REGULATION OF GLUCAGON-LIKE POLYPEPTIDE-1 FROM THE ISOLATED-PERFUSED CANINE ILEUM BY CIRCULATING GLUCOSE AND INSULIN

Glucagon-like peptide-1 (GLP-1) is one of incretin hormones which are released from the gut and stimulates insulin secretion. GLP-1 secretio n is stimulated by the ingestion of various nutrients such as glucose, fat and mixed meal, and by the administration of various gut peptides including bombesin, enkephalin and gastric inhibitory polypeptide (GI P). However, feedback control, found in the secretion of GIP, of GLP-1 has not been well understood. In this experiment, using the isolated perfused canine ileum, we studied whether circulating insulin or gluco se modulates the release of GLP-1 induced by the intra-luminal adminis tration of glucose. The release of GLP-1 from the ileum increased by i ntra-luminal 278 mM (5%) glucose alone. This increase was reduced duri ng the intra-arterial infusion of 15 mM glucose, although intra-arteri al glucose alone slightly increased GLP-1 release. Intra-luminal gluco se-induced GLP-1 secretion also appeared to be suppressed by intraarte rial 2 nM insulin infusion. Therefore, intra-luminal glucose-induced G LP-1 secretion could be controlled by circulating glucose and insulin.