VIP and PACAP

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VIP and PACAP Edward J. Goetzl*, Julia K. Voice and Glenn Dorsam Immunology and Allergy, University of California, San Francisco, 533 Parnassus Avenue, Room UB8B, Box 0711, San Francisco, CA 94143-0711, USA * corresponding author tel: 415-476-5339, fax: 415-476-6915, e-mail: [email protected] DOI: 10.1006/rwcy.2000.13003.

SUMMARY

BACKGROUND

Vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating peptide (PACAP) are homologous mediators that are released from cholinergic, nonadrenergic noncholinergic, and other neurons. They are recognized by members of a subfamily of G protein-coupled receptors. VIP and PACAP are distributed widely, but with anatomical peaks, in the nervous and endocrine systems, lungs, intestines, and immune organs. Their early appearance in embryogenesis and the deleterious effects of pharmacological antagonism in utero both suggest that VIP and PACAP are critical mediators of development. In adult mammals, VIP and PACAP normally have potent neural, endocrine, other physiological, and immune effects and potential pathological roles in esophageal achalasia, Hirschsprung's disease of the colon, cystic fibrosis, diabetes, and asthma.

VIP and PACAP are constituents of one structural superfamily of neuroendocrine hormones which also includes secretin, glucagon, glucagon-like peptide, and growth hormone-releasing hormone (Table 1) (Said and Mutt, 1988). VIP and PACAP are linked by some functional similarities based on their sharing of two of the three G protein-coupled cellular receptors in one subset.

Discovery VIP was first identified as a potent vasodilator in extracts of porcine intestine (Said and Mutt, 1970) and was subsequently found to be a 28 amino acid neuroendocrine peptide distributed widely in the nervous, endocrine, gastrointestinal, respiratory, and

Table 1 Structures, determinants of expression, and cellular sources of VIP, PACAP38, and PACAP27 Peptide

Amino acid sequence: signature structures

Regulation of expression

Sources

VIP

H-S-D-A-V-F-T-D-N-Y-T-R-L-R-KQ-M-A-V-K-K-Y-L-N-S-I-L-N-NH2 Human, pig, cow, dog  helix ˆ aa 13±20/26

Cyclic AMP, Ca2+, neuropoietic cytokines

NS, endo, GI, resp, and immune systems

PACAP38

H-S-D-G-I-F-T-D-S-Y-S-R-Y-R-KQ-M-A-V-K-K-Y-L-A-A-V-L-G-K-RY-K-Q-R-V-K-N-K-NH2 Human, ovine, rat

PACAP27

H-S-D-G-I-F-T-D-S-Y-S-R-Y-R-K-Q-M-AV-K-K-Y-L-A-A-V-L-NH2

CNS, endo, GU, GI, and resp systems

NS, nervous system; CNS, central nervous system; endo, endocrine; GI, gastrointestinal; GU, genitourinary; resp, respiratory.

1398 Edward J. Goetzl, Julia K. Voice and Glenn Dorsam immune systems of mammals (Said and Mutt, 1972). PreproVIP, the precursor cleaved to yield VIP, is also the source of biologically active peptide histidine isoleucine (PHI) or peptide histidine methionine (PHM), depending on which species is the source, and a peptide histidine valine (PHV), which is a Cterminally extended form of PHI and PHM. PACAP was first found in extracts of ovine hypothalamus as a potent stimulus of adenylyl cyclase activity in rat cultured anterior pituitary cells, and was subsequently determined to consist of one predominant 38 amino acid peptide (Miyata et al., 1989) and a C-terminally truncated 27 amino acid variant (Table 1) (Miyata et al., 1990). PACAP was detected most prominently in the central nervous system, with highest concentrations in the hypothalamus, substantial levels in testis and adrenal medulla, and lower levels in other areas of the central nervous system, ovary, lung, eye, intestines, and pancreas.

Structure VIP, PACAP38, and PACAP27 are linear peptides with a C-terminal amide and without any complex substituents (Table 1).

Main activities and pathophysiological roles VIP and PACAP are potent mediators of neural development and survival, hormone secretion, smooth muscle function, glandular secretion, and cellular migration, adhesion, and production of cytokines and other proteins (Table 2).

