Studies with Cholecystokinin. II. Cholecystokinetic Potency of Porcine Gastrins I and II and Related Peptides in Three Systems

Abstract

A sulfated tyrosine residue seems to be an essential structural feature of a number of peptides possessing cholecystokinetic activity. The unsulfated forms of porcine gastrin and cerulein, a decapeptide isolated from frog skin, possessed weaker cholecystokinetic activities than their sulfated counterparts on the isolated rabbit gallbladder, the isolated guinea pig gallbladder, and the exposed guinea pig gallbladder in situ. The hypothesis is presented that, physiologically, gastrin II (the sulfated form) may act as a cholecystokinetic hormone since it a) possesses the required structural specificity and b) was cholecystokinetic at physiological levels. Since gastrin I is equipotent with gastrin II in stimulating acid secretion by the stomach while hypopotent in cholecystokinetic potency, it may be a metabolic precursor of gastrin II or an artifact produced by the desulfation of gastrin II during the extraction and purification of the latter. (Endocrinology84: 1277, 1969)