STIMULATION OF (PRO-)INSULIN BIOSYNTHESIS AND RELEASE BY GASTRIC INHIBITORY POLYPEPTIDE IN ISOLATED ISLETS OF RAT PANCREAS

Abstract

(Pro-)-Insulin biosynthesis [3H]L incorporation) and insulin secretion were studied in collagenase-isolated rat islets incubated for 3 h at 1 and 2 mg/ml glucose in the presence of gastric inhibitory polypeptide (GIP). GIP augmented [3H]Leu incorporation and release of insulin at both glucose concentrations. In a 2nd series of experiments, an amino acid mixture had no influence on the insulotrophic action of GIP. Combined stimulation of insulin release by GIP and glucagon did not result in higher insulin output than observed in the presence of each substance alone. GIP, in contrast to many other gastrointestinal peptides however similar to glucagon, enhances not only release but also biosynthesis of insulin. This insulinotrophic action can be observed already at a glucose concentration of 1 mg/ml. The results underline the outstanding role which GIP appears to play in the regulation of .beta.-cell function.