1. Laboratory of Molecular and Cellular Biology (N.J.S.), Bethesda, Maryland 20892
2. Molecular and Cellular Endocrinology Branch (F.B-D., M.C.S.), National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Bethesda, Maryland 20892
3. Department of Radiology (J.L.D.), Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892