1. From the Medical Care Line (S.H.S., R.E.R.), Michael E. DeBakey VA Medical Center, Houston, Tex; the Departments of Pediatrics (K.N.P., R.V.B., A.R.B., R.E.R.) and Medicine (S.H.S., J.-F.D., A.R.B., R.E.R.), Baylor College of Medicine, Houston, Tex; and the Department of Physiology (C.A.M.), University of Kentucky, Lexington.