1. From the Divisions of Clinical Pharmacology (J.M.L., J.V.G., L.J.M., J.D.M., N.J.B.), Nephrology and Hypertension (J.M.L.), and Cardiovascular Medicine (D.E.V.), the Departments of Medicine and Pharmacology, and the Department of Biostatistics (C.Y.), Vanderbilt University Medical Center; Nashville, Tenn; and the Veterans Affairs Medical Center (D.E.V.), Nashville, Tenn.