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Chemical, immunological and biological properties of peptides like vasoactive-intestinal-peptide and peptide-histidine-isoleucinamide extracted from the venom of two lizards (Heloderma horridum and Heloderma suspectum).

Having previously isolated helodermin, the major peptide like vasoactive-intestinal-peptide and peptide-histidine-isoleucinamide, from the venom of the lizard Heloderma suspectum, we decided on a systematic exploration of all (VIP-PHI)-like peptides present in the venom of another lizard of the Helodermatidae family: Heloderma horridum. Six (VIP-PHI)-like peptides (PHH1 to 6) were purified to homogeneity from the venom of the lizard H. horridum with PHH3 and PHH4 representing two minor forms. All peptides cross-reacted in radioimmunoassays for helodermin and PHI but not for VIP. They yielded four fragments (T1 to T4) after trypsin digestion. T1, T2 and T3 showed the same retention time by reverse-phase HPLC and the same amino acid composition; the differences were confined to T4, the C-terminal sequence. PHH5 and PHH6 were found to be identical to synthetic helospectins I and II respectively. PHH1 and PHH3 probably resulted from a secondary modification of PHH5, while PHH2 and PHH4 derived from PHH6. Thus, the VIP-like peptides, previously called helospectins, are in fact typical of H. horridum venom. We confirmed that helodermin is the major (VIP-PHI)-like peptide of the venom of H. suspectum and observed its absence in H. horridum venom. Also, we found that positions 8 and 9 of helodermin are occupied by two Glu residues instead of two Gln as previously published. Helospectin-like material was also present in H. suspectum venom but in very small amount. In both venoms all VIP-like peptides were equally potent and efficient when tested for (a) their ability to occupy VIP as well as secretin receptors in rat pancreatic membranes and VIP receptors in rat liver membranes, and (b) the ensuing activation of adenylate cyclase in both membrane preparations.

Adenylyl Cyclases↗

Functional expression of receptors for calcitonin gene-related peptide, calcitonin, and vasoactive intestinal peptide in the human thymus and thymomas from myasthenia gravis patients.

The molecular and functional expression of serpentine membrane receptors for vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), and calcitonin (CT) were characterized in human thymus and thymomas from myasthenia gravis (MG) patients and thymic epithelial cells either in primary culture (PTEC) or transformed by the simian virus 40 large T (SV40LT) oncogene (LT-TEC). Using RT-PCR combined with Southern analysis, we identified the PCR products corresponding to the receptor (-R) transcripts for VIP, CGRP, and CT in thymus from control subjects and MG patients with either hyperplasia or thymoma. Similar expressions of the VIP- and CGRP-R transcripts were observed in PTEC, whereas the CT-R message was not detected. In LT-TEC, the signals for VIP-R, CGRP-R, and CT-R transcripts were seen with a lower intensity than those in control and MG thymus. In agreement with our molecular analysis, 1) VIP was the most potent peptide among VIP-related peptides (VIP > PACAP > PHM > PHV) to stimulate cAMP production through specific type 1 VIP receptors in both PTEC and LT-TEC; 2) cAMP generation was induced by CGRP in PTEC and by CT in LT-TEC; 3) in frozen thymic sections and by flow cytometry, type 1 VIP-R, CGRP-R, and CT-R were localized in epithelial cells; and 4) in parallel, the transcription of the acetylcholine receptor alpha subunit (the main autoantigen in MG) was induced by CGRP and CT in PTEC and LT-TEC, respectively. Our data suggest that the neuroendocrine peptides VIP, CGRP, and CT may exert functional roles during MG and malignant transformation of the human thymus.

Adolescent↗

Interaction of neuropeptides and cultured glial (Müller) cells of the chick retina: elevation of intracellular cyclic AMP by vasoactive intestinal peptide and glucagon.

