 1. That L-arginine administered orally prior to sleep will prevent the early morning decline in plasma levels of L-arginine and nitric oxide; 2. That L-arginine administered prior to sleep will attenuate or prevent the early morning decline in endothelial function; and 3. That the effects of L-arginine, taken prior to sleep, on plasma levels of L-arginine and nitric oxide and on endothelial function will be more marked with 15 grams of L-arginine versus 5 grams of L-arginine or placebo, indicative of a dose response effect. 