The vasoactive intestinal peptide receptor-effector system is developmentally regulated in rat jejuno-ileal epithelial cells

The specific binding of vasoactive intestinal peptide (VIP) to its specific receptors as well as the stimulatory effect of the neuropeptide on cyclic AMP accumulation were studied in jejuno-ileal epithelial cells from 14-, 20- and 60-day-old rats. The potency and specificity of the VIP receptor-effector system did not vary during development. However, the concentration of VIP receptors and the efficiency of VIP stimulation of cyclic AMP generation increased from suckling to adult conditions, and VIP levels in jejuno-ileal tissue followed a parallel course.     

Ileal vasoactive intestinal peptide (VIP) levels and VIP receptor/effector system in ileal epithelial cells after colectomy in the rat

The interaction of VIP (binding to specific receptors and stimulation of cyclic AMP accumulation) with ileal epithelial cells and the levels of the neuropeptide in the ileal segment were determined after colectomy (removal of cecum and colon followed by ileorectal anastomosis) in the rat. The number of VIP receptors (but not the affinity) and the efficiency (but not the potency) of the neuropeptide upon stimulation of cyclic AMP accumulation in ileal epithelial cells increased 21 (but not 7) days after colectomy, whereas VIP ileal levels followed an inverse pattern. These changes could be interpreted in terms of a consequence or a cause of some of the phenomena that appear after colectomy, i.e., chronic watery diarrhea.     

Lindane effect upon the vasoactive intestinal peptide receptor/effector system in rat enterocytes

Isolated rat enterocytes exposed to the insecticide lindane (the gamma-isomer of hexachlorocyclohexane, HCCH) showed an important decrease in the efficiency of the neuropeptide vasoactive intestinal peptide (VIP) upon the stimulation of cyclic AMP accumulation. The effect of lindane was time- and dose-dependent, optimal conditions being reached after 5 min incubation of cells at 25 degrees C with 0.5 mM of this organochlorine compound. Lindane action exhibited an important degree of specificity since the isomer alpha-HCCH and endrin reproduced the same inhibitory pattern but beta-HCCH and dieldrin were inactive. The inhibition of VIP-induced cyclic AMP accumulation could not be explained by a lindane-dependent reduction in the binding of VIP to its specific receptors. Among various possibilities, the results suggest the modification of membrane fluidity by lindane and/or the activation of Ca2+-dependent protein kinase C by this compound leading to phosphorylation of Gs/adenylate cyclase.     

Cholesterol modulation of membrane fluidity and VIP receptor/effector system in rat prostatic epithelial cells.

Treatment of rat prostatic epithelial cells with cholesteryl hemisuccinate (ChH) resulted in a time- and dose-dependent inhibition of the stimulatory effect of the neuropeptide vasoactive intestinal peptide (VIP) on cyclic AMP accumulation, with a 40% decrease in the response to a maximally effective VIP concentration. Cell treatment with ChH led also to a similar blocking of isoproterenol (a beta-adrenergic agonist) action but did not modify forskolin (which is assumed to act directly on the catalytic unit of adenylate cyclase) activity upon cyclic AMP levels. The levels of the transduction protein Gs were similar in membranes from both control and ChH-treated cells as suggested by experiments on cholera toxin-catalyzed ADP-ribosylation. The inhibitory effect of ChH was accompanied by an increase of membrane microviscosity as estimated by measurements of fluorescence polarization. Experiments on VIP binding indicated that increasing cholesterol concentration in the plasma membrane led to a higher VIP binding capacity without changes in the affinity of VIP receptors. These data suggest that membrane cholesterol incorporation diminishes the coupling efficiency between adenylate cyclase and the VIP-receptor complex or other receptor systems (i.e., desensitization) due to an increase of plasma membrane rigidity.     

Influence of castration and testosterone treatment on the vasoactive intestinal peptide receptor/effector system in rat prostatic epithelial cells

The interaction of vasoactive intestinal peptide (VIP) with prostatic epithelial cells was studied after castration and testosterone replacement in pubertal and mature rats. The number of VIP receptors (but not the affinity) decreased 2 days after castration and returned to normal when subsequently treated with testosterone for 4 days. However, the stimulatory effect of VIP upon cyclic AMP accumulation was unaffected by the androgen withdrawal elicited by the surgical procedure. The results suggest the importance of androgens in the biosynthesis of VIP receptors and also in their coupling to adenylate cyclase by affecting the membrane fluidity.     

