1. From the Division of Clinical Pharmacology (A.G., A.D., C.S., S.Y.P., G.F., I.B.), Department of Medicine (A.G., R.A., A.D., C.S., S.Y.P., G.F., I.B.) and Pharmacology (I.B.), and the Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Nashville, Tenn.