The isolation and chemical characterization of a novel vasoactive intestinal peptide-related peptide from a teleost fish, the cod, Gadus morhua

The serendipitous origin of chordate secretin peptide family members

Background

The secretin family is a pleotropic group of brain-gut peptides with affinity for class 2 G-protein coupled receptors (secretin family GPCRs) proposed to have emerged early in the metazoan radiation via gene or genome duplications. In human, 10 members exist and sequence and functional homologues and ligand-receptor pairs have been characterised in representatives of most vertebrate classes. Secretin-like family GPCR homologues have also been isolated in non-vertebrate genomes however their corresponding ligands have not been convincingly identified and their evolution remains enigmatic.

Results

In silico sequence comparisons failed to retrieve a non-vertebrate (porifera, cnidaria, protostome and early deuterostome) secretin family homologue. In contrast, secretin family members were identified in lamprey, several teleosts and tetrapods and comparative studies revealed that sequence and structure is in general maintained. Sequence comparisons and phylogenetic analysis revealed that PACAP, VIP and GCG are the most highly conserved members and two major peptide subfamilies exist; i) PACAP-like which includes PACAP, PRP, VIP, PH, GHRH, SCT and ii) GCG-like which includes GCG, GLP1, GLP2 and GIP. Conserved regions flanking secretin family members were established by comparative analysis of the Takifugu, Xenopus, chicken and human genomes and gene homologues were identified in nematode, Drosophila and Ciona genomes but no gene linkage occurred. However, in Drosophila and nematode genes which flank vertebrate secretin family members were identified in the same chromosome.

Conclusions

Receptors of the secretin-like family GPCRs are present in protostomes but no sequence homologues of the vertebrate cognate ligands have been identified. It has not been possible to determine when the ligands evolved but it seems likely that it was after the protostome-deuterostome divergence from an exon that was part of an existing gene or gene fragment by rounds of gene/genome duplication. The duplicate exon under different evolutionary pressures originated the chordate PACAP-like and GCG-like subfamily groups. This event occurred after the emergence of the metazoan secretin GPCRs and led to the establishment of novel peptide-receptor interactions that contributed to the generation of novel physiological functions in the chordate lineage.

Immunomodulation of innate immune responses by vasoactive intestinal peptide (VIP): its therapeutic potential in inflammatory disease

Since the late 1970s a number of laboratories have studied the role of vasoactive intestinal peptide (VIP) in inflammation and immunity. These studies have highlighted the dramatic effect of VIP on immune cell activation and function, and studies using animal models of disease have indicated that VIP has significant therapeutic and prophylactic potential. This review will focus on the effects of VIP on innate immune cell function and discuss the therapeutic potential for VIP in inflammatory diseases of humans.

Persistence of duplicated PAC1 receptors in the teleost, Sparus auratus

Background:

Duplicated genes are common in vertebrate genomes. Their persistence is assumed to be either a consequence of gain of novel function (neofunctionalisation) or partitioning of the function of the ancestral molecule (sub-functionalisation). Surprisingly few studies have evaluated the extent of such modifications despite the numerous duplicated receptor and ligand genes identified in vertebrate genomes to date. In order to study the importance of function in the maintenance of duplicated genes, sea bream (Sparus auratus) PAC₁ receptors, sequence homologues of the mammalian receptor specific for PACAP (Pituitary Adenylate Cyclase-Activating Polypeptide), were studied. These receptors belong to family 2 GPCRs and most of their members are duplicated in teleosts although the reason why both persist in the genome is unknown.

Results:

Duplicate sea bream PACAP receptor genes (sbPAC₁A and sbPAC₁B), members of family 2 GPCRs, were isolated and share 77% amino acid sequence identity. RT-PCR with specific primers for each gene revealed that they have a differential tissue distribution which overlaps with the distribution of the single mammalian receptor. Furthermore, in common with mammals, the teleost genes undergo alternative splicing and a PAC₁Ahop1 isoform has been characterised. Duplicated orthologous receptors have also been identified in other teleost genomes and their distribution profile suggests that function may be species specific. Functional analysis of the paralogue sbPAC₁s in Cos7 cells revealed that they are strongly stimulated in the presence of mammalian PACAP₂₇ and PACAP₃₈ and far less with VIP (Vasoactive Intestinal Peptide). The sbPAC₁ receptors are equally stimulated (LOG_EC50 values for maximal cAMP production) in the presence of PACAP₂₇ (-8.74 ± 0.29 M and -9.15 ± 0.21 M, respectively for sbPAC₁A and sbPAC₁B, P > 0.05) and PACAP₃₈ (-8.54 ± 0.18 M and -8.92 ± 0.24 M, respectively for sbPAC₁A and sbPAC₁B, P > 0.05). Human VIP was found to stimulate sbPAC₁A (-7.23 ± 0.20 M) more strongly than sbPAC₁B (-6.57 ± 0.14 M, P < 0.05) and human secretin (SCT), which has not so far been identified in fish genomes, caused negligible stimulation of both receptors.

