Isolation of a novel 38 residue-hypothalamic polypeptide which stimulates adenylate cyclase in pituitary cells

Publisher Summary This chapter discusses prostaglandins and thromboxanes. The prostaglandins are C 20 acids formed from polyunsaturated fatty acids by oxygenation and cyclization. The thromboxanes, which were originally found in platelets, have now been identified in a variety of tissues. Rapid progress is being made in understanding their biological roles. Earlier studies on vascular and airway smooth muscle demonstrated that endoperoxides had unique effects that could not be attributed to conversion into the stable prostaglandins. Because aspirin, an inhibitor of endoperoxide formation, inhibits the second wave of aggregation, it was suggested that the endoperoxides play a role in the release reaction. The potency of the endoperoxides in causing contractions of the isolated rabbit aorta was of particular interest. However, the occurrence of thromboxanes is not limited to platelets. The transformation of arachidonic acid into thromboxane B 2 has also been observed in lung tissue, spleen, kidney, leukocytes, umbilical artery, and brain.

Prostaglandins and thromboxanes.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally alpha-amidated peptide that was first isolated 20 years ago from an ovine hypothalamic extract on the basis of its ability to stimulate cAMP formation in anterior pituitary cells (Miyata et al., 1989. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-secretin-growth hormone-releasing hormone-glucagon superfamily. The sequence of PACAP has been remarkably well conserved during evolution from protochordates to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide, the activity of which remains unknown. Two types of PACAP binding sites have been characterized: type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP, whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes: the PACAP-specific PAC1-R, which is coupled to several transduction systems, and the PACAP/VIP-indifferent VPAC1-R and VPAC2-R, which are primarily coupled to adenylyl cyclase. PAC1-Rs are particularly abundant in the brain, the pituitary and the adrenal gland, whereas VPAC receptors are expressed mainly in lung, liver, and testis. The development of transgenic animal models and specific PACAP receptor ligands has strongly contributed to deciphering the various actions of PACAP. Consistent with the wide distribution of PACAP and its receptors, the peptide has now been shown to exert a large array of pharmacological effects and biological functions. The present report reviews the current knowledge concerning the pleiotropic actions of PACAP and discusses its possible use for future therapeutic applications.

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

Distribution of peptide- and catecholamine-containing neurons in the gastro-intestinal tract of rat and guinea-pig: immunohistochemical studies with antisera to substance P, vasoactive intestinal polypeptide, enkephalins, somatostatin, gastrin/cholecystokinin, neurotensin and dopamine beta-hydroxylase.

Insulin secretion is controlled by a complex set of factors that include not only glucose but amino acids, catecholamines, and intestinal hormones. We report that a novel glucagon-like peptide, co-encoded with glucagon in the glucagon gene is a potent insulinotropic factor. The glucagon gene encodes a proglucagon that contains in its sequence glucagon and additional glucagon-like peptides (GLPs). These GLPs are liberated from proglucagon in both the pancreas and intestines. GLP-I exists in at least two forms: 37 amino acids GLP-I(1-37), and 31 amino acids, GLP-I(7-37). We studied the effects of synthetic GLP-Is on insulin secretion in the isolated perfused rat pancreas. In the presence of 6.6 mM glucose, GLP-I(7-37) is a potent stimulator of insulin secretion at concentrations as low as 5 X 10(-11) M (3- to 10-fold increases over basal). GLP-I(1-37) had no effect on insulin secretion even at concentrations as high as 5 X 10(-7) M. The earlier demonstration of specific liberation of GLP-I(7-37) in the intestine and pancreas, and the magnitude of the insulinotropic effect at such low concentrations, suggest that GLP-I(7-37) participates in the physiological regulation of insulin secretion.

/pdf/insulinotropin-glucagon-like-peptide-i-7-37-co-encoded-in-32lldpwvng.pdf

Insulinotropin: glucagon-like peptide I (7-37) co-encoded in the glucagon gene is a potent stimulator of insulin release in the perfused rat pancreas.

Vasoactive intestinal polypeptide immunoreactivity is present in high concentrations in clonal lines of neuronal and glial origin. The central nervous system and sympathetic ganglia are also rich in the peptide. The findings suggest that this peptide, hitherto thought limited to the gastrointestinal tract, is widely distributed in neural tissue and may have broad physiological significance.

https://science.sciencemag.org/content/sci/192/4242/907.full.pdf

Vasoactive intestinal polypeptide: abundant immunoreactivity in neural cell lines and normal nervous tissue.

