Vasoactive Intestinal Polypeptide Stimulation Research Articles

Dynamics of a disinhibitory prefrontal microcircuit in controlling social competition

Social competition plays a pivotal role in determining individuals' social status. While the dorsomedial prefrontal cortex (dmPFC) is essential in regulating social competition, it remains unclear how information is processed within its local networks. Here, by applying optogenetic and chemogenetic manipulations in a dominance tube test, we reveal that, in accordance with pyramidal (PYR) neuron activation, excitation of the vasoactive intestinal polypeptide (VIP) or inhibition of the parvalbumin (PV) interneurons induces winning. The winning behavior is associated with sequential calcium activities initiated by VIP and followed by PYR and PV neurons. Using miniature two-photon microscopic (MTPM) and optrode recordings in awake mice, we show that VIP stimulation directly leads to a two-phased activity pattern of both PYR and PV neurons-rapid suppression followed by activation. The delayed activation of PV implies an embedded feedback tuning. This disinhibitory VIP-PV-PYR motif forms the core of a dmPFC microcircuit to control social competition.

Cyclic AMP-dependent protein kinase A and EPAC mediate VIP and secretin stimulation of PAK4 and activation of Na+,K+-ATPase in pancreatic acinar cells.

Rat pancreatic acinar cells possess only the p21-activated kinase (PAKs), PAK4 of the group II PAK, and it is activated by gastrointestinal hormones/neurotransmitters stimulating PLC and by a number of growth factors. However, little is known generally of cAMP agents causing PAK4 activation, and there are no studies with gastrointestinal hormones/neurotransmitters activating cAMP cascades. In the present study, we examined the ability of VIP and secretin, which stimulate cAMP generation in pancreatic acini, to stimulate PAK4 activation, the signaling cascades involved, and their possible role in activating sodium-potassium adenosine triphosphatase (Na+,K+-ATPase). PAK4 activation was compared with activation of the well-established cAMP target, cyclic AMP response element binding protein (CREB). Secretin-stimulated PAK4 activation was inhibited by KT-5720 and PKA Type II inhibitor (PKI), protein kinase A (PKA) inhibitors, whereas VIP activation was inhibited by ESI-09 and HJC0197, exchange protein directly activated by cAMP (EPAC) inhibitors. In contrast, both VIP/secretin-stimulated phosphorylation of CREB (pCREB) via EPAC activation; however, it was inhibited by the p44/42 inhibitor PD98059 and the p38 inhibitor SB202190. The specific EPAC agonist 8-CPT-2- O-Me-cAMP as well 8-Br-cAMP and forskolin stimulated PAK4 activation. Secretin/VIP activation of Na+,K+-ATPase, was inhibited by PAK4 inhibitors (PF-3758309, LCH-7749944). These results demonstrate PAK4 is activated in pancreatic acini by stimulation of both VIP-/secretin-preferring receptors, as is CREB. However, they differ in their signaling cascades. Furthermore, PAK4 activation is needed for Na+,K+ATPase activation, which mediates pancreatic fluid secretion. These results, coupled with recent studies reporting PAKs are involved in both pancreatitis/pancreatic cancer growth/enzyme secretion, show that PAK4, similar to PAK2, likely plays an important role in both pancreatic physiological/pathological responses. NEW & NOTEWORTHY Pancreatic acini possess only the group II p21-activated kinase, PAK4, which is activated by PLC-stimulating agents/growth factors and is important in enzyme-secretion/growth/pancreatitis. Little information exists on cAMP-activating agents stimulating group II PAKs. We studied ability/effect of cyclic AMP-stimulating agents [vasoactive intestinal polypeptide (VIP), secretin] on PAK4 activity in rat pancreatic-acini. Both VIP/secretin activated PAK4/CREB, but the cAMP signaling cascades differed for EPAC, MAPK, and PKA pathways. Both hormones require PAK4 activation to stimulate sodium-potassium adenosine triphosphatase activity. This study shows PAK4 plays an important role in VIP-/secretin-stimulated pancreatic fluid secretion and suggests it plays important roles in pancreatic acinar physiological/pathophysiological responses mediated by cAMP-activating agents.

