glucagon-like-peptide-1-(7-36) and gallocatechol

Glucagon-like peptide 1 (GLP-1), secreted from intestinal L cells, glucose dependently stimulates insulin secretion from β-cells. This glucose dependence prevents hypoglycemia, rendering GLP-1 analogs a useful and safe treatment modality in type 2 diabetes. Although the amino acid glutamine is a potent elicitor of GLP-1 secretion, the responsible mechanism remains unclear. We investigated how GLP-1 secretion is metabolically coupled in L cells (GLUTag) and in vivo in mice using the insulin-secreting cell line INS-1 832/13 as reference. A membrane-permeable glutamate analog (dimethylglutamate [DMG]), acting downstream of electrogenic transporters, elicited similar alterations in metabolism as glutamine in both cell lines. Both DMG and glutamine alone elicited GLP-1 secretion in GLUTag cells and in vivo, whereas activation of glutamate dehydrogenase (GDH) was required to stimulate insulin secretion from INS-1 832/13 cells. Pharmacological inhibition in vivo of GDH blocked secretion of GLP-1 in response to DMG. In conclusion, our results suggest that nonelectrogenic nutrient uptake and metabolism play an important role in L cell stimulus-secretion coupling. Metabolism of glutamine and related analogs by GDH in the L cell may explain why GLP-1 secretion, but not that of insulin, is activated by these secretagogues in vivo.

Topics: Administration, Rectal; Animals; Catechin; Cell Line; Enteroendocrine Cells; Enzyme Activation; Enzyme Inhibitors; Enzyme-Linked Immunosorbent Assay; Female; Glucagon-Like Peptide 1; Glucose; Glutamate Dehydrogenase; Glutamates; Glutamine; Insulin; Insulin Secretion; Insulin-Secreting Cells; Mice, Inbred C57BL; Mitochondria; Models, Biological; Peptide Fragments; Rats; Single-Cell Analysis