Journal of Applied Physiology, Vol 53, Issue 1 16-20, Copyright © 1982 by American Physiological Society
Elicitation of supramaximal thermogenesis by aminophylline in the rat
L. C. Wang and E. C. Anholt
Previous studies in rats indicate that maximal thermogenesis during severe
cold exposure is suppressed by overnight fasting. Since fasting depresses
sympathetic activity and the activity of adrenergic receptors, both of
which affect substrate mobilization in cold, the present study attempted to
restore maximal thermogenesis in fasted rats by exogenous sympathomimetics
and a hypoxanthine (aminophylline). In overnight-fasted rats, exogenous
sympathomimetics had no effect in further enhancing maximal thermogenesis
induced by exposure to severe cold (in He-O2 at -10 degrees C), indicating
maximization of endogenous sympathetic discharge and saturation of
adrenergic receptor binding during severe cold exposure. In contrast,
aminophylline (1.25-37.5 mg/kg ip) elicited "supramaximal thermogenesis"
beyond control maximums in both fasted (+19.4%) and fed +14.4%) conditions
in a dose-dependent manner, resulting in improved cold tolerance and
prevention of hypothermia. Since aminophylline acts distally to adrenergic
receptors to increase intracellular adenosine 3',5'-cyclic monophosphate
concentration, it is possible that such increases could enhance substrate
mobilization to support supramaximal thermogenesis in severe cold.
