Journal of Applied Physiology, Vol 53, Issue 2 367-372, Copyright © 1982 by American Physiological Society
Leucine and urea metabolism in acute human cold exposure
R. D. Goodenough, G. T. Royle, E. R. Nadel, M. H. Wolfe and R. R. Wolfe
Four healthy males voluntarily underwent acute cold exposure at 10 degrees
C. Metabolic rate doubled for the 100-min exposure. [1-13C]leucine and
[15N2]urea were used as tracers of protein metabolism via a primed constant
infusion. Total and plasma transported leucine oxidation approximately
doubled, but the oxidation of leucine derived from protein in the tissue
where oxidation occurred ("intracellular oxidation") did not change as it
did when the same subjects underwent mild exercise. Rate of appearance of
urea and leucine in plasma were not significantly different between control
and cold. Although the rate of protein synthesis calculated from the
leucine data did not change, the rate of catabolism increased. Net protein
catabolism based on the urea data agreed well with the leucine data at rest
but did not exhibit a significant increase during exposure. However, net
protein catabolism based on the leucine data did increase significantly
during acute cold exposure. Further, there appears to be a qualitative
difference in the protein catabolism associated with the voluntary muscular
activity of exercise and muscular shivering aimed at thermogenesis.