Vasoactive intestinal peptide (VIP) and, to a lesser extent, glucagon were found to increase intracellular cyclic AMP rapidly in cultured glial (Müller) cells of the chick embryo retina. Although VIP elicited higher cyclic AMP accumulation than glucagon at each concentration tested, the half-maximal concentrations were similar, i.e., 6 X 10(-8) M for VIP and 8 X 10(-8) M for glucagon. Secretin had a minimal effect on cyclic AMP accumulation even at a very high (5 X 10(-6) M) concentration. Several other peptide and nonpeptide putative agonists also had little effect on cyclic AMP accumulation. The cultured Müller cell may thus be a useful model for examining VIP and glucagon effects on glial elements of the CNS.

Animals↗

Activation of choline acetyltransferase by vasoactive intestinal peptide.

Addition of vasoactive intestinal peptide (VIP) to brain homogenates increased the activity of choline acetyltransferase (ChAT) but not that of acetylcholinesterase or glucose-6-phosphate dehydrogenase. Activity of ChAT was increased in the anterior hypothalamus and in the dorsal and ventral hippocampus, but not in the parietal cortex or posterior hypothalamus. Increased activity occurred rapidly after VIP addition to homogenates and was maximal at 10(-7)M concentration. Kinetic analysis indicates that the Vmax of the enzyme is increased and the Km for choline, but not acetyl-coenzyme A, is decreased in the presence of VIP. Results support a possible VIP-cholinergic interaction in the CNS.

Acetylcholinesterase↗

Fetal metabolism and placental transfer of vasoactive intestinal peptide in sheep.

Vasoactive Intestinal Peptide (VIP) is a 28-amino-acid putative neurotransmitter that may have a role in the regulation of myometrial blood flow and uterine contractility. The chronically cannulated fetal sheep preparation was used to examine the fetal clearance and placental transfer of VIP. Metabolic Clearance Rate (MCR) and placental transfer of VIP were measured by alternate steady-state infusion of VIP into the mother and fetus. Plasma concentrations of VIP were measured by radioimmunoassay. MCR was similar in the pregnant (45 +/- 10 ml/kg/min) and nonpregnant ewes (35 +/- 5 ml/kg/min). However, compared to both pregnant and nonpregnant ewes, fetal MCR was significantly increased at 77 +/- 15 ml/kg/min, indicating highly developed clearance mechanisms in the fetus. VIP did not cross the placenta in either direction. Both the placenta and fetal liver metabolized VIP and contributed to the elevated fetal clearance of VIP. The results show that VIP in fetal tissue is unlikely to influence maternal uterine activity with any VIP-mediated effects emanating from maternal and/or placental sources.

Animals↗

Stimulation of insulin and glucagon secretion by vasoactive intestinal peptide.

In vivo, vasoactive intestinal peptide (VIP) produces simultaneous increases in blood glucose and insulin levels. In order to determine whether VIP, like its homologues, also stimulates insulin secretion directly, studies were made in controlled glucose media employing the vascularly perfused cat pancreas. VIP stimulated insulin secretion significantly in the presence of constant physiological concentrations of glucose. The highest insulin response to VIP (100.3+/-8.1 muU/min) approached the highest insulin response to glucose (119.9 +/- 12.0 muU/min). In the absence of glucose, the insulin response to VIP was insignificant. Unexpectedly, VIP was found to be a more effective stimulant of glucagon than of insulin secretion. The highest glucagon response to VIP (327+/-51% of control levels) was attained in the presence of physiological concentrations of glucose and equalled the glucagon response obtained upon withdrawal of glucose from the perfusate. The glucagon response to VIP was blocked by increasing the glucose in the perfusate. These studies indicate the VIP present in pancreatic islets might play a role in the local control of pancreatic endocrine function.

Animals↗

Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs.

