Glucagon-like peptide-1 (GLP-1) is a novel insulinotropic peptide which is rapidly degraded by the enzyme dipeptidyl peptidase-4 (DPP-4). In addition to its attractive merit in type 2 diabetes, interest in the cardioprotective effects of GLP-1 has been increased with various reports and evidence. Previously, the investigators could show exenatide, GLP-1 receptor agonist protects ischemic/reperfusion injury-induced endothelial dysfunction through opening of KATP (ATP-sensitive potassium) channels in human ischemic/reperfusion injury model. But, recent clinical studies showed 2 different DPP-4 inhibitors, alogliptin and saxagliptin, did not decrease major adverse cardiovascular events even though improving glycemic control. The investigators will investigate the role of sitagliptin in human ischemic/reperfusion (IR) injury model of forearm conductance vessels as previous described method.