography, with little additional risk of morbidity. It appears to be an effective means of localizing small gastrinomas and in¬ sulinomas. Endoscopic ultrasonography is a useful localizing technique in experienced hands, particularly for tumors in the pancreatic head, and somatostatin receptor scintigraphy with indium-ill-labeled pentetreotide accurately delineates the ex¬ tent of metastatic disease (Fig. 176-4), but is unlikely to have sufficient resolution to identify primary tumors less than 1 cm in diameter. Perioperative localization of small lesions may be aided by the use of intraoperative ultrasonography or duodenal trans¬ illumination34 (see Chap. 153).

1517

formed on patients under local anesthesia and, if embolization first is undertaken with small particles to block the distal arteries, recanalization or the opening of anastomotic vessels is rare. Pa¬ tients should be pretreated with a course of antibiotic therapy (e.g., aminoglycoside, metronidazole, and penicillin), which should continue for 10 days after the procedure, because a ne¬ crotic tumor can easily become the seat of secondary infection with fatal consequences (Fig. 176-5). Cytotoxic therapy with streptozocin, a glucosamine nitro¬ sourea, is dramatically effective with VIPomas. Response rates exceed 90%, and remissions may last more than a year. The agent is less effective with other types of tumors but, occasionally, ex¬ cellent remissions are achieved. The main side effect of strepto¬ zocin is renal toxicity, and particular care must be exercised in patients with reduced renal function because the drug is cleared renally. With good hydration and careful monitoring to assess the development of proteinuria, most patients have no complica¬ tions. Rarely, hepatic and hematologic toxicity is observed. The agent causes acute fever and nausea and is best given at night with aspirin and antiemetic sedation. A typical course might be 0.5 g/m2 body surface, given on alternate days on five occasions with careful monitoring of urinary protein throughout. Strepto¬ zocin is usually given in combination with 5-fluorouracil, al¬ though the advantage of this is unclear, with one study showing a non-statistically significant benefit.37 The combination of streptozotocin and doxorubicin has been reported to be the most effective chemotherapeutic regimen, with a response rate of over 60%, associated with prolongation of survival. 8 Symptomatic treatment varies with the tumor type. How¬ ever, the long-acting somatostatin analogue (octreotide acetate) gives effective 24-hour blood levels with a dosage of 100 pg sub¬ cutaneously every 8 hours and allows the suppression of hor-

TUMOR TREATMENT The optimal treatment is complete surgical resection, but this is possible only in a few noninsulinoma pancreatic endocrine tu¬ mors (see Chap. 154).34a If complete resection cannot be achieved, tumor debulking can be helpful, because these tumors grow slowly and palliation can be achieved. A few patients with metastatic disease confined to the liver and resectable primary tumor may be candidates for hepatic transplantation.35 Hepatic metastases are particularly dependent on their arterial supply; therefore, hepatic artery embolization may cause considerable regression of the hepatic deposits.36 The technique can be per¬

FIGURE 176-6.

Truncal rash in a patient with a glucagonoma. (From Bloom SR, Polak JM. Glucagonoma syndrome. Am J Med 1987;82(Suppl 5B): 25.)

1518

PART X: DIFFUSE HORMONAL SECRETION

mone secretion from most tumor types, often with the further advantage of independent end-organ suppression (see Chap. 166).39-40 This treatment works best with VIPomas, acting to in¬ hibit release of VIP and inhibit the action of VIP on the intestinal mucosa.40-41 Octreotide can produce rapid resolution of necrolytic migratory erythema but has less effect on the other features of the glucagonoma syndrome. If VIPomas escape from the effects of octreotide acetate and conventional antidiarrheal agents, they may respond to high-dose corticosteroids, although side effects are severe. The features of the gastrinoma syndrome are the re¬ sult of gastrin-stimulated acid secretion by the stomach, and this can always be completely abolished using parietal proton pump inhibitors, such as omeprazole.41-42 The rash of the glucagonoma syndrome (Fig. 176-6) is also responsive to zinc therapy, both locally and orally (e.g., 200 mg zinc sulfate daily). Good control of diabetes by administration of insulin and a high-protein diet is also helpful. The weight loss of the glucagonoma syndrome and of the somatostatinoma syn¬ drome are difficult to combat.

REFERENCES 1. Modlin IM, Brennan MF The diagnosis and management of gastrinoma. Surg Gynecol Obstet 1984; 158:97. 2. Zollinger RM. Gastrinoma: the Zollinger-Ellison syndrome. Semin Oncol 1987; 14:247. 3. Wolfe MM, Jensen RT. Zollinger-Ellison syndrome: current concepts in diagnosis and management. N Engl J Med 1987;317:1200. 3a. Jensen RT, Fraker DL. Zollinger-Ellison syndrome. Advances in treatment of gastric hypersecretion and the gastrinoma. JAMA 1994;271:1429. 4. Thom AK, Norton JA, Axiotis CA, Jensen RT. Location, incidence, and malignant potential of duodenal gastrinomas. Surgery 1991; 110:1086. 5. Mallinson CN, Bloom SR, Warin AP, et al. A glucagonoma syndrome. Lan¬ cet 1974; 2:1. 6 Wood SM, Polak JM, Bloom SR. The glucagonoma syndrome. In: Lefebvre PJ, ed. Handbook of experimental pharmacology. Berlin: Springer-Verlag, 1983: 411. 7. Bloom SR, Polak JM. Glucagonoma syndrome. Am J Med 1987;82(Suppl 5B):25. 8. Boden G. Insulinoma and glucagonoma. Semin Oncol 1987; 14:253. 9. Uttenthal LO, Ghiglione M, George SK, et al. Molecular forms of glucagon¬ like peptide-1 in human pancreas and glucagonomas. J Clin Endocrinol Metab 1985;61:472.

26. Penman E, Lowry PJ, Wass JAH, et al. Molecular forms of somatostatin in normal subjects and patients with pancreatic somatostatinomas. Clin Endocrinol (Ox f) 1980; 12:611. 27. Bloom SR, Polak JM. Somatostatin. Br MedJ 1987;295:288. 28. Allen JM, Yeats JC, Causon R, et al. Neuropeptide Y and its flanking pep¬ tide in human endocrine tumors and plasma. J Clin Endocrinol Metab 1987;64: 1199. 29. Howard JM, Gohara AF, Cardwell RJ. Malignant islet cell tumor of the pancreas associated with high plasma calcitonin and somatostatin levels. Surgery 1989; 105(2 pt. 1):227. 30. Esch F, Bohlen P, Link NC, et al. Characterization of a 40-residue peptide from a human pancreatic tumor with growth hormone releasing activity. Biochem Biophys Res Commun 1982; 109:152. 31. Christofides ND, Stephanou A, Suzuki H, et al. Distribution of immunoreactive growth hormone-releasing hormone in the human brain and intestine and its production by tumors. J Clin Endocrinol Metab 1984;59:747. 32. Suzuki H, Christofides ND, Chretien M, et al. Elevated concentration of a novel pituitary protein (7B2) in human foetal pancreas and in pancreatic islet tumours. Diabetic Med 1985;2:305A. 33. Tjon A, Tham R, Jansen J, et al. MR, CT, and ultrasound findings of met¬ astatic vipoma in pancreas. J Comput Assist Tomogr 1989; 13:142. 34. Hammond PJ, Jackson JA, Bloom SR. Localization of pancreatic endo¬ crine tumours. Clin Endocrinol (Oxf) 1994;40:3. 34a. Vassilopoulou-Sellin R, Ajani J. Islet cell tumors of the pancreas. Endo¬ crinol Metab Clin North Am 1994;23:53. 35. Arnold J, O'Grady J, Bird G, et al. Liver transplantation for primary and secondary hepatic apudomas. BrJ Surg 1989; 76:248. 36. Ajani JA, Carrasco H, Charnsangavej C, et al. Islet cell tumors metastatic to the liver: effective palliation by sequential hepatic artery embolization. Ann In¬ tern Med 1988; 108:304. 37. Moertel C, Hanley JA, Johnson LA. Streptozotocin alone compared with streptozotocin plus fluorouracil in the treatment of advanced islet cell carcinoma. N Engl J Med 1980;303:1189. 38. Moertel CG, Lefkopoulo M, Lipsitz S, et al. Streptozocin-doxorubicin, streptozocin-fluorouracil or chlorozotocin in the treatment of advanced islet-cell carcinoma. N Engl J Med 1992;326:519. 39. Neuroendocrine gut and pancreatic tumours: biological response modi¬ fiers. Acta Oncol 1989;28:301. 40. Jockenhovel F, Lederbugen S, Olbrich T, et al. The long-acting somato¬ statin analog octreotide alleviates symptoms by reducing posttranslational conver¬ sion of prepro-glucagon to glucagon in a patient with malignant glucogoma. Clin Invest 1994,72:127. 41. Bloom SR, Greenwood C, eds. Somatostatin 85, chemical physiological and clinical advances. Scand J Gastroenterol 1986;21:S119. 42. Clissold SP, Campoli-Richards DM. Omeprazole: a preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in peptic ulcer disease and Zollinger-Ellison syndrome. Drugs 1986;32:15.

10. Boden G, Owen OE. Familial hyperglucagonemia: an autosomal domi¬ nant disorder. N Engl J Med 1977;296:534. 11. Williams G, Lofts F, Fuessl H, Bloom SR. Treatment with danazol and plasma glucagon concentration. Br MedJ 1985; 291:1155. 12. Verner JV, Morrison AB. Islet cell tumor and a syndrome of refractory diarrhea and hypokalemia. Am J Med 1958; 25:374. 13. Bloom SR, Polak JM, Pearse AGE. Vasoactive intestinal peptide and wa¬ tery diarrhea syndrome. Lancet 1973;2:14. 14. Mekhjian HS, O'Dorisio TM. VIPoma syndrome. Semin Oncol 1987; 14: 282. 15. Bloom SR, Christofides ND, Delamarter J, et al. Diarrhoea in VIPoma patients associated with cosecretion of a second active peptide (peptide histidine isoleucine) explained by single coding gene. Lancet 1983; 2:1163. 16. Bloom SR, Polak JM. VIPomas. In: Said SI, ed. Vasoactive intestinal pep¬ tides. New York: Raven Press, 1982:457. 17. Blackburn AM, Bryant MG, Adrian TE, Bloom SR. Pancreatic tumors pro¬ duce neurotensin. J Clin Endocrinol Metab 1981;52:820. 18. Vinik Al, Strodel WE, Eckhauser FE, et al. Somatostatinomas, PPomas, neurotensinomas. Semin Oncol 1987; 14:263. 19. Calam J, Unwin R, Peart WS. Neurotensin stimulates defaecation. Lancet 1983; 1:737. 20. Polak JM, Bloom SR, Adrian TE, et al. Pancreatic polypeptide in insulino¬ mas, gastrinomas, VIPomas and glucagonomas. Lancet 1976; 1:328. 21. Adrian TE, Lettenthal LO, Williams SJ, Bloom SR. Secretion of pancreatic polypeptide in patients with pancreatic endocrine tumors. N Engl J Med 1986; 315: 287. 22. Choksi UA, Sellin RV, Hickey RC, Samaan NA. An unusual skin rash associated with a pancreatic polypeptide-producing tumor of the pancreas. Ann Intern Med 1988; 108:64. 23. Stacpoole PW, Kasselberg AG, Berelowitz M, Chey WY. Somatostat¬ inoma syndrome: does a clinical entity exist? Acta Endocrinol (Copenh) 1983; 102: 80. 24. Pipeleers D, Couturier E, Gepts W, et al. Five cases of somatostatinoma: clinical heterogeneity and diagnostic usefulness of basal and tolbutamide-induced hypersomatostatinemia. J Clin Endocrinol Metab 1983;56:1236. 25. Griffiths DF, Williams GT, Williams ED. Duodenal carcinoid tumours, phaeochromocytoma and neurofibromatosis: islet cell tumour, phaeochromocytoma and the von Hippel-Lindau complex: two distinctive neuroendocrine syn¬ dromes. Q J Med 1987; 64:769.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

177

THE ENDOCRINE KIDNEY ALAN DUBROW

Along with the vital importance of the kidney in volume homeostasis, the endocrine kidney plays a prominent role in nor¬ mal physiology and disease. The essential components of this endocrine organ include the renin-angiotensin system (RAS), prostaglandins, the renal kallikrein-kinin system, vitamin D me¬ tabolites, erythropoietin, and endothelin.

RENIN-ANGIOTENSIN SYSTEM The interrelationship of structure and function is evident in the juxtaglomerular apparatus in the juxtaposition of the macula densa segment of the early distal convoluted tubule with the glo¬ merular vascular pole (Fig. 177-1). From this structural delinea¬ tion, the concept of affector and effector limbs of the RAS was postulated.1 This complex system operates at three levels: through the systemic circulation, within the vasculature itself, and by direct renal effects. Renin is a proteolytic enzyme with relative specificity for the

Ch. 177: The Endocrine Kidney

1519

Proximal convoluted tubule

Basement membrane FIGURE 177-1.

Erythrocytes Glomerular capillaries

Glomerular basement membrane

Mesangial cell Endothelium

Capsular (parietal) epithelium

Glomerular (visceral) epithelium

JG cells

Lacis cells Efferent arteriole

/

Distal tubule

Smooth muscle cells in media

Leu-Leu bond or NH2-terminal fragment of angiotensinogen. It is synthesized and stored primarily within the juxtaglomerular apparatus, in the distal portion near the afferent arteriole, al¬ though it also is found in salivary glands and the central nervous system.2 Renin, consisting of two peptide chains linked by disul¬ fide bridges, also exists as a prorenin (an inactive zymogen) that is activated by proteolytic enzymes. It is bound to renin binding protein, and may be stabilized by an endogenous renin inhibitor. Angiotensinogen is a large a^-globulin that primarily is synthe¬ sized by the liver but also is found in the kidney.3 The action of renin on angiotensinogen generates angiotensin I, a 10-amino acid peptide with little physiologic effect. Angiotensin converting enzyme (ACE), a nonspecific COOH-terminal dipeptidase, forms the physiologically active angiotensin II by the clearing of HisLeu; the enzyme is diffusely located in lung, brain, kidney, and endothelial surfaces.4 The location of angiotensin within the kid¬ ney and in the renal lymph, along with the intrarenal demonstra¬ tion of angiotensin II receptors, complete the elements necessary for an intrarenal and extrarenal RAS.5 The control of RAS activity, ranging from renin synthesis and release through angiotensinogen concentration and ACE ac¬ tivity, is multifactorial (see Chap. 77). The system is designed to regulate arterial pressure, organ perfusion, and extracellular fluid volume status through modulation of both sodium chloride and water homeostasis; moreover, it can be modulated by pressure, volume status, and vasoactive hormones, as well as by the sym¬ pathetic nervous system.6-7

INTRARENAL RENIN-ANGIOTENSIN SYSTEM Within the kidney, the RAS has a significant role in regulat¬ ing both glomerular filtration rate (GFR) and renal blood flow

Afferent arteriole

The juxtaglomerular (JG) apparatus is a triangular-shaped formation situated at the hilus of the glomerulus. It comprises the macula densa, consisting of modified, small, cuboidal epithelial cells at the commencement of the distal renal convoluted tubule, which are immediately adjacent to the afferent arteriole. The granular cells (myoepithelioid, epitheli¬ oid, or JG cells) are located within the media of the distal region of the afferent arteriole at its junction with the glomerulus. These are modified smoothmuscle cells possessing secretory granules that con¬ tain renin. The extraglomerular mesangial cells (agranular, lacis, or Goormaghtigh cells) lie adjacent to the macula densa, filling the space between the ar¬ terioles and the distal tubular cells. They possess con¬ tractile myofibrils and also appear to contain renin. Renin is found principally in cells near the distal afferent arteriole and is released by conditions that de¬ crease extracellular fluid volume or blood pressure (decreased effective intravascular volume), or that augment sympathetic output. The specific mecha¬ nisms of renin release from the JG apparatus are not agreed on, although it is stimulated by intracellular cyclic adenosine monophosphate and inhibited by calcium. The baroreceptor concept postulates that de¬ creased renal arteriolar pressure is sensed by the gran¬ ular cells, which then increase renin output. The mac¬ ula densa concept postulates the presence of receptors sensitive to the decreased transport or concentration of sodium and chloride in the distal tubules, which then increase renin output. Additional influences in¬ clude direct stimulation of renin release by sympa¬ thetic discharge and by humoral factors such as an¬ giotensin II, endothelin, vasopressin, and adenosine, all of which are inhibitory. (Modified from Ham AW. Histology. Philadelphia: JB Lippincott, 1969.)

(RBF), major determinants of renal function that influence sys¬ temic pressure and volume homeostasis. The system is set to pro¬ tect against any excessive reductions of GFR, in response to either hypotension or volume depletion, which could impair renal ex¬ cretion of metabolic products, acids, or toxins. A reduction in re¬ nal perfusion stimulates renin synthesis and release, angiotensin generation and conversion, and angiotensin II-enhanced effer¬ ent glomerular tone through the angiotensin I receptor, main¬ taining the GFR despite a reduction in renal perfusion.8 This sys¬ tem operates with other systems regulating GFR and in concert with other vasoactive modulators, such as vasopressin, endo¬ thelin, and adenosine.8 9 If released angiotensin II had the effect on afferent glomeru¬ lar arterioles that it does on efferent glomerular arterioles, GFR would decline. The sustained GFR that occurs with renal hypo¬ perfusion may represent the intrarenal net effect of the RAS ac¬ tivity interacting with other vasoactive regulators (e.g., vasodila¬ tation caused by prostaglandins or kinins). Perhaps, the occurrence of increased efferent resistance without increased afferent resistance serves a second purpose, by permitting the excretion of toxins and metabolic products while enhancing the conservation of sodium chloride and water, which induces extra¬ cellular volume expansion and improves renal perfusion. Local renal angiotensin II formation can enhance renal tubular reab¬ sorption directly and through renal hemodynamic changes (e.g., efferent constriction, diminished peritubular capillary hy¬ drostatic pressure, and increased capillary colloid oncotic pressure).10 Angiotensin I derived outside the kidney can be converted to angiotensin II within the kidney. Thus, it can be difficult to distinguish the source of the RAS affecting renal function. More-

1520

PART X: DIFFUSE HORMONAL SECRETION

over, caution must be exercised in extrapolating from study re¬ sults derived from the use of ACE inhibitors and in extrapolating from pathologic states to normal physiologic events. The interde¬ pendence of the various vasoactive and volume-control systems further increases the difficulty in assessing the physiologic effect of changes in one parameter without measuring any possible al¬ tered parameters of the other systems (Table 177-1). Neverthe¬ less, there appears to be a disproportionate increase in the RAS activity in experimental diabetes. 1 Renal renin gene production also is altered in pathophysiologic states such as salt depletion, ureteral obstruction, Bartter syndrome, and high-protein feeding.

TABLE 177-2 Stimuli of Renal Prostaglandin Production PEPTIDE HORMONES Vasopressin Bradykinin Angiotensin II Endothelin-1 MISCELLANEOUS STIMULI Calcium Intravenous loop diuretics

PROSTAGLANDINS

a-Adrenergic catecholamines Adenosine triphosphate

The oxygenation of arachidonic acid through either the cyclooxygenase or the lipoxygenase pathway leads to the forma¬ tion of various biologically important compounds known collec¬ tively as eicosanoids (see Chap. 170). Included are prostaglan¬ dins, thromboxanes, leukotrienes, and hydroxy-fatty acids. Before its conversion to eicosanoids, arachidonic acid must be released from membrane-bound phospholipids by the action of phospholipases. In the kidney, various chemical and hormonal stimuli serve to activate phospholipase (Table 177-2). Eicosanoids, including prostaglandins, have been called autacoids. Autacoids are compounds that act near their sites of synthesis. Different regions of the kidney synthesize prostaglan¬ dins, whose sites of physiologic activity are at or near their sites of synthesis. Thus, prostaglandins synthesized in the renal cortex regulate cortical processes, such as glomerular filtration, and prostaglandins synthesized in the medulla exert their effects on medullary sodium and water metabolism and on medullary blood flow.12,13 In addition, there are several prostaglandin re¬ ceptor subtypes with distinct cellular localization as well as sec¬ ond messenger responses. The PGE receptor, for example, con¬ sists of three subtypes that confer multiple functions in different segments of the nephron.14 The loci of renal prostaglandin synthesis are the glomeruli, arterioles, collecting ducts, and medullary interstitial cells. In hu¬ mans, prostacyclin (PGI2) is the principal prostaglandin synthe-

TABLE 177-1 Modulators of Renin-Angiotensin System Activity PROSTAGLANDINS Stimulation:

Prostaglandin E2 Prostacyclin (6-keto-F2a)

Modulation:

Macula densa

Inhibition:

Nonsteroidal antiinflammatory drugs

SYMPATHETIC NERVOUS SYSTEM Stimulation:

/8-Agonists

Inhibition:

/3-Antagonists a-Agonists

IONS Stimulation:

Diminished serum ionized calcium Diminished serum [K+]

Inhibition:

Increased serum ionized calcium Increased serum [K+]

MISCELLANEOUS Stimulation:

Kallikrein/kinins Glucagon Parathyroid hormone Nitric oxide Endothelin Adenosine

Inhibition:

Vasopressin Angiotensin II Somatostatin Caffeine

Dietary supplementation with arachidonic acid precursors Interleukin-la Tumor necrosis factor a Serotonin Endotoxin Estradiol DISEASES Glomerulonephritis Cirrhosis Congestive heart failure Bartter syndrome Renal ischemia Ureteral obstruction (Modified from Dunn MJ. Renal endocrinology. Baltimore: Willaims & Wilkins, 1983:4.)

sized by the glomeruli, where it participates in the regulation of GFR. PGI2 also is the major prostaglandin synthesized by arteri¬ oles, acting to regulate RBF by modulating vascular resistance. The medullary collecting duct and medullary interstitial cells, in contrast, synthesize predominantly PGE2 and virtually no PGI2. The nonsteroidal antiinflammatory drugs (NSAIDs; e.g., as¬ pirin and indomethacin) inhibit in vivo cyclooxygenase activity by 75% to 90%, as assessed by measurements of urinary prosta¬ glandins.16 This is a reasonable index of renal prostaglandin pro¬ duction, because prostaglandins synthesized by other organs are not excreted in the urine.12 The major renal effects of prostaglandins are control of renal vascular resistance, regulation of glomerular filtration, stimula¬ tion of renin secretion, enhancement of water excretion, increase of sodium chloride excretion, and stimulation of erythropoietin release. PGE2 and PGI2 are vasodilators and increase RBF, but they have little effect on glomerular filtration under physiologic con¬ ditions.1718 In any clinical setting characterized by effective intra¬ vascular volume depletion (e.g., diuretic-induced or dietary so¬ dium restriction, congestive heart failure, cirrhosis, or nephrotic syndrome), the RAS is activated, and prostaglandins assume a critical role in offsetting vasoconstriction and preserving GFR. Probably, vasodilative prostaglandins relax the glomerular mes¬ angium and blood vessels, thereby augmenting the filtration sur¬ face area and the ultrafiltration coefficient.15 The renal vasculature and glomeruli are sensitive to the va¬ soconstrictor peptides, angiotensin II and vasopressin. Both these hormones stimulate the release of PGI2 and PGE2, which modu¬ late the constrictor response. NSAID inhibition of prostaglandin synthesis leads to an augmentation of the vasoconstrictor effects and can cause significant reductions in both RBF and GFR. How¬ ever, in healthy animals and humans, vasodilative prostaglan¬ dins appear to exert little control over RBF or GFR. The acute administration of NSAIDs does not reduce renal function unless

Ch. 177: The Endocrine Kidney they are given in a setting of increased vasoconstriction. In that circumstance, vasodilative prostaglandins would be expected to serve a counterbalancing effect to the vasoconstriction.19'20 PGE2 is the principal eicosanoid participating in the regula¬ tion of tubular reabsorption of sodium and water. Sodium chlo¬ ride reabsorption is enhanced in the medullary thick ascending limb of the loop of Henle and in the cortical and medullary col¬ lecting ducts when PGE2 is inhibited. The major sites of inhibi¬ tion of vasopressin-mediated water reabsorption are in the corti¬ cal and medullary collecting ducts.17 These effects appear to be largely independent of RBF, representing instead direct actions on renal tubular cells. The inhibition of prostaglandin synthesis with indomethacin reduces the urinary sodium chloride concen¬ tration, interferes with the effects of diuretic agents, decreases urinary osmolarity, and, in certain clinical settings, can induce a net positive sodium balance and edema.121714 There is a complex system of negative-feedback relation¬ ships preserving GFR. Stimuli that induce renal vasoconstriction stimulate the synthesis of vasodilative PG12 and PGE2. These prostaglandins, in turn, may modulate their own actions by stim¬ ulating renin secretion. The danger of NSAID administration un¬ der circumstances of stimulated renin or vasopressin release can¬ not be overemphasized.

1521

the kidney act in a paracrine manner, mediating intrarenal vaso¬ dilatation and perhaps regulating blood flow to specific regions of the kidney. The administration of mineralocorticoids, as well as angio¬ tensin II and vasopressin, appears to stimulate renal kallikrein excretion.27-29 Moreover, kinins infused into the renal artery stimulate the synthesis of PGE2 in the collecting duct and me¬ dulla and PGI2 in the arterioles.30 Prostaglandins stimulate and prostaglandin synthesis inhibitors suppress the renal release of kallikreins, completing the negative-feedback circuit.31 The physiologic role played by these interactions remains speculative, however. An isolated increase in the activity of the RAS would produce both peripheral and renal vasoconstriction, which could impair RBF. Angiotensin II and aldosterone, however, stimulate the release of renal kallikrein and prostaglandins, which would augment RBF and offset vasoconstrictor influences. Studies using both ACE inhibitors and aprotinin, an inhibi¬ tor of kallikrein, suggest that kinins released within the kidney cause natriuresis, diuresis, and the release of prostaglandins. It is unclear whether these effects are due to a direct effect of kinins on distal nephron sodium transport, to changes in RBF and dis¬ tribution, or both.

VITAMIN D RENAL KALLIKREIN-KININ SYSTEM The renal kallikrein-kinin system, whose activity appears to be interrelated with the renin-angiotensin and prostaglandin sys¬ tems, may participate in the control of RBF and function by alter¬ ing the tone of renal and extrarenal blood vessels, and by directly regulating intrarenal sodium and water excretion. The role of the kallikrein-kinin system in normal and pathologic processes will be clarified further with the information forthcoming from mo¬ lecular cloning of the kallikrein genes21 (see Chap. 163). Kallikreins are serine proteases that release kinins from plasma substrates, known as kininogens. Renal kallikrein appears to favor low-molecular-weight kininogen, forming a compound known as Lys-bradykinin or kallidin. The kinins formed are inac¬ tivated rapidly by enzymes called kininases, which are found in blood and other tissues. There are two major kininases, kininase I and kininase II; kininase II, a peptidyl dipeptidase, also is known as ACE. The activity of the renal kallikrein-kinin system usually is studied by measuring urinary kallikrein. However, methodologic problems have been posed by the lack of specificity of some of the methods used to measure kallikrein.22 Urinary kallikrein is synthesized by the kidney; 90% of renal kallikrein is found in the cortex, with little in the medulla or papilla.23 The granular por¬ tions of the distal convoluted and cortical collecting tubules form a single segment known as the collecting tubule, which is the site of kallikrein synthesis. The discrete tubular localization of kallikrein suggests a specific role of renal kallikrein at this site.24 Micropuncture evidence has confirmed that renal kallikreins are secreted into the urine at the level of the distal tubule, and that urinary kinins are formed.23'25 Kininase II and other pepti¬ dases in the proximal tubular lumen prevent filtered kinins from reaching distal nephron segments. Urinary kinins appear to be formed from low-molecular-weight kininogen, and the kidney may produce its own kininogen. Numerous complex interactions occur among the kallikreinkinin, renin-angiotensin-aldosterone, vasopressin, and prosta¬ glandin systems of the kidney. Urinary kallikrein converts inac¬ tive renin (or prorenin) to active renin in vitro, and the in vivo activation of renin by kallikrein has been suggested.26 Converting enzyme (kininase II), which is found in high concentrations in vascular endothelial cells of the lung, has the concurrent func¬ tions of converting angiotensin I to angiotensin II and inactivat¬ ing kinins, which promote vasoconstriction. More than 90% of kinins found in the venous circulation are inactivated in a single passage through the lung, suggesting that kinins formed within

Vitamin D3, or cholecalciferol, functions both as a vitamin and as a steroid prohormone, which is converted to an active form, 1,25-dihydroxyvitamin D3 (l,25[OH]2D3; see Chap. 53). The kidney, as the major site of this final and most closely regu¬ lated step of synthesis, is the principal regulator of vitamin D3 action.32,33 7-Dehydrocholesterol, derived from cholesterol in the skin, is converted by ultraviolet irradiation to previtamin D3, and then, when thermal conditions are appropriate, to vitamin D3 (see Chaps. 53 and 179). This endogenous vitamin D3, as well as vi¬ tamin D3 or D2 ingested from dietary sources, is bound to vitamin D-binding protein and transported to the liver. Hydroxylation of vitamin D3 in the liver forms 25-hydroxycholecalciferol (25[OH]D3), which is bound to vitamin D-binding protein for transport to the kidney. Although 25(OH)D3 is the predominant circulating form of vitamin D3 in the plasma, only 1% to 2% of vitamin D-binding protein is saturated with this substance. 25(OH)D3 is converted in the kidney to l,25(OH)2D3 by the enzyme la-hydroxylase. This enzyme has been localized to renal proximal tubule mitochondria and is substrate specific.34 It is a closely regulated enzyme and can be affected by several factors. Parathyroid hormone, hypocalcemia, and hypophosphatemia all stimulate hydroxylation, whereas vitamin D3 and l,25(OH)2D3 inhibit activity. Other hormonal changes can affect l,25(OH)2D3 synthesis: increased levels of sex hormones (e.g., pregnancy), prolactin, or growth hormone stimulate enzyme activity, whereas exogenous glucocorticoids suppress it. l,25(OH)2D3 has many sites of action. The intestinal absorp¬ tion of both calcium and phosphorus are enhanced. The absorp¬ tion of calcium, by active transport in the duodenum, is exqui¬ sitely sensitive to this hormone.35 The skeletal effect of the vitamin D family of compounds also is important, albeit less well understood. Calcium and phosphorus supplementation heals rickets only when vitamin D or its metabolites also are adminis¬ tered concomitantly. In addition, l,25(OH)2D3 exerts a permis¬ sive effect on parathyroid hormone-mediated bone resorption. The effects of the vitamin D metabolites on renal transport are unclear and may depend on the vitamin D and parathyroid hormone status.36 The acute administration of l,25(OH)2D3 ex¬ erts an antiphosphaturic effect when renal cyclic adenosine monophosphate (cAMP) is stimulated concomitantly by phosphaturic agents. The calcitriol receptor is localized to the distal tubule, the collecting duct, the proximal tubule, and the parietal epithelial cells of the glomerulus.37 The abnormalities of vitamin D metabolism in patients with

1522

PART X: DIFFUSE HORMONAL SECRETION

advanced renal failure are caused by impaired production of l,25(OH)2D3. Decrements of glomerular filtration of up to 40 mL/min usually are not associated with vitamin D deficiency and disordered calcium homeostasis. Below that level, the character¬ istic osteodystrophy of renal disease may supervene (see Chap. 60).

ERYTHROPOIETIN Erythropoietin is the primary regulator of erythrocyte pro¬ duction (see Chap. 207). It is a nondialyzable glycoprotein with a molecular mass of 39,000 daltons, containing carbohydrates (notably sialic acid) that are essential for biologic function. Mea¬ surement by various methods, including the polycythemic mouse bioassay, in vitro marrow culture, and radioimmunoassay, have estimated human serum levels at about 15 mU/mL.38 The role of the kidney in erythropoietin production was es¬ tablished with the demonstration that rats without kidneys (but not those with comparable uremia but intact kidneys) failed to increase plasma erythropoietic activity in response to hypoxia.39 Until recently, bioassays of renal tissue failed to detect erythro¬ poietic activity, leading to several hypotheses explaining the kid¬ ney's role in erythropoietin production. It was proposed that the kidneys release an enzyme, erythrogenin, that converts a circulating erythropoietinogen into ac¬ tive erythropoietin.40 Alternatively, it was suggested that the kid¬ neys produce an erythropoietin "proform" that is activated in plasma, or that the hormone is produced in the kidneys but is protected from inhibitors by a plasma factor. Recent studies have negated these theories by isolating significant amounts of active erythropoietin from kidney tissue.4 The postulated enzyme "erythrogenin" has not been isolated. The intrarenal site of erythropoietin production remains controversial. Evidence suggesting cortical glomerular synthesis of the hormone is derived principally from studies demonstrating erythropoietin activity in supernatant cultures of cortical glomer¬ uli, localization of fluorescein-labeled globulins to glomerular tufts, and localization of horseradish peroxidase-labeled anti¬ bodies to epithelial foot processes of glomerular cells.42 Elowever, the glomerular basement membrane may nonspecifically trap antigen-antibody complexes, and the significance of these find¬ ings has been questioned. The juxtaglomerular apparatus also has been considered as a site for erythropoietin synthesis, because changes in juxtaglo¬ merular cell granularity have been correlated with tissue oxygen tension. Others attribute these changes to alterations in blood volume, rather than to any control mechanisms related to eryth¬ rocyte production.43,44 With in situ hybridization, localization of erythropoietin mRNA was noted in cortical cells of anemic rat kidneys, which suggested interstitial or capillary endothelial cells as the site of erythropoietin production.45 Extrarenal sources probably account for less than 10% of erythropoietin in adults, but may contribute significant amounts in nephrectomized animals. The liver and possibly the reticuloendothelial system are the major proposed extrarenal sites of erythropoietin production.42 Erythropoietin is produced in response to renal tissue hyp¬ oxia, as determined by the balance between renal oxygen supply and consumption. Because the kidney's arterial-venous oxygen difference is relatively small, renal tissue oxygen content reflects the systemic oxygen supply.42 Serum levels of the hormone are increased in response to systemic hypoxia, such as that caused by high altitude and altered oxygen dissociation. Changes in RBF produce tissue hypoxia and stimulate erythropoietin production. Polycythemia can occur with significant renal artery stenosis, af¬ ter transplantation with alterations in renal vasculature, and in the presence of renal cysts compressing surrounding renal parenchyma. A proposed mechanism by which hypoxic stimuli induce

erythropoietin production states that hypoxia may allow in¬ creased calcium entry into the glomerular cell, activating phos¬ pholipase and triggering the synthesis of prostaglandins, includ¬ ing PGI2.38 PGI2 or its metabolite 6-keto-PGF2a subsequently activates adenylate cyclase, increasing renal cAMP and initiating or enhancing erythropoietin production. Erythropoietin, which is considered a cytokine, acts on sev¬ eral steps in the production of erythrocytes.43 Erythroid colony¬ forming units are exquisitely sensitive to erythropoietin and may be the principal sites of regulation of erythrocytes by this hor¬ mone. Moreover, erythropoietin causes the early release of large "stress" reticulocytes, accelerates bone marrow transit time, and increases the hemoglobin concentration of individual red blood cells. Thus, the erythroid marrow can increase production to 6 to 10 times basal rates in response to prolonged stimulation.43 The anemia of chronic renal failure has many causes.46 Se¬ rum levels of erythropoietin are lower in patients with chronic renal failure than in patients with comparable anemia but normal renal function. Shortened red blood cell survival times and the presence of inhibitors of erythropoiesis have been demonstrated. Red blood cell survival can be improved by dialysis, resulting in a lessening of the anemia.4' Studies in patients receiving mainte¬ nance hemodialysis have demonstrated the correction of anemia with recombinant human erythropoietin,48'49 and this form of therapy is available for such patients. The synthetic hormone ap¬ pears to be equally effective in correcting the anemia of patients with chronic renal insufficiency that has not progressed to endstage renal failure. Other effects of erythropoietin include antinatriuresis through the production of renal angiotensin II.50

ENDOTHELIN Endothelin is among the most potent renal peptides, regu¬ lating renal homeostasis by several actions (see Chap. 174). En¬ dothelin has direct vasoconstrictive and tubular transport actions that affect the control of RBF, GFR, and sodium and water excre¬ tion. Endothelin is produced in multiple renal sites and also is capable of binding to endothelin-B receptors in renal areas such as the inner medullary collecting duct in an autocrine fashion. Stimulation of endothelin-B receptors inhibits vasopressininduced cAMP formation and thereby affects water balance. The effect on renal sodium excretion is highly complex and not fully elucidated. However, renal natriuretic effects include decreased renin secretion and inhibition of Na+-K+ adenosine triphospha¬ tase. Antinatriuretic effects include effects on GFR and direct effects on Na+ reabsorption. Endothelin has been implicated in the pathogenesis of essential hypertension, pregnancy-induced hypertension, atherosclerosis, cerebral and myocardial vaso¬ spasm, acute renal failure due to radiocontrast agents, cyclospor¬ ine nephrotoxicity, and renal glomerulopathies. 8

REFERENCES 1. Goormaghtigh N. Existence of an endocrine gland in the media of the renal arterioles. Proc Soc Exp Biol Med 1939; 42:688. 2. Cantin M, Gutowska J, Lacasse ], et al. Ultrastructural immunocytochemical localization of renin and angiotensin II in the juxtaglomerular cells of the isch¬ emic kidney in experimental renal hypertension. Am J Pathol 1984; 115:212. 3. Morris B, Johnston Cl. Renin substrate in granules from rat kidney cortex. BiochemJ 1976; 154:625. 4. Hall ER, Kato J, Erdos EG, et al. Angiotensin I-converting enzyme in the nephron. Life Sci 1976,-18:1299. 5. Burns KD, Homma T, Harris RC. The intrarenal renin-angiotensin system. Semin Nephrol 1993,101:169. 6. Di Bona GF. Neural regulation of renal tubular sodium reabsorption and renin secretion: integrative aspects. Clin Exp Hypertens [A] 1987;9:1515. 7. Osborn JL, Johns EJ. Renal neurogenic control of renin and prostaglandin release. Miner Electrolyte Metab 1989; 15:51. 8. Hall JE. Regulation of renal hemodynamics. Int Rev Physiol 1982; 26:243. 9. Navar LG. Renal autoregulation: perspectives from whole kidney and sin¬ gle nephron studies. Am J Physiol 1978;234:F357.

Ch. 178: The Endocrine Genitourinary Tract

1523

10. Schuster VL, Kokko JP, Jacobson HR. Angiotensin II directly stimulates transport in rabbit proximal convoluted tubules. J Clin Invest 1984; 73:507. 11. Anderson S, Tung FF, Jugelfinger JR. Renal renin-angiotensin system in diabetes: functional immunohistochemical, and molecular biological correlations. Am J Physiol 1993; 265 :F477. 12. Dunn MJ. Renal prostaglandins. In: Dunn MJ, ed. Renal endocrinology. Baltimore: Williams & Wilkins, 1983:1. 13. Levenson DJ, Simmons CE Jr, Brenner BM. Arachidonic acid metabolism, prostaglandins and the kidney. Am J Med 1982; 72:354. 14. Sugimoto Y, Namba T, Shigemoto R, et al. Distinct cellular localization of mRNAs for three subtypes of prostaglandin E receptor in kidney. Am J Physiol 1994;266:F823. 15. Scharschmidt LA, Lianos E, Dunn MJ. Arachidonate metabolites and the control of glomerular function. Fed Proc 1983;42:3058. 16. Dunn MJ, Zambraski EJ. Renal effects of drugs that inhibit prostaglandin synthesis. Kidney Int 1980; 18:609. 17. Anderson RJ, Berl T, McDonald KM, Schrier RW. Prostaglandins: effects on blood pressure, renal blood flow, sodium and water excretion. Kidney Int 1976; 10:205. 18. Gerber JG, Nies AS, Friesinger GL, et al. The effect of PGI2 on canine renal function and hemodynamics. Prostaglandins 1978; 16:519. 19. Dunn MJ. Nonsteroidal anti-inflammatory drugs and renal function. Annu Rev Med 1984;35:411. 20. Terragno NA, Terragno DA, McGiff JC. Contribution of prostaglandins to the renal circulation in conscious, anesthetized and laparotomized dogs. Circ Res 1977; 40:590. 21. Lin FK, Lin CH, Chou CC, et al. Molecular cloning and sequence analysis of the monkey and human tissue kallikrein genes. Biochim Biophys Acta 1993; 1173:325. 22. Marin-Grez M, Carretero OA. A method for measurement of urinary kal¬ likrein. J Appl Physiol 1972; 32:428. 23. Scieli AG, Carretero OA, Oza NB. Distribution of kidney kininogenases. Proc Soc Exp Biol Med 1976; 151:57. 24. Beasley D, Oza NB, Levinsky NG. Micropuncture localization of kallikrein secretion in the rat nephron. Kidney Int 1987; 32:26. 25. Imai M. The connecting tubule: a functional subdivision of the rabbit dis¬ tal nephron segments. Kidney Int 1979; 15:346. 26. Sealey JE, Atlas SA, Laragh JH. Linking the kallikrein and renin system via activation of inactive renin. Am J Med 1978;65:994. 27. Mills IH. Kallikrein, kininogen and kinins in control of blood pressure. Nephron 1979;23:61. 28. Margolius HS, Horowitz D, Pisano JJ, Keiser HR. Urinary kallikrein excre¬ tion in normal man. Relationships to sodium intake and sodium-retaining steroids. Circ Res 1974; 35:812. 29. Fejes-Toch G, Zahajszky T, Filep J. Effect of vasopressin on renal kallikrein excretion. Am J Physiol 1980;239:F388. 30. Terragno NA, Lonigro AJ, Malik KU, McGiff JC. The relationship of the renal vasodilator action of bradykinin to the release of prostaglandin E-like sub¬ stances. Experientia 1972; 28:437. 31. Nasjletti A, Malik KU. Relationships between the kallikrein-kinin and prostaglandin system. Life Sci 1979;25:99. 32. Coburn JW, Slatopolsky E. Vitamin D, parathyroid hormone and renal osteodystrophy. In: Brenner B, Rector F, eds. The kidney. Philadelphia: WB Saun¬ ders, 1985:1657. 33. Reichel H, Koeffler HP, Norman AW. The role of the vitamin D endocrine system in health and disease. N Engl J Med 1989; 320:980. 34. Slatopolsky E. Renal regulation of extrarenal function: bone. In: Seldin DW, Giebisch G, eds. The kidney: physiology and pathophysiology. New York: Raven Press, 1985:823. 35. Lemman J Jr, Gray RW. Vitamin D metabolism and the kidney. In: Dunn NJ, ed. Renal endocrinology. Baltimore: Williams & Wilkins, 1983:114. 36. Norman AW. Vitamin D metabolites l,25(OH)2D and 24,25(OH)2D. In: Massry SG, Glassock RJ, eds. Textbook of nephrology. Baltimore: Williams & Wil¬ kins, 1980:2. 37. Kumar R, Schaefer J, Grande JP, Roche PC. Immunolocalization of calcitriol receptor, 24-hydroxylase cytochrome P-450, and calbindin D28K in hu¬ man kidney. AmJ Physiol 1994;266:F477. 38. Fischer JW, Nelson PK, Beckman B, Burdowski A. Kidney control of eryth¬ ropoietin production. In: Dunn MJ, ed. Renal endocrinology. Baltimore: Williams &

47. Anagnostou A, Kurtzman NA. Hematological consequences of renal fail¬ ure in the kidney. In: Brenner BM, Rector FC, eds. Philadelphia: WB Saunders, 1986: 1631. 48. Bommer J, Alexiou C, Meuller-Beuhl U, et al. Recombinant human eryth¬ ropoietin therapy in haemodialysis patients—dose determination and clinical expe¬ rience. Nephrol Dial Transplant 1987; 2:238. 49. Eschbach JW, Kelly MR, Haley NR, et al. Treatment of the anemia of progressive renal failure with recombinant human erythropoietin. N Engl J Med 1989;321:158. 50. Brier ME, Bunke CM, Lathon PV, Aronoff GR. Erythropoietin-induced antinatriuresis mediated by angiotensin II in perfused kidneys. J Am Soc Nephrol 1993; 3:1583. 51. Inagami T, Kawamura M, Naruse K, Okamura T. Localization of compo¬ nents of the renin angiotensin system within the kidney. Fed Proc 1986;45:1414. 52. Mendelsohn FAO, Aguilera G, Saavedra JM, et al. Characteristics and regulation of angiotensin II receptors in pituitary, circumventricular organs and kid¬ ney. Clin Exp Hypertens [A] 1983;5:1081. 53. Cumming AD, Jeffrey S, Lambie AT, Robson JS. The kallikrein-kinin and renin-angiotensin systems in nephrotic syndrome. Nephron 1989; 51:185. 54. Erslev AJ, Caro J. Physiologic and molecular biology of erythropoietin. Med Oncol Tumor Pharmacother 1986; 3:159. 55. Kurtz A. Erythropoietin: structure, function, origin. Adv Nephrol 1987; 16:

Wilkins, 1983:142. 39. Jacobsen LO, GoldwasserE, Fried W, Pezak L. Role of the kidney in erythropoiesis. Nature 1957; 179:633. 40. Gordon AS, Cooper GW, Zanjani ED. The kidney and erythropoiesis.

Information concerning the different peptides in the genito¬ urinary tract varies considerably, from the mere demonstration of immunoreactivity in tissue extracts (e.g., thyrotropin-releasing hormone, (8-endorphin) to detailed studies on cellular localiza¬ tion and function (e.g., vasoactive intestinal peptide [VIP], sub¬ stance P).

Semin Hematol 1967;4:337. 41. Fried W, Barone-Vazelas J, Berman M. Detection of high EP titers in renal extracts of hypoxic rats. J Lab Clin Med 1981;97:82. 42. Powell JS, Adameon JW. Hematopoiesis and the kidney. In: Seldon DW, Giebisch G, eds. The kidney: physiology and pathophysiology. New York: Raven

371. 56. Nicolson AG, Haites NE, McKay NG, et al. Induction of nitric oxide syn¬ thase in human mesangial cells. Biochem Biophys Res Commun 1993; 193:1269. 57. Simonson MS. Endothelins: multifunctional renal peptides. Physiol Rev 1993;73:375. 58. Perico N, Remuzzi G. Role of endothelin in glomerular injury. Kidney Inter 1993;43:576.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

178_

THE ENDOCRINE GENITOURINARY TRACT JAN FAHRENKRUG The intrinsic control of some functions in the genitourinary tract cannot be attributed to cholinergic and adrenergic nerves. The demonstration of prostaglandins and regulatory peptides in urogenital tissues suggests that these substances may account for these local, noncholinergic, nonadrenergic physiologic events. Several peptides have been found in the urogenital tract (Ta¬ ble 178-1). With the exception of relaxin, all peptides originally were isolated from extragenital sources, mainly the brain or the gastrointestinal tract. Although chromatographic studies suggest that these immunoreactive peptides are identical to their extragenital counterparts, confirmation awaits isolation and sequencing.

PEPTIDE HORMONES OF THE GENITOURINARY TRACT

Press, 1985. 43. Spivak JL. The mechanism of action of erythropoietin. Int J Cell Cloning

SUBSTANCE P

1986;4:139. 44. Erslev AJ. Production of erythrocytes. In: Williams WJ, Beutler E, Erslev AJ, Lichtman MA, eds. Hematology. New York: McGraw Hill, 1983:142. 45. Koury ST, Bondurant MC, Koury MJ. Localization of erythropoietin syn¬ thesizing cells in murine kidneys by in situ hybridization. Blood 1988; 71:524. 46. Paganini EP, Garcia J, Abdulhadi M, et al. The anemia of chronic renal failure. Overview and early erythropoietin experience. Cleve Clin J Med 1989;56:

Substance P (see Chap. 167) is found in nerve fibers of the smooth muscle layers of the fallopian tube and uterus and around blood vessels in the vagina.1 There are substance-Pcontaining nerve terminals in the vaginal epithelium and clitoris, which probably represent primary sensory neurons. In the male genital tract, substance-P-containing nerves are concentrated

79.

1524

PART X: DIFFUSE HORMONAL SECRETION

mainly in a group of fibers in the corpuscular receptors un¬ derneath the epithelium of the glans penis.2 In the urinary tract, similar nerve fibers are encountered in the lamina propria and the muscle layer, especially in the detrusor muscles.3

and the two peptides seem to be colocalized, which is explained readily by a common precursor molecule for VIP and PHM.9 PHM in the female genital tract is present mainly in a Cterminally extended form, which is more biologically active than PHM itself.10

CALCITONIN GENE-RELATED PEPTIDE Afferent nerves immunoreactive for calcitonin gene-related peptide (CGRP) occur in the female genital tract, mainly associ¬ ated with blood vessels, nonvascular smooth muscle, squamous epithelium, and uterine and cervical glands.4 In men CGRP nerves are prevalent in the penis.5 In subpopulations of the gen¬ ital CGRP immunoreactive cells and nerves, the peptide seems to be colocalized with substance P or the enzyme responsible for synthesis of nitric oxide, a messenger molecule, which may serve as a neurotransmitter.5'6

VASOACTIVE INTESTINAL PEPTIDE AND PEPTIDE HISTIDINE ISOLEUCINE Vasoactive intestinal peptide (see Chap. 168) is localized in nerve fibers throughout the female genital tract.7 This peptide occurs in large, electron-dense granules in nerve terminals that seem to innervate epithelial cells, blood vessels, and smooth muscle cells. A particularly rich supply of fibers are found in the cervical os and the isthmic part of the fallopian tube. The VIP nerves in the female genital tract are intrinsic, originating mainly from local ganglia in the paracervical tissue. In the male genital tract, VIP nerves are abundant in the erectile tissue of the corpus cavernosum and around arteries and arterioles.2,8 The nonvascu¬ lar smooth muscle and glands in the prostate and seminal vesicles also are associated with VIP nerves. In the urinary tract, VIPimmunoreactive nerves are distributed widely in all regions, but are particularly dense in the bladder, mainly beneath the epithe¬ lium and the muscle layer of the trigone.3 Nerve fibers showing peptide histidine methionine (PHM) immunoreactivity have a distribution pattern identical to VIP,

TABLE 178-1 Peptide Hormonal Substances in the Female and Male Genitourinary Tracts

NEUROPEPTIDE Y Neuropeptide Y (NPY) has a widespread distribution in both the male and female genital tracts, located in the nerve fibers associated with vascular and nonvascular smooth muscula¬ ture.2" 12 In the urinary tract, NPY nerves are seen in the muscle layer, particularly in the trigonal area.3

GALANIN Galanin-immunoreactive nerve fibers are found in the fe¬ male and male genital tracts, with the exception of ovary and testis. Galanin nerve fibers are found within smooth muscle and in close relationship to arteries and veins.13 Galanin fibers are, however, most abundant in the female paracervical tissue, where they surround ganglion cells.14

ENKEPHALINS In the female genital tract, the two enkephalin pentapeptides (see Chap. 165) are present in nerve fibers within the smooth muscle layers of the uterine cervix and in local ganglia surrounding nonimmunoreactive cell bodies.15 The latter local¬ ization is interesting in view of their suspected neuromodulatory role. In the urinary tract, a few single fibers are found along bun¬ dles of smooth muscle cells.

GASTRIN-RELEASING PEPTIDE Gastrin-releasing peptide (bombesin-like peptides; see Chap. 161) is found throughout nerve fibers scattered in the smooth musculature of the male and female genital tracts. In men, it is found mainly in the musculature of the seminal vesi¬ cles, urethra, and vas deferens. In the urinary bladder, gastrin¬ releasing peptide has a diffuse distribution, in contrast to VIP, substance P, and NPY, which are concentrated in the trigone of the bladder.

GUT-BRAIN PEPTIDES Substance P Vasoactive intestinal peptide Peptide with NH2-terminal histidine and COOH-terminal methionine amide

SOMATOSTATIN Nerve fibers containing somatostatin (see Chap. 166) are dis¬ tributed sparsely in the genital tract, occurring mainly in the smooth musculature.2

Neuropeptide Y Leucine-enkephalin Methionine-enkephalin Gastrin releasing peptide/bombesin-like peptides

HYPOTHALAMIC-RELEASING HORMONES Thyrotropin-releasing hormone Somatostatin

OXYTOCIN AND OXYTOCIN-NEUROPHYSIN Immunoreactivity to oxytocin (see Chap. 26) is found in large luteal cells of nonpregnant cows.16 Furthermore, oxytocinimmunoreactive cells have been localized within the interstitial tissue of the rat testis.17 The role of oxytocin within the genital tract is unknown, but this peptide does possess luteolytic action.

NEUROHYPOPHYSIAL HORMONES Oxytocin

/3-ENDORPHIN

Neurophysin

Immunostaining for /3-endorphin (see Chaps. 16 and 165) is found in the cytoplasm of Leydig cells and in the epithelium of the epididymis, seminal vesicles, and vas deferens of rats.18

PITUITARY PEPTIDES /3-Endorphin

OTHERS Renin Relaxin Calcitonin gene-related peptide Galanin

RENIN Immunoreactivity to renin (see Chaps. 77 and 177) occurs in the apical region of endometrial cells and in perivascular cells of the myometrium.19 Intramural renin may play a local role in the regulation of vascular tone and the tone of the uterine muscle.

Ch. 178: The Endocrine Genitourinary Tract and endometrial renin may be involved in the cessation of bleed¬ ing that follows an abrasion.

RELAXIN Relaxin originally was isolated from the corpus luteum of pregnant sows.21' Relaxin immunoreactivity is found in both the nongestational and gestational corpus luteum and in the secre¬ tory endometrium of nonpregnant women.203 It has been sug¬ gested that relaxin is involved in the maintenance of uterine qui¬ escence and in the softening of the uterine cervix.

GENITOURINARY FUNCTIONS OF PEPTIDE HORMONES Probably, the regulatory peptide substances of the genito¬ urinary tract are synthesized, stored, and released locally. The mechanism whereby communication occurs between the peptide-containing cells and their target cells is not fully un¬ derstood. In autocrine secretion, the peptide probably acts locally on the cell of origin. In paracrine secretion, the peptide exerts a local action on neighboring cells of the genitourinary tract by extracellular fluid transport systems. Any effects mediated by au¬ tocrine or paracrine secretion may be either quick or prolonged, and may include trophic effects and influences on cell differentiation. The final mode of communication used by the peptides con¬ fined to nerve fibers (i.e., neurocrine) is synaptic transmission. The targets of this communication are mainly vascular cells and nonvascular muscle cells, to effect control of blood flow and smooth muscle activity.

PEPTIDERGIC CONTROL OF BLOOD FLOW Vasoactive intestinal peptide, PHM, and substance P cause uterine vasodilation by directly affecting vascular smooth mus¬ cle.21 VIP also increases vaginal blood flow.22 There is strong ev¬ idence that this peptide participates as the noncholinergic vasodilatory transmitter in the control of uterine blood flow and is responsible for the increase in vaginal blood flow and vaginal lubrication evoked by sexual excitement.23 VIP loses its ability to increase vaginal blood flow after the menopause, but the vasodilatory response can be restored by hormonal replacement ther¬

12

i o

1525

apy (Fig. 178-1), indicating that the milieu of sex steroids can influence VIP function.24 In humans, VIP is a possible mediator of erection: intracavernous VIP injection causes erection, and during visually induced erection, there is a local release of this peptide (Fig. 178-2).23 A suggested contribution to penile erection by CGRP26 27 and nitric oxide28 remains to be clarified.

PEPTIDERGIC CONTROL OF SMOOTH MUSCLE ACTIVITY The activity of genital smooth musculature seems to be un¬ der dual peptidergic control by excitatory substance P nerves and inhibitory VIP nerves and NPY nerves.29,30 In addition, CGRP has an inhibitory effect on the substance P-stimulated uterine contractions.6 Moreover, VIP is able to abolish both spontaneous and oxytocin- and prostaglandin F2a-induced mechanical and myoelectrical activity in the uterus.7 VIP also is an inhibitory neu¬ rotransmitter in the urinary tract.31 In the bladder, VIP seems to decrease the muscular tone during passive filling, thus maintain¬ ing normal compliance until micturition occurs. Micturition in¬ volves cholinergic detrusor contraction and a VIP-induced tri¬ gone relaxation.

PATHOPHYSIOLOGIC IMPLICATIONS Abnormalities in the peptidergic nerves of the genitourinary tract are known to occur in two disease states, both of them in¬ volving VIP. Normal persons can inhibit bladder detrusor con¬ tractions until they are ready to urinate. Patients with bladder instability cannot, and may manifest symptoms such as increased frequency, nocturia, urgency, incontinence, and enuresis. In pa¬ tients with urodynamically proven idiopathic detrusor instability (i.e., no evidence of outflow obstruction, neuropathy, or struc¬ tural lesions), the number of VIP nerves is greatly decreased in all layers, but particularly in the muscle.32 In the penile tissue of impotent diabetics with autonomic neuropathy, there is a de¬ creased number of VIP nerves.33 In many patients with erectile failure, VIP alone is not sufficient to induce full erection, but in combination with a small dose of the a-adrenoceptor block¬ ing drug, phentolamine, VIP is now successfully used as self¬ injection therapy for male impotence.34 Undoubtedly, as the physiologic roles of regulatory peptides in the genitourinary tract are deciphered, many more clinical ex¬ amples of pathologic dysfunction will be found.

-

8 -

■o

o —

o $

■a E o>

FIGURE 178-1.

-

0

-

2

-

Effect of vasoactive intestinal peptide (VIP) on vaginal blood flow in postmenopausal women receiving no medication (open circles) and in postmeno¬ pausal women receiving hormonal replacement ther¬ apy (closed circles). Figures are given as means ± SEM of six experiments. 1 .fusion of saline solution did not change vaginal olo< J fl )w (not shown). Asterisks indi¬ cate significar t diFiiei ce from before VIP injection, P

Dose of VIP (pg)

0.1% residual activity) of HPRT are as¬ sociated with early (teenage)-onset gout and uric acid crystal for¬ mation (infancy), but neurologic symptoms either are absent or mild. Rarely, mothers of HPRT-deficient male children exhibit mild degrees of purine overproduction and late-onset gout, indi¬ cating that this disorder can be inherited as an incomplete Xlinked dominant trait in unusual situations. HPRT deficiency can be diagnosed readily by assay of eryth¬ rocyte lysates. A deficiency of this enzyme has two important consequences for purine synthesis: first, PRPP accumulates be¬ cause it is not used in this salvage reaction, and second, purine nucleotide formation through salvage mechanisms is reduced (see Fig. 186-1). Consequently, there is increased activity of the first enzyme in the de novo pathway of purine synthesis (see Fig. 186-3).

MANAGEMENT OF PURINE OVERPRODUCTION FIGURE 186-5.

Lesch-Nyhan syndrome. Choreoathetosis of upper extremities and scissoring of lower extremities is typical of the spasticity observed in this disorder.

HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE DEFICIENCY Hypoxanthine-guanine phosphoribosyltransferase, another enzyme encoded by a gene on the X chromosome, catalyzes a significant reaction in the salvage pathway in which the purine bases, hypoxanthine and guanine, are phosphoribosylated to form purine nucleotides (see Fig. 186-1). This is one of the best studied of the human enzymatic deficiencies, including compre¬ hensive metabolic studies in patients, biochemical analyses of cultured cells, and documentation of amino acid changes in the HPRT protein and base substitutions in the HPRT gene.8,9 Two clinical syndromes are associated with this enzyme defect, which is inherited as an X-linked recessive disorder. Highgrade deficiencies (-OH -N

N HO^N ALLOPURINOL

~\

N

OXYPURINOL

N FIGURE 186-6.

Substrates and inhibi¬ tors of xanthine oxidase.

1600

PART XI: HERITABLE ABNORMALITIES OF ENDOCRINOLOGY AND METABOLISM

added effect of decreased purine production. Although there still is no satisfactory treatment for the neurologic symptoms associ¬ ated with HPRT deficiency, the production of a mouse model for Lesch-Nyhan syndrome11 and the prospect of germ line gene modification1- raise the potential for somatic gene therapy and possibly even future treatment and prevention of this devastat¬ ing disorder.

DISORDERS OF PURINE SALVAGE HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE DEFICIENCY Hypoxanthine-guanine phosphoribosyltransferase deficiency is a disorder of both purine base salvage and purine synthesis. Failure to reuse hypoxanthine (and guanine) contributes to the excessive rate of uric acid production observed in patients with this enzyme defect. In normal persons, a large portion of the hy¬ poxanthine produced each day through purine nucleotide catab¬ olism is salvaged by the HPRT reaction. Loss of this salvage mechanism contributes to the excess production of uric acid char¬ acteristic of this disorder.

ADENINE PHOSPHORIBOSYLTRANSFERASE DEFICIENCY Reutilization of the purine base, adenine, is catalyzed by APRT (see Fig. 186-1). This enzyme is the product of a gene different from that for HPRT. The salvage of adenine is quantita¬ tively much less significant than that of hypoxanthine because human cells have a limited capacity to produce adenine. Thus, APRT deficiency has no discernible effect on purine nucleotide synthesis, and patients with this enzyme defect do not exhibit increased rates of purine synthesis and uric acid production. When adenine is not phosphoribosylated by APRT, this purine base becomes available for oxidation by XO (see Fig. 186-1). The affinity of APRT for adenine is considerably greater than that of XO, and in normal individuals, essentially all of the adenine is metabolized through the salvage pathway. Symptoms in patients with APRT deficiency are the conse¬ quence of failure to “scavenge” or reuse the small amount of adenine produced or ingested each day.13 Oxidation of adenine to 2,8-dihydroxyadenine leads to the formation of an extremely insoluble purine base, and crystals of 2,8-dihydroxyadenine form in the urine, causing renal calculi.14 Complete deficiency of APRT is inherited as an autosomal recessive trait and can be diagnosed readily by assay of erythrocyte lysates. Recurrent radiolucent renal calculi may form in children and young adults with this enzyme defect. Renal insufficiency has developed in some patients. Occasionally, the stones have been misdiagnosed as uric acid calculi because of the similar physical properties of 2,8-dihydroxyadenine and uric acid. The treatment of this disor¬ der depends on early recognition of the type of stone being formed and institution of appropriate dietary (low purine) and drug therapy (allopurinol to inhibit XO). Partial deficiency of APRT (30%-50% of normal activity) also has been reported. This abnormality appears to be a common genetic polymorphism of no clinical significance.

DISORDERS OF PURINE CATABOLISM Disorders in one portion of the purine pathway frequently lead to secondary changes in other parts of this pathway, as well as producing derangements in other metabolic pathways. This is best illustrated by the group of disorders categorized as defects in purine catabolism. Inherited defects in other pathways may alter purine catabolism, secondarily, and the resultant derangements in purine metabolism contribute to the symptoms observed in these patients.

ADENOSINE DEAMINASE DEFICIENCY Adenosine deaminase deaminates both adenosine and deoxyadenosine to form inosine and deoxyinosine, respectively (see Fig. 186-1). Deficiency of this enzyme activity, which is inherited as an autosomal recessive disorder, leads to profound lymphope¬ nia.15 Patients having this enzyme defect have reduced numbers of T and B cells, decreased immunoglobulin levels, and diminu¬ tion in cellular and humoral immune responses. ADA deficiency accounts for a significant number of patients with severe com¬ bined immunodeficiency (SCID). These patients suffer recurrent infections, and without therapy, they often die within the first few years of life. ADA deficiency can be diagnosed by assay of any easily ob¬ tained tissue, such as erythrocytes. The deficiency leads to the accumulation of both adenosine and deoxyadenosine. The buildup of these naturally occurring purine nucleosides, particu¬ larly deoxyadenosine, may alter lymphocyte growth and func¬ tion through derangements in purine, nucleic acid, or transmeth¬ ylation reactions. The accumulation of deoxy-ATP may inhibit ribonucleotide reductase, leading to a decrease in DNA synthesis and lymphocyte replication. An accumulation of S-adenosylhomocysteine may inhibit transmethylation reactions. It is unclear why a generalized deficiency of ADA has such profound effects on lymphocytes while most other organs function normally, but the susceptibility of lymphocytes to ADA deficiency may be ex¬ plained partly by other features of purine metabolism in lympho¬ cytes that lead to the accumulation of deoxy-ATP or other purine intermediates in these cells. The removal of deoxyadenosine and adenosine by replace¬ ment of ADA activity through red blood cell transfusion or bone marrow transplantation has restored immune function in some of these patients. Several SCID patients have been treated with injections of polyethylene glycol-modified bovine ADA, result¬ ing in significant clinical improvement.16 The successful cloning of the gene responsible for ADA deficiency has opened new ave¬ nues of therapeutic intervention for this disorder. In one of the first uses of gene transfer therapy, patients with SCID have been given infusions of genetically corrected T cells, resulting in im¬ proved immune status.17

PURINE NUCLEOSIDE PHOSPHORYLASE DEFICIENCY Purine nucleoside phosphorylase catalyzes the reaction in which inosine, deoxyinosine, guanosine, and deoxyguanosine undergo phosphorolysis to purine bases (see Fig. 186-1). PNP deficiency is characterized by recurrent infections with nonbacterial organisms, reflecting the primary defect in cellular immu¬ nity. Laboratory tests reveal lymphopenia and a diminished number of T cells. Although there are normal numbers of B cells, their function may be significantly impaired.18 A confirmation of the diagnosis is obtained by the assay of erythrocyte lysates or other cell extracts. The deficiency of PNP, which is inherited as an autosomal recessive trait, leads to the accumulation of several purine nucle¬ osides, the most important of which is deoxyguanosine. Thus, deoxyguanosine triphosphate concentrations become elevated in T lymphocytes, leading to the inhibition of ribonucleotide reduc¬ tase, a reduction in DNA synthesis, and the death of T cells. The prognosis in PNP deficiency usually is better than in ADA defi¬ ciency; the replacement of PNP activity by bone marrow trans¬ plantation or red blood cell infusion has been less successful.

XANTHINE OXIDASE DEFICIENCY Xanthine oxidase catalyzes the last reactions in the purine catabolic pathway, that is, oxidation of hypoxanthine to xanthine and of xanthine to uric acid (see Fig. 186-1). This disorder is sus¬ pected in individuals with persistently low ( 13

5

I

Abnormal short stature or slow growth with good general health can arise from various disorders. Optimum therapy de¬ pends on accurate diagnosis. Children with growth disorders are classified into two types: those in whom persistent short stature is the dominant feature, and those in whom slowing of growth, with or without short stature, is the major problem. Common causes of short stature are congenital and include familial delayed puberty, GH deficiency. Turner syndrome, intrauterine growth failure, skeletal dysplasia, and normal genetic short stature. Common causes of slow growth are acquired and include deprivation, acquired GH defi¬ ciency/insensitivity, hypothyroidism, mild Crohn disease, Cush¬ ing disease, and drug-induced diseases. Typical growth curves for the two types of growth problems are shown in Figures 192-4 and 192-5.

SHORT STATURE WITH OR WITHOUT SLOWING OF GROWTH FAMILIAL DELAYED PUBERTY FIGURE 192-4.

Typical growth curve of a girl with long-standing short

stature, probably a congenital disorder.

Associated with sexual maturation is a spurt in growth. The peak height velocity occurs at 14.1 ± 0.9 years in boys and at

1643

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

12.2 ± 0.8 years in girls (mean ± SD).6 Children who mature somewhat later than average are shorter than most of their peers throughout their teenage years. Almost always, a close relative has experienced a late but normal puberty. Because children with familial delayed puberty continue to grow for a longer period than usual, they achieve normal adult height. Anecdotal experi¬ ence leads the authors to believe that, as adults, these men and women continue to look younger than their peers and are psy¬ chologically normal. PRESENTING MANIFESTATIONS

During the first decade of life, patients with familial delayed puberty, who usually are boys, have modest short stature (e.g., heights consistently 1 to 2 SD below the mean). During the sec¬ ond decade, they complain of absent puberty and an even greater height discrepancy compared with their peers (2 to 3 SD below the mean). Patients vary in expressing their concern about their youthful appearance and sexual immaturity. Results of the sys¬ tem review are negative. The musculature is good and, except for delayed or absent sexual maturation, results of the physical examination are normal. This condition is much more common in boys than in girls, with a ratio of about 10:1. CONFIRMING THE DIAGNOSIS

The diagnosis of familial delayed puberty is suggested by a family history of late puberty. Ultimately, the diagnosis is con¬ firmed when progressive sexual maturation and a pubertal growth spurt are observed. The bone age is delayed, but usually is within normal limits. Laboratory tests can be performed to detect rising serum tes¬ tosterone levels, elevated serum luteinizing hormone levels dur¬ ing sleep, or elevated luteinizing hormone levels in response to stimulation with gonadotropin releasing hormone. In the experi¬ ence of the authors, however, such tests are no more sensitive than a careful physical examination for the initial signs of pu¬ berty (lengthening of the scrotum and growth of the testes in boys, or breast budding and growth of pubic hair in girls). In 45 sexually infantile boys aged 10.0 to 15.3 years, plasma testosterone levels were measured at 8:00 pm and again the next morning at 8:00 AM.7 Of those boys who had significant over¬ night elevations in testosterone, 58% and 89% achieved testicu¬ lar volumes of 4 mL or more after 12 and 21 months, respectively. Of those boys who had morning testosterone concentrations of 0.7 nmol/L (20 ng/dL) or more, 77% entered puberty within 12 months and 100% did so within 15 months. Boys in whom the initial signs of puberty have not devel¬ oped by the age of 13.5 to 14 years and girls in whom they have not developed by the age of 13 to 13.5 years probably do not have familial delayed puberty and require study for other causes of short stature or sexual immaturity (e.g., hypopituitarism. Turner syndrome, acquired hypothyroidism, hyperprolactin¬ emia, or overzealous exercise).4-8-9 THERAPY AND PROGNOSIS

Because familial delayed puberty is a variation of normal, supportive rather than hormonal therapy is needed. The natural history of the condition should be explained to patients and their parents: the children will continue to grow, but for a longer time than usual, and ultimately will achieve normal adult height. They will mature sexually, but at a later age than usual. On return vis¬ its; the authors demonstrate to these patients that they have grown, gained weight, and acquired secondary sexual character¬ istics (Fig. 192-6), Many patients benefit from talking to a relative who has had a similar growth pattern, looking at old class pictures of that relative, and sharing humorous or trying experiences. Occasionally, a boy is so upset by the delayed puberty that a short course of therapy is suggested with testosterone enanthate,

FIGURE 192-6.

Eighteen-year-old boy with proportionate short stat¬

ure, good musculature, recent appearance of secondary sexual character¬ istics. Tanner stage III genitalia, and a bone age of 14 years. His father completed sexual maturation and achieved full height at 21 years of age. Diagnosis: familial delayed puberty.

50 to 100 mg given intramuscularly once a month for 3 to 6 months.10 This results in some growth of the genitalia, an in¬ crease in muscle mass, and an increase in height, without undue acceleration of skeletal maturation. Used judiciously, such hor¬ monal therapy does not seem to compromise final adult height. A satisfactory response to an oral preparation, testosterone undecanoate in arachis oil, 40 mg/d for 15 to 24 months, has been reported.11 Oxandrolone, 1.25 or 2.5 mg/d for 3 to 12 months, was ad¬ ministered to 40 boys with familial delayed puberty when the volume of the testes was 4 mL, resulting in sustained growth ac¬ celeration.12 (Ordinarily, boys experience an increase in height when the testes reach a volume of 10 mL.) Although young women with familial delayed puberty or their parents rarely ask for female sex hormone therapy, ethinyl estradiol, 5 jug PO daily for 3 weeks out of 4 for 3 to 6 months, accelerate growth and, at least in some patients, initiate breast development. Among 42 individuals with previously diagnosed constitu¬ tional delay of growth and puberty, both boys and girls achieved normal heights (about 1 SD below the mean and 5 cm below target heights), based on mid-parental heights.12 The discrepancy has been ascribed to a selection bias: the shortest children were referred for pediatric endocrinology consultation.13 The 40 boys treated with oxandrolone grew to mean adult heights slightly greater than the predicted heights.12 Adult men with histories of constitutionally delayed puberty have decreased radial and spinal bone mineral density and may be at increased risk for osteoporotic fractures in old age.14

CONGENITAL GROWTH HORMONE DEFICIENCY The anterior pituitary gland secretes GH; the hypothalamus secretes growth hormone releasing hormone and somatostatin

Ch. 192: Short Stature and Slow Growth in the Infant and Child

1649

or growth hormone release-inhibiting hormone. With the use of recombinant DNA probes, genes have been located on the long arm of chromosome 17 for GH, on chromosome 20 for growth hormone releasing hormone, and on chromosome 3 for somatostatin.15 GH is essential for extrauterine growth. Congenital GH de¬ ficiency varies from mild to marked in severity and results from disorders of the pituitary or hypothalamus. The underlying dis¬ order can be controlled genetically: X-linked recessive, autosomal dominant, or autosomal recessive. Congenital GH deficiency can be associated with craniofacial midline defects (e.g., cleft lip or palate, single maxillary central incisor, septo-optic dysplasia); it can arise from anatomic defects in the pituitary or from difficul¬ ties in pregnancy (e.g., early vaginal bleeding); or it can occur consequent to breech or forceps delivery and difficulties in the neonatal period (e.g., prematurity). Often, however, the origin of the deficiency is unknown. Other deficiencies of hypothalamic-pituitary hormones can be present. Thus, the natural history is variable and not fully de¬ lineated. Some patients with severe hypopituitarism probably die in the newborn period, whereas those who merely lack normal amounts of GH have pathologic short stature as adults (Fig. 192-7). Adults with hypopituitarism develop atherosclerotic changes and die at an early age.16 PRESENTING MANIFESTATIONS

Most patients with GH and gonadotropin deficiency have short stature early in life and extreme short stature as well as sexual infantilism during the second decade. In the experience of the authors, children with isolated GH deficiency come to the attention of physicians relatively late and with only moderately severe short stature. Other family members (e.g., parents or sib¬ lings) may be abnormally short. Some parents report that their

FIGURE 192-8.

Seven-year-old boy with proportionate, but abnormal,

short stature and low levels of growth hormone. Note youthful appear¬ ance, pudgy anterior thoracic and anterior abdominal walls, small normal external genitalia, and mottling of skin of lower extremities.

FIGURE 192-7.

Adult with abnormal but proportionate short stature,

obesity, and growth hormone deficiency; mother of boy in Figure 192-8.

short children lack physical strength and energy, and that their permanent teeth erupted later than usual. Those who have both ACTH and GH deficiency may have had symptoms of hypogly¬ cemia (e.g., seizures, somnolence, irritability) during the new¬ born period and intermittently during the first decade of life. Neonatal hyperbilirubinemia can be associated with congenital GH deficiency. Small external genitalia (penile length < 2.5 cm) can be one of the presenting manifestations in male neonates with hypopituitarism, and reflects GH deficiency, gonadotropin deficiency, or both. Septo-optic dysplasia is a defect of neuronal migration char¬ acterized by some or all of the following: absence of the septum pellucidum, optic nerve hypoplasia, hypopituitarism, diabetes insipidus, and mental retardation. Newborns with septo-optic dysplasia can have searching nystagmus secondary to blindness, as well as symptomatic hypoglycemia. On physical examination, these patients have unusually youthful appearances, small-timbre voices, and pudgy torsos with dimpled abdominal fat. Boys can have an absence of good muscle development and small but normal external genitalia. Sexual infantilism can be present in both boys and girls (Fig. 192-8). Children with septo-optic dysplasia can have small optic globes, small optic nerve heads on funduscopic examination, normal or impaired vision, and normal or impaired intellect. The authors evaluate proportional but unusually short chil¬ dren with bone age radiographs and measurements of serum insulin-like growth factor I (IGF-I) concentrations. In GH-deficient patients, bone ages usually are more than 2 SD below the mean and IGF-I concentrations are below the normal range for both chronologic and bone age. However, the serum IGF-I con¬ centrations of normal children and those of children with hypo¬ pituitarism overlap, particularly during the first 5 years of life.

1650

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN THE GROWING CHILD AND IN THE AGED

Thus, a low IGF-I concentration is a sensitive but nonspecific in¬ dicator of GH deficiency in this age group. Measurement of the serum concentration of IGF binding protein III is a more specific test for GH deficiency in young children.17 CONFIRMING THE DIAGNOSIS

In normal children, GH concentrations vary throughout the 24-hour period and peak several times during the night, coinci¬ dent with slow-wave sleep. The GH response to at least two pharmacologic agents has been used extensively to diagnose GH deficiency in euthyroid short children. For the past 30 years, cli¬ nicians have challenged euthyroid short children under basal conditions with two stimulating agents or procedures known to increase blood levels of GH in normal children. Available stimulating agents include insulin, arginine, glucagon, clonidine, Ldopa, and propranolol. Exercise also stimulates GH release in about 80% of normal children. The authors find arginine espe¬ cially useful because it rarely produces symptoms. Insulininduced hypoglycemia permits simultaneous evaluation of ACTH, cortisol, and GH, but patients require close monitoring for the possibility of a serious hypoglycemic reaction.23 In 1984, a subgroup of children was identified who had fea¬ tures of GH deficiency and normal GH responses to pharmaco¬ logic stimulation, but decreased spontaneous secretion of GH in serial blood samples collected every 20 minutes during a 24-hour period. These children had short stature, delayed bone age, and low serum IGF-I concentrations, and their subnormal growth ve¬ locity more than doubled after 1 year of GH therapy. This condi¬ tion has been called GH neurosecretory dysfunction. In these pa¬ tients, GH secretion (expressed as mean GH concentration, peak

Time

Time

FIGURE 192-10.

Representative 24-hour growth hormone (GH) secre¬ tory patterns in GH-deficient children, children with GH neurosecretory dysfunction, and control subjects. The GH-deficient children and those with GH neurosecretory dysfunction are in pubertal stage I. The control subject in the left lower panel is Tanner stage I and the control subject in the right lower panel is Tanner stage IV. (From Spiliotis BE, August GP, Hung W, et al. Growth hormone neurosecretory dysfunction: a treatable cause of short stature. JAMA 1984; 251:2251.)

Dysfunction

FIGURE 192-9. Mean 24-hour growth hormone (GH) concentrations in three patient groups (GH deficient, GH neurosecretory dysfunction, and control). The bar represents mean ± SEM. (From Spiliotis BE, August GP, Hung W, et al. Growth hormone neurosecretory dysfunction: a treatable cause of short stature. JAMA 1984; 251:2223.)

frequency and amplitude, and area under the curve) was lower than in a normal control group, but higher than in children with classic GH deficiency1819 (Figs. 192-9 and 192-10). In another study, integrated overnight GH secretory profiles were determined by pooling blood samples obtained through an indwelling catheter at 20-minute intervals from 8:00 pm to 8:00 am on two consecutive nights in the hospital. The subjects had heights below the 3rd percentile for age, height velocities below the 25th percentile for age, or both. The investigators used the Hybritech immunoradiometric assay. Maximum stimulated GH concentrations correctly categorized 80% of children who had maximum nocturnal GH concentrations above or below 4 ng/ mL. The remaining 20% of children had stimulated GH concen¬ trations below 4 ng/mL but spontaneous GH concentrations above this level. These investigators believe that it is common for stimulated GH concentrations to underestimate spontaneous GH secretion, and that the measurement of spontaneous GH secre¬ tion on a single night is more reliable for identifying children with low endogenous GH secretion than is the use of GH stimulation testing alone.18,19 About 10 years after its initial description, the topic of GH neurosecretory dysfunction remains controversial.20-23 The de¬ bate is fueled by the variability of GH secretion from day to day, both during sleep21 and in response to stimulation tests22; by the

Ch. 192: Short Stature and Slow Growth in the Infant and Child limited use of electroencephalographic monitoring to document sufficient slow-wave sleep in most studies of spontaneous GH secretion; and by the absence of an ideal test of GH secretion. The positive short-term response to GH therapy described in patients with GH neurosecretory deficiency no longer is considered diag¬ nostic of GH deficiency, and the final heights of children with low spontaneous GH secretion who receive GH therapy are only minimally increased above those of untreated patients.24-25 Growth Hormone Assays. Many laboratories measure serum GH. However, because of variations in methodology, a single sample assayed in different laboratories yields different values.26 Serum GH concentrations measured by a traditional radioimmu¬ noassay using a polyclonal antibody are between 1.9 and 2.8 times higher than those determined by the newer immunoradiometric monoclonal antibody-based assay. Ideally, each labora¬ tory assaying serum GH should determine the normative con¬ centrations in different age groups of healthy, normally growing children. In addition, the extent of GH deficiency varies among pa¬ tients. Table 192-2 lists two agents frequently used for outpatient GH testing and the serum GH values usually considered diag¬ nostic of “classic” or "partial" GH deficiency. Although this clas¬ sification is used by several pediatric endocrinologists in the United States, the terminology and the GH concentrations used to separate conditions of subnormal from normal GH secretion are somewhat controversial. Because an impaired GH response to any of the stimulating agents can occur in 5% to 10% of normal individuals, at least two stimulation tests should be performed, preferably on two separate days, to minimize the risk of false¬ negative results. Any GH value higher than 10 ng/mL generally is considered good evidence against GH deficiency. Measurement of the GH concentration in a timed (12- or 24-hour) urine collection has the theoretic advantages of being noninvasive and reflecting the secretion of GH over many hours. However, data suggest that it is not a useful screening test for GH deficiency. Although this method identifies children with GH ex¬ cess, confirmation by serum GH measurements is still needed.27 During the 1960s, serum GH levels were measured in chil¬ dren who slept in the hospital, remained in bed in the morning, fasted, and had blood samples collected before, during, and after the administration of a stimulating agent.28 Because of current insurance regulations, blood for nonbasal GH measurements of¬ ten must be collected in ambulatory patients. The stimulated se¬ rum GH levels of normal ambulatory children are unknown. Peak and integrated GH concentrations vary in normal chil¬ dren according to age: they are extremely high in the newborn period29 and somewhat elevated during puberty. In 44 integrated studies performed in nine prepubertal normal boys over a 1- to 3-year period, the mean 24-hour integrated concentrations of

1651

GH for individual profiles ranged from 1.1 to 7.0 ng/mL, with an intersubject coefficient of variation of 46%. However, values for repeated studies performed on the same individual varied less, with a coefficient of variation of 26%. The physiologic release of GH is regulated over time within characteristic, individually determined limits that vary predictably, but reciprocally, with body mass index.30 Serum IGF-I (somatomedin C) levels generally reflect GH secretion. These concentrations vary with age and sex; they are lower in younger children and higher in older/pubertal children and in girls.31 In normally short children, normal random serum IGF-I levels strongly suggest that GH secretion is sufficient. A single serum GH determination is useful only if the concentration is in the GH-sufficient range. Diagnostic Imaging. With the use of magnetic resonance im¬ aging, almost 450 children with hypopituitarism and 46 healthy short children have been evaluated for pituitary abnormali¬ ties.32,33 In a study of 101 consecutive patients with congenital idiopathic GH deficiency, 59 had ectopia of the posterior pitu¬ itary or an interrupted pituitary stalk and 42 had a normal poste¬ rior pituitary. The pituitary volume was extremely small in the patients with ectopia and in those with normal glands that had severely narrowed stalks; the mean volume was significantly lower in these patients than in healthy short children. The inves¬ tigators hypothesized defective induction of the mesobasal struc¬ ture of the brain in the early embryo. The incidence of empty sella was 9% among patients with isolated GH deficiency and 35% among those with multiple pituitary hormone deficiencies.

THERAPY AND PROGNOSIS

From the late 1950s until the mid-1980s, many clinicians investigated the response to treatment with human pituitaryderived GH. However, the Food and Drug Administration with¬ drew this substance because of the possibility that it was contam¬ inated with the Creutzfeldt-Jakob agent, which has caused the deaths of 12 patients treated with pituitary-derived human growth hormone (hGH) produced in the United States.34 Because the incubation period can be as long as 35 years, patients who received hGH for the first time in 1985 may still be at risk for Creutzfeldt-Jakob disease in the early 21st century. For babies and children with GH deficiency, biosynthetic hGH is the drug of choice. It is commercially available in two forms, methionyl hGH (met-hGH, somatrem) and the natural se¬ quence hGH (somatropin), both of which are equally effective in promoting linear growth. The current annual cost of biosynthetic GH for a 20-kg patient treated with 0.3 mg/kg/wk is about $13,500. In GH-deficient patients with abnormal short stature, the

TABLE 192-2 Pharmacologic Agents Commonly Used for Outpatient Testing of Growth Hormone (GH) Secretion

Drug and Dose

Sampling Times

Clonidine hydrochloride 0.15

0, +60, +75, +90, +120 min (minimum: single sample at +75

mg/m2 po (maximum: 0.2 mg)*

min)

L-dopa 350 mg/m2 (maximum: 500 mg) plus propranolol 0.75 mg/kg po (maximum: 40 mg)|

0, +30, +60, +90, +120 min (minimum: two samples, at +60 and +90 min, respectively)

* Side effects are mild and include somnolence and mild hypotension. 4 Side effects are mild and include nausea, vomiting, and mild bradycardia.

Normal GH Response (Polyclonal Radioimmunoassay)

Normal GH Response (Hybritech Immunoradiometric Assay)

At least one value above 10 ng/mL; values between 7 and 10 ng/mL suggest partial GH deficiency; values < 7 ng/mL suggest complete GH deficiency

At least one value above 7 ng/ mL; values between 5 and 7 ng/mL suggest partial GH deficiency; values < 5 ng/mL suggest complete GH deficiency

At least one value above 10 ng/mL; values between 7 and 10 ng/mL suggest partial GH deficiency; values < 7 ng/mL suggest complete GH deficiency

At least one value above 7 ng/ mL; values between 5 and 7 ng/mL suggest partial GH deficiency; values < 5 ng/mL suggest complete GH deficiency

1652

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

goal is to achieve normal stature during the first 3 to 4 years of GH therapy. Ideally, these children should grow at a rate of 1.5 X the mean growth rate for the bone age; for example, an 8-yearold boy with a bone age of 4 years should grow at a rate of 1.5 X 7 cm/yr, or 10.5 cm/yr. Younger, smaller patients often respond well to smaller and less frequent doses, such as 0.15 mg/kg/wk given in three sepa¬ rate injections on Monday, Wednesday, and Friday.35,36 For those who achieve an optimum growth rate over a period of 6 months, the same dose per kilogram of body weight is continued at the same frequency. For those who grow significantly less, the fre¬ quency is increased to daily injections and, if necessary, the dose is increased to 0.3 mg/kg/wk or even 0.45 mg/kg/wk. Older, larger patients should begin at 0.3 mg/kg/wk. For those with hypoglycemia, daily injections are mandatory during the first de¬ cade. Once normal height has been achieved, the authors aim for a mean growth rate for bone age and offer "vacations" from treatment (e.g., for camping trips). European and a few American pediatric endocrinologists have treated patients with higher doses of GF1 (0.6 mg/kg/wk). The intranasal administration of hGH results in a plasma peak similar to the physiologic and en¬ dogenous peak. 37 Significant systemic levels of GH can be achieved in vivo by gene transfer into muscle cells, using either viral or DNA vectors.38,39 Complications of Growth Hormone Therapy. Although some patients develop serum antibodies to GH during biosynthetic GH therapy, these antibodies do not produce immune complex dis¬ ease and rarely inhibit growth. They do interfere with serum GH measurements. If antibodies are going to develop, they usually do so within 3 to 6 months and their appearance can be transient, especially in patients with low levels of binding. The methionyl GH is more likely to result in the formation of antibodies than is the natural sequence GH. A few patients with GH deficiency have developed leukemia before, during, or after therapy with either pituitary-derived or biosynthetic GH. At risk are those who have undergone irradia¬ tion for brain tumors with or without GH therapy. In the United States, the incidence of leukemia in nonirradiated patients is no higher than in the general population.40 Another study described a few patients who developed pseudotumor cerebri that abated when GH treatment was discontinued.41 Children with GH deficiency who have gonadotropin sufficiency may need special attention. Because they are being treated with GH, puberty can begin at an inappropriately short height and final adult height can be compromised. The efficacy of gonadotropin releasing hormone analogues in retarding the onset of puberty in these patients is being evaluated. Preliminary data suggest that such combined therapy may be helpful among those with central sexual precocity and severely compromised growth potential; it slows their sexual and skeletal maturation and may allow them to achieve normal adult height.42 Indications for Growth Hormone Treatment in Patients Without Growth Hormone Deficiency. Although many GH-sufficient chil¬ dren who are abnormally short respond temporarily to therapy with GH, there are no data (except for Turner syndrome) to indi¬ cate which of these children should be treated. Extensive re¬ search shows that children with Turner syndrome, renal in¬ sufficiency, and glucocorticoid-induced dwarfism experience accelerated growth. Less intensively studied children who also respond to GH treatment include those with intrauterine growth failure, Down syndrome, hypophosphatemic rickets, meningo¬ myelocele, and Prader-Willi syndrome. The decision to treat with GH must be made by each patient's physician and family.43-47 Final adult heights were reported for 15 normally short pa¬ tients who were treated with GH for 4 to 10 years. The mean final heights did not differ from the mean pretreatment predicted adult heights.24 For long-term results of GH therapy in girls with Turner syndrome, see below.

Growth Hormone Insensitivity (Laron Syndrome). In 1966, three siblings were described who had hypoglycemia and other clinical and laboratory signs of GH deficiency, but abnormally high concentrations of immunoreactive serum GH and decreased concentrations of IGF-I.48 Since then, more than 200 such pa¬ tients, mostly of Mediterranean or Indian descent, have been de¬ scribed.49 Patients with Laron dwarfism have GH insensitivity due to a GH receptor deficiency. Therapy with IGF-I, 80 to 120 Mg/kg twice daily, accelerated the growth of five patients with Laron syndrome to 6.0 to 11.9 cm/yr.50 Although short-term therapy with biosynthetic GH has pro¬ duced no significant side effects, the safety of long-term therapy is unknown. Experience with other hormone therapies has shown that adverse effects can take years to evolve (e.g., stilbestrol given to a woman pregnant with a female fetus led to subse¬ quent malignancy of the girl's external genitalia). Thus, the au¬ thors urge a cautious approach to hGH therapy. Meanwhile, the following guidelines are suggested: 1. Do not use for normal genetic short stature. 2. Consider for abnormal short stature of indeterminable cause for a 1-year period. 3. Validate the efficacy of treatment by obtaining careful height measurements during the 6 months before therapy and for the first year of therapy. 4. Continue therapy only if it is successful.

TURNER SYNDROME Turner syndrome is a sporadic phenomenon associated with a missing female sex chromosome or a short arm of a female sex chromosome in some or all of the peripheral lymphocytes (see Chaps. 87 and 89). In addition to marked short stature, these girls have absent to diminished endocrine and germinal function of the ovaries. Many have isolated, mild learning difficulties; dys¬ morphic features; minor anatomic renal abnormalities; acquired hypothyroidism; congenital heart disease; and an increased inci¬ dence of wrist fracture and scoliosis.51 Girls with Turner syn¬ drome grow to an adult height of 127 to 157 cm (50 to 60 inches). Although sterility is the rule, an occasional patient has been fertile. PRESENTING MANIFESTATIONS

Most patients with Turner syndrome seek help for patho¬ logic short stature during the first decade of life or for short stat¬ ure and sexual immaturity during the second decade. The short stature is proportional and the adult height correlates with cor¬ rected mid-parental height.52 About 15% of cases are diagnosed shortly after birth because of dysmorphic features, particularly puffy hands or feet and redundant skin at the nape of the neck. A few are identified by pediatric cardiology. Parents usually remark that these girls have remarkably even dispositions and are particularly gifted in caring for young children. The physical examination generally reveals a short, stocky girl with slightly unusual facies: narrow maxilla and pal¬ ate, relatively small mandible, epicanthal folds, and ptosis of the lids. There may be many nevi, mild hypertension, webbing of the neck, an organic heart murmur, cubitus valgus, short legs, nar¬ row fingernails, and residual lymphedema of one or both feet. Affected teenagers develop pubic hair, but little breast tissue or maturation of the vagina and labia. However, the most constant physical finding is proportionate abnormal short stature. ESTABLISHING THE DIAGNOSIS

The diagnosis of Turner syndrome depends on documenting the missing female sex chromosome by karyotyping peripheral lymphocytes. Most patients have either a missing female chro¬ mosome (45,X) or a mosaic pattern (45,X/46,XX). On occasion.

Ch. 192: Short Stature and Slow Growth in the Infant and Child the karyotype of the peripheral lymphocytes is normal, and the diagnosis can be established only by karyotyping cultured fi¬ broblasts from skin or from ovarian biopsy samples.53 About 9% of patients with Turner syndrome have Y chro¬ mosomal material; because its presence predisposes to the for¬ mation of gonadoblastoma, a potentially malignant lesion, these patients should be examined regularly for signs of virilization. In addition, Y chromosomal material should be sought carefully, using both fluorescence and polymerase chain reaction of the gene from the sex-determining region of the Y chromosome.54 If this chromosome is demonstrated on cytogenetic examination, prophylactic gonadectomy should be performed. The short stature of patients with Turner syndrome is unre¬ lated to any clear-cut hormonal deficiency. However, 24-hour integrated concentrations of GH and serum concentrations of IGF-I are much lower in these patients than in age-matched nor¬ mal pubertal girls.55 Some patients with Turner syndrome have elevated spontaneous GH pulse-frequency patterns also associ¬ ated with relatively low IGF-I levels. 6 Serum gonadotropin values can be helpful before the age of 5 years and again after the age of 10 years. Patients with elevated levels probably do not have functional ovarian tissue. Pelvic ul¬ trasound examination confirms the absence of ovarian tissue. Bone age is slightly retarded. THERAPY AND PROGNOSIS

Since 1983, therapy with biosynthetic GH, initiated at 0.125 mg/kg three times a week, alone or in combination with oxandrolone, has been under study in 70 girls with Turner syn¬ drome.57 Thirty patients have completed treatment; their mean height is 151.9 cm, which is greater than their originally projected mean adult height of 143.8 cm. The authors initiate therapy with biosynthetic GH, 0.3 to 0.375 mg/kg/wk, in seven equal daily doses given subcutaneously. Some patients do not desire treat¬ ment, particularly those who have a normal degree of short stat¬ ure (often the offspring of relatively tall parents). For complete feminization, most of these girls require re¬ placement therapy with an estrogen and progesterone. Therapy is begun with 5 to 10 ^g of ethinyl estradiol or 0.3 to 0.6 mg of conjugated estrogen given daily for 3 to 6 months. Thereafter, the estrogen is given on days 1 to 23 of each calendar month and medroxyprogesterone acetate, 2.5 to 5.0 mg, is given on days 10 to 23. Later, these patients can choose in vitro fertilization or adoption.

INTRAUTERINE GROWTH RESTRICTION/PREMATURITY Intrauterine growth restriction occurs in association with en¬ vironmental, maternal, placental, and fetal factors.58 It is unclear whether there are different types of intrauterine growth restric¬ tion or whether the condition should be diagnosed solely on the basis of a birth weight that is low for gestational age.59,60 Neonates with body weights under the 10th percentile are con¬ sidered to have intrauterine growth restriction. Two types of intrauterine growth restriction have been iden¬ tified: symmetric and asymmetric. At birth, children with the sym¬ metric type (type I) have the same degree of growth restriction in body weight, crown-heel length, and head circumference. More¬ over, postnatal growth is sluggish. Children with the asymmetric type (type II), which probably results from malnutrition, have small skeletal dimensions for their gestational age as well as sig¬ nificant reductions in soft-tissue mass. These children tend to have more severe growth retardation. Fetuses with intrauterine growth restriction are identified by ultrasound. Therapies under investigation for fetal growth retardation include nutritional sup¬ plementation, oxygen therapy, and aspirin.60 Parents do not readily report that a short child had intrauter¬ ine growth restriction. Important in the evaluation is a review of

1653

past measurements. A child who was abnormally short but is accelerating in growth probably does not require further labora¬ tory evaluation. A child who remains abnormally short, how¬ ever, should undergo additional testing. Babies born before 37 weeks' gestation are considered pre¬ mature. Through the efforts of neonatologists, premature babies of extremely low birth weight (< 1000 g) now survive. Although larger, healthy premature babies achieve normal length by 18 months of age, those with extremely low birth weight may not "catch up" until 8 years of age.61-63 Some prematurely born chil¬ dren have intracranial damage and GH deficiency. In a study of 105 children who had intrauterine growth fail¬ ure and remained small (3 SD below the mean at a median chro¬ nologic age of 8.7 years and a median bone age of 7 years),64 GH was administered at a median dose of 0.5 IU/kg/wk (about 0.25 mg/kg/wk) and a median frequency of five injections per week. The median height scores for chronologic age after 1, 2, and 3 years of GH treatment were — 2.5 SD, — 2.1 SD, and — 1.9 SD, respectively. The effects of treatment on final adult height are not known.

SKELETAL DYSPLASIAS AND OTHER SYNDROMES Skeletal dysplasias are associated with innate disorders of the cartilage and bone, probably metabolic in origin, so that the bones grow abnormally in length, shape, or both.65-68 Although most of the skeletal dysplasias are transmitted as autosomal dominant traits, a few are autosomal recessive. The basic reasons for the anomalies are unknown. Final adult height varies with the underlying bone dysplasia from 61 to 152 cm (2 to 5 feet). Severe bone dysplasias can be associated with impaired hearing, weakness of the legs, and cardiopulmonary insufficiency. The reader is referred to an international classification of the several dozen skeletal dysplasias.65 Most of the patients have dis¬ proportionately short stature: the extremities usually are more affected than the trunk, or one portion of the extremities is more affected than the other. The diagnosis generally can be made from careful examination of a radiographic skeletal survey.69 Bone age determinations are not reliable in these disorders. ACHONDROPLASIA

Presenting Manifestations. Achondroplasia is the most common skeletal dysplasia, with a frequency of 1:26,000. The inheritance is autosomal dominant; 80% of cases are spontane¬ ous mutations.70 Progressive deceleration of the growth rate be¬ gins in infancy. The mean adult height is 131 cm (5H/2 inches) in boys and 124 cm (49 inches) in girls. The proximal limb shorten¬ ing is readily apparent. The head is large, with a low nasal bridge and a prominent forehead. The usual lumbar lordosis is markedly exaggerated (Fig. 192-11). Because of hypotonia and the large head, motor development is slower than usual but intellectual function is normal. In about half the adults, spinal cord or root compression occurs as a consequence of kyphosis, spinal steno¬ sis, or an intravertebral disk lesion. Diagnosis. The diagnosis of achondroplasia is clinical. Ra¬ diographs reveal a large calvarium; short ribs with anterior cup¬ ping; small, cube-shaped vertebral bodies; anterior "beaking" of the first or second lumbar vertebra, or both; small iliac wings with narrow greater sciatic notches; and short, broad tubular bones. Therapy and Prognosis. Because the hydrocephalus arrests, shunt procedures rarely are necessary. For severely bowed legs, osteotomies are indicated. Short eustachian tubes can lead to fre¬ quent middle ear infections, and antibiotics and tympanic tubes may be indicated. For weakness of the lower extremities, ortho¬ pedic surgery can be helpful. These babies usually are delivered by cesarean section. Percutaneous limb-lengthening procedures can elongate the femur and tibia by up to 15 cm each71 (Fig. 192-12). These tech-

1654

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

is being assessed; however, there is concern about worsening the narrowing of the foramen magnum and the spinal stenosis. HYPOCHONDROPLASIA

Hypochondroplasia is an autosomal dominant condition with widely variable severity. Short stature is obvious by 3 years of age.73 The final adult height varies from 117 to 153 cm (46 to 60 inches). Presenting Manifestations. These patients usually seek help in late childhood or adolescence for minimally disproportionate short stature with relatively short limbs, stubby hands and feet, and limitation of elbow extension and supination (Fig. 192-13). Diagnosis. Especially helpful are radiographs that show mild V-shaped metaphyseal indentation and flaring, prominent bony sites of muscle attachment, bowing of the lower limbs, short femoral necks, a bony spinal canal narrowing caudally, and hypoplasia of the iliac bones with small greater sciatic notches (Fig. 192-14). Therapy and Prognosis. The efficacy of GH therapy is being assessed. Pregnant women with this disorder may require cesar¬ ean section. MULTIPLE EPIPHYSEAL DYSPLASIA SYNDROME

FIGURE 192-11. Young adult with achondroplasia. Note the relatively large head, short limbs, and exaggerated lumbar lordosis. (From Rimoin DL, et al. Growth Genetics & Hormones 1991;7(3):5.)

niques are feasible in achondroplasia because of the excessive soft tissue and the tortuous nerves and blood vessels. Centers offering this surgery have widely varying age requirements, from 6 years and older to 14 years and older. The most common rea¬ sons for seeking surgery are poor body image and functional dis¬ ability; one report describes a 94% satisfaction rate in 35 patients 2 to 5 years after surgery.72 The efficacy of long-term GH therapy

FIGURE 192-12. Same young adult as in Figure 192-11 after having undergone leg lengthening for achondroplasia. The final height was 61.5 inches (156.2 cm). (From Rimoin DL, et al. Growth Genetics & Hormones 1991;7(3):5.)