Functional receptors for vasoactive intestinal peptide in cultured vascular smooth muscle cells from rat aorta

Specific binding sites for vasoactive intestinal peptide (VIP), a potent vasodilatory polypeptide, and its effect on formation of intracellular cyclic AMP levels were studied in cultured vascular smooth muscle cells (VSMC) from rat aorta. Specific binding of ¹²⁵I-labeled-VIP to cultured VSMCs was time- and temperature-dependent. Scatchard analysis of binding studies suggested the presence of two classes of high and low affinity binding sites for VIP; the apparent K_d and the number of maximal binding capacity were ∼8×10⁻⁹ M and 60,000 sites/cell (high-affinity sites) and ∼4×10⁻⁸ M and 140,000 sites/cells (low-affinity sites), respectively. Unlabeled VIP competitively inhibited the binding of ¹²⁵I-labeled-VIP to its binding sites, whereas neither peptides structurally related to VIP, nor other vasoactive substances affected the binding. VIP stimulated formation of intracellular cyclic AMP in cultured VSMCs in a dose-dependent manner; the stimulatory effect of VIP on cyclic AMP formation was not blocked by propranolol and was additive with isoproterenol. The present study first demonstrates the presence of specific receptors for VIP in VSMCs functionally coupled to adenylate cyclase system. It is suggested that VIP exerts its vasodilatory effect through its specific receptors distinct from β-adrenergic receptors.     

Differential effect of arachidonic acid on the vasoactive intestinal peptide receptor/effector system in rat prostatic epithelium during sexual maturation

The effects of alterations in the membrane lipid environment on vasoactive intestinal peptide (VIP) binding and VIP-stimulated cyclic AMP accumulation have been analyzed by arachidonic acid treatment of prostatic epithelial cells from rats at puberty and maturity, two critical developmental periods with characteristic lipidic and androgenic statuses. Treating cells with 0.1 mM arachidonic acid for 15 min at 37°C increased the affinity of VIP receptors and the potency of the neuropeptide (up to five times) in the formation of cyclic AMP at maturity, but not at puberty. The average plasma membrane fluidity (as measured by fluorescence polarization of diphenylhexatriene) remained unmodified after arachidonic acid treatment of cells. The modifications observed in mature rats were specific for the VIP receptor/effector system, since cyclic AMP stimulation by isoproterenol or forskolin was not affected by cell treatment with arachidonic acid. These results are compatible with the existence of a particular lipidic microdomain surrounding the VIP receptor in the cell membrane that would be altered by exposure to arachidonic acid (either directly or through conversion of arachidonic acid to its metabolites, as suggested by experiments on inhibition of the arachidonic acid cascade). This would make it possible for the activation of protein kinase C to phosphorylate VIP receptors in cells from mature rats, but not in those from pubertal animals with a very different membrane lipid composition (as suggested by the corresponding values of membrane fluidity and transition temperature).     

GABAB Receptor-Mediated Enhancement of Vasoactive Intestinal Peptide-Stimulated Cyclic AMP Production in Slices of Rat Cerebral Cortex

Basal and vasoactive intestinal peptide (VIP)-stimulated accumulations of cyclic AMP were measured in slices of rat cerebral cortex. Neither gamma-aminobutyric acid (GABA) nor the selective GABAB receptor agonist (-)-baclofen stimulated basal cyclic AMP accumulation, whereas VIP caused a large dose-dependent increase in cyclic AMP levels. However, in the presence of 100 microM (-)-baclofen, the effects of VIP on cyclic AMP accumulation were significantly enhanced, with the responses to 1 microM and 10 microM VIP being approximately doubled. The enhancing effects of (-)-baclofen was dose related (1-1,000 microM), but an enhancing effect was not observed with 100 microM (+)-baclofen. In the presence of the GABA uptake inhibitor nipecotic acid (1 mM), GABA caused a similar dose-related enhancement of the VIP response. The ability of either GABA or (-)-baclofen to augment VIP-stimulated production of cyclic AMP was not mimicked by the GABAA, agonists isoguvacine and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and was not antagonized by the GABAA antagonist bicuculline. The putative GABAB antagonist 5-aminovaleric acid (1 mM) significantly reduced the effect of (-)-baclofen. The ability of (-)-baclofen to enhance VIP-stimulated accumulation of cyclic AMP was observed in slices of rat cerebral cortex, hippocampus, and hypothalamus. These results indicate that GABA and (-)-baclofen can enhance VIP-stimulated accumulation of cyclic AMP in rat brain slices via an interaction with specific GABAB receptors.     

