Endothelium determines flow-dependent dilation of the epicardial coronary artery in dogs.

The mechanisms of epicardial coronary artery dilation after reactive hyperemia were studied in instrumented conscious dogs. A pair of ultrasonic crystals, an electromagnetic flow probe and a cuff occluder were placed on the left circumflex coronary artery in 12 mongrel dogs under sterile conditions. Reactive hyperemia after 20 s of coronary occlusion dilated the epicardial coronary artery by 120 +/- 14 micron (3.8 +/- 0.6%, p less than 0.01) from 3.167 +/- 0.345 mm. This reactive dilation was abolished by flow-limiting coronary stenosis. However, vasodilation after nitroglycerin was 168 +/- 26 micron (5.1 +/- 0.5%) and 162 +/- 27 micron (4.9 +/- 0.6%), respectively, before and after flow limitation. After removal of the endothelium by a balloon catheter, dilation of the epicardial coronary artery after reactive hyperemia was markedly attenuated to 7 +/- 4 micron (p less than 0.01 versus before denudation), despite the presence of a similar degree of reactive hyperemia. The extent of coronary dilation after nitroglycerin was unchanged before and after de-endothelialization. Thus, the endothelium contributed to reactive dilation but not to the nitroglycerin-induced dilation. The negative feedback control of coronary diameter to changes in flow velocity may relate to the regulation of coronary artery tone.