The multiple epiphyseal dysplasia syndrome is associated with moderately short adult stature of 145 to 170 cm (57 to 67 inches), mottled epiphyses, and early osteoarthritis. It is inherited as an autosomal dominant trait with wide variability in expression. Presenting Manifestations. Moderately short stature and waddling gait are evident by 2 to 10 years of age. Patients com-

FIGURE 192-13.

Nineteen-year-old boy with hypochondroplasia and abnormal short stature, but with normal proportions.

Ch. 192: Short Stature and Slow Growth in the Infant and Child

1655

FIGURE 192-14. Hypochondroplasia. Left, 10-year-old with slight ulnar shortening and metaphyseal flaring, with bulbous radial enlargement and elongation of the styloid process (arrow). Middle, 7-year-old with elonga¬ tion of the distal fibula and slight "squaring off" of the proximal tibial epiphysis. Right, Adult with more marked "squaring" of the proximal tibial epiphysis (arrow), with sharp flare of the metaphysis and elongation of the distal fibula with varus deformity of the ankle mortise. (From Beals RK. Hypochondroplasia: a report of five kindreds. J Bone Joint Surg 1969;51:728.)

plain of pain and stiffness in the joints, especially the hips, as early as 5 years but usually not until the fourth decade. Diagnosis and Therapy. On radiographs, the epiphyses are late in ossifying, and are small, irregular, and mottled; eventu¬ ally, osteoarthritis occurs. There is a short femoral neck, mild metaphyseal flare, and short metacarpals and phalanges (Fig. 192-15). No definitive therapy is available.

NORMAL OR ABNORMAL GENETIC SHORT STATURE Abnormal genetic short stature occurs when a child and a parent have heights 4 SD or more below the mean. Normal genetic short stature occurs when a child is short because the parents are normally short (i.e., within 2 SD of the mean).

OTHER SYNDROMES Syndromes that feature proportionately short stature in the absence of chromosomal trisomy, dysostosis, or major dysmor¬ phic features are shown in Table 192-3.

PRESENTING COMPLAINTS These patients, often boys from middle- or upper-class fam¬ ilies, seek help because they are somewhat smaller than their

FIGURE 192-15. Multiple epiphyseal dysplasia syn¬ drome. Late and irregular mineralization of epiphyses (arrow), which may be small or aberrant in shape, or both. (From Jones KL. Osteochondrodysplasias. Skeletal dysplasias and other disorders. In: Jones KL, ed. Smith's recognizable patterns of human malformation, ed 4. Philadelphia: WB Saunders, 1988:331.)

1656

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

TABLE 192-3 Syndromes Featuring Proportionate Short Stature in the Absence of Chromosomal Trisomy, Dysostosis, or Major Dysmorphic Features Syndrome

Genetics

Clinical Features

Fetal alcohol74,75

Environmental

Prenatal and postnatal growth deficiency of variable degree; facial dysmorphism (short palpebral fissures, smooth philtrum, microcephaly); developmental delay; average IQ: 60-70

Aarskog76,77

X-linked semidominant

Moderate short stature; hypertelorism, downward slanting of palpebral fissures, anteverted nostrils, broad philtrum; brachydactyly; inguinal hernias; “shawl" scrotum, cryptorchidism

Cockayne78

Autosomal recessive

Short stature; retinopathy; deafness; mental retardation; enophthalmos; beaked nose; cataracts; skin sensitivity to ultraviolet light

Fanconi pancytopenia77,79

Autosomal recessive

Mild to moderate short stature of prenatal and postnatal onset; hypoplasia or aplasia of the thumb; strabismus, microcephaly; mental retardation in 20% of patients; skin pigmentation; small genitalia/cryptorchidism in males; progressive bone marrow failure, generally starting at 5-10 years of age and resulting in severe pancytopenia and death; increased chromosomal breakage in vitro

Laurence-Moon-Biedl77,80

Autosomal recessive

Moderately short stature; obesity; polydactylia and/or syndactylia; retinitis pigmentosa; mental retardation; small genitalia in males, variable hypogonadism

Prader-Willi77,81-83

Sporadic

Severe hypotonia and poor feeding in early infancy, developmental delay; mental retardation; progressive obesity starting in the first few years of life; short stature of moderate degree (average adult height 147 cm in females, 155 cm in males); small hands and feet; small penis, cryptorchidism, hypogonadism in both sexes; almond-shaped palpebral fissures, narrow biparietal diameter; occasionally, diabetes mellitus (type II); deletion of the long arm of chromosome 15 is detected in over 60% of the cases, and virtually all the remaining patients have maternal disomy of 15q

Russell-Silver77,84

Sporadic

Short stature of prenatal onset (intrauterine growth retardation) and continuing postnatally; mildly to moderately short stature in childhood; triangular face with downturned corners of the mouth, asymmetry of the extremities; clinodactyly of the fifth finger

Ullrich-Noonan77,85

Sporadic or autosomal dominant

Moderately short stature; epicanthal folds, ptosis, low-set ears, webbed neck; shield chest;

Sporadic

Prenatal and postnatal growth deficiency; mildly to moderately short stature in childhood; short palpebral fissures, depressed nasal bridge, anteverted nares, prominent lips with open mouth; mental retardation (average IQ; 50-60) with friendly personality; supravalvular aortic stenosis or other congenital heart disease or arterial anomaly; occasional hypercalcemia in early infancy ("idiopathic hypercalcemia in infancy")

Williams77,86

mental retardation; pulmonic stenosis, septal defects; small penis, cryptorchidism, occasional hypogonadism; occasional lymphedema of the dorsum of hands and feet; improperly called Turner-like syndrome

peers. The results of the physical examination, including signs of sexual maturation, are normal.

ESTABLISHING THE DIAGNOSIS The diagnosis is clinical. The authors measure the height of both parents and plot the data on the growth curve at 18 years of age. The parents' heights and the patient's height in terms of standard deviations are comparable. For example, if the patient's height is 2 SD below the mean, the height of one or both parents also should be about 2 SD below the mean (i.e., 152 cm [60 inches] for the mother and 164 cm [64y2 inches] for the father). Further evaluation is unnecessary. Bone age is within normal lim¬ its. If the patient's height in standard deviations is significantly less than that of his parents (e.g., 4 SD below the mean), normal genetic short stature is not the cause and further evaluation is indicated. If the patient's height and a parent's height are further than 2 SD below the mean, both may have abnormal short stat¬ ure and should be studied for a genetically controlled disease such as congenital GH deficiency or skeletal dysplasia (e.g., hypochondroplasia, multiple epiphyseal dysplasia syndrome).

THERAPY AND PROGNOSIS No therapy is available for normal genetic short stature. It is uncertain whether drug therapy for these normal children will ever be indicated, given the difficulty of evaluating the long-term effects of drugs such as GH in healthy youngsters with normal short stature. Most parents are reassured by the knowledge that their nor¬ mally short child is healthy and will grow to adulthood, like themselves, as a normally short and functional individual.

Affected teenage boys should be encouraged to engage in sports that they enjoy and that are safe (e.g., wrestling, baseball, swim¬ ming, tennis, ice skating, sailing) and to avoid sports that pose a potential risk (e.g., tackle football). They should be reassured that normally short girls are delighted to date normally short young men. Those parents, usually fathers, who find the diagnosis difficult to accept should be reassured repeatedly. Therapy for abnormal genetic short stature depends on the underlying disease.

SLOW GROWTH WITH OR WITHOUT SHORT STATURE DEPRIVATION SYNDROME Deprivation, caloric or emotional, slows weight gain and, eventually, linear growth. The type I deprivation syndrome has more of a nutritional component and the type II syndrome has more of a psychosocial component.87,88 Type I deprivation syndrome is seen in babies and young children. For various reasons, these patients have not received enough food or, in some cases, enough attention. The parent or caregiver may be disorganized, inadequately trained, misguided, overwhelmed, or disturbed. This condition also has been de¬ scribed in the second decade of life.89 Type II deprivation syn¬ drome, the childhood variety, affects children older than 3 years and, occasionally, teenagers. Parents or caregivers, who fre¬ quently are alcoholics, abuse these children emotionally. Al¬ though the disorder occurs more often in the lower socioeco¬ nomic classes, the authors have documented the deprivation syndrome in the upper classes. Boys are affected most com-

Ch. 192: Short Stature and Slow Growth in the Infant and Child

1657

monly.90 At the initial evaluation, hypopituitarism, including GH deficiency, often is present. Without intervention, the prognosis for normal growth and development is guarded to dismal for pa¬ tients with both types of deprivation syndrome. PRESENTING MANIFESTATIONS Infants with type I deprivation syndrome have slowing of growth, a scrawny appearance, and a relatively alert demeanor, although some look dejected. Kwashiorkor (see Chap. 126) rarely occurs in the United States. Eight patients, aged 14 to 27 months, were described to have consumed excessive amounts of fruit juice with resultant failure to thrive (abnormally low weight).91 However, these patients recovered after nutritional intervention. Sixteen extensively studied patients with nutritional dwarfing, aged 10 to 16 years, were found to have inappropriate eating habits and subnormal weight gain (accompanied by a propor¬ tionate decline in growth velocity), but no signs of emaciation. Parents reported that these children became satiated early during the course of a meal.89 Children with type II deprivation syndrome, the "psychoso¬ cial dwarfs," generally are withdrawn, grow extremely slowly, and have delayed sexual maturation. Most have an appropriate weight for their height, and some resemble celiac dwarfs, with protuberant abdomens and wasted buttocks. Eventually, the his¬ tory emerges of polydipsia, polyphagia, stealing of food, eating from garbage cans, and drinking from toilet bowls. Developmentally, patients in both groups perform suboptimally. ESTABLISHING THE DIAGNOSIS The gold standard for establishing the diagnosis of depriva¬ tion syndrome is the observation of accelerated weight gain in babies, and accelerated growth as well as weight gain in older children, when patients have new caretakers (e.g., hospitals or foster homes; Fig. 192-16; see chap 20). Feeding should be in¬ creased gradually to the recommended number of calories per kilogram of the ideal body weight for the patient's age. In infants, definitive weight gain occurs in about 2 weeks; in older children, accelerated growth and weight gain can take several months. Laboratory studies are of little help in establishing the diagnosis. The bone age is retarded, particularly in psychosocial dwarfs. Infants whose linear growth rates are slowing (e.g., drop¬ ping from the 50th to the 20th percentile from the ages of 6 to 12 months, respectively) present diagnostic difficulties. They may be perfectly normal and simply experiencing a shift from an intra¬ uterine growth rate influenced by maternal factors to an extrauterine growth rate dictated by their own genetic backgrounds (i.e., mid-parental height). These normal infants establish their permanent normal growth rate (e.g., along the 20th percentile) by the age of 18 to 24 months. THERAPY AND PROGNOSIS When the caretaker is disturbed, a new caretaker must be located. For some parents of malnourished infants, education in feeding is helpful. If a biologic parent is the psychologically dis¬ turbed caretaker, psychotherapy is essential. If the parent refuses psychotherapy or the infant does not improve rapidly, the phys¬ ician must use every means necessary to place the child in a new permanent home. With intervention, the long-term overall prognosis for chil¬ dren with type I deprivation syndrome is generally good. For children with type II deprivation syndrome, the long-term prog¬ nosis for growth and sexual maturation is favorable, and intellec¬ tual ability improves to some extent. However, both intellectual function and emotional development are likely to be perma¬ nently compromised.92

ACQUIRED GROWTH HORMONE DEFICIENCY Acquired abnormalities of the hypothalamic-pituitary area that inhibit GH synthesis or secretion produce a marked slowing

FIGURE 192-16. Young boy who stopped gaining weight and stopped growing after 12 months of age. During a long hospitalization at 33 months of age, he gained weight and grew. Diagnosis: deprivation.

or cessation of growth. Examples of such abnormalities include craniopharyngioma; histiocytosis X; severe trauma to the head; preventive cranial irradiation for acute lymphoblastic leukemia; and therapeutic irradiation with more than 20 to 40 Gy (2000 to 4000 rad) for neoplasms of the brain, face, head, or neck. Besides GH, other hypothalamic-pituitary hormones can be deficient, and vision and personality can become compromised.93

PRESENTING MANIFESTATIONS In addition to the growth problem, patients have a variety of complaints, including pituitary tumor with diabetes insipidus (Fig. 192-17), visual problems or increased intracranial pressure; and histiocytosis X with greasy, scaly scalp lesions, chronically draining ears, and hepatosplenomegaly (Fig. 192-18). Pituitaryhypothalamic hormones besides GH also can be deficient. Pa¬ tients who have received high-dose cranial irradiation are at risk for inappropriately early (precocious) puberty of central nervous system origin, girls more commonly than boys.94,95

CONFIRMING THE DIAGNOSIS As with congenital idiopathic GH deficiency, acquired GH deficiency is documented by serum GH determinations obtained during two stimulation studies performed while the patient is eu¬ thyroid. Eventually, the bone age in acquired GH deficiency is retarded. In some patients with prior cranial irradiation, only a neurosecretory disorder of GH secretion occurs.96

1658

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

FIGURE

192-17. Enlarged sella turcica {arrow) in a 15-year-old boy with a pituitary tumor, who had cessation of growth and sexual infantilism.

THERAPY AND PROGNOSIS The details of optimum therapy have not been determined for these tumors but include excision and irradiation. For histio¬ cytosis X, most pediatric oncologists recommend the use of glu¬ cocorticoids and antimetabolites. Replacement hormonal ther¬ apy must include GH as well as any other hormones that are deficient. For patients with precocious puberty, therapy with a long-acting gonadotropin releasing hormone analogue can be considered. With a few exceptions, the prognosis for survival and growth has improved.9 Final adult heights are known for 30 pa¬

FIGURE 192-18. Chronic scaly, greasy scalp lesion of histiocytosis X.

tients with craniopharyngiomas who were treated with pituitary hGH. Most achieved a final height above the 3rd percentile, but none above the 50th percentile. Because these patients usually receive GH therapy before growth retardation is severe, the prog¬ nosis for achieving a normal adult height is better than that for patients with congenital GH deficiency. Because of the localized invasive nature of some of the tumors, vision can be permanently impaired and the life span shortened. Parents often ask whether therapy with hGH will exacerbate the neoplasia. Two studies suggest that hGH therapy itself does not increase the chance of tumor recurrence.98,99

Ch. 192: Short Stature and Slow Growth in the Infant and Child

ACQUIRED PRIMARY HYPOTHYROIDISM73 Normal levels of thyroid hormone are essential for optimal linear growth during extrauterine life. Hence, an inadequate amount of thyroid hormone results in slowing of growth. Auto¬ immune chronic lymphocytic thyroiditis causes most of the ac¬ quired hypothyroidism seen in children and teenagers. Girls are at greater risk, as are patients with Down syndrome, Turner syn¬ drome, Klinefelter syndrome, or insulin-dependent diabetes mellitus. Occasionally, hypothyroidism is associated with a failure of ectopically placed thyroid tissue (e.g., lingual; see Chap. 46).

PRESENTING MANIFESTATIONS Besides abnormally slow growth, most patients have only minimal complaints, such as decreased physical activity, in¬ creased need for sleep, and mild constipation. They usually per¬ form well in school. Occasionally, pallor and rough, dry skin are marked. In patients with myxedema, the thyroid often cannot be visualized or palpated. Sexual maturation generally is delayed but can be precocious in cases of severe hypothyroidism. Postmenarchal girls have amenorrhea and, rarely, galactorrhea.

ESTABLISHING THE DIAGNOSIS Primary hypothyroidism is associated with a low serum thy¬ roxine concentration and an elevated thyroid-stimulating hor¬ mone level. Delayed bone age, elevated serum prolactin and cre¬ atine phosphokinase levels, anemia (normocytic or macrocytic), and, on occasion, an enlarged sella caused by hyperplasia or ad¬ enomatous transformations of the pituitary thyrotropic cells also can be found. The presence of antithyroid antibodies (thyroglobulin, microsomal, or thyroid peroxidase), usually in low titers, suggests chronic lymphocytic thyroiditis. Compared with adults, children and teenagers with chronic thyroiditis have relatively low antithyroid antibody levels, often less than 1:64. The authors suggest that the laboratory be asked to provide the exact titer. The authors often are asked to rule out hypothyroidism in children with exogenous obesity. Usually, this can be accom¬ plished by physical examination. Patients with exogenous obe¬ sity have normal growth or tall stature, rosy cheeks, and soft, warm skin. These physical findings are incompatible with hypothyroidism.

1659

prefer, L-thyroxine can be administered once a week at a dose of 1.1 mg/m2.100 The dose should be regulated so that patients are clinically euthyroid and have normal serum thyroxine and thyroid-stimulating hormone levels. Because generic prepara¬ tions are not uniform in their thyroid hormone content, brand name preparations should be used.101,102 The prognosis for growth and good health is excellent (Fig. 192-19). With replacement therapy, some children experience a temporary deterioration in school performance, difficulty in in¬ terpersonal relationships (particularly with parents), and loss of scalp hair. Thyroid hormone replacement causes the enlarged ec¬ topic thyroid tissue to disappear, the enlarged pituitary to shrink, and the anemia, precocious puberty, elevated prolactin level, and elevated creatine phosphokinase value to resolve. If the bone age is unduly advanced, the sexual precocity may not resolve. Rarely, pseudotumor cerebri develops, but this abates with a reduction in the dose of thyroxine. During therapy with physiologic doses of L-thyroxine, the authors and others have observed accelera¬ tion in bone maturation without a proportional spurt in growth. Hence, patients may be shorter than expected as adults. For such individuals, the authors suggest using the smallest dose possible to maintain a euthyroid state, both clinically and biochemically. Girls continue to grow after menarche, with a mean velocity of 4.1 cm/y.103

ATYPICAL CROHN DISEASE104 Crohn disease, a chronic inflammatory disease of the bowel of unknown etiology but with a strong genetic component, often interferes with growth and sexual maturation, probably as a result of chronic undernutrition and, secondarily, low serum concentrations of IGF-I.105 Several factors contribute to the nutritional problems, including increased nutrient losses and malabsorption.

PRESENTING MANIFESTATIONS Growth failure can herald Crohn disease. The weight often is more compromised than the height and puberty is delayed but the patient looks well. Perianal fistulas are common. On ques¬ tioning, patients may describe intermittent attacks of abdominal pain and diarrhea.

THERAPY AND PROGNOSIS

CONFIRMING THE DIAGNOSIS

The authors treat patients who have hypothyroidism with lthyroxine, 3.5 ± 0.3 Mg/kg daily (100 /ug/m2/d). For those who

Barium contrast radiographs of the small and large bowels often are characterized by an irregular mucosa or a cobblestone-

FIGURE 192-19. A, Hypothyroid 14-year-old girl with slowing of growth during previous 4 years, scant secondary sexual characteristics, and little physical energy. B, After 6 months of therapy with thyroxine.

i860

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

like pattern, a thickened bowel, and the presence of enteric fis¬ tulas. The segmental distribution of the lesions frequently is diagnostic. Biopsy samples of the rectal mucosa obtained by co¬ lonoscopy show typical granulomas. The erythrocyte sedimenta¬ tion rate usually is elevated, the bone age is retarded, and the hemoglobin and serum albumin levels occasionally are depressed. THERAPY AND PROGNOSIS

Control of the disease and provision of adequate nutrition are the prerequisites for growth, but an optimal method of ac¬ complishing these goals has not been identified. Growth may ac¬ celerate with initial daily glucocorticoid therapy followed by alternate-day therapy in cases of stable disease. Calories have been administered by central or peripheral in¬ travenous hyperalimentation, elemental diets, and specialized formulas.inb When the underlying disease is controlled, good nu¬ trition alone, regardless of the method used to deliver it, stimu¬ lates growth. When disease activity cannot be stabilized and growth cannot be achieved with medical and nutritional support, surgical intervention should be considered. For growth to occur, resection must be performed before late puberty, all actively dis¬ eased bowel must be resected, and a prolonged disease-free post¬ operative period must be achieved. Ongoing nutritional therapy may augment the accelerated growth rate.10? The effects of various treatment plans on growth rate and final adult height require evaluation in large cooperative studies.

CUSHING DISEASE OR SYNDROME Patients with Cushing syndrome secrete excess amounts of cortisol and other adrenocortical hormones, usually continuously but sometimes periodically.108 The underlying disease can be caused by an ACTH-secreting microadenoma of the pituitary (basophilic or mixed basophilic chromophobic, with a resultant bilateral adrenal hyperplasia) or by an adrenal tumor. Rarely, it is caused by a corticotropin releasing hormone (CRH)-secreting tumor.10q The natural history of Cushing disease (adrenal hyper¬ plasia) is not known, but rare cases of spontaneous remission have been reported.110111 Because many of the adrenal tumors are malignant, the mortality rate is high (see Chaps. 73 and 81). After the age of 7 years, the most common underlying problem is an ACTH-producing pituitary adenoma.112,113 PRESENTING MANIFESTATIONS

Although Cushing disease is rare in the young, babies as well as teenagers can be affected. Usually, help is sought for the increasingly abnormal appearance: moon facies, obesity (espe¬ cially of the trunk and face), purplish striae, hypertension, acne, emotional lability, and virilization. A review of growth data in¬ variably reveals a pathologically slow growth rate over the past months or years. The slowing of growth occasionally precedes the abnormal appearance by several months or years (Fie 192-20). CONFIRMING THE DIAGNOSIS

The diagnosis of Cushing disease depends on the demon¬ stration of pathologically elevated cortisol secretion, that is, ele¬ vated urinary free cortisol levels that cannot be suppressed with low doses of dexamethasone (see Chap. 75). The response to the administration of larger doses of dexamethasone helps to localize the lesion. Suppression with high doses of dexamethasone sug¬ gests the presence of adrenocortical hyperplasia caused by an ab¬ normality of the hypothalamic-pituitary area, whereas failure to suppress is strongly suggestive of an adrenocortical tumor. Hy¬ pochloremic hypokalemic metabolic alkalosis can be present and, in those cases caused by pituitary adenomas, late evening serum ACTH levels may be elevated. In a study of a short boy with

FIGURE 192-20. Seventeen-year-old boy with Cushing syndrome caused by bilateral adrenal hyperplasia. Note “moon" facies, buffalo hump, and obesity, especially of the trunk.

periodic Cushing syndrome, the CRH test was found to be help¬ ful. ACTH and cortisol concentrations were undetectable both in the basal state and after stimulation with CRH. As expected, the patient had bilateral micronodular adrenal hyperplasia at surgery. In searching for a pituitary lesion, radiographs of the sella turcica, computed tomography of the pituitary area, magnetic resonance imaging, and, eventually, direct transsphenoidal visu¬ alization of the pituitary are helpful. For demonstrating the pres¬ ence of an adrenal tumor, a radiograph of the abdomen can be useful to look for calcification of certain areas indicative of such a tumor. To reveal the tumor itself, ultrasound, computed tomog¬ raphy, magnetic resonance imaging, and radioactive iodocholesterol uptake can be used (see Chap. 85). In almost 300 patients, when plasma was sampled from the inferior petrosal sinuses with the conjunctive use of CRH, it was possible to distinguish those with Cushing disease from those with ectopic ACTH secretion.114 THERAPY AND PROGNOSIS

Transsphenoidal microsurgery is the treatment of choice for patients with adrenal hyperplasia from a demonstrated pituitary tumor115 (see Chap. 25). Results are excellent when the tumor is visualized and removed at surgery. Many of these patients be¬ come permanently glucocorticoid deficient. The former ap¬ proach, bilateral adrenalectomy, rarely is indicated. Long-term remission has been reported with pituitary irradiation (see Chap. 24). Ketoconazole can facilitate regression of the stigmata of Cushing disease.116 Surgical excision is the treatment of choice for demonstrable adrenal tumors (see Chap. 86). Well-localized adenomas have a good prognosis. However, microscopic examination does not always distinguish benign from malignant lesions. The results of chemotherapy for the malignant tumors are disappointing. After successful therapy, the signs and symptoms of Cush¬ ing syndrome disappear and many children grow in an acceler¬ ated fashion. As a group, they achieve a reasonable adult

Ch. 192: Short Stature and Slow Growth in the Infant and Child height.112 The effects of exogenous corticosteroids on growth are discussed in the next section.

IATROGENIC EFFECTS ON GROWTH STIMULANT MEDICATION Certain neurostimulant drugs, especially methylphenidate but also pemoline and methamphetamine, can inhibit weight gain and growth before puberty but probably not after puberty. Desipramine does not inhibit the linear growth of children.117-120 PRESENTING MANIFESTATIONS Patients with attention deficit disorders who have been treated with neurostimulant drugs can have moderate slowing of growth and weight gain or even weight loss. Generally, these patients have received "high-normal” doses (e.g., > 1 mg/kg/d) of methylphenidate hydrochloride for many months. Anorexia is common and dose-dependent, but abates with continued ther¬ apy. The results of physical examination usually are normal. DIAGNOSIS The diagnosis is clinical and can be confirmed only when linear growth accelerates after cessation of the medication. Dis¬ continuing therapy during summer vacations seems to result in accelerated growth, but catch-up is incomplete. If linear growth does not increase during a drug "holiday," patients should be evaluated for other causes of slow growth. THERAPY AND PROGNOSIS No definitive therapy is available, except for discontinuing drug therapy, decreasing a large dose, or substituting desipra¬ mine. Thus, judicious prescribing of these drugs is important. During withdrawal, some children become temporarily hyperac¬ tive or depressed.

GLUCOCORTICOIDS121 Shortly after pharmacologic doses of glucocorticoids were observed to inhibit somatic growth in immature animals, the same effect was noted in children. The most viable of the pro¬ posed mechanisms for growth delay is inhibition of C-terminal type I procollagen.122 Sexual maturation is delayed, and the prog¬ nosis for normal adult height is guarded. PRESENTING MANIFESTATIONS Often, these patients have slowing of growth after the ad¬ ministration of pharmacologic doses of glucocorticoids (equiva¬ lent to more than 20 mg/m2/d of cortisone acetate, given intra¬ muscularly; or to more than 50 mg/m2/d of hydrocortisone, given orally in divided doses). On physical examination, these patients often resemble patients with Cushing syndrome. DIAGNOSIS, THERAPY, AND PROGNOSIS The diagnosis is clinical and depends on the results of the physical examination and the demonstration of catch-up growth after cessation of therapy or institution of an alternate-day regi¬ men. In some patients, the slowing of growth is related to the underlying disease for which they are receiving therapy (e.g., Crohn disease, juvenile rheumatoid arthritis, severe asthma). Children who receive single doses of glucocorticoids on al¬ ternate days generally do not demonstrate growth delay. Some evidence suggests that these drugs should be given in the morn¬ ing. When glucocorticoid therapy is discontinued, catch-up growth usually is dramatic. For patients who must continue to take drugs containing glu¬ cocorticoids, such as renal transplant recipients, therapy with GH

1661

accelerates linear growth, perhaps by overcoming the glucocorti¬ coid-induced inhibition of C-terminal type I procollagen synthesis.

PSYCHOSOCIAL MANAGEMENT OF SHORT STATURE* As a group, short children have normal intellectual function. Many girls with Turner syndrome have impaired space percep¬ tion that causes difficulties with direchon sense and with geome¬ try. A few patients with GH deficiency caused by tumors or by cranial irradiation experience varying degrees of intellectual im¬ pairment, and many have diminished ambition. Short children and short adults can have many problems with psychological adjustment, and their medical therapy is only one dimension of the care necessary to meet the multifaceted and variable needs of this population.123-130 In their interactions with short children, adults tend to infantilize, to overprotect, and to expect less than might be appro¬ priate from other children of the same age. Hence, some short children behave in a manner more appropriate for "height age" than for chronologic age. Short persons tend to be at a physical disadvantage in bodycontact sports. If pubertal development is delayed or absent, physical strength is less than expected for age. In their interac¬ tions with peers, especially those of the same sex, short children may be socialized according to height age. Many patients with¬ draw into total isolation from their peers, with or without in¬ creased interaction with adults or preferential interaction with younger children. A few boys avoid male peers and associate nonromantically with girls. Accompanying these withdrawal syndromes are a lack of assertiveness and intense feelings of in¬ feriority. Some patients with short stature establish "joking rela¬ tionships" with peers and become class clowns or mascots. A few become overly assertive. Although the "cuteness" of patients with short stature can lead to a degree of popularity during childhood, peer avoidance and rejection commonly occur during adolescence. The short stature itself, and the often associated sexual infantilism, seri¬ ously compromise participation in heterosexual dating and result in further alienation from the peer group. Age-appropriate de¬ velopment of general social, heterosexual, and educationalvocational skills is at risk; patients may drop out of school or, later, avoid employment. The final outcome depends largely on parental attitudes and behavior. It is dismal when parents reject these children and remarkably good when they are supportive. The overall goals for short children are to become financially self-supportive, to pursue a career commensurate with their in¬ tellectual capacity, to function well socially, and to attain a rea¬ sonable degree of contentment. Physicians should interact with these patients in an ageappropriate manner. Because short patients are highly sensitive to seemingly innocuous jokes and remarks, teasing should be avoided. For adolescents and adults with severe short stature who have difficulty getting on the examining table, a stool or other assistance should be offered but physicians should never lift them, except by mutual agreement. On occasion, a short staff member provides a desirable role model. In terms of the physical environment, children with marked short stature should develop age-appropriate autonomy both in and out of the home. In the home, sturdy boxes or stepladders should be placed in various locations; clothing rods and light switches should be lowered. For older children, smaller bicycles and, subsequently, specially equipped automobiles allow inde¬ pendence in transportation. * Portions of this section have been adapted from Meyer-Bahlberg HL. Psychosocial management of short stature. In: Schaffer D, Ehrhardt AA, Greenhill LL, eds. The clinical guide to child psychiatry. New York: Free Press, 1985:110-144.

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PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

Schools should provide chairs that allow the children's feet to rest on the floor, and should furnish assistance on school buses, as well as discrete, private explanations to classmates. Teachers may need encouragement in treating short children in a manner appropriate for their chronologic age. Before children with severe short stature are enrolled, the authors recommend that parents visit the school, explain the problem, and request assistance. Parents should attempt to provide age-appropriate clothing by shopping at stores that cater to short persons or by obtaining tailor-made clothes. Usually, short teenagers try to groom them¬ selves in a stylish manner and should be supported in their efforts. In dealing with other adults, short children should be in¬ structed to be direct and politely assertive, using such statements as "I have a growth problem and would like to look at clothes appropriate for my age.” Parents can assist younger short chil¬ dren by explaining to family, neighbors, and friends that the children have growth problems and need a few special considerations. Because relationships with peers can be difficult for some short children, the authors encourage them to pursue interests and develop skills that are not size-dependent (e.g., handicrafts, playing a musical instrument, computers, fishing, debating, ski^n8' gymnastics, and gainful employment) and to pursue these activities with other people, either peers or adults. Attempts to compete in sports that can be dangerous to the undersized (e.g., tackle football) are discouraged. If patients are annoyed by re¬ peated teasing, they should be encouraged to make direct com¬ ments, such as "I have a medical problem and your teasing makes me feel bad.” If teasing persists, they can tease back with a state¬ ment such as Your breath smells.” Mastering karate may help children who are experiencing physical harassment. Adolescent patients should be encouraged to find paying, part-time jobs as a useful preparation for permanent employ¬ ment and a means of increasing self-esteem and fostering contact with peers and adults. They may need support in dealing with the occasional employer who is prejudiced against short persons. Two national organizations have been formed that provide sensible support for short persons and their families: Little People of America, (2720 Arlington Drive, Alexandria, Virginia 22306) especially for adult dwarfs; and the Human Growth Foundation (7777 Leesburg Pike #202-S, Falls Church, Virginia 22043), for younger patients and their parents.

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42. Lee PA. Concomitant growth hormone and gonadotropin releasing hor¬ mone analogue therapy. Pediatr Res 1992;31:79A. 43 Hopwood NJ, Hintz RL, Gertner JM, et al. Growth response of children with non-growth-hormone deficiency and marked short stature during three years of growth hormone therapy. J Pediatr 1993; 123:215. 44. Allen DB, Frasier SD, Foley TP Jr, Pescowitz OH. Growth hormone for children with Down syndrome. (Editorial) J Pediatr 1993; 123:742. 45. Wilson DM, Lee PD, Morris AH, et al. Growth hormone therapy in hypophosphatemic rickets. Am J Dis Child 1991; 145:1165. 46. Rotenstein D, Reigel DH, Flom LL. Growth hormone accelerates growth of short children with neural tube defects. J Pediatr 1989; 115:417. 47. Angulo M, Castro-Magana C, Uy J. Pituitary evaluation and growth hor¬ mone treatment in Prader-Willi syndrome. J Pediatr Endocrinol 1991;4:167. 48. Laron Z, Pertzeland A, Mannheimer S. Genetic pituitary dwarfism with

Ch. 192: Short Stature and Slow Growth in the Infant and Child high serum concentrations of growth hormone—a new inborn error of metabolism? J Med Sci 1966;2:152. 49. Rosenfeld RG, Rosenbloom Al, Guevara-Aguirre J. Growth hormone (GH) insensitivity due to primary GH receptor deficiency. Endocr Rev 1994; 15:369. 50. Clemmons DR, Underwood LE. Uses of human insulin-like growth factorI in clinical conditions. J Clin Endocrinol Metab 1994; 79:4. 51. Ross JL, Long LM, Feuillan P, et al. Normal bone density of the wrist and spine and increased wrist fractures in girls with Turner's syndrome. ] Clin Endocri¬ nol Metab 1991; 73:355. 52. Massa GG, Vanderschuerer-Lodeweyekx M. Age and height at diagnosis in Turner syndrome: Turner influence of parental heights. Pediatrics 1991; 88:1148. 53. Goldstein DE, Kelly TE, Johanson AJ, Blizzard RM. Gonadal dysgenesis with 45, XO/46, XX mosaicism demonstrated only in a streak gonad. J Pediatr 1977;90:604. 54. Medelej R, Lobaccaro PB, Belon C, Leheup B. 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85. Collins E, Turner G. The Noonan syndrome. J Pediatr 1973; 83:941. 86. Jones KL, Smith DW. The Williams elfin facies syndrome: a new perspec¬ tive. J Pediatr 1975;86:718. 87. Powell GF, Brasel JA, Blizzard RM. Emotional deprivation and growth retardation simulating idiopathic hypopituitarism. I. Clinical evaluation of the syn¬ drome. N Engl J Med 1967a;276:1271. 88. Powell GF, Brasel JA, Raiti S, et al. Emotional deprivation and growth retardation simulating idiopathic hypopituitarism. II. Endocrine evaluation of the syndrome. N Engl J Med 1967b;276:1279. 89. Sandberg DE, Smith MM, Fornari V, et al. Nutritional dwarfing: is it a consequence of disturbed psychosocial functioning? Pediatrics 1991;88:926. 90. Rudolf MCJ, Hochberg Z. Annotation. Are boys more vulnerable to psy¬ chosocial growth retardation? Dev Med Child Neurol 1990;32:1022. 91. Smith MM, Lifshitz F. Excess fruit juice consumption as a contributing factor in nonorganic failure to thrive. Pediatrics 1994; 93:438. 92. Money J, Annecillo C, Kelly JF. Growth of intelligence: failure and catch¬ up associated respectively with abuse and rescue in the syndrome of abuse dwarfism. Psychoneuroendocrinology 1983; 8:309. 93. Kaplan SA. Growth and growth hormone: disorders of the anterior pitu¬ itary. In: Kaplan SA, ed. Clinical pediatric and adolescent endocrinology. Philadel¬ phia: WB Saunders, 1982:20. 94. Burstein S. Growth disorders after cranial irradiation in childhood. (Edi¬ torial) J Clin Endocrinol Metab 1994; 78:1280. 95. Oglivy-Stuart AL, Clayton PE, Shalet SM. Cranial irradiation and early puberty. J Clin Endocrinol Metab 1994,-78:1282. 96. Blatt J, Bercu BB, Gillin JC, et al. Reduced pulsatile growth hormone secre¬ tion in children after therapy for acute lymphoblastic leukemia. J Pediatr 1984; 104: 182. 97. Winter RJ, Green OC. Irradiation-induced growth hormone deficiency: blunted growth response and accelerated skeletal maturation to growth hormone therapy. J Pediatr 1985; 106:609. 98. 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Growth failure and inflammatory bowel disease. Approach to treatment of a complicated adoles¬ cent problem. Pediatrics 1983;72:481. 105. Kirschner BS. Growth and development in chronic inflammatory bowel disease. Acta Paediatr Scand Suppl 1990; 366:98. 106. Polk DB, Hattner JAT, Kerner JA Jr. Improved growth and disease activ¬ ity after intermittent administration of a defined formula diet in children with Crohn's disease. J Parenter Enter Nutr 1992; 16:499. 107. Lipson AB, Savage MO, Davies PSW, et al. Acceleration of linear growth following intestinal resection for Crohn's disease. Eur J Pediatr 1990; 149:687. 108. Muguruza MTG, Chrousos GP. Periodic Cushing syndrome in a short boy: usefulness of the ovine corticotropin releasing hormone test. J Pediatr 1989; 115:270. 109. Preeyasombat C, Sikikulchayanonta V, Mahaclok Elert-Wattana P, et al. Cushing's syndrome caused by Ewing's sarcoma secreting corticotropin releasing factor-like peptide. Am J Dis Child 1992; 146:1103. 110. 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PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

122. Allen DB, Goldberg BD. Stimulation of collagen synthesis and linear growth by growth hormone in glucocorticoid treated children. Pediatrics 1992; 89: 416. 123. Stabler B, Underwood LE, eds. Growth, stature and adaptation. Chapel Hill: University of North Carolina Press, 1994. 124. Stabler B. Growth hormone insufficiency during childhood has implica¬ tions for later life. Acta Paediatr Scand Suppl 1991; 377:9. 125. Stabler B, Siegel PT, Clopper RR. Growth hormone deficiency in children has psychological and educational co-morbidity. Clin Pediatr (Phila) 1991; 130:3. 126. Rieser PA. Educational, psychologic and social aspects of short stature. Journal of Pediatric Health Care 1992; 6:325. 127. Siegel PT, Clopper R, Stabler B. Psychological impact of significantly short stature. Acta Paediatr Scand Suppl 1991; 377:14. 128. Tynan WD. Disorder of growth. Psychologic aspects of pediatric endo¬ crine disorders. In: Hung W, ed. Clinical pediatric endocrinology. St Louis: MosbyYear Book, 1992. 129. Stabler B, Clopper RR, Siegel PT, et al. The national cooperative growth study. Academic achievement and psychological adjustment in short children. J Dev Behav Pediatr 1994; 15:1. 130. Wood D, Halfon N, Scariata D, et al. Impact of family relocation on children's growth, development, school function, and behavior. In: Impact of relo¬ cation on children. JAMA 1993; 270:1334.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

193

AGING AND ENDOCRINOLOGY DAVID A. GRUENEWALD AND ALVIN M. MATSUMOTO The number of elderly people is growing faster than the pop¬ ulation at large. In 1990, those older than 65 years represented 12.6% of the U.S. population, and by 2030 they are projected to represent 22%.' Because endocrine diseases such as osteoporosis, type II diabetes mellitus, and hypothyroidism are common in the elderly, endocrinologists are expected to see an increasing pro¬ portion of older patients in their practices. With aging, changes occur in many parameters of endocrine and metabolic function, such as decreased growth hormone (GH) and gonadal steroid levels, increased cholesterol levels, and adi¬ posity. Some of these changes clearly predispose to morbidity and mortality in later life (such as the effects of ovarian failure on bone mass and fracture risk), whereas the effects of other agerelated alterations (such as declining GH and testosterone levels) are of uncertain significance. Furthermore, the clinical presenta¬ tion, diagnosis, treatment, and prognosis of certain endocrine disorders may be altered with aging, greatly increasing the clini¬ cal challenges of evaluation and management. In turn, endocrine diseases in geriatric patients often have profound effects on func¬ tional status and the quality of life; often, these issues are more important to patients than the underlying diseases per se. Fre¬ quently, the goal of medical management in the elderly patient is not necessarily to eliminate the disease, but rather to help the patient to achieve the highest possible level of functioning and quality of life.

PRINCIPLES OF GERIATRIC ENDOCRINOLOGY Several principles of geriatric endocrinology illustrate the greater complexity and challenge of evaluating frail older pa¬ tients with endocrine disease. These include the atypical presen¬ tations of illness; the presence of multiple coexisting medical problems; the large number of symptoms, signs, and abnormal laboratory findings often present in individual elderly patients; underreporting of symptoms; and problems in the cognitive, psy¬ chiatric, social, economic, and functional domains. Failure to ap¬

preciate and to appropriately assess older patients with these is¬ sues in mind may result in missed or incorrect diagnoses, inappropriate treatments, and poor functional outcomes. Impaired Homeostasis. Aging is characterized by a decline in the functional reserve of major body organs, leading to a di¬ minished ability to restore equilibrium after environmental stresses. This age-related impairment of homeostatic regulation is evident in many endocrine functions, but may become clinically evident only during acute or significant long-term stress. For ex¬ ample, fasting blood glucose levels exhibit little change with nor¬ mal aging, but after challenge with a glucose load, glucose levels increase much more in the healthy elderly compared with young adults. With aging, the function of endocrine systems may be maintained through homeostatic mechanisms or changes in hor¬ mone metabolism, or both, that offset the loss of function. For example, to compensate for a reduction in the testicular secretion of testosterone, pituitary luteinizing hormone (LH) secretion and serum LH levels are increased in many elderly men, and testos¬ terone metabolism is decreased. However, in some cases, such changes are insufficient to maintain normal function, even under basal conditions. This is illustrated by aldosterone production, which declines disproportionately to its clearance rate with aging/ leading to age-related decreases in basal plasma aldoste¬ rone levels. Nonspecific and Atypical Symptomatology. Endocrinopathies in the elderly commonly present with nonspecific, muted, or atypical symptoms and signs. For example, hypothyroidism and hyperthyroidism may present with similar nonspecific symptoms in the elderly, for example, weight loss, fatigue, weak¬ ness, constipation, and depression. Also, the presentation of en¬ docrine disease in geriatric patients may be atypical compared with that in younger patients. Examples include the apathy, de¬ pression, and psychomotor retardation of apathetic hyperthy¬ roidism, and the hyperosmolarity and marked hyperglycemia without ketoacidosis of the hyperosmolar nonketotic state. In other patients, regardless of the source of the illness, its manifes¬ tations may occur in the most compromised body system. Thus, in an older patient with underlying gait and balance abnormali¬ ties, falling may be the primary symptom of diseases as diverse as pneumonia, myocardial infarction, uncontrolled diabetes mel¬ litus, or hypothyroidism. In addition to falls, common presenta¬ tions of illness include other geriatric syndromes that result in disability, such as delirium, urinary incontinence, and dementia.2 Endocrine disorders may produce or be associated with any or all of these syndromes; thus, it is important that endocrinologists have a basic understanding of these disorders. Several excellent reviews of these geriatric syndromes are available.1-3 Concomitant Medical Disorders. In addition to atypical or nonspecific presentations of disease, the presence of multiple medical problems and medications may render the evaluation of older patients more difficult. For example, decreased serum thy¬ roxine (T4) and triiodothyronine (T3) levels may occur in elderly patients who are systemically ill but are euthyroid (euthyroid sick syndromes), giving a misleading impression of an endocrine ab¬ normality. Furthermore, with aging it is increasingly common for illnesses such as hypothyroidism to present without any symp¬ toms. The presence of disease may be appreciated only on routine laboratory screening, as in the case of asymptomatic hypercalce¬ mia secondary to hyperparathyroidism. Laboratory Values in the Elderly. The evaluation of the older patient is further complicated by the fact that normal ranges for endocrine laboratory tests often are developed in healthy young subjects, and may not reflect normal values in healthy elderly people. Moreover, normative data for older populations are often confounded by the inclusion of subjects with ageassociated diseases. Finally, most studies of aging and endocrine function in humans are cross-sectional rather than longitudinal, and, therefore, may not accurately predict age-related changes within a given individual. Indeed, variability between individuals is a hallmark of aging.

Ch. 193: Aging and Endocrinology Assessment and Therapy. Based on the forgoing considera¬ tions, the onset of functional decline may be an important—and sometimes the only—clue to the development of an acute illness or exacerbation of a chronic disease in geriatric patients. Accord¬ ingly, a structured functional assessment should be a part of the evaluation. Functional assessment can detect impairments in physical function, cognition, emotional status, sensory capabili¬ ties, and activities of daily living that are not detected by standard clinical examinations.4 These impairments are often much more important to patients than the underlying diseases that give rise to them. Such an assessment can also help to determine the re¬ sponse to treatment and to predict the patient's ultimate degree of disability.4 Patients with evidence of functional impairment on screening examination5 may benefit from more comprehensive functional assessment by an interdisciplinary care team. How¬ ever, because comprehensive evaluation is time-consuming and expensive, it should be targeted to the most appropriate patients: frail or ill elderly people with a real or anticipated functional de¬ cline, including patients on the verge of requiring institutional¬ ization, those with inadequate primary medical care, and those with poor economic and social support systems.6 Treatment decisions involving geriatric patients with endo¬ crine disease must consider age-associated factors, such as alter¬ ations in clearance rate and target organ effects, coexisting medi¬ cal illnesses, and other medications taken by the patient. Older patients consume a disproportionate share of medications com¬ pared with the population at large. Moreover, drug toxicities are more frequent and severe in elderly compared with young pa¬ tients receiving the same drug regimen.2 Dysfunction in multiple organ systems, together with cognitive and visual impairment, further predispose older patients to adverse drug effects. Thus, older people are at high risk for the development of medication side effects, as well as drug interactions secondary to polyphar¬ macy. To minimize these risks, dosage levels for hormone re¬ placement and medications must be adjusted for changes in the clearance rate, and patients should receive the lowest dosage of medication needed to achieve the therapeutic effect. New medi¬ cations should be initiated using low doses and increased grad¬ ually as needed. Finally, the medication regimen should be re¬ viewed periodically, discontinuing medications that are no longer needed.

HYPOTHALAMUS AND PITUITARY HYPOTHALAMIC REGULATION Studies directly assessing the effects of aging on parameters of hypothalamic neuroendocrine function in humans have not been performed. However, some of these effects can be inferred from age-related alterations in circadian and ultradian rhythms (e.g., pulsatile release) of pituitary hormones, and by determining pituitary hormonal responsiveness to administration of hypotha¬ lamic releasing hormones, or agents that either block end-organ feedback (e.g., clomiphene and metyrapone) or that stimulate hypothalamic-pituitary hormonal secretion (e.g., stimulation of antidiuretic hormone [ADH] secretion by hypertonic saline ad¬ ministration or stimulation of GH secretion by insulin-induced hypoglycemia). For example, age-related blunting of the circa¬ dian rhythm of LH pulse frequency has been observed in healthy elderly men, suggesting altered regulation of the gonadotropin¬ releasing hormone (GnRH) pulse generator with aging.7 Further¬ more, LH pulse frequency is relatively decreased despite reduced testosterone levels in some healthy elderly patients, implying de¬ creased GnRH pulse frequency in these older men.8 However, adrenocorticotropic hormone (ACTH) pulse frequency, cortisol levels, and ACTH response to corticotropin-releasing hormone (CRH) stimulation are the same in healthy elderly as in young men, suggesting that in contrast to the reproductive axis, hypo¬

1665

thalamic regulation of pituitary-adrenocortical function may be unimpaired by aging.9 Hypothalamic-pituitary feedback sensitivity to some endorgan hormones is altered with aging. For example, most studies have found increased feedback sensitivity to testosterone with aging,10 whereas most evidence suggests that glucocorticoid feedback sensitivity is decreased with aging.91112

POSTERIOR PITUITARY ANTIDIURETIC HORMONE There is considerable evidence for a state of relative ADH excess in healthy elderly humans. Most studies13 have found in¬ creased basal ADH levels with aging, and release of ADH after an osmotic stimulus (e.g., hypertonic saline infusion) is greater in the elderly than in young subjects. The pharmacologic inhibition of pituitary ADH secretion (e.g., with ethanol infusion) is im¬ paired in elderly compared with young adult subjects.14 In addi¬ tion, free water clearance by the kidney decreases with aging in proportion to declining glomerular filtration rate.15 This agerelated reduction in free water clearance is primarily responsible for the common occurrence of hyponatremia in older patients,15 although relative ADH excess and the increased prevalence of conditions such as congestive heart failure, hypothyroidism, and the use of sulfonylurea or diuretic medication may also predis¬ pose the elderly to hyponatremia. Also, the elderly are at increased risk for dehydration and hypernatremia. Although ADH secretory capacity is unimpaired with aging, the renal response to ADH is blunted, resulting in a diminution of maximal urinary concentrating capacity. Other factors which predispose the elderly to water depletion include the impairment in thirst responses to dehydration (observed even in healthy older people), and the common occurrence of states that limit access to free water (e.g., altered mental status and surgery).16

ANTERIOR PITUITARY GROWTH HORMONE The GH axis undergoes significant alterations in many healthy elderly people. Nocturnal pulsatile GH secretion declines progressively after 40 years of age, such that by 70 to 80 years of age, about half of all individuals have no significant GH secretion at night. Plasma insulin-like growth factor I levels show a corre¬ sponding decline that is reversible by exogenous GH supplemen¬ tation.17 The GH response to various secretagogues (e.g., insulininduced hypoglycemia, arginine, levodopa) and to GH releasing hormone is normal or reduced with aging. Nevertheless, a nor¬ mal GH response may be useful in verifying intact pituitary (somatotrope) function. Many age-associated changes in body composition, such as increased adiposity and decreased muscle and bone mass, are similar to those associated with GH deficiency in younger pa¬ tients.1718 This observation has led to the hypothesis that de¬ creased GH secretion with aging contributes to alterations in body composition in older adults. GH administration over a 12to 18-month period has been reported to increase lean body mass in older men,19 and to a lesser degree in women.20 Biochemical indices of bone turnover increase with GH treatment; the bone mass appears to remain stable or to increase slightly.20 The doserelated side effects of GH treatment include carpal tunnel syn¬ drome, fluid retention, and, in men, possibly gynecomastia.18-20 These preliminary findings suggest a potential role for GH ther¬ apy in the treatment of age-related disorders of body composi¬ tion, but further studies are needed to determine the long-term benefits and risks of GH treatment in the elderly. PROLACTIN No clinically significant changes occur in basal prolactin lev¬ els. However, several medications commonly used in the elderly

1666

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

inhibit dopamine secretion and sometimes cause elevated prolac¬ tin levels, including phenothiazines and cimetidine. ADRENOCORTICOTROPIC HORMONE No significant age-related changes occur in basal ACTH and cortisol levels, or in the ACTH and cortisol responses to secretagogues (e.g., insulin-induced hypoglycemia, metyrapone, and CRH). The cortisol response to insulin-induced hypoglycemia is a reliable method for determining the presence of primary or sec¬ ondary adrenal insufficiency, but is not usually used in frail older patients because of the significant risk of severe hypoglycemia or myocardial infarction. The standard metyrapone test often is not well-tolerated by older patients, who commonly develop dizzi¬ ness, nausea, and vomiting after receiving the drug; intravenous infusions of metyrapone have been proposed as a safer and better-tolerated method for elderly patients.21 The ACTH stimu¬ lation test is usually used to confirm the presence of adrenal in¬ sufficiency, and expected responses do not change with normal aging. THYROID-STIMULATING HORMONE Thyroid-stimulating hormone (TSH) levels are commonly suppressed in the elderly (as in younger patients) by factors such as glucocorticoid use and fasting associated with severe illness. Conversely, 3% of elderly men and 7% of elderly women have TSH levels greater than 10 ;uU/mL, reflecting an increased prev¬ alence of subclinical primary hypothyroidism in the elderly.22 The TSH response to exogenous thyrotropin-releasing hormone (TRH) is diminished, or even absent, in healthy elderly people, particularly in men. Therefore, together with the widespread availability of supersensitive TSH assays, the TRH stimulation test is generally not useful in the assessment of older subjects suspected of having hyperthyroidism, although a normal TSH response to TRH excludes hyperthyroidism. GONADOTROPINS In postmenopausal women, follicle-stimulating hormone (FSH) levels are increased to a greater extent than LH levels. LH and FSH levels remain fairly constant with aging after the meno¬ pause, although systemic illnesses may result in a decrease in gonadotropin levels. Postmenopausal women exhibit an exag¬ gerated gonadotropin response to GnRH because of a loss of neg¬ ative feedback from ovarian hormones.23 Aging men exhibit in¬ creased basal LH and FSH levels compared with younger men, but gonadotropin levels often remain within the normal range. Testosterone levels are decreased in many healthy older men

TABLE 193-1 Alterations in Thyroid Physiology With Aging T4 production j T4 clearance

l

T4 to T3 conversion | T3 clearance j Serum free T4 «-»• Serum total T4 40 years) fasting serum glucose less than 250 mg/dL, dura¬ tion of diabetes less than 5 years, normal or excessive body weight, and previous insulin therapy of 40 U a day or less.104 Underweight older diabetics often do not respond to oral agents because they are relatively insulin deficient. However, many el-

Ch. 193: Aging and Endocrinology

1677

derly patients are sensitive to the hypoglycemic effects of these

pear to be a marker of disease in patients who are already ill, or

medications. Therefore, treatment should begin with low doses (e.g., glipizide 2.5-5.0 mg or glyburide 1.25-2.5 mg each morn¬

may be a harbinger of future disease onset.113114 The management of hyperlipidemia is discussed in detail in Chapter 158. Clinical trials in middle-aged adults have shown

ing), with small incremental increases every 1 to 2 weeks if needed. The elderly are at higher risk than younger patients for pro¬ longed hypoglycemia caused by oral agents.'07 Chlorpropamide is not recommended for use in the elderly because of its long halflife, which may increase the risk of prolonged hypoglycemia. In addition, chlorpropamide also may cause hyponatremia because of inappropriate ADH secretion. Second-generation sulfonylureas (glipizide and glyburide) are preferable because they are nonionically bound to albumin in the circulation. As a result, these agents are not displaced from albumin by other anionic drugs, such as warfarin and salicylates, and drug interactions are less likely to occur. Either of these agents is acceptable for use in most older type II diabetics; the reported incidence of hypoglyce¬ mia is similar in patients taking glyburide compared with glipi¬ zide.108 In general, oral hypoglycemic agents should not be pre¬ scribed for patients with severe renal or hepatic failure, which may lead to drug accumulation and toxicity. Oral agents are the treatment of choice in most elderly pa¬ tients who require hypoglycemic medication. Sulfonylureas are particularly useful in obese or normal-weight elderly patients with visual problems, arthritis, or memory deficits, in whom in¬ sulin administration may be problematic. However, insulin is needed in older insulinopenic patients and in patients with type II diabetes whose blood glucose cannot be adequately controlled with diet modifications, exercise, and oral hypoglycemic agents. In these patients, it is best to begin with a low insulin dose and to increase slowly as needed, while ensuring that the patient is never hypoglycemic. As with younger patients receiving insulin, prerequisites for safe insulin therapy include accurate home blood glucose monitoring and record-keeping, and a stable pat¬ tern of food intake and activity throughout the day. In older pa¬ tients who are unable to adjust their food intake regimen, the insulin regimen may have to be adjusted instead. Patients with visual or manual dexterity problems may require devices such as syringe magnifiers or dose gauges to help draw up the correct amount of insulin, or premeasured insulin syringes. The insulin regimen should be kept as simple as possible to reduce medication errors and to improve compliance. Most el¬ derly patients requiring insulin can be adequately managed with a single daily dose of intermediate-acting insulin in the morning. The “dawn phenomenon" is markedly reduced or absent in nor¬ mal elderly people,109 so it is generally inappropriate in elderly

that the lowering of elevated cholesterol levels reduces morbidity and mortality from coronary heart disease (CHD), particularly in those with established atherosclerotic disease.115 However, there have been no trials in an exclusively elderly population to deter¬ mine whether reducing cholesterol levels will reduce rates of CHD in these patients, and published treatment guidelines are based on data from younger populations.116 Most geriatricians do not aggressively treat hypercholesterolemia in older patients because of concerns about efficacy, cost, side effects, and the pos¬ sibility of minimal benefit in patients with limited longevity.110 However, in selected older patients, the active management of hypercholesterolemia may be beneficial in view of the corre¬ lations between total, LDL, and HDL cholesterol levels and CHD risk in the elderly; the increased prevalence of both hypercholes¬ terolemia and CHD in elderly compared with young adults; and the evidence from studies in younger adults that CHD rates can be reduced and coronary artery plaque regression can be achieved with lipid-lowering therapy.116 17 Any decision to treat elderly patients with hypercholesterolemia should carefully weigh individual factors, including overall health, patient moti¬ vation, the impact of atherosclerotic disease on the quality of life, and the potential risks and benefits of therapy. In general, the older the patient, the less the anticipated benefit from treatment of hypercholesterolemia. Moreover, many older people with hy¬ percholesterolemia have other chronic illnesses such as conges¬ tive heart failure, stroke, chronic renal failure, chronic lung dis¬ ease, and malignancies; these patients are unlikely to derive much benefit from lipid-lowering therapy. However, otherwise healthy patients with established atherosclerotic disease and a good life expectancy may be ideal candidates for treatment.115 The highest treatment priority in all hypercholesterolemic elderly patients should be to modify other CHD risk factors (hy¬ pertension, smoking, diabetes mellitus, and associated obe¬ sity).116 According to the guidelines of the National Cholesterol Education Program Expert Panel,115 the approach to the initiation of treatment and the goals of treatment are similar in elderly and younger adults, and are based on both LDL cholesterol levels and CHD risk status. As in young adults, the older patients with one or more risk factors besides age (smoking, family history of CHD, diabetes, hypertension, HDL < 35 mg/dL) who are good candi¬ dates for cholesterol-lowering therapy should receive dietary in¬ tervention for LDL levels of 130 mg/dL or greater, and drug

Chaps. 138 and 139).

treatment for LDL levels of 160 mg/dL or greater. However, the presence of CHD lowers these treatment initiation levels to 100 mg/dL or higher, and 130 mg/dL or higher, respectively.115 Al¬

LIPIDS

though published treatment guidelines have suggested a goal of less than 130 mg/dL for LDL levels in older patients with CHD risk factors and 100 mg/dL or less for those with established

diabetics to give a single dose in the evening, which might induce prolonged and unrecognized early morning hypoglycemia (see

Average total serum cholesterol levels increase during early

CHD,115 it may not be possible to lower LDL levels to less than 130 mg/dL in many older persons without incurring malnutri¬

adulthood but level off beyond approximately 50 years of age in men and 60 years of age in women, while the body weight

tion or unacceptable adverse drug effects. All of the cholesterol-lowering drugs have the potential for

reaches a plateau.' In senescence, cholesterol and triglyceride lev¬ els have been found to decline together with body weight, al¬

significant toxicity in older patients, and should be used in the lowest effective dose. Bile salt resins may cause constipation and bloating, and can interfere with the absorption of many medica¬ tions including warfarin, digoxin, L-thyroxine, and antibiotics.

though all of these may remain stable in ambulatory healthy elders.110 Both HDL and LDL cholesterol levels have been re¬ ported to decline with time in healthy older men and women.111 As with body weight, extremes of cholesterol levels are associ¬ ated with an increased mortality risk, whereas the lowest mortal¬ ity risk is observed in those with intermediate cholesterol lev¬

Nicotinic acid has a high incidence of side effects in older pa¬ tients, including flushing of the skin, worsening of diabetes mel¬ litus, elevation of liver function tests, and dry mouth and eyes.

els.112 The association of hypocholesterolemia with an increased likelihood of mortality appears to be confined to elderly people with hypocholesterolemia of relatively recent onset, particularly among hospitalized and institutionalized patients. In contrast, long-standing or lifelong hypocholesterolemia confers a lower

Gastrointestinal side effects and flushing can be minimized by initiating the drug at low dosages, and giving it only with meals. In general, the 3-hydroxy-3-methylglutaryl coenzyme A reduc¬ tase inhibitors appear to be better tolerated by older patients than the other cholesterol-lowering agents. However, compared with other cholesterol-lowering drugs, there is relatively less experi¬

risk of cardiovascular disease.110 Declining cholesterol levels ap¬

ence with these agents in older patients, so they should be used

1678

PART XIII: ENDOCRINE AND METABOLIC DYSFUNCTION IN GROWING CHILDREN AND IN THE AGED

with caution. The side effects are dose related and include gas¬ trointestinal upset, elevation of liver function test results, and a severe myopathy syndrome that more often occurs with the con¬ comitant use of other lipid-lowering agents (gemfibrozil and nic¬ otinic acid) or some other drugs (e.g., erythromycin and cyclosporine).

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51. Lufkin EG, Wahner HW, O'Fallon WM, et al. Treatment of postmeno¬ pausal osteoporosis with transdermal estrogen administration. Ann Intern Med 1992; 117:1.

20. Marcus R, Holloway L, Butterfield G. Clinical uses of growth hormone in older people. J Reprod Fert 1993;46(Suppl):115. 21. Tsagarakis S, Grossman A. The hypothalamic-pituitary-adrenal axis in senescence. In: Morley JE, Korenman SG, ed. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:70. 22. Kunitake JM, Pekary AE, Hershman JM. Aging and the hypothalamicpituitary-thyroid axis. In: Morley JE, Korenman SG, eds. Endocrinology and metab¬ olism in the elderly. Boston: Blackwell Scientific Publications, 1992:92. 23. Marshburn PB, Carr BR. The menopause and hormone replacement ther¬ apy. In: Hazzard WR, Bierman EL, Blass JP, et al, eds. Principles of geriatric medi¬ cine and gerontology, ed 3. New York: McGraw-Hill, 1994:867. 24. Tenover JS. Male hormonal changes with aging. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:243. 25. Mokshagundam S, Barzel US. Thyroid disease in the elderly. J Am Geriatr Soc 1993; 41:1361. 26. Davis PJ, Davis FB. Endocrine diseases. In: Calkins E, Ford AB, Katz PR, eds. Practice of geriatrics, ed 2. Philadelphia: WB Saunders, 1992:483. 27. Mooradian AD, Morley JE, Korenman SG. Endocrinology in aging. Disease-A-Month 1988;34:398. 28. Bagchi N, Brown TR, Parish RF. Thyroid dysfunction in adults over age 55 years: a study in an urban U.S. community. Arch Intern Med 1990; 150:785. 29. Sawin CT, Geller A, Kaplan MM, et al. Low serum thyrotropin in older persons without hyperthyroidism. Arch Intern Med 1991; 151:165. 30. Sawin CT, Bigus ST, Land S, Bacharach P. The aging thyroid: relationship between elevated serum thyrotropin levels to thyroid antibodies in elderly patients Am J Med 1985;79:591. 31. Griffin JE. Review: hypothyroidism in the elderly. Am J Med Sci 1990; 299334. 32. Gregerman RI, Katz MS. Thyroid diseases. In: Hazzard WR, Bierman EL,

42. Kochersberger G, Bales C, Lobaugh B, Lyles KW. Calcium supplementa¬ tion lowers serum parathyroid hormone levels in elderly subjects. J Gerontol Med Sci 1990;45:M159. 43. Lips P, Wiersinga A, van Ginkel FC, et al. The effect of vitamin D supple¬ mentation on vitamin D status and parathyroid function in elderly subjects. J Clin Endocrinol Metab 1988;67:644. 44. Chestnut CH III. Osteoporosis. In: Hazzard WR, Bierman EL, Blass JP, et al, eds. Principles of geriatric medicine and gerontology, ed 3. New York: McGrawHill, 1994:897. 45. Kane RL, Ouslander JG, Abrass IB. Immobility. In: Kane RL, Ouslander JG, Abrass IB, eds. Essentials of clinical geriatrics, ed 3. New York: McGraw-Hill, 1994:221. 46. Riggs BL, Melton LJ III. Involutional osteoporosis. N Engl J Med 1986;3141676.

52. Horowitz M, Need AG, Morris HA, Nordlin BEC. Management of osteo¬ porosis. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:183. 53. Lyles KW. Hyperparathyroidism. In: Hazzard WR, Andres R, Bierman EL, Blass JP, et al, eds. Principles of geriatric medicine and gerontology, ed 3. New York: McGraw-Hill, 1994:923. 54. Brickman AS. Primary hyperparathyroidism in the elderly. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:215. 55. Meneilly GS, Greenspan SL, Rowe JW, Minaker KL. Endocrine systems. In: Rowe JW, Besdine RW, eds Geriatric medicine, ed 2. Boston: Little, Brown & Co., 1988:402. 56. Terry LC, Halter JB. Aging of the endocrine system. In: Hazzard WR, Bier¬ man EL, Blass JP, et al, eds. Principles of geriatric medicine and gerontology, ed 3. New York: McGraw-Hill, 1994:791. 57. Barton RN, Horan MA, Weijers JWM, et al. Cortisol production rate and the urinary excretion of 17-hydroxycorticosteroids, free cortisol, and 6-betahydroxycortisol in healthy elderly men and women. J Gerontol Med Sci 1993-48M213. 58. Friedman M, Green MF, Sharland DE. Assessment of hypothalamicpituitary-adrenal function in the geriatric age group. J Gerontol 1969; 24:292. 59. Pavlov EP, Harman SM, Chrousos GP, et al. Responses of plasma adrenocorticotrophin, cortisol, and dehydroepiandrosterone to ovine corticotrophinreleasing hormone in healthy aging men. J Clin Endocrinol Metab 1986; 62:767. 60. Flood C, Gherondache C, Pincus G, et al. The metabolism and secretion of aldosterone in elderly subjects. J Clin Invest 1967;46:961. 61. Tsunoda K, Abe K, Goto T, et al. Effect of age on the renin-angiotensinaldosterone system in normal subjects: simultaneous measurement of active and inactive renin, renin substrate and aldosterone in plasma. J Clin Endocrinol Metab 1986;62:384. 62. Barrett-Connor E, Khaw KT, Yen SSC. A prospective study of dehydro¬ epiandrosterone sulfate, mortality, and cardiovascular disease. N Engl J Med 1986;315:1519.

Ch. 193: Aging and Endocrinology 63. Veith RC, Featherstone JA, Linares OA, Halter JB. Age differences in plasma norepinephrine kinetics in humans. ] Gerontol 1986; 41:319. 64. Sowers JR, Rubenstein LZ, Stem N. Plasma norepinephrine responses to posture and isometric exercise increase with age in the absence of obesity. J Gerontol 1983; 38:315. 65. SupianoMA, Halter JB. The aging sympathetic nervous system. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:465. 66. Urban RJ. Neuroendocrinology of aging in the male and female. Endocri¬ nol Metab Clin North Am 1992;21:921. 67. Kronenberg F. Hot flashes: epidemiology and physiology. Ann NY Acad Sci 1990; 592:52. 68. Barrett-Connor E, Langer RD. Cardiovascular events, estrogens, and the menopause. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Cambridge, MA: Blackwell Scientific Publications, 1992:336. 69. Wahl P, Walden C, Knopp R, et al. Effect of estrogen/progestin potency on lipid/lipoprotein cholesterol. N Engl J Med 1983; 308:862. 70. Sullivan JM, Vander Zwaag R, Hughes JP, et al. Estrogen replacement and coronary artery disease: effect on survival in postmenopausal women. Arch Intern Med 1990; 150:2557. 71. Gruchow HW, Anderson AJ, Barboriak JJ, Sobocinski KA. Postmeno¬ pausal use of estrogen and occlusion of coronary arteries. Am Heart J1988; 115:954. 72. Swerdloff RS, Wang C. Androgen deficiency and aging in men. West J Med 1993; 159:579. 73. Morley JE, Melmed S. Gonadal dysfunction in systemic disorders. Metab¬ olism 1979;28:1051. 74. Deslypere JP, Kaufman JM, Vermeulen T, et al. Influence of age on pulsa¬ tile luteinizing hormone release and responsiveness of the gonadotrophs to sex hor¬ mone feedback in men. J Clin Endocrinol Metab 1987; 64:68. 75. Tenover JS. Effects of testosterone supplementation in the aging male. J Clin Endocrinol Metab 1992;75:1092. 76. Morley JE, Perry HM III, Kaiser FE, et al. Effects of testosterone replace¬ ment therapy in old hypogonadal males: a preliminary study. J Am Geriatr Soc 1993;41:149. 77. Pfeiffer E, Verwoerdt A, Wang HS. Sexual behavior in aged men and women. Arch Gen Psychiatry 1968; 19:753. 78. Schiavi RC, Schreiner-Engel P, Mandeli J, et al. Healthy aging and male sexual function. Am J Psychiatry 1990; 147:766. 79. Kinsey AC, Pomeroy WD, Martin CE. Sexual behavior in the human male. Philadelphia: WB Saunders, 1948:1. 80. Kaiser FE. Impotence in the elderly. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publica¬ tions, 1992:262. 81. Morley JE. Impotence. Am J Med 1986; 80:897. 82. Van Italie TB. Health implications of overweight and obesity in the United States. Ann Intern Med 1985; 103:983. 83. Forbes GB, Reina JC. Adult lean body mass declines with age: some longi¬ tudinal observations. Metabolism 1970; 19:653. 84. Shimokata H, Tobin JD, Muller DC, et al. Studies in the distribution of body fat: I. Effects of age, sex, and obesity. J Gerontol Med Sci 1989;44:M66. 85. Novak LP. Aging, total body potassium, fat-free mass, and cell mass in males and females between ages 18 and 85 years. J Gerontol 1972; 27:438. 86. Andres R. Mortality and obesity: the rationale for age-specific heightweight tables. In: Hazzard WR, Bierman EL, Blass JP, et al, eds. Principles of geriatric medicine and gerontology, ed 3. New York: McGraw-Hill, 1994:847. 87. Lee IM, Manson JE, Hennekens CH, Paffenbarger RS. Body weight and mortality: a 27-year follow-up of middle-aged men. JAMA 1993;270:2823-2828. 88. Launer LJ, Harris T, Rumpel C, Madans J. Body mass index, weight change, and risk of mobility disability in middle-aged and older women: the epide¬ miologic follow-up study of NHANES I. JAMA 1994;271:1093-1098. 89. Goldberg AP, Coon PJ. Diabetes mellitus and glucose metabolism in the elderly. In: Hazzard WR, Bierman EL, Blass JP, et al, eds. Principles of geriatric medicine and gerontology, ed 3. New York: McGraw-Hill, 1994:825. 90. Flarris MI, Hadden WC, Knowler WC, Bennett PH. Prevalence of diabetes and impaired glucose tolerance and plasma glucose levels in U.S. population aged 20-74 years. Diabetes 1987;36:523. 91. Porte DJ, Kahn SE. What geriatricians should know about diabetes melli¬ tus. Diabetes Care 1990; 13(Suppl 2):47. 92. Abbott RD, Donahue RP, MacMahon SW, et al. Diabetes and the risk of stroke: the Honolulu Heart Program. JAMA 1987, 257:949.

1679

93. Ametz BB, Kallner A, Theorell T. The influence of aging on hemoglobin A1C. J Gerontol 1982;37:648. 94. Rosenthal MJ, Morley JE. Diabetes and its complications in older people. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:373. 95. Gradman TJ, Laws A, Thompson LW, Reaven GM. Verbal learning and/ or memory improves with glycemic control in older subjects with non-insulindependent diabetes mellitus. J Am Geriatr Soc 1993;41:1305. 96. Andres R. Diabetes and aging. In: Brocklehurst JC, Tallis RC, Fillit HM, eds. Textbook of geriatric medicine and gerontology, ed 4. Edinburgh: Churchill Livingstone, 1992:724. 97. Graf RJ, Halter JB, Porte D Jr. Glucosylated hemoglobin in normal subjects and subjects with maturity onset diabetes: evidence for a saturable system in man. Diabetes 1978; 27:834. 98. Panzram G, Zabel-Langhennig R. Prognosis of diabetes mellitus in a geo¬ graphically defined population. Diabetologia 1981;20:587. 99. Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med 1993;329:977. 100. Kerson CM, Baile GR. Do diabetic patients inject accurate doses of insu¬ lin? Diabetes Care 1981;4:333. 101. Funnell MM. Role of the diabetes educator for older adults. Diabetes Care 1990; 13(Suppl 2):60. 102. Franz MJ, Horton ESS, Bantle JP, et al. Nutrition principles for the man¬ agement of diabetes and related complications. Diabetes Care 1994; 17:490. 103. Mooradian AD, Osterweil D, Petrasek D, Morley JE. Diabetes mellitus in elderly nursing home patients: a survey of clinical characteristics and management. J Am Geriatr Soc 1988;36:391. 104. Mooradian AD. Management of diabetes in the elderly. In: Morley JE, Korenman SG, eds. Endocrinology and metabolism in the elderly. Boston: Blackwell Scientific Publications, 1992:388. 105. Schwartz RS. Exercise training in treatment of diabetes mellitus in elderly patients. Diabetes Care 1990; 13(Suppl 2):77. 106. Halter JB, Morrow LA. Use of sulfonylurea drugs in elderly patients. Diabetes Care 1990; 13(Suppl 2):86. 107. Asplund K, Wiholm BF, Lithner F. Glibenclamide-associated hypoglyce¬ mia: a report of 57 cases. Diabetologia 1983;24:412. 108. Feldman JM. Review of glyburide effect after one year on the market. Am J Med 1985;79(Suppl 3B):102. 109. Meneilly GS, Elahi D, Minaker KL, Rowe JW. The dawn phenomenon does not occur in normal elderly subjects. J Clin Endocrinol Metab 1986;63:292. 110. Hazzard WR. Dyslipoproteinemia. In: Hazzard WR, Bierman EL, Blass JP, et al, eds. Principles of geriatric medicine and gerontology, ed 3. New York: McGraw-Hill, 1994:855. 111. Garry PJ, Hunt WC, Koehler KM, et al. Longitudinal study of dietary intakes and plasma lipids in healthy elderly men and women. Am J Clin Nutr 1992;55:682. 112. Jacobs D, Blackburn H, Higgins M, et al. Report of the conference on low blood cholesterol: mortality associations. Circulation 1992;86:1046. 113. Kritchevsky SB, Wilcosky TC, Morris DL, et al. Changes in plasma lipid and lipoprotein cholesterol and weight prior to the diagnosis of cancer. Cancer Res 1991; 51:3198. 114. Noel MA, Smith TK, Ettinger WH Jr. Characteristics and outcomes of hospitalized older patients who develop hypocholesterolemia. J Am Geriatr Soc 1991;39:455. 115. National Cholesterol Education Program Expert Panel. Summary of the second report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel II). JAMA 1993;269:3015. 116. Denke MA, Grundy SM. Hypercholesterolemia in elderly persons: re¬ solving the treatment dilemma. Ann Intern Med 1990; 112:780. 117. Blankenhorn DH, Azen SP, Kramsch DM, et al, and the MARS Research Group. Coronary angiographic changes with lovastatin therapy: the monitored ath¬ erosclerosis regression study (MARS). Ann Intern Med 1993; 119:969. 118. American College of Obstetricians and Gynecologists. Hormone replace¬ ment therapy. Tech Bull 1992; 166:1. 119. Lipson LG. Diabetes in the elderly: diagnosis, pathogenesis, and therapy. Am J Med 1986;80(Suppl 5A):10.

PART

XIV

INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY KENNETH L. BECKER, editor

194.

INFLUENCE OF HORMONES AND MESSENGER PEPTIDES ON NORMAL BRAIN FUNCTION. 1682

195.

CEREBRAL EFFECTS OF ENDOCRINE DISEASE. 1691

196.

PSYCHIATRIC-HORMONAL INTERRELATIONSHIPS. 1696

197.

RESPIRATION AND ENDOCRINOLOGY. 1703

198.

THE CARDIOVASCULAR SYSTEM AND ENDOCRINE DISEASE. 1713

199.

GASTROINTESTINAL MANIFESTATIONS OF ENDOCRINE DISEASE. 1721

200.

THE LIVER AND ENDOCRINE DYSFUNCTION. 1726

201.

EFFECTS OF NONRENAL HORMONES ON THE NORMAL KIDNEY. 1740

202.

RENAL METABOLISM OF HORMONES. 1746

203.

EFFECTS OF ENDOCRINE DISEASE ON THE KIDNEY. 1754

204.

ENDOCRINE DYSFUNCTION DUE TO RENAL DISEASE. 1759

205.

NEUROMUSCULAR MANIFESTATIONS OF ENDOCRINE DISEASE. 1762

206.

RHEUMATIC MANIFESTATIONS OF ENDOCRINE DISEASE. 1770

207.

HEMATOLOGIC ENDOCRINOLOGY. 1776

208.

INFECTIOUS DISEASES AND ENDOCRINOLOGY. 1784

209.

THE EYE IN ENDOCRINOLOGY. 1793

210.

OTOLARYNGOLOGY AND ENDOCRINE DISEASE. 1817

211.

DENTAL ASPECTS OF ENDOCRINOLOGY. 1821

212.

THE SKIN AND ENDOCRINE DISORDERS. 1830

1682

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

194_

INFLUENCE OF HORMONES AND MESSENGER PEPTIDES ON NORMAL BRAIN FUNCTION ABBA J. KASTIN, WILLIAM A. BANKS, BILAL AHMED, AND JAMES E. ZADINA

The extensive effects of hormones constitute an important aspect of this textbook. Although not all hormones are peptides and not all peptides are hormones, both hormones and peptides are found in the brain. Hormones from the pituitary are released into the blood, and other hormones and peptides are synthesized in the periphery. Regardless of how these substances reach the blood, most of them exert actions on the brain. The effects of the large and growing number of bioactive peptides on the central nervous system (CNS) are numerous and have been tabulated elsewhere.1 They are summarized in Table 194-1.

MECHANISMS OF BRAIN HORMONE-PEPTIDE INTERACTIONS At least five general mechanisms exist by which blood-borne hormones and peptides can affect brain function. First, they can act at peripheral sites to stimulate a signal that is relayed to the brain, as illustrated by the vagal mediation of cholecystokinin (CCK)-induced satiety. Second, they can alter the level of an¬ other substance that directly affects brain function. For example, insulin induces coma through its effect on serum glucose. Third, they can act at circumventricular organs (areas of the brain that lie outside the blood-brain barrier [BBB]), with neuronal relay of information to brain areas behind the BBB. For instance, some of the effects of angiotensin on water-drinking behavior seem to be mediated through circumventricular organs. Fourth, they can regulate the transport of other substances across the BBB. For example, a-melanocyte-stimulating hormone (a-MSH), arginine vasopressin (AVP), adrenocorticotropic hormone (ACTH), bradykinin, and insulin alter the permeability of the BBB to glucose, technetium pertechnetate, antipyrine, albumin, amino acids, inulin, and sucrose. Fifth, they can cross the BBB in intact form to affect the brain directly. Steroid hormones cross the BBB mainly by direct membrane permeation. Thyroid hormones have spe¬ cific, saturable, carrier-mediated transport systems; the major route for triiodothyronine is directed from the blood to the brain, and that for thyroxine is directed from the brain to the blood.2,3 The passage of peptides across the BBB, once a controversial issue, has received increasing attention. The fact that peptides can cross the BBB in amounts sufficient to affect brain function is now widely appreciated.4 Such passage may play an important role in mediating some of the physiologic effects of peptide hor¬ mones on brain function. Many of the peptides and cytokines that can affect brain function, including cyclo (His-Pro), MHS release-inhibiting factor-1 (MIF-1), Tyr-MIF-1, AVP, thyrotro¬ pin-releasing hormone (TRH), delta sleep-inducing peptide, aMSH, pancreatic polypeptide, met-enkephalin, /1-endorphin, in¬ terleukin-1, and tumor necrosis factor, cross the BBB. For some peptides, passage has been linked directly to spe¬ cific effects on brain function.5 More speculative actions have been considered for other peptides, such as a possible role for the BBB transport system for met-enkephalin in alcohol addiction.6 Peptides and their analogues that can cross the BBB may have

therapeutic uses.7 Treatment of anorexia with CCK antagonists, addiction with opiate analogues, and human immunodeficiency virus infection of the CNS with peptide T analogues have all been suggested. Changes in BBB permeability to peptides, hor¬ mones, and other blood-borne substances occur with stroke, de¬ mentias, and other diseases (i.e., multiple sclerosis); these changes may play a role in altered brain function. Furthermore, changes in BBB function during maturation and aging suggest a dynamic role for the BBB in the development, maintenance, and deterioration of brain-hormone interactions throughout life.

LEARNING Learning no longer can be considered a single process. It consists of several steps, of which memory is only one compo¬ nent. Much of the early work with vasopressin (VP) and memory was confounded by the cardiovascular and endocrine effects of this peptide hormone. Therefore, many of the later studies used analogues of VP that were changed from the parent VP to pre¬ vent these effects, although some CNS effects also could have been eliminated inadvertently. During the last decade, 30 studies were performed in healthy human volunteers and summarized elsewhere.8 The results are largely inconclusive, with some stud¬ ies showing that memory was dramatically improved and others showing no improvement. The effects of CCK and its analogues on memory also have been studied in animals, with somewhat similar results.9 Before information can reach memory, it must be processed; this involves attention and arousal. Melanocyte-stimulating hor¬ mone (MSH) was used as the tool to dissect learning and to show that an effect on learning does not necessarily mean an effect on memory. Differentiation of the processes of attention and memory was shown in a laboratory experiment in which rats were trained to avoid electric shock by entering a safe chamber in a Y-maze.10 Then, the position of the safe chamber was changed. Classic memory theory predicted that the rats would continue to enter the previously safe chamber where they were now getting shocked, whereas attention theory predicted that they would make the reversal shift more rapidly so as to enter the other chamber that was now safe. Administration of MSH resulted in faster reversal. Other experiments in both rats and humans show that attention or arousal are better explanations than memory for the effects of MSH on learning. The first clinical study to illustrate this effect on attention involved the somatosensory-evoked response to stimulation of the hand.11 Administration of MSH caused a significant increase in the electrical activity of the brain when the subject was undis¬ turbed, whereas the effect disappeared when the subject was dis¬ tracted by performance of another task. Not only did the evoked response return when the subject was told to pay attention to what was happening to his hand, but the response was so great after MSH that it was strikingly evident on the electroencephalo¬ gram even without the computer-averaging usually required for detection of evoked potentials. Thus, attention was responsible for the effect. Substances discovered for one activity frequently are found to have effects on other activities. The concept of the multiple actions of peptides has been extended to many endogenous hor¬ mones and peptides.1- Besides MSH, these now include cyto¬ kines (see Chap. 169).

SLEEP Cytokines such as interleukin-1 and tumor necrosis factor may be involved in sleep, a poorly understood process.13 During infections, sleep usually is increased. Muramyl dipeptide is a

Ch. 194: Influence of Hormones and Messenger Peptides on Normal Brain Function component of bacterial cell walls that can induce sleep, and some components of viruses also are somnogenic. Just as substances discovered for other purposes have been found to have sleep-promoting activity, delta sleep-inducing peptide, discovered by its somnogenic properties, can exert other actions.14 This illustrates the misleading nature of nomencla¬ ture,15 as well as the multiple actions of peptides.12 Some of the inconsistent results with delta sleep-inducing peptide on sleep might be explained by the inverted U-shaped dose-response curve typical of the behavioral actions of many peptides, but other hormones and peptides probably are involved in the pro¬ cess of sleep. Somnogenic properties have been found for vaso¬ active intestinal peptide, corticotropin releasing hormone (CRH), MSH, and growth hormone releasing hormone, although nega¬ tive study results also have been reported for these compounds. Other substances with apparent sleep-promoting properties in¬ clude factor S and uridine.

EATING AND DRINKING CONTROL OF INGESTION Ingestion represents a complex set of behaviors that involves the seeking, acquisition, selection, regulation of amount and rate of ingestion (oral metering), and integration with other behaviors such as defecation, social interactions, and (in some species) stor¬ age of food. Ingestion includes at least three broad categories: (1) caloric intake or feeding, (2) water intake or drinking, and (3) noncalorically driven intakes or cravings, such as for salt or alco¬ hol. Many hormones can exert effects on aspects of ingestion and its integration with other behaviors.16'17 Most recent work has focused on the roles of peptides and cytokines.

SUPPRESSION OF FEEDING Many hormones can suppress eating. These include peptide hormones such as CCK, glucagon, bombesin, enterostatin, TRH, cyclo(His-Pro), pancreatic polypeptide, CRH, neurotensin, and cytokines such as the interleukins and tumor necrosis factor. Some hormones may exert their effects only when the animal or subject is on a certain diet or may affect the selection of nutrients.18 CCK inhibits feeding in many species after its administration into either the brain or the periphery.16 In humans, CCK can elicit increased feelings of satiety and decreased feelings of hunger. In most species, the action of peripherally administered CCK on feeding is mediated through the vagus nerve, as it is for somato¬ statin, TRH, and glucagon. There is a diversity in hormonal action on satiety. For exam¬ ple, bombesin stimulates CCK, and its effect on satiety can be blocked by CCK antagonists such as proglumide. However, the effect of bombesin cannot be explained completely by its action in releasing CCK because this is not mediated through the vagus nerve, nor does bombesin induce satiety after injection into the hypothalamus, as does CCK. Bombesin has been proposed as an integrative hormone, a subset of regulatory hormones with ac¬ tions in both the CNS and the periphery.19

STIMULATION OF FEEDING Although many substances suppress feeding, fewer sub¬ stances have been shown to increase feeding. These stimulatory compounds include the opiates, galanin, norepinephrine, neuro¬ peptide Y, peptide YY, and motilin.18,20 The influence of opiates on feeding appears to be modulated by levels of adrenal and sex steroid hormones. Studies with naloxone and quaternary nalox¬ one (which, unlike naloxone, does not cross the BBB) show that the action of opiates is centrally mediated but may involve mech¬ anisms different from those of peptides like CCK or neuropeptide Y.21 Levels of 0-endorphin in the cerebrospinal fluid, but not in

1683

the plasma, are elevated in Prader-Willi syndrome, in which in¬ creased food intake, weight, and feelings of hunger apparently decrease after treatment with naloxone. Hormones may be im¬ portant not only in the determination of whether individuals eat, but also in what they prefer to eat. The possible actions of opiates in food selection may involve reinforcement of learned and naive food preferences.

CENTRAL REGULATION OF GASTRIC ACTIVITY The CNS regulation of gastric secretions is modulated by hormones in the brain.22 Centrally administered bombesin, gastrin-releasing peptide, calcitonin, norepinephrine, opiates, in¬ terleukin-1, and A VP decrease gastric acid secretion, whereas TRH and pentagastrin increase secretion. Several of these sub¬ stances also induce a cytoprotective effect against the develop¬ ment of stress ulcers. Some of these peptides have no effect, or opposite effects, when administered peripherally. The peptides may work by modulating GABAergic and adrenergic inputs into the brain nuclei that are responsible for maintaining vagal tone to the stomach. The role that these peptides play in stress-induced ulcers and ulcers occurring with CNS trauma (Cushing ulcers) is not clear. Many other aspects of gastrointestinal function are affected by centrally acting hormones. These include the actions of bloodborne pancreatic polypeptide on pancreatic exocrine function ex¬ erted through the brain.

DRINKING Many of the behaviors involved in drinking, such as the seeking, procuring, and ingesting of water, are influenced by AVP and angiotensin II.23 The opiates can stimulate centrally me¬ diated drinking behavior, whereas peptides with opiate antago¬ nist activity, such as MIF-1 (Pro-Leu-Gly-NH2) and Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), can inhibit opiate-stimulated drinking at the usually tested doses.20 Other hormones shown to alter drinking behaviors include aldosterone and some of the gastro¬ intestinal hormones.

CRAVINGS Salt craving, although intimately related to thirst and fluid status, has an aspect of regulation independent from that of wa¬ ter drinking.23 Angiotensin II induces natriuresis and atrial natri¬ uretic hormone increases salt retention when given into the brain, effects that are opposite to those induced when these sub¬ stances are given peripherally. The tachykinins, testosterone, and aldosterone also affect appetite for salt. The relationship between control of salt craving and hypertension remains unclear. The craving for alcohol is influenced by brain hormones. For example, concentrations of met-enkephalin and serotonin in the brain are inversely related to the amount of alcohol an animal will drink when presented with alcohol. This correlation exists for animals addicted to alcohol as well as those that have never tasted alcohol.24

DEVELOPMENT OF THE BRAIN Circulating hormones, together with complex genetic, nutri¬ tional, and environmental factors, play a critical role in normal brain development. One of the most dramatic examples of this phenomenon is the role of gonadal steroid hormones. In adult animals, androgens and estrogens are important for the activa¬ tion of neural and endocrine events leading to successful mating and reproduction. In developing animals, these steroids also play an important role during critically timed periods to prepare neu¬ ral structures for later response to the appropriate activating mes¬ sengers.25,26 In the rat, this critical period occurs around the time

1684

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

TABLE 194-1 Some CNS Effects of Peptides

Activity Aggression Analgesia Anxiety Attention Behavior (other) Bladder contraction Catalepsy Cerebral blood flow Cerebrovascular Blood pressure Cardiac output Heart rate Defense Depression Drinking Electrophysiology ETOH consumption Feeding Gastrointestinal Absorption Luminal pressure Motility Secretion Grooming Hormone release

ACTH

ACTH analogues

4

4

Amylin

ANF

Angiotensin

II

AVP

AVP analogue

BBS

4

4 (slight)

t (RS)

Complex

Ind

Caerulein

4 t Ind

t

Ind

Ind

Ind

t

0

t

t

t

t

0

t

0

t

4

Var (SD, DD)

4 (slight)

4 Ind

4

f or

4 (RS)

Complex 4

0: GH,

Learning Memory Metabolic

t(C)

0: ACTH

Nerve regeneration Neurotransmitter Panic

f DA

| Melatonin;

t

t

Complex

4

t (RS) t 4 t

4, Complex t f cortisol

0

4

cortisol

Seizures Self-stimulation Sexual Signal transduction Sleep

ANF analogues

t t

f 4 Glucose util (C)

f AVP

Var

0 4 Ach

4 (slight)

fLat

Social Temperature Ventilation Vocalization Weight Yawning

4 (C), t

AC, adenylate cyclase; Ach, acetylcholine; ACTH, adrenocorticotropin; ANF, atrial natriuretic factor; aPP, avian pancreahc polypeptide; AVP, arginine vasopressin; BBS, bombesin; CCK, cholecystokinin; CGRP, calcitonin gene-related peptide; CRF, cOrticotropm-releasing factor; DA, dopamine; DSIP, delta sleep-inducing peptide; EGF, epidermal grovth factor; End, endorphin; Enk, enkephalin; ETOH, ethanol; 5HT, serotonin; LH, luteinizing hormone; MSH, melanocyte-stimulating hormone; NE, norepinephrine; NPY, neuropeptide Y; PACAP, pituitary adenylate cyclase activating polypeptide; Pi, phosphoinositol; PP, ?n^r?utlC Poly.PePtlde; Prl' prolactin; PYY, peptide YY; sPP, salmon pancreatic polypeptide; TCA, tricyclic antidepressants; 1KH, thyrotropin-releasing hormone; TV, tidal volume; VIP, vasoactive intestinal peptide; f, increased; decreased; 0, no effect; C, conditioned; DD, dose-dependent; GS, glucose-specific; ind, induced; integ, integrated; lat, latency; mult, multiple; RS, routespecihc; SD, strain- or species-dependent; syn, synthesis; util, utilization; var, variable. (Modified from Ahmed et al. Peptides 1994:15).

of birth (the last few days of gestation and the first few days of life). In the human, this period is between the fourth and seventh month of fetal life. Stress during this period can interfere with development.26-28 After genetically induced differentiation of primordial go¬ nadal tissue into either testes or ovaries, the hormonal secretions from these organs, especially androgen from the testes, deter¬ mines whether neural structures will become male- or femaletypical. Rats with the female genotype that have been injected with androgen during the critical period show an altered pattern of release of luteinizing hormone-releasing hormone (LHRH). In

the normal female, the hypothalamus regulates release of this hormone in a cyclic pattern. In the female given androgen, the release pattern is shifted to the more tonic pattern typical of the male. As a consequence, the female is no longer able to ovulate. After injection of androgen in the adult period, these rats show reproductive behavioral patterns normally observed in the male. Conversely, male rats that have had their testes removed during the critical period show a shift of the pattern for the re¬ lease of LHRH from tonic to cyclic. Ovaries implanted in these animals as adults show female-typical cycles, and their reproduc¬ tive behavior in response to estrogen is the stereotypical female

1685

Ch. 194: Influence of Hormones and Messenger Peptides on Normal Brain Function

19-

Calcitonin

Casomorphin

Casomorphin analogues

CCK

Ceruletide

CGRP

1 t

t(SD)

t

CRF

Deltorphin

DSIP

Dynorphin

1 1

1

1

Ind

Dermorphin

t

( Hunger

t

Ind

Ind

Var (RS)

t

t or | (RS)

Var (RS)

t

t orl (C)

1(C)

t

t 0 or f (GS, DD) Ind 0 or ^

1 (RS, SD)

Prevents f (C)

1

f Insulin

t

1

| (SD, RS) 1(C) t f MSH, ACTH, AVP

t f Protein syn

f GH

1

t

Mult f /3-End (C) Var(C) Var (RS) t fcAMP

Ca2+ var

Complex

0 Prevents l (C) f TV (RS)

pattern. Manipulation of the androgen level (by castration of the male or injection into the female) at a time other than the critical period does not produce these dramatic results. Thus, the neural mechanisms for both the control of LHRH release and complex reproductive behaviors are profoundly affected by the hormonal milieu present in a specific, critical period of development of the nervous system. Although, in recent years, many peptides also have been shown to affect brain function in adult animals, the role of these peptides in brain development has only begun to be explored. The earliest studies involving the exogenous administration of

t

1 t

peptides to newborn rats used TRH (which caused increased emotionality in later life) and fragments and analogues of the MSH-ACTH family of peptides. Animals, especially males, given MSH-ACTH peptides during the first week of life showed im¬ provement in various tasks related to learning, memory, and at¬ tention in later life.29 Another major group of peptides that have been investi¬ gated for their role in the development of later brain functions are the opiate peptides.29-32 The administration of /3-endorphin to rats at about the time of birth altered sensitivity to heatinduced pain, brain opiate receptors, components of sociosexual

1686

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

TABLE 194-1 Some CNS Effects of Peptides (continued)

Activity Aggression Analgesia Anxiety Attention Behavior (other)

Dynorphin analogue

EGF

Complex

l

0Endorphin

Endothelin

Enkephalin, leu

Enkephalin, met

FMRF

FMRF analogues

Complex f, f (SD)

Mult

Defense Depression Drinking Electrophysiology ETOH consumption

Enkephalin analogues

Complex

t

Ind

Bladder contraction Catalepsy Cerebral blood flow Cerebrovascular Blood pressure Cardiac output Heart rate

FeedinS

Eledoisin

1

Ind

f

|

f

f

yar

f

Var (SD)

f

f

Var

|

\

(slight)

t

Var (SD, DD)

j

\

|

jnj |

t

Var

Integ

Complex

Complex

|

Gastrointestinal Absorption Luminal pressure Motility Secretion Grooming Hormone release Learning Memory Metabolic

f Glucose

Nerve regeneration Neurotransmitter Panic Peptide release Seizures Self-stimulation Sexual Signal transduction Sleep Social Temperature Ventilation Vocalization Weight Yawning

f Enk-met Complex

0

f

Var

t

Var

1

AC, adenylate cyclase; Ach, acetylcholine; ACTH, adrenocorticotropin; ANF, atrial natriuretic factor; aPP, avian pancre¬ atic polypeptide; AVP, arginine vasopressin; BBS, bombesin; CCK, cholecystokinin; CGRP, calcitonin gene-related peptide; CRF, corticotropin-releasing factor; DA, dopamine; DSIP, delta sleep-inducing peptide; EGF, epidermal growth factor; End, endorphin; Enk, enkephalin; ETOH, ethanol; 5HT, serotonin; LH, luteinizing hormone; MSH, melanocyte-stimulating hormone! NE, norepinephrine; NPY, neuropeptide Y; PACAP, pituitary adenylate cyclase activating polypeptide; Pi, phosphoinositol; PP, pancreatic polypeptide; Prl, prolactin; PYY, peptide YY; sPP, salmon pancreatic polypeptide; TCA, tricyclic antidepressants; TRH, thyrotropin-releasing hormone; TV, tidal volume; VIP, vasoactive intestinal peptide; f, increased; decreased; 0, no effect; C, conditioned; DD, dose-dependent; GS, glucose-specific; ind, induced; integ, integrated; lat, latency; mult, multiple; RS, routespecific; SD, strain- or species-dependent; syn, synthesis; util, utilization; var, variable. (Modified from Ahmed et al. Peptides 1994:15).

behavior, and various measures involving attention, learning, and activity. CRH, when given to neonatal rats, dramatically changed their growth pattern and eye opening, as well as the plasma and adrenal corticosterone concentrations seen in later development. As adults, these animals showed altered behavior in an open field.31 One of the many physiologic roles proposed for substance P is that of a neurotransmitter in sensory neurons, particularly in areas known to influence the perception of pain. The injection of substance P into neonatal rats produced a long-term increase in the sensitivity of the animals to pain.33 When VP was given dur¬

ing the first week of life, it induced a long-lasting deficit in the ability of the kidney to respond to VP.34 Whether neonatal VP can induce a similar deficit in the ability of the brain to respond to VP is not known, but Brattleboro rats, with their hereditary deficiency of this hormone, show retarded brain development. Thus, the functions of, and responsiveness to, hormonal ste¬ roids and peptides in an adult animal can be permanently affected by changing concentrations of these substances during development. As illustrated by reproductive and other behaviors, it appears that a delicate balance of these messenger molecules during the formative period can be influential in determining

Ch. 194: Influence of Hormones and Messenger Peptides on Normal Brain Function

Galanin

GRF

Glucagon

Glycyl-Lglutamine

Hemorphin

Hemorphin analogues

t

t

1

1

Kassinin

Kentsin

Neokyotorphin

MIF-1

t (RS)

t

1 1

t

1687

MIF-1 analogue

t(C) Ind

f TCA effect 1 Ind f(RS)

f or 1 (DD)

Complex

1

0 0

t

f or 0 (RS)

f GH

t I REE

1 histamine

f Galanin

1 AC

fCa2+

1(C)

whether brain development proceeds in an optimal or deficient manner.

REPRODUCTIVE BEHAVIOR AND THE BRAIN There is perhaps no area of behavioral physiology in which hormones play so commanding a role as in reproductive behav¬ ior. This involves gonadal hormones, the classic neurotransmit¬ ters, and, more recently, peptide hormones. LHRH was the first peptide to be tested for its effects on

mating behavior. It induced the stereotypic female mating pos¬ ture called lordosis in female rats that were given doses of estro¬ gen too low to induce the lordosis by themselves.35,36 This effect could be seen in animals without pituitaries, indicating that it acted directly on the brain, rather than through the pituitarygonadal axis.36 It might be expected that structural modifications of LHRH that block ovulation would also block mating behavior, whereas analogues that act as potent agonists for pituitary luteinizing hor¬ mone release would also stimulate lordosis. This does not always occur. Some analogues known to block ovulation are capable of

1688

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

TABLE 194-1 Some CNS Effects of Peptides (continued)

Tyr-MIF-1 Activity Aggression Analgesia Anxiety Attention Behavior (other)

Morphiceptin

a-MSH

MSH analogues

Neuromedin N

Neuropeptide FF

Neuropeptide K

1 or f(C)

Ind

\

0 0

1(C) HQ Complex 1

f f f or | LH (C)

f GH, Prl

Learning Memory Metabolic

t Complex

Nerve regeneration Neurotransmitter Panic

Social Temperature Ventilation Vocalization Weight Yawning

Neuromedin C

0

t

Defense Depression Drinking Electrophysiology ETOH consumption Feeding

Peptide release Seizures Self-stimulation Sexual Signal transduction Sleep

Neurokinin B

t

Bladder contraction Catalepsy Cerebral blood flow Cerebrovascular Blood pressure Cardiac output Heart rate

Gastrointestinal Absorption Luminal pressure Motility Secretion Grooming Hormone release

Neurokinin A

i

t DA

t Var

Complex fcAMP

| (C)

Prevents f (C)

AC, adenylate cyclase; Ach, acetylcholine; ACTH, adrenocorticotropin; ANF, atrial natriuretic factor; aPP, avian pancre¬ atic polypeptide; AVP, arginine vasopressin; BBS, bombesin; CCK, cholecystokinin; CGRP, calcitonin gene-related peptide; CRF, corticotropin-releasing factor; DA, dopamine; DSIP, delta sleep-inducing peptide; EGF, epidermal growth factor; End, endorphin; Enk, enkephalin; ETOH, ethanol; 5HT, serotonin; LH, luteinizing hormone; MSH, melanocyte-stimulating hormone; NE, norepinephrine; NPY, neuropeptide Y; PACAP, pituitary adenylate cyclase activating polypeptide; Pi, phosphoinositol; PP, pancreatic polypeptide; Prl, prolactin; PYY, peptide YY; sPP, salmon pancreatic polypeptide; TCA, tricyclic antidepressants; TRH, thyrotropin-releasing hormone; TV, tidal volume; VIP, vasoactive intestinal peptide; f, increased; f, decreased; 0, no effect; C, conditioned; DD, dose-dependent; GS, glucose-specific; ind, induced; integ, integrated; lat, latency; mult, multiple; RS, routespecific; SD, strain- or species-dependent; syn, synthesis; util, utilization; var, variable. (Modified from Ahmed et al. Peptides 1994:15).

stimulating lordosis, whereas for others, the reverse is true,37 fur¬ ther indicating separate as well as concerted actions at the brain and pituitary. Other peptides also may be involved in mating and in repro¬ ductive function.38 The opiate peptides, for example, can inhibit or abolish elements of male copulatory behavior. 0,39 The inhibi¬ tion of lordosis by CRH appears to be partially mediated by its ability to release /3-endorphin, because opiate blockade by nalox¬ one or /3-endorphin antiserum reverses the CRH-induced inhibi¬ tion of behavior. Both the CRH-induced and the /3-endorphininduced inhibition can be overcome by the administration of

LHRH.39 Proopiomelanocortin-derived peptides of the MSHACTH family also affect lordosis.39 Thus, even with a behavior for which the requirements for steroid hormones have been ex¬ tensively documented, a new understanding of hormonal influ¬ ences on brain function is being discovered in parallel with the ongoing discovery of new peptides in the brain.

