Vasoactive Intestinal Polypeptide Concentrations Research Articles

Chronic but not Acute Exposure to Stress is Associated with Hypothalamic Vasoactive Intestinal Polypeptide (VIP) Release into Median Eminence

The influence of stress on hypothalamic VIP release into the pituitary portal blood has not been assessed at present despite the fact that this peptide has been implicated in the control of several pituitary hormones and especially in the release of prolactin (PRL) caused by stress. In the present work the effect of stress on the in vivo release of VIP into the pituitary portal blood of male rats was evaluated by means of push-pull perfusion (PPP) of median eminence (EM). VIP content in the PPP liquid was successfully measured and their levels agree well with pituitary portal blood levels measured by other authors. Whereas plasma PRL levels strongly increased during acute immobilization (IMO), no changes in VIP secretion into the ME were observed. VIP release into the ME was also unaffected by exposure to ether. In contrast, in chronically immobilized rats a significant increase in VIP release into the ME was obtained in response to acute IMO. The present data argue against a major role of hypothalamic VIP in PRL release caused by acute stress and show that chronic stress qualitatively alters the signal of hypothalamic VIP to the pituitary.

Identification of vasoactive intestinal polypeptide (VIP) binding protein in bovine pineal gland

Vasoactive intestinal polypeptide (VIP) containing nerves are present in close proximity to epithelial, endocrine, and vascular smooth muscle cells. The pineal gland, known also as a “neuroendocrine transducer organ” contains a high content of VIP which prompted us to characterize the binding sites for VIP in this organ. [Tyr 10− 125I]VIP was bound selectively and specifically to pineal membrane preparations in a time-dependent fashion. Scatchard analysis demonstrated a single class of high affinity binding sites with a dissociation constant ( K d ) value of 5.7 ± 0.52 nmol/1 and a receptor density ( B max) value of 440 ± 35 fmol/mg protein. A Hill Plot with a slope of 1.013 indicated the absence of cooperativity. Covalent crosslinking with [Tyr 10− 125I]VIP followed by SDS electrophoresis and autoradiography, revealed that the VIP binding protein exhibited a molecular weight of 51.8 ± 0.5 kDa. The precise function of pineal VIP binding protein remains to be delineated.

Release of immunoreactive somatostatin, vasoactive intestinal polypeptide (VIP), and galanin during propulsive complexes in isolated pig ileum

We studied the release of immunoreactive somatostatin, VIP, and galanin during net aboral propulsive complexes (NAP) in isolated, perfused, 80-cm segments of porcine ileum. Net aboral propulsive complexes were induced by controlled infusion of liquid (perfusion medium, 3.5 ml/min) into the proximal opening of the ileum segment. In response to liquid infusion, the ileum segments generated propulsive complexes rapidly propagating along the entire segment in the aboral direction, resulting in emptying of the luminal contents. The NAPs occurred with an average interval of 7 minutes. The concentrations of galanin, somatostatin, and VIP in the venous effluent, which in control experiments without luminal infusion did not change, increased significantly (by 63.6 ± 23.7%, 43.8 ± 31.8%, and 38.8 ± 14.6%, respectively) during NAPs and emptying. Atropine (10 −6 mol/l) and hexamethonium (10 −5 mol/l) abolished both NAP generation and peptide responses. It is concluded that the enteric neruopeptides, somatostatin, VIP, and galanin, all of which have pronounced intestinal motor effects, may participate in the generation of net aboral propulsive complexes in the ileum of the pig, possibly mainly in descending relaxation.

Action of pituitary adenylate cyclase-activating polypeptide on ion transport in guinea pig distal colon.

