Physiological Reviews EDITORIAL BOARD H. E. Morgan, Editor R. C. Rose, Associate Editor Department of Physiology, Pennsylvania State University, Hershey, Pennsylvania 17033 D. V. Bates F. S. Grodins J. G. Nicholls Allen M. Scher D. Tosteson E. Windhager FROM Corresponding M. E. Holman (Australia & New Zealand) Setsuro Ebashi (Japan) Gerhard Malnic (Latin America) AMERICAN SOCIETY OF BIOLOGICAL CHEMISTS European Joseph Larner D. F. Steiner FROM SOCIETY OF PHYSIOLOGISTS AMERICAN INSTITUTE OF A. E. Harper BIOPHYSICAL SOCIETY G. Eisenman FROM SOCIETY FOR NEUROSCIENCE C. D. Woody PUBLICATIONS COMMITTEE, A. P. Fishman, Committee Ivan Assenmacher (France) Jean Crabb6 (Belgium) Christian Crone (Denmark) Hans Lindner (Israel) Stefan Mellander (Sweden) Klaus Thurau (Germany) D. R. Wilkie (England) NUTRITION FROM Editorial D. S. Parsons, Committee Chairman Department of Biochemistry University of Oxford South Parks Road Oxford, England 0x1 3QU GENERAL J. W. Hastings P. H. von Hippel FROM Members AMERICAN Chairman Stephen R. Geiger, Publications W. A. Sonnenberg, Business Manager PHYSIOLOGICAL Paul Horowitz SOCIETY F. E. Yates Manager and Executive Laurie S. Chambers, Editor Copy Editor PHYSIOLOGICAL REVIEWS is published quarterly in January, April, July, and October by The American Physiological Society. Subscription Price: $30.00 per year postpaid in the United States; $32.00 in Canada; $33.00 in all other countries. Subscriptions from outside the United States are payable in U.S. currency or full equivalent. Subscriptions are accepted on a calendar-year basis only. Single Copies and Back Issues: When available, $9.00 each postpaid. Change of Address: The Journal must be advised of a change of address at least six weeks prior to date of issue, with the subscriber’s old and new address given. Undelivered copies resulting from an address change will not be replaced. Second-class Physiological postage Society. paid at Washington, All rights reserved. D.C., and at additional mailing offkes. Printed in the United States of America. Subscriptions and orders should be sent to: PHYSIOLOGICAL REVIEWS, 9650 Rockville Pike, Bethesda, Copyright 1976 by The Maryland 20014 American