Effect of exercise training on aging-induced changes in rat papillary muscle.

BACKGROUND The effects of aging on papillary muscle have been widely demonstrated, but no data on the effects of exercise on the age-related changes are available. OBJECTIVE To analyze the effects of aging on the morphological and quantitative properties of papillary muscle and investigate whether a long-term moderate exercise program would exert a protective effect against the effects of aging. METHODS We used electron microscopy to study the density of myocytes, capillaries and connective tissue and the cross-sectional area of myocytes of the papillary muscle of the left ventricle of 6- and 13-month-old untrained and exercised Wistar rats. RESULTS As expected, the volume density of myocytes declined significantly (p<0.05) with aging. The length density of myocardial capillaries also declined with aging, but not significantly. The interstitial volume fraction of the papillary muscle tissue increased significantly (P<0.05) with age. The number of myocyte profiles showed a reduction of 20% that was accompanied by myocyte hypertrophy in the aged rats (P<0.05). Animals submitted to a 60-minute daily session,, 5 days/wk at 1.8 km x h(-1) of moderate running on a treadmill for 28 weeks showed a reversion of all the observed aging effects on papillary muscle. CONCLUSION The present study supports the concept that long-term exercise training restrains the aging-related deleterious changes in the papillary muscle.