GENE AND GENE REGULATION

Accession numbers Human VIP: M33027, M37460, M54930, M38563, M36634 Human PACAP: E02721, E02722 Rat PACAP: E02724

Chromosome location The 8.8 kb gene encoding preproVIP has been localized in human chromosome 6p24 (Table 3). Expression of preproVIP is regulated with cell type specificity by intracellular cyclic AMP and Ca2+, phorbol esters,

and several members of the neuropoietic family of cytokines (Table 3) (Yamagami et al., 1988; Fink et al., 1991). The 6.9 kb gene encoding preproPACAP is located in rat chromosome 9 and human chromosome 18p11 (Hosoya et al., 1992; Cai et al., 1995).

Regulatory sites and corresponding transcription factors Neural cell-specific full expression of the preproVIP gene is mediated by a tissue-specific element (TSE) consisting of a 425 bp domain with two AT-rich octamer-like sequences between ÿ4.7 and ÿ4.2 kb upstream of the transcription start site (Hahm and Eiden, 1998). The TSE interacts with four additional promoter proximal domains defined by mutational analyses in human neuroblastoma cell lines, including a 17 bp cyclic AMP-responsive element (CRE) enhancer immediately proximal to the TSE and a series within ÿ1.55 kb of the start site composed of an enhancer with E-boxes and MEF2-like motifs (ÿ1.55 to ÿ1.37 kb), a repressor STAT motif (ÿ1.37 to ÿ1.28 kb), and an enhancer AP-1-binding sequence (ÿ1.28 to ÿ0.9 kb). Phorbol esters use distinct messenger pathways but trans-acting proteins of similar DNA-binding specificity to regulate the VIP precursor protein gene convergently through the CRE enhancer (Fink et al., 1991). Ca2+-mediated increases in preproVIP mRNA levels in human neuroblastoma cell lines contrast with those evoked by cAMP in being cAMP-independent, slower in time course and requiring de novo protein synthesis. Although increases in Ca2+ induce differential rises in several transcription factors relative to cAMP, no promoter element was unequivocally coupled to the effects of Ca2+. The 180 kb neuropoietic cytokine response element (CyRE) is located between the first of the three TSE-interactive domains and the CRE in the same neuroblastoma cell lines. Coordinated binding of the STAT1 and STAT3 proteins to one CyRE site and a complex of c-Fos, JunB and JunD to an AP-1 site of the CyRE stimulates cytokine- and cell type-specific transcription of the preproVIP gene (Symes et al., 1997). Little specific information is available about transcriptional control of the gene encoding the PACAP precursor protein.

Cells and tissues that express the gene The genes encoding preproVIP and preproPACAP are widely expressed in many types of cells and tissues (Table 1).

VIP and PACAP 1399 Table 2 Effects of VIP, PACAP38, and PACAP27 on cellular and tissue differentiation, organogenesis, survival, and functions Peptide

Target cell/tissue/system

Effects on development and functions

Neural tube (NT), murine

Patterning

Neural PACAP VIP

CNS, murine

Post-NT closure early neurogenesis

VIP

CNS, murine

Neuronal survival, excitotoxin resistance

PACAP

NS

Neurite outgrowth

VIP/PACAP

CNS

Neuronal proliferation, differentiation

VIP

Cerebral astrocytes, rat

IL-6 generation

VIP

Adrenal gland

Production/secretion, many hormones

PACAP/VIP

Rodent GI

Secretin secretion

Endocrine

PACAP/VIP

Rat GI

Serotonin release

PACAP/VIP

Rodent pancreas

Insulin secretion

VIP

Guinea pig, rat, human

Smooth muscle relaxation

PACAP

Rat, opossum

Smooth muscle relaxation

VIP

Rat, dog, hamster

Vasodilatation, reversal of vasoconstriction

VIP/PACAP

Cat, ferret, dog, human

Water and mucus secretion

VIP

Rat small intestine

Inhibition of transport

PACAP

Rat

Catecholamine secretion

Human/mouse T cells

Enhancement of adhesion

Non-neuroendocrine physiological

Immune and inflammatory VIP

Stimulation of migration Activation of matrix metalloproteinases VIP

Human/mouse T+ B cells

Decreased generation of IgG, increased production of IgE, IgA

VIP

Human/mouse T cells

Decreased IL-2, IL-4, IL-10, and IL-13

VIP/PACAP

Mouse/human macrophages

Induction of chemotaxis

Increased IL-5, IFN Inhibition of TNF generation and secretion VIP

Rodent mast cells

Inhibition of histamine release Elicitation of mediator release

VIP

Human blood mononuclear leukocytes

Inhibition of NK activity

VIP

Human skin

Adhesive protein expression by leukocytes Leukocyte infiltration

1400 Edward J. Goetzl, Julia K. Voice and Glenn Dorsam Table 3 Chromosomal location and genomic organization of VIP and PACAP genes Peptide

