1. Department of Physiology and Pharmacology, Medical School, University of Nottingham, Nottingham, U.K.
2. U.S. Department of Agriculture, Human Nutrition Research Centre on Aging at Tufts University, Boston, Massachusetts, U.S.A.
3. Hebrew Rehabilitation Centre for Aged, Boston, Massachusetts, U.S.A.
4. Division on Aging, Harvard Medical School, Boston, Massachusetts, U.S.A.