COMPARISON BETWEEN SEASONAL AND THERMAL ACCLIMATION IN WHITE RATS: V. METABOLIC AND CARDIOVASCULAR RESPONSE TO NORADRENALINE

Abstract

White rats cold-acclimated at a constant temperature in the laboratory are known to be more sensitive to noradrenaline than warm-acclimated controls. The present study reveals that this responsiveness to noradrenaline is linearly related to the temperature at which the animals are conditioned. Concomitant measurements (after intramuscular injection of noradrenaline) of oxygen consumption, blood pressure, and heart rates on white rats acclimatized to outdoor summer or winter conditions revealed a much greater metabolic and cardiovascular sensitivity to noradrenaline in winter than in summer rats. The slight degree of shivering upon exposure to 6 °C which was observed in the outdoor winter rats, as well as their great sensitivity to noradrenaline, suggests that under both indoor and outdoor environmental conditions, increased cold resistance is obtained through similar metabolic mechanisms.