Nonadrenergic noncholinergic neurotransmitter of feline trachealis: VIP or nitric oxide?

We tested the hypothesis that vasoactive intestinal peptide (VIP) or nitric oxide (NO) is the nonadrenergic noncholinergic (NANC) neurotransmitter in feline trachealis. Isometric tension was measured in trachealis (open or closed tracheal rings) in vitro. Propranolol (10 microM) and atropine (1 microM) were present throughout the experiment, and smooth muscle tone was increased to 60-90% maximal with 5-hydroxytryptamine. We used three methodologies to reduce the relaxation function of VIP, which in turn should reduce NANC-mediated relaxation. 1) The putative VIP antagonist peptide T (10 microM) did not affect VIP concentration-response curves or electrical field stimulation- (EFS) induced NANC responses. 2) Incubation of tissue in specific VIP antiserum (16 h at 4 degrees C) did not reduce EFS-induced NANC relaxations relative to tissue incubated in normal rabbit serum (P > 0.05). On the basis of our passive immunization techniques, it is not possible to absolutely reject VIP as the NANC transmitter. We speculate that nonspecific peptidases present in normal serum and VIP antiserum reduce EFS-induced responses similarly. 3) VIP desensitization, confirmed by a significant rightward shift (P < 0.01) in the VIP concentration-response curve, was achieved by exposing tissues (n = 11) to 1.0 microM VIP for 30 min. Desensitization did not reduce the EFS-induced NANC relaxatory response (P < 0.05) compared with control tissues, suggesting that VIP is not the NANC mediator.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptides and skin inflammation

Neuropeptides (NP) are protein compounds contained both in the central and peripheral nervous system. They can be antidromically released from sensory nerves and are implicated in the so-called neurogenic inflammation. They also exert a number of functions within the immune system and are thought to act as trophic as well as mitogenic substances. Several NP have been detected in human skin by immunohistochemical and radioimmunological techniques, and recent reports have demonstrated that NP could be involved in the mechanisms of certain dermatoses. The involvement of NP in either physiological or pathophysiological skin conditions is discussed. Moreover, a few questions, which still need to be addressed, are raised, and future directions this field of research should take are outlined.

Evidence for involvement of nitric oxide in the regulation of hypothalamic portal blood flow

Vasoactive intestinal polypeptide and peptide histidine isoleucine, two peptides with a common precursor and with strong vasodilatory actions, have been suggested to be involved in control of blood flow through the hypothalamic portal blood vessels, in this way regulating the amounts of releasing and inhibitory factors reaching the anterior pituitary. Using the indirect immunofluorescence technique, we now show that this system also contains the enzyme nitric oxide synthase, as well as acetylcholinesterase. It is therefore likely that the control of blood flow through the portal vessels is mediated via relaxation of smooth muscle cells with a high myogenic tone by neuronal release of four vasodilatory compounds, acetylcholine, vasoactive intestinal polypeptide, peptidine histidine isoleucine, and nitric oxide, i.e. a classic neurotransmitter, two neuropeptides and a gas.

Convergent serotonin and GABA innervation of VIP neurons in the suprachiasmatic nucleus demonstrated by triple labeling in the rat

By means of a combination of serotonin (5-HT) uptake radioautography and dual immunocytochemistry, vasoactive intestinal polypeptide (VIP) neurons in the suprachiasmatic nucleus are demonstrated to simultaneously receive both 5-HT and GABA afferents at their somatic and dendritic levels. These data constitute a further step towards the improved characterization of the morphological substrate of the integrative function of these neurons, which are known to play an important role in the delivery of light-mediated rhythmic signals to other parts of the brain.

