Aplicação do laser de baixa intensidade antes ou após exercício resistido tem impacto similar no estresse oxidativo muscular em ratos?

Abstract

Oxidative stress comprises the circumstance in which there is an imbalance between the generation of oxidizing agents and the antioxidant defense systems, which results in injury and cellular dysfunction. Exercise can significantly break homeostasis by inducing muscle damage, inflammation and oxidative stress, resulting in a delayed recovery process. The high incidence of muscle injuries mainly during intense training sections has directly affected the growing number of studies that seek a way to minimize oxidative damage and, consequently, to accelerate the tissue repair. Low-level laser therapy (LLLT) has been introducing as an approach to atenuate muscle damage and oxidative stress induced by exercise, but it has not been showed whether the antioxidant effects of LLLT can be dependent on the time of application. The aim of the present study was to investigate the effect of LLLT before or after a resistance exercise (REx) session on muscle oxidative stress. Thirty-seven female Wistar rats were initially allowed to adapt to the act of climbing for three consecutive days and following (post-24 h of rest) the maximum load test. Rats were then kept at rest for 72 h and were assigned to one of the following experimental groups: Sham, non-exercised submitted to placebo-LLLT; RE, exercised submitted to placebo-LLLT; L+RE, pre-exercise LLLT; RE+L, post-exercise LLLT. REx session comprised four climbs bearing the maximum load with a 2 min time interval between each climb. An 830-nm DMC Laser Photon III was applied on three points in gastrocnemius muscles with the radiant energy of 4J. Animals were euthanized 24 hours after the exercise ended, and muscle tissue was removed to evaluate malondialdehyde (MDA), oxidized protein (OP) and nitric oxide (NO) levels. Activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) was also assessed. There was significantly higher MDA and OP content in the RE group, meanwhile CAT activity was downregulated by REx. All LLLT groups had prevention of increased OP, however, increased MDA was prevented only in the RE+L group. These positive results were associated with higher SOD activity. GPx activity increased in the L+RE group compared to Sham, and no significant treatment effect was found for CAT activity. There was no effect of REx and LLLT on NO levels. In conclusion, the timing of LLLT application was decisive to attenuate REx-induced muscle oxidative stress. These effects were potentiated when LLLT was applied after REx. The prevention of muscle lipoperoxidation and the increase of antioxidant enzymatic activity are dependent on the time of LLLT application.