Exercise Endocrinology 9783110866483, 9783110095579

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Exercise Endocrinology

Exercise Endocrinology Editors K. Fotherby • S. B. Pal

w DE

G

Walter de Gruyter • Berlin • New York 1985

Editors K. Fotherby, Ph. D..,ER.I.C. Department of Steroid Biochemistry Royal Postgraduate Medical School University of London Ducane Road London W12 OHS United Kingdom S. B. Pal, D. Phil.., Dr. rer. biol. hum., M. I. Biol. Universität Ulm Department für Innere Medizin Steinhövelstraße 9 D-7900 Ulm ER. of Germany

Library of Congress Cataloging in Publication Data Exercise endocrinology. Includes bibliographies and index. 1. Exercise—Physiological aspects. 2. Endocrinology. I. Fotherby, K. (Kenneth), 1927. II. Pal, S. B., 1928[DNLM: 1. Endocrine Glands—physiology. 2. Exertion. 3. Hormones—physiology. WE 103 E956] QP301.E95 1985 612'.76 84-27409 ISBN 3-11-009557-2

CIP-Kurztitelaufnahme der Deutschen Bibliothek Exercise endorinology / ed. K. Fotherby ; S. B. Pai. Berlin ; New York : de Gruyter, 1985. ISBN 3-11-009557-2 (Berlin . . . ) ISBN 0-89925-030-0 (New York) NE: Fotherby, Kenneth [Hrsg.]

311009557 2 Walter de Gruyter • Berlin • New York 0-89925-030-0 Walter de Gruyter, Inc., New York Copyright © 1985 by Walter de Gruyter & Co., Berlin 30 All rights reserved, including those of translation into foreign languages. No part of this book may be reproduced in any form - by photoprint, microfilm or any other means nor transmitted nor translated into a machine language without written permission from the publisher. Printing: Gerike GmbH, Berlin. Binding: Dieter Mikolai, Berlin. Printed in Germany.

PREFACE

During the past few years there has been a marked increase in interest in exercise physiology. This has arisen partly as a result of the higher standards required in most sports and in order to achieve this to make the most efficient use of the strength, energy and stamina of the sports-person. An improvement of 1 % or less in performance can have a significant effect on the final result. Consequently most studies carried out so far have used "trained" athletes. However, another reason for this growing interest is the participation of large numbers of people, usually "untrained", in sporting events who, unlike the "trained" athlete, are often performing below their maximum level so that we need to know also what the physiological changes are under these conditions. In the physiological adaptations to exercise, the endocrine system plays a central role, governing as it does the metabolic changes that are involved in energy production and also to some extent the cardiovascular and psychological changes. This monograph reviews within selected areas these endocrine changes and the resultant effects which accompany exercise in both the "trained" and "untrained" subject. It also highlights how patchy our knowledge is concerning these changes, how variable many of them appear to be and how much work is necessary in this interesting area of physiology and endocrinology.

K. Fotherby August 1984

S. B. Pal

CONTRIBUTORS

Numbers in parentheses indicate the page on which the authors1 articles begin A. Aakvaag, Hormone and Isotope Laboratory, Aker Hospital, Oslo 5, Norway (25). H. Adlercreutz, Department of Clinical Chemistry, University of Helsinki, Meilahti Hospital, SF-00290 Helsinki 29, Finland (65) . G. A. Bernath, Section of Geriatrics and Gerontology, The Medical College of Wisconsin and Wood, VA Medical Center, Milwaukee, Wisconsin, U.S.A. (99). G. W. Black, Department of Behavioral Medicine, SRI International, Menlo Park, California 94025, U.S.A. (263). W. M. Bortz, Health Care Division, Palo Alto Medical Clinic, Palo Alto, California 94301, U.S.A. (263). T. W. Boyden, Section of Endocrinology, Department of Internal Medicine, Veterans Administration Medical Center, Tucson, Arizona 85723, U.S.A. (121). G. Brandenberger, Centre d'Etudes Bioclimatiques, 21 rue Becquerel, 6 7087 Strasbourg Cedex, France (47). R. J. A. Butland, St. George's Hospital, Blackshaw Road, London SW17 OQT, U.K. (183). D. B. Carr, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts, U.S.A. (157). E. H. Duthie, Section of Geriatrics and Gerontology, The Medical College of Wisconsin and Wood, VA Medical Center,

VIII Milwaukee, Wisconsin,

U.S.A.

(99).

P. A. F a r r e l l , D e p a r t m e n t of H u m a n K i n e t i c s ,

School of

Allied

H e a l t h Professions, University of W i s c o n s i n - M i l w a u k e e , Wisconsin

53201, U.S.A.

(139).

S. M . F i s h m a n , H a r v a r d M e d i c a l S c h o o l , B o s t o n , U.S.A.

Milwaukee,

Massachusetts,

(157).

S. R . G a m b e r t , D i v i s i o n of G e r o n t o l o g y a n d G e r i a t r i c D e p a r t m e n t of Medicine, N e w York Medical College, New York

10595, U.S.A.

Medicine,

Valhalla,

(99).

M . P. H e y e s , D e p a r t m e n t of N u c l e a r M e d i c i n e , M c M a s t e r Hamilton, Ontario, Canada Daniela Jezovä, of P h y s i o l o g i c a l

University,

(239) .

Institute of E x p e r i m e n t a l Endocrinology, S c i e n c e s , S l o v a k A c a d e m y of S c i e n c e s ,

lava, Czechoslovakia

Centre

Bratis-

(201).

K . K u o p p a s a l m i , D e p a r t m e n t of C l i n i c a l C h e m i s t r y , of Helsinki, M e i l a h t i Hospital,

University

SF-00290 Helsinki 29,

Finland

(65) . I. N . M e f f o r d , C h e m i s t r y D e p a r t m e n t , B o s t o n C o l l e g e , Hill, Massachusetts

02167, U.S.A.

(263).

G . M e t i v i e r , D e p a r t m e n t of K i n a n t h r o p o l o g y , Ottawa, Ottawa, Ontario, Canada

Chestnut

University

of

(225) .

P . K . O p s t a d , N o r w e g i a n D e f e n c e R e s e a r c h E s t a b l i s h m e n t , N - 2 007 Kjeller, Norway

(25).

R . W . P a m e n t e r , U n i v e r s i t y of A r i z o n a , T u c s o n , A r i z o n a U.S.A.

(121) .

Esther D.R. Pruett, (1) .

85724,

I n s t i t u t e of W o r k P h y s i o l o g y , O s l o ,

Norway

IX J. R. S u t t o n , D e p a r t m e n t of M e d i c i n e , M c M a s t e r Hamilton, Ontario, Canada

University,

(239) .

M. V i g a s , I n s t i t u t e of E x p e r i m e n t a l E n d o c r i n o l o g y , C e n t r e of P h y s i o l o g i c a l S c i e n c e s , S l o v a k A c a d e m y of S c i e n c e s , Czechoslovakia

Bratislava,

(201).

M a r c i a M. W a r d , D e p a r t m e n t of B e h a v i o r a l M e d i c i n e , SRI t i o n a l , M e n l o P a r k , C a l i f o r n i a 94025, U . S . A .

(263).

Interna-

CONTENTS

Insulin and Exercise in Non-Diabetic and Diabetic Man Esther D. R. Pruett

1

Hormonal Response to Prolonged Physical Strain, Effect of Caloric Deficiency and Sleep Deprivation A. Aakvaag and P. K. Opstad

25

Cortisol Responses to Exercise and their Interactions with Diurnal Secretory Peaks G. Brandenberger

47

Interaction between Catabolic and Anabolic Steroid Hormones in Muscular Exercise K. Kuoppasalmi and H. Adlercreutz 65 Age, Exercise and the Endocrine System G. A. Bernath, E. H. Duthie, S. R. Gambert

99

Exercise and the Thyroid T. W. Boyden, R. W. Pamenter

121

Adrenocorticotropic Hormone and Exercise P. A. Farrell

139

Exercise and Endogenous Opioids D. B. Carr and S. M. Fishman

157

Catecholamine Responses to Exercise R. J. A. Butland

183

Effect of ß-Adrenergic Blockade on the Endocrine Response to Exercise in Man v v Daniela Jezova and M. Vigas

201

XII

Pituitary and Gonadal Secretory Variations and Control Mechanism during Physical Exercise G. Metivier

225

Endocrine Responses to Exercise at Altitude J. R. Sutton, M. P. Heyes

239

Exercise and Plasma Catecholamine Release Marcia M. Ward, I. N. Mefford, G. W. Black, W. M. Bortz .. 263 Subject Index

295

INSULIN AND EXERCISE IN NON-DIABETIC AND DIABETIC MAN

Esther D. R. Pruett Institute of Work Physiology, Oslo, Norway *

Although insulin is only one of many factors involved in the regulation of metabolism, it is generally recognized as the hormone having the greatest direct effect on glucose metabolism. Its lack, or a failure to function properly, causes diabetes mellitus. Exercise has long been used as a therapeutic tool for the diabetic. It enhances the effect of exogenous insulin to bring about a lowering of blood glucose and has been used in conjunction with treatment by insulin since the isolation of the hormone by Banting and Best (1). The exact relationship between insulin and exercise is only partly understood because the processes by which insulin mediates the transport of glucose and other molecules into cells is not fully understood. The biochemical and physiological mechanisms resulting in secretion of insulin from the beta cells of the Islets of Langerhans of the pancreas have been exhaustively studied (2). Plasma insulin levels have been investigated and their behaviour under many conditions of rest, exercise, health and disease are known. New evidence concerning the mode of action of insulin arises from the discovery and isolation of the insulin receptor. But the receptor is only part of the biochemistry and physiology involved in the action of insulin. Exercise causes changes in blood levels of many hormones in addition to insulin and each has an influence upon the others and upon exercise metabolism. Cardiac output, blood flow, oxygen uptake, metabolic rate, energy substrate utilization and other parameters all undergo severe adjustments. In this chapter, •Present address: 80 Palmers Mill Road, Media, Pa. 19063, U.S.A.

Exercise Endocrinology © 1985 by Walter de Gruyter & Co., Berlin • New York - Printed in Germany

2 only insulin is discussed, with little reference to other metabolic changes occurring simultaneously, with the exception of changes in blood glucose levels and glucose utilization.

