Journal of Applied Physiology, Vol 64, Issue 3 906-912, Copyright © 1988 by American Physiological Society
Effects of cold exposure on inhibition by isoproterenol of release of alanine in the rat
T. Yamada, M. Shiota and T. Sugano
Department of Veterinary Physiology, College of Agriculture, University of Osaka Prefecture, Japan.
The effects of isoproterenol on the release of alanine during perfusion
with pyruvate and valine were studied in perfused hindlimbs from rats that
had been kept for 5 or 20 days at 4 degrees C. In hindlimbs perfused with
Krebs bicarbonate buffer in a flow-through mode, the rate of release of
alanine during perfusion with 2 mM pyruvate plus 5 mM valine was 250
nmol.min-1.leg-1, a rate that is comparable with that reported in hindlimbs
perfused with complex medium. Neither the pyruvate-stimulated nor valine
plus pyruvate-stimulated rates of release of alanine changed after 20 days
of exposure to cold. Isoproterenol inhibited the release of alanine during
perfusion with pyruvate, with valine, and with valine plus pyruvate in
hindlimbs from a control group of rats. However, in hindlimbs from
cold-exposed groups, isoproterenol failed to inhibit the release of alanine
during perfusion with valine plus pyruvate and stimulated the release of
alanine during perfusion with valine. Aminooxyacetate inhibited the effects
of valine, pyruvate, and isoproterenol. The results obtained suggested that
cold exposure decreases the responses to isoproterenol of the mechanism of
alanine release and causes an increased supply of alanine to the liver.
