Comparison of vasoactive intestinal peptide (VIP) and secretin in gastric secretion and mucosal blood flow

Recent advances in vasoactive intestinal peptide physiology and pathophysiology: focus on the gastrointestinal system

Vasoactive intestinal peptide (VIP), a gut peptide hormone originally reported as a vasodilator in 1970, has multiple physiological and pathological effects on development, growth, and the control of neuronal, epithelial, and endocrine cell functions that in turn regulate ion secretion, nutrient absorption, gut motility, glycemic control, carcinogenesis, immune responses, and circadian rhythms. Genetic ablation of this peptide and its receptors in mice also provides new insights into the contribution of VIP towards physiological signaling and the pathogenesis of related diseases. Here, we discuss the impact of VIP on gastrointestinal function and diseases based on recent findings, also providing insight into its possible therapeutic application to diabetes, autoimmune diseases and cancer.

Inhibitory effect of sorbin on pepsin secretion in conscious cats and rabbits

Sorbin, a 153 amino acid polypeptide isolated from porcine upper small intestine and its shortest synthetic derivative, the C-terminal heptapeptide (C7-sorbin), substituted by D alaninamide in the last position (D7-sorbin), have proabsorptive and antisecretory effect in the different parts of the intestine. We showed that labeled C7-sorbin accumulated not only in the enterocytes and the enteric nervous system but also in the gastric chief cells in the rat. The chief cell secretion of pepsin was then studied in two other species, the cat and the rabbit, simultaneously with the acid secretion of parietal cells. Lipase secretion was studied in the rabbit because lipase is exclusively secreted by the upper cells of the fundic glands, which do not secrete pepsin. The animals were equipped with a gastric fistula, fully innervated, and a Heidenhain pouch, vagally denervated, during a continuous perfusion of pentagastrin (PG) 2 microg/kg. h and vasoactive intestinal peptide (VIP) 4 microg/kg. h. D7-sorbin (100 pmol/kg. h) inhibited cat and rabbit pepsin secretion from the innervated gastric fistula secretion and from the cat denervated Heidenhain pouc secretion, but was without effect on acid secretion and lipase secretion. These data indicate that the inhibitory effect of sorbin is specific on chief cells because the acid parietal cell secretion in both species and lipase upper cell secretion of the fundic glands, in the rabbit, are not implicated.

Characteristics of the muscularis mucosae in the acid-secreting region of the rabbit stomach

It has been suggested that muscularis mucosae excitation may augment gastric acid secretion, implying that this muscle should contract to secretagogues or stimulation of its motor innervation. The aim of this study was to characterize in vitro the responses of the muscularis mucosae in the rabbit gastric corpus to substances that modulate acid release and to intrinsic nerve stimulation. Muscularis mucosae from both fundic and antral ends of the corpus had identical mechanical properties, contracted to ACh, ADP, ATP, and histamine but relaxed to vasoactive intestinal polypeptide. Fundic but not antral muscularis mucosae contracted to bombesin and PGE2 and PGF2alpha, whereas adenosine, AMP, CCK, gastrin, secretin, and somatostatin were without effect on any preparation. In both regions electrical field stimulation evoked TTX-sensitive responses consisting of an atropine-resistant contraction followed by an NG-nitro-L-arginine methyl ester- and indomethacin-resistant relaxation. It is concluded from the regional variability in the pharmacological properties of the gastric muscularis mucosae that if its motor activity is linked to acid secretion this would be achieved by a neurally mediated relaxation rather than a paracrine- and/or endocrine-induced alteration in tone.

