Rewarming From Natural Hibernation and From Artificial Cooling

Abstract

Ground squirrels (Citellus) and golden hamsters (Mesocricetus) were provided with thermocouples in various bodily locations. Large temperature gradients existed both during cooling and during warming; the chest was uniformly the warmest region, due to production of heat in chest muscles and in heart, with probable constriction of blood vessels conducting blood from the chest. Critical body temperatures from which self-rewarming was possible when in cold air were in ground squirrel lower than in golden hamster, and much lower than in white rat. Rates of warming stood in the same order among spp. Maximal O2 consumptions observed at appropriate stages either during cooling or during rewarming in ground squirrel and hamster far exceeded those in rats of comparable size. Heat productions estimated from the O2 consumptions were found to be sufficient to provide the temperature gradients noted. Whether ground squirrels were recovering from hibernation or from artificial cooling, like warming rates, temperature gradients and heat productions prevailed. Hibernators thus manifest both high heat productions and large temperature gradients during self-rewarming; nonhibernators manifest neither.