Epicardial coronary artery diameter and coronary blood flow were measured by a sonomicrometer and electromagnetic flow probe, respectively, in conscious dogs. Reactive dilation appeared following the full appearance of reactive hyperemia. Serotonin induced coronary dilation as well as reactive dilation disappeared after endothelial balloon-denudation. Thus, endothelial linings play an important role in regulation of the epicardial coronary arterial tone in physiological states. Reduced level of endothelium-related relaxation in response to serotonin was also noted in Göttingen miniature pigs. When severe and persistent spasms were provoked in pigs, intramural hemorrhage was frequently induced along the thickened intima. The latter phenomenon suggests the important relevance of spasms in the progression of atherosclerosis or evolution of myocardial infarction.
