Chronic Exposure to GLP-1R Agonists Promotes Homologous GLP-1 Receptor Desensitization In Vitro but Does Not Attenuate GLP-1R–Dependent Glucose

Glucagon-like peptide-1 (GLP-1) stimulates glucose-de-pendent insulin secretion and inhibits food intake, gas-tric emptying, and glucagon secretion, actions that promote reduction of fasting and postprandial glycemia in subjects with type 2 diabetes. The rapid degradation of native GLP-1 has engendered interest in more stable longer-acting GLP-1 receptor agonists such as exendin-4 (Ex-4); however, the potential consequences of sus-tained GLP-1 receptor activation leading to receptor desensitization has not been extensively studied. We have now examined a range of GLP-1 receptor–depen-dent responses following treatment with Ex-4 using INS-1 cells in vitro and both wild-type control and MT–Ex-4 transgenic mice in vivo. Although both GLP-1 and Ex-4 acutely desensitized GLP-1 receptor–depen