ORIGINAL ARTICLE Effects of graded exercise-induced dehydration and rehydration on circulatory markers of oxidative stress across the resting and exercising human leg Orlando Laitano • Kameljit Kaur Kalsi • James Pearson • Makra Lotlikar • Alvaro Reischak- Oliveira • Jose ´ Gonza ´lez-Alonso Received: 21 April 2011 / Accepted: 4 September 2011 / Published online: 20 September 2011 Ó Springer-Verlag 2011 Abstract Exercise in the heat enhances oxidative stress markers in the human circulation, but the contribution of active skeletal muscle and the influence of hydration status remain unknown. To address this question, we measured leg exchange of glutathione (GSH), glutathione disulfide (GSSG), superoxide dismutase activity (SOD) and isopros- tanes in seven males at rest and during submaximal one- legged knee extensor exercise in the following four condi- tions: (1) control euhydration (0% reduction in body mass), (2) mild-dehydration (2%), (3) moderate-dehydration (3.5%), (4) rehydration (0%). In all resting and control exercise conditions, a net GSH uptake was observed across the leg. In contrast, a significant leg release of GSH into the circulation (-354 ± 221 lmol/min, P \ 0.05) was observed during exercise with moderate-dehydration, which was still present following full rehydration (-206 ± 122 lmol/min, P \ 0.05). During exercise, mild and moderate-dehydration decreased both femoral venous erythrocyte SOD activity (195 ± 6 vs. 180 ± 5 U/L, P \ 0.05) and plasma isoprostanes (30 ± 1.1 vs. 25.9 ± 1.3 pg/L, P \ 0.05), but during rehydration these were not different from control. In conclusion, these findings suggest that active skeletal muscles release GSH into the circulation under moderate dehydration and subsequent rehydration, possibly to enhance the antioxidant defense. Keywords Superoxide Á Isoprostanes Á Glutathione Introduction Prolonged exercise in the heat induces marked dehydration and hyperthermia if the fluid lost through sweating is not replaced during exercise. While the deleterious effects of dehydration on cardiovascular, thermoregulatory and met- abolic function are well documented (Sawka and Coyle 1999; Gonza ´lez-Alonso et al. 2008), whether dehydration induces disruption of the cellular redox balance, diminishes antioxidant defense and increases reactive oxygen species (ROS) formation in skeletal muscle remains unknown. This is important because they may lead to oxidative stress (McAnulty et al. 2005; Paik et al. 2009), which can cause damage or downregulation of important cellular structures such as skeletal muscle mitochondrial DNA (Marcuello et al. 2005). One of the main cellular redox regulators that may be affected by dehydration during exercise is glutathione (GSH) (Meister 1988; Inayama et al. 2002). GSH is a major component of the antioxidant defense as it is the primary preventative pathway to avert hydroperoxide-induced cell damage that occurs under oxidative stress (Gohil et al.1988; Communicated by Susan A. Ward. O. Laitano Á K. K. Kalsi Á J. Pearson Á J. Gonza ´lez-Alonso (&) Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex UB8 3PH, UK e-mail: j.gonzalez-alonso@brunel.ac.uk O. Laitano Á A. Reischak-Oliveira Exercise Research Laboratory, Federal University of Rio Grande do Sul, School of Physical Education, Porto Alegre, Brazil Present Address: O. Laitano Colegiado de Educac ¸a ˜o Fı ´sica, Universidade Federal do Vale do Sa ˜o Francisco-UNIVASF, Av. Jose ´ de Sa ´ Manic ¸oba S/N-Centro, Petrolina PE CEP: 56304-917, Brazil e-mail: Orlando.Laitano@univasf.edu.br M. Lotlikar Department of Anaesthetics, Ealing Hospital, NHS Trust, Southall, Middlesex, UK 123 Eur J Appl Physiol (2012) 112:1937–1944 DOI 10.1007/s00421-011-2170-2