The aim of the present study was to investigate the action of pituitary adenylate cyclase-activating polypeptide (PACAP) on ion transport in the guinea pig distal colon. Submucosal/mucosal segments from distal colon were mounted in Ussing flux chambers, and increases in short-circuit current (Isc) were used as an index of secretion. Serosal addition of PACAP-38 and PACAP-27 produced concentration-dependent (10(-10)-10(-6) M) increases in Isc. Furosemide and chloride-free solutions significantly reduced the PACAP-evoked responses. Tetrodotoxin (TTX) completely blocked PACAP-evoked responses. Atropine significantly reduced the PACAP-evoked responses but did not abolish the responses. The results suggest that PACAP evokes chloride secretion through cholinergic and noncholinergic neural mechanism. Vasoactive intestinal polypeptide (VIP), peptide histidine-isoleucine amide, and helodermin evoked Isc in a concentration-dependent manner. Atropine reduced but did not abolish the VIP- and related peptides-evoked responses. TTX also significantly decreased the responses to higher concentrations of VIP and related peptides but did not abolish the responses. The results suggest that VIP and related peptides act on both submucosal neurons and the epithelial cell itself. VIP tachyphylaxis significantly decreased PACAP-38- and PACAP-27-evoked responses. These results provide evidence that PACAP recognizes, in some part, VIP receptors in the submucosal neurons to evoke chloride secretion.

Synergistic regulation of vasoactive intestinal polypeptide expression by cyclic AMP and calcium in newborn but not adult rat sensory neurons in culture

There is a spontaneous induction of vasoactive intestinal polypeptide (VIP) expression in adult rat dorsal root ganglion sensory neurons when grown in culture. The mechanism of this induction may be the same as that responsible for the increased VIP expression in sensory neurons following peripheral axotomy in vivo. This study investigates the effects of depolarization and cyclic AMP on VIP expression (measured by radioimmunoassay) in cultures of newborn and adult rat sensory neurons. Unlike adult neurons, newborn rat sensory neurons, supported in culture with nerve growth factor, did not spontaneously express VIP. However, potassium-evoked depolarization and drugs that increase intracellular cyclic AMP concentrations (forskolin, 8-bromo cyclic AMP, isobutylmethylxanthine) interacted synergistically to stimulate high levels of VIP expression in newborn rat neurons. The contribution of depolarization to this effect could be mimicked by the L-type calcium channel agonist Bay K 8644 and blocked by the channel antagonist nifedipine, implying the involvement of calcium influx through L-type channels. While depolarization and forskolin individually had small effects on VIP content of adult rat sensory neuron cultures, there was no synergism of the kind seen in newborn rat cultures. Immunostaining showed that VIP was localized within approximately 30% of both newborn and adult rat sensory neurons. Thus, a subpopulation of newborn rat sensory neurons exhibit marked plasticity of VIP expression in an integrated response to activation of cyclic AMP- and calcium-dependent signalling pathways. This property is no longer present in mature neurons, however, where VIP expression is regulated by as yet undetermined factors.

Photic regulation of peptides located in the ventrolateral subdivision of the suprachiasmatic nucleus of the rat: daily variations of vasoactive intestinal polypeptide, gastrin-releasing peptide, and neuropeptide Y

We have determined, by enzyme immunoassay, daily and circadian patterns of the concentrations of three peptides, which are located in the ventrolateral subdivision of the suprachiasmatic nucleus (SCN): vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and neuropeptide Y (NPY). The contents of VIP and GRP, which are synthesized in the SCN, did not show circadian rhythms in constant darkness (DD). Under light-dark (LD) conditions, GRP content increased and VIP content decreased over the course of the light period and then gradually recovered during the dark period. Responsiveness of these peptides to light suggests that VIP and GRP may transmit visual information on duration of illumination. NPY, which is transported from the intergeniculate leaflet of the lateral geniculate body, showed a circadian rhythm with a peak at circadian time 12 hr in DD. This endogenous rhythm was remarkably modulated by photic stimulation. Under LD conditions, the NPY content in the SCN exhibited a bimodal rhythm with peaks at both the light-dark and dark-light transition points. Thus, NPY may convey visual information on the transitions. All these results indicate that the levels of VIP, GRP, and NPY are mainly regulated by light stimulation and suggest that peptides in the ventrolateral SCN are involved in the mediation of photic information to the pacemaker.