[Role of gut hormones in irritable bowel syndrome]

In irritable bowel syndrome (IBS), motility disturbances occur from the upper gastrointestinal tract to the distal colon, where regulatory peptides have a wide-spread distribution. Studies on basal and postprandial plasma levels of different gut hormones show that VIP, CCK, and motilin may be closely related to the symptoms including abdominal pain, diarrhea and constipation. In addition, peptide YY and NPY have effects on absorption in the intestine, and some opioid peptides exert actions on colonic motility in IBS patients. Recent studies revealed that gall bladder in IBS has an abnormal sensitivity to CCK-8, indicating that IBS patients has an generalized abnormality of the smooth muscle of the digestive tract. Gut hormones, which act as hormones, neurotransmitters and neuromodulators depending on their releasing site, may therefore play an important role in IBS patients.

VIP inhibits CCK-induced gallbladder contraction involving a beta-adrenoceptor mediated pathway in the rainbow trout, Oncorhynchus mykiss, in vivo

The effects of VIP on CCK-induced contractions of the gallbladder were studied in the rainbow trout, Oncorhynchus mykiss, in vivo. Gallbladder pressures were measured via a catheter inserted into the gallbladder, and drugs were injected through a catheter in the dorsal aorta. CCK-induced contractions of the gallbladder wall were reduced in a dose-dependent manner by VIP. The effect of VIP was inhibited by the beta-adrenergic antagonist sotalol, indicating an adrenergic link in the VIP inhibition of the CCK-induced contraction. It is suggested that activation of VIP nerves could facilitate postprandial filling/refilling of the gallbladder despite the increased plasma levels of CCK during this period.

Vasoactive intestinal peptide is a secretagogue in bovine chromaffin cells pretreated with pertussis toxin

Vasoactive intestinal peptide (VIP) evokes little or no secretion of catecholamines from cultured bovine chromaffin cells. However, pretreatment of chromaffin cells with pertussis toxin (PTX, 100 ng/ml for > or = 4 h) revealed that VIP is a secretagogue. In PTX-treated cells catecholamine secretion evoked by VIP occurs with minimal elevation of cyclic AMP and is only slightly enhanced by cyclic nucleotide phosphodiesterase inhibitors. Forskolin, a direct activator of adenylate cyclase, causes delayed secretion of catecholamines from chromaffin cells treated with PTX, but only with pronounced elevation of cyclic AMP levels. Stimulation of catecholamine secretion by histamine, known to activate phosphatidylinositol-specific phospholipase C in chromaffin cells, is also enhanced by preincubation of the cells with PTX. These results suggest that in the bovine chromaffin cell a PTX-sensitive G-protein mediates tonic inhibition of secretion, possibly by preventing activation of phospholipase C.

Effect of immunisation against vasoactive intestinal polypeptide on gastric corpus tone and motility in the ferret

The role of vasoactive intestinal polypeptide in the control of gastric corpus tone and motility was investigated using auto-antibodies to neutralise endogenous vasoactive intestinal polypeptide. Six ferrets were immunised with vasoactive intestinal polypeptide thyroglobulin conjugate in Freund's complete adjuvant which resulted in a significant increase in plasma vasoactive intestinal polypeptide binding activity compared with unimmunised control animals. In acute experiments the level of spontaneous motility in the period immediately after completion of the surgical preparation was 15 times higher in immunised v control animals (p < 0.02). Surprisingly, however, there was no deficit in the ability of the corpus to accommodate fluid. Peak pressure at the end of a 20 ml ramp distension was not different in immunised animals (5.7 (0.6) cm H2O) compared with controls (4.8 (0.3) cm H2O). It is concluded that the non-adrenergic non-cholinergic inhibitory mechanisms regulating corpus tone and motility are different and that vasoactive intestinal polypeptide acts primarily to regulate phasic contractile activity. Alternatively, because of plasticity in the mechanisms controlling corpus tone, the effect of vasoactive intestinal polypeptide may have been superceded during the timecourse of the immunisation procedure.