Insulin Secretion Most of the information concerning the processes controlling the secretion of insulin from the pancreas comes from the study of cultured beta cells in vitro and animal studies. Insulin secretion in the human is nearly impossible to measure accurately since the portal vein cannot be catheterized. Thus any arteriovenous (A-V) differences in plasma insulin levels involving the pancreas must be taken across the entire splanchnic region and therefore includes both increases from insulin secretion and decreases due to utilization or destruction in the liver. The liver is believed to take up as much as one half of the entire amount of newly secreted hormone before it reaches the hepatic vein.Proinsulin (3) or the discarded C-peptide chain (4) from the break-down of proinsulin to insulin have been measured in an attempt to elucidate changes in insulin secretion in vivo. Proinsulin has about one fifth of the biological activity of insulin and must be assumed to be taken up by the liver to a certain extent. C-peptide is not thought to be biologically active, but that, in itself, does not preclude uptake by the liver. Dilution methods employing infusion of

1 31 I-insulin have

been used to assess pancreatic secretion in normal and obese humans and during mild exercise (5, 6). In these studies no changes in insulin secretion during exercise were detected. Since infusion of even small amounts of labeled insulin during exercise may itself change the response of the body, the method has limited value, especially in studies involving severe exercise. Changes in plasma insulin levels in response to exogenous glucose under various circumstances have been intensively studied.

3

However, changes in plasma insulin concentration need not result entirely from changes in insulin secretion. One study (7) measured arterial-deep venous differences in plasma insulin concentration during forearm exercise. The arterial concentration remained constant, while the A-V difference changed from zero at rest to a steady negative value indicating a net release of insulin during exercise. This suggests a release, or dissociation, of bound insulin from the insulin receptor on the muscle cell during exercise.

Plasma Insulin Levels During Exercise Methods of study Techniques, especially radioimmunoassay, for measuring plasma insulin levels in man are now extremely reliable (8, 9, 10). Bioassays require large amounts of sample, and the results of the determination are distorted by insulin-like activity of other substances. Since the discovery of the insulin receptor, a radioreceptor assay may be used (11) which tests the biochemical specificity of the hormone rather than its immunologic properties. Methods of study in insulin-treated diabetics The generation of insulin antibodies in the blood by exogenous insulin precludes the direct use of the radioimmunoassay of plasma insulin concentrations from insulin-treated diabetics. The method can be adapted for use on plasma from these patients either by removing the insulin-antibody complex and free antibodies by ethylene glycol precipitation and measuring the remaining "free" insulin (12), or by breaking down the insulinantibody complex using an acid-ethanol method (13), removing the antibodies and measuring the "total" insulin by radioimmunoassay. The physiological significance of "total" and "free" insulin is not quite clear.

4

Studies involving insulin-treated diabetics have not generally included measurement of plasma insulin levels but rely on changes in blood glucose concentrations (BGC). Results in thin normal individuals Physical training tends to reduce basal plasma immunoreactive insulin (IRI) levels in healthy individuals (14, 15). In thin normal subjects plasma IRI levels decrease during prolonged exercise, even in cases of such severe exercise that there is an eventual increase rather than a decrease in BGC (16, 17, 18, 19, 20, 21). In whole-body exercise studies, the time when the blood sample is taken is critical. Plasma IRI concentration increases immediately and dramatically upon cessation of exercise (19), so that any measurement not carried out while the subject is still exercising may be misleading. Since a decrease in plasma IRI is generally accompanied by increased hepatic glucose output and decreased glucose uptake by skeletal muscle, the decrease in IRI during exercise suggests that the exercising body is conserving liver glycogen to preserve function of the central nervous system, rather than for the use of the exercising muscles. Splanchnic glucose production increases as exercise is prolonged, both from hepatic glycogen stores and from gluconeogenesis (21, 22, 23). BGC remains fairly constant until the subject approaches exhaustion, when it decreases, often to the point of hypoglycemia (18). Even though insulin levels continually decrease, utilization of glucose from the circulation by muscle does take place (21, 24, 25). The amount used increases with the severity and duration of the exercise. Results in obesity and maturity-onset diabetes Basal plasma IRI levels in maturity-onset diabetics and obese patients are generally higher than in healthy individuals, and the phenomenon of insulin resistance is present (26, 27) . In these individuals, while the insulin and insulin-like components

5

of the blood appear to be similar, there is a resistance to the action of insulin at the target cell level (28) . The same BGC lowering effect can eventually be reached in these patients, but the amount of insulin required is several times larger than in thin, normal subjects. In the obese or the well-regulated diabetic patient, exercise may be beneficial. When these patients undergo long-term physical training, basal IRI levels can be reduced, an effect that may be reversed if the training ceases (26, 29). The reduction in basal IRI level is usually accompanied by a decrease in insulin resistance (30) . After physical training, diabetic subjects may also show a decrease in blood glucose levels implying normalization of glucose metabolism (30, 31). Single bouts of exercise in untrained obese and maturityonset diabetic subjects often brings about a temporary decrease in plasma IRI, just as in thin, normal subjects. If the maturityonset diabetic patient does not have a well-regulated metabolism and is ketotic, BGC, IRI, and ketone body concentrations may increase rather than decrease during exercise (27, 32) In such cases, rather than being beneficial, exercise may be detrimental (33, 34) . Results in insulin-treated diabetics Blood glucose concentrations do not always show the same type of decrease in insulin-treated diabetics as in healthy individuals as the exercising subject approaches exhaustion (34, 35). There are instances in which the decrease is rapid and dramatic, and other instances when there is little or no decrease in BGC. A high pre-exercise BGC does not turn out to be a necessary criterion for endurance in the insulin-treated diabetic (35). The amount and the rate of decrease in BGC in diabetic subjects during exercise appears to depend on the injection site of the insulin, elapsed time between injection and exercise, elapsed time between feeding and exercise, frequency of injection (including use of the implantable insulin delivery

6 system), the insulin preparation used, the presence of antibodies in the blood of the subject, counterregulatory effects of other hormones, environmental factors, and the state of mind of the exercising subject (33, 34, 36, 37, 38, 39, 40, 41, 42, 43) . An interesting study using ^H-insulin at the injection site (32) showed an increase in the rate of appearance of the label in the circulation during exercise, especially from sites involved directly in the exercise. An increase in plasma insulin concentration during exercise in the insulin-treated diabetic would be expected to cause a more rapid decrease in BGC than in the non-diabetic individual, in whom normal regulation of the plasma level occurs. Intramuscular utilization of blood glucose would be expected to increase while release of hepatic glucose would be inhibited and hypoglycemia would occur. A-V differences across the splanchnic region (23, 44) show a continued release in hepatic glucose in insulin-treated diabetics as well as in normal subjects, and the amount of release is not necessarily related to the concomitant change in BGC in the diabetic patient. Exercise is beneficial in well-regulated insulin-treated diabetics, as it is in non-insulin-treated diabetics. Again, however, if insulin and diet therapy are not adequate to prevent ketosis, increases in both BGC and ketone bodies may occur (34, 45, 46, 47, 48, 49, 50, 51) especially during long-term, severe exercise. It is important to remember that the timing and the site of the insulin injection in relation to the exercise play a major role in the action of insulin. Long-term training in the insulin-treated diabetic can be beneficial (34) and some insulin-treated diabetics have become successful professional athletes. The reaction of the insulintreated diabetic to exercise is a highly individual affair, depending upon all the aforementioned factors. Exercise, as therapy or as a profession, must be tailored to each patient, according to his ability to adjust his insulin dose and diet to the amount of exercise performed. One positive reaction to exercise in the well-regulated diabetic is subjective. He comes

7 to realize that his disease does not necessarily relegate him to the ranks of the severely handicapped. He may live a normally active life within the restrictions imposed by his ability to regulate his metabolism through diet, exercise and insulin therapy. It has been suggested that regular physical training in the diabetic may retard the recognized development of cardiovascular disease in the insulin-treated diabetic. Longitudinal studies confirming this hypothesis are not at present available, however.

Tissue Sensitivity to Insulin Insulin resistance, or the inability of blood glucose concentrations to decrease normally in response to increased plasma insulin concentrations, is a factor in a number of disease conditions. To measure this, tissue sensitivity to insulin has traditionally been studied, using the oral (OGTT) or the intravenous (IVGTT) glucose tolerance test. The rapidity with which a peroral or infused glucose load disappears from the circulation, and the insulin response to the load, have become important diagnostic tools. Criteria for judging insulin response to OGTT and IVGTT have been established by several investigators (9, 52, 53, 54), and use of the tests in the study of prediabetic and obese individuals and in the diagnosis of diabetes mellitus is widespread. In insulin-resistant patients, the initial insulin response to the glucose load may be much greater than in healthy individuals. On the other hand, in highly trained athletes, this response is moderate, even compared with that of healthy, untrained subjects (15). The IVGTT and OGTT have also been used to study changes in tissue sensitivity to insulin due to exercise in non-diabetic, diabetic, and obese subjects (26, 30, 31, 55, 56, 57). In general, exercise increases the disappearance rate of ingested or infused glucose from the blood after exercise (57) and plasma

8 IRI also disappears simultaneously. The increase in the disappearance rate of the glucose load is dependent upon the severity and duration of the preceding exercise (56, 57). Glucose tolerance curves for diabetic subjects resemble more and more those of non-diabetic subjects as the severity of the preceding exercise increases (56). Arterial-hepatic vein glucose differences during and after glucose infusion following exercise show continued output of glucose from the liver in both diabetic and non-diabetic subjects (23). Later research (44) shows that hepatic glucose output is greater in the diabetic subject than in the non-diabetic during infusion after exercise, possibly indicating an increase in gluconeogenesis in the diabetic subject. In any case, the liver is found not to contribute to the elimination of infused glucose from the circulation during the initial hour of recovery after exercise in the diabetic subject, and contributes only slightly in non-diabetics. The infused glucose is, instead, taken up by the muscle to replenish the glycogen depots. The GTT methods for measuring tissue sensitivity to insulin have recently been supplemented by use of the euglycemic insulin clamp technique (58, 59). This method consists of raising the plasma insulin concentration by infusion to a level about 100 liU/ml above the normal for the individual being studied and infusing sufficient glucose, the amount regulated by a feedback mechanism, to maintain the normal resting BGC of the individual. The amount of glucose necessary to maintain this BGC in the face of the hyperinsulinemia is taken as a measure of the sensitivity of the tissues to insulin action. Most of the work done so far by this method has been on normal and obese subjects at rest. It would seem that the use of the technique might well contribute to knowledge of tissue sensitivity in exercise. In fact, a recent study (60) reported that insulin and exercise are found to act together to enhance glucose disposal in man and that muscle is the primary tissue responsible for glucose uptake after hyperinsulinemia and exercise in healthy subjects.

