Essential amino acid (EAA) ingestion enhances postexercise muscle protein synthesis, and in particular, the anabolic response of older adults appears sensitive to the quantity of ingested leucine. The effect of leucine ingestion on muscle breakdown following resistance exercise (RE) is less understood. The purpose of this study was to identify the impact of postexercise leucine ingestion on the ubiquitin proteasome and autophagosomal-lysosomal systems following acute RE in older men. Subjects (72±2yr) performed RE and 1h postexercise ingested 10g of EAA containing a leucine quantity similar to quality protein (Control, 1.8g leucine, n=7) or enriched in leucine (Leucine, 3.5g leucine, n=8). Stable isotope infusion and muscle biopsies (vastus lateralis) obtained at rest and 2, 5, and 24h postexercise were used to examine protein content (western blot), mRNA expression (RT-qPCR) and muscle protein fractional breakdown rate (FBR). MuRF1 mRNA increased in both groups at 2 and 5h (p<0.05). LC3 mRNA increased and the LC3BII/LC3BI ratio decreased at all postexercise time points in Control (p<0.05). Conversely, LC3 mRNA only increased at 2h and the LC3BII/LC3BI ratio only decreased at 2 and 5h in Leucine (p<0.05). TRAF6 mRNA increased (p<0.05) in Control at 5h. FBR was not statistically different between groups or from basal 24h postexercise (p>0.05). These data indicate that ingesting a larger quantity of leucine following RE may further reduce postexercise skeletal muscle autophagy in older men, however it does not appear to influence the acute postexercise elevation in markers of the ubiquitin proteasome system or the breakdown of intact proteins.
- skeletal muscle
- protein breakdown
- fractional breakdown rate
- Copyright © 2016, Journal of Applied Physiology