Lactate administration induces skeletal muscle synthesis by influencing Akt/mTOR and MuRF1 in non-trained mice but not in trained mice

Background: The perception regarding lactate has changed over the past decades, with some of its physiological roles having been revealed. However, the effects of exogenous lactate on skeletal muscle synthesis remain unclear. Therefore, this study aimed to confirm the effects of long-term and post-exercise lactate administration on skeletal muscle synthesis. Methods: : 32 ICR mice were randomly assigned to non-trained + placebo (Non/Pla), non-trained + lactate (Non/Lac), tranied + placebo (Tr/Pla), or trained + lactate (Tr/Lac) groups. Lactate (3 g/kg) or same volume of saline was immediately administered after exercise training (70% VO 2max ). Lactate administration and/or exercise training was performed 5 days/week for 5 weeks. Results: : After the experimental period, lactate administration tended to increase skeletal muscle weight and significantly enhanced the gastrocnemius muscle weight. Furthermore, lactate administration increased the mRNA levels of Akt ( p = 0.000) and mTOR ( p = 0.009), decreased protein expression of MuRF1 ( p = 0.001), and reduced blood IGF1 levels ( p = 0.039). However, lactate administration after exercise training had no additional effects on almost factors. Conclusions: : These results suggest that long-term lactate administration have a potential to stimulate skeletal muscle synthesis, but lactate administration after exercise training may not be extra beneficial for increasing skeletal muscle because of the lactate administration timing.