Hemorheology and vascular endothelial cells.

The vascular endothelium is a biologically active monolayer of cells provid ing an interface between the blood how and tissues. Vascular Endothelial Ce lls (VEC) have two functional states. The endothelium is normally anti-thro mbotic and anti-adhesive to ensure blood fluidity. During aggressions, such as atherosclerosis, inflammation states, metabolic diseases (through chemi cal or mechanical stimuli), VEC can reverse its functions by expressing sto red material or by slower involvement of previously are repressed genes. Endothelial cells have three types of anti-thrombotic properties: vase regu lating properties: VEC release vasomotor components, such as endothelin (va soconstriction), prostacyclin and nitric oxide (vasodilatation). Endothelial cells also have antithrombotic and hemostatic properties. They express proteoglycans on their surface, including some negative-charge, pla sminogen, sulfate glycoaminoglycans (heparane-sulfate), and secrete plasmin ogen tissular activator (t-PA) and tissular factor inhibitor. One fundament al action of the endothelium in that area is the production and expression of thrombomodulin, a thrombin receptor. This function has a major anticoagu lation effect, controlling continual thrombin generation at the sub-endothe lium and blood cell interface. Moreover, endothelial cells show anti-adhesi on properties. During cardio-vascular diseases, all of these properties may be reversed. Thus, the VEC have a determinant role in hemodynamic control through these various metabolic activities, such as control of homeostasis, vascular tone , blood fluidity, coagulating properties, cellular adhesion. Otherwise, man y studies have demonstrated that local blood how conditions have a crucial role on the VEC properties (mechanoactivation and mechanotransduction conce pt). In conclusion, knowledge of all the properties of the endothelial cell s and control of the phenomena which define their functions is a key elemen t in understanding cardiovascular diseases.