Elevated Venous Concentrations of Vasoactive Intestinal Polypeptide in Cord Blood of Infants with Fetal Distress

Concentrations of vasoactive intestinal polypeptide (VIP) in cord plasma were determined in 70 neonates (birth weight, mean +/- SD, 3,213.5 +/- 50.9 g, gestation 39.5 +/- 0.2 weeks), 22 of whom had fetal distress. Arterial VIP levels in cord blood were not significantly different between infants with and without fetal distress. The mean venous VIP in cord blood of distressed infants (28.1 +/- 8.4 pg/ml, mean +/- SE) was significantly (p < 0.05) higher than that of normal neonates (12.6 +/- 3.4 pg/ml). The mean placental content of VIP was 5.1 +/- 0.3 ng/g wet tissue, although a correlation with the venous concentration in the cord was not demonstrated. Venous VIP levels were elevated 24 h after birth (34.6 +/- 13.7 pg/ml) and decreased on the 5th day of life to 12.9 +/- 3.8 pg/ml, which was not significantly different from the mean VIP level in childhood (14.7 +/- 3.1 pg/ml). These results demonstrate that, in the perinatal period, plasma VIP levels are elevated on two occasions: at delivery associated with fetal distress (cord vein), and at 24 h of age. VIP in the former seems to be of placental and/or maternal origin.

Concentrations of vasoactive intestinal polypeptide in corpus cavernosum and peripheral venous blood during prostaglandin E1-induced erection.

Vasoactive intestinal polypeptide (VIP) has been suggested to play a role as a nonadrenergic, noncholinergic neurotransmitter or neuromodulator involved in the process of erection. Until now, data about fluctuating concentrations of VIP in corpus cavernosum (CC) blood have been controversial. The present study describes a modified radioimmunoassay method that was developed in our laboratory for the determination of VIP in plasma. Examination of 12 patients suffering from impotentia coeundi (6 men with psychogenic impotence, 2 with induratio penis plastica, and 4 with impotence of vascular origin) showed that the concentrations of VIP in corpus cavernosum blood during pharmacologically induced erection did not increase in organically healthy men or in men with impotentia coeundi of vascular origin. The VIP concentrations in peripheral venous blood and those in CC blood were similar.

Autonomic and peptidergic innervation of human nasal mucosa.

The localization and distribution of vasoactive intestinal polypeptide (VIP), peptide histidine methionine (PHM), the novel peptide helospectin, neuropeptide tyrosine (NPY) and its C-flanking peptide (C-PON), substance P and calcitonin gene-related peptide (CGRP) were studied in the middle and inferior turbinate of the human nose using sensitive immunocytochemical and radioimmunological methods. For light microscopy, double immunofluorescence and immunogold-silver staining methods were applied. Ultrastructural immunoelectronmicroscopy was performed using a pre-embedding method. In addition, semithin Epon resin sections were immunostained. The concentrations of VIP, NPY, CGRP, substance P and neurokinin A were measured using radioimmunological methods. A dense network of autonomic and peptidergic nerve fibers in the normal human nasal mucosa was demonstrated. Colocalization studies showed the coexistence of peptides with components of the autonomic nervous system. Scattered chromogranin A-, CGRP and bombesin-flanking peptide (BFP)-immunoreactive endocrine-like cells were detected within the lamina propria and in groups within exocrine ducts. Highest radioimmunoassay (RIA) tissue concentrations were detected for VIP, followed by NPY, substance P, CGRP and neurokinin A.