Daily Changes in GT1–7 Cell Sensitivity to GnRH Secretagogues That Trigger Ovulation

Circadian rhythms in behavior and physiology are orchestrated by a master biological clock located in the suprachiasmatic nucleus (SCN). Circadian oscillations are a cellular property, with ‘clock’ genes and their protein products forming transcription-translation feedback loops that maintain 24-hour rhythmicity. Although the expression of clock genes is thought to be ubiquitous, the function of local, extra-SCN timing mechanisms remains elusive. We hypothesized that extra-SCN clock genes control local temporal sensitivity to upstream modulatory signals, allowing system-specific processes to be carried out during individual, optimal times of day. To test this possibility, we examined changes in the sensitivity of immortalized GnRH neurons, GT1–7 cells, to timed stimulation by two key neuropeptides thought to trigger ovulation on the afternoon of proestrus, kisspeptin and vasoactive intestinal polypeptide (VIP). We noted a prominent daily rhythm of clock gene expression in this cell line. GT1–7 cells also exhibited daily changes in cellular peptide expression and GnRH secretion in response to kisspeptin and VIP stimulation. These responses occurred without changes in GnRH transcription. These findings are consistent with the notion that GnRH cells are capable of intrinsic circadian cycles that may be fundamental for coordinating daily changes in sensitivity to signals impacting the reproductive axis.

Effect of chronic, extrinsic denervation on functional NANC innervation with vasoactive intestinal polypeptide and substance P in longitudinal muscle of rat jejunum1

Intestinal denervation contributes to enteric motor dysfunction after intestinal transplantation [small bowel transplantation (SBT)]. Our aim was to determine long-term effects of extrinsic denervation on functional non-adrenergic, non-cholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P. Contractile activity of jejunal longitudinal muscle from six age-matched, naïve control rats (NC) and eight rats 1 year after syngeneic SBT were studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently in both groups, greater in NC than in SBT. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor l-N(G)-nitro arginine prevented inhibition by exogenous VIP and electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than in SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and increased the EFS-induced inhibitory response. Immunohistofluorescence showed staining for tyrosine hydroxylase in the jejunoileum 1 year after SBT suggesting sympathetic reinnervation. In rat jejunal longitudinal muscle after chronic denervation, response to exogenous VIP and substance P is decreased, while endogenous release of both neurotransmitters is preserved. These alterations in excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

The increase in prolactin-secreting cells in incubating chicken hens can be mimicked by extended treatment of pituitary cells in vitro with vasoactive intestinal polypeptide (VIP)

Incubation of eggs by birds and lactation in mammals are regulated by pituitary prolactin (PRL) and associated with an increase in pituitary PRL-producing cells or lactotrophs. However, the mechanisms controlling this increase in lactotroph numbers are not known. PRL secretion in birds is regulated by vasoactive intestinal polypeptide (VIP). This study was designed to determine whether VIP treatment could modulate lactotroph abundance in culture. Anterior pituitary cells were isolated from laying Japanese White Silkie hens and cultured for 2 or 6 days in the absence or presence of VIP. PRL-secreting cells were identified by reverse hemolytic plaque assay. Treatment with VIP for 6 days substantially increased the abundance of PRL-secreting cells from 47.5% under basal conditions to 70.6% of all pituitary cells following VIP stimulation. However, 2-day VIP treatment had no effect. Furthermore, the extent to which the hens were allowed to accumulate eggs in a clutch prior to isolation of the pituitaries did not affect the lactotroph response to VIP in vitro . These findings indicate that chronic VIP stimulation may be responsible for the increased abundance of lactotrophs found in the pituitary glands of incubating hens.

