The glucoincretin hormone glucagon-like peptide-1 (GLP-1) augments glucose-stimulated insulin secretion and is in use as an effective treatment for diabetes. However, after its secretion from the intestine, the insulinotropic GLP-1 (7-36) amide hormone is rapidly inactivated by enzymatic cleavage by the diaminopeptidyl peptidase-4 giving rise to GLP-1 (9-36) amide. Inasmuch as most of the circulating GLP-1 is in the form of the metabolite GLP-1 (9-36) amide it has been suggested that it has insulin-like actions on peripheral insulin-sensitive tissues. In earlier studies, infusions of GLP-1 (9-36) amide in obese insulin-resistant subjects showed a marked suppression of hepatic glucose production. However, it remained uncertain whether the effects on glucose production were due to direct effects on hepatocytes, involved central or portal vein-mediated actions, or were mediated by insulin secretion. Here we show that GLP-1 (9-36) amide directly suppresses glucose production in isolated mouse hepatocytes ex vivo independent of the GLP-1 receptor. These findings support direct insulinomimetic actions of the GLP-1 metabolite on gluconeogenesis in hepatocytes that are independent of insulin action and the GLP-1 receptor, and suggest that GLP-1 (9-36) amide-based peptides might present a novel therapy for the treatment of excessive hepatic glucose production in individuals with insulin-resistant diabetes.
Copyright Georg Thieme Verlag KG Stuttgart New York.