Colonic vasoactive intestinal polypeptide in ulcerative colitis

Vasoactive intestinal polypeptide (VIP) is a 28 amino acid peptide which is localised in both the central and peripheral nervous system. In the human colon VIP is found in all layers and the highest concentrations have been found in the myenteric plexus. It is known that VIP has various effects on intestinal functions: i) it is a potent stimulant of mucosal water and electrolyte secretion: ii) it is involved in the peristaltic reflex: and iii) plays an inhibitory role on immune cell function. Based on these biological effects it has been hypothesized that the intestinal mucosal immune system and inflammation may be influenced by alterations in the tissue concentrations of VIP. Some authors have demonstrated no changes in the VIP colonic content of patients with ulcerative colitis, whereas others have demonstrated a reduction. Our results, using specific radioimmunoassay, showed that there is a significant decrease of VIP in both rectal and colonic mucosa of patients with ulcerative colitis as compared to controls. The VIP decrease is selective since substance P and calcitonin gene-related peptide were unchanged in the mucosal tissue of ulcerative colitis patients and furthermore the VIP alteration is correlated to the degree of mucosal inflammation. These findings suggest that the reduction of VIP mucosal content, even if it represents a non-specific event, could influence local inflammatory response and the activity of the disease.

The cortical lesion of Huntington's disease: further neurochemical characterization, and reproduction of some of the histological and neurochemical features by N-methyl-D-aspartate lesions of rat cortex.

Huntington's disease is a progressive neurodegenerative disease in which the basal ganglia are preferentially affected. Recent evidence, however, suggests involvement of the cerebral cortex as well, with sparing of neurochemically defined subsets of gamma-aminobutyric acid (GABA)-ergic interneurons. In the present study, we examined changes in concentrations of the amino acid neurotransmitters GABA, glutamate, and aspartate in nine cortical regions from 23 patients with advanced Huntington's disease and 12 control brains. GABA concentrations were significantly increased in eight of the nine regions, consistent with a sparing of GABAergic local circuit neurons in the context of progressive cortical atrophy. Small but significant increases in glutamate were found in six of the nine regions, while aspartate levels were generally unaffected. Striate cortex (Brodmann's area 17) showed the most profound increases in GABA and glutamate. We also investigated the effects of powdering the excitotoxins N-methyl-D-aspartate (NMDA) or kainic acid onto the dura of rats. The resulting lesions were examined at 1 week and 6 months. The NMDA-induced lesions showed striking sparing of parvalbumin-positive neurons (a subset of GABAergic interneurons), and this sparing was reflected in neurochemical measurements of GABA; kainic acid lesions failed to display this selectivity. Somatostatin, cholecystokinin, and vasoactive intestinal polypeptide concentrations were spared by the NMDA-induced lesions, and substance P levels were significantly increased. These results provide evidence that NMDA excitotoxic lesions of cerebral cortex can produce a selective pattern of neuronal damage similar to that which occurs in Huntington's disease.

Influence of vasoactive intestinal polypeptide and NGnitro-L-arginine methyl ester on cholinergic neurotransmission in the rat gastric fundus

The possible modulating effect of vasoactive intestinal polypeptide (VIP) and nitric oxide (NO), on cholinergic neurotransmission was assessed in longitudinal muscle strips of rat gastric fundus. VIP and NO arc the putative co-transmitters of the inhibitory non-adrenergic non-cholinergic (NANC) neurones in this tissue. VIP concentration dependently inhibited cholinergic contractions induced by 2-min transmural stimulation, relaxed tissues, the tone of which was continuously raised by transmural stimulation, and shifted to the right the frequency-response curves for contraction induced by transmural stimulation with a cumulative increase of frequency. The same effect was found when contractions were induced with methacholine. suggesting that only functional antagonism at the postsynaptic smooth muscle cell level is involved. On 30-min incubations. 3 × 10−4 M NGnitro-L-arginine methyl ester (L-NAME) potentiated cholinergic responses to 20-s transmural stimulation, while not influencing contractions of similar amplitude evoked by mcthacholine; the cholinergic responses to 2-min transmural stimulation were also not influenced. The potentiating effect of L-NAME was prevented by L-arginine but not D-arginine. These results suggest that endogenous NO released from the inhibitory NANC neurones during short trains of transmural stimulation interferes with cholinergic ncurotransmission either by functional antagonism of acetylcholine at the postsynaptic level or by presynaptic inhibition of acctylcholine release.

