THE ANTIOXIDANT EFFECTS OF URTE AND GENERATION OF ALLANTOIN DURING EXHAUSTIVE EXERCISE / 体力科学

ABSTRACT

Allantoin is one of the oxidation products of uric acid resulting from attack by oxygen free radicals. In this study we attempted to clarify the antioxidant effect of uric acid during exercise, and the influence of other antioxidants on urate <I>in vitro</I>. Seven healthy male subjects performed exhaustive (100%VO<SUB>2max</SUB>) and mild endurance (40%VO<SUB>2max</SUB>) cycling exercise, and serum uric acid and allantoin were measured before and up to 24 h after the exercise. Various radicals were added to uric acid, ascorbic acid and glutathione were mixed with phosphate buffer or fresh human serum, and changes in each of the antioxidants (protein sulfhydryl groups in serum were measured instead of glutathione in buffer) and allantoin were examined. The serum allantoin level increased immediately after exhaustive exercise and remained high for up to 2 h, while uric acid increased at 0.5 h and remained at a high level at 24 h during recovery. On the other hand, no significant changes in allantoin and uric acid were observed after mild endurance exercise. Superoxide anion radicals (O<SUB>2</SUB><SUP>-</SUP>) generated by a hypoxanthine-xanthine oxidase (HX-XOD) system formed allantoin with decreasing levels of other antioxidants in buffer and serum, although uric acid was generated by this system. To determine the influence of uric acid newly produced by the HX-XOD system, different kind of antioxidants in buffer were used to examine allantoin generation. Allantoin was generated in the order uric acid only>no antioxidants>three kinds of antioxidants during 20 min of reaction. Hydroxyl radicals (·OH) generated by the Fenton reaction also formed allantoin as other antioxidants decreased, while hydrogen peroxide did not oxidize uric acid to allantoin despite the fact that other antioxidants were consumed in the buffer and serum. These results suggest that O<SUB>2</SUB><SUP>-</SUP> and ·OH oxidize uric acid to allantoin during exhaustive exercise, whereas, ascorbic acid, glutathione and protein sulfhydryl groups inhibit allantoin generation. Moreover, uric acid previously present in the body may be used for radical scavenging more effectively than that newly generated by exhaustive exercise.