Interaction of vasoactive intestinal peptide with rat small intestinal epithelial cells after intestinal resection

Specific binding of vasoactive intestinal peptide (VIP) and VIP-stimulated c y c l i c AMP accumulation were studied in small intestinal epithelial cells (both of crypt and villous levels) 3, 7 and 14 d after a 60% resection of the small intestine . The affinity, but not the binding capacity, of VIP receptors decreased during the adaptive hyperplastic response. Basal cyclic AMP levels were similar in cells of both control and resected rats. Resection induced a decrease of potency, but not of efficiency, of VIP on the stimulation of cyclic AMP accumulation.     

The effects of experimental uremia in rats on duodenal VIP levels and the interaction of VIP with duodenal epithelial cells

The effects of experimental uremia on the concentration of vasoactive intestinal peptide (VIP) in duodenum as well as on the interaction of this neuropeptide with the corresponding epithelial cells were studied in rats. Duodenal VIP concentration was significantly decreased in uremic rats as compared to control animals. The specific binding of VIP to duodenal epithelial cells increased in rats with uremia due to an increase in the number of VIP receptors rather than a change in the binding affinity or in the extent of VIP degradation. On the other hand, the efficacy but not the potency of VIP upon cyclic AMP generation varied in parallel to that observed at the receptor level.     

Interaction of porcine vasoactive intestinal peptide with dispersed pancreatic acinar cells from the guinea pig. Structural requirements for effects of vasoactive intestinal peptide and secretin on cellular adenosine 3':5'-monophosphate.

Secretin and vasoactive intestinal peptide (VIP), but not glucagon, stimulate accumulation of cyclic AMP in dispersed guinea pig pancreatic acinar cells. Secretin stimulated cellular accumulation of cyclic AMP by interacting with a single class of high affinity receptors. On the other hand, the dose-response curve for VIP-stimulated cellular cyclic AMP was biphasic and reflected interaction of this peptide with two classes of receptors. Results obtained with synthetic fragments of VIP and secretin indicate that the receptor having a high affinity for VIP has a low affinity for secretin, interacts with, but does not distinguish among, secretin, secretin 5-27 and [6-tyrosine] secretin or among secretin 14-27, VIP 14-28, VIP 15-28, and increases cellular cyclic AMP when occupied by VIP, but not when occupied by secretin, [6-tyrosine] secretin, or secretin 1-14. The receptor having a low affinity for VIP has a high affinity for secretin, interacts with and distinguishes among secretin, secretin 5-27, and [6-tyrosine] secretin, interacts with secretin 14-27 but not with VIP 14-28 or VIP 15-28, and increases cellular cyclic AMP when occupied by VIP, secretin, [6-tyrosine] secretin, or secretin 1-14.     

Effects of Vasoactive Intestinal Peptide and Other Peptides on Cyclic AMP Accumulation in Intact Pieces and Isolated Horizontal Cells of the Teleost Retina

The effects of vasoactive intestinal peptide (VIP) and several other peptides have been examined on cyclic AMP accumulation in intact pieces and isolated horizontal cells of the teleost (carp) retina. VIP was the most effective peptide examined, inducing a dose-related response, and an approximately fivefold increase in cyclic AMP production when used at a concentration of 10 microM. Porcine histidine isoleucine-containing peptide and secretin, peptides structurally related to VIP, also stimulated cyclic AMP accumulation, but at concentrations of 10 microM induced responses which were only approximately 40% and 10%, respectively, of the response observed with 10 microM VIP. In contrast, several other peptides, including glucagon, neurotensin, somatostatin, luteinizing hormone-releasing hormone, alpha-melanocyte-stimulating hormone, cholecystokinin octapeptide26-33, gastrin-releasing peptide, thyrotropin-releasing hormone, and VIP10-28 were totally inactive. The response to 10 microM VIP was not antagonized by several dopamine antagonists, indicating the presence of a population of specific VIP receptors coupled to adenylate cyclase, distinct from the population of dopamine receptors coupled to adenylate cyclase also known to be present in this tissue. Finally, experiments involving the use of fractions of isolated horizontal cells indicate that these neurons possess a population of VIP receptors coupled to cyclic AMP production which would appear to share a common pool of adenylate cyclase with a population of similarly coupled dopamine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of ligation of pancreatic and bile ducts on the interaction of vasoactive intestinal peptide with rat duodenal epithelial cells

