Vasoactive Intestinal Peptide Antiserum Research Articles

Pituitary adenylate cyclase activating polypeptide and vasoactive intestinal peptide inhibit feeding in the chick brain by different mechanisms

Intracerebroventricular (ICV) injections of pituitary adenylate cyclase-activating polypeptide-38 (PACAP) and vasoactive intestinal peptide (VIP) inhibit feeding in chicks. However, the precise anorexigenic mechanisms have not been investigated, since both peptides activate the VPAC receptor in mammals. We investigated which receptor mediates the anorexigenic effects of these peptides in chicks. ICV co-injection of PACAP (6–38), a PAC1 receptor antagonist, attenuated the anorexigenic effect of PACAP but not VIP. On the other hand, ICV co-injection of [ d-p-Cl-Phe6, Leu17]-VIP, a VPAC receptor antagonist, did not affect the effects of both peptides. Although these results imply that the effect of VIP was not specific, a subsequent experiment demonstrated that ICV injection of anti-chicken VIP antiserum stimulated feeding and suggested that endogenous VIP inhibits feeding in the chick brain. Collectively, the data suggest that the anorexigenic mechanism of PACAP is different from that of VIP and that an undiscovered VIP receptor may be present in the chicken brain.

Involvement of Vasoactive Intestinal Peptide on Insulin-Like Growth Factor I-Induced Proliferation of Rat Pituitary Lactotropes in Primary Culture: Evidence for an Autocrine and/or Paracrine Regulatory System

In previous studies we demonstrated that insulin-like growth factor I (IGF-I) induces pituitary vasoactive intestinal peptide (VIP) gene expression and secretion, and that IGF-I-induced prolactin (PRL) release is mediated by VIP. In this study, we investigate the mitotropic action of IGF-I and VIP on pituitary lactotropes, and their possible interplay in this effect. Cultured male rat pituitary cells were treated with rhIGF-I (10^–7M) and/or VIP (10^–7M) for 48 h. 5-Bromo-2′-deoxyuridine (BrdU) (10 µM) was added for labeling proliferation of pituitary cells. BrdU-labeling indices indicative of the proliferation rate of lactotropes were determined by double-labeling immunofluorescence staining for PRL and BrdU. Treatment with either IGF-I or VIP increased BrdU-labeling indices of lactotropes, but there was no further increase upon combined incubation with both factors, suggesting an interaction between the signal transduction pathways of IGF-I and VIP. VIP antiserum partially suppressed IGF-I-induced BrdU-labeling indices of lactotropes. We also investigated the intracellular signal transduction pathways in the action of IGF-I and VIP on the proliferation of lactotropes. Treatment of pituitary cells with an inhibitor of the mitogen-activated protein kinase (MAPK) pathway completely abolished IGF-I-induced lactotrope proliferation, whereas it partially suppressed VIP-induced BrdU-labeling indices. The protein kinase A (PKA) inhibitor, which abolished the mitogenic action of VIP, markedly suppressed IGF-I-induced lactotrope proliferation. These results indicate that both IGF-I and VIP stimulate lactotrope proliferation, and that IGF-I-induced lactotrope proliferation is partially mediated by VIP produced locally. Also, this study suggests that interactions between MAPK and cyclic adenosine 3′,5′-monophosphate-PKA signaling pathways are implicated in the lactotrope proliferation induced by IGF-I and VIP.

Vasoactive intestinal peptide and nitric oxide promote survival of adult rat myenteric neurons in culture.

Several motility disorders originate in the enteric nervous system (ENS). Our knowledge of factors governing survival of the ENS is poor. Changes in the expression of vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS) in enteric neurons occur after neuronal injury and in intestinal adaptation. The aim of this study was to evaluate whether VIP and nitric oxide (NO) influence survival of cultured, dissociated myenteric neurons. Neuronal survival was evaluated after 0, 4, and 8 days in culture. Influence of VIP and NO on neuronal survival was examined after culturing in the presence of VIP, NO donor, VIP antiserum, or NOS inhibitor. A marked loss of neurons was noted during culturing. VIP and NO significantly promoted neuronal survival. Corroborating this was the finding of an enhanced neuronal cell loss when cultures were grown in the presence of VIP antiserum or NOS inhibitor.