The goldfish vasoactive intestinal polypeptide receptor: functional studies and tissue distribution

Vasoactive intestinal polypeptide (VIP)1 is a neuropeptide that has numerous physiological actions and is widely distibuted in the body of most vertebrate species yet studied. A full-length VIP receptor cDNA was obtained by screening a goldfish brain and pituitary cDNA library. Functional expression of this receptor in mammalian COS-7 cells showed that it is coupled to cAMP production in a VIP (Atlantic cod, Gadus morhua) concentration-dependent manner; the EC50 of the VIP receptor in response to cod VIP stimulation was determined to be at 1.0 nM. At 100 nM of peptide, the relative potency of various peptides in stimulating cAMP in the transfected cells was cod VIP>human VIP>human PACAP-38>human PACAP-27>human secretin>dogfish glucagon>carp GHRH. The receptor was able to bind specifically to VIP and PACAP as indicated by competitive displacement assays. By reverse-transcriptase polymerase chain reaction, the transcripts of this receptor were detected in goldfish brain, pituitary gland, gall bladder, kidney, gill, small and large intestine, heart, muscle and spleen. The expression pattern of goldfish VIP receptor is similar to that of mammals and thus further evidence of the conservation of VIP function in vertebrates. Characterization of the VIP1 receptor from goldfish is the first step in understanding 2 of the most important neuropeptides, VIP and PACAP, and their interaction with multiple receptor system in lower vertebrates.

Interaction Between Adrenergic and Peptide Stimulation in the Rat Pineal: Pituitary Adenylate Cyclase‐Activating Peptide

The 27 amino acid peptide, pituitary adenylate cyclase-activating polypeptide (PACAP-27), and its 38 amino acid analogue, PACAP-38, stimulate serotonin-N-acetyltransferase (NAT) activity and N-acetylserotonin (NAS) and melatonin content of pineal glands from adult rats. Maximal stimulation of rat pineal NAT by PACAP-38 is not increased further significantly by concurrent stimulation with the two related peptides, vasoactive intestinal polypeptide (VIP) and/or peptide N-terminal histidine C-terminal isoleucine (PHI). Isoproterenol was a more potent inducer of NAT activity than any of these peptides alone or in combination. PACAP-38 also stimulates melatonin production by chicken pineal cells in culture as does VIP. Stimulation by both was not greater than after either alone. Prior stimulation of rat pineal NAT activity with VIP, PHI, or PACAP-38 reduces the magnitude of subsequent stimulation with PACAP-38 or forskolin. Concurrent stimulation of alpha-receptors or treatment with active phorbol ester augments rat pineal response to PACAP-38 stimulation just as it increases the response to VIP, PHI, and beta-receptor stimulation. Pineals from newborn rats respond to PACAP-38 with an increase in NAT activity and the increase is augmented by concomitant alpha 1-adrenergic stimulation. The putative PACAP inhibitor PACAP (6-38) and the putative VIP inhibitor (Ac-Tyr,D-Phe)-GRF 1-29 amide, in 100-1,000-fold excess, did not affect the stimulatory activity of any of the peptides. Pineal melatonin concentration parallels changes in pineal NAT activity.

Different neurotransmitter systems are involved in the development of esophageal achalasia

Clinical and pharmacological evidence suggests that several neurotransmitters are involved in the control of the esophageal motilility; in fact, besides the well known cholinergic and sympathetic innervation, Vasoactive Intestinal Polypeptide (VIP)-containing fibers as well as dopamine (DA)-containing nerve endings have been identified within the esophageal wall. Lower Esophageal Sphincter (LES) achalasia is a neuromuscular disorder characterized by the absence of peristalsis in the body of the esophagus and by the failure of the LES to relax in response to swallowing. Stimulation of both VIP receptors and D-2 DA receptors induce a decrease in LES pressure, while D-1 receptors mediate LES contractions. In the present study we show that both VIP and DA system is disregulated in LES achalasia. In particular, this disease is associated not only with the lack of VIP nerves in the LES, but also with a failure in the responsiveness of postsynaptic receptors to VIP stimulation. Furthermore, we demonstrate a selective functional loss of the D-2 DA receptor component, without changes in the D-1 DA receptor mediated responses.