PAIN Pain is a protective sensory experience that warns of tissue damage and danger. However, anecdotal experience from wars,

Ch. 194: Influence of Hormones and Messenger Peptides on Normal Brain Function

Neurotensin

Neurotensin analogues

NPV

Var (RS)

Complex

l 0 (SD)

NPY analogues

Oxytocin

Ind

Ind

PACAP

Pancreastatin

PP (salmon, avian)

PYY

1689

Sauvagine

Senktide

1(C)

1

Var (SD) USD) Ind

Ind

t (slight)

t

t(C)

Var

1 (slight)

t

1

Var

t

f (sPP) or

\ (RS)

1 (sPP)

f

t

Integ

t

t

1

Complex

0

0 Ind

Integ

0 or f (slight; SD)

Complex

i

Var

0 j Tone

f (aPP)

t

t

i

URS) | MSH,

\

0 (aPP)

t

t

t

f MSH

t LH (C)

t LH(C)

t

t

| NE

Mult

t

Var (RS) 1(C)

UQ f Pi,

t

| cAMP

fCa2+

UQ

USD)

1 0 or

1

UQ

|

t

childbirth, and the dentist's chair indicate that situational vari¬ ables can drastically modify the perception of pain. This plasticity suggests complex neural mechanisms for modulating the experi¬ ence of, and emotional reaction to, pain. Peptide hormones, which often are referred to as neuromodulators, play a critical role in the perception of pain. The first family of peptides discovered to be involved in in¬ fluencing pain perception were the opiate peptides.40 These arise from at least three distinct genes, and the response they induce depends on which of several types of opiate receptors in the brain and spinal cord they activate. Several areas in the CNS contain

high concentrations of opiate peptides and their receptors, and are sensitive to opiates. Microinjections of opiates and electrical stimulation in these areas produce a selective suppression of no¬ ciceptive dorsal horn neurons and, consequently, cause analge¬ sia. These areas include the periaqueductal gray in the midbrain, the rostral ventromedial medulla, and the superficial layers of the dorsal horn of the spinal cord. Substance P may be one of the excitatory transmitters in the nociceptive neurons that is inhib¬ ited by this descending system. This peptide, however, has been reported to be capable of both inducing analgesia and reducing pain thresholds.40

1690

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

TABLE 194-1 Some CNS Effects of Peptides (continued)

Somatostatin Activity Aggression Analgesia Anxiety Attention Behavior (other)

Somatostatin analogue

t

Substance P

Substance P analogue

0

4

t Ind

Ind

Bladder contraction Catalepsy Cerebral blood flow Cerebrovascular Blood pressure Cardiac output Heart rate

Thermal peptides

TRH

TRH analogues

Vasotocin

VIP

t

4 t t

t

4(C) t(C)

4

Urotensin

t

Mult

Ind

Ind

4 (SD)

;

t

t

Var (SD)

Var (SD, DD)

t

t

Prevents

4

(C) Defense Depression Drinking Electrophysiology ETOH consumption Feeding Gastrointestinal Absorption Luminal pressure Motility Secretion Grooming Hormone release Learning Memory Metabolic

Social Temperature Ventilation Vocalization Weight Yawning

Ind

t

t t t

Ind

t 4

4 t (DD)

GH integ

t GH, TSH var

t

t

MSH var; f TSH, Prl

t t t f TSH, Prl

t

Nerve regeneration Neurotransmitter Panic Peptide release Seizures Self-stimulation Sexual Signal transduction Sleep

Ind

t

t

4(C)

f GH

t t

4 f Glucose, f FFA

f DA

f 5HT

f Enk

| Galanin

f MSH (C)

fEnd(C)

4 f Ca2+

f cAMP Mult

t t 4

4 f or 0

t

AC, adenylate cyclase; Ach, acetylcholine; ACTH, adrenocorticotropin; ANF, atrial natriuretic factor; aPP, avian pancre¬ atic polypeptide; AVP, arginine vasopressin; BBS, bombesin; CCK, cholecystokinin; CGRP, calcitonin gene-related peptide; CRF, corticotropin-releasing factor; DA, dopamine; DSIP, delta sleep-inducing peptide; EGF, epidermal growth factor; End, endorphin; Enk, enkephalin; ETOH, ethanol; 5HT, serotonin; LH, luteinizing hormone; MSH, melanocyte-stimulating hormone; NE, norepinephrine; NPY, neuropeptide Y; PACAP, pituitary adenylate cyclase activating polypeptide; Pi, phosphoinositol; PP, pancreatic polypeptide; Prl, prolactin; PYY, peptide YY; sPP, salmon pancreatic polypeptide; TCA, tricyclic antidepressants; TRH, thyrotropin-releasing hormone; TV, tidal volume; VIP, vasoactive intestinal peptide; f, increased; /, decreased; 0, no effect; C, conditioned; DD, dose-dependent; GS, glucose-specific; ind, induced; integ, integrated; lat, latency; mult, multiple; RS, routespecific; SD, strain- or species-dependent; syn, synthesis; util, utilization; var, variable. (Modified from Ahmed et al. Peptides 1994:15).

Other peptides also have been shown to have bidirectional effects on pain or to modulate or antagonize the effects of mor¬ phine or stress on pain responses. These peptides include MIF-1, Tyr-MIF-1, Tyr-W-MIF-1, CCK-8, MSH, FMRF-NH2, neuropep¬ tide FF, and /3-endorphin when cleaved to its 1-27 fragment. Most of these peptides are thought to exert their actions as opiate antagonists at sites other than the opiate receptor, serving to re¬ store homeostasis by regulating signal pathways that counteract the effects of opiates. Nonetheless, some peptides that can act at the opiate receptor could antagonize the effects of morphine and other opiates.41 These actions depended on the state of the tissue

tested. Under opiate-naive conditions, Tyr-MIF-1 and hemorphin (a blood-derived peptide isolated on the basis of morphine¬ like actions) acted as opiate agonists. Under opiate-tolerant conditions, however, the peptides were able to antagonize mor¬ phine. Thus, antiopiate peptides could play a role in tolerance and dependence by at least two mechanisms: (1) occupancy of opiate receptors with less efficacy than morphine, or (2) actions at nonopiate sites with results that counteract opiates. These pro¬ cesses, alone or in combination, could provide a dynamic, wide range of control of pain perception, emphasizing the influence of peptides and hormones on the functioning of the brain.

Ch. 195: Cerebral Effects of Endocrine Disease

REFERENCES 1. Ahmed B, Kastin AJ, Banks WA, Zadina JE. CNS effects of peptides: a cross¬ listing of peptides and their central actions published in the journal Peptides from 1986-1993. Peptides 1994; 15:1105. 2. Banks WA, Kastin AJ, Michals EA. Transport of thyroxine across the bloodbrain barrier is directed primarily from brain to blood in the mouse. Life Sci 1985; 37: 2407. 3. Nilsson C, Lindvall-Axelsson M, Owman C. Neuroendocrine regulatory mechanisms in the choroid plexus-cerebrospinal fluid system. Brain Res Rev 1992; 17:109. 4. Banks WA, Kastin AJ. Editorial review: peptide transport systems for opi¬ ates across the blood-brain barrier. Am J Physiol 1990;259:E1. 5. Banks WA, Kastin AJ. Physiological consequences of the passage of pep¬ tides across the blood-brain barrier. Rev Neurosci 1993;4:365. 6. Banks WA, Kastin AJ. The potential for alcohol to affect the passage of peptide and protein hormones across the blood-brain barrier: a hypothesis for a disturbance in brain-body communication. In: Zakhari S, ed. NIAAA research monograph 23, alcohol and the endocrine system. Bethesda, MD: National Insti¬ tutes of Health, National Institute on Alcohol Abuse and Alcoholism, 1993:401. 7. Banks WA, Audus KL, Davis TP. Permeability of the blood-brain barrier to peptides: an approach to the development of therapeutically useful analogs. Pep¬ tides 1992; 13:1289. 8. Fehm-Wolfsdorf G, Born J. Behavioral effects of neurohypophyseal pep¬ tides in healthy volunteers: 10 years of research. Peptides 1991; 12:1399. 9. Crawley JN, Corwin RL. Biological actions of cholecystokinin. Peptides 1994; 15:731. 10. Sandman CA, Miller LH, Kastin AJ, Schally AV. Neuroendocrine influ¬ ence on attention and memory. J Comp Physiol Psychol 1972; 80:54. 11. Kastin AJ, Miller LH, Gonzalez-Barcena D, et al. Psycho-physiologic cor¬ relates of MSH activity in man. Physiol Behav 1971; 7:893. 12. Kastin AJ, Olson RD, Sandman CA, et al. Multiple independent actions of neuropeptides on behavior. In: Martinez JL, Jensen RA, Messing RB, et al, eds. Endogenous peptides and learning and memory processes. New York: Academic Press, 1981:563. 13. Krueger JM, Obal F Jr. Sleep factors. In: Saunders NA, Sullivan CE, eds. Sleep and breathing. New York: Marcel Dekker, 1994:79. 14. Graf MV, Kastin AJ. Delta-sleep-inducing peptide (DSIP): an update. Pep¬ tides 1986; 7:1165. 15. Kastin AJ, Banks WA, Zadina JE, Graf MV. Brain peptides: the dangers of constricted nomenclatures. Life Sci 1983; 32:295. 16. Morley JE, Silver AJ. Role of the endocrine brain in the control of eating and drinking. In: Motta M, ed. Brain endocrinology. New York: Raven Press, 1991: 431. 17. Plata-Salaman CR. Regulation of hunger and satiety in man. Dig Dis 1991;9:253. 18. Bray GA. The nutrient balance hypothesis: peptides, sympathetic activity, and food intake. Ann NY Acad Sci 1993:676:223. 19. McCoy JG, Avery DD. Bombesin: potential integrative peptide for feeding and satiety. Peptides 1990; 11:595. 20. Olson GA, Olson RD, Kastin AJ. Endogenous opiates: 1992. Peptides 1993;14:1339. 21. Sakatani N, Inui A, Inoue T, et al. The role of cholecystokinin octapeptide in the central control of food intake in the dog. Peptides 1987;8:651. 22. Johnson AK, Gross PM. Sensory circumventricular organs and brain ho¬ meostatic pathways. FASEB J 1993; 7:678. 23. Epstein AN. Neurohormonal control of salt intake in the rat. Brain Res Bull 1991; 27:315. 24. Blum K, Elston SFA, DeLallo L, et al. Ethanol acceptance as a function of genotype amounts of brain [met]-enkephalin. Proc Natl Acad Sci USA 1983; 80: 6510. 25. Goy RJ, McEwen BS. Sexual differentiation of the brain. Cambridge, MA: MIT Press, 1980. 26. Dorner G. Sexual differentiation of the brain. Vitam Horm 1980;38:325. 27. Zadina JE, Kastin AJ. Developmental and long-term effects of perinatal stress and peptides released during stress. In: Pancheri P, Zichella L, eds. Bio¬ rhythms and stress in the physiopathology of reproduction. New York: Hemisphere Publishing Corporation, 1988:485. 28. Ward IL. The prenatal stress syndrome: current status. Psychoneuroendo¬ crinology 1984; 9:3. 29. Sandman CA, Kastin AJ. The influence of fragments of the LPH chains on learning, memory and attention in animals and man. Pharmacol Ther 1981; 13:39. 30. Meyerson BJ. Influence of early /3-endorphin treatment on the behavior and reaction to /3-endorphin in the adult male rat. Psychoneuroendocrinology 1985; 10:135. 31. Zadina JE, Kastin AJ, Coy DH, Adinoff BA. Developmental, behavioral, and opiate receptor changes after prenatal or postnatal /3-endorphin, CRF, or TyrMIF-1. Psychoneuroendocrinology 1985; 10:367. 32. Harrison LM, Zadina JE, Banks WA, Kastin AJ. Effects of neonatal treat¬ ment with Tyr-MIF-1, morphiceptin and morphine on development, tail-flick, and blood-brain barrier transport. Dev Brain Res 1993; 75:207. 33. Handelmann GE, Selsky JH, Helke CJ. Substance P administration to neo¬ natal rats increases adult sensitivity to substance P. Physiol Behav 1984;33:297. 34. Handelmann GE, Russell JT, Gainer H, et al. Vasopressin administration to neonatal rats reduces antidiuretic response to adult kidneys. Peptides 1983; 4: 827.

1691

35. Moss RL, McCann SM. Induction of mating behavior in rats by luteinizing hormone-releasing factor. Science 1973; 181:177. 36. Pfaff DW. Luteinizing hormone-releasing factor potentiates lordosis be¬ havior in hypophysectomized ovariectomized female rats. Science 1973; 182:1148. 37. Zadina JE, Kastin AJ. Multi-independent actions of peptides in the brain: LHRH, MIF-1 and CRF. Am Zool 1986; 26:951. 38. Fabbri A, Jannini EA, Gnessi L, et al. Neuroendocrine control of male reproductive function. The opioid system as a model of control at multiple sites. J Steroid Biochem 1989; 32:145. 39. Sirinathsinghji DJS. Modulation of lordosis behavior in the female rat by corticotropin releasing factor, /3-endorphin and gonadotropin releasing hormone in the mensencephalic central gray. Brain Res 1985;336:45. 40. Terenius L. The endogenous opioids and other central peptides. In: Melzack R, Wall PD, eds. Textbook of pain. New York: Churchill-Livingstone, 1984: 133. 41. Zadina JE, Kastin AJ, Kersh D, Wyatt A. Tyr-MIF-1 and hemorphin can act as opiate agonists as well as antagonists in the guinea pig ileum. Life Sci 1992; 51: 869.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

195_

CEREBRAL EFFECTS OF ENDOCRINE DISEASE HOYLE LEIGH

Hormones affect all organs of the body, and the brain is no exception (see Chap. 194). For example, even in utero, testoster¬ one determines the formation of the “male brain", characterized, by an absence of hypothalamic gonadotropic cyclicity; this early hormonal influence is associated with long-term behavioral effects. As many chapters of this textbook demonstrate, normal cerebral development and function are dependent on a normal hormonal milieu. Not surprisingly, many endocrine abnormali¬ ties can cause effects on the brain that are manifested by disor¬ ders in behavior, mood, and cognitive functions—symptoms that usually are attributed to psychiatric disorders.113 In a study of 658 consecutively evaluated outpatients who had psychiatric syndromes, 9.1% had a medical disorder that explained their psychiatric complaints, and 46% had a previously undiagnosed medical illness.2,3 In this study, 21 patients had an endocrine dis¬ order; their average age was 37 years. In a parallel study of 100 psychiatric inpatients, endocrine disorders were found in 17% of the 80 patients who had diag¬ nosed physical illnesses. The endocrine dysfunction was respon¬ sible for more than one third of all medical disorders that caused the psychiatric symptoms. Most patients were unaware that their psychiatric difficulties were because of medical illness, and their physicians had difficulty distinguishing the physical disorders that were associated with the psychiatric syndromes from "purely" psychiatric disorders given the psychiatric symptoms alone. Clearly, endocrine dysfunction must be ruled out before making the diagnosis of a "functional" disorder in any patient who manifests psychiatric symptomatology. Cerebral cortical dysfunction usually is manifested by cogni¬ tive difficulties (i.e., disturbances with orientation, memory, ab¬ straction, and judgment). Limbic system dysfunction is manifested by problems with emotions (e.g., depression, mania, anxiety, and anhedonia [absence of pleasure from otherwise pleasurable acts]), as well as difficulties with instinctual behaviors such as appetite, sex, and aggression. Endocrine diseases often cause effects in many parts of the brain, so that one commonly sees complex psychiatric syndromes, such as psychosis (which in¬ cludes disturbances of thought processes—a cortical function— as well as disturbances in emotions, such as flat affect or anxiety) and depressive syndrome (which includes depressive affect as well as anhedonia, suicidal ideations, and "vegetative" changes such

1692

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

as loss of appetite and sleep disturbance). Anxiety is one of the most common presenting symptoms of an endocrine dysfunc¬ tion; endocrinopathy accounts for 25% of anxiety disorders in which a specific medical cause is found.4 Table 195-1 lists de¬ scriptions of psychiatric syndromes.

HYPOTHALAMIC DISORDERS Lesions of the hypothalamus may cause bulimia (see Chap. 127) hypersomnia, anorexia, or impotence (see Chap. 11). The associated autonomic dysfunction may mimic or actually pro¬ duce an anxiety attack. Hypothalamic disorders often cause cere¬ bral effects indirectly through their effects on the pituitary gland (see Chaps. 19 and 20). Drowsiness, confusion, irritability, hyperphagia, and depression are common psychiatric symptoms of hypothalamic disorders.5

THE PITUITARY GLAND In acromegaly, drowsiness, lethargy, and diminished libido have been reported. Personality change—decreased initiative, lack of spontaneity, and mood changes—may be prominent. In hypopituitarism, there is typically a slow onset of a com¬ bination dementia-delirium, which sometimes is present up to 2 years before coming to medical attention.6 The mental symp¬ toms—commonly, confusion, disorientation, and drowsiness— may be the dominant feature. Lethargy, anergy (asthenia), and depression may ensue. Psychosis and paranoid symptoms also may occur. There may be a personality change with brief epi¬ sodes of irritability, argumentativeness, and a lack of initiative. When the onset of the hypopituitarism is rapid, however, the symptoms may be dramatic: lethargy rapidly progressing to stu¬ por. In reversing the organic brain syndrome of hypopituitar¬ ism, both thyroid and corticosteroid replacement therapy is necessary.7

THE THYROID GLAND The mechanism whereby thyroid dysfunction affects the CNS is probably related to changes in CNS receptor sensitivity to neurotransmitters and to changes of cellular metabolism. In

hyperthyroidism, there may be an increase in the sensitivity of receptors to catecholamines, a decrease in the monoamine oxi¬ dase activity levels, and an increase in norepinephrine turnover rates.8 In hypothyroidism, there is depressed oxygen and glucose utilization by the CNS, decreased cerebral blood flow, and in¬ creased cerebrovascular resistance. Neurotransmitter receptors are also desensitized to the effects of catecholamines.

HYPERTHYROIDISM Some degree of thyrotoxic encephalopathy has been ob¬ served in 20% to 40% of cases of hyperthyroidism, but severe cognitive disorders are uncommon, except in the elderly. De¬ creased ability to concentrate and deficits in recent memory are common symptoms of the organic brain syndrome in hyperthy¬ roidism. Also, in some patients antithyroid drugs may contribute to an organic brain syndrome. Hyperthyroidism probably exacerbates preexisting thought disorder and prepsychotic personality traits. Symptoms of frank psychosis may occur in up to one fifth of hyperthyroid patients. The symptoms may be schizophreniform, with prominent para¬ noid symptoms, or they may manifest as manic psychoses with grandiose delusions, agitation, and irritability. Visual and audi¬ tory hallucinations may occur. Marked delirious states may signal impending thyroid storm in up to 5% of patients with this severe condition.7 Depression, along with anxiety and psychomotor agitation or retardation, may be the first symptoms of hyperthyroidism.9 Chronic fatigue is an early symptom. Severe depression may pre¬ cede the obvious clinical onset of thyrotoxicosis; it is one of the most outstanding psychiatric features of the illness and may con¬ tinue after thyrotoxicosis subsides. In some elderly patients, par¬ ticularly those with long-lasting thyroid illness, the depressive syndrome may be characterized by apathy and lethargy ("apa¬ thetic hyperthyroidism"),1011 accompanied by weight loss and tachycardia, with or without the presence of high-output conges¬ tive heart failure.1213 Antidepressant therapy usually is in¬ effective. The syndrome resolves with appropriate treatment of the thyrotoxicosis. Anxiety, along with hyperactivity, nervousness, and motor tension with tremor, is observed in nearly half of hyperthyroid patients. Emotional lability and overreactivity is a hallmark of early hyperthyroidism. Diminished hearing, paresthesias, weak¬ ness, and at times bizarre neurologic symptoms may seem hys-

TABLE 195-1 Psychiatric Syndromes Commonly Seen in Endocrinopathies Organic Brain Syndrome: cerebral state characterized by global cognitive impairment because of a physical cause (e.g., delirium and dementia). Delirium: clouded state of consciousness having acute onset, and fluctuating course. There is shifting, and difficulty in focusing, and sustaining attention. Perceptual disturbances such as illusions, hallucinations (especially visual and tactile types), and misinterpretations are common. Sleep-wakefulness cycle is often disturbed, leading to hypervigillance and difficulty in falling asleep. The patient exhibits somnolence or agitation, or alternates between the two states of motor activity. Key features of delirium are memory impairment (especially recent memory), and disorientation to time, place, and, infrequently, to person Confusion may be more severe in the evening. r Dementia: loss of previously acquired intellectual abilities to the extent of social or occupational impairment. Persistent personality changes may accompany the disturbances in memory, abstract thinking, and other higher cortical functions. Level of consciousness does not fluctuate in dementia. Psychosis: syndrome characterized by disturbances in thought content and process, and by perceptual aberrations. Delusions, ideas of reference, and paranoid ideation are common. Thought processes may be incoherent, leading to looseness of association, poverty of content, and bizarre use of language. Hallucinations and illusions especially visual, olfactory, or gustatory—are common in psychoses caused by endocrinopathies. Although the sensorium is usually clear in functional psychoses such as schizophrenia, features of delirium or dementia often coexist in endocrinopathic psychoses. Depression: in a psychiatric context, denotes a syndrome characterized by affective, cognitive, and neurovegetative symptoms and signs. Whereas dysphoria is characteristic of depression, apathy and anhedonia are not infrequent. Feelings of hopelessness and helplessness, and suicidal thoughts are common. There otten is a decreased ability to concentrate and indecisiveness (pseudodementia of depression). Neurovegetative symptoms include insomnia (particularly, early morning awakening), hypersomnia, appetite changes (decrease or increase), and loss of libido. Psychomotor retardation or agitation may occur. The Manic Syndrome: a state of elated, expansive, or irritable mood, with marked distractibility and flight of ideas. Self-esteem is often inflated, and patients mvo ve themselves in activities with a high potential for self-harm without consideration of consequences. Hyperactivity, pressured speech, and a decreased need for sleep are common. Anxiety: a common cerebral effect of endocrine disorders. The features include motor tension, inability to relax, autonomic hyperactivity with sweating, tachycardia, cold moist hands, dry mouth, lightheadedness, paresthesias, and often gastrointestinal or genitourinary complaints. Endocrine disorders account for approximately one quarter of anxiety disorders in which a specific medical diagnosis is found.4

Ch. 195: Cerebral Effects of Endocrine Disease terical. Marital problems are common. Criminal behavior has been reported. Panic attacks and agoraphobia may occur.14 Most psychiatric symptoms of thyrotoxicosis are reversible with appropriate treatment of the underlying disease, but the manic or depressive syndrome may persist for considerable peri¬ ods after a euthyroid state has been established.

HYPOTHYROIDISM Nearly every known type of psychiatric syndrome occurs in myxedema. Psychiatric symptoms often precede a physically rec¬ ognizable myxedematous state.15 Organic brain syndrome occurs in about one third of these patients, impaired cognition occurs in more than 90%, and impaired recent memory is common. Delir¬ ium is unusual except in very rapid onset cases (e.g., postthyroid¬ ectomy or antithyroid drug-induced hypothyroidism). A slowonset dementia of long duration that has various degrees of reversibility is typical.16 In elderly patients with concomitant ce¬ rebrovascular disorder, psychotic organic brain syndrome is com¬ mon.7 There appears to be no consistent relationship between the severity of the physical symptoms and the severity of the psychiatric disorder. Permanent intellectual and morphologic deficits occur if cre¬ tinism is not treated within the first year of life. In juvenile hypo¬ thyroidism, the mental disorder may appear 1 to 2 years after obvious somatic signs arise. Older children and adults show im¬ paired recent memory; labored, slow mentation; and poor con¬ centration. The "Witzelsucht" or facetious humor of frontal lobe disorders also can be seen. There may be slowing and decreased amplitude on electroencephalography, and seizures may be pres¬ ent in severe cases. Psychosis has been reported in over 40% of hypothyroid pa¬ tients. The psychosis is often rapid in onset, but it may be insidi¬ ous in some patients. There are no specific symptoms for myx¬ edema psychosis; however, depression, paranoid delusions, and vivid hallucinations are common. Thyroid replacement usually helps and leads to reversal of the symptoms within several weeks. The duration of hypothyroidism does not seem to be cor¬ related with the response to treatment. Older patients seem to respond more rapidly to treatment. The psychosis may be irre¬ versible if treatment is delayed. Depression appears to be a concomitant of all grades of hy¬ pothyroidism, from the subclinical to the overt. It is marked in nearly half of myxedema patients. The incidence may be greater for those who have a first-degree relative who has a history of depression; suicidal and paranoid ideations often accompany this depression. The patients appear to be lethargic and have dimin¬ ished mental effort and sexual interest. Patients may eventually become indifferent to their delayed cognitive processes. Typi¬ cally, the depression does not respond to antidepressant medica¬ tion and may also be resistant to thyroid replacement, requiring electroconvulsive therapy.17 On the other hand, patients who have had depression for years may respond within a few days after the initiation of replacement therapy. No significant corre¬ lation between the severity of depression and the severity of myxedema has been observed. In one study, nearly 10% of 100 patients with depression or anergia with unremarkable physical, neurologic, and routine laboratory evaluations were found to be hypothyroid.18 Mania may be the presentation of "myxedema madness," but the less dramatic and more common hypomanic symptoms include excitement, agitation, hostility, and hyperactivity. Thy¬ roid hormone-induced mania is a distinct entity observed during the initial treatment of hypothyroid patients.19 Nearly all of the affected patients have psychiatric symptoms at the time medica¬ tion is commenced. One half of the patients have a past or family history of psychiatric disorder. More than 90% of the patients are women and have been hypothyroid for at least 6 months. The thyroid hormone therapy usually is excessive for a beginning dosage (see Chap. 44). In these cases, mania begins 4 to 7 days

1693

after medication is started, and lasts 1 to 2 weeks, resolving with¬ out sequelae, although the patient is at significant personal risk while manic. The syndrome consists of psychomotor agitation, persecutory delusions, elation, and irritability. Increased cate¬ cholamine activity and an abrupt increase in receptor sensitivity, both precipitated by too rapid thyroid replacement, seem to play a role in this syndrome. Anxiety and uncontrollable excitability may mark the pre¬ sentation of some patients with myxedema. The anxiety is not related to the severity of myxedema, and it may persist even after thyroid replacement. There may be a personality change with chronic invalidism. Often, no recovery is expected if the mental illness has a duration longer than 2 years; the highest recovery rate (80%) from this condition is in those older than 50 years of age who have organic brain syndromes caused by the hypothyroidism. Once thyroid hormone therapy is commenced, the recovery from the mental disturbances of hypothyroidism often lags behind the restoration of normal metabolism, but occasionally mental im¬ provement may precede major somatic changes.

THE PARATHYROID GLAND AND DISORDERS OF CALCIUM METABOLISM Parathyroid disorders affect the CNS by causing aberrations in calcium, phosphorus, and magnesium metabolism. Calcium enhances both the release and depletion of norepinephrine and dopamine /3-hydroxylase.

HYPERPARATHYROIDISM AND HYPERCALCEMIA Confusion and delirious states may dominate the clinical picture in hyperparathyroidism.20-23 The incidence of organic brain syndrome is about 5% to 10%. The serum calcium level is closely correlated with the severity of psychiatric symptoms.17 Serum calcium levels of 12 to 16 mg/dL usually are associated with personality changes and affective disturbances. Acute or¬ ganic brain syndromes with altered levels of consciousness, para¬ noid ideation, and hallucinations often occur at levels of 16 to 19 mg/dL. Somnolence and coma supervene at levels higher than 19 mg/dL. The hypomagnesemia that occasionally is associated with hypercalcemia (see Chap. 67) also may play a role in the mental disturbances of some patients. These disorders include disor¬ ientation, confusion, and hallucinations. Also, reversible demen¬ tia may occur in the hypercalcemia of lithium-associated hyperparathyroidism. Psychosis occurs in 5% to 20% of patients with hyperpara¬ thyroidism, largely depending on the level of serum calcium. The preponderant symptoms are hallucinations and delusions. Psy¬ chosis may appear abruptly while plasma calcium levels rise rap¬ idly, necessitating rapid medical or surgical intervention. In such cases, paranoid states may begin to clear within 48 hours after the resection of a parathyroid adenoma. Depression occurs in 5% to 20% of patients and may be as¬ sociated with headaches. Usually, calcium levels are in the 12 to 16 mg/dL range, and fatigue with anergia develops first, at times insidiously, over years or decades. Anxiety and irritability are seen in up to one third of the patients. Personality changes in¬ clude fatigue, weakness, and anorexia. The postoperative reversal24 of many of the cerebral symp¬ toms associated with hyperparathyroidism does not seem to be related to the duration of the illness, the severity of mental symp¬ toms, or the patient's age. The depression of hyperparathyroid¬ ism usually reverses promptly after resection of the adenoma.

HYPOPARATHYROIDISM More than 40% of patients with hypoparathyroidism have an organic brain syndrome that may occur in the absence of tet-

1694

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

any or seizures. Usually, this occurs within the first 3 to 4 months of the illness and tends not to recur with relapses. Sometimes, the psychiatric disturbances are the first and only manifestations of the disease observed—carpopedal spasm and convulsions may occur later.7 A syndrome resembling delirium tremens may oc¬ cur; typically, it resolves without sequelae when normal calcium levels are maintained. Intellectual impairment is common in both hypoparathy¬ roidism and pseudohypoparathyroidism. In pseudopseudohypo¬ parathyroidism, intellectual impairment is seen in almost all of the patients who have psychiatric manifestations. Psychosis occurs in nearly 20% of patients with surgical hypoparathy¬ roidism and less frequently in patients with idiopathic hypo¬ parathyroidism.243 Periodic psychosis associated with pseudo¬ pseudohypoparathyroidism has been reported.25 Depression is a common feature of patients with hypopara¬ thyroidism as well as hyperparathyroidism. Feelings of guilt are described only rarely in depressed hypoparathyroid patients. In¬ terestingly, the presence of guilt has been a clue to the hyper¬ parathyroid etiology of an affective disorder. Well-defined mood swings have been reported in cases of surgical hypoparathy¬ roidism. Anxiety and irritability are common.26 Personality changes, such as obsessions, phobias, tics, social withdrawal, and irritability, may be prominent.27 Intellectual impairment improves with treatment of the hypocalcemia in most patients with surgical and idiopathic hypoparathyroidism and in one third of patients with pseudohypoparathyroidism.

THE ADRENAL CORTEX The CNS effects of disorders of the adrenal cortex are related to the effects of corticosteroids, and perhaps also to the effects of changes of the levels of adrenocorticotropin (ACTH) and cortico¬ tropin releasing hormone. The concomitant abnormalities in glu¬ cose metabolism, electrolytes, and blood pressure also may play a role; however, the exact mechanisms are unknown.

CUSHING SYNDROME Probably, Cushing syndrome is the endocrinopathy having the highest frequency of mental changes. Cerebral symptoms are more common in endogenous Cushing syndrome than in exoge¬ nous corticosteroid administration. Psychiatric symptoms pre¬ date the physical stigmata in 50% of the cases of Cushing syn¬ drome. The greatest percentage of all mental changes in Cushing syndrome occurs in the bilateral adrenocortical hyperplasia sec¬ ondary to a pituitary tumor (i.e., Cushing disease).7 Organic brain syndrome occurs in about one third of pa¬ tients with Cushing syndrome or with exogenous hypercortisolism, and can mimic the impaired concentration, delirium, and dementia of any organic, toxic, or metabolic disorder. Psychosis occurs in 5% to 20% of patients with Cushing syn¬ drome. Often, it is clinically indistinguishable from schizophre¬ nia; the onset may be rapid, and it may occur early or late in the course of the illness; it is not related to the emotional reaction to the physical changes of the disorder.28 Paranoid states are more likely to occur in patients with the highest serum cortisol levels, but often these states do not seem to be related to predisposing personality factors. Psychotic episodes occur in a similar percentage of patients who are receiving pharmacologic doses of corticosteroids.7 Psy¬ chosis is twice as likely to occur during the first week of treat¬ ment. There is no characteristic pattern in corticosteroid-induced psychosis. The pattern ranges from schizophreniform, to affec¬ tive, to organic brain syndrome. The psychosis usually responds to chlorpromazine, 200 mg, or the equivalent, daily, and sponta¬ neous recovery occurs 2 weeks to 7 months after discontinuation

of corticosteroids.29 Occasionally, the psychosis may occur only after the corticosteroids are discontinued. Depression occurs in more than half of the patients with Cushing syndrome. Some may attempt suicide. Suicidal ideation may first develop when physical signs and symptoms begin to resolve. Depression often antedates the physical findings. The depression in Cushing patients is often volatile, with rapid shifts in mood. Sadness and crying may occur without any depressing thought content. The duration of each depressive episode may last 1 to 2 days. Patients with high levels of both serum cortisol and ACTH generally have more serious depressive symptoms. Corticosteroid-induced euphoria, often with increased ap¬ petite and libido, occurs in at least 20% to 40% of patients receiv¬ ing these medications, but it has been observed in fewer than 5% of those with endogenous Cushing syndrome.7 In Cushing syndrome, loud rapid speech, increased energy, elation with hy¬ peractivity, and rapid thoughts may be seen early in the disease process; later, this may lead to agitation, depression, or psychosis, as the disease progresses. Acute episodes of anxiety occur in up to one third of the patients with Cushing syndrome, and a milder degree of anxiety is common in patients receiving corticosteroids. Perceptual disor¬ ders occur in more than 10% of patients with Cushing syndrome, and these may be misinterpreted as hysterical in origin. The treatment of Cushing syndrome (see Chap. 73) often induces a psychological improvement paralleling the resolution of physical signs. Corticosteroid-induced psychosis, however, may persist for some time, even after discontinuation of the drug.

ADDISON DISEASE Psychiatric symptoms are present in almost all cases of se¬ vere Addison disease (see Chap. 74). Memory impairment occurs in 75% of patients, and more severe organic brain syndrome in 5% to 20%. A profound perceptual impairment may occur, with a decreased threshold to tactile, auditory, gustatory, and olfac¬ tory stimuli, accompanied by impaired recognition and inter¬ pretation of sensory stimuli.13 Psychosis occurs in one quarter of the cases and may include the symptoms of seclusiveness, negativism, poor judgment, agi¬ tation, hallucinations, delusions, and bizarre and catatonic posturing. About a third of addisonian patients show depression, man¬ ifested by apathy or sad affect, fatigue, poverty of thought, and lack of initiative. Depression may antedate the physical signs. A subjective return of interest and energy occurs within days of corticosteroid replacement in Addison disease. However, the psychosis may persist for months after adequate replacement therapy. Also, acute mania can occur when a chronically hypoadrenal patient is administered corticosteroids for the first time.

ADRENAL MEDULLA Pheochromocytoma is often associated with an anxiety syn¬ drome and sensations of impending doom.

THE SEX HORMONES Many forms of hypothalamic-pituitary-gonadal dysfunction may produce loss of libido and potentially reversible impo¬ tence. In hypogonadal men, androgen therapy may produce the side effects of insomnia, pressured thought, and irritability (see Chap. 114). Seventy to ninety percent of women of childbearing age are considered to have some degree of the premenstrual tension syn¬ drome, consisting of various emotional symptoms—emotional lability, irritability, depression, anxiety, crying spells, and fatigue (see Chap. 96).30 Changes in appetite and craving for sweets may occur. However, fewer than one third of these women are re-

Ch. 195: Cerebral Effects of Endocrine Disease ported to change their daily routine because of the symptoms. The symptoms usually begin soon after ovulation, increase grad¬ ually, reaching a maximum about 5 days before menstruation. They dissipate rapidly once menstruation begins, and a peak of well-being often occurs during the mid- and late-follicular phase. The “maternity blues," which occurs 1 to 2 weeks postpartum may be due to withdrawal of endogenous progesterone.31 In some women, anxiety, fatigue, emotional lability, depres¬ sion, insomnia, tension, and difficulty in concentration are asso¬ ciated with the menopause (see Chap. 97). The degree of symp¬ tomatology seems to be related to the rate of withdrawal of the hormones (the most severe symptoms being associated with sur¬ gical menopause).

HYPOGLYCEMIA, DIABETES, AND PANCREATIC DISORDERS Anxiety occurs in 20% to 40% of patients with hypoglyce¬ mia. Behavioral disturbances associated with hypoglycemia can be quantified.32 The perceptual disturbances associated with hy¬ poglycemia together with fainting, confusion, and paresthesias may mimic hysteria. On the other hand, early symptoms of dia¬ betes (e.g., blurred vision, polydipsia, polyuria, anorexia) also may mimic hysteria. Many patients with hypoglycemia manifest an organic brain syndrome. However, cognitive function appears to be spared during mild reductions of plasma glucose and is dissociated from the adrenergic activation. 3 Mild delirium may occur at plasma glucose levels below 30 mg/dL and coma may occur at levels below 10 mg/dL (see Chap. 152). The rate of fall in plasma glu¬ cose is more important than the absolute level; therefore, a pre¬ cipitous decrease to a normal level in a severe diabetic may cause delirium. On the other hand, high plasma glucose levels may cause a hyperosmolar encephalopathy. Both the clinical deterio¬ ration and the posttherapy improvement in the psychiatric symp¬ toms of patients with hypoglycemia tend to lag behind the meta¬ bolic and electroencephalographic changes. Psychomotor retardation, depersonalization, and altered states of conscious¬ ness, which may mimic psychosis, are common in hypoglycemia. Chronic hypoglycemia of any etiology may present with depression.333 Also, chronic hypoglycemia may mimic schizo¬ phrenia. In diabetics, varying degrees of intellectual deterioration may occur because of the multiple episodes of insulin-induced hypoglycemia and because of cerebral atherosclerosis.34 Interestingly, more than 50% of patients with pancreatitis have symptoms of psychosis, such as hallucinations (more com¬ monly visual than auditory), which are not dependent on alcohol history.35 Inexplicably, depression and anxiety may be the presenting symptoms in patients with carcinoma of the pancreas and may predate physical signs and symptoms by 6 months to several years. At least 10% of pancreatic cancer patients have an associ¬ ated psychiatric disorder of significant proportion; depression, anxiety, insomnia, and a feeling of impending doom are typically noticed. The sensorium is clear and, initially, a mild weight loss and complaints of pain are seen to variable extents. The depres¬ sion is mild to moderate, without delusional content; feelings of guilt, worthlessness, or suicide are remarkably absent. The de¬ pression is usually resistant to antidepressant drugs. It is not known whether or not the cerebral symptomatology associated with carcinoma of the pancreas is humorally mediated.

REFERENCES 1. Reus VI. Behavioral disturbances associated with endocrine disorders. Annu Rev Med 1986; 37:205. la. Fava GA. Affective disorders and endocrine disease: new insights from psychosomatic studies. Psychosomatics 1994:341. 2. Hall RCW, Popkin MK, DeVaul RA, et al. Physical illness presenting as psychiatric disease. Arch Gen Psychiatry 1978;35:1315.

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3. Hall RCW, Gardner ER, Stickney SK, et al. Physical illness manifesting as psychiatric disease: II. Analysis of a state hospital inpatient population. Arch Gen Psychiatry 1980; 37:989. 4. Hall RCW, Beresford TP, Gardner ER, Popkin MK. The medical care of psychiatric patients. Hosp Community Psychiatry 1982; 33:25. 5. Martin JB, Riskind PN. Neurologic manifestations of hypothalamic dis¬ ease. Prog Brain Res 1992;93:31 6. Lipowski ZJ. Delirium: acute brain failure in man. Springfield, IL: Charles C Thomas, 1980. 7. Leigh H, Kramer SI. The psychiatric manifestations of endocrine disease. Adv Intern Med 1984; 29:413. 8. Ettigi PG, Brown GM. Brain disorders associated with endocrine dysfunc¬ tion. Psychiatr Clin North Am 1978;1:117. 9. Trzepacz PT, McCue M, Klein I, et al. A psychiatric and neuropsychologi¬ cal study of patients with untreated Graves' disease. Gen Hosp Psychiatry 1988; 10: 49. 10. Mintzer MJ. Hypothyroidism and hyperthyroidism in the elderly. J Fla Med Assoc 1992; 79:231. 11. Palacios A, Cohen MA, Cobbs R. Apathetic hyperthyroidism in middle age. Int] Psychiatry Med 1991; 21:393. 12. Eitigi PG, Brown GM. Brain disorders associated with endocrine dysfunc¬ tion. Psychiatr Clin North Am 1978; 1:117. 13. Devaris DP, Mehlman I. Psychiatric presentations of endocrine and met¬ abolic disorders. Primary Care 1979;6:245. 14. Orenstein H, Peskind A, Raskind MA. Thyroid disorders in female psy¬ chiatric patients with panic disorder or agoraphobia. Am J Psychiatry 1988; 145: 1428. 15. Logotheis J. Psychiatric behavior as the initial indicator of adult myx¬ edema. J Nerv Ment Dis 1963; 136:561. 16. Smith CL, Granger CV: Hypothyroidism producing reversible dementia: a challenge for medical rehabilitation. Am J Phys Med Rehabil 1992; 71:28 17. Pitts FN, Guze SB. Psychiatric disorders and myxedema. Am J Psychiatry 1961,118:142. 18. Gold MS, Pottash AC, Mueller EA III, Erxtein I. Grades of thyroid failure in 100 depressed and anergic psychiatric inpatients. Am ] Psychiatry 1981; 138:253. 19. Josephson AM, McKenzie TB. Thyroid-induced mania in hypothyroid patients. Br] Psychiatry 1980; 137:222. 20. Gatewood JW, Organ CH, Mead BT. Mental changes associated with hy¬ perparathyroidism. Am] Psychiatry 1975; 132:129. 21. Agras S, Oliveau DC. Primary hyperparathyroidism and psychosis. Can Med Assoc J 1964; 91:1366. 22. Sier HC, Hartnell ], Morley JE, et al. Primary hyperparathyroidism and delirium in the elderly. J Am Geriatr Soc 1988;36:157. 23. Solomon BL, Schaaf M, Smallridge RC. Psychologic symptoms before and after parathyroid surgery. Am J Med 1994;96:101. 24. Joborn C, Hetta ], Lind L, et al. Self-rated psychiatric symptoms in pa¬ tients operated on because of primary hyperparathyroidism and in patients with long-standing mild hypercalcemia. Surgery 1989; 105:72. 24a. Pollard A], Prendergast M, al-Hammouri F, Rayner PH, Shaw NJ. Different subtypes of pseudohypoparathyroidism in the same family with an un¬ usual psychiatric presentation of the index case. Arch Dis Child 1994:99. 25. Periodic psychosis associated with pseudo-pseudohypoparathyroidism. J Nerv Ment Dis 1991; 179:637 26. Lawlor BA. Hypocalcemia, hypoparathyroidism, and organic anxiety syndrome. J Clin Psychiatry 1988; 49:317. 27. Peterson P. Psychiatric disorders in primary hyperparathyroidism. J Clin Endocrinol Metab 1968,-28:1491. 28. Spillane JD. Neurosis and mental disorders in Cushing's syndrome. Brain 1951; 74:72. 29. Hall RCW, Popkin MK, Stickney SK, Gardner ER. Presentation of steroid psychoses. ] Nerv Ment Dis 1979,-167:229. 30. Wilson CA, Keye WR, Jr. A survey of adolescent dysmenorrhea and pre¬ menstrual symptom frequency. ] Adolesc Health 1989,-10:317. 31. Harris B, Lovett L, Newcombe RG, et al. Maternity blues and major en¬ docrine changes: Cardiff Puerperal Mood and Hormone Study II. Br Med J 1944;308:949. 32. Cox DI, Irvine A, Gonder-Frederick L, et al. Fear of hypoglycemia: quan¬ tification, validation, and utilization. Diabetes Care 1987; 10:617. 33. Ipp E, Forster B. Sparing of cognitive function in mild hypoglycemia: dis¬ sociation from the neuroendocrine response. J Clin Endocrinol Metab 1987; 65:806. 33a. Roy M, Collier B, Roy A. Excess of depressive symptoms and life events among diabetics. Comprehens Psychiatr 1994:129. 34. Rovet JF, Ehrlich RM, Hoppe M. Specific intellectual deficits in children with early onset diabetes mellitus. Child Dev 1988; 59:226. 35. Schuster MM, Iber FL. Psychosis and pancreatitis. Arch Intern Med 1965; 116:228.

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PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

196_

PSYCHIATRIC-HORMONAL INTERRELATIONSHIPS MITCHEL A. KLING, ISAAC NEUHAUS, AND PHILIP W. GOLD

Studies of neuroendocrine regulation in patients with major psychiatric illness suggest an intimate linkage between neurohormonal functional activity and major components of the symptom complexes of illnesses, such as major depression and anorexia nervosa. For instance, several aspects of the syndromes of mood and eating disorders suggest hypothalamic dysfunction. Thus, patients with depression often manifest disturbances in appetite, libido, reproductive function (e.g., oligomenorrhea, amenor¬ rhea), water metabolism, cortisol secretion, and disturbances of the temporal organization of physiologic processes whose circa¬ dian periodicity is thought to be governed by hypothalamic pace¬ makers. Patients with anorexia nervosa show profound alter¬ ations in eating behavior, as well as marked changes in hypothalamic-pituitary regulation, gonadotropin secretion, and in plasma cortisol secretion. Along with efforts to explore the mechanism of these abnormalities in psychiatric populations, in¬ terest in neuroendocrine systems also reflects the fact that the monoaminergic neurotransmitters, long thought to play a domi¬ nant role in major psychiatric illness, also modulate the synthesis and release of a number of hypothalamic peptides and pituitary hormones; thus, examination of pituitary hormones in plasma can shed light on the functional activity of central biogenic amine systems. Moreover, the hypothalamic hormones are widely dis¬ tributed within brain, exert specific receptor-mediated bioactiv¬ ity, and influence the functional activity of brain neurotransmit¬ ter systems (see Chap. 194). Several hypothalamic hormones also have the effect of coordinating complex behaviors and physio¬ logic processes of relevance to adaptation and the maintenance of internal homeostasis.

DEPRESSIVE DISORDERS Major depression is a condition defined by the occurrence of one or more episodes of the so-called major depressive syn¬ drome. Despite being based exclusively on clinical criteria, the diagnosis of major depression leads to valid predictions concern¬ ing heritability, clinical manifestations, natural history, and re¬ sponse to treatment. Although the psychological pain of the dis¬ order is perhaps the cruelest symptom, patients with affective illness also manifest symptoms suggestive of abnormalities in hy¬ pothalamic loci controlling appetite, sexual function, circadian rhythms, and anterior pituitary function. In many cases, major depression is a recurrent illness, consisting of either recurrent de¬ pressive episodes alone (unipolar affective illness, also called major depression) or recurrent manic and depressive episodes (bipolar disorder). Episodes of major depression also may be superim¬ posed on a more chronic, indolent depressive process (dysthymia) or associated with certain personality disorders, resulting in socalled double depressions, or may occur within the context of other psychiatric disorders or medical conditions. In the latter case, the diagnosis of organic mood syndrome may be made. Data from adoption and twin studies strongly suggest that vulnerability to mood disorders is heritable, whereas environ¬ mental factors are required for phenotypic expression of these illnesses. A putative linkage marker for bipolar illness has been

identified on chromosome 18,1 although several previous candi¬ date markers were not confirmed with subsequent study. One of the factors hampering the search for such markers is the lack of specific biological abnormalities in depressive illness, which would make phenotype definition more reliable. The diagnosis is made by carefully validated clinical criteria based on the evalua¬ tion of psychologic and physiologic symptoms. The standard di¬ agnostic criteria in the United States are those of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition,2 which incorporates clinical signs of physiologic disturbances and psy¬ chologic symptoms. Clinical observations strongly suggest that the principal pathophysiologic alterations in major depressive syndrome re¬ flect changes in neuroendocrine regulation. Thus, major depres¬ sive illness is characterized by either anorexia or hyperphagia, decreased libido and menstrual irregularities, early morning awakening, an apparent phase advance of rapid eye movement (REM) sleep and body temperature rhythms, and a diurnal vari¬ ation in mood. Moreover, the finding of sustained hypercortisolism in patients with major depression3-7 represents one of the best validated and most completely studied somatic abnormali¬ ties in biologic psychiatry. Other neuroendocrine abnormalities observed in depressed patients include blunted thyrotropin (TSH) responses to thyrotropin-releasing hormone (TRH),8 hy¬ persecretion of growth hormone (GH),9 and partial neurogenic diabetes insipidus.10

SPECIFIC NEUROENDOCRINE ABNORMALITIES IN PATIENTS WITH MAJOR DEPRESSIVE ILLNESS HYPOTHALAMIC-PITUITARY-ADRENAL AXIS

The existence of significant hypercortisolism in patients with major depression has been demonstrated by a number of inde¬ pendent measures, including estimation of cortisol production rate,3 serial sampling of the diurnal cortisol secretory pattern,4 urinary free cortisol excretion,5 and escape of plasma cortisol lev¬ els from dexamethasone suppression.6 7 Studies suggest that the hypercortisolism reflects a defect at or above the level of the hy¬ pothalamus that results in the hypersecretion of corticotropin re¬ leasing hormone (CRH).1112 Thus, depressed patients manifest elevated plasma cortisol levels in association with an attenuated response of plasma corticotropin (ACTH) to the administration of exogenous CRH. This finding suggests a normal response of the pituitary corticotrope cell to cortisol negative-feedback in de¬ pression and, thus, a suprapituitary locus of hypercortisolism. These attenuated ACTH responses to CRH contrast with those observed in patients with Cushing disease, which generally are augmented despite profound hypercortisolism,12 suggesting a loss of pituitary responsiveness to the negative feedback of corti¬ sol. Moreover, depressed patients demonstrate increased adreno¬ cortical responsiveness to ACTH, as assessed either directly after ACTH infusions13 or indirectly from the relative responses of ACTH and cortisol to CRH infusion.1112 This increased adreno¬ cortical responsiveness to ACTH is consistent with the idea that the depressive process is associated with the development of adrenal hyperplasia because of prolonged hyperstimulation. This explains the finding that basal plasma ACTH levels tend to be normal in depression, because smaller amounts of ACTH would be required to generate the same cortisol response from hyper¬ plastic compared with normoplastic adrenal glands. Direct measurements of CRH have been made in patients with depressive illness. Because CRH levels in peripheral blood are low and may reflect secretion from peripheral sites as well as any putative hypothalamic release, most studies have focused on measuring CRH levels in the cerebrospinal fluid (CSF). These studies have suggested that CSF CRH levels are either frankly elevated14 15 or are inappropriately elevated for the degree of hy¬ percortisolism manifested by these patients.16 CSF CRH levels decrease after successful treatment with electroconvulsive ther-

Ch. 196: Psychiatric-Hormonal Interrelationships apy17 and antidepressants such as fluoxetine.18 Preliminary data using sequential sampling of CSF through lumbar catheters tend to confirm these findings (Fig. 196-1). Nevertheless, some inves¬ tigators have reported decreased CSF CRH levels in depressed patients. These differences may reflect the existence of distinct syndromes of depression, with patients having classic melan¬ cholic depression showing evidence of CRH hypersecretion and those with more “atypical'' symptoms of fatigue, hyperphagia, hypersomnia, and mood reactivity having a pathologic decrease in CRH secretion.16 The existence of such pathophysiologic dis¬ tinctions remains to be definitively established, but is an area of active investigation because of the potential for identifying bio¬ logical markers that may be useful in diagnosis and in genetic studies. The putative hypersecretion of CRH in melancholic depres¬ sion is supported by data obtained in experimental animals that the intracerebroventricular administration of CRH initiates a se¬

ries of complex physiologic and behavioral changes classically associated with stress (and depression). These include hypercortisolism,19 as well as activation of the sympathetic nervous sys¬ tem,20 decreased feeding,21 hypothalamic hypogonadism22 with decreased sexual behavior,23 and context-dependent changes in motor activity.24,25 The possibility that decreases in CRH may ac¬ count for symptoms such as fatigue, hyperphagia, and hyper¬ somnia in "atypical" depressions is under study. HYPOTHALAMIC-PITUITARY-GONADAL AXIS

The observation of a female preponderance in the preva¬ lence of unipolar depression26 stimulated interest in the potential role of gonadal dysfunction in the pathophysiology of this disor¬ der. Indeed, early studies showed alterations in luteinizing hor¬ mone (LH) secretion in postmenopausal women with depres¬ sion.27 Moreover, major depression is frequently associated with

FIGURE 196-1.

B

TIME (H)

1697

Effect of electroconvulsive treatment (ECT) on pattern of cerebrospinal fluid (CSF) immunoreactive corticotropinreleasing hormone (IR-CRH) measured by serial sampling over 30 hours (A), and plasma cortisol measured every 30 min dur¬ ing study (B), in a 28-year-old white woman with melancholic depression. Patient was medication free for both pretreatment and posttreatment studies. Shaded area in A rep¬ resents mean ± 1 SD of sinusoidal fit for di¬ urnal rhythm of CSF IR-CRH in six healthy volunteers (Kling MA, Geracioti TD, De Beilis MD, et al. A significant diurnal rhythm of CSF immunoreactive corticotropin-releasing hor¬ mone in healthy volunteers: physiologic im¬ plications. ] Clin Endocrinol Metab 1994;79: 233.). Before ECT, increased CSF IR-CRH values in early morning hours are superim¬ posed on apparently normal diurnal rhythm and are associated with, and slightly lag, in¬ creased plasma cortisol values during late evening and early morning hours. After ECT, no such elevations in early morning CSF IRCRH levels are observed whereas the plasma cortisol pattern reverts toward normal. (Fig¬ ure is from Kling MA, Geracioti TD, Licinio ], et al. Effects of electroconvulsive therapy on the CRH-ACTH-cortisol system in melancholic de¬ pression: preliminary findings. Psychopharmacol Bull 1994;30:489.)

1698

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

loss of libido and, in some women, with menstrual disturbances, including secondary amenorrhea. Luteinizing hormone-releas¬ ing hormone (LHRH) secretion is believed to be under the tonic inhibitory control of /3-endorphin secreted by the arcuate nucleus of the hypothalamus.28 The injection of CRH into the arcuate nucleus appears to stimulate /3-endorphin secretion from these neurons,2 providing a possible mechanism for the inhibition of reproductive function associated with intracerebroventricular administration of this peptide. Moreover, glucocorticoids inhibit reproductive function at the hypothalamic, pituitary, and adre¬ nal levels.28 Hence, the pituitary-adrenal activation associated with depression can potentially act at multiple levels to inhibit both behavioral and physiologic aspects of reproductive function. HYPOTHALAMIC-PITUITARY-THYROID AXIS

A number of disturbances in the regulation of thyroid func¬ tion have been reported in depression.29 Most notable are a blunted response of TSH to exogenous TRH administration8 and an attenuation of the normal nocturnal rise of plasma TSH lev¬ els.30 However, while basal plasma thyroxine (T4) levels tend to be normal in depression, controversy exists about whether these above abnormalities represent a primary central nervous system (CNS) disturbance that causes the hypersecretion of TRH, or whether thyrotrope responsiveness to TRH is impaired either by some nonspecific pituitary dysfunction or by increased secretion of some factor inhibitory to thyrotrope function. Exogenous thy¬ roid hormones in physiologic doses (e.g., 25-50 triiodothyro¬ nine [T3]/d) can augment responses to antidepressants.31,32 It has been argued that these replacement doses act by suppression of the effects of thyroid hormone on the CNS,29 because most of the T3 in brain derives from intracellular deiodination of peripherally secreted T4/ rather than direct transport of T3 from blood. Alter¬ natively, it has been proposed that these doses correct a putative underlying alteration of /3-adrenoceptor function in depression.33 Glucocorticoids have a number of effects on thyroid func¬ tion, including a tendency to attenuate the responsivity of the thyrotrope to TRH. Moreover, Cushing syndrome is associated with a pattern of thyroid dysfunction similar to that observed in depression, including an attenuation of the nocturnal TSH rise, as well as a shift in thyroid hormone metabolism that causes de¬ creased peripheral conversion of T4 to T3. Both of these findings are manifestations of the so-called euthyroid sick state, a phe¬ nomenon that occurs in depression.34 However, the precise rela¬ tionship, if any, between hypothalamic-pituitary-adrenal dys¬ function and these thyroid alterations, and their clinical significance, remains to be fully elucidated (see Chap. 36). GROWTH HORMONE

A number of studies suggest alterations in GH regulation in depression. The GH responses to insulin-induced hypoglycemia, amphetamine, L-dopa, and clonidine are attenuated. However, the regulation of GH secretion involves the influences of a multi¬ plicity of neurotransmitters (e.g., norepinephrine, dopamine, se¬ rotonin, 7-aminobutyric acid, and acetylcholine) that modulate the secretion of growth hormone releasing hormone (GHRH) and the release-inhibiting hormone, somatostatin (see Chap. 14). Moreover, GH secretion is subject to negative-feedback control by the somatomedins, most notably insulin-like growth factor type I (IGF-I, somatomedin C). The mean 24-hour plasma GH levels are increased in major depression, mostly because of an increased daytime or nonsleeprelated secretion that more than counterbalances a decrease in sleep-dependent secretion.9 These results are consistent with the notion that GH secretion tends to be increased in depression. Data suggest that this putative hypersecretion of GH in depres¬ sion derives, as does the hypercortisolism in this disorder, from a suprapituitary disturbance. Thus, depressed patients show atten¬ uated responses of GH to GHRH in association with increased

basal IGF-I levels,35,36 providing further evidence for increased GH functional activity and intact somatotrope feedback respon¬ siveness. The CSF levels of somatostatin are consistently reduced in depression,37 suggesting that a relative deficiency of this pep¬ tide within the CNS may contribute to dysregulation of GH se¬ cretion in this disorder. The observation of a negative correlation between postdexamethasone cortisol levels and CSF somato¬ statin levels in depressed patients,38 and of decreased CSF so¬ matostatin levels in Cushing syndrome patients,39 suggests that hypercortisolism may, likewise, contribute to this putative so¬ matostatin deficiency in depression. OTHER NEUROENDOCRINE ABNORMALITIES

Because the secretion of many anterior pituitary hormones is regulated by classic monoaminergic neurotransmitters such as norepinephrine, serotonin, and acetylcholine, all of which have been implicated in the pathophysiology of depression, a number of investigators have advocated using anterior pituitary secretion as an indication of the functional status of these classic neuro¬ transmitter systems in the brains of patients with affective disor¬ ders. The studies of GH responses to provocative stimuli consti¬ tute one example of such an approach. Others have focused on prolactin as a potential index of serotonin function in depression because of evidence that serotonin is excitatory to prolactin se¬ cretion. Such studies would, in theory, be of importance in view of the use of serotonin uptake inhibitors in the treatment of de¬ pression. However, such approaches are subject to limitations, such as those indicated above with respect to GH, because the hypothalamic regulation of prolactin, like that of other anterior pituitary hormones, is complex and multidetermined. Moreover, monoamine transmitters such as serotonin are present in multiple cell groups in the brain, and studies of anterior pituitary hormone responses are predicated on the assumption that dys¬ regulation of such monoamine systems includes the hypotha¬ lamic cell groups as well as those elsewhere in the brain.

ANOREXIA NERVOSA Anorexia nervosa is a syndrome characterized by decreased food intake and increased motor activity in the obsessive pursuit of thinness (see Chap. 127). A related condition, bulimia nervosa, is characterized by episodic food binges and purging and may either coexist with anorexia or occur as a separate entity without weight loss. These syndromes occur predominantly in young women, with an age of onset near the time of puberty. Neuroen¬ docrine abnormalities are among the cardinal manifestations of anorexia nervosa. The best described of these include hypercor¬ tisolism,40-42 hypothalamic hypogonadism,40-42 alterations in the secretion of plasma and CSF vasopressin,43 and decreased meta¬ bolic indices including reduced thyroid function.44 Some of these changes have also been observed in patients with bulimia, as de¬ tailed later.

SPECIFIC NEUROENDOCRINE ABNORMALITIES IN PATIENTS WITH EATING DISORDERS HYPOTHALAMIC-PITUITARY-ADRENAL AXIS

The underweight phase of anorexia nervosa is associated with profound hypercortisolism40-42; plasma and urinary free cortisol levels overlap with those seen in Cushing disease and often exceed those seen in all but the most severe depressions. However, in distinction to Cushing syndrome, the diurnal rhythm of plasma cortisol levels is preserved, although attenu¬ ated.45 This pattern is comparable with that observed in extreme starvation. Pituitary-adrenal responses to CRH are qualitatively similar to those observed in depression and further suggest a CNS source of hypercortisolism. Thus, ACTH responses to CRH are attenuated in underweight anorexics in the face of elevated

Ch. 196: Psychiatric-Hormonal Interrelationships basal plasma cortisol levels (see Fig. 196-2), compatible with nor¬ mal corticotrope responsiveness to cortisol negative-feedback, and suggesting that the hypercortisolism derives from an abnor¬ mality at or above the hypothalamus that causes the hypersecre¬ tion of CRH.46 A relatively greater response of cortisol compared with that of ACTH after CRH administration suggests that a de¬ gree of adrenal hyperresponsiveness to ACTH has developed during the course of this illness. Finally, as in depression, basal plasma ACTH levels are not significantly different from normal (Fig. 196-2), suggesting that the development of adrenal hyper¬ responsiveness causes a lower ACTH requirement, to maintain the degree of hypercortisolism observed in these patients, than that required in persons with normal adrenal responsiveness. With short-term (3-4 weeks) recovery of normal or near¬ normal weight, plasma and urinary free cortisol levels return to normal,46 suggesting resolution of the central defect that gener¬ ates the hypercortisolism in the underweight phase. However, ACTH responses to CRH remain attenuated (see Fig. 196-2). Cor¬ tisol responses to CRH are normal in these patients, suggesting persistence of the apparent adrenal hyperresponsiveness to ACTH observed during the underweight phase. In patients stud¬ ied after longer periods of weight recovery (> 6 months), both ACTH and cortisol responses to CRH were normal, suggesting that these abnormalities are not inherent pathophysiologic fea¬ tures of the illness, but appear to be related to the time of the weight loss and its immediate aftermath. Similar findings have been obtained after administration of the glucocorticoid receptor antagonist RU 486,47 which further suggests that the increased cortisol output in underweight patients is not purely because of glucocorticoid resistance. In further support of the hypothesis that hypercortisolism reflects hyperstimulation of the pituitary-adrenal axis by CRH

1699

are data that CSF CRH levels are significantly elevated in un¬ derweight anorexics.48 Although CSF CRH levels partially nor¬ malized after the short-term correction of weight loss and seemed fully normalized in patients studied after 6 or more months of weight recovery, CSF CRH levels correlated positively with de¬ pression ratings in these weight-corrected subjects.48 This finding reflected the fact that some patients remained both depressed and hypercortisolemic after correction of the weight loss, which is associated with the persistence of higher levels of CRH in the CSF. Patients with bulimia tend to show more subtle evidence of disturbed pituitary-adrenal function than do underweight pa¬ tients with anorexia nervosa. Normal-weight patients with bu¬ limia (studied at > 80% average body weight) show a higher rate of nonsuppression of plasma cortisol in response to 1-mg over¬ night dexamethasone administration than do control subjects, but this frequency is considerably less than that in underweight anorexic patients.49 Evidence of increased ACTH and cortisol se¬ cretion has been shown in normal-weight bulimic patients in as¬ sociation with attenuated ACTH and cortisol responses to CRH administration,50 although some have found normal ACTH and cortisol responses to CRH.46 Further studies are required to clar¬ ify these apparent discrepancies.

ALTERATIONS IN ARGININE VASOPRESSIN SECRETION

Patients with anorexia nervosa demonstrate a number of ab¬ normalities in the regulation of arginine vasopressin (AVP) se¬ cretion.43 In particular, the underweight phase of the illness is associated with gross defects in the response of plasma AVP to osmotic stimuli such as hypertonic saline infusion. Hence, an¬ orexic patients manifest either low basal levels of AVP that show

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1816

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

swelling, which produces elevation, and for atrophy. Although the direct ophthalmoscope does not provide a stereoscopic view, with experience, elevation of the optic disc is readily appreciated. In papilledema, there is edema of the optic discs due to increased intracranial pressure. On examination, there is a bilateral eleva¬ tion of the optic discs with a diminished or absent central depres¬ sion (see Fig. 209-20). When axons become swollen, axonal transport is interrupted. The exact mechanism for this interrup¬ tion is unknown, but it is probably a result of mechanical obstruc¬ tion caused by increased cerebrospinal fluid pressure compress¬ ing the optic nerve just behind the globe. The blood vessels, particularly the small vessels lining the rim of the disc, appear to be engorged, and spontaneous venous pulsations usually are absent. Flame-shaped hemorrhages may also be found along the disc margin, which is obscured by the swollen axons. In the early stages of papilledema, visual acuity either is not affected or is only mildly diminished, and the blood vessels do not leak fluo¬ rescein or cause hard exudate deposits in the retina. The differential diagnosis of papilledema is extensive, and includes systemic and ocular conditions. Endocrine conditions, including hyperthyroidism, parathyroid deficiency, Addison dis¬ ease, pregnancy, and diabetes, may cause papilledema. Pseudotu¬ mor cerebri, a common cause of disc elevation, refers to papille¬ dema associated with elevated cerebrospinal fluid pressure in the presence of normal or small-sized ventricles by computed tomog¬ raphy and normal cerebrospinal fluid composition. It occurs in hypoparathyroidism and is associated with the typical clinical manifestations of papilledema.49 Sometimes, this finding may be evident years before more severe symptoms, such as seizures, appear. Other causes of pseudotumor cerebri include systemic corticosteroid therapy, oral contraceptive use, pregnancy, and obesity. Hyperparathyroidism also has been associated with unilat¬ eral papilledema. The pathogenesis of this condition appears to be compression of the optic nerve secondary to increased bone vascularity.50 Papillitis or optic neuritis is another cause of optic disc edema. It is primary inflammation of the optic nerve, is usually unilateral, and causes an acute impairment of vision. Greater than 60% of patients with optic neuritis will develop multiple sclerosis. Endocrine causes of optic neuritis include diabetes mellitus and thyroid disorders. Another cause of optic disc edema is ischemic optic neuropa¬ thy. This condition results from an ischemic infarction of the in¬ terior portion of the optic nerve. It causes acute visual loss. One of its many associations is diabetes mellitus. Optic nerve drusen are hyaline-like bodies within the optic nerve. If they are superficial, the drusen look like yellow globules clustered on the surface of the optic nerve head. If they are lo¬ cated deeper within the nerve head, they are not directly visible and are a cause of pseudopapilledema. Optic atrophy is recognized by optic disc pallor, with associ¬ ated changes in retinal vessels, that is accompanied by visual dys¬ function. Pathologically, this is due to shrinkage of the optic nerve as a result of any process that causes degeneration of the axons in the anterior visual system. Many endocrine and meta¬ bolic abnormalities are associated with optic atrophy. Finally, the term optic nerve hypoplasia refers to an optic disc that is underdeveloped. The disc is usually pale and smaller than normal. It is one of the causes of decreased vision or blindness in newborn infants. Septo-optic dysplasia, or de Morsier syndrome, is optic nerve hypoplasia associated with midline cerebral de¬ fects, such as absence of the septum pellucidum. Optic nerve hy¬ poplasia is also associated with various pituitary abnormalities, including dwarfism, diabetes insipidus, and neonatal hypoglyce¬ mia.51-53 It is standard practice for an ophthalmologist who is caring for an infant with optic nerve hypoplasia to obtain a mag¬ netic resonance imaging study to rule out an absent septum pel¬ lucidum and to refer the patient for a pediatric endocrine evaluation.

FIGURE 209-20.

Patient with papilledema; there is swelling of the optic disc as a result of increased intracranial pressure. Note the loss of the central cup.

OCULAR EFFECTS OF METABOLIC DISEASES Many metabolic abnormalities are accompanied by signifi¬ cant ocular changes (Table 209-2). In some cases, changes noted in the eye are the first indication of the underlying metabolic ab¬ normality, and may lead directly to the diagnosis. For example, congenital cloudy corneas suggest the presence of one of the mu¬ copolysaccharidoses, whereas lens dislocation suggests homocystinuria (see Chap. 185) or Marfan syndrome. Examination of the fundus in patients with hyperlipidemias sometimes reveals arteries that appear creamy white instead of blood red (particularly in patients with hypertriglyceridemia; see Table 209-2 and Chap. 157). Mucolipidoses and glycogen storage diseases54 manifest a cherry-red spot, indicating an abnormal de¬ position in the retina that spares the central fovea and creates the red-centered white appearance. Many of these findings can be identified readily by an expe¬ rienced clinician, without sophisticated instrumentation. Fre¬ quently, this responsibility falls to the physician who first exam¬ ines the patient. Thus, it is essential that endocrinologists be skilled and diligent in the basic ocular examination.55 When a particular finding or lesion has been identified or is suspected, a more detailed and complete ocular examination can be con¬ ducted by an ophthalmologist.

EFFECTS OF BLINDNESS ON THE ENDOCRINE SYSTEM The bulk of the interaction of endocrinology with ophthal¬ mology consists of the effect of the endocrine system on the eyes. Blindness is a case in which an ocular condition can have an effect on the endocrine system. The role of light in synchronizing the circadian rhythms of various hormones has been investigated by researchers studying blind subjects. No difference was found in the diurnal rhythms of follicle-stimulating hormone and testosterone in a study com¬ paring these rhythms in blind and sighted men. However, there was an apparent “phase shift” in circulating cortisol levels in the blind subjects, and the cortisol cycle appeared to be independent of the follicle-stimulating hormone and testosterone diurnal cy¬ cles.56 Peak levels of serum cortisol in these individuals occurred between 8:00 am and 4:00 pm, whereas in sighted subjects, peak

Ch. 209: The Eye in Endocrinology levels occurred at 8:00 am and progressively declined between 8:00 AM and 4:00 PM. Blindness also appears to have effects on other hormonal levels and functions. Long-term testicular function was altered when 1-month-old rats were blinded.57 Testosterone secretion in blinded rats was consistently lower than that in control animals. In humans, blindness was reported to be associated with de¬ creased urinary excretion of 17-ketosteroids and gonadotropins, and this effect was more pronounced when blindness occurred before puberty. Pineal gland activity (see Chap. 12) appeared to mediate the decrease in gonadal function associated with blindness.

REFERENCES 1 Feldman F, Bain J, Matuk A. Daily assessment of ocular and abnormal vari¬ ables throughout the menstrual cycle. Arch Ophthalmol 1978; 96:1835. 2. Leach NO, Wallis NE, Lothringer LL, Olson JA. Corneal hydration changes during the normal menstrual cycle. J Reprod Med 1971;6:15. 3. Sunness J. The pregnant woman's eye. Surv Ophthalmol 1988; 32: 219,228,231,233. 4. Pritchard JA, MacDonald PC, Grant NF. Williams obstetrics, ed 17. Nor¬ walk, CT: Appleton-Century-Crofts, 1985:137. 5. Sanke RL. Blepharoptosis as a complication of pregnancy. Ann Ophthalmol 1984; 16:720. 6. Schachner SM, Reynolds AC. Horner's syndrome during lumbar epidural analysis for obstetrics. Obstet Gynecol 1982;59(Suppl):315. 7. Landesman R. Retinal and conjunctival vascular changes in normal and toxemic pregnancy. Bull NY Acad Med 1955;31:376. 8. Millodot M. The influence of pregnancy on the sensitivity of the cornea. Ophthalmology 1977;61:646. 9. Horven 1, Gjonnaess H. Corneal indentation pulse and intraocular pressure in pregnancy. Arch Ophthalmol 1974;91:92. 10. Dieckmann WJ. The toxemias of pregnancy, ed 2. St Louis: CV Mosby 1952:240. 11. Sadowsky A, Serr DM, Landau J. Retinal changes and fetal prognosis in the toxemias of pregnancy. Obstet Gynecol 1956; 8:426. 12. Fry WE. Extensive bilateral retinal detachment in eclampsia with complete reattachment. Arch Ophthalmol 1929; 1:609. 13. Hallum AV. Eye changes in hypertensive toxemia of pregnancy. JAMA 1936; 106:1649. 14. Arvlkumaran S, Gibb DMF, Rauf M, et al. Transient blindness associated with pregnancy-induced hypertension. Br J Obstet Gynaecol 1988; 92:847. 15. Beck RW, Gamel JW, Willcourt RJ, et al. Acute ischemic optic neuropathy in severe preeclampsia. Am J Ophthalmol 1980; 90:342. 16. Bedrossian R. Central serous retinopathy and pregnancy. (Letter) Am J Ophthalmol 1974;78:152. 17. Digre KB, Varner MW, Corbett JJ. Pseudotumor cerebri and pregnancy. Neurology 1984;34:721. 18. Maycock RL, Sullivan RD, Greening RR, Jones R. Sarcoidosis and preg¬ nancy. JAMA 1957,164:158. 19. Snyder DA, Tessler HH. Vogt-Koyanayi-Harada. Am J Ophthalmol 1980;90:69. 20. Cassar J, Hamilton AM, Kohner EM. Diabetic retinopathy in pregnancy. Int Ophthalmol Clin 1978; 18:179. 21. Ohrt V. The influence of pregnancy on diabetic retinopathy with special regard to the reversible changes shown in 100 pregnancies. Acta Ophthalmol (Copenh) 1984,'62:603. 22. Moloney JBM, Drury ML The effect of pregnancy on the natural course of diabetic retinopathy. Am J Ophthalmol 1982; 93:745. 23. Seddon JM, MacLaughlin DT, Albert PM, et al. Uveal melanomas present¬ ing during pregnancy and the investigation of estrogen receptors in melanomas. Br J Ophthalmol 1982; 66:695. 24. Warren DW: Hormonal influences on the lacrimal gland. Int Ophthalmol Clin 1994:34( 1): 19. 25. Radnot M, Follman P. Ocular side-effects of oral contraceptives. Ann Clin Res 1972;5:197. 26. Davidson SI. Reported adverse effects of oral contraceptives on the eye. Trans Ophthalmol Soc UK 1971;91:561. 27. Stowe GC, Zakov ZN, Albert DM. Central retinal vascular occlusions as¬ sociated with oral contraceptives. Am J Ophthalmol 1978;86:798. 28. Svarc Ed, Werner D, Isolated retinal hemorrhages associated with oral contraceptives. Am J Ophthalmol 1977;84:50. 29. Rock T, Dinar Y, Romem M. Retinal periphlebitis after hormonal treat¬ ment. Ann Ophthalmol 1989; 21:75. 30. Giovannini A, Consolani A. Contraceptive-induced unilateral retinopa¬ thy. Ophthalmologica 1979; 179:302. 31. VokeJ. Colour vision and the pill. Nurs Times 1974;70:139. 32. Gerner E. Ocular toxicity of tamoxifen. Ann Ophthalmol 1989; 21:420. 33. Netland PA, Dallon RL. Thyroid ophthalmopathy. In: Albert GM, Jakobiec FA, eds. Principles and practice of ophthalmology, vol 5. Philadelphia: WB Saunders, 1994:2937. 34. Roy FH. Ocular differential diagnosis, ed 5. Philadelphia: Lea & Febiger, 1993:289,316.

1817

35. Mahto RS. Ocular features of hypoparathyroidism. Br J Ophthalmol 1972;56:546. K 36. Blake J. Eye signs in idiopathic hypoparathyroidism. Trans Ophthalmol Soc UK 1976; 96:448. 37. Lundberg PO. Hereditary myopathy, oligophrenia, cataract, skeletal ab¬ normalities and hypergonadotropic hypogonadism. Eur Neurol 1973; 10:261. 38. Chlack LT Jr. Mechanism of "hypoglycemic'' cataract formation in the rat lens. 1. The role of hexokinase instability. Invest Ophthalmol 1975; 14:746. 39. Merin S, Crawford JS. Hypoglycemia and infantile cataract. Arch Oph¬ thalmol 1971; 86:495. 40. Saadat H, Bahrami Y. Blindness: a postoperative complication of pheochromocytoma. Virginia Med 1977;104:38. 41. Hagler WS, Hyman BN, Waters WC. Von Hippel's angiomatosis retinae and pheochromocytoma. Trans Am Acad Ophthalmol Otolaryngol 1971; 75:1022. 42. Brown AC, Pollard ZF, Jarret H. Ocular and testicular abnormalities in alopecia areata. Arch Dermatol 1982; 118:546. 43. Chang RJ, Davidson BJ, Carlson HE, et al. Hypogonadotropic hypogo¬ nadism associated with retinitis pigmentosa in a female sibship: evidence for go¬ nadotropin deficiency. J Clin Endocrinol Metab 1981; 53:1179. 44. Edwards JA, Sethi PK, Scoma AJ, et al. A new familial syndrome charac¬ terized by pigmentary retinopathy, hypogonadism, mental retardation, nerve deaf¬ ness and glucose intolerance. Am J Med 1976;60:23. 45. Rizzo JF, Berson EL, Lessell S. Retinal and neurologic findings in LaurenceMoon-Bardet-Biedl phenotype. Ophthalmology 1986;93:1452. 46. Lee ES, Galle PC, McDonough PG. The Laurence-Moon-Bardet-Biedl syndrome. Case report and endocrinologic evaluation. J Reprod Med 1986;31:353. 47. Brownlie BEW, Newton OAG, Singh SP. Ophthalmopathy associated with primary hypothyroidism. Acta Endocrinol (Copenh) 1975;79:69L 48. Pellock JM, Behrens M, Lewis L, et al. Kearn's Sayre syndrome and hypo¬ parathyroidism. Ann Neurol 1978;3:455. 49. Bajandas FJ, Smith JL. Optic neuritis in hypoparathyroidism. Neurology 1976; 26:451. 50. Murphy KJ. Papilloedema due to hyperparathyroidism. Br J Ophthalmol 1974;58:694. 51. Costin G, Murphree AL. Hypothalamic-pituitary function in children with optic nerve hypoplasia. Am J Dis Child 1985; 139:249. 52. Hoyt WF, Koplan SL, Grumbach MM, et al. Septo-optic dysplasia and pituitary dwarfism. Lancet 1970; 1:893. 53. Sheridan SJ, Robb RM. Optic nerve hypoplasia and diabetes insipidus. J Pediatr Ophthalmol 1978; 15:82. 54. Collins JE, Leonard JV. Hepatic glycogen storage disease. Br J Hosp Med 1987;38:168. 55. Newell FW. Ophthalmology. Principles and concepts, ed 5. St Louis: CV Mosby, 1985:165. 56. Bodenheimer S, Winter JSD, Faiman C. Diurnal rhythms of serum gonad¬ otropins, testosterone, estradiol and cortisol in blind men. J Clin Endocrinol Metab 1973;37:472. 57. Kinson G, Liu CC. Long-term testicular responses to blinding in rats. Life Sci 1974; 14:2179.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

210_

OTOLARYNGOLOGY AND ENDOCRINE DISEASE STEPHEN G. HARNER Endocrine diseases can manifest themselves in four ways that are of concern to the otolaryngologist. The first is when head and neck manifestations are a major component of the disease (e.g., the hearing loss that occurs in Pendred syndrome) (see Chap. 46). The second is when certain findings are commonly associated with the disease, but are not invariably present (e.g., mixed hearing loss and Paget disease). Another situation of con¬ cern is when certain findings are occasionally present and are thought to be a part of the disease process, but the relationship is unclear (e.g., facial palsy in pregnancy). Finally, there are those associations between clinical findings and endocrine disease that have been accented but may be no more than a chance relation¬ ship (e.g., Meniere disease and diabetes mellitus). A thorough otolaryngologic work-up includes the patient's history; a specialized physical examination; tests, such as audi¬ ometry, electronystagmography, posturography, and brainstem evoked response audiometry; appropriate radiographic studies;

1818

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

endoscopic examination; voice analysis; and biopsy. The features evaluated include hearing loss, voice change, nasal obstruction, neck masses, and dizziness. On this basis, the etiology of the dis¬ order and the appropriate mode of therapy are determined.

HYPOTHALAMUS Several of the processes that cause altered hypothalamic ac¬ tivity appear to be associated with a vasomotor rhinitis. More¬ over, some genetically induced syndromes affect the hypothala¬ mus and have other associated otolaryngologic findings. Laurence-Moon-Biedl syndrome (a syndrome characterized by retinitis pigmentosa, polydactylism, mental defects, and hypogo¬ nadism) and Alstrom syndrome (an autosomal recessive disorder marked by hypogonadism, atypical retinitis pigmentosa, and di¬ abetes mellitus) often are associated with obesity and sensorineu¬ ral hearing loss as well (Fig. 210-1). Deafness is associated with diabetes insipidus in the DIDMOAD syndrome1 (diabetes insipi¬ dus, diabetes mellitus, optic Atrophy, and deafness). In olfactorygenital dysplasia (Kallmann syndrome), anosmia is the primary feature (see Chap. 114). Craniopharyngiomas (see Chap. 13) are congenital cysts that arise in the basisphenoid and may erode into the pituitary and hypothalamus. This tumor usually appears as a cystic mass in the sphenoid and nasopharynx; it may be de¬ tected on the basis of clinical signs or on an imaging study of the sinuses. The treatment options include transseptal and transnasal resections.

PITUITARY GLAND In acromegaly, the tongue is increased in size. Also, most affected patients have a change in voice that consists of decreased pitch and a huskier sound. Occasionally, the recurrent laryngeal nerve is stretched, causing vocal cord paralysis; if there is no spontaneous improvement, the voice change can be treated by injection of the vocal cord with Teflon. A patient may develop diabetes insipidus as a result of trauma to the skull base secondary to an operation or a disease process that is otolaryngologic in origin. Large pituitary tumors can infiltrate the sinuses. The major interest of the otolaryngologist in pituitary dis¬ ease has been patient management. The transseptal-transsphenoidal surgical approach is primarily a team procedure in which the rhinologist provides access for the neurosurgeon.2 This type of cooperative effort has markedly improved the management and outcome of these patients (see Chap. 25).

125

250

500

1000

THYROID With hyperthyroidism (thyrotoxicosis. Graves disease), a pa¬ tient may have a goiter and Graves ophthalmopathy. Often, the otolaryngologist is involved in the surgical management of the ophthalmopathy. Transantral orbital decompression is the most widely used surgical procedure for this condition.3 This proce¬ dure allows removal of the inferior and medial orbital walls, thereby providing space for the excess tissue in the sinuses. No external incisions are necessary, and complications are minimal (see Chap. 42). A number of pertinent findings are associated with myx¬ edema (hypothyroidism). There may be a conductive hearing loss secondary to serous otitis media (Fig. 210-2). Also, there may be a sensorineural hearing loss. The conductive loss usually resolves with treatment, but the sensorineural loss generally persists. Generalized mucosal edema produces nasal obstruction, thick¬ ened tongue, facial edema, hoarseness, and slowed speech. Al¬ though diagnosis is rarely a problem, if doubt arises, biopsy of the nasal mucosa will reveal an increase in acid mucopolysaccharide content. Carcinoma of the thyroid may present as a mass in the gland, a neck mass of unknown cause, or a cause of vocal cord paralysis. Vocal cord paralysis secondary to recurrent laryngeal nerve in¬ volvement or surgical trauma often will respond to Teflon injec¬ tion, thyroplasty, arytenoidectomy, or other appropriate ther¬ apy.4 When the tumor is under control, it is customary to wait 6 months before instituting therapy. However, if the prognosis is poor and the patient is having trouble with aspiration or a weak voice, the therapy is done immediately. Acute bacterial thyroid¬ itis (see Chaps. 45 and 208) may be associated with a large neck mass, hoarseness, vocal cord paralysis, or a compromised airway. In such cases, tracheostomy or vocal cord injection may be indicated. An infant with congenital hypothyroidism (cretinism) usu¬ ally presents with a severe sensorineural hearing loss (see Fig. 210-1), a broad flat nose, and a high-pitched cry5 (see Chap. 46). Correction of the hypothyroidism will improve the voice, but the hearing loss will remain. In Pendred syndrome6—a rare congen¬ ital syndrome associated with bilateral sensorineural hearing loss and a euthyroid goiter—the hearing loss involves highfrequency sound primarily, is of varying severity, and is nonreversible. The goiter results from a defect in the organification of the thyroid hormone. Thyroid function tests are normal, and the diagnosis is confirmed by using a perchlorate washout test. There is no treatment, but genetic counseling may be appropriate.7 An¬ other nontreatable syndrome—Hollander syndrome—is charac-

2000

4000

8000

Speech Audiometry Type of speech signal

FIGURE 210-1.

Typical sensori¬ neural hearing loss, which is equal in both ears. The air and bone re¬ sponses are identical. Notice that bone conduction cannot be tested at intensities greater than 70 dB. Speech reception threshold is the sound intensity at which the subject begins to hear words. Speech dis¬ crimination is the ability to un¬ derstand a list of unrelated words. Sensorineural hearing loss is the most common type of loss. Treat¬ ment usually involves the use of hearing aids and aural rehabilita¬ tion.

62

R_dB I_dB

Most comfortable level

R_dB I_dB

Discomfort level

R_dB I_dB

Speech discrimination scores

60

Right-% at-dB sensation level Right _% at_dB sensation level Left

68

°° .% at_dB sensation level

Left-% at-dB sensation level

Right ear Left ear

Q

Q

X

D

60

Speech reception threshold

Ch. 210: Otolaryngology and Endocrine Disease 125

250

500

lOOO

2000

4000

1819

8000

Speech Audiometry Type of speech signal

30

5

Speech reception threshold

R_dB i

Most comfortable level

R_dB I_dB

Discomfort level

R_dB I_dB

Speech discrimination scores: Right ^ % at

dB sensation level

Right

dB sensation level

% at

Left —12£.% at-dB sensation level Left-% at-dB sensation level

Left ear

X

3

terized by progressive sensorineural hearing loss and euthyroid goiter.

CALCIUM AND PHOSPHATE METABOLISM Patients with hyperparathyroidism may have hearing loss, dysphagia, fasciculations of the tongue, tumors of the facial bones, and lesions of the oral mucosa. The hearing loss is senso¬ rineural and nonreversible (see Fig. 210-1). The lesions seen in the facial bones are called brown tumors (osteitis fibrosa cystica). These lesions are benign, are most often located in the maxilla, and need not be excised unless they cause functional or cosmetic problems. The nodular lesion of the oral mucosa, called epulis, requires no therapy. Hyperparathyroidism is an important com¬ ponent of multiple endocrine neoplasia (MEN) (see Chap. 182). In MEN type 1, the findings may include those of hyperparathy¬ roidism, pituitary tumor, and pancreatic tumor. In MEN type 2A, hyperparathyroidism, pheochromocytoma, and medullary thy¬ roid carcinoma (occasionally presenting as a neck mass) are found. In MEN type 2B, the findings include medullary thyroid cancer, pheochromocytoma, and neuromas involving the mu¬ cosa lining the lips, oral cavity, nose, larynx, and eyes; hyper¬ parathyroidism is rare. These neuromas are histologically benign, but their presence should alert the clinician to the possibility of a MEN syndrome. In any patient suspected of having MEN type 2A or 2B, it is imperative to screen for pheochromocytoma preoperatively. If a secreting pheochromocytoma is present, anes¬ thesia and surgery are exceedingly risky.8 Hypercalcemia that is unrelated to parathyroid malfunction may be seen with malignant lesions involving the head and neck region, or with sarcoidosis (see Chap. 58). Careful head and neck examination should reveal any primary cancer. Sarcoidosis causes many characteristic findings in the head and neck re¬ gion.910 Granular lesions of the nasal mucosa, ulcers of the lar¬ ynx, neck masses, and swelling of the salivary glands are com¬ monly seen. Hypoparathyroidism with hypocalcemia produces nerve irritability, which causes laryngeal stridor, laryngospasm, and a positive Chvostek sign (see Chap. 59). Frequently, this hy¬ poparathyroidism is a sequela of a surgical procedure in the neck. Severe hypocalcemia and hypomagnesemia can cause bilateral vocal cord paralysis.11 Hypophosphatasia, as well as hyperphosphatasia, has been reported to occur in infants found to have an associated hearing loss.12

METABOLIC BONE DISEASE Several metabolic diseases of bone produce significant oto¬ laryngologic findings, one of which is Paget disease of the bone

hr

FIGURE 210-2. An audiogram demonstrates normal hearing in the left ear and conductive hearing loss in the right ear. Notice that the air conduction levels in the right ear are separated from the bone conduc¬ tion markers. The speech reception threshold corresponds to the air con¬ duction levels. Speech discrimina¬ tion scores are normal in both ears. This type of hearing loss usually is associated with some malfunction in the ossicular chain, tympanic mem¬ brane, or external ear canal. Correc¬ tion usually is possible.

(see Chap. 64). This is a disease process that has truly protean manifestations that are revealed in middle and old age. Skull changes are relatively common, as is involvement of the temporal bone. Clinically, a significant number of these patients have hearing loss. Classically, this loss begins as a mixed hearing loss and then becomes purely sensorineural (Fig. 210-3). Moreover, these patients can have tinnitus and vertigo, which seem to be related to the disease.13 Calcitonin therapy may halt the progress of the involvement.14 Osteogenesis imperfecta is a genetically induced disease with varying levels of involvement15 (see Chaps. 65, 69, and 183). Affected patients may have a conductive hearing loss sec¬ ondary to involvement of the ossicular chain. Clinically and his¬ tologically, the condition is identical to otosclerosis. Surgical treatment and use of hearing aids may be necessary. At opera¬ tion, if the incus is involved, it may not be possible to perform a stapedectomy. In fibrous dysplasia (see Chap. 65), the maxilla is the bone most commonly involved in the head (Fig. 210-4). Mass lesions can form anywhere, leading to cosmetic and functional prob¬ lems.16 ]/ These lesions can be debulked or removed, but they have a tendency to recur. Malignant transformation is rare, but is more likely if the patient has been irradiated.18 Osteopetrosis (Albers-Schonberg disease) may have otologic complications, as well. The involvement varies greatly from pa¬ tient to patient, but the temporal bone is commonly affected. Temporal bone disease causes sensorineural and conductive hearing losses. Usually, these are not treatable except with a hearing aid. Moreover, facial paralysis may be seen; this tends to be recurrent, and decompression often is advised. Dental caries occur frequently and are severe. This condition may cause osteo¬ myelitis of the mandible, which is difficult to control.

ADRENAL CORTEX Patients with adrenal insufficiency (Addison disease) may present with sunken eyes, dry tongue, and hyperpigmentation of the skin and tongue (see Chap. 74). Endolymphatic hydrops (Meniere syndrome), dysosmia, and dysgeusia all have been re¬ ported to occur with adrenal insufficiency. Adrenocortical hyper¬ activity (Cushing disease) causes moon facies and prominent su¬ praclavicular fat pads.

PREGNANCY The most common abnormality related to pregnancy is a se¬ vere vasomotor rhinitis. This usually arises in the second or third

1820

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY 125

250

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Speech Audiometry Type of speech signal

75

50

dB

Speech reception threshold

R-dB

Most comfortable level

R_dB I_dB

Discomfort level

R_dB L_dB

Speech discrimination scores

30

Right-% at-dB sensation level Right_% at_dB sensation level

84

Left_% at-dB sensation level Left-% at-dB sensation level

Right ear Left ear

Air conduction

Bone conduction

O X

C D

FIGURE 210-3. This audiogram reflects the type of hearing loss that is often seen with Paget disease of the bone. In the left ear, there is a mixed hearing loss: part of the loss is sensorineural and part is conductive. Notice the separation, in the low frequencies, between air conduction and bone conduction levels on the left side. The speech reception threshold corresponds to the air conduction level, but speech discrimination remains fairly good at this point. The hearing level in the right ear is fairly typical of end-stage Paget disease of the temporal bone. This is a fairly severe sensorineural hearing loss with poor speech discrimination. In this example, the mixed hearing loss might occur relatively early in the course of the disease, whereas the sensorineural hearing loss might occur relatively late.

trimester. There are no predisposing factors. Treatment with de¬ congestants is of limited benefit. Another unusual finding is hoarseness, which arises from vascular engorgement of the true and false vocal cords. An extremely dry throat—-laryngitis sicca gravidarum—occasionally is seen. All of these conditions resolve after delivery. Finally, the incidence of facial paralysis is three times greater in pregnant women than in nonpregnant women; the cause for this is unknown, and treatment usually is limited to careful observation.19

FIGURE 210-4.

Radiograph of a patient with fibrous dysplasia of the left maxilla. Severe cystic involvement (arrow), overall expansion of the bone, and extreme thinning of the cortex (arrowhead) are evident. Notice the asymmetry of the orbits, as well as the gross deformity of the left orbit.

DIABETES MELLITUS There have been reports that sensorineural hearing loss ap¬ pears earlier and is more severe in diabetics than in the normal population. However, when diabetics are compared with a gen¬ eral population of the same age and sex, there appears to be no difference in hearing levels.20 Other conditions that have been thought to be more prevalent in diabetics are Meniere syndrome, facial nerve palsy (Bell palsy), and vocal cord paralysis, but none of these have been conclusively shown to be more common in these patients than in the population as a whole. Infections are a great problem in diabetics. Two infectious processes are unique and will be reviewed in some detail. The first is malignant (necrotizing) external otitis, a disease that affects elderly diabetics.21 It is a unilateral process that begins as a rou¬ tine external otitis. Despite therapy, it evolves from a soft tissue infection into an osteomyelitis of the temporal bone, and eventu¬ ally involves the base of the skull. Pseudomonas aeruginosa is the major pathogen. The cardinal symptoms are severe otalgia and otorrhea. There is granulation tissue at the anterior junction of the bony and the cartilaginous external auditory canal. The clini¬ cal appearance is deceptively mild, and the course of the disease is prolonged. Once the bone is involved, cranial nerve deficits develop. The facial nerve is the one most commonly affected, but cranial nerves VI through XII can be involved. If more than one cranial nerve is involved, the prognosis is poor. The treatment must be aggressive and multifaceted. Local treatment consists of placing an antibiotic-soaked wick in the ear canal; systemic ther¬ apy has been an aminoglycoside and one of the synthetic peni¬ cillins. There is evidence2* that prolonged therapy with a cepha¬ losporin or fluoroquinolone may be effective. Treatment must be continued for at least 4 weeks, and probably for 6 weeks. Surgical management is limited to debridement of the temporal bone, usually a radical mastoidectomy. It is imperative to control the diabetes concurrently, and to monitor renal function. Treatment must be continued until all clinical evidence of the disease disap¬ pears, the erythrocyte sedimentation rate normalizes, the gallium bone scan improves, and there is radiographic evidence of reso¬ lution.23'24 At one time, the mortality rate associated with this disease was 50%, but is now around 10% (see Chap. 146).

Ch. 211: Dental Aspects of Endocrinology The second infection of concern is mucormycosis. The two forms seen in the head and neck region are the rhino-orbitalcerebral form and the otic form.25-28 The nasal form presents with blindness, ophthalmoplegia, proptosis, facial swelling, palatal ul¬ cer, or disorders of consciousness. Examination reveals brick red or black areas within the nasal cavity. Biopsy confirms the clinical impression of mucormycosis. The otic presentation usually is ac¬ companied by otorrhea, followed by facial paralysis and then al¬ tered sensorium. Treatment must be prompt and aggressive. The diabetes must be controlled, because ketoacidosis and dehydra¬ tion are invariably present at the onset of the disease. Systemic therapy is initiated with amphotericin B. Surgical debridement is more important in mucormycosis than in malignant otitis ex¬ terna. Surgical management involves the removal of all necrotic tissue and the establishment of drainage from areas of infection. If the facial or optic nerve is involved, decompression is indi¬ cated. The mortality rate associated with this condition is 40%.

HYPOGLYCEMIA

1821

15. Bergstrom L. Osteogenesis imperfecta: otologic and maxillofacial aspects. Laryngoscope 1977;87(Suppl):l. 16. Feldman MD, Rao VM, Lowry LD, Kelly M. Fibrous dysplasia of the para¬ nasal sinuses. Otolaryngol Head Neck Surg 1986;95:222. 17. Reddy KTV, Jefferis AF, Vinayok BC, Grieve DV. Fibrous dysplasia of the temporal bone. Ann Otol Rhinol Laryngol 1994; 103:74. 18. Sofferman RA. Cysts and bone dyscrasias of the paranasal sinuses. In: English GM, ed. Otolaryngology, vol 2. Philadelphia: Harper & Row, 1985:13. 19. Hilsinger RL jr, Adour KK. Idiopathic facial paralysis, pregnancy, and the menstrual cycle. Ann Otol Rhinol Laryngol 1975;84:433. 20. Hamer SG. Hearing in adult-onset diabetes mellitus. Otolaryngol Head Neck Surg 1981;89:322. 21. Chandler JR. Malignant external otitis and osteomyelitis of the base of the skull. Am J Otol 1989; 10:108. 22. Meyers BR, Mendelson MH, Parisier SC, Hirschman SZ. Malignant ex¬ ternal otitis: comparison of monotherapy vs. combination therapy. Arch Otolaryn¬ gol Head Neck Surg 1987,-113:974. 23. Levenson MJ, Parisier SC, Dolitsky J, Bindra G. Ciprofloxacin: drug of choice in the treatment of malignant external otitis (MEO). Laryngoscope 1991; 101: 821. 24. Benecke JE Jr. Management of osteomyelitis of the skull base. Laryngo¬ scope 1989; 99:1220. 25. Blitzer A, Lawson W. Mycotic infections of the nose and paranasal si¬ nuses. In: English GM, ed. Otolaryngology, vol 2. New York: Harper & Row, 1985:4. 26. Sugar AM. Mucormycosis. (Review) Clin Infect Dis 1992;l(Suppl 14):

So-called reactive postprandial hypoglycemia29 has been as¬ sociated with Meniere syndrome, fluctuating hearing loss, and episodic vertigo.30 Although some authors believe that hypogly¬ cemia plays a major role in the evolution of these symptom com¬ plexes, the objective data are not impressive. The subjective na¬ ture of the symptoms and the tendency for remission to occur make scientific evaluation difficult.

LIPID METABOLISM Hyperlipidemia causes characteristic xanthomas of the face and may be associated with sensorineural hearing loss.31 It had been thought that patients with Meniere syndrome, fluctuating hearing loss, episodic imbalance, and premature hearing loss of¬ ten had hyperlipidemia.32 Most of those studies had flaws in their design, and it is doubtful that hyperlipidemia is a significant fac¬ tor in these conditions. In abetalipoproteinemia, which is a rare recessive disorder, the presenting features include ataxia, acanthocytosis, and sensorineural hearing loss.33

REFERENCES 1. Ito H, Takamoto T, Nitta M, et at. DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness) syndrome associated with myocardial disease. Jpn Heart J 1988;29:371. 2. Wilson CB. Role of surgery in the management of pituitary tumors. Neurosurg Clin North Am 1990; 1:139. 3. Hamer SG. Orbital decompression techniques. In: Gorman CA, Waller RR, Dyer JA, eds. The eye and orbit in thyroid disease. New York: Raven Press, 1984: 221. 4. Netterville JL, Aly A, Ossoff RH. Evaluation and treatment of complica¬ tions of thyroid and papathyroid surgery. Otolaryngol Clin North Am 1990; 23:529. 5. Chaouki ML, Maoui R, Benmiloud M. Comparative study of neurological and myxoedematous cretinism associated with severe iodine deficiency. Clin Endo¬ crinol (Oxf) 1988; 28:399. 6. Friis J, Johnsen T, Feldt-Rasmussen U, et al. Thyroid function in patients with Pendred's syndrome. J Endocrinol Invest 1988; 11:97. 7. Maisel RH, Brown DR, Ritter FN. Endocrinology. In: Paparella MM, Shumrick DA, eds. Otolaryngology, vol 1. Philadelphia: WB Saunders, 1980:779. 8. van Heerden JA, Sheps SG, Hamberger B, et al. Pheochromocytoma: cur¬ rent status and changing trends. Surgery 1982;91:367. 9. McCaffrey TV, McDonald TJ. Sarcoidosis of the nose and paranasal si¬ nuses. Laryngoscope 1983;93:1281. 10. Hybels RL, Rice DH. Neuro-otologic manifestations of sarcoidosis. La¬ ryngoscope 1976; 86:1873. 11. Lye WC, Leong SO. Bilateral vocal cord paralysis secondary to treatment of severe hypophosphatemia in a continuous ambulatory peritoneal dialysis pa¬ tient. Am J Kidney Dis 1994;23:127. 12. Schuknecht HF. Pathology of the ear. Cambridge, MA: Harvard Univer¬ sity Press, 1974:172. 13. Hamer SG, Rose DE, Facer GW. Paget's disease and hearing loss. Otola¬ ryngology 1978;86:869. 14. El Samma M, Linthicum FH Jr, House HP, House JW. Calcitonin as treat¬ ment for hearing loss in Paget's disease. Am J Otolaryngol 1986; 7:241.

