The effect of exhaustive treadmill running exercise on purine nucleotide degradation was examined, in both slow-twitch and fast-twitch muscle fibers in rats. Rats were divided into three groups: resting control groups without allopurinol administration (n = 5) and with allopurinol administration (n=24), and an exercise group with allopurinol administration (n=48). Purine metabolites were assayed by high performance liquid chromatography at 0,30,60,120,180, and 300 min after exercise. Plasma uric acid concentration was suppressed by allopurinol in both the exercise and control groups. There was a significant increase in plasma inosine concentration immediately after exercise, which returned to basal levels within 30 min of recovery. Plasma hypoxanthine and xanthine concentrations increased immediately after the exhaustive exercise, and remained significantly higher than resting controls until 60 and 300 min of the recovery phase, respectively. In extensor digitorum longus muscle, the content of adenosine 5'-triphosphate decreased, but inosine 5'-monophosphate and inosine increased immediately after exercise. Hypoxanthine level in extensor digitorum longus muscle was increased following exercise, and this remained higher than resting controls at 120 min of recovery. Decreased adenosine 5'-triphosphate content in soleus muscle was observed immediately after exercise. Although inosine 5'-monophosphate in soleus muscle did not show a significant change, inosine content was elevated immediately after exercise. Significant increases in hypoxanthine levels were observed from 0 to 60 min of the recovery phase. It was found that hypoxanthine levels in soleus muscle and extensor digitorum longus muscle increased to about the same degree. These results suggest that adenine nucleotide degradation and the subsequent formation of uric acid precursors occurred continuously during and following exhaustive exercise, in slow-twitch muscle fibers as well as fast-twitch muscle fibers, which may later on result in exercise-induced prolonged hyperuricemia.