Conclusion:

The existence of functionally divergent duplicate sbPAC₁ receptors is in line with previously proposed theories about the origin and maintenance of duplicated genes. Sea bream PAC₁ duplicate receptors resemble the typical mammalian PAC₁, and PACAP peptides were found to be more effective than VIP in stimulating cAMP production, although sbPAC₁A was more responsive for VIP than sbPAC₁B. These results together with the highly divergent pattern of tissue distribution suggest that a process involving neofunctionalisation occurred after receptor duplication within the fish lineage and probably accounts for their persistence in the genome. The characterisation of further duplicated receptors and their ligands should provide insights into the evolution and function of novel protein-protein interactions associated with the vertebrate radiation.

Binding and multiple hydrolytic sites in epitopes recognized by catalytic anti-peptide antibodies

Autoantibodies purified from humans catalyse the hydrolysis of the neurotransmitter, vasoactive intestinal peptide (VIP). Evidence that the hydrolysis of VIP is due to antibodies includes: the antibody preparations are free of detectable non-immunoglobulin (non-Ig) contamination; the hydrolytic activity is removed by precipitation with anti-human IgG antibody; human B lymphoblastoid cells transformed with Epstein-Barr virus secrete hydrolytic antibodies in culture; the Fab fragments of the antibodies exhibit VIP hydrolysis; and affinity chromatography on immobilized VIP permits purification of specific antibodies with greatly enriched hydrolytic and binding activities. One of the catalytic antibody preparations hydrolyses the Gln-16-Met-17 bond. Studies with synthetic VIP fragments showed that the epitope recognized by this antibody is formed by VIP(15-28). Important binding interactions are contributed by VIP(22-28), a sequence four residues distant from the scissile bond. Antibodies from a second subject hydrolyse six peptide bonds in VIP, clustered between residues 14 and 22. These bonds link amino acids of different charge, size and hydrophobicity, suggesting that the hydrolytic repertoire of the antibodies is considerable. The antibodies do not hydrolyse peptides unrelated in sequence to VIP. Cleavage of several peptide bonds in VIP by polyclonal antibody preparations may be due to several antibodies, each with a unique cleavage specificity. Alternatively, a single antibody may make catalytically productive contact at multiple peptide bonds in the substrate, because of conformational flexibility of VIP or of the antibody active site. Purified light chains from the catalytic antibodies hydrolysed VIP more rapidly than did intact antibodies. The residues constituting the catalytic site of an antibody may be encoded in germline V-region genes or may arise during maturation of the antibody response.

Isolation and characterization of four VIP-related peptides from red-bellied newt, Cynops pyrrhogaster

Four novel bioactive peptides were isolated from the red-bellied newt, Cynops pyrrhogaster, using a bioassay system monitoring the rectum contraction of the Japanese quail, Coturnix japonica. As these peptides are structurally related to vasoactive intestinal polypeptide (VIP), we termed these peptides newt VIP-related peptides 1, 2, 3, and 4 (NVRP-1, -2, -3, and -4). The primary sequences of these peptides were determined to be HSDAVFTDNYSRLLGKTALKNYLDGALKKE (NVRP-1), HSDAVFTDNYSRLLAKTALKNYLDGALKKE (NVRP-2), HSDAVFT-DNYSRLLGKIALKNYLDEALKKE (NVRP-3), and HSDAVFTDNYSRLLGKT-ALKNYLDSALKKE (NVRP-4). The N-terminal regions of these NVRPs possessed homology at the amino-acid level to various VIP, while the NVRP C-termini differed from VIPs significantly. All of the VIP consist of 28 amino-acid residues with amidated forms at the C-termini, whereas NVRPs possess 30 amino-acid residues and have free forms at the C-termini. NVRPs exert relaxant activities on isolated quail rectums in a dose-dependent manner, with threshold concentrations between 1 x 10(-8) and 3 x 10(-8) M. NVRPs also exhibited potent relaxant activities acting on the newt duodenum at 3 x 10(-8) M. As yet, this is the first isolation of biologically active VIP-related peptides from urodele.

