Biochemical changes in skeletal muscles of denning bears (Ursus americanus).

1. Biopsies of the extensor hallucis longus (EHL) and gastrocnemius (G) muscles of four captive black bears (Ursus americanus) were obtained prior to denning (PRE), during denning (DEN) and following the Spring arousal (POST). 2. Glycogen, triglyceride and protein concentrations did not differ significantly between the three groups. Likewise, the activity of citrate synthase, a mitochondrial oxidative enzyme, was not significantly different between the three groups. 3. DNA concentrations in DEN samples increased 30% compared to other groups while RNA concentrations were significantly elevated in POST samples. The RNA/DNA ratios were significantly depressed during DEN. 4. These results suggest a degree of muscle atrophy during DEN, with the potential for an increased capacity for muscle protein synthesis following the Spring arousal.