Effects of pituitary adenylate cyclase activating polypeptide-27 on alkaline secretory and mucosal ulcerogenic responses in rat duodenum

Effects of pituitary adenylate cyclase activating polypeptide (PACAP) on duodenal mucosal HCO3- secretion and ulcerogenic responses induced by mepirizole in anesthetized rats were examined and compared with those of vasoactive intestinal polypeptide (VIP). Animals were given mepirizole (200 mg/kg, s.c.) for induction of duodenal ulcers, and gastric acid and duodenal HCO3- secretions were measured with or without pretreatment of PACAP-27 or VIP. Mepirizole increased acid secretion and induced hemorrhagic lesions in the proximal duodenum within 6 h. Intravenous bolus injection or infusion of PACAP-27 (4 and 8 nmol/kg or 8 nmol/kg/h) increased duodenal HCO3- secretion even in the presence of mepirizole, without effect on acid secretion, and significantly reduced the severity of duodenal lesions caused by mepirizole. In contrast, VIP (8 nmol/kg, i.v.) given by bolus injection significantly decreased acid secretion induced by mepirizole, in addition to stimulation of HCO3- secretion, and prevented duodenal lesions in response to mepirizole. These results suggest that PACAP-27 increases duodenal HCO3- secretion and this action may be important in maintaining the duodenal mucosal integrity against acid, and VIP affords duodenal protection by both increasing duodenal HCO3- secretion and decreasing acid secretion. The reason for the different effects of PACAP and VIP on acid secretion is unknown.

Intrinsic innervation of the stomach of the fetal pig: an immunohistochemical study of VIP-immunoreactive nerve fibres and cell bodies

Using an immunohistochemical technique, the presence and distribution of vasoactive intestinal polypeptide (VIP) was investigated in cryostat sections, both tangential and transverse, of the fetal pig's stomach. In all fetuses and in all gastric segments investigated, VIP-like immunoreactive (IR) nerve-cell bodies were seen in all intramural ganglia, and VIP-IR nerve fibres were found in all layers of the gastric wall except the tunica serosa. Consequently, VIP-IR nerve fibres were found to form a periglandular network, to accompany arterioles, to interconnect the intramural ganglia, to encircle both VIP-IR-negative and -positive neurons, and were found in all muscle layers. Despite the fact that VIP-IR seems to be restricted to the intramural nervous elements, some non-specific-reacting VIP-IR glandular cells were noticed in the basal parts of the fundic, antral and pyloric gastric glands. The distribution pattern of VIP in the fetal pig resembles that of the adult pig. This suggests a possible functional role for VIP during fetal life and/or puts forward the suggestion that the stomach of a fetal pig from the second half of the gestation period is prepared, from then on, for postnatal function. High similarities with regard to the general distribution pattern of VIP in the stomach have also been noted between the fetal pig and humans, proving once more that the fetal pig can serve as a good animal model in several research areas. Finally, the morphological data provided here may, combined with the physiological significance of VIP, contribute to a better insight into the physiopathology of economically important gastro-intestinal disorders in the pig, such as gastric ulceration.

Pituitary adenylate cyclase activating polypeptide-27 (PACAP-27) inhibits pentagastrin-stimulated gastric acid secretion in conscious rats

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel neuropeptide and has two amidated forms, PACAP-27 and PACAP-38. Its chemical structure is similar to that of vasoactive intestinal peptide (VIP). In our previous studies, we found that PACAP has a stimulatory effect on rat exocrine pancreas secretion and an inhibitory effect on rat gastrointestinal motility. These effects of PACAP-27 were greater than those of PACAP-38 and VIP. In the present study, we examined the effect of PACAP-27 on basal and pentagastrin (PG)-stimulated gastric acid secretion in conscious rats and compared its effect with that of VIP. Rats were equipped with a chronic gastric fistula and a permanent IV line and separately housed in metabolic cages. The effects of PACAP-27 and VIP at doses of 1.25, 2.5, 5 and 10 nmol/kg/h on basal and PG (24 micrograms/kg/h)-stimulated gastric acid secretion were tested. Our results showed that: (1) VIP had no significant effect on basal and PG-stimulated gastric acid secretion at the tested doses. (2) PACAP-27 had no effect on basal acid secretion but had a dose-dependent inhibitory effect on PG-stimulated gastric acid secretion. The highest inhibition by PACAP-27, 68.2 + 8.1%, was achieved at 5 nmol/kg/h. We suggest that PACAP may have a regulatory role in gastric acid secretion.

