Effects of leucine on whole-body leucine, valine and threonine
metabolism in humans.
Hoffer, L. John, Arlene Taveroff, Line Robitaille, Mazen J. Hamadeh,
and Orval A. Mamer.
McGill Nutrition and Food Science Centre and The McGill Medical
Research Council of Canada, Biomedical Mass Spectrometry Unit, McGill
University, Montreal, Quebec, H3A 1A3 Canada
APStracts 4:0038E, 1997.
We tested whether expansion of the plasma leucine pool distorts
leucine or valine tracer kinetics, causing errors in the derived
values of whole body proteolysis. Seven normal adults received a 10 h
primed-continuous tracer infusion of L-[5,5,5-2H3]leucine, L-[1
-13C]valine, and L-[1-13C]threonine, during the final 7 h of which L
-leucine was infused at a rate that more than tripled the plasma
leucine concentration. Leucine, valine and threonine rates of
appearance were converted to a common value of whole body proteolysis
based on their concentrations in body proteins. The conversion of
labeled leucine and valine to their corresponding branched-chain
[alpha]-keto and [alpha]-hydroxy acids was also monitored. Prior to
the unlabeled leucine infusion, postabsorptive whole-body proteolysis
was estimated similarly by the three tracers (approximately 160 mg
protein/kg.h). The leucine infusion reduced proteolysis by an average
of 21% (P < 0.006) as estimated using valine or threonine
kinetics, and by 10% using leucine kinetics (P < 0.02). No
delay in the conversion of valine to KIVA occurred during the leucine
infusion. Thus, all three tracers indicated similar postabsorptive
rates of whole body proteolysis and a reduction of proteolysis during
leucine administration, although the magnitude of the effect was
underestimated using the leucine tracer.
Received 15 August 1996; accepted in final form 24 January 1997.
APS Manuscript Number E403-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 20 February 1997