EXERCISE TRAINING-INDUCED ADAPTATIONS IN THE CORONARY CIRCULATION

Aerobic exercise training induces an increase in coronary blood flow c apacity that is associated with altered control of coronary vascular r esistance and, therefore, coronary blood flow. The relative importance of metabolic, myogenic, endothelium-mediated, and neurohumoral contro l systems varies throughout the coronary arterial tree, and these cont rol systems contribute in parallel to regulating coronary vascular res istance to differing degrees at each level in the coronary arterial tr ee. In addition to this nonuniformity of the relative importance of va scular control systems in the coronary arterial tree, it appears that exercise training-induced adaptations are also distributed spatially, in a nonuniform manner throughout the coronary tree. As a result, it i s necessary to examine training-induced adaptations throughout the cor onary arterial tree. Adaptations in endothelium-mediated control play a role in training-induced changes in control of coronary vascular res istance, and there is evidence that the effects of training may be dif ferent in large coronary arteries than in the microcirculation. Also, there is evidence that the mode, frequency, and intensity of exercise training bouts and duration of training may influence the adaptive cha nges in endothelial function. Exercise training has also been shown to induce changes in responses of coronary vascular smooth muscle to vas oactive agents and alterations in the cellular-molecular control of in tracellular Ca2+ in coronary vascular smooth muscle of conduit coronar y arteries and to enhance myogenic reactivity of coronary resistance a rteries. Exercise training also appears to have different effects on v ascular smooth muscle in large coronary arteries than in the microcirc ulation. For example, adenosine sensitivity is increased in conduit co ronary arteries and large resistance arteries after training but is no t altered in small coronary resistance arteries of trained animals. Al though much remains to be studied, evidence clearly indicates that chr onic exercise alters the phenotype of coronary endothelial and vascula r smooth muscle cells and that plasticity of these cells plays a role in adaptation of the cardiovascular system in exercise training.