9

The Insulin Receptor Since the beginning of the search for the mechanism of insulin action, it has been recognized that in each cell that requires the action of insulin there must be some natural component that serves to recognize the biologically active hormone. This component, having recognized the presence of insulin, must alter, or cause to be altered, the permeability of the plasma membrane for glucose and other molecules as the cell requires. Experimental evidence for an insulin receptor in the plasma membrane of fat cells (61) was found as early as 1969 and they have now been described on the surface of the plasma membrane of liver, fat, muscle and blood cells from rodents, and from blood and fat cells from humans (62, 63, 28). The receptor has been isolated (61) and the structure provisionally determined (64). The receptor is defined as a natural component of the cell that binds a hormone in a saturable fashion and with a specific proportionality to the biological activity of the hormone (65). Binding of the hormone to the receptor is a necessary, but not a sufficient, condition for action. The insulin-bound receptor per se does not appear to be involved in the transport of glucose into the cell (61, 66, 67). The insulin-receptor complex either becomes internalized and degraded by lysosomal activity and the degradation products eliminated from the cell (67, 68), or it becomes dissociated (28) and the insulin made available for future binding. Some step, distal to the receptor-binding operation, apparently carries out the function required by the particular cell involved. Many theories have been proposed for this step, some of which have been experimentally ruled out, and some for which a certain amount of experimental evidence is available (67, 68). None of the evidence for these theories is conclusive, however. The work of Czech (69) finds evidence consistent with the hypothesis that the insulin-receptor interaction leads to activation of a membrane protease that catalyzes the release of a peptide mediator or mediators of insulin action. This hypothesis, at least, allows for the determination

10

by each cell of the extent to which it will utilize the available insulin according to its individual needs. Study of the insulin receptor in man is strictly limited, owing to the problem of sampling. Since, at the present time, isolation of the insulin receptor from mammalian tissue requires a purification of the order of 500,000 times (62) , the tissues that may be used are limited to components of the blood and in some few cases to adipose tissue cells. The blood component selected by most investigators has been the circulating monocyte, although lymphocytes (68) and erythrocytes (70) have been used. The monocyte is not a primary target for insulin action. However, it does have receptors. Their total population and affinity for insulin change with various circumstances. Therefore, the monocyte has been taken as a mirror for insulinreceptor interactions of adipocytes, hepatocytes and muscle cells (71) in humans. The following arguments are made for the validity of the choice of the monocyte: 1) In lean or obese mice, lymphocytes, adipocytes, and muscle cells all have receptors that react 1 25 similarly to binding with I-insulin. Obese mice show a decrease in receptors on all these tissues compared with tissues from lean mice (72). 2) Adipocytes and monocytes from obese humans have receptors that behave similarly (73) . 3) Studies of the soleus muscle of lean and obese mice (74) show evidence of "spare" receptors, which corresponds to information available for receptors on circulating human monocytes. 4) Studies of tissue sensitivity to insulin, measured with the euglycemic insulin clamp technique performed concurrently with binding studies of monocytes in humans, show a high correlation between 125 I-insulin binding to monocytes and tissue sensitivity to insulin in both control and obese subjects at rest (58, 75). 5) Cultured macrophages from rodents have receptors similar to hepatic and other tissue receptors in rodents and to receptors on human monocytes (76), and display sensitivity to insulin at physiological concentrations. 6) Patients with syndromes that include high insulin resistance among the symptoms (acanthoses

11

nigricans and some other endocrine malfunctions) show an impair1 25 ment of I-insulin binding to monocytes that correlates closely with insulin resistance observed clinically (77, 78). There is also evidence suggesting that insulin-receptor interaction may not be identical on all cells (79). Degradation rate as well as association and dissociation rates may differ in receptor populations from different cells of the same animal or from the same type of cell in different animals. Accepting the validity of the choice of the circulating monocyte as a mirror for the insulin-receptor interaction on all cells at a given instant, the information cannot give us great insight into the total mechanism of insulin action. Since all of the tissues of the body do not react similarly at any given time to the action of insulin, even though the receptor population and its affinity for the hormone might be the same on all cells, there must be at least one step, after the binding step, that brings about, or permits, the required action in any particular type of cell.

Studies of

125

I-Insulin Binding to Human Monocytes

In most of the binding studies reported, blood is drawn from the subject at a pertinent time, centrifuged, and the buffy coat treated to remove the mononuclear cells (80). These cells 1 25 are incubated with various concentrations of I-insulin, and the data from the counted samples is subjected to three types of analysis: 1) The amount of labeled insulin bound to monocytes is plotted as a function of the total insulin concentration in the medium. 2) Scatchard plots (81) of bound/free insulin as the ordinate and bound insulin as the abcissa are made. 3) The affinity of the receptor for insulin at various points on the Scatchard plots is calculated and plotted as a function of the log of the percentage of the receptors occupied at that point (76). This is called the affinity profile of the receptor. The projected intercept of the Scatchard plot on the abcissa is

12 taken as a measure of the total insulin receptor concentration available for binding to the insulin in the blood sample. In the case of the insulin receptor, Scatchard plots are not straight-line functions, indicating that there is more than one affinity for insulin binding on a given set of receptors. In fact, studies of the binding phenomenon indicate a site-site negative cooperativity that changes the affinity of the receptors for insulin as more and more receptors are bound

(28, 82).

These and other findings lead to the conclusion that insulin is a primary regulator of its own receptor concentration and affinity

(68, 73, 76) . Using the methods just described it is found that under

certain conditions the total number of receptors available for binding on a given cell may be changed, and under other conditions, the affinity of these receptors may be changed. There are a number of queries that may be raised concerning the validity of these types of analysis of the data obtained from bind1 25 ing studies (83). Studies using binding of I-insulin to mononuclear cells show that, in general, binding is inversely proportional to ambient insulin concentrations

(65). Thus, in obese,

prediabetic, and maturity-onset diabetic subjects, in whom high basal plasma IRI concentrations as well as high insulin resistance are found, the level of binding of insulin to monocytes is considerably lower than in healthy, thin individuals (58, 63, 68, 70, 73, 76, 79). This may be due to a defect in the receptor itself (61), to counterregulatory hormones, or the presence of insulin receptor antibodies (61, 78). In non-ketotic, non-insulin-treated diabetics (63), however, cells from 20 diabetic subjects bound 50% less insulin than cells from non-diabetic control subjects. This difference was accounted for by a lower total receptor population on the cells from the diabetics, and not by a difference in the affinity profile of the receptors. The pH value of the medium in vitro causes a change in receptor affinity for insulin. In patients with ketosis, the lowered blood pH may be a contributing factor in insulin resistance (28) .

13

A situation that lowers ambient insulin concentration in a subject is also likely to bring about an increase in binding of insulin to receptors, a condition that can be reversed. Such situations include long-term dieting and physical training on the one hand (84, 85), and short-term starvation and exercise bouts on the other (76, 86). In general, when changes occur over a long period of time, the change is apparently in the size of the receptor population available for binding. When changes in binding occur over short periods of time and under more acute stress, however, the change appears to be in the affinity profile of the receptor population for binding to insulin. In healthy subjects, ambient insulin concentrations are 125 relatively low and binding of I-insulin to circulating monocytes relatively high. Physical training in such subjects is found to decrease the basal insulin concentrations, to increase tissue sensitivity to insulin (15) and to increase insulin binding to monocytes (75). The increase in binding comes about because of an increase in the total receptor population. When untrained, healthy subjects are submitted to heavy or moderate exercise (84, 87), binding to circulating monocytes is found to increase, and the change is brought about by an increase in the affinity of the receptor for insulin. If fully trained athletes, on the other hand, are subjected to bouts of exercise (14), insulin binding to the monocyte receptor is found to decrease rather than increase as in the untrained subjects. The change is, again, in the affinity of the receptor for insulin, but it is towards a lesser rather than a greater affinity. This difference may reflect the larger muscle glycogen stores, the increased utilization of free fatty acids (22) and the lesser dependence of the muscle cell in the highly trained subject on support from blood glucose to carry out the work. Whether or not this is so, the difference in behaviour of receptors on monocytes from trained and untrained individuals during exercise lends some credence to the hypothesis that the monocyte may be taken as a mirror for insulin-receptor interaction on

14

other body cells. Binding studies using monocytes from insulin-treated diabetics have yielded little helpful information. The results of such studies depend largely on the state of metabolic regulation of the subject (88) . An increased binding to monocytes after exercise in insulin-treated diabetics, suggested that the same change occurred in muscle, contributing to the increase in glucose tolerance after exercise in these patients (89, 90).

Summary Direct knowledge concerning changes in insulin secretion in humans is not available. Studies of changes in plasma insulin concentrations, which decrease during exercise, have traditionally led us to believe that secretion of insulin also decreases, and it probably does. New information from studies of insulin receptors, however, shows that binding of insulin to receptors on the circulating blood cells generally increases as ambient insulin concentrations decrease. This may be caused by changes in the total receptor population of the cell or in the receptors' affinity for insulin. Insulin bound to the receptor can become dissociated from it and remain available for future binding or the insulin-receptor complex can become internalized and made permanently unavailable for use. A net release of insulin from working muscle indicates that decreases and increases in IRI levels may partly be caused by changes in binding of insulin to its receptors. Insulin may be destroyed as well as utilized be hepatic tissue. Thus, pancreatic secretion may be only part of the series of events that regulates circulating insulin concentrations during exercise. It is reasonable to think that the decrease in plasma IRI concentrations during exercise causes a decreased uptake by exercising muscles of the glucose available from the liver. A-V difference experiments show an increased uptake of glucose by working muscle as exercise is prolonged, in spite of decrea-

15

sing insulin concentrations and, except in athletes, receptor binding of insulin increases during exercise, at least on circulating monocytes. This could bring about a decrease in plasma IRI and, at the same time, allow for increased uptake of glucose in the exercising muscle, if it also happens on the muscle cell. The A-V difference study, showing a net release of insulin from the exercising muscle, is at variance with this hypothesis. From studies of blood glucose and plasma insulin concentrations, glucose tolerance is increased in most individuals as a result of exercise. The increase in the rate of disappearance of exogenous glucose from the blood is followed closely by the increase in the rate of disappearance of insulin, although the initial response of insulin to the glucose load differs in different types of individuals. When the body's glycogen depots have been replenished, the tolerance for infused glucose returns to the pre-exercise state. With long-term training, however, tissue sensitivity to insulin can be normalized in patients showing pre-training abnormalities in insulin reaction to a glucose load. The normalization in disappearance rate after exercise occurs in insulin-treated diabetics as well as in subjects with native insulin, as long as their metabolism is well regulated. The carry-over to future glucose tolerance tests does not occur, however, although it may be possible to decrease insulin dosage in regularly exercising insulin-treated diabetics. Further light on changes in tissue sensitivity to insulin 125 comes from binding studies of I-insulin to insulin receptors on monocytes from the blood of different types of individuals. Patients with abnormally high ambient insulin concentrations, insulin resistance, and low insulin-receptor binding before exercise can, after training, exhibit normalization of the insulin binding to the receptors as well as of the ambient insulin concentration, insulin resistance and glucose tolerance. Binding to monocytes from blood of untrained subjects during exercise increases whereas that of athletes decreases probably reflecting a difference in metabolic needs between

