Effect of DPP4 Inhibition on Vasoconstriction

Subjects will receive sitagliptin 100 mg daily for 7 days prior to one of the study days.

Subjects will receive a placebo capsule daily for 7 days prior to one of the study days.

During the study days, neuropeptide Y will be infused through an intra-arterial line. There will be four doses of neuropeptide Y used (0.1, 0.3, 1.0, and 3.0 nmol/min) and each dose will be infused for 10 minutes.

Ninety minutes after the last dose of neuropeptide Y, enalaprilat will be infused through the intra-arterial line at 0.33 µg/min/100mL of forearm volume. After 30 minutes, a second infusion of neuropeptide Y will begin. Similar to the previous neuropeptide infusion, four doses of neuropeptide Y will be used (0.1, 0.3, 1.0, and 3.0 nmol/min) and each dose will be infused for 10 minutes.

Valsartan 160 mg/d for 7 days prior to one of the study days.