Hypothyroidism increases vasoactive intestinal polypeptide (VIP) immunoreactivity and gene expression in the rat hypothalamic paraventricular nucleus.

Vasoactive intestinal polypeptide (VIP) is produced by neurons in the rat hypothalamic paraventricular nucleus (PVN) and may have an important role as a prolactin-releasing factor. Recent work from our laboratories has shown that thyroid hormone regulates the content of VIP and VIP mRNA in the rat anterior pituitary, but its effect on VIP in the PVN is not known. To determine whether thyroid hormone alters VIP biosynthesis in the PVN, we studied the effect of hypothyroidism on the content of immunoreactive (IR)-VIP and VIP mRNA in PVN neurons using histochemical techniques. By immunocytochemistry, only scattered IR-VIP fibers were present in the PVN of control animals whereas IR-VIP perikarya and fibers were present in hypothyroid rats. By in situ hybridization histochemistry, no labeled neurons were recognized in the PVN in control animals whereas PVN neurons were labeled in hypothyroid rats. These findings raise the possibility that hypothyroidism exerts negative feedback regulation on VIP-producing neurons in the PVN and suggest that this may be important to modulate the stimulatory effects of VIP on anterior and/or posterior pituitary function.

Patterns of innervation of vasoactive intestinal polypeptide, neuropeptide Y, and gastrin-releasing peptide immunoreactive nerves in the feline pancreas.

In this study, we performed a detailed analysis of the immunoreactive (IR) patterns and tissue distribution of vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and gastrin-releasing peptide (GRP) in the feline pancreas by means of immunohistochemical and radioimmunological techniques. Immunoreactivity for each peptide is localized to varicose nerve fibers distributed throughout the exocrine and endocrine pancreas, with some differences in the density and pattern of fiber distribution. In the acinar and stromal compartments, VIP-IR processes have a higher density than NPY- and GRP-containing fibers, the latter being the least abundant. The vasculature receives a particularly prominent NPY innervation, while GRP- and VIP-IR fibers are found occasionally in association with blood vessels. Around ducts, NPY- and VIP-IR nerves are more numerous than those positive for GRP-IR, which are quite sparse. One of the most interesting findings of the present work is the visualization of all peptide-IRs both in neuronal cell bodies and fibers within the intrapancreatic ganglia. VIP-IR is observed in virtually all ganglion cells, while GRP- and NPY-IRs are seen in a few neuronal cells. VIP and NPY tissue levels are much higher than GRP concentrations in all regions of the pancreas. VIP content in the head and body is greater than in the tail. The morphological relationship of VIP-, NPY-, and GRP-IR fibers with different pancreatic structures is consistent with specific peptidergic neural inputs in the regulation of pancreatic functions.

Interleukin-1 alpha and tumor necrosis factor-alpha differentially regulate enkephalin, vasoactive intestinal polypeptide, neurotensin, and substance P biosynthesis in chromaffin cells.