The amino acid sequence of the porcine vasoactive intestinal octacosapeptide is His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Thr-Arg-Leu-Arg-Lys-Gln-Met-Ala-Val-L ys-Lys-Tyr-Leu-Asn-Ser-Ile-Leu-Asn-NH2. Its amino acid residues 1, 2, 6 and 7, counted from the N-terminus, are identical to those in the corresponding positions in both porcine glucagon and secretin. The residues in positions 3, 12, 13, 14 and 23 are identical to those in secretin, but not in glucagon, and position 10 is occupied by a tyrosyl and position 28 by an asparaginyl residue, like in glucagon but not in secretin. If in addition to identical amino acid residues also chemically similar residues, such as isoleucine in position 26 of the octacosapeptide, as compared to leucine in secretin and glucagon, are taken into consideration then the similarity between these three polypeptides is still more evident.



At a more remote level there is some structural resemblance also between these peptides and the other four peptides from the intestinal wall, cholecystokinin-pancreozymin, motilin, the gastric inhibitory peptide and substance P, the structures of which are known.



The elucidation of the structure of the octacosapeptide was facilitated by the finding that pancreatic kallikrein preferentially cleaved only one of the three bonds in its N-terminal cyanogen bromide heptadecapeptide that are susceptible to cleavage with trypsin.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1974.tb03373.x

Structure of the porcine vasoactive intestinal octacosapeptide. The amino-acid sequence. Use of kallikrein in its determination.

A L-His-L-Ser-L-Asp-L-Ala-L-Val-L-Phe-L-Thr-L-Asp-L-Asn-L-Tyr-L-Thr-L-Ar g-L-Leu-L-Arg-L-Lys-L-Gln-L-Met-L-Ala-L-Val-L-Lys-L-Lys-L-Tyr-L-Leu-L- Asn-L-Ser-L-Ile-L-Leu-L-Asn-NH2 biological actions including systemic vasodilation, hypotension, increased cardiac output, respiratory stimulation, and hyperglycemia, was isolated from intestines of animals such as a hog. The isolation procedure for purification includes two steps of ion-exchange chromatography, gel chromatography and countercurrent distribution separation.

Vasoactive intestinal peptide

The actions of the vasoactive intestinal polypeptide make it a potential candidate for mediating certain manifestations of the watery-diarrhea syndrome. Peptide levels were measured by radioimmunoassay in 25 controls and 30 patients with chronic watery diarrhea. Plasma levels were too low to measure ( < 200 pg per milliliter) in 22 of the controls, averaging 79 ± 64 pg per milliliter (S.D.). Levels were elevated in 26 of 28 plasma samples (5.1 ± 2.5 ng per milliliter), and ineach of 13 tissue extracts (5.1 ± 10.9 μg per gram); in all, 28 patients had elevated levels in plasma or tissue or both. Thirteen patients had pancreatic islet-cell adenoma, four islet-cell hyperplasia, five bronchogenic carcinoma, and one each pheochromocytoma and ganglioneuroblastoma.The findings indicate that the peptide is a probable mediator of the watery-diarrhea syndrome, that the syndrome may result from a variety of non-pancreatic tumors, and that this or a related peptide may also be secreted by these tumors. (N En...

Elevated plasma and tissue levels of vasoactive intestinal polypeptide in the watery-diarrhea syndrome due to pancreatic, bronchogenic and other tumors.

The vasoactive intestinal polypeptide was present in synaptosomal (nerve ending) preparations from cerebral cortex, hypothalamus, and striatum of rat brain in higher concentrations than in these tissues as a whole. The total content and relative specific activity of the peptide increased with progressive purification of the synaptosomal fractions and generally followed the distribution of known synaptosomal constituents--dopamine, norepinephrine, and lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27). The peptide was also released from synaptosomal pellets with increased K+ concentration, and this release was Ca2+-dependent. The findings suggest a role for vasoactive intestinal polypeptide as a transmitter or modulator of synaptic function.

https://www.pnas.org/content/pnas/74/8/3424.full.pdf

Sami I. Said

Papers

Vasoactive intestinal polypeptide: abundant immunoreactivity in neural cell lines and normal nervous tissue.

Structure of the porcine vasoactive intestinal octacosapeptide. The amino-acid sequence. Use of kallikrein in its determination.

Vasoactive intestinal peptide

Elevated plasma and tissue levels of vasoactive intestinal polypeptide in the watery-diarrhea syndrome due to pancreatic, bronchogenic and other tumors.

Vasoactive intestinal polypeptide in brain: localization in and release from isolated nerve terminals