THE CALORIGENIC RESPONSE OF COLD-ACCLIMATED WHITE RATS TO INFUSED NORADRENALINE

Abstract

The increase in oxygen consumption during continuous intravenous injection of various doses of L-noradrenaline was measured in anesthetized rats fully acclimated to 6[degree]C. The metabolic response was found to be linearly related to the logarithm of the amount of noradrenaline infused per minute. The calorigenic response to infusion of noradrenaline at a level of 1 ug per minute was then measured in rats undergoing acclimation to cold. The calorigenic response was found to increase with time of exposure to the cold environment, thus paralleling previous observations in the time course of gain in cold resistance, increase in food consumption, and loss of dependence on shivering during acclimation of white rats to cold. Also, the same maximal increase in oxygen consumption was obtained on infusion of noradrenaline into functionally eviscerated and sham-operated cold-acclimated rats, thus indicating that the liver and abdominal viscera (kidneys excluded) are not involved in the calorigenic response to noradrenaline. It is proposed, as a working hypothesis, that striated muscle is the site of the major alteration in sensitivity to noradrenaline induced by acclimation to cold. Difficulties associated with consideration of striated muscle as the source of non-shivering thermogenesis in the cold-acclimated rat are discussed.