Species

Chromosome and other genomic characteristics

PACAP

Rat

9

Human

18p11

VIP

Human

6p24

Figure 1 Amino acid sequences for VIP, PACAP38, and PACAP27. VIP HSDAVFTDNY TRLRKQMAVK KYLNSILN

and immune proteases frequently cleave VIP rapidly on the carboxyl-side of Asp3, Thr7, Tyr10, Tyr22, Ser25, as well as the expected tryptic sites, and a monoclonal catalytic anti-VIP antibody cleaves on the carboxyl side of Lys20, but none acts in the predicted  helical domain. Extensive studies of the binding and functional activities of a wide range of linear and cyclical analogs of VIP have established a model pharmacophore, which requires the entire native sequence for optimum potency and is highly dependent on Asp3, Phe6, Thr7, Tyr10, Tyr22, and Leu23 (O'Donnell et al., 1991). Far less is known of the structural determinants of activity of PACAP.

PACAP38 HSDGIFTDSY SRYRKQMAVK KYLAAVLGKRYKQRVKNK

CELLULAR SOURCES AND TISSUE EXPRESSION

PACAP27 HSDGIFTDSY SRYRKQMAVK KYLAAVL

Cellular sources that produce

PROTEIN

Sequence See Figure 1.

Description of protein The conformation of VIP and biologically active fragments of VIP have been analyzed by physicochemical studies, computational methods, and susceptibility to peptidolysis (Haghjoo et al., 1996; Filizola et al., 1997). Circular dichroism (CD) estimates of the secondary structure of an analog of VIP1-28 and of various substituents of VIP1-28 in methanolic aqueous solutions showed helical content of 60±70% and suggested an  helical domain spanning amino acids 13±20. However, the CD spectra in aqueous buffer resembled random coils with only approximately 25%  helix. The results of proton NMR studies of the same VIP structures in methanolic aqueous solutions were consistent with a single extended  helix from amino acids 11 to 27 and with the tendency to form turns at the N-terminus. Calculations designed to predict lowest energy configurations of amino acids 1±11, when attached to an amino acid 12±28  helix, suggested bent or multi-turn configurations for VIP1±11 compatible with those proposed by NMR data. The presence of an  helix spanning amino acids 13±20 is also supported by the findings that different neuroendocrine

VIP is distributed widely in the nervous, endocrine, gastrointestinal, respiratory, and immune systems of mammals (Said and Mutt, 1972). PACAP is present at highest levels in the central nervous system, but there are also substantial levels in testis and adrenal medulla, and lower levels in other areas of the nervous system, ovary, lung, eye, intestines, and pancreas. VIP and PACAP are both found principally in neurons of the cholinergic and nonadrenergic noncholinergic systems of the CNS and peripheral nerves, as well as intrinsic neural networks of the endocrine, reproductive, gastrointestinal, immune, and respiratory systems (Said and Mutt, 1988) (Table 1). Some tumor cells produce and store these neuropeptides, perhaps as a manifestation of dedifferentiation, but there is no apparent relationship to tumor biology. Mast cells, basophils, eosinophils, macrophages, and T cells may also contain low levels of immunoreactive VIP, but a large fraction of VIP in immune cells consists of truncated or otherwise altered variants with lower potency and less activity than intact VIP1-28 (Wershil et al., 1993). VIP and PACAP are both expressed at levels predominantly determined by the balance between transcriptionally regulated synthesis and susceptibility to peptidolysis, and exert many different types of effects in numerous organ systems.

Eliciting and inhibitory stimuli, including exogenous and endogenous modulators See Table 1.

VIP and PACAP 1401

RECEPTOR UTILIZATION VIP and PACAP are specifically recognized by three distinct members of a separate subfamily of G protein-coupled receptors. Both forms of PACAP bind to the PAC1 receptor with approximate Kd values of 1 nM while VIP binds to PAC1 with much lower affinity (Kd ˆ 1 mM). In addition, VPAC1 and VPAC2 bind VIP and the PACAPs with similar affinities (Kd ˆ 3±10 nM), and bind secretin, GRF, and other members of this neuropeptide superfamily with much lower affinities that vary with the species of origin of the VPACs.

