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 in vitro. Seven healthy male subjects performed exhaustive (100%VO_2max) and mild endurance (40%VO_2max) 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 (O₂^-) 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 O₂^- 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.

The purpose of this research was to study the effects of Tu-Chung extract (Eucommia ulmoides OLIV.) administration on serum testosterone and the possible mechanisms in hindlimb- suspended rats. 25 five-week old male Wistar rats were used. All rats were randomly divided into two groups : those treated with Tu-Chung extract (Tu-Chung G, n=suspended for 37 days in hindlimb. 1 mg/ml Tu-Chung extract was administered orally once daily at a dose of 1 ml/100 g body weight. Distilled water was administered in a similar way to the control group. The following results were observed :
1. Serum testosterone concentration in Tu-Chung G was significantly higher than in Cont. G (P<0.001) .
2. There was no significant difference between Tu-Chung G and Cont. G in serum LB concentrations.
3. The Testicular cAMP level in Tu-Chung G was significantly higher than that in Cont. G (P<0.01) .
4. 24-h urinary excretion of 17-ketosteroid in Tu-Chung G was significantly higher than that in Cont. G (P<0.001) .
5. There were no significant differences between the two groups in the weights per body weight of the kidneys, adrenal grand and testes. These results suggest that the adininstration of Tu-Chung extract inducing high serum testosterone concentrations in hindlimb-suspended rats might be due to enhanced testicular and adrenal functions, not pituitary.