Skeletal muscle response to endurance training in $IL-6^{-/-}$ mice

We examined effects of moderate-intensity endurance training on muscle COX/CS activities and $V'O_{2max}$ in control WT and $IL-6^{-/-}$ mice. Animals were exercised for 10 weeks on treadmill for 1 h, 5 days a week at velocity of 6 m·$min^{-1}$ which was increased by 0.5 m·$min^{-1}$ every 2 weeks up to 8 m·$min^{-1}$. Training triggered an increase of enzyme activities in soleus muscle of WT mice (COX: 480.3±8.9 U·$g^{-1}$ in sedentary group vs. 773.3±62.6 U·$g^{-1}$ in trained group, P<0.05 and CS: 374.0±6.0 U·$g^{-1}$ in sedentary group vs. 534.2±20.5 U·$g^{-1}$ in trained group, P<0.01, respectively) whereas no changes were observed in soleus of $IL6^{-/-}$ mice. Moreover, in mixed gastrocnemius muscle of trained $IL-6^{-/-}$ mice enzyme activities tended to be lower (COX: 410.7±48.4 U·$g^{-1}$ for sedentary vs. 277.0±36.5 U·$g^{-1}$ for trained group and CS: 343.8±24.6 U·$g^{-1}$ for sedentary vs. 251.7±27.1 U·$g^{-1}$ for trained group). No changes in $V'O_{2max}$ were observed in WT and $IL-6^{-/-}$ mice after training. Concluding, moderate-velocity endurance training-induced increase in COX and CS activities in muscles of WT mice only which suggests that IL-6 regulates training-induced skeletal muscle responses to exercise.