S126. 27. Abedi E, Sismanis A, Choi K, Pastore P. Twenty-five years' experience treating cerebro-rhino-orbital mucormycosis. Laryngoscope 1984;94:1060. 28. Gussen R, Canalis RF. Mucormycosis of the temporal bone. Ann Otol Rhinol Laryngol 1982;91:27. 29. Betteridge DJ. Reactive hypoglycemia. Br Med J 1987;295:286. 30. de Vincentiis I, Ralli G. New pathogenetic and therapeutic aspects of Me¬ niere's disease. Adv Otorhinolaryngol 1987;37:97. 31. Sikora MA, Morizono T, Ward WD, et al. Diet-induced hyperlipidemia and auditory dysfunction. Acta Otolaryngol (Stockh) 1986; 102:372. 32. Spencer JT Jr. Hyperlipoproteinemia and inner ear disease. Otolaryngol Clin North Am 1975;8:483. 33. Liston S, Meyerhoff WH. Metabolic hearing loss. In: English GM, ed. Otolaryngology, vol 1. Philadelphia: Harper& Row, 1985:9.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

211_

DENTAL ASPECTS OF ENDOCRINOLOGY ROBERT S. REDMAN Most of the major circulating hormones are important in the normal growth and development of the orofacial region, includ¬ ing the teeth, and most of them also participate in the mainte¬ nance of the health and integrity of these structures. Conse¬ quently, hormonal abnormalities commonly have dental and oral manifestations. Many of these oral signs and symptoms, and the endocrinopathies and other disorders with which they may be associated, are summarized in Tables 211-1 and 211-2.

ONTOGENY OF THE OROFACIAL STRUCTURES When considering the potential for hormonal effects on the development of mature oral structures, two phenomena must be examined. First, regarding tooth development, the various stages of odontogenesis occur at different ages for each pair of teeth. The first primary teeth are initiated at about 6 weeks after concep¬ tion, whereas the last secondary teeth (the third molars) finish root formation at about 20 years after birth.1 Thus, significant deviations from the normal chronology of tooth eruption (Fig. 211-1) can be an important sign of endocri-

1822

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

TABLE 211-1 Dental and Orofacial Abnormalities That May Be Associated With Specific Metabolic or Endocrine Disorders Dental or Oral Abnormality

Metabolic or Endocrine Disorders

TEETH Enamel hypoplasia, hypocalcification

Cretinism; juvenile myxedema; rickets; hypophophatasia; pseudohypophosphatasia; hypoparathyroidism, including APECS; pseudohypoparathyroidism; fluorosis

To be distinguished from: amelogenesis imperfecta; results of local trauma or severe systemic illnes in infancy or early childhood

Dentinal hypoplasia, hypocalcification

Cretinism; juvenile myxedema; rickets; familial hypophosphatemia, hypophosphatasia and pseudohypophosphatasia; hypoparathyroidism and APECS

Short roots, enlarged pulp chambers

Cretinism; myxedema

To be distinguished from: dentinogenesis imperfecta; results of trauma or illness in early childhood

To be distinguished from: Regional odontodysplasia Short roots, occluded pulp chambers

Pseudohypoparathyroidism

To be distinguished from: dentinogenesis imperfecta; dentinal dysplasia Dentinal defects leading to periapical infection

Vitamin D-resistant rickets (familial hypophosphatemia)

Delayed eruption

Cretinism; myxedema; hypopituitarism; rickets

Precocious eruption

Hyperthyroidism; congenital adrenal hyperplasia; precocious puberty

BONES OF THE MAXILLA AND MANDIBLE Hypocalcification (developmental)

Cretinism; juvenile myxedema; rickets; hypophosphatasia; pseudohypophosphatasia; familial hypophosphatemia

Hypocalcification (postdevelopmental)

Decreased estrogen (postmenopause); hyperparathyroidism; vitamin D deficiency; long-term inadequate dietary calcium or high dietary phosphate:calcium ratio

Loss of lamina dura

Hyperparathyroidism; vitamin D deficiency (osteomalacia and rickets); renal dialysis

Central (intraosseous) giant cell lesions

Hyperparathyroidism; renal dialysis

Underdevelopment; relative maxillary prognathism

Pituitary dwarfism; cretinism; juvenile myxedema

Postpubertal enlargement

Acromegaly (greater degree of enlargement in the mandible than in the maxilla)

To be distinguished from: Paget disease (in which the enlargement is usually greater in the maxilla) ORAL MUCOSA Macroglossia (secondary to edema)

Hypothyroidism at any age

To be distinguished from: cellulitis; lymphangioma; amyloidosis; relative or absolute hyperplasia (true macroglossia), as in Down syndrome and acromegaly

Glossodynia; metallic taste

Diabetes; decreased estrogen (postmenopause); also occurs in those with pernicious or iron deficiency anemia and those ingesting bismuth and lead

Candidiasis Acute pseudomembranous type (involving the tongue, buccal mucosa, gingiva)

Greater incidence in diabetics than in normal population, even when precipitated by systemic antibiotic therapy. If patient is resistant to antifungal therapy, hypoparathyroidism, APECS, hyperadrenocorticism, and corticosteroid therapy should be considered. Also occurs in immune deficiencies, both congenital and acquired (AIDS)

Chronic hyperplastic type (involving the tongue, buccal mucosa, and especially the labial angular commissures)

Hypoparathyroidism, APECS; hyperadrenocorticism; also occurs in those with immune deficiencies, including AIDS

To be distinguished from: Angular cheilosis associated with closed bite or nutritional deficiencies; premalignant dyskeratosis; carcinoma

Type associated with median rhomboid glossitis/central papillary atrophy

Greater prevalence in diabetics than in general population

To be distinguished from: Benign migratory glossitis; glossitis secondary to anemia or vitamin B deficiency.

Patches of melanin pigmentation of buccal, 'abial, and gingival mucosa

Hypoadrenocorticism

Aphthae; herpes labialis

Frequently associated with menses

Hyperplastic gingivitis; pyogenic granuloma

Increased female sex hormones, as occurs in hypergonadism or pregnancy, with use of oral contraceptives, or with estrogen therapy; diabetes

To be distinguished from: amalgam tattoo, bismuth or lead deposits; pigmentations associated with African or Mediterranean ancestry; nevus; melanoma; Peutz-Jeghers syndrome

To be distinguished from: gingivitis secondary to phenytoin (Dilantin) therapy; vitamin C deficiency Periodontitis that is progressive despite • therapy, or that is associated with recurrent exacerbations

Poorly controlled diabetes; hyperthyroidism; hypothyroidism; hyperparathyroidism; hyperadrenocorticism; renal dialysis; also occurs in immune deficiencies

SALIVARY GLANDS Xerostomia

Bilateral, generalized enlargement, especially the parotid glands

Diabetes; postirradiation atrophy and fibrosis of salivary glands secondary to iodine-131 therapy for thyroid carcinoma; also occurs in Sjogren syndrome; after conventional radiation therapy to the head and neck; and with some medications Diabetes; also occurs in alcoholism; chronic undernutrition; sarcoidosis; Sjogren syndrome and with iodine therapy (iodine mumps) or bismuth ingestion

APECS, autoimmune polyendocrinopathy candidiasis syndrome.

Ch. 211: Dental Aspects of Endocrinology

1823

TABLE 211-2 Reported Effects of Various Endocrine Conditions on the Sense of Taste Abnormality/Disorder

Effect

HYPOGONADOTROPIC HYPOGONADISM (KALLMANN SYNDROME)

Decreased sense of taste (largely attributable to loss of sense of smell); defects are irreversible

HYPOTHYROIDISM

Distortion of taste (dysgeusia), as well as hyposmia; decreased taste acuity, especially to bitter stimuli. Defects are reversible with thyroid hormone therapy

HYPERCALCEMIA

Bitter taste in mouth; reversible with normalization of serum calcium levels

PSEUDOHYPOPARATHYROIDISM

Impaired taste for sour and bitter (as well as impaired olfaction)

ADDISON DISEASE

Lowered threshold for the sensation of saltiness; reversible with corticosteroid therapy

GONADAL DYSGENESIS

Variable disorders of gustatory (as well as olfactory) functions

DIABETES MELLITUS

Blunted sensation for sweetness and generalized decreased taste acuity for saltiness and bitterness; metallic taste

* Taste (gustation) is an extremely adaptive chemical sense. The thousands of taste buds are located mostly on the dorsal surface of the tongue, but also are located on palatal, pharyngeal, and buccal mucosae. Taste buds consist of supporting cells and gustatory cells. The latter cells, which respond to dissolved substances, are supplied afferently by the facial nerve (anterior two thirds of the tongue), glossopharyngeal nerve (posterior one third of the tongue), and vagus nerve (throat); the impulses eventu¬ ally arrive in the parietal cortex, where they are intermixed with sensations of touch, temperature, and smell.

nopathy, as well as of metabolic or nutritional problems. Further¬ more, any part of a tooth that has completely calcified undergoes no significant further developmental changes in shape or compo¬ sition. Thus, the duration, as well as the severity, of hormonal changes will determine which parts of which teeth will be affected. Once the teeth have fully formed and erupted, they can be altered only by destructive processes, such as periodontitis and caries, and their capacity for repair is limited. Therefore, ab¬ normalities of shape or mineralization that are restricted to cer¬ tain teeth also may serve as a permanent record, indicating when and for how long an endocrinopathy has been a factor (Fig. 211-2). Second, the maxilla, mandible, and most of the facial bones grow by intramembranous ossification, except for epiphy¬ seal plate-like growth in a rim of hyaline cartilage on the head of each mandibular condyle. This cartilage persists in the adult.2 Thus, with appropriate hormonal stimulation, during adulthood, the facial bones and both jaws can enlarge by accretion, but the mandible also can elongate from the condyles.

PITUITARY Experiments3 in which the incisors continuously erupt have indicated the relative importance of the pituitary and several of its target endocrine gland hormones in the production of dental and alveolar bone abnormalities in hypopituitarism. In hypophysectomized rats, the rate of eruption progressively slows, then ceases, and the incisors become reduced in size and mis¬ shapen. Amelogenesis, morphogenesis, and rate of eruption are largely restored by thyroxine, whereas dentinogenesis and alve¬ olar bone growth nearly normalize with growth hormone sup¬ plementation. Decreased levels of adrenocortical hormones also may participate in the abnormal morphogenesis of the incisors.

HYPOPITUITARISM In pituitary dwarfism (growth hormone deficiency), there is delayed eruption of both primary and secondary dentitions, and delayed shedding of the primary teeth.3-7 The crowns of the teeth reportedly are smaller than normal, although some researchers

have suggested that the crowns appear smaller only because they are incompletely erupted.3 Also, the roots of the teeth are notice¬ ably stunted.3-7 The overall growth of the jaws is retarded, with the maxilla being less affected than the mandible.3,4 In this con¬ dition, the alveolar (tooth-supporting) regions of both jaws grow at a disproportionately reduced rate. Consequently, the dental arches are too small to accommodate all of the teeth, causing crowding and malocclusion.3 4,6 7 Hypofunction of the salivary glands also may occur, leading to increased dental caries and periodontitis.7 In adult-onset panhypopituitarism, there are no specific effects on the teeth, but characteristic orofacial changes include thinning of the mucosa of the lips and an immobile facial expression.3

HYPERPITUITARISM Growth hormone excess that occurs before puberty (gigan¬ tism) causes progressive, symmetrical enlargement of the jaws, tongue, and teeth,3,4 7 and the eruption of the teeth is acceler¬ ated.3-6 Orofacial features of acromegaly emerge when the hy¬ perpituitarism continues past, or begins after, 8 to 10 years of age.3-7 The jaws and facial bones enlarge disproportionately in relation to most of the bones of the skull because resumption of osseous growth is more vigorous in the intramembranous bones. Moreover, endochondral ossification resumes in the hyaline car¬ tilage of the heads of the mandibular condyles, and the mandib¬ ular angles become flattened. This causes progressively more se¬ vere mandibular prognathism. The palatal arch is flattened, and panoramic dental radiographs may demonstrate enlarged maxil¬ lary sinuses. The periosteum of the jaws may become ossified at points of attachment of the muscles and tendons. The crowns of the teeth are not enlarged, but there often is excessive deposition of cementum on the roots (hypercementosis). The tongue may become so large that indentations form where it encroaches on the teeth. Partly from this pressure, and partly from the enlarge¬ ment of the jaws, the teeth become spaced and outwardly tipped (Fig. 211-3). The nose and lips also are enlarged, adding to the general coarsening of the facial features. Enlargement of the bones of the face and skull, and spacing

1824

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

MAXILLA

FIGURE 211-2. Severe hypoplasia of enamel and dentin. The parents of this 7-year-old girl were unsure of the nature of her illness in early childhood. The limitation of the dental defect to the incisal third of the secondary teeth, of which only the central incisors (c) have erupted, would be compatible with the onset of an endocrinopathy, such as hypo¬ thyroidism, shortly after birth and its subsequent diagnosis and appro¬ priate treatment at about 14 to 16 months of age. (Courtesy of Douglas J. Sanders, DDS.)

FIGURE 211-1. Chronology of eruption of the permanent, or second¬ ary, teeth. Eruption time, as depicted in this diagram, is defined as the time when the tooth first pierces the gingiva and becomes visible in the oral cavity. The numbers within the teeth designate the mean eruption times in years and months; e.g., the maxillary central (next to the midline) incisors erupt at the age of 7 years, 5 months in boys, and 7 years, 2 months in girls. The third molars (so-called wisdom teeth) contain no numbers because their eruption times are extremely variable, and are, therefore, of little use as a sign of metabolic or hormonal disturbance. Of the deciduous teeth (not shown), the mandibular incisors usually erupt first, beginning at about 6 months after birth, followed by the first molars, canines, and second molars. Notice that when the deciduous molars are shed, they are replaced by the permanent premolars. All of the deciduous teeth usually have erupted by the age of 2 years. Like the permanent teeth, the deciduous teeth tend to erupt earlier in girls than in boys. (Mod¬ ified from Sinclair D. Human growth after birth. London: Oxford University Press, 1978:103.)

weeks of age. When this rise is prevented by thyroidectomy, the weaning process, tooth eruption, and maturation of the salivary glands are all retarded, but not prevented.8,9 Rodent parathyroid glands are enclosed in the poles of the thyroid gland, and surgical removal of the thyroid eliminates both glands. However, similar developmental retardation occurs when hypothyroidism is in¬ duced by propylthiouracil, and is prevented with timely replace¬ ment of thyroxine.8,9 This indicates that the effects are attribut¬ able to the lack of thyroxine, and not to any disturbance of parathyroid hormone. Furthermore, the administration of thy¬ roxine to suckling mice and rats induces precocious development of salivary glands,9 as well as of the teeth.3 Also, in mature rats and mice, deficiency of thyroxine causes up to 50% reductions in salivary flow and of gland stores of amylase, protease, and other salivary proteins.9,10 These findings suggest that decreased sali¬ vary function, as well as the previously observed enamel hypocalcification, may contribute to the increased dental caries that occur in juvenile hypothyroidism. It is noteworthy that the major salivary glands actively con¬ centrate iodine from body fluids.11 This does not complicate ra-

and hypercementosis of the teeth can occur in osteitis deformans (Paget disease of bone).3 5 However, in contrast to that associated with acromegaly, the enlargement in this disease is limited to the bones; the lips may become thinner because of stretching, and the maxilla tends to enlarge disproportionately to the mandible, producing an anterior open bite and a maxillary prognathism. Also, the jaws and skull bones are especially inclined to exhibit radiolucency (osteoclastic stage) and fuzzy (cotton-wool) radio¬ density (osteoblastic stage).

THYROID The serum concentration of thyroid hormone is low in neo¬ natal rats and mice, but increases to adult levels between 2 and 3

FIGURE 211 -3. The maxillary anterior teeth of a 52-year-old man with acromegaly are pictured. Notice the wide spaces between the teeth, as well as their anterior inclination.

Ch. 211: Dental Aspects of Endocrinology

1825

salivary glands also may be seriously damaged.11 The resulting xerostomia may be permanent, and rampant caries and peri¬ odontal destruction will follow unless long-term, specific dental care is instituted in a timely manner. Appropriate care includes scrupulous oral hygiene, frequent professional dental cleanings, saliva substitutes for oral moistness and comfort, and the daily topical application of a fluoride gel onto the teeth.

HYPOTHYROIDISM

FIGURE 211-4.

Periapical radiographs of mandibular molars. A, In a normal patient, the lamina dura (arrow) and the bony trabeculae are thick and dense. B, By contrast, the lamina dura is virtually absent and the trabeculae are thinner and much less radiodense in this patient with hy¬ perparathyroidism. (Courtesy of John N. Trodahl, DDS.)

dioiodine uptake or scanning tests of the thyroid because of the relatively small amounts used, the lesser uptake by the salivary glands, and the anatomic separation of these organs and the thy¬ roid gland. But if radioiodine is used to destroy residual thyroid tissue in a patient who has had surgery for thyroid carcinoma, the

FIGURE 211-5. Radiograph of a central giant cell granu¬ loma in the mandible of a 7-year-old girl. The circumscribed, multilocular, radiolucent region (arrows) initially appeared (when the child was 5 years old) as a small radiolucent area in the premolar region. There was no evidence of hyperpara¬ thyroidism in this patient. (Courtesy ofL. Stefan Levin, DDS.)

Cretinism is characterized by maxillary prognathism be¬ cause the underdevelopment of the maxilla is less severe than that of the mandible.3 4,7 Radiographic examination often reveals hypocalcification of the jaws, and sometimes there is abnormal development of the sinuses or nonunion of the mandibular sym¬ physis.4 The characteristic facies consists of a concave nasal bridge and flared alae nasi; stiff facial expression, thickened lips and enlarged tongue, owing to doughy, nonpitting edema; and a mouth held partly open because of the lack of room for the tongue inside the underdeveloped mandible.3,4'7 The somewhat similar facies in Down syndrome arises from a disproportionately underdeveloped maxilla and a relative macroglossia that is not associated with edema.3 In both juvenile myxedema and cretin¬ ism, there is retarded development of the teeth, frequently with hypocalcification, enamel hypoplasia (see Fig. 211-2), persistence of large pulp chambers, and open apical foramina.4,6 Eruption of both dentitions and shedding of the primary dentition are gener¬ ally (but erratically) delayed.3-7 This, and the underdevelopment of the jaws, causes a malocclusion that may be severe and may be complicated by spreading and flaring of the teeth secondary to pressure from the enlarged tongue. Hypothyroidism at any age seems to predispose affected pa¬ tients to excessive dental caries,4,5,7 as well as to accelerated alve¬ olar bone loss in both dentulous areas (periodontitis) and eden¬ tulous ridges (atrophy).5 The increased caries and periodontitis are related to hyposalivation and to the drying effects of mouth breathing caused by the enlarged, protruding tongue.7 Adults with myxedema also develop thickened lips and a swollen tongue (from edema); pressure from the latter, in conjunction with an exacerbation of periodontitis, may cause spreading and splaying of the teeth.3-6 Generally, the earlier childhood hypo¬ thyroidism is treated, the greater is the success in preventing or reversing orofacial maldevelopment, except for the affected parts of dentin and enamel that have completed all phases of development. Hypothyroid patients often are unable to tolerate prolonged dental procedures. Also, they usually have an exaggerated re¬ sponse to premedication with narcotics or barbiturates.4 '

1826

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

HYPERTHYROIDISM In children, hyperthyroidism accelerates the development of the teeth and jaws, but maldevelopment is unusual.3,6 Malocclu¬ sion results occasionally when shedding of primary teeth and eruption of secondary teeth are disportionately precocious to jaw growth. Usually, the teeth are normal in terms of size, morphol¬ ogy, and calcification. Periodontitis may begin at an unusually early age, and both caries and periodontitis reportedly are ex¬ acerbated in hyperthyroidism at any age. In severe hyperthyroid¬ ism, there can be rapid bone demineralization, which is mani¬ fested radiographically as osteoporosis of the jaws and loss of alveolar bone in both dentulous and edentulous areas. Patients with hyperthyroidism are likely to be poor dental patients because they are unable to hold still for dental proce¬ dures and are likely to develop cardiac arrhythmias.3"5,7 The anx¬ iety, stress, and trauma associated with dental treatment thus may precipitate a medical emergency in the dental office. In par¬ ticular, the use of epinephrine and other vasoconstrictors in local anesthetics is contraindicated.7

CALCIUM AND PHOSPHORUS METABOLISM Hypoplasia of enamel and dentin, marked chronologic devi¬ ations in eruption and exfoliation of teeth, loss of radiodensity of the jawbones (especially the lamina dura), and the presence of giant cell lesions in the jaws may alert the dentist to previously undiagnosed disorders of calcium and phosphorus metabolism. Abnormalities of mineral metabolism that produce oral signs and symptoms include disturbances of particular nutritional factors (calcium, fluoride, vitamin D), hormones (parathyroid hormones, adrenal corticosteroids), and renal function.

NUTRITIONAL FACTORS Calcium deficiency may be an important factor in osteopo¬ rosis, which may accentuate alveolar bone loss in edentulous ridges.3 Fluoride deficiency has only one overt effect: a greatly in¬ creased susceptibility to dental caries. It may also contribute to osteoporosis when calcium intake is inadequate. Dental fluorosis, or mottled (hypoplastic) enamel, occurs with increasing fre¬ quency and severity when fluoride concentrations exceed 1.0 ppm in the drinking water if it is ingested while tooth develop¬ ment and calcification are in progress3 (see Chap. 7). Vitamin D deficiency in children (rickets) causes hypocalcification of the dentin, enamel, and alveolar bone, and delays the eruption of both dentitions.3,12 The hypocalcified dentin is characterized histologically by a wide predentin zone and exces¬ sive amounts of interglobular dentin. The crowns may be pitted, stained, or even deformed. In dental radiographs, the crown may have radiolucent spots or striations. In adults with vitamin D de¬ ficiency (osteomalacia), the maxilla and mandible are hypomineralized.1* Radiographic examination reveals prominent marrow spaces, thin cortices, fading or loss of trabeculae, and thinning or even loss of the lamina dura (Fig. 211-4). The teeth are not affected, and may seem unusually dense in contrast to the re¬ duced mineral content of the bone. In vitamin D-resistant rickets (familial hypophosphatemia), the dentinal hypocalcification is more severe than in ordinary rickets, and is associated with hypoplasia.3 Frequently, there are clefts and tubular defects near the pulp horns, and oral microor¬ ganisms often invade the pulp in the absence of caries. Conse¬ quently, multiple periapical infections and fistulas develop. The lamina dura may be reduced or absent, and the cementum may be hypoplastic. Both hypophosphatasia and pseudohypophosphatasia cause premature exfoliation of the deciduous teeth, apparently because of a lack of cementogenesis. Occasionally, the teeth and

alveolar bones are sufficiently hypocalcified to be demonstrably less radiodense, and the pulp chambers may be abnormally large.3,6

PARATHYROID HORMONE In hypoparathyroidism of infancy or early childhood, there may be hypoplasia or even aplasia of the teeth.3 The hypoplasia affects both enamel and dentin, and often results in short, blunted roots, malformed teeth, delayed eruption, and impac¬ tion. When it occurs as part of the autoimmune polyendocrinopathy candidiasis syndrome (APECS),3,13 superficial mucocu¬ taneous candidiasis frequently precedes any of the other signs or symptoms (see Fig. 211-11A; see Chaps. 59 and 191). Acute exacerbations of the oral mucosal lesions usually can be con¬ trolled with topical antifungal agents, but are subject to recur¬ rence when therapy is discontinued. Angular cheilosis, however, is nearly constant, and seldom completely regresses with anti¬ fungal therapy. Enamel hypoplasia occurs in many cases. Fre¬ quently, the enamel is affected before the onset of any of the endocrinologic disorders. This supports the notion that the syn¬ drome may be caused by episodes of autoimmune destruction limited to certain organs. Tooth eruption and occlusion seem to be unaffected. Hypoparathyroidism occurring after puberty does not affect tooth development or eruption, but may cause circumoral paresthesia, and predispose to oral candidiasis.7 Pseudohypoparathyroidism is characterized by microdon¬ tia, occluded pulp chambers, short roots, hypoplastic enamel, os¬ teodentin, and multiple impacted teeth.3,5 Hyperparathyroidism, whether primary or secondary, pro¬ duces characteristic changes in dental radiographs.3"7,12 The bones of the maxilla and mandible are generally less radiodense than normal, and often have a ground-glass appearance. Fre¬ quently, the lamina dura is greatly reduced or even lost (see Fig. 211-4). In time, discrete radiolucent areas appear and enlarge (Fig. 211-5). These are osteoclastomas that are histologically identical to the giant cell granuloma, a lesion that occurs most commonly in the jaws. Thus, if a circumscribed lesion of the max¬ illa or mandible is diagnosed as a central (arising from within the bone) giant cell granuloma, the patient should be referred for investigation of possible hyperparathyroidism. The less uncom¬ mon peripheral (arising from or near the surface of the bone) giant cell granuloma apparently is not associated with hyperparathy¬ roidism14; however, referral to an endocrinologist still would be

FIGURE 211-6. Hyperplastic marginal gingivitis (arrowheads) was evi¬ dent in this 22-year-old woman who was 8 months' pregnant at the time of this examination. Five weeks after delivery of her baby, the patient returned for dental treatment, at which time the gingivitis had completely regressed.

Ch. 211: Dental Aspects of Endocrinology

1827

FIGURE 211-8.

FIGURE 211-7. Parotid gland hypertrophy (arrow) in a 28-year-old pa¬ tient with poorly controlled type I diabetes.

prudent if there is more than a superficial cupping of the underly¬ ing bone, or if multiple lesions occur. Dental treatment of the patient with parathyroid disease must involve a consultation between the dentist and the phys¬ ician, because abnormal blood calcium levels can precipitate medical emergencies such as cardiac arrhythmias, bronchospasm, laryngospasm, and convulsions.7

RENAL FUNCTION Azotemic osteodystrophy may affect oral and facial bones via negative calcium balance (osteoporosis or osteomalacia) or secondary hyperparathyroidism (as described earlier), or both.312 Patients with renal failure who are treated by dialysis or renal transplantation are prone to accelerated alveolar bone loss and, therefore, require recurrent dental treatment.15

ADRENAL Experiments3 in young rats and mice indicate that corticoste¬ roids are much less important than growth hormone and thyrox¬ ine in odontogenesis. However, they are nearly as essential as thyroxine in the maturation of the salivary glands that is associ¬ ated with weaning.9 Glucocorticosteroids also affect the compo¬ sition of saliva in mature rats10 (see Thyroid). High doses of cor¬ ticosteroids, administered during pregnancy, cause an increased

Severe marginal gingivitis and early periodontitis de¬ veloped in a 38-year-old man 8 months after the onset of type II diabetes. Notice the shiny, swollen gingival margins (black arrows) and gingival bleeding (white arrows). The gingivae were much improved 2 weeks after dental prophylaxis and resumption of acceptable oral hygiene practices.

incidence of cleft palate in mice and rabbits, but only in strains that are prone to the spontaneous development of this defect.3 Therefore, the clinical significance of this observation is unclear.

HYPOADRENOCORTICISM The appearance of irregularly shaped, blotchy melanin patches on the oral mucosa is often an early sign of Addison dis¬ ease3”7 (see Chap. 74). The color varies from brown to blue-black, and characteristically affects the buccal mucosa near the commis¬ sures first, then spreads posteriorly. In time, the tongue and gin¬ giva may be affected. Melanin pigmentation of the oral mucosa is common in persons from the Mediterranean region or those of African ancestry, but the involved areas tend to be evenly col¬ ored, and there is a correlation between the inherent darkness of the person's skin and the extent and darkness of the oral pigmen¬ tation. The pigment usually affects the attached, but not the mar¬ ginal, gingivae. The gingival pigmentation associated with heavy metal poisoning affects mostly the marginal gingivae; with lead poisoning, the deposits are gray, whereas with bismuth poison¬ ing, they are blue-black.3 Other oral pigmented spots that must be considered include ephelides, pigmented macules, nevi, melanomas, amalgam tat¬ toos (silver amalgam dust embedded in tissues during polishing and shaping of restorations), and the labial, lingual, and buccal mucosal spots associated with Peutz-Jeghers syndrome. Dental procedures may precipitate an adrenal crisis in pa-

FIGURE 211-9. Panoramic dental radiograph of the patient de¬ picted in Figure 211-8. Significant alveolar bone loss is evident among the maxillary incisors, where the crests of the interdental ridges (white arrows) were 2 to 3 mm below the lateral cementoenamel junctions (black arrows).

1828

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

tients with Addison disease or in those who recently were receiv¬ ing long-term, high-dose corticosteroid therapy.3~'7 The dentist should confer with the patient's physician regarding the need for antibiotic coverage, a preoperative boost in corticosteroid dosage, or hospitalization (see Chaps. 74 and 76).

HYPERADRENOCORTICISM Cushing syndrome, as well as exogenous corticosteroid ther¬ apy, can cause osteoporosis and an increased susceptibility to periodontitis and oral candidiasis.3,4 The gingivae may be edematous and bleed easily.7 In children, accelerated tooth de¬ velopment has been reported, but most cases have occurred in conjunction with the adrenogenital syndrome, in which in¬ creased androgen levels are common.3,6 The dentist should know whether a patient is receiving adre¬ nocortical medication because all but the lowest doses signifi¬ cantly interfere with healing and the patient's resistance to infec¬ tion. Other considerations in the dental management of patients with hypoadrenocorticism include caution in the use of sedatives that can depress respiration, and, for hyperadrenocorticism, care to provide adequate support of weakened vertebrae.7 Likewise, patients requiring long-term treatment with corticosteroids should receive timely dental care, so that periodontal bone loss and serious oral infections may be avoided. Hyperaldosteronism decreases both the flow rate and the sodium:potassium ratio in saliva. A failure of the sodiurmpotassium ratio to normalize after adrenal surgery indicates incomplete re¬ moval of the causative adenoma.16

SEX HORMONES The granular ducts in the submandibular salivary glands of rats and mice differentiate after puberty. The number and size of the granules in these ducts, as well as the amount of proteases, epidermal growth factor, nerve growth factor, and a host of other enzymes and hormones they contain, all are greater in male than in female rodents.17 Gonadectomy eliminates this sexual dimor¬ phism, decreasing the volume of granular ducts less in the fe¬ males than in the males. Consistent with these observations is the fact that, when testosterone is administered to female rodents or to gonadectomized rodents of either sex, a much greater de¬ gree of differentiation of the granular ducts is achieved than with any of the female hormones. These differences in hormonal re¬ sponsiveness appear to be mediated by a greater number of an¬ drogen receptors in the glands, and by a much larger proportion of these receptors being occupied by testosterone, and thus acti¬ vated, in male than in female rodents.17 Alternatively, estrogen receptors are found in salivary glands of female rats, and the per¬ oxidase activity in these glands is estrogen responsive.18

FIGURE 211-10. This panoramic dental radiograph shows advanced periodontal destruction and alveolar bone loss in a 64-year-old man. Onset of type II diabetes had occurred at the age of 60 years. In the intervening 3 years, there had been three acute exacerbations, accompanied by abscess formation and mobility of teeth, when the patient had neglected his oral hygiene. With each episode, the pa¬ tient's need for insulin increased significantly until dental treatment brought the oral infection under control. Notice that the crest of the alveolar bone (arrows) has receded to a line that is midway between the crowns and the root apices (tips) of the teeth. (Courtesy of Cullen C. Ward, DDS.)

FEMALES Pregnancy frequently produces a florid marginal gingivitis (Fig. 211-6), from which a pyogenic granuloma ("pregnancy tu¬ mor") sometimes emerges.3'5,719 The gingivitis and smaller pyo¬ genic granulomas (those less than 1.0 cm in diameter) usually will regress completely after parturition. Scrupulous oral hygiene tends to minimize these gingival lesions, but does not prevent them entirely. Oral contraceptives also seem to exacerbate gingi¬ vitis. Pregnancy and estrogen therapy also have been implicated in the development of both peripheral and central giant cell gran¬ ulomas.20 Some women tend to develop recurrent herpes labialis or oral mucosal aphthae in conjunction with menstruation. Postmenopausal oral changes can include osteoporosis, mild to moderate atrophy of the oral epithelium, and glossodynia.3-5

MALES Testosterone and other androgens are primarily responsible for the generally larger size attained by males, and this size differential encompasses the jaws and orofacial bones. The greater bone mass causes greater general radiodensity on dental radiographs; thus, gender must be considered when evaluating bone density.

PANCREAS Experimentally induced diabetes in rats has significant effects on the salivary glands.20 Growth and development are markedly retarded, with the granular ducts being most affected. In older rats, there is atrophy of the granular ducts and accum¬ ulation of lipid droplets in the acinar cells. Glandular stores of the salivary enzymes peroxidase and protease are greatly diminished. Insulin and glucagon immunoreactivity are present in the parenchymal cells of both rat and human salivary glands. Al¬ though purified extracts are bioactive, salivary gland glucagon is not released by stimuli that effect pancreatic glucagon secretion.21,22

INSULIN Diabetes mellitus adversely affects resistance to oral infec¬ tion and, in turn, significant oral infection can adversely affect the management of diabetes. Therefore, dental care is an important adjunct to the management of diabetes in patients with natural teeth.3,4,7,23 Oral signs and symptoms of diabetes mellitus include periodontitis, enlarged salivary glands (Fig. 211-7), taste impair¬ ment (hypogeusia),24 disturbances of taste (especially the pres-

Ch. 211: Dental Aspects of Endocrinology

1829

FIGURE 211-11. Three different types of oral candidiasis occurring in diabetic patients. A, Acute pseudomembranous oral candidiasis (thrush) in a 42-year-old woman. A lateral view of the retracted left buccal mucosa shows raised, curd-like plaque (arrowheads). On¬ set of the disease occurred 1 week after the patient began a 2-week course of penicillin therapy. Nystatin oral suspension was prescribed, and the lesions healed within 3 days despite continuation of the penicillin. Nystatin was discontinued at the conclusion of the penicillin therapy, and the candidiasis did not recur. CR, cheek retractor; T, tongue. B, Median rhomboid glossitis (arrow) is evident as a bald patch on the dorsum of the tongue just anterior to the vallate papillae. This benign, usually asymptomatic anomaly is re¬ ported to be disproportionately represented among diabetics; most of the patients studied have been infected superficially with Candida organisms. However, few of these lesions regress with antifungal therapy. C, A focus of chronic, hyperplastic candidiasis in a 64year-old diabetic man. The thin, firm, white plaque on an erythematous base is a recurrent lesion. A previous patch had been shown to be a result of infection with Candida albicans (confirmed by biopsy and culture), and a good response had been achieved after 2 weeks of treatment with nystatin tablets dissolved in the mouth twice daily. This subsequent lesion also disappeared after 2 weeks of nystatin therapy. Frequently, the plaque compo¬ nent is missing or is not prominent; therefore, this type of lesion is easily mistaken for median rhomboid glossitis.

ence of a metallic taste), glossodynia, dry mouth, and increased susceptibility to oral candidiasis. A slow but inexorably progressive periodontitis, associated with a poor response to treatment, occurs in some diabetic indi¬ viduals even when their blood glucose is generally well con¬ trolled. When diabetes is poorly controlled, rapidly progressive periodontal destruction is a frequent occurrence (Figs. 211-8 through 211-10). Multiple and recurrent periodontal abscesses are characteristic of both situations. The substitution of blood glycated hemoglobin or of fructosamine for blood glucose, as the indicator of diabetes control, has clarified and strengthened the previously somewhat inconsistent correlation between such con¬ trol and the severity of periodontal disease.25 In some poorly controlled diabetic patients, the parotid glands are enlarged, often to a greater extent than are the other salivary glands. The enlargement is bilateral, firm, smooth, and painless, and often persists after the diabetes is brought under control. Similarly enlarged parotid glands can occur in general¬ ized undernutrition, chronic alcoholism, and Sjogren syndrome (see Table 211-1). The xerostomia and altered taste that are seen in some dia¬ betic patients are caused mostly by polyuria and resultant dehy¬ dration, but they also may be partially attributable to salivary gland dysfunction. These symptoms are relieved when the dia¬ betes is controlled. Oral candidiasis is more common among diabetics than in the general population because of reduced immunologic resis¬ tance, decreased salivary flow, and increased glucose in the oral fluids and tissues of the former.23,26 The increased prevalence is independent of ABH(O) secretor status.24 The best-known form of this disease is acute pseudomembranous candidiasis, or thrush, in which soft, creamy white plaques cover an erythematous mu¬ cosa (Fig. 211-11A). This form usually responds to topical anti¬ fungal therapy and recurs infrequently in diabetics whose dis¬

ease is well controlled. Two similar, but apparently etiologically distinct, lesions affecting the dorsum of the tongue are more com¬ mon among diabetics than among normal subjects.27 One of these—median rhomboid glossitis—(see Fig. 211-1 IB) is a devel¬ opmental anomaly that often is characterized by a superficial in¬ fection with Candida organisms. The other is a focal variety of chronic hyperplastic candidiasis. It sometimes occurs close to the same site as does median rhomboid glossitis, but usually is more anterior, and differs from the latter in the frequent appearance of a thin white plaque (see Fig. 211-11C). Median rhomboid glossitis seldom improves permanently with topical antifungal therapy, whereas the focal, chronic, hyperplastic form of candidiasis is very responsive to therapy, but often recurs in the same or in a different location. Extensive and tenacious oral involvement with pseudomem¬ branous or chronic hyperplastic candidiasis is most likely to be a sign of a suppressed or defective immune system. For example, this type of involvement is common in patients with APECS13 and the acquired immune deficiency syndrome (AIDS).28

REFERENCES 1. Ten Cate AR. Tooth eruption. In: Bhaskar SN, ed. Orban's oral histology and embryology, ed 10. St. Louis: CV Mosby, 1986:361. 2. Sharawy M, Bhussry BR, Suarez FR. Temporomandibular joint. In: Bhaskar SN, ed. Orban's oral histology and embryology, ed 10. St. Louis: CV Mosby, 1986:395. 3. Shafer WG, Hine MK, Levy BM, Tomich CE. A textbook of oral pathology, ed 4. Philadelphia: WB Saunders, 1983;56:616. 4. Holub DA, Beckerman, T, Gottsegen R, Silverman SI. Diseases of endo¬ crine origin. In: Zegarelli, EV, Kutscher AH, Hyman GA, eds. Diagnosis of diseases of the mouth and jaws, ed 2. Philadelphia: Lea & Febiger, 1978:63. 5. Snyder MB. Endocrine disease and dysfunction. In: Lynch MA, ed. Burket's oral medicine: diagnosis and treatment, ed 8. Philadelphia: JB Lippincott, 1984:812. 6. Pindborg JJ. Pathology of the dental hard tissues. Copenhagen: Munksgaard, 1970; 140:178.

1830

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

7. Bricker SL, Langlais RP, Miller CS. Endocrine system. In: Bricker SL, Langlais RP, Miller CS, eds. Oral diagnosis, oral medicine, and treatment planning, ed 2. Philadelphia: Lea & Febiger, 1994:421. 8. Blake HH, Henning SJ. Effect of propylthiouracil dose on serum thyroxine, growth and weaning in young rats. Am ] Physiol 1985;248:R524. 9. Kumegawa M, Yajima T, Maeda N, et al. Synergistic effects of diet, thyrox¬ ine and glucocorticoid hormones on amylase activity in parotid glands of growing rats. Arch Oral Biol 1981; 26:631. 10. Johnson DA. Regulation of salivary glands and their secretions by masti¬ catory, nutritional, and hormonal factors. In: Sreebny LM, ed. The salivary system. Boca Raton, FL: CRC Press, 1987:135. 11. Wiesenfeld D, Webster G, Ferguson MM, et al. Salivary gland dysfunc¬ tion following radioactive iodine therapy. Oral Surg 1983; 55:138. 12. Pines KL, Zegarelli EV, Kutscher A, Holub DA. Metabolic diseases affect¬ ing the bones and teeth. In: Zegarelli EV, Kutscher AH, Hyman GA, eds. Diagnosis of diseases of the mouth and jaws, ed 2. Philadelphia: Lea & Febiger, 1978:47. 13. Myllamiemi S, Perheentupta J. Oral findings in the autoimmune polyendocrinopathy-candidiaisis syndrome (APECS) and other forms of hypoparathy¬ roidism. Oral Surg 1978;45:721. 14. Smith BR, Fowler CB, Svane TJ. Primary hypoparathyroidism presenting as a peripheral giant cell granuloma. J Oral Maxillofac Surg 1988;46:65. 15. Sowell SB. Dental care for patients with renal failure and renal transplants. J Am Dent Assoc 1982; 104:171. 16. Wotman S, Goodwin FJ, Mandel ID, Laragh JH. Changes in salivary elec¬ trolytes following treatment of primary aldosteronism. Arch Intern Med 1969; 124: 477. 17. Gresik EW. The granular convoluted tubule (GCT) of rodent submandib¬ ular glands. Microsc Res Technique 1994; 27:1. 18. Laine M, Tenuovo J. Effects on peroxidase activity and specific binding of the hormone 17/3-oestradiol and rat salivary glands. Arch Oral Biol 1983; 28:847. 19. Flagged JJ III, Heldt LV, Gareis FJ. Recurrent giant cell granuloma occur¬ ring in the mandible of a patient on high dose estrogen therapy for the treatment of Soto's syndrome. J Oral Maxillofac Surg 1987;45:1074. 20. Anderson LC, Suleiman AH, Garrett JR. Morphological effects of diabetes on the granular ducts and acini of the rat submandibular gland. Microsc Res Tech¬ nique 1994;27:61. 21. Bhathena SJ, Smith SS, Voyles NR, et al. Studies on submaxillary gland immunoreactive glucagon. Biochem Biophys Res Commun 1977; 74:1574. 22. Smith PH, Toms BB. Immunocytochemical localization of insulin- and glucagon-like peptides in rat salivary glands. J Histochem Cytochem 1986; 34:627. 23. Murrah VA. Diabetes mellitus and associated oral manifestations: a re¬ view. J Oral Pathol 1985; 14:271. 24. Le Floch J-P, Le Lievre G, Sadorn J, et al. Taste impairment and related factors in type 1 diabetes mellitus. Diabetes Care 1989; 12:173. 25. Unal T, Firatli E, Sivas A, Meric H, Hikmet O. Fructosamine as a possible monitoring parameter in non-insulin dependent diabetes patients with periodontal disease. J Periodontol 1993;64:191. 26. Lamey P-J, Darwaza A, Fisher BM, et al. Secretor status, candidal carriage and candidial infection in patients with diabetes mellitus. J Oral Pathol 1988; 17: 354. 27. Redman RS. Glossitis, mediah rhomboid type. In: Buyse ML, ed. Ency¬ clopedia of birth defects. Cambridge, MA: Blackwell Scientific Publications, 1990: 417. 28. Pindborg JJ. Oral candidiasis in HIV infection. In: Robertson PB, Greenspan JS, eds. Perspectives on oral manifestations of AIDS. Littleton, MA: PSG Publishing, 1988:77.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

212_

THE SKIN AND ENDOCRINE DISORDERS JO-DAVID FINE AND KENNETH L. BECKER

The endocrine system greatly influences the skin, both dur¬ ing the normal maturational and aging processes and in the course of several endocrine- or metabolically related disease states.1 In many cases, skin findings may be the first disease indi¬ cators to be recognized by the astute clinician. In this chapter, the major cutaneous manifestations of several physiologic and disease states are emphasized; detailed discussions of the extracutaneous and biochemical aspects of these conditions can be found elsewhere in this textbook.

CUTANEOUS MANIFESTATIONS OF PHYSIOLOGIC ENDOCRINE STATES NEONATAL, PREPUBERTAL, AND POSTPUBERTAL PERIODS Newborn human skin appears to contain most, if not all, of the well-characterized structural antigens, including epidermal cell surface antigens, keratins, basement membrane components, and collagens, which are present in adult skin. Despite this, some differences exist—most notably, the amount and distribution of terminal hair, the activity of glandular structures, and the pig¬ mentation in some areas of the body. Many of these differences are regulated by the endocrine system. For example, terminal hair development in the axillary and pubic regions in both sexes, and in the bearded area in males, is absent until puberty, unless pre¬ cocious puberty supervenes. Similarly, significant sebaceous and apocrine gland activity and their associated diseases, including acne and hidradenitis suppurativa, as well as genital hyperpig¬ mentation, usually are lacking in normal individuals until the on¬ set of puberty. Seborrheic dermatitis, a common inflammatory condition of sebaceous glands characterized by mild erythema and scale, usually becomes clinically manifest at or after puberty. However, seborrheic dermatitis occasionally is observed tran¬ siently in neonates (as are mild clitoral hypertrophy and vaginal discharge in the female neonate and gynecomastia in the male neonate) as a result of the presence of circulating maternal hor¬ mones within the infant. As discussed in Chapter 98, measurable aberrations in one or more hormones may be seen in some indi¬ viduals with severe acne, and such patients may experience clin¬ ical improvement with administration of dexamethasone or an¬ drogen antagonists.

PREGNANCY During pregnancy, increased pigmentation develops in the genital and perianal regions, areolae, umbilicus, and linea nigra; such hyperpigmentation subsides several months after the com¬ pletion of pregnancy. Similarly, increased gingival tissue and in¬ flammation, and an increase in the number or size of some skin tumors, including neurofibromas, nevi (moles), and skin tags (fi¬ broma molluscum gravidarum), may occur.2 At least in the case of nevi, this is most likely attributable to the effects of elevated estrogen levels on estrogen receptors present on nevus cell mem¬ branes. Another pigmentary disorder that is usually associated with pregnancy (or the use of oral contraceptives) is melasma, sometimes referred to as the "mask of pregnancy." This condi¬ tion is characterized by the development of irregular, brownish discoloration, which at times becomes confluent, along the lateral aspects of the face, cheeks, forehead, and upper lip. In contrast to other pigmentary changes associated with pregnancy, however, melasma may persist for years afterward in some individuals, and may become more pronounced with repeated sunlight exposure. Other skin findings that may be associated with pregnancy include hyperhidrosis, hypertrichosis, urticaria, dermatographism, cutaneous flushing, diffuse hair loss, and nail abnormalities. Vascular cutaneous changes may include palmoplantar telangi¬ ectases, palmar erythema, and spider angiomas. Other skin dis¬ eases that may be exacerbated by pregnancy include acne, ec¬ zema, erythema multiforme, and malignant melanoma. In addition to these, several other specific skin conditions may arise during pregnancy, including herpes gestationis, pruritic urticarial papules and plaques of pregnancy (PUPPP), impetigo herpeti¬ formis, pruritus gravidarum, papular dermatitis of pregnancy (of Spangler), and immune progesterone dermatitis of pregnancy. Herpes gestationis is a markedly pruritic vesiculobullous dis¬ order that usually arises during the second or third trimester, waxes and wanes during the course of the pregnancy, flares at

Ch. 212: The Skin and Endocrine Disorders the time of delivery, and slowly diminishes in disease activity several weeks to months later.3 Some patients experience disease recurrence, at times earlier or more severe, during successive pregnancies. In addition, affected individuals frequently experi¬ ence flares during menses or after the initiation of treatment with oral contraceptives, suggesting a significant influence by the en¬ docrine system in the perpetuation of disease activity. Despite this, however, no consistent aberrations in hormonal levels have been demonstrated in such patients. Because of the severity of symptoms and extent of disease, most patients require treatment throughout pregnancy with systemic corticosteroids or dapsone. Other evidence suggesting that this disease is also immunologically mediated includes the demonstration of C3 and, less fre¬ quently, immunoglobulin G (IgG), which is bound, in vivo, to the basement membrane zone of lesional and perilesional skin. Additionally, in some patients' sera, there are circulating IgG au¬ toantibodies or a complement-fixing factor (herpes gestationis factor) capable of binding in vitro to the basement membrane zone of normal human skin. The latter serum factors may be transmitted transplacentally to the infant, resulting in the tran¬ sient development of similar eruptions in some newborn infants. Two other important aspects of this disease include an increased risk of morbidity and mortality (up to 30%) in the fetus4 and a markedly increased frequency of histocompatibility antigens HLA-DR3 and HLA-DR4 in affected mothers.5 By contrast, PUPPP is a markedly pruritic eruption that is seen in the latter portion of the third trimester and is characterized by the presence of variably sized red papules, urticarial plaques, and infrequent vesicles, often initially arising within the striae distensae.6 As op¬ posed to herpes gestationis, no fetal problems, immunologic ab¬ normalities, or associations with HLA are seen in PUPPP. Immune progesterone dermatitis of pregnancy is a rare dis¬ order characterized by the appearance, during the first trimester, of a papulopustular eruption over the extremities, anterior thighs, and buttocks.7 Affected patients have been reported to have numerous laboratory abnormalities, including peripheral eosinophilia, hypergammaglobulinemia, elevated serum hista¬ mine levels, elevated plasma /3-estradiol levels, and slightly de¬ creased urinary levels of 17-hydroxysteroids and 17-ketosteroids. Intradermal challenge with progesterone reportedly reproduces the disease histologically. Similarly, symptoms have been exacerbated and reduced in such patients after the intro¬ duction of progesterone- and estrogen-containing oral contra¬ ceptives, respectively. Papular dermatitis of pregnancy (of Spangler) is a rare, se¬ verely pruritic eruption that can develop at any time during the course of pregnancy, clears rapidly after delivery, and may recur in future pregnancies.8 As with herpes gestationis, a 30% inci¬ dence rate of fetal mortality (stillbirths, spontaneous abortions) has been reported in untreated cases. This eruption is character¬ ized by the development of erythematous papules, crusts, exco¬ riations, and postinflammatory hyperpigmentation. Associated endocrinologic abnormalities include elevated urinary levels of human chorionic gonadotropin, decreased plasma hydrocorti¬ sone levels with foreshortened half-life, and reduced or lownormal 24-hour urinary estrogen levels. Although no longer an acceptable mode of therapy, affected patients in the past were treated successfully with diethylstilbestrol. In addition, fetal loss appeared to be prevented by treatment with systemic corticosteroids. Two other conditions seen during pregnancy are impetigo herpetiformis and intrahepatic cholestasis of pregnancy. The for¬ mer, a variant of severe, generalized, pustular psoriasis, occurs during the third trimester, is characterized by a high incidence of fetal and maternal mortality, and is associated with several endocrine abnormalities, including hypoparathyroidism and de¬ creased urinary levels of pregnanediol, androsterone, and dehydroepiandrosterone. Intrahepatic cholestasis of pregnancy (pru¬ ritus gravidarum) occurs during the third trimester, and may recur in subsequent pregnancies or after the initiation of oral con¬

1831

traceptive therapy. This disorder is characterized by laboratory and clinical findings that are consistent with cholestasis, includ¬ ing hyperbilirubinemia, jaundice, generalized pruritus, nausea, and vomiting.

CUTANEOUS MANIFESTATIONS OF DISEASES OF SPECIFIC ENDOCRINE GLANDS PITUITARY GLAND At least three disorders of hypersecretion by the anterior pi¬ tuitary gland are associated with skin findings. In acromegaly (see Chap. 14), these include coarse, leathery, thickened skin with increased markings and deepened furrows (on the scalp, referred to as cutis verticis gyrata because of its resemblance to the gyri of the cerebral cortex); hyperhidrosis; increased skin oil¬ iness; hyperpigmentation; an increased amount and coarseness of body hair; increased numbers and sizes of skin tags (fibroma molluscum); thickening of the eyelids, nose, and lower lip; and acanthosis nigricans, the latter of which is characterized by hy¬ perpigmentation and a velvet-like or increasingly papillomatous exaggeration of skin markings in usually symmetrical but local¬ ized regions (lateral neck, axillae, inguinal folds) (Figs. 212-1 and

212-2). In Cushing disease, as well as in other conditions leading to the overproduction of adrenocorticotropic hormone (ACTH), generalized hyperpigmentation may develop as a result of the stimulation of epidermal melanocytes by this hormone and by related peptides of its precursor molecule. Pituitary microadeno¬ mas causing hyperprolactinemia may present with associated hirsutism. Skin findings associated with panhypopituitarism include absent axillary and pubic hair, soft and finely textured skin (with fine facial wrinkling in some patients), and generalized pallor (in¬ cluding the nipples) (Fig. 212-3). If hypogonadism is also present, a juvenile scalp hair pattern (i.e., lacking frontal recession) is observed.

THYROID GLAND In hyperthyroidism, the skin appears red, smooth, and warm, velvety, and moist to touch, the latter being attributable to generalized hyperhidrosis.9 The face may be flushed and the palms may exhibit a marked redness (localized or diffuse), both

FIGURE 212-1. Radiograph of the foot of a patient with acromegaly (right) and a normal person (left). The heel pad distance is measured at the shortest distance between the calcaneous and plantar surface of the skin. In one study, most acromegalics had heel pad distance values ex¬ ceeding 20 mm (mean 25.6 mm), whereas nearly all of the normal sub¬ jects had values of 20 mm or less.26 Although this phenomenon is of pathophysiologic interest, a valid diagnosis is based upon growth hor¬ mone studies.

1832

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

FIGURE 212-3. A 30-year-old man with panhypopituitarism subse¬ quent to the surgical removal of a nonfunctioning pituitary tumor. The skin is soft and wrinkled. There is marked pallor and an absence of facial hair. Notice the extraocular muscle palsy that is secondary to cranial nerve involvement by the lesion.

loss), and, at times, rather diffuse alopecia. Diffuse hyperpigmen¬ tation of the skin, similar to that seen in Addison disease, may occur in hyperthyroidism, although oral involvement is report¬ edly absent in the latter condition. The nails may become soft, shiny, and onycholytic (referring to separation of the nail from the distal nail bed [Fig. 212-5]), or concave, widened, irregular, and darkened, or both. Other skin findings may include vitiligo (an autoimmune phenomenon manifested by discrete areas of depigmentation), urticaria, dermatographism, and generalized pruritus (Fig. 212-6; see Chap. 41). By contrast, the skin in hypothyroidism (see Chap. 44) ap¬ pears boggy but nonpitting, coarse, dry (the result of diminished eccrine and sebaceous gland activity), cool (owing to reduced

FIGURE 212-2. A, Cutis verticis gyrata in a man with acromegaly. The skin of the scalp has a corrugated appearance, and forms elevated folds and intervening furrows that are not obliterated by traction. This condi¬ tion may also be familial (occurring mostly in men, and associated with increased facial creases), idiopathic, or secondary, as in acromegaly. B, Acrochordons (skin tags, fibroma molluscum) on the back of a man with acromegaly. These soft, sessile or pedunculated lesions vary in size from 1 to 3 mm and, in whites, are flesh colored or brownish. They may appear on the neck, eyelids, upper chest, back, axillae, groin, or other folds of the body. They are characterized by a hyperplastic epidermis and a central connective tissue core. They are often seen in obesity and in association with acanthosis nigricans. The lesions may be removed by electrodessication, cautery, or by scissors or a scalpel. of which are a reflection of cutaneous vasodilatation and in¬ creased blood flow. The scalp hair is finely textured, soft, and somewhat fragile Other hair changes may include hirsutism, leukotrichia (Fig. 212-4), alopecia areata (a presumptive autoim¬ mune disorder characterized by circular, well-circumscribed hair

FIGURE 212-4.

A photograph of young man, who is now euthyroid, taken several weeks after a course of radiation therapy for Graves dis¬ ease. During this time, he developed leukotrichia of the left sideburn (ar¬ row). Notice the slight residual exophthalmos on the right.

Ch. 212: The Skin and Endocrine Disorders

FIGURE 212-5. Onycholysis (Plummer sign) in a hyperthyroid man with Graves disease. Notice the separation of the nails from the nail beds (arroivs).

core body temperature and cutaneous vasoconstriction), and pale. In more profound disease, nonpitting puffiness or edema may be observed in the face, eyelids, and hands; when the face is markedly affected, it may appear to be expressionless, owing to the loss of normal skin creases and markings. The tongue also may become markedly enlarged in myxedema. When hypopitu¬ itarism is also present, normally pigmented areas, such as the nipples, may become lightened. Some background yellowish dis¬ coloration may also be observed in hypothyroidism, reflecting carotene accumulation within the horny layer of the skin as a result of associated carotenemia. The hair appears dull, coarse, and brittle. In some patients, diffuse hair loss may occur, includ¬ ing over the scalp, the lateral thirds of the eyebrows (referred to

1833

as madarosis), the beard, and the genital regions. The nails are thin, striated, and brittle. In some patients, pruritus may be sig¬ nificant, possibly a reflection of extensive skin dryness and sec¬ ondary inflammation. Localized or symmetrically distributed, matted telangiectases (the latter on the fingertips) and eruptive or tuberous xanthomas have also been observed in some patients with myxedema (Figs. 212-7 through 212-9). In congenital hypothyroidism (cretinism), skin findings in¬ clude thickened, dry, cool, yellowish skin; coarse scalp hair; and a livedo pattern on the extremities (see Chap. 46). Other findings may include enlargement of the tongue, protuberant lips, thick¬ ened and everted eyelids, a flattened nose, and confluence of the eyebrows. At puberty, pubic and axillary hair is either sparse or absent. Pretibial myxedema is seen most commonly in patients with Graves disease, although it may occur less frequently in those who are euthyroid or hypothyroid. Pretibial myxedema most of¬ ten develops symmetrically on the anterior lower extremities, al¬ though occasionally, it is observed elsewhere (including the dor¬ sal aspects of the hands, arms, face, and trunk). Typically, these lesions appear as skin-colored, yellowish, or somewhat viola¬ ceous plaques or nodules with a waxy texture, dilated follicular orifices ("peau d'orange"), and, at times, overlying hypertricho¬ sis (see Chap. 41). Such lesions can be readily differentiated from necrobiosis lipoidica diabeticorum, because the latter have overlying telangiectatic vessels, tend to ulcerate centrally, and usually become atrophic rather than verrucous with time (see Chap. 147). With progression, areas of pretibial myxedema may become so thickened that they simulate the late acral skin changes of ele¬ phantiasis (elephantiasis verrucosa nostra). In some patients, the latter changes may actually produce distal deformative swelling. Occasionally, patients with pretibial myxedema also develop ac¬ quired keratoderma (excessive hyperkeratinization) of the palms, which rapidly improves with thyroxine therapy. Studies1011 in tissue culture suggest that patients with pretibial myxedema con¬ tain within their sera one or more heat-stable factors capable of inducing mucopolysaccharide biosynthesis by normal fibro¬ blasts. In addition, this response appears to be site-specific to the skin, because it occurs in fibroblasts from the pretibial areas of normal subjects and of patients with pretibial myxedema, but not in fibroblasts from other regions of the body. Such findings correlate with the usually pretibial distribution of lesions, as well as the histologic and biochemical findings of increased mucin, hyaluronic acid, and dermatan sulfate within the affected dermis. Thyroid acropathy is characterized by diaphyseal, periosteal

FIGURE 212-6.

A, Progressive depigmentation, re¬ ferred to as vitiligo, involving the hand. B, Dermatographism, a form of physical urticaria, on the trunk of an affected patient.

1834

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY proliferation of the distal long bones and phalanges, with overlying swelling of soft tissues. It is seen in some patients with pretibial myxedema and exophthalmic thyrotoxicosis (see Chap. 42). Finally, there appears to be an increased incidence of hyper¬ thyroidism and hypothyroidism in patients with dermatitis her¬ petiformis. This an intensely pruritic autoimmune vesiculobullous disorder that usually affects young adults and is characterized by the following: grouped, symmetrical formation and crusting of vesicles (most often on the elbows, knees, but¬ tocks, shoulders, and scalp); histologic, if not clinical, evidence of associated gluten-sensitive enteropathy; and immunoglobulin A (IgA) in vivo bound within the uppermost portion of the der¬ mis.12 Although the nature of these associations is poorly un¬ derstood, they may simply reflect the increased prevalence of the HLA-B8 haplotype in patients with thyroid disorders and derma¬ titis herpetiformis.

PARATHYROID GLANDS The skin findings in hypoparathyroidism may include scali¬ ness, dryness, and, in autoimmune hypoparathyroidism, altered pigmentation (hyperpigmentation or vitiligo).13 Hair loss, which may either be mild or extensive, also may occur. The nails may be thin, brittle, and horizontally ridged. Associated skin disorders may include impetigo herpetiformis (see the previous discussion on the skin signs of pregnancy), candidiasis (Fig. 212-10), and exfoliative dermatitis.

ADRENAL GLANDS

FIGURE 212-7. A, Severe dryness of the skin in a 45-year-old man with hypothyroidism secondary to Hashimoto's thyroiditis. B, Nonpitting puffiness of the hands in a 22-year-old woman with hypothyroidism of 2 years' duration subsequent to radiation therapy for Graves disease.

In Cushing syndrome (see Chap. 73), body fat tends to be¬ come centripetally distributed, leading to the characteristic ap¬ pearance of exaggerated fat pads in the supraclavicular areas, posterior base of the neck (buffalo hump [Fig. 212-22A]), and cheeks (moon facies). The skin is somewhat atrophic as a result of the loss of dermal collagen and mucopolysaccharides, which.

Ch. 212: The Skin and Endocrine Disorders

1835

all may be involved, and may appear blue-black in longstanding disease. Other mucosal surfaces, including the conjunctiva and vagina, also may become hyperpigmented. Similarly, hair be¬ comes darker in color and nails may develop darkened longitu¬ dinal bands (see Chap. 16). In addition to hyperpigmentation, a subset of patients with Addison disease will also develop areas of vitiligo. PANCREAS The most common pancreatic disorder with skin manifesta¬ tions is diabetes mellitus. Associated findings are discussed in de¬ tail in Chapter 147. Also, Chapter 157 discusses the skin mani¬ festations of the hyperlipemias, some of which may be associated with disordered carbohydrate metabolism. Glucagon-producing islet cell tumors of the pancreas are as¬ sociated with a distinctive eruption—referred to as necrolytic mi¬ gratory erythema—as well as systemic symptoms and findings that include weakness, weight loss, and diarrhea. Laboratory evaluation may reveal markedly elevated plasma glucagon lev¬ els, normocytic normochromic anemia, elevated sedimentation rate, hyperglycemia, hypocholesterolemia, and hypoaminoacidemia1^ (see Chap. 176). The eruption itself often is characterized by a symmetrical and annular or arciform array of erythema, scale, papules, ero¬ sions, crusts, flaccid bullae, and postinflammatory hyperpigmen¬ tation. Typically, the advancing border may appear vesiculopustular, whereas the receding border is denuded. This eruption usually develops on the face, lower abdomen, groin, perineum, buttocks, thighs, and distal extremities. On the basis of this mor¬ phology, only a limited differential diagnosis exists, including pemphigus, zinc deficiency (inherited [acrodermatitis enteropathica] or acquired), and extensive candidiasis. Other findings associated with glucagonoma include glossi¬ tis, stomatitis, angular cheilitis, blepharitis, scalp alopecia, and thin and friable nails. Usually, necrolytic migratory erythema rapidly disappears after successful surgical removal of the gluca¬ gon-secreting tumor. Although this eruption is a very specific cu¬ taneous marker for underlying glucagonoma in a few affected patients, there has been no evidence of associated malignant disease. Several other diseases involving the pancreas, in addition to diabetes mellitus and glucagonoma, are associated with skin FIGURE 212-9. A 46-year-old man with hypothyroidism (A) before and (B) 6 months after treatment with thyroid hormone. Notice the more alert appearance, the darker skin, the increased sebaceous secretion, and the increased facial hair after therapy.

at least in part, contributes to its noticeably fine texture, the de¬ velopment of violaceous striae (on abdomen, thighs, arms), easy bruisability, plethoric-appearing facies, and prolonged wound healing. In addition, hirsutism and acne (see Fig. 212-1 IB) may develop, the latter of which may, at times, be severe. Some pa¬ tients with pigmented nodular adrenocortical disease, a condi¬ tion that may be associated with hypercortisolemia, have the Carney syndrome, which consists of spotty pigmentations of the skin, myxomatous masses, and endocrine disorders14 (Fig. 212-12). In adrenal virilizing syndromes, female patients may exhibit multiple cutaneous findings. These may include hirsutism, marked male-pattern alopecia or baldness, thickening of the skin, male escutcheon, and acne (see Chap. 75). In Addison disease (see Chap. 74), the major cutaneous finding is generalized hyperpigmentation of the skin and associ¬ ated mucous membranes. This pigmentation, which is tan to bronze in color, is accentuated in exposed areas (i.e., the face), in flexural folds and creases (palms, knuckles, elbows), in sites of trauma (i.e., scars), and in skin regions that are normally pig¬ mented (areolae, genitalia, some nevi, linea alba in pregnant women). In the oral cavity, the gums, buccal mucosa, and tongue

FIGURE 212-10. Brittleness, dystrophy, discoloration, and loss of the distal nail plate are evident in a patient with candidiasis of the nails.

1836

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

A

FIGURE 212-12. This young woman with multiple facial freckles has pigmented nodular adrenocortical disease (Carney syndrome). (From Carney JA, Gordon H, Carpenter PC, et al. The complex of myxomas, spotty pigmentation and endocrine overactivity. Medicine 1985;64:270.) state. The bronze skin discoloration in hemochromatosis has been attributed to increased melanin content within the epider¬ mis, whereas the bluish hue is believed to be the result of iron deposition within sweat glands. This discoloration initially de¬ velops on exposed areas of the body, and is most intense over the face, arms, genitalia, and body folds. FIGURE 212-11. A, A 25-year-old woman with a cervicodorsal fat pad (buffalo hump) (arrows) associated with Cushing disease. Also notice the increased amount of fine hair over the woman's back. B, Sudden onset of acne on the back of a young man being treated with high doses of prednisone.

changes, including pancreatitis, adenocarcinoma of the pancreas, and hemochromatosis. In acute or fulminant pancreatitis, for ex¬ ample, suppurative panniculitis may develop. These lesions, which reflect saponification and necrosis of subcutaneous tissue secondary to the effects of elevated serum levels of lipolytic en¬ zymes, are variably sized, painful nodules that are palpable deep within the skin and that characteristically suppurate, exuding an oily discharge to the skin surface. Identical lesions may also occur in the setting of pancreatic adenocarcinoma. Recurrent migratory superficial thrombophlebitis, usually seen on the upper extremi¬ ties, is also a marker for internal malignant disease, including pancreatic adenocarcinoma. In hemochromatosis (a disorder of excessive iron absorption or parenteral iron loading), multiple or¬ gans may be involved, including the pancreas. The latter may lead to the development of diabetes.16 The cutaneous findings associated with hemochromatosis (see Chap. 7) include localized to generalized bronze or bluish-gray discoloration, dryness, skin atrophy, hair loss (truncal, axillary, supra-pubic), palmar ery¬ thema and spider angiomas, of which the latter two features most likely reflect cirrhosis and its associated hyperestrogenic

MISCELLANEOUS CONDITIONS INVOLVING THE SKIN AND ENDOCRINE SYSTEM ACANTHOSIS NIGRICANS As previously described, acanthosis nigricans is usually a lo¬ calized process characterized by hyperpigmentation, papillo-

FIGURE 212-13. The vulva and medial thighs of this woman with ac¬ anthosis nigricans are hyperpigmented and have a velvet-like appear¬ ance (see Chap. 140).

Ch. 212: The Skin and Endocrine Disorders

1837

matous hyperproliferation, and dermal glycosaminoglycan de¬ position of the skin.17 For practical purposes, acanthosis nigricans can be thought of as arising primarily in three subsets of patients. In the first subset, a very mild clinical variant, sometimes referred to as “benign” acanthosis nigricans, develops along the sides of the neck, the axillary vaults, or the inguinal folds and perineal region. This form is associated with obesity and with onset at puberty or afterward (Fig. 212-13). However, this so-called be¬ nign acanthosis nigricans also has been reported in a number of other unrelated conditions, such as acromegaly, pituitary and hy¬ pothalamic tumors or lesions (sarcoidosis), Cushing disease, adrenal insufficiency, polycystic ovary syndrome, chondrodys¬ trophy, Wilson disease, lupoid hepatitis, hepatic cirrhosis, Rud syndrome (lamellar ichthyosis, dwarfism, hypogonadism, mental retardation and epilepsy), Bloom syndrome (photosensitivity, fa¬ cial telangiectasia, short stature, and neoplasia), and drug use (diethylstilbestrol, corticosteroids, and nicotinic acid). The second group of patients with associated “benign” acanthosis nigricans, which is often extensive or generalized in distribution, are those with syndromes of insulin-resistant diabetes mellitus (see Chap. 140). In the third form of the disease, which is often referred to as “malignant” acanthosis nigricans, the eruption appears de novo, usually after the age of 50 to 55 years, and is associated with occult malignant disease, the most common of which is ad¬ enocarcinoma of the stomach (see Chap. 213).

MULTIPLE ENDOCRINE NEOPLASIA The cutaneous manifestations that occur in patients with various types of multiple endocrine neoplasia (MEN) may reflect the particular organs involved (e.g., the parathyroid, pituitary, and pancreatic islet cells in MEN type 1). In addition, patients with MEN type 1 may develop multiple lipomas, epidermal in¬ clusion cysts, and leiomyomas. In MEN type 2A, no specific skin markers are present, whereas in MEN type 2B (medullary carci¬ noma of the thyroid and pheochromocytoma), extensive neuro¬ mas may occur and may involve the mucous membranes. Addi¬ tionally, there may be evidence of diffuse lentigos, cafe au lait spots, neuromas, or neurofibromas (see Chap. 182).

FIGURE 212-15. Severe calcinosis cutis in a patient who has hyper¬ parathyroidism secondary to prolonged renal failure and who is on dial¬ ysis. Multiple ischemic ulcerations of the fingers are visible (arrows).

ever, a subset of patients may develop vitiligo before, at the same time, or after the appearance of one or more endocrine condi¬ tions, including thyroid disease, Addison disease, diabetes melli¬ tus, and hypoparathyroidism. For example, approximately 7% of patients with Graves disease, and 15% of those with Addison disease, have been reported to have vitiligo. Furthermore, vitiligo may be seen in some patients who are diagnosed as having auto¬ immune polyglandular failure syndrome, and various autoanti¬ bodies (including antibodies directed against thyroid, adrenal,

VITILIGO Vitiligo, which was mentioned earlier, is a presumptive au¬ toimmune condition characterized by the development of sym¬ metrical depigmentation (either localized or generalized) of the skin. It usually occurs in the absence of endocrine disease; how-

FIGURE 212-14. Scleredema (Buschke disease) in a man with type II diabetes mellitus. Notice the thickened, infiltrated, peau d'orange ap¬ pearance of the skin of the back.

FIGURE 212-16. Discrete, hypopigmented macules (arrows), referred to as cafe au lait spots, are visible on the backs of the legs of a patient with neurofibromatosis.

1838

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

and parietal cells) may be detectable in the sera of some patients with vitiligo, even in the absence of definable endocrinopathy (see Chap. 191).

LIPODYSTROPHIES Lipodystrophies are characterized by localized, partial, or generalized loss of subcutaneous tissue. Localized lipodystrophy (see Chaps. 139 and 147) primarily occurs in sites of insulin in¬ jection. Although it has been a problem in the past, lipodystro¬ phy is seen less commonly in patients who are using the newer, more purified or synthetic insulin preparations. In partial (pro¬ gressive cephalothoracic) lipodystrophy, which has a 20% inci¬ dence of associated diabetes mellitus, an initial loss of subcuta¬ neous tissue in the facial area leads to marked coarsening of the facial features. With time, this process slowly progresses inferiorly. A generalized form of lipodystrophy (Lawrence-Seip syn¬ drome), which is characterized by autosomal recessive transmis¬ sion and onset at puberty, also may occur. This form is associated with insulin-resistant diabetes mellitus and hyperthyroidism. Affected patients may also manifest cirrhosis, epilepsy, or mental retardation (see Chap. 140).

SCLEREDEMA OF BUSCHKE Scleredema of Buschke is characterized by the sudden onset of diffuse symmetrical, nonpitting, woody induration of the skin. This usually develops first in the posterior and lateral aspects of the neck or face, but it may progress over a period of several weeks to months to include the upper trunk, back, and arms and, rarely, other areas of the body. The affected skin is usually freshcolored; when the induration is pronounced, some areas may ac¬ tually have a peau d'orange appearance (Fig. 212-14). The face, when affected, may become expressionless. Although this disor¬ der usually affects only the skin, other tissues may become in¬ volved, including the tongue, pharynx, conjunctiva, heart, and pleura. Diabetes mellitus is seen in many of these patients. The etiology of this condition is unknown. Both adults and children may be affected, and many experience a preceding infection, which is most often streptococcal in nature. Histochemical stud¬ ies suggest increased collagen synthesis and, in some cases, in¬ creased deposition of acid mucopolysaccharides within the der¬ mis. In most patients, this disorder spontaneously resolves within 6 to 24 months; however, in others, it may persist for years or indefinitely.

OTHER METABOLIC DISORDERS WITH CUTANEOUS MANIFESTATIONS Albright syndrome consists of the triad of localized hyper¬ pigmentation, often unilateral lesions of fibrous dysplasia affect¬ ing the long bones of the extremities or pelvis, and precocious puberty. The characteristic skin lesion in this syndrome is a soli¬ tary, often large, brown macule with jagged borders that is lo¬ cated on the same side of the body as the underlying bony ab¬ normalities. In addition, oral hyperpigmentation may be seen in some patients. Neurofibromatosis is an autosomal dominant disorder char¬ acterized by the development of usually widespread tumors (neurofibromas) on the skin, as well as in other organs, including the nervous system, eye, gastrointestinal tract, and bone.21 Less than 1% of patients with neurofibromatosis develop a pheochromocytoma. A pathognomonic skin finding in neurofibromatosis is axillary freckling. Other characteristic skin lesions include cafe au lait spots (Fig. 212-16) (more than 75% of affected patients have six or more with a diameter of at least 1.5 cm), soft pedun¬ culated or firmer nonpedunculated neurofibromas, and rarely, large lobulated masses (plexiform neuromas) containing tumors arranged along peripheral nerves.22 Werner syndrome23 is an autosomal recessive condition that is associated with endocrine abnormalities, such as diabetes mel¬ litus, hypogonadism, osteoporosis, metastatic subcutaneous calcifications, and impotence. The skin typically shows patches of scleroderma-like changes and marked, premature wrinkling (Fig. 212-17). Many other metabolic disorders, both acquired and inher¬ ited, have prominent cutaneous manifestations. Although a de¬ tailed discussion of each of these conditions is beyond the scope of this chapter, salient features of several of these diseases are summarized in Table 212-1.24-27

PIGMENTARY ALTERATIONS AND THE ENDOCRINE SYSTEM As previously discussed, many endocrine disorders are char¬ acterized by generalized or focal, increased or decreased pigmen-

CUTANEOUS CALCIFICATION Calcification may occur in localized or more generalized ar¬ eas of skin and other organs as a result of (1) preceding tissue injury (dystrophic calcification), (2) markedly elevated calciumphosphorus product (metastatic calcification), or (3) unknown reasons (as in the case of calcinosis circumscripta or universalis). When present within the skin, asymptomatic papules or nodules are usually seen. In some situations, these lesions may break down, leading to drainage of chalky material. With regard to en¬ docrine conditions associated with metastatic calcification to the skin, hyperparathyroidism and hypoparathyroidism must be considered in the differential diagnosis (Fig". 212-15). In one unique clinical disorder—calciphylaxis—painful ischemic ulcer¬ ations may develop on the fingers, legs, and thighs of patients with secondary or tertiary hyperparathyroidism who are un¬ dergoing maintenance hemodialysis or who have functioning re¬ nal homografts.181' Although the mechanism for this phenome¬ non is still poorly understood, it appears in part to involve arterial insufficiency and ischemic necrosis in conjunction with medial calcification of dermal and subcutaneous arterioles and arteries. Although patients on chronic dialysis commonly develop meta¬ static calcification of various organs, the skin is involved only rarely.20

FIGURE 212-17. A 48-year-old woman with Werner syndrome. She appears senile, has alopecia of the scalp, graying of the hair, and thinned, wrinkled skin. (From Epstein C] et al. Medicine 1966;45:177.)

Ch. 212: The Skin and Endocrine Disorders

1839

TABLE 212-1 Selected Metabolic Disorders With Cutaneous Manifestations

Disease

Mode of Transmission

Clinical Findings Metabolic Defect

Skin

Extracutaneous

Fair complexion; blond or light

Blue eyes; neurologic deterioration; skele¬ tal changes (microcephaly, short stat¬ ure, syndactyly, pes planus); pyloric stenosis

DISORDERS OF AMINO ACID METABOLISM*24'27 PHENYLKETONURIA

AR

Phenylalanine hydroxylase de¬ ficiency (owing to defective dihydrobiopterin biosynthesis, or deficient dihydropteridine reductase in 10% of affected patients)

HOMOCYSTINURIA

ALKAPTONURIA

HARTNUP'S DISEASE

AR

AR

AR

?AR

tremities); atrophoderma; lin¬ ear scleroderma

Cystathionine synthetase defi¬ ciency

Fair complexion; fine, light hair; malar blush; livedo reticularis

Ocular changes (e.g., glaucoma, dislo¬

Homogentisic acid oxidase defi¬ ciency

Gray discoloration (eyelids, tar¬

Ocular discoloration (gray) (sclera, con¬ junctiva, cornea); spinal changes (e.g., lumbosacral spondylosis); severe de¬ generative arthritis; calculi (prostatic, renal); aortic valve murmurs

Defective amino acid transport

Photoeruption (pellagra-like); abnormal hair

Neurologic changes (ataxia, dementia,

Absent tyrosine aminotransferase

Painful palmoplantar keratoses

Corneal ulcers and clouding; photopho¬ bia

(renal, intestinal)

TYROSINEMIA (TYPE II; RICHNER-HANHART SYNDROME)24

hair; atopic eczema; scleroder¬ moid changes (in lower ex¬

sal plate, pinna, hands, nasal tip, malar face, flexural areas)

cated lens, proptosis); neurologic ab¬ normalities (seizures, mental retarda¬ tion); skeletal disorders (disproportion, various deformities, vertebral osteopo¬ rosis, high arched palate); hepatomeg¬ aly; premature atherosclerosis (strokes, myocardial infarcts); thromboembolic phenomena

spasticity); short stature; diarrhea; glos¬ sitis, stomatitis

DISORDERS OF LIPID METABOLISM* FABRY DISEASE

XR

Galactosidase A deficiency

Angiokeratomas (diffuse; espe¬ cially affecting the umbilicus, knees); telangiectases; turtleback nails; defective sweating

Angiokeratomas (oral mucosa, tongue, conjunctiva); severe peripheral neural¬ gias; fever; distal arthropathy; corneal opacities; aneurysmal dilatations (con¬ junctival veins); renal failure; hyper¬ tension; atherosclerosis; pulmonary disease

REFSUM DISEASE

AR

Phytanic acid a-hydroxylase de¬ ficiency

Acquired ichthyosis

Ocular changes (night blindness, altered visual fields, retinitis pigmentosa, cata¬ racts); impaired hearing; neurologic ab¬ normalities (e.g., ataxia, polyneuropa¬ thy); renal disease; skeletal deformities

DISORDERS OF METAL METABOLISM* WILSON DISEASE

AR

Abnormal copper metabolism

Hyperpigmentation (legs); easy bruisability; azure lunulae (nails)

Pigmented corneal ring (Kayser-Fleischer ring); neurologic changes (cerebellar, pyramidal, pseudobulbar); psychiatric symptoms; hepatic disease (hepatitis, cirrhosis); hypersplenism; hemolytic anemia; skeletal changes; renal calculi, arthralgias; cardiac disease (rare)

MENKES SYNDROME

XR

Abnormal copper transport

Abnormal hair (pili torti)

Failure to thrive; hypothermia; recurrent infections (respiratory and gastrointes¬ tinal); neurologic abnormalities (retar¬ dation, seizures, spasticity); deafness; blindness

ACRODERMATITIS ENTEROPATHICA26

AR

Zinc deficiency

Symmetrical erosions, crusts, vesicles; hyperkeratotic areas (periorificial, acral, perianal, intergluteal); nail dystrophy; alopecia

Failure to thrive; malabsorption; diarrhea; growth retardation; photophobia

* See Chap. 185. f See Chap. 157. * See Chap. 7. AR, autosomal recessive; XR, X-linked recessive.

1840

PART XIV: INTERRELATIONSHIPS BETWEEN HORMONES AND THE BODY

tation of the skin. Techniques are available to quantify skin pig¬ mentation.28 For example, hyperpigmentation may occur with Addison disease, ACTH-producing tumors of the pituitary gland, paraneoplastic ACTH secretion, and POEMS syndrome (periph¬ eral neuropathy, organomegaly, endocrine dysfunction, mono¬ clonal gammopathy, and skin pigmentation). 2,29 Hypopigmentation may accompany panhypopituitarism, hypogonadism (particularly in the male patient), and vitiligo (in polyglandular autoimmune deficiency).

REFERENCES 1. Fine JD, Moschella SL. Diseases of nutrition and metabolism. In: Moschella SL, Hurley HJ, eds. Dermatology, ed 2. Philadelphia: WB Saunders, 1985:1422. 2. Costello MJ. Eruptions of pregnancy. NY State J Med 1941;41:849. 3. Katz SI, Hertz KC, Yaoita H. Immunopathology and characterization of the herpes gestationis factor. J Clin Invest 1976;57:1434. 4. Lawley TJ, Stingl G, Katz SI. Fetal and maternal risk factors in herpes ges¬ tationis. Arch Dermatol 1978; 114:552. 5. Shornick JK, Stastny P, Gilliam JM. High frequency of histocompatibility antigens HLA-DR3 and DR4 in herpes gestationis. J Clin Invest 1981;68:553. 6. Lawley TJ, Hertz KC, Wade TR, et al. Pruritic urticarial papules and plaques of pregnancy. JAMA 1979;241:1696. 7. Bierman SM, Ackerman AB, Katz SI. Autoimmune progesterone dermatitis of pregnancy. Arch Dermatol 1973; 107:896. 8. Spangler AS, Emerson K Jr. Estrogen levels and estrogen therapy in papular dermatitis of pregnancy. Am J Obstet Gynecol 1971; 110:534. 9. Lang PC. Cutaneous manifestations of thyroid disease. Cutis 1978;21:862. 10. Cheung H, Nicoloff JT, Kamiel MB, et al. Stimulation of fibroblast biosyn¬ thetic activity by serum of patients with pretibial myxedema. J Invest Dermatol 1978;71:12. 11. Jolliffe DS, Gaylarde PM, Brock AP, Sarkany I. Pretibial myxedema: stim¬ ulation of mucopolysaccharide production of fibroblasts by serum. Br J Dermatol 1979; 100:557.

12. Zone JJ, Petersen MJ. Dermatitis herpetiformis. In: Thiers BH, Dobson RL, eds. Pathogenesis of skin disease. New York: Churchill Livingstone, 1986:159. 13. DePadova-Elder SM, Ditre CM, Kantor GR, et al. Candidiasis endocrinopathy syndrome. Arch Dermatol 1994; 130:19. 14. Carney JA, Gordon H, Carpenter PC, et al. The complex of myxomas, spotty pigmentation and endocrine overactivity. Medicine 1985; 64:270. 15. Kahan RS, Perez-Figaredo RA, Neimanis A. Necrolytic migratory ery¬ thema. Distinctive dermatosis of the glucagonoma syndrome. Arch Dermatol 1977;113:792. 16. Bassett ML, HalidayJW, Powell LW. Hemochromatosis—newer concepts: diagnosis and management. DM 1980; 26:1. 17. Matsuoka LY, Wortsman J, Gavin JR, Goldman J. Spectrum of endocrine abnormalities associated with acanthosis nigricans. Am J Med 1987;83:719. 18. Gipstein RM, Coburn JW, Adams DA, et al. Calciphylaxis in man: a syn¬ drome of tissue necrosis and vascular calcification in 11 patients with chronic renal failure. Arch Intern Med 1976; 136:1273. 19. Mehregan DA, Winkelmann RK. Cutaneous gangrene, vascular calcifica¬ tion, and hyperparathyroidism. Mayo Clin Proc 1989;64:211. 20. de Graaf P, Ruiter DJ, Scheffer E, et al. Metastatic skin calcification: a rare phenomenon in dialysis patients. Dermatologica 1980; 161:28. 21. Hofman KJ. Diffusion of information about neurofibromatosis type 1 DNA Testing. Am J Med Genet 1994;49:299. 22. Martuza RL, Eldridge R. Neurofibromatosis 2. N Engl J Med 1988; 318: 684. 23. Bauer EA, Uitto J, Tau ML, Holbrook KA. Werner's syndrome: evidence for preferential regional expression of a generalized mesenchymal cell defect. Arch Dermatol 1988; 124:90. 24. Goldsmith LA. Tyrosine-induced skin disease. BrJ Dermatol 1978; 98:119. 25. Fine JD, Wise TG, Falchuk KH. Zinc in cutaneous disease and dermato¬ logic therapeutics. In: Moschella SL, ed. Dermatology update: reviews for physi¬ cians. New York: Elsevier, 1982:299. 26. Steinbach HL, Russell W. Measurement of the heel pad as an aid to diag¬ nosis of acromegaly. Radiology 1964;82:418. 27. Case Records of the Massachusetts General Hospital. Case 10-1987. N Engl J Med 1987;316:606. 28. Bech-Thomsen N, Angelo HR, Wulf HG. Arch Dermatol 1994; 130:464. 29. Schulz W, Domenico D, Nand S. POEMS syndrome associated with poly¬ cythemia vera. Cancer 1989;63:1175.

PART

XV

HORMONES AND CANCER KENNETH L. BECKER, editor

213. 214. 215. 216. 217. 218. 219.

PARANEOPLASTIC ENDOCRINE SYNDROMES. 1842 THE CARCINOID TUMOR AND THE CARCINOID SYNDROME. 1853 HORMONES AND CARCINOGENESIS: LABORATORY STUDIES. 1856 SEX HORMONES AND HUMAN CARCINOGENESIS: EPIDEMIOLOGY.. 1861 ENDOCRINE TREATMENT OF BREAST CANCER. 1868 ENDOCRINE ASPECTS OF PROSTATE CANCER. 1875 ENDOCRINE CONSEQUENCES OF CANCER THERAPY. 1884

1842

PART XV: HORMONES AND CANCER Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

213_

PARANEOPLASTIC ENDOCRINE SYNDROMES KENNETH L. BECKER AND OMEGA L. SILVA

DEFINITION Along with being a local disorder of tissue growth and a source of potential metastases, cancers often have important sys¬ temic metabolic manifestations. These remote biologic effects sometimes can dominate the other clinical effects of the malig¬ nant process.1,2 As discussed in other chapters of this text, many humoral manifestations are attributable to a neoplasm of a tissue that normally is the predominant site of production of the hor¬ mone (e.g., pituitary prolactinoma and galactorrhea; adrenal cor¬ tical adenoma and Cushing syndrome; thyroid adenoma and hy¬ perthyroidism). However, if clinical manifestations are the result of hormones secreted by tumors emanating from tissues that nor¬ mally do not secrete them into the blood at significant levels, they are termed paraneoplastic endocrine syndromes. Despite the extraordinary cellular differentiation and orga¬ nization seen in humans, most normal tissues retain the ability to secrete many hormones, albeit some more efficiently than others (see Chap. 171). This inherent secretory capacity is shared by the neoplasms derived from these tissues. A cancer often reflects the innate humoral characteristics and secretory potentials of its cell of origin. Thus, conceptually, the elaboration of a hormone by a neoplasm is not really "ectopic"; it is "eutopic," but quantita¬ tively abnormal.

PATHOGENESIS Some tumors that produce paraneoplastic endocrine syn¬ dromes (e.g., small-cell lung cancer,3 carcinoid tumor, Merkel cell tumor) arise from the so-called diffuse neuroendocrine system

TABLE 213-1 Criteria for Defining a Paraneoplastic Endocrine Syndrome* * • Documentation, in a patient with a neoplasm, of the presence of a syndrome known to be caused by a certain hormone. • Measurement of increased levels of the hormone in the serum, the urine, or both. (Investigatively, it may be informative to compare the potency of the hormone by immunologic means [e.g., radioimmunoassay], by its receptor affinity [e.g., radioreceptor assay], and by its biologic effects [e.g., bioassay].) • Determination of an arteriovenous gradient for the hormone, indicating active secretion. 8 Demonstration of hormone concentrations in the neoplastic tissues that are ' greater than those found in the normal adjacent tissue. (Such studies can be performed quantitatively [e.g., radioimmunoassay or bioassay] or qualitatively [immunohistochemical methods].) • Demonstration in the tumor of messenger RNA coding for the hormone in question. • Demonstration that removal of the tumor (by surgery) or other antitumor effect (e.g., by chemotherapy) causes remission of the paraneoplastic syndrome. • Return of the hormonal syndrome with recurrence of the tumor. * Not all these criteria must be met in any given patient before the clinical diagnosis of a paraneoplastic endocrine syndrome can be established.

(see Chap. 171). Although the primordial tissues engendering such neoplastic lesions initially were thought to have a common embryonic origin, this theory is no longer tenable. The neuroen¬ docrine cancers do not share common embryonic precursors. Also, many paraneoplastic syndromes originate from tumors that are not neuroendocrine. Attempting to explain why a tumor produces hormones, in¬ vestigators have stressed the fact that the DNA complement within each normal somatic cell is identical; that is, in each spe¬ cific cell, some functions normally are repressed (e.g., a gene that codes for a certain hormone). Therefore, hormone-secreting can¬ cers are viewed as exhibiting selective derepression of the ge¬ nome, allowing synthesis of the hormone. Others attribute the hormonal elaboration by cancer to a failure of differentiation of undifferentiated, totipotential stem cells.

CRITERIA Certain traditional criteria have been proposed for accepting a group of symptoms and signs as a paraneoplastic endocrine syndrome4 (Table 213-1). However, these idealized criteria have not been met for several bona fide paraneoplastic syndromes, and often are unnecessary for making the diagnosis.

GENERAL PRINCIPLES A common feature of most paraneoplastic endocrine syn¬ dromes is the elaboration of peptide hormones. De novo steroid synthesis by cancer usually requires adrenal, gonadal, or placen¬ tal tissue, and de novo thyroid hormone synthesis requires thy¬ roidal or teratomatous tissue (see Chap. 199). Moreover, biogenic amines (i.e., histamine, serotonin) play significant roles in some paraneoplastic manifestations. Prosta¬ glandin secretion also may be important (see Chap. 170). When encountering most paraneoplastic endocrine syn¬ dromes, the physician already is conscious of the associated neo¬ plasm. Nonetheless, sometimes the syndrome precedes the diag¬ nosis of the tumor; indeed, marked endocrine effects may mask the tumor, averting attention to inappropriate therapeutic ap¬ proaches. Although a paraneoplastic endocrine syndrome might constitute an interesting but relatively harmless occurrence (e.g., acanthosis nigricans, hypertrophic osteoarthropathy), it also might contribute directly to the patient's premature demise (e.g., hypercalcemia, syndrome of inappropriate antidiuresis [SIAD]). Although tumors sometimes produce the same hormone as related normal cells, they often produce and secrete much greater quantities.5 Moreover, such tumors frequently secrete other hor¬ mones, which may be secreted by their normal cellular counter¬ parts in minute amounts. The clinical effects of the polyhormonal potential of many of these tumors are unknown. Generally, hormones secreted by cancers are not unique in chemical structure. Nonetheless, there frequently is an abnormal distribution of the molecular forms of the secreted peptide. In particular, there often is a predominance of precursor forms with high molecular weight; this probably reflects a deficient or in¬ complete posttranslational modification, or it may signify an al¬ ternative means of secretion.6 Because these precursors often have less or no bioactivity, a clinical syndrome may not occur, despite an extraordinarily high level of radioimmunoassayable hormone in the serum. Most tumors producing such peptides re¬ main clinically silent. Furthermore, the finding of high serum hormone levels em¬ anating from a tissue other than a classic endocrine gland is not a specific indicator of neoplasia. Irritated, hyperplastic, or premalignant tissues or lesions also may secrete increased levels of pep¬ tide hormones (e.g., in chronic obstructive pulmonary disease, chronic bronchitis of smokers, regional ileitis, and ulcerative colitis).

Ch. 213: Paraneoplastic Endocrine Syndromes Morphologically, in contrast to normal, anatomically dis¬ crete endocrine organs, hormone-secreting neoplasms often do not possess a highly structured and coordinated neural control. Metabolically, the neoplastic cells in most paraneoplastic syndromes often do not respond to the usual physiologic control mechanisms that modulate normal hormone secretion (i.e., phys¬ iologic secretagogues, feedback suppression). Although there are exceptions, this relative autonomy may be of considerable diag¬ nostic utility. Last, the hormonal secretion by cancer may serve as an im¬ portant biomarker for its presence, its response to therapy, and its relapse.

1843

PARANEOPLASTIC CORTICOTROPIN RELEASING HORMONE SYNDROME Corticotropin releasing hormone (CRH) has been found in bronchial carcinoid tumors and in small-cell carcinoma of the lung. Rarely, high serum levels of this hormone stimulate the pi¬ tuitary gland to produce excess adrenocorticotropic hormone (ACTH). In such cases, the increased ACTH levels cause bilateral adrenal hyperplasia, and the resultant hypercortisolism results in Cushing syndrome1112 (see Chap. 73).

PARANEOPLASTIC ADRENOCORTICOTROPIC HORMONE SYNDROME

SPECIFIC PARANEOPLASTIC ENDOCRINE SYNDROMES This chapter discusses the paraneoplastic endocrine syn¬ dromes of certain cancers, including those in which the humoral mediator is suspected but not yet identified. Brief mention also is made of possible humoral syndromes that arise as a result of the effect of neoplasia on noncancerous tissue. Hormone-secreting tumors of the pancreas and of the neuroendocrine cells of the gut (e.g., insulinoma, gastrinoma) are discussed elsewhere (see Chaps. 152 and 176). Although several humoral syndromes as¬ sociated with other neuroendocrine tumors are mentioned, they also are discussed in other chapters.

PARANEOPLASTIC GROWTH HORMONE RELEASING HORMONE SYNDROME Although far less common than hypothalamic-pituitary ac¬ romegaly, the syndrome of acromegaly that is secondary to the tumoral secretion of growth hormone releasing hormone (GHRH) is a fascinating and instructive example of a paraneo¬ plastic endocrine syndrome. Normally, GHRH circulates at low or undetectable levels, although appreciable levels are found in the hypothalamic-hypophysial portal system. Some tumors se¬ crete large amounts of GHRH, causing acromegaly. The secreted GHRH is the same as that in the human hypothalamus; both the 44 and 40 amino acid hormones are found.7 Two lesions, in particular, may produce the syndrome: bron¬ chial carcinoid and pancreatic islet cell tumor. In addition, GHRH is found in some carcinoid tumors involving the gastrointestinal tract and thymus, as well as in pheochromocytoma, medullary thyroid cancer, and small-cell lung cancer. However, although it is also in the blood of some patients with these tumors, it does not necessarily cause symptoms and signs of acromegaly. Patients with the full-blown syndrome of paraneoplastic GHRH secretion have the classic appearance of acromegaly (see Chap. 14), but often of more rapid onset. The serum levels of GHRH often exceed 200 pg/mL. The high serum levels of the hormone cause hyperplasia of the pituitary somatotropes, with consequent hypersecretion of growth hormone. As in hypothalamic-pituitary acromegaly, serum growth hormone lev¬ els are not suppressed after the administration of oral glucose; however, in contrast to classic acromegaly, patients with the paraneoplastic GHRH syndrome may have a markedly increased serum growth hormone response to insulin-induced hypoglyce¬ mia.8 Usually, the sella turcica is not enlarged, and examination by computed tomography or nuclear magnetic resonance im¬ aging yields normal results. However, occasionally, an enlarged sella is seen9; some cases apparently eventuate with pituitary tumors. Pituitary surgery is not indicated in this syndrome. If feasi¬ ble, the cancerous lesion should be removed. If surgery is suc¬ cessful, it should cause regression of the acromegalic syndrome. Medical treatment with bromocriptine often successfully sup¬ presses the growth hormone level; the somatostatin analogue, octreotide acetate, also has been useful in this regard.10

The paraneoplastic ACTH syndrome (or so-called ectopic ACTH syndrome) is caused by the secretion of ACTH by a nonpituitary neoplasm, which results in bilateral adrenal hyperplasia and manifestations of Cushing syndrome. This condition is more common than Cushing disease. Two thirds of the cases of para¬ neoplastic ACTH syndrome are attributable to bronchogenic cancer. The principal offender is small-cell cancer of the lung; occasionally, pulmonary adenocarcinoma also has been impli¬ cated. Another common cause is the relatively benign bronchial carcinoid tumor.13 Other, less frequent causes are thymic tumor (usually benign, and often of carcinoid histology), islet cell carci¬ noma of the pancreas, medullary thyroid cancer, pheochromocy¬ toma, and colon carcinoma. Manifestations of the syndrome are influenced not only by the level of ACTH secretion, but also by the bioactivity of the hormone. Many nonpituitary tumors that secrete ACTH typically remain biologically silent because of the secretion of bioinactive precursors of ACTH—so-called big ACTH—that make up pre¬ proopiomelanocortin and its related products, including multiple immunologic forms of /3~endorphin.14 Simultaneous assays of receptor-active ACTH and immunoactive ACTH have confirmed the inactivity of many of the secreted hormones. Thus, although about one third of patients with small-cell cancer of the lung have increased serum ACTH levels by radioimmunoassay, only 1% to 2% have hypercortisolism. Clinically, because of the close association with small-cell lung cancer, it is not surprising that many patients with the syn¬ drome are men older than 40 years who abuse tobacco. (This is in direct contrast to Cushing disease, which occurs in younger persons and has a strong female predilection.) The tumor type is important; patients with slow-growing bronchial carcinoid often have a gradual, insidious disease onset, a duration of symptoms that may span months to several years, and a prolonged period during which the classic cushingoid features develop (facial plethora, moon facies, easy bruising, hirsutism, truncal obesity, and atrophy of the extremities).15 In such patients, the tumor may be occult and difficult to localize.16 Because of the increased secretion of ACTH and its pre¬ cursor (proopiomelanocortin), there is an increased level of melanocyte-stimulating hormone (MSH) activity (a-MSH within the ACTH molecule, and /3-MSH within the /3-bpotropin mole¬ cule; see Chap. 16). Consequently, these patients may manifest marked hyperpigmentation that is similar in appearance to that encountered in Addison disease (Fig. 213-1). Patients with more aggressive malignant disease (e.g., small¬ cell lung cancer [see Fig. 213-1], pancreatic adenocarcinoma) of¬ ten do not have centripetal obesity. Commonly, the onset is acute, the symptoms have been present for several weeks at the time of examination, and there is obvious, rapid weight loss. Of¬ ten, the serum ACTH level is even higher than that in patients with carcinoid tumor, and the resultant hyperpigmentation is more pronounced. Other manifestations may include edema, muscle weakness, hypertension, severe hypokalemic alkalosis, and hyperglycemia. However, a clear-cut parallelism between clinical findings, tumor type, and duration of the neoplasm is not always present.

1844

PART XV: HORMONES AND CANCER

FIGURE 213-1.

Patient with paraneoplastic ACTH syndrome second¬

ary to small-cell cancer of the lung. Note the darkening of the skin, the fullness of the cheeks and the supraclavicular fossae, and the cervicodorsal hump.