Gastric somatostatin release: evidence for direct mediation by calcitonin gene-related peptide and vasoactive intestinal peptide

It has previously been demonstrated that somatostatin (SRIF) directly inhibits parietal cell secretion. However, the significance of SRIF as a paracrine agent and mechanisms of local gastric SRIF release are not clear. Vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) are neuropeptides which have been localized in the gastric fundus and have been demonstrated to inhibit gastric acid secretion in vivo. The present study examines the hypothesis that CGRP and VIP act via the release of gastric fundic SRIF. The study utilized rabbit isolated gastric glands prepared by collagenase digestion. Glands were incubated alone, or with 10(-10)-10(-6) M CGRP or 10(-10)-10(-6) M VIP for 30 min. Supernatant SRIF was measured using a specific radioimmunoassay. Unstimulated SRIF release was 101 +/- 16 fmole/ml. CGRP (10(-7) and 10(-6) M) and VIP (10(-7) and 10(-6) M) resulted in significant SRIF release. The maximum release of SRIF by CGRP (506 +/- 113 fmole/ml) was significantly greater than that by VIP (293 +/- 33 fmole/ml) (P less than 0.05). However, both these concentrations of SRIF are comparable to the ID50 concentration (4.5 X 10(-10) M) for SRIF inhibition of acid secretion by isolated parietal cells as assessed by [14C]aminopyrine accumulation. These results are consistent with the hypothesis that CGRP and VIP inhibition of acid secretion may be mediated, at least in part, by the local release of SRIF from the gastric fundus. These data further support the significance of paracrine interactions in the modulation of cellular secretory function.

The effect of neurotensin and secretin on gastric acid secretion and mucosal blood flow in man

Neurotensin stimulates pancreatic secretion directly and by potentiating the effect of secretin. Neurotensin also inhibits gastric secretion. Secretin inhibits gastric secretion as well, but whether it also interacts with neurotensin is not known. Secretin is known to inhibit gastric mucosal blood flow (GMBF). The effect of neurotensin on GMBF is not known. Acid secretion (triple lumen perfused orogastric tube) and GMBF ([14C]aminopyrine clearance) were therefore measured in 6 subjects during neurotensin, secretin and neurotensin plus secretin infusions. Neurotensin plus secretin reduced acid secretion by a median 130 (range 34-394) mumol/min which was significantly greater than either neurotensin at 36 (7-67) mumol/min or secretin 54 (20-347) mumol/min alone (P less than 0.05). This effect appeared independent of GMBF. Neurotensin plus secretin reduced GMBF by 14 (12-27) ml/min but not significantly more than neurotensin at 11 (3-20) ml/min or secretin 18 (2-27) ml/min alone. Further, there was no correlation between changes in acid output and GMBF during infusion of the peptides. We conclude that the inhibitory effects of neurotensin and secretin on gastric secretion are at least additive and together they may function as an 'enterogastrone'.

Calcitonin gene related peptide inhibits basal, pentagastrin, histamine, and bethanecol stimulated gastric acid secretion

This study was designed to examine the effect of calcitonin gene related peptide on gastric acid secretion in the rat. Calcitonin gene related peptide (1 pmol-1 nmol/rat) injected intravenously inhibited basal gastric acid secretion in awake, freely moving rats. Calcitonin gene related peptide decreased gastric secretion stimulated by histamine, pentagastrin, or bethanecol in anaesthetised rats. The inhibitory effect was immediate and most pronounced in the first hour and diminished during the second hour. The N- and C-terminal fragments of calcitonin gene related peptide, CGRP1-14 and [Tyr23]CGRP23-37, did not affect gastric acid secretion. [acetamidomethyl-cys2,7]CGRP, the linear cysteine-protected molecule devoid of the disulphide bridge, was not biologically active. After truncal vagotomy or atropine sulphate, calcitonin gene related peptide did not inhibit gastric secretion. These studies indicate that calcitonin gene related peptide administered peripherally inhibits basal and stimulated gastric acid secretion in the rat. Both C- and N-terminal residues as well as the disulphide bridge are necessary for the inhibitory effect on gastric secretion. Inhibition of gastric acid secretion by calcitonin gene related peptide may depend on intact vagal cholinergic fibres.

