EFFECTS OF EXERCISE TRAINING ON REGULATION OF TONE IN CORONARY-ARTERIES AND ARTERIOLES

A large number of studies now support the concept that exercise traini ng alters functional control of the coronary circulation. Recent work has approached this area using ex vivo coronary arterial preparations (proximal coronary arteries, near-resistance arteries, resistance arte rioles) isolated from exercise-trained animals and contracting indepen dently of confounding in vivo influences. The combined results of thes e studies indicate that training-induced alterations in vascular contr ol mechanisms do not occur uniformly throughout the coronary vascular tree. Proximal epicardial coronary arteries (approximately 2.0 mm diam eter) isolated from exercise-trained pigs exhibited significantly redu ced contractile responsiveness to the alpha-adrenergic receptor agonis t, norepinephrine, but unaltered contractile responsiveness to K+, ace tylcholine, and endothelin. Also, proximal arteries from exercise-trai ned animals demonstrated enhanced sensitivity to the vasodilator effec ts of adenosine. At the other end of the vascular spectrum, in resista nce arterioles (<150 mu m diameter) the relaxation responses to adenos ine were unaffected by exercise training, but bradykinin-induced vasod ilation (endothelium-dependent) was significantly enhanced. In near-re sistance arteries (150-240 mu m diameter) responses to both bradykinin and adenosine were enhanced by exercise training. Thus, exercise trai ning is associated with intrinsic vessel size-dependent alterations in coronary smooth muscle and endothelium-mediated regulatory mechanisms .