Xenopsin-related peptide generated in avian gastric extracts.

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.