Effect of chronic hypoxia on oxidative enzyme activity in rat skeletal muscle

To determine the effects of chronic hypoxia on oxidative capacity in skeletal muscle, 10-week-old Wistar male rats were exposed continuously to normobaric hypoxia (10% O2) for 4 weeks. To unify the level of activity in skeletal muscle of the lower limbs, some rats were treated by surgical sciatic denervation. After the experimental period, rats were anesthetized and their plantaris and soleus muscles were removed. Muscle samples were homogenized and analyzed for the mitochondrial enzymes malate dehydrogenase (MDH) and 3-hydroxyacyl-CoA dehydrogenase (HAD) activities by spectrophotometer. Sciatic denervation caused a decrease in MDH and HAD activities in both the plantaris and the soleus. Hypoxia also reduced MDH activity in the denervated plantaris muscle. As the ATP demands in the plantaris of hypoxic rats might be equal to that of normoxic rats, the reduction of MDH levels by hypoxia was not caused by a decreased level of muscle activity during hypoxic exposure. Our results indicate that chronic hypoxia has a negative effect on the oxidative enzyme MDH activity in rat skeletal muscle.