Celulas Endoteliales

Endothelial Cells

Endothelial cells, a monolayer of cells lining blood vessels, help to separate intravascular and extravascular spaces. They produce antiplatelet and antithrombotic agents that main- tain blood vessel patency and also vasodilators and vaso- constrictors that regulate vascular tone. Injury to a vessel wall interrupts the endothelial barrier and exposes local pro- coagulant signals (Fig. 2-18B).

Endothelial cells are gatekeepers in inflammatory cell recruitment: they may promote or inhibit tissue perfusion and inflammatory cell influx. Inflammatory agents such as bradykinin and histamine, endotoxin and cytokines induce endothelial cells to reveal adhesion molecules that anchor and activate leukocytes, present major histocompatibility complex (MHC) class I and II molecules and generate key vasoactive and inflammatory mediators. These mediators include:

■ Nitric oxide (NO•): Originally identified as “endothelial- derived relaxation factor,” NO• is a low–molecular-weight vasodilator that inhibits platelet aggregation, regulates vas- cular tone by stimulating smooth muscle relaxation and reacts with ROS to create highly reactive radical species (see above).

■ Endothelins: Endothelins-1, -2 and -3 are low–molecular- weight peptides produced by endothelial cells. They are potent vasoconstrictor and pressor agents, which induce prolonged vasoconstriction of vascular smooth muscle.

■ Arachidonic acid–derived contraction factors: Oxygen radicals generated by the hydroperoxidase activity of cyclooxygenase and prostanoids such as TXA2 and PGH2 induce smooth muscle contraction.

■ Arachidonic acid-derived relaxing factors: The biological opponent of TXA2, PGI2 inhibits platelet aggregation and causes vasodilation.

■ Cytokines: IL-1, IL-6, TNF-

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