16

the muscle cells of trained and untrained individuals. A great deal of information is now available concerning the insulin receptor itself, its structure, its behaviour on the cell surface and what happens to the insulin-receptor complex after binding occurs. The function of the receptor as a separate unit is much better understood than its function as a part of the metabolic processes of a single cell or of the entire body. That the size of the total receptor population and the affinity of the receptor for the hormone can be changed, given long-term or short-term changes in circumstances, is becoming established. Whether or not the model used in the mathematical analysis of available data gives a clear and correct picture of what is happening to the receptor population of the cells is open to question. The validity of the selection of a single type of cell in the human as a model for insulin-receptor interaction on all cells under, for example, exercise stress, is in need of clarification. The simultaneous use of soleus muscle and monocyte receptors from exercised rodents might give useful information. If the choice of the monocyte as a mirror is validated, then the interpretation of the data to explain why receptor concentrations and affinity change under various circumstances finds firmer footing. The difference in the direction of change in the affinity of receptors from exercising, untrained subjects and those from athletes poses the interesting question of whether the causes of these changes can be metabolic in origin. Finally comes the question of the transport of glucose and other molecules through the cell membrane as mediated by the binding of insulin to its receptor. This vital mechanism must ultimately be under the control of the cell itself because of its individual needs. The possible release of peptide mediators of insulin action after activation of a membrane protease by the occupied insulin receptor, for which there is some evidence, is promising.

17

References

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6. Nikkilä, E.A., Taskinen, M.-R.: The insulin secretion rate in obesity. Postgrad. Med. J. (suppl.) 47, 412-417 (1971). 7. Kaijser, L., Eklund, B., Riccardi, G., Carlson, L.A.: Insulin and substrate exchange in the forearm during prolonged forearm work. Scand. J. clin. Lab. Invest. 321328 (1979). 8. Hales, C.N., Rändle, P.J.: Immunoassay of insulin with insulin-antibody precipitate. Biochem. J. 8£$, 1 37-146 (1 963). 9. Jörgensen, K.R.: Evaluation of the double antibody radioimmunoassay of insulin and the determination of insulin in plasma and urine in normal subjects. Acta Endocrinol. 60, 327-351 (1969). 10. Yalow, R.S., Berson, S.A.: Immunoassay of endogenous plasma insulin in man. J. clin. Invest. 39, 1157-1175 (1960). 11. Gavin, J.R., Kahn, C.R., Gordon, P., Neville, D.M.: Radioreceptor assay of insulin: comparison of plasma pancreatic insulins and proinsulins. J. clin. Endocrinol. Metab. 41, 438-445 (1975). 12. Nakagawa, S., Nakayama, H., Sasaki, T., Yoshima, K., Yu, Y.Y., Shimozaki, K., Aoki, S., Mashimo, K.: A simple method for the determination of free insulin levels in insulintreated patients. Diabetes 22, 590-600 (1973). 13. Heding, L.G.: Determination of total serum insulin in insulin-treated diabetic patients. Diabetologia 8, 260-266(1972). 14. Koivisto, V.A., Soman, V. , Conrad, P., Hendler, R., Nadel, E., Felig, P.: Insulin binding to monocytes in trained athletes. J. clin. Invest. 64, 1011-1015 (1979). 15. Lohmann, D., Liebold, F., Heilmann, W., Senger, H., Pähl, A.: Diminished insulin response in highly trained athletes. Metabolism 27, 521-524 (1978). 16. Cochran, B. Jr., Marbach, E.P., Poucher, R., Steinberg, T., Gwinup, G.: Effect of acute muscular exercise on serum im-

18

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19

30. Saltin, B., Lindegärde, F., Houston, M., Hörlin, R., Nygaard, E., Gad, P.: Physical training and glucose tolerance in middle-aged men with chemical diabetes. Diabetes 28, (suppl. 1), 30-32 (1979). 31. Ruderman, N.B., Ganda, O.P., Johansen, K.: The effect of physical training on glucose tolerance and plasma lipids in maturity-onset diabetes. Diabetes 2J5, (suppl. 1), 8992 (1979). 32. Berger, M. , Halban, P.A., Assal, J.P., Offord, R.E., Vranic, M., Renold, A.E.: Pharmokinetics of subcutaneously injected insulin: effects of exercise. Diabetes 28 (suppl. 1), 53-57 (1979). 33. Koivisto, V.A., Sherwin, R.S.: Exercise in diabetes: therapeutic implications. Postgrad. Med. 66^, 87-96 (1 979). 34. Richter, E.A., Ruderman, N.B., Schneider, S.H.: Diabetes and exercise. Am. J. Med. 70, 201-209 (1981). 35. Pruett, E.D.R., Maehlum, S.: Muscular exercise and metabolism in juvenile diabetics. I. Energy metabolism during exercise. Scand. J. clin. Lab. Invest. 3£, 139-147 (1973). 36. Dandona, P., Hooke, D., Bell, J.: Exercise and insulin absorption from subcutaneous tissue. Brit. med. J. _1_, 479480 (1978). 37. Johansen, K. : Physical training and diabetes mellitus. J. Endocrinol. Invest. 367-371 (1978). 38. Kemmer, F.W., Berchtold, P., Berger, N., Start, A., Clippers, H.J., Gries, F.A., Zimmerman, H.: Exercise-induced fall of blood glucose in insulin-treated diabetics unrelated to alteration of insulin metabolism. Diabetes 28, 1131-1137(1979). 39. Koivisto, V.A., Felig, P.: Effects of leg exercise on insulin absorption in diabetic patients. New Engl. J. Med. 298, 79-83 (1978). 40. Lawrence, R.D.: The effect of exercise on insulin action in diabetes. Brit. med. J. 1926: 648-650 (1926). 41. Murray, F.T., Zinman, B., McClean, P.A., Denoga, A., Albisser, A.M., Leibel, B.S., Nakhoosa, A.F., Stokes, E.F., Marliss, E.B.: The metabolic response to moderate exercise in diabetic man receiving intravenous and subcutaneous insulin. J. clin. Endocrinol. Metab. £4, 708-720 (1977). 42. Zinman, B., Murray, F.T., Vranic, M., Albisser, A.M., Leibel, B.S., McClean, P.A., Marliss, E.B.: Glucoregulation during moderate exercise in insulin-treated diabetics. J. clin. Endocrinol. Metab. £5, 641-652 (1977). 43. Zinman, B., Vranic, M., Albisser, A.M., Leibel, B.S., Marliss, E.B.: The role of insulin in the metabolic response to exercise in diabetic man. Diabetes 28, (suppl. 1) 76-81 (1979).

20

44. Wahren, J.: Glucose turnover during exercise in healthy man and in patients with diabetes mellitus. Diabetes 28, (suppl. 1 ), 82-88 (1 979) . 45. Berger, M., Berchtold, P., Cüppers, H.J., Drost, H., Kley, H.K., Müller, W.A., Wiegelmann, W., Zimmermann-Telschow, H., Gries, F.A., Krüskemper, H.L., Zimmermann, H.: Metabolic and hormonal effects of muscular exercise in juvenile type diabetes. Diabetologia 1_3, 355-365 (1 977). 46. Berger, H., Hagg, S., Ruderman, N.B.: Glucose metabolism in perfused skeletal muscle. Interaction of insulin and exercise on glucose uptake. Biochem. J. 146, 231-238 (1975). 47. Larsson, Y.: Physical exercise and juvenile diabetes Summary and conclusions. Acta Paediatr. Scand. Suppl.2 38, 120-122 (1980). 48. Sherwin, R.S., Koivisto, V.: Keeping in step: does exercise benefit the diabetic ? Diabetologia 20, 84-86 (1981). 49. Wahren, J., Hagenfeldt, L., Felig, P.: Splanchnic and leg exchange of glucose, amino acids, and free fatty acids during exercise in diabetes mellitus. J. clin. Invest. 55, 1303-1314 (1975). 50. Wahren, J., Hagenfeldt, L.: Free fatty acids and ketone body metabolism during exercise in diabetes. Acta Paediatr. Scand. Suppl. 283, 39-43 (1980). 51. Hagenfeldt, L.: Metabolism of free fatty acids and ketone bodies during exercise in normal and diabetic man. Diabetes 28, (suppl. 1) 66-70 (1979). 52. Cerasi, E., Luft, R.: Plasma-insulin response to sustained hyperglycaemia induced by glucose infusion in human subjects. The Lancet 28, 1359-1361 (1963). 53. Cerasi, E., Luft, R.: The plasma insulin response to glucose infusion in healthy subjects and in diabetes mellitus. Acta Endocrinol. 55, 278-304 (1967). 54. Cerasi, E., Luft, R.: Further studies on healthy subjects with low and high insulin response to glucose infusion. Acta Endocrinol. 55, 305-329 (1967). 55. Lindegärde, F., Saltin, B.: Daily physical activity, work capacity and glucose tolerance in lean and obese normoglycaemic middle-aged men. Diabetologia 2CI, 1 34-1 38 (1981 ). 56. Maehlum, S., Pruett, E.D.R.: Muscular exercise and metabolism in male juvenile diabetics. II. Glucose tolerance after exercise. Scand. J. clin. Lab. Invest. 32^, 149-153 (1 973). 57. Pruett, E.D.R., Oseid, S.: Effect of exercise on glucose and insulin response to glucose infusion. Scand. J. clin. Lab. Invest. 26, 277-285 (1970). 58. DeFonzo, R.A., Soman, V., Sherwin, R.S., Hendler, R., Felig, P.: Insulin binding to monocytes and insulin action in human

21

obesity, starvation, and refeeding. J. clin. Invest. 62, 204-213 (1978). 59. Sherwin, R.S., Kramer, K.J., Tobin, J.D., Insel, P.A., Liljenquist, J.E., Berman, M., Andres, R.: A model of the kinetics of insulin in man. J. clin. Invest. 5^3, 1481-1492 (1 974) . 60. DeFonzo, R.A., Ferrannini, E., Sato, Y., Felig, P., Wahren, J.: Synergistic interaction between exercise and insulin on peripheral glucose uptake. J. clin. Invest. 6j$, 1468-1474 (1981). 61. Cuatrecasas, P.: The insulin receptor. Diabetes 2_1_ (suppl. 2), 396-402 (1972). 62. Cuatrecasas, P.: Membrane receptors. Ann. Rev. Biochem. 43, 169-214 (1974). 63. Olefsky, J.M.: The insulin receptor: its role in insulin resistance of obesity diabetes. Diabetes 2J5, 1154-1162 (1976). 64. Czech, M.P., Massague, J., Pilch, P.F.: The insulin receptor: structural features. Trends Biochem. Sci. 6, 222-225 (1981) . 65. Gordon, P.: Hormone receptor interactions. Diabetes 28 (suppl. 1), 8-12 (1979). 66. Haring, H.U., Biermann, E., Kemmler, W.: Coupling of insulin binding and insulin action on glucose transport in fat cells. Am. J. Physiol. 240, E556-E565 (1981). 67. Marshall, S., Olefsky, J.M.: The endocytotic-internalization pathway of insulin metabolism: relationship to insulin degradation and activation of glucose transport. Endocrinology T07, 1937-1945 (1980). 68. Archer, J.A., Gordon, P., Gavin, J.R., Lesniak, M.A., Roth, J.: Insulin receptors in human circulating lymphocytes.J. clin. Endocrinol. Metab. 36, 627-633 (1973). 69. Czech, M.P.: Insulin action. Am. J. Med. 70, 142-149

(1981).