VIP-, substance P- and met-enkephalin-immunoreactive innervation of the human gastroduodenal mucosa and Brunner's glands

VIP-, substance P- and met-enkephalin-containing innervation of the human gastroduodenal mucosa and Brunner's glands was studied by immunocytochemistry on whole mount tissue preparations. A dense VIP-containing nerve supply was found around fundic and pyloric glands, while the few and scattered substance P-immunoreactive fibres tended to run across the full thickness of the gastric mucosa. In the duodenum, both VIP and substance P were present in a striking nerve network in the villi as well as in the muscularis mucosae and around blood vessels. Both peptides were also immunostained in nerve bundles and neuronal perikarya between the lobules of Brunner's glands, while only very few fibres reached the proximity of acinar cells. Met-enkephalin-immunoreactivity was detected in a small number of nerve fibres, virtually confined to the basal parts of the mucosa and to the duodenal submucous plexus.

Gastric inhibitory peptide (GIP), pancreatic glucagon and vasoactive intestinal peptide (VIP) are cAMP-inducing hormones in the human gastric cancer cell line HGT-1. Homologous desensitization of VIP receptor activity

GIP (EC50 = 8 X 10(-9) M, 5-fold stimulation), pancreatic glucagon (EC50 = 10(-8)M, 13-fold) and porcine or chicken VIP (EC50 = 2.5 X 10(-9) M, 10-fold) are shown to activate the cAMP generating system in HGT -1 cells. Combinations of GIP, pancreatic glucagon and VIP indicate the occurrence of 3 separate sets of recognitions sites for these 3 peptides. Accordingly, chronic treatment of cultured HGT -1 cells by VIP (10(-8) M) during 6 days resulted in homologous desensitization of VIP receptor activity. Other peptides structurally related to the secretin-glucagon family, to neurotensin, or to gastrin are either ineffective or very weak agonist (hpGRF). GIP or pancreatic glucagon are inactive on the human colonic cell line HT-29, indicating the gastric specificity of the effect of GIP and glucagon in transformed epithelial cells originating from the human gastrointestinal tract. This implies that GIP and (pancreatic-entero) glucagon peptides may regulate gastric secretions directly, under similar mechanisms that those we evidenced in the rat.

VIP inhibits histamine-induced ultrastructural changes related to acid secretion by parietal cells

We have studied the in vitro effect of VIP and histamine on ultrastructure of the parietal cells in isolated guinea pig fundic glands. The morphological changes induced by histamine in the parietal cells can be compared to those observed after histamine stimulation in vivo or in vitro on gastric mucosa preparations. In contrast, VIP incubation did not produce the ultrastructural changes related to gastric acid secretion, in resting parietal cells. Pretreatment of the glands by VIP resulted in a remarkable suppression of the histamine effect, since the parietal cells assumed an almost resting state. The data (1) indicate that the parietal cells in isolated gastric glands of the guinea pig retain in vitro the capacity to undergo the ultrastructural changes that are related to acid secretion in vivo after histamine or cAMP and (2) suggest that VIP is an inhibitor of histamine-induced gastric acid secretion in the guinea pig. It is proposed that VIP could act directly on the parietal cell via cAMP-phosphodiesterase activation, or indirectly via gastric somatostatin and/or prostaglandin secretions, inhibiting the H2 receptor-cAMP system of the parietal cell.

Circulatory effects of VIP in anesthetized man

VIP was given intravenously over 1 min at the doses 0.1 and 0.2 micrograms X kg X min-1 to twenty-one anesthetized patients undergoing abdominal surgery. Intra-arterial blood pressure was monitored and various blood flows were measured simultaneously by electromagnetic technique. Following VIP, intra-arterial blood pressure was decreased. The blood flows were increased in the gastroduodenal-, and the left gastric arteries. The flow in the hepatic artery proper was increased only following the 0.2 micrograms dose. The flow in the superior mesenteric artery varied considerably inter-individually. In branches supplying only the small intestine, it seemed to be unaffected. The flow in the splenic artery was decreased in normal-sized spleens, but unaffected in enlarged spleens. The flow in the external iliac artery initially decreased and thereafter increased. Changes in vascular resistances showed that VIP acted as a vasodilator in the splanchnic region except in the superior mesenteric vasculature, where it was ineffective. In normal spleens it was a vasoconstrictor. In the external iliac artery, an initial insignificant vasoconstriction was followed by vasodilation. It seemed that VIP acts directly on the vessels and has a specific pattern of vasoactivity of probable physiological significance.

