Exercise-Induced Prolonged Hyperuricemia by Continuous Production and Release of Hypoxanthine in Fast-Twitch Muscle in Rats

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To elucidate the mechanism of exercise-induced prolonged hyperuricemia, post-exercise changes in purine metabolites in plasma and plantaris muscle were examined in rats. Rats were divided into three groups including a resting control group with allopurinol (n=24) and without allopurinol (n=5), and an exercise group with allopurinol (n=48). The levels of purine metabolites were assayed by HPLC in eight or four animals each at 5,30,60,120,180, and 300 min after exhaustive exercise on the treadmill or rest. Plasma uric acid was suppressed by allopurinol both in exercise and resting control groups. Plasma inosine and hypoxanthine in the exercise group were increased between 5 and 30 min. Plasma xanthine was also increased from 5 to 180 min. Although ATP in plantaris muscle did not change at 5 min, inosine monophosphate showed an tendency to increase. Muscle inosine and hypoxanthine were increased at 5 min. Muscle hypoxanthine recovered slowly compared to inosine and the level was elevated even at 120 min. These changes of plasma and muscle purine metabolites suggest that hypoxanthineis continuously produced in fast-twitch muscles and then released from muscle to blood after exhaustive exercise, causing exercise-induced prolonged hyperuricemia.