The specific binding of vasoactive intestinal peptide (VIP) and the stimulatory effect of the neuropeptide on cyclic AMP in duodenal epithelial cells were modified 3 days following pancreaticobiliary exclusion. The binding capacity, but not the affinity, of VIP receptors decreased (by about 50%) as a consequence of the surgical manipulation. VIP was equally potent but showed a lower efficiency (about 45%) in stimulating cyclic AMP after ligation of the pancreatic and bile ducts. These observations may be either a consequence or a cause of the adaptive response of duodenal epithelium, the last possibility suggesting a role of VIP in the mechanisms of growth and differentiation of intestinal mucosa.     

Homologous regulation of adenylate cyclase-coupled receptors for vasoactive intestinal peptide (VIP) on human mononuclear leucocytes

The effect of agonists on VIP receptor regulation has been investigated in mononuclear human blood leucocytes. VIP receptor number and affinity, as well as VIP-stimulated cyclic AMP accumulation were measured after pretreatment with VIP, PHM-27 or secretin. Pretreatment for 30 min with 0.1 μM VIP caused 28% (S.E.M. = 15) reduction in specific binding, and 52% (S.E.M. = 12) reduction in cyclic AMP accumulation, while 3 h of pretreatment caused 59% (S.E.M. = 10) and 68% (S.E.M. = 12) reduction. Only VIP concentrations at the nanomolar level and higher were shown to have any effect. B_max of the high-affinity receptor was reduced by 66% (S.E.M. = 8) after 30 min, and 95% (S.E.M. = 3) after 3 h of exposure to 0.1 μM VIP. No significant change was observed in receptor affinity, in B_max of the low-affinity receptor, in ED₅₀, or in ED₁₀₀ of VIP-stimulated cyclic AMP accumulation. Pretreatment with PHM-27 (0.1 μM, 3 h) caused 24% reduction in [¹²⁵I]VIP binding and 25% reduction in cyclic AMP accumulation, while no effect was detected after pretreatment with secretin (0.1 μM, 3 h).     

Cyclic AMP response to vasoactive intestinal peptide andβ-adrenergic or cholinergic agonists in isolated epithelial cells of rat ventral prostate

Vasoactive intestinal peptide (VIP) and the -adrenergic agonist isoproterenol stimulated cyclic AMP formation through independent receptors in isolated epithelial ceils of rat ventral prostate. The specific -adrenergic antagonist propranolol inhibited the stimulatory effect of isoproterenol but not that of VIP. Besides small differences in the efficiency of both agents, results indicated that isoproterenol was 500 times less potent than VIP. Acetylcholine did not modify the basal cyclic AMP levels but inhibited the accumulation of the cyclic nucleotide in the presence of either VIP or isoproterenol. The inhibitory action of muscarinic receptors was calcium-dependent. The coexistence of receptors for cholinergic, adrenergic and peptidergic agents which can regulate cyclic AMP suggests that the functions of prostatic epithelium may be interdependently controlled by multiple neural effectors.     

Stimulatory effect of vasoactive intestinal peptide (VIP) on cyclic AMP production in rat peritoneal macrophages.

Vasoactive intestinal peptide (VIP) stimulated cyclic AMP production in rat peritoneal macrophages. The stimulatory effect of VIP was dependent on time, temperature and cell concentration, and was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). At 15 degrees C, the response occurred in the 0.1-1000 nM range of VIP concentrations. Half maximal stimulation of cellular cyclic AMP (ED50) was obtained at 1.2 +/- 0.5 nM VIP, and maximal stimulation (about 3-fold basal level) was obtained between 100-1000 nM. The cyclic AMP system of rat peritoneal macrophages showed a high specificity for VIP. The order of potency observed in inducing cyclic AMP production was VIP greater than rGRF greater than hGRF greater than PHI greater than secretin. Glucagon, insulin, pancreastatin and octapeptide of cholecystokinin did not modify cyclic AMP levels at concentrations as high as 1 microM. The beta-adrenergic agonist isoproterenol increased the cyclic AMP production and show additive effect with VIP. Somatostatin inhibits the accumulation of cyclic AMP in the presence of both vasoactive intestinal peptide and isoproterenol. The finding of a VIP-stimulated cyclic AMP system in rat peritoneal macrophages, together with the previous characterization of high-affinity receptors for VIP in the same cell preparation, strongly suggest that VIP may be involved in the regulation of macrophage function.     

