Exercise training in swine promotes growth of arteriolar bed and capillary angiogenesis in heart

Exercise training induces coronary vascular adaptations. The goal of this study was to contrast the effects of training on capillary and arteriolar growth. Minipigs were trained for 1, 3, 8, and 16 wk and compared with controls. Maximal O2 consumption increased continuously throughout the study. Capillary and arteriolar densities and diameters, and proliferation of vascular cells in these vessels, were determined in perfusion-fixed tissue. The arterioles were subdivided into five groups according to diameter: 10-19.9, 20-30, 31-40, 41-70, and 71-120 microgram. The total vascular bed cross-sectional area increased by 37% at 16 wk, mainly because of an increase in the number of the small arterioles and an increase in the diameter of the larger vessels. Capillary density increased at 3 wk and then returned to control levels by 16 wk; concomitantly, the number of arterioles (20-30 microgram) increased at 16 wk. We speculate that the "extra" capillaries observed at 3 wk were the source of the new arterioles.