The Effect of Dipeptidyl Peptidase-4 Inhibition on GLP-1 Induced Insulin Secretion and Glucose Turnover During Mild Stable Hyperglycemia in Young and Old Normal Volunteers

The purpose of the present proposal is to 1) examine the role of dipeptidyl peptidase (DPP-4) inhibition on insulin release during a hyperglycemic clamp while GLP-1 is being infused and, 2) further elucidate the role of the metabolite of GLP-1, that is GLP-1 9-36 amide (GLP-1m). During stable and very reproducible elevated plasma glucose levels the effect of increased active incretin levels with DPP-4 inhibitors should result in increased plasma insulin levels. Therefore the aim of this protocol is to document whether plasma insulin levels are increased following GLP-1 infusion in the presence or absence of DPP-4 inhibitors. Additionally, the investigators have shown that some improvement in glucose homeostasis during GLP-1 administration is due in part to the metabolite of GLP-1, i.e. GLP-1 (9-36) amide (GLP-1m). Therefore, the investigators will also test the role of the latter by infusing GLP-1m when the volunteers are being treated with DPP-4 inhibitors.