PLASMA ACCUMULATION OF HYPOXANTHINE, URIC-ACID AND CREATINE-KINASE FOLLOWING EXHAUSTING RUNS OF DIFFERING DURATIONS IN MAN

During exhausting exercise adenylate kinase in the muscle cells is activated and a degradation of adenosine 5'-diphosphate occurs. Consequently, degradation products of adenosine 5'-monophosphate including hypoxanthine and uric acid, accumulate in plasma. The aim of this study was to compare the concentration changes of hypoxanthine and uric acid in plasma following running of varying duration and intensity. In addition, plasma creatine kinase activity was measured to assess the possible relationship between metabolic stress and protein release. Four groups of competitive male runners ran 100 m (n = 7), 800 m (n = 11), 5000 m (n = 7) and 42 000 m (n = 7), respectively, at an exhausting pace. Subsequent to the 100 m event (mean running time 11 s) plasma concentrations of hypoxanthine and uric acid increased by 364% and 36% respectively (P < 0.05), indicating a very high rate of adenine nucleotide degradation during the event. Following the 800-m event (mean running time 125 s), hypoxanthine and uric acid concentrations had increased by 1598% and 66%, respectively (P < 0.05). Both the events of longer duration, 5000 m and 42 000 m, also caused a significant increase in plasma concentration of hypoxanthine (742% and 237% respectively, P < 0.05) and plasma uric acid (54% and 34% respectively, P < 0.05). Plasma activities of creatine kinase were significantly increased at 24 h only following the 5000 m and 42 000 m events (64% and 1186% respectively, P < 0.05). Changes in plasma creatine kinase activity showed no correlation with changes in plasma concentration of either hypoxanthine or uric acid for the 5000 m and 42 000 m events (r = 0.00-0.45, P > 0.05). These findings suggest that metabolic stress induced by exhausting exercise cannot be considered an important factor for the release of intracellular proteins. It was, furthermore, concluded that the rate of elimination of adenine nucleotides from cells was markedly elevated with the increasing intensity of exercise and only moderately affected by the duration of running.