[Vascular endothelium (author's transl)]

Studies during recent years have shown the importance of the vascular endothelium in several physiological and pathological circumstances. The culture of endothelial cells has permitted the direct study of endothelial functions. The endothelium is a selective barrier between blood and tissues: the molecules cross it, according to their size, either through the intercellular junctions or through the cells by pinocytotic vesicles. The permeability is modulated by vasomotor agents and modified during endothelial regeneration, especially for the lipids. The endothelium plays a prominent part in the maintenance of the blood flow through its nonthrombogenic properties. It metabolizes circulating thrombogenic substances (arachidonic acid, adenosine diphosphate) and produces potent antiaggregating agents (prostacyclin and adenosine). It may also release a plasminogen activator promoting thrombolysis. The endothelial cells contribute to the formation of the basement membrane by synthesizing collagen and fibronectin, which are involved in platelet adhesion and aggregation to exposed subendothelium. On the other hand, the endothelium has a modulating influence on the local blood flow by producing vasoconstrictors (angiotensin II and III) and vasodilating agents (adenosine and prostacyclin). It is not necessary to elucidate the coordination of these functions and their relationship to the endothelial disorders in vascular diseases.