Suprasensitivity to calcitonin gene-related peptide but not vasoactive intestinal peptide in women with chronic pelvic pain

Chronic pelvic pain in women is associated with radiological evidence of pelvic venous dilatation and reduced flow, termed 'pelvic congestion'. The aim of this study was to elucidate a possible role in this condition for vasoactive intestinal peptide and calcitonin gene-related peptide, both localized in perivascular nerves in the ovaries and uterus. Healthy volunteers and women with chronic pelvic pain and venous congestion received intravenous infusions of vasoactive intestinal peptide (n = 15), calcitonin gene-related peptide (n = 15) or a bland infusate (n = 7). Changes in the uterovaginal and skin blood flow were assessed by continuous measurement of vaginal, axillary, cheek and hand temperature. During calcitonin gene-related peptide infusion median hand temperature changes were +0.97 degrees C in women with pelvic pain and -0.03 degrees C in healthy volunteers (p < 0.05). There were no differences between groups in hand and cheek temperature responses to vasoactive intestinal peptide infusion. Vasoactive intestinal peptide and calcitonin gene-related peptide appeared to dilate the uterovaginal vasculature in healthy subjects but not in those with pelvic pain. Vasoactive intestinal peptide and calcitonin gene-related peptide did not provoke pain in healthy subjects but in those with pelvic pain, symptoms were significantly exacerbated during calcitonin gene-related peptide infusion but not by vasoactive intestinal peptide. Changes in plasma follicle stimulating hormone, luteinizing hormone and oestradiol during either infusion were not significant. These findings indicate greater sensitivity to calcitonin gene-related peptide in women with pelvic pain and suggest a possible underlying neurovascular disorder.

Development of cerebral arterial innervation: synchronous development of neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-containing fibers and some observations on growth cones

The pre- and postnatal development of sympathetic fibers containing neuropeptide Y (NPY) and parasympathetic fibers containing vasoactive intestinal polypeptide (VIP) supplying the cerebral arteries were studied with immunohistochemistry in rats. The innervation patterns and densities of NPY and VIP fibers were similar at all stages of development and similar to that previously reported for norepinephrine (NE). There was a striking reorganization of the innervation pattern of all three fiber systems between the first and second postnatal weeks. At all stages of development prior to the first postnatal week, growth cones were present on individual fibers at the distal part of major cerebral arteries and the middle segment of the basilar artery. The growth cones had a range of shapes from blunt to stellate, lanceolate or filiform. NPY and VIP immunoreactive granules were commonly present. The present results taken with our earlier developmental study of NE fibers (J. Comp. Neurol., 271 (1988) 435-444), demonstrate that: (1) both sympathetic and parasympathetic perivascular nerves on immature cerebral vessels develop with similar sequences: first longitudinal fibers and fiber bundles are present; these transform to a meshwork pattern and finally transform again into the mature, predominantly circumferential pattern; (2) both the classical (NE) and peptidergic transmitters (NPY) within the sympathetic system appear to develop identically in terms of time of appearance, innervation patterns, densities and reorganization.(ABSTRACT TRUNCATED AT 250 WORDS)

A peptidergic component to vagally induced tracheal vasodilation in the dog

The purpose of the study was to determine the extent that peptidergic afferent and efferent pathways contribute to vagally induced vasodilation in the trachea of the dog. The change in vascular resistance of the tracheal branch of the cranial thyroid artery and the trachealis responses were determined in 28 anesthetized, paralyzed, and mechanically ventilated dogs. After propranolol (2 mg/kg) and phentolamine (1.5 mg/kg), stimulation of the superior laryngeal nerves (NS; 15 Hz, 7 V, 2 ms, 30 s) caused a decrease in vascular resistance of 11.7 +/- 0.8% and a tracheal contraction of 5.2 +/- 4.7 cmH2O. Atropine (1.5 mg/kg) reduced the fall in vascular resistance to 4.7 +/- 0.8% (P less than 0.01), whereas tracheal contraction was abolished. Thiorphan (1.5 mg), a neutral endopeptidase inhibitor, augmented the decrease in vascular resistance (8.8 +/- 0.6%; P less than 0.01) to NS. After hexamethonium (0.5 mg/kg), NS still caused a small decrease in TVR (2.9 +/- 0.9%; P less than 0.05), which was abolished by capsaicin. In atropinized dogs, capsaicin reduced the fall in vascular resistance after NS; the residual vasodilation was virtually abolished by hexamethonium. Acetylcholine (10(-3) mg/kg) decreased vascular resistance (15.7 +/- 3.0%), and the effect was abolished by atropine. We conclude that there is noncholinergic nonadrenergic vagally induced tracheal vasodilation that is peptidergic. The peptidergic vasodilation appears to be mediated by both afferent and efferent pathways.

