1. From the Laboratory of Cardiovascular Science (T.M.V., A.E.L., W.Z., A.M.R., S.S., D.Y., Y.-Y.Z., R.-P.X., H.C., M.D.S., V.A.M., E.G.L.), Gerontology Research Center, National Institute on Aging, NIH, Baltimore, Md; and the Department of Integrative Physiology and The Cardiovascular Research Institute (S.D., M.B., S.J., J.L.C.), University of North Texas Health Science Center, Fort Worth. Current address for Y.-Y.Z.: Schering-Plough Research Institute, Lafayette, NJ.