The Localization of Vasoactive Intestinal Peptide (VIP)-Like Immunoreactivity in Gonadotropes of the Rat Anterior Pituitary

Abstract The anterior pituitary gland has recently been shown to contain a number of bioactive peptides other than inherent pituitary hormones. One of these peptides is vasoactive intestinal peptide (VIP). The localization of VIP has not known and so the present study was undertaken to determine which type of pituitary cell contains this peptide. The adult rat anterior pituitary was immunohistochemically examined with two VIP antisera. One of these antisera successfully stained some pituitary cells. Both the double immunostaining technique and the flip-flop section method revealed VIP-like immunoreactivity, mainly in gonadotropes. This immunostaining was lost when the anti-VIP was preabsorbed with synthetic VIP or with pituitary adenyl cyclase activating peptide (PACAP), 68% of the 1–28 portion of which is homologous to VIP. When tested with anti-PACAP, however, no immunoreactivity was observed in anterior pituitary tissue. These results indicate that VIP is localized in gonadotropes in the anterior pitui...

Inhibition of vasodilator neurotransmission in the sheep middle cerebral artery by VIP antiserum.

1. Middle cerebral artery rings from the sheep were relaxed by vasoactive intestinal peptide (VIP) (20-200 nM) or by stimulation of the vasodilator nerves, electrical field stimulation (EFS). 2. VIP antiserum 1:256 inhibited the relaxation produced by both exogenous VIP (from 70 +/- 5 to 32 +/- 9% of 5-HT-induced tone at 200 nM VIP) and by EFS (from 43 +/- 5 to 26 +/- 6% of 5-HT-induced tone after 20 min), while pre-immune serum was inactive. 3. Capsaicin (1 microM) produced a transient relaxation but did not alter the response to EFS which was subsequently inhibited by addition of L-NOArg (100 microM). VIP-induced relaxation was antagonized by L-NOArg (50 microM) (from 68 +/- 5 to 46 +/- 2% relaxation of 5-HT-induced tone) but not by D-NOArg. 4. Exogenous VIP produced an approximately 2.4-fold increase in cyclic GMP content which was prevented by preincubation with L-NOArg (100 microM) but not D-NOArg. 5. VIP and neuronal NOS immunoreactivity was co-localized to the same adventitial nerve fibres in the sheep middle cerebral artery. 6. These results provide evidence that neurogenic relaxation in the sheep middle cerebral artery is, at least in part, mediated by VIP, involving activation of NO synthase.

Mechanisms of fluid losses in small‐bowel obstruction

Abstract: Small‐bowel obstruction (SBO) is a serious condition induced by hindrance of the propagation of intestinal contents. Mortality of 5% is still relatively high, but has decreased since the beginning of this century when it was around 60%. The condition is characterized by severe abdominal pain, accumulation of gas and fluids in the obstructed intestine and dehydration of the patient. The mechanisms responsible for the profuse fluid losses remain unclear. The aim of this thesis was to elucidate some aspects of the pathophysiology by using an experimental in vivo model in rats. In anaesthestized animals jejunum was ***string‐ligated approximately 10 cm distal of the ligament of Treitz. The laparotomy was closed and the animals allowed to recover. Next day the animals were reanaesthetized, tracheostomy was performed and the femoral artery and vein catheterized. Complete obstruction of the jejunum during 18 h resulting in fluid secretion which was subsequently measured using a gravimetric technique allowing continuous registration of intestinal net fluid transport (NFT). After a control period of 30 min with stable net fluid secretion drugs or saline were administered. Mean NFT of the following 2 h was compared to the mean NFT of the control period. In some animals Evans blue dye (20 mg · kg−1) was given as marker of blood vessel permeability. Some aspects of the study were investigated in human gastrointestinal tissue.Results show that a pronounced inflammation occurs in the obstructed bowel wall, as suggested by extravasation of plasma Evans blue‐albumin visualized by fluorescence microscopy and quantified by spectrophotometry. This was paralleled by net fluid secretion in the obstructed intestine. The importance of inflammation for the mechanisms of fluid losses was illustrated by the actions of the anti‐inflammatory agents, hydrocortisone and indomethacin, which reversed secretion into net fluid absorption. We proposed that the inflammation‐induced secretion of SBO was partly mediated through the enteric nervous system (ENS). This is supported by results showing that lidocaine, a local anaesthetic, with anti‐inflammatory properties, inhibited both inflammation and secretion, and anti‐inflammatory action of lidocaine was also shown in a human model where it reduced release of prostaglandins. The importance of ENS was further supported by results showing that the neurotransmitters vasoactive intestinal peptide (VIP) and somatostatin are involved in the regulation of fluid transport. VIP antiserum significantly reduced the net secretion, while the somatostatin analogue octreotide reversed net secretion into net absorption. Octreotide, which inhibits the release of many peptides including VIP, also reduced the Evans blue‐albumin extravasation. The secretion of SBO was also shown to be under influence of the sympathoadrenal system since clonidine, an α2‐adrenoceptor agonist, and propranolol, a β‐adrenoceptor antagonist, inhibited net fluid secretion. There were no significant effects on NFT after administration of α1‐ or β1‐adrenoceptor agonists or antagonists.In conclusion, the present work shows that obstruction of the small intestine will induce a pronounced inflammatory reaction in the bowel wall, most prominent in the external muscle layer. This inflammation probably triggers the profuse fluid losses by direct action on the enterocytes and by activation of enteric neurons. The anti‐inflammatory agents hydrocortisone, indomethacin, lidocaine and octreotide significantly reduced both the fluid losses and the increased Evans blue‐albumin extravasation. Neuropeptides of the ENS are also important, and neutralization of VIP using VIP antiserum or inhibiting the release of VIP by octreotide both reduced fluid losses. The fluid transport in obstructed gut seems also to be under tonic control of adrenergic neurons, as stimulation of α2‐adrenoceptors and blockade of β2‐adrenoceptors reduced fluid losses, while blockade of α2‐adrenoceptors and stimulation of β2‐adrenoceptors increased the net fluid secretion. Treatment of patients with small bowel obstruction with anti‐inflammatory drugs may prove beneficial