Adrenocortical Steroids Modify Neurotransmitter-Stimulated Cyclic AMP Accumulation in the Hippocampus and Limbic Brain of the Rat

Glucocorticoid hormones are known to affect limbic system structures that have high levels of specific receptors for glucocorticoids, especially the hippocampus (HIPP). To understand how glucocorticoids may affect synaptic transmission, we have tested the effects of adrenal removal and glucocorticoid replacement on neurotransmitter-stimulated cyclic AMP accumulation in brain slices from the rat limbic system. Adrenalectomy (ADX) caused an enhancement of vasoactive intestinal peptide (VIP)-stimulated cyclic AMP accumulation in HIPP, amygdala (AMYG), and septum (SEP). In HIPP, ADX increased the cyclic AMP response to isoproterenol (ISOP) and decreased the response to histamine (HIST). In the AMYG and SEP, ADX did not affect significantly the action of ISOP, but ADX did decrease the response to HIST in AMYG. Administration of dexamethasone or corticosterone reversed the effects of ADX on cyclic AMP accumulation in the HIPP. The dexamethasone action on VIP-stimulated cyclic AMP accumulation takes place within 48 h and is most apparent in the mid-range of the VIP dose-response curve. These results demonstrate that glucocorticoids regulate neurotransmitter-stimulated cyclic AMP generation in a fashion that is specific, both for the neurotransmitter involved and for the brain regions affected.     

Modulation of cyclic AMP accumulation in GH3 cells by a phorbol ester and thyroliberin

4 beta phorbol-12, 13-dibutyrate (PDBu) stimulated cyclic AMP accumulation in GH3 pituitary tumour cells in the presence of isobutylmethylxanthine. This effect persisted after preincubation of cells with cholera or pertussis toxins. In contrast, vasoactive intestinal polypeptide (VIP)-stimulated cyclic AMP accumulation was inhibited by PDBu in a dose dependent fashion (IC50 = 5.1 nM). Thyroliberin (TRH) had a similar, but non-additive, stimulatory effect on cyclic AMP accumulation with PDBu, however it did not inhibit VIP stimulation. These results suggest that TRH may stimulate cyclic AMP accumulation through protein kinase C and that stimulation of adenylate cyclase by PDBu and TRH may occur distal to the guanine nucleotide binding regulatory proteins, Ns and Ni.     

Stimulatory effects of Gila monster venom on rat pancreatic acini

The effects of Gila monster venom on dispersed rat pancreatic acini were compared with those of secretin and VIP. The efficacy of the venom in terms of amylase release was much higher (a 24-fold increase over basal secretion) than that of secretin (a 4-fold increase) and VIP (+ 40% only). On the other hand, cyclic AMP levels increased 12-fold with the venom, as compared to 18-fold with secretin and 16-fold with VIP. The venom, VIP and secretin all displaced 125I-VIP and the competition curve with the venom was steeper, suggesting that all VIP-recognizing receptors bound the venom with the same affinity. VIP receptors were, however, not responsible for the release of amylase provoked by the venom since VIP (and secretin) did not inhibit the secretory action of the venom. The venom exerted no effect on 45Ca efflux and its secretory effect did not depend on the presence of external calcium. Besides, the effect of CCK-8 on amylase release was additive with the effect of the venom. A first exposure to the venom induced a refractoriness to itself with respect to amylase release but not in terms of cyclic AMP increase. In conclusion, Gila monster venom may contain one component binding to VIP/secretin receptors with resulting cyclic AMP elevation. A second venom component may be responsible for the high secretory efficacy, without involving cyclic AMP or calcium efflux.     

Effect of gastroduodenostomy on intestinal vasoactive intestinal peptide (VIP) levels, and VIP binding and VIP stimulation of cyclic AMP in intestinal epithelial cells from rat

The concentration of VIP in duodenum and jejunum as well as the interaction of VIP (binding and stimulation of cyclic AMP accumulation) with epithelial cells from both gut segments were studied in rats after surgical bypass of the pylorus by gastroduodenostomy. Duodenal VIP concentration increased in rats with gastroduodenostomy as compared to sham-operated animals. The binding capacity (but not the affinity) of VIP binding sites and the efficiency (but not the potency) of VIP on cyclic AMP accumulation decreased in the condition of gastroduodenostomy. However, no modifications in either VIP concentration and interaction could be seen at the jejunal level.