 Vascular Studies. Subjects will be asked to return to the Clinical Research Unit one week after the euglycemic insulin clamp for vascular studies Visit 4. Change in forearm blood flow following brachial artery infusion of acetylcholine endothelial NO-dependent and sodium nitroprusside endothelial-independent will be used to assess the arterial vasodilatory response to physiological stimuli. All test substances will be infused into the non-dominant arm. After local skin anesthesia with lidocaine, a 20-gauge needle attached to an arterial line Arrow International, Erding, Germany will be used to cannulate the brachial artery. A pressurized 0.9 saline solution bag will be connected to the arterial line, and a constant drip will be started at t -60 min to keep the arterial line patent throughout the study. Subjects will then be allowed to rest for 60 minutes. At time t -5 min, five consecutive measurements of forearm blood flow will be performed using a mercury strain gauge plethysmography Hokanson Plethysmograph, Model EC4, Hokanson, Bellevue, WA, combined with a rapid cuff inflator. Test substances will be infused according to a variation of the original design of Bergholm et al, as follows. After completion of baseline measurements, an intra-brachial infusion of sodium nitroprusside at 3 microgmin will be started and continued for 12 minutes the last 6 minutes are used to establish the local vascular effect of sodium nitroprusside. At time t 12 min, the infusion rate of sodium nitroprusside is increased to 10 microgmin and the infusion continued for an additional 6 minutes. At time t 18 min, the sodium nitroprusside infusion is stopped and 2 ml of blood is withdrawn to clear the arterial line. Saline is then infused for 30 minutes and at time t 48 min, an intra-brachial infusion of acetylcholine at a constant rate of 15 microgmin is started and continued for 8 minutes the last 6 minutes are used to establish the local vascular effect of acetylcholine. At time t 54 min, the infusion rate of acetylcholine is doubled to 30 microgmin and the infusion continued for and additional 6 minutes. Forearm blood flow is measured five consecutive times during the last 3 minutes of each intra-brachial infusion period, i.e., at time t 9-12 min and t 15-18 min, respectively during the low and high nitroprusside dose, and at time t 51-54 min and t 57-60 min, respectively during the low and high acetylcholine dose. At time t 60 min, the acetylcholine infusion is stopped and the study terminated. At the end of the experiment the arterial line is removed and compression to the area applied for 10 minutes. The radial pulse is verified every 5 minutes during the 30-min period after the experiment is terminated, before subjects are allowed to leave. Subjects will be contacted within 24 hrs and 1week after completion of the study to ascertain that there have been no complications. 