The control of production and release of haemostatic factors in the endothelial cell.

Endothelial cell products contribute to many aspects of the regulation of haemostasis. They include potent inhibitors of platelet aggregation (prostacyclin and nitric oxide) rapidly released in response to agonists such as thrombin. Similar agonists also induce the formation of platelet-activating factor by endothelium. Endothelial cell surface ectonucleotidase enzymes control the catabolism of platelet-active adenine nucleotides. The main source of the circulating coagulant cofactor von Willebrand factor is the endothelium, where it is stored in granules for agonist-triggered exocytosis and also secreted constitutively. Surface anticoagulant activities are due to the presence of antithrombin and thrombomodulin. Endothelial cells also secrete plasminogen activator and its inhibitor. Many of these reactions are significantly modulated by exposure of endothelium to cytokines or bacterial endotoxin, the most striking example being the new synthesis and surface expression of the procoagulant tissue factor (thromboplastin).