ABSTRACT
The endothelium is a complex, unique organ with a vast surface area and an aggregate mass equal to that of the liver. The endothelial disposition of angiotensin-converting enzyme (ACE) led to the development of assays useful for the identification of endothelial cells in culture and to the development of orally effective antihypertensive drugs that target ACE. A blood-borne agonist interacting with receptors on the endothelial cells (EC) leads to release of a mediator that modulates smooth muscle relaxation. ECs have both thrombotic and thrombo-resistant properties. The hemostatic potential of the endothelium results from a complex balance between active factors that have opposing biological actions and between active factors and specific inhibitors. ECs inhibit thrombus formation by interfering with the coagulation cascade, inhibiting platelet adhesion/aggregation, and activating fibrinolytic pathways. Many substances produced by ECs affect local vasomotor tone and a complex interaction exists between those elements that control hemostasis: vascular modeling and vasomotor reactivity.
