Skeletal muscle metabolic enzymes are altered by hyperbaric oxygenation treatments

To test whether repeated HBO exposures would increase activity of skeletal muscle metabolic enzymes, 27 rabbits (3 groups) were exposed 90 min/day, 5 days/wk to either 100% O2 at 243 kPa (HBO), 100% O2 at 101 kPa (HIO), or 21% O2 at 101 kPa (CON). Four animals per group were killed after 2 wk treatment, and the remaining five per group were killed after 8 wk of treatment. Soleus, plantaris, and tibialis anterior muscles were removed, and the activities of adenylate kinase, alpha-glycerophosphate dehydrogenase, and citrate synthase were measured. After 8 wk there was no difference in enzyme activity between groups for either plantaris or tibialis anterior. In the soleus after 8 wk there was no difference between groups in adenylate kinase activity, but alpha-glycerophosphate dehydrogenase activity was 56% greater (P < 0.05) in HBO than in HIO and 50% greater than in CON, and citrate synthase activity in HBO was 24% greater (P < 0.05) than that in HIO and 36% greater than that in CON. Inasmuch as the soleus is a postural muscle, these results suggest that long-term HBO treatments can increase enzyme activity in an actively contracting muscle.