IN VITRO ACTIVITIES

In vitro findings Effects of VIP and PACAPs may be considered in four broad categories: neural; endocrine; nonneuroendocrine physiological, including vascular, muscular, glandular and metabolic; and immune and inflammatory (Table 2). The principal neural effects of VIP and PACAP are regulation of proliferation and gene expression by differentiating neurons during early embryogenesis (Gressens et al., 1993; Waschek et al., 1998). The highest fetal tissue level of VIP was observed on embryonic day 11 in rodents when no VIP mRNA was detected in the tissues, which led to the demonstration that maternal nerves are the major source (Hill et al., 1996). Pharmacological antagonism of VIP on embryonic days 9±11 in vivo resulted in growth retardation and microcephaly, which were prevented by administration of exogenous VIP (Gressens et al., 1994). Limited results of several studies have documented stimulatory effects of VIP and/or PACAP on neuronal survival, outgrowth of neurites, cellular differentiation, and generation of cytokines in vitro (Said and Mutt, 1988). VIP and PACAP also modulate release of neuropeptides from some sensory nerves (Said and Mutt, 1988). Endocrine effects of VIP are predominantly directed at regulation of secretion of numerous hormones. VIP enhanced secretion of cortisol, aldosterone, and androgens by cultured mixtures of human adrenal cortical and chromaffin cells (Bornstein et al., 1999). That -adrenergic antagonists blocked augmentation of corticosteroid production by VIP suggested that a major primary effect of VIP is induction of catecholamine generation by medullary cells. This possibility was supported by direct findings of VIP enhancement of adrenal catecholamine release (Przywara et al., 1996). VIP stimulated release of

secretin and inhibited secretion of serotonin from intrinsic plexus nerves of the rodent gastrointestinal tract (Chang et al., 1998). VIP and PACAP raised [Ca2+]i and stimulated release of insulin by pancreatic cells through several different mechanisms in vitro (Leech et al., 1995). This capability of VIP was demonstrated in vivo by the findings that transgenic overexpression of VIP in mice under control of the insulin promoter increased the pancreatic cell content and level of secretion of VIP in association with enhanced secretion of insulin and improved glucose tolerance (Kato et al., 1994). Other physiological effects of VIP and/or PACAP result from smooth muscle and vascular activities, and actions on transport and secretory systems (Table 2). VIP and PACAP mediate vasodilatation and relaxation of smooth muscle in several organ systems of some species. The powerful systemic and pulmonary vasodilatory actions of neurally delivered VIP and PACAP are endothelial cell-independent and regionally expressed, as exemplified by the greater effect in proximal than peripheral pulmonary airways. Nonadrenergic noncholinergic neural responses, that relax smooth muscles of most organs and are the principal relaxant of human pulmonary airways, are mediated and modulated by VIP, PACAP, and endogenous nitric oxide (NO). Although the inhibitory role of NO has been directly established in contractions induced by electrical field stimulation and cholinergic activation, a dependence on crude probing tools such as protease degradation of neuropeptides and the lack of useful pharmacological agents for VIP and PACAP has prevented unequivocal confirmation of the involvement of the neuropeptides. In some instances, weak antagonists of VIP and PACAP have attenuated neurally mediated relaxation of intestinal smooth muscle. The relaxing effects of VIP and PACAP are expected to be more prominent in proximal pulmonary airways and directed to cholinergic mechanisms, as VIPergic nerves are concentrated around airway ganglia. The mechanisms by which VIP and PACAP relax smooth muscle have been only partially elucidated, but include changes in L-type Ca2+ channel currents mediated by cAMPdependent protein kinase and protein kinase C (Leech et al.,1995). The dense networks of VIP- and PACAP-containing nerves around many different types of secretory epithelial cells and submucosal glands suggested a role in regulating fluid and mucus production. In many model systems, VIP and PACAP stimulate glandular secretion, as would be expected for adenylyl cyclase agonists, and often show preferential effects on one component of the process. For example, VIP stimulates secretion of mucus glycoproteins more