Inhibition of VIP-stimulated ion transport by a novel Y-receptor phenotype in rabbit distal colon.

Neurocrine, endocrine, and paracrine regulators are critical to the control of colonic secretion. These studies have investigated the inhibition of vasoactive intestinal polypeptide (VIP)-stimulated ion transport by peptide YY (PYY) and other Y-class effectors in rabbit distal colonic mucosa mounted in Ussing chambers. PYY decreased basal short-circuit current (Isc) but did not significantly change either basal Na+ or Cl- flux. PYY inhibited VIP-stimulated increases in Isc by up to 86% and abolished VIP-induced Cl- secretion. PYY decreased VIP-generated increases in Isc by a tetrodotoxin-insensitive mechanism. PYY inhibited cholera toxin-stimulated as well as forskolin-stimulated increases in Isc but failed to alter stimulation by 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP). PYY decreased VIP-stimulated increases in tissue cAMP by 88% and forskolin-stimulated increases by 84%. PYY, neuropeptide Y (NPY), (Leu31,Pro34)-NPY, and pancreatic polypeptide (PP) all demonstrated potent inhibition of VIP-stimulated increases in Isc. PYY-(13-36) demonstrated little effect on VIP stimulation. Thus the rabbit distal colon possesses a novel Y-class receptor phenotype that demonstrates high affinity for all three PP-fold peptides, NPY, PYY, and PP.

Vasoactive Intestinal Polypeptide‐Related Peptides Modulate Tyrosine Hydroxylase Gene Expression in PC12 Cells Through Multiple Adenylate Cyclase‐Coupled Receptors

We investigated the receptor mechanisms by which vasoactive intestinal polypeptide (VIP) and related peptides exert their effects on tyrosine hydroxylase (TH) gene expression. VIP, secretin, and peptide histidine isoleucine (PHI) each produced increases in TH gene expression, as measured by increases in TH mRNA levels and TH activity. The concentrations at which the effects of these peptides were maximal differed for TH activity and TH mRNA. Moreover, maximal increases in TH activity were 130-140% of control, whereas maximal increases in TH mRNA were 250% of control. The concentration dependence of the increases in TH mRNA in response to the three peptides was analyzed by fitting the data to nonlinear regression models that assume either one or two components to the response. The data for secretin fit best to a model that assumes a single component to the increase in TH mRNA levels. The data derived for PHI and VIP fit best to models that assumed two components to the TH mRNA response. These data suggested that there may be more than one receptor or signal transduction mechanism involved in the response to the various peptides. We examined whether the peptides exerted their effects through common or multiple second messenger systems. The ability of maximally active concentrations of these peptides to stimulate increases in TH mRNA was not additive, indicating that the peptides work through a common receptor or signal transduction pathway. Each peptide stimulated increases in protein kinase A (PKA) activity. Secretin and VIP were ineffective in increasing TH mRNA levels in a PKA-deficient mutant PC12 cell line (A126-1B2). Moreover, the adenylate cyclase antagonist 2',5'-dideoxyadenosine prevented the increase in TH mRNA produced by each peptide. Thus, each peptide requires an intact cyclic AMP second messenger pathway to produce changes in TH gene expression, suggesting that the complex pattern of response to VIP and PHI revealed by concentration-response analysis was due to the actions of these peptides at multiple receptors. To evaluate this possibility, we examined the effect of several peptide receptor antagonists on the increase in TH gene expression elicited by VIP, PHI, and secretin. The secretin antagonist secretin (5-27) (20 microM) had no significant effect on VIP or PHI stimulation of TH gene expression, but reduced the effect of secretin. The VIP antagonist VIP (10-28) (20 microM) reduced the effect of VIP on increasing TH mRNA, but had no significant effect on the response of TH mRNA to secretin or PHI.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacological approach to the insulin-resistance/polymetabolic syndrome