70. Spanheimer, R.G., Bar, R.S., Ginsberg, B.H., Peacock, M.L., Martino, I.: Comparison of insulin binding to cells of fed and fasted obese patients. J. clin. Endocrinol. Metab. 54, 40-47 (1982). 71. Gavin, J.R., Roth, J., Jen, P., Freychet, P.: Insulin receptors in human circulating cells and fibroblasts. Proc. natn. Acad. Sci. U.S.A. 69, 747-751 (1972). 72. Le Marchand, Y., Loten, E.G., Assimacopoulos-Jeannett, K., Forgue, M.-E., Freychet, P., Jeanrenaud, B.: Effect of fasting and streptozotocin in the obese-hyperglycemic mouse. Diabetes 2£, 582-590 (1977). 73. Olefsky, J.M.: Decreased insulin binding to adipocytes and circulating monocytes from obese subjects. J. clin. Invest. 57, 1 165-1 172 (1976) .

22

74. Le Marchand-Brustel, Y., Jeanrenaud, B., Freychet, P.: Insulin binding and effects in isolated soleus muscle of lean and obese mice. Am. J. Physiol. 234, E348-E358 (1978). 75. Soman, V.R., Koivisto, V.A., Deibert, D., Felig, P., DeFonzo, R.A. : Increased insulin sensitivity and insulin binding to monocytes after physical training. New Engl. J. Med. 3CM, 1200-1 204 (1 979). 76. Bar, R.S., Gordon, P., Roth, J., Kahn, C.R., De Meyts, P.: Fluctuations in the affinity and concentration of insulin receptors on circulating monocytes of obese patients. J. clin. Invest. 58, 1123-1135 (1976). 77. Kahn, C.R., Flier, J.S., Bar, R.S., Archer, J.A., Gordon, P., Martin, M.M., Roth, J.: The syndromes of insulin resistance and acanthosis nigricans. Insulin-receptor disorder in man. New Engl. J. Med. 294, 739-745 (1976). 78. Le Marchand-Brustel, Y., Gordon, P., Flier, J.S., Kahn, C. R., Freychet, P.: Anti-insulin receptor antibodies inhibit insulin binding and stimulate glucose metabolism in skeletal muscle. Diabetologia 1_4 , 31 1-317 (1978). 79. Gliemann, J., Beck-Nielsen, H., Pedersen, 0., Sonne, 0.: Role of insulin receptors in insulin resistance. Ann. Clin. Res. V2, 264-268 (1980). 80. Boyum, A.: Separation of leucocytes from blood and bone marrow. Scand. J. clin. Lab. Invest. 2J_ (suppl. 97), 7-109 (1968). 81. Scatchard, G.: The attractions of proteins for small molecules and ions. Ann. N.Y. Acad. Sci. 51_, 660-672 (1 949). 82. De Meyts, P., Bianco, A.R., Roth, J.: Site-site interactions among insulin receptors. J. biol. Chem. 51_, 1877-1888 (1976). 83. Wiley, H.S., Cunningham, D.D.: A steady state model for analyzing the cellular binding, internalization and degradation of polypeptide ligands. Cell 25, 433-440 (1981). 84. Koivisto, V., Soman, V., Nadel, E., Tamborlane, W.V., Felig, P.: Exercise and insulin: insulin binding, insulin mobilization, and counterregulatory hormone secretion. Fed. Proc. 39, 1481-1486 (1980). 85. LeBlanc, J., Nadeau, A., Boulay, M., Rousseau-Migneron, S.: Effect of physical training and adiposity on glucose metabolism and 1^5 1-insulin binding. J. appl. Physiol. 46, 235-239 (1 979) . 86. Koivisto, V.A., Soman, V.R., Felig, P.: Effects of acute exercise on insulin binding to monocytes in obesity. Metabolism 29, 168-172 (1980). 87. Soman, V.R., Koivisto, V.A., Grantham, P., Felig, P.: Increased insulin binding to monocytes after acute exercise in normal man. J. clin. Endocrinol. Metab. 47_, 216-219 (1 978) .

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88. Fantus, I.G., Ryan, J., Gordon, P.: The insulin receptor in insulin-dependent diabetes mellitus. Metabolism 30, 510-517 (1981). 89. Pedersen, 0., Beck-Nielsen, H., Heding, L.: Increased insulin receptors after exercise in patients with insulindependent diabetes mellitus. New Engl. J. Med. 302, 886892 (1 980) . 90. Pedersen, 0., Beck-Nielsen, H., Sörensen, N.S., Heding, H.: Effects of exercise on insulin receptors on erythrocytes and monocytes from insulin dependent diabetics. Acta Paediatr. Scand. Suppl. 283, 78-80 (1980).

HORMONAL RESPONSE TO PROLONGED PHYSICAL STRAIN, EFFECT OF CALORIC DEFICIENCY AND SLEEP DEPRIVATION

A. Aakvaag and P. K. Opstad Hormone and Isotope Laboratory, Aker Hospital, Oslo 5, and Norwegian Defence Research Establishment, N-2007 Kjeller, Norway

Introduction A multitude of endocrine changes occur during exercise. These changes involve pituitary, thyroid, pancreas, adrenals and gonads. In most studies the endocrine response has been expressed as changes of hormone levels in plasma. These alterations are frequently considered to be reflections of changes in hormone production. It should, however, be pointed out that heavy physical exercise also affects the metabolism of hormones (1). The metabolic clearance rate of aldosterone was reduced by about 25% during an exercise on a bicycle ergometer at about 60% of the individual maximum oxygen uptake (1). There is reason to believe that this reduction in metabolic clearance rate reflects reduced hepatic metabolism of aldosterone due to diminished hepatic blood flow and/or diminished hepatic extraction and metabolism. Since hepatic metabolism is such an important process for the removal of steroid hormones from the plasma, it may be assumed that this effect may be a more or less general one in relation to changes of steroid levels during exercise. Kidney clearance of hippuran was also drastically reduced during the same bicycle exercise, which may imply that renal metabolism and excretion of steroid hormones may also be impaired with significant impact on hormone levels in plasma during exercise. The mechanisms by which physical exercise affects the

Exercise Endocrinology © 1985 by Walter de Gruyter & Co., Berlin - New York - Printed in Germany

26 endocrine system are only vaguely known and the stimulus of physical exercise is a very complex one. The response to physical exercise is dependent upon both the duration and the degree of exercise. Prolonged physical exercise may have the opposite effect to short-term exercise. This has clearly been seen for testosterone levels in plasma. Galbo et al. (2) showed an increase in serum testosterone levels during the initial period (40 min) of heavy exercise and a subsequent decline on continued exercise until exhaustion, although the levels had not reached the pre-exercise levels. Dessypris et al. (3) recorded a 40% reduction in plasma testosterone levels after a marathon run. Sutton et al. (4) observed no change in plasma testosterone levels in swimmers during 2 0 to 90 min of strenuous exercise, whereas rats that swam for 60 min reduced their plasma testosterone levels to 34% of controls (5). These discrepancies are probably related to the complexity of the physiological stimulus that physical exercise represents, alterations in both hormone metabolism and excretion on the one hand, and alteration in hormone production on the other, and furthermore, changes in distribution volume of the hormone. One may assume that after some time of exercise the homeostatic mechanisms controlling hormone levels in plasma will compensate for the changes in hormone levels induced by alterations in hormone metabolism and excretion. Therefore, it may be suggested that prolonged exercise may be more relevant than short-term experiments in relation to the question of the effect of exercise on the function of endocrine organs, when using plasma hormone levels as parameters for this function. In this discussion we will therefore concentrate on our own work, where we have studied the endocrine alterations during a complex stimulus of prolonged, 4 to 5 days, heavy physical exercise, combined with sleep deprivation and caloric deficiency. By subsequent corrections of the various factors of this complex situation, by giving caloric supplementation and extra sleep, one might gain an understanding of which factor is responsible

27 for which endocrine alteration, and thereby an insight into the underlying mechanism of hormonal changes. It should be pointed out that the term "prolonged" has different meanings for different authors. Galbo et al. (2) considered an exercise lasting for 80 min a prolonged one, others consider a marathon run of 3 to 5 h (3) or a 90 km cross-country ski-race of 5 to 8 h (6) prolonged strenuous exercise. In our observation prolonged means 4 to 5 days, and one of the objectives was to study whether signs of adaptation might occur during this long period.

Design of Study The uniqueness of our study is the very long period of physical strain. The subjects under investigation underwent a continuous exhaustive physical strain lasting for 4 to 5 days. The subjects were cadets of the Norwegian Military Academy participating in a ranger training course as a part of their military training program. The average age of the candidates was about 24 y and they were all in excellent mental and physical condition. The course lasted from Monday morning until the following Friday afternoon or Saturday morning. The continuous simulated combat activities allowed the subjects to get only short periods of sleep, estimated to be a total of about 1 to 2 h during the course. Continuous heart rate studies have shown that the energy consumption during the course was from 9000 to 11 000 kcal/24 h and this average activity level was at about 30% of their V

max

0 throughout the z

entire period. Randomly selected groups of the cadets were given extra sleep and extra caloric supplementation in order to investigate the effect of sleep deprivation and caloric deficiency on the various endocrine parameters.