Laboratory studies of patients with the paraneoplastic ACTH syndrome may reveal normal or decreased serum potas¬ sium levels. Hypokalemia occurs much more commonly in this syndrome than in either pituitary Cushing disease or Cushing syndrome secondary to adrenal adenoma. Any unprovoked hy¬ pokalemia (i.e., a patient not taking diuretics or laxatives) merits further investigation. There may be metabolic alkalosis and hy¬ perglycemia. The demonstration of hypercortisolism is essential to the diagnosis. Commonly, the serum cortisol level is extremely high—higher than that seen in most patients with Cushing dis¬ ease (although the serum cortisol elevation in patients with car¬ cinoid tumor often is moderate). The normal diurnal cortisol rhythmicity (see Chap. 5) is abolished, and there often is a large day-to-day variability in the serum cortisol level. Rarely, periodic hypersecretion may be encountered, with intervals of days to weeks of normal levels interspersed among periods marked by increased values. Increased levels of serum dehydroepiandrosterone sulfate and urinary 17-ketosteroids may help to distin¬ guish between Cushing syndrome caused by paraneoplastic ACTH production and Cushing syndrome caused by unilateral adrenal adenoma, the latter of which is characterized by normal values. , Although there are exceptions, many patients with the para¬ neoplastic ACTH syndrome do not exhibit suppression of serum cortisol or urinary 17-hydroxycorticosteroid levels with daily ad¬ ministration of 8 mg of dexamethasone orally (2 mg every 6 hours for 2 days). However, most patients with Cushing disease do exhibit such suppression (see Chaps. 72 and 73). In contrast to the marked responsiveness of serum 11 -deoxycortisol and uri¬ nary 17-hydroxycorticosteroid levels to the administration of metyrapone that usually occurs with Cushing disease, those with the paraneoplastic ACTH syndrome generally are unresponsive. In the paraneoplastic ACTH syndrome, serum ACTH levels

usually are high, and there may be simultaneous production of several other hormones, such as calcitonin, arginine vasopressin (AVP), somatostatin, or vasoactive intestinal peptide. (The socalled (8-MSH-secreting tumor does not constitute a clinical en¬ tity that is distinct from the paraneoplastic ACTH syndrome.) The injection of CRH may induce a further increase in serum ACTH levels in Cushing disease, but not in the paraneoplastic ACTH syndrome.17 Localization studies are essential to the workup of these pa¬ tients. Chest radiography, sputum cytology, and bronchoscopy often facilitate the diagnosis of small-cell lung cancer. Results of computed tomographic and magnetic resonance imaging studies of the pituitary are normal. Similar studies of the chest or abdo¬ men may reveal the tumor, and imaging of the abdomen often demonstrates bilateral adrenal hyperplasia. (In one instance, a pheochromocytoma that secreted ACTH was diagnosed in a pa¬ tient with bilateral enlarged adrenals, one of which also con¬ tained a focal mass.) Bilateral, simultaneous, inferior petrosal si¬ nus sampling of patients with paraneoplastic ACTH syndrome generally reveals no unilateral ACTH gradient, and demonstrates ACTH levels that are less than those derived from venous cathe¬ terization samples of the tumor effluent (e.g., mediastinal veins). Somatostatin receptor scintigraphy may be used to demonstrate the location of the tumor-producing lesion.18 Occasionally, per¬ cutaneous needle aspiration of tumor tissue, with assay of the intracellular ACTH, has confirmed the diagnosis.19 The ideal therapy for the paraneoplastic ACTH syndrome is extirpation of the neoplasm. If this is not feasible, some patients respond, albeit transiently, to chemotherapy. If the neoplasm cannot be treated successfully, adrenocortical hyperactivity can be mitigated with drugs, such as o' p' DDD, aminoglutethimide, metyrapone, or ketoconazole.20 In addition, such drugs can be administered before surgery in patients whose primary neo¬ plasms are resectable, but whose Cushing syndrome initially might make an operation too hazardous.

PARANEOPLASTIC ARGININE VASOPRESSIN SYNDROME The syndrome of inappropriate antidiuresis is characterized by the excretion of a hypertonic urine despite an expanded extra¬ cellular volume. SIAD can arise from central mechanisms (acute or chronic disorders of the central nervous system, drugs), or from peripheral mechanisms, in which case the secretion of AVP by a neoplasm is a common offender.21 This paraneoplastic AVP syndrome also has been termed tumoral hyponatremia22 (see Chaps. 26 and 28). AVP and oxytocin, as well as the carrier protein neurophysin, are found within such cancers, and cell cultures of the tumor also secrete the precursor peptide, propressophysin. In 80% of cases, the tumor causing SIAD is small-cell cancer of the lung23; although it often is an incidental finding, as many as one third of patients with this type of cancer have some degree of the syn¬ drome. Other tumors that have been known to cause SIAD in¬ clude those involving the pancreas, thymus, and breast. Occa¬ sionally, a cancerous lesion that does not directly secrete AVP can produce this syndrome through a central mechanism (e.g., metastases to the brain). The symptoms and signs of SIAD are attributable to water intoxication and hyponatremia, and may range in severity from having no effect to being life-threatening. There may be nausea, weakness, and central nervous system effects, such as confusion or obtundation, all of which may be easily misconstrued as being caused by the malignant disease. The central nervous system effects may progress to convulsions and, sometimes, frank coma. Laboratory studies reveal hyponatremia (and consequent hypoosmolality: < 270 mOsm/kg) and hypochloremia; serum potas¬ sium levels usually are normal. A concurrently voided specimen of urine will show inappropriate levels of sodium (or increased osmolality) in comparison to the serum hypoosmolality. The de-

Ch. 213: Paraneoplastic Endocrine Syndromes termination of serum AVP is not essential to the diagnosis; levels of the hormone need not appear to be inappropriately high. Some patients with pulmonary disorders, such as acute pneumonitis or advanced tuberculosis, also may manifest SIAD, allegedly as a result of alterations in thoracic baroreceptor control mechanisms. However, the syndrome is more likely attributable to AVP secretion by stimulated or hyperplastic pulmonary neu¬ roendocrine cells (see Chap. 172). The hyponatremia of tumor-associated SIAD must be dis¬ tinguished from that occurring with solute depletion, as well as from other conditions, such as adrenal insufficiency, hypopitu¬ itarism, hypothyroidism, congestive heart failure, cirrhosis of the liver, and renal disease. The initial therapy is water restriction. In emergencies, intravenous saline with furosemide-induced diure¬ sis is used; various drugs (lithium, hydantoin sodium, demethylchlortetracycline) also have been used (see Chap. 28). Many pa¬ tients with small-cell cancer of the lung exhibit a striking remission after radiotherapy, combined chemotherapy, or both, in which case the SIAD ceases, only to return with recurrence of the neoplasm. However, in rare instances, patients with this can¬ cer may be cured. Some patients with hyponatremia and inappropriate sodium loss have paraneoplastic secretion of atrial natriuretic hormone. This may occur in patients with small-cell cancer of the lung.24,25

PARANEOPLASTIC HYPERCALCEMIA The most common paraneoplastic endocrine syndrome is hypercalcemia. It also constitutes the most frequent form of hy¬ percalcemia seen in hospitalized patients (see Chap. 58). Of all the paraneoplastic syndromes, hypercalcemia is the most lifethreatening. Although the basic mechanism usually is excess bone resorption, increased tubular reabsorption of calcium also may be a factor. The symptoms and signs of the hypercalcemia associated with malignant disease do not differ markedly from those seen in other forms of hypercalcemia. The confusion and weakness may be attributed erroneously to the spread of the cancer or to che¬ motherapy. With the exception of lymphoma, multiple myeloma, and breast cancer, the associated hypercalcemia usually occurs late in the course of the disease. Its history is short, the onset often is abrupt, there may be erratic day-to-day variations in the level, and it is often a harbinger of imminent death. Nephrocalcinosis or nephrolithiasis usually is not seen, and there is no subperiosteal bone resorption or bone cysts; only rarely is there extraosseous metastatic calcification. Commonly, the hypercalce¬ mia is precipitated by volume depletion, resulting in a decreased glomerular filtration rate with renal retention of calcium. The condition is worsened by immobilization. Among solid tumors, the principal causes of the hypercalce¬ mia associated with malignant disease are breast cancer (50% of all patients with metastatic mammary cancer have an episode of hypercalcemia); lung cancer; squamous cell cancer of the head, neck, esophagus, and cervix; and cancer of the kidney, ovary, and bladder. Of the lung cancers associated with hypercalcemia, squamous cell carcinoma is the most common, adenocarcinoma occurs less frequently, large-cell cancer is uncommon, and small¬ cell carcinoma is rare. Of the hematologic malignant diseases causing hypercalcemia, multiple myeloma is the most common; among the leukemias, acute leukemia is the most common; and among the lymphomas, the histiocytic variety is particularly prone to cause the syndrome. The humoral factors causing the paraneoplastic hypercalce¬ mia of malignant disease are discussed in Chapter 58. Hardly ever do solid tumors produce parathyroid hormone (PTH).25a Rather, solid tumors often secrete PTH-related protein (PTHrp), which binds to PTH receptors and induces bone resorption and phosphaturia.26-28 There is some homology between PTHrelated protein and PTH in the amino terminal region. However,

1845

it does not react with antisera to PTH. PTHrp is the principal tumor-derived factor causing the hypercalcemia of malignancy, but its expression by a cancer does not necessarily obligate the occurrence of the hypercalcemia.29 PTHrp is expressed at low levels in normal tissues (see Chap. 51). Its gene expression and secretion are regulated, in part, by peptide growth factors, such as transforming growth factor /3 and epidermal growth factor.30 Cellular transformation by the ras and src oncogenes has been shown to increase the gene expression markedly.31 In patients with PTHrp-induced hypercalcemia, the serum calcium levels do not necessarily correlate with the serum hormonal levels. Nevertheless, the elevated serum levels of PTHrp, as well as the hypercalcemia, may return to normal after successful surgical removal of the tumor.32 It seems likely that, in addition to its hypercalcemic effect, PTHrp stimulates the growth of some malignant cells in an autocrine fashion.29,33 Other humoral factors that are produced either by solid tu¬ mors or by hematologic neoplasms have been implicated in hy¬ percalcemia, again because of their bone-resorbing effects. For example, multiple myeloma often produces osteoclast activating factors, which are made up of one or several cytokines (e.g., in¬ terleukin-1/3, lymphotoxin) emanating directly from the neoplas¬ tic plasma cell.34 Multiple myeloma also may produce tumor ne¬ crosis factor /3, a cytokine that is normally secreted by monocytes and macrophages and that also causes bone resorption. Several other growth factors resorb bone and are secreted by various neo¬ plasms in patients with associated hypercalcemia, including epidermal growth factor and transforming growth factor (see Chap. 49). In some patients with lymphoma, the hypercalcemia may be due to increased la-hydroxylation of 25-hydroxyvitamin D (25[OH]D) by malignant histiocytes.35 Normal activated T lym¬ phocytes also can induce this transformation. Although prosta¬ glandin E2 is produced by some neoplasms, serum levels do not appear to be sufficiently high to enhance bone resorption to the extent of producing hypercalcemia; moreover, inhibitors of pros¬ taglandin synthesis have no effect on most patients with neoplas¬ tic hypercalcemia. Usually, the initial therapy for the hypercalcemia of malig¬ nant disease is intravenous physiologic saline; rehydration alone may dramatically reduce or even normalize the hypercalcemia. Other modes of therapy (plicamycin, calcitonin, phosphate, cor¬ ticosteroids, gallium nitrate36) are discussed elsewhere (see Chaps. 52, 57, and 58). However, the most effective and least toxic therapy for the hypercalcemia associated with solid tumors is intravenous pamidronate sodium.37 Patients with the highest PTH-related protein levels tend to be somewhat more resistant to therapy and have the worst prognosis. Nevertheless, they usu¬ ally respond to higher doses and increased frequency of pami¬ dronate therapy.

PARANEOPLASTIC OSTEOMALACIA Osteomalacia or rickets secondary to the secretion of a hu¬ moral substance by a tumor (paraneoplastic osteomalacia, onco¬ genous osteomalacia) is being diagnosed with surprising fre¬ quency (see Chap. 62). Affected patients have a deficiency of serum calcitriol, as well as renal phosphate wasting.38,39 The syn¬ drome has been reproduced by transplantation of tumor tissue into athymic nude mice. The mechanism appears to be twofold: an inhibition of la-hydroxylation, which prevents 25(OH)D from being metabolized to the more active 1,25-dihydroxyvitamin D (l,25[OH]2D), and an effect on the proximal nephron, which promotes phosphaturia. In this regard, tumor extracts from patients with this syndrome have been found to stimulate PTH-responsive renal adenylate cyclase. Clinically, paraneoplastic osteomalacia most commonly oc¬ curs in young adults. The symptoms often are severe, and include skeletal pain, muscle weakness and cramps, and, sometimes,

1846

PART XV: HORMONES AND CANCER

fracture. The illness may confine the patient to the chair or bed. The symptoms of this syndrome may be present for months or years before being recognized. The lesions producing paraneoplastic osteomalacia have been well described as “strange tumors in strange places."40 Most of them are slow-growing, benign, and extremely vascular mes¬ enchymal tumors involving soft tissue or bone.41 Frequently, they are small (as small as 1 cm in diameter) and difficult to find, although they also may be large. Hemangiomatous lesions are encountered most often—specifically, cavernous hemangioma, hemangiopericytoma, angiofibroma, angiosarcoma, and others. Other tissue diagnoses include soft-tissue myxoma, osteo¬ blastoma, ossifying mesenchymal tumor, neurofibromatosis, schwannoma, and prostatic cancer. In many of these lesions, multinucleated giant cells, resembling osteoclasts, have been de¬ scribed. The unusual locations of these tumors have included the nasopharynx, the maxilla, and the palm of the hand (Fig. 213-2). Paraneoplastic osteomalacia should be suspected in any pa¬ tient with osteomalacia for which there is no obvious cause (e.g., malabsorption syndrome) or familial history. Most patients have hypophosphatemia; serum alkaline phosphatase levels usually are increased. Serum calcium levels are normal or only slightly decreased. It is unknown why the stimulation of PTH-responsive receptors is not accompanied by hypercalcemia; perhaps only re¬ nal receptors, and not those of bone, are stimulated. Serum 25(OH)D levels are normal; however, despite the presence of hy¬ pophosphatemia (which should stimulate la-hydroxylation), serum levels of l,25(OFI)2D are decreased. Serum PTH and calcitonin levels are normal. Even with hypophosphatemia, phosphaturia occurs, as demonstrated by a decreased tubular re¬ absorption of phosphate. The proximal renal tubular dysfunction may be accompanied by aminoaciduria and glucosuria (plasma glucose levels are normal). Histomorphologic analysis of a biopsy of nondecalcified iliac crest bone will confirm the excess osteoid.

FIGURE 213-2. A nontender, firm nodule (arrows) measuring 2 X 3 cm is evident on the palm of this 34-year-old man with severe osteomalacia. Bone pain and muscle weakness disappeared after removal of the lesion, and previously undetectable serum levels of 1,25-dihydroxyvitamin D returned to normal. The lesion was a benign tumor composed of hyaline cartilage and osteoclast-like giant cells. (From Weiss D, Barr RS, Weidner N, et al. Postgrad Med } Oncogenic osteomalacia: strange tumors in strange places. 1985; 61:349.)

When it is found in association with osteoblastic metastases, prostate cancer, as well as breast cancer, also may cause osteo¬ malacia (and sometimes hypocalcemia) because of the high calcium and vitamin D requirements of the rapidly forming new bone. These patients manifest hypophosphatemia, increased al¬ kaline phosphatase levels, and, importantly, low serum 25(OH)D levels. 2 Another clinical entity that may be confused with para¬ neoplastic osteomalacia is found rarely in patients with multiple myeloma or chronic lymphatic leukemia. It is termed light chain nephropathy, and causes decreased tubular reabsorption of phos¬ phate and hypophosphatemia, as well as aminoaciduria, glucos¬ uria, and impaired renal acidification.43 Presumably, vitamin D metabolism is normal. Therapy for paraneoplastic osteomalacia consists of extirpa¬ tion of the tumor, which is followed by spontaneous cure of the bone abnormality. After operation, serum l,25(OH2)D levels rapidly normalize. Even the partial removal of an offending tu¬ mor may be beneficial. If surgery cannot be performed, or if the causative neoplasm cannot be found, treatment includes large doses of l,25(OH)2D daily (up to 3 ^g/day) plus oral phosphate. Often, the clinical response to this treatment is only partial. The patient's serum should be monitored, because hypercalcemia may occur if the bone lesions heal.

PARANEOPLASTIC SECRETION OF HUMAN CHORIONIC GONADOTROPIN Human chorionic gonadotropin (hCG) is a glycoprotein hor¬ mone of about 45,000 daltons that is made up of two dissimilar, noncovalently joined subunits, each of which is encoded by different genes. The a subunit is identical to that in luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone, whereas the /? subunit differs, and confers biologic specificity to the hormone (see Chaps. 17 and 18). The principal source of serum hCG is the syncytiotrophoblast cell of the normal placenta (see Chaps. 106, 109, and 110). Moreover, hCG is widely distributed at low concentrations in many, perhaps all, normal tissues; however, except in pregnancy, serum hCG levels are extremely low or undetectable. Large amounts of hCG may be secreted from trophoblastic tumors, including gestational tumors (hydatidiform mole, cho¬ riocarcinoma), gonadal tumors with trophoblastic elements, and extragonadal nongestational choriocarcinoma (see Chaps. 109 and 110). Hormone production in these cases is not really para¬ neoplastic because the tumor involves tissue components that normally would be expected to produce considerable amounts of the hormone. However, nontrophoblastic tumors also may pro¬ duce levels of hCG that are sufficiently high to cause clinical manifestations. Interestingly, ovarian and testicular tumors (see Chaps. 99 and 122) commonly secrete hCG. Although areas suggestive of trophoblastic tissue may be found on histologic examination, this is not obligatory. For example, 25% of so-called pure seminomas of the testis are associated with increased serum hCG levels. As mentioned earlier, extragonadal, nongestational, choriocarcinomatous-appearing lesions occur rarely. These lesions are usually midline in location (mediastinum, pineal gland, retroperitoneum, bladder), and are more prevalent in men44 than in women. Rarely, they may be nonmidline (lung, kidney, colon). It is un¬ known whether such lesions are caused by incomplete or aber¬ rant migration of primordial germ cells, metastases from occult (or regressed) lesions of the gonads or placenta, metaplastic differentiation of epithelial cells, or persistence of totipotential cells from early embryogenesis. The nontrophoblastic tumors that may secrete large amounts of hCG include lung cancer (mostly large-cell), gastro¬ intestinal tumors (especially those involving the stomach and functioning islet cell lesions), breast cancer, melanoma, and hepatoblastoma. The serum gonadotropin levels are not suppressible with androgen or estrogen administration.45

Ch. 213: Paraneoplastic Endocrine Syndromes The clinical manifestations of tumoral secretion of hCG de¬ pend on the level of the hormone and the age and sex of the patient. Most patients, particularly those with nontrophoblastic tumors, have no symptoms. Infants or children with the rare ma¬ lignant hepatoblastoma may have precocious pseudopuberty.46 Boys, in particular, are affected, perhaps because of the luteiniz¬ ing hormone-like activity of hCG and its lack of folliclestimulating hormone activity. The precocious puberty is isosexual, manifested by the early appearance of secondary sex characteristics, increased body hair, and an enlarged penis. Be¬ cause of the absence of follicle-stimulating hormone, the testes usually exhibit interstitial cell hyperplasia without seminiferous tubule maturation or spermatogenesis, and they remain rather small in size. One third of these hepatoblastomas are resectable, and the symptoms may remit. Similar cases may occur among patients with trophoblastic teratomas or pinealomas. Women with high levels of serum hCG often have dysfunc¬ tional uterine bleeding, whereas affected men commonly have gynecomastia and, often, impotence. It is uncertain whether the gynecomastia is the result of the stimulation of secretion of sex steroids from the testes or of the direct production of sex hor¬ mones by the tumor tissue. Thyrotoxicosis can occur with high levels of serum hCG because of its thyroid stimulating hormone¬ like effects47; this condition may be seen in some women with choriocarcinoma (see Chaps. 17, 41, and 110) but it also occurs, albeit rarely, in men with testicular cancer. Care should be exercised in interpreting serum hCG levels because sensitive assays may detect hCG in normal persons, and slight increases may occur in patients with gastrointestinal in¬ flammatory diseases, such as ulcerative colitis, regional ileitis, and, rarely, duodenal ulcer. In addition, some hCG radioimmu¬ noassays cross react with other glycoprotein hormones. Antisera raised to the isolated, purified /3 subunit of hCG (the so-called /? subunit assay) also detect intact hCG, but do not cross react with luteinizing hormone. In addition, new, highly specific subunit assays are available.48 49 Boys with precocious pseudopuberty secondary to hCG have serum testosterone levels that are inap¬ propriately high for their age. Adult men and women have no consistent pattern of abnormality in terms of either serum andro¬ gen or estrogen levels. Some men with gynecomastia secondary to increased serum hCG may have a decreased androgenestrogen ratio. Patients with hCG-induced thyrotoxicosis have abnormal results on several thyroid function tests.

PARANEOPLASTIC HYPOGLYCEMIA Occasionally, patients have hypoglycemia secondary to extrapancreatic tumors.50 Usually, these are large neoplasms lo¬ cated within the thorax or abdomen; often, the abdominal lesions are behind the peritoneum. Many of these tumors, which most commonly are mesenchymal, fibrous neoplasms, are benign; oth¬ ers are sarcomas. The cell types that have been encountered include fibroma, fibrosarcoma, mesothelioma, neurofibroma, neurofibrosarcoma, liposarcoma, rhabdomyosarcoma, spindle cell sarcoma, heman¬ giopericytoma, and leiomyosarcoma.51 Lymphoma and lympho¬ sarcoma also have been implicated. Other tumors have included bronchial or ileal carcinoid, gastric and colon carcinoma, hyper¬ nephroma, adrenal carcinoma, and hepatoma; the last of these often occurs in men. The mechanism of the hypoglycemia is uncertain. Because the tumors are large, they were thought to arise as a result of the utilization of glucose by the neoplastic tissue. However, this is not a valid conclusion. Nor do the tumors release insulin; in most studies, radioimmunoassayable serum insulin levels are dimin¬ ished. In some reports, serum levels of nonsuppressible insulin¬ like protein, a high-molecular-weight substance whose action is not suppressed by insulin antibody, are increased.52 Usually, se¬ rum growth hormone levels are suppressed. In other studies, in¬ creased levels of a labile insulin growth factor (IGF)-like material

1847

similar53 or identical54 to IGF-II have been found in serum. In one study, this material was receptor-active and presumably bound to insulin receptors, but by immunoassay, was not recognized as IGF-II.55 Acidic gel filtration of sera of patients with tumorassociated hypoglycemia demonstrated the presence of a largemolecular-weight IGF-II (big IGF-II), an incompletely processed IGF-II precursor; levels normalized after removal of the tumor.56 Still another mechanism was postulated on the basis of a case report in which there was a large increase in the number of insu¬ lin receptors. This increase suggests an augmented utilization of glucose by normal body tissues resulting from an acquired, hor¬ mone-induced proliferation of receptors.57 Care should be taken not to confuse paraneoplastic hypo¬ glycemia with the glycolysis that may occur in vitro in blood ob¬ tained from patients with hematologic malignant disease who have greatly increased leukocyte counts (e.g., those with acute or chronic myeloid leukemia).58 In such patients, the freshly drawn blood is normoglycemic. Clinically, patients with paraneoplastic hypoglycemia man¬ ifest symptoms when fasting; in severe cases, symptoms may oc¬ cur spontaneously. Patients may have histories of sweating, hun¬ ger, headache, visual disturbances, or confusion. If the onset is gradual, there may be behavioral problems. Commonly, the in¬ gestion of food brings relief. However, patients with intractable disease may become comatose despite the fact that they are not in a fasting state. The treatment of paraneoplastic hypoglycemia involves sur¬ gery. Most patients do not survive unless the lesion is resectable, in which case the hypoglycemia may resolve—either perma¬ nently if the lesion is benign, or transiently if it is malignant. Be¬ fore operation, continuous glucose infusion may be necessary. Diazoxide therapy is helpful only occasionally.

PARANEOPLASTIC HYPERRENINISM Occasionally, renin may be produced autonomously by a neoplasm (also called tumoral hyperreninism or primary hyperreninism). Because renin normally is produced by the kidney, it is not surprising that this syndrome most commonly occurs in conjunction with renal neoplasms. In patients with a benign re¬ nal cyst, renin excess probably is attributable to localized isch¬ emia of the adjacent renal cortex. However, in rare cases, the excess may be caused by primary renin secretion by a juxtaglo¬ merular tumor (also called renal hemangiopericytoma). These tu¬ mors usually are small, occur in children and young adults, and, on microscopic examination, resemble the normal juxtaglomeru¬ lar apparatus.59 In addition, young children with paraneoplastic hyperreninism may have a Wilms tumor (nephroblastoma). In adults, renal adenocarcinoma occasionally is implicated. Extrarenal tumors also can cause hyperreninism.60 Such le¬ sions have included adenocarcinoma of the pancreas, adenocar¬ cinoma and small-cell carcinoma of the lung, ovarian cancer (es¬ pecially the Sertoli cell type61), adrenocortical adenoma, and a benign, tumor-like condition of the subcutaneous tissue termed angiolymphoid hyperplasia with eosinophilia.62 In some of these tu¬ mors, most of the secreted renin is in the form of relatively inac¬ tive precursors. Normally, the hormone is biosynthesized as a preprorenin molecule and then is converted into prerenin, which subsequently is processed into a smaller, active renin. This posttranslational processing may be deficient in neoplasms. Most patients with paraneoplastic hyperreninism have se¬ vere hypertension that is resistant to therapy, although occasion¬ ally, the hypertension may be mild. Usually, /3-adrenergic block¬ ade is unsuccessful, and captopril, an angiotensin converting enzyme inhibitor, is only variably effective. Retinal hemorrhages may occur and, because of the secondary hyperaldosteronism, there may be a persistent hypokalemia. The plasma renin levels may be extremely high. Generally, procedures that increase renin in normal persons (i.e., salt restriction, diuresis, or both) do not further increase hormonal levels in patients with this syndrome

1848

PART XV: HORMONES AND CANCER

because of a loss of the physiologic regulatory controls. Never¬ theless, attempts to use saralasin, an angiotensin II antagonist, or other pharmacologic blockade agents as diagnostic tools have yielded inconsistent results. When hyperreninism has been caused by a renal lesion, venous catheterization studies have demonstrated lateralization of the hyperreninism, whereas an in¬ creased venous tumor-kidney renin ratio has been demonstrated in cases in which an extrarenal lesion has been involved. The hypertension and hypokalemia usually respond to chemother¬ apy or to extirpative surgery.

PARANEOPLASTIC ERYTHROCYTOSIS Erythrocytosis (polycythemia) may be caused by various be¬ nign or malignant tumors that contain and secrete erythropoietin. Not surprisingly, because erythropoietin is produced by the nor¬ mal kidney, various renal lesions have been found to secrete this hormone (e.g., hypernephroma, which is responsible for 50% of such cases; renal cyst; and Wilms tumor). However, extrarenal tumors also can produce the syndrome. Three extrarenal tumors, in particular, seem to be involved more often than others: uterine fibroma, cerebellar hemangi¬ oblastoma, and hepatocellular carcinoma.63,64 Cerebellar heman¬ gioblastoma, a tumor that occurs predominantly in girls, may be associated with increased erythropoietin levels in the cerebrospi¬ nal fluid, as well as in the blood. The lesion, when transplanted to the athymic nude mouse, has caused erythrocytosis. One study of hepatocellular cancer in South African blacks revealed that, although 23% of the 65 patients had increased serum levels of erythropoietin, only 1 patient had erythrocytosis. This finding suggests that either the secreted hormone often is inactive, or there is an inhibition of erythropoiesis, a phenomenon that oc¬ curs in advanced cancer. Other tumors causing this syndrome include pheochromocytomas65 and ovarian tumors. Because of the hormonal stimulation that is involved in the proliferation and differentiation of erythrocyte progenitor cells, patients with paraneoplastic erythrocytosis have an increased red blood cell count, increased hemoglobin and hematocrit values, and an elevated red blood cell mass. There is no splenomegaly as may occur in polycythemia vera. Erythropoietin is found within the tumor, either by immunostaining methods or by direct assay. Moreover, serum and urine erythropoietin levels, as measured by radioimmunoassay or bioassay, may be increased. Erythropoietin levels also are increased in secondary eryth¬ rocytosis attributable to cyanotic heart disease or chronic obstruc¬ tive pulmonary disease. However, in these patients, the cause is tissue hypoxia, and blood gas determinations demonstrate hypoxemia. In polycythemia vera, a primary bone marrow disor¬ der, serum erythropoietin is either decreased or undetectable. Remission of paraneoplastic erythrocytosis generally is effected by successful, complete excision of the tumor. Perioper¬ ative complications, such as hemorrhage and thromboembolism, may occur. Therefore, prophylactic phlebotomies have been ad¬ vocated to reduce the red blood cell mass before surgery.

COMBINED PARANEOPLASTIC ENDOCRINE SYNDROMES Commonly, cancers that cause an endocrine syndrome as a result of the secretion of a specific hormone also are found to secrete other hormones, such as neurotensin, calcitonin, somato¬ statin, or vasoactive intestinal peptide. In most such cases, no clinical manifestations are evident. Occasionally, however, pa¬ tients may manifest combined endocrine syndromes, as in the case of a small -cell cancer of the lung that secretes ACTH and vasopressin, resulting in Cushing syndrome and inappropriate secretion of ADH, or an ACTH- and CRH-secreting bronchial carcinoid tumor that produces adrenal hyperplasia both directly and through pituitary stimulation.66 Small-cell cancer of the tra¬ chea has been reported to cause both Cushing syndrome due to

ACTH secretion and paraneoplastic osteomalacia.67 There have been reports of a gastrin- and GHRH-secreting pancreatic islet cell tumor that has caused both the Zollinger-Ellison syndrome and acromegaly,68 as well as a gastrin- and ACTH-secreting pan¬ creatic islet cell tumor that has produced the Zollinger-Ellison syndrome and Cushing syndrome.69 Often, primary liver cell car¬ cinoma is associated with erythropoietin-induced polycythemia, as well as with hypercalcemia and hypoglycemia.70

PARANEOPLASTIC SECRETION OF OTHER KNOWN PEPTIDE HORMONES WITH NO ASSOCIATED ENDOCRINE SYNDROME Calcitonin is one of the most common hormones to be se¬ creted by tumors. In addition to medullary thyroid carcinoma (see Chap. 40), hypercalcitonemia occurs in 10% to 30% of other malignant neoplasms. In these cases, there is preferential secre¬ tion of procalcitonin. Particularly high values are seen in small¬ cell lung cancer and pulmonary carcinoid tumors (see Chap. 172). Clinically, the measurement of this hormone in blood or urine may be a biomarker for the progression of a tumor, or its response to therapy.71 There is no specific syndrome known to be caused by hypercalcitonemia. Serum calcium levels and bone architecture remain normal. Neurotensin, somatostatin, and cholecystokinin also are com¬ monly secreted by tumors without obvious clinical effects. Con¬ ceivably, these hormones may participate in the general systemic effects that often accompany malignant disease, such as fatigue, depression, nausea, anorexia, and weight loss. Rare and insufficiently documented cases of the extrapituitary production of thyroid-stimulating hormone have been re¬ ported. However, most patients with hyperthyroidism secondary to associated nonpituitary, nonthyroidal malignant disease are thyrotoxic because of the thyroid-stimulating effects of high se¬ rum levels of hCG produced by trophoblastic tumors (see Chaps. 17 and 41). Human chorionic somatomammotropin, also termed human placental lactogen, has been reported to have been produced by a large-cell lung cancer in a patient who also had gynecomastia. However, subsequent documentation of a specific syndrome has not been forthcoming. There have been alleged cases of lung cancer in which tu¬ moral secretion of growth hormone was associated with hyper¬ trophic pulmonary osteoarthropathy. However, the validity of this phenomenon remains uncertain. There is little evidence of a syndrome attributable to prolac¬ tin secretion by a tumor of nonpituitary origin. Although this hormone has been found in both the normal and cancerous uter¬ ine cervix, the patients with malignancy do not usually have hyperprolactinemia.72

SUSPECTED PARANEOPLASTIC ENDOCRINE SYNDROMES HYPERTROPHIC OSTEOARTHROPATHY Hypertrophic osteoarthropathy (Bamberger-Marie syn¬ drome) is a progressive, bilaterally symmetric, periosteal reaction involving the bones of the fingers and toes. It commonly affects the distal long bones and joints as well. The thickened, clubbed¬ appearing digits have been referred to as acropachy (Fig. 213-3B). Often, the disease is associated with a malignant process. Patients may note progressive disfigurement, or, if the onset is sudden, patients may be surprised when the examiner calls attention to the enlarged fingers. If present, the arthralgia of the fingers, wrists, knees, and ankles may be confused with rheuma-

Ch. 213: Paraneoplastic Endocrine Syndromes

1849

FIGURE 213-3. A patient with pachydermoperiostitis (thickened fa¬ cies, hypertrophic osteoarthropathy, and underlying malignancy). The pa¬ tient had epidermoid carcinoma of the lung. A, Note the coarsening of the fa¬ cial features, including the prominent creases of the forehead, the deep na¬ solabial folds, and the broad nose. The skin is very oily. B, Marked clubbing of the digits is evident. C, Radiographs of a patient with this syndrome reveal periostitis of the long bones (ar¬ rowheads), especially the distal ends.

toid arthritis. On physical examination, the digits have a widened transverse diameter. Obliteration of the normal angle between the distal phalanges and the nails adds to the drumstick appear¬ ance. The nails may be fluctuant to the touch and slightly mobile. In addition, the hands and feet may appear enlarged, and the wrists and ankles may be thickened. In such cases, there also may be periarticular swelling of the soft tissues, which are tender and slightly warm. Occasionally, joint effusions may be palpated. A sample of the synovial fluid will be "noninflammatory"; seldom are there more than 500 leukocytes per cubic millimeter. Rarely, the facial skin may be thickened and seborrheic, with deep furrows, increased nasolabial folds, a corrugated brow, and a broad nose. These findings may impart an acromegalic appear¬ ance to the patient (see Fig. 213-3A). On x-ray examination, there often is evidence of periosteal new bone formation in the proxi¬ mal phalanges. There also may be involvement of the metacarpals, the distal ends of the radius and ulna, the tibia and fibula, and the distal femur (see Fig. 213-3C). In severe cases, there is thick, multilayered, new bone formation with periosteal eleva¬

tion and an underlying rarefaction of the outer portions of the original cortex, which imparts an "onionskin" appearance. Later, there may be fusion of old and new bone. A radionuclide bone scan usually reveals increased uptake of contrast material in the involved areas. The underlying pathology in many patients with hypertro¬ phic osteoarthropathy is malignant disease. Probably 90% of such cases are attributable to intrathoracic cancers, of which the predominant form is bronchogenic cancer. The most common cell type is epidermoid cancer (especially if there is pleural in¬ volvement or necrosis within the tumor), followed by adenocar¬ cinoma, and, occasionally, large-cell cancer. (Small-cell cancer of the lung rarely causes this syndrome.73) Other intrathoracic le¬ sions that may be implicated include mesothelioma, mediastinal lymphoma, metastatic cancer involving the lungs, and thymoma. Uncommon, extrathoracic causes include carcinoma of the naso¬ pharynx or gastrointestinal tract, and osteogenic sarcoma. The syndrome also may occur in childhood.74 FFypertrophic osteoarthropathy also may occur in chronic

1850

PART XV: HORMONES AND CANCER

nonmalignant conditions, such as bronchiectasis, cyanotic con¬ genital heart disease, subacute bacterial endocarditis, ulcerative colitis, or cirrhosis of the liver. In addition, endocrinologists may see this condition in patients with the hyperthyroidism associ¬ ated with Graves disease, but not in the hyperthyroidism accom¬ panying toxic adenomatous goiter (see Chap. 41). Another form of hypertrophic osteoarthropathy—hereditary acropathy—is unassociated with cancer or with any of the pre¬ viously mentioned benign conditions. Sometimes, this condition is inherited as a mendelian dominant trait; commonly, it begins in puberty. The term pachydermoperiostosis75 should be reserved for the primary or idiopathic variety of hypertrophic osteo¬ arthropathy (Fig. 213-4), whereas pachydermoperiostitis is the correct term for the secondary form, which is associated with a known, underlying condition. Clinically, a severe case of hypertrophic osteoarthropathy may be mistaken for rheumatoid arthritis. Occasionally, the finding of hypertrophic osteoarthropathy may precede a clinical diagnosis of malignant disease, and hence, may first call attention to the presence of the neoplasm. Rarely, a patient may not mani¬ fest any signs or symptoms indicating the presence of an underly¬ ing malignant lesion for several months. In many patients, the erythrocyte sedimentation rate is increased, which probably re¬ flects the presence of a neoplasm. The serum alkaline phospha¬ tase level may be normal or increased. Most likely, hypertrophic osteoarthropathy is humorally mediated. The mediastinum, and the pleura in particular, is rich in vagal innervation, and it has been postulated that an abnormal vagal afferent reflex, instituted by a thoracic lesion, can induce a local or central release of vasoactive or growth-promoting substances. Aspirin and other nonsteroidal antiinflammatory agents may provide symptomatic relief if joint pain or joint effusions occur. Successful surgical extirpation or chemotherapy may re¬ verse the joint swellings, and may even induce partial remission of the bone changes.76,77

ACANTHOSIS NIGRICANS Acanthosis nigricans is an acquired, bilaterally symmetric, cutaneous lesion characterized by a piling up of the skin, which assumes a brown to black coloration and a velvety consistency. Commonly, there also are many local, tiny, pedunculated, papil¬ lomatous overgrowths (so-called skin tags). Usually, the condi¬ tion is nonpruritic. The darkened, verrucous-appearing skin lesion occurs in flexural areas, such as the axillae, the back and sides of the neck, the antecubital fossae, beneath the folds of pendulous abdominal fat, behind the knees, between the thighs, and, sometimes, on the face (circumoral and nasolabial regions; see Chap. 212). In these relatively moist regions, the piling up of the epidermis par¬ allels the body creases in a striate fashion. The condition occurs in all races. Histologic examination reveals hyperkeratosis, a thickened stratum corneum, papillary hypertrophy, and an in¬ crease in the pigmented basal layers. Traditionally, acanthosis nigricans has been classified as ei¬ ther benign or malignant. A common, but not universal, charac¬ teristic associated with the benign variety is a cellular resistance to insulin action (see Chap. 140). In some manner, this metabolic defect, which does not always result in frank diabetes, induces an overgrowth of epidermal cells that may be hormonally mediated, perhaps involving blood-borne trophic factors. The more com¬ mon benign form of acanthosis nigricans usually occurs in rela¬ tively young persons who are obese or who have obesity-related ovarian dysfunction (polycystic ovary syndrome; see Chaps. 93 and 98). Other associated metabolic or endocrine conditions in¬ clude congenital lipodystrophy, acromegaly, and Cushing dis¬ ease. In nearly all cases, the coexistent skin lesions progress with time. The malignant form of acanthosis nigricans, so named be¬ cause of its association with internal tumors, may occur at any age, but is most common among older persons.78 Often, affected patients are not obese. The most common causative lesion is gas¬ trointestinal adenocarcinoma (e.g., involving the stomach [in two thirds of the cases], the gallbladder, or the rectum). Other causes include ovarian carcinoma and lymphoma. The neoplasm invari¬ ably is highly malignant and usually is inoperable because of the presence of metastases. Although acanthosis nigricans can pre¬ cede any clinical manifestations of the underlying neoplasm, it generally coincides with detection of the tumor and worsens with the progress of the malignant lesion. Some believe that pruritic involvement of the palms and soles by acanthosis nigricans is a clue to the presence of underlying neoplasia. Occasionally, cases have been reported in which successful surgery or chemothera¬ peutic treatment of the neoplasm was associated with reversibil¬ ity of the skin lesion.

MISCELLANEOUS POSSIBLY PARANEOPLASTIC ENDOCRINE SYNDROMES

FIGURE 213-4. Patient with pachydermoperiostosis (thickened facies, hypertrophic osteoarthropathy, no associated malignancy). Affected pa¬ tients have marked clubbing of the digits, as well as radiographic evi¬ dence or periostitis of the long bones, especially the distal ends. This con¬ dition is inherited as a mendelian dominant trait.

Several other syndromes that are associated with neoplasms may be humorally mediated. Paraneoplastic eosinophilia, de¬ scribed in association with large-cell cancer of the lung, is char¬ acterized by marked eosinophilia and diffuse eosinophilic infil¬ tration of nearly all tissues. Increased serum eosinophilic colonystimulating factor and eosinophilic chemotactic factor have been detected. Lung cancer also may be associated with an absolute neutrophilia and, in some instances, thrombocytosis. In such cases, there may be secretion of granulocyte/macrophage colonystimulating factors.80,81 In some patients, the neutrophilia rapidly resolves after surgical removal of the primary lesion. Acquired hypertrichosis lanuginosa ("malignant down")82 is found in pa¬ tients with late-stage, widespread cancer, commonly involving the gastrointestinal tract. The face, neck, and trunk exhibit long, fine, silky, unpigmented hair (Fig. 213-5). Conceivably, the con¬ dition may be due to the secretion of a growth factor.

Ch. 213: Paraneoplastic Endocrine Syndromes

1851

activity in adipocytes, and induces a loss of triglycerides from this tissue89; it also causes an anemia.90 The extent to which this substance, or other cytokines, might contribute to the cachexia of cancer, either by direct production from the neoplasm91 or by other tissues that react to the malignant lesion, is unknown. Tu¬ mor cells, as well as T lymphocytes, may produce humoral tumor angiogenesis factors92 that stimulate new blood vessel growth, which, in turn, assists in the perpetuation and propagation of the malignant neoplasm. Last, some tumor cells produce humoral factors that inhibit the growth of other cell lines of cancer (e.g., secretion of transforming growth factor /3 by breast cancer cell lines after treatment with antiestrogens inhibits the growth of an estrogen receptor-negative human breast cancer cell line93).

REFERENCES

FIGURE 213-5. Woman with acquired hypertrichosis lanuginosa asso¬ ciated with a metastatic sarcoma.

The sign ofheser-Trelat (sudden onset of seborrheic keratoses in association with an internal malignant lesion) may be caused by the production of transforming growth factor a by the neo¬ plasm. Such a condition has been postulated in one patient with melanoma, and also was associated with acanthosis nigricans and multiple acrochordons (skin tags).83 The spontaneous regression of metastases, after excision of the primary lesion, has been described in about 80 patients, mostly men, whose pulmonary metastases regressed after nephrectomy for renal cell carcinoma.84 A similar phenomenon has been de¬ scribed in malignant melanoma. Conceivably, the removal of the primary lesion arrests the secretion of a growth factor that either had been stimulating or maintaining the viability of the metastases. Several other syndromes associated with cancer have no ev¬ idence of humoral mediation, but merit further endocrine inves¬ tigation. The Eaton-Lambert myasthenic syndrome, characterized by proximal muscle weakness in association with small-cell can¬ cer of the lung, was formerly thought to be mediated by a hor¬ mone. It is caused by an autoantibody to the tumor that crossreacts with determinants at the motor nerve terminal.85 Similarly, the cerebellar degeneration associated with malignant disease may be attributable to autoantibodies.86 Severe constipation, oc¬ curring in several patients with ovarian carcinoid tumors, has been attributed to peptide YY secretion, a substance known to inhibit intestinal motility.87 Malignant hemangioendothe¬ liomas have been reported to secrete endothelin and to cause hypertension.88

HORMONE-MEDIATED EFFECT OF NEOPLASIA ON THE BODY Neoplasia frequently is associated with asthenia, negative nitrogen balance, and severe wasting; sometimes, these symp¬ toms occur even if the causative lesion is relatively small. Usually, there is weight loss despite deliberate attempts to overeat. The hormone, tumor necrosis factor a, which is produced by endotoxin-stimulated macrophages, inhibits lipoprotein lipase

1. De Bustros A, Baylin SB. Hormone production by tumors: biological and clinical aspects. Clin Endocrinol Metab 1985; 14:221. 2. Howlett TA, Rees LH. Ectopic hormones. In: Cohen MP, Foa PP, eds. Spe¬ cial topics in endocrinology and metabolism, vol 7. New York: Liss, 1985:1. 3. Becker KL, Gazdar AF. What can the biology of small cell cancer of the lung teach us about the endocrine lung? Biochem Pharmacol 1985; 34:155. 4. Lupulescu A. Cancer and ectopic hormones: clinical and biological aspects. In: Hormones and carcinogenesis. New York: Praeger Publishers, 1983:276. 5. LeRoith D, Roth ]. Syndromes associated with inappropriate hormone syn¬ thesis by tumors: an evolutionary interpretation. Recent Results Cancer Res 1985;99:209. 6. Gumbiner B, Kelly RB. Two distinct intracellular pathways transport secre¬ tory and membrane glycoproteins to the surface of pituitary tumor cells. Cell 1982,-28:51. 7. Frohman LA, Jansson J-O. Growth hormone-releasing hormone. Endocr Rev 1986; 7:223. 8. Boizel R, Halimi S, Labat F, et al. Acromegaly due to a growth hormone¬ releasing hormone-secreting bronchial carcinoid tumor. ] Clin Endocrinol Metab 1987,-64:304. 9. Ezzat S, Asa SL, Stefaneanu L, et al. Somatotroph hyperplasia without pituitary adenoma associated with a long standing growth-hormone releasing hormone-producing bronchial carcinoid. J Clin Endocrinol Metab 1994;78:555. 10. Barkan AL, Shenker Y, Grekin RJ, Vale WW. Acromegaly from ectopic growth hormone-releasing hormone secretion by a malignant carcinoid tumor. Suc¬ cessful treatment with long-acting somatostatin analogue SMS 201-995. Cancer 1988; 61:221. 11. Carey RM, Varma SK, Drake CR Jr, et al. Ectopic secretion of corticotropin¬ releasing factor as a cause of Cushing's syndrome. A clinical morphologic, and bio¬ chemical study. NEnglJ Med 1984; 311:13. 12. Zarate A, Kovacs K, Flores M, et al. ACTH and CRF-producing bronchial carcinoid associated with Cushing's syndrome. Clin Endocrinol (Oxf) 1986; 24:523. 13. Hofland J, Schneider Aj, Cuesta MA, Meijer S. Bronchopulmonary carci¬ noids associated with Cushing's syndrome—report of a case and an overview of the literature. Acta Oncol 1993;32:571. 14. White A, Clark AJL. The cellular and molecular basis of the ectopic ACTH syndrome. Clin Endocrinol (Oxf) 1993;39:131. 15. Cederna P, Eckhauser FE, Kealey GP. Cushing's syndrome secondary to bronchial carcinoid secretion of ACTH: a review. Am Surg 1993; 59:438. 16. Howlett TA, Drury PL, Perry L, et al. Diagnosis and management of ACTH-dependent Cushing's syndrome: comparison of the features in ectopic and pituitary ACTH production. Clin Endocrinol (Oxf) 1986; 24:699. 17. Chrousos GP, Schulte HM, Oldfield EH, et al. The corticotropin-releasing factor stimulation test: an aid in the evaluation of patients with Cushing's syn¬ drome. N Engl J Med 1984;310:622. 18. de Herder WW, Krenning EP, Malchoff CD, et al. Somatostatin receptor scintography. Its value in tumor localization in patients with Cushing syndrome caused by ectopic corticotropin or corticotropin-releasing hormone secretion. Am J Med 1994;96:305. 19. Doppman JL, Loughlin T, Miller DL, et al. Identification of ACTHproducing intrathoracic tumors by measuring ACTH levels in aspirated specimens. Radiology 1987; 163:501. 20. Shepherd FA, Hoffert B, Evans WK, et al. Ketoconazole. Use in the treat¬ ment of ectopic adrenocorticotropic hormone production and Cushing's syndrome in small cell lung cancer. Arch Intern Med 1985; 145:863. 21. Robertson GL. Cancer and inappropriate antidiuresis. In: Ruddon RW, ed. Biological markers of neoplasia: basic and applied aspects. Amsterdam: Elsevier North Holland, 1978:277. 22. Verbalis JG. Tumoral hyponatremia. Arch Intern Med 1986; 146:1686. 23. Sorensen JB, Kristjansen PEG, Osterlind K, et al. Syndrome of inappropri¬ ate antidiuresis in small-cell lung cancer. Acta Med Scand 1987; 222:155. 24. Bliss DP Jr, Battey JF, Linnoila RI, et al. Expression of the atrial natriuretic factor gene in small cell lung cancer tumors and tumor cell lines. J Natl Cancer Inst 1990; 82:305. 25. Kamoi XX, Ebe T, Hasegawa A, et al. Hyponatremia in small cell lung cancer: mechanisms not involving inappropriate ADH secretion. Cancer 1987;60: 1089.

1852

PART XV: HORMONES AND CANCER

25a. Rizzoli R, Pache J-C, Didierjean L, et al. A thymoma as a cause of true ectopic hyperparathyroidism. J Clin Endocrinol Metab 1994; 79:912. 26. Stewart AF, Mangin M, Wu T, et al. Synthetic human parathyroid hormone-like protein stimulates bone resorption and causes hypercalcemia in rats. ] Clin Invest 1988; 81:596. 27. Strewler GJ, Stern PH, Jacobs JW, et al. Parathyroid hormone-like protein from human renal carcinoma cells. J Clin Invest 1987;80:1803. 28. Stewart AF, Elliot J, Burtis WJ, et al. Synthetic parathyroid hormone-like protein—(1-74): biochemical and physiological characterization. Endocrinology 1989; 124:642. 29. Dunne FP, Rollason T, Ratcliffe WA, et al. Parathyroid hormone-related gene expression in invasive cervical tumors. Cancer 1994; 74:83. 30. Tait DL, McDonald PC, Casey ML. Parathyroid hormone-related protein expression in gynecic squamous carcinoma cells. Cancer 1994;73:1515. 31. Li X, Drucker DJ. Parathyroid hormone-related peptide is a downstream target for ras and src activation. J Biol Chem 1994; 269:6263. 32. Ratcliffe WA, Bonden SJ, Dunne FP, et al. Expression and processing of parathyroid hormone-related protein in a pancreatic endocrine cell tumor associ¬ ated with hypercalcemia. Clin Endocrinol (Oxf) 1994; 40:679. 33. Iwamura M, Abrahamsson PA, Foss KA, et al. Parathyroid hormonerelated protein: a potential autocrine growth regulator in human prostate cancer cell lines. Urology 1994;43:675. 34. Garrett IR, Durie BGM, Nedwin GE, et al. Production of lymphotoxin, a bone-resorbing cytokine, by cultured human myeloma cells. N Engl J Med 1987;317:526. 35. Mudde AH, Van den Berg H, Boshuis PG, et al. Ectopic production of 1,25 dihydroxyvitamin D by B-cell lymphoma as a cause of hypercalcemia. Cancer 1987,-59:1543. 36. Warrell RP Jr, Israel R, Frisone M,.et al. Gallium nitrate for acute treatment of cancer-related hypercalcemia. Ann Intern Med 1988; 108:669. 37. Wimalawansa SJ. Significance of plasma PTH-rp in patients with hyper¬ calcemia of malignancy treated with bisphosphonate. Cancer 1994; 73:2223. 38. Ryan EA, Reiss E. Oncogenous osteomalacia. Review of the world litera¬ ture of 42 cases and report of two new cases. Am J Med 1984; 77:501. 39. Siris ES, Clemens TL, Dempster DW, et al. Tumor-induced osteomalacia. Kinetics of calcium, phosphorus, and vitamin D metabolism and characteristics of bone histomorphometry. AmJ Med 1987;82:307. 40. Weiss D, Barr RS, Weidner N, et al. Oncogenic osteomalacia: strange tu¬ mors in strange places. Postgrad Med J 1985; 61:349. 41. Weidner N, Santa Cruz D. Phosphaturic mesenchymal tumors. A poly¬ morphous group causing osteomalacia or rickets. Cancer 1987;59:1442. 42. Charhon SA, Chapux MC, Delvin EE, et al. Histomorphometric analysis of sclerotic bone metastases from prostatic carcinoma with special reference to os¬ teomalacia. Cancer 1983;51:918. 43. Rao DS, Parfitt AM, Villaneuva AR, et al. Hypophosphatemic osteomala¬ cia and adult Fanconi syndrome due to light-chain nephropathy. Am J Med 1987;82:333. 44. Kathuria S, Jablokow VR. Primary choriocarcinoma of mediastinum with immunohistochemical study and review of the literature. J Surg Oncol 1987; 34:39. 45. Becker KL, Cottrell J, Moore CF, et al. Endocrine studies in a patient with a gonadotropin-secreting bronchogenic carcinoma. J Clin Endocrinol Metab 1968; 28: 809. 46. Navarro C, Corretger JM, Sancho A, et al. Paraneoplastic precocious pu¬ berty. Report of a new case with hepatoblastoma and review of the literature. Can¬ cer 1985;56:1725. 47. Norman RJ, Green-Thompson RW, Jialal I, et al. Hyperthyroidism in ges¬ tational trophoblastic neoplasia. Clin Endocrinol (Oxf) 1981; 15:395. 48. Hay DL. Histological origins of discordant chorionic gonadotropin secre¬ tion in malignancy. J Clin Endocrinol Metab 1988;66:557. 49. O Connor JF, Schlatterer JP, Birken S, et al. Development of highly sensi¬ tive immunoassays to measure human chorionic gonadotropin, its /3-subunit, and core fragment in the urine: application to malignancies. Cancer Res 1988,-48:1361. 50. Daughaday WH. Hypoglycemia in patients with non-islet cell tumors. Endocrinol Metab Clin North Am 1989; 18:91. 51. Touyz R, Plitt M, Rumbak M. Hypoglycemia associated with a lung mass Chest 1986;89:289. 52. Li TC, Reed CE, Stubenbord WT Jr, et al. Surgical cure of hypoglycemia associated with cystosarcoma phylloides and elevated nonsuppressible insulin-like protein. Am J Med 1983; 74:1080.

59. Pedrinelli R, Graziadei L, Taddei S, et al. A renin-secreting tumor. Neph¬ ron 1987; 46:380. 60. Morris BJ, Pinet F, Michel JB, et al. Renin secretion from malignant pul¬ monary metastatic tumour cells of vascular origin. Clin Exp Pharmacol Physiol 1987; 14:227. 61. Korzets A, Nouriel H, Steiner Z, et al. Resistant hypertension associated with a renin-producing ovarian Sertoli cell tumor. AmJ Clin Pathol 1986; 85:242. 62. Fernandez LA, Olsen TG, Barwick KW, et al. Renin in angiolymphoid hyperplasia with eosinophilia. Arch Pathol Lab Med 1986; 110:1131. 63. Rosenlof K, Fyhrquist F, Gronhagen-Riska C. Erythropoietin and renin substrate in cerebellar hemangioblastoma. Acta Med Scand 1985; 218:481. 64. Okabe T, Urabe A, Kato T, et al. Production of erythropoietin-like activity by human renal and hepatic carcinomas in cell culture. Cancer 1985;55:1918. 65. Shulkin BL, Shapiron B, Sisson JC. Pheochromocytoma, polycythemia, and venous thrombosis. AmJ Med 1987;83:773. 66. Schteingart DE, Lloyd RV, Akil H, et al, Cushing's syndrome secondary to ectopic corticotropin-releasing hormone-adrenocorticotropin secretion. J Clin En¬ docrinol Metab 1986;63:770. 67. van Heyningen C, Green AR, MacFarlane IA, Burrow CT. Oncogenic hy¬ pophosphatemia and ectopic corticotrophin secretion due to oat cell carcinoma of the trachea. J Clin Pathol 1994; 47:80. 68. Wilson DM, Ceda GP, Bostwick DG, et al. Acromegaly and ZollingerEllison syndrome secondary to an islet cell tumor. J Clin Endocrinol Metab 1984;59: 1002. 69. Maton PN, Gardner JD, Jensen RT. Cushing's syndrome in patients with the Zollinger-Ellison syndrome. N Engl J Med 1986; 315:1. 70. Teniola SO, Ogenleye IO. Paraneoplastic responses in primary liver cell carcinoma in Nigeria. Trop Geogr Med 1994; 46:20. 71. Silva OL, Broder LE, Doppman JL, et al. Calcitonin as a marker for bron¬ chogenic cancer: a prospective study. Cancer 1979; 44:680. 72. Macfee MS, McQueen J, Strayer DE. Immunocytochemical localization of prolactin in carcinoma of the cervix. Gynecol Oncol 1987;26:314. 73. Yacoub MH. Relation between the histology of bronchial carcinoma and hypertrophic pulmonary osteoarthropathy. Thorax 1965;20:537. 74. Ilhan I, Kutluk T, Gogus S, et al. Hypertrophic pulmonary osteoarthropa¬ thy in a child with thymic carcinoma: an unusual presentation in childhood. Med Pediatr Oncol 1994;23:140. 75. Rimoin DL. Pachydermoperiostosis (idiopathic clubbing and periostitis): genetic and physiologic considerations. N Engl J Med 1965;272:923. 76. Evans WK. Reversal of hypertrophic osteoarthropathy after chemother¬ apy for bronchogenic carcinoma. J Rheumatol 1980; 7:93. 77. Nishi K, Matsamura M, Myou S, et al. Two cases of pulmonary hypertro¬ phic osteoarthropathy associated with primary lung cancer, in which symptoms were rapidly improved by resection of the primary lesions. Nippon Kyobu Shikkan Gakkai Zasshi 1994;32:271. 78. Curth HO, Hilberg AW, Machacek GF. The site of histology of the cancer associated with malignant acanthosis nigricans. Cancer 1962; 15:364. 79. Kodama T, Takada K, Kameya T, et al. Large cell carcinoma of the lung associated with marked eosinophilia. Cancer 1984; 54:2313. 80. Ascensao JL, Oken MM, Ewing SL, et al. Leukocytosis and large cell lung cancer. Cancer 1987; 60:903. 81. Adachi N, Yamaguchi K, Morikana T, et al. Constitutive production of multiple colony-stimulating factors in patients with lung cancer associated with neutrophilia. Br J Cancer 1994;69:125. 82. Hovenden AL. Acquired hypertrichosis lanuginosa associated with malig¬ nancy. Arch Intern Med 1987; 147:2013. 83. Nakano E, Sonoda T, Fujiaka H, et al. Spontaneous regression of pulmo¬ nary metastases after nephrectomy for renal cell carcinoma. Eur Urol 1984; 10:212. 84. Ellis DL, Kafka SP, Chow JC, et al. Melanoma, growth factors, acanthosis nigricans, the sign of Leser-Trelat, and multiple acrochordons. N Engl J Med 1987,-317:1582. 85. Roberts A, Perera S, Lang B, et al. Paraneoplastic myasthenic syndrome IgG inhibits 45 Ca2+ flux in a human small cell carcinoma line. Nature 1985; 317: 737. 86. Wang A-M, Leibowich S, Ridker PM, David WS. Paraneoplastic cerebellar degeneration in a patient with ovarian carcinoma. AJNR Am J Neuroradiol 1988;9: 216. 87. Motoyama T, Katayama Y, Watanabe H, et al. Functioning ovarian carci¬ noids induce severe constipation. Cancer 1992;70:513.

53. Ron D, Powers AC, Pandian MR, et al. Increased insulin-like growth fac¬ tor II production and consequent suppression of growth hormone secretion: a dual mechanism for tumor-induced hypoglycemia. J Clin Endocrinol Metab 1989-68701.

88. Yokokawa K, Tahara H, Kohno M, et al. Hypertension associated with endothelin-secreting malignant hemangioendothelioma. Ann Intern Med 1991; 114:213.

54. Horiuchi T, Shinohara Y, Sakamoto Y, et al. Expression of insulin-like growth factor II by a gastric carcinoma associated with hypoglycemia. Virchows Arch 1994; 424:449.

89. Beutler B, Cerami A. Cachectin (tumor necrosis factor): a macrophage hor¬ mone governing cellular metabolism and inflammatory response. Endocr Rev 1988;9:57.

55. Merimee TJ. Insulin-like growth factors in patients with non-islet cell tu¬ mors and hypoglycemia. Metabolism 1986;35:360. 56. Zapf J. IGFs: function and clinical importance. Role of insulin-like growth factor (IGF) II and IGF binding proteins in extrapancreatic tumor hypoglycemia J Intern Med 1993;234:543. 57. Stuart CA, Price MJ, Peters EJ, et al. Insulin receptor proliferation: a mech¬ anism for tumor-associated hypoglycemia. J Clin Endocrinol Metab 1986;63:879. 58. Al Hilali MM, Majer RV, Penney O. Hypoglycemia in acute myelomonoblastic leukaemia: report of two cases and review of published work BMJ 1984;289.1443.

90. Moldawer LL, Marano MA, Wei H, et al. Cachectin/tumor necrosis factor¬ ed alters red blood cell kinetics and induces anemia in vivo. FASEB J 1989;3:1637. 91. Balkwill F, Burke F, Talbot D, et al. Evidence for tumor necrosis factor/ cachectin production in cancer. Lancet 1987; 1:1229. 92. Hadar EJ, Ershler WB, Kreisle RA, et al. Lymphocyte-induced angiogen¬ esis factor is produced by L3T4+ murine T lymphocytes, and its production declines with age. Cancer Immunol Immunother 1988;26:31. 93. Knabbe C, Lippman ME, Wakefield LM, et al. Evidence that transforming growth factor-beta is a hormonally regulated negative growth factor in human breast cancer cells. Cell 1987; 48:417.

Ch. 214: The Carcinoid Tumor and the Carcinoid Syndrome Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

214_

THE CARCINOID TUMOR AND THE CARCINOID SYNDROME PAUL N. MATON

Carcinoids were thought to occur in 1% of autopsies, but data demonstrate that they frequently occur in the acidproducing (oxyntic) mucosa of the stomach in patients who are hypergastrinemic.1 Nonetheless, most carcinoids remain local¬ ized and are not clinically significant. The major interest in these tumors relates to the few that produce 5-hydroxytryptamine and other substances and cause flushing, diarrhea, heart disease, and asthma—the carcinoid syndrome.2 3

CELL OF ORIGIN Carcinoids are neuroendocrine tumors that usually arise from enterochromaffin (EC) cells, which are found scattered throughout the body, but occur principally in the submucosa of the intestine and main bronchi.2,3 The EC cell population is het¬ erogeneous, which may explain the variety of features associated with carcinoid tumors (Table 214-1). Some EC cells are argentaffinic, whereas others are argyrophilic (see Chap. 171). Further¬ more, some EC cells contain peptides, such as substance P, en¬ kephalins, or motilin.2 The prior-mentioned gastric carcinoids do not arise from EC cells, but from enterochromaffin-like (ECL) cells that may be important in the production of histamine.1,4

1853

type 1, there is a generalized hypertrophy of ECL cells that in some cases leads to the formation of multiple carcinoids.1,4 The many (sometimes hundreds) small polyps that are seen are ini¬ tially dependent on gastrin but may become autonomous. Metastases to lymph nodes are rare, but are more common in sporadic (nonhypergastrinemia-associated) ECL cell carcinoids (see Table 214-2). Eighty percent of small intestinal carcinoids (which may be multiple) occur within 60 cm (2 ft) of the ileocecal valve and 85% of bronchial carcinoids are in the main bronchi. The primary tumors tend to remain small and extend outward, away from the lumen. They then spread to local lymph nodes. Marked fibrotic reaction may occur, which, with midgut carcinoids, may distort the gut and mesentery, and sometimes cause intestinal obstruc¬ tion or vascular occlusion. Further spread occurs to the liver, and distant metastases may occur at almost any site, including osteo¬ lytic and osteoblastic bone metastases.2,5,6 Carcinoids may contain various peptides and amines, and some carcinoids, particularly those of the foregut, can produce other clinical syndromes, with or without the carcinoid syn¬ drome. Carcinoids that secrete insulin, growth hormone, cor¬ ticotropin /3-melanocyte-stimulating hormone, gastrin, calci¬ tonin, substance P, growth hormone releasing hormone, and bombesin-like peptides have been described.2 The carcinoid syndrome is much rarer than carcinoid tu¬ mors: the estimated incidence is about 3 cases per million popu¬ lation per year. The syndrome occurs only when vasoactive sub¬ stances reach the systemic circulation and, therefore, most gut carcinoids cause the syndrome only when hepatic metastases are present. Even then, the carcinoid syndrome occurs only in a few cases (see Table 214-2), and the histamine-type syndrome caused by gastric carcinoids has been described in less than 10 cases. All were sporadic ECL cell carcinoids. Ovarian and bronchial tu¬ mors, which drain directly into the systemic circulation, can cause the carcinoid syndrome without metastases; however, with bronchial carcinoids, metastases are usually present. Rarely, medullary carcinoma of the thyroid and small-cell tumors of the lung cause the syndrome.

CLINICAL FEATURES PATHOLOGY The relative distribution of carcinoid tumors, their propen¬ sity to metastasize, and their ability to cause the carcinoid syn¬ drome are shown in Table 214-2. Most gastric ECL cell carcinoids are under the influence of gastrin. In patients with hypergastrinemia due to gastric atrophy (with or without pernicious anemia) or Zollinger-Ellison syndrome with multiple endocrine neoplasia

CARCINOIDS WITHOUT SYSTEMIC FEATURES Carcinoids without systemic features occur most commonly in the appendix (see Table 214-2) and usually are found inciden¬ tally at surgery.2,3,5,6 Small intestinal carcinoids are usually symp¬ tomless but, occasionally, cause intestinal obstruction or vascular occlusion. Ileal tumors generally are not demonstrated by simple

TABLE 214-1 Carcinoid Tumors: Characteristics and Embryological Derivation Site of Tumor Foregut

Mid gut

Hindgut

HISTOLOGIC FEATURES

Trabecular

Solid mass of cells

Mixed

APPEARANCE OF CYTOPLASMIC GRANULES (ELECTRON MICROSCOPY)

Variable density, 180 pm diameter

Uniformly dense, 230 pm diameter

Variable density, 190 pm diameter

NSE

Positive

Positive

Positive

SILVER

STAINING

Argyrophilic; or negative

Argentaffin

Negative

TUMOR PRODUCTS

5-HTP, peptides; histamine (gastric)

5-HT

None

METASTASES TO BONE AND SKIN

Common

Unusual

Common

NSE, neuron-specific enolase; 5-HTP, 5-hydroxytryptophan; 5-HT, 5-hydroxytryptamine.

1854

PART XV: HORMONES AND CANCER

radiology; therefore, barium infusion studies or angiography are required.7 Duodenal and gastric carcinoids most often are inci¬ dentally found at endoscopy. Colonic, rectal, and esophageal car¬ cinoids also may be found incidentally, or may cause obstruc¬ tion.73 Bronchial carcinoids may be discovered as a coin lesion on chest radiographs or may be seen at bronchoscopy; they also may present with cough, wheeze, hemoptysis, or with segmental ob¬ struction and infection. Mediastinal and ovarian carcinoids ap¬ pear as masses.71’ Most carcinoids occur as an isolated disease, but there are associations between foregut carcinoids and multiple endocrine neoplasia type 1, between gastric carcinoids and hypergastrinemia whether due to achlorhydria or Zollinger-Ellison syndrome, especially as part of multiple endocrine neoplasia type l,8 and between ampullary carcinoids and von Recklinghausen disease.2 The diagnosis of all carcinoids without systemic features depends on the histologic structure.

THE CARCINOID SYNDROME The carcinoid syndrome2,3'5,6 is characterized by flushing, di¬ arrhea, and heart disease, although the relative importance of the symptoms varies in different patients, reflecting differences in tumor origin, bulk, tumor products, and length of history. The primary tumor may have been removed many years before the development of the syndrome, or it may never have become clin¬ ically evident. However, most patients with the carcinoid syn¬ drome will have an ileal tumor, with evident hepatic metastases at the time of presentation (see Table 214-2).

TABLE 214-2 Ability of Carcinoid Tumors to Metastasize and Produce the Carcinoid Syndrome No. of Cases

Total

With Metastases

With Carcinoid Syndrome

FOREGUT Esophagus

2

—

197 21 32 115 5 18 5 7 4 >500* 74

17 12 17 23 1 6 —

— —

9 4 1 1 _

1 2 >100* 19

— —

66 -

MIDGUT Jejunum Ileum Meckel diverticulum Appendix Colon Liver Ovary Testis Cervix

56 1013 44 1687 89 4 34 2 33

20 355 8 34 53 —

91 6 6 5

573

The flushing may be due to the release of kinins in some patients.12,13 Carcinoids contain kallikrein, an enzyme that, when released into the circulation spontaneously or stimulated by al¬ cohol or catecholamines, acts on plasma kininogens to generate bradykinin2,5 (see Chap. 163). In gastric carcinoids, the distinc¬ tive flush is mediated by histamine (see Chap. 180). 5-Hydroxy tryptamine (serotonin) is largely responsible for the diarrhea through its effects on gut motility. It also contributes to the asthma and is probably implicated in the cardiac fibrosis. The diversion of tryptophan to the tumor for 5-hydroxytryptamine synthesis can lead to reduced protein synthesis, with hypoalbuminemia, and to nicotinic acid deficiency, with pellagra.14 The prostaglandins15 and many gut peptides16 probably are not mediators of the flushing or diarrhea in most patients. The role of other peptides such as substance P or other tachykinins (neurokinin A, neuropeptide K) has yet to be fully evaluated.13

—

2 —

8

17 1 1

HINDGUT Rectum

PATHOGENESIS OF THE CARCINOID SYNDROME

—

Stomach-) With gastric atrophy With ZES Sporadic^ Duodenum Pancreas Gallbladder Bile duct Ampulla Larynx Bronchus Thymus

Carcinoid flushing is erythematous, and principally affects the upper part of the body. Some patients are unaware of the flushing, whereas others are distressed. Flushes may be brief or prolonged. They often are spontaneous, but they may be precip¬ itated by alcohol, certain foods, abdominal palpation, or anxiety. Several patterns of flushing have been described,3 but only two are clinically distinctive. Gastric carcinoids may produce a bright red, geographic flush, often precipitated by food9; bronchial car¬ cinoids may cause severe prolonged flushes with salivation, lacrimation, sweating, facial edema, palpitations, diarrhea, and hy¬ potension. After many months of flushing, a fixed, facial telangiectasia, edema, and cyanotic plethora may occur. Diarrhea occurs in most cases, although it is less evident with gastric carcinoids. In some patients, diarrhea is related to epi¬ sodes of flushing; in others, the two seem independent. Watery diarrhea is more frequent than malabsorption and is due to in¬ creased motility and possibly intestinal secretion; but intermit¬ tent intestinal obstruction, cholorrheic diarrhea after previous in¬ testinal resection for tumor, or vascular insufficiency or lymphatic obstruction may occur in some patients. Abdominal pain may be due to these abnormalities or to necrosis of hepatic metastases. Heart disease occurs in up to 30% of patients. Insidious right heart failure, often worsens during periods of flushing, and, in such cases, tricuspid regurgitation or stenosis is typical; less com¬ monly, pulmonary stenosis may occur. The left side of the heart also may be involved, usually in association with bronchial car¬ cinoids. The heart disease is caused by a unique form of fibrosis that involves the endocardium and valves. 3 Fibrosis in other sites can cause constrictive pericarditis, retroperitoneal fibrosis, pleural thickening,10 and Peyronie disease. Wheezing occurs in 10% of patients and can be the present¬ ing feature. A pellagra-like syndrome may occur, and confusional states have been described with foregut carcinoids. Rarely, patients experience arthralgia or a myopathy.11

18

1

* Only approximate data are available. t From Rindi G, Luinetto O, Cornaggia M, et al. Three subtypes of gastric argyrophil carcinoid and the gastric neuroendocrine carcinoma: a clinical pathologic study. Gastro¬ enterology 1993; 104:994. | Not associated with hypergastrinemia. ZES, Zollinger-Ellison syndrome.

DIAGNOSIS OF THE CARCINOID SYNDROME Once the carcinoid syndrome has been considered, the diag¬ nosis is often not difficult and rests on clinical features, measure¬ ment of the principal 5-hydroxytryptamine metabolite in urine (5-hydroxyindoleacetic acid [5-HIAA]) and, occasionally, on the provocation of flushing with epinephrine.2,3,5,6 In a patient who flushes, who has an enlarged liver, and in whom urinary 5-HIAA excretion is more than 30 mg/day (normal < 10), the diagnosis is obvious. Diagnostic difficulties may arise in patients who flush

Ch. 214: The Carcinoid Tumor and the Carcinoid Syndrome for other reasons, in patients with carcinoid syndrome in whom the flushing is not apparent, or in patients with modestly elevated urinary 5-HIAA. The differential diagnosis of flushing includes menopausal flushing, reactions to alcohol and glutamate, side effects of drugs (such as chlorpropamide, calcium channel block¬ ers, and nicotinic acid), other tumors, chronic granulocytic leuke¬ mia, idiopathic flushing, and systemic mastocytosis17,18 (see Chap. 180). None of these conditions increases urinary 5-HIAA, and in none does epinephrine provoke flushing as it does in the carcinoid syndrome. A positive response to epinephrine also may help to confirm the diagnosis of carcinoid syndrome in patients without apparent flushing. When urinary 5-HIAA is only mod¬ estly elevated, other causes must be excluded; excretion rates of up to 25 mg/day have been described in Whipple disease, celiac disease, tropical sprue, and pancreatic islet tumors other than car¬ cinoids. Furthermore, the ingestion of 5-hydroxytryptaminecontaining foods, such as pineapples, avocados, walnuts, or ba¬ nanas, can increase 5-HIAA excretion, and more than 30 drugs are known to cause falsely high or low urinary 5-HIAA values.19 If there is any doubt about the diagnosis, urinary collections should be performed with the patient abstaining from all medications.

PROGNOSIS In the carcinoid tumor registry, the age-adjusted 5-year sur¬ vival in patients with local disease was 99% for appendiceal tu¬ mors and greater than 75% for tumors from all sites. In patients with distant metastases, the 5-year survival was 30% or less.20 In the largest reported series of patients with the carcinoid syn¬ drome, the median survival from first flush was 3 years but ranged up to 17 years.6 The median survival in patients with heart disease was 14 months, and in patients with a large tumor burden (5-HIAA > 150 mg/day), it was 11 months. The progno¬ sis for ECL cell gastric carcinoids associated with hypergastrinemia is much better, with no deaths being attributable to these tumors. However, sporadic ECL gastric carcinoids are more ma¬ lignant (see Table 214-2).

TREATMENT CONTROL OF THE TUMOR Except in the case of gastric ECL cell carcinoids that are of low malignancy and can be observed for some years, surgery should be considered in all patients because the resection of local disease can result in cure of carcinoid tumors, and cure of the carcinoid syndrome due to some bronchial and ovarian tumors.21 Resection of isolated hepatic metastases detected by routine methods such as CT scan or possibly using somatostatin ana¬ logue scintigraphy22 also may be markedly beneficial in selected cases5,6; however, in the presence of extensive metastases, partial hepatic resection is not warranted, nor is removal of the primary tumor unless it is causing local problems. Interestingly, the ap¬ propriate surgery for multiple gastric carcinoids in patients with gastric atrophy is not removal of the tumors, but removal of the gastric antrum, leading to normalization of plasma gastrin and tumor regression.4 Chemotherapy for carcinoid tumors has been disappointing, with responses occurring in a minority and lasting only a mean of 7 months.6 Single agents have produced responses in up to 30%, streptozocin being the most effective agent. Various combi¬ nations of streptozocin with 5-fluorouracil, cyclophosphamide, and doxorubicin have produced response rates of up to 35%.6 Given the variation in tumor growth, questionable efficacy and undoubted toxicity of chemotherapy, and the availability of

1855

other symptomatic therapy, chemotherapy should be reserved for advanced tumors that are actively growing. a-Interferon, 3 to 6 million IU/day subcutaneously, reduces tumor size in about 15% and stabilizes tumor size in another 30% to 40%.6,23-25 Oc¬ treotide acetate, used mainly for its effect on symptoms (see later), reduces tumor bulk in about 5% and stabilizes tumor size in another 20%.26-28 Radiotherapy is useful only for symptomatic therapy of bone and skin metastases. Hepatic artery occlusion leads to selective necrosis of hepatic metastases. Surgical ligation of the hepatic artery has been used to necrose the hepatic tumor in the carcinoid syndrome,6 but per¬ cutaneous arterial embolization is less traumatic, more selective, and can be repeated.29-31 Embolization, alone or in combination with chemotherapy,6 can produce a striking relief of symptoms and reduction in urinary 5-HIAA levels, even in patients with symptoms that are resistant to other modes of therapy. Complete remissions of up to 30 months have been reported; second re¬ missions may follow repeat embolizations, and survival may be prolonged.

CONTROL OF SYMPTOMS Many patients have considerable hepatic tumor, yet they re¬ main well, apart from occasional flushing or diarrhea.2,5 They should be advised to avoid precipitants of flushing and to sup¬ plement their diet with nicotinamide. Heart failure can be treated with diuretics, asthma with albuterol (salbutamol) (which does not precipitate flushing), and diarrhea with loperamide. If pa¬ tients require further therapy, various other agents may be tried. For diarrhea, cyproheptadine, 4 to 8 mg every 6 hours, is the best oral agent.32 In the rare patient with carcinoid syndrome due to a gastric carcinoid, a combination of diphenhydramine 50 mg ev¬ ery 6 hours, together with an H2 antagonist (e.g., cimetidine 300 mg every 6 hours), has proved effective for flushes.33 However, for most patients, the most effective agent for both diarrhea and flushes is the long-acting somatostatin analogue octreotide ace¬ tate (100-500 fig every 8-12 hours subcutaneously), which has produced responses in more than 80% of patients.27,28,34 oclnterferon, used principally for its effect on the tumor, reduces flushing and diarrhea in about 50% of patients.6,23-25 (see Chap. 166). if drugs fail to control symptoms, hepatic embolization should be considered. Progressive cardiac disease can be halted only by removal of the tumor and cure of the carcinoid syn¬ drome, but the occasional, carefully selected patient may benefit from tricuspid valve replacement.5 35 Anesthetics, surgery, chemotherapy, and hepatic artery oc¬ clusion can precipitate extremely severe flushing with hypoten¬ sion—a carcinoid crisis. The risk of developing such a crisis can be reduced by appropriate premedication, careful monitoring, the judicious use of anesthetic drugs and techniques, and avoidance of flush-provoking agents, such as catecholamines.29,30,36 Should a crisis occur, hypotension should be treated with octreotide ace¬ tate 100 fig intravenously, which should be available whenever patients with the carcinoid syndrome undergo procedures.37 If octreotide acetate is not available methoxamine, 3 to 5 mg, can be used. Other pressor agents should be avoided.

REFERENCES 1. Rindi G, Luinetto O, Cornaggia M, et al. Three subtypes of gastric argyrophil carcinoid and the gastric neuroendocrine carcinoma: a clinical pathologic study. Gastroenterology 1993; 104:994. 2. Maton PN, Hodgson HJF. Carcinoid tumours and the carcinoid syndrome. In: Bouchier IAD, Allan RN, Hodgson HJF, Keighly MRB, eds. Textbook of gastro¬ enterology. London: Bailliere-Tindall, 1984:620. 3. Feldman JM, Zakin D, Dannenberg AJ. Carcinoid tumors and syndrome. Semin Oncol 1987; 14:237. 4. Maton PN, Dayal Y. Clinical implications of hypergastrinemia. In: Zakim DH, Dannenberg AJ, eds. Peptic ulcer disease and other acid-related disorders. New York: Academic Research Associates, 1991:213.

1856

PART XV: HORMONES AND CANCER Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

5. Grahame-Smith DG. The carcinoid syndrome. London: William Heinemann, 1972. 6. Moertel CG. An odyssey in the land of small tumors. J Clin Oncol 1987;5: 1503. 7. Jeffree MA, Barter SJ, Hemingway AP, Nolan DJ. Primary carcinoid tumors of the ileum: the radiological appearances. Clin Radiol 1984;35:451. 7a. Spread C, Berkel H, Jewell L, et al. Colon carcinoid tumors: A populationbased study. Dis Colon Rectum 1994;37:482. 7b. Wang DY, Chang D-B, Kuo S-H, et al. Carcinoid tumors of the thymus. Thorax 1994;49:357. 8. Hakanson R, Sundler F, eds. Mechanisms for the development of gastric carcinoids: proceedings of an international symposium. Digestion 1986;35(Suppl 1): 1 • 9. Roberts LJ, Mamey SR, Oates JA. Blockade of the flush associated with metastatic gastric carcinoid by combined H, and H2 receptor antagonists: evidence for an important role of H2 receptors in human vasculature. N Engl J Med 1979; 300: 236. 9a. Wikowske MA, Hartman LC, Mullaney CJ, et al. Progressive carcinoid heart disease after resection of primary ovarian carcinoid. Cancer 1994; 73:1889. 10. Moss SF, Lehner PJ, Gilbey SG, et al. Pleural involvement in the carcinoid syndrome. Q J Med 1993;86:49. 11. Lederman RJ, Bukowski RM, Nickelson P. Carcinoid myopathy. Cleve Clin J Med 1987;54:299. 12. Lucas KJ, Feldman JM. Flushing in the carcinoid syndrome and plasma kallikrein. Cancer 1986;58:2290. 13. Grahame-Smith DG. What is the cause of the carcinoid flush? Gut 1987;28:1413. 14. Swain CP, Tavill AS, Neale G. Studies of tryptophan and albumin metab¬ olism in a patient with carcinoid syndrome, pellagra and hypoproteinemia. Gastro¬ enterology 1976; 74:484. 15. Metz SA, McRae JR, Robertson PR. Prostaglandins as mediators of para¬ neoplastic syndromes: review and update. Metabolism 1981;30:299. 16. Long RG, Peters JR, Bloom SR, et al. Somatostatin, gastrointestinal pep¬ tides and the carcinoid syndrome. Gut 1981;22:549. 17. Wilkin JK. Flushing reactions: consequences and mechanisms. Ann Intern Med 1981;95:468. 18. Aldrich LB, Moattari R, Vinik AI. Distinguishing features of idiopathic flushing and carcinoid syndrome. Arch Intern Med 1988; 148:2614. 19. Young DS, Pestaner LC, Gibberman V. Effects of drugs on clinical labora¬ tory tests. Clin Chem 1975;21:398D. 20. Godwin JD. Carcinoid tumors: an analysis of 2837 cases. Cancer 1975; 36: 560. 21. Norton JA. Neuroendocrine tumors of the pancreas and duodenum. Curr Probl Surg 1994; 31.. 22. Kwekkeboom DJ, Krenning EP, Bakker WH, et al. Somatostatin analog scintigraphy in carcinoid tumors. Eur J Nucl Med 1993; 20:283. 23. Oberg K, Eriksson B. Role of interferons in the management of carcinoid tumors. BrJ Hematol 1991; 79(Suppl 1):74. 24. Janson ET, Oberg K. Long-term management of the carcinoid syndrome: treatment with octreotide alone and in combination with alpha interferon. Acta Oncol 1993; 32:225. 25. Oberg K, Norheim 1, Lind E, et al. Treatment of malignant carcinoid tu¬ mors with human leukocyte interferon. Cane Treat Rep 1986; 70:1296. 26. Arnold R, Benning R, Neuhaus C, et al. Gastroenteropancreatic endocrine tumors: effect of Sandostatin on tumor growth. The German Sandostatin Study Group. Metabolism 1992;41(Suppl 2): 116. 27. Kvols LK, Moertel CG, O'Connell MJ, et al. Treatment of the malignant carcinoid syndrome. N Engl J Med 1986;315:663. 28. Gorden P, Comi RJ, Maton PN, Go VLW. Somatostatin and somatostatin analogue (SMS 201-995) in treatment of hormone-secreting tumors of the pituitary and gastrointestinal tract and non-neoplastic diseases of the gut. Ann Intern Med 1989; 110:35. 29. Maton PN, Camilleri M, Griffin G, et al. The role of hepatic arterial embo¬ lisation in the carcinoid syndrome. Br Med J 1983;287:932. 30. Martensson H, Norbin A, Bengmark S, et al. Embolisation of the liver in the management of metastatic carcinoid tumors. J Surg Oncol 1984;27:152. 31. Mitty HA, Warner RRP, Newman LH, et al. Control of carcinoid syndrome with hepatic artery embolisation. Radiology 1985; 155:623. 32. Moertel CG, Kvols LK, Rubin J. A study of cyproheptadine in the treat¬ ment of metastatic carcinoid tumor and the malignant carcinoid syndrome. Cancer 1991;67:33. 33. Oates JA. The carcinoid syndrome. N Engl J Med 1986; 315:702. 34. Bloom SR, Greenwood C, eds. Proceedings of somatostatin '85: chemical, physiological and clinical advances. Scand J Gastroenterol 1986;21(Suppl 119): 1. 35. Codd JE, Prozda J, Merjavy J. Palliation of carcinoid heart disease. Arch Surg 1987; 122:1076. 36. Tomebrandt K, Nobin A, Ericsson M, Thompson D. Circulation, respira¬ tion and serotonin levels in carcinoid patients during neuroleptic anaesthesia. An¬ aesthesia 1983; 38:957. 37. Marsh HM, Martin JK Jr, Kvols LK, Moertel CG. Carcinoid crisis during anesthesia: successful treatment with somatostatin analogue. Anesthesiology 1987;66:89.

CHAPTER

215_

HORMONES AND CARCINOGENESIS: LABORATORY STUDIES JONATHAN J. LI, SATYABRATA NANDI, AND SARA ANTONIA LI

The resurgence of research in experimental hormonal carci¬ nogenesis is partly due to the realization that 25% of human tu¬ mors originate in endocrine tissues or their target organs. Spe¬ cifically, it began with the discovery of an unusual, early occurrence of vaginal cancer in young women exposed in utero to diethylstilbestrol (DES; see Chap. 216).1 Since then, correlations have been made between oral contraceptives and other estrogens and endometrial, hepatic, cervical, ovarian, and breast tumors.2,3 These observations have resulted in a growing awareness of the carcinogenic potential of both natural and synthetic hormones.4 That hormones can induce neoplasms in experimental animals has been known for more than 50 years; for nearly every clinical neoplasm with a hormonal association, there is a corresponding animal tumor model that can be induced by hormones. Using different mammalian cells, hormone-induced cell transforma¬ tions, both mutagenic and neoplastic, have also been shown in culture. Yet, the precise way in which hormones affect cell trans¬ formation, whether in vivo or in vitro, remains obscure. This is not necessarily surprising, because hormonal modulation of cel¬ lular processes, such as growth, differentiation, and metabolism, is complex, and many pertinent aspects are poorly understood. Although much is known about the metabolism of hormones, both natural and synthetic, essential information concerning its influence on hormonal carcinogenicity is lacking. Of the various hormonal agents, sex hormones, particularly the estrogens, have been the most implicated in cellular transformation in both hu¬ mans and experimental animals. In addition, both androgens and progestins have been associated with tumor induction in various species, including humans.

GENERAL CONSIDERATIONS OF HORMONAL CARCINOGENESIS Hormonal carcinogenesis can be defined as the induction of tumors (benign or malignant) in endocrine organs and in their target tissues by endogenously produced or exogenously admin¬ istered (synthetic or natural) hormones. The general characteris¬ tics of hormonal carcinogenesis are (1) tissue and species specific¬ ity; (2) long induction period; (3) sustained and prolonged exposure at high levels; (4) cellular proliferation or hyperstimulation because of hormonal exposure; and (5) potential metabolic activation of the parent hormone to reactive metabolites. Perhaps related to some of these tumorigenic effects is the ability of hormones to act as transplacental teratogens. Hormones have been implicated, directly or indirectly, in the induction and growth of various experimental tumors, including those of the testis, ovary, prostate, vagina, uterus, mammary gland, liver, kidney, thyroid, anterior pituitary, and lymphoid or¬ gans.5-10 A variety of methods, including exogenous hormone administration (e.g., estrogens) and endocrine gland ablation (gonadectomy, thyroidectomy, and others), with or without other agents (oncogenic viruses, chemical carcinogens, ionizing radia¬ tion, goitrogens), have been used to cause tumors in endocrine

Ch. 215: Hormones and Carcinogenesis: Laboratory Studies organs and target tissues. The common denominator of these ma¬ nipulations appears to be prolonged and severe derangements in normal homeostasis and regulatory relationships between the hormones and their target organs.11,12 One hypothesis is that hormones may only modify the host or the target tissue during one or more phases of the events initi¬ ated by carcinogenic agents, such as viruses, chemicals, or ioniz¬ ing radiation. Modification by hormones might involve (1) pro¬ motional or cocarcinogenic effects, (2) modification of the host immune system, (3) activation of viruses, (4) modification of re¬ ceptors for carcinogens or metabolic conversion of a procarcino¬ gen into a proximal carcinogen in the target cells, and (5) regula¬ tion of the growth of the tumor cells or initiation of DNA synthesis after the carcinogenic stimulus, which appears to be essential for the fixation of transformed cells. Another hypothesis suggests that hormones play a dual role in carcinogenesis initiated by other agents.13 First, they are nec¬ essary for DNA synthesis and mitosis of the initially transformed cells for their conversion into fixed transformed cells with herita¬ ble characteristics. Second, hormones, by increasing the rate of cell division, shorten the reproductive life span of normal target cells, eventually causing a reduction in the normal-transformed cell ratio in the population—a condition that is thought to allow emergence of tumor cells by overriding the inhibitory influence of normal cells. A third hypothesis, perhaps the most relevant to this chapter, is that hormones may act as initiators of carcinogen¬ esis in various ways, such as by acting as a mutagen; by increas¬ ing the frequency of cell replication in target tissues, which in turn increases the probability of error in DNA copying; by induc¬ ing chromosomal abnormalities; or by producing hormonal metabolites that act on cellular macromolecules.14-18

1857

induction of mammary cancer is the low or negligible spontane¬ ous tumor incidence at this organ site. The susceptibility to estro¬ gens, of either the steroidal or stilbene type, in different rat strains is notable, and indicates that genetic factors play an important role in mammary gland tumor induction in this species as well. In addition, it is probable that pituitary hormones act as synergists, because hypophysectomy abolishes the induction of these tu¬ mors. In intact rats that continuously receive estrogens, malig¬ nant tumors of the breast and adenomas of the pituitary fre¬ quently develop together. This is in contrast to mice and hamsters, in which there appears to be no correlation between the tendency to develop pituitary tumors and the susceptibility to mammary cancers. Moreover, in the induction of mammary carcinomas, progesterone has a synergistic effect in certain strains of various species. A few mammary tumors also have been induced in beagle dogs by several oral contraceptive agents.21

UTERINE-CERVICAL-VAGINAL Uterine-cervical or vaginal squamous cell carcinomas occur after prolonged estrogen administration in C3H, C57, and BC mouse strains.7 No spontaneous occurrence of such tumors has been reported, and it generally is believed that these tumorigenic effects are produced by the direct carcinogenic action of estro¬ gens. Prolonged testosterone administration also causes uterinecervical tumors in female hybrid mice. Particularly pertinent is the induction of uterine mesotheliomas in a nonhuman primate species (squirrel monkey) after prolonged treatment with either DES or estradiol benzoate.22

PITUITARY

EXPERIMENTAL ANIMAL MODELS Various rodent and one primate species develop tumors in response to sex hormone treatment. Although some of these hormone-induced tumor models either involve viral mediation or arise from stimulation of the production of other pertinent hor¬ monal factors, many are considered to result from the direct car¬ cinogenic action of the hormonal agent involved. The induction of tumors by hormones characteristically occurs in hormoneresponsive target organs. This includes the hamster kidney, which contains both estrogen receptors and inducible progester¬ one receptors.16

MAMMARY GLAND Lacassagne19 first demonstrated that prolonged estrone ad¬ ministration induced a high incidence of mammary cancer in male mice; it was assumed that this hormone was directly carci¬ nogenic. However, with the discovery in this species of onco¬ genic viruses, such as mammary tumor virus, this assumption was seriously challenged. Several viruses are associated with the induction of mammary neoplasms in mice, and it is now gener¬ ally believed that hormones cannot effect a high incidence of mammary gland cell transformation in the absence of mammary tumor virus or chemical carcinogen exposure in this species. It also is evident that mammary tumor induction in mice is not caused by hormonal imbalance. However, genetic factors also are pertinent in mammary gland cell transformation in the mouse. In C3H female mice, a carcinogenic dose-response curve for oral administration of DES has been reported. These data indicate that 6.25 parts per billion of DES in the diet lead to significantly increased tumor formation.20 The lack of a viral association in rats has indicated that mammary tumor induction by estrogens in susceptible strains may result from direct hormonal action. However, a role for pituitary hormones, as well as unknown viral or other environmental factors, cannot be ruled out. Unlike the mouse, a distinct advantage of the rat in experimental hormonal

Some strains of mice and rats are highly susceptible to the induction of pituitary tumors by estrogens, whereas other strains are largely resistant. Males appear to be more susceptible to estrogen-induced pituitary tumors than are females. Once pitu¬ itary tumors develop in mice, they do not regress after estrogen treatment ceases. Histologically, these tumors are described as chromophobe adenomas. The predominant secretion of these tu¬ mors is prolactin, but growth-promoting properties as well as adrenocorticotropin-like effects have been reported. These pitu¬ itary tumors can be induced by either natural steroidal estrogens or synthetic steroidal and stilbene estrogens. Intermediate-lobe pituitary adenomas also have been produced in rats and ham¬ sters after prolonged estrogen treatment. Present evidence indi¬ cates that these pituitary tumors are induced by direct hormonal action.

TESTES The induction of testicular tumors in mice with estrogens has been studied extensively. Initially, it was reported that malignant tumors of the interstitial cells develop in the A1 strain of mice that receive estradiol.23 Since then, similar testicular tumors have been induced with high incidence in some mouse strains, includ¬ ing BALB/c, ABi, and ACrg, but not in several other strains. Al¬ terations in androgen biosynthetic enzyme systems and transient induction of DNA synthesis as a consequence of estrogen treat¬ ment, together with a greater nuclear estrogen content in Leydig cells of susceptible mice, may contribute to their neoplastic trans¬ formation.24 The pituitary apparently plays a permissive role in estrogen-induced testicular tumors because hypophysectomy prevents the appearance of these tumors.

OVARY Granulosa cell tumors of the ovary develop in 25% to 50% of BALB/c mice that have been implanted with progesterone pel¬ lets. 19-Norprogesterone is more effective than progesterone in

1858

PART XV: HORMONES AND CANCER

producing these tumors. The contraceptive agents, norethindrone and norethynodrel, produce a 52% ovarian tumor inci¬ dence. Similar ovarian tumors have been shown when ovaries were transplanted into the spleens of ovariectomized rats, mice, guinea pigs, and rabbits. In these animals, the chronic excess of gonadotropins is presumed to be responsible for promoting ovar¬ ian tumor development.

kidney is proposed (Fig. 215-2). Briefly, estrogens induce prolif¬ eration of preexisting estrogen-sensitive interstitial cells as well as reparative proliferation secondary to cellular damage. This proliferation of interstitial cells leads to aneuploid cells and chro¬ mosomal instability, resulting in gene amplification and suppres¬ sion (specifically, proto-oncogene, growth factor, and suppressor gene expression), eventually leading to tumor formation.

KIDNEY

LIVER

The most intensively studied experimental model in hor¬ monal carcinogenesis is the estrogen-induced renal carcinoma of the Syrian hamster25 (Fig. 215-1). Chronic exposure of male, ei¬ ther castrated or intact (but not female), Syrian hamsters to either steroidal or stilbene estrogens results in essentially 100% inci¬ dence of multiple bilateral renal neoplasms.16 Chemoprevention of renal tumorigenesis can be effected completely by concomitant administration of the estrogen with androgen, progesterone, antiestrogen, or ethinyl estradiol.16 Evidence strongly indicates that the estrogen-induced renal tumor arises from undifferenti¬ ated committed epithelial stem cells in the interstitium.26,27 Not all estrogens are equally active in inducing these renal tumors.16 With the exception of ethinyl estradiol, which elicits only a 10% renal tumor incidence, potent estrogens (17/3-estradiol, DES, hexestrol, and 11/3-methoxyethinylestradiol [Moxestrol]) exhibit high incidences of renal neoplasms compared to weak estrogens (estriol, 4-hydroxyestrone). Moreover, estrogens that possess low or negligible estrogenic activity (17a-estradiol, /3-dienestrol, 2hydroxy-estradiol) do not induce kidney tumors. The lack of strong carcinogenic activity of ethinyl estradiol in the hamster kidney, despite its evident potent estrogenic activity, may be the result of its unique and consistent hormonal effects on the prolif¬ eration of a subset of renal tubule cells that are unaffected by other potent estrogens that are highly carcinogenic in this model.27 One of the most unusual features of the hamster kidney is its ability to behave as an estrogen-responsive and estrogendependent organ. Estrogen treatment elevates its own receptor level and induces progesterone receptors in the kidney, which are characteristic of estrogen action in target tissues.16 A revised comprehensive model for estrogen carcinogenicity in the hamster

Few hepatic tumors have been produced in mice, rats, and hamsters with various synthetic estrogens and progestins.28 Al¬ though the number of animals was low, some studies have re¬ ported a 50% to 100% incidence of liver neoplasms after long¬ term estrogen treatment. A new model has been discovered for studying estrogen car¬ cinogenicity in the liver. In the presence of 0.3% a-naphthoflavone in the diet, either DES or ethinyl estradiol administration induces an 80% to 100% incidence, respectively, of hepato¬ cellular carcinomas in castrated male hamsters.29 Because anaphthoflavone is not known to behave as a carcinogen or to possess substantial mutagenic activity, it is believed to modify the metabolism of synthetic estrogens, thus enhancing their car¬ cinogenicity by increasing the amount of parent hormone. How¬ ever, a cocarcinogenic role for a-naphthoflavone cannot be ruled out in the induction of these hamster liver tumors.

PROSTATE Long-term exposure of either Noble or Lobund Wistar rats to testosterone results in prostatic carcinomas.30,31 Tumor incidence was 50% when testosterone treatment was applied for 13 months and estrone was substituted for 6 months.30 Maximum tumor yields were obtained when testosterone plus estradiol was given for 19 months, with the incidence approaching 90%.32 Similar simultaneous exposure to testosterone plus estradiol for 4 months resulted in consistent dysplastic lesions in the dorsolat¬ eral lobe of the prostate in Noble rats.33 When testosterone was replaced by dihydrotestosterone, the active androgen in many species, prostatic tumors were not seen.34 These data suggest that estradiol may be involved in the etiology of these prostatic neo¬ plasms, because testosterone can be aromatized to estradiol. Cur¬ rent evidence suggests that estrogen acting on the androgensupported prostate induces cell proliferation in this tissue through a receptor-mediated process.35

UTERUS, DUCTUS DEFERENS, SCENT GLAND Many induced tumors in the Syrian hamster and rat require two hormones for their production, either androgen and estrogen or estrogen and progesterone. For example, leiomyosarcomas are induced in the uterine horns and ductus deferens, and an un¬ known type of tumor is induced in the scent gland after the long¬ term administration of estrogen and androgen in combina¬ tion.36 The relationship between these hormones in inducing these tumors is not well understood.

PERINATAL Perinatal effects of estrogens have been studied extensively in the mouse.37 When these animals receive prenatal and neona¬ tal exposure to DES or estradiol, cervicovaginal adenosis and ad¬ enocarcinoma occur in females and testicular lesions occur in the rete testis of males. The mechanism for these transplacental and perinatal effects is unknown. FIGURE 215-1.

Bilateral primary renal carcinomas induced with con¬ tinuous administration of 17/3-estradiol for 9 months. Hormone pellets were renewed every 2.5 months to maintain estrogen levels. Serum and kidney estradiol levels were about 2166 pg/mL and 4.5 pg/mg of pro¬ tein, respectively, throughout the treatment period. Total absorption of 17/3-estradiol over he treatment period was 31 mg (based on average mean daily absorption values).

HORMONES AS COCARCINOGENS OR PROMOTERS Finally, hormones can act as cocarcinogens or promoters in conjunction with either physical carcinogens (e.g., radiation) or chemical carcinogens (dimethylbenzanthracene [DMBA], diethylnitrosamine [DEN], N-nitrosobutylurea [NBU]) at different or-

Ch. 215: Hormones and Carcinogenesis: Laboratory Studies

1859

FIGURE 215-2. Multistep model for estrogen-induced carcinogenesis in the hamster kidney. E, estrogen; ER+, estrogen receptor positive. gan sites. For example, either DES or ethinyl estradiol plus x-ray treatment yield a high incidence of mammary tumors in AC1 rats that are relatively insensitive to radiation treatment alone.38 These same hormones are capable of promoting mammary tu¬ mors and hepatic neoplasia in rats exposed to DMBA and DEN/ NBU, respectively.

IN VITRO CELL CULTURE MODELS Fformonal effects on in vitro cell transformation and muta¬ genic assays have important implications regarding the role of these substances in oncogenic processes. Hormonal agents have yielded some negative results in numerous in vitro tests, includ¬ ing lack of gene mutations in the Salmonella typhimurium assay. However, positive findings in other in vitro cell assay systems are significant, and strongly suggest the possibility that hormones may possess epigenotoxic characteristics that could affect in vivo malignant cell transformation.39

SYRIAN HAMSTER EMBRYO CELL SYSTEM One of the most intensively studied in vitro assays is the Syrian hamster embryo cells in culture.40 In this assay system, DES and some of its metabolites induce morphologic and neo¬ plastic transformation of Syrian hamster embryo cells. However, no detectable gene mutations at two genetic loci were found. In the presence of the rat postmitochondrial supernatant fraction, DES also induced unscheduled DNA synthesis.

man fibroblasts and lymphocytes in culture by DES, but not by 17/3-estradiol. The major drawback of all short-term assays is that the cells used are not considered target cells for sex hormones and are not primarily epithelial in origin.

