Journal of Applied Physiology, Vol 38, Issue 3 436-442, Copyright © 1975 by American Physiological Society
Nonshivering thermogenesis and cold resistance in rats under severe cold conditions
O. Heroux, E. Page, J. Leblanc, J. Leduc, R. Gilbert, A. Villemaire and P. Rivest
Following either chronic exposure to 6 degrees C, or outdoor winter
exposure, or chronic treatment with tyramine rats were exposed to -40
degrees C and their oxygen consumption and colonic temperature monitored.
Fall in body temperature with time of exposure followed a sigmoid curve
which had an inflection point around 32.9 degrees C. Both the time required
for body temperature to reach this point and hypothermic resistance defined
as the total O2 consumed up to the inflection time were useful indices of
resistance to severe cold; Three days before the cold tests, capacity for
norepinephrine-induced nonshivering thermogenesis was measured in all
animals by examination of their metabolic response to tyraminemthe
magnitude of response to tyramine correlated well with hypothermic
resistance only for those rats chroncally treated with tyramine. It is
concluded that it is impossible to predict with any reasonable degree of
confidence the cold resistance of a rat from its tyramine response. In
cold-acclimated rats, factors in addition to norepinephrine sensitivity are
significantly involved in cold resistance and deserve further studies.
