Effects Of Lactate Infusion On Resistance Exericse Induced MTORC1-signaling And Protein Synthesis In Human Muscle

Abstract

Lactate has recently been highlighted as a potential signaling molecule. In myotubes, lactate incubation increase mTORC1-signaling, reduce myostatin expression and induce myotube growth. This indicates that lactate could be a potential mediator of muscle adaptations to resistance exercise. PURPOSE: Here we wanted to study the acute molecular response in human skeletal muscle to resistance exercise performed with our without a venous infusion of lactate. The primary outcomes of the study was intracellular signaling, rate of protein synthesis (FSR) and blood/muscle levels of lactate and pH. METHODS: 16 healthy females and males participated in the study which consisted of two resistance exercise sessions performed under venous infusion of sodium lactate or saline, in a randomized, blinded and counterbalanced fashion. In the overnight fasted state infusion was employed during ~60 min of rest and unilateral knee-extension exercise. Blood was sampled repeatedly during trials and muscle biopsies were collected at rest and at 0, 90, 180 min and 24 h after exercise. Oral D2O ingestion was used to determine FSR during 24 h of recovery. RESULTS: With saline, blood lactate levels reached 3.0 mmol/l post exercise, while lactate infusion resulted in 130% greater lactate levels post exercise that also remained higher than at rest and saline up to 90 min of recovery. Post exercise muscle levels of lactate were 20% higher with lactate compared to saline infusion (32 vs 27 mmol/kg d.w). Lactate infusion had an alkalizing effect in blood with pH being 7.44 after exercise with lactate and 7.34 with saline. This effect was not noted in muscle were pH was reduced by 0.06 units after exercise in both trials. Exercise increased the phosphorylation of mTORS2448 (~40%), S6K1T389 (~3-fold) and S6S240/244 (~9-fold) during recovery, without any differences between trials. Effects of exercise without any influence of lactate infusion was also noted for eEF2T56, AMPKT172, PRAS40T246 and p44T202/T204. FSR over 24h of recovery did not differ between saline (0.067 %/h) and lactate infusion (0.060 %/h). CONCLUSIONS: In this model blood lactate levels did not modulate resistance exercise induced mTORC1-signaling or FSR. As only small differences were noted for muscle levels of lactate, its potential role as signaling molecule should not be discarded.