VIP-antiserum and indomethacin inhibit calcium and bicarbonate secretion by the inflamed feline gallbladder mucosa.

Ionized calcium (Ca2+) and bicarbonate (HCO(3)-) are important ions for gallstone formation. In the present study the effect of indomethacin and vasoactive intestinal peptide-antiserum (VIP-antiserum) on the Ca2+, HCO(3)- and fluid secretion in the inflamed gallbladder were tested in a validated experimental model in cats. The animals were studied in acute experiments 6 weeks after cystic duct ligation and gallstone implantation. During basal conditions there was a continuous secretion of Ca2+, HCO(3)- and fluid into the lumen of the inflamed gallbladder. Indomethacin and VIP-antiserum inhibited the Ca2+, HCO(3)- and fluid secretion across the inflamed gallbladder mucosa. Intraluminal amiloride inhibited the absorption of Ca2+, HCO(3)- and fluid after indomethacin infusion. An impaired absorption of Ca2+, HCO(3)- and fluid in the inflamed gallbladder is probably important for the solubility of calcium salts in the early stages of inflammation in the gallbladder mucosa.

Importance of vasoactive intestinal peptide and somatostatin for fluid losses in small-bowel obstruction.

Previous observations have shown vasoactive intestinal peptide (VIP) to be an important secretagogue in the gut, whereas somatostatin has been reported to inhibit VIP release and fluid secretion. The possible role of VIP as mediator of the inflammation and fluid losses in obstructive ileus was investigated in vivo and in a chronic rat model with thread ligation of the jejunum. Extravasated Evans blue (Eb)-stained albumin was quantified by spectrophotometry. Net fluid secretion was measured by a gravimetric technique. VIP antiserum was used to inhibit the effects of endogenous VIP. A somatostatin analogue, octreotide, was used to inhibit the release of VIP. Results showed a pronounced plasma Eb-albumin extravasation in the wall of the obstructed gut, which was significantly inhibited by VIP antiserum (p < 0.05) or octreotide (p < 0.01). Obstruction of the jejunum resulted in net fluid secretion that was significantly reduced by administration of octreotide (p < 0.01) or VIP antiserum (p < 0.05). Net fluid secretion in control animals remained constant. These findings suggest that VIP is an important mediator of the pathophysiology in mechanical intestinal obstruction and that somatostatin may be involved in the endogenous control of fluid losses.

Nitric oxide pathway in cat esophagus: localization of nitric oxide synthase and functional effects.