The pattern of expression of at least four neuropeptides contained in adrenomedullary chromaffin cells is altered by exposure to the cytokines interleukin-1 alpha (IL-1 alpha) and tumor necrosis factor-alpha (TNF alpha), alone or in combination with stimulation of other second messenger pathways. Vasoactive intestinal polypeptide (VIP) was elevated 2- to 3-fold by 1 nM IL-1 alpha within 48 h of exposure, while neurotensin and substance P synthesis were unaffected, and met-enkephalin levels were decreased 25-35%. Stimulation of VIP and substance P biosynthesis by forskolin was markedly enhanced by IL-1 alpha, while forskolin stimulation of enkephalin and neurotensin biosynthesis was unaffected. IL-1 alpha amplified the effect of phorbol myristate acetate to increase the VIP content of chromaffin cells, but antagonized phorbol ester-induced elevation of neurotensin levels. TNF alpha also demonstrated a neuropeptide-specific pattern of modulation of second-messenger effects on chromaffin cell neuropeptide levels similar to those seen with IL-1 alpha. The neuroendocrine actions of IL-1 alpha described above, unlike IL-1 action in the immune system, do not appear to be mediated through IL-2 as this cytokine did not affect VIP or enkephalin expression in the presence or absence of protein kinase stimulation. Neither IL-1 alpha nor TNF alpha affected the calcium-coupled stimulation of neuropeptide secretion and biosynthesis that occurs in response to cell depolarization in these and other neuroendocrine cells in vitro and in vivo. These data provide a functional demonstration of IL-1 and TNF receptors in chromaffin cell cultures and suggest a physiological role for cytokine production in the adrenal medulla. Since both the magnitude and direction of neuropeptide synthesis modulation by IL-1 alpha and TNF alpha are highly peptide-specific, it appears that these cytokines do not merely augment second messenger pathways that affect neuropeptide synthesis, but potentially regulate the activity of factors controlling the pattern of neuropeptide gene expression in chromaffin cells.

Gut regulatory peptides and intestinal permeability in acute infantile gastroenteritis.

The plasma concentrations of seven gut regulatory peptides were measured in 11 infants suffering from acute gastroenteritis. Samples were taken at the time of the acute illness, upon reintroduction of feeding, and three months after recovery. These results were compared with controls. In the infants with diarrhoea, a massive increase in the fasting plasma mean (SEM) concentrations of enteroglucagon was found at the time of illness (1292 (312) v 79 (27) pmol/l), with concentrations of pancreatic glucagon, peptide tyrosine tyrosine, and motilin also being increased (17.8 (3.1) v 6.3 (1.1) pmol/l, 114.6 (15.2) v 37.0 (11.0) pmol/l, 217.6 (44.1) v 98.5 (18.3 pmol/l) respectively). The preprandial concentrations of motilin were found to be still increased at recovery (183.9 (35.4) pmol/l), but the concentrations of the other three peptides had returned to normal values. No differences in plasma concentrations of vasoactive intestinal polypeptide, neurotensin, or pancreatic polypeptide were found. An increased intestinal permeability was demonstrated at the time of diarrhoea by the urinary ratio of lactulose to mannitol, suggesting simultaneous gut damage. The effects of regulatory peptides may be relevant to the pathophysiology of gastroenteritis in infants.

Effects of age and streptozotocin-induced diabetes on contents and effects of substance P and vasoactive intestinal polypeptide in the lower urinary tract of the rat.

The urinary bladder and urethral content of substance P and vasoactive intestinal polypeptide and the in vitro effects of the peptides on the bladder were studied at 6 weeks and 6 months of streptozotocin-induced diabetes in the rat. The results were compared with those obtained in age-matched control animals. Both short-term and long-term streptozotocin treatment induced a clearcut increase in bladder weight. Bladder substance P content was increased in both groups of diabetic animals but substance P concentration was similar in control and diabetic animals. Vasoactive intestinal polypeptide content was slightly higher in diabetic animals than in controls but vasoactive intestinal polypeptide concentration was significantly lower in the bladders from both short-term and long-term diabetic animals. The bladder contractile response to substance P was similar in all groups of animals and vasoactive intestinal polypeptide was found to be devoid of contractile or relaxatory effects in the rat bladder. No change in urethral weight was seen with diabetes. There were no clear-cut changes in the urethral contents or concentrations of substance P and vasoactive intestinal polypeptide. The study also enabled comparisons between younger (3 months) and older (9 months) rats. This comparison showed a decrease in the concentrations and contents of substance P and vasoactive intestinal polypeptide between young and older rats. The changes were seen in both the bladder and the urethra and were similar in diabetic and normal animals.

