Muscle full effect after oral protein time-dependent concordance and discordance between human muscle protein synthesis and mTORC1 signaling

Background We previously showed that human muscle protein synthesis (MPS) increased during infusion of amino acids (AAs) and peaked at approximate to 120 min before returning to baseline rates despite elevated plasma AA concentrations Objective We tested whether a protein meal elicited a similar response and whether signaling responses that regulate messenger RNA translation matched MPS changes Design Eight postabsorptive healthy men (approximate to 21 y of age) were studied during 8 5 h of primed continuous infusion of [1 2-C-13(2)] leucine with intermittent quadriceps biopsies for determination of MPS and anabolic signaling After 2 5 h subjects consumed 48 g whey protein Results At 45-90 min after oral protein bolus me in (+/- SEM) myofibrillar protein synthesis increased from 003 +/- 0 003% to 0 10 +/- 001%/h thereafter myofibrillar protein synthesis returned to baseline rates even though plasma essential AA (EAA) concentrations remained elevated (+130% at 120 mm +80% at 180 min) The activity of protein kinase B (PKB) and phosphorylation of eukaryotic initiation factor 4G preceded the rise of MPS and in creases in phosphorylation of ribosomal protein kinase S6 (S6K1) and 4E binding protein 1 (4EBP1) was superimposable with MPS responses until 90 min However, although MPS decreased thereafter all signals with the exception of PKB activity (which mirrored insulin responses) remained elevated which echoed the slowly declining plasma EAA profile The phosphorylation of eukaryotic initiation factor 2 alpha increased only at 180 min Thus, discordance existed between MPS and the mammalian target of rapamycin complex 1 (mTORC1) and signaling (ie S6K1 and 4EBP1 phosphorylation) Conclusions We confirm our previous findings that MPS responses to AAs are transient even with oral protein bolus However changes in MPS only reflect elevated mTORC1 signaling during the upswing in MPS Am J Clin Nutt 2010 92 1080-8