Incubation of eggs by birds and lactation in mammals are regulated by pituitary prolactin (PRL) and associated with an increase in pituitary PRL-producing cells or lactotrophs. However, the mechanisms controlling this increase in lactotroph numbers are not known. PRL secretion in birds is regulated by vasoactive intestinal polypeptide (VIP). This study was designed to determine whether VIP treatment could modulate lactotroph abundance in culture. Anterior pituitary cells were isolated from laying Japanese White Silkie hens and cultured for 2 or 6 days in the absence or presence of VIP. PRL-secreting cells were identified by reverse hemolytic plaque assay. Treatment with VIP for 6 days substantially increased the abundance of PRL-secreting cells from 47.5% under basal conditions to 70.6% of all pituitary cells following VIP stimulation. However, 2-day VIP treatment had no effect. Furthermore, the extent to which the hens were allowed to accumulate eggs in a clutch prior to isolation of the pituitaries did not affect the lactotroph response to VIP in vitro. These findings indicate that chronic VIP stimulation may be responsible for the increased abundance of lactotrophs found in the pituitary glands of incubating hens.

Effect of 3-isobutyl-1-methylxanthine and zaprinast on non-adrenergic non-cholinergic relaxation in the rat gastric fundus

Vasoactive intestinal polypeptide (VIP) and nitric oxide (NO) have been proposed as inhibitory non-adrenergic non-cholinergic (NANC) neurotransmitters in the rat gastric fundus. The smooth muscle relaxant actions of VIP and NO are mediated by cAMP and cGMP, respectively; therefore the effect of inhibitors of phosphodiesterases responsible for cyclic nucleotide breakdown on relaxation induced by VIP, NO and electrical field stimulation was investigated. The non-specific phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), the cGMP-specific phosphodiesterase inhibitor, zaprinast, the adenylate cyclase activator, forskolin, and the cyclic nucleotide analog, 8-bromo cGMP, produced concentration-dependent relaxation of rat gastric fundus strips precontracted by PGF 2α. IBMX potentiated isoprenaline-induced relaxation but not relaxation induced by sodium nitroprusside, VIP, NO or electrical field stimulation. Zaprinast potentiated the relaxation induced by sodium nitroprusside, while having no influence on relaxation due to any other stimulus. The combination of both phosphodiesterase inhibitors did not significantly affect the electrically induced relaxation. It is concluded that both cAMP and cGMP mediate relaxation in the rat gastric fundus. Further research is needed to investigate the role of the cyclic nucleotides during NANC relaxation of this tissue.

Functional Vasoactive Intestinal Polypeptide (VIP) Receptors in Human Neuroblastoma Subclones That Contain VIP Precursor mRNA and Release VIP-like Substances

Three phenotypically distinct subclones (SH-SY-5Y, SH-EP, SH-IN) of the human neuroblastoma cell line SK-N-SH were found to possess vasoactive intestinal polypeptide (VIP) precursor mRNA, release immunoreactive VIP, and express high-affinity VIP receptors coupled to adenylate cyclase. The apparent molecular mass for the receptor polypeptide, as determined by covalent cross-linking of 125I-VIP, was 49 kDa. After 2 days in culture, a concentration of immunoreactive VIP equivalent to the binding affinity of VIP to its receptor was found in the medium in two of these clones (SH-IN and SH-EP). Conditioned medium from SH-IN cells competitively displaced 125I-VIP binding and increased cAMP levels in SH-EP cells, indicating that all of the necessary components for a potential autocrine action of VIP exist in SK-N-SH cells. After numerous cell passages, the SH-EP subclone converted to a distinct phenotype in which VIP precursor mRNA and VIP immunoreactivity in the cell and medium were no longer detectable. In correlation, the VIP receptor number increased, and the EC50 for VIP stimulation of cAMP production shifted to a lower concentration. This points to the possibility that the continuous presence of endogenous VIP in earlier passage SH-EP cells causes a modification in VIP receptor number and cell responsiveness to VIP.

