Exchange of purines in human liver and skeletal muscle with short-term exhaustive exercise

The exchange of purines in liver and active skeletal muscle with short-term exhaustive exercise was investigated. Eight male subjects performed two similar 10-min bouts of exhaustive supine cycling, separated by 75 min of rest. Immediately after termination of the second bout, a tourniquet was applied to the upper part of the thigh for 10 min. After the first bout, the arterial concentration of hypoxanthine and uric acid increased from 4.1 +/- 0.3 (SE) to a peak value of 36.3 +/- 7.9 mumol/l (P < 0.05) and from 335 +/- 23 to a peak value of 421 +/- 28 mumol/l (P < 0.05), respectively. There was a net release of hypoxanthine from the muscle at 12 and 45 min postexercise and an uptake of hypoxanthine and inosine in the liver at 7 and 42 min postexercise. Uric acid was released from the liver at 7 and 42 min after exercise. Before the second exercise bout and at 2 and 10 min after the release of the tourniquet, there was a significant net uptake of uric acid by the muscle. The present study demonstrates that, after strenuous short-term exercise, the main source of plasma hypoxanthine is the muscle, with no net contribution of this purine from the liver. Hypoxanthine in the blood is taken up by the liver where most of it is converted to uric acid. After exercise and a short period of ischemia, uric acid is taken up by the muscle.