Regional vascular influences of vasoactive intestinal polypeptide

Vasoactive intestinal polypeptide (VIP) has powerful vasodilating effects, shown by a striking conductance increase especially in the vertebral artery (+100%), the left descending coronary artery (+200%), the left gastric artery (+550%), the superior pancreaticoduodenal artery (+200%), and the gastroduodenal artery (+220%). The conductance increase was also significant in the common and the proper hepatic artery (+60% and 50%, respectively). Total peripheral conductance was progressively increased by 45%; arterial pressure was reduced by 20%. Blood flow was assessed with non-cannulating electromagnetic flow sensors in anesthetized dogs. VIP was injected in a brachial vein at intervals of 1 min in amounts of 1-1024 ng X kg-1, following a logarithmic scale. The pulsatile flow and pressure signals were analog-digital-converted and processed simultaneously by a computer program to obtain mean flow (ml X min-1) and mean pressure (mmHg) values for every 3 sec. The hemodynamic data were presented as conductances. No response was observed in the inferior mesenteric artery, the renal artery, or the femoral artery. Major vasoactivity thus occurred in cerebral, cardiac, gastric, hepatic, and pancreatic regions.

Histamine and VIP interactions with receptor-cyclic AMP systems in the human gastric cancer cell line HGT-1

In HGT-1 cells incubated at 20 degrees C for 15 min with 1 mM 3-isobutyl-1-methylxanthine (IBMX), histamine (10(-4)M) increased basal cAMP levels from 2.12 +/- 0.14 to 22.9 +/- 2 pmol per 10(6) cells, with a potency of 6.4 X 10(-6)M. IBMX was added in order to inhibit cAMP degradation by low and high Km cAMP-phosphodiesterases (cAMP-PDE). The use of specific H1, H2 agonists or antagonists indicated that the histamine effect was due to an interaction with typical H2 -receptors that are involved in gastric acid secretion. Cyclic AMP levels were also increased (10-fold) by vasoactive intestinal peptide VIP (3 X 10(-11) - 10(-8)M). Porcine peptide having N-terminal histidine and C-terminal isoleucine amide (PHI) and secretin were respectively 80 and 3600 times less potent than VIP and did not produce additive effect when tested in combinations with VIP. This observation indicates that these two peptides, structurally related to VIP, are acting through the recognition sites for VIP. Combination of VIP and histamine results in additive stimulation on intact cells as well as on membrane-bound adenylate cyclase, suggesting the existence of two cell populations bearing respectively the two sets of receptors. Two other human cancer cell lines originating from nongastric tumors (HT-29 and HL-60) possess only VIP or histamine receptors, respectively, indicating the gastric cellular originality of the HGT-1 cells. It is concluded that HGT-1 cells possess both VIP and histamine H2 receptors with similar pharmacological properties to those characterized in normal human fundic glands (1,2). Therefore, this cell line can be a good model to study drugs used therapeutically during the treatment of patients for gastric ulcer or cancer.

A new neuroregulator: the vasoactive intestinal peptide or VIP

VIP is a neuroregulator occurring in the central and peripheral nervous system which exhibits the function of neurotransmitter in the brain, neuroendocrine substance at the pituitary level, and neuroparacrine substance in peripheral organs. The structure and the specificity of the molecule as studied by antibody and receptor, and its location in brain and peripheral organs are summarized as well as its numerous biological effects. The method used to demonstrate the involvement of VIP in a physiological regulation is described and illustrated by two examples: the effect of VIP on gut epithelium and the neuroendocrine action of VIP in inducing prolactin release from pituitary cells. The consequence of this recent progress in the knowledge of VIP release and action in human physiology and disease is indicated.