In the cat lower esophageal sphincter (LES) and esophageal body, nitric oxide synthase (NOS) immunoreactive nerves were abundant in the circular smooth muscle layer, especially in the LES region. NADPH diaphorase staining showed an identical pattern. The ability to form L-citrulline from L-arginine corresponded roughly to the distribution of NOS. Confocal microscopic analysis indicated colocalization within neurons of vasoactive intestinal peptide (VIP) in 65% of NOS-positive nerves. In LES circular smooth muscle preparations, electrically induced relaxations (single train stimuli) were generally abolished by NG-nitro-L-arginine (L-NNA). Continuous electrical stimulation for 2 min evoked a relaxation in the presence of L-NNA. This relaxation was inhibited by VIP antiserum and followed by a decrease in guanosine 3',5'-cyclic monophosphate, but not by any consistent change in adenosine 3',5'-cyclic monophosphate levels. K+ (124 mM) induced a biphasic relaxation, with L-NNA inhibiting the first phase but not the second. We conclude that nitric oxide (NO) has a major role as the mediator responsible for relaxation in the cat esophagus. NO seems also to initiate the release and enhance the effect of another transmitter.

Inflammation reduces mucosal secretion of hydrogen ions and impairs concentrating function and luminal acidification in feline gallbladder.

The gallbladder mucosa normally absorbs fluid and secretes H+ ions. The fluid secretion in inflamed gallbladders is induced by prostaglandins and mediated by intramural vasoactive intestinal peptide (VIP)-ergic nerves. The influence of inflammation on gallblader contents due to secretion of H+ into the lumen. In animals with inflamed gallbladder this acid secretion was reduced; there was secretion of HCO3- and no evident acidification of the gallbladder contents. Injection of VIP antiserum or indomethacin restored H+ secretion and inhibited HCO3- and fluid secretion by the inflamed gallbladder mucosa. An impaired acidification of the gallbladder contents due to mucosal inflammation may reduce the solubility of calcium salts in gallbladder bile and increase the risk of their precipitation in the lumen. Mucosal inflammation reduces H+ secretion and impairs acidification of the gallbladder contents.

Induction of vasoactive intestinal peptide gene expression and prolactin secretion by insulin-like growth factor I in rat pituitary cells: evidence for an autoparacrine regulatory system.

The effects of recombinant human insulin-like growth factor I (IGF-I) on both vasoactive intestinal peptide (VIP) and PRL production and gene expression were studied using rat anterior pituitary cell cultures grown in serum-free defined medium. We also examined whether pituitary VIP could be involved in the PRL response to IGF-I and hence in a paracrine regulatory system. Exposure of cultured anterior pituitary cells to IGF-I (2.6 nM) for 3 h caused a significant decrease in both VIP content and media PRL. Treatment with IGF-I (from 0.65-5.2 nM) for 48 h increased VIP production and VIP messenger RNA (mRNA) accumulation, whereas only an increase in media and intracellular PRL content without changes in mRNA was observed. In all these experiments, IGF-I led to a decrease in both GH secretion and expression. Immunoglobulins G purified from VIP antiserum inhibited IGF-I-induced PRL release without affecting intracellular and mRNA levels. The inhibition of both GH secretion and gene expression induced by IGF-I was not blocked by VIP antiserum. In conclusion, these results indicate that IGF-I induces VIP gene expression, and its secretion and also increases PRL secretion. The effect of IGF-I on PRL release is specifically mediated by VIP through a paracrine or autocrine mechanism.

Induction of vasoactive intestinal peptide gene expression and prolactin secretion by insulin-like growth factor I in rat pituitary cells: evidence for an autoparacrine regulatory system

The effects of recombinant human insulin-like growth factor I (IGF-I) on both vasoactive intestinal peptide (VIP) and PRL production and gene expression were studied using rat anterior pituitary cell cultures grown in serum-free defined medium. We also examined whether pituitary VIP could be involved in the PRL response to IGF-I and hence in a paracrine regulatory system. Exposure of cultured anterior pituitary cells to IGF-I (2.6 nM) for 3 h caused a significant decrease in both VIP content and media PRL. Treatment with IGF-I (from 0.65-5.2 nM) for 48 h increased VIP production and VIP messenger RNA (mRNA) accumulation, whereas only an increase in media and intracellular PRL content without changes in mRNA was observed. In all these experiments, IGF-I led to a decrease in both GH secretion and expression. Immunoglobulins G purified from VIP antiserum inhibited IGF-I-induced PRL release without affecting intracellular and mRNA levels. The inhibition of both GH secretion and gene expression induced by IGF-I was not blocked by VIP antiserum. In conclusion, these results indicate that IGF-I induces VIP gene expression, and its secretion and also increases PRL secretion. The effect of IGF-I on PRL release is specifically mediated by VIP through a paracrine or autocrine mechanism.

