Understanding the incretin pathway has led to significant advancements in the treatment of type 2 diabetes (T2D). Still, the exact mechanisms are not fully understood. In a randomized, placebo-controlled, 4-period, crossover study in 24 patients with T2D dipeptidyl peptidase-4 (DPP-4) inhibition and its glucose lowering actions were tested after an oral glucose tolerance test (OGT). The contribution of GLP-1 was examined by infusion of the GLP-1 receptor (GLP-1r) antagonist exendin-9. DPP-4 inhibition reduced glycemia and enhanced insulin levels and the incretin effect. Glucagon was suppressed and gastric emptying (GE) was decelerated. Exendin-9 increased glucose levels and glucagon secretion. It attenuated insulinemia and the incretin effect. It accelerated GE. Under the GLP-1r antagonist the glucose-lowering effects of DPP-4 inhibition were reduced by about 50%. However, a significant effect on insulin secretion remained during GLP-1r blockade, while the inhibitory effects of DPP-4 inhibition on glucagon and GE were abolished. So in this cohort of diabetic patients with a substantial incretin effect, GLP-1 contributed about 50% to the insulin excursion after an OGT both with and without DPP-4 inhibition. Thus, a significant DPP-4 sensitive glucose lowering mechanism contributes to glycemic control in diabetic patients that may be not mediated by circulating GLP-1.
- Received September 20, 2013.
- Accepted November 22, 2013.
- © 2013 by the American Diabetes Association.
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