Hibernation as a model for studies on thermogenesis and its control.

Abstract

Mammalian hibernation is characterized by the alternation of prolonged periods of hypothermia and spontaneous arousals with a temporary return to euthermia. Of special interest to the physiology of effectors of thermogenesis are the following points: a) In the second part of the arousal process, the metabolic rate reaches 6 to 8 times BMR, with a body temperature about 10 degrees C lower. Enzymatic adaptations provide for the maintenance of normal reaction rates and regulatory potentials at low temperatures, but how very high thermogenetic rates can be achieved still remains largely unexplained. b) Entrance into hibernation involves a resetting of the hypothalamic thermostat to a lower level, but this is probably not the only intervening regulation. Evidence is presented in favor of a control of thermogenesis at the effector level, in terms both of baseline levels and of loop gains. One likely control factor is acid-base state, which can be changed rapidly and reversibly by ventilation and is characterized by a strong acidosis in hibernation.