Nonadrenergic noncholinergic neurotransmitter of feline trachealis: VIP or nitric oxide?

We tested the hypothesis that vasoactive intestinal peptide (VIP) or nitric oxide (NO) is the nonadrenergic noncholinergic (NANC) neurotransmitter in feline trachealis. Isometric tension was measured in trachealis (open or closed tracheal rings) in vitro. Propranolol (10 microM) and atropine (1 microM) were present throughout the experiment, and smooth muscle tone was increased to 60-90% maximal with 5-hydroxytryptamine. We used three methodologies to reduce the relaxation function of VIP, which in turn should reduce NANC-mediated relaxation. 1) The putative VIP antagonist peptide T (10 microM) did not affect VIP concentration-response curves or electrical field stimulation- (EFS) induced NANC responses. 2) Incubation of tissue in specific VIP antiserum (16 h at 4 degrees C) did not reduce EFS-induced NANC relaxations relative to tissue incubated in normal rabbit serum (P > 0.05). On the basis of our passive immunization techniques, it is not possible to absolutely reject VIP as the NANC transmitter. We speculate that nonspecific peptidases present in normal serum and VIP antiserum reduce EFS-induced responses similarly. 3) VIP desensitization, confirmed by a significant rightward shift (P < 0.01) in the VIP concentration-response curve, was achieved by exposing tissues (n = 11) to 1.0 microM VIP for 30 min. Desensitization did not reduce the EFS-induced NANC relaxatory response (P < 0.05) compared with control tissues, suggesting that VIP is not the NANC mediator.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple peptide immunoreactivities in the nervous system of Aeschna cyanea (Insecta, Odonata)

By use of the indirect immunoperoxidase method, the brain, the suboesophageal ganglion and the corpora cardiaca of the dragonfly Aeschna cyanea have been shown to be immunoreactive to proctolin antiserum and to several mammalian peptide antisera including unsulfated cholecystokinin octapeptide (CCK-8 NS) (Andriès et al. 1989), vasoactive intestinal peptide (VIP), human somatoliberin (hGRF) (Andriès et al. 1984) and motilin antisera. Immunohistochemical studies have been performed on material fixed in a solution of picricacid paraformaldehyde or in Bouin Hollande's sublimate solution. Antisera were applied on alternate sections or, according to the elution-restaining method of Tramu et al. (1978), one after another on the same section. Multiple peptide immunoreactivities appear expressed in the brain and the suboesophageal ganglion. Cells reactive to both hGRF and VIP antisera show also gastrin/CCK-like immunoreactivity and some of them are also detected by motilin antiserum. Besides, some cells immunopositive to CCK-8 NS and motilin antisera do not show hGRF or VIP immunoreactivity. At least, two pairs of protocerebral cells appear immunoreactive to both CCK-8 NS and proctolin antisera. Therefore, the present observations support our previously developed idea (Andriès et al. 1989) that the population of CCK-like cells is heterogenous.

Dual effects of vasoactive intestinal peptide (VIP) on leucocyte migration

Vasoactive intestinal peptide, at different concentrations, was tested on the migration of leucocytes by using the sealed capillary migration test. Vasoactive intestinal peptide, at 10(-7)-10(-9)M, inhibited, while at 10(-12)-10(-14)M, stimulated mononuclear leucocyte migration. The migration of polymorphonuclear leucocytes was inhibited by vasoactive intestinal peptide at 10(-6)-10(-9)M, a stimulation was found at 10(-13)-10(-14)M. The inhibiting effect of vasoactive intestinal peptide on leucocyte migration was abolished when vasoactive intestinal peptide was split into C- and N-terminal fragments, while a stimulating effect was retained in the N-terminal fragment, at 10(-14)M, for mononuclear cells. Helodermin and peptide T, as well as two other members of the secretin-glucagon family, secretin and gastric inhibitory peptide, had no effect on the migration. When VIP antiserum was tested, it had an inhibiting effect, which was not seen with control serum, supporting a physiological effect of the lower vasoactive intestinal peptide concentrations. Vasoactive intestinal peptide seems to have dual effects on mononuclear and polymorphonuclear leucocyte migration and, generally, intact vasoactive intestinal peptide seems to be needed for these effects.