Localisation of VIP-binding sites exhibiting properties of VPAC receptors in chromaffin cells of rainbow trout (Oncorhynchus mykiss)

The current model for the neuronal control of catecholamine release from piscine chromaffin cells advocates that the neurotransmitters vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are co-released with acetylcholine from preganglionic fibres upon nerve stimulation. Both VIP and PACAP elicit the secretion of exclusively adrenaline from rainbow trout chromaffin cells, which presumably arises from the activation of VPAC type receptors. Thus, the goals of the present study were (1) to localise VPAC receptors in the chromaffin cell fraction of the posterior cardinal vein (PCV) of trout and (2) to test the hypothesis that the selective secretion of adrenaline elicited by VIP could be explained by the absence of the VPAC receptors from the noradrenaline-containing cells. Fluorescent labelling of chromaffin cells using aldehyde-induced fluorescence of catecholamines and antisera raised against dopamine beta-hydroxylase (DbetaH) revealed a distinct layer of chromaffin cells lining the walls of the PCV. Furthermore, specific VIP-binding sites were demonstrated on chromaffin cells using a biotinylated VIP that was previously established as being bioactive. Although multiple labelling experiments revealed that a number of DbetaH-positive cells were immunonegative for phenylethanolamine N-methyl transferase (PNMT; noradrenaline-containing cells versus adrenaline-containing cells, respectively), labelling of VIP-binding sites was similar to that of DbetaH labelling, suggesting that all chromaffin cells possess VIP-binding sites. Pharmacological assessment of the VIP-binding sites indicated that they exhibited characteristics of VPAC receptors. Specifically, the labelling of VIP-binding sites was prevented after pre-treatment of PCV tissue sections with unlabelled VIP, PACAP or the specific VPAC receptor antagonist VIP 6-28. By contrast, sections pre-treated with the PAC(1) receptor blocker PACAP 6-27 displayed normal labelling of VIP-binding sites. Finally, partial cDNA clones for the trout VPAC(1) and VPAC(2) receptor were obtained and sequenced. Tissue distribution experiments using RT-PCR revealed the presence of VPAC(1) receptor mRNA but not that of the VPAC(2) receptor in the PCV tissue. The results provide direct evidence that VIP and PACAP can elicit the secretion of adrenaline from the chromaffin tissue via specific VIP-binding sites that exhibit properties of VPAC receptors. However, the selective secretion of adrenaline by VIP or PACAP cannot be explained by a lack of VIP-binding sites on the noradrenaline-containing cells.

Comparative distribution of VIP in the central nervous system of various species measured by a new radioimmunoassay

Vasoactive intestinal polypeptide (VIP) occurs in high concentrations throughout the gut and the nervous system. The presence of VIP has been shown in a number of species, mainly by immunohistochemistry. The aim of the present study was to develop a new, highly specific VIP radioimmunoassay to investigate the distribution of VIP in the central nervous system of various vertebrate and invertebrate species. Different areas of the brain and spinal cord were removed from rats, chickens, turtles, frogs and fishes. The cerebral ganglia and the ventral ganglionic chain were investigated in the earthworm. The tissue samples were processed for VIP radioimmunoassay. Our results show that the antiserum used in the radioimmunoassay turned to be C-terminal specific, without significant affinity to other members of the VIP peptide family. Detection limit of the assay was 0.1 fmol/ml. Highest concentrations were found in the turtle diencephalon, followed by other brain areas in the turtle and rat. All other brain areas in the examined species contained significant levels of VIP. Immunoreactivity was also shown in the cerebral and ventral ganglia of the earthworm. In summary, our results show comparative quantitative distribution in representative species of the phylogenetic line, using the same experimental conditions.