Effects of chronic atropine administration on regional vasoactive intestinal polypeptide concentrations in rat brain

We studied the effects of 14 days' treatment with atropine sulfate (10 or 20 mg/kg per day) or atropine methyl bromide (20 mg/kg per day) on the concentration of vasoactive intestinal polypeptide like-immunoreactivity (VIP-LI) in the rat brain. VIP-Li in the anterior pituitary as well as brain areas dissected from treated and control rats was measured by radioimmunoassay. VIP-LI in the hypothalamus, and especially in the suprachiasmatic nucleus, was not affected by chronic atropine sulfate administration. Conversely, the same treatment induced a decrease in VIP-LI in the cerebral cortex, dorsal raphe, locus coeruleus, ventrolateral and dorsolateral medulla. In these structures, the decrease in VIP-LI was probably due to muscarinic receptor blockade in the central nervous system rather than in the peripheral nervous system since variations in VIP-LI were not observed after atropine methyl bromide treatment. These findings suggest the existence of a muscarinic control of VIP-LI in discrete brain areas of the rat and particularly in caudal brainstem structures.

&lt;b&gt;Expression of oncogenes and angiotensinogen gene in human ileal renin-secreting &lt;/b&gt;&lt;b&gt;carcinoma &lt;/b&gt;

Norepinephrine (NE), epinephrine (E), vasoactive intestinal polypeptide (VIP), met-enkephalin (met-E), somatostatin (SRIF), calcitonin (CT), and ACTH were measured using highly sensitive chemical methods and radioimmunoassays in tissue extracts obtained from 14 adrenal and 2 extraadrenal pheochromocytomas. We also determined the concentrations of NE, E, VIP, and met-E in plasma from 8 normal subjects and 13 patients with pheochromocytomas. There was a wide variation in the tissue contents of these peptides (VIP; 17.8±7.9 ng/g tissue, metE; 5175±2292 ng/g tissue, SRIF; 16.2±5.8 ng/g tissue, CT; 18.6±6.1 ng/g tissue, ACTH; 8.0±1.1 ng/g tissue), respectively, and in all tumors catecholamine concentrations (NE; 3.6±0.8 mg/g tissue, E; 1.5±0.6 mg/g tissue) were much higher (p<0.001)

Peptide Contents of Neuropeptide Y, Vasoactive Intestinal Polypeptide, andβ-Calcitonin Gene-Related Peptide and Their Messenger Ribonucleic Acids after Dexamethasone Treatment in the Isolated Rat Islets of Langerhans

A number of neuropeptides including neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), and beta-calcitonin gene related peptide (beta-CGRP) are known to influence insulin secretion. In order to investigate whether they might have a local autocrine/paracrine effect within the islets of Langerhans we screened isolated islets by Northern blot analysis and RIA for a number of peptides and found evidence for the presence of messenger RNA (mRNA) encoding NPY, VIP, and beta-CGRP. Dexamethasone treatment for 12 days increased the content of NPY, VIP, and beta-CGRP significantly from 1.3 +/- 0.3 to 19.8 +/- 1.6; 0.25 +/- 0.03 to 0.91 +/- 0.1; 2.2 +/- 0.2 to 4.8 +/- 0.1 fmol/islet respectively, mean +/- SEM (n = 4, P less than 0.05) and remained elevated 24 h after recovery. However when the results were normalized and expressed as a ratio of insulin content only NPY and VIP were significantly raised. Five days post treatment VIP was still significantly elevated compared to controls. mRNA for NPY increased 10-fold and for VIP increased 2 1/2 times after dexamethasone whereas mRNA for beta-CGRP was not significantly different from controls. Neither capsaicin nor 6-hydroxydopamine affected islet content or message of NPY, VIP, and beta-CGRP. Immunoreactive NPY and its mRNA were detected in two cultured beta-cell lines, HIT T-15 and RIN m5F cells whereas VIP and beta-CGRP were undetectable. The local islet synthesis of neuropeptides, which are known to influence islet hormone release pharmacologically, suggests the possibility that they may play a role in intraislet paracrine regulation.