EFFECT OF SEROTONIN (5-HT) ON INSULIN-SECRETION

Abstract

The effect on insulin secretion of serotonin (5-HT) administered intraportally to anesthetized adult dogs was studied. The influence of 5-HT on insulin release was also studied in mouse pancreatic islets isolated by a collagenase method. In in vivo studies, 6 mg of 5-HT rapidly injected in the portal vein of dogs induced hypoglycemia and a significant increase of immunoreactive insulin plasma levels (IRI) in blood samples taken from the pancreatoduodenal vein. The phenomenon was registered throughout 3 consecutive 10 min periods after serotonin administration. With 3 mg of 5-HT, IRI increases were not observed. When serotonin was slowly infused at doses of 3 and 6 mg, no increases of IRI were recorded. In in vitro studies, 5-HT at 100 .mu.g/ml stimulated the output of insulin in the presence of a low concentration of glucose (0.6 mg/ml); when the islets were incubated with glucose at a higher concentration (3.0 mg/ml) there was a lower insulin release in the presence of serotonin (100 .mu.g/ml) than that obtained with glucose alone at the same concentration (3.0 mg/ml). Serotonin probably stimulates insulin release under certain conditions in the intact dog and in the isolated pancreatic islets of the mouse incubated in vitro.