28

Hormonal Changes Gonadal hormones Testosterone levels in plasma were found to be substantially reduced during the exercise period (Fig. 1) (7, 8). The reduction occurred within 12 h (Fig. 1D), at a time that sleep deprivation could not be a factor, and remained low during the entire exercise period. One may assume that this decrement is caused by impaired secretion of testosterone, otherwise one would have to postulate an increase in metabolic clearance rate of about 10 fold. This is hardly conceivable in light of the effect of exercise on aldosterone metabolism (1). LH remained essentially unchanged during the course with a slight tendency to increase (7, 8), which suggests that diminished stimulation of the testis from the pituitary is not the cause of this reduction in testosterone output. It is, however, difficult to accept an effect on the testis only, because one would then expect a rise in LH due to the diminished negative feedback effect of testosterone on LH secretion. It therefore seems that one has to postulate an effect of prolonged heavy physical exercise on both the testis and the hypothalamus-pituitary. The complex nature of the experimental situation with prolonged heavy physical exercise, sleep deprivation and caloric deficiency prompted modifications in the experimental situation that might provide data that could relate the reduced testosterone levels to specific factors. The significance of sleep deprivation was tested in two experiments. In the first of these, three groups of cadets were tested, two getting some sleep during one night, 3 h for group 2 and 6 h for group 3. Groups 2 and 3 had significantly higher testosterone levels on day 4, in the morning after the night of the extra sleep (Fig. 1B). In the other experiment the cadets were divided into two groups, one getting 3 h sleep per night sometime between 11 p.m. and 3 a.m. The control group had no

29

P

V 1 2

i

i ff

3 4 5 6 8

i

*

i *t-i

r-

i ii

12 »8 1 2 3 4 5 6 1

I

1 1 > l 2 3 4 5 28 1 2 3 4 5

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DAYS

Fig. 1

Serum levels of testosterone in men during prolonged strenuous exercise as described in the text. Closed arrows indicate start of the program, open arrows the end. Blood samples were taken between 7 and 8 a.m. except in panel D, days 1 and 5, when samples were also taken at 8 p.m. Symbols : x x Basic program. Panel B: • Participants with 6 h extra sleep during the night between day 3 and 4. • • Participants with 3 h extra sleep during the night between day 3 and 4. Panel C: • • Participants with 3 h extra sleep each night. Panel D: • • Participants with caloric supplementation of about 6400 kcal, rendering them essentially isocaloric. Vertical bars indicate SEM. (Data from references 7, 8, 9, 27).

heavy physical exercise during these 3 h. The sleep group (Fig. 1C) had significantly higher levels of serum testosterone in the morning than the other group.

30 In a subsequent experiment the cadets were divided in groups, one getting extra caloric supplementation of 6400 kcal per day in addition to the basic diet of 1500 kcal. The supplementary diet consisted of 105 g protein, 125 g fat and 1230 g carbohydrate (9). The dietary supplementation did not affect the testosterone response (Fig. 1D). It is evident from the data of Fig. 1 that a rapid recovery of the testicular function occurred after the end of the program. From panel A and B it can be seen that on day 6, when the sample was taken after 6 h sleep, there was already a significant increase in the serum testosterone level, in agreement with the previously discussed effect of sleep. However, as pointed out, the marked reduction in serum testosterone level within 12 h (Fig. 1D) excludes sleep deprivation as the sole factor behind the reduction in serum testosterone level.

From panels A, C and D, it can be

seen that the values on days 6 to 23 after the program were invariably and significantly higher than before the program. This "rebound" phenomenon may be related to the increased serum level of testosterone binding globulin seen during and after this program (7). This combat course also involved some psychological stress, which may in part be responsible for the response demonstrated. It is well documented that surgical (10) and psychological stress (11) induce a marked reduction in the serum testosterone levels, but contrary to the observation in this study, there is a slow recovery of the testicular function after surgery. The serum levels of other gonadal hormones were also affected during this period of prolonged heavy physical exercise, some of which may be related to the change in serum testosterone. The levels of androstenedione, 5a-dihydrotestosterone (DHT) and oestradiol were all reduced during exercise (Fig. 2 and 3). The reduced androstenedione levels (to less than 50% of the starting values) are interesting in light of the concept that this steroid in man is primarily of adrenal origin (12) and also compared to the increased androstenedione levels after a marathon run (3). Since adrenocortical activity is augmented during this

31

3.0 O ? 2.0& E 1.0-

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Ui

Z o

4.5-

Q UJO

S? 35 i- E in c 0 W 2.5-1

z
-'' 11.6

O Q

O 1.4

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Fig. 6

Serum levels of triiodothyronine in men during prolonged strenuous exercise as described in the text. See Fig. 1 for explanation of symbols, panel A corresponds to Fig. 1B, panel B to Fig. 1C and panel C to Fig. 1D. (Data from references 8, 20 and 27).

Cortisol (Fig. 7) and urinary excretion of free Cortisol and 17-ketogenic steroids (7). It was also found that the normal diurnal variation of serum Cortisol disappeared (Fig. 7C). These data suggest that increased Cortisol secretion may be a major factor in the increased serum Cortisol levels seen in this type of prolonged physical exercise. It should be noticed that there tended to be an adaptation to the situation with reduction in serum levels as the program continued, after the initial peak value observed in the early phase (Fig. 7). A similar adaptation was not observed for the

39

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Fig. 7

Serum levels of Cortisol in men during prolonged strenuous exercise as described in the text. See Fig. 1 for explanation of symbols, panel A corresponds to Fig. 1A, panel B to Fig. 1C and panel C to Fig. 1D. (Data from references 7, 20 and 27).

other hormones, which tends to rule out Cortisol per se as a mediator of the responses discussed before. The renin - aldosterone system The blood levels of aldosterone increased dramatically during heavy exercise in the form of a 90 km cross-country ski-race; a concomitant increase in plasma renin activity (PRA) was observed (1). In a subsequent experiment it was found that exercise for 2-1/2 h on an ergometer bicycle at an exercise level of 60% of Vmax 0z0 gave rise to dramatically increased levels of aldosterone and PRA and a significant reduction of the metabolic clearance rate (MCR) (1). These observations led to the conclusion that the increased serum levels of aldosterone during

40

heavy exercise were due to both increased secretion and reduced metabolic removal from the serum. Evidence was presented that PRA was a major stimulant to the aldosterone increase, a significant correlation was observed between log PRA and the increment in aldosterone, and furthermore, when the bicycle experiment was repeated after administration of the renin blocker, methyldopa, the reduced response of PRA was accompanied by a reduced aldosterone response (1). In our experiments on prolonged physical exercise, the response of aldosterone and PRA was also studied (Fig. 8). Both the serum aldosterone levels and PRA increased dramatically during the first two days with a clear tendency to fall off during the later part of the experiment. This suggested that either some sort of adaptation was taking place or that an exhaustion of the renin - aldosterone system occurred. When the experimental persons were subjected to an ergometer bicycle experiment of 15 min 1 s duration at 60% of V

on day 3, max ¿. they were able to respond with increased serum levels of aldosterone and increased PRA (Fig. 9). The increments were in fact larger on day 3 than on the control day, whereas the per cent increase was quite similar. There was therefore no evidence for

exhaustion of the renin - aldosterone system, and the reduction of aldosterone and PRA during the later part of the experiment was probably due to some sort of adaptation to the exercise. The experimental situation did not allow any metabolic studies so that changes in the electrolyte and water balance of the individuals are unknown. There were, however, no changes in serum electrolyte concentrations and the individuals were not dehydrated as judged from serum protein levels and haematocrit values. It therefore seems that it was the exercise itself that induced the changes in the renin - aldosterone system, a suggestion which is supported by the increase during acute exercise (Fig. 9). However, caloric supplementation produced a significantly lower response of PRA and aldosterone during both prolonged and acute exercise (unpublished observations).

41

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Catecholamines Physical exercise is known to stimulate the release of adrenaline and noradrenaline, and the response is related to the caloric intake; exercise after fasting resulted in higher plasma levels of adrenaline and noradrenaline than observed when the exercise took place after normal caloric intake (24).

42

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Serum levels of aldosterone and plasma renin activity during and after 15 min of exercise on a bicycle ergometer at 60% of V max z Symbols: x x Before prolonged exercise. • • On day 3 of program (Fig. 8).

It has also been shown that the catecholamine response to exercise is dependent upon the condition of training, the response after training being lower than before (25). In our studies, the urinary excretion of adrenaline and noradrenaline increased dramatically and remained elevated throughout the program (7, 13). The plasma levels of adrenaline, noradrenaline and also dopamine were increased during a subsequent study (26). When these subjects, who were under caloric deficiency, were subjected to a bicycle ergometer experiment

43 of 30 min duration at 50% of V

0„, an increased response was max Z observed in agreement with the data of Galbo et al. (24). From the work of Galbo et al. the diet prior to exercise appeared to determine the catecholamine response (24). Catecholamines are known to stimulate renin release, therefore one may speculate that the increased plasma levels of adrenaline and noradrenaline caused the increased PRA and aldosterone levels. In that context it should be pointed out that caloric supplementation induced a diminished response of PRA and aldosterone, which may be relevant to the effect of caloric supplementation on the catecholamine response to exercise discussed above.

Conclusions Prolonged physical exercise severely affects blood levels of many hormones. The alterations are due to changes both in hormone secretion and, at least for some hormones, reduced metabolic removal and possibly changes in distribution volume. Increased levels of Cortisol in combination with decreased level of testosterone will bring the subjects into a situation of catabolism which may be beneficial in providing chemical energy for the work to be done. The multifactorial situation with prolonged physical exercise, sleep deprivation and caloric deficiency makes it difficult to establish which is the factor responsible for the reduced testicular function. Caloric deficiency appears to be of little importance, whereas sleep deprivation seems to play a significant role in the reduction of testicular function. The reduction in serum levels of androstenedione parallel to testosterone in the presence of elevated Cortisol concentrations suggests a major testicular contribution of this steroid, contrary to the commonly accepted views, or it may be explained by a separate factor, other than ACTH, controlling adrenal androgen secretion.

44

The renin-angiotensin-aldosterone system is highly activated during prolonged exercise and this system may be further stimulated during acute exercise with no signs of exhaustion. It seems likely that this activation is related to stimulation of the adrenergic system. The renin-aldosterone response to exercise was reduced when methyldopa was administered prior to exercise and feeding, which reduces catecholamine response to exercise, also reduced PRA and aldosterone responses.

