Heterogeneity of endothelium-dependent responses in mammalian blood vessels

A number of naturally occurring substances can evoke endothelium-dependent responses in isolated blood vessels. In most arteries studied, acetylcholine, adenosine diphosphate (ADP), adenosine triphosphate (ATP), arachidonic acid, bradykinin, and thrombin cause endothelium-dependent relaxations. In veins, however, the endothelium-dependent inhibitory effect of acetylcholine, ATP, and thrombin often is transient and/or modest, as it is masked by the direct stimulating action of these substances on the venous smooth muscle; arachidonic acid evokes endothelium-dependent augmentation of the contractile response to norepinephrine. Aggregating platelets cause an endothelium-dependent relaxation of certain but not all arteries and veins that is probably mediated by released serotonin and ADP. The endothelium of the coronary artery may enhance the relaxations caused by catecholamines. Vasopressin causes endothelium-dependent relaxations in cerebral and coronary arteries but not in systemic blood vessels. Hypoxia causes endothelium-dependent increases in tension in systemic arteries and in pulmonary arteries and veins but not in limb veins. The heterogeneity in endothelium-dependent responsiveness may reflect variations in sensitivity of either endothelial or vascular smooth-muscle cells of different anatomical origin.