METABOLISM AND COVALENT BINDING STUDIES Investigations, both in animal models and in short-term in vitro cell culture assays, provide important indirect evidence for the bioactivation of sex hormones as a pertinent aspect of hormone-induced tumor cell transformation. Estrogens have been studied the most. There is no doubt that the estrogens can form reactive species capable of covalent binding to cellular mac¬ romolecules. 167 However, it remains controversial whether such reactive intermediates are involved in initiating oncogenesis in whole animals. From animal studies, there is a growing aware¬ ness that there are no intrinsic differences between stilbene es¬ trogens, as exemplified by DES, and steroidal estrogens, such as estradiol, in precipitating tumor formation in most model sys¬ tems. Both stilbene and steroidal estrogens can undergo orthohydroxylations to form catechols that subsequently can be oxidized to similar reactive species.41 The significance of this finding is uncertain. The covalent binding of oxidative reactive estrogen metabo¬ lites to DNA and microsomal proteins has been demon¬ strated.42 43 However, the significance of these results is disputed, and their relationship to either mutagenicity or carcinogenicity remains an unproven possibility.16

BALB/c 3T3 CELL SYSTEM Another in vitro cell system that has been studied in consid¬ erable detail is the BALB/c 3T3 cell system. Estradiol, DES, and estrone induce a statistically significant cell transformation fre¬ quency. The natural steroidal estrogens require three-fold to five¬ fold the concentration of DES to produce an equivalent transfor¬ mation frequency.

OTHER CELL SYSTEMS In other systems studied, DES induces gene mutations in mouse lymphoma cells in the presence of rat liver postmitochon¬ drial supernatant, and unscheduled DNA synthesis in HeLa cells in the presence of the same postmitochondrial supernatant frac¬ tion. Sister chromatid exchanges have been induced in hu¬

GROWTH FACTOR AND ONCOGENE INVOLVEMENT An analysis of carcinogenesis, especially hormonal carcino¬ genesis, needs to include consideration of the possible role of growth factors and oncogenes in these processes. This is espe¬ cially pertinent because many growth factors produced by nor¬ mal cells are involved, singly or in combination with other mito¬ gens, in the proliferation of specific target cells, both normal and neoplastic. Growth factors, such as insulin-like growth fac¬ tors, and transforming growth factors can be produced by transformed cells. It is likely that transformed cells may both syn¬ thesize and respond to growth factors and, consequently, prolif¬ erate independently through autocrine secretion. Thus, growth

1860

PART XV: HORMONES AND CANCER

factors, which are basically peptide hormones, can be involved in the regulation of growth, both of normal and neoplastic endo¬ crine tissues and of their target cells. In vitro studies with serumfree media have clearly shown the proliferative effects of epider¬ mal growth factor on endocrine target cells. Oncogenes, including cellular proto-oncogenes, are thought to play an important role in carcinogenesis in animals and hu¬ mans, perhaps through their proliferative functions. Oncogenes could participate in carcinogenesis in several ways, including the possibility that some of them may be coding for growth factors or growth factor receptors. It has been shown that the one gene of simian sarcoma virus (sis) is almost identical with a gene cod¬ ing for a precursor of one polypeptide chain of platelet-derived growth factor (PDGF).44 The expression of the c-sis proto¬ oncogene is known to be under androgenic control in a ductus deferens smooth-muscle tumor cell line (DDT, MF-2). Moreover, these cells synthesize and secrete a PDGF-like growth factor, which is implicated in the autocrine regulation of DDT,MF-2 cell proliferation.45 In addition, studies of the amino acid sequence of immunoaffinity-purified epidermal growth factor receptor have shown that the v-erb-B oncogene of avian erythroblastosis virus may encode for a truncated receptor lacking the external ligand binding domain for epidermal growth factor.46 These findings provide direct evidence that oncogenes may contribute to the ma¬ lignant transformation of cells by inappropriate production of growth factors or through expression of uncontrolled growth fac¬ tor receptor functions, causing unregulated cell proliferation.47 Although little is known about the expression of oncogenes by endocrine target cells, prolonged hormonal stimulation, a pre¬ requisite for hormonal carcinogenesis, may cause, in some un¬ known way, inappropriate expression of autocrine growth fac¬ tors or inappropriate activation of their receptors, thus allowing a normal cell to become neoplastic. Estrogen, which is considered to be carcinogenic, has been postulated to stimulate a growth factor that then acts on estrogen target tissues, causing cell proliferation.46 In conclusion, many chemical and physical agents are known to be involved in carcinogenesis in animals and humans. These have been classified into various categories, such as initia¬ tors, promoters, cocarcinogens, and others. It is likely that hor¬ mones possess one or more of these characteristics, depending on the experimental model system in question. A unique and funda¬ mental feature of carcinogenesis resulting from hormonal imbal¬ ance is the consistent finding that transformation usually follows a discrete pathway from normal cell hyperplasia to hormonedependent neoplasia to hormone-responsive or hormone-inde¬ pendent neoplasia (i.e., autonomous tumors). Both hormoneinduced and chemical carcinogen-induced tumors require a long latent period. Unlike hormonal carcinogenesis, however, cancers that are induced by chemical carcinogens in endocrine glands or in their target tissues usually do not depend on hormones for their growth. An exception to this general rule is the chemical carcinogen-induced mammary cancer in rats. The nature of hor¬ monal involvement and whether hormones have a direct or indi¬ rect influence in one or more parts of the sequences of events leading to carcinogenesis still require elucidation.

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eds. The hormones, physiology, chemistry and applications. New York: Academic Press, 1964:559. 7. Bischoff F. Carcinogenic effects of steroids. Adv Lipid Res 1969; 7:165. 8. Lingerman CH. Carcinogenic hormones. Recent results in cancer research. Berlin-Heidelberg: Springer-Verlag, 1979. 9. International Agency for Research on Cancer. Evaluation of carcinogenic risk of chemicals to man. Sex hormones, ed 2, vol 21. Lyon, France: IARC, 1979. 10. Chandburg RR. Pharmacology of estrogens, international encyclopedia of pharmacology and therapy, sect 106. Oxford: Pergamon Press, 1981. 11. Rivera EM, Bern HA. Hormones and cancer. In: Vernadakis A, Timiras PS, eds. Hormones in development and aging. Jamaica, NY: Spectrum Publications, 1982:645. 12. Hertz R. An appraisal of the concepts of endocrine influence on etiology, pathogenesis, and control of abnormal and neoplastic growth. Cancer Res 1957; 17: 423. 13. Nandi S. Role of hormones in mammary neoplasia. Cancer Res 1978; 38:4046. 14. 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Neoplastic and nonneoplastic re¬ sponses to chronic feeding of diethylstilbestrol in C3H mice. J Toxicol Environ Health 1984; 14:551. 21. Etreby MFE, Graf K-J. Effect of contraceptive steroids on mammary gland of beagle dog and its relevance to human carcinogenicity. Pharmacol Ther 1979; 5: 369. 22. McClure HM, Graham CE. Malignant uterine mesotheliomas in squirrel monkeys following diethylstilbestrol administration. Lab Anim Sci 1973;23:493. 23. Bonser GM, Robison JM. The effects of prolonged estrogen administration upon male mice of various strains: development of testicular tumors in the Strong A strain. J Pathol Bacteriol 1940;51:9. 24. Sato B, Spomer W, Huseby RA, Samuels LT. The testicular estrogen re¬ ceptor system in two strains of mice differing in susceptibility to estrogen-induced Leydig cell tumors. Endocrinology 1979; 104:822. 25. Kirkman H. Estrogen-induced tumors of the kidney in Syrian hamsters. Natl Cancer Inst Monogr 1959; 1:1. 26. Gonzalez A, Oberley TD, Li JJ. Morphological and immunohistochemical studies of the estrogen-induced Syrian hamster renal tumor: probable cell of origin. Cancer Res 1989;49:1020. 27. Oberley TD, Gonzalez A, Lauchner J, et al. Characterization of early kid¬ ney lesions in estrogen-induced tumors in Syrian hamster. Cancer Res 1991; 51: 1991. 28. Schardein JL. Studies of the components of oral contraceptive agents in albino rats. I. Estrogenic component. J Toxicol Environ Health 1980; 6:885. 29. Li JJ, Li SA. High incidence of hepatocellular carcinomas after synthetic estrogen administration in Syrian golden hamsters fed a-naphthoflavone: a new tumor model. J Natl Cancer Inst 1984; 73:543. 30. Noble RL. Prostate carcinoma of the Nb rat in relation to hormones. Int Rev Exp Pathol 1982; 23:113. 31. Pollard M, Snyder DL, Lochert PH. Dihydrotestosterone does not induce prostate adenocarcinoma in L-W rats. Prostate 1987; 10:325. 32. Drago JR. The induction of Nb rat prostatic carcinomas. Anticancer Res 1984; 4:255. 33. Leav I, Ho S-M, Ofner P, et al. Biochemical alterations in sex hormone induced hyperplasia and dysplasia of the dorsolateral prostates of Noble rats. J Natl Cancer Inst 1988;80:1045. 34. Bruchovsky N, Lesser B. Control of proliferative growth in androgen re¬ sponsive organs and neoplasms. Adv Sex Horm Res 1976;2:1. 35. Ho SM, Yu M, Leav I, Viccione T. The conjoint action of androgens and estrogens in the induction of proliferative lesions in the rat prostate. In: Li JJ, Nandi S, Li SA, eds. Hormonal carcinogenesis. New York: Springer-Verlag, 1992:18. 36. Kirkman H. Hormone-related tumors in Syrian hamsters. Prog Exp Tumor Res 1972; 16:201. 37. Bern HA, Talamantes FJ. Neonatal mouse models and their relation to disease in the human female. In: Herbst SL, Bern HA, eds. Developmental effects of diethylstilbestrol (DES) in pregnancy. New York: Thieme-Stratton, 1981:129. 38. Holtzman S, Stone JP, Shellabarger CJ. Synergism of estrogens and x-rays in mammary carcinogenesis in female AC1 rats. J Natl Cancer Inst 1981;67:455. 39. Li JJ. Perspectives in hormonal carcinogenesis: animal models to human disease. In Huff J, Barrett C, Boyd J, eds. Cellular and molecular mechanisms of hormonal carcinogenesis. Environmental influences. New York: John Wiley & Sons, 1995 (in press). 40. Tsutsui T, Degen GH, Schiffmann D, et al. Dependence on exogenous metabolic activation for induction of unscheduled DNA synthesis in Syrian hamster embryo cells by diethylstilbestrol and related compounds. Cancer Res 1984; 44:184. 41. Li SA, Klicka JK, Li JJ. Estrogens 2-/4-hydroxylase activity, catechol estro-

Ch. 216: Sex Hormones and Human Carcinogenesis: Epidemiology gen formation, and implications for estrogen carcinogenesis in the hamster kidney. Cancer Res 1985; 45:181. 42. Tsibris JCM, McGuire PM. Microsomal activation and binding to nucleic acids and proteins. Biochem Biophys Res Commun 1977;78:411. 43. Randerath K, Liehr JG, Gladek A, Randerath E. Age-dependent covalent DNA alteration (I-compounds) in rodent tissues: species, tissues, and sex specifici¬ ties. Mutat Res 1989; 219:121. 44. Waterfield MD. Oncogenes may encode a growth factor or part of the receptor for a growth factor. Br J Cancer 1984;50:242. 45. Smith RG, Nag A, Syms AJ, Norris JS. Steroid regulation of receptor con¬ centration and oncogene expression. J Steroid Biochem 1986; 24:51. 46. Downward J, Yarden Y, Mayes E, et al. Close similarity of epidermal growth factor receptor and x-erb-B oncogene protein sequences. Nature 1984; 307521. 47. Ikeda T, Danielpour D, Sirbasku DA. Isolation and properties of endocrine and autocrine type mammary tumor cell growth factors (estromedin). Prog Cancer ResTher 1984;31:171.

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

216_

SEX HORMONES AND HUMAN CARCINOGENESIS: EPIDEMIOLOGY ROBERT N. HOOVER

Because of the central role that the hormonal milieu plays in various carcinogenic processes, it is essential that clinical endo¬ crinologists be aware of malignancies to which their patients may be predisposed, either because of the nature of their illness or because of the nature of the hormonal therapy being instituted.

CARCINOGENESIS AND ENDOGENOUS SEX HORMONE STATUS Endogenous hormone status has long been thought to be an important factor in the etiology of a number of human malignan¬ cies, and this belief has been based on animal carcinogenesis studies (see Chap. 215), the responsiveness of a number of tu¬ mors to hormonal manipulation (see Chaps. 217 and 218), the relationship of risk of certain tumors to a variety of reproductive and other factors thought to influence hormonal status, and the simple fact that some organs depend on hormonal status for their normal function.1 Speculation about a hormonal cause has fo¬ cused on malignancies of the female breast and the reproductive tract. However, some evidence for hormonal carcinogenesis has been observed for a variety of other tumors, including prostate, testis, thyroid, and gallbladder cancers, and malignant mela¬ noma. Despite these long-standing suspicions, with the possible exception of endometrial cancer, there has been little success in identifying the specific hormonal factors that might be responsi¬ ble for these tumors.

1861

cies.2 Moreover, enthusiasm has grown for the widespread treatment of relatively healthy segments of the population (e.g., oral contraception, menopausal replacement therapy). There is considerable interest in the use of estrogens for postmenopausal prevention of osteoporosis and osteoporotic fractures3 (see Chaps. 63 and 97). Some evidence supports the long-suspected potential of menopausal estrogens to prevent clinical coronary heart disease.4 Because of this enthusiasm, appropriate evalua¬ tions of the carcinogenic consequences of these exposures has become important to public health, as well as to understanding the biology of the tumors involved.

ENDOMETRIAL CANCER ENDOGENOUS FACTORS IN ENDOMETRIAL CANCER The cancer for which the evidence for both an endogenous and an exogenous hormonal cause is best established is endome¬ trial cancer. Various factors related to endogenous hormone production have been associated with endometrial cancer.5 Medical condi¬ tions related to increased risk include functional (estrogensecreting) ovarian tumors, the polycystic ovary syndrome, diabe¬ tes mellitus, and hypertension. Reproductive factors also have consistently been found to be related to increased risk, including nulliparity and a late natural menopause. Some dietary factors also seem to influence risk, including obesity as a risk factor and vegetarian diet as a possible protective factor.6 Age, a determi¬ nant of levels of most endogenous hormones, also influences en¬ dometrial cancer risk in a unique manner. Endometrial cancer rates are extremely low in women younger than 45 years of age, rise precipitously among women in their late 40s and throughout their 50s (much more dramatically than for other tumors), and then decline from about age 60 years and older (Fig. 216-1).

EXOGENOUS SEX HORMONES AND ENDOMETRIAL CANCER Exogenous hormones also have been linked to endometrial cancer.7

CARCINOGENESIS AND EXOGENOUS SEX HORMONE THERAPY Within the last 40 years, a new element in the area of hor¬ monal influences on cancer risks has been added, that of exoge¬ nous sex hormone exposure. Pharmacologic levels of estrogens, progestins, androgens, and pituitary trophic hormones, alone or in combination, have been administered to large segments of the population for various reasons. These large-scale "natural exper¬ iments" have provided more specific insights into the relation¬ ship between hormonal factors and several different malignan¬

FIGURE 216-1. Age-specific incidence rates for breast and uterine cor¬ pus cancers among white women during 1986 through 1990. (Data from the S iraeillance, Epidemiology and End Results Program. Adapted from Deve. a iS. Cancer patterns among women in the United States. Semin Oncol

Nurs ii press.)

1862

PART XV: HORMONES AND CANCER

ESTROGENS AND ENDOMETRIAL CANCER

Estrogen replacement therapy of the menopause for 2 years or longer is associated with an excess relative risk (RR) of endo¬ metrial cancer. Table 216-1 shows estimated RRs (i.e., the risk of the disease among those exposed to estrogen therapy compared with the risk among those not exposed).8-15 The RR among users compared with nonusers ranges from twofold to eightfold. It in¬ creases even further with long duration of use and with high av¬ erage daily doses. Thus far, every type of estrogen that has been investigated has shown this relationship, including conjugated equine estrogens, ethinyl estradiol, and diethylstilbestrol (DES). The highest risk occurs among current users. The risk declines with each year after cessation of use, although apparently there is some residual excess risk even 10 years after cessation. The risk is highest for early stage malignancies, but there is a twofold to threefold excess risk for the advanced stages of disease as well. (After early positive studies, some investigators questioned whether the association might be spurious because of the oppor¬ tunities for enhanced detection of latent endometrial cancer among estrogen users. Various approaches yielded evidence con¬ sistent with a causal relationship between menopausal estrogen treatment and an increased risk of endometrial cancer.) EFFECT OF ESTROGEN-PROGESTERONE IN SEQUENCE

There has been a profound trend away from unopposed es¬ trogen treatment of menopausal symptoms and toward treat¬ ment with a sequence of an estrogen, which is then combined with a progestin. Substantial evidence16 supports that such cyclic treatment reduces the frequency of hyperplasia and atypical hy¬ perplasia associated with unopposed estrogen treatment. The first epidemiologic data on risk of endometrial cancer itself has appeared. Although based on small numbers of observations, use of the combined regimen is related to substantially lower risks than those associated with the estrogen-only regimen. Neverthe¬ less, whether exclusive use of the combined regimen is related to any excess risk remains unclear. However, it is certain that such use does not prevent the background or “expected" numbers of cancers, nor does it remove the excess risk induced by any prior use of the estrogen-only regimen.15"18

ORAL CONTRACEPTIVES AND ENDOMETRIAL CANCER

Oral contraceptives also have been studied extensively in re¬ lation to endometrial cancer, after the observations in the early 1970s that young women receiving sequential oral contraceptives (particularly dimethisterone and ethinyl estradiol [Oracon]) were developing endometrial cancer.19 Subsequent investigations esti-

TABLE 216-1 Relative Risks* of Endometrial Cancer Associated With Menopausal Estrogen Use From Selected Case-Control Studies

Overall RR

RR Among Long-Term Userst

Health plan

7.6

13.9

Retirement community

5.6

8.8

Reference

Source of Controls

Ziel and Finkel8 Mack et al.9 Gray10

Private practice

3.1

11.6

Antunes et al.11

Hospital patients

4.3

15.0

Weiss et aiq12

Community

7.9

14.3

Hulka et al.13

Gynecology patients

1.8

4.1

Shapiro et al.14

Hospital patients

3.9

6.0

Brinton et al.15

Community

3.0

6.0

* Risk of cancer relative to a risk of 1.0 for women who never used menopausal estrogens. | Definition of long-term varied from 2: 5 to & 10 years. $ Refers to continuous users. RR, relative risks.

TABLE 216-2 Relative Risks* of Endometrial Cancer Associated With Combination Oral Contraceptive Use From Five Case-Control Studies RR Among Long-Term Userst

Reference

Source of Controls

Weiss and Sayvetz20

Community

0.5

Kaufman et al.21

Hospital patients

0.5

0.3

Hulka et al.22

Community

0.4

0.3

Stanford et al.25

Community

0.4

0.2

CDC24

Community

0.5

0.6

Overall RR

* Risk of cancer relative to a risk of 1.0 for women who never used oral contracep¬ tives. f Definition of long-term varied from a 4 to 2; 10 years CDC, Centers for Disease Control; RR, relative risks.

mated that such women were at a twofold to eightfold excess risk of this tumor. On the other hand, nonsequential, combination oral contraceptives clearly are related to decreased risks of endo¬ metrial cancer (Table 216-2). RRs of 0.4 to 0.5 have been ob¬ served, indicating a 50% to 60% protection associated with such use.18"25 There is also some evidence of increased levels of pro¬ tection with increased years of use. The effects of stopping use are unclear. Three studies22,24'25 have noted that the protection was substantial among current users and subsided after cessa¬ tion. These studies, however, disagreed on the duration of pro¬ tection after stopping. In addition, most studies have observed profound interaction between other endometrial cancer risk fac¬ tors and the associations with combination oral contraceptive use. Specifically, the protective effect is attenuated among the obese,26 among long-term estrogen users,25 and among the mul¬ tiparous. Although the same interactions have not been found in all studies, these observations are consistent with a number of these risk factors operating through common or highly correlated hormonal mechanisms.

MECHANISMS OF ACTION A unified theory27 of how these risk factors operate has been proposed (Fig. 216-2). Most known risk factors are associated with increased levels of circulating estrogens, particularly estro¬ gens not bound to protein. Clearly, also related are the age effects, and the use of combination oral contraceptives, which probably modify the increased risk associated with estrogen level through the modulating effects of progestogens. Furthermore, al¬ though nulliparity, diabetes, hypertension, and race have not yet been included in this scheme, they possibly will be as our knowl¬ edge of basic endocrinology expands. The model suggests several promising lines of future clinical, epidemiologic, and laboratory research. The way that obesity affects the peripheral conversion of estrogen precursors deserves more attention. When in a woman's life does obesity matter most? Some data suggest that weight loss decreases circulating estrogens; other data do not. Does the number of adipocytes or their content determine peripheral conversion? What accounts for the reduced risk among vegetarians? The effects of progester¬ one also deserve further study, including resolving whether the protection given by combination oral contraceptives is transient, and measuring the effects of the new combination-type meno¬ pausal estrogen regimen. Perhaps most important to our understanding of carcino¬ genesis will be the clarification of the precise mechanism by which circulating estrogens produce endometrial cancer. Several possibilities have been proposed: that estrogens are complete car¬ cinogens themselves; that they promote initiated cells; or that they simply stimulate growth and, thereby, offer a greater oppor¬ tunity for abnormal cells to arise or for carcinogens to act on vul-

Ch. 216: Sex Hormones and Human Carcinogenesis: Epidemiology LATE MENOPAUSE

r

> OBESITY

----> INCREASED CONVERSION OF -> ESTROGEN PRECURSORS

1863

FUNCTIONAL OVARIAN TUMORS INCREASED CIRCULATING ESTROGENS (ESPECIALLY •FREE" ESTROGENS)

l> OMNIVOROUS

COMBINATION ORAL -> CONTRACEPTIVES

PROGESTERONE ---> FACTOR

DIABETES NULLIPARITY

■>

???

160 mg/dL without CHD but with two or more risk factors, or if LDL > 190 mg/dL without CHD and fewer than two risk factors;40 41 (2) hypertriglyceridemia after maximal effort at diet Rx, risk factor modification, and exercise if (a) triglycerides 250-500 mg/dL and LDL elevated, HDL depressed, or a positive family history of coronary artery disease or (b) triglycerides >500 mg/dL. (Diet Rx is the cornerstone of Rx of hyperlipidemias. Diet Rx must be continued concurrently with any drug Rx. Factors to which hyperlipidemia may be secondary [e.g., hypothyroidism, diabetes mellitus, alcohol consumption], must be treated with specific Rx. Lipid levels should be monitored at regular intervals. Oat bran, a soluble fiber, and psyllium mucilloid have lipid lowering effects. Although not now specifically recommended for Rx of hypercholesterolemia, they may play an adjunctive role. For mechanisms of action of individual lipid-lowering agents see Chapter 158.)

Ch. 223: Compendium of Endocrine-Related Drugs

1927

I. Bile Acid Sequestrants INDICATIONS: (1) Adjunctive Rx of elevated LDL cholesterol; (2) pruritus associated with biliary tree obstruction. Unlabeled use in diabetic diarrhea and hyperthyroidism. (Maximum possible lowering of LDL with these agents alone is about 20%.)

DOSE: All dosages cited are for adults. Other drugs should be taken 1 h before or 4 h after, to avoid their malabsorption. SIDE EFFECTS: Their use is contraindicated in the presence of total biliary tree obstruction or hypersensitivity [pruritus, urticaria] to bile acid sequestrants. Side effects include GI manifestations such as nausea and constipation, which usually decline over several months of Rx; interference with absorption of fat-soluble vitamins and various medications including digoxin, thyroxine, and anticoagulants [see Chap. 158]. Safety for use in pregnancy or during nursing has not been determined. Their use may lead to elevation in triglyceride levels. For a complete listing of other possible side effects, see Refs 1-3.

A. CHOLESTYRAMINE

Questran 4 g cholestyramine 19 g powder; 378 g powder/can and 9 g single-dose packets of powder Questran Light 4g/5 g powder (1.6 cal/package) Cholybar_4g cholestyramine/bar (raspberry, 60 cal/bar, or caramel 50 cal/bar)

DOSE: Begin with 4 g bid. Titrate upward at 1 wk intervals to 12 g bid or 8 g tid. Mix dose well in -6 oz of preferred liquid, soup, pureed fruit, or jello, before taking.. ~bT COLESTIPOl.

TCol~stid

300 & 500 g bottles; 5 g single dose packets

DOSE: Begin with 5 g po bid. Titrate upward at 1 wk intervals to 15 g bid or 10 g tid. Mix as for cholestyramine above. Maximum dose is 16 g/d. II. Fibric Acid Derivatives INDICATIONS: Type II, IV and V hyperlipidemias. (These agents predominantly lower triglycerides and VLDL levels. They lower LDL cholesterol less predictably. Gemfibrozil increases HDL levels.) ~a7clT)FIBRATE

rCiofibrate

500 mg caps

Atromid-S

500 mg caps

INDICATIONS: Advocated for Rx of type III hyperlipidemia that does not respond to dietary Rx, and for diet-resistant types IV and V for which triglyceride values are higher than 750 mg/dL and there is risk of pancreatitis .42 DOSE: 1 g po bid.

SIDE EFFECTS: Side effects of ciofibrate include cholelithiasis, myositis, and enhanced action of warfarin. May be associated with excess mortality from gastrointestinal disease, including Ca [see Chap. 158], May lead to elevations of serum AST and ALT, and proteinuria. B. GEMFIBROZIL~|~Gemfibrozil_300 mg caps_Lopid_300 mg caps & 600 mg tabs INDICATIONS: Advocated for hypertriglyderidemia in adults with serum triglyceride values higher than 750 mg/dL [types IV and V] who do not respond to dietary Rx and in whom there is risk of pancreatitis. (In the Helsinki Heart Study, subjects with types Ila, lib, and IV hyperlipidemias received 600 mg bid of gemfibrozil. Mean HDL rose about 8.5% and LDL fell about 33%. In 5 yr, total cardiac endpoints were 27.3/1000 in the gemfibrozil group versus 41.4 in the placebo group. There were slightly more deaths overall in the gemfibrozil |roup because of accidents or violence and intracranial hemorrhage. There was no significant difference in total number of cancers between groups.43) DOSE: 600 mg po bid ac.

SIDE EFFECTS:

Side effects of gemfibrozil include gastrointestinal discomfort,' leukopenia, and enhanced action of warfarin.

III. HMG-CoA REDUCTASE INHIBITOR A. LOVASTATIN B. PRAVASTATIN C. SIMVASTATIN D. FLUVASTATIN

Mevacor Pravacol Zocor Lescol

elevation of serum AST and ALT, hypokalemia, anemia.

10, 20 & 40 mg tabs 10, 20 & 40 mg tabs 5, 10, 20 & 40 mg tabs 20 & 40 mg tabs

INDICATIONS: Elevated LDL cholesterol.2 (Highly effective in lowering LDL cholesterol. In the MARS study,45 80 mg lovastatin lowered total cholesterol by 32%, LDL cholesterol by 38%, and apolipoprotein B by 26%. Lovastatin raised HDL by 8.5%. For angiographic lesions > 50%, average sclerosis increased by 0.9% in the placebo group and decreased by 4.1% in the lovastatin group. Regression occurred in 13 patients receiving placebo and 28 patients receiving lovastatin. Simvastatin has been reported to lower overall mortality over 5 yr in the 4S study. Effectiveness among these drugs is similar.) DOSE: See Chapters 157 and 158.

SIDE EFFECTS Check liver-associated enzymes q 4-6 wk during first 15 mo of Rx, then periodically. Use with caution if liver disease history. May cause myalgia; discontinue if markedly elevated plasma CPK. Increased association with rhabdomyolysis in transplant recipients on cyclosporine, erythromycin, gemfibrozil, and niacin use. Side effects among these drugs are similar.

IV. NEOMYCIN SULFATE

(tabs) Neomycin sulfate Neo-tabs

mg/tab 500 500

(5 mL oral soln) Mycifradin Sulfate Neo-fradin

INDICATIONS: Unlabeled use: Elevated LDL cholesterol in type Ila hyperlipidemia,

47

mg 125 125

only if there is prior failure to respond to conventional Rx

and high risk of ischemic heart disease.

DOSE: Adult dosage for the unlabeled use below: 0.5 g/d to a maximum of 2 g/d. SIDE EFFECTS: Contraindicated in renal insufficiency because it may cause nephrotoxicity and ototoxicity. V. NICOTINIC ACID

Nicotinic acid Nicotinic acid

25, 50, 100, 250 & 500 mg tabs 125, 250, 400 & 500 mg timedrelease caps

Niacor Nico-400

500 mg tabs 400 mg timed release caps

wmam

1928

PART XVII: ENDOCRINE DRUGS AND VALUES Nicotinic acid 100 caps Nia-Bid 400 Niac 300 Niacels_400

mg/mL injection

Nicobid

125, 250 & 500 mg timed-release

mg timed-release caps mg timed-release caps mg timed-release caps

Nicolar Nicotinex Slo-Niacin

500 mg tabs (contains tartrazine) 50 mg/5 mL elixir 250, 500 & 750 timed release tabs

INDICATIONS: (1) Advocated as adjunctive Rx in diet nonresponders with elevated LDL cholesterol or triglycerides;48 (2) elevated triglycerides; (3) used in lower doses for Rx of niacin deficiency. DOSE: Begin with 100 mg po tid. Increase slowly up to 2 g tid, with or after meals. SIDE EFFECTS: If flushing occurs, it may be alleviated by administration of one aspirin given 30 min before the scheduled dose. Nicotinic acid may exacerbate glucose intolerance, and the slow-release preparations are associated with increased risk of liver toxicity. VI. PROBUCOL

Lorelco

250 & 500 mg tabs

INDICATIONS: Advocated for diet nonresponders with elevated LDL cholesterol. (Probucol may cause lowering of HDL cholesterol.) DOSE: 500 mg po bid, with morning and evening meals. SIDE EFFECTS: Probucol is not advocated for patients with arrhythmias, recent or progressive myocardial damage.49 Prolonged QT on EKG, arrhythmias, diarrhea, decreased sense of taste and smell.

Drug

Trade Names and Preparations

LITHIUM I. LITHIUM CARBONATE

II. LITHIUM CITRATE

Lithium carbonate Eskalith Eskalith CR Lithane

300 300 450 300

mg mg mg mg

tabs; 150, 300 & 600 mg caps caps & tabs controlled-release tabs tabs

Lithobid Lithonate Lithotabs

300 mg slow-release tabs 300 mg caps 300 mg tabs

Lithium Citrate 8 mEq lithium ( as citrate, equiv to 300 mg lithium carbonate)/5 mL syrup Cibalith-S_8 mEq lithium ( as citrate, equiv to 300 mg lithium carbonate)/5 mL syrup

INDICATIONS: Manic episodes of bipolar disorder and maintenance Rx [see Ref 1]. Unlabeled uses: Rx of the syndrome of inappropriate secretion of antidiuretic hormone [SIADH] and of hyperthyroidism [see Chaps. 28 and 41].50 DOSE: For unlabeled use in SIADH (below), the dose is 600-1200 mg/d, in divided doses. For acute mania, about 600 mg po tid is used. Dosage must be individualized according to serum levels and clinical response. SIDE EFFECTS: Lithium in the Rx of SIADH may be associated with multiple side effects and inconsistent results.22 The drug may cause neurologic, cardiovascular, and other toxicities. It interferes with the action of ADH on the renal tubule. Lithium and sodium compete for reabsorption in the proximal renal tubule. Use may exacerbate hyponatremia. Serum levels must be followed closely to avoid toxicity, although side effects may occur at levels which are not very high. Hypothyroidism may occur with long-term Rx. Hyperthyroidism also has occurred.

Drug

Trade Names and Preparations

MAGNESIUM I. MAGNESIUM CHLORIDE (MgCL2)

Magnesium chloride Slow-Mag

Solutions: 20% (1.97 mEq/mL) in 50 mL vials 64 mg tabs (approx 12% elemental Mg)

Almora Magtrate

500 mg tabs (approx 5.4% elemental Mg) 500 mg tabs (approx 5.4% elemental Mg) & 54 mg/5 mL

Milk of Magnesia Concentrated Phillips Milk of Magnesia

325 mg tabs; 390 mg/mL & 7.75% liquid (approx 41% elemental Mg)

IV. MAGNESIUM LACTATE

Mag-Tab SR

84 mg Mg, caplets, sustained release

V. MAGNESIUM OXIDE (MgO)

Mag-200 Mag-Ox 400 MaOx Uro-Mag

400 400 420 140

VI. MAGNESIUM SULFATE (MgS04)

Magnesium Sulfate

Epsom Salt

Solutions: 10% (0.8 mEq/mL) in 20 & 50 mL vials & 20 mL amps; 12.5% (1 mEq/mL) in 20 mL vials; 50% (4 mEq/mL) in 2, 10, 20 & 50 mL vials, 5 & 10 mL syringes, and 2 & 10 mL amps (approx 10% elemental Mg) 40 mEq magnesium sulfate/5 g granules

Chelated Magnesium

500 mg tabs (100 mg magnesium)

II. MAGNESIUM GLUCONATE

III. MAGNESIUM HYDROXIDE (Mg[OH]2)

VII. MAGNESIUM AMINO ACIDS CHELATE

800 mg/5 mL (sorbitol, sugar. Strawberry, orange & vanilla creme flavors)

mg mg mg mg

tabs tabs tabs (with tartrazine) caps (84.5 mg magnesium)

DOSE: If using MgS04 for mild magnesium deficiency in adults, 1 g (8.1 mEq) (2 mL of 50% soln) is given IM q 6 h for 4 doses. For severe

Ch. 223: Compendium of Endocrine-Related Drugs

1929

magnesium deficiency in adults with seizures or tetany, one may give up to 2 mEq/kg (0.5 mL of the 50% MgS04 soln) IM; or 5 g (40 mEq as the 50% MgS04 soln in 1 L D-5-W) IV over 3 h [also see Chap. 67]. For other doses see Refs 2 and 3. INDICATIONS: (1) Hypomagnesemia; (2) hyperalimentation; (3) control of hypertension, encephalitis, and convulsions associated with acute nephritis in children; (4) toxemia/eclampsia of pregnancy; (5) saline laxative. [1 g elemental Mg=82.3 mEq or 41.2 mmol ] (Mild depletion of magnesium may be corrected with po magnesium carbonate, chloride, gluconate, hydroxide, or oxide salts. Magnesium chloride has greater solubility and may be absorbed better than the other preparations. Moderate to severe depletion usually is treated by the administration of parenteral magnesium sulfate. Urine output should be maintained at 100 mL q 4 h and serum magnesium levels should be closely monitored during parenteral Rx.) DOSE: For po magnesium supplementation in adults and older children, 5 mg magnesium/kg/d is given. SIDE EFFECTS: Excess oral magnesium salts cause diarrhea. Use with caution in patients with renal insufficiency. Magnesium toxicity is characterized by flushing, hypotension, paralysis, hypothermia, and cardiac and CNS depression [see Chap. 67].

Drug

Trade Names and Preparations

MEGESTROL ACETATE__ Megestrol Acetate

20 & 40 mg tabs

Megace_20 & 40 mg tabs & 40 mg/mL suspn

INDICATIONS: Palliative Rx of advanced: (1) Ca of the breast [see Chap. 217];51 (2) Ca of the endometrium. Unlabeled use: metastatic prostate Ca, particularly in combination with estradiol or diethyIstilbestrol; treatment of anorexia, cachexia, or weight loss in AIDS; treatment of hot flushes induced by prostate Ca Rx. See Chapters 119 and 218. (Megestrol acetate is a progestational antiandrogen.) DOSE: In breast Ca, 40 mg po qid. In endometrial Ca, 40-320 mg po qd, in divided doses. For appetite stimulation, 80 mg qid. SIDE EFFECTS: Weight gain.

Use with caution if prior thromboembolic disease.

Trade Names and Preparations

Drug MENOTROPINS (hMG) Pergonal

75 IU each of FSH and LH activity per 2 mL amp of hMG 150 IU each of FSH and LH activity per 2 mL amp of hMG

INDICATIONS: (1) Induction of ovulation in selected patients who do not respond to clomiphene, or do not produce endogenous gonadotropins; (2) with hCG in Rx of hypogonadotropic or idiopathic male infertility when no response to clomiphene. (hMG is a preparation of human menopausal gonadotropins extracted from the urine of postmenopausal women.) DOSE: See Chapter 94 for protocol for ovulation induction using hMG-hCG. In male infertility, the dosage of hMG is 25-75 IU 3 x/wk with hCG injections 2 x/wk. SIDE EFFECTS: Hyperstimulation syndrome, gynecomastia._____

Trade Names and Preparations

Drug METYROSINE Demser

250 mg caps

INDICATIONS: Pheochromocytoma, particularly in the preoperative preparation of patients for surgery. Also may be used if surgery is not possible or in cases of malignant pheochromocytoma. (Metyrosine, a-methyl-L-tyrosine, inhibits tyrosine hydroxylase, which is the enzyme that catalyzes the first, rate-limiting step in the synthesis of catecholamines. It is important to maintain adequate hydration during Rx [see Chap. 83].) DOSE: Starting dosage is 250 mg po q 6 h. May be increased by 250 to 500 mg/d to a maximum dose of 4 g/d in divided doses. SIDE EFFECTS:

It is not recommended for use in children 500 mg/d is required, dose should be divided.

D. TOLBUTAMIDE_~|~Tolbutamide_500 mg tabs_Orinase

250 & 500 mg tabs

DOSE: Tolbutamide: Begin Rx with 1-2 g po/d. Maximum dose is 3 g/d in 2 divided doses.

II. “Second-Generation Agents” A. GLIPIZIDE Glucotrol 5 & 10 mg scored tab Glucotrol XL 5 & 10 mg scored tab DOSE: Glucotrol: Begin Rx with 5 mg po/d. If elderly or if liver disease, begin with 2.5 mg/d. Maximum dosage is 40 mg/d. Give bid if dose is >15 mg/d. Should be taken 30 min before meals, since food delays its absorption. Starting dose of Glucotrol XL is 5 mg qd; maximum dose is 20 mg qd not at meal times.

B. GLYBURIDE DiaBeta 1.25, 2.5 & 5 mg scored tabs Micronase 1.25, 2.5 & 5 mg scored tabs (Glibenclamide) Glynase 1.5, 3 & 6 mg scored tabs DOSE: Glyburide: Begin Rx with 2.5 to 5 mg po/d. If elderly, start with 1.25 or 1.5 mg. Give bid if dose is >10 mg/d. Should be taken with meals. Maximum dose is 20 mg/d.

INDICATIONS: Type II diabetes mellitus, if diet and exercise Rx alone are not successful in achieving adequate serum glucose control. (The designations "first-" and "second-generation” for oral hypoglycemic agents are based on the time-course of their development rather than a clear-cut Rx advantage of the second group over the first. The second-generation agents are more potent on a mg/mg basis and the two groups differ in their lipophilic properties. If a patient is well-controlled on one agent, there usually is no reason to switch to another.)

SIDE EFFECTS: Adverse reactions to oral hypoglycemic agents include hypoglycemia, gastrointestinal disturbances, cholestatic jaundice, skin rashes, and hematologic dyscrasias. Patients should be told to notify physician if they have symptoms of hypoglycemia or hyperglycemia, or if they develop fever, sore throat, or unusual bruising or bleeding. See Chapter 138 for a full discussion of these agents. The duration of action of any one of these agents [see Chap. 138] should be taken into consideration when making a Rx decision regarding its use. The long t'A of chlorpropamide gives it a prolonged hypoglycemic effect. Hypoglycemia may need to be aggressively treated, including hospitalization. In addition to IV dextrose, charcoal hemoperfusion shortened the t'A of chlorpropamide in one patient with drug-induced hypoglycemia in association with renal failure. Rx with octreotide has also been reported to be useful in drug-induced hypoglycemia. Drugs that compete for protein-binding sites may potentiate hypoglycemic effects of first-generation agents. Acetohexamide is the only sulfonylurea with uricosuric properties. Difference in bioequivalence of generics for these agents may be a problem. Chlorpropamide may be used in Rx of nephrogenic diabetes insipidus in a dose of 125-250 mg/d. Tolazamide has a mild diuretic effect that may make it useful in patients with a tendency for fluid retention. Rx with sulfonylureas is contraindicated in the presence of known hypersensitivity to these agents, in type I diabetes mellitus, in pregnancy or lactation, and in the presence of significant liver or renal disease. Sulfonylureas, particularly chlorpropamide, may cause a disulfuram-like reaction when used in conjunction with alcohol. They may cause hyponatremia owing to potentiation of the effect of vasopressin on the kidney (particularly chlorpropamide). The toxicities associated with the use of tolbutamide, glyburide, and glipizide generally are low.

Drug

Trade Names and Preparations

OXYTOCIN Oxytocin Pitocin

10 U/mL for injection 10 U/mL for injection

Syntocinon

10 U/mL for injection 40 U/mL in nasal spray

INDICATIONS: (1) Medical induction of labor; (2) to augment labor in selected patients with uterine dysfunction; (3) prevention of postpartum uterine atony or hemorrhage; (4) promotion of milk letdown in lactation. (Oxytocin is an octapeptide produced in the hypothalamus and stored in the posterior pituitary. It has uterine-stimulating, vasopressor, and antidiuretic properties, and stimulates the milk let-down reflex.) DOSE: For doses and routes consult Refs 1-3. 5IDE EFFECTS: All synthetic oxytocic products are potentially dangerous to mother and fetus and should be used only in a closely monitored setting. Monitor for overstimulation of the uterus, hypertension, water intoxication, and fetal distress.

Ch. 223: Compendium of Endocrine-Related Drugs Drug

1931

Trade Names and Preparations

PARATHYROID HORMONE (TERIPARATIDE ACETATE)_ _Parathar_200 U hPTH powder in a 10 mL vial with a 10 mL vial of diluent_ INDICATIONS: Dx agent to assist in determining whether hypocalcemia may be due to hypoparathyroidism or pseudohypoparathyroidism. (Teriparatide acetate is a synthetic form of human parathyroid hormone made up of the 1-34 fragment [NH2-terminal region] of native PTH.) DOSE: For dosages, see Chapter 227. SIDE EFFECTS: Subjects may note paresthesias, a metallic taste, pain at the injection site, nausea, cramps, urge to defecate, or diarrhea.

Trade Names and Preparations

Drug

PERGOLIDE MESYLATE__ Permax

0.05, 0.25 and 1 mg tabs

INDICATIONS: Adjunctive Rx in Parkinson disease. Unlabeled use in hyperprolactinemic states.55 (Dopamine receptor agonist at D, and D2 receptors. It is 10-1000 times more potent than bromocriptine in lowering prolactin.) DOSE: 0.05 mg/d on first 2 days. Increase gradually by 0.1 or 0.5 mg q 3 days for 12 days. response is achieved. Administer tid.

Increase by 0.25 mg/day q 3 days until optimal

SIDE EFFECTS: Side effects include hypotension (to which tolerance often develops), hallucinosis (no tolerance observed), atrial premature contractions, and sinus tachycardia.

Trade Names and Preparations

Drug

PHENOXYBENZAMINE__ Dibenzyl ine

10 mg caps

INDICATIONS: Management of pheochromocytoma to control hypertension [see Chap. 83]. Unlabeled use in micturition disorders (neurogenic bladder, sphinctorial outlet obstruction, partial prostatic obstruction) in a dose of 5-60 mg/d. (Phenoxybenzamine is an a-adrenergic receptor¬ blocking agent. If tachycardia develops during its use, a B-adrenergic receptor-blocking agent may be added. Important to maintain adequate hydration during Rx.) DOSE: In adults, initial dosage is 10 mg po bid. May be increased qod until the desired blood pressure response is achieved. Usual dose is 20-40 mg, bid or tid. Dosage must be individualized. For doses in children, see Chapter 84. SIDE EFFECTS: Side effects include postural hypotension, cardiac arrhythmias, miosis, and inhibition of ejaculation. Should be used with caution in patients with atherosclerosis or renal disease.

Trade Names and Preparations

Drug PHENTOLAMINE Regitine

5 mg/1 mL vial

INDICATIONS: Management of pheochromocytoma for the control of blood pressure in hypertensive crisis or in the perioperative period. Unlabeled use in the control of hypertensive crisis associated with withdrawal from clonidine or propranolol Rx or secondary to MAO inhibitor/sympathomimetic amine interactions. Also may be useful in controlling other effects of excessive epinephrine, such as respiratory depression and convulsions [see Chap. 83]. It also has been used in combination with papaverine and prostaglandin E] as an intracavemosal injection for impotence. (Phentolamine is an a-adrenergic receptor-blocking agent. It causes cardiac stimulation. It has a rapid onset and short duration of action. Maintain adequate hydration during Rx.) DOSE: Phentolamine, 5 mg, in the adult, or 1 mg in the child, is given IV or IM 1-2 h preoperatively, or IV as needed for control of blood pressure. These doses may be repeated. SIDE EFFECTS: Side effects include severe hypotension, tachycardia, cardiac arrhythmias, flushing, nausea, vomiting, and diarrhea. Should be used with extreme caution in patients with atherosclerosis because myocardial and cerebrovascular infarction have occurred following its use.

Trade Names and Preparations

Drug PHOSPHORUS I. Oral

II. Intravenous

K-Phos Neutral Neutra-Phos

250 mg phorphorus/tab 250 mg phosphorus/cap

Neutra-Phos-K Uro-KP-Neutral

250 mg phosphorus/cap or 75 mL soln 250 mg phosphorus/tab

Potassium phosphate Sodium phosphate

or 75 mL soln 224 mg monobasic & 236 mg dibasic potassium phosphate/mL (3 mmol phosphate & 4.4 mEq potassium/mL) in 5 & 15 mL vials and 50 mL bulk additive vials 276 mg monobasic & 142 mg dibasic sodium phosphate/mL (3 mmol phosphate & 4 mEq sodium/mL) in 15 & 30 mL vials

1932

PART XVII: ENDOCRINE DRUGS AND VALUES

INDICATIONS: (1) Phosphate depletion; (2) dietary phosphorus supplementation, particularly if the diet is restricted or if needs are increased; (3) Rx of hypercalcemia in certain circumstances when serum phosphate levels are low [see Chaps. 57 and 58]; (4) hypophosphatemic rickets [see Chap. 62]; (5) X-linked hypophosphatemic rickets [see Chap. 69]; (6) Adult hypophosphatasia [see Chap. 62], (1 mmol of phosphorus = 31 mg. K-Phos Neutral tabs have 1.1 mEq K+ and 13 mEq Na+ each. They contain dibasic sodium phosphate anhydrous, monobasic sodium phosphate, and monobasic potassium phosphate. Neutra-Phos has 7.1 mEq K+ and 7.1 mEq Na+/cap or 75 mL of po soln. It contains monobasic and dibasic sodium and potassium phosphates. Neutra-Phos-K contains 14.2 mEq K+/cap or per 75 mL of po soln. It contains dibasic and monobasic potassium phosphate. Uro-KP-Neutral tabs contain 1.3 mEq K+ and 10.8 mEq Na+each. They consist of disodium and dipotassium phosphate anhydrous and monobasic sodium anhydrous phosphate.) DOSE: For phosphate depletion, 2.5 to 3.5 g of phosphate po/d in 4 equally divided doses. For hypercalcemia with low serum phosphate, 250 mg po qid. For hypophosphatemic rickets, 2-4 g po/d in divided doses. For X-linked hypophosphatemic rickets, 1-4 g po/d. For adult hypophosphatasia, 1.25-3 gpo/d. SIDE EFFECTS: Phosphorus replacement products contain significant amounts of sodium or potassium and should be used with caution if a patient is on a sodium or potassium-restricted diet. Serum calcium, phosphate, and creatinine levels should be followed closely in any patient being treated, since renal failure may occur. Use is contraindicated in the presence of severely impaired renal function, hyperphosphatemia, Addison disease, or hyperkalemia. Should be used with caution in certain conditions including renal insufficiency, liver disease, dehydration, and congestive heart failure. Most commonly experienced side effects are gastrointestinal upset and diarrhea. IV phosphorus Rx should be used only if absolutely necessary in the rare patient with life-threatening hypophosphatemia who cannot be controlled using any other approach, and then with extreme caution because it may cause severe soft tissue calcification, renal cortical necrosis, and shock [see Chap. 58].

Drug

Trade Names and Preparations

PLICAMYCIN (MITHRAMYCIN) Mithracin

2500 pg/vial, which when reconstituted with 4.9 mL sterile water contains 500 gg plicamycin/mL

INDICATIONS: (1) Malignant testicular tumors refractory to surgery or radiation Rx; (2) refractory hypercalcemia of malignancy, including parathyroid Ca, which threatens to impair neurologic or renal function [see Chap. 58].56 Unlabeled use: may be helpful in severe Paget disease to limit bone resorption and reduce the high-output cardiac state in patients unresponsive to other forms of Rx. Because of toxicity, its use here should be limited [see Chap. 64], (Plicamycin is a cytotoxic antibiotic produced by Streptomyces plicatus. Lowers serum calcium levels by inhibition of bone resorption. Fall in serum calcium generally seen within 12 h. Effect lasts for 3-7 d. Repeat doses at intervals of 4-7 d, as needed. Plicamycin is used infrequently as a chemotherapeutic agent because of its toxicity.) DOSE: For refractory hypercalcemia of malignancy, 25 gg/kg by IV infusion over 4-6 h and then reevaluate for response and toxicity. For severe Paget disease, 15-25 pg/kg has been given 1-2 x/wk by IV infusion over 4-6 h over a limited number of weeks. SIDE EFFECTS: Because of toxicity, should NOT be used routinely in Rx of most hypercalcemic patients. Toxicity more common with cumulative doses. Adverse reactions include: hemorrhagic diathesis, thrombocytopenia, hepatotoxicity, nephrotoxicity. This drug should be used only with extreme caution in patients with impaired renal or hepatic function [see Chap, 58],

Drug PROGESTINS

Trade Names and Preparations

(Caution: progestins during pregnancy may be teratogenic. Rule out pregnancy before use.)

ETHYNODIOL DOSE: Constituent with estrogen, of oral contraceptive pills. II. HYDROXYPROGESTERONE CAPROATE IN OIL

Hydroxyprogesterone caproate Duralutin Gesterol L.A. 250 DOSE: For menstrual disorders, 125 to 250 mg IM.

125 & 250 mg/mL in oil 250 mg/mL in oil 250 mg/mL in oil

Hyutin Hyprogest 250

250 mg/mL in oil 250 mg/mL in oil

III. LEVONORGESTREL DOSE: Constituent with estrogen, of oral contraceptive pills. IV. MEDROXYPROGESTERONE ACETATE

Oral: Medroxyprogesterone acetate Amen Curretab

10 mg tabs 10 mg tabs 10 mg tabs

Injection: Depo-Provera

150 mg/mL aqueous suspn for IM injection

Cycrin Provera

2.5, 5 & 10 mg tabs 2.5, 5 & 10 mg tabs

DOSE: For amenorrhea and dysfunctional uterine bleeding, 5-10 mg po qd x 5-10 d. For endometriosis, 30 mg po/d. For replacement hormonal Rx, 5-10 mg po/d for each of the last 12 to 15 d of the mo in which estrogen is administered. V. MEGESTROL ACETATE

Megestrol acetate 20 & 40 mg tabs Megace 20 & 40 mg tabs & 40 mg/mL suspn Palliative Rx: breast Ca, 40 mg po qid; endometrial Ca, 40 to 320 mg po/d in divided doses. In cachexia initial dose is 800 mg/d. VI. NORETHINDRONE Norlutin 5 mg tabs DOSE: For amenorrhea and dysfunctional uterine bleeding, 5-20 mg po/d days 5-25 of the menstrual cycle. For endometriosis, 10 mg po/d x 14 d, then increase dose by 5 mg increments every 2 wk to maximum dose of 30 mg/d. Also used in doses of 0.35-2 mg/pill as constituent of oral contraceptive pills. VII. NORETHINDRONE ACETATE

Norlutate

5 mg tabs

Aygestin

5 mg tabs

mmm

Ch. 223: Compendium of Endocrine-Related Drugs

1933

DOSE: For replacement Rx, 2.5 mg po/d days 16-25 of the menstrual cycle. For amenorrhea and dysfunctional uterine bleeding, 2.5-10 mg po/d days 5-25. For endometriosis, 5 mg po/d x 14 d, then increase the dose by 2.5 mg increments q 2 wk to a maximum dose of 15 mg/d. Constituent of oral contraceptive pills in dosages of 1, 1.5 and 2.5 mg/pill.

VII. NORGESTREL

Ovrette

0.075 mg/tab

DOSE: Also available as a constituent, with estrogen, of oral contraceptive pills.

X. PROGESTERONE A. Progesterone in Oil B. Progesterone Powder

Progesterone in oil

mg/mL 50

Gesterol

mg/mL 50

Progestaject

mg/mL 50

Progesterone 1, 2, 4, 5, 8, 10, 16, 25, 50, 100 & 1000 g (for prescription compounding) DOSE: For Dx use in amenorrhea, 100 to 200 mg IM. For dysfunctional uterine bleeding, 50-100 mg.

INDICATIONS: (1) Ethynodiol diacetate used in po contraceptive pills; (2) hydroxyprogesterone caproate used for menstrual disorders; (3) medroxyprogesterone used for amenorrhea and dysfunctional uterine bleeding, endometriosis, and replacement hormonal Rx in combination with estrogens; (4) megestrol acetate used for palliative Rx of breast Ca and endometrial Ca; (5) norethindrone used for amenorrhea and dysfunctional uterine bleeding, endometriosis, and po contraceptive pills; (6) norethindrone acetate used for replacement hormonal Rx in combination with estrogens, amenorrhea and dysfunctional uterine bleeding, endometriosis, and constituent of contraceptive pills; (7) norgestrel used as progestin-only contraceptive pill and constituent of contraceptive pills; (8) progesterone used for dysfunctional uterine bleeding and for Dx evaluation of amenorrhea. (Progestins are used for wide variety of Dx and Rx purposes including contraception, dysfunctional uterine bleeding, amenorrhea, premenstrual syndrome, endometriosis, postmenopausal replacement Rx, palliative Rx of endometrial and breast Ca, suppression of postpartum lactation, chronic anovulatory syndrome and hypoventilation syndromes. Ethynodiol diacetate is converted to norethindrone in vivo. Duration of action of hydroxyprogesterone caproate is 9-17 d. Levonorgestrel has no first-pass effect. It has pronounced androgenic effects. Medroxyprogesterone acetate is commonly used in clinical practice in the evaluation of amenorrhea to induce endometrial sloughing, and in combination with estrogens for replacement Rx. In replacement Rx, doses of 2.5 or 5 mg medroxyprogesterone acetate/d may be given if progestin side effects are a problem. Duration of Rx with this agent as well as dose may be responsible for the endometrial protective effect of progestins.57 Depo-Provera is used as a contraceptive agent. The androgenic effects of norethindrone are minor to moderate. Norethindrone acetate is twice as potent as norethindrone. It has no androgenic effects. Norgestrel has pronounced androgenic effects. Progesterone is not effective when given po. It also is used in the Progestasert intrauterine device. For use of progestins in oral contraception and menopause [see Chaps. 97, 101 and 102].) SIDE EFFECTS: Breakthrough bleeding, change in menstrual flow, amenorrhea, breast tenderness, masculinization, jaundice.

Drug

Trade Names and Preparations

SOMATOSTATIN ANALOGUE OCTREOTIDE ACETATE

Sandostatin

0.05, 0.10 & 0.50 mg in 1 mL amp

INDICATIONS Indicated for control of symptoms in patients with metastatic carcinoid and vasoactive intestinal peptide-secreting tumors [see Chap. 176]58 and Rx of acromegaly [see Chap. 23],59 as well as unlabeled use in a variety of disorders [see Chap.166]. (Octreotide acetate is a longacting somatostatin analogue that suppresses growth hormone levels for 8-12 h after SC administration. Octreotide acetate generally is well tolerated in the Rx doses used. Octreotide acetate in the Rx of endocrine tumors is most successful for VIPomas [see Chap. 176]. Somatostatin analogues also are being evaluated for the Rx of other tumors of neuroendocrine origin and in patients with diabetes mellitus for their potential to attenuate the dawn phenomenon and postprandial hyperglycemia.) DOSE: Rx is initiated with 50 pg SC 1-2 times/d. The dosage then is increased according to the response obtained and to patient tolerance [see Chap. 166], SIDE EFFECTS: Rx may be associated with cholelithiasis; it is recommended that patients on extended Rx be evaluated periodically by ultrasound of the gallbladder and bile ducts. Adverse reactions, which may be seen in 3-10% of patients, include nausea, injection site pain, diarrhea, abdominal pain/discomfort, loose stools, and vomiting.

Drug

Trade Names and Preparations

SPIRONOLACTONE Spironolactone

25 mg tabs

Aldactone

25, 50 & 100 mg tabs

INDICATIONS: (1) Primary aldosteronism [see Chap. 78]; (2) certain edematous conditions when some potassium retention is desired or other Rx fails, e.g., congestive heart failure, cirrhosis of the liver with ascites, nephrotic syndrome; (3) essential hypertension; (4) hypokalemia. Unlabeled use: hirsutism [see Chap. 98].60 (Spironolactone is an aldosterone antagonist. It binds competitively in the distal renal tubule and promotes sodium excretion and potassium retention. It also has antiandrogenic effects.)

DOSE: For primary aldosteronism, 100-400 mg po/d in divided doses. For certain edematous conditions, the initial dosage is 100 mg/d in single or divided doses. The maintenance dosage is 25-200 mg/d. For essential hypertension, 50-100 mg/d in single or divided doses. For hypokalemia, 25100 mg/d. For hirsutism, dosages of 50-200 mg/d have been used. Many hirsute patients require 200 mg/d.

SIDE EFFECTS: Should not be used in a patient with significantly impaired renal function from any cause, or in any patient who is hyperkalemic. Must be evaluated periodically for the presence of hyperkalemia and/or hyponatremia. Has been shown in rats to produce dose-related adenomas of the thyroid and testis, malignant breast tumors, proliferative changes in the liver, and hepatocellular Ca.1 The drug and its metabolites may cross the placenta and into breast milk. They can cause feminization of the male rat fetus. Should not be used in pregnancy. Side effects also include abdominal cramps and diarrhea, lethargy, headaches, confusion, ataxia, impotence, gynecomastia, menstrual irregularities,' postmenopausal bleeding, skin rashes, and fever.

1934

PART XVII: ENDOCRINE DRUGS AND VALUES

Trade Names and Preparations

Drug

TAMOXIFEN CITRATE__ __Novaldex_10 mg tabs_Tamoxifen_10 mg tabs_ INDICATIONS: (1) Adjunctive Rx in postmenopausal women with estrogen receptor-positive breast Ca; (2) also may be used in premenopausal breast Ca patients who are estrogen receptor-positive [see Chap. 217]; (3) advanced breast Ca in women and men. Unlabeled use in mastalgia [10 mg/d x 4 mo] and for decreasing the size and pain of gynecomastia. (A nonsteroidal antiestrogenic agent.) DOSE: The usual dosage is 10 or 20 mg po bid. SIDE EFFECTS: Side effects include nausea, vomiting, and hot flashes. Bone pain and hypercalcemia may follow initiation of Rx due to tumor flare.

Drug

Trade Names and Preparations

THYROID HORMONE I. Natural Products A. DESICCATED THYROID (THYROID U.S.P.)

B. THYROGLOBULIN

Thyroid U.S.P. Armour Thyroid Thyrar S-P-T Thyroid Strong

15, 30, 60, 120, 180 & 300 mg tabs 15, 30, 60, 90, 120, 180, 240 & 300 mg tabs Bovine: 30, 60 & 120 mg tabs Pork thyroid in soybean oil: 60, 120, 180 & 300 mg caps 50% stronger than thyroid U.S.P.: 30, 60 & 120 mg tabs; 30, 60, 120 & 180 mg sugar-coated tabs

Proloid

30, 60, 90, 120 & 180 mg tabs

DOSE: Doses must be individualized with follow-up thyroid function tests to assess levels. The starting dose of desiccated thyroid is 15-30 mg po qd, depending on clinical setting. Maintenance dosages are 60-120 mg/d. Maintenance dosage of thyroglobulin is 65-200 mg/d. (64.8 mg=l gr).

II. Synthetic Preparations A. LEVOTHYROXINE SODIUM (L-THYROXINE, T4)

(Note: doses are in micrograms) Levothyroxine sodium 100 (white), 150 (blue), 200 (pink) & 300 (green) pg tabs Levothroid 25 (orange), 50 (white), 75 (gray), 100 (yellow), 125 (purple), 150 (blue), 175 (turquoise), 200 (pink) & 300 (green) pg tabs. Available as an IV preparation: 200 & 500 pg/vial Levoxyl 25 (orange), 50 (white), 75 (purple), 88 (olive) 100 (yellow), 112 (rose), 125 (brown), 150 (blue) (formerly Levoxine) 175 (turquoise), 200 (pink) & 300 (green) pg scored tabs. Available as an IV preparation: 200 & 500 pg/vial Synthroid 25 (orange), 50 (white), 75 (violet), 88 (olive), 100 (yellow), 112 (rose), 125 (brown), 150 (blue), 175 (lilac), 200 (pink) & 300 (green) pg scored tabs. Available as an IV preparation: 200 & 500 pg/vial Levo-T 25, 50, 75, 100, 125, 150, 200 & 300 pg tabs

DOSE: I he initial and maintenance dosage of levothyroxine used depends on the age of the patient, the indication for its use, the severity of hypothyroidism, and the presence of concurrent medical conditions, such as coronary artery disease. A reasonable eventual maintenance dosage in adults is 1.7 pg/kg/d.62 Dosage must always be titrated to clinical response and thyroid function tests. Levothyroxine is administered IV in the Rx of myxedema coma.

B. LIOTHYRONINE SODIUM (T,)

Cytomel DOSE: The usual dosage of T3 in adults is 25-75 pg qd. C. LIOTRIX (T4 & T3) Euthroid Thyrolar

(Note: doses are in micrograms) 5, 25 & 50 pg tabs Triostat (Some subdivide the dosage tid.)

10 pg/mL injection

Strengths: “'A” (orange & tartrazine), “1” (brown & tartrazine), “2” (violet) & “3” (gray & tartrazine) Strengths: “'A” (violet/wh.), “!4” (peach/wh.), “1” (pink/wh.), “2” (green/wh.) & “3” (yellow/wh.)

INDICATIONS: Thyroid preparations are used for (1) Rx of hypothyroidism and (2) TSH suppression. Natural thyroid products are derived from beef or pork sources. Desiccated thyroid and thyroglobulin are thought by many to be obsolete. Their standardization is inexact and their shelf-lives are limited. Levothyroxine is the synthetic sodium salt of the L isomer of T4. Its t'A is about 1 wk. A steady-state serum level is reached after about 4 wk on a given dose. FDA standardization procedures recently have been improved. Bioequivalence may vary between brands, and it is suggested that they not be interchanged. See Chapters 44 and 193 for initiation guidelines for adults and Chapter 46 for pediatric doses. 0.1 mg [100 pg] of levothyroxine = approximately 1 gr thyroid USP. Liothyronine sodium is the synthetic sodium salt of the L isomer of T3. T3 is rapidly metabolized and excreted. Its t'A is 1-2 d. Serum levels fluctuate widely. Postabsorptive T3 peaks could be dangerous in the elderly and in subjects with coronary artery disease. Liothyronine is not recommended for routine thyroid hormone replacement Rx. T3 is used (1) to prepare patients for scanning for presence of metastatic thyroid Ca in order to allow for a relatively short period between discontinuation of thyroid hormone Rx and scanning; (2) may be used in the performance of a T3 suppression test, where it must be used with caution because it may precipitate angina pectoris or myocardial infarction; (3) myxedema coma [use injectable form q 4 hr at a rate of 65 pg/d. The initial dose ranges from 25 to 50 pg. In patients with known cardiovascular disease, start with 10 to 20 pg. Liotrix is a mixture of synthetic T4 and T3 in a 4:1 ratio. Generally, there is no clinical advantage to its use over that of T4 alone. All strengths of Euthroid, except "2", contain tartrazine. 60 mg of Liotrix = approximately 1 gr thyroid USP. The reference strength of Euthroid "1"=60 pg T4 + 15 pg T3. This provides a so-called 'thyroid equivalent' of 60 mg. Reference strength of Thyrolar "1"=50 pg T4 + 12.5 pg T3. This provides a "thyroid equivalent" of 60 mg. SIDE EFFECTS: Side effects of thyroid hormone Rx generally reflect hyperthyroidism secondary to overdosage. reactions may occur to vehicles in tablets.

Rarely, hypersensitivity

Ch. 223: Compendium of Endocrine-Related Drugs

1935

Trade Names and Preparations THYROTROPIN (TSH) Thytropar

10 IU of thyrotropin/vial with vial of diluent

INDICATIONS: Used to increase the uptake of radioactive iodine (1) in management of thyroid Ca to demonstrate differentiated thyroid Ca or metastases and to increase uptake of Rx doses of radioactive iodine; (2) to show the presence of normal thyroid tissue in patients with autonomously functioning thyroid nodules; (3) to increase the uptake of Rx doses of radioactive iodine in toxic adenomatous goiters. (Thyrotropin [thyroid stimulating hormone/TSH] is derived from bovine anterior pituitary glands. Potency is given in international thyrotropic units.) DOSE: 10 IU thyrotropin is given SC or IM qd for 1-3 d before the administration of a tracer or Rx dose of radioactive iodine. SIDE EFFECTS: Can induce or exacerbate hyperthyroidism and should be used with caution. Patients with adrenal insufficiency should receive adequate glucocorticoid replacement during Rx with thyrotropin, to avoid adrenal crisis. Other side effects include nausea, vomiting, urticaria and headache. Hypotension, arrhythmias, thyroid swelling and anaphylaxis also may occur.

Drug

Trade Names and Preparations

THYROTROPIN RELEASING HORMONE (TRH, Protirelin)__ | Thypinone

500 pg/mL in 1 mL

Relefact TRH

500 pg/mL in 1 mL amps

INDICATIONS: Dx agent in the assessment of (1) thyroid function; (2) pituitary or hypothalamic dysfunction; (3) adequacy of thyrotropin suppression in patients on thyroid hormone Rx [see Chap. 227], (Protirelin is a synthetic tripeptide thyrotropin releasing hormone. It causes release of thyroid stimulating hormone and prolactin from the anterior pituitary. In acromegaly, about 2/3 of patients will have a paradoxical rise of growth hormone levels in response to protirelin.) DOSE: In the TRH stimulation test, protirelin is administered as a 500 pg bolus in adults. In children aged 6-16 years, 7 pg/kg, up to 500 pg. SIDE EFFECTS: Side effects, usually minor, occur in about 50% of patients and include transient hypo- or hypertension, nausea, flushing, urge to urinate, abdominal discomfort, a metallic taste in the mouth, and headache. Occasionally a patient may experience chest or throat tightness. Rarely, seizures may occur in persons with predisposing central nervous system disease and amaurosis has occurred transiently in patients with pituitary tumors.

Drug

Trade Names and Preparations

VASOPRESSIN DERIVATIVES I. DESMOPRESSIN ACETATE

DDAVP

Nasal soln of 0.1 mg/mL (0.1 mg= 400 IU arginine vasopressin) in 2..5 mL vials with applicator tubes calibrated to 0.05, 0.10, 0.15 & 0.20 mL; also available as 1.5 mg/mL in 5 mL pump bottle. Injection of 4 pg/mL in 1 mL amps Nasal soln of 0.1 mg/mL (0.1 mg = 400 IU arginine vasopressin) in 20 pg/2 mL intranasal pipets

Concentraid

DOSE: In Rx of neurogenic diabetes insipidus, dose of DDAVP in adults is intranasal 0.1-0.4 mL/d either as single dose or divided into 2-3 doses. Morning and evening dosages should be adjusted separately. The SC or IV dose of DDAVP is 0.5-1 mL/d in 2 divided doses, separately adjusted. See Refs 1-3 for pediatric doses. II. LYPRESSIN

Diapid

0.185 mg/mL in 8 mL bottles of nasal spray (1 spray = approx 2 posterior pituitary pressor U)

DOSE: The usual dose for adults and children is 1 or 2 sprays into each nostril qid. nocturia. III. VASOPRESSIN

Pitressin Synthetic

An additional bedtime dose may be required to prevent

20 pressor U/mL in 0.5 or 1 mL amps for injection, IM or SC

DOSE: Pitressin synthetic, 5-10 U, usually yields a full physiologic response in adults. In diabetes insipidus, the dosage is 5-10 U bid to tid IM or SC as needed, or intranasally on cotton pledgets, by spray or by dropper. IV. VASOPRESSIN TANNATE IN OIL

Pitressin Tannate In Oil

5 pressor U/mL in 1 mL amps for injection, IM

DOSE: Dosage of pitressin tannate in oil is 0.3-1.0 mL IM only. Repeat as needed. INDICATIONS: (1) Central diabetes insipidus; (2) prevention and Rx of postoperative abdominal distention; (3) primary nocturnal enuresis (DDAVP); (4) congenital bleeding disorders. Unlabeled uses include (1) management of bleeding esophageal varices; (2) congenital and acquired bleeding disorders.63 (These agents are derivatives of vasopressin, a posterior pituitary hormone. They have pressor and antidiuretic hormone activity. See Chapter 27 for their use in diabetes insipidus. Desmopressin acetate is l-deamino-8-D-arginine vasopressin. It is a synthetic analogue of arginine vasopressin. A single dose has an antidiuretic effect that lasts 8-20 h. By injection, its antidiuretic effect is about 10 times as potent as by the nasal route. DDAVP presently is the drug of choice in Rx of diabetes insipidus.64 Lypressin is 8-lysine vasopressin, which has antidiuretic activity and vasopressor effects. The peak of antidiuretic effect is 30-60 min. Its duration of action is 3-8 h. It is useful in patients who become unresponsive or have reactions to other preparations. May induce vasoconstriction if taken in excess. Pitressin is synthetic 8-arginine vasopressin. The duration of action of vasopressin is 2-8 h, and of vasopressin tannate is 24-96 h.) SIDE EFFECTS: Fluid and electrolyte status should be monitored closely to avoid fluid overload and hyponatremia. Use with caution in patients with atherosclerosis or hypertension. Side effects include hypersensitivity reactions, tremor, vertigo, abdominal cramps, bronchoconstriction, and anaphylaxis.

1936

PART XVII: ENDOCRINE DRUGS AND VALUES

Trade Names and Preparations

Drug VITAMIN D CALCIFEDIOL (25[OH]D3)

Caiderol

20 & 50 pg/cap

INDICATIONS: (1) Renal osteodystrophy in the presence of hypocalcemia, hyperparathyroidism, osteomalacia, or proximal myopathy [see Chap. 60]; (2) hypoparathyroidism [see Chap. 59]; and (3) osteoporosis. (Calcifediol is 25-hydroxycholecalciferol or 25(OH)D3. The time to optimal Rx effect is 2-4 wk. Serum calcium levels must be monitored closely and patients should be warned of the symptoms of hypercalcemia. For a discussion of individual agents, see Chapter 62.) DOSE: For renal osteodystrophy, 20 to 100 pg po/d. For hypoparathyroidism, 50-200 pg po/d. Some give Rx on alternate days. II. CALCITRIOL (1,25[0H]2D3)

Oral: Rocaltrol

0.25 & 0.5 pg/cap

Injection: Calcijex

1 & 2 pg/mL for IV injection

INDICATIONS: (1) Renal failure in the presence of hypocalcemia, osteodystrophy, tertiary hyperparathyroidism, osteomalacia, or proximal myopathy [see Chap. 60]; (2) hypoparathyroidism [see Chap. 59]; (3) pseudohypoparathyroidism; (4) osteomalacia; (5) tumor-induced osteomalacia; (6) X-linked hypophosphatemic rickets [see Chaps. 62 and 69]; (7) vitamin D-dependent rickets type 1 [see Chaps. 62 and 69]; and (8) vitamin Ddependent rickets type II [see Chap. 69], (Calcitriol is 1,25-dihydroxycholecalciferol [l,25(OH)2D3]. The time to optimal Rx effect for this preparation is 1-3 d. Because of its short time to onset and offset of action, calcitriol is preparation of choice in Rx of hypocalcemia in pregnancy. It is commonly used in the Rx of renal osteodystrophy in the presence of the indications listed here. In the Rx of osteomalacia, if hypophosphatemia is present, phosphate also is added to the Rx regimen. In vitamin D-dependent rickets, type II, parenteral calcium Rx may be necessary to heal the bone disease. Calcium levels should be checked at least twice weekly until the dose of calcitriol is established [see Ref 2].) DOSE: Starting po dosage is 0.25 pg/d. In dialysis patients, increase by 0.25 pg as needed at 4-8 wk intervals up to 1 pg/d. In hypoparathyroidism, increase at 2-4 wk intervals to 0.5-2 pg/d in adults; to 0.25-0.75 pg/d in children 1-5 yr. Other doses: 0.5-3 pg/d in 0.5-2 pg/d in X-linked hypophosphatemic rickets; 0.5-3 pg po/d in vit. D-dependent rickets, type I. Also see Chapter 69; doses as high as 15-20 pg/d may be required in vitamin D-dependent rickets, type II III. CHOLECALCIFEROL (Vitamin D3)

Delta-D Vitamin D3

400 IU tabs 1000 IU tabs

INDICATIONS: (1) Dietary vitamin D supplementation and (2) Rx of vitamin D deficiency. DOSE: 400-1000 IU po/d. IV. DIHYDROTACHYSTEROL (DHT)

DHT Hytakerol

0.125, 0.2 & 0.4 mg tabs; 0.2 mg/mL Intensol soln (20% ethanol); 0.2 mg/5 mL oral soln (4% ethanol) 0.125 mg caps; 0.25 mg/mL in oil

INDICATIONS: (1) Flypoparathyroidism and tetany [see Chap. 59], Unlabeled use: Renal osteodystrophy in the presence of hypocalcemia, secondary hyperparathyroidism, osteomalacia, or proximal myopathy. (DHT is a synthetic reduction product of tachysterol and is very similar to vitamin D3. It is hydroxylated in the liver, but does not require renal activation. Its time to optimal Rx effect is 1-2 wk. It has only weak antirachitic activity [1/450 that of vitamin D], 1 mg of DHT is equivalent to about 3 mg [120,000 IU] of vitamin D2 [see Ref 2], Monitor serum calcium.) DOSE: In renal osteodystrophy, DHT dose is 0.20-2.0 mg po/d. In hypoparathyroidism, maintenance dose is 0.2-1 mg po/d. ERGOCALCIFEROL (Vitamin D2)

Drops: Calciferol Drops Drisdol

8,000 IU/mL in 60 mL dropper 8,000 IU/mL in 60 mL dropper bottle

Caps or Tabs: Vitamin D Calciferol Deltalin Gelseals Drisdol

50,000 IU/cap 50,000 IU/cap 50,000 IU/cap 50,000 IU/cap (with tartrazine) (Many over-the-counter small-dosage forms are available, e.g., 400, 800 & 1000 IU/cap or tab) Injection, IM: Calciferol in oil

500,000 IU/mL

INDICATIONS: (1) Hypoparathyroidism [see Chap. 59]; (2) pseudohypoparathyroidism; (3) malabsorption of vitamin D; (4) vitamin D-resistant rickets; (5) vitamin D-deficient rickets [see Chap. 62]; and (6) vitamin D-dependent rickets type II [see Chaps. 62 and 69], (Ergocalciferol is vitamin D2. 1.25 mg provides 50,000 IU of vitamin D activity. Its time to optimal Rx effect is 4-6 wk. This is the least expensive vitamin D preparation available. 400 IU/d of vitamin D2 satisfies daily allowances for most age groups.2 Monitor serum calcium. Vitamin D-dependent rickets type II may respond to Rx with vitamin D2. For malabsorption, ergocalciferol may be given IM.) DOSE: In hypoparathyroidism in adults, dosage is 1.25-5 mg (50,000-200,000 IU) po/d [see Chap. 59], In vit. D-resistant rickets: 12,000 to 500,000 IU/d po in adults; 1000-16,000 IU/d po in children. If compliance is a problem, 600,000 IU may be given po or IM for 1 dose [also see Chap. 69], In vit. D-deficient rickets: 5,000-10,000 IU/d po until bone is healed. The dose then is reduced to 400 IU po/d. SIDE EFFECTS: Vitamin D products may cause hypercalcemia and the calcium-phosphate product should not exceed 70. Early symptoms include weakness, headache, somnolence, nausea, vomiting. Late symptoms include polyuria, polydipsia, irritability, generalized vascular calcification.

Ch. 224: Effects of Drugs on Endocrine Function and Values

REFERENCES 1. Physicians' desk reference. Oradell, NJ: Medical Economics, 1995. 2. Drug facts and comparisons. Philadelphia: JB Lippincott, 1995. 3. AMA drug evaluations. Chicago: American Medical Association, 1994. 4. Thoren M, et al. Acta Endocrinol (Copenh) 1985; 109:451. 5. Miller JW, Crapo L. Endocrine Rev 1993; 14:443. 6. Koppeschaar HP et al. Clin Endocrinol (Oxf) 1986;25:661. 7. Engelhardt D, Weber MM. J Steroid Biochem Molec Biol 1994;49:261. 8. Glass AR. J Clin Endocrinol Metab 1986;63:1121. 9. Pepper GM et al. ] Clin Endocrinol Metab 1987;65:1047. 10. Dicksteir, G et al. JAMA 1986; 255:1167. 11. Otokida K et al. Tohoku J Exp Med 1986,-150:407. 12. Med Lett Drug Ther 1985;27:87. 13. Dmowski WP. Clin Obstet Gynecol 1988;31:829. 14. Wang YS et al. J Clin Endocrinol Metab 1987;65:679. 15. Flores JF et al. Cancer 1994; 73:2527. 16. Ott SM et al. J Clin Endocrinol Metab 1994; 78:968. 17. Gucalp R et al. Arch Intern Med 1994; 154:1935. 18. Barone JA et al. Ann Pharmacother 1994; 154:1935. 19. Meldrum D. Arch Pathol Lab Med 1992; 116:406. 20. Landolt AM et al. Clin Endocrinol (Oxf) 1994; 40:485. 21. Chrousos GP et al. Ann Intern Med 1985; 102:344. 22. Miyagawa CL Drug Intell Clin Pharm 1986;20:527. 23. Carroccio A et al. Scand J Gastroenterol 1994; 24:300. 24. Paganini EP et al. Adv Intern Med 1993; 38:223. 25. Stoner E. Arch Intern Med 1994; 154:83. 26. Fruzzetti F et al. J Clin Endocrinol Metab 1994; 79:831. 27. Boivin G et al. World Rev Nutr Diet 1993; 73:80. 28. Budden FH et al. J Bone Miner Res 1988;3:127. 29. Labrie F. Cancer 1993; 72:3816. 30. Martin KA et al. J Clin Endocrinol Metab 1993; 77:125. 31. Martin KA et al. J Clin Endocrinol Metab 1990; 71:1081 A. 32. Lee PA, Page JG. J Pediatr 1989; 114:321. 33. Rittmaster RS. J Clin Endocrinol Metab 1988;67:651. 34. Loy RA. Current Opin Obstet Gynecol 1994;6:262. 35. Lantosjetal. JAMA 1989:261:1020; 1989;262:30. 36. Frohman LA. Acta Paediatr Scand Suppl 1988; 343:3. 37. Goode PN et al. World J Surg 1986; 10:586. 38. Koskinen PJ et al. Diabetes Care 1988; 11:318. 39. Eriksson B, Oberg K. Acta Oncol 1993;32:203. 40. Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults. JAMA 1993:269:3002, 3009, 3015. 41. Consensus Conference. JAMA 1984;251:1196. 42. Grundy SM, Vega GL. Am J Med 1987; 83:9. 43. Frick MH et al. N Engl J Med 1987;317:1237. 44. Todd PA, Ward A. Drugs 1988;36:314. 45. Blankenhorn DH et al. Ann Intern Med 1993; 119:969. 46. Scandinavian Simvastatin Survival Study Group. Lancet 1994;344:1383. 47. Hoeg JM et al. Am J Cardiol 1987;59:812. 48. Walldios G, Wahlberg G. Adv Exp Med Biol 1985; 183:281. 49. StrandbergTE et al. Gen Pharmacol 1988,-19:317. 50. Bistriceanu M et al. Endocrinologie 1986; 24:109. 51. Sedlacek SM. Semin Oncol 1988; 15(Suppl 1):3. 52. Stewart AF et al. Ann Intern Med 1985; 102:776. 53. Travis W. Ann Surg 1990;212:621. 54. Curtis P, Safransky H. Birth 1988; 15:199. 55. Lamberts SW, Quik RF. J Clin Endocrinol Metab 1991;72:635. 56. Ralston SH et al. Lancet 1985;2:907. 57. Lufkin EG et al. Mayo Clin Proc 1988; 63:453. 58. Gcrden P et al. Ann Intern Med 1989; 110:35. 59. Johnson MR. Eur J Endocrinol 1994; 130:229. 60. Erenus M et al. Fertil Steril 1994; 61:613. 61. Heifer EL et al. J Clin Endocrinol Metab 1988;66:208. 62. Hennessey JV et al. Ann Intern Med 1986; 105:11. 63. Mannucci PM. Blood 1988; 72:1449. 64. Chanson P. Acta Endocrinol (Copenh) 1988; 117:513.

1937

Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker.

J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

224_

EFFECTS OF DRUGS ON ENDOCRINE FUNCTION AND VALUES MEETA SHARMA

A great number of drugs may suggest, mimic, or cause disor¬ ders of endocrine or metabolic function. Some of these are negligible and relatively well tolerated; others may be severe or even lifethreatening. With some drugs, the disorder occurs rarely; with others, it occurs very frequently. Moreover, a great number of drugs, although not affect¬ ing endocrine function, influence the analysis of one or several endocrine-metabolic tests. This can cause an increase or decrease in the apparent value or may render the test difficult or impossi¬ ble to perform. Such effects may lead to the erroneous diagnosis of an endocrine-metabolic disorder when none is present or may mask the bona fide presence of such a disorder. This chapter consists of an extensive alphabetical list of many of the drugs that exert one or several of the previously described effects. Most of the drugs are not hormonal. However, if some hormonal agents exert effects on endocrine function or values other than the purpose for which they are prescribed, they may be listed as well. It should be emphasized that some of the apparent drug effects are based on clinical or laboratory informa¬ tion that may have been reported in the literature only once or twice, and there may be insufficient data to prove causality. Table 224-1 includes findings that suggest or indicate endo¬ crine-metabolic dysfunction (e.g., gynecomastia caused by spiro¬ nolactone), effects on laboratory values (e.g., hyperkalemia caused by spironolactone), and/or interferences with a test on an analytical basis (e.g., an increase of urinary 17-hydroxycorticosteroids by a metabolite of spironolactone). Most of the drugs listed have been approved by the Food and Drug Administration. However, a few are in use only in nations other than the United States. In addition, several agents are included that are only in¬ vestigational. Although most of the signs and symptoms are endocrine-metabolic in nature, other clinically relevant findings are included in order to assist in making the correct diagnosis. Several of the drugs are grouped into chemical categories, but some of the constituent drugs within these categories are listed separately if they have been individually associated with certain reported effects. Unless otherwise specified, tests are of the blood. Urine tests are specified as "ur," analytical effects are specified as "an.” The analytical effect often depends upon the method utilized to perform the test. The term "exp" indicates an effect in experimental ani¬ mals. The term "inc" refers to an increase of a laboratory value, and "dec" indicates a decrease of a laboratory value. For references or further information, contact Dr. Meeta Sharma, Department of Endocrinology, George Washington University Medical Center, 2150 Pennsylvania Avenue, NW, Washington, DC 20037.

1938

PART XVII: ENDOCRINE DRUGS AND VALUES

Table 224-1. Alphabetical List of Effects of Drugs on Endocrine Function and Values* ABBREVIATIONS

ABG ACE ACTH ADH AIP alk an AMI BMR BPH BUN cAMP CBG chol cone CPK dec CRF CS DHEA DHEAS DHT DI esp ESRD exp FFA FSH GFR GH GHRH GIP GT GTT G-6-PD HDL HMG-CoA HPA HPG HVA IGF-I inc inc/dec I/T IV LDH

= =

= = = = =

= = =

= = = = = = = = = = = = =

= = = = = = = = = = = = = = = =r = = = = =

= =

arterial blood gases angiotensin converting enzyme adrenocorticotropic hormone antidiuretic hormone acute intermittent porphyria alkaline analytical interference atrial natriuretic hormone basal metabolic rate benign prostatic hyperplasia blood urea nitrogen cyclic adenosine monophosphate corticosteroid binding globulin cholesterol concentrated creatine phosphokinase decreased chronic renal failure corticosteroids dehydroepiandrosterone dehydroepiandrosterone sulfate dihydrotestosterone diabetes insipidus especially end-stage renal disease experimental in animals free fatty acids

follicle stimulating hormone glomerular filtration rate growth hormone growth hormone releasing hormone gastric inhibitory peptide glucose tolerance glucose tolerance test glucose-6-phosphate dehydrogenase high density lipoproteins 3-hydroxy-3-methylglutaryl coenzyme A reductase hypothalamic-pituitary-adrenal axis hypothalamic-pituitary-gonadal axis homovanillic acid insulin-like growth factor I increased either increased or decreased intrathecal intravenous lactic dehydrogenase

01,-ADRENERGIC BLOCKERS:

. r..

-1 | LDL LFTs LH NADH

dec fertility (exp), testicular

=

= =

=

1 NIDDM NSAIDS OC’s PP

= =

| PPt PRA preg PSA pt PTH RBC RBF RIA RTA SG SHBG SIADH T, T4 TBG TBPA TC TG ■ tot TSH tt4 ur vit VLDL VMA . vol w/ w/o 1 xs 5-FU 5-HIAA ll-(OH)CS 17-(OH)CS 17-KGS 17-KS ? 1 1

= = = = = = = = = = = -

1

1 1 1

= =

=

= = -

= = = = = = = = =

low density lipoproteins liver function tests luteinizing hormone reduced form of nicotinamide-adenine dinucleotide non-insulin-dependent diabetes mellitus non-steroidal anti-inflammatory drugs oral contraceptives pancreatic polypeptide precipitation of an effect plasma renin activity pregnancy prostate specific antigen patient parathyroid hormone red blood cells renal blood flow radioimmunoassay renal tubular acidosis specific gravity sex hormone binding globulin syndrome of inappropriate ADH tri-iodothyronine tetra-iodothyronine thyroxine-binding globulin thyroxine-binding prealbumin total cholesterol triglycerides total thyroid-stimulating hormone total thyroxine urine vitamin

=

very low density lipoproteins vanillylmandelic acid volume with without excess; toxic dose 5-fluorouracil

= = = = = =

5-hydroxyindoleacetic acid 11-hydroxycorticosteroids 17-hydroxycorticosteroids 17-ketogenic steroids 17-ketosteroids suspected but undocumented effect

= = =

(ur), inc tot metanephrines (ur) (an), inc VMA (ur) (an), inc

atrophy (exp).

catecholamines (an), inc catecholamines (ur) (an), inc triglycerides,

a-D-GALACTOSIDASE ENZYME: inc galactose. a-METHYLDOPA: dec libido, gynecomastia, breast enlargement,

dec LDL chol, dec HDL chol, dec chol (an), inc apolipoprotein C

III,

inc ketones (ur) (an), inc or dec glucose (an), inc creatinine (an), inc

galactorrhea, hyperprolactinemia, failure to ejaculate, dec 5-HIAA

uric acid (ur) (an).

(ur), dec PRA, inc Na\ inc BUN, dec GH, inc Cl , inc alk

ACEBUTOLOL (also see P-blockers):

phosphatase, dec VMA (ur), inc porphyrins (ur), inc coproporphyrin

dec FFA, slight dec HDL chol (HDL/chol ratio unchanged), dec GT.

dec chol, dec LDL chol,

The author and editor appreciate the assistance of Roberta L. Brown, Pharm. D., in the verification of this table and other pertinent pharmaceutical information in this textbook.

IBM— Ch. 224: Effects of Drugs on Endocrine Function and Values ACE INHIBITORS: hyperkalemia, dec angiotensin II, dec aldosterone, inc PRA, sodium and fluid loss, dec ANH, inc prostaglandin synthesis, transient inc in BUN/creatinine, inc bilirubin, inc uric acid, inc glucose, dec glucose.

ACETAMINOPHEN: inc alk phosphatase (xs), dec glucose (effect of metabolite), inc 5-HIAA (ur) (an), inc metanephrines (ur) (an), hypoglycemia, jaundice. ACETAZOLAMIDE (also see carbonic anhydrase inhibitors): dec Ca2*, inc Ca2* (ur), inc estrogens (ur), dec estrogens (ur) (an), inc glucose (in prediabetics), inc 17-(OH)CS (ur) (an), inc 17-KGS (ur) (an), inc 17-KS (ur) (an), inc Mg2+, inc/dec Mg2* (ur), dec P043, inc P043 (ur), dec K*, inc K* (ur), inc Na* (ur), dec pH, inc iodide (ur).

1939

aluminum intoxication (in renal failure), osteomalacia (xs), osteoporosis (in uremic pts), dec P043, milk-alkali syndrome. AMANTADINE: inc alk phosphatase, anorexia, edema, urinary retention.

AMIKACIN (see aminoglycosides). AMILORIDE: dec libido, impotence, polyuria, alopecia, dec Ca2* (ur), inc Mg2*, inc K*, dec Na*, dec Cl , inc BUN, inc aldosterone, inc angiotensin II, natriuresis (at start of therapy), inc PRA, inc uric acid.

AMINOCAPROIC ACID: impairment of fertility (exp), kidney concretions (in renal disease), inc CPK, rhabdomyolysis, inc K* (esp in renal disease), dry ejaculation (in one hemophiliac).

ACETOHEXAMIDE (also see sulfonylureas): mild diuresis, inc

AMINOGLUTETHIMIDE: goiter, hypothyroidism, adrenal

uric acid (ur), inc alk phosphatase, inc glucose, inc insulin, inc chol. ACETOPHENAZINE (see phenothiazines): inc alk phosphatase, inc chol.

insufficiency (esp during stress), pseudohermaphroditism in fetus, masculinization and hirsutism in women, precocious sex

ACETYLSALICYLIC ACID: inc chol, inc glucose (an), inc triglycerides, dec tot T„, inc T3 uptake, inhibits binding of T4 and T3 by TBG and TBPA.

ACTH: Cushingoid state (xs), osteoporosis (xs), hyperpigmentation

development in men, inhibits conversion of chol to A5 pregnenolone, dec glucocorticoids, dec mineralocorticoids, dec estrogens, dec androgens, dec Na*, inc alk phosphatase, dec T4 by RIA, inc TSH. AMINOGLYCOSIDES: dec Mg2*, dec vit B12, dec Ca2*, dec Na*, dec K*, inc creatinine, inc BUN, inc casts (ur), dec pH, inc alk phosphatase, inc bilirubin, malabsorption syndrome, alopecia, oliguria, proteinuria, Fanconi-like syndrome. AMIODARONE: hyperthyroidism, hypothyroidism, inhibits peripheral conversion of T4 to T,, thyroid follicular adenoma, thyroid carcinoma, congenital goiter/hypothyroidism/hyperthyroidism in babies of mothers taking amiodarone, dec fertility, dec libido, alopecia, blue discoloration of skin, inc T4 by RIA (most cases), inc/dec TSH response to TRH, inc reverse T3, inc TG, inc/dec chol, inc glucose, inc alk phosphatase.

(xs), thin fragile skin (xs), acne (xs), adrenal hemorrhage, sodium and fluid retention, suppression of skin test reactions, menstrual irregularities, suppression of growth in children (xs), hirsutism, dec carbohydrate tolerance, inc insulin requirements/oral hypoglycemics in diabetics, secondary adrenocortical and pituitary unresponsiveness (esp during stress), embryocidal effects, hyperadrenalism in fetus, dec l31I uptake, inc DHEA, inc DHEAS, inc cortisol, inc estriol (in preg), inc GH, inc 17-(OH)progesterone, inc pregnanediol, hypokalemic alkalosis, inc K* (ur), inc Ca2* (ur), dec estradiol (ur) (an), dec estriol (ur) (an), dec estrogen (ur) (an). ACYCLOVIR: testicular atrophy (exp), inc BUN, inc creatinine,

AMITRIPTYLINE (see tricyclic antidepressants). AMLODIPINE: hair loss, polyuria, anorexia, sexual difficulties,

anuria, edema, anorexia, inc sediment (ur), dec K\ renal failure (xs).

nocturia.

ADENOSINE: inc epinephrine, inc norepinephrine, dec

AMOBARBITAL (see barbiturates). AMOXAPINE (see tricyclic antidepressants). AMPHETAMINES: impotence, anorexia, changes in libido, inc

spermatogenesis (exp), inc abnormal sperm (exp).

ALANINE: inc glucose, inc GH, inc insulin, inc P043, dec K*. ALBUTEROL (also see sympathomimetics): mild dec aldosterone, dec Ca2\ inc HDL chol, dec corticosteroids, dec Mg2*, dec P043, dec K\ inc PRA, given IV aggravates diabetes and ketoacidosis. ALDESLEUKIN (IL-2): hypothyroidism, inc bilirubin, inc BUN, inc creatinine, inc alk phosphatase, dec Mg2*, acidosis, inc/dec Ca2*, inc/dec P043 , inc/dec K*, inc uric acid, dec albumin, dec protein, inc/dec Na*, alkalosis, hypoglycemia, hyperglycemia, dec chol, anorexia, pancreatitis, oliguria, anuria, proteinuria, dysuria, alopecia, fatigue, weight gain, weight loss, malignant hyperthermia. ALDOSTERONE: inc HC03, dec Cl , inc Mg2* (ur), dec K*, inc K* (ur), dec Na*(ur), inc corticosteroids (an). ALFENTANIL (also see narcotic analgesics): hypercarbia. ALGLUCERASE: catalyzes hydrolysis of glucocerebroside to glucose and ceramide, improved mineralization in pts with type I Gaucher disease. ALLOPURINOL: ppt of gout, cholestatic jaundice, inc alk phosphatase, hepatitis, uremia, alopecia, renal failure, infertility(?), gynecomastia(?), hyperlipidemia(?), salivary gland swelling(?), hypercalcemia(?), impotence, dec libido, albuminuria(?).

ALPRAZOLAM (see benzodiazepines). ALSEROXYLON (see Rauwolfia derivatives). ALTRETAMINE: inc alk phosphatase, anorexia, fatigue, inc creatinine, inc BUN, alopecia. ALUMINUM: inc aluminum (in renal failure), inc alk phosphatase, dec l,25(OH)2D, (in renal failure), dec PTH (in renal failure), dec P043 (in renal failure).

ALUMINUM-MAGNESIUM HYDROXIDE (also see antacids):

cortisol, inc FFA, dec glucose, inc GH, inc HVA (ur), inc epinephrine (ur), inc norepinephrine (ur), inc corticosteroids (greatest in evening), reversible inc T4, inc Tv AMPHOTERICIN: dec Na*, inc alk phosphatase (xs), inc chol (an), dec Mg2* (xs), inc/dec K*, inc BUN, nephrocalcinosis, hyposthenuria, RTA. AMPICILLIN: dec urinary excretion of DHEA and DHEAS (in preg), dec estriol (ur), dec 17-KGS (ur), dec 17-KS (ur), dec pregnanediol (ur), dec progesterone. AMPICILLIN-SULBACTAM: inc LDH, inc alk phosphatase, dec albumin, dec tot proteins, inc BUN, inc creatinine, inc hyaline casts (ur). AMRINONE LACTATE: anorexia, dec K*. ANABOLIC STEROIDS: acne, oligospermia, priapism, epididymitis, gynecomastia, testicular atrophy, change in libido, impotence, inc risk of prostatic hypertrophy and prostate cancer (in elderly), acceleration of epiphyseal maturation more rapidly than linear growth (in children), virilization (in women), male pattern baldness (in men), masculinization of female fetus, inc chol/HDL chol ratio, inc LDL chol, dec creatinine, dec glucose, inc P043 , inc Na*, inc lean muscle mass (however, muscle tissue may be deficient in P043 and structurally flawed), edema, inc Ca2*, inc glucose in diabetics, altered metyrapone test, inc alk phosphatase, dec LH, dec FSH, dec T4, dec TBG, inc T3 resin uptake, dec radioactive iodine uptake, retention of Na*, Cl , H20, K\ P043, and Ca2*.

ANDROGENS: priapism, excessive sexual stimulation, virilization, clitoromegaly, hirsutism, male pattern baldness, acne, amenorrhea, menstrual irregularities, polycythemia, precipitation of

1940

PART XVII: ENDOCRINE DRUGS AND VALUES

AIP, edema, gynecomastia, ? male contraception, oligospermia and dec ejaculatory volume (xs), virilization of external genitalia of female fetus, accelerate linear growth rate, advance bone maturation, prostatic hypertrophy, prostatic carcinoma, inc libido, inc tot Ca2+ (in immobilized pts and pts with metastatic breast cancer), stimulates osteolysis, inc acid phosphatase (in women), inc ceruloplasmin, dec LH, dec FSH, dec testosterone, dec free testosterone, dec DHT, dec SHBG, inc 17-KS (ur), dec TBG, dec T4 by RIA, dec T, by RIA, inc T3 resin uptake, inc TSH, inc uric acid, inc chol, dec TG, retention of N2, Na\ K\ H20, P, and Cl , dec Ca2+ (ur), inc protein anabolism, dec protein catabolism. ANISINDIONE: albuminuria. ANTACIDS: Aluminum containing: constipation, aluminum intoxication, osteomalacia, hypophosphatemia. Magnesiumcontaining: hypermagnesemia in pts with renal failure. Magnesium oxide: milk-alkali syndrome. Calcium carbonate: milk-alkali syndrome (xs). Sodium bicarbonate: milk-alkali syndrome (xs). Soluble bismuth salts: milk-alkali syndrome (xs). ANTIBIOTICS: dec K\ ANTICHOLINERGIC AGENTS: suppression of lactation, impotence, prostatic hypertrophy, dec pancreatic polypeptide, difficulty in achieving or maintaining an erection. ANTICONVULSANTS: inc alk phosphatase, inc SHBG, inc apolipoprotein Al, dec folate, dec vit B6, dec vit B12, dec vit E. ANTIHISTAMINES: anorexia, early menses, induced lactation, gynecomastia, inhibition of ejaculation, dec libido, impotence, high or prolonged glucose tolerance curves, inc glucose (ur), inc chol, excessive perspiration. ANTINEOPLASTIC AGENTS: inc K\ dec hydroxyproline. ANTISPASMODICS (see anticholinergic agents). APROBARBITAL (see barbiturates). ARGININE: When given IV induces pronounced inc in human GH (intact pituitary function). ASPARAGINASE: dec insulin, dec C-peptide, hyperglycemia, glycosuria, polyuria, dec FFA, azotemia, proteinuria, inc alk phosphatase, inc bilirubin, dec thyroxine, dec albumin, inc/dec chol (xs), inc/dec tot lipids, edema, malabsorption syndrome, anorexia, pancreatitis, weight loss. ASPIRIN (also see salicylates): dec vit C. ATENOLOL (see B-adrenergic blockers). ATOVAQUONE: inc alk phosphatase, inc amylase, dec Na\ hyperglycemia, hypoglycemia, anorexia, inc creatinine. ATROPINE (also see anticholinergic agents): dec gastrin, abolishes cholecystokinin response to meals. AZATADINE (see antihistamines). AZATHIOPRINE: inc uric acid (rapid tissue destruction), dec uric acid (in pts w/ gout), dec uric acid (ur), inc alk phosphatase, dec chol, inc K+, dec sperm count. AZTREONAM: diaphoresis, hepatitis, jaundice, breast tenderness, vaginitis, inc alk phosphatase, inc creatinine. P-ADRENERGIC BLOCKERS: dec melatonin, dec PRA, sexual dysfunction, blunt premonitory signs and symptoms of acute hypoglycemia, mask signs of hyperthyroidism, inc TG, inc chol, inc LDL chol, inc VLDL chol, dec HDL chol, hypoglycemia, hyperglycemia, interfere with GTT, cause unstable diabetes, impotence, dec libido, alopecia, acne, gout. BACITRACIN: albuminuria, cylindruria, azotemia. BACLOFEN: ovarian cysts, weakness, dizziness, lethargy/fatigue, urinary frequency, palpitations, anorexia, taste disorder, enuresis, urinary retention, dysuria, impotence, inability to ejaculate, nocturia, hematuria, rash, pruritus, ankle edema, excessive perspiration, weight gain, inc alk phosphatase, inc glucose, dec appetite (I/T), dehydration (I/T), urinary incontinence (I/T), sluggish bladder (I/T),

bladder spasms (I/T), sexual dysfunction (I/T), alopecia (I/T), facial edema (I/T), weight loss (I/T). BARBITURATES: inc metabolism of vit D via enzyme induction, rickets, osteomalacia, skin rashes, oliguria (xs), inc steroid requirements in adrenal insufficiency, inc alk phosphatase (xs), dec BMR, inc CPK (xs), inc creatinine (xs), dec glucose, dec 17-(OH)CS (ur), inc 13II uptake, inc porphyrins (ur), acute attack of porphyria, inc T, uptake, dec T4, competes with T4 for TBPA, inc testosterone, inc free testosterone, inc DHT. BECLOMETHASONE DIPROPIONATE (inhalation): suppression of HP A function. BELLADONNA ANTICHOLINERGICS (see anticholinergic agents). BENAZEPRIL (also see ACE inhibitors): impotence, dec libido, hyponatremia. BENDROFLUMETHIAZIDE (also see thiazide diuretics): metabolic acidosis (in diabetics), false-negative phentolamine and tyramine tests (an). BENZODIAZEPINES: anorexia, excessive salivation, palpitations, sweating, changes in libido, menstrual irregularities, hair loss, hirsutism, gynecomastia, galactorrhea, inc alk phosphatase. BENZQUINAMIDE: sweating, shivering, flushing, salivation, fatigue, anorexia, inc temp. BENZTHIAZIDE (see thiazide diuretics). BEPRIDIL: difficulties.

follicular adenomas of thyroid (exp), anorexia, sexual

BETAMETHASONE (see glucocorticoids). BETAXOLOL (see B-adrenergic blockers). BILE ACID SEQUESTRANTS: inc fecal loss of bile acids, inc chol, inc LDL chol, inc/dec TG, malabsorption of fat soluble vits (A, D, E, K), hyperchloremic acidosis, osteoporosis, diuresis, anorexia, inc libido, inc phosphorus, inc chloride, dec Na\ dec K+. BISMUTH SALTS (see antacids). BISOPROLOL (also see P-adrenergic blockers): inc uric acid, inc creatinine, inc BUN, inc K\ inc glucose, inc phosphorus. BITOLTEROL (also see sympathomimetics): proteinuria. BLEOMYCIN: hyperpigmentation, hyperkeratosis, alopecia, nail changes, skin tenderness, anorexia, weight loss. BRETYLIUM: dec catecholamines, dec VMA (ur). BROMOCRIPTINE: dec catecholamines, dec VMA (ur), dec prolactin, inc testosterone, dec T4 (in hypothyroid patients), inc alk phosphatase, inc CPK (transient), inc BUN (transient). BROMPHENIRAMINE (see antihistamines). BUMETANIDE (also see loop diuretics): inc alk phosphatase, chloruresis, natriuresis, no effect on glucose tolerance, premature, ejaculation, difficulty maintaining erection. BUPRENORPHINE: fatigue, loss of appetite, sweating, urinary retention, flushing, malaise. BUPROPION: weight loss, weight gain, anorexia, inc appetite, menstrual complaints, impotence, urinary frequency, urinary retention, excessive sweating, inc salivary flow, cutaneous temperature disturbance, palpitations, dec libido, fatigue, edema, alopecia, acne, hirsutism, gynecomastia, glycosuria, jaundice (xs), inc libido, dec sexual function, nocturia, vaginal irritation, testicular swelling, painful erection, retarded ejaculation, dysuria, dyspareunia, painful ejaculation, menopause, ovarian disorder. BUSPIRONE HCI: fatigue, palpitations, sweating, cold intolerance, galactorrhea, thyroid abnormality, anorexia, inc appetite, salivation, urinary frequency, urinary hesitancy, menstrual irregularity, amenorrhea, spotting, dysuria, nocturia, inc/dec libido, delayed ejaculation, impotence, edema, hair loss, acne, thinning of nails, weight gain, weight loss, malaise.