Comparison of the effect of vasoactive intestinal polypeptide and non-adrenergic non-cholinergic neurone stimulation in the cat gastric fundus

The possible involvement of vasoactive intestinal polypeptide (VIP) in the non-adrenergic non-cholinergic (NANC) relaxation of the cat gastric fundus was studied in circular and longitudinal muscle strips. Cumulative transmural stimulation induced a frequency-dependent relaxation, while cumulative administration of VIP induced a concentration-dependent relaxation. Tetrodotoxin almost completely antagonized the relaxation induced by transmural stimulation (1 Hz), but did not influence the relaxation induced by VIP (10 −7 M); the latter was not influenced by hexamethonium or propranolol plus phentolamine. Trypsin (30 min incubation) and VIP antiserum (1 h incubation) prevented the relaxation induced by VIP and reduced that induced by transmural stimulation, but did not influence the relaxation induced by isopropylnoradrenaline. Two putative VIP receptor antagonists, [AcTyr 1]hGRF-(1–40)OH and [4Cl-D-Phe 6,Leu 17]VIP, did not influence the relaxation induced by VIP or transmural stimulation. These results are compatible with the hypothesis that VIP is involved in the NANC relaxation of the cat gastric fundus, although participation of a non-VIP component cannot be excluded.

Synergistic action of postsynaptic alpha-adrenergic receptor stimulation on vasoactive intestinal polypeptide-induced increases in pineal N-acetyltransferase activity.

The alpha-adrenergic agonists phenylephrine and methoxamine, at concentrations that have little effect on pineal N-acetyltransferase activity, markedly enhance stimulation of this enzyme by vasoactive intestinal polypeptide (VIP). This augmentation can be blocked by the alpha 1-adrenergic antagonists phenoxybenzamine and prazosin and, at 10 but not 1 microM, by the alpha 2-antagonist yohimbine. The time course for VIP stimulation is not altered by concomitant alpha-adrenergic stimulation. Augmented activity does not require concomitant alpha-adrenergic stimulation, but alpha-adrenergic agonists must be present for augmentation to be maintained. Phorbol 12,13-diacetate or -dibutyrate but not 4 alpha-phorbol can substitute for phenylephrine, a finding suggesting that protein kinase C is involved in the augmentation. These results are, in general, analogous to alpha-adrenergic magnification of N-acetyltransferase induction by beta-adrenergic agonists.

Vasoactive intestinal polypeptide regulation of rabbit renal adenylate cyclase activity in vitro.

1. The effect of vasoactive intestinal polypeptide (VIP) upon adenylate cyclase activity was determined in purified cortical basolateral membranes and in glomeruli and tubular elements obtained from rabbit kidney. 2. In purified basolateral membranes prepared from cortex, 1 microM-VIP consistently stimulated adenylate cyclase activity above basal levels (1.55 +/- 0.09-fold (mean +/- S.E. of mean), n = 10 animals). Half-maximal stimulation was observed at 17 +/- 11 nM-VIP (S.D., n = 9). 3. Related peptides, e.g. secretin, glucagon, gastric inhibitory peptide, human pancreatic growth hormone releasing factor, and peptide having N-terminal histidine and C-terminal isoleucine amide (PHI), were without effect or gave lower stimulations of adenylate cyclase activity when tested at 1 microM. 4. Significant VIP degradation was observed under the assay conditions used but this did not substantially alter the response or selectivity to VIP. 5. In separate preparations of isolated glomeruli and proximal tubules addition of 1 microM-VIP resulted in a 3.3 +/- 1.1-fold (S.D., n = 3) and 2.2 +/- 1.0-fold (S.D., n = 3) stimulation (respectively) of adenylate cyclase activity. 6. In isolated medullary tubule suspensions, isolated by collagenase-hyaluronidase digestion of outer (red) medulla, and in thick ascending-limb-enriched preparations prepared by Percoll density gradient fractionation, 1 microM-VIP significantly increased adenylate cyclase activity by 2.4 +/- 0.6-fold (S.D., n = 3) and 2.1 +/- 0.7-fold (S.D., n = 3) respectively. 7. A possible role for VIP in the regulation of renal function in the rabbit is discussed in relation to the occurrence of VIP stimulation of adenylate cyclase activity in several renal cellular elements.