References 1. Sundsfjord, J.A., Stramme, S.B., Aakvaag, A.: Plasma aldosterone, plasma renin activity and Cortisol during exercise. In: "Research on Steroids", Eds. Breuer, H., Hughes, A., Klopper, A., Conti, C., Jungblut, P., Lerner, L., NorthHolland Publishing Company, Amsterdam, Oxford; American Elsevier Publishing Co., New York, vol. VI, pp. 133-140 (1973). 2. Galbo, H., Hummer, L., Petersen, I.B., Christensen, N.J., Bie, N.: Thyroid and testicular hormone responses to graded and prolonged exercise in man. Europ. J. Appl. Physiol. 36, 101-106 (1977). 3. Dessypris, A., Kuoppasalmi, K., Adlercreutz, H.: Plasma Cortisol, testosterone, and androstenedione and LH in a non-competitive marathon run. J. Steroid Biochem. 33-37 (1976). 4. Sutton, J.R., Coleman, M.J., Casey, J., Lazarus, L.: Androgen responses during physical exercise. Brit. med. J. 163, 520-522 (1973). 5. Bliss, E.L., Frischat, A., Samuels, L.: Brain and testicular function. Life Sei. 231-238 ( 1 972). 6. Kirkeby, K., Stramme, S.B., Bjerkedal, I., Hertzenberg, L., Refsum, H.E.: Effects of prolonged strenuous exercise on lipids and thyroxine in serum. Acta Med. Scand. 202, 463467 (1977). 7. Aakvaag, A., Bentdal, 0., Quigstad, K., Walstad, P., R^nningen, H., Fonnum, F.: Testosterone and testosterone binding globulin in young men during prolonged stress. Int. J. Androl. _1_, 22-31 (1978). 8. Aakvaag, A., Sand, T., Opstad, P.K., Fonnum, F.: Hormonal changes in serum in young men during prolonged physical strain. Europ. J. Appl. Physiol. 39, 283-291 (1978).

45

9.

Opstad, P.K., Aakvaag, A.: Decreased serum levels of oestradiol, testosterone and prolactin during prolonged physical strain and sleep deprivation and the influence of a high caloric diet. Europ. J. Appl. Physiol. 49, 343-348 (1982).

10. Carstensen, H., Amer, B., Amer, I., Wide, L.: The postoperative decrease of plasma testosterone in man in relation to plasma FSH and LH. J. Steroid Biochem. 45-55 (1973). 11. Kreutz, L.E., Rose, R.M., Jennings, J.R.: Suppression of plasma testosterone levels and psychological stress. Arch. Gen. Psychiatry 26, 479-482 (1972). 12. Wieland, R.G., de Courcey, C., Levy, R.P., Zala, A.P., Hirschman, H.: C-19-O2 steroids and some of their precursors in blood from normal human adrenals. J. clin. Invest. 44, 159-168 (1965). 13. Holmboe, J., Bell, H., Norman, N.: Urinary excretion of catecholamines and steroids in military cadets exposed to prolonged stress. Forsvarsmedicin Y\_, 183-191 (1975). 14. Vermeulen, A., Ando, S.: Prolactin and adrenal androgen secretion. Clin. Endocrinol. (Oxf.) 8, 295-303 (1978). 15. Ito, T., Horton, R.: The source of plasma dihydrotestosterone in man. J. clin. Invest. ^0, 1621-1627 (1971). 16. McDonald, P.C., Madden, J.N., Brenner, P.F., Wilson, J.D., Siiteri, P.K.: Origin of oestrogen in normal men and women with testicular feminization. J. clin. Endocrinol. Metab. 49, 905-916 (1979). 17. Doerr, P., Pirke, K.M.: Response of plasma testosterone and luteinizing hormone to Cortisol or dexamethasome over a 26-hour period in normal adult males. Acta Endocrinol. (Kbh.) Suppl. J_99, 228 (1 975). 18. Hajjar, R.A., Stratton Hill, C., Samaan, N.A.: Adrenal mediation of the effect of excess ACTH on testosterone levels in males. Acta Endocrinol. (Kbh.) 80, 339-343 (1975). 19. Evain, D., Morera, A.M., Saez, tors in rat testis; their role DNA synthesis of Leydig cells. of Endocrinology, Abstract No.

J.M.: Glucocorticoid recepin the steroidogenesis and 5th International Congress 524 (1976).

20. Opstad, P.K., Aakvaag, A.: The effect of a high calorie diet on hormonal changes in young men during prolonged physical strain and sleep deprivation. Europ. J. Appl. Physiol. 46 , 31-39 (1 981 ) . 21. Irvine, C.H.G.: Effect of exercise on thyroxine degradation in athletes and non-athletes. J. clin. Endocrinol. Metab. 28, 942-948 (1 968) . 22. Johannessen, A., Hagen, C., Galbo, H.: Prolactin, growth hormone, thyrotropin, 3,5,3'-triiodothyronine, and thyroxine responses to exercise after fat- and carbohydrate-

46

enriched diet. J. clin. Endocrinol. Metab. 52^ 56-61 (1981). 23. Davidson, M.B., Chopra, I.J.: Effect of carbohydrate and noncarbohydrate sources of calories on plasma 3,5,3'-triiodothyronine concentrations in man. J. clin. Endocrinol. Metab. 48, 577-581 (1979). 24. Galbo, H., Christensen, N.J., Mikines, K.J., Sonne, B., Hilsted, J., Hagen, C., Fahrenkrug, J.: The effect of fasting on the hormonal response to graded exercise. J. clin. Endocrinol. Metab. 52, 1106-1112 (1981). 25. Hartley, L.H.: Growth hormone and catecholamine response to exercise in relation to physical training. Med. Sci. Sports 7, 34-36 (1 975) . 26. Opstad, P.K., Aakvaag, A., Rognum, T.O.: Altered hormonal response to short-term bicycle exercise in young men after prolonged physical strain, caloric deficit, and sleep deprivation. Europ. J. Appl. Physiol. 4J5 , 51-62 (1 980). 27. Opstad, P.K., Aakvaag, A.: The effect of sleep on the plasma levels of hormones during prolonged physical strain and calorie deficiency. Europ. J. Appl. Physiol. 5, 97-107 (1983).

CORTISOL RESPONSES TO EXERCISE AND THEIR INTERACTIONS WITH DIURNAL SECRETORY PEAKS

G. Brandenberger Centre d'Etudes Bioclimatiques, 21, rue Becquerel, 67087 Strasbourg Cedex, France

In the process of adaptation to stress, Cortisol, which provides evidence of the activation of the hypothalamo-hypophysoadrenal axis is of major interest. Selye (1, 2), long ago underlined the essential role of this hormone, which, together with the catecholamines, is involved in preparing the organism to confront given situations. Within this framework, numerous studies have sought to determine the influence of muscular exercise, a complex stress, on Cortisol secretion, and to reveal the privileged role of this hormone in adaptive reactions. But the precise metabolic role for the increased Cortisol release during exercise is not known (3). The studies were based first of all on the analysis of urinary metabolites and then on the analysis of blood samples taken at long intervals. The development of more sensitive techniques made it possible to monitor plasma Cortisol levels at shorter intervals and to measure urinary free Cortisol. In these investigations, it is often assumed that an increase in adrenal steroid secretion is followed by an increase in the urinary output of steroid metabolites or in plasma corticosteroid levels. But, in fact, little reliance can be placed on urinary metabolites as an index of glandular activity, and only limited information on adrenal secretion rates is provided by plasma Cortisol levels which reflect the net results of Cortisol production, of changes in protein-binding and of metabolic clearance. Furthermore, measurement of total plasma Cortisol does not give information on the biologically active free

Exercise Endocrinology © 1985 by Walter de Gruyter & Co., Berlin • New York - Printed in Germany

48

hormone (4); it is only this fraction that is exchangeable with the extravascular and intracellular compartments and which can react with the specific receptors at most target levels. On the contrary, urinary excretion of free Cortisol is a valuable index to the adrenocortical secretion rate and to the biologically active plasma fraction (5, 6). But analysing urine collected over a long period only reveals the overall effect of muscular exercise and does not reveal transitory hormonal variations. Few studies have been made of Cortisol turnover in man during physical exercise. Exercise increases the rate of Cortisol uptake by peripheral tissues and when the work load exceeds a critical level, stimulation of the adrenal cortex results in massive Cortisol secretion which is sufficient to raise the plasma level and in turn to promote a further ingress of Cortisol into the tissues (7). On the contrary, Leclercq and Poortmans (8) did not reveal any significant increase in the rate of Cortisol catabolism during exercise or in the recovery phase, although the analytical methods and the work load were comparable. Cashmore et al. (9) found that the rise in Cortisol level was concomitant with a significant inflection in the cortisol-specific activity curve and concluded that changes in Cortisol level indicated fairly accurately the time when Cortisol secretion increased (Fig. 1). Most studies have measured the response of urinary excretion or plasma corticosteroid levels to physical exercise, with apparently conflicting results. Decreased, unchanged or increased levels have been found, and it has been asserted that several variables, such as the load and the duration, the state of training and adaptation, can influence the extent and direction of these changes. During short-term exercise, with low or moderate work loads, the plasma Cortisol level varies little and not systematically. Cornil et al. (10) found that short exercise on the bicycle ergometer produced a fall in plasma corticosteroid levels in sedentary subjects. Similarly, Raymond et al. (11) found a reduction in serum corticosteroids in normal healthy

49

Fig. 1

Changes in Cortisol concentration (triangles), and specific activity (squares) and ^H-cortisol concentration (circles) in two subjects during progressive exercise experiments. The box at the bottom of each figure indicates the period of exercise and the respective treadmill gradient. (From ref. 9, with permission) .

subjects who performed low intensity treadmill exercise, whereas Rose et al. (12) showed that there were no significant differences in plasma levels from control values in well-trained subjects after running a mile. In contrast, Staehelin et al. (13) and Lehnert et al. (14) reported an increase in plasma corticosteroid in subjects who performed moderate intensity exercise on the bicycle ergometer. In moderate to heavy exercise, plasma Cortisol levels rise progressively. Davies and Few (15) suggested that a workload of some 60% of a subject's maximum aerobic power (VC^ max) was the critical level, above which a rise in plasma Cortisol occurred in subjects performing treadmill exercises. This increase was also observed in supramaximal exercise (16, 17, 18), and the activity of the pituitary-adrenocortical system was a good