Effects of pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) on the cardiovascular system in sheep

The cardiovascular effects of PACAP and VIP were studied in intact conscious sheep; PACAP (0.008, 0.04, 0.2, and 1.0 nmol/min) and VIP (0.07, 0.2, 0.6, and 1.8 nmol/min) were infused in conscious sheep for periods of 10 min. For each peptide there was a dose-dependent increase in heart rate. At the highest doses tested, pulse pressure and mean arterial pressure tended to increase and decrease, respectively. However, only the decrease in mean arterial pressure following the highest dose of VIP reached significance. At the highest doses tested, heart rate increased nearly threefold during the infusion while mean arterial pressure declined by 18.5%. In individual animals the decrease in blood pressure and increase in heart rate occurred simultaneously, so that we were unable to conclude whether the increase in heart rate was due to a baroreceptor reflex.

Effects of vasoactive intestinal peptide, peptide histidine methionine, and neuropeptide Y on intracavernous pressure in the rabbit

In anesthesized white rabbits blood was extracorporeally circulated from the left carotid artery into the penile corporeal bodies with a constant flow rate. Corpus cavernosum pressure (CCP) responses to intracavernous injections of drugs were recorded in animals with aortic nonocclusion and aortic occlusion, respectively. Vasoactive intestinal polypeptide (VIP, 1 microgram, 5 micrograms, and 20 micrograms), dissolved in 0.5 mL volumes, induced no significant increases in CCP compared with equivalent volumes of solvent, but the peptide increased the time interval until return of CCP to steady state level. Peptide histidine methionine induced a significant increase in the maximal CCP obtained in nonocclusion, and the time interval until return of CCP to steady state levels was increased in both aortic nonocclusion and occlusion. Neuropeptide Y produced an increase in the maximal CCP in animals with aortic occlusion, and a minor increase in the time interval until return of CCP values to steady state levels in both aortic nonocclusion and occlusion. Thus, all the peptides tested were capable of influencing the smooth muscle tissues involved in penile outflow regulation.

Release of vasoactive intestinal polypeptide from the rat gastric fundus

1. Auxotonic responses and release of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) induced by electrical field stimulation (EFS) were studied in longitudinal muscle strips from the gastric fundus of reserpinized rats suspended between parallel platinum electrodes in Krebs solution containing atropine (1 microM), 5-hydroxytryptamine (3 microM) and bovine serum albumin (50 mg l-1). 2. EFS (supramaximal voltage, 1 ms, 0.25-32.0 Hz, trains of 2 min) induced frequency-dependent relaxations. 3. EFS at frequencies greater than or equal to 8 Hz also produced significant increases in VIP-LI release. 4. VIP-LI release induced by EFS at 16 Hz no longer occurred in the presence of tetrodotoxin (1 microM) or a Ca(2+)-free medium. 5. Detection of VIP-LI upon activation of inhibitory non-adrenergic, non-cholinergic neurones indicates that VIP meets the 'detectable release' criterion for an inhibitory neurotransmitter in the rat gastric fundus.

