Journal of Applied Physiology AJP: Heart and Circulatory Physiology
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J Appl Physiol 94: 1572-1582, 2003. First published December 20, 2002; doi:10.1152/japplphysiol.00884.2002
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Vol. 94, Issue 4, 1572-1582, April 2003

N-acetylcysteine infusion alters blood redox status but not time to fatigue during intense exercise in humans

I. Medved1, M. J. Brown2, A. R. Bjorksten3, J. A. Leppik1, S. Sostaric1, and M. J. McKenna1

1 Muscle, Ions, and Exercise Group, Centre for Rehabilitation, Exercise, and Sport Science, School of Human Movement, Recreation, & Performance, Victoria University of Technology, 2 Department of Anaesthesia, Austin and Repatriation Medical Centre, and 3 Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Melbourne, Victoria, Australia 8001

Infusion of the antioxidant N-acetylcysteine (NAC) reduces fatigability in electrically evoked human muscle contraction, but due to reported adverse reactions, no studies have investigated NAC infusion effects during voluntary exercise in humans. We investigated whether a modified NAC-infusion protocol (125 mg · kg-1 · h-1 for 15 min, then 25 mg · kg-1 · h-1) altered blood redox status and enhanced performance during intense, intermittent exercise. Eight untrained men participated in a counterbalanced, double-blind, crossover study in which they received NAC or saline (control) before and during cycling exercise, which comprised three 45-s bouts and a fourth bout that continued to fatigue, at 130% peak oxygen consumption. Arterialized venous blood was analyzed for glutathione status, hematology, and plasma electrolytes. NAC infusion induced no severe adverse reactions. Exercise decreased the reduced glutathione (P < 0.005) and increased oxidized glutathione concentrations (P < 0.005); NAC attenuated both effects (P < 0.05). NAC increased the rise in plasma K+ concentration-to-work ratio (P < 0.05), indicating impaired K+ regulation, although time to fatigue was unchanged (NAC 102 ± 45 s; saline 107 ± 53 s). Thus NAC infusion altered blood redox status during intense, intermittent exercise but did not attenuate fatigue.

reactive oxygen species; glutathione; potassium


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