EflFects of the Gastric Inhibitory Polypeptide Present in Impure Pancreozymin-Cholecystokinin on Plasma Insulin and Glucagon in the Rat

Plasma insulin (IRI) and glucagon (IRG) responses to intravenous infusions of porcine duodenojejunal mucosal extracts containing identified intestinal hormones in various degrees of purity were examined in the urethane anesthetized rat. The pancreozymin-cholecystokinin (PZ-CCK) content of an intestinal extract containing 10% by weight of PZ-CCK (10% PZ-CCK) did not account for the effects of the preparation on the endocrine pancreas. While the infusion of 10% PZ-CCK greatly increased both fasting and glucose-stimulated elevations of plasma IRI and significantly increased plasma IRG, highly purified PZ-CCK increased plasma IRI only modestly, and had no effect on plasma IRG. Gastric inhibitory polypeptide, a derivative of 10% PZ-CCK, was found to be capable of reproducing to a large extent the effects of 10% PZ-CCK on plasma IRI and IRG. The present study shows that in the rat gastric inhibitory polypeptide is a potent insulinotropic agent, also capable of increasing plasma glucagon, and suggests that this peptide accounts for effects on the endocrine pancreas previously attributed to PZ-CCK (Endocrinology94: 1139, 1974)