A mediator derived from arginine mediates inhibitory junction potentials and relaxations in lower esophageal sphincter: an independent role for vasoactive intestinal peptide

This study provides mechanical and electrophysiological evidence to show that a metabolite of arginine, not vasoactive intestinal peptide (VIP), is the putative nonadrenergic noncholinergic (NANC) inhibitory mediator in canine and opossum lower esophageal sphincters (LES). Relaxations of spontaneous active tension by electrical field stimulation (FS) at parameters that induced tetrodotoxin (TTX)-sensitive responses were abolished by L-N omega-arginine methyl ester (L-NAME) at 10(-4) M and restored by L-arginine (10(-3) M) but not D-arginine (10(-3) M). TTX-insensitive relaxations to 5-ms pulses were unaffected by L-NAME, L- or D-arginine. VIP (10(-6) M) caused maximum relaxations of basal tension in both the opossum and canine LES. However these relaxations, unlike those from FS were unaffected by L-NAME. Methylene blue (5 x 10(-5)M) increased basal tension of the LES in each species, and did not inhibit the relaxation to FS or VIP, but often increased the amplitudes of these responses due to the increase in basal tension. In parallel experiments NANC inhibition of body circular muscle from opossum esophagus was abolished by methylene blue. Electrophysiological studies using micro-electrodes revealed that NANC inhibition was associated with inhibitory junction potentials in the canine LES. These were inhibited by L-NAME and restored by L-arginine but not D-arginine. In contrast, 10(-6) M VIP in canine LES did not induce any change in membrane potential during a 20-min superfusion. Sodium nitroprusside also hyperpolarized sphincteric muscle and its effects were not affected by L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoregulation of neuroblastoma growth by vasoactive intestinal peptide

Elevated serum levels of vasoactive intestinal peptide (VIP) are associated with some cases of neuroblastoma and correlate with a favorable prognosis. VIP has previously been shown in our laboratory to cause the in vitro growth inhibition and morphological differentiation of the human neuroblastoma cell line, LA-N-5. It is now shown that LA-N-5 cells express immunoreactive VIP and bear specific VIP receptors. Antagonism of endogenous VIP, either by competitive inhibition or receptor blockade, increased cell proliferation, suggesting that VIP is operative in normal growth regulation. Intracellular and extracellular levels of VIP were also shown to increase significantly during the retinoic acid-induced differentiation of these cells. Furthermore, a concomitant marked increase in VIP receptor expression was demonstrated with cellular differentiation. These receptors remain functional as evidenced by a matching increase in the level of detectable cAMP generated in response to exogenous VIP. It is concluded that VIP is a normal autoregulator of neuroblastoma cell growth and differentiation, and that retinoic acid-mediated differentiation may be, in part, due to endogenous VIP.

Demonstration of [125I]VIP binding sites and effects of VIP on cAMP-formation in rat insulinoma (RINm5F and RIN14B) cells

Vasoactive intestinal polypeptide (VIP)-immunoreactive nerves have been demonstrated in close association with the islets of Langerhans, and VIP has been shown to stimulate insulin and somatostatin secretion. Using [125I]VIP and membranes prepared from rat insulinoma (RIN) cells, i.e., the subclones m5F (m5F; mainly insulin-secreting) and 14B (14B; mainly somatostatin-secreting), it was found that VIP (10(-10)-10(-7) M) competitively inhibited the binding of [125I]VIP. A single class of high affinity binding sites with Kd values of 0.40 +/- 0.06 nM and 0.36 +/- 0.08 nM for m5F and 14B, respectively, with a corresponding number of binding sites (Bmax) of 163 +/- 20 and 254 +/- 51 fmol/mg protein was observed. The rank order of potency in inhibiting [125I]VIP binding was in both cell lines: VIP greater than helodermin greater than pituitary adenylate cyclase activating polypeptide 1-27 (PACAP27) greater than peptide histidine isoleucine (PHI) greater than secretin. VIP caused a dose-dependent increase in cAMP-formation in both m5F and 14B cell membranes with EC50 values of 3.0 and 3.5 nM, respectively, but VIP (1.10(-9)-3.10(-6) M) had no effect on insulin secretion (over 2 h) from the m5F cells. Thus, the data suggest that the VIP-receptors in these neoplastic rat cell lines, despite an apparent coupling to adenylate cyclase activity, seem to be functionally uncoupled to an effect on insulin secretion following an acute exposure to VIP.