VIP and PGE1 activate adenylate cyclase in rat intestinal epithelial cell membranes via different mechanisms

The effect of vasoactive intestinal polypeptide (VIP) and of prostaglandin E1 (PGE1) alone and in combination was tested in an adenylate cyclase (AC) preparation from rat intestinal epithelial cell membranes. AC activity increased linearly with time up to 15 min in the absence or presence of VIP or PGE1, respectively. NaF, VIP and PGE1 concentration-dependently stimulated AC activity. The dose-response curve of VIP in the presence of PGE1 was shifted to the left and the maximal effect of VIP was significantly enhanced. The dose-response curve obtained experimentally was significantly different from theoretical additive dose-response curve, indicating that PGE1 potentiates the effect of VIP on AC activity. The possible mechanisms of potentiation are discussed. The results suggest that VIP and PGE1 activate AC via two different but not entirely independent mechanisms.

Influence of vasoactive intestinal polypeptide on net water flux and cyclic adenosine 3',5'-monophosphate formation in the rat jejunum

1. The effects were studied of vasoactive intestinal polypeptide (VIP), theophylline, and morphine on net water flux and cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels in the jejunum of anaesthetized rats in vivo and of VIP and morphine on adenylate cyclase activity in rat epithelial cell membranes in vitro. 2. Infusion of VIP (0.1-2 x 10(-9) mol/min/kg) dose dependently caused a reversal from net water absorption to net secretion; 2 x 10(-9) mol/min/kg enhanced the mucosal cyclic AMP content by 67%. 3. Theophylline (5 mg/ml, intraluminally) enhanced the effect of intra-arterial infusion of VIP (2 x 10(-9) mol/min/kg) as to net water secretion and increase in mucosal cyclic AMP content. 4. Pretreatment with morphine (5 mg/kg, s.c.) did not influence the effects of VIP on net water flux and on mucosal cyclic AMP content. 5. Atropine (2 mg/kg, s.c.) also failed to reduced the effect of VIP (0.4 x 10(-9) mol/min/kg) on net water flux. 6. Stimulation of adenylate cyclase activity was a function of VIP concentration over a range of 1 x 10(-10)-1 x 10(-7) M. Morphine (up to 1 x 10(-3) M) failed to influence stimulation of adenylate cyclase by VIP. 7. The finding that low doses of VIP, which already have an effect on net water flux, fail to increase cyclic AMP levels makes it likely that other mediators besides cyclic AMP are involved in the effect of VIP on net water flux. Some of the present results, however, support the assumption that VIP stimulates intestinal fluid secretion by increasing mucosal cyclic AMP levels.

Stimulation of gastric acid secretion and suppression of VIP-like immunoreactivity by bombesin in the Atlantic codfish, Gadus morhua

Cods were equipped with cannulae for drainage of the stomach and for separate perfusion of the stomach (pure sea-water) and intestine (diluted sea-water). Acidity and volume of gastric effluence were measured. Plasma immunoreactive gastrin and vasoactive intestinal polypeptide (VIP) were assayed in some experiments. The high rate of "basal" acid secretion was further elevated by i.m. administration of bombesin, but not by pentagastrin. Exogenous VIP inhibited acid secretion. Following 5 h of bombesin infusion, plasma gastrin-IR was unaffected while VIP-IR was depressed compared to saline-treated controls. The possibility that bombesin stimulates acid secretion by inhibiting VIP-release is discussed.

Comparison of pancreatic responses to portal and systemic secretin and VIP in cats

This study was designed to compare pancreatic bicarbonate responses to secretin and vasoactive intestinal peptide (VIP) administered either by peripheral or portal route in 24 anesthetized cats. Continuous intravenous infusion of graded doses of secretin (rang from 0.04 to 0.68 nmol/kg per h), stimulated pancreatic volume flow and bicarbonate outputs dose dependently and not statistically differently when given into the peripheral or portal vein. VIP infused in graded doses (range from 0.60 to 9.62 nmol/kg per h) into the peripheral vein produced pancreatic volume flow and bicarbonate outputs not statistically different from those obtained with secretin. In contrast, the biological activity of VIP administered intraportally was reduced by 60% at lower VIP doses (0.60 and 1.20 nmol/kg per h) and by 40% at 2.40 nmol/kg per h, whereas at higher doses it was not significantly changed. This study provides evidence that VIP in the cat is a secretin-like full agonist of pancreatic bicarbonate secretion and that it is only partially inactivated by the liver.