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.     

Decreased binding of vasoactive intestinal peptide to intestinal epithelial cells from hypothyroid rats

The binding of vasoactive intestinal peptide (VIP) and stimulation of adenylate cyclase by VIP were studied in intestinal epithelial cells during hypothyroidism. Experimental hypothyroidism was induced in rats by the administration of KC10(4). The binding capacity, but not the affinity, of VIP receptors decreased in the hypothyroid rats. Besides, the stimulation of cyclic AMP production by VIP was also diminished in cells from hypothyroid rats. These observations indicate a decrease of the responsiveness of intestinal epithelial cells to VIP in the hypothyroid status, suggesting a role of the peptide in the pathophysiologic mechanism of intestinal manifestations during hypothyroidism.     

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.     

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.     

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.     

Analysis of progress curves for enzyme-catalysed reactions. Automatic construction of computer programs for fitting integrated rate equations.

In epithelial cells isolated from rat small intestine, we have studied the influence of vasoactive intestinal peptide (VIP), a neurotransmitter which markedly increases enterocyte cyclic AMP, and of two cyclic AMP analogues (8-bromo cyclic AMP and N6,2'-O-dibutyryl cyclic AMP) on the rate of glycolysis, fructose 2,6-bisphosphate concentration and 6-phosphofructo-2-kinase activity, as well as on the rate of 3-O-methyl-D-[14C]glucose uptake. Our results show that, without affecting the rate of 3-O-methyl-D-[14C]glucose accumulation, VIP and cyclic AMP analogues were able to inhibit glucose consumption and L-lactate formation by isolated rat enterocytes. These effects occurred parallel to a significant decrease in the cellular concentration of fructose 2,6-bisphosphate and to a partial inactivation of 6-phosphofructo-2-kinase. These findings support the hypothesis that VIP inhibits glycolysis in rat enterocytes through a cyclic AMP-dependent mechanism.     

Effects of age and androgens upon functional vasoactive intestinal peptide receptors in rat prostatic epithelial cells

The specific binding of vasoactive intestinal peptide (VIP) and the stimulatory effect of VIP upon cyclic AMP accumulation in isolated epithelial cells of rat ventral prostate were age dependent. The number of VIP receptors decreased but the efficiency of VIP on cyclic AMP accumulation increased in prostatic epithelium when considering the periods 35-65 days and 3-6 months. Since these features could be related to the known age-related decrease of androgen and androgen-receptor levels, we studied the effect of testosterone and its 5 alpha-reduced metabolite dihydrotestosterone upon both steps of VIP action. The two steroid hormones exerted a non-competitive inhibition on VIP-induced cyclic AMP accumulation but did not modify VIP binding to its specific receptors. This modulatory effect of androgens might involve their interaction with specific sites on the cell membrane leading to modifications of membrane activities including adenylate cyclase, as has been suggested by an increasing number of recent reports.     

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.     

Effect of intestinal ischaemia on intestinal VIP levels and VIP interaction with intestinal epithelial cells from rat

1. The number (but not the affinity) of vasoactive intestinal peptide (VIP) receptors in small intestinal epithelial cells decreased following intestinal ischaemia in rats as compared to sham-operated animals. 2. There was a parallel decrease of the efficiency (but not the potency) of the neuropeptide upon cyclic AMP formation at the same level after intestinal ischaemia. 3. The surgical manipulation did not modify the level of VIP immunoreactivity in the gut segment studied. 4. These results suggest that the VIPergic system is not directly involved in the high loss of water and electrolytes that appears following intestinal ischaemia.     

Vasoactive-intestinal-polypeptide-stimulated adenosine 3'',5''-cyclic monophosphate accumulation in GH3 pituitary tumour cells. Reversal of desensitization by forskolin.

The interaction between forskolin and vasoactive intestinal polypeptide (VIP) in the regulation of cyclic AMP production in GH3 pituitary tumour cells was investigated. Both forskolin (10nM-10 microns) and VIP (10pM-10nM) increased the cyclic AMP content of GH3 cells. Forskolin (50-100nM) was additive with VIP in stimulating cyclic AMP accumulation when low concentrations (less than 1 nM) of the peptide were used, but exhibited a synergistic interaction with higher VIP concentrations (10-100 nM). These effects on cyclic AMP accumulation were reflected in a leftward shift in the concentration-response curve for VIP-stimulated prolactin release from GH3 cells, a process known to be regulated by intracellular cyclic AMP concentrations. The synergy observed did not appear to be related to changes in cyclic nucleotide phosphodiesterase activity, since it was even more marked in the presence of isobutylmethylxanthine, a phosphodiesterase inhibitor. Studies of the time-course of VIP-induced changes in GH3-cell cyclic AMP content revealed that, with high concentrations of VIP, production ceased within 2 min of addition. This attenuation of cyclic AMP synthesis was still observed in the presence of isobutylmethylxanthine, but was markedly inhibited by low concentrations of forskolin (50-100nM). The results suggest that VIP-induced cyclic AMP production rapidly becomes desensitized. This process, which is prevented by forskolin, may be related to changes in the ability of the guanine nucleotide regulatory protein to couple receptor occupancy to activation of adenylate cyclase.     

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.     

