The effect of serotonin (5-HT) on insulin secretion.

The present study was aimed at observing the effect on insulin secretion of serotonin (5-HT) administered intraportally to anesthetized adult dogs. The influence of 5-HT on insulin release was also studied in mouse pancreatic islets isolated by a collagenase method. In the 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 three consecutive 10 min periods after serotonin administration. With 3 mg of 5-HT the IRI increases were not observed. When serotonin was slowly infused at doses of 3 and 6 mg, no increases of IRI were recorded. In the in vitro studies, 5-HT at 100 mug/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 mug/ml) than that obtained with glucose alone at the same concentration (3.0 mug/ml). The results obtained suggest that serotonin stimulates insulin release under certain conditions in the intact dog and also in the isolated pancreatic islets of the mouse incubated in vitro.