Postprandial resynthesis of myofibrillar proteins is translationally rather than transcriptionally regulated in human skeletal muscle

Feeding stimulates protein synthesis in skeletal muscles, although the regu latory mechanisms are incompletely understood. The aim of this study was to determine whether this could be detected at the gene transcription level f or postprandial stimulation of the synthesis of muscle proteins. Healthy ma le volunteers were investigated after an overnight fast. Open muscle biopsi es were performed in the starved state and 3 h after meal intake, consistin g of 0.15 gN/kg, 12 kcal/kg. Blood samples were drawn every 15 to 30 min fo r 5 h. Myosin mRNA and insulin growth factor-I (IGF-I) mRNA were measured b y solution hybridization assay in homogenized muscle specimens. After food intake, plasma glucose concentrations increased from 5.0 +/- 0.1 to 7.3 +/- 0.3 (P less than or equal to 0.001), and insulin concentration rose from 3 .8 +/- 0.5 mU/L before to 75.3 +/- 11.4 15 min after the meal (P less than or equal to 0.001). Plasma concentration of free fatty acids declined after food intake (P less than or equal to 0.001). Plasma concentrations of amin o acids increased from basal values (2864 +/- 128 mu M) to 4419 +/- 262 mu M (P less than or equal to 0.05) 90 min after meal ingestion. Myosin mRNA c oncentration in the biopsied muscle tissue was higher during starvation and was reduced by 20% after food intake: 10.8 +/- 1.3 amol mRNA/mu g DNA in t he starved state and 8.5 +/- 1.3 amol mRNA/mu g DNA after food intake (P le ss than or equal to 0.05). Feeding did not alter IGF-I mRNA concentrations in muscle: 0.51 +/- 0.05 and 0.55 +/- 0.06 amol/mu g DNA in the starved and fed state, respectively (P less than or equal to 0.38). Improved protein b alance by stimulation of protein synthesis has been related to increased pl asma amino acids. Interestingly, in the short term, this was not related to increases in gene transcription of either myofibrillar proteins (myosin) o r muscle IGF-I. Thus, postprandial stimulation of protein synthesis appears not to be regulated by increased gene transcription but by increased trans lation using the increased concentrations of amino acids. In contrast, as f ar as the 2X myosin mRNA level is concerned, this is enhanced during starva tion, which facilitates rapid recovery once the availability of substrate i s resumed. (C) Elsevier Science Inc. 2000.