Endothelial function in different organs.

The endothelial lining represents an organ of 1.5 kg in an adult which is distributed throughout the body and serves multifunctional purposes. It regulates vascular growth processes and adaptations and controls the delicate equilibrium between coagulation-hemostasis and fibrinolysis. The endothelium is not only a simple diffusion barrier between the intravascular and extravascular space of blood and lymph vessels thus regulating permeability (ie, the fluid, metabolite and catabolite exchange), but synthetizes, releases, converts, activates and/or inactivates various vasoactive hormones. Thus, it regulates vascular tone and organ blood supply as well as lymphatic flow and expression of surface receptors for the activation of leukocytes eg, during inflammation. In different organs it has additional, organ specific functions (eg, cerebral endothelial lining/blood brain barrier, endothelium mediated changes in renal, splenic and hepatic function and in skeletal muscle perfusion) by generating various autacoids such as nitric oxide, prostaglandins, endothelins, hyperpolarizing factors, and so on. These autacoids are not only vasoactive compounds but also modulate the activation of transcription factors. The endothelial autacoids exert an important role in vascular homeostasis (eg, by direct inhibition of atherogenesis and by inhibition of proatherogenic genes).