Ch. 224: Effects of Drugs on Endocrine Function and Values BUSULFAN: ovarian suppression, amenorrhea, menopausal symptoms, sterility, azoospermia, testicular atrophy, hyperpigmentation, alopecia, porphyria cutanea tarda, dry and fragile skin, syndrome resembling adrenal insufficiency, gynecomastia, cholestatic jaundice.

BUTABARBITAL (see barbiturates). BUTORPHANOL: sweating, lethargy, sensation of heat, impaired urination, palpitations, anorexia, edema. BUTYROPHENONE: inc prolactin. CABERGOLINE: dec prolactin.

1941

CELLULOSE SODIUM PHOSPHATE: inc PTH, hyperparathyroid bone disease, dec intestinal Ca2* absorption, hypomagnesiuria, hyperoxaluria, dec Mg2*, dec Cu2*, dec Zn2*, dec Fe2*. CEPHALOSPORIN: false-positive glucose (ur) (an), inc protein (ur) (an), inc 17-KS (ur) (an), inc creatinine (an), anorexia, inc alk phosphatase, inc bilirubin, inc LDH, hepatitis, inc BUN (transient), dec creatinine clearance, vaginitis, flushing.

CHENODEOXYCHOLIC ACID: dec hepatic synthesis of chol and cholic acid, inc chol, inc LDL chol, dec TG, inc alk phosphatase, inc/dec HDL chol.

CAFFEINE: inc chol, inc LDL chol, inc dopamine (ur), inc epinephrine (ur), inc glucose, inc/dec glucose tolerance, inc 5-HIAA (ur), inc VMA (ur) (an), diuresis, inc uric acid (an), inc

CHLORAL HYDRATE: ppt of AIP, malaise, ketonuria, jaundice (xs), albuminuria (xs), interferes with CuS04 test for glycosuria,

catecholamines (acute), inc PRA (acute), inc linoleic acid, severe acidosis in infants (xs).

interferes with fluorometric tests for urine catecholamines, interferes with urine 17-(OH)CS determinations.

CALCIFEDIOL (see vitamin D).

CHLORAMBUCIL: jaundice, sterility, azoospermia, amenorrhea. CHLORAMPHENICOL: inc alk phosphatase (xs), inc bilirubin

CALCITONIN: dec P043, inc P043 (ur), dec alk phosphatase, dec hydroxyproline (ur), dec bone resorption, dec elevated Ca2+ in patients with carcinoma, multiple myeloma, and primary hyperparathyroidism, nocturia, inc urinary frequency, mild tetanic

(xs), dec glucose(?), inc 17-KS (ur) (an), inc sugar (ur) (an), dec uric acid (an).

symptoms (rare), dec C-peptide, inc glucagon, dec glucose tolerance (?), dec insulin, inc Mg‘+ (ur), inc K* (ur), dec prolactin, inc Na* (ur), inc Ca2* (ur).

reversible cholestatic jaundice.

CALCITRIOL (see vitamin D). CALCIUM CARBONATE (see antacids).

photosensitization.

CALCIUM EDTA: proteinuria, microscopic hematuria, renal tubular necrosis. CALCIUM: inc calcitonin (if given IV), inc gastrin, hypercalcemia (xs) (and in ESRD), hypercalciuria (xs), inc 1 l-(OH)CS, dec 17(OH)CS (ur), inc insulin (newborns), dec 131I uptake, dec Mg2* (an), dec Mg2* (ur) (an).

CAPREOMYCIN: hypokalemia, inc BUN, abnormal urine sediment, Bartter syndrome (one patient), renal injury, inc creatinine. CAPTOPRIL (also see ACE inhibitors): proteinuria (clears in 6 months), nephrotic syndrome, in diabetic nephropathy may improve proteinuria, false-positive acetone (ur) (an), anorexia, alopecia, impotence, polyuria, hyponatremia, gynecomastia, dec catecholamines, glycosuria.

CARBAMAZEPINE: dec tot Ca2*, inc Cu, dec DHEAS, dec free T4 index, inc/dec TBG, inc/dec TSH, dec T4, dec free T4, dec T3, dec free T3, dec vasopressin, dec 25-(OH)vit D, dec androstenedione, osteomalacia, inc cortisol (an), inc glucose (ur), inc 1 l-(OH)CS (an), inc 17-(QH)CS (ur) (an), dec 17-KS (ur) (an), dec P043, false¬ negative preg tests (ur), inc SHBG, dec Na\ dec testosterone, dec free testosterone, inc BUN, inc albumin (ur), anorexia, jaundice, hepatitis, oliguria, impotence, SIADH.

CARBIDOPA: neuroleptic malignant syndrome, dec BUN, dec creatinine, dec uric acid.

CARBINOXAMINE (see antihistamines). CARBONIC ANHYDRASE INHIBITORS: dec HCO,, inc Zn2* (whole blood), hypokalemia, inc Na* (ur), inc K* (ur), inc HCO, (ur), inc H20 (ur), alkaline diuresis, anorexia, glycosuria, renal calculi, crystalluria, polyuria, phosphaturia, acidosis, dec libido, impotence.

CARBOPLATIN: inc alk phosphatase, inc BUN, inc creatinine, inc bilirubin, dec Mg2*, dec Ca2*, dec K*, dec Na*, alopecia. CARMUSTINE: impaired fertility, progressive azotemia, inc alk phosphatase, inc bilirubin. CARTEOLOL (see B-adrenergic blockers). CASCARA (see laxatives). CASTOR OIL (see laxatives). CATECHOLAMINES: inc ANH, inc gastrin, inc lactate.

CHLORDIAZEPOXIDE (see benzodiazepines). CHLORMEZANONE: flushing, edema, inability to void, CHLORPROMAZINE (also see phenothiazines): inc chol, CHLORPROPAMIDE (also see sulfonylureas): inc/dec chol, dec Na*, disulfiram-like syndrome with alcohol, SIADH, treatment of neurogenic DI, inc alk phosphatase, inc ADH (ur), inc Ca2* (an), dec HDL chol, dec HDL3 chol, dec LDL chol, dec glucose, inc insulin, inc T, uptake, dec T4, dec free H20 clearance (ur), dec urobilinogen (ur), inc uroporphyrin (ur), may ppt cutaneous porphyria, dec serum osmolality, inc urine osmolality, water retention, dilutional hyponatremia. CHLORPROTHIXENE (see thiothixene). CHLORTHALIDONE (see thiazide diuretics). CHLORTHIAZIDE (also see thiazide diuretics): alopecia. CHLORZOXAZONE: urine discoloration, hepatitis. CHOLECALCIFEROL (see vitamin D). CHOLESTYRAMINE (also see bile acid sequestrants): dec folate, dec bile acids, inc Ca2* (ur), dec tot phospholipids, inc Na*, dec tot lipids, dec T, (dec intestinal absorption of T4), inc/dec TG, inc vit A, dec vit E. CHORIONIC GONADOTROPIN: inc production of gonadal steroids (Leydig cells: androgens; corpus luteum: progesterone), ovarian hyperstimulation, fluid retention, multiple births, dec LH, dec FSH, precocious puberty, gynecomastia. CHROMIUM: inc glucose tolerance factor needed for activation of insulin-mediated reactions, improved glucose tolerance. CIMETIDINE (also see H2 antagonists): inc alk phosphatase, inc HDL chol, dec estradiol, inc FSH, inc gastrin, dec glucose, inc HDL2 chol, dec insulin, dec PTH, inc prolactin, dec sperm count, inc/dec testosterone, dec T3, inc reverse T3, inc BUN, inc uric acid, dec vit B12 (ur), inc androstenedione, inc creatinine, inc estradiol (in males), antiandrogenic effect, gynecomastia, alopecia (rare), impotence, galactorrhea, inhibits cytochrome P450 oxidase system. CIPROFLOXACIN: gynecomastia, inc alk phophatase, inc creatinine, inc BUN, crystalluria (rare), inc LDH, inc bilirubin, hematuria, proteinuria, albuminuria, inc amylase, inc uric acid, inc/dec glucose, inc/dec K*, inc TG, inc chol, acidosis, polyuria, renal calculi, anorexia, hyperpigmentation, exacerbation of myasthenia gravis. CISAPRIDE: inc pancreatic polypeptide, inc cholecystokinin. CISPLATIN: dec Mg2*, inc uric acid, dec Ca2*, inc Cu2* (ur), dec creatinine clearance, dec K\ dec Na*, inc Na* (ur), inc BUN, inc Zn

1942

PART XVII: ENDOCRINE DRUGS AND VALUES

(ur), dec P043, tetany, SIADH, anorexia. CITRATE: dec Mg2+ (in tranfusions), inc Al3\ dec Ca2\ dec chol (an), inc glucose (an), dec pH (an), dec P043 (an), inc K+ (ur), dec selenium (an), dec a-tocopherol (an), dec TG (an), inc uric acid, dec uric acid (ur), dec vit A (an), inc urine volume, dec Zn2+ (an). CLADRIBINE: fatigue, diaphoresis, malaise, dec appetite, edema, hyperuricemia.

CLEMASTINE (see antihistamines). CLINDAMYCIN (also see lincosamides): anorexia, inc alk phosphatase, inc bilirubin. CLOFAZIMINE: skin pigmentation, acne, anorexia, hepatitis, jaundice, inc glucose, discolored urine/sweat/sputum, bone pain, edema, inc albumin, inc bilirubin, inc K\ CLOFIBRATE: inc or dec alk phosphatase, dec chol, dec LDL chol, dec VLDL chol, inc HDL chol, dec FFA, dec tot lipids, inc apolipoprotein Al, dec TG, dec VMA (ur) (an), inc CPK, dec glucose, inc/dec glucose tolerance, dec insulin, inc/dec T4, dec TSH, dec T3 uptake, inc TBG, dec free T4, dec l31I uptake, alopecia, impotence, dec libido, proteinuria, polyphagia, weight gain, inc perspiration, gynecomastia(?), dec uric acid, inc uric acid (ur). CLOMIPHENE: inc androstenedione, inc dehydroepiandrosterone, inc DHEAS, inc DHT, inc estradiol, inc estrogens (ur), inc FSH, inc LH, inc progesterone, inc testosterone, inc free testosterone, inc sperm count, dec chol, inc TBG, inc/dec T4, dec T3, inc TSH, dec free T4 index, induction of ovulation in selected anovulatory women, inc output of pituitary gonadotropins, dec number of available estrogenic receptors, ovarian stimulation, inc multiple pregnancies, vasomotor flushes, abnormal uterine bleeding, breast tenderness, reversible hair loss, abnormal ovarian enlargement, inc mid-cycle ovarian pain, ovarian cyst formation, prolonged luteal phase of menstrual cycle, birth defects.

CLOMIPRAMINE (also see tricyclic antidepressants): ejaculatory failure, impotence.

CLONAZEPAM (also see benzodiazepines): inc salivation. CLONIDINE: dec catecholamines, dec catecholamines (ur), dec VMA (ur), dec epinephrine (ur), dec norepinephrine (ur), dec aldosterone (ur), dec PRA, inc Na*, inc GH, inc IGF-I (in children with GH deficiency), dec cortisol, dec corticotropin, transient inc glucose, weight gain, transient inc CPK (rare), gynecomastia, hair thinning and alopecia, impotence, dec sexual activity, loss of libido, nocturia, anorexia.

CLORAZEPATE (see benzodiazepines). CLOZAPINE: fatigue, weakness, lethargy, sweating, salivation, anorexia, incontinence, abnormal ejaculation, urinary urgency, urinary frequency, urinary retention, weight gain.

CODEINE (also see narcotic analgesics): inc amylase, inc lipase, oliguria, antidiuretic effect, inc LDH, inc protein (ur), inc BUN. COLCHICINE: dec folate, dec vit B12, inc alk phosphatase, inc bilirubin, dec cholesterol, inc corticosteroids (ur) (an), inc 17(OH)CS (ur) (an), dec sperm count, loss of hair, reversible azoospermia.

COLESTIPOL (also see bile acid sequestrants): dec carotene level, dec cholesterol, dec TBG, inc TSH, dec T4, dec free T4, dec T3, inc T3 uptake, dec CBG, inc/dec TG, inc alk phosphatase. COLISTIMETHATE SODIUM: dec urine output, inc BUN, inc creatinine.

CORTISONE (see glucocorticoids). CROMOLYN SODIUM: dec 17-(OH)CS. CURARE PREPARATIONS: inc histamine release, excessive salivation, flushing, respiratory paralysis in myasthenia gravis. CYANIDE: dec alk phosphatase (an), inc protein (an), dec uric acid (an). CYCLOBENZAPRINE: malaise, anorexia, thirst, urinary

frequency/retention, hepatitis, jaundice, inc alk phosphatase, sweating, edema, SIADH(?), inc/dec glucose(?), weight changes(?), change in libido(?), alopecia(?), impotence(?), testicular swelling(?), gynecomastia(?), galactorrhea(7), breast enlargement^). CYCLOPHOSPHAMIDE: dec osmolality, dec Na\ inc ADH, SIADH, inc alk phosphatase, inc bilirubin, inc chol, dec 131I uptake, inc osmolality (ur), inc LH (in males), dec testosterone, testicular atrophy, inc plasma volume, dec urine volume, interferes with oogenesis and spermatogenesis, sterility, amenorrhea, dec estrogen, dec LH (in males), dec FSH (in females), ovarian fibrosis, oligospermia, azoospermia, anorexia, alopecia, pigmentation of skin and nails, renal function impairment, hemorrhagic cystitis. CYCLOPROPANE: inc alk phosphatase, inc bilirubin, inc catecholamines, dec catecholamines (an), inc glucose, dec pH, malignant hyperthermia. CYCLOSERINE: dec vit B6, inc alk phosphatase, inc bilirubin, dec l31I uptake, renal function impairment, dec vit B12, dec folate. CYCLOSPORINE: inc chol, inc LDL chol, inc apolipoprotein B, dec HDL chol, inc TG, dec Mg2\ inc Mg2+ (ur), dec aldosterone, inc alk phosphatase, inc bilirubin, inc chloride, inc creatinine, dec GFR, dec RBF, inc K\ inc protein (ur), dec PRA, inc BUN, inc uric acid, development of diabetes in kidney transplant patients, preserves Bcell function and may ameliorate newly-diagnosed insulin-dependent diabetes, hirsutism, acne, anorexia, gynecomastia, inc glucose, weight loss. CYPROHEPTADINE: inc alk phosphatase, inc amylase, inc bilirubin, dec glucose, antiserotonin effect.

CYPROTERONE (also see antihistamines): inc androstenedione, inc/dec chol, dec DHEAS, dec estradiol, dec estrone, dec glucose, dec glucose tolerance, inc insulin, insulin resistance (when given with ethinyl estradiol), inc/dec tot phospholipids, inc TG, dec progesterone, dec sperm count, dec testosterone, dec free testosterone. CYTARABINE: hyperuricemia, acute pancreatitis, bone pain, anorexia, hepatic dysfunction, jaundice, alopecia, renal dysfunction. DACARBAZINE: anorexia, malaise, alopecia, facial flushing, inc BUN, inc creatinine, abnormal LFTs (rare). DACTINOMYCIN: anorexia, hepatitis, alopecia, acne, inc pigmentation of previously irradiated skin, malaise, hypocalcemia, renal toxicity. DANAZOL: inc androstenedione, dec HDL chol, inc LDL chol, inc TG, dec cortisol, inc/dec cortisol (an), inc free cortisol, dec DHEA, inc DHEAS, dec estradiol, dec FSH, dec LH, inc glucagon, dec glucose tolerance, dec HDL2, dec HDL3, inc 17-KS (ur), inc K\ dec progesterone, inc prolactin, dec SHBG, inc/dec testosterone, inc/dec testosterone (an), inc free testosterone, dec TSH, dec T4, dec T4 (an), dec TBG, inc free T4, dec T„ direct enzymatic inhibition of sex steroid synthesis, competitively inhibits binding of steroids to their cytoplasmic receptors, fluid retention, dec glucose tolerance, inc insulin requirements (in diabetics), acne, hirsutism, testicular atrophy, hair loss, changes in libido, carpal tunnel syndrome, virilization, clitoral hypertrophy (in female fetus), labial fusion (in female fetus). DANTROLENE SODIUM: malignant hyperthermia, malaise, anorexia, hepatitis, inc alk phosphatase, inc bilirubin, inc crystals (ur), difficult erection, nocturia, acne, abnormal hair growth. DAPSONE: anorexia, proteinuria, nephrotic syndrome (xs), male infertility, hypoalbuminemia, inc methemoglobin. DAUNORUBICIN: testicular atrophy (exp), hyperuricemia, red discoloration of urine, reversible alopecia. DEMECLOCYCLINE (also see tetracycline): nephrogenic diabetes insipidus.

DESERPIDINE (see rauwolfia derivatives).

Ch. 224: Effects of Drugs on Endocrine Function and Values

DESIPRAMINE (also see tricyclic antidepressants): inc alk

1943

phosphatase, inc bilirubin, inc FFA, inc/dec glucose, inc GH, inc norepinephrine, inc prolactin, dec urine volume, inc ACTH.

DILTIAZEM: inc HDL chol, inc PRA, hyperglycemia, inc CPK, inc alk phosphatase, anorexia, polyuria, hair loss, gynecomastia, sexual difficulties, fetal skeletal abnormalities (xs).

DESLANOSIDE (see digoxin). DESSICATED THYROID (see thyroid hormone). DEXAMETHASONE (also see glucocorticoids): dec

DIMENHYDRINATE: lassitude, anorexia, palpitations, difficult/painful urination.

catecholamines, dec VMA (ur), dec ACTH, dec 17-(OH)CS (ur), inc amylase, dec androsterone (ur), inc Ca2+, dec corticosteroids, inc corticosteroids (ur) (an), dec cortisol, dec DHEA (ur), dec DHEAS, dec 6-endorphin, dec estrogens (ur), inc glucose, inc glucose (ur), dec glucose tolerance, dec 17-KGS (ur), inc 17-KS (ur) (an), negative nitrogen balance, dec K\ inc K* (ur), dec prolactin, inc SHBG, inc Na* (ur), dec testosterone, dec T4, dec Tv

creatinine, hypoglycemia, inc uric acid, inc alk phosphatase, inc lactate, anorexia, impotence, gynecomastia (rare).

DEXCHLORPHENIRAMINE (see antihistamines). DEXTRAN 40: dilutional acidosis, hypernatremia (with edema), inc glucose (an), dec protein (an).

DEXTRAN 70 (see dextran 40). DEXTROTHYROXINE SODIUM: dec chol, inc glucose (in diabetics), dec l31I uptake, dec LDL chol, dec tot lipids, dec 0lipoproteins, dec TG, inc T4, inc T, (an), hair loss, exophthalmos, lid lag, diuresis, menstrual irregularities, changes in libido. DEZOCINE: sweating, flushing, edema, inc alk phosphatase, urinary frequency, urinary hesitancy, urinary retention.

DIAZEPAM (also see benzodiazepines): inc GH, inc TSH, dec T3 uptake, dec T„, inc alk phosphatase, inc bilirubin, positive dopa screening test (ur) (an), inc estradiol, dec glucose (ur) (an), inc 5HIAA (ur) (an), dec 13II uptake, inc porphyrins (ur).

DIAZOXIDE: inc glucose, dec pancreatic insulin release, inc alk phosphatase, azotemia, dec creatinine clearance, dec NaCl (ur), dec H;0 (ur), fluid retention, dec HCO, (ur), inc uric acid, dec uric acid (ur), dec urinary output, nocturia, inc albumin (ur), inc glucose (ur), inc FFA, ketoacidosis, non-ketotic hyperosmolar coma, inc I, dec Cl (ur), dec K* (ur), inc Na\ dec Na+(ur), inc plasma volume, inc PRA, dec cortisol, dec cortisol (ur) (an), dec glucagon-stimulated insulin release, dec libido, inc catecholamines, fetal or neonatal hyperbilirubinemia, altered carbohydrate metabolism in neonates, alopecia and hypertrichosis lanuginosa in infants of mothers taking drugs in last 19-60 days of preg, galactorrhea, gout, lanugo-like hirsutism (on forehead, back, and limbs), loss of scalp hair, advance in bone age.

DICHLORPHENAMIDE (see carbonic anhydrase inhibitors). DICLOFENAC SODIUM (also see NSAIDS): inhibition of bone resorption, inc chol, inc glucose (an), inc BUN. DIDANOSINE (DDI): pancreatitis, inc amylase, phenylketonuria, hyperuricemia, anorexia, inc alk phosphatase, inc bilirubin, edema, dec K\ impotence, kidney calculus, nocturia, renal failure, diabetes mellitus (in children), diabetes insipidus (in children).

DIETHYLSTILBESTROL: inc tot Ca2+, inc bilirubin, inc coproporphyrin (ur), inc CBG, dec estradiol (ur) (an), dec estriol (ur) (an), dec FSH, dec LH, dec glucose tolerance, inc 17-(OH)CS (ur), inc 6-P(OH)cortisol (ur), inc prolactin, inc SHBG, dec DHT, dec testosterone, dec free testosterone, inc TBG, dec uric acid, inc uric acid (ur), dec vit A.

DIFLUNISAL (also see salicylates): anorexia, hepatitis, dysuria, renal dysfunction, light-headedness, pruritus, diaphoresis, fatigue, edema. DIGITOXIN (see digoxin). DIGOXIN IMMUNE FAB: hypokalemia. DIGOXIN: dec DHT, dec testosterone, dec free testosterone, inc estrone, inc estrogens, dec LH, dec PRA, dec Mg2*, dec mI uptake, inc 17-(OH)CS (ur) (an), 17-KS (ur) (an), dec glucose (ur) (an), anorexia, gynecomastia.

DIHYDROTACHYSTEROL (see vitamin D).

DIMERCAPROL: salivation, burning sensation in penis (xs). DIPHENHYDRAMINE (also see antihistamines): dec l31I uptake. DISOPYRAMIDE: hypokalemia, inc chol, inc TG, inc BUN, inc

DISULFIRAM: inc acetone, inc acetoacetate, inc alk phosphatase, inc chol, inc (i(OH)butyrate, dec l3lI uptake, dec norepinephrine, dec VMA, impotence.

DOBUTAMINE: inc norepinephrine, inc PRA. DOCUSATE (see laxatives). DOMPERIDONE: gynecomastia, inc prolactin, inc TSH. DOPAMINE: inc catecholamines (ur) (an), inc dopamine (ur), inc epinephrine (ur), inc glucose, inc GH, dec LH, inc norepinephrine, inc K* (ur), dec prolactin, inc Na* (ur), dec TSH, dec TSH response to TRH, dec T4, inc uric acid (an), inc urine volume. DOXAPRAM: inc epinephrine, inc BUN, proteinuria.

DOXAZOSIN (also see a,-adrenergic blockers): dec chol, dec LDL chol, inc HDL chol, dec VLDL chol, dec triglycerides, inc norepinephrine, inc PRA, gout, dec libido, sexual dysfunction, polyuria, alopecia. DOXEPIN (see tricyclic antidepressants). DOXORUBICIN: hyperuricemia, red discoloration of urine, reversible complete alopecia, hyperpigmentation of nail beds and dermal creases, onycholysis, anorexia, facial flushing.

DOXYCYCLINE (see tetracycline). DRONABINOL: dec seminal fluid volume (exp), dec spermatogenesis (exp), palpitations, anorexia, hepatitis, flushing, sweating, urinary retention (xs).

EDTA: hypocalcemia, hyperuricemia, dec alk phosphatase, dec ACE (an), dec HCO, , dec chol, inc glucose (an), dec glucose (ur), inc BUN, dec K+ (an), inc K* (ur), inc Na* (an), inc sugar (ur) (an), dec tot lipids.

ENALAPRIL (also see ACE inhibitors): anorexia, alopecia, impotence, glycosuria, hypoglycemia (rare).

ENCAINIDE: inc glucose, inc insulin/oral hypoglycemic requirements in diabetics, anorexia.

EPHEDRINE (also see sympathomimetics): dec cortisol, inc epinephrine (ur), inc glucose, inc 5-HIAA (ur) (an), dec l3lI uptake. EPINEPHRINE (also see sympathomimetics): inc calcitonin, inc cAMP, inc glucagon, inc glucose, inc dose of insulin/oral hypoglycemics in diabetics, inc thyrotoxic symptoms in hyperthyroid patients, inc BMR, inc catecholamines, inc chol, inc FFA, inc gastrin, dec iron, inc lactate, inc lipoproteins, dec PO„\ inc tot phospholipids, inc/dec K+, dec Na+ (ur), inc TBG, dec tyrosine, inc uric acid, inc VMA (ur), dec urine volume, metabolic acidosis (xs). ERGOCALCIFEROL (see vitamin D). ERGONOVINE: proteinuria, inc BUN, renal damage (xs), inc porphyrins (ur), acute porphyria, inc aminolevulinic acid (ur).

ERGOT ALKALOIDS: dec prolactin, inc porphyrins (ur), ppt of acute porphyria, inc BUN, proteinuria (xs).

ERYTHRITYL TETRANITRATE (see nitrates). ERYTHROMYCIN: inc alk phosphatase, inc amino acids (ur) (an), inc bilirubin, inc catecholamines (ur) (an), dec chol (xs), dec glucose (xs), dec mI uptake, inc 17-(OH)CS (ur) (an), inc 17-KS (ur) (an), dec folate (an). ERYTHROPOIETIN: exacerbation of porphyria (in CRF), hyperkalemia(?) (in CRF).

1944

PART XVII: ENDOCRINE DRUGS AND VALUES

ESMOLOL (see 13-adrenergics blockers). ESTAZOLAM (also see benzodiazepines): dec libido, inc/dec appetite, acne, frequent urination, menstrual cramps, urinary hesitancy/urgency, vaginal discharge/itching, hematuria, nocturia, oliguria, penile discharge, urinary incontinence, thirst, swollen breast, thyroid nodule(?), weight gain/loss. ESTRAMUSTINE PHOSPHATE SODIUM: dec glucose tolerance, worsening of diabetic control, fluid retention, edema,

FINASTERIDE: inhibits 5 a-reductase, dec DHT in prostate, liver, skin, inc FSH, inc LH, inc testosterone, improvement in symptoms of BPH, dec PSA, regression in size of enlarged prostate, inc urinary flow, impotence, dec libido, dec volume of ejaculate. 5-FLUOROURACIL: inc 5-HIAA (ur), inc TBG, inc T„ by RIA, inc T3, dec T3 resin uptake, inhibition of spermatogonial differentiation (exp), fetal teratogenicity, anorexia, alopecia, inc skin pigmentation, inc alk phosphatase, inc bilirubin. FLECAINIDE: inc alk phosphatase, anorexia, impotence, dec libido, polyuria, alopecia.

anorexia, thirst, thinning hair, breast tenderness, breast enlargement, inc bilirubin, changes in Ca2+ and phosphorus metabolism. ESTROGENS: inc angiotensin II, inc PRA, inc Ca2\ dec carotene, inc ceruloplasmin, inc HDL, inc TG, inc phospholipids, dec chol, inc Cu, inc cortisol, inc DHT, dec folate, dec FSH, dec LH, inc glucose, dec glucose tolerance, worsening of diabetic control(?), inc GH, inc 17-(OH)CS (ur), dec (OH)proline (ur), dec IGF-I, dec 17-KGS (ur),

FLUCYTOSINE: inc alk phosphatase (xs), inc bilirubin (xs), inc creatinine (an), anorexia, jaundice, azotemia, crystalluria, hypoglycemia, hypokalemia.

inc Mg2’, inc prolactin, inc SHBG, inc Na’, inc testosterone, inc TBG, inc T4, inc T,, dec T, resin uptake, free T, unaltered, inc vit A, dec vit C, dec Zn2’, dec pregnanediol (ur), dec response to metyrapone tests, hypercalcemia (in breast cancer with bone metastases), breakthrough bleeding, spotting, change in menstrual flow, dysmenorrhea, pre-menstrual syndrome, amenorrhea during and after treatment, chloasma, alopecia, hirsutism, ppt of AIP, changes in libido, mastodynia, fluid retention, edema, protein anabolism, thinning of cervical mucus, inhibition of ovulation, prevent postpartum breast discomfort, maintain tone and elasticity of urogenital structures, shaping of skeleton, conservation of Ca2’ and P04\ promote bone formation.

FLUDARABINE: anorexia, malaise, tumor lysis syndrome (hyperuricemia, hyperphosphatemia, hypocalcemia, metabolic acidosis, hyperkalemia, hematuria, urate crystalluria, renal failure), edema, hyperglycemia, proteinuria, osteoporosis. FLUDROCORTISONE: dec aldosterone (ur), inc amylase, inc HCO, , inc glucose, dec glucose tolerance, dec K’, inc Na’, inc renal tubular reabsorbtion of Na*, inc K’ (ur), inc H’ (ur), dec ACTH, dec adrenal cortical secretion, inc liver glycogen, negative nitrogen balance, edema, hypokalemic alkalosis (xs), weight gain (xs), hemorrhagic pancreatitis (xs). FLUMAZENIL: inc sweating, fatigue, hot flushes, shivering, flushing.

ETHACRYNIC ACID (also see loop diuretics): acute symptomatic hypoglycemia with convulsions in uremic patients (xs). ETHAMBUTOL: inc uric acid, inc creatinine, dec creatinine clearance, inc BUN, dec uric acid (ur), ppt of acute gout, anorexia, abnormal liver function.

FLUORIDES: hypocalcemia (xs), hypoglycemia (xs), delayed hyperkalemia (xs), tetany (xs), dec alk phosphatase, dec chol (an), inc Na’(an), inc BUN, inc uric acid.

ETHCHLORVYNOL (PLACIDYL): cholestatic jaundice (hypersensitivity). ETHIONAMIDE: hepatitis, worsening of diabetic control, jaundice, acne, alopecia, pellagra-like syndrome, impotence, gynecomastia, menorrhagia. ETHOSUXIMIDE (see succinjmides). ETHOTOIN (see hydantoins). ETHYL NOREPINEPHRINE (see sympathomimetics). ETIDRONATE: dec Ca2’, inc BUN, inc creatinine, dec bone turnover, dec P04’, dec Mg2’, dec mineralization of osteoid during bone accretion, focal osteomalacia, inc pain at pagetic sites. ETODOLAC (see NSAIDS). ETOPOSIDE (see podophyllotoxin derivatives). FAMOTIDINE (also see H2 antagonists): alopecia, impotence, loss of libido, anorexia, acne, dec gastric HC1. FELODIPINE: inc PRA, inc aldosterone (ur), inc norepinephrine, polyuria, sexual difficulties, dose-dependent inc in benign Leydig cell tumors and testicular hyperplasia (exp). FENCLOFENAC: dec T„, dec T,, free T4 normal, dec reverse T3, (most potent drug that interferes with thyroid hormone binding). FENFLURAMINE: dec blood glucose, inc glucose tolerance, impotence, polyuria, menstrual upset, hair loss, gynecomastia, inc cortisol (an), inc GH, inc ketones, dec (3-lipoproteins, dec TG. FENOPROFEN (also see NSAIDS): inc T3 (an), inc free T3 (an) (Amerlex-MKit), inc creatinine, dec creatinine clearance (ur), inc protein (ur). FENTANYL (also see narcotic analgesics): diaphoresis. FILGRASTIM (G-CSF): inc uric acid (reversible), inc alk phosphatase (reversible), anorexia, worsening of pre-existing alopecia, proteinuria (xs), osteoporosis (xs).

FLUCONAZOLE: nausea, salivation (xs), urinary incontinence (xs), adrenal insufficiency^), hepatitis.

FLUOXETINE HC1: rash, urticaria, edema, carpal tunnel syndrome, proteinuria, serum sickness, dec appetite, significant weight loss, hyponatremia, SIADH, hypoglycemia, hyperglycemia (after drug discontinuation), fatigue, sweating, pelvic pain, hypothermia, hirsutism, acne, alopecia, skin discoloration, thirst, inc appetite, inc salivation, jaundice, hyperchlorhydria, dec libido, inc libido, hot flushes, palpitations, bone necrosis, painful menstruation, sexual dysfunction, frequent micturition, abnormal ejaculation, amenorrhea, breast pain, dysuria, impotence, fibrocystic breast, menorrhagia, vaginitis, urinary incontinence, dyspareunia, albuminuria, galactorrhea, kidney calculus, polyuria, urolithiasis, vaginal hemorrhage, pyuria, salpingitis, generalized edema, hypothyroidism, weight gain, goiter, gout, hypercholesterolemia, hyperlipemia, hyperthyroidism, dec K’, dehydration. FLUOXYMESTERONE (see androgens). FLUPHENAZINE (see phenothiazines). FLURAZEPAM (also see benzodiazepines): inc bilirubin, inc alk phosphatase. FLUTAMIDE: hot flashes, loss of libido, impotence, gynecomastia, hepatitis, edema, anorexia, inc creatinine, inc bilirubin (xs), breast tenderness, inhibits androgen uptake, inhibits nuclear binding of androgen in target tissues. FOLIC ACID: inc folate (an), dec mI uptake. FOSCARNET SODIUM: hypothermia, anorexia, inc amylase, dec K’, dec Ca2’, dec Mg2*, inc/dec P04\ dec Na’, dec weight, inc alk phosphatase, inc BUN, acidosis, cachexia, thirst, hypercalcemia, dehydration, glycosuria, inc CPK, diabetes mellitus, abnormal glucose tolerance, hypervolemia, hypochloremia, dec protein, acne, alopecia, inc creatinine, dec creatinine clearance, inc albumin (ur), polyuria, ADH disorders, dec gonadotropins, gynecomastia, penile inflammation, perineal pain (in females). FOSINOPRIL (also see ACE inhibitors): dec libido, sexual dysfunction, gout.

Ch. 224: Effects of Drugs on Endocrine Function and Values FUROSEMIDE (also see loop diuretics): renal calcifications in premature infants (if mother taking drug), inc aldosterone, inc angiotensin II, inc ADH, inc PRA, dec Ca2+, dec Cl , inc chol, inc LDL, inc VLDL, inc TG, inc dopamine (ur), inc glucose, dec glucose tolerance, dec insulin, dec Mg2*, inc norepinephrine, inc norepinephrine (ur), inc PTH, inc P043, dec K\ inc prolactin, dec Na\ inc T3 uptake, dec T4, dec T3, inc BUN, dec plasma volume. GALLIUM NITRATE: dec Ca2\ dec Ca2* resorption from bone, dec bone turnover, inc BUN, inc creatinine, transient dec P043, dec HCO,, dec (OH)proline (ur), dec PTH. GANCICLOVIR: anorexia, alopecia, hematuria, inc creatinine, inc BUN, edema, dec glucose. GASTRIN: dec Ca2*, dec ionized Ca2\ inc glucagon. GEMFIBROZIL: dec chol, inc HDL, dec LDL, dec VLDL, dec TG, inc apolipoprotein AI, inc apolipoprotein All, inc alk phosphatase, inc CPK, inc glucose, alopecia, dec libido, myopathy, impotence, dec male fertility, weight loss, benign Leydig cell tumors (exp). GENTAMICIN (also see aminoglycosides): pseudotumor cerebri. GLIPIZIDE (also see sulfonylureas): mild diuresis. GLUCAGON: dec Ca2\ dec chol, dec dopamine (ur), dec gastrin, inc glucose, inc lipolysis, inc hepatic gluconeogenesis, inc glycogenolysis, inc FFA, dec glucose tolerance, inc GH, inc insulin, dec TG, dec tot lipids, dec Mg2*, inc norepinephrine (ur), inc K*, inc VMA (ur), counteracts severe hypoglycemia in diabetics. GLUCOCORTICOIDS: Na* and fluid retention, hypokalemia, alkalosis, metabolic alkalosis, thin fragile skin, hirsutism, acne, amenorrhea, post-menopausal bleeding, menstrual irregularities, suppression of growth in children, dec carbohydrate tolerance, inc insulin/sulfonylurea requirements in diabetics, protein catabolism, negative N2 balance, exophthaImos(?), dec motility and number of spermatozoa, Cushing syndrome (xs), osteoporosis (xs), sexual dysfunction (xs), diabetes (xs), dec ACTH, inc ANH, dec Ca2\ inc Ca2* (ur), dec K\ inc chol, inc TG, inc glucose, inc glucose (ur), dec GH, inc 17-(OH)CS (ur), dec (OH)proline (ur), inc 17-KGS (ur), dec osteocalcin, inc PTH, dec TBG (high dose), dec TSH (high dose), dec T3, dec T, (minimal), dec mI uptake, dec TSH response to TRH, dec 25-(OH)vit D, inc Zn2*. GLUTETHIMIDE: edema, nocturnal diaphoresis, porphyria. GLYBURIDE (also see sulfonylureas): mild diuresis. GLYCERIN (see osmotic diuretics). GLYCERIN SUPPOSITORY (see laxatives). GLYCYRRHIZA: pseudoaldosteronism, dec aldosterone, inc estrogens (ur) (an), inc pH, alkalosis, dec K\ inc K+ (ur), dec PRA, inc BUN, nephropathy (xs). GOLD COMPOUNDS: inc alk phosphatase (xs), inc aminolevulinic acid (ur), inc bilirubin (xs), inc chol, inc coproporphyrin (ur), dec creatinine clearance (ur), proteinuria (xs), inc BUN, alopecia, anorexia, chrysiasis. GONADORELIN ACETATE: inc LH, inc FSH, inc gonadal steroids, induction of ovulation in female with hypothalamic amenorrhea, ovarian hyperstimulation, multiple preg. GONADOTROPINS: inc androsterone (ur), inc estrogens (ur), inc etiocholanolone (ur), 17-(OH)CS (ur), inc 17-KS (ur), inc pregnanediol (ur), inc pregnanetriol (ur), inc testosterone, inc testosterone (ur). GOSERELIN ACETATE: hot flashes, sexual dysfunction, dec erections, lethargy, edema, sweating, anorexia, gout, hyperglycemia, inc weight, breast swelling, breast tenderness, inc bone pain (transient), inc testosterone (transient), impairment of fertility (exp), gonadal suppression. GRISEOFULVIN: inc alk phosphatase, inc aminolevulinic acid (ur), inc coproporphyrin (ur), inc porphyrins, ppt of acute porphyria

1945

attack, proteinuria (transient), inc creatinine, inc BUN, dec uric acid, dec creatinine clearance (ur), menstrual irregularities. GROWTH HORMONE: inc P043, inc Ca2* (ur), inc intestinal Ca2* absorption, retention of Na* and/or 1C, inc tubular reabsorption of P043, inc glucose, glucosuria, linear growth, skeletal growth, inc alk phosphatase, inc cellular protein synthesis, dec N2 excretion (ur), nitrogen retention, dec BUN, impaired glucose tolerance, inc insulin levels, insulin resistance, dec insulin sensitivity, dec body fat stores, lipid mobilization, inc FFA, inc synthesis of chondroitin S042' and collagen, inc protein, inc (OH)proline (ur), gynecomastia, carpal tunnel syndrome, dec T4, dec TSH response to TRH, hyperthyroidism(?), pseudotumor cerebri, inc GH antibodies, slipped capital epiphyses, acromegaly (xs). GUAIFENESIN: dec uric acid, inc VMA (ur) (an), inc 5-HIAA (ur) (an). GUANABENZ: natriuresis, dec chol, dec TG, dec norepinephrine, dec PRA, dec apolipoprotein E, inc glucagon, gynecomastia, disturbances of sexual function. GUANADREL: salt and H20 retention, anorexia, nocturia, impotence, ejaculation disturbances, weight gain or loss. GUANETHIDINE: dec catecholamines (ur), inc epinephrine (ur), dec norepinephrine (ur), dec PRA, inc Na\ Na* retention, inc VMA (early, ur), dec VMA (late, ur), inc BUN, dec glucose, inc glucose tolerance, inc chloride, antidiabetic activity, hypoglycemia, priapism, inhibition of ejaculation, impotence, scalp hair loss, inc response to tyramine test. GUANFACINE: dec chol, dec TG, dec PRA, dec catecholamines, inc GH, impotence, dec libido, testicular disorder. H2 ANTAGONISTS: dec gastric acid secretion. HALAZEPAM (see benzodiazepines). HALOPERIDOL: inc alk phosphatase, inc bilirubin, dec chol, inc glucose, dec glucose, inc prolactin. HALOTHANE: inc alk phosphatase, positive antimicrosomal antibodies, inc fluoride, inc glucose, inc GH(?), dec testosterone, inc T4, inc free T„ index, inc BUN, inc uric acid. HEMIN: dec amino levulinic acid (ur), dec uroporphyrinogen (ur), dec porphobilinogen (ur). HEPARIN: dec aldosterone, dec TG, inc FFA, inc K*, dec Na\ inc TSH, dec T4, inc free T4, dec hormone binding to TBG, induced hypoaldosteronism (esp in CRF and diabetes), adrenal hemorrhage leading to acute adrenal insufficiency, ovarian (corpus luteum) hemorrhage, osteoporosis (chronic xs), transient alopecia, priapism. If heparin is 10% of tot vol of a sample for ABG analysis, can cause errors in HCO,', base excess and C02 pressure; inc/dec Ca2+ (an), inc chol (rebound after stopping drug), inc CS (an), inc glucose, dec 5HIAA, inc/dec insulin (an), inc P043. HEROIN: inc alk phosphatase, inc chol, dec creatinine clearance (ur), inc K*, rhabdomyolysis, proteinuria, inc TBG, inc T4, inc free T4, inc T4 binding to TBG, mild inc T3. HISTAMINE: In vitro diagnostic aid for gastrointestinal function: inc epinephrine, inc GH, inc 17-(OH)CS (ur), inc norepinephrine, inc K*, inc VMA (ur), dec plasma volume, dec urine volume. HISTRELIN: inc LH (acute), inc FSH (acute), inc gonadal steroids (acute), dec LH (chronic), dec FSH (chronic), dec gonadal steroids (chronic), regression of secondary sexual characteristics in children with precocious puberty, dec linear growth velocity, dec skeletal maturation, dec testicular steroidogenesis, dec testicular volume, dec estradiol, cessation of menses, hypogonadism (if HPG axis does not reactivate after drug discontinuation), vaginal dryness, metorrhagia, mastodynia, breast edema, breast discharge, dec breast size, dyspareunia, polyuria, nocturia, glycosuria, libido changes, hot flashes, vaginal bleeding, vaginitis, dysmenorrhea, goiter, hyperlipidemia, acne, alopecia.

1946

PART XVII: ENDOCRINE DRUGS AND VALUES

HMG-COA REDUCTASE INHIBITORS: inc HDL, dec LDL, dec chol, dec VLDL, dec TG, inc transaminases, inc CPK, myopathy, rhabdomyolysis, inc myoglobin (ur), gynecomastia, loss of libido, erectile dysfunction, alopecia. HYDANTOINS (also see phenytoin): hyperglycemia, dec insulin release, worsening of glucose control in diabetics, ppt of AIP, hepatitis, interferes with metyrapone and 1 mg dexamethasone tests, gynecomastia, weight gain, edema, goiter, hypothyroidism, dec T4, dec free T4, jaundice (xs), Peyronie disease. HYDRALAZINE: inc aldosterone, inc/dec PRA, inc BUN, inc uric acid (an), inc alk phosphatase, inc Ca2* (an), inc catecholamines (ur) (an), dec chol, inc/dec glucose (an), dec 17-(OH)CS (ur) (an), inc 17-KGS (ur) (an), dec vit B6, anorexia, impotence. HYDRAZINES: inc alk phosphatase (xs), inc bilirubin (xs), dec glucose, potentiate action of insulin in diabetics, dec 5-HIAA (ur), inc tot metanephrines (ur), inc normetanephrine (ur), dec VMA (ur). HYDROCHLOROTHIAZIDE (also see thiazide diuretics): alopecia. HYDROCODONE (see narcotic analgesics). HYDROCORTISONE (see glucocorticoids). HYDROFLUMETHIAZIDE (see thiazide diuretics). HYDROMORPHONE (see narcotic analgesics). HYDROXYCHLOROQUINE SULFATE: retinopathy, alopecia, bleaching of hair, anorexia, weight loss, lassitude, ppt of porphyria. HYDROXYUREA: dec TG (an), inc BUN, inc uric acid, inc creatinine, renal dysfunction, anorexia, alopecia, inc hepatic enzymes. HYDROXYZINE: inc CS (ur) (an), inc 17-(OH)CS (ur) (an), inc 17-KGS (ur) (an). IBUPROFEN (see NS AIDS) IDARUBICIN: hyperuricemia, hair loss, alopecia, testicular atrophy (exp), inhibition of spermiogenesis and sperm maturation (exp). IFOSFAMIDE: hemorrhagic cystitis, alopecia, anorexia, RTA, inc BUN, inc creatinine, metabolic acidosis, inc bilirubin. IMIPENEM-CILASTATIN: hepatitis, inc salivation, palpitations, facial edema, oliguria, anuria, polyuria, acute renal failure, hyperhidrosis, inc alk phosphatase, inc bilirubin, dec Na\ inc K\ inc Cl , inc BUN, inc creatinine, inc protein (ur), inc casts (ur). IMIPRAMINE (also see tricyclic antidepressants): dec 5-HIAA (ur), inc bilirubin, inc chol, dec mI uptake, inc metanephrines (ur) (an), dec VMA (ur). IMMUNE SERUMS: nephrotic syndrome (rare). INDAPAMIDE (also see thiazide diuretics): frequent urination, polyuria. INDOMETHACIN (also see NSAIDS): dec aldosterone, inc alk phosphatase (xs), inc glucose (rare), inc K\ dec PRA, dec Na\ dec Na* (ur), inc TSH response to TRH, inc BUN, renal insufficiency, dec uric acid, inc urine volume. INOSIPLEX: inc uric acid, uricosuria. INSULIN: inc ACTH, inc gastrin, inc glucagon, dec P04', dec K\ dec Ca‘\ dec chol, inc corticosteroids, inc cortisol, inc epinephrine, inc norepinephrine, dec FFA, dec glucose, inc GH, dec Mg2+, inc prolactin, dec Na* (ur), inc T4, inc Tv dec reverse T3, inc VMA (ur), hypogylcemia (xs), lipoatrophy, lipohypertrophy, insulin allergy, inc insulin antibodies causing insulin resistance. INTERFERON a-2A: proteinuria, anovulation (exp), menstrual cycle irregularities (exp), fatigue, anorexia, loss of libido, hot flashes, partial alopecia, weight loss, transient impotence, excessive salivation, inc alk phosphatase, inc uric acid, inc BUN, in creatinine, hypocalcemia, inc fasting glucose, inc phosphorus, fertility impairment (exp), dec estradiol, dec progesterone, edema, aggravation of diabetes mellitus, gynecomastia, virilism, thyroid

disorder, bone pain, amenorrhea, leukorrhea, menorrhagia, nocturia, polyuria, acne, frequent micturition. INTERFERON a-n3: dec estradiol, dec progesterone, menstrual irregularities (exp), sweating, malaise, anorexia, thirst, inc salivation, hot flashes, dysuria, inc alk phosphatase, inc bilirubin. INTERFERON (i-lB: malaise, generalized edema, pelvic pain, palpitations, inc salivation, pancreatitis, salivary gland enlargement, Cushing syndrome, diabetes, SIADH, inc alk phosphatase, inc BUN, hypercalcemia, glycosuria, hypoglycemia, ketosis, thirst, goiter, inc bilirubin, proteinuria, weight loss, weight gain, sweating, alopecia, dysmenorrhea, menstrual disorder, metrorrhagia, menorrhagia, urinary urgency, breast pain, urinary retention, dec libido, hirsutism, anuria, breast engorgement, gynecomastia, impotence, kidney calculus, nocturia, oliguria, polyuria, urinary incontinence. INTERFERON y-lB: irregular menstrual cycles (exp), fatigue, weight loss, anorexia, hyponatremia, hyperglycemia, pancreatitis, reversible renal insufficiency. IODIDES: inc Cl (an), inc chol (an), inc 17-(OH)CS (ur) (an), inc ionized Ca2t (an), dec mI uptake, inc TSH, inc T4, dec Tr IODIDE ,3,I (therapeutic): inc in clinical symptoms of hyperthyroidism, acute thyroid crisis, sialoadenitis, temporary thinning of hair, thyroid destruction, hypothyroidism. IODINE-CONTAINING PRODUCTS: overactivity/underactivity of thyroid gland, goiter, thyroid adenoma, myxedema, dec mI uptake, inc TSH, fetal goiter with or without hypothyroidism (in pregnant women), inc acne, hyperkalemia (KI), inc Cl (an), inc chol (an), inc 17-(OH)CS (ur) (an), inc ionized Ca2+ (an). IOPANOIC ACID: dec mI uptake, inc TSH, inc T„, dec T,, dec uric acid, inc uric acid (ur). IPODATE (also see iopanoic acid): inc BUN, inc urobilin (ur). IPRATROPIUM: alopecia. IRON DEXTRAN: hemosiderosis (xs), inc glucose (an), inc protein (ur). ISOCARBOXAZID (see monoamine oxidase inhibitors). ISOETHARINE (see sympathomimetics). ISONIAZID: inc bilirubin, dec pyridoxine, dec folate, pellagra, hyperglycemia, metabolic acidosis, gynecomastia, hypocalcemia/hypophosphatemia due to altered vit D metabolism, inc alk phosphatase, dec chol (xs), dec mI uptake, inc ketones (ur), inc sugar (ur) (an), inc uric acid (an), dec 5-HIAA (ur), inc K+. ISOPROTERENOL (also see sympathomimetics): inc catecholamines (ur), inc catecholamines, inc cAMP, dec urine volume, inc epinephrine (ur), inc FFA, inc glucose, inc VMA (ur). ISOSORBIDE (also see nitrates): inc Cl (ur), inc K* (ur), inc Na\ inc Na+(ur), inc BUN (xs), inc urine volume, inc creatinine clearance. ISOSORBIDE DINITRATE (see nitrates). ISOSORBIDE MONONITRATE (also see nitrates). ISOTRETINOIN: inc alk phosphatase, inc apolipoprotein B, inc chol, dec HDL chol, inc LDL chol, inc VLDL chol, inc TG, dec T4, dec free T4, dec T3, worsening of diabetic control, thinning of hair, hirsutism, proteinuria, abnormal menses, inc fasting glucose, inc uric acid, inc CPK, PTH deficiency in fetus. ISRADIPINE: polyuria, sexual difficulties, dose-dependent inc in benign Leydig cell tumors and testicular hyperplasia (exp). ITRACONAZOLE: hepatitis, hypercholesterolemia (exp), nausea, anorexia, edema, fatigue, malaise, dec libido, impotence, gynecomastia, mastalgia (in males), hypokalemia, albuminuria, adrenal insufficiency. KANAMYCIN (also see aminoglycosides): inc granular casts (ur), malabsorption syndrome. KETAMINE HC1: anorexia, hypersalivation. KETOCONAZOLE: dec chol, dec cortisol, dec DHT, dec

Ch. 224: Effects of Drugs on Endocrine Function and Values estradiol, inc FSH, inc 17-(OH)progesterone, inc LH, dec testosterone, dec free testosterone, inc TG, dec l-25(OH), vit D, dec acid phosphatase (xs), dec free cortisol (ur), dec osmolality, dec Na\ dec sperm count, dec ACTH-induced corticosteroid levels, impotence, gynecomastia, oligospermia.

1947

crisis (xs), inc creatinine (an).

LINCOMYCIN (also see lincosamides): vaginitis, inc alk phosphatase (xs), inc bilirubin (xs), dec chol (xs), dec folate (an), dec glucose (xs), dec mI uptake. LINCOSAMIDES: jaundice, azotemia, oliguria, proteinuria.

KETOPROFEN (see NSAIDS). KETOROLAC (see NSAIDS). LABETALOL (also see B-blockers): inc/dec aldosterone (ur), inc

LIOTHYRONINE SODIUM (see thyroid hormone). LIOTRIX (see thyroid hormone). LISINOPRIL (also see ACE inhibitors): anorexia, impotence, dec

catecholamines (ur) (an), inc epinephrine (an), inc epinephrine (ur) (an), inc glucose, inc HDL, inc tot metanephrines (ur) (an), inc

libido, gout.

norepinephrine, inc prolactin, inc/dec PRA, inc TG, transient inc BUN, transient inc creatinine, blocks signs and symptoms of acute hypoglycemia, ejaculation failure, impotence, priapism, reversible alopecia.

LACTULOSE (also see laxatives): worsening of diabetic control(?) (syrup contains galactose and lactose).

LAXATIVES: In excess most laxatives can cause inc PRA, inc aldosterone, inc HCO/, inc pH, dec Ca2\ dec Cl , dec Na\ dec K\ dec protein, steatorrhea, osteomalacia (xs), and vit and mineral deficiencies. Saline laxatives include magnesium sulfate, magnesium hydroxide, magnesium citrate, and sodium phosphate. (In renal failure the latter may cause dec Ca2*, inc P043, inc Na\ acidosis). Irritant/stimulant laxatives include cascara, senna, phenolphthalein, biscodyl, casanthranol, castor oil. Bulk-producing laxatives include methylcellulose, psyllium, polycarbophil. Lubricant laxative: mineral oil. Surfactant: docusate. Miscellaneous: glycerin suppository, lactulose. LEUCOVORIN/5-FU: alopecia, anorexia. LEUPROLIDE ACETATE: inc pituitary hyperplasia (exp), inc benign pituitary adenoma (exp), dec bone density, suppression of pituitary-gonadal system, dec testicular size, impotence, dec libido, gynecomastia, breast tenderness, hot flashes, sweating, anorexia, bone pain, vaginitis, acne, weight gain, weight loss, testicular pain, diabetes, inc Ca2*, alopecia, hair growth, inc uric acid, body odor, accelerated sexual maturity, inc alk phosphatase, inc chol, inc LDL, inc TG, dec HDL, penile swelling, prostatic pain, hypoglycemia, inc BUN, inc creatinine, inc libido, dec protein, thyroid enlargement. LEVAMISOLE: inc copulation period (exp), dec fertility (exp), alopecia, fatigue, renal failure, inc creatinine, inc alk phosphatase, inc bilirubin, anorexia, urinary infection. LEVODOPA: inc ACTH, inc dopamine (ur), dec cortisol, inc insulin, inc C-peptide, inc FFA, inc FSH, inc GH, inc homovanillic acid (ur), dec 5-HIAA (ur), dec prolactin, dec vit B6, inc alk phosphatase, inc catecholamines (an), inc estrogens (ur) (an), inc/dec glucose, dec 17-(OH)CS (ur), dec 13II uptake, inc ketones (ur) (an), dec tot metanephrines (ur), inc norepinephrine (ur), dec normetanephrine (ur), dec K*, inc Na*(ur), inc sugar (ur) (an), dec TSH, dec TSH response to TRH in hypothyroidism, inc T4, dec TG, inc/dec BUN, inc/dec uric acid (an), inc/dec VMA (ur), dec VMA (ur) (an), dark sweat/urine, change in weight, priapism, edema, hair loss. LEVONORGESTREL: irregular menstrual bleeding, intermenstrual spotting, amenorrhea, fluid retention, dec insulin sensitivity in diabetics, dec chol, inc LDL chol(?), inc/dec HDL chol, dec TG, dec SHBG, slight dec thyroxine, inc T3 uptake, acne, mastalgia, weight gain, hirsutism, hypertrichosis, scalp hair loss, inc/dec androstenedione, inc apolipoprotein B, dec estradiol, inc glucose, dec P043, inc/dec testosterone.

LEVORPHANOL (see narcotic analgesics). LEVOTHYROXINE SODIUM (see thyroid hormone). LICORICE: inc Na\ dec K*, dec aldosterone, dec renin, inc free cortisol (urine).

LIDOCAINE: metabolic acidosis (xs), malignant hyperthermic

LITHIUM: inc aldosterone (ur), inc alk phosphatase (bone isoenzyme), inc ADH, inc HCO, (ur) (on 1st day of therapy), inc Ca , dec Ca2 (ur), inc chol, dec cortisol, inc creatinine, dec creatinine clearance (ur), inc glucose, dec glucose tolerance, inc/dec I uptake, inc Mg2+, inc Mg'* (ur), dec norepinephrine (ur), dec osmolality (ur), inc PTH, dec P043, inc K*, dec Na+, inc Na* (ur), dec specific gravity (ur), dec free thyroxine, inc/dec T4 by RIA, dec T3 by RIA, dec T, resin uptake, dec free T4 index, inc TSH, dec uric acid, inc uric acid (ur), mild inc VMA (ur), inc urine volume, acquired nephrogenic diabetes insipidus, glycosuria, transient hyperglycemia, hypothyroidism, euthyroid goiter, hyperthyroidism (rare), Na* depletion, thinning of hair, alopecia, impotence, sexual dysfunction. LOMUSTINE: inc alk phosphatase, inc bilirubin, azotemia, alopecia.

LOOP DIURETICS: dec Na*, dec K*, dec Mg2+, dec Ca2*, tetany (xs), hypochloremic alkalosis, dehydration, azotemia, inc BUN, inc Cr, inc Na* (ur), inc Mg2* (ur), inc Cl (ur), inc uric acid, gout (xs), inc glucose, dec glucose tolerance, ppt of diabetes, inc chol, inc LDL chol, inc TG, slight dec HDL chol. LORATADINE (also see antihistamines): menorrhagia, dysmenorrhea.

LORAZEPAM (see benzodiazepines). LOVASTATIN (also see HMG-COA reductase inhibitors): inc alk phosphatase, abnormalities in TFTs, testicular atrophy, dec spermatogenesis (exp).

LOXAPINE: inc prolactin, galactorrhea, amenorrhea, impotence, false-positive preg tests, neuroleptic malignant syndrome, gynecomastia, inc LFTs.

LYMPHOCYTE IMMUNE GLOBULIN: hyperglycemia (in renal transplantation), inc alk phosphatase (in aplastic anemia), edema, hepatitis, abnormal renal function tests. MAGNESIUM-CONTAINING DRUGS: hypermagnesemia (xs) (and in renal disease), inc Ca2* (an), inc alk phosphatase (an), dec ACE. MANNITOL (also see osmotic diuretics): inc osmolality, inc Ca2* (ur), dec Cl , dec P043 (an), inc K*, inc/dec Na\ inc Na* (ur), dec uric acid, inc uric acid (ur), acidosis, marked diuresis, edema, urinary retention, dry mouth, thirst, dehydration. MAZINDOL: dec glucose, testicular pain, polyuria, impotence, menstrual upset, gynecomastia. MECAMYLAMINE: anorexia, dec libido, impotence, inc uric acid. MECHLORETHAMINE: anorexia, delayed menses, oligomenorrhea, amenorrhea, impaired spermatogenesis, azoospermia, tot germinal aplasia. MECLIZINE: anorexia, urinary frequency, difficult urination, urinary retention, palpitations, cholestatic jaundice (cyclizine).

MECLOFENAMATE (see NSAIDS). MEDROXYPROGESTERONE: fluid retention, inc glucose, dec glucose tolerance (esp in diabetics), inc insulin, dec progesterone, dec estradiol, dec pregnanediol (ur), dec testosterone, dec cortisol, dec gonadotropins, dec 17-(OH)CS (ur), dec SHBG, inc Mg2*, inc PO„3, may dec T, uptake, inc/dec chol, inc/dec TG, inc/dec LDL

1948

PART XVII: ENDOCRINE DRUGS AND VALUES

chol, inc/dec HDL chol, prolonged contraceptive effect, hirsutism, sensation of preg, lack of return of fertility, changes in breast size, breast lumps, nipple bleeding, prevention of lactation, irregular menstrual bleeding, spotting, heavy menstruation, amenorrhea, dec libido, anorgasmia, acne, pelvic pain, mastalgia, alopecia, bloating, hot flashes, galactorrhea, melasma, chloasma, dyspareunia, inc libido, inc bone loss initially, risk factor for osteoporosisf?). MEFENAMIC ACID (also see NS AIDS): inc bile (ur) (an). MEFLOQUINE: hair loss, telogen effluvium, loss of appetite, fatigue. MEGESTROL: dec 11-deoxycortisol (in breast cancer), dec estradiol, dec FSH, dec LH, dec glucose, inc insulin, inc prolactin, dec SHBG, weight gain, inc appetite, fluid retention, nausea, vomiting, edema, breakthrough bleeding, galactorrhea, tumor flare (with or without hypercalcemia), hyperglycemia, alopecia, carpal tunnel syndrome, rash. MELPHALAN: inc bilirubin (xs), inc 5-HIAA (ur), inc BUN (xs), nausea, vomiting, anorexia, skin ulceration, skin necrosis (at injury site), oral ulceration. MENOTROPINS: ovarian follicular growth/maturation, abnormal ovarian enlargement (xs), hyperstimulation syndrome (xs), multiple births.

MEPERIDINE (also see narcotic analgesics): inc creatinine kinase, inc glucose, inc histamine, dec ACTH, dec 17-(OH)CS (ur), dec 17-KS (ur), inc LDH, inc lipase, inc amylase, inc pC02, dec p02, dec urine volume, inc ADH, sweating, nausea, anorexia, taste alterations, facial flushing, urinary retention or hesitancy, oliguria, antidiuretic effect, dec libido, dec potency, edema, interference with thermal regulation, pruritus.

MEPHENYTOIN (see hydantoins). MEPHOBARBITAL (see barbiturates). MEPROBAMATE: inc alk phosphatase (xs), inc aminolevulinic acid (ur), ppt of acute porphyria, inc bilirubin (xs), inc chol (xs), inc estrogens (ur) (an), inc 17-(OH)CS (ur) (an), inc/dec 17-KGS (ur) (an), inc/dec 17-KS (ur) (an), inc porphyrins (ur), urticaria, stomatitis, hyperpyrexia, oliguria. MERCAPTOPURINE: inc alk phosphatase (xs), inc bilirubin (xs), inc glucose (an), inc uric acid (ur), hyperuricemia, pancreatitis. MERCURY COMPOUNDS: dec HCO, (xs), dec Ca2t (xs), red urine, inc glucose (ur), Fanconi syndrome (xs), dec Mg2\ dec pH (xs), inc P04’ (ur), dec K+ (xs), dec protein, albuminuria, dec Na+ (xs), dec BUN (an), dec uric acid (xs), inc uric acid (ur) (xs). MESALAMINE: acne, dysmenorrhea, menorrhagia, hair loss, anorexia, inc appetite, inc alk phosphatase, inc BUN, inc Cr. MESCALINE: inc free fatty acids.

MESNA: inc ketones (ur) (an), bad taste, fatigue, nausea, vomiting. MESORIDAZINE (see phenothiazines). METAPROTERENOL (see sympathomimetics). METARAMINOL: metabolic acidosis (xs). METFORMIN: dec HCO/, lactic acidosis (xs), dec carotene, inc form-imino glutamic acid (ur), dec TG, dec vit Bl2, megaloblastic anemia (xs), dec xylose (ur). METHACHOLINE: inc amylase, inc bilirubin, inc lipase, inc norepinephrine (ur), itching, nausea, vomiting, worsening of thyrotoxicosis.

METHACYCLINE (see tetracycline). METHADONE (also see narcotic analgesics): inc cortisol, false¬ positive preg tests (an), inc T4, inc TBG, dec free T4, inc T,, inc pC02, nausea, anorexia, urinary retention, oliguria, antidiuretic effect, dec libido, dec potency, interference with thermal regulation. METHANOL: inc acetone (ur) (xs), inc amylase (xs), dec HCO/ (xs), acidosis (xs), dec ionized Ca2+ (an), inc ketones (xs), proteinuria (xs), inc BUN (xs), inc uric acid (xs).

METHAZOLAMIDE (see carbonic anhydrase inhibitors). METHDILAZINE (see antihistamines). METHENAMINE: inc catecholamines (an), crystalluria, inc/dec estrogens (ur) (an), inc 17-(OH)CS (ur) (an), dec 5-HIAA (ur) (an), dec mI uptake, dec urine pH, proteinuria (xs), inc sugar (ur) (an), inc urobilinogen (ur)(an), inc VMA (ur) (an), nausea, stomatitis, anorexia, dysuria, hematuria, frequency, urgency, pruritus, uriticaria. METHERGOLINE: decTSH. METHICILLIN: dec HCO/ (xs), dec Ca2+(?), inc 17-KS (ur) (an), inc P043'(xs), inc K* (xs), proteinuria (xs), inc TG (an), inc BUN (xs), inc uric acid (xs), glossitis, stomatitis, abnormal taste, oliguria (xs), hematuria (xs), pyuria (xs), hyaline casts (xs), nephropathy (xs), vaginitis, anorexia, hyperthermia, inc alk phosphatase, hypernatremia, dec tot proteins, dec albumin. METHIMAZOLE: inc alk phosphatase, inc chol, inc glucose (an), dec mI uptake, inhibits synthesis of thyroid hormone, dec T4, dec T3, dec T3 uptake, inc TSH (xs), insulin autoimmune syndrome (may cause hypoglycemic coma), aplasia cutis (in fetus), goiter (in fetus), cretinism, skin pigmentation, hair loss. METHIONINE: inc insulin, dec urine pH.

METHOCARBAMOL (ROBAXIN): brown/green/blue urine, inc 5-HIAA (ur) (an), inc VMA (ur) (an), pruritus, rash, flushing, metallic taste, light-headedness.

METHOTREXATE: inc alk phosphatase (xs), nausea, vomiting, rash, pruritus, alopecia, anorexia, dysuria, fever, sweating, vaginal discharge, inc BUN (xs), inc creatinine (xs), renal failure, inc chol (an), dec folate, inc P04’ (an), dec sperm count, dec TG (an), inc/dec uric acid.

METHOXAMINE: inc cortisol, inc ACTH, uterine hypertonus. METHOXYFLURANE: inc fluoride, inc oxalate, inc alk phosphatase (xs), dec Ca2\ inc Cl (xs), inc osmolality, inc Na\ inc BUN, inc uric acid, inc urine volume.

METHSUXIMIDE (see succinimides). METHYCHLOTHIAZIDE (also see thiazide diuretics): SIADH. METHYLCELLULOSE (see laxatives). METHYLDOPA: inc alk phosphatase (xs), inc porphyrins (ur), ppt of acute attack of porphyria, inc coproporphyrin (ur), inc apolipoprotein C III, inc catecholamines, dec catecholamines (ur), inc chloride, dec chol (an), dec HDL, dec LDL, dec VLDL, inc/dec glucose (an), dec GH, dec 5-HIAA (ur), inc ketones (ur) (an), inc metanephrines (ur) (an), inc prolactin, inc Na\ salt retention, edema, inc glucose (ur) (an), inc triglycerides, dec TG (an), inc BUN, inc/dec uric acid (an), inc VMA (ur) (an), inc plasma volume, gynecomastia, galactorrhea, dec libido, dec potency, breast enlargement, lactation, amenorrhea, impotence, failure to ejaculate. METHYLPHENIDATE: inc epinephrine (ur), urticaria, anorexia, weight loss, scalp hair loss, palpitations.

METHYLPREDNISOLONE (also see glucocorticoids): inc amylase (xs), dec ACE (an), inc HCO, , dec ACTH, dec cortisol, inc creatinine clearance, dec glucose tolerance, inc lipase (xs), inc lactate (xs), dec K+, dec p02, dec testosterone, dec GnRH, inc trypsin (xs), inc plasma volume.

METHYLTESTOSTERONE (also see androgens): inc alk phosphatase (xs), inc bilirubin (xs), inc Ca2+ (in females with breast cancer), inc chol (xs), dec sperm count, dec TBG, dec urobilinogen (ur).

METHYLTHIOURACIL: inc alk phosphatase (xs), inc bilirubin (xs), dec T4 (dec iodination of tyrosine).

METHYLXANTHINES: inc catecholamines, inc VMA (ur). METHYPRYLON: inc aminolevulinic acid (ur), inc 17-(OH)CS (ur) (an), inc 17-KGS (ur) (an), inc 17-KS (ur) (an), inc porphyrins (ur), ppt of acute porphyria, inc sugar (ur) (an), pyrexia, pruritus. METHYSERGIDE: dec serotonin, inc BUN (xs), penile fibrotic

Ch. 224: Effects of Drugs on Endocrine Function and Values plaques (simulating Peyronie disease), facial flush, localized brawny edema, hair loss, weight gain. METQCLOPRAMIDE: inc aldosterone (transient), inc ACTH, inc cortisol, inc GH, inc 18-(OH)corticosterone, dec K+, inc prolactin, inc TSH, hypoglycemia, galactorrhea, amenorrhea, gynecomastia, impotence, fluid retention, porphyria, nipple tenderness (in males), neuroleptic malignant syndrome, inc catecholamines (in hypertensives), hypertensive crisis in patients with pheochromocytoma. METOLAZONE (see thiazide diuretics). METOPROLOL (see P-adrenergic blockers). METRONIDAZOLE: gynecomastia, inc/dec glucose (an), dec 17KS (ur), dec LDH (an), dec TG (an), nausea, anorexia, polyuria, dyspareunia, dec libido, dryness of vagina, dysuria. METYRAPONE: inc androstenedione, dec aldosterone, inc 11deoxycortisol, dec cortisol, inc ACTH, inc 11-deoxycorticosterone, dec corticosterone, inhibits endogenous adrenal corticosteroid synthesis, mild natriuresis, may induce acute adrenal insufficiency in pts with low adrenal secretory capacity, dec Na\ dec C1‘, inc K\ inc 17-(OH)CS (ur), 17-KGS (ur), dec 17-KS (ur) (an), inc porphyrins (ur), ppt of AIP, dec testosterone. METYROSINE: dec catecholamines, therapy of pheochromocytoma, crystalluria, urolithiasis (exp), inc catecholamines (ur) (an), impotence, failure to ejaculate, galactorrhea, slight breast swelling. MEXILETINE: hair loss, impotence, dec libido. MICONAZOLE: inc CPK, dec Na+, pruritus, nausea, anorexia, flushing, hyperlipemia (due to vehicle). MIDAZOLAM HC1: excessive salivation, hives. MIFEPRISTONE (RU 486): heavy bleeding, uterine pain. MILRINONE: hypokalemia. MINERAL OIL (also see laxatives): dec absorption of vits A, D, E, K. MINERALOCORTICOIDS: inc ANH, inc HC03, dec K\ inc Na+. MINOCYCLINE (see tetracycline). MINOXIDIL: hypertrichosis (but may exacerbate hair loss), alopecia, light-headedness, fractures, edema, facial swelling, weight gain, urinary tract infections, renal calculi, urethritis, prostatitis, epididymitis, vaginitis, vulvitis, vaginal discharge, itching, sexual dysfunction, fatigue, menstrual changes, fluid retention, breast tenderness, inc alk phosphatase, inc BUN, inc creatinine, inc HDL chol, dec LDL chol. MISOPROSTOL: menstrual spotting, hypermenorrhea, dysmenorrhea, post-menopausal vaginal bleeding. MITHRAMYCIN: inc alk phosphatase, dec Ca2\ inc Ca2* (ur), inc creatinine (xs), dec hydroxyproline (ur), inhibition of bone resorption, dec P043 , dec K+, inc protein (ur) (xs), inc BUN (xs), inhibition of spermatogenesis (exp), anorexia, nausea, inc bilirubin. MITOMYCIN: alopecia, inc creatinine, anorexia, fatigue, edema, hemolytic uremic syndrome. MITOTANE: inc alk phosphatase (xs), dec 17-(OH)CS (ur), inc 6P-(OH)cortisol (ur), proteinuria (xs), hematuria (xs), renal damage (xs), inc T3 uptake, competes for sites on TBG, dec T4, lactic acidosis, adrenal insufficiency, anorexia, nausea, hyperpyrexia, generalized aching, dec glucocorticoids. MITOXANTRONE: hyperuricemia, jaundice, alopecia. MOLINDONE: inc FFA, inc prolactin, galactorrhea, amenorrhea, gynecomastia, impotence, neuroleptic malignant syndrome. MONOAMINE OXIDASE INHIBITORS: inc catecholamines, inc epinephrine, inc norepinephrine, dec glucose, inc metanephrines (ur), inc prolactin, inc dopamine, galactorrhea, inc serotonin, inc VMA (ur), hypertensive crisis, nausea, edema, hyperhidroses, inc transaminases, anorexia, weight changes, palpitations, dysuria,

1949

incontinence, urinary retention, sexual disturbances, hypernatremia, hypermetabolic syndrome, impaired H20 excretion compatible with SIADH, acidosis (xs), hyperpyrexia (xs), hepatitis (xs), jaundice (xs), inc alk phosphatase (xs), dec chol (xs), dec glucose (xs), inc glucose tolerance, dec 5-HIAA (ur). MONOCTANOIN: hypokalemia. MORICIZINE: impotence, anorexia, dec libido. MORPHINE (also see narcotic analgesics): inc alk phosphatase, dec BMR, dec cortisol, inc CPK, dec enteroglucagon, inc epinephrine, dec gastric inhibitory peptide, inc gastrin, inc glucose, inc histamine, dec 17-(OH)CS (ur), dec insulin, dec 17-KS, dec lactate, inc lipase, dec motilin, dec norepinephrine, dec PP, inc prolactin, galactorrhea(7), gynecomastia(?), inc sugar (ur) (an), inc TSH, dec VMA (ur), dec urine volume, stimulates ADH release, sweating, nausea, taste alterations, facial flushing, ureteral spasm, urinary retention or hesitancy, oliguria, dec libido, dec potency, pruritus, edema, interference with thermal regulation. MUMPS VIRUS VACCINE (LIVE): parotitis, orchitis. MUROMONAB-CD3: flushing, diaphoresis, hepatitis, inc BUN, inc creatinine, inc cellular casts (ur). NABUMETONE (see NSAIDS). NADOLOL (see B-adrenergic blockers). NAFARELIN ACETATE: inc LH, inc FSH, inc ovarian steroidogenesis at onset of therapy; repeated dosing leads to dec LH, dec FSH and dec secretion of gonadal steroids; arrests secondary sexual development, slows linear growth and skeletal maturation, estrogen withdrawal bleeding (within 6 weeks after initiation of therapy) then ceasing of menstruation, dec pelvic pain, dec dysmenorrhea, dec dyspareunia, arrests breast development in females, arrests genital development in males, dec pubic hair growth, slight dec in bone density/bone mass, inc ovarian cysts, acne, transient breast enlargement, body odor, seborrhea, hot flashes, asymmetry and enlargement of pituitary gland, pituitary microadenoma(?) (children), inc/dec libido, vaginal dryness, hirsutism, chloasma, lactation, breast engorgement, inc TG, inc chol, inc P04', dec Ca2+. NALIDIXIC ACID: inc alk phosphatase (xs), inc bilirubin (xs), inc creatinine, inc glucose (an), inc BUN, inc 17-KGS (ur) (an), inc 17KS (ur) (an), inc sugar (ur) (an), inc VMA (ur) (an), pruritus, cholestatic jaundice (xs), metabolic acidosis (xs). NALOXONE: inc cortisol, inc FSH, inc LH, nausea, sweating, palpitations. NALTREXONE: edema, loss of appetite, delayed ejaculation, dec potency, inc/dec sexual interest, acne, alopecia, oily skin, inc thirst, weight loss, weight gain. NANDROLONE (see anabolic steroids). NAPROXEN (also see NSAIDS): inc 17-KGS (ur) (an), inc 5HIAA (ur) (an), inc alk phosphatase (an), inc HCO, (an), dec Cl (ur), inc P043 (an), dec TG (an), inc ZnJ* (ur). NARCOTIC ANALGESICS: inc amylase, dec BMR, inc CPK, dec 17-(OH)CS (ur), inc glucose, inc lipase, sweating, nausea, vomiting, taste alterations, anorexia, facial flushing, ureteral spasm, spasm of vesical sphincters, urinary retention or hesitancy, oliguria, anti¬ diuretic effect, dec libido, dec potency, pruritus, diaphoresis, edema, interference with thermal regulation. NEOMYCIN: inc amino acids (ur) (an), dec ammonia ion, dec Ca * (ur), inc Cau (feces), dec carotene, inc casts (ur) (xs), dec TG, dec FFA, dec chol, dec LDL, dec estrogens (ur), dec lactose tolerance, dec Mg2\ dec K\ dec thyroglobulin, dec T,, inc BUN (xs), dec vit A, dec vit B,,, inc fecal fat, malabsorption syndrome. NETILMICIN (also see aminoglycosides): hyperkalemia. NIACIN: dec chol, dec LDL, dec TG, dec VLDL, inc action of lipoprotein lipase, dec lipolysis in adipose tissue, inc histamine, dec

1950

PART XVII: ENDOCRINE DRUGS AND VALUES

FFA, dec (3 lipoproteins, dec phospholipids, dec pre-B lipoproteins, inc ketones (ur), hyperglycemia, inc/dec glucose tolerance, inc insulin, hyperuricemia, dec uric acid clearance, inc alk phosphatase, inc apolipoprotein Al, inc catecholamines (an), inc GH, dec K* (ur), inc Na+ (ur), inc sugar (ur) (an). NICARDIPINE: dec T4, inc TSH, polyuria, sexual difficulties, inc Na+ (ur), dose-dependent inc in thyroid hyperplasia or neoplasia (follicular adenoma, carcinoma) (exp). NICOTINE: inc ADH, inc catecholamines (ur), inc epinephrine, inc FFA, inc glucose, inc 1 l-(OH)CS, inc 5-HIAA (ur), inc neurophysin, inc norepinephrine, inc catecholamine release from adrenal medulla, inc cortisol, impaired fertility (exp), anorexia, excessive salivation, taste perversion, dysmenorrhea, sweating, edema. NITRATES: dec chol (an), inc appetite, impotence, methemoglobinemia (xs), inc urine volume. NITRAZEPAM: inc HCO, (an), dec glucose (an), inc 5-HIAA (ur), fatigue, pruritus. NITROFURANTOIN: inc alk phosphatase (xs), inc anithyroglobulin antibodies, dec HC03 (xs), inc BUN (xs), dec glucose tolerance, inc Na+ (an), inc sugar (ur) (an), methemoglobinemia (xs), anorexia, pruritus, transient alopecia, dec glucose, inc bilirubin, inc creatinine.

NITROGLYCERIN (also see nitrates): inc catecholamines, inc VMA (ur), inc epinephrine (ur), inc norepinephrine (ur), inc TG (an). NITROPRUSSIDE: inc TSH, inc T4, dec hormone binding to TBG, dec free T4, hypothyroidism, dec vit B12, cyanide toxicity (xs), methemoglobinemia (xs), thiocyanate toxicity (xs).

NIZATIDINE (also see H2 antagonists): gynecomastia (rare), impotence, loss of libido, inc uric acid, inc alk phosphatase.

NORTRIPTYLINE (also see tricyclic antidepressants): inc alk phosphatase (xs), inc/dec glucose. NOVOBIOCIN: inc alk phosphatase (xs), dec 131I uptake, pseudojaundice, inc bilirubin, alopecia, jaundice (xs). NSAIDS: dec aldosterone, inc creatinine, reversible acute renal failure, inc K\ proteinuria, dec PRA, dec Na\ H20 retention, interstitial nephritis, papillary necrosis, inhibition of PG synthesis, jaundice (xs), anorexia, hematuria, inc BUN, dec creatinine clearance, change in taste, skin discoloration, hyperpigmentation, inc/dec appetite, inc/dec weight, glycosuria, hyperglycemia, hypoglycemia, flushing, sweating, menstrual disorders, impotence, vaginal bleeding, diabetes mellitus, thirst, pyrexia, breast changes, gynecomastia, facial edema, libido changes, mastodynia, renal calculi(?), leukorrhea(?), displaces T4 from TBG. NYSTATIN: inc amino acids (ur) (an). OCTREOTIDE: dec serotonin, dec gastrin, dec VIP, dec insulin, dec glucagon, dec secretin, dec motilin, dec pancreatic polypeptide, dec GH, cholelithiasis, mild transient hypoglycemia/hyperglycemia, dec insulin requirements in diabetics, aggravation of fat malabsorption, dec libido, frigidity(?), hair loss, galactorrhea(?), secondary hypothyroidism, urine hyperosmolarity, hyperdipsia, inc CPK, dec Ca2+(?). OLSALAZINE: alopecia(?), impotence(?), menorrhagia(?), proteinuria (?). OMEGA-3 POLYUNSATURATED FATTY ACIDS: inc fasting glucose (in NIDDM), inc mean glucose (in NIDDM), impaired insulin secretion/inc insulin sensitivity. OMEPRAZOLE: dec gastrin, dec gastric acid secretion, dec cyanocobalamin (malabsorption), gynecomastia, hypoglycemia, weight gain, alopecia, electrolyte disturbances!?), hepatitis, jaundice, hypoglycemia (?), glycosuria, testicular pain. ONDANSETRON HC1: hepatitis, hypokalemia.

OPIATES: inc aldosterone, inc cortisol, inc epinephrine, inc norepinephrine, inc PRA. ORAL CONTRACEPTIVES: (The effects vary with the contents): dec 17-(OH)progesterone, dec 17-KGS (ur), dec pregnanediol (ur), dec progesterone, inc lactate, inc oxytocin, inc PRA, inc renin substrate, inc Na+, inc testosterone, inc SHBG, dec free testosterone, inc DHT, inc TT4, inc TBG, dec T, RU, inc vit A, dec vit B6, dec vit Bl2, dec vit C, dec zinc, dec folate, dec Mg2\ inc aminolevulinic acid (ur), inc amylase, inc coproporphyrin, inc CBG, dec DHEAS, inc GH, inc lipase, inc/dec P04', inc uroporphyrin (ur), inc menstrual cycle regularity, dec blood loss, dec dysmenorrhea, dec ovarian cysts, dec ectopic preg, dec fibrocystic disease of breasts, breast enlargement, dec lactation (post-partum), fluid retention, pre¬ menstrual-like syndrome(?), changes in libido, hirsutism, loss of scalp hair, breakthrough bleeding, spotting, amenorrhea, fertility impairment, ppt of porphyria, melasma, breast tenderness, dec alk phosphatase, dec albumin, inc angiotensin I, inc aldosterone, inc amylase, inc calcitonin, inc glucose, dec glucose tolerance, inc copper, inc ceruloplasmin, dec P043 ,inc selenium, inc cortisol, inc transcortin, inc corticosteroids, inc C-peptide, inc insulin, dec response to metyrapone test, inc prolactin, galactorrhea(?), growth factor for prolactinomas(?), dec FSH, dec LH, inc FFA, inc TG, inc tot phospholipids, may inc LDL, inc chol, dec HDL (low-dose estrogen), inc apolipoprotein Al (high dose estrogen), dec apolipoprotein Al (low dose estrogen), inc glycosylated hemoglobin. OSMOTIC DIURETICS: inc Na* (ur), inc Cl (ur), hypovolemia (xs), dilute urine, hypernatremia, hyponatremia, hyperkalemia, hypokalemia, acidosis, inc BUN (xs), electrolyte loss (xs). OUABAIN: dec catecholamines (ur).

OXACILLIN (also see penicillins): inc alk phosphatase (xs), inc bilirubin (xs), inc creatinine, inc 17-KS (ur) (an), inc protein (an), proteinuria (xs), inc BUN (xs), hyperkalemia (xs). OXANDROLONE (see anabolic steroids). OXAPROZIN (see NSAIDS). OXAZEPAM (also see benzodiazepines): inc cortisol, inc alk phosphatase (xs), inc bilirubin (xs), inc glucose (an), dec l31I uptake, inc sugar (ur) (an). OXYBUTYNIN: dec sweating, impotence, suppression of lactation, dec lacrimation.

OXYCODONE (see narcotic analgesics). OXYMETAZOLINE: dec corticosteroids.

OXYMETHOLONE (see anabolic steroids). OXYMORPHONE (see narcotic analgesics). OXYPHENBUTAZONE (also see phenylbutazone): inc alk phosphatase (xs), inc amylase, inc bilirubin (xs), inc Cl , inc Na\ marked salt retention, inc creatinine, dec creatinine clearance, inc uric acid crystals (ur), inc glucose, dec glucose (an), dec mI uptake, dec T4, inc T, uptake, inc BUN, kidney damage, inc uric acid (an), dec uric acid, inc plasma volume, dec urine volume, edema, salivary gland enlargement, metabolic acidosis, respiratory alkalosis, proteinuria (xs), thyroid hyperplasia (?), goiters associated with hyperthyroidism/hypothyroidism(?), pancreatitis(?), excessive perspiration (xs). OXYPHENISATIN: dec albumin (xs), inc alk phosphatase (xs), positive antimitochondrial antibodies, inc bilirubin (xs), dec mI uptake.

OXYTETRACYCLINE (see tetracycline). OXYTOCIN: contraction of lacteal glands, milk ejection (in lactating females), uterine stimulation, anti-diuresis, inc plasma volume, water intoxication (xs), dec Na* (xs), hypertonic uterine contractions (xs), uterine rupture (xs), insulin-like action during labor(?).

Ch. 224: Effects of Drugs on Endocrine Function and Values

PACLITAXEL: impaired fertility (exp), alopecia, inc bilirubin, inc alk phosphatase. PAMIDRONATE: hypocalcemia, hypophosphatemia, hypomagnesemia, hypokalemia, hypothyroidism (90-mg dose), bone pain. PANCREATIN (see pancreozymin). PANCRELIPASE (see pancreozymin). PANCREOZYMIN: inc amylase, inc glucose (IV), inc insulin (IV), inc lipase (an), hyperuricosuria (xs), hyperuricemia (xs). PANCURONIUM: inc epinephrine/norepinephrine (if given with halothane anesthesia), salivation, rash. PAPAVERINE: inc alk phosphatase (xs), metabolic acidosis (xs), hyperglycemia (xs), hypokalemia (xs), erections (intracavemous). PARA-AMINOSALICYLATE SODIUM: crystalluria, dec vit B12, jaundice, hepatitis, goiter with or without myxedema. PARALDEHYDE: inc alk phosphatase (xs), dec HCO/ (xs), metabolic acidosis (xs), inc bilirubin (xs), inc corticosteroids (ur) (an), inc glucose (transient), inc 17-(OH)CS (ur) (an), inc 17-KGS (ur) (an), inc ketones (transient), proteinuria (xs), inc BUN (xs), strong unpleasant breath. PARAMETHADIONE: inc alk phosphatase (xs), inc bilirubin (xs), dec Ca2+, inc chol (xs), inc creatinine (xs), dec 25-(OH)D3, proteinuria (xs), inc BUN (xs), nephrosis (xs), myasthenia gravislike syndrome (xs), nausea, anorexia, weight loss. PARATHYROID HORMONE (TERIPARATIDE ACETATE): hypercalcemia (xs), hypertensive crisis, inc hydroxyproline (ur), inc prolactin, inc pH (ur), inc HC03 (ur), inc Cl (ur), inc Mg2\ dec P04^, inc urine volume. PAROMOMYCIN (see aminoglycosides). PAROXETINE: hypercholesterolemia, hypocalcemia, hypoglycemia, hypokalemia, hyponatremia, diabetes mellitus, hyperthyroidism, hypothyroidism, thyroiditis, dec preg rate (exp), inc pre- and post-implantation preg losses (exp), atrophy of seminiferous tubules (exp), arrested spermatogenesis (exp), abnormal ejaculation, sweating, dry mouth, adrenergic syndrome, pelvic pain, salivary gland enlargement, urinary frequency, abortion, amenorrhea, breast pain, cystitis, dysmenorrhea, dysuria, menorrhagia, nocturia, polyuria, urethritis, urinary incontinence/retention/urgency, vaginitis, breast atrophy/carcinoma/neoplasm, female lactation, hematuria, renal calculus/pain, abnormal kidney function, mastitis, nephritis, oliguria, prostatic carcinoma, vaginal moniliasis, acne, alopecia, photosensitivity, skin discoloration, edema, weight gain/loss, hyperglycemia, thirst, inc alk phosphatase, inc bilirubin, gout, dehydration. PECTIN: dec chol. PEMOLINE: anorexia, weight loss, inc acid phosphatase, prostatic enlargement, hepatitis, jaundice, growth suppression (with long term use in children), hyperpyrexia (xs), sweating (xs), flushing (xs). PENBUTOLOL (see p-adrenergic blockers). PENICILLAMINE: dec Cu, dec Hg, dec cystine, dec vit B6, inc alk phosphatase (xs), inc amino acids (ur) (an), positive antinuclear antibodies, positive anti-DNA antibodies, inc bilirubin (xs), inc chol, dec chol (an), inc CPK, proteinuria (xs), inc BUN (xs), inc Zn2*, myasthenic syndrome, skin rashes, oral ulcerations, hypoglycemia (rare), anti-insulin antibodies, skin friability, generalized pruritus, thyroiditis (rare), altered/blunted/loss of taste, pancreatitis, inc alk phosphatase, hematuria, hyperpyrexia, falling hair/alopecia, mammary hyperplasia, elastosis perforans serpiginosa, hot flashes, excessive wrinkling, inc excretion of Zn2\ Hg, and Pb, nephrotic syndrome (xs). PENICILLINS: dec albumin (an), inc a-levulinic acid (ur) (an), inc CPK when given as intramuscular injection (as occurs with other

1951

other drugs administered by this route), dec estrogens (ur), inc 17(OH)CS (ur) (an), dec l3lI uptake, inc 17-KGS (ur) (an), inc 17-KS (ur) (an), inc Hg (ur), inc/dec K\ proteinuria (xs), inc protein (ur) (an), inc sugar (ur) (an), inc T3 uptake (competes for TBPA sites), dec T„, inc BUN (xs), inc uric acid (an), dec uric acid, inc alk phosphatase, hypernatremia, dec albumin, dec tot proteins, vaginitis, anorexia, hyperthermia, oliguria (xs), hematuria (xs), hyaline casts (xs), pyuria (xs), nephropathy (xs), glossitis, stomatitis, abnormal taste.

PENTAERYTHRITOL TETRANITRATE (see nitrates). PENTAGASTRIN: inc calcitonin, slight inc GH, inc histamine (ur), inc pepsin (gastric juice), inc prolactin, flushing, light¬ headedness, sweating, warmth.

PENTAMIDINE: dec folate, hypoglycemia, hyperglycemia, inc creatinine (xs), inc BUN (xs), renal toxicity (xs), pancreatic islet cell necrosis, inc insulin, diabetes mellitus, hypocalcemia, anorexia, rash, bad taste, hyperkalemia, dec appetite, hypersalivation, pancreatitis.

PENTAZOCINE: inc porphyrins (ur), attack of acute porphyria, inc epinephrine, dec 1 l-(OH)CS (ur), dec 17-(OH)CS (ur), inc lipase, inc norepinephrine, dec pH, anorexia, edema of face, urinary retention, change in rate/strength of uterine contractions in labor.

PENTOBARBITAL (see barbiturates). PENTOSTATIN: seminiferous tubular degeneration (exp), anorexia, sweating, skin discoloration, weight loss, inc BUN, inc creatinine, jaundice, hepatitis, pelvic pain, acidosis, inc CPK, dehydration, diabetes mellitus, inc gamma globulins, gout, abnormal healing, dec chol, weight gain, hyponatremia, bone pain, acne, alopecia, inc albumin (ur), glycosuria, fibrocystic breast, inc gynecomastia, polyuria, oliguria, vaginitis, inc LFTs. PERCHLORATE: inc ionized Ca2+ (an), proteinuria (xs), inc BUN (xs), nephrotic syndrome (xs). PERGOLIDE: dec prolactin, uterine neoplasms (exp), impaired fertility (xs) (exp), facial edema, palpitation, nausea, anorexia, malaise, pelvic pain, hypothyroidism, diabetes mellitus, SIADH, thyroid adenoma, weight loss, dehydration, dec K+, inc/dec glucose, gout, inc chol, acidosis, inc uric acid, cachexia, skin discoloration, alopecia, hirsutism, urinary incontinence, dysmenorrhea, dysuria, mastalgia, menorrhagia, impotence, vaginitis, priapism, kidney calculus, lactation, fibrocystic breast, pyuria, amenorrhea, uricaciduria, withdrawal bleeding, urethral pain, breast engorgement, urolithiasis.

PERPHENAZINE (see phenothiazines). PHENACEMIDE: inc alk phosphatase, inc bilirubin, dec creatinine (an), proteinuria (xs), anorexia, weight loss, skin rash, hepatitis, inc creatinine, nephritis, fatigue, palpitations. PHENAZOPYRIDINE HCI (PYRIDIUM): yellowish tinge of skin/sclera, interferes with urine determinations by spectrometry, rash, pruritus, methemoglobinemia, renal toxicity (xs), hepatic toxicity (xs), red-orange urine.

PHENELZINE (also see monoamine oxidase inhibitors): pyridoxine deficiency, weight gain. PHENFORMIN: inc folate, lactic acidosis, dec glucose.

PHENINDAMINE (see antihistamines). PHENMETRAZINE: inc epinephrine (ur), inc 5-HIAA (ur), dec l3'l uptake.

PHENOBARBITAL (also see barbiturates): dec creatinine, inc alk phosphatase, osteomalacia, inc aminolevulinic acid, inc bilirubin (xs), hypocalcemia, inc ceruloplasmin, inc Cu, dec folate, dec glucose (ur) (an), inc amino acids (ur) (an), dec 17-(OH)CS (ur), inc 6B-(OH)cortisol (ur), inc 5-HIAA (ur) (an), inc hydroxyproline (ur), dec 25-(OH) vit D3, inc lactate, dec P043, dec T4, dec free T„ index. PHENOTHIAZINES: acne, lactation, breast enlargement (in females), SIADH, mastalgia, menstrual irregularities, changes in

1952

PART XVII: ENDOCRINE DRUGS AND VALUES

libido, hyperglycemia/hypoglycemia, hyponatremia, glycosuria, pituitary tumor correlated with hyperprolactinemia, heavy menses, dry mouth, anorexia, salivation, perspiration, urinary retention/frequency/incontinence, polyuria, enuresis, priapism, ejaculation inhibition, hyperpyrexia, enlarged parotid glands, inc appetite, polyphagia, inc weight, polydipsia, chromosomal aberrations in spermatocytes (exp), abnormal sperm (exp), severe neurotoxicity in thyrotoxic patients, gynecomastia; interferes with urinary ketone determinations, preg tests and steroid determinations; inc catecholamines, dec HDL chol, inc chol, inc glucose, dec VMA (ur), inc vasopressin, dec FSH, dec LH, dec DHT, dec testosterone, dec free testosterone, dec GH, dec 17-(OH)CS (ur), dec 17-KS (ur), dec pregnanediol (ur), inc prolactin, inc TBG, inc tot T4, dec T3 uptake, dec BUN (xs), inc/dec uric acid, inc alk phosphatase (xs), dec estrogens (ur), block ovulation, dec glucose tolerance, dec gonadotropins (ur), dec 5-HIAA (ur) (an), inc l3lI uptake, dec 17KGS (ur) (an), inc tot metanephrines (ur) (an), dec PO„5 (an), inc bilirubin (xs), renal dysfunction (xs), galactorrhea, amenorrhea, impotence, inc in mammary neoplasms (exp), neuroleptic malignant syndrome, tardive dyskinesia, alterations in LFTs, discoloration of urine to pink/red-brown, hair loss, papillary hypertrophy of tongue. PHENOXYBENZAMINE: inhibition of ejaculation, dec Na\ inc ADH. PHENSUXIMIDE (see succinimides). PHENTOLAMINE: inc catecholamines, inc 5-HIAA (ur) (an), dec glucose (xs). PHENYLBUTAZONE: inc sodium, salt retention, inc alk phosphatase (xs), inc bilirubin (xs), inc Cl , inc chol (one patient), inc glucose, dec 17-(OH)CS (ur), inc 66-(OH)cortisol (ur), dec mI uptake, respiratory alkalosis, proteinuria (xs), dec T4, dec free T4, inc T3 uptake, dec free T4 index, inc TSH, inc BUN (xs), inc uric acid (low dose), dec uric acid (high dose), inc plasma volume, dec urine volume, edema, salivary gland enlargement, metabolic acidosis, hyperglycemia, thyroid hyperplasia, goiters associated with hyperthyroidism and hypothyroidism, pancreatitis. PHENYLEPHRINE: inc glucose, inc tot metanephrines (ur) (an), inc amino acids (ur) (an). PHENYLPROPANOLAMINE: inc amino acids (ur) (an), palpitations, renal failure (xs), rhabdomyolysis (xs), dysuria. PHENYTOIN (also see hydantoins): inc alk phosphatase, dec Ca2+, inc Cu, inc ceruloplasmin, inc chol, inc HDL chol, inc corticosteroids, inc apolipoprotein Al, dec calcitonin, dec DHEAS, dec cortisol, dec 11-deoxy cortisol, inc GH, dec 17-(OH)CS (ur), dec 17-KS (ur), dec P04’, inc prolactin, inc PTH (in epileptic children), inc FSH, inc LH, inc glucose, dec insulin, inc/dec glucose tolerance, inc/dec free T4, inc T3 uptake, inc/dec T3, dec free T3, inc SHBG, inc testosterone, dec free testosterone, inc transcortin, dec 25-(OH) vit D, dec ADH, inc vit A, hyperglycemia, gynecomastia, goiter, clinical hyperthyroidism (rare), hirsutism, alopecia, dec binding of T4 and T3 by TBG (xs) PHOSPHATES: inc PTH, dec alk phosphatase (an), dec Ca2+ (an), crystalluria (xs), dec ionized Ca2+ (slight), dec Mg2t (ur), dec K+. PHOSPHORUS REPLACEMENT PRODUCTS: weight gain, low urine output, unusual thirst, bone/joint pain (xs), osteomalacia (xs), extraskeletal calcifications (xs), inc alk phosphatase (xs), inc bilirubin (xs), inc creatinine (xs), dec glucose (xs), proteinuria (xs), inc BUN (xs). PHYTATE: dec Ca2\ dec Fe2\ dec P045, dec Zn2+. PIMOZIDE: Neuroleptic malignant syndrome, thirst, inc appetite, inc salivation, anorexia, impotence, nocturia, urinary frequency, sweating, weight gain, weight loss, loss of libido, menstrual disorder, breast secretions. PINDOLOL (see B-adrenergic blockers).

