DPP4 Inhibition & Beta Cell Function

Subjects will receive sitagliptin prior to the start of the experiment involving 1/2 of the subjects receiving Exendin-9 (a GLP-1 receptor blocker) first over 60 minutes ; followed by a bolus arginine (5g) infusion after 30 minutes into the Ex-9 infusion, with blood draws over the next 30 minutes. Followed by a 60 minute washout and the procedure is repeated , this time with saline instead of Ex-9 (these procedures are reversed - saline first then Ex-9 - half of the time).

Subjects will receive Placebo (instead of sitagliptin) prior to the start of the experiment involving 1/2 of the subjects receiving Exendin-9 (a GLP-1 receptor blocker) first over 60 minutes ; followed by a bolus arginine (5g) infusion after 30 minutes into the Ex-9 infusion, with blood draws over the next 30 minutes. Followed by a 60 minute washout and the procedure is repeated , this time with saline instead of Ex-9 (these procedures are reversed - saline first then Ex-9 - half of the time).