ROLE OF VASCULAR ENDOTHELIUM IN EXERCISE-INDUCED DILATION OF LARGE EPICARDIAL CORONARY-ARTERIES IN CONSCIOUS DOGS

Background The role of vascular endothelium in the control of epicardi al coronary artery vasomotion during treadmill exercise remains unclea r. Therefore, we examined the consequences of in vivo balloon endothel ial denudation on external coronary diameter of the left circumflex ar tery during exercise in conscious dogs. Methods and Results Seven dogs instrumented for the measurement of arterial blood pressure, external coronary artery diameter, and coronary blood flow were studied during exercise before and up to 21 days after balloon endothelial denudatio n of the proximal left circumflex artery. Endothelial denudation was c onfirmed by abolition of the epicardial coronary artery dilation induc ed by acetylcholine (0.3 mu g/kg IV) and reactive hyperemia. Epicardia l coronary vasodilation was observed in the control state during tread mill exercise (+5.2+/-1.0%). In contrast, a marked vasoconstriction wa s observed 3 (-4.6-+/-0.6%) and up to 6 days after endothelial denudat ion. Complete epicardial coronary artery dilation in response to acety lcholine and exercise was restored 9 days after endothelial denudation . In addition, epicardial coronary artery vasomotor responses to acety lcholine and treadmill exercise were closely correlated (r=.82, P<.001 ). Reactive dilation was not completely restored 21 days after endothe lial denudation, but reactive hyperemia and exercise vasomotor respons es during the 21 days follow-up were correlated (r=.70, P<.001). Vasod ilation induced by nitroglycerin (1 mu g/kg IV) was reduced by 25% (P< .01) 3 days after endothelial denudation and returned to its correspon ding control level 3 days later. Prazosin (50 mu g/kg IV) significantl y attenuated the exercise-induced coronary artery constriction after e ndothelial denudation (+1.5+/-1.4% versus -4.6+/-1.0%). Conclusions Th ese data demonstrate that endothelium is essential for the mediation o f epicardial coronary dilation during exercise and may protect these v essels against the vasoconstrictor effect of endogenous catecholamines .