A fragment of vasoactive intestinal peptide, VIP(10-28), is an antagonist of VIP in the colon carcinoma cell line, HT29

The 19 amino acid carboxyl terminus fragment of vasoactive intestinal peptide (VIP), VIP(10-28), inhibits [125I]VIP binding in intact HT29 colonic adenocarcinoma cells and in membranes from these cells. However, VIP(10-28) alone has no effect on adenylate cyclase activity (membranes) or cyclic AMP synthesis (intact cells) in HT29 cells although VIP receptor agonists are markedly stimulatory. The indicated antagonist character of VIP(10-28) was confirmed by rightward parallel shifts of VIP dose response curves in the presence of VIP(10-28) in adenylate cyclase and cyclic AMP synthesis experiments. The equilibrium dissociation constant values for VIP(10-28) from these experiments agree with values from inhibition binding studies. The lack of effect of VIP(10-28) on forskolin dose response curves in HT29 adenylate cyclase assays indicates the specificity of the VIP(10-28) antagonism, thus suggesting that VIP(10-28) may be a useful tool in studying VIP receptor regulation and other aspects of the mechanisms of VIP action. The potential regulatory role of a proteolytically generated fragment of VIP acting antagonistically at VIP receptors is discussed.     

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.     

Autoradiographic distribution of vasoactive intestinal polypeptide receptors in rabbit and rat small intestine

Vasoactive intestinal peptide (VIP) is found in the enteric nervous system of all layers of the small intestine. In the gastrointestinal tract, VIP receptors coupled to adenylate cyclase are present on epithelial, smooth muscle and possibly mononuclear cells. This study analyzes the distribution of VIP binding using in vitro autoradiographic techniques. VIP binding was present in high density in the mucosal layer of rabbit duodenum, jejunum and ileum. Low VIP binding was noted over the smooth muscle layers or the lymphoid follicles. Similar results were obtained in rat small intestine. The density of VIP binding was greatest in duodenal mucosa but was present in lower density in jejunal and ileal mucosa. Again, low VIP binding was noted in the smooth muscle layers or lymphoid follicles. Thus, autoradiographic maps of small intestine indicate that VIP receptors are found primarily in the small intestinal mucosa.     

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.     

Regulation of GH3-cell function via adenosine A1 receptors. Inhibition of prolactin release, cyclic AMP production and inositol phosphate generation.

We examined the mechanism by which adenosine inhibits prolactin secretion from GH3 cells, a rat pituitary tumour line. Prolactin release is enhanced by vasoactive intestinal peptide (VIP), which increases cyclic AMP, and by thyrotropin-releasing hormone (TRH), which increases inositol phosphates (IPx). Analogues of adenosine decreased prolactin release, VIP-stimulated cyclic AMP accumulation and TRH-stimulated inositol phospholipid hydrolysis and IPx generation. Inhibition of InsP3 production by R-N6-phenylisopropyladenosine (R-PIA) was rapid (15 s) and was not affected by the addition of forskolin or the removal of external Ca2+. Addition of adenosine deaminase or the potent adenosine-receptor antagonist, BW-A1433U, enhanced the accumulation of cyclic AMP by VIP, indicating that endogenously produced adenosine tonically inhibits adenylate cyclase. The potency order of adenosine analogues for inhibition of cyclic AMP and IPx responses (measured in the presence of adenosine deaminase) was N6-cyclopentyladenosine greater than R-PIA greater than 5'-N-ethylcarboxamidoadenosine. This rank order indicates that inhibitions of both cyclic AMP and InsP3 production are mediated by adenosine A1 receptors. Responses to R-PIA were blocked by BW-A1433U (1 microM) or by pretreatment of cells with pertussis toxin. A greater amount of toxin was required to eliminate the effect of R-PIA on inositol phosphate than on cyclic AMP accumulation. These data indicate that adenosine, in addition to inhibiting cyclic AMP accumulation, decreases IPx production in GH3 cells, possibly by directly inhibiting phosphoinositide hydrolysis.     

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.     

α2-Adrenoceptors Mediate Inhibition of Cyclic AMP Production in the Spinal Cord After Stimulation of Cyclic AMP with Forskolin but Not After Stimulation with Capsaicin or Vasoactive Intestinal Peptide

In slices obtained from the ventral and the dorsal guinea pig spinal cord both forskolin and vasoactive intestinal peptide (VIP) caused a dose-dependent stimulation of the production of cyclic AMP. By contrast capsaicin stimulated cyclic AMP formation only in the dorsal cord; no effect was observed in the ventral cord. The alpha 2-adrenergic agonist UK-14,304 dose-dependently inhibited the production of cyclic AMP in both the dorsal and ventral aspects of the cord when the formation of cyclic AMP had been stimulated with 3 microM forskolin, the maximal inhibition amounting to 25-32%. Also the basal (i.e., unstimulated) production of cyclic AMP was inhibited, the inhibition amounting to about 16-18%. However, after stimulation of cyclic AMP formation in the dorsal cord with capsaicin, UK-14,304 was virtually ineffective in inhibiting the accumulation of cyclic AMP. Also, when the formation of cyclic AMP was stimulated with VIP, UK-14,304 was virtually ineffective in inhibiting the formation of cyclic AMP both in the ventral and the dorsal parts of the cord. When cyclic AMP production had been stimulated with forskolin the ability of UK-14,304 to inhibit the formation of cyclic AMP was not attenuated by capsaicin, either in the ventral or in the dorsal cord. The results are discussed with the notion that cyclic AMP inhibitory spinal cord alpha 2-adrenoceptors are located on cells accessible to stimulation of cyclic AMP with forskolin but not with capsaicin or VIP.     

Effect of bilateral adrenalectomy on VIP receptor/effector system in rat intestinal epithelial cells

The number of vasoactive intestinal peptide (VIP) receptors and the efficiency of VIP in the stimulation of cyclic AMP accumulation in rat jejunal epithelial cells increased after bilateral adrenalectomy. However, this condition increased neither receptor affinity nor VIP potency. In addition, jejunal VIP levels followed a parallel increase. These changes reversed to control conditions after glucocorticoid replacement with dexamethasone indicating that adrenalectomy modifies the intestinal VIP receptor/effector system and suggest a relationship between corticosteroids and VIP in the functions of intestinal epithelium.