Allantoin formation and urate and glutathione exchange in human muscle during submaximal exercise

Seven males performed two exhaustive cycling bouts (EX1 and EX2) at a work- rate of 90% of maximal oxygen uptake, separated by 60 min. During EX1 there was a significant accumulation of urate (from 0.16 +/- 0.02 to 0.27 +/- 0. 03 mu mol/kg d.w.) and allantoin (from 0.39 +/- 0.05 to 0.69 +/- 0.14 mu mo l/kg d.w.) in the Muscle. An uptake Of Urate was observed in early recovery from EX1 (0-9 min: 486 +/- 136 mu mol: p <.05). There was no exchange of t otal glutathione or cysteine over the muscle either during or after exercis e, and muscle and plasma total glutathione remained unaltered (p <.05). The glycogen levels were lowered by 40% at the onset of EX2 yet the level of o xidative stress in EX1 and EX2 was similar as evidenced by a similar increa se in muscle allantoin in both exercise bouts. The data suggest that urate is utilized as antioxidant in human skeletal muscle and that reactive oxyge n species are formed in Muscle during intense submaximal exercise. No net e xchange of glutathione appears to occur over the muscle either at rest, dur ing exercise or in recovery. Moreover, when an exhaustive exercise bout is repeated with lowered glycogen levels, the level of oxidative stress is not different than that of the first bout. (C) 2001 Elsevier Science Inc.