Xenin 8

Stimulatory effect of xenin-8 on insulin and glucagon secretion in the perfused rat pancreas.[Pubmed:12873795]

Regul Pept. 2003 Aug 15;115(1):25-9.

Xenin is a 25-amino acid peptide of the neurotensin/xenopsin family identified in gastric mucosa as well as in a number of tissues, including the pancreas of various mammals. In healthy subjects, plasma xenin immunoreactivity increases after meals. Infusion of the synthetic peptide in dogs evokes a rise in plasma insulin and glucagon levels and stimulates exocrine pancreatic secretion. The latter effect has also been demonstrated for xenin-8, the C-terminal octapeptide of xenin. We have investigated the effect of xenin-8 on insulin, glucagon and somatostatin secretion in the perfused rat pancreas. Xenin-8 stimulated basal insulin secretion and potentiated the insulin response to glucose in a dose-dependent manner (EC(50)=0.16 nM; R(2)=0.9955). Arginine-induced insulin release was also augmented by xenin-8 (by 40%; p<0.05). Xenin-8 potentiated the glucagon responses to both arginine (by 60%; p<0.05) and carbachol (by 50%; p<0.05) and counteracted the inhibition of glucagon release induced by increasing the glucose concentration. No effect of xenin-8 on somatostatin output was observed. Our observations indicate that the reported increases in plasma insulin and glucagon levels induced by xenin represent a direct influence of this peptide on the pancreatic B and A cells.

Metabolism and potency of xenin and of its reduced hexapseudopeptide psi fragment in the dog.[Pubmed:14654163]

Life Sci. 2003 Dec 26;74(6):697-707.

Xenin is a 25 amino acid peptide hormone, secreted into the circulation by specific endocrine cells in the duodenal mucosa. Plasma concentrations are elevated after sham feeding and feeding. In the present study the metabolism of xenin and of a C-terminal fragment was investigated. Xenin, its C-terminal hexapeptide, and a pseudopeptide analog psi (CH2NH) hexapeptide in which a psi reduced bond is introduced in the biologically important dibasic motif of the C-terminus were infused or injected intravenously in 14 anaesthetized dogs. Plasma disappearance time, metabolic clearance rate, the generation of metabolites, and biological effects on exocrine pancreatic secretion were determined employing radioimmunoassay, high pressure liquid chromatography, mass spectrometry (MALDI-MS), and sequence analysis. Half time after steady state infusion of xenin was 3.1 min(-1), that of psi xenin 6 was 6.2(-1) (p<0.01) Plasma concentrations of psi xenin 6 were significantly elevated (p<0.01), pancreatic secretion of volume was augmented by a factor of 50, and output of protein by a factor of 30 compared to unmodified xenin 6. MALDI-MS and sequencing after infusion of xenin revealed a C-terminal octapeptide fragment as primary metabolite. Introduction of a reduced pseudobond in the dibasic motif of xenin dramatically enhances biological potency. This indicates that such a reduced pseudopeptide may be useful in the treatment of bowel paralysis.

Xenopsin-related peptide generated in avian gastric extracts.[Pubmed:2460902]

Regul Pept. 1988 Sep;22(4):303-14.

Two avian counterparts to amphibian xenopsin have been identified as H-Phe-His-Pro-Lys-Arg-Pro-Trp-Ile-Leu-OH (XP-2) and its partial sequence H-His-Pro-Lys-Arg-Pro-Trp-Ile-Leu-OH (XP-1) isolated from extracts of turkey proventriculus and skin. Both peptides were shown to be present within these and other tissues primarily (99%) in precursor form(s), from which they were liberated by the action of endogenous enzyme(s) during extraction. Synthetic and native preparations of XP-2 increased vascular permeability in rats and released histamine from isolated rat mast cells at submicromolar concentrations. The ubiquitous distribution of this XP-related sequence and its pharmacologic capabilities suggest potential roles in the general regulation of tissue blood flow and fluid exchange.