Endothelium-related coronary dilation after balloon denudation was compared with the extent of luminal lining of the regenerated endothelial cells. Under conditions of asepsis, a pair of 10-MHz piezoelectric crystals, an electromagnetic flow probe, and a cuff occluder were placed on the left circumflex coronary artery. Seven to 10 days after this instrumentation, the dogs were anesthetized and the endothelium was removed with the use of a balloon catheter. Immediately after balloon denudation, coronary dilations following reactive hyperemia (reactive dilation) and acetylcholine 3 micrograms/kg iv were reduced to 19 +/- 5 (P less than 0.01) and 10 +/- 4% (P less than 0.01) of control, respectively. In 2, 5, and 7-10 days after denudation, reactive dilation in the conscious dogs was 24 +/- 7 (n = 16), 71 +/- 10 (n = 11), and 75 +/- 9% (n = 5) of control, respectively. Acetylcholine-induced coronary dilation in conscious state was 52 +/- 12 (n = 9), 116 +/- 17 (n = 7), and 94 +/- 24% (n = 2) of control in 2, 5, and 7-10 days after denudation, respectively. There was a positive linear relation between the extent of reactive dilation and acetylcholine-induced dilation from 2 to 10 days after denudation (r = 0.734). The amount of reactive hyperemia, nitroglycerin-induced coronary dilation, and ergonovine-induced coronary constriction remained constant during the experimental period. The area covered by the endothelial cells at the denuded site was 8 +/- 3 (n = 5), 18 +/- 9 (n = 6), 64 +/- 9 (n = 6), and 81 +/- 11% (n = 3) of the denuded area in 0, 2, 5, and 7-10 days after denudation, respectively, which linearly related to the percent recovery of reactive dilation (r = 0.912). Thus reactive dilation or acetylcholine-induced coronary dilation depended on the presence of endothelium, irrespective of the shape or alignment of the regenerated tissues. These findings may be clinically relevant because anatomical integrity of the endothelium might be assessed in vivo by reactive dilation or acetylcholine-induced coronary dilation.