PIPECURONIUM BROMIDE: hypoglycemia, hyperkalemia, inc creatinine, anuria. PIPERIDINES: inc 17-(OH)CS (ur) (an), dec ionized Ca2+ (an), inc 17-KS (ur) (an). PIRBUTEROL (see sympathomimetics). PIROXICAM (see NS AIDS). PIZOTIFEN: inc 5-HIAA (ur). PODOPHYLLOTOXIN DERIVATIVES: anorexia, alopecia, pigmentation, renal dysfunction, hepatic dysfunction. POLYMYXIN B: albuminuria, cylindruria, azotemia, facial flushing, inc amino acids (ur) (an), inc creatinine (xs), dec K+ (xs), proteinuria (xs), inc BUN (xs). POLYTHIAZIDE (see thiazide diuretics). POTASSIUM CHLORIDE: inc CF, dec glucose, inc K+, dec vit B,2. POTASSIUM IODIDE: inc amylase, parotitis, inc corticosteroids (ur) (an), inc 17-(OH)CS (ur) (an), inc TSH, dec T4, dec T3. POVIDONE-IODINE: inc glucose (an) (if swab used with fingerstick). PRAVASTATIN (see HMG-COA reductase inhibitors). PRAZEPAM (see benzodiazepines). PRAZOSIN (also see a-1-adrenergic blockers): dec chol, inc HDL, dec VLDL, inc FFA, inc glucose, dec glucose tolerance, inc insulin, inc lipoprotein lipase, dec PRA, inc TSH (slight), inc T4 (slight), dec TG, inc VMA (ur) (an), inc metabolites of norepinephrine (ur) (an), impotence, alopecia. PREDNISOLONE (see glucocorticoids). PREDNISONE (also see glucocorticoids): dec alk phosphatase, inc amylase, pancreatitis (xs), dec ACE, inc HCO,, hypokalemic alkalosis, dec bilirubin, dec Ca2\ inc chol, inc HDL, inc cortisol (an), dec creatinine clearance, dec 1,25-dihydroxy vit D3, inc glucose, dec glucose tolerance, inc PTH, dec K\ inc Na\ dec T3 binding capacity, dec testosterone, inc TSH, dec TBG, inc TG, dec T3, inc/dec reverse T3, inc uric acid. PRILOCAINE: dose-dependent methemoglobinemia. PRIMAQUINE: inc bilirubin, rusty yellow/brown urine, dec RBCreduced glutathione, hemolysis in G-6-PD deficiency, methemoglobinemia in NADH methemoglobin reductase deficiency. PRIMIDONE: inc amino acids (ur) (an), crystalluria (xs), dec folic acid, dec free testosterone, dec T4, dec free T, index, fatigue, anorexia, skin eruptions, impotence. PROBENECID: inc alk phosphatase (xs), urinary calculi, dec estriol (ur), dec glucose, dec 17-KS (ur), proteinuria (xs), inc sugar (ur) (an), inc BUN (xs), dec uric acid, inc uric acid (ur), anorexia, urinary frequency, ppt of gout. PROBUCOL: dec chol, dec LDL, dec HDL, dec TG, dec GH, inc HCO, , dec Ca~+, inc BUN, inc glucose, inc uric acid, inc CPK, inc alk phosphatase (xs), impotence, nocturia, hyperhidrosis, enlargement of multinodular goiter. PROCAINAMIDE: anorexia, inc K+ (an), worsening of myasthenia gravis, inc alk phosphatase (xs), positive antinuclear/antihistone antibodies, inc bilirubin (xs). PROCAINE: inc porphobilinogen (ur) (an), inc urobilinogen (ur) (an). PROCARBAZINE: anorexia, nocturia, hematuria, gynecomastia in prepubertal and early pubertal boys, flushing, hyperpigmentation, alopecia, jaundice, hepatic dysfunction, diaphoresis, inc bilirubin. PROCHLORPERAZINE (see phenothiazines). PROGESTERONE: (Effects vary according to the progestational agent): inc aldosterone (ur) (an), inc alk phosphatase (xs), dec chol, inc corticosteroids (an), dec HDL, inc cortisol (an), dec glucose, dec 17-(OH)CS (ur), dec LH, inc Mg2+, dec pregnanediol (ur), inc protein, sodium retention, inc TBG, inc cystine, inc melatonin,

Ch. 224: Effects of Drugs on Endocrine Function and Values

1953

inhibits secretion of pituitary gonadotropins, prevents follicular maturation and ovulation, fluid retention, dec glucose tolerance (esp

anorexia, atrophic glossitis, malaise, light-headedness, dermatitis, abnormal skin pigmentation, hyperphenylalaninemia.

in diabetics), amenorrhea, breast tenderness, acne, melasma, chloasma, alopecia, hirsutism, masculinization of female fetus (during preg).

QUATERNARY ANTICHOLINERGICS (see anticholinergic agents). QUAZEPAM (see benzodiazepines). QUINACRINE: inc alk phosphatase (s), inc bilirubin (xs), yellow

PROGESTINS (see progesterone). PROGESTOGENS: inc aminolevulinic acid (ur), inc porphyrins (ur), acute porphyria. PROMAZINE (also see phenothiazines): inc alk phosphatase (xs), inc bilirubin (xs), inc chol (xs), dec 17-(OH)CS (ur), dec 5-HIAA (ur) (an), dec mI uptake, 17-KS (ur) (an), inc prolactin, inc protein (ur). PROMETHAZINE (also see antihistamines): false-negative or false-positive preg tests, inc blood glucose, inc alk phosphatase, inc bilirubin, inc catecholamines, dec corticosteroids (ur) (an), dec 17(OH)CS (ur) (an), dec 5-HIAA (ur) (an), dec mI uptake, dec P04v (an).

PROPAFENONE: fertility impairment (exp), dec spermatogenesis (exp), anorexia, alopecia, inc alk phosphatase, hyponatremia, SIADH, impotence, inc glucose. PROPOFOL: hypersalivation, enlarged parotid gland, metabolic acidosis, flushing, diaphoresis, green urine, oliguria, urine retention, hyperkalemia, hyperlipemia, inc BUN, inc creatinine, inc osmolality, dehydration, hyperglycemia, inc TG. PROPOXYPHENE (also see narcotic analgesics): reversible jaundice, abnormal liver function tests, inc alk phosphatase (xs), dec glucose, dec 17-(OH)CS (ur), dec 17-KS (ur), dec 13II uptake, reversible jaundice. PROPRANOLOL (also see p-adrcnergic blockers): dec aldosterone, dec C-peptide, dec FFA, dec glucagon, dec glucose, inc GH, dec insulin, inc LH (in males), dec LH (in females), inc K\ inc prolactin (in males), dec TBG, dec T„, inc free T4, inc TSH, dec T3, inc reverse T3, inc BUN (xs), inc alk phosphatase (xs). PROPYLTHIOURACIL: inhibits synthesis of thyroid hormone, dec T4, dec T3, dec peripheral conversion of T4 to T3, inc TSH (xs), pituitary adenomas(?), thyroid hyperplasia(?), goiter/cretinism in fetus, skin pigmentation, hair loss, insulin autoimmune syndrome (can cause hypoglycemic coma), inc alk phosphatase (xs), inc amylase, inc bilirubin (xs), dec FFA, inc glucose (an), dec IMI uptake, inc BUN (anaphylactic nephritis), inc uric acid (an), inc antinuclear antibodies. PROSTAGLANDIN E2: stimulation of uterus, uterine evacuation, hot flashes, breast tenderness, excessive thirst, uterine sacculation (xs), uterine rupture (xs), dehydration (xs), proliferation of bone, cervical ripening, inc T4, inc T3. PROTAMINE: inc catecholamines (an), dec lipase, inc tot lipids, dec lipoprotein lipase.

PROTRIPTYLINE (see tricyclic antidepressants). PSEUDOEPHEDRINE: inc amino acids (ur) (an), palpitations, dysuria, weakness (xs).

PSYLLIUM (see laxatives). PYRAZINAMIDE: dec albumin (xs), inc alk phosphatase (xs), inc bilirubin (xs), dec globulin (xs), inc ketones (ur) (an), inc 17-KS (ur), dec protein (xs), inc uric acid, gout, fever, porphyria, dysuria, anorexia, inc Fe cone, rashes, pruritus, acne, photosensitivity, interstitial nephritis, worsening of glucose control in diabetics(?). PYRIDOSTIGMINE: inc GH secretion, inc GH response to GHRH, urinary frequency, incontinence, urinary urgency, diaphoresis, rash, urticaria, flushing, alopecia. PYRIDOXINE: dec oxalate, dec folic acid (xs), prolactin suppression^), inhibition of lactation(?).

PYRILAMINE (see antihistamines). PYRIMETHAMINE: dec folate, hemolysis in G-6-PD deficiency,

skin, deep yellow urine, inc cortisol (an), inc cortisol (ur) (an), inc 1 l-(OH)CS (an), hemolysis in G-6-PD deficiency, acute porphyria attack, anorexia, dermatitis, yellow pigmentation of skin (xs).

QUINAPRIL (see ACE inhibitors). QUINETHAZONE (see thiazide diuretics). QUINIDINE: anorexia, abnormalities of pigmentation, inc CPK, acidosis (xs), inc alk phosphatase (xs), false inc catecholamines (an), inc catecholamines (ur) (an), inc corticosteroids (ur) (an), inc 17(OH)CS (ur) (an), inc 17-KS (ur) (an), dec mI uptake, inc anti¬ nuclear antibodies. QUININE: inc bilirubin, inc catecholamines (an), inc corticosteroids (ur) (an), dec glucose, inc insulin, inc 17-(OH)CS (ur) (an), inc 17-KGS (ur) (an), hepatitis. RADIOGRAPHIC AGENTS: inc histamine, dec VMA (ur), inc inorganic iodide, dec uric acid, inc amylase, dec catecholamines (ur), inc creatinine (xs), crystalluria, dec 17-KGS (ur) (an), dec P04’ clearance (ur), proteinuria, interferes with serum protein electrophoresis (an), inc specific gravity (ur), inc sugar (ur) (an), inc TSH, inc T4 (an), dec T3, inc reverse T3, inc BUN, azotemia (xs), renal failure (xs). RAMIPRIL (also see ACE inhibitors): anorexia, impotence, inc Na\ dec Na+(ur). RANITIDINE (also see H2 antagonists): impotence, loss of libido, inc creatinine, gynecomastia (rare), dec aldosterone, dec cortisol, inc/dec prolactin, dec T4, dec free T4, inc T3, inc free T3, dec TSH response to TRH, dec vit B12, inc gastrin, dec serotonin, dec 5-HIAA (urine). RAUWOLFIA DERIVATIVES: mammary fibroadenomas (exp), malignant tumors of the seminal vesicles (exp), malignant adrenomedullary tumors (exp), inc serum prolactin, inc/dec catecholamines (ur), dec 17-KS (ur), dec 17-(OH)CS (ur), dec VMA (ur), anorexia, pseudolactation, galactorrhea, amenorrhea, impotence, gynecomastia, dec libido, breast engorgement, weight gain, inc Na\ edema.

RESCINNAMINE (see rauwolfia derivatives). RESERPINE (also see rauwolfia derivatives): dec catecholamines, inc/dec catecholamines (ur), inc HVA (ur), inc 5HIAA (ur), inc prolactin, dec serotonin, inc/dec VMA (ur), inc corticosteroids (ur) (an), inc FFA, inc glucose, dec norepinephrine (ur), dec T4, false-negative tyramine test, galactorrhea, amenorrhea, gynecomastia, impotence, dec libido. RESORCINOL: green-blue urine, inc creatinine (an), dec ' “I uptake, inc methemoglobin. RIBOFLAVIN: inc catecholamines (an), inc catecholamines (ur) (an), yellow-orange urine, inc urobilin (ur) (an). RIFABUTIN: fertility impairment (exp), rash, anorexia, discolored urine, taste perversion, inc alk phosphatase, hepatitis, skin discoloration.

RIFAMPIN: inc alk phosphatase (xs), inc bilirubin, inc casts (ur), dec chol (an), red-orange saliva/sweat/urine, dec corticosteroids, dec cortisone, inc C-peptide, inc glucose, dec hydrocortisone, dec 25(OH) vit D, inc insulin, inc P04v (an), inc prolactin, dec protein, inc testosterone, inc TSH, dec T4, dec free T4, inc T3, inc BUN, renal failure, inc uric acid, porphyria exacerbation, anorexia, pancreatitis, hepatitis, rash, pruritus, fatigue, osteomalacia, hematuria, hemoglobinuria, menstrual disturbances, edema of face and extremities, inhibits assays for folate and B,, (an).

1954

PART XVII: ENDOCRINE DRUGS AND VALUES

RITODRINE: dec contactility of uterine smooth muscle, inc insulin (IV), inc glucose (IV), dec K* (IV), inc FFA (IV), inc cAMP (IV), glycosuria, lactic acidosis, hypoglycemia (neonatal), hypocalcemia (neonatal). SALICYLATES: inc creatinine, dec estriol (ur), dec FFA, dec folate, dec hydroxyproline (ur), inc ketones, dec TSH, dec T4, inc uric acid, dec vit B12, inc bilirubin, dec T3, dec renal function, compete with thyroid hormone for binding sites on TBPA and TBG, dec glucose (ur) (an), interfere with 5-HIAA (ur) (an), inc VMA (ur) (an), dec VMA (ur) (an) (Pisano method), anorexia, hepatoxicity, rashes, thirst, respiratory alkalosis (xs), metabolic acidosis (xs), dehydration (s), hyperthermia (s), hypokalemia (xs), slight inc glucose, hypoglycemia (xs). SALSALATE (also see salicylates): dec albumin, nephrotic syndrome, inc creatinine, proteinuria, dec T4, dec T3, displaces T4 from TBG. SALT SUBSTITUTES (potassium-containing): inc K* (xs). SARGRAMOSTIM (GRANULOCYTE MACROPHAGE

SPECTINOMYCIN: inc alk phosphatase, dec creatinine clearance (ur), inc BUN, dec urine volume, urticaria, dizziness. SPINAL ANESTHESIA: dec Cl (ur), dec effective renal plasma flow, dec GFR, dec Na* (ur), dec urobilinogen (ur), dec urine volume. SPIRONOLACTONE: hyperkalemia, hyponatremia, gynecomastia* reversible hyperchloremic metabolic acidosis, inability to achieve or maintain erection, amenorrhea, irregular menses, post-menopausal bleeding, inc aldosterone, inc Cl (ur), inc angiotensin II, inc Ca2‘, inc/dec chol, dec HDL, inc LDL, inc 18(OH)corticosterone, inc insulin, inc 17-(OH)CS (ur) (an), inc 17KGS (ur) (an), inc 17-KS (ur) (an), inc PRA, dec testosterone, inc/dec TG, inc/dec uric acid, inc corticosteroids (an), inc cortisol (an), inc corticosteroids (an), inc cortisol (an), inc DOC, dec glucose tolerance, inc estradiol (ur), inc 1 l-(OH)CS (an), sexual dysfunction, dec plasma volume, inc LH, displaces DHT from receptors, inc BUN.

STANOZOLOL (see anabolic steroids).

COLONY STIMULATING FACTOR): fluid retention, anorexia, alopecia, inc creatinine (in pre-existing renal dysfunction), inc bilirubin (in pre-existing hepatic dysfunction).

STREPTOKINASE: inc alk phosphatase, inc CPK, inc creatinine, nephrotoxicity (xs), proteinuria (xs), inc BUN.

SCOPOLAMINE (see anticholinergic agents). SECOBARBITAL (see barbiturates). SECRETIN: inc HCO/ (ur), inc Ca2\ dec gastrin, inc glucose, inc

hemolytic anemia, nephrotoxicity, proteinuria (xs), inc sugar (ur) (an), inc BUN (xs).

insulin, inc lipase, inc Na* (ur), dec titratable acidity (ur).

SELEGILINE (also see monoamine oxidase inhibitors): hair loss, weight loss, prostatic hyperplasia, facial hair, anorgasmia (xs), dec penile sensation (xs).

SENNA (also see laxatives): red/orange/rust urine, inc estradiol (ur) (an), inc estrogens (ur) (an), dec estrone (ur) (an).

SERTRALINE: significant weight loss, dec uric acid, uricosuria, inc sweating, male sexual dysfunction, ejaculatory delay, anorexia, fatigue, inc salivation, flushing, palpitations, edema, acne, alopecia, hypertrichosis, anorexia, inc appetite, dysmenorrhea, intermenstrual bleeding, amenorrhea, mastalgia, menorrhagia, micturition frequency, dysuria, nocturia, polyuria, fatigue, hot flushes, thirst, dehydration, inc chol, inc TG, hypoglycemia, exophthalmos, gynecomastia. SILVER: dec chloride, inc pH, proteinuria (xs), nephrotoxicity (xs), dec Na+, inc BUN (xs).

SIMVASTATIN (also see HMG-COA reductase inhibitors): dec vital sperm, inc abnormal sperm, dec fertility (exp). SODIUM BICARBONATE (also see antacids): inc pH, alkalinization of urine, dec K*, inc protein (ur) (an), inc urobilinogen (ur). SODIUM CHLORIDE: ionized Ca2* (an).

dec bilirubin (an), inc cortisol (ur), inc

STREPTOMYCIN (also see aminoglycosides): inc bilirubin,

STREPTOZOCIN: inc acetoacetate, dec HCO,, polyuria, dec FFA, dec gastrin, inc glucose (ur), inc insulin, inc lactate, hypokalemia, inc pyruvate, polydipsia, nephrotoxicity, dec fertility (exp), hypoalbuminemia, abnormalities of glucose tolerance, hypoglycemia, nephrogenic DI, lethargy. STRONTIUM: inc Mg2* (ur) (an). SUCCIMER: inc ketones (ur) (an), dec uric acid (an), dec CPK (an), appetite loss, inc alk phosphatase, inc chol, proteinuria. SUCCINIMIDES: inc aminolevulinic acid (ur), inc porphyrins (ur), ppt of acute porphyria, anorexia, weight loss, inc libido, alopecia, hirsutism, urinary frequency, renal damage, hematuria, vaginal bleeding, microscopic hematuria, proteinuria (xs), nephrosis (xs). SUCCINYLCHOLINE: inc CPK, inc histamine, inc ionized Ca2+, inc myoglobin, inc K\ malignant hyperthermia, metabolic acidosis (xs), inc salivation, hyperkalemia, myoglobinuria. SUCRALFATE: aluminum toxicity (in renal failure), aluminum osteodystrophy, osteomalacia, encephalopathy, in conjunction with other aluminum-containing products may inc Al1* levels; dec PO„3 (in renal failure).

SUFENTANIL (also see narcotic analgesics): chills. SULFACYTINE (see sulfonamides). SULFADIAZINE (also see sulfonamides): inc alk phosphatase,

SODIUM NITROPRUSSIDE: dec 131I uptake, dec T4, thyroidal inhibition (in renal dysfunction).

dec Ca‘* (an), inc chol (xs), crystalluria, dec l3lI uptake, proteinuria (xs), hematuria, dec urine volume.

SODIUM POLYSTYRENE SULFONATE: hypokalemia, hypocalcemia/hypercalcemia, sodium retention. SODIUM SALTS: dec aldosterone, inc HC03', inc Ca2+ (an), inc/dec Ca2+ (ur), dec Cl , inc ionized Ca2\ inc pH, dec K\ dec PRA, inc Na*.

SULFAMETHIZOLE (see sulfonamides). SULFAMETHOXAZOLE (also see sulfonamides): inc alk

SOMATOSTATIN (also see octreotide): dec Na\ water

SULFATE-CONTAINING DRUGS (if present in high concentration): dec Ca2* (an), dec Ca2\ inc Ca2+ (ur), dec K\

intoxication, dec TSH, dec TSH response to TRH, inhibitor of TSH release, dec T4, dec T3, dec free T3. SORBITOL: inc glucose, hyperglycemia in diabetics, dec intestinal absorption of Bl2, acidosis, electrolyte loss, marked diuresis, edema, urinary retention, dry mouth, thirst, dehydration, inc bilirubin, inc lactate, dec pyruvate. SOTALOL (also see p-blockers): inc chol, dec HDL, inc LDL, dec FFA, inc tot metanephrines (ur) (an), inc TG.

phosphatase, inc T, (an).

SULFASALAZINE (also see sulfonamides): oligospermia, infertility in men, inc alk phosphatase.

kaliuresis, dec Na\ natriuresis.

SULFHYDRYL COMPOUNDS: dec alk phosphatase (an). SULFINPYRAZONE: renal failure (xs), inc uric acid (ur), ppt of acute gouty arthritis, urolithiasis, renal colic, jaundice (xs).

SULFISOXAZOLE (also see sulfonamides): false-positive urinary protein. SULFONAMIDES: ppt of acute porphyria, false-positive urinary

Ch. 224: Effects of Drugs on Endocrine Function and Values glucose, methemoglobinemia, anorexia, pancreatitis, dec folic acid, crystalluria, hematuria, proteinuria, inc creatinine, nephrotic syndrome, toxic nephrosis, oliguria, anuria, alopecia, goiter production, diuresis, hypoglycemia, acidosis (xs), dec Ca2t (an), inc alk phosphatase (xs), inc cholesterol (xs), dec l31I uptake, dec T„, inc T3 uptake, inc BUN (an), dec uric acid, uricosuric effect, uremia. SULFONYLUREAS: inc acetaldehyde, inc alk phosphatase, inc bilirubin, hypoglycemia, dec l3lI uptake, dec Na\ inc T3 uptake, dec T4, dec TG, dec glucose, hypoglycemia (xs), SIADH, porphyria cutanea tarda, hepatic porphyria, inc BUN, inc creatinine, dec TG, inc insulin, inc C-peptide, potentiation of effect of ADH, dec glucagon release from the liver. SULINDAC (also see NSAIDS): inc alk phosphatase (xs), dec creatinine clearance, dec prostaglandin F201, dec PR A, dec thromboxane B2. SUMATRIPTAN SUCCINATE: malaise, flushing, sweating, warm/hot sensation, thirst, polydipsia, dehydration, hunger, dec appetite, dysuria, dysmenorrhea, renal calculus, urinary frequency. SYMPATHOMIMETICS: hypokalemia (xs), anorexia, alopecia. TAMOXIFEN: dec alk phosphatase, inc Ca2+, dec chol, dec LDL, inc VLDL, inc estradiol, dec FSH, inc/dec LH, dec prolactin, inc sperm count, inc T„, inc TBG, inc free T4, inc T3, inc TG, endometrial hyperplasia, endometrial polyps, hyperlipidemia, hot flashes, vaginal bleeding, vaginal discharge, menstrual irregularities, ovarian cysts, loss of appetite.

TEMAZEPAM (see benzodiazepines). TENIPOSIDE (see podophyllotoxin derivatives). TERAZOSIN (also see a,-adrenergic blockers): dec chol, dec LDL chol, dec VLDL chol, impotence, dec libido, sexual dysfunction, gout, hemodilution, weight gain. TERBUTALINE (also see sympathomimetics): inc HDL, inc glucose, inc insulin, inc/dec K\ dec T4, inc T3. TERFENADINE (also see antihistamines): alopecia, galactorrhea, dysmenorrhea.

TESTOLACTONE: anorexia, alopecia, edema, nail growth disturbances, dec estradiol, inc Ca2\ inc 17-KS (ur), inc creatinine (ur).

1955

THIAMINE: inc uric acid (an), inc urobilinogen (an). THIAMYLAL (see barbiturates). THIAZIDE DIURETICS: dec free cortisol (ur), dec C-peptide, dec insulin, dec Mg2*, dec osmolality, inc BUN, inc creatinine, dec K*, dec Na*, hypochloremic alkalosis, inc uric acid, inc Ca2+, hyperglycemia, inc chol, inc LDL chol, inc TG, inc Na* (ur), inc Cl (ur), inc K* (ur), inc HC03 (ur), dec Ca2* (ur), dec uric acid (ur), dec formation and recurrence of calcium nephrolithiasis, dec incidence of osteoporosis in post-menopausal women, dec urine volume (therapy of nephrogenic DI), impotence, dec libido, inc insulin or oral hypoglycemic requirement in diabetics, azotemia (xs), fetal/neonatal jaundice, fetal/neonatal hypoglycemia and electrolyte imbalances. THIOCYANATE: proteinuria (xs), inc BUN (xs), nephrosis (xs). THIOGUANINE: jaundice, inc alk phosphatase, anorexia, hyperuricemia. THIOPENTAL (also see barbiturates): inc histamine, salivation, shivering, nausea. THIORIDAZINE (also see phenothiazines): dec LH, dec testosterone. THIOTEPA: inc uric acid, nephropathy (xs), anorexia, amenorrhea, interferes with spermatogenesis, chemical/hemorrhagic cystitis. THIOTHIXENE: inc alk phosphatase (xs), inc bilirubin (xs), reversible cholestasis, inc/dec glucose, false-positive urine preg tests, inc prolactin, galactorrhea, amenorrhea, gynecomastia(?), impotence, neuroleptic malignant syndrome. THIOURACIL: dec T„ inc reverse T,, inc alk phosphatase (xs), inc bilirubin (xs), inc chol (xs). THYROID HORMONE: dec chol, dec HDL, dec LDL, inc SHBG, dec TSH, inc metabolic rate of body tissues; exacerbation of intensity of symptoms if given in diabetes mellitus, diabetes insipidus or adrenal insufficiency; ppt of hyperthyroid state, dec bone density (xs), weight loss, menstrual irregularities, partial loss of hair in first few months of therapy, inc glucose, inc (OH)proline (ur), dec 13II uptake, inc protein, dec catechol-O-methyl-transferase, dec estriol (ur), dec monoamine oxidase, dec norepinephrine, inc T4,

TESTOSTERONE (also see androgens): inc aldosterone (ur) (an),

inc T3, inc free T„ index.

inc alk phosphatase, inc androstenedione, inc Ca2+, inc chol, dec CBG, inc corticosteroids (an), dec DF1EA, inc estradiol, inc 17(OH)CS (ur) (an), dec 17-(OH)progesterone, dec 17(OH)pregnenolone, dec progesterone, dec SHBG, dec TBG, Na* retention, H20 retention, inc urine volume. TETRACYCLINE: dec Ca2\ inc alk phosphatase (xs), aminoaciduria (xs), inc amylase (xs), inc Bence-Jones protein (ur) (xs), dec HC03 (xs), acidosis (xs), inc catecholamines (an), dec chol (xs), inc estrogens (ur) (an), dec folate, inc/dec glucose (an), l3lI uptake, inc/dec PO„3, Fanconi syndrome (outdated product), inc/dec K+, proteinuria (xs), hypernatremia (xs), inc sugar (ur) (an), dec testosterone, dec free testosterone, inc BUN (xs), inc/dec uric acid (an), inc urine volume, anorexia, pseudotumor cerebri, brown-black microscopic discoloration of thyroid gland. TETRAHYDROCANNABINOL: inc epinephrine (ur), inc norepinephrine (ur), dec testosterone, dec DHT, dec free testosterone, dec uric acid, inc C-peptide, dec cAMP, dec glucose, inc insulin, dec LH (in women), inc K*. THALLIUM: inc BUN (xs), proteinuria (xs), inc casts (ur) (xs). THEOPHYLLINE: inc cAMP, diuresis, inc catecholamines (ur), hyperglycemia (xs), proteinuria (xs), SIADH, alopecia, hypokalemia (xs), hypercalcemia (xs), dec HCO, (xs), acidosis (xs), dec alk phosphatase (an), inc FFA, dec P043, dec Na\ inc/dec somatostatin

THYROTROPIN: inc 13,I uptake, inc T4, inc T3. THYROXINE (see thyroid hormone). TICLOPIDINE: inc chol, inc TG, anorexia, hyponatremia, inc alk phosphatase (xs), inc bilirubin (xs).

TIMOLOL (see B-adrenergic blockers). TIOPRONIN: wrinkling and friability of skin, proteinuria, nephrotic syndrome (xs), dec vit B6.

TOBRAMYCIN (also see aminoglycosides): cylindruria. TOCAINIDE: anorexia, alopecia, myasthenia gravis, polyuria, positive antinuclear antibodies.

TOLAZAMIDE (also see sulfonylureas): mild diuresis. TOLBUTAMIDE (also see sulfonylureas): false-positive reaction for albumin in urine (metabolite precipitates when acidified after boiling test).

TOLMETIN (also see NSAIDS): inc protein (ur) (an). TOSYLATE BRETYLIUM: dec catecholamines (ur). TRANYLCYPROMINE (see monoamine oxidase inhibitors). TRAZODONE: priapism, inc/dec libido, impotence, retrograde

(an), inc uric acid, inc urine volume.

ejaculation, early menses, missed periods, breast enlargement and engorgement, lactation, hypersalivation, SIADH, methemoglobinemia, inc bilirubin, hematuria, delayed urine flow, inc urinary frequency, urinary incontinence/retention, inc/dec appetite, sweating, weight gain/loss, malaise, alopecia. TRH: inc epinephrine, inc norepinephrine, inc prolactin, inc TSH,

THIABENDAZOLE: inc alk phosphatase (xs), inc chol (xs), inc

inc T4, inc T3.

glucose, proteinuria (xs), inc crystals (ur) (an), anorexia, hematuria,

TRIAMCINOLONE (also see glucocorticoids): inc amylase, inc

enuresis, facial flush.

Ca2+ (ur), dec cortisol, inc glucose, dec glucose tolerance, negative

1956

PART XVII: ENDOCRINE DRUGS AND VALUES

nitrogen balance, hypokalemic alkalosis, inc K* (ur) (xs), inc Na* (ur). TRIAMTERENE: hyperkalemia, mild N2 retention, renal stones(?), metabolic acidosis, inc glucose, azotemia (xs), inc creatinine (xs), inc uric acid, gout(?), inc aldosterone, dec HCO, , dec catecholamine (ur) (an), inc Cl , green-blue color of urine, dec creatinine clearance, crystalluria, dec folate, dec GFR, inc Mg2*, dec Na\ sexual dysfunction(?). TRIAZOLAM (also see benzodiazepines): dec cortisol (ur). TRICHLORMETHIAZIDE (also see thiazide diuretics): false¬ positive phentolamine and tyramine tests (an). TRICYCLIC ANTIDEPRESSANTS: Neuroleptic malignant syndrome, inc arrhythmias in hyperthyroid patients, inc/dec glucose, acne, inc alk phosphatase, gynecomastia, testicular swelling, breast enlargement, menstrual irregularity, galactorrhea (in females), inc/dec libido, painful ejaculation, impotence, nocturia, urinary frequency, dysuria, lactation (non-puerperal), vaginitis, leukorrhea, mastodynia, amenorrhea, inc prolactin, inc ADH, SIADH, inc norepinephrine, inc cortisol. TRIFLUOPERAZINE (see phenothiazines). TRIFLUPROMAZINE (see phenothiazines). TRILOSTANE: dec glucocorticoids, dec aldosterone, dec cortisol (ur), inc 17-KS (ur), inc ACTH, adrenal hypertrophy, inc adrenal adenoma(?), adrenal cortical hypofunction (in stress). TRIMEPRAZINE (see antihistamines). TRIMETHADIONE (also see paramethadione): attack of acute porphyria. TRIMETHAPHAN: inc histamine. TRIMETHOPRIM-SULFAMETHOXAZOLE: inc TSH, dec T4, dec free T„, inc alk phosphatase, inc BUN, inc creatinine, crystalluria, dec folate, dec Na*, impairs free water clearance, anorexia, pancreatitis, oliguria (xs), anuria (xs). TRIMIPRAMINE (see tricyclic antidepressants). TRIPELENNAMINE (see antihistamines). TRIPROLIDINE (see antihistamines). TRYPSIN: dec ionized Ca2* (an). TRYPTOPHAN: inc amino acids (an), inc chol (an), phosphaturia, inc uric acid (an), eosinophilia-myalgia syndrome. TUBOCURARINE: inc creatinine kinase, inc histamine, respiratory alkalosis, excessive salivation. TYRAMINE: inc amino acid (an), inc glucose, inc tyrosine (an), inc uric acid (an), inc urobilinogen (an). TYROPANOIC ACID: impairs conversion of T4 to T„ inc T., dec T3-

TYROSINE: inc bilirubin (an), crystalluria, inc uric acid (an), inc urobilinogen (an). URACIL MUSTARD: amenorrhea, impaired spermatogenesis, azoospermia, hair loss, inc alk phosphatase, inc bilirubin. UREA (also see osmotic diuretics): dec bilirubin (an), inc chol (an), inc creatinine (an), inc creatinine (ur) (an), inc ionized Ca2* (an), inc osmolality (an), inc urine osmolality (an), dec porphobilinogen (ur) (an), hypokalemia, hyponatremia, inc BUN, dec urobilinogen (ur) (an), inc urine volume, dehydration (xs), inc aldosterone, inc angiotensin II, inc PR A. UROFOLLITROPIN: stimulation of ovarian follicular growth, abnormal ovarian enlargement, multiple preg, breast tenderness, ectopic preg, hair loss. URSODEOXYCHOLIC ACID: hair thinning. VALPROIC ACID: inc GH, dec selenium, inc TSH, dec T4, dec free T4, inc alk phosphatase (xs), inc amylase, inc FFA (an), dec P(OH)butyraie, dec ketones, inc ketones (ur) (an), inc lactate, inc organic acids (ur), dec prolactin, inc pyruvate, dec free testosterone, hyperammonemia, dec spermatogenesis (exp), testicular atrophy

(exp), anorexia, weight loss, inc appetite, weight gain, transient hair loss, irregular menses, secondary amenorrhea, galactorrhea, parotid gland swelling, breast enlargement, hyperglycemia, hypocarnitinemia, edema, acute pancreatitis (xs). VANCOMYCIN: inc casts (ur), inc creatinine, nephrotoxicity (xs), dec creatinine clearance (xs), proteinuria, red man syndrome. VASOPRESSIN: inc ACTH, inc cortisol, inc GH, inc reabsorption of water, water intoxication (xs), SIADH (xs), inc corticosteroids, inc CPK, inc creatinine (xs), rhabdomyolysis (xs), dec Na* (xs), inc BUN (xs), dec urine volume. VIDARABINE (ADENINE ARABINOSIDE): fluid overload, anorexia, inc bilirubin, weight loss. VINBLASTINE: dec uric acid, aspermia, amenorrhea, anorexia, malaise, SIADH (xs). VINCRISTINE: dec osmolality, dec Na+, inc vasopressin, inc Na+ (ur), SIADH (xs), water intoxication (xs), inc uric acid, inc osmolality (ur), azoospermia, amenorrhea, uric acid nephropathy (xs), pain in the parotid gland, bone pain, anorexia, polyuria, dysuria, urinary retention, weight loss, alopecia. VINDESINE SULFATE: parotid pain, SIADH, alopecia, transient hepatic dysfunction. VINYL ETHER: inc bilirubin (xs), inc glucose, inc BUN (xs). VITAMIN A: inc alk phosphatase (xs), inc bilirubin (an), dec mI uptake, inc Ca2*, alopecia (xs), hypomenorrhea (xs), polydipsia (xs), polyuria (xs), hypercalcemia (xs). VITAMIN B COMPLEX: inc catecholamines (an), dec estrogens (ur) (an). VITAMIN B12: hypokalemia (xs), inc RBC requirements of K* with conversion of megaloblastic to normal erythropoiesis. VITAMIN C: false-positive urine glucose (xs), ppt of cystine/oxalate/urate renal stones (xs), dec triglycerides, inc oxalate (esp in renal failure). VITAMIN D: inc Ca2*, inc P04\ inc calculi (ur), inc chol (an), proteinuria (xs), inc BUN (xs), inc creatinine (xs), hypercalcemia (xs), metastatic soft tissue calcification (xs), generalized vascular calcification (xs), nephrocalcinosis (xs), hypercalciuria (xs), hyperphosphatemia (xs), muscle pain, bone pain, polyuria, polydipsia, anorexia, nocturia, mild acidosis, dec libido, hypercholesterolemia (xs). VITAMIN E: dec aminolevulinic acid (ur), dec uroporphyrin (ur), gynecomastia. VITAMIN K: inc bilirubin (in neonates or G-6-PD deficiency), inc catecholamines (an), inc 17-(OH)CS (ur) (an), inc porphyrins (ur), inc protein (ur). XANTHINE: inc chloride (ur), crystalluria, inc K* (ur), inc protein (an), inc Na‘ (ur), diuresis, inc urine volume. YOHIMBINE HC1: antidiuresis, skin flushing, sweating, penile erectile stimulation. ZALCITABINE: pancreatitis, anorexia, fatigue, dec weight, edema, inc amylase, jaundice, salivary gland enlargement, diabetes mellitus, hyperglycemia, dec Ca2*, impotence, hot flushes, hepatitis, jaundice, acne, alopecia, gout, polyuria, renal calculus, inc alk phosphatase. ZIDOVUDINE (AZT): diaphoresis, anorexia, acne(?), polyuria(?), urinary frequency(?). ZINC: significant dec HDL (xs), copper deficiency, dec alk phosphatase (an), inc Ca2+ (an), inc Mg2* (ur) (an). ZOLPIDEM TARTRATE: fatigue, lethargy, anorexia, palpitations, inc sweating, flushing, impotence, edema, hot flashes, dec weight, inc appetite, dec libido, hyperbilirubinemia, hyperglycemia, gout, hypercholesterolemia, hyperlipidemia, inc BUN, periorbital edema, thirst, menstrual disorder, vaginitis, breast pain, breast fibroadenosis, acne, dysuria, polyuria, renal pain, acute renal failure, micturition frequency.

Ch. 225: Reference Values in Endocrinology Principles and Practice of Endocrinology and Metabolism, Second Edition, edited by Kenneth L. Becker. J.B. Lippincott Company, Philadelphia, © 1995.

CHAPTER

225

REFERENCE VALUES IN ENDOCRINOLOGY D. ROBERT DUFOUR

Laboratory tests are widely used by endocrinologists in the diagnosis and monitoring of disease. On receiving the results of such tests, the first thing physicians do is check to see whether the results are "normal" by comparing them to a list of values prepared by the laboratory, which commonly are referred to as "normal ranges." Textbooks often provide such lists. Although comparing a test result to a published standard may seem simple, there are many considerations that may influence the interpreta¬ tion. In this chapter, instead of simply providing a list of normal values, the factors that may affect the interpretation of test results and common situations that may change test results are dis¬ cussed. Table 225-2, at the end of the chapter, lists common fac¬ tors that may influence the results of each of these tests.

REFERENCE RANGES—DO THEY MEAN “NORMAL”? DEFINITIONS OF NORMAL Although one review documented seven possible meanings for the word normal, to most endocrinologists and their patients, normal is synonymous with absence of disease.1 By corollary, ab¬ normal indicates the presence of disease, which has caused a change from the normal, healthy state. A second common mean¬ ing for normal, which is derived from statistics, is often used by scientists: a bell-shaped frequency distribution, in which 95% of all results are within 2 SD of the average value. Although these two definitions do not necessarily describe the same thing, they fre¬ quently are used interchangeably in medicine, particularly in in¬ terpreting laboratory results.2,3

REFERENCE VALUES All clinical pathology laboratories publish a list of reference values. Until recently, they were called tables of normal values, with the laboratory using the term normal to indicate the second definition given earlier. Reference value now is widely used to in¬ dicate that the value provides a reference, something to be used for comparison with a test result, rather than a declaration of values expected in normal, healthy persons.4 This subtle but im¬ portant difference is the source of much confusion among physi¬ cians seeking to interpret the results of laboratory tests. Less com¬ monly, reference values may be established for disease, such as expected values of glycated hemoglobin in persons with varying degrees of glycemic control. Because the principles and assump¬ tions used in establishing such reference values are similar, this type of reference range is not discussed further here. ESTABLISHMENT OF A REFERENCE RANGE

Reference ranges can be established in several ways. A sam¬ ple of suitable size is needed to guarantee the statistical validity of results. Usually, 100 to 200 persons constitute a sample large enough to be valid but small enough to be workable. For many

1957

difficult or expensive procedures, published reference ranges may be based on results from fewer than 20 persons. Representative Sampling. The first assumption is that the sample is representative of the population that ultimately will be tested. Most volunteers are hospital employees, blood donors, or medical students. None of these groups is necessarily represen¬ tative of the population that eventually will be examined.5 This is a particular problem in inner city and charity hospitals, in which the usual sources of volunteers are not likely to be from the same population as the patients. If the sample is not repre¬ sentative, the reference range may or may not be valid, but its validity cannot be tested. Absence of Disease. A second assumption is that there are no persons in the sample group with the diseases to be tested for. This is important only for tests that are used in distinguishing persons with disease from healthy persons. An example is the current widespread effort to screen the U.S. population for risk factors for coronary artery disease. From autopsy studies, it is known that there is a high incidence of atherosclerosis in persons without symptoms.6 Serum cholesterol is thought to be related to the development of atherosclerotic plaques/ 8 To develop a reference range for serum cholesterol levels to separate persons without atherosclerosis from those with atherosclerosis, it would be necessary to select a sample of persons without atherosclero¬ sis. This is not commonly done. Until recently, most laboratories used reference ranges derived from "normal" volunteers, many of whom actually had atherosclerosis. This led to extremely wide reference ranges in which virtually no one except those with fa¬ milial hypercholesterolemia had abnormal results.9 Currently, "reference" values for cholesterol are based on risk of develop¬ ment of coronary artery disease, rather than selection of "typical" values.10 (Other common disorders that may affect laboratory tests are diabetes, hypertension, and alcohol abuse.) Conditions of Testing. Although the method used for ob¬ taining samples is not commonly considered, differences in pa¬ tient preparation and the technique used for venipuncture can affect test results.11 Specimens from fasting patients have lower levels of certain constituents (e.g., glucose), and there are diurnal variations of certain other constituents (e.g., cortisol), but the effects of fasting and diet on most laboratory tests are ignored or unknown. If all volunteers are requested to come in after an overnight fast (a common instruction given by laboratories), then reference ranges will be valid only for comparing samples ob¬ tained under those conditions.5 In most clinical settings, patients are seen at other times of the day for blood drawing, and they may have results outside the reference range solely for that reason. In an elegant series of experiments, the effect of various forms of prevenipuncture position on test results was evalu¬ ated.12 Drawing blood after 30 minutes of standing and walking before the person sat down increased the apparent concentra¬ tions of proteins and protein bound molecules (which affects many of the tests related to endocrine evaluation) by 3% to 5% over those obtained after the same person had been sitting for 30 minutes. If the person had been supine for 30 minutes before venipuncture, there was a 5% to 10% decrease in the same con¬ stituents. Because the first condition describes the common pro¬ cedure for obtaining blood from outpatients, and the second de¬ scribes the usual method of obtaining blood from inpatients, different interpretations of results could easily be made. In virtu¬ ally all laboratories, reference ranges are derived using samples obtained from ambulatory persons, so that some results are 8% to 15% higher than expected for supine inpatients. Statistical Interpretation. MEAN AND STANDARD DEVIATION. The typical approach in evaluating the data is to consider the central 95% of all values as the reference range. In most laboratories, this is determined by calculating the mean and SD, and by defining the reference limits as the mean ± 2 SD. There are several problems with this seem¬ ingly simple statistical procedure. The assumption is that the data

1958

PART XVII: ENDOCRINE DRUGS AND VALUES

are graphically distributed in a bell-shaped fashion, the Gaussian or normal distribution. For many parameters, distribution of re¬ sults is not symmetric but is skewed to one side or the other.13 Often, the degree of skewing of the data is not enough to invali¬ date the assumption that values within 2 SD of the mean include 95% of all data points. Some statistical tests demonstrate whether the degree of skewing is too great to use this assumption.14 Many laboratories neither inspect the data for skewing nor use these statistical tests to determine whether skewing is too great; they simply define the reference range as the mean ± 2 SD. Figure 225-1 illustrates the consequences of this approach. If values are skewed toward higher concentrations, more than 5% of the sam¬ ple have results above the upper reference limit, and the converse is true for values skewed to lower concentrations. Even if valid sampling techniques are used, such statistical errors lead to in¬ correct reference limits. Evaluation of the sensitivity of several statistical techniques to differences in data distributions has shown that some are virtually unaffected by skewing of results.15 LIMITATIONS OF GAUSSIAN STATISTICS. Feinstein detailed an even more important problem of this method for defining limits of a reference range: Gaussian statistics describe the distribution of repeated measurements of the same parameter.16 For example, if 100 different scales were used to measure one person's weight, there would be a 95% chance that the actual weight would lie within 2 SD of the average value for all weights. In describing results obtained from populations, there is no valid statistical rea¬ son for selecting these limits as defining an expected range of normality. Once limits are set to include only the central 95% of all values as normal, then 5% of results from the sample are considered to be outside the reference limits, even though all per¬ sons in the sample originally were considered normal. Thus, if reference limits are used as a guide to what is normal in the med¬ ical sense, then 5% of results from the sample must indicate dis¬ ease. This same condition holds true for each test performed. If each test assays an independent variable, and results for each test are distributed randomly in the population, then the likelihood that n tests are within the reference range is (0.95)n. The likeli¬ hood (p) of all independent test values being within reference ranges (assuming that reference limits include 95% of all values) for different values of n is as follows: n = 1, p = 0.95; n = 2, p = 0.90; n = 6, p = 0.74; n = 10, p = 0.60; n = 12, p = 0.54; n = 15, p — 0.46; n = 20, p = 0.36; n = 24, p = 0.29. As n becomes larger and approaches the number of tests commonly included in screening profiles by many laboratories, most patients should

have at least one result outside the reference limits solely because of the chance distribution of results. This statistical fact frequently produces results outside refer¬ ence values, even for apparently healthy persons. The author has been using results of medical students' laboratory tests to illus¬ trate this phenomenon to the students for several years. In sam¬ ples taken from 597 healthy medical students, using reference values defined as within 2 SD of the average, only 65% of stu¬ dents had all "normal” test results, whereas 27% had one "ab¬ normal test result and 8% had more than one "abnormal" test result. Using the central 95% of the distribution as the reference values (because several tests showed statistically significant skewness), the results were similar (64% all "normal," 27% one "abnormal," 9% two or more "abnormal"), although in about 15% of students, the two methods disagreed on the number of abnormal" results. Several recent publications have highlighted this statistical phenomenon, and used it to suggest that wide¬ spread screening programs are unlikely to be beneficial, because most "abnormal" results are probably the result of random sta¬ tistical occurrences.1718 The statistical assumptions of inde¬ pendence become more complicated, however, because many commonly measured tests change in parallel, rather than inde¬ pendently (i.e., sets of compounds such as serum electrolytes; calcium, phosphate, and magnesium; blood urea nitrogen and creatinine; and triiodothyronine [T3], thyroxine [T4], and thyroid-stimulating hormone [TSH]). Another assumption limiting the use of reference values is that results are randomly distributed in the population) and that an individual is no more likely to have any one result than an¬ other. Many studies have shown that each individual maintains concentrations of many critical parameters within an extremely narrow range and, thus, results would not be randomly distrib¬ uted in the population. 1Q~21 The ratio of average variation within an individual to the variation within a population has been termed the index of individuality; an index below 1.4 suggests that standard reference ranges will be insensitive markers of signifi¬ cant changes in the condition of a person. As an example, the range of cholesterol values seen in the medical students (central v5 /o of values) is from 126 to 252 mg/dL. In contrast, the average day-to-day variation in cholesterol levels in a person with an av¬ erage blood cholesterol level is about 6% (1 SD). Thus, significant changes in serum cholesterol can occur without producing an "abnormal" result. Other common tests with small individual variation include calcium, alkaline phosphatase, and thyroid function tests. IMPLICATIONS OF A REFERENCE RANGE

The usefulness of reference ranges depends on the tech¬ niques used to establish them. Even if all of the influences have been considered, it does not follow that a result within the refer¬ ence range indicates health or that a result outside the reference range indicates disease. Because the reference range is a descrip¬ tive statistic of the sample (and, if valid sampling techniques were used, of the population), then results outside the reference range indicate only that an individual is not from the same population. This could be due to disease, to population differences, or to physiologic variations in the individual. Similarly, a result within the reference range does not guarantee health, because some dis¬ eases may have a high enough incidence in the population that the test cannot separate healthy and diseased individuals. These observations have led to several alternatives to reference ranges.

MEDICAL DECISION LEVELS TEST RESULTS FIGURE 225-1. This skewed distribution of test results is typical of the pattern observed with many serum constituents. Using the mean ± 2 SD as reference limits would falsely classify results between 0 and 5 as nor¬ mal and results between 40 and 45 as abnormal.

Medical decision levels are cutoff points that reliably indi¬ cate disease or the need for additional action.22 The limits for these values usually are wider than reference ranges, so that finding a result beyond these limits as a result of chance alone would be uncommon. Because they indicate the need for medical intervention, there is less reason to consider qualifying factors in

Ch. 225: Reference Values in Endocrinology

1959

interpreting results. Tables of medical decision levels are found in several articles, and one book gives medical decision levels for 137 tests.23 Decision levels may prove useful for analytes, which are commonly subject to minor, physiologic variations. SENSITIVITY AND SPECIFICITY

Sensitivity and specificity are terms commonly used in eval¬ uating the usefulness of medical tests. In their common defini¬ tions, sensitivity refers to the ability to detect disease, and speci¬ ficity refers to the ability to exclude disease. One limitation of medical decision levels is that, although they are highly specific for disease, they tend to be less sensitive and are of less use in screening persons for early stages of a disease process that pro¬ duces gradual changes in test results. Figure 225-2 shows the effect of changing the reference limits of a test to improve either sensitivity or specificity: it is impossible to improve simulta¬ neously the sensitivity and specificity of a given test. RELATIVE OPERATING CHARACTERISTIC CURVES

Relative operating characteristic (ROC) curves are a graphic depiction of sensitivity and specificity over a continuous range of cutoff points or decision levels.24 Typically, sensitivity is plotted in an ascending fashion on the y-axis and specificity is plotted in a descending fashion on the x-axis. Such graphs are useful in selecting optimal decision points to use in diagnosing disease, and for comparing the performance of diagnostic tests. The point closest to the upper left hand corner of the graph (perfect perfor¬ mance) correctly classifies the greatest percentage of patients. For comparison of two or more tests, the curve closer to the upper left hand corner performs better in clinical usage. Decision points can be selected to give high sensitivity or high specificity, de¬ pending on the use of the test. In using medical decision levels, the specificity is increased to virtually 100%, meaning that all abnormal results indicate disease. Figure 225-3 illustrates a typi¬ cal ROC curve for a diagnostic test, with several possible cutoff points indicated, showing why medical decision levels have a lower sensitivity than other possible decision levels. A logical approach would be to use ROC curves to define an appropriate decision level to use for any purpose, such as screen-

FIGURE 225-3.

This relative operating characteristic curve illustrates the results obtained in several screening programs for primary hyper¬ parathyroidism. Point A represents a serum calcium level of 10.0 mg/dL; all patients with primary hyperparathyroidism continuously have serum calcium levels above this value, but about 30% of normal persons have one or more values above this. Point B represents the upper reference limit of 10.5 mg/dL. About 90% of serum calcium values from patients with primary hyperparathyroidism fall above this level, and about 5% to 8% of values from normal persons are above it, usually due to hemoconcentration. Point C is the medical decision level of 11.0 mg/dL recom¬ mended by Statland.24 Only 70% of values from patients with primary hyperparathyroidism are above this level, but it reliably indicates an ele¬ vated serum calcium value of clinical significance.

ing for disease or confirming a diagnosis, but there have been many difficulties. First, production of an ROC curve requires knowledge of the sensitivity and specificity of a test for a disease in a population; for most disorders, these are unknown.25 Sec¬ ond, the use of sensitivity and specificity has been criticized, be¬ cause values usually are derived by applying the test to patients with known disease, which was confirmed by some other tech¬ nique of equal or greater specificity and sensitivity. The original results for sensitivity and specificity are unlikely to remain valid when the same test is used for patients with lesser manifestations of disease.26 INTERLABORATORY DIFFERENCES

Because laboratories use many different techniques for mea¬ suring most analytes, different cutoff values may be needed for different laboratories. Thus, it will be some time before there are enough universally applicable formulas available for diagnosis of disease by laboratory tests alone.

INDIVIDUAL REFERENCE RANGES

Glucose Concentration (mg/dL) FIGURE 225-2.

The distribution of fasting glucose results in patients with normal glucose tolerance (solid line) and "diabetic" glucose toler¬ ance (dotted line) illustrates the impossibility of improving both sensitiv¬ ity and specificity simultaneously. Using a fasting glucose of 140 mg/dL (solid bar) to predict abnormal glucose tolerance excludes all persons with normal glucose tolerance (specificity 100%), but it misses 40% of those with abnormal glucose tolerance (sensitivity 60%). Using a fasting glu¬ cose of 115 mg/dL (open bar), sensitivity is improved to 100%, but speci¬ ficity falls to 75%. With any value between these two points, specificity improves and sensitivity falls. Moving below 115 or above 140 mg/dL lowers specificity or sensitivity, respectively, without improving the other component.

Another approach is the use of individual reference ranges.42' The concentrations of many analytes are closely regulated in most individuals, so that the variation within a person is much smaller than the variation between persons.'421 With the feasi¬ bility of doing widespread population screening for different dis¬ ease states, and the common practice of doing "profiles" of labo¬ ratory tests as part of periodic physical examinations, there exists a database for determining a person's typical concentrations of several analytes. If the results of laboratory tests are available on computers, it is easier to perform this analysis. One way in which these ranges can be useful is in diagnosing myocardial infarction. In a commonly used approach, standard reference ranges are em¬ ployed and serum isoenzyme determinations of creatine kinase

1960

PART XVII: ENDOCRINE DRUGS AND VALUES

are obtained only if the enzyme levels exceed the reference limit. In several studies, many patients with apparent myocardial in¬ farction had extremely low baseline values for serum creatine ki¬ nase and showed acute rises in the level of this enzyme that did not exceed the upper reference limit.28,29 Thus, comparing a pa¬ tient's test results to his or her own values improves the sensitiv¬ ity of creatine kinase measurements for diagnosing myocardial infarction.30 The use of individual reference ranges should better define the expected limits of normal physiologic changes and provide the ultimate in sensitivity for early detection of disease. As dis¬ cussed earlier, intraindividual variation is generally much less than the variation seen in the population.31 The major impedi¬ ments are the extremely high cost of screening the population for every conceivable test and the enormous amount of data storage capacity required. Another possible problem is the lack of accept¬ able reference ranges for allowable changes in an individual. Al¬ though the studies cited provide approximate reference ranges for intraindividual variation, they are not all-inclusive, and there is a wide difference in the values given. Moreover, there are data to suggest that intraindividual variation is greater in persons with certain disease processes.32 A range that may detect early changes in healthy persons may be a false-positive indicator of impending complications in persons with disorders such as diabetes. Despite these problems, the use of individual reference ranges probably will increase.

PHYSICAL AND EMOTIONAL STRESS

Exercise leads to the release of catecholamines, prolactin, and muscle-specific enzymes into the circulation.39 Stress leads to catecholamine release; prolonged stress can cause marked changes in the concentrations of various blood lipids and hormones. AGE

The values of many serum constituents change markedly in concentration during a person's lifetime. Although it is accepted that values may differ in children (see Chaps. 9, 20, 46, 69, 81, 88 through 90, 155 and 192), changes also occur at other times in life. For example, testosterone and renin decrease with increasing age in adults, and alkaline phosphatase and parathyroid hor¬ mone (PTH) continue to increase in persons older than 50 years. (Also see Chap. 193.) RACE

For many commonly measured parameters, values in per¬ sons of African ancestry are different from those in persons of European ancestry; differences in other races have not been eval¬ uated as carefully. For example, African Americans tend to have higher values for high-density lipoprotein cholesterol and PTH, but lower values for vitamin D metabolites and renin. SEX

COMMON CAUSES OF “ABNORMAL” ENDOCRINE TEST RESULTS Although reference ranges often are used to define "nor¬ mal," it is common to see results outside reference limits without any evidence of an underlying disease process. In this section, some frequent causes of variation in laboratory test results are described; a more complete listing is available in the table at the end of this chapter.

PHYSIOLOGIC INFLUENCES ON ENDOCRINE TEST RESULTS The effects of normal physiologic changes in a patient are not often considered in interpreting laboratory results, yet they are commonly the explanation for an unexpected test result. DIET

Occasionally, dietary factors are responsible for unexpected changes, either from the ingestion of food (e.g., transient alkalo¬ sis, intracellular shifts in phosphate, release of intestinal alkaline phosphatase into the circulation, elevated levels of hormones) or from the chemical substances in food that cause physiologic changes (e.g., caffeine-induced catecholamine release).33,34 DIURNAL AND PULSATILE RHYTHMS

Diurnal variation is a well-known phenomenon for cortisol and adrenocorticotropic hormone, but lesser degrees of diurnal variation also are found for other hormones, including prolacun, TSH, and testosterone.35'37 Marked diurnal variation in serum iron concentrations is a common finding, and many hormones, such as gonadotropins, growth hormone, and prolactin, are re¬ leased in a pulsatile fashion, making it difficult to interpret a sin¬ gle test result.38 For measurement of most pituitary hormones, pooling several serum samples and assaying the pooled specimen provides a more accurate indication of average hormone concen¬ tration and pituitary function.

There are obvious differences in sex hormones and prolactin, but women and men often have different concentrations of many of the analytes commonly measured. Serum levels of free T4 and copper are higher in women, but lower values for renin, aldoste¬ rone, and most blood lipids also are the rule. MENSTRUATION AND PREGNANCY

During the normal menstrual cycle, in addition to the obvi¬ ous changes in estrogens and progesterone, vasopressin, prolac¬ tin, and PTH increase. The onset of menstruation causes a fall in serum sodium and phosphate levels, and a rise in renin and aldosterone concentrations. Pregnancy induces some unexpected changes: levels of PTH, calcitonin, cortisol, and aldosterone in¬ crease, and fasting levels of glucose and glycohemoglobin (he¬ moglobin A1C) fall. The effects of pregnancy may last long after the baby is delivered; recent studies have shown lower levels of prolactin and dehydroepiandrosterone in women who have borne children in comparison to those who have never been pregnant. HEIGHT AND WEIGHT

A person's height and weight are related to the concentra¬ tions of several substances. In children, there is a positive corre¬ lation between height and serum alkaline phosphatase levels. Weight is much more closely associated with the concentrations of several parameters, especially in obese persons, who have higher serum concentrations of cortisol, insulin, and glucagon, but lower than normal levels of gonadotropins and sex hormone¬ binding globulin. Weight loss in obese persons causes changes, such as a fall in renin and aldosterone levels (see Chap. 125). ALTITUDE

Changes in the concentrations of many analytes are found in persons living at altitudes above 5000 ft. Although some of these changes are transient, occurring only during the process of acclimatization, others appear to persist. Persons living at these heights tend to have higher levels of erythropoietin and lower levels of renin, angiotensin II, and aldosterone.

Ch. 225: Reference Values in Endocrinology

EFFECTS OF DRUGS ON ENDOCRINE TEST RESULTS There are two mechanisms for drug effects on laboratory tests.43 The first is a direct pharmacologic effect of the drug, such as hypokalemia due to diuretic therapy. Although most endocri¬ nologists are familiar with this particular effect, there are many unfamiliar drug effects. For example, anticonvulsants increase al¬ kaline phosphatase (and related enzymes such as 7-glutamyltranspeptidase), prolactin, and vasopressin levels, but decrease total and free T4 and 25-hydroxyvitamin D levels, as well as uri¬ nary excretion of corticosteroid metabolites.44 A second type of drug interference results from crossreaction in the assay. Two common examples are phenothiazines, which crossreact in some assays for urinary metanephrine, and certain cephalosporins, which crossreact in many assays for creati¬ nine. 43,46 Usually, information on the medications being taken by each patient tested is not given to the laboratory; even if this were available, it would be virtually impossible to screen all test re¬ quests manually to detect possible drug-test interferences. How¬ ever, with the increasing use of computers, it should be possible to construct a program to review the pharmacy record for each patient and search for drug interferences when abnormal results are encountered. Several comprehensive lists of drug effects on laboratory tests are available,47-48 and a compendium of drug effects on endocrine laboratory tests is provided in Chapter 224.

HEMOCONCENTRATION Hemoconcentration causes an increase in proteins (e.g., al¬ bumin) and, consequently, in protein bound substances in the blood. The common causes of hemoconcentration are dehydra¬ tion, postural differences, and the use of tourniquets during blood collection, but evaporation of serum after collection may produce the same effect. Ambulatory patients have a mild degree of relative hemoconcentration as a result of the shift of extracel¬ lular fluid from intravascular to extravascular locations, caused by the increased hydrostatic pressure found in the upright posi¬ tion.12 This causes an increase of 3% to 5% in the concentration of proteins and protein bound substances (e.g., some hormones, lipids, and ions such as Mg, Ca, and Fe). A similar hemoconcentrating effect is produced by leaving a tourniquet on for as little as 40 seconds while drawing blood.12 The suggested approach is to use a tourniquet only after a vein has been located and the skin has been prepared; longer use can cause 5% to 10% hemocon¬ centration. Fist clenching during blood collection, with a tourni¬ quet applied, leads to leakage of muscle contents, especially po¬ tassium, which can increase by 1 to 1.5 mmol/L in as little as 1 minute. The combined effects of posture and tourniquet use may cause a 10% to 20% increase in the apparent concentration of proteins. In one study, 15% of all persons evaluated for hyper¬ calcemia eventually were found to have normal serum calcium levels; hypercalcemia was artifactual as a result of concentration of serum proteins.49 In the author's laboratory, about 5% to 10% of persons with "hypercalcemia" have a serum albumin level greater than 4.5 g/dL on initial study; usually, their calcium level is within the reference range if their blood was collected (without prolonged use of a tourniquet) after they sat for 30 minutes. In a year, two patients were admitted for the evaluation of "hyper¬ calcemia," which was found to be caused by hemoconcentration.

CHANGES AFTER COLLECTION OF SPECIMENS Difficulties occasionally arise from changes that occur in the test tube during or after specimen collection. Some of the more common specimen-related problems include hemolysis, which increases the apparent concentration of all abundant substances within cells, such as potassium, phosphate, magnesium, and en¬ zymes; and delay in transport of the specimen to the laboratory,

1961

which allows utilization and exhaustion of glucose, after which the cells leak their intracellular contents.50-51 Less commonly, ex¬ tremely high white blood cell or platelet counts cause difficulties; the former increases the rate of glucose use, and the latter leads to the release of potassium during coagulation.52-53 In rare instances, there is an interaction between a substance in the collection tube and the patient's blood that causes artifactual abnormalities, such as an increase in potassium induced by heparin in patients with extremely high lymphocyte counts.54 Renin levels increase with storage in ice water, as a result of the conversion of prorenin to renin.55

CLERICAL AND ANALYTIC ERRORS A final source of unexpected test results may be the labora¬ tory itself if the results reported are not matched to the correct patient. Although all laboratories strive to minimize errors, such mistakes do occur. Clerical errors in specimen identification, which can occur at any time from collection to final reporting, are the single most common cause (25%) of erroneous results.56 Less commonly, actual errors in performing the test cause incorrect results. Explainable causes of abnormal laboratory test results al¬ ways should be considered. These factors are likely if the result is only minimally outside the reference limits; if there is evidence of hemoconcentration, such as a serum albumin level above the reference limit; if patients are receiving multiple medications; or if results from the current specimen differ markedly from previ¬ ous results in a patient who is clinically stable. In any of these circumstances, it is best to contact the laboratory and submit a new specimen. Many reference laboratories perform repeated testing at no charge or at a reduced rate to maintain good cus¬ tomer relationships and to document possible causes of unex¬ pected results.

METHODS OF ANALYSIS AND THEIR LIMITATIONS Endocrinologists need to be aware of several common meth¬ ods used to measure the concentrations of relevant compounds in the blood. In some laboratories, two or three different methods may be available to measure the same analyte. The method used may depend on the time of day the specimen is received, because some methods may be easier to perform and, thus, used for emer¬ gency testing. Occasionally, this may lead to differing results, be¬ cause interfering substances may not react identically to the tested compound and may not have the same effect on apparent concentration. For example, one method used for bicarbonate testing shows a positive interference from salicylate, whereas most commonly used methods do not show any cross reactions. If bicarbonate levels were determined using the former method, there would be no anion gap or a negative anion gap, which would lead to markedly different interpretations of the patient's condition. No method is completely free of all interference or abso¬ lutely specific for any compound. This section reviews the most common techniques used in laboratories and mentions some difficulties encountered in using these methods. Sensitivity and specificity refer, in this section, to analytic sensitivity (ability to detect a small amount of a substance) and analytic specificity (ability to detect a substance in the presence of interfering compounds).

SPECTROPHOTOMETRY Spectrophotometry and its variants are the techniques used for most simple analyses. A spectrophotometer is an instrument that allows light of a specific wavelength to pass through a solu-

1962

PART XVII: ENDOCRINE DRUGS AND VALUES

tion to a detector. Spectrophotometric techniques rely on a direct linear relationship between the concentration of a substance and the amount of light absorbed as it passes through the solution. This relationship, called Beer's law, holds true when substances are present in pure form in an aqueous solution. In biologic fluids, the multitude of substances present poses a difficult problem for the analyst. If a substance is strongly colored and present in high concentration, direct measurement of the amount of light ab¬ sorbed can be used; this technique is used for hemoglobin deter¬ minations and for bilirubin measurement on some instruments. For most substances, however, this simple approach does not work, because many other compounds absorb light at the same wavelength. The most common approach used to eliminate these interferences is to combine the substance of interest with another compound to give a highly colored reaction product that will absorb light at an order of magnitude greater than that of any interfering substances. For many analytes, such as glucose, calcium, and phosphate, this step is enough to give the measure¬ ment adequate specificity. For example, glucose combines with o-toluidine to give a product with an intense blue color. The ap¬ parent concentration of glucose measured by this reaction is within 10% of the value obtained using the accepted reference method.57 For other substances, the method is specific enough to use for routine analyses, but some commonly encountered com¬ pounds also react. An example is the reaction of creatinine with picrate, known as the Jaffe reaction, a method used by most lab¬ oratories to measure creatinine.58 In urine and in most sera, the method is an accurate approximation of creatinine concentration. Ketone bodies cross react in the most commonly used application of this method. In patients with alcoholic or diabetic ketoacidosis, it is common for the apparent concentration of creatinine to be markedly elevated, leading to a false perception of renal insuffi¬ ciency59 (Fig. 225-4). For other substances, such as urinary steroid and catecholamine metabolites, many drugs crossreact, and for vanillylmandelic acid, food substances crossreact, making the in¬ terpretation of spectrophotometric methods difficult at best.

ENZYMATIC METHODS

In cases where interfering substances are commonly en¬ countered, simple chemical reactions often are not adequate. Be¬ cause enzymes are similar to antibodies in having a site that rec¬ ognizes a specific structural or chemical sequence, they tend to be more specific than simple chemical reactions. Enzymatic proce-

CREATININE IN KETOACIDOSIS

dures do not eliminate all interferences; just as an antibody may crossreact with substances having a structure similar to its target antigen, an enzyme may show similar traits. An example is the crossreaction of isopropanol, commonly used to prepare the skin for venipuncture, in the measurement of ethanol by alcohol de¬ hydrogenase; this has caused contention over evidence involving persons accused of driving while intoxicated.60 Most enzyme measurements involve a sequence of reactions, and only the final product is measured. If another substance reacts in one of the steps or interferes with one of the reactions, then the result is inaccurate. This is an occasional problem with urine that contains high concentrations of ascorbic acid, an antioxidant that prevents the development of the colored product used for detecting glucosuria with glucose oxidase test strips.61 ATOMIC ABSORPTION SPECTROPHOTOMETRY

The most specific spectrophotometric method is atomic ab¬ sorption spectrophotometry, which uses a lamp containing a strip of the metal being measured. Atomic absorption is both ex¬ tremely sensitive and specific for the elements measured and is a reference technique for the determination of the true concentra¬ tions of metals such as calcium and magnesium. It can be used only to determine the concentrations of metals, limiting its appli¬ cability, and the lengthy preparation time limits the number of specimens that can be analyzed. The extremely low concentra¬ tions of some trace metals makes the measurements highly de¬ pendent on careful technique to prevent contamination, which can occur from such diverse sources as rubber stoppers on collec¬ tion tubes, wooden applicator sticks, and the glass used in the collection of blood or the preparation of the specimens.62

ELECTROCHEMISTRY Another common technique is electrochemistry, in which molecules or ions either produce a chemical reaction that gener¬ ates electrons or interact with a selective membrane and create a difference in electrical potential. Electrochemical methods are commonly used for blood gases and electrolytes; they are highly specific for the substance being measured. To prevent interfer¬ ence, most electrochemical methods measuring sodium involve the dilution of specimens before measurement; thus, they mea¬ sure the concentration of electrolytes in plasma. In normal situa¬ tions, plasma is composed of 93% water and 7% solids, such as proteins and lipoproteins. In contrast, the body regulates sodium activity, which is related more closely to concentration in the wa¬ ter phase than to total plasma concentration. In normal situa¬ tions, there is little practical importance to this distinction. How¬ ever, in situations where protein or lipid makes up a larger percentage of plasma, such as in multiple myeloma and in severe hypertriglyceridemia, methods that measure sodium concentra¬ tion in plasma produce a falsely low result, termed pseudohypo¬ natremia. (This phenomenon also is observed in older flame pho¬ tometric techniques, which also required specimen dilution). Some newer instruments, especially those using whole blood measurements as are commonly found in critical care settings, measure sodium activity directly without dilution, so pseudohy¬ ponatremia does not occur.63

IMMUNOLOGIC METHODS

FIGURE 225-4. Changes in blood urea nitrogen (BUN) and creatinine seen in a patient with diabetic ketoacidosis. Point A represents the time at which serum ketones began to rise, and point B represents the last time that serum ketones were positive at a dilution of 1:32 or greater. At point C, ketones were no longer detectable. Changes in serum creatinine par¬ allel changes in ketones, but BUN remains virtually unchanged during the entire episode. Because the chemical reaction used in most creatinine assays is nonspecific, ketone bodies produce the same colored product.

Because antibodies have relatively high specificity in their reactions and because they or their targets can be labeled with radioisotopes, fluorescent molecules, or enzymes to increase sen¬ sitivity, immunologic methods are ideal for measuring com¬ pounds in extremely low concentrations. Yalow published a review of radioimmunoassay and its limitations; similar con¬ siderations apply to other types of immunoassay.64 An illus¬ tration of the principles of immunoassay is given in Figure

Ch. 225: Reference Values in Endocrinology

A Antibody A Antigen * Label

1963

constituent atom, such as T3 and T4, many antibodies lack speci¬ ficity in reactivity. Three common examples are the antibody for cortisol, which cross reacts with endogenous and exogenous glu¬ cocorticoids; the antibody used to detect amphetamine in urine, which cross reacts with many prescription and nonprescription drugs having a structure similar to amphetamine; and the anti¬ body to digoxin, which crossreacts with inactive digoxin metab¬ olites and endogenous digoxin-like substances.65-67 POLYCLONAL AND MONOCLONAL ANTIBODIES

A

B

FIGURE 225-5. The common feature of all immunoassays is that a lim¬ ited amount of labeled antigen competes for antibody binding sites with unlabeled antigen present in the standards or in a patient's serum. A, In homogeneous immunoassays, the label behaves differently if bound to antibody or if free within solution; therefore, no separation step is neces¬ sary, simplifying the measurement. This is the principle of enzymemultiplied immunoassays (EMIT) and fluorescence polarization inhibi¬ tion assays, which are the simplest immunoassay techniques to perform. B, In heterogeneous immunoassays, the remaining free labeled antigen must be separated from that bound to antibody before measurement. This is most often accomplished by precipitating unbound antigen by binding it to a nonspecific absorbent, such as charcoal or a resin; alterna¬ tive methods include precipitating antigen-antibody complexes and fix¬ ing antigen or antibody to a solid medium, such as the sides of a test tube or small beads. This methodology is typical of radioimmunoassay (R1A) and fluorescence immunoassay (FIA). C, Antibody may be labeled in¬ stead of labeling the antigen; this is the principle of immunometric meth¬ ods, such as enzyme-linked immunosorbent assay (ELISA) and immunoradiometry. The major advantages are that antibodies are generally easier to label and that sensitivity and specificity can be improved by using two antibodies.

RADIOIMMUNOASSAY AND OTHER IMMUNOASSAYS

The basic principle underlying immunoassays is that a la¬ beled compound competes with unlabeled compound in the pa¬ tient's serum for a limited number of binding sites on the anti¬ body molecules. In radioimmunoassay, the label is a radioactive isotope, usually iodine or tritium; however, the label also could be a fluorescent compound, as in fluorescence immunoassays or fluorescence polarization inhibition assays, or an enzyme, as in enzyme multiplied immune technique. The higher the concen¬ tration of unlabeled compound in the patient's serum, the less labeled compound will bind to the antibody. After an incubation period to allow for equilibrium, the amount of label attached to the antibody is measured. In many methods, a separation step is required to remove any residual, free labeled compound; such methods are called heterogeneous, because they measure label in only one of at least two separate specimens. With some labels, the bound and free labeled compound behave differently, so that no separation step is required; such methods are termed homoge¬ neous assays. In a similar method, the label may be attached to an antibody, or antibodies from two different species may be used. These methods are immunometric assays. Such "sandwich” methods are commonly used if the antigen is difficult to obtain in the pure form or is difficult to label without changing the reaction between antigen and antibody.

Generally, antibodies against hormones are prepared either by immunizing an animal with the hormone bound to an immu¬ nogen, by using adsorption to remove antibodies to the immuno¬ gen (used with small molecular weight substances that are poorly immunogenic by themselves), or by using the purified hormone. Different species of animals and different animals within the same species may recognize different antigenic determinants, which may mean that the antibodies react differently when used for testing. This is a common problem with peptide hormones, which have so many possible antigenic determinants that each antibody often reacts differently, resulting in a different reference range for each antibody-dependent method.68 Monoclonal antibodies have the potential to alleviate some of these difficulties, because limitless amounts of a monoclonal antibody can be made, allowing continuous use of an antibody that reacts with a highly specific antigenic determinant of the hormone.69 Not surprisingly, there already has been at least one report of a problem unique to monoclonal antibodies. Some pa¬ tients' sera contain antibodies to mouse immunoglobulin (most commonly, mouse cells are used to manufacture monoclonal an¬ tibodies), which may cross react in the final reaction.'11 This prob¬ lem can occur with any immunometric assay, such as TSH, hu¬ man chorionic gonadotropin, and tumor markers. Another problem involves the use of antibodies that sepa¬ rate bound from free forms of hormones, such as T4. Some of the antibodies used for assays of free T4 have a higher affinity for T4 than do the thyroid binding proteins. In the euthyroid sick syndrome (see Chap. 36), in which there is thought to be a difference in protein binding affinity for T4, there is a marked discrepancy in results for different immunoassays for free T4 measurements when compared to each other and to the reference equilibrium dialysis method/1- " ANTIGENICITY VERSUS BIOACTIVITY

Antibodies detect the presence of an antigen; they say noth¬ ing about the bioactivity of the antigen being measured. Al¬ though this is not likely to pose a problem for small hormones such as T4, it is of considerable importance in measuring peptide hormones that may circulate as large molecular weight inactive prohormones or that are cleaved in the circulation to metabolites having little or no bioactivity. This problem became apparent early in the development of immunoassay, when it was noticed that most patients with lung carcinomas had elevated serum ad¬ renocorticotropic hormone levels, but that they usually had no evidence of adrenal hyperfunction. This was caused by a larger, inactive form of the hormone that crossreacted in the assay (see Chap. 213).74 Other hormones, such as calcitonin, insulin, and glucagon, also have circulating inactive precursors. With pitu¬ itary dysfunction, TSH peptide deficient in carbohydrate may be produced; although this has reduced bioactivity, it reacts better than does intact TSH in immunoassays. The commonly used midmolecule PTH assay predominantly measures an inactive fragment that accumulates if renal function is impaired.'"

ANTIBODY SPECIFICITY

COMPETITIVE PROTEIN BINDING AND RADIORECEPTOR ASSAYS

The first problem in interpretation involves antibody speci¬ ficity. Although some antibodies are highly specific and can differentiate compounds that vary only in the presence of a single

Two other techniques are similar in principle to radioimmu¬ noassay. Competitive protein binding uses a natural serum car-

1964

PART XVII: ENDOCRINE DRUGS AND VALUES

rier protein, such as corticosteroid-binding globulin or thyroid¬ binding globulin, and a labeled hormone that "competes" for the same binding sites as does the hormone in the patient's serum; an example is the Murphy-Patee test for T4. This technique is virtually limited to steroid and thyroid hormones, because pep¬ tide hormones seldom have carrier proteins. Competitive protein binding assays are subject to the same interferences as are immu¬ noassays. Moreover, they usually are less specific, showing cross¬ reactions with more related compounds than do immunoassays. In radioreceptor assays, the binder is a cellular receptor, ei¬ ther in intact cells or purified in a subcellular fraction. Radiore¬ ceptor assays have the theoretic advantage of recognizing only the active part of the hormone, thus eliminating one of the limi¬ tations of immunoassays. Radioreceptor assays can be used for steroid, peptide, and catecholamine classes of hormones, and they have virtually the same applicability as immunoassays. Fur¬ thermore, both naturally occurring and synthetic hormones can be measured with radioreceptor techniques. The basic principle is the same as in immunoassay: competition for binding sites be¬ tween radioactively labeled hormone and unlabeled hormone in the patient's serum. Despite these theoretic advantages, radioreceptor assays have not found widespread applicability, mainly because they lack specificity. For example, TSH, luteinizing hormone, and hu¬ man chorionic gonadotropin all combine with TSH receptors; prolactin, growth hormone, and human placental lactogen all bind to cellular prolactin receptors; and both PTH and PTHrelated protein bind to PTH receptors. Moreover, the small num¬ ber of binding sites often reduces sensitivity below that which can be achieved with immunoassays. Because it usually is easier to obtain naturally occurring compounds (e.g., carrier proteins) than to manufacture new ones (e.g., antibodies), competitive pro¬ tein binding and radioreceptor assays tend to become available first. Generally, they are replaced after antibodies with sufficient sensitivity and specificity become available, as in the case of T4.

ASSAYS FOR FREE HORMONE Because it is the free hormone that often is the bioactive form, and protein bound hormones commonly are an inactive reservoir, great attention has been paid to developing assays for free hormone. There are difficulties in developing antibodies that accurately measure free hormone in the presence of much larger concentrations of protein bound hormone. This has led to a search for other body fluids that might accurately reflect free hor¬ mone levels, and it has been discovered that salivary hormone levels correlate extremely well with free plasma levels for most steroid hormones analyzed. Salivary hormone concentrations are independent of the rate of production of saliva, and show the same circadian and other rhythmic variations as do plasma hor¬ mone concentrations. These assays have not gained wide accep¬ tance but are likely to become more important in the future.76

CHROMATOGRAPHY Chromatographic methods use differences in the solubility of compounds to achieve their separation (Fig. 225-6 and Table 225-1). They frequently are the only or the best means of sepa¬ rating and measuring substances that are closely related structur¬ ally. Although such methods are reliable, accurate, specific, and highly sensitive (orders of magnitude more sensitive than immu¬ noassays when coupled to mass spectrographic detectors), they are not commonly used in clinical laboratories because of their relatively high cost per test, the often extensive sample prepara¬ tion required before analysis, and the small number of specimens that can be analyzed each day. They remain the only method available for analyzing some compounds, and often are used in the preliminary purification of closely related substances, such as the vitamin D metabolites, steroid metabolites, and catechol¬ amine metabolites.

□ Stationary phase A Compound A • Compound B

FIGURE 225-6. In all chromatographic methods, substances are sepa¬ rated based on whether they have a greater affinity for the stationary or the mobile phases. Compound A is similar to the stationary phase in one physical property ("straight sides") and is separated from compound B as the mobile phase passes over the stationary phase.

BIOASSAY Bioassay was one of the first modes of testing used in endo¬ crinology, but more easily performed techniques, such as immu¬ noassay, have almost totally replaced this method. However, there has been renewed interest in new and highly sensitive in vitro bioassays for hormones. In a typical in vitro bioassay for a hormone activating adenylate cyclase, the change in cyclic aden¬ osine monophosphate in the cell culture medium is used as an indicator of active hormone concentration. The advantage of bio¬ assays is that they directly measure active hormone. In vitro bio¬ assays have been developed for most hormones.77 An example is a bioassay for PTH using cells from an osteosarcoma; the test for thyroid-stimulating immunoglobulins is, in effect, a bioassay, because the final product measured is cyclic adenosine mono¬ phosphate induced by the antibody-TSH receptor interaction. Such assays are not yet commercially available for most hor¬ mones, but they could replace immunoassays after they have been validated by wider use. Their theoretic advantage is that they should detect only active hormone. However, at least in the case of PTH, PTH-related protein can bind to the PTH receptor and activate adenylate cyclase.78,79

USE OF LABORATORY TESTS IN DIAGNOSIS Although the major purpose of this chapter is to familiarize the endocrinologist with the techniques used in laboratories that can influence the interpretation of laboratory tests, it would not be complete without a brief discussion of the uses of laboratory tests in endocrine diagnosis.

“ABNORMAL” TEST RESULTS—BAYES’ THEOREM Not all endocrine results that fall outside the reference range indicate disease. The physician then must answer this question: What is the likelihood that this result indicates a particular dis-

Ch. 225: Reference Values in Endocrinology

1965

TABLE 225-1 Types of Chromatographic Separation Type of Chromatography

Stationary Phase

Mobile Phase

THIN LAYER

Polar

COLUMN

Advantages

Disadvantages

Endocrine Applications

Nonpolar

Easy to use; little expertise needed; can be used to purify compounds

Limited resolution and limited applications

Amino acids; lecithin/ sphingomyelin ratio

Polar

Nonpolar

Easy to use, little expertise needed; may be used as an initial preparation step to eliminate interfering substances

Slow separation, limiting the number of specimens that may be analyzed

Purification steps for vanillylmandelic acid, fractionation of urine androgens

AFFINITY

Specific adsorbent

Varies

Can be highly specific for compound of interest, because the binding site recognizes a unique structure

Limited applications; more expensive than simple column chromatography

Glycated hemoglobin

ION EXCHANGE

Cation exchange: polyanions Anion exchange: polycations

Varies

Separates compounds based on differences in charge; compounds of charge differing from the type of resin elute most rapidly

Limited applications in clinical laboratories

Glycated hemoglobin

MOLECULAR SIEVE

Sephadex resins

Varies

Separates compounds based on differences in size; larger compounds will elute most rapidly

Limited applications

Separation of different size forms of peptide hormones (e.g., gastrin, glucagon)

HIGH-PERFORMANCE LIQUID (HPLC)

Normal: polar Reversed: nonpolar

Nonpolar Polar

Relatively rapid separation; may be automated; can be used to separate most compounds; can separate parent compound and metabolites; can be used to purify compounds; more sensitive than any procedures given above

More expensive than first two; requires some degree of experience in performing assays

Catecholamines, catecholamine metabolites, preparatory separation of vitamin D metabolites

GAS-LIQUID (GLC)

Liquid adsorbed to inert support

Inert gas

Can resolve substances indistinguishable by other methods; relatively rapid, compared with other chromatographic methods; may be coupled to mass spectrometry for positive identification and sensitivity much greater than other chromatographic methods

Requires high capital outlay and expert technical assistance; compounds must be volatile or able to be made volatile by derivitization

Estrogens, progestagens

ease in this patient? There are several statistical models that could be used to answer the question; the most widely publicized is Bayes' theorem. Bayes' theorem answers the question directly, giving a nu¬ meric probability that the test result indicates a given disease. The principles of Bayes' theorem are given in Figure 225-7. The information needed to answer the question includes the fre¬ quency with which abnormal results are found in persons with the disease (sensitivity), the frequency with which normal results are found in persons without the disease (specificity), and the frequency of the disease in the population. The answer is called the predictive value of a positive result. Figure 225-8 illustrates the importance of disease prevalence on the predictive value. The percentage of abnormal results that indicate disease decreases as the frequency of the disease decreases. Since the introduction of Bayes' theorem into medical use, it has found increasing use as a model for the diagnostic process, and several reviews highlighting it have appeared in the internal medicine literature.1,80,81 The weaknesses of Bayes' theorem for making medical decisions have not been emphasized. The first limitation is its use of a single decision level for predicting the presence of disease. For example, in the evaluation of hypercal¬ cemia, a serum calcium level of 10.6 mg/dL would be treated the same as a calcium level of 12.1 mg/dL or a calcium level of 16.5 mg/dL; few practicing endocrinologists would make this same conclusion. A second obstacle is the difficulty of using Bayes' the¬ orem for more than one variable. Although applications for

multiple variables do exist, they are not commonly used, and they further compound the first limitation by looking at only a single decision level for each variable studied. Furthermore, equal emphasis is placed on each result. However, physicians are well aware that certain findings are virtually pathognomonic, whereas others are extremely nonspecific. A further drawback lies not in the theorem itself, but in the way it has been used. In screening for rare diseases (e.g., neonatal hypothyroidism) or even in screening for relatively common en¬ docrine disorders (e.g., primary hyperparathyroidism), most ab¬ normal results from screening tests do not indicate the presence of disease. This has led many to criticize screening of asymptom¬ atic persons as worthless, because most abnormal results are false positives.17,18 However, the purpose of screening tests is not to make diagnoses, but to identify persons who are at high risk for having a disease. For example, as shown in Figure 225-8, only about 8% of infants with an elevated TSH level have congenital hypothyroidism. What the screening program does, however, is virtually rule out hypothyroidism in 99.75% of the screened newborns. It now is a much simpler task to find the affected in¬ fants by performing further tests on the few infants with elevated TSH levels. Without screening, discovering infants with hypo¬ thyroidism would be like finding a needle in a haystack; screen¬ ing puts the needle in a pin cushion. Bayes' theorem is an inadequate model for the diagnostic process. Although its popularization has focused attention on the inherent uncertainty in the interpretation of any data, other

1966

PART XVII: ENDOCRINE DRUGS AND VALUES

mathematical models and artificial intelligence systems (e.g., In¬ ternist) provide much closer approximations to the probability of diagnoses based on data obtained.82

A Cushings

High Cortisol

Normal Cortisol

Total

23.75

1.25

25 Predictive Value =

Obese

REFERENCE VALUES IN ENDOCRINOLOGY (TABLE 225-2) Reference values should be used as a relative means of com¬ parison, not as an absolute declaration of health or disease. Table 225-2 is an attempt to provide the proper context for the endocri¬ nologist to interpret results for an individual patient. Reference values are given first in the conventional units used in the United States. The conversion factor to transform these results to SI units and the reference range in SI units also are given. SI refers to Systeme International, which is an attempt to create a universally accepted scientific nomenclature; this sys¬ tem is used widely in Europe and in other parts of the world. The SI system recommends expressing concentration in moles (or fractions thereof) of a substance per liter, rather than in weight per volume. Young outlined the rationale for making this conver¬ sion. In summary, the major advantage of SI units is that they make interrelations between substances much easier to un¬ derstand.651 A good example is in the formula for calculated os¬ molality, in which glucose is divided by 18 and blood urea nitro¬ gen by 2.8 to convert from weight units to moles (osmolality is related to moles of a substance in solution). In this example, ex¬ pressing concentration in moles makes the calculation easy, and eliminates the need for remembering the appropriate factors for conversion. Other advantages of using SI units include a better understanding of relationships between a compound and its target or receptor, and a universal reporting system, which should improve the international usefulness of scientific studies. It has been recommended that peptide hormone concentra¬ tions still be expressed in standard mass nomenclature. This de¬ cision is difficult to understand, because hormones with active forms of different molecular weights cannot be expressed accu¬ rately using such mass nomenclature. Hormone concentrations are reported in mass units; however, because all immunoassays detect molar concentrations of a substance, hormone immunoas¬ says make use of some conversion factor. For the many hormones with multiple circulating forms, the conversion factor may be ei¬ ther an average molecular weight of all forms present, a weighted average, or the molecular weight of the most abundant or most

Sensitivity = Likelihood of "abnormal" result in presence of disease

True Positive Results (TP) Total Persons With Disease

Specificity = Likelihood of “normal" result in absence of disease

True Negative Results (TN) Total Persons Without Disease

[TP] = True Positives (Total) = Sensitivity x Prevalence [FP] = False Positives (Total) = (1—Specificity) x (1 —Prevalence) Predictive Value of Positive = Likelihood that a positive result indicates the presence of disease _ _(Sensitivity) (Prevalence)_ (Sensitivity x Prevalence) + [(1—Specificity) x (1—Prevalence)]

_EEl_ -

EP] + [FP]

FIGURE 225-7. Bayes' theorem. The predictive value of a positive result answers the question: What is the likelihood that a positive result indi¬ cates the presence of disease? For any disease, increasing sensitivity or specificity of the tests used increases the predictive value. The major de¬ terminant of predictive value is disease prevalence. If the prevalence is low, then the term TP becomes small compared with FP, because TP = Sensitivity X Prevalence. The equation then reduces to TP/FP, or TP/ (1 — Specificity) X (1 — Prevalence). Because (1 — Prevalence) is approxi¬ mately 1, the predictive value is (Sensitivity/[1 - Specificity]) X Prevalence.

B Hyperpara¬ thyroid

3.75

71.25

27.5

72.5

Calcium >10.5

Calcium s10.5

0.9

0.1

23.75 27 5

86%

75

1 Predictive Value = QJ =3.8% 25.9 1000

25

975

25.9

975.1

High TSH

Normal TSH

Hypothyroid

0.9

0.1

1

Euthyroid

10

3990

4000

Normal

c

Predictive Value = — = 8.3% 10.9

10.9

FIGURE 225-8. Examples of the use of Bayes' theorem. A, In obese pa¬ tients with abdominal striae and centripetal obesity, the frequency of Cushing syndrome is about 25%. In testing 100 patients by using urinary free cortisol levels, the sensitivity and specificity are each about 95%. The predictive value of elevated urinary free cortisol levels in this setting is 86%, thus increasing the certainty of diagnosis from 25% to the higher figure by using this one test. B, In screening for primary hyperparathy¬ roidism, about 90% of all serum calcium values in affected persons are above 10.5 mg/dL. Because this is the upper reference limit, 2.5% of normal persons have a serum calcium value above this figure by chance alone. In screening studies, the prevalence of hyperparathyroidism is about 1:1000. The likelihood that a serum calcium value above 10.5 mg/ dL represents primary hyperparathyroidism, using only the result of the calcium test, is 3.5%. C, Neonatal hypothyroidism screening programs sometimes use measurements of thyroid-stimulating hormone (TSH) in cord blood for the initial test. Because about 10% of cases are due to hypothalamic-pituitary insufficiency, the sensitivity is 90%. The cutoff value is more than 3 SD above the mean value for normal neonates; this excludes 99.75% of normal infants. Because the prevalence of hypothy¬ roidism is about 1:4000 newborns, the predictive value of an elevated TSH level is about 8%, but most affected infants have an elevated TSH level. Thus, in screening 4000 infants, only 11 infants need further stud¬ ies to find the one infant with hypothyroidism.

physiologically important form (i.e., the immunoassay standard). Because the exact conversion factors may vary, Table 225-2 gives the conversion factor only for hormones with a single predomi¬ nant circulating form. The major disadvantage of conversion to SI units is that phy¬ sicians in the United States would be required to learn a new set of reference ranges for all commonly ordered tests. Canada adopted SI units without major difficulty. In the late 1980s, sev¬ eral journals announced their intention to convert to SI units for all published scientific articles; however, most have returned to the use of conventional units. The reference ranges given in Table 225-2 are those used in the author's laboratory or in the reference laboratories the author uses, employing the method listed first under "Methodologic Considerations." Reference ranges are for serum or plasma un¬ less otherwise specified. For some tests, reference ranges pub¬ lished in the literature are included, with the reference number in superscript. Some of these reference ranges are based on re¬ sults from fewer than 20 persons. These ranges may not be ap¬ plicable to other methods or laboratories, and readers are urged to use reference ranges published by the laboratory they most commonly use. For tests in which reference ranges often differ

Ch. 225: Reference Values in Endocrinology by an order of magnitude (because of the lack of an acceptable standard or differences in reactivity of antibodies), the reference range carries the notation “method dependent." For each test, the author has attempted to define the com¬ mon intraindividual, physiologic, drug-related, and methodologic factors influencing the results for a particular test. For each test, these comments apply to the specimen type (e.g., urine or serum) listed first, using the method listed in the "Methodologic Considerations" column unless otherwise specified. Intraindi¬ vidual variation includes day-to-day variation, within-day vari¬ ation, and changes occurring during the menstrual cycle. Physi¬ ologic changes include commonly encountered alterations in expected physiology, such as exercise, obesity, pregnancy, and the effects of age, sex, and race. The effects of renal insufficiency

1967

and alcohol or tobacco use on test results also are given when indicated. This is not a comprehensive list of reference ranges in children; instead, the magnitude and direction of such changes is given. For more information on pediatric reference ranges, the reader should consult pertinent chapters of this book. In addi¬ tion, there are two textbooks devoted to pediatric chemistry that include endocrine values.652'653 The heading for drug effects in¬ cludes only pharmacologic effects of drugs; crossreactions are listed under "Methodologic Considerations," as are any special collection or handling requirements. Several general references and the publication on drug effects are the sources of much of the data in this table.47'48'652-65” In addition, specific references for each individual test are listed under the test name. (see References on page 2002)

1968

PART XVII: ENDOCRINE DRUGS AND VALUES

TABLE 225-2 Reference Values in Endocrinology Test Name

Reference Range (Conventional)

Conversion Factor

Reference Range (SI Units)

Intraindividual Variation

0.02-0.2 mmol/L

Probably similar to ketones.

ACE (see ANGIOTENSIN CONVERTING ENZYME ACETOACETATE (see also KETONES)83'84'660

0.02-0.2 mmol/L

1

ACETONE (see KETONES) ACID PHOSPHATASE85 87

0-0.5 U/L

1

0-0.5 U/L

ACTH (see ADRENOCORTICOTROPIC HORMONE)

Highest in afternoon with nadir in am. Within-day variation 25%-50%. Dayto-day variation 50%100%.

“

-

3',5-ADENOSINE MONOPHOSPHATE (see CYCLIC AMP) ADH (see VASOPRESSIN) ADRENOCORTICOTROPIC HORMONE88 93

7- 51 ng/L

1

7-51 ng/L

INC: highest shortly before waking, released in episodic spikes during the day, lowest in early sleep.

ALBUMINURIA, MINIMAL94 96

0-60 Mg/L

ALDOSTERONE97-102'661

Serum:

0-60 Mg/L

Supine < 16 ng/dL

0.0277

Upright 4-31 ng/dL

100%), progestational agents.

Higher in men than women and in whites than blacks; increases with age, especially after age 50 yr.

DEC: HMG-CoA reductase inhibitors, phenytoin, phenobarbital, valproic acid.

INC: supine position, volume expansion, renal failure, pregnancy, starvation, ethanol.

INC: glucocorticoids, mineralocorticoids, catecholamines.

DEC: volume depletion.

DEC: angiotensin converting enzyme inhibitors.

Higher in women than men, increases with increasing age in adults. In children, highest in first week, falls to adult levels by 4-6 d.

INC: during sleep. DEC: exercise, prolonged fast.

Immunoassay: standardization is not uniform, so that results differ markedly from one laboratory to another.

INC: volume depleting agents, mineralocorticoids, carbenicillin, glucocorticoids. DEC: carbonic anhydrase inhibitors, spironolactone.

Immunoassay: standardization is not uniform, so that results differ markedly from one laboratory to another.

RIA: probably labile, specimens should be collected in EDTA and plasma frozen immediately after separation. If plasma not extracted before analysis, overestimation of ANH occurs, possibly due to alteration of the iodine-labeled ligand. Hemolysis, heparin cause falsely low results.

Spectrophotometric: C02 content usually measured in venous blood; this is 1-2 mmol/L higher than HC03. In arterial blood gases, HC03 is calculated; in acute illness, differences in ionic strength may make this calculation incorrect, while C02 content is accurate. With all methods, delay in analysis causes decrease in concentration. With one ion-selective electrode, salicylate, ketones, and naproxen interfere, causing falsely high results.

(continued)

1972

PART XVII: ENDOCRINE DRUGS AND VALUES

TABLE 225-2 Reference Values in Endocrinology (continued) Reference Range (Conventional)

Test Name

Conversion Factor

CADMIUM160-161

25 ng/dL.

Urinary aldosterone.

>100 Mg/d-

Low-dose: 0.001-mg IV bolus. Prolonged: 0.25 mg IV over 6 h; some suggest repeat daily for 3 days. If adrenal insufficiency is being considered, give dexamethasone 1 mg PO before ACTH.

>7 Mg/dL.

RENIN-ANGIOTENSIN-ALDOSTERONE AXIS STIMULATORY 1. Sodium Restriction85-89

10-20 mmol sodium diet until urine Na 5 ng/mL/h.

4 h. Plasma aldosterone at

>25 ng/dL.

4 h.

* Note: The methodology, interpretation, and utility of some of these procedures are disputed; for further clinical infor¬ mation and recommendations, see the indicated chapters.

Response greater in PM than AM. Day-to-day variation 20%-30%.

Ch. 227: Dynamic Procedures in Endocrinology

2021

Physiologic Factors_Drug Effects_Methodologic Considerations_Special Considerations/Interpretation

DEC: acute illness, obesity, pregnancy, acute stress (for overnight and 2-day low-dose tests). In renal failure and alcohol abuse, lack of suppression is common with low-dose overnight and 2-day tests. Nonsuppression is more common in children and in those > age 65 yr, especially if cortisol is measured at 4 pm, as is recommended in psychiatric uses of the test).

INC: amphetamines, carbamazepine, nonsteroidal antiinflammatory agents, benzodiazepines. DEC:

Cortisol assay is important in interpreting results of overnight testing because some assays may be imprecise at low levels (near the 5-/ig/dL decision level). Urine 17-OH steroids or free cortisol may be inaccurate in patients with renal failure.

diphenylhydantoin, barbiturates, estrogens (high doses), rifampicin.

The low-dose tests show lack of suppression in almost all cases of Cushing syndrome, regardless of cause; the high-dose tests show suppression with Cushing disease, but usually not with other causes of Cushing syndrome. With the low-dose overnight test, lack of suppression is common in affective psychiatric disorders. Lack of suppression in low-dose tests is common in patients with diabetes mellitus, but is not related to diabetic control. Poor dexamethasone absorption has been reported in patients with chronic renal failure. It is important to verify ingestion of dexamethasone; in doubtful cases, plasma dexamethasone concentration is useful (see Chaps. 72, 76, and 196).

Response is similar in newborn infants, children, adults, and the elderly.

INC: estrogens, theophylline. DEC: calcium channel blockers, glucocorticoids, ketoconazole.

If assays that show crossreactivity with prednisone and cortisone are used (competitive protein binding and many immunoassays), there may be a high basal value with no response to infusion in patients receiving the medications.

Diminished or no response is seen in patients with primary adrenal insufficiency, and in patients who had been treated with supraphysiologic doses of glucocorticoids in whom normal pituitary-adrenal responsiveness has not returned. Low-dose ACTH shows diminished response in patients receiving long-term corticosteroids, and has been suggested to show decreased response in early adrenal insufficiency. Patients with secondary (pituitary) adrenal insufficiency usually respond. Patients with Cushing disease often hyperrespond, and those with adrenal carcinoma or ectopic ACTH production usually do not. As many as 50% of patients with adrenal adenomas show a response to ACTH. In normal individuals, the response decreases as basal serum cortisol increases; lack of response may occur if basal cortisol is >20 /ig/dL (see Chaps. 72 and 76).

Response decreases with increasing age.

Drugs that alter aldosterone excretion also affect dynamic responses (see Table 225-2).

Response decreases with increasing age.

Drugs that alter aldosterone excretion also affect dynamic responses. In addition, ranitidine decreases response to posture (see Table 225-2).

This degree of sodium restriction often is not achieved in practice, particularly in children. Appropriate sample collection is essential because renin activity increases if specimens are not kept at room temperature until plasma frozen; aldosterone is labile (see Table 225-2 for additional information on collection).

In persons with aldosteronoma, there typically is no change in aldosterone, whereas an increase may be seen in persons with hyperplasia of the zona glomerulosa. In primary or secondary hypoaldosteronism, there is a blunted aldosterone response; renin increases only in primary hypoaldosteronism. Hypokalemia and hypopituitarism blunt the response to volume depletion; in hypopituitarism, cortisol alone does not correct the response, but cortisol plus thyroxine do (see Chap. 77-79 and 177). The pattern of change is similar to sodium restriction. Hypokalemia and hypopituitarism blunt the response to volume depletion; in hypopituitarism, cortisol alone does not correct the response, but cortisol and thyroxine do (see Chaps. 77-79 and 177).

(continued)

2022

PART XVII: ENDOCRINE DRUGS AND VALUES

TABLE 227-1 Dynamic Procedures to Evaluate Endocrine Functions (continued)* Name of Procedure

How Performed

Substance Measured

Expected Response

Oral: 120-mmol Na diet until urine Na >60 mmol/12 h.

Plasma renin activity