Vasoactive intestinal peptide (VIP) is a potent inotrope and coronary vasodilator. To test whether VIP also exerts regional myocardial electrophysiological (EP) effects, dose-response and time-course effects of intracoronary injections (10(-10)-10(-4) M) were obtained in 4 intact hearts and 12 in situ normoperfused right ventricular flap preparations in chloralose-anesthetized dogs. Under constant rate, activation (A), recovery (R), and A-R interval (ARI) maps were constructed from multiplexed unipolar surface electrograms recorded simultaneously from 32 sites. Effects were compared with those of isoproterenol (Iso) and forskolin (For). The main finding with all agonists was the uniform shortening of ARIs in a dose-response fashion with a maximum of 30 +/- 4 ms or 20% from control. Although the maximal EP changes were similar for all agonists, they occurred at different molecular concentrations (10(-6) Iso, 10(-5) VIP, and 10(-4) For). Also, whereas the duration of EP effect did not exceed 5 min for Iso and For, it was markedly sustained for VIP, outlasting its contractile but paralleling its vasodilatory effect. The physiological endoepicardial differences in ARI and the recovery sequence were preserved for all agonists. Thus VIP, in addition to coronary vasodilation and myocardial inotropy, exerts a strong balanced global myocardial EP effect, similar to, but more sustained than, the adrenergic effect. The difference in duration of inotropic and EP effects may point to different mediating mechanisms.

Animals↗

Five discrete cis-active domains direct cell type-specific transcription of the vasoactive intestinal peptide (VIP) gene.

Vasoactive intestinal peptide (VIP) is a neuromodulator expressed with great anatomical specificity throughout the nervous system. Cell-specific expression of the VIP gene is mediated by a tissue specifier element (TSE) located within a 2.7-kilobase (kb) region between -5.2 and -2.5 kb upstream from the transcription start site, and requires an intact promoter proximal VIP-CRE (cyclic AMP-responsive element) (Hahm, S. H., and Eiden, L. E. (1997) J. Neurochem. 67, 1872-1881). We now report that the TSE comprises a 425-base pair domain located between -4.7 and -4.2 kb containing two AT-rich octamer-like sequences. The 425-base pair TSE is sufficient to provide full cell-specific regulation of the VIP gene, when fused to the 5' proximal 1.55 kb of the VIP gene. Mutational analysis and gel shift assays of these octamer-like sequences indicate that the binding of proteins related to the ubiquitously expressed POU-homeodomain proteins Oct-1 and/or Oct-2 to these octamer-like sequences plays a central role for the function of the TSE. The TSE interacts with three additional discrete domains besides the cAMP response element, which are located within the proximal 1.55 kb of the VIP gene, to provide cell-specific expression. An upstream domain from -1.55 to -1.37 kb contains E-boxes and MEF2-like motifs, and deletion of this domain results in complete abrogation of cell-specific transcriptional activity. The region from -1.37 to -1. 28 kb contains a STAT motif, and further removal of this domain allows the upstream TSE to act as an enhancer in both SH-EP and HeLa cells. The sequence from -1.28 to -0.9 kb containing a non-canonical AP-1 binding sequence (Symes, A., Gearan, T., Eby, J., and Fink, J. S. (1997) J. Biol. Chem. 272, 9648-9654), is absolutely required for TSE-dependent cellspecific expression of the VIP gene. Thus, five discrete domains of the VIP gene provide a combination of enhancer and repressor activities, each completely contingent on VIP gene context, that together result in cell-specific transcription of the VIP gene.

Base Sequence↗

Enzymatic synthesis of vasoactive intestinal peptide analogs by transglutaminase.

Vasoactive intestinal peptide is an amino acceptor and donor substrate for tissue transglutaminase (TGase) in vitro. This peptide contains a single glutamine residue, Gln16, which was identified as the amino acceptor substrate. Different gamma(glutamyl16)amine derivatives of vasoactive intestinal peptide were synthesized enzymatically in vitro. The modification is very fast when compared with that of many native substrates of TGase. The analogs 1,3-diaminopropane, putrescine, cadaverine, spermidine, spermine, glycine ethyl ester and mono-dansylcadaverine of the peptide were purified by high-performance liquid chromatography on a reverse-phase column and were analyzed by electrospray mass spectrometry. When amines were absent in the assay mixture as an external amino donor, lysine residue occurring in the peptide was an effective amino donor site for TGase. Only one of the three lysine residues of vasoactive intestinal peptide, namely Lys21, was demonstrated to be involved in both inter- and intramolecular cross-link formation.

Amines↗

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.

Cell Migration Inhibition↗

[Neuroendocrine activation in acute myocardial infarction: state of the art and preliminary results on intestinal vasoactive peptide].