1402 Edward J. Goetzl, Julia K. Voice and Glenn Dorsam than chloride transport or water secretion in pulmonary airways, but has greater enhancing activity for serous than mucus secretions in nasal mucosa (Barnes et al., 1991). Other effects on secretion and transport include induction of catecholamine release from adrenal chromaffin cells (Przywara et al., 1996) and inhibition of alanine absorption by the jejunum (Barada et al., 1998). VIP affects the cystic fibrosis transmembrane conductance regulator (CFTR), defective cellular trafficking of which is the most common cause of cystic fibrosis. Cl secretion and selective apical membrane expression of the CFTR were both significantly increased by VIP at concentrations as low as 10 nM (Lehrich et al., 1998). Although high concentrations of VIP and PACAP may affect the localization and activities of mast cells and inflammatory leukocytes in vitro, concentrations attainable in vivo will rarely initiate or influence inflammatory or hypersensitivity reactions directly. The principal immunological and inflammatory effects of VIP are T cell-dependent (Table 2). Less is known of the actions of PACAP on T cells and most preliminary analyses have shown less binding by T cells of PACAP than VIP. VIP alters thymocyte maturation with preferential promotion of development of helper T cells (Pankhaniya et al., 1998). The results of in vitro studies have also identified three major effects of VIP on human blood and rodent tissue T cells, and on cultured lines of T cells with defined VIP/PCAP receptors. First, VIP evokes T cell migration through basement membranes and connective tissues by increasing expression of adhesive proteins, stimulating chemotaxis and inducing secretion of specific matrix metalloproteinases (MMPs) (Johnston et al., 1994; Xia et al., 1996). VIP facilitates interactions of T cells with endothelium and connective tissues by increasing expression of P- and Eselectins and enhancing T cell 1 integrin-dependent binding to VCAM-1 and fibronectin (Smith et al., 1993; Johnston et al., 1994). Chemotaxis of T cells through micropore filters coated with mixtures of basement membrane components is stimulated by VIP at concentrations as low as 0.1 nM and requires T cell secretion of MMPs-2 and -9 to create channels in the basement membrane matrix (Xia et al., 1996). Basement membrane transmigration of T cells stimulated by VIP, but not that elicited by some chemokines, is suppressed by MMP inhibitors. VIP induction of all aspects of T cell migration is mediated selectively by VPAC2, whereas in some subsets of T cells VPAC1 signaling inhibits migration in response to other chemotactic factors (see chapter on PACAP and VIP Receptors). Second, concentrations of VIP attained in tissues mounting immune responses inhibit T cell production

and secretion of IL-2, IL-4, IL-10, and IL-13 by transcriptional and posttranslational mechanisms (Ganea and Sun, 1993; Sun and Ganea, 1993). In some subsets of mouse T cells, VIP enhances antigeninduced secretion of IL-5 (Mathew et al., 1992). Similarly, IFN production by antigen-challenged cloned and purified mouse TH1 cells is augmented markedly by VIP, without an effect on IFN production elicited by mitogen, anti-CD3 antibody, or ionophore plus phorbol ester (Jabrane-Ferrat et al., 1999). VIP and PACAP also regulate cytokine production by macrophages, as exemplified by inhibition of TNF generation through transcriptional mechanisms dependent on both suppression of NFB binding and alterations in the composition of the CRE-binding complex (Delgado et al., 1998). Third, T cell-dependent generation of IgG and, in some circumstances IgM, is inhibited more than 90% by VIP, that concurrently enhances production of IgA and IgE (Goetzl et al., 1990; Boirivant et al., 1994). A maximal effect depends on maintenance of the level of VIP by repeated introduction into the culture medium. Effects of VIP on NK cells and B cells are not well documented to date.

Bioassays used VIP and PACAP are assessed by bioassays of effects on cellular differentiation and function, secretion of hormones, proteins and mucous glycoproteins, smooth muscle relaxation and vascular dilatation, and cellular migration and adhesion (Table 2).

IN VIVO BIOLOGICAL ACTIVITIES OF LIGANDS IN ANIMAL MODELS

Normal physiological roles The results of analyses in four distinct settings illustrate the promise of potent and distinct activities for VIP and PACAP, and also demonstrate the problems of obtaining unequivocally definitive results. First, pharmacological antagonism of VIP on embryonic days 9±11 in vivo resulted in growth retardation and microcephaly, that were prevented by administration of exogenous VIP (Gressens et al., 1994). Although this finding supports the likely involvement of VIP in ontogeny, the only available

