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.     

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 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.     

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.     

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.     

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.     

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.     

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).     

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.     

The interaction of vasoactive intestinal peptide (VIP) with isolated bovine thyroid plasma membranes

The binding of vasoactive intestinal peptide (VIP) and stimulation of adenylate cyclase were studied in bovine thyroid plasma membranes. The binding depended on time, temperature and was saturable and specific. Binding studies suggested the presence of two classes of binding sites: a class with high affinity (Kd = 13 nM) and low capacity (6411 sites/pg), and a class with low affinity (Kd = 480 nm) and high capacity (105,300 sites/pg) at 15 degrees C. Secretin, glucagon, insulin and somatostatin did not displace the tracer from the membranes. VIP stimulated cyclic AMP production. Maximal cyclic AMP production (2-fold above basal values) was observed with 100 nM VIP and half-maximal response was obtained at 5 nM VIP at 15 degrees C.     

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.     

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).     

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.     

Characterization and age dependence of the stimulatory effect of VIP on cyclic AMP accumulation in rat Leydig cells

The neuropeptide vasoactive intestinal peptide (VIP) has been shown to stimulate cyclic AMP accumulation in Leydig cells isolated from rat testis. The effect was dependent on time, temperature and cell concentration. At 15° half-maximal and maximal stimulation were observed at about 1 and 100 nM VIP, respectively. The interaction was specific since an order of potencies chicken VIP> rat VIP> secretin>glucagon and no effect of neurotensin and substance P were obtained. The efficiency of VIP was lower in pubertal rats and then increased in young-adult and adult animals. These results together with the known presence of VIP in the testis support the idea that VIP may be involved in the regulation and function of Leydig cells during development.     

Effect of resection of small intestine on the interaction of vasoactive intestinal peptide with rat colonic epithelial cells

Vasoactive intestinal peptide (VIP) receptors and VIP-dependent cyclic AMP production were studied in rat colonic epithelial cells 3 days after a 60% resection of the small intestine. Basal cyclic AMP levels were similar in both control and resected animals. The potency, but not the efficiency, of the peptide on the stimulation of cyclic AMP production was diminished in cells from resected rats. Accordingly, the affinity of VIP receptors, but not the binding capacity, decreased as a consequence of the loss of a part of the small intestinal mucosa. These observations are consistent with the known inhibitory role of cyclic AMP on cell proliferation in colonic epithelium and other tissues and suggest a participation of VIP acting through the cyclic nucleotide in the compensatory hyperproliferative response of the colon following massive resection of the small intestine.     

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.     

Activation of cyclic AMP-dependent protein kinases by vasoactive intestinal peptide (VIP) in isolated intestinal epithelial cells from rat.

VIP stimulates protein kinase activity in intestinal epithelial cells isolated from rat jejuno-ileum. The stimulation is time-dependent and is potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. The response occurs in the 0.1–10 nM range of VIP concentrations, half-maximal stimulation being observed with 0.7 nM VIP. The VIP-induced protien kinase activation is thus observed at concentrations similar to those promoting the accumulation of cyclic AMP (11). Secretin also stimulates protien kinase activity but with a 100-times lower potency than VIP, in agreement with the fact that secretin is a VIP agonist of 100-times lower potency with respect to cyclic AMP increase. Prostaglandins E₁ and E₂ (10^?5 M), are also found to increase protein kinase activity.     

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.     

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.     

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.