Regional capillary and myocyte distribution in normal and exercise trained male and female rat hearts

Adult Sprague-Dawley male and female rats were exercise trained for five months by either treadmill running or swimming. Significant differences in left ventricular regional capillary density and myocyte cross-sectional area were found. In control rats the epicardial regions had greater capillary density than endocardial regions. Endocardial myocyte cross-sectional areas were greater than those of epicardial myocytes in both sexes. Male rats had larger endocardial myocytes and larger hearts than females. After exercise training, myocyte size increased in the epicardial region but not in the endocardial region, while capillary density increased significantly only in the endocardial region. Similar changes were seen in both male and female rats with comparable degrees of exercise induced hypertrophy. These data suggest that exercise training "normalizes" the distribution of capillaries in the myocardium. Capillary density increased only in the regions where myocyte cross-sectional area did not increase. Further, the effects of exercise on male and female rat hearts is not different when the degree of exercise induced hypertrophy is similar.