Cardiac energetics and performance of exercised and food-restricted rats during aging

The effects of exercise and food restriction on hemodynamic and metabolic characteristics of the heart during aging were studied in male, retired breeder, Fischer 344 rats. At the age of 10 mo they were divided into three groups: 1) sedentary and ad libitum fed (S); 2) sedentary and food restricted by alternate-day feeding (R); and 3) exercised 20 min/day on a treadmill and ad libitum fed (E). Isolated, perfused working hearts were analyzed at 10 (S only), 18, 24, and 30 mo. Groups E and R demonstrated significant improvements (P less than 0.01) at 18 mo for cardiac output (ml.min-1.g-1), pressure work (kg.m.min-1.g-1), and efficiency (%). These performance parameters declined (P less than 0.01) after 18 mo in all groups; however, at 24 mo, E maintained higher values (P less than 0.01) for these parameters than S or R. At 30 mo, all groups were similar. Levels of high-energy phosphate compounds or lactate release were not affected by age or treatment. An age-related increase (P less than 0.05) in left ventricular hexokinase activity was observed in all groups. Activities of rate-determining enzymes of Krebs cycle or content of cytochromes were not affected by age. We conclude from this metabolic profile that energy production is not impaired in the aged Fischer 344 rat heart.