Vasoactive intestinal polypeptide (VIP) inhibits rat alveolar macrophage phagocytosis and chemotaxis in vitro

Vasoactive intestinal polypeptide (VIP) has been shown to inhibit lymphocyte function and is believed to modulate the immune response. We explored the possible immunomodulatory effects of VIP on alveolar macrophage (AM) function by examining its influence on AM phagocytosis and chemotaxis. Rat AMs were collected by bronchoalveolar lavage and incubated for 90 min with polystyrene beads in the presence or absence of VIP in concentrations from 10(-11) M to 10(-5) M. VIP significantly (P less than 0.0001) inhibited AM phagocytosis of polystyrene beads at concentrations of 10(-11) to 10(-6) M, with a maximal inhibition of 35% at 10(-6) M (but no inhibition at 10(-5) M). AMs were also incubated for 90 min in a chemotaxis chamber with endotoxin-activated rat serum (EARS) as a chemoattractant, with or without VIP in concentrations from 10(-9) to 10(-6) M. VIP significantly (P less than 0.0001) inhibited AM chemotaxis by at least 30% at concentrations of 10(-9) to 10(-6) M, with a maximal inhibition of 46% at 10(-7) M. These results indicate that VIP, in concentrations from 10(-11) to 10(-6) M, inhibits rat AM function as assessed by phagocytosis of polystyrene beads and chemotaxis to EARS. The inhibition of alveolar macrophage function is another mechanism by which VIP may modulate the immune response in the lung.

Neuropeptidergic innervation of intramuscular hemangiomas

Intramuscular hemangiomas are idiopathic lesions which are either tumoral or developmental in origin. A close association of abnormal blood vessels with nerve fibers is found and may suggest that nerves have a primary inciting role in the development of these lesions. In the current study, the number of nerve fibers in different zones around the tumors, as well as the type of neuropeptides present in these fibers, was quantitatively assessed by computer-assisted image analysis of immunohistochemical staining of histological slides. The number of nerve fibers as determined by positive staining by anti-protein S-100 antibodies was found to be elevated in the immediate vicinity of the abnormal blood vessels. The density of the nerve fibers rapidly declined with increasing distance from the hemangiomas, reaching normal values at distances of over 2 mm. Furthermore, hemangiomas contain a significantly higher number of calcitonin gene-related peptide (CGRP), substance P, and Met-enkephalin-positive fibers. The most significant rise in number is that of CGRP-positive fibers. This neuropeptide is a known mitogen, which could be responsible for the growth of the hemangiomatous blood vessels. Substance P is a nociceptive neurotransmitter and its presence can explain the pain which often accompanies even tiny intramuscular hemangiomas.

Effects of vasoactive neuropeptides on human saphenous vein

OBJECTIVE

To assess the role of neuropeptides in the control of vascular tone in the human saphenous vein the actions of substance P, vasoactive intestinal peptide, calcitonin gene related peptide, neuropeptide Y, and somatostatin on this blood vessel were examined.

METHODS

In vitro organ bath techniques were used with preparations of saphenous veins obtained from 29 patients (aged 41-66) who were undergoing coronary bypass surgery.