Acute myocardial infarction (AMI) is known to be associated with a complex neuroendocrine activation, especially concerning sympathetic and renin-angiotensin systems, cortisol, atrial natriuretic peptide and endothelin. Results of our study show that the vasoactive intestinal peptide (VIP), also, is early involved in the neuroendocrine activation occurring in AMI. Plasma concentration of VIP, significantly increased in AMI patients within 6 hours after the onset of chest pain, soon decreased and remained below than normal along the first week. At the 14th day of the AMI, plasma levels of VIP returned into the normal range. A significant increase of VIP plasma concentration is detectable in the first hours of AMI in survived as compared with died patients. The phenomenon seems to be a suitable process to provide an endogenous support to the ischemic heart and to counteract the negative effects of other neuroendocrine activated factors.

Adult↗

Distribution and colocalization of calcitonin gene-related peptide, tachykinins, and vasoactive intestinal peptide in normal and idiopathic unstable human urinary bladder.

The distribution of nerves containing calcitonin gene-related peptide (CGRP), substance P (SP), neurokinin A (NKA), and vasoactive intestinal peptide (VIP) was examined in the human urinary bladder, using both single- and double-label immunohistochemistry. Nerves containing CGRP and tachykinins were typically present within the subepithelial region, encircling intramural ganglia and around blood vessels. These nerves were sparsely distributed, and only very rarely projected to the smooth muscle bundles of the detrusor. In contrast, VIP-containing nerves formed a dense subepithelial plexus and also projected to the detrusor muscle bundles. The double-label studies revealed that approximately 26% +/- 10% of CGRP-immunoreactive nerves also contained SP and NKA, but that no CGRP fibers coexpressed VIP. Conversely, all SP-immunoreactive fibers also contained CGRP, and many coexpressed NKA. At least three neurochemically distinct populations of nerves can therefore be discerned in the human bladder: VIP/-, CGRP/-, and CGRP/SP/ +/- NKA. The density of CGRP and SP-immunoreactive nerves within the subepithelium of 14 women with urodynamically-proven idiopathic detrusor instability was increased by 82% (p = 0.003) and 94% (p = 0.036), respectively, relative to that of 14 control women with no symptoms of frequency or urgency. This effect was not due to an increase in overall nerve density, because immunoreactivity for the general nerve marker, protein gene product, was not significantly different between the two groups (p = 0.21). The results indicate that at least some patients with detrusor instability demonstrate increases in a specific class of nerve fibers containing CGRP and SP. These peptides are characteristic of sensory neurons in a number of species, suggesting that abnormalities in the afferent arm of the micturition reflex may be associated with detrusor instability.

Adult↗

[Intestinal vasoactive peptide receptors in enterocytes : specific binding and stimulation of cyclic AMP].

Receptors for the vasoactive intestinal peptide (VIP) were characterized on enterocytes isolated from Rat small intestine. Native VIP inhibited competitively the binding of 125I-VIP to enterocytes and strongly stimulated cyclic AMP production; both these effects were observed for concentrations of VIP as low as 0.5-1.0 ng/ml (0.15-0.30 nM) which are compatible with the VIP concentration in the gut.

Animals↗

Peptide specificity for stimulation of corticotropin secretion: activation of overlapping pathways by the vasoactive intestinal peptide family and corticotropin-releasing factor.

