Lower recovery of muscle protein lost during starvation in old rats despite a stimulation of protein synthesis

Sarcopenia could result from the inability of an older individual to recove r muscle lost during catabolic periods. To test this hypothesis, we compare d the capacity of 5-day-refed 12- and 24-mo-old rats to recover muscle mass lost after 10 days without food. We measured gastrocnemius and liver prote in synthesis with the flooding-dose method and also measured nitrogen balan ce, S-methylhistidine excretion, and the gene expression of components of p roteolytic pathways in muscle comparing fed, starved, and refed rats at eac h age. We show that 24-mo-old rats had an altered capacity to recover muscl e proteins. Muscle protein synthesis, inhibited during starvation, returned to control values during refeeding in both age groups. The lower recovery in 24-mo-old rats was related to a lack of inhibition of muscle proteolysis during refeeding. The level of gene expression of components of the proteo lytic pathways did not account for the variations in muscle proteolysis at both ages. In conclusion, this study highlights the role of muscle proteoly sis in the lower recovery of muscle protein mass lost during catabolic peri ods.