Exercise and dietary cholesterol alter rat myocardial capillary ultrastructure

The effects of a cholesterol-rich diet and exercise training on the myocardial capillary network and capillary ultrastructure were examined using Sprague-Dawley rats subjected to a 7-week exhaustive swimming scheme. A total of 16 animals were randomly divided into four groups consisting of normal dietinactive, normal dietexercise, cholesterol dietinactive, and cholesterol dietexercise. Following the experimental regimen the largest heart-mass-to-body-mass ratios were measured for the exercised rats fed a normal diet and the smallest ratios were found for the cholesterol-fed inactive rats. The capillary-to-fiber ratios and the capillary densities of the exercise-trained animals fed normal and cholesterol-containing diets were higher than those of either of the inactive groups. Diet and exercise had significant and opposing effects on the number of capillary pinocytotic vesicles and no significant effect on vesicle size. The capillary endothelium of the exercise-trained animal groups occupied a smaller proportion of the capillary area when compared to diet-matched inactive groups. The results of this study imply that exercise training and a cholesterol-containing diet have opposite effects on the heart-mass-to-body-mass ratio and capillary pinocytotic vesicle number. Furthermore, exercise increases the capillary network of the myocardium and may facilitate receptor-mediated transport in heart capillaries.