Vasoactive intestinal peptide is a hypothalamic prolactin-releasing neuropeptide in the turkey ( Meleagris gallopavo)

The hypothesis that vasoactive intestinal peptide (VIP) functions as a hypothalmic prolactin (PRL)-releasing peptide in the turkey was tested by determining the effects of hypothalamic VIP immunoneutralization and pituitary VIP receptor blockade on hypothalamic extract (HE)-induced PRL secretion from dispersed anterior pituitaries. Incubation of cells with porcine VIP (pVIP; 0.5 or 10 n M) significantly stimulated PRL secretion. This effect was inhibited in a dose-related manner by 1-hr preincubation of pVIP with a VIP antisera ( A S ; 1:500–1:50,000). Likewise, HE (0.3 equivalent)-stimulated PRL secretion was inhibited by preincubation with VIP A S ( P < 0.0001). A 96–98% reduction in PRL secretion was obtained from cells cultured with HE, that was previously incubated with 1 500 dilution of antiserum. Pretreatment of pituitary cells for 15 min with [4Cl- d-Phe 6,Leu 17] VIP, a VIP receptor antagonist (10 −5 M), significantly depressed the PRL response to 0.5 n M VIP (9.9 ± 0.5 μg/500,000 cells vs 4.9 ± 0.1 μg/500,000 cells; 22.4 ± 0.9 μg/500,000 cells vs 14.7 ± 0.4 μg/500,000 cells) or 0.3 eq HE (8.8 ± 0.6 μg/500,000 cells vs 5.2 ± 0.2 μg/500,000 cells; 15.3 ± 0.3 μg/500,000 cells vs 8.2 ± 0.2 μg/500,000 cells). These results suggest that hypothalamic stimulation of PRL secretion appears to be mediated by receptors specific for VIP and that VIP is an endogenous hypothalamic PRL-releasing peptide in the turkey.

Role of peptide histidine isoleucine in relaxation of cat lower esophageal sphincter

Vasoactive intestinal peptide (VIP) is a candidate as an inhibitory neurotransmitter mediating relaxation of the lower esophageal sphincter (LES) because VIP antiserum reduces LES relaxation in response to neural stimulation. Vasoactive intestinal peptide antiserum, however, does not completely block LES relaxation. Thus it is possible that other neurotransmitters may be involved. Peptide histidine isoleucine has structural homologies with VIP, is synthesized with VIP from a common precursor protein, coexists in some nerve cells, and is coproduced with VIP in some tumors. In numerous organ systems VIP and peptide histidine isoleucine (PHI) produce similar effects, with PHI being less potent than VIP by approximately one log number. In the LES both VIP and PHI produce tetrodotoxinresistant dose-dependent relaxation, with PHI being almost equipotent with VIP. We therefore tested the hypothesis that PHI may be a second neurotransmitter, partly responsible for relaxation of the cat LES, by using a highly specific rabbit PHI antiserum that exhibits minimal cross-binding with VIP, secretin, and glucagon. In 3 animals, LES and brain tissue were extracted in 0.1 N HCl and assayed with a PHI radioimmunoassay. The antiserum cross-reacted with cat brain and LES showing PHI concentrations >100 ng/g, with the LES containing equal or greater concentrations of PHI than brain tissue. In other animals consecutive LES circular muscle strips were cut, mounted in 1-ml muscle chambers, and stimulated with 6-s square-wave trains of 0.1-, 0.2-, 0.4-, and 0.8-ms pulses at 1, 2, and 5 Hz. These parameters produced relaxation that was completely blocked by tetrodotoxin, and reduced by VIP antiserum, but not affected by adrenergic or cholinergic receptor antagonists. Some strips were incubated in 5% or 10% PHI antiserum, whereas others were incubated in the same concentration of preimmunization serum from the same animal. Incubation in normal serum did not significantly affect relaxation, whereas in the antiserum-treated strips, LES relaxation was reduced by a significant amount (20%–30%) at all parameters of stimulation tested. Incubation in antiserum however had no effect on relaxation induced by VIP (10−8–10−8M). These data suggest that PHI may play a role in LES relaxation induced by electrical stimulation.

Role of dopamine and vasoactive intestinal peptide in the control of pulsatile prolactin secretion.

