Aging and exercise training effects on myocardial structure and function in rat heart

Aging is characterized by a progressive decline in cardiac function. On the other hand, endurance exercise training has been shown to retard or prevent a number of deleterious effects of aging. Yet, little information exists concerning cardiac adaptation in response to exercise training in very old animals. Although the ability of the myocardium to perform external work is a critical component of ventricular function, previous studies of myocardial adaptations have generally been limited to examining the parameters of activation and relaxation. Therefore, we determined the effects of aging and exercise training on power output properties in the myocardium. Force-velocity properties were measured in permeablized myocytes. Velocity of shortening was determined during loaded contractions using a force-clamp technique. Power output was calculated by multiplying the force and shortening velocity values. Normalized peak power output was decreased by 24% in myocytes from old rats (33 mo) vs. young adult (9 mo), partially due to an increase in beta-myosin heavy chain (MHC) content relative to total MHC.; 30-month old Fisher 344/Brown Norway hybrid (F344BNF1) rats underwent 11 weeks of exercise training at either moderate intensity (MI) or high intensity (HI). Peak power output was increased by 41% in MI, but not HI, compared to controls. Maximal isometric tension or maximal unloaded shortening velocity (Vmax) were not different among groups. Increased peak power output occurred in the absence of training-induced changes in either MHC or myosin light chain-1 isoform contents. In addition, we investigated the structural changes in the heart in response to exercise training. With advancing age, alteration of the cardiac contractile properties accompanies structural modifications that have been shown to occur in the myocardium. We found interstitial fibrosis was significantly increased with HI compared with MI or C. These results suggest that MI is associated with a significant increase the ability of the myocardium to do work without affecting structural remodeling. We conclude aging is associated with decreased peak power output, but MI has a positive effect on myocardial contractile function in aged animals but that our HI program may have represented too high a workload for the hearts of aged animals.