THE ENDOTHELIAL ORGAN

The endothelium, in addition to its antithrombogenic properties, exerts a variety of effects on vascular homeostasis, the most prominent being the control of vascular tone and cell growth. These effects are mainly mediated either directly or indirectly by endothelium-derived autacoids such is nitric oxide, prostacyclin, endothelin-1, and possibly prostaglandin H-2. In normotension, during which the endothelium produces mainly nitric oxide and prostacyclin, the vasodilator and growth inhibitory influence predominates. Hypertension, on the other hand, is associated with a shift toward enhanced constriction and vascular hypertrophy. These effects are associated with a decreased production of nitric oxide and prostacyclin and increased production of endothelin-1 and prostaglandin H-2. Although the evidence is circumstantial, anti-hypertensive therapy with angiotensin-converting enzyme inhibitors appears to redress the imbalance in endothelial production of vasodilator and vasoconstrictor autacoids and to reverse morphological changes within the vascular wall.