Effect Of Repeated Bouts Of Resistance Exercise On Skeletal Muscle Proteolytic Response In Rat.

Abstract

Resistance training (RT) increases the skeletal muscle mass and strength. It has been reported that activation of the mammalian target of rapamycin (mTOR) signaling, which is important for skeletal muscle protein synthesis, is attenuated by increasing exercise bout. However, the effect on proteolytic response is unclear. PURPOSE: The present study aimed to investigate the changes in proteolytic responses to repeated bouts of resistance exercised. METHODS: Male Sprague-Dawley rats were randomly assigned into four groups: Sedentary (SED), resistance-exercised with 1bout (1B), 2bouts (2B), 3bouts (3B). RT protocol consisted of 50 repetitions of maximal isometric contraction of the right gastrocnemius muscle by direct electric stimulation under anesthesia. Muscle samples were collected 3h and 6h after the final exercise session. RESULTS: Phosphorylation of p70S6K increased in all trained groups (1B: 15 fold, 2B: 10 fold, 3B: 8 fold, P<0.05). And there was also significant difference between 1B and 3B. The protein ubiquitination increased in all trained groups of 1.2-fold in SED (P<0.05). And Light chain 3 (LC3), which is a marker for autophagy, increased in all trained groups of 1.5-fold in SED (P<0.05). MuRF-1 mRNA showed a significant 5.1-fold increase with training (P<0.05). However, there were no effect of repeated bouts of RT in muscle proteolytic response. CONCLUSIONS: The present results suggest that the muscle protein proteolytic response was activated by RT. In addition, the activation of mTOR signaling attenuated with the increase in RT bouts, but the level of activation of proteolytic response did not change.