RESULTS

Substance P, vasoactive intestinal peptide, and calcitonin gene related peptide relaxed pre-constricted vessels in a dose dependent manner with a rapid onset of action, taking one to two minutes to reach a plateau at each dose. Substance P (10(-9) to 10(-6) mol/l) induced relaxation with a maximum response (mean (SEM)) 23.0 (6.6)% of the total relaxation induced by glyceryl trinitrate 1 microgram/ml and a 50% maximal effective concentration of 6.8 x 10(-9) mol/l. Vasoactive intestinal peptide (10(-10) to 10(-7) mol/l) produced a relaxation of 27.0 (5.1)% at 10(-7) mol/l. The maximum responses induced by substance P and vasoactive intestinal peptide were significantly reduced, to 3.7 (2.8)% and 4.7 (2.0)% respectively, after removal of the endothelium. Calcitonin gene related peptide (10(-10) to 10(-7) mol/l) elicited only 14.3 (2.6)% relaxation at 10(-7) mol/l, and this was not affected by removal of the endothelium. By contrast, neuropeptide Y and somatostatin exerted concentration dependent constriction on resting vessels. Neuropeptide Y (10(-10) to 10(-7) mol/l) caused prolonged contraction (roughly 20 minutes to reach a maximum plateau at each dose). At 10(-7) mol/l, the constriction amounted to 28.0 (12.0)% of the response to 90 mM KCl, in ring segments with or without endothelium. Somatostatin (10(-10) to 10(-6) mol/l) quickly caused contraction with a maximum response of 42.7 (15.0)% and a maximum response of 42.7 (15.0)% and a 50% maximal effective concentration of 6.7 x 10(-6) mol/l. The constriction was greatly increased when endothelium was removed, with a maximum response of 78.2 (16.8)% and a 50% maximal effective concentration of 4.3 x 10(-7) mol/l.

CONCLUSIONS

Vasoactive peptides have diverse effects on the vascular tone these effects are endothelium dependent. The exact physiological role and implication for performance of bypass grafts require further investigation.

Vasoactive intestinal peptide stimulation of aldosterone secretion by the rat adrenal cortex may be mediated by the local release of catecholamines

The effects of vasoactive intestinal peptide (VIP) on adrenocortical function were investigated using several different preparations of adrenocortical tissue. VIP caused a significant increase in perfusion medium flow rate and in aldosterone and corticosterone secretion by the isolated perfused rat adrenal gland, with a threshold of 1 pmol in 200 microliters, but did not affect basal steroid secretion by collagenase-dispersed adrenocortical cells at any concentration used, from 10 pmol/l to 10 mumol/l. The presence of VIP (100 nmol/l) had no significant effect on the response of zona glomerulosa cells to stimulation by ACTH at any concentration. In incubations of intact adrenal capsular tissue, VIP (10 mumol/l) caused a significant stimulation of aldosterone secretion, and also induced a significant release of adrenaline into the incubation medium. Addition of (-)alprenolol (100 nmol/l), a beta-adrenergic antagonist, to the incubation medium significantly attenuated the response of capsular tissue to VIP. It is concluded that the effects of VIP on aldosterone, which are only seen when the architecture of the zona glomerulosa is preserved, may be mediated by the local release of adrenaline.

Pituitary adenylate cyclase-activating polypeptide relaxes rat gastrointestinal smooth muscle

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a new member of the secretin/glucagon peptides family, being most homologous to vasoactive intestinal peptide (VIP). The present study was designed to investigate a possible effect of PACAP on the rat gastrointestinal smooth muscle in vitro. We demonstrated that 1) PACAP reduced basal smooth-muscle contractions in all portions of the gastrointestinal tract, but the effect of VIP was region-specific. The inhibitory effect of PACAP in midcolon was approximately 100 times greater than that of VIP. 2) PACAP significantly inhibited smooth-muscle contractions induced by acetylcholine or carbachol. The inhibitory effect of PACAP was not affected by hexamethonium and was additive to the inhibitory effect of atropine and pirenzepine. 3) PACAP inhibited smooth-muscle contractions induced by substance P, cholecystokinin, and galanin, even after atropine treatment. Although the exact mechanism of the inhibitory action of PACAP remains to be clarified, PACAP appears to exert its effect in the rat at a site other than muscarinic receptors, probably through a direct effect on gastrointestinal smooth muscle in vitro.