Light and agonist alter vasoactive intestinal peptide binding and intracellular accumulation of adenosine 3',5'-monophosphate in the rat pineal gland.

We examined the effects of environmental light and prior treatment with an agonist on vasoactive intestinal polypeptide (VIP) binding and VIP stimulation of cAMP accumulation in the rat pineal gland. VIP binding to pinealocytes and cAMP accumulation in response to VIP were significantly increased in animals kept exposed to constant light compared to those in animals experiencing a dark night before the experiments. Scatchard analysis of [125I]VIP binding indicated the presence of two classes of binding sites: high affinity, low capacity sites and low affinity, high capacity sites. The increased VIP binding to pinealocytes in rats maintained in constant light was attributed to an increase in the number of available VIP receptors at both high and low affinity sites. The affinity of VIP binding to cells was not affected by exposure of the animals to light. VIP stimulation of cAMP accumulation was not inhibited by d,l-propranolol. Prior treatment of pinealocytes with VIP decreased [125I]VIP binding by reducing the number of receptors and significantly inhibited subsequent VIP stimulation of cAMP accumulation. Prior treatment with norepinephrine did not alter the number of VIP receptors. Our results strongly suggest that VIP is a neuromodulator of pineal function.

Modulation of cyclic AMP accumulation in GH 3 cells by a phorbol ester and thyroliberin

4β phorbol-12,13-dibutyrate (PDBu) stimulated cyclic AMP accumulation in GH 3 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 (IC 50=5.1nM). 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, N s and N i.

The effect of avian pancreatic polypeptide as a VIP antagonist

Vasoactive intestinal polypeptide (VIP) has been shown to be present in some neurones of the myenteric plexus by immunohistochemical techniques. It was reported that avian pancreatic polypeptide (APP) inhibited the vasodilation induced by VIP and chorda-lingual nerve stimulation in the cat submandibular gland (Lundberg et al.,Acta.Physiol.Scand.,1980,110,199). The purpose of the present experiment is to investigate whether APP acts as a VIP antagonist by using various tissues innervated by non-cholinergic, non-adrenergic nerves in the gastrointestinal tract. APP was isolated and purified from chicken pancreas by the method of Kimmel et al. (J.Biol.Chem., 1975,250,9369). The isolated APP (0.48-12nmole) caused a dose-dependent inhibition of the vasodilation induced by VIP and chorda-lingual nerve stimulation in the cat submandibular gland as reported by Lundberg et al. ‘1980). In the cat colon, APP (0.4-10nmole) elicited a dose-dependent vasoconstriction and partially inhibited the atropine-resistant vasodilation induced by VIP and pelvic nerve stimulation, but not significantly that induced by bradykinin. On the other hand, APP failed to inhibit the relaxation caused by either transmural electrical stimulation or VIP in the presence of atropine and guanethidine in isolated chick rectum and fundic strips of guinea-pig and rat. Furthermore, APP had no inhibitory effect on the gastric relaxation induced by the vago-vagal reflex and by the close arterial injection of VIP in the dog stomach. The results suggest that APP may act as an antagonist for the VIP-induced vasodilation of vascular smooth muscles, but not for the VIP-and the non-adrenergic nerve stimulation-induced relaxation of gastrointestinal smooth muscles.