Chronic exercise and cardiac vascularization.

Male albino rats were trained on a motorized treadmill for 8 weeks, using eight training regimens which varied in severity from 0.313 m . s-1, 3 days/week for 30 min each day, to 0.447 m . s-1, 5 days/week for 60 min each day. At the end of the 8 week training period, the animals were anesthetized and Pelikan ink infused retrogradely through the aorta, into the coronary arteries and capillaries of the heart. The hearts were sectioned, stained and examined for the number of capillaries per mm2 and the capillary/muscle fiber (C/F) ratios. Six of the eight exercise groups had capillary densities significantly lower than the density in the sedentary control group of 3,022 cap mm-2. Likewise, five of the exercise groups had significantly lower C/F ratios than the sedentary group ratio of 1.077. The difficulties inherent in identification of cardiac muscle fibers make the C/F ratio a weaker measurement for determining cardiac vascularity. The lower capillary density in the trained hearts could be produced by muscle fiber hypertrophy which would push the capillaries farther apart. It is concluded that exercise training does not stimulate the multiplication of cardiac capillaries. The beneficial effect of exercise on the heart is probably a result of enlargement of the coronary arteries or the collateral circulation.