Evolution of vertebrate neuropeptides

This review describes some of the most typical features in the evolution of neuropeptides. Neuropeptides are synthesized like other polypeptides and proteins, with an amino acid sequence determined by the DNA sequence of the corresponding gene. Mutations of bases in the coding regions of the DNA lead to changes in amino acid sequence, and explain the differences in amino acid sequence of a certain neuropeptide in different animal species. The more distantly related two species are, the more substitutions can be found in one and the same neuropeptide. The biologically active part of the neuropeptide is usually the most conserved part. Neuropeptides also form families of closely related peptides, where several members may occur in one animal species. This is due to gene or exon duplications followed by mutations. Gene splicing and posttranslational processing decides the gene product in a single cell. Difference in sequence may cause difference in function, but more often than not, members of a family appear to produce the same effect. Three neuropeptide families, the tachykinins, the neuropeptide Y family, and the vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating peptide family will be described in more detail.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Presence of pituitary adenylate cyclase-activating polypeptide (PACAP) and its relaxant activity in the rectum of a teleost, the stargazer, Uranoscopus japonicus

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide and a member of the secretin/glucagon superfamily of peptides that include vasoactive intestinal polypeptide. PACAP is not only present in the central nervous system but also in peripheral organs, such as the gastrointestinal tract, gonads and adrenal glands, and plays various roles in mammals. Recently, we isolated and characterized PACAP, which is very similar to PACAP of mammalian origin, from the brain of a teleost, the stargazer, Uranoscopus japonicus. In the present study, the expression of PACAP mRNA was detected in the stargazer rectum using the reverse transcriptase/polymerase chain reaction (RT-PCR) method. The distribution of PACAP-like immunoreactivity in the rectum was also examined immunohistochemically, using an antiserum raised against PACAP 27, and PACAP-like immunoreactive neuronal cell bodies and fibers were found in the myenteric plexuses and the smooth muscle layers of the rectum. The present study also investigated the relaxant activity of synthesized homologous PACAP on rectal contraction. Stargazer PACAP, like that of mammalian origin, inhibited contractions stimulated by acetylcholine or potassium chloride. PACAP-induced inhibition was not affected by preincubation with atropine, propranolol, or phentolamine. These results suggest that PACAP may act directly as an inhibitory neuropeptide in the stargazer rectum.

PACAP and nitric oxide inhibit contractions in the proximal intestine of the atlantic cod, Gadus morhua

The possible inhibitory roles of pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and nitric oxide in the control of intestinal motility were investigated in the Atlantic cod, Gadus morhua. Circular and longitudinal smooth muscle preparations developed spontaneous contractions that were inhibited by atropine (10(−)(5)mol l(−)(1)). PACAP 27 and PACAP 38 (10(−)(7)mol l(−)(1)) reduced the amplitude of the contractions but did not usually affect the resting tension. In the circular preparations, the mean active force developed (above resting level; +/− s.e.m.) was reduced from 0. 62+/−0.18 mN to 0.03+/−0.03 mN (N=10) by PACAP 27 and from 0.53+/−0. 20 mN to 0.31+/−0.13 mN (N=7) by PACAP 38, while neither cod nor mammalian VIP (10(−)(10)-10(−)(6)mol l(−)(1)) had any effect. In the longitudinal preparations, PACAP 27 reduced the force developed from 1.58+/−0.22 mN to 0.44+/−0.25 mN (N=8) and PACAP 38 reduced it from 1.61+/−0.47 mN to 0.75+/−0.28 mN (N=5). The nitric oxide donor sodium nitroprusside (NaNP) almost abolished the contractions in the circular preparations, reducing the mean force developed from 0. 47+/−0.05 mN to 0.02+/−0.06 mN (10(−)(6)mol l(−)(1); N=9) and 0+/−0. 07 mN (10(−)(5)mol l(−)(1); N=8). In the longitudinal preparations, NaNP reduced the force developed from 2.03+/−0.36 mN to 0.33+/−0.22 mN (10(−)(6)mol l(−)(1); N=8) and 0.19+/−0.30 mN (10(−)(5)mol l(−)(1); N=8). The L-arginine analogue N(G)-nitro-L-arginine methyl ester (L-NAME; 3×10(−)(4)mol l(−)(1)) enhanced the contractions in both circular and longitudinal preparations, increasing the mean force developed from 0.51+/−0.12 mN to 0.94+/−0.21 mN (N=8) and from 1.49+/−0.36 mN to 3.34+/−0.67 mN (N=7), respectively. However, preincubation with L-NAME before a second addition of PACAP 27 (10(−)(7)mol l(−)(1)) did not affect the response to PACAP, neither did preincubation with the guanylate cyclase inhibitor 6-anilinoquinoline-5,8-quinone (LY83583; 10(−)(5)mol l(−)(1)), while the inhibitory response to NaNP (3×10(−)(7)mol l(−)(1)) was abolished by LY83583. The PACAP analogue PACAP 6–27 (3×10(−)(7)mol l(−)(1)) had no effect on the response to either NaNP (3×10(−)(7)mol l(−)(1)) or PACAP 27 (10(−)(8)mol l(−)(1)) in the circular preparations. These findings indicate the presence of both a cholinergic and a nitrergic tonus in the smooth muscle preparations of the cod. Although PACAP and NaNP both inhibit contractions, there is no evidence of any interactions between the two substances. In addition, NaNP, but not PACAP, probably acts via stimulating the production of cyclic GMP. In conclusion, both PACAP and nitric oxide may act as inhibitory transmitters, using distinct signalling pathways, in the control of intestinal motility in the Atlantic cod.

