Avoidance of skeletal muscle atrophy in spontaneous and facultative hibernators.

Smooth and skeletal muscle changes were compared from overwintering white-tailed prairie dogs, spontaneous hibernators that undergo regular, low-temperature torpor bouts, and black-tailed prairie dogs, facultative hibernators that use sporadic, moderate-temperature torpor bouts. The objectives were to assess the abilities of these two species with dramatically different torpor patterns (1) to conserve skeletal muscle morphology, protein, and strength and (2) to use labile protein in the small intestine and liver during the winter season of reduced activity and food intake. Mass and protein concentration of the extensor digitorum longus (EDL), soleus, liver, and small intestine, as well as skeletal muscle strength and fiber morphology for the EDL and soleus, were compared before and after hibernation in both species. Both species appeared to be similar to overwintering black bears and underwent very little strength and protein loss, as compared with euthermic models of immobility and long-term fasting. Although the two species used vastly different hibernation strategies, none of the changes in parameters related to muscle atrophy and labile-protein use during the hibernation season differed significantly between them. Therefore, it appears that regardless of the phenotypic expressions of hibernation, the outcome is the conservation of skeletal muscle.