Papel do exercício resistido na atrofia muscular induzida por dexametasona
Krug, André Luis de Oliveira
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The use of glucocorticoids as treatment for allergic and inflammatory conditions has become commom nowadays, although, chronically it can causes many side effects such as peripheral insulin resistance, hyperglycemia and hyperinsulinemia, hypertension, dyslipidemia, body weight loss and muscle atrophy. On the other hand, resistance training (RT) has been recommended as non-pharmacological treatment for some pathological conditions, however little is known about its effects on muscle atrophy induced by chronic treatment with dexamethasone (DEX). The aim of this study was to verify the preventive effect of RT (80% of maximal carrying capacity) on DEX-induced muscle atrophy as well as the responsible mechanisms for this response. Forty-three wistar rats (200-250g) were allocated into four groups: sedentary control (SC), sedentary treated with DEX (SD), trained control (TC) and trained treated with DEX (TD). After a familiarization period on the ladder, a maximal voluntary carrying capacity test (MVCC) was performed to determinate the training intensity and the rats underwent or RT (80% MCCT, 4 days/week, 70 days) or remained sedentary. The MVCC was performed in the beginning, after 4 weeks, before and after the DEX treatment. Through the last ten days, the animals received DEX (0.5 mg/kg/day, i.p.) or saline solution. After 24 hours of the last training session, the animals were euthanized and the flexor hallucis longus (FHL), tibialis anterior (TA) and soleus (SOL) muscles were collected and weighted for further analysis of mTOR, p70S6K, FOXO3a, Atrogin-1 and MuRF-1 protein levels. The results were presented as mean ± SEM, α<0.05. DEX treatment evoked adrenal gland atrophy (-47%), body weight loss (-21%) and food intake reduction (-28%). The RT increased MVCC of trained animals (+215%). Also, DEX treatment reduced FHL and TA muscles mass (-19.6% e -17.7%, respectively), which was associated with the MuRF-1 protein level increase (+37% e +45,5%, respectively). We did not observe any alterations in mTOR, p70S6K, FOXO3a and Atrogin-1 protein levels after DEX treatment. RT was be able to attenuate FHL muscle atrophy due to blockade of MuRF-1 increase (-3.5%). In addition, it did increase mTOR (+63% for TC e TD) e p70S6K (+46% and +49% for TC e TD, respectively) protein levels in FHL muscle. FOXO3a and Atrogin-1 protein levels were not altered by RT. SOL muscle was not affected by neither treatment nor training. Therefore, these results allow us to suggest that DEX-induced muscle atrophy observed in the FHL and TA muscles can be associated with increases in MuRF-1 protein level. RT-induced attenuation of FHL muscle atrophy involved increases in mTOR and p70S6K protein levels associated with maintenance of MuRF-1 protein levels.