The hypothalamic peptide vasoactive intestinal peptide (VIP) stimulates ACTH and endorphin secretion by the AtT20/D16 clonal strain of mouse pituitary tumor cells. The dose dependence for VIP stimulation of hormone release is biphasic, indicating that VIP is able to activate at least two classes of receptors in D16 cells (ED50 = 1.6 and 160 nM). We show that at high concentrations (ED50 greater than or equal to 150 nM), other natural peptides with primary structures homologous to that of VIP also increased ACTH secretion by D16 cells, whereas structurally unrelated peptides did not. The stimulatory actions of GH-releasing factor (GRF) and porcine heptacosapeptide with amino-terminal histidine and carboxy-terminal isoleucine amide (PHI) were mediated by high affinity VIP receptors because their effects were not additive with that of 10 nM VIP. In addition, GRF and PHI behaved as antagonists at low affinity VIP receptors; both peptides inhibited stimulation by 1 microM VIP. In contrast, glucagon and gastric inhibitory polypeptide appeared to stimulate ACTH release via low affinity VIP receptors because their effects were additive with that of 10 nM, but not 1 microM, VIP. Since all of the VIP-like peptides increased ACTH secretion only at high concentrations, they were unlikely to represent a physiological ligand for the receptor activated by high concentrations of VIP. Therefore, we determined whether cross-reactivity occurred between VIP-like peptides and corticotropin-releasing factor (CRF), a potent stimulator of ACTH secretion both in vitro and in vivo. The dose-response curve for CRF stimulation of ACTH secretion by D16 cells extended over more than a 1000-fold range of concentrations and was biphasic (ED50 = 2.6 and greater than 300 nM), indicating that CRF interacted with multiple receptor types in D16 cells. However, since the effect of 10 nM CRF was additive with that of 1 microM VIP, the CRF receptor was not the site at which high concentrations of VIP stimulated ACTH release. In contrast, the effect of 1 microM CRF was not additive with that of 1 microM VIP or other VIP-like peptides. Therefore, high concentrations of CRF and the previously recognized VIP-like peptides stimulated ACTH secretion by overlapping pathways. Comparison of the amino acid sequence of CRF with those of the VIP-like peptides showed that 18 of the 41 amino acids in CRF match a corresponding amino acid in at least 1 member of the VIP peptide family.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗

Effect of gastroduodenostomy on intestinal vasoactive intestinal peptide (VIP) levels, and VIP binding and VIP stimulation of cyclic AMP in intestinal epithelial cells from rat.

The concentration of VIP in duodenum and jejunum as well as the interaction of VIP (binding and stimulation of cyclic AMP accumulation) with epithelial cells from both gut segments were studied in rats after surgical bypass of the pylorus by gastroduodenostomy. Duodenal VIP concentration increased in rats with gastroduodenostomy as compared to sham-operated animals. The binding capacity (but not the affinity) of VIP binding sites and the efficiency (but not the potency) of VIP on cyclic AMP accumulation decreased in the condition of gastroduodenostomy. However, no modifications in either VIP concentration and interaction could be seen at the jejunal level.

1-Methyl-3-isobutylxanthine↗

Effect of GHRH and peptides from the vasoactive intestinal peptide family on cAMP production of human cancer cell lines in vitro.

Antagonistic analogs of GHRH inhibit growth of various human cancers both in vivo and in vitro. To elucidate the mechanism of direct action of the antagonistic analogs of GHRH on tumor cells, cultured human cancer cells were exposed to GHRH, vasoactive intestinal peptide (VIP), secretin, glucagon, neuropeptide-Y (NPY), pituitary adenylate cyclase-activating peptide (PACAP), and VIP analogs in a superfusion system, and changes in cAMP and IGF-II release from the cells were measured. Various human cancer cell lines, such as mammary (MDAMB-468 and ZR-75-1), prostatic (PC-3), pancreatic (SW-1990 and Capan-2), ovarian (OV-1063), and colorectal (LoVo) responded to pulsatile stimuli with GHRH (0.5-20 nM), VIP (0.02-10 nM), and PACAP-38 (0.05-5 nM) with a rapid, transient increase in cAMP release from the cells. The VIP antagonist, PG-97-269, and the adenylate cyclase inhibitor, MDL-12330A, but not SQ-22536 or pertussis toxin, blocked the cAMP responses to these peptides. Stimulation of the cells with 100 nM secretin, glucagon or NPY did not alter the cAMP release. Our results suggest that GHRH receptors different from the type expressed in the pituitary are involved in mediating these effects. As cAMP is a potent second messenger controlling a wide variety of intracellular functions, including those required for cell growth, our results indicate that GHRH might have a direct stimulatory effect on growth of human cancers. Blockade of the autocrine/paracrine action of GHRH with its antagonistic analogs may provide a new approach to tumor control.

Cyclic AMP↗