Intravenous Catheter: Trained staff will place two intravenous catheters. Placement of the catheters will be in any arm veins deemed most suitable for ease of access. However, one will be placed in the antecubital fossa (infusion), and one in the antecubital, hand, or wrist vein (blood sample) of the opposite arm for each of the two study visits. The blood sampling IV catheter will be used to draw up to 15 mL blood samples at specific time points throughout each study visit to measure concentrations of glucose and insulin as well as for markers of inflammation and oxidative stress. All procedures are identical during each trial (placebo/L-NMMA/BQ123). The specific time points, which are approximate due to small variations in MRI scan times, are as follows: