Hibernation, a state of natural tolerance to profound reduction in organ blood flow and oxygen delivery capacity

Hibernation represents a seasonal physiological adaptation, which allows conservation of energy and down-regulation of cellular functions. Hibernating animals exhibit multiple biological alterations which contribute to their dramatic ability to tolerate the ischaemic conditions associated with reduced rates of respiration and blood flow while in the hibernating state. There is accumulating evidence that mammalian hibernation involves a controlled suppression of interactive physiological responses that preserves homeostatic balance. Mammalian hibernation is a regulated state of torpor with a profound suppression of energy requirements that has evolved in at least six mammalian orders as a strategy to cope with seasonal cold and shortages of food and water (Wang, 1988). A hibernation bout may last up to several weeks in some mammals and consists of entry into,. maintenance of, and arousal from hibernation. Arousal is maintained for a few hours to a few days before the animal initiates another bout of hibernation. During entrance into hibernation, metabolic rate drops to extremely low levels. In studies by Frerichs et al. (1995), glucose utilization was determined by the autoradiographic [I4C] deoxyglucose technique by direct chemical measurement (HPLC) of precursor and products in samples dissected from funnel-frozen brain. The calculated glucose metabolic rate (CM~lc) in ground squirrels in deep hibernation was only . ,