Journal of Applied Physiology, Vol 49, Issue 6 975-978, Copyright © 1980 by American Physiological Society
Modulation of maximum thermogenesis by feeding in the white rat
L. C. Wang
The present study investigated the availability of substrates as a limiting
factor in acute cold exposure. By use of a self-control experimental
design, thermogenesis was measured in rats at -10 degrees C under 21%
O2-79% He following different feeding regimes. Overnight fasting resulted
in the lowest total heat production (9,949 +/- 189 cal/120 min, mean +/-
SE, n = 11), maximum rate of thermogenesis (1,320 +/- 23 cal/15 min), and
final body temperature (31.0 +/- 0.3 degrees C). The values were
significantly lower than those found after overnight rationing (10,630 +/-
231, 1,386 +/- 29, and 32.8 +/- 0.5, respectively) or ad libitum feeding
(10,821 +/- 224, 1,395 +/- 27, and 33.5 +/- 0.3). Rats fasted overnight but
fed intragastrically a 5-ml substrate mixture (3 kcal/ml) 60 min prior to
cold exposure resulted in the highest values for all parameters (11,553 +/-
207, 1,488 +/- 23, and 33.7 +/- 0.4). The increases were not due to the
specific dynamic action of food. Since the levels of maximum thermogenesis
and cold tolerance can be modulated by feeding, it is evident that
substrate availability limits thermogenesis in severe cold independent of
respiratory-cardiovascular functions and cellular oxidative capabilities.
