A model of skeletal muscle leucine kinetics measured across the
human forearm.
Tessari, Paolo, Sandro Inchiostro, Michela Zanetti, Rocco Barazzoni.
Department of Metabolism, University of Padova, Italy
APStracts 2:0049E, 1995.
We propose a new six-compartment model of intracellular muscle kinetic
of leucine and of its transamination product, [alpha]-ketoisocaproate
(KIC), by combining systemic tracer infusions of 14C-leucine and 15N
-leucine, with the arterial-deep venous catheterization of the human
forearm. Venous 14C-KIC SA is taken as representative of
intracellular 14C-leucine SA, while net 15N-leucine disposal is used
to calculate leucine inflow and outflow across forearm cell
membrane(s). In postabsorptive normals, model-derived rates of
intracellular leucine release from, and incorporation into, protein
were nearly equal to 32% (p=0.03) and nearly equal to 37% greater
(p=0.025), respectively, than those calculated using a conventional
A-V approach. Forearm fasting proteolysis exceeded protein synthesis
(p<0.025), while leucine oxidation was greater than zero
(p<0.01), suggesting a net negative leucine (i.e. protein) balance.
Leucine inflow from blood to cell represented nearly equal to 30% of
arterial leucine delivery; therefore nearly equal to 70% of arterial
leucine by-passed intracellular metabolism. This model provides both
a comprehensive description of regional leucine and KIC kinetics, and
new estimates of protein degradation and synthesis across the human
forearm.
Received 31 October 1994; accepted in final form 24 February
1995.
APS Manuscript Number E444-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.