ABSTRACT
A mammalian hibernator is confronted with somewhat contradictory requirements: reducing energy spending during the cold season, meeting the thermogenic requirements of endothermic arousal, and maintaining most of tissue function and metabolic regulation over the temperature range thus achieved. This chapter provides a synthetic view of temperature regulation of the hibernation cycle. In addition, the hibernator is exposed to the constraints set by the laws of thermodynamics, as expressed by the equation of heat flux or by temperature effects at tissue level. The thermodynamic laws of heat fluxes and enzyme kinetics necessarily apply to all animals. Hibernating mammals utilize them in combination with changes in temperature regulation to achieve a complex cycle of entrance, torpor and arousal. To break the barrier on the entry into hibernation, a first possibility is isothermal metabolic depression, i.e. temporary reduction of metabolic rate below the normal resting metabolic rate, e.g. to face an adverse situation.