VIP and PACAP 1403 pharmacological agents employed lack potent antagonistic activity and possess some partial agonist functions. Second, in trials of bronchodilator activity, intratracheal VIP alone only weakly and transiently (t1/2 ˆ 4 minutes) reversed the bronchoconstriction evoked in guinea pig lungs by intravenous administration of 50 mg/kg of histamine. In contrast, the effects of N-terminally acetylated and amino acidsubstituted analogs of VIP with higher in vitro potencies were greater and longer-lasting, with durations of up to 4 hours (O'Donnell et al., 1994). However, these analogs also increased bronchial blood flow more effectively, which may have led to more efficient clearance and metabolism of the histamine. Bioavailable VIP analogs also prevented the bronchoconstriction, bronchial edema, and lung tissue eosinophilic responses of sensitized guinea pigs to intratracheal antigen challenge. Third, acute infusion of 10 nmol of VIP into the afferent lymphatics of lymph nodes in sheep reduced efferent flow of lymphocytes by approximately 75% for many hours (reviewed in Goetzl et al., 1990). VIP demonstrated selectivity in control of lymphocyte traffic, as B cells were affected more than T cells and CD8+ T cells more than CD4+ T cells. The underlying mechanisms remain obscure, however, and oppose results of related studies. Physiologically, increases in flow of both lymph and the blood that is a source for lymphatic lymphocytes after administration of VIP would be expected to produce the opposite result. Further, the rank order of frequency of VIP receptors is CD4+ T cells > CD8+ T cells  B cells, as are the magnitude of in vitro effects of VIP. Fourth, prominent effects of VIP are observed in in vivo compartmental immune responses. VIP is released into fluid of the anterior chamber of the eye at nanomolar concentrations after local antigen challenge of immunized animals or introduction of immunologically active cytokines (Taylor et al., 1994; Ferguson et al., 1995). The capacity of this VIP to suppress production of IFN and delayed-type hypersensitivity reactions in the anterior chamber was shown by loss of suppression after specific absorption or antagonism of VIP. In another series of studies of neuromodulation of regional immunity, intratracheal antigen challenge of primed mice resulted in release of VIP into pulmonary tissues. The concentration of VIP attained nanomolar levels in bronchoalveolar lavage fluid with a peak 1±3 days after that of substance P and concurrent with the time of maximal infiltration of CD4+ T cells (Kaltreider et al., 1997). More than 50% of the CD4+ T cells responding to antigen expressed VPAC1 and/or VPAC2, as assessed by quantification of mRNA encoding the receptors

and immunochemical analyses. The lack of useful in vivo pharmacological antagonists prevented further definition of the immunoregulatory roles of VIP in this model. More definitive investigations of the in vivo effects of VIP and PACAP will require not only the development of selective agonists and antagonists, but also of forms of delivery of the peptides that stabilize active configurations and minimize proteolytic inactivation. One such recent effort involves the use of liposomal VIP in a hamster cheek pouch model that allows intravital microscopic evaluation of vascular events and in situ administration of vasoactive mediators. VIP on sterically stabilized liposomes assumes a predominantly  helical conformation. Suffusion of either phenylephrine or angiotensin II vasoconstricted hamster cheek pouch blood vessels significantly and liposomal VIP, but not aqueous VIP, attenuated this vasoconstriction with maximal effect at 30 minutes after administration (Ikezaki et al., 1998). Optimal concentrations of numerous other vasodilators failed to reverse phenylephrine or angiotensin II-evoked vasoconstriction, emphasizing the distinctive effectiveness of liposomal VIP.

Transgenic overexpression Transgenic upregulation of expression of VIP in pancreatic islet cells resulted in greater secretion of insulin and improved glucose tolerance in mice (Kato et al., 1994).

Interactions with cytokine network VIP regulates negatively and positively the generation of cytokines by macrophages and lymphocytes.

PATHOPHYSIOLOGICAL ROLES IN NORMAL HUMANS AND DISEASE STATES AND DIAGNOSTIC UTILITY

Role in experiments of nature and disease states In the absence of animals or humans with genetically determined deficiencies of VIP or PACAP, and without antagonists having reliable bioavailability, conclusions about pathogenetic participation are based on findings of abnormally high or low levels in

1404 Edward J. Goetzl, Julia K. Voice and Glenn Dorsam involved tissues in relation to expression of a disease. Deficiencies of VIPergic nerves, assessed by morphometric criteria, have been observed at the affected tissue sites of patients with esophageal achalasia and Hirschsprung's disease of the colon, where absence of VIP may contribute to each characteristic disorder of gastrointestinal motility (Said and Mutt, 1988; reviewed in Goetzl et al., 1990). Similarly, subsets of patients with cystic fibrosis or asthma have diminished respiratory airway content of VIP, that may account in part for the respective abnormalities of exocrine secretion and bronchial reactivity (Said and Mutt, 1988; Goetzl et al., 1990). Other reductions in tissue content of VIP observed transiently in acute inflammatory or metabolic illnesses have been attributed to cytokine- or drug-induced reductions in synthesis, accelerated biodegradation, and/or increased use through binding to greater numbers of cellular receptors.

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LICENSED PRODUCTS VIP cyclic analog agonists (Astra, Stockholm from Hoffman LaRoche, Inc.)