Muscle protein synthesis (MPS) increases after consumption of a protein containing meal, but returns to baseline values within 3h, in spite of continued elevations of plasma amino acids and mammalian target of rapamycin (mTORC1) signaling. This study evaluated the potential for supplemental leucine (Leu), carbohydrates (CHO), or both to prolong elevated MPS after a meal. Male Sprague-Dawley rats (~270 g) trained to consume three meals daily were food deprived for 12 h, and then blood and gastrocnemius muscle collected 0, 90, or 180 min after a standard 4 g test meal (20% whey protein). At 135 min post-meal, rats were orally administered 2.63 g CHO, 270 mg Leu, both, or water (Sham control). Following test meal consumption, MPS peaked at 90 min then returned to basal (time 0) rates at 180 min even though ribosomal protein S6 kinase (S6K1) and eIF4E binding protein-1 (4E-BP1) phosphorylation remained elevated. In contrast, rats administered Leu and / or CHO supplements at 135 min post meal maintained peak MPS through 180 min. MPS was inversely associated with the phosphorylation states of translation elongation factor 2 (eEF2), the "cellular energy sensor" adenosine monophosphate-activated protein kinase alpha (AMPKα) and its substrate, acetyl-CoA carboxylase (ACC), and with increases in the ratio of AMP/ATP. We conclude that the incongruity between MPS and mTORC1 at 180 min reflects a block in translation elongation due to reduced cellular energy. Administering Leu or CHO supplements ~2 h after a meal maintains cellular energy status and extends the postprandial duration of MPS.
- translation initiation
- translation elongation
- branched-chain amino acids
- Copyright © 2011, American Journal of Physiology - Endocrinology and Metabolism