Both healthy control subjects and patients with type 2 diabetes are subjected to 4 experimental days (in a randomized order) with continuous infusion of GLP-1 and pre-treatment with 25 mg sitagliptin, 100 mg sitagliptin, 200 mg sitagliptin and placebo, respectively. Afterwards, we are going to measure the whole-body DPP-4 activity by comparing plasma levels of active (intact) GLP-1 and total GLP-1, and relate to plasma DPP-4 activity.