Generation of xenopsin-related peptides during acid extraction of gastric tissues.

Biologically active xenopsin-related peptide(s) were shown by radioimmunoassay to be liberated in nearly micromolar concentrations from substrate(s) with Mr greater than 70,000 during acid extraction of mammalian and avian stomach. The reaction displayed an enzyme-like temperature sensitivity, had a pH optimum of 2, and was fully inhibited in the presence of pepstatin A. Treatment of a stabilized gastric substrate with hog pepsin was found to mimic the reaction, producing immunoreactive xenopsin(s) which behaved similarly during high pressure liquid chromatography. Although some of the generated immunoreactivity co-chromatographed with xenopsin, it differed immunochemically when examined with a battery of region-specific antisera. Highly purified rat gastric immunoreactive xenopsin displayed xenopsin-like biologic effects, producing hypotension in the anesthetized rat and contracting the isolated guinea pig ileum. These findings suggest that there may be a renin/angiotensin-like system for the generation of xenopsin-related peptides in the stomach.