[Tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI)]

Tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor 1 (PAI-1) are the most important factors involved in the regulation of blood fibrinolysis. t-PA converts zymogen plasminogen to plasmin on the surface of endothelial cells to maintain blood fluidity and on the surface of the thrombus to efficiently lyse the thrombus. In circulating plasma, PAI-1 inactivates t-PA by forming an equimolar complex with t-PA to suppress the hyperfibrinolysis of the blood. Both proteins are synthesized by the vascular endothelial cells and secreted from the cells in resting state and in response to several stimuli such as thrombin, endotoxin, cytokines and growth factors. In various diseases such as DIC, thromboembolism and bacterial infection, the plasma concentrations of those two factors vary as a consequence of several stimuli, representing the altered fibrinolytic balance caused by the disease. Measurements of these factors and evaluation of the fibrinolytic balance will be important for determination of the most appropriate method of treatment. Moreover, the high plasma concentration of PAI-1 will be a prognostic marker of the disease and may be a risk factor of thrombotic events. In clinical treatment, t-PA is now widely used as a valuable fibrinolytic agent especially in myocardial infarction.