Myocardial protein synthesis during aging and endurance exercise in rats.

Rates of protein synthesis, and RNA and cytochrome c concentrations, were assayed in hearts of 9- and 25-month-old sedentary rats and 25-month-old rats trained to run 5 days/week for 21 weeks. Isolated working hearts were perfused with modified Krebs-Henseleit bicarbonate buffer labelled with [14C]phenylalanine. Protein synthesis rate decreased with age, as did RNA content and efficiency of protein synthesis, an indication of the activity per ribosome. None of these three parameters were altered by endurance training. Cytochrome c concentration, which also decreased significantly between 9 and 25 months, was increased in the 25-month-old endurance trained heart to the level of the 9-month-old sedentary heart. We conclude that the depressed protein synthetic system of aged animals is less of a liability in the endurance trained than in the sedentary animal as a consequence of the associated improvement in functional capacity that serves to minimize homeostatic disequilibrium in response to environmental challenges.