Acute but not chronic activation of brain glucagon-like peptide-1 receptors enhances glucose-stimulated insulin secretion in mice.

ABSTRACT

AIM: To investigate the role of brain glucagon-like peptide-1 (GLP-1) in pancreatic ß-cell function. METHODS: To determine the role of brain GLP-1 receptor (GLP-1R) on ß-cell function, we administered intracerebroventricular (i.c.v.) infusions of GLP-1 or the specific GLP-1 antagonist exendin-9 (Ex-9), in both an acute and a chronic setting. RESULTS: We observed that acute i.c.v. GLP-1 infusion potentiates glucose-stimulated insulin secretion (GSIS) and improves glucose tolerance, whereas central GLP-1R blockade with Ex-9 impaired glucose excursion after a glucose load. Sustained activation of central nervous system GLP-1R, however, did not produce any effect on either GSIS or glucose tolerance. Similarly, ex vivo GSIS performed in islets from mice chronically infused with i.c.v. GLP-1 resulted in no differences compared with controls. In addition, in mice fed a high-fat diet we observed that acute i.c.v. GLP-1 infusion improved glucose tolerance without changes in GSIS, while chronic GLP-1R activation had no effect on glucose homeostasis. CONCLUSIONS: Our results indicate that, under non-clamped conditions, brain GLP-1 plays a functional neuroendocrine role in the acute regulation of glucose homeostasis in both lean and obese rodents.