Effects of exercise on oxidative activities in rat liver mitochondria

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Abstract
The oxidation rates of substrates in the citric acid cycle were found to be greater in liver mitochondria from exercised rats than in those from rested rats, whereas the P/O (phosphate-to oxygen) ratios were unchanged. The most pronounced effects of exercise were obtained in the presence of those substrates which were oxidized most slowly, thus suggesting an increase in the effective capacity of the citric acid cycle. The above effects accompanied increases in the steady-state percentage of reduced pyridine nucleotide in the liver mitochondria. Exercise apparently stimulated the individual dehydrogenase activities by increasing the level or the availability of mitochondrial diphospho-pyridine nucleotide (DPN). When DPN was added the differences in the rates of oxygen uptake between the control and the experimental mitochondria were reduced or eliminated. Other factors which influenced the exercise-induced responses in oxygen uptake in liver mitochondria appeared to be abnormally high endogenous levels of both oxaloacetate and pyruvate in the experimental mitochondria. An increase in the former substrate would stimulate pyruvate oxidation, whereas an increase in the latter substrate would accelerate malate oxidation.