The effects of amino acids to stimulate synthesis and attenuate
degradation of skeletal muscle proteins in man.
Svanberg, E., A-C M[diaeresis]oller-Loswick, D. E. Matthews, U.
K[diaeresis]orner, M. Andersson & K. Lundholm.
Departments of Surgery & Anaesthesiology, Sahlgrenska University
Hospital, University of G[diaeresis]oteborg, G[diaeresis]oteborg,
Sweden and Departments of Medicine & Surgery, Cornell University
Medical College, New York, NY
APStracts 3:0123E, 1996.
Synthesis and degradation of globular and myofibrillar proteins across
arm and leg muscles were examined during stepwise increased iv.
infusion of amino acids (0.1, 0.2, 0.4 & 0.8 g N/kg/day) to
healthy volunteers. Protein dynamics were measured by a primed
constant infusion of L-[ring-2H5]phenylalanine and the release of 3
-methylhistidine from skeletal muscles. Arterial concentrations and
flux of glucose, lactate and free fatty acids were unchanged despite
increasing concentrations of plasma amino acids from 2.6 to 5.8 mM.
Plasma insulin, IGF-I and plasma concentrations of IGF-I binding
proteins-1 and 3 remained at fasting levels throughout the
investigation. Amino acid infusion caused a significant uptake of the
majority of amino acids across arm and leg tissues, except tyrosine,
tryptophan and cysteine, probably due to low concentrations of these
amino acids in the formulation. The balance of globular proteins
improved significantly (p<0.01) due to stimulation of synthesis
and attenuation of degradation across arm and leg tissues, despite
insignificant uptake of tyrosine, tryptophan and cysteine.
Degradation of myofibrillar proteins was uninfluenced by provision of
amino acids. The results demonstrate that neither insulin nor
circulating IGF-I explained improved protein balance in skeletal
muscles following elevation of plasma amino acids. Rather, some amino
acids in themselves trigger cellular reactions that initiate peptide
formation. Limited availability of some extracellular amino acids was
overcome by increased reutilization of the intracellular amino acid.
Received 29 January 1996; accepted in final form 4 June 1996.
APS Manuscript Number E52-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96