Maintenance of the adaptation of skeletal muscle mitochondria to exercise in old rats

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Abstract
The purpose of this study was to determine whether the adaptive increase in mitochondrial enzymes in skeletal muscle induced by a constant exercise program is altered by aging. Male pathogen-free Long-Evans rats were exercised by means of swimming for 3h/d, 5d/wk beginning at age 6 months and studied at ages 9 and 24 months. The levels of activity of the four mitochondrial enzymes used as indicators of the capacity for aerobic metabolism (citrate synthase, succinate DH, 3-hydroxyacyl-CoA-DH, and 3-ketoacid-CoA-transferase) were significantly increased in epitrochlearis muscle in both the 9-month and 24-month-old swimmers. The increases ranged from approximately 20% for 3-hydroxyacyl-CoA-DH to 50–60% for 3-ketoacid-CoA-transferase. Neither the 24-month-old sedentary rats nor the 24-month-old swimmers had significantly lower muscle enzyme levels than the comparable 9-month-old rats. Thus, it appears that aging does not result in a progressive decline in the capacity of muscle for aerobic metabolism or a progressive impairment in the ability to maintain an increase in muscle mitochondrial enzymes in response to chronic exercise in healthy rats.

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