The researchers plan to enroll a total of 15 non-obese (BMI < 27 kg/m2) otherwise healthy adults into a randomized, double-blinded, cross-over study of the impact of recombinant methionyl human leptin 0.2 mg/kg SC, hereafter called rL, (Amgen Inc, Thousand Oaks, Calif) versus placebo SC (sorbitol and sodium acetate, pH 4.0 of same volume) in 15 non-obese adults. Subjects will have baseline vascular studies performed by brachial artery ultrasonography-flow-mediated dilatation and nitroglycerin mediated dilatation and blood drawn for measures of leptin levels. They will then receive rL SC or placebo SC (randomized order). They will then have vascular studies performed and blood levels drawn every 2 hours for 6 hours total. After completion of day 1, patients will return 1-4 weeks later and repeat the protocol crossed-over to the alternate intervention (rL or placebo).