The present studies were designed to obtain a detailed characterization of pulsatile PRL secretory patterns under basal conditions and to explore the role of dopamine (DA) and vasoactive intestinal peptide (VIP) in the genesis of PRL pulses. Adult intact male rats received chronic indwelling jugular canula and were bled at 3-min intervals for periods ranging from 90-150 min. Pulse analysis was performed using the algorithm Detect. Blockade of DA receptors with domperidone, pimozide, or haloperidol resulted in a 2-fold increase in PRL pulse frequency, with no change in pulse duration. All quantitative parameters, i.e. peak and trough values, pulse amplitude, and area under the pulse, were significantly increased after dopaminergic blockade. Blockade of endogenous VIP activity was achieved by passive immunization with a potent VIP antiserum. This treatment, by itself, did not modify basal PRL levels or PRL pulsatility parameters. However, when VIP antiserum was administered in combination with domperidone, a reduction in all quantitative pulse parameters was observed. Heterogeneity of PRL pulses was evaluated by frequency distribution analysis, using the area under the pulse divided by basal secretion, to evaluate the mass of hormone secreted per pulse normalized to the basal rate of secretion. Untreated animals presented pulses within a range of different masses. Dopaminergic blockade resulted in a great reduction in big mass pulses, and the distribution of pulses was restricted primarily to small mass pulses. The increased pulse frequency after dopaminergic blockade, therefore, results mainly from an increase in the appearance of small mass pulses. These results indicate that DA exerts a tonic inhibitory action on the frequency as well as the qualitative parameters of PRL pulses. They also suggest that big mass PRL pulses are dopaminergic in origin, i.e. they may result from temporary interruptions in DA activity. Small mass PRL pulses appear to result from other neural stimulatory inputs. Endogenous VIP enhances quantitative PRL pulse parameters, but this activity is only apparent after removal of DA inhibition.

Effects of passive immunization against vasoactive intestinal peptide on serum prolactin and LH levels.

Recent findings suggest that vasoactive intestinal peptide (VIP) may be a physiological regulator of prolactin secretion and may also be involved in the control of LH secretion. In the present work we have studied the effect of the blockade of endogenous VIP by means of the injection of a specific rabbit anti-VIP serum, in male and female rats with hyperprolactinemia. The administration of 0.5 ml of the VIP antiserum in ovariectomized rats given an acute or chronic treatment with 17 beta-estradiol induced a significant decrease in serum prolactin and LH levels as compared with estrogenized-control rats injected with normal rabbit serum. Anti-VIP serum also reduced serum LH levels in ovariectomized rats not treated with estrogens. The administration of the same antiserum decreased serum prolactin levels in male rats implanted with 2 anterior pituitary glands under the kidney capsule. On the other hand, the injection of the anti-VIP serum in the morning in proestrus rats brought about an increase in serum prolactin and LH levels in the afternoon of the same day. These results confirm previous data showing that VIP is a stimulator of prolactin release, and may also participate in the control of LH secretion in ovariectomized rats acting as a facilitatory factor. During proestrus however, VIP may act in an opposite way, inhibiting, rather than stimulating, prolactin and LH release.

VIP augments cholinergic-induced glycoconjugate secretion in tracheal submucosal glands.

Using isolated submucosal glands from feline trachea, we examined the effect of vasoactive intestinal peptide (VIP) on mucus glycoprotein secretion and glandular contraction by measuring released radiolabeled glycoconjugates and induced tension, respectively. VIP (10(-10) to 10(-6) M) produced a dose-dependent increase in [3H]glycoconjugate release of up to 300% of controls, which was inhibited by VIP antiserum and not inhibited by atropine, propranolol, or phentolamine. VIP at a low concentration (10(-9) M), which did not produce any significant increases over controls, produced a 2.4- to 5-fold augmentation of the glycoconjugate release induced by 10(-9) to 10(-7) M methacholine (MCh). Atropine or VIP antiserum abolished the augmentation. VIP did not produce any alteration in isoproterenol- or phenylephrine-evoked glycoconjugate secretion. VIP (up to 10(-5) M) did not produce any alteration in the tension, even when the gland had contracted with MCh, or any augmentation of contraction induced by MCh (10(-9) to 10(-7) M). These results indicate that VIP induces mucus glycoprotein release from secretory cells and also that it potentiates the secretion induced by cholinergic stimulation.