Neuropeptide families: evolutionary perspectives

Examination of neuropeptide families can provide information about phyletic relationships and evolutionary processes. In this article the oxytocin/vasopressin family, growth hormone releasing factor (GRF) superfamily and the substance P/tachykinin family have been considered in detail because they have been isolated from an extraordinarily diverse array of species from several vertebrate classes and invertebrate phyla. More important is that the nucleotide sequence of mRNA or cDNA encoding many of these peptides has been determined, which has allowed evolutionary distances to be estimated based on the DNA mutation rate. The origin of a given family lies in a primordial gene that arose many millions of years ago, and through time, exon duplication and insertion, gene duplication, point mutation and exon loss, the family developed into the forms that are now recognised. For example, in birds, GRF and pituitary adenylate cyclase activating peptide (PACAP) are encoded by the same gene, which probably arose as a result of exon duplication and tandem insertion of the ancestral GRF gene. In mammals GRF is the sole product on one gene, and PACAP is the product of a gene that also produces PACAP-related peptide (PRP), which is homologous to GRF. Thus it appears that between birds and mammals the GRF/PACAP gene duplicated: exon loss gave rise to the mammalian GRF gene, while mutation led to the formation of the mammalian PRP/PACAP gene. The neuropeptide Y superfamily is considered briefly, as is cionin, which is an invertebrate peptide that is closely related to the mammalian gastrin/cholecystokinin family.

Vip-induced relaxation of small arteries of the rainbow trout, Oncorhynchus mykiss, involves prostaglandin synthesis but not nitric oxide

Small arteries (internal diameter 376 +/- 69 microns) from the proximal intestine region of the rainbow trout were mounted in a myograph apparatus where changes in isometric tension could be recorded. VIP (vasoactive intestinal polypeptide) caused a concentration-dependent relaxation (10(-9)-3 x 10(-7) M) of vessels precontracted with the alpha-adrenoceptor agonist phenylephrine (10(-5) M). The nitric oxide synthase inhibitor L-NAME (10(-4) M) did not affect the VIP-relaxation, neither did the lipoxygenase inhibitor esculetin (10(-5) M). However, the cyclooxygenase inhibitor indomethacin (10(-6) M) shifted the concentration-response curve significantly to the right. The VIP-relaxation was still present after mechanical removal of the endothelium. Sodium nitroprusside (10(-9)-10(-6) M) caused a concentration-dependent relaxation of the precontracted vessel, indicating the presence of soluble guanylate cyclase in the vascular smooth muscle cells. VIP-immunoreactivity was found in varicose nerve fibers in these vessels, but nitric oxide synthase-immunoreactivity could not be demonstrated. These results suggest that in rainbow trout, as in mammals, VIP is an endogenous vasodilating neuropeptide. No endothelium-dependent mechanism seems to be involved, neither is production of nitric oxide. Instead the relaxation is mediated, at least in part, via prostaglandin synthesis.

Vasoactive intestinal polypeptide immunoreactive nerves in the gill arch of teleost fish, Carassius auratus L

The localization of vasoactive intestinal polypeptide (VIP)-immunoreactive (ir) nerve cell bodies and fibers has been studied in the gill arches of goldfish (Carassius auratus, L.) using the peroxidase-antiperoxidase (PAP) immunohistochemical method. It was found that VIP-ir nerve cell bodies are localized in connective tissue on the oral side of the gill arch; these cells were present as single cells, in couples or as small clusters. Moreover, a dense network of VIP-ir fibers was observed beneath the lining epithelium of the raker cushion. The possible involvement of this peptide in mucus secretion in the gill arches of teleost is discussed.

