ABSTRACT
This chapter focuses on a description of the heterogeneity in endothelium-dependent responsiveness and discusses the limited information available concerning certain of the factors which possibly could determine it. Canine coronary arteries with endothelium relax to acetylcholine, whereas contractions are seen in coronaries from other species such as the sheep, pig, and cattle. The occurrence of endothelium-dependent relaxations to acetylcholine in human epicardial coronary arteries is controversial. Within the same species, differences exist in endothelium-dependent relaxations to a given agonist among different vascular beds. Obvious examples include the following: acetylcholine, platelet products and thrombin, and histamine. Within the same vascular bed endothelium-dependent relaxations to acetylcholine become more prominent as the diameter of the blood vessel decreases. The endothelium-dependent contractions evoked by arachidonic acid in canine veins are unaltered by chronic increases in blood flow.
