Are proteins and uric acid potent free radical scavengers? Are they playing a role as antioxidant defense in human body frequently exposed to free radical attacks (sportsmen)? These questions were examined in "in vitro" and "in vivo" experiments. In experiments in vitro: A system generating free radicals was found to inhibit lactate dehydrogenase (LDH) activity but this effect is obliterated by the presence of superoxide dismutase (SOD). Urate was found to protect bovine serum albumin (BSA) against free radical-induced peroxidation, measured by carbonyl group formation. BSA inhibited almost completely the free radical-induced lipid peroxidation (measured by TBARS method). In experiments in vivo: The amounts of urea and uric acid were measured in 24 h urine collected from 119 male elite athletes and 35 medical students. From the urea content, the protein catabolism was computed. It was found that athletes consuming appropriate amounts of protein had normal uricuria. A low-protein diet, accompanied by performing exercise of high volume and intensity, as in case of professional sports, resulted in reduction of uricuria. The results suggest that both protein and uric acid play a significant role in athlete's body by protecting against tissue damage caused by an excess of free radicals.
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