50

indicator of effort during exercise. Similarly, Bloom et al. (19) showed that the Cortisol values rose with a high workload but fell at low and moderate exercise rates. However, Kuoppasalmi et al. (20) and Wade and Claybaugh (21) observed no significant increase in plasma Cortisol levels after 10 or 20 min. exercise at nearly maximum aerobic power. The results of Bonen (22) may account for this lack of response; he indicated that urinary free Cortisol excretion rates correlate positively with % VC>2 max when exercise is sufficiently intense. However, exercise duration must also be considered since Cortisol excretion rates and exercise intensity only correlated in one group who worked at 80% VC^ max for 30 min. , but not in another group who worked at 75% VC>2 max for 10 min. It is therefore difficult to define the lower limit of exercise intensity which increases Cortisol levels, since Cortisol excretion rates depend on the combination of exercise intensity and duration. These conclusions are supported by Brandenberger and Follenius (23) who observed similar transient Cortisol rises with prolonged exercise with low or moderate work loads. The latency, the rate of change in levels and the magnitude did not differ significantly for light or moderate work loads. More strenuous work was required to produce a more rapid Cortisol response (24) . However, the increase in plasma Cortisol level was significantly lower than that induced by less intense but longer lasting exercise. With prolonged exercise, the Cortisol level can rise far above that at rest. The marathon is an extremely strenuous endurance test; the mean Cortisol levels of runners after a non-competitive marathon were 3 to 4 times higher than the control values (25, 26). Maron et al. (27) observed lower increases, roughly 1.8 times the basic levels at the end of a marathon, while Sundsfjord et al. (28) found that after a 70 km cross-country race, plasma Cortisol reached a mean level 3 times higher than before the race. A decrease in the plasma glucocorticoid level is generally found at exhaustion (3). Dessypris et al. (25) observed a much lower Cortisol level than before

51

the race in a marathon runner who had given up at the 15th kilometre. Nevertheless, exhaustion is more often seen in animals, perhaps because animals can more readily be forced to exercise to complete exhaustion (29, 30). Viru and Akke (31) suggested that this decrease in glucocorticoid in severe exercise "is one manifestation of a general defence reaction against the fatal depletion of the resources of the organism". On the contrary, Suzuki et al. (32) found a marked increase in corticosteroids in completely exhausted dogs, whereas in animals which showed no signs of fatigue after exercise, the corticosteroid secretion rates were within the range of physiological variations at rest. Some evidence suggests that the corticosteroid response to exercise depends on fitness. Several authors have reported lower plasma corticosteroid levels in trained animals after acute exercise than in untrained animals (33, 34, 35). But long-term training has also been shown to cause adrenal hypertrophy and an increase in plasma corticosteroids, with a subsequent return to the initial level (3). Severson et al. (36) found a variable age-dependent response in plasma corticosterone levels in trained rats undergoing an acute bout of swimming. In man, lower Cortisol responses have been reported for trained subjects. Metivier et al. (37) found a progressive rise in plasma-cortisol in untrained individuals on low intensity bicycle ergometer exercise, whereas there was an initial decrease in well trained individuals followed by no change during the work period. Similarly, White et al. (38) demonstrated that the pattern of serum corticosteroid response to graded exercise can be influenced by intensive training. They observed significantly lower corticosteroid levels for identical work loads before and after training. Sutton (39) also described a tendency for plasma Cortisol to decrease in fit subjects during exercise, whereas it rose in unfit subjects (Fig. 2). Other studies have failed to demonstrate that training leads to any significant reduction in corticosteroid response patterns. Hartley et al. (40) observed no significant differen-

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2 max) results in increased plasma levels of Cortisol (12, 15). ACTH levels measured before and after 20 min treadmill runs at two submaximal workloads (29) are shown in Fig. 1 with values found in a run to exhaustion lasting 12.6 min + 3.3 (SD) and denoted as the 100% VC>2 max. Resting levels of ACTH were in agreement with those considered normal by Yamaguchi et al. (24) for mid-morning periods. An insignificant increase in ACTH occurred after 20' of running at 65% VC>2 max. The 80% VC>2 max run resulted in a significant increase to 128 pg/ml + 46 (SD) immediately after the run. The run to exhaustion resulted in a further rise in ACTH to 292 _+ 181 pg/ml. Interestingly, this later level (292 pg/ml) is similar to the level found by Donald (30) in response to insulin induced hypoglycemia. This similarity is especially intriguing in light of the fact that plasma glucose levels in our study were increased by 35 mg/dl after the run to exhaustion. Increased glucose levels were also found during the 80% VO^ max run when ACTH was significantly elevated. The studies demonstrate that the stimulus for ACTH release is not hypoglycemia. The rise in glucose during the high intensity runs is consistent with the known hyperglycemic effects of ACTH and Cortisol. Gambert et al. (31) have provided data on nine untrained subjects in response to 20 min of treadmill running at 85% of the predicted maximal heart rate (Fig. 1, mean values determined from graphically presented data in the original article). It is difficult to ascribe a particular percent of VC>2 max to this workload, however, it may be assumed that this level of exertion was approximately equal to 70% VO^ max. The mean increase in ACTH after the run was 31.2 _+ 6.0 pg/ml for five men and 5.2 + 2.0 pg/ml for four women. This sex difference was not evident in our study which included 3 male and 3 female subjects. This four-fold increase reported by Gambert et al. (31) is greater than the 2.24 fold increase we reported after a 80% V0 2 max run for 2 0 min. It should be noted that Gambert et al. (31)

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monitored by a spirometer. Of the unspecified but "large number" who were investigated, only eight, aged 21 _+ 2 y, completed this test, reaching maximal effort "between 8 and 15" minutes. No data was presented on the .remainder. Plasma samples were obtained at baseline, maximal exertion, and 15 and 30 minutes after stopping. Extracts of plasma were chromatographed on Sephadex G-75 to separate p-EP from p-LPH, and levels of the former peptide were then measured by radioimmunoassay. ACTH was also measured in the samples. Levels of P-EP were 320 pg/ml at baseline, rising over five-fold at maximum effort and then promptly declining. ACTH levels averaged 80 pg/ml to start and rose over ten-fold, then promptly declined. Fifteen endurance-trained males, running for between four and seven hours along a 45.9 km course on a steep, high-altitude mountain trail, were studied by Appenzeller et al. (43). Preand post-run p-EP levels were 116 and 200 pg/ml, a "highly significant" difference which held true for the entire group and also for subgroups either younger or older than 40. The rise tended to be greater in the younger group; numbers in each subgroup were not given nor were details of the assay described. Of five reports in 1981, Colt et al. (44) described preand post-run levels of total immunoactive p-EP equal to 11.8 and 17.6 pg/ml, respectively, in twenty runners covering 6.4 to 12.8 km at a "self-regulated comfortable speed". None of these subjects and six additional ones covered the same course more rapidly, so that "the effort was close to maximal", and had preand post-run total p-EP levels of 8.2 and 28.0 pg/ml. These 15 subjects had incremental rises of total p-EP which correlated negatively with years of prior training. In addition, P-EP and p-LPH were each measured separately after separation on G-50 Sephadex prior to and after the strenuous run in seven subjects, of whom five had rises in both peptides. The molar ratio of PEP to p-LPH determined in this last portion of the study averaged 24%. The assays of p-EP and p-LPH applied in this study were developed by the authors (45). Berk and colleagues (46) analyzed serum samples in six

167

athletes and six non-athletes performing graded treadmill exercise according to the Bruce protocol. Samples were drawn fasting basally, at each stage, and 15, 30, and 60 minutes after exercise. Percentage increases over basal levels were presented for maximal exertion, and the stage immediately preceding, along with post-exercise values in male and female athletes and nonathletes. In all groups, endorphin levels doubled during exercise. Peak values occurred at the stage just before maximal exertion but in non-athletes there was a second, post-exercise rise which was especially marked for the women, in whom postexertion values rose six-fold within 15 minutes. Details regarding the number of subjects, their ages, or assay techniques were not provided. Bortz et al. (47) studied participants in a 100-mile race across snow-covered mountains and desert canyons. The course encompassed a 17,000 foot increase and 22,000 drop in altitude, and was completed by only half of the 250 starters despite rigorous entry criteria. The fastest time to finish was 18.5 h. Fifty-one entrants were sampled 12 days prior to the race, 12 provided specimens at the 60-mile point, and 34 at the finish. 3-EP immunoactivity, assayed by means of an antibody directed against the carboxy terminal and so presumably reacting with 3-LPH as well, rose 85% above control levels at the 60-mile point and had fallen to 139% of baseline by the finish. Both these values were significantly higher than baseline. A study from the authors' laboratory (48) examined the effects of aerobic training upon the exercise-induced rise of plasma |3-EP and 3-LPH in seven healthy, endocrinologically screened but previously inactive women aged 18 to 30 y. Females were studied because of interest in the relationship between EOs and menstrual dysfunction which often accompanies athletic stress (49 and see below). To simulate typical athletic training, subjects trained six days per week to attain 85% of maximum heart rate for progressively greater fractions of each day's one-hour training session. Subjects were instructed to eat so as to maintain a constant weight. A sham exercise test was conducted in

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the early follicular phase of the menstrual cycle before conditioning, after which submaximal exercise tests were performed monthly just before the start of training, and twice thereafter. During each test, subjects pedalled on a bicycle ergometer for one hour against work loads adjusted so as to result in progressively rising heart rates until maintaining a constant pulse of 85% maximal in the final 15 minutes (50). Two baseline blood samples were withdrawn atraumatically before acute testing, another specimen was drawn at the close of the one-hour test, and a fourth specimen was taken 30 minutes later. Assays of total immunoactive S-EP (= 3-EP + 3~LPH) were performed (48, 51). Gel chromatography of pooled plasma extracts revealed that the increases in total 3-EP resulted from rises of both 3-EP and 3-LPH (Fig. 3). Baseline levels of total 3-EP averaged approximately 30 pg/ml, and there was a steady increase in the exercise-induced increment in total 3-EP from 57% to 145% during eight weeks of conditioning. Cortisol and ACTH were also measured. ACTH rose in parallel with total 3-EP, but Cortisol rose only during the last two exercise tests, when the release of ACTH and 3-EP was greatest. A six-fold greater increase in 3-EP immunoactivity and ACTH in men compared to women was seen in an acute study (52). The subjects were five men and four women aged 24 to 36 y, all described as healthy but sedentary apart from one of the women who ran 10 miles per week. No data were given regarding the phase of the menstrual cycle in the women. All subjects ran on a treadmill for 20 minutes to maintain pulse rates at 80% of predicted maximum. Pre- and post-exercise blood samples were obtained in all cases, and in two volunteers more frequent specimens were taken to delineate the time course of the responses. Total 3 _ EP immunoactivity was measured in plasma extracts by means of an antibody with 20% cross-reactivity by weight to 3-LPH. Because the ratio of 3 _ EP to 3-LPH was not determined, it is problematic to express their results in fmol/ml in terms of pg/ml, although a crude estimate would be 45 and 8 pg/ml for men and women, respectively. Baseline levels of ACTH and immuno-

169

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