Protein metabolism and urea recycling in rodent hibernators.

A review of the metabolism of hibernators supports the argument that protein utilization is an essential aspect of hibernation. Several lines of evidence in support of this hypothesis are discussed, including (1) the field preferences of some hibernators for a diet rich in protein prior to hibernation, (2) the gluconeogenic maintenance of glycogen stores during hibernation, (3) the maintenance of plasma amino acid levels during hibernation and their elevation during the process of arousal, (4) changes in levels of nonprotein nitrogen with hibernation, (5) the potential for urea recycling by intestinal microflora in active fasted animals, and (6) the lack of correlation between loss of lean body mass and urea recovery during the hibernating season. These data serve to emphasize the contribution of protein metabolism to the overall energetic adjustments required for survival at a lower body temperature.