Distribution of PACAP (pituitary adenylate cyclase-activating polypeptide)-like and helospectin-like peptides in the teleost gut

Pituitary adenylate cyclase-activating polypeptide (PACAP) and helospectin are two vasoactive intestinal polypeptide (VIP)-related neuropeptides that have recently been demonstrated in the mammalian gut; the aim of this study was to reveal their occurrence and localisation in the gastrointestinal tract, swimbladder, urinary bladder and the vagal innervation of the gut of teleosts, using immunohistochemical methods on whole-mounts and sections of these tissues from the Atlantic cod, Gadus morhua and the rainbow trout, Oncorhynchus mykiss. Both PACAP-like and helospectin-like peptides were present in the gut wall of the two species. Immunoreactive nerve fibres were found in all layers but were most frequent in the myenteric plexus and along the circular muscle fibres. Immunoreactivity was also demonstrated in nerves innervating the swimbladder wall, the urinary bladder and blood vessels to the gut. Immunoreactive nerve cell bodies were found in the myenteric plexus of the gut and in the muscularis mucosae of the swimbladder. In the vagus nerve, non-immunoreactive nerve cells were surrounded by PACAP-immunoreactive fibres. Double staining revealed the coexistence of PACAP-like and helospectin-like peptides with VIP in all visualized nerve fibres and in some endocrine cells. It is concluded that PACAP-like and helospectin-like peptides coexist with VIP in nerves innervating the gut of two teleost species. The distribution suggests that both PACAP and helospectin, like VIP, are involved in the control of gut motility and secretion.

Vasodilator action of guinea pig vasoactive intestinal polypeptide (VIP): comparison with common mammalian VIP

The vascular activity of guinea pig (gp) and common mammalian (p) VIP were compared in anesthetized guinea pigs and dogs. In the guinea pig, intravenous injections of gpVIP and pVIP increased pancreatic blood flow and reduced the systemic arterial pressure and pancreatic vascular resistance in a dose-related manner. There were no significant differences in the vasodilator actions of these two VIPs, indicating that the overall cardiovascular actions of gpVIP and pVIP are similar in guinea pigs. In the dog, gpVIP, when given intra-arterially, was less potent (about 1/4) than pVIP in its action on femoral blood flow, suggesting that the blood vessels of the dog hind leg are more sensitive to its own VIP than to gpVIP. Oxidation of pVIP and gpVIP with H2O2 greatly reduced their vasodilator effects on the femoral arterial blood flow. The vascular effects were restored to control levels by reduction of the oxidized peptides with mercaptoethanol, which suggests that methionine residues of gpVIP and pVIP are important in the vasodilator effect on the femoral arterial bed in dogs.

VIP inhibits CCK-induced gallbladder contraction involving a beta-adrenoceptor mediated pathway in the rainbow trout, Oncorhynchus mykiss, in vivo

The effects of VIP on CCK-induced contractions of the gallbladder were studied in the rainbow trout, Oncorhynchus mykiss, in vivo. Gallbladder pressures were measured via a catheter inserted into the gallbladder, and drugs were injected through a catheter in the dorsal aorta. CCK-induced contractions of the gallbladder wall were reduced in a dose-dependent manner by VIP. The effect of VIP was inhibited by the beta-adrenergic antagonist sotalol, indicating an adrenergic link in the VIP inhibition of the CCK-induced contraction. It is suggested that activation of VIP nerves could facilitate postprandial filling/refilling of the gallbladder despite the increased plasma levels of CCK during this period.

Isolation and primary structure of VIP from sheep brain

The amino acid sequence of the vasoactive intestinal polypeptide (VIP) is well conserved between species. Thus, all mammalian VIPs isolated so far, except that of the guinea pig, have the same amino acid sequence. This study describes the isolation and primary structure of sheep brain VIP. The purification was followed with a bioassay and a VIP receptor assay. The amino acid sequence of the isolated sheep VIP is identical to that of the pig, human, ox, rat, rabbit, goat and dog VIP.