Tissue activator plasminogen and urokinase are the main physiological activators of plasminogen. The tissue activator of plasminogen is produced by endothelial cells and causes a partial pro-theolysis of plasminogen, resulting in the transformation into plasmin. A distinctive feature of the tissue activator is a high affinity for fibrin, which accelerates its effect on plasminogen hundreds of times. As a result, the tissue activator activates with greater speed those molecules of plasminogen that are adsorbed on the filaments of fibrin.
Thus, the action of the tissue plasminogen activator is limited to the fibrin of the thrombus. Once in the bloodstream, the tissue activator binds to a specific inhibitor and therefore has little effect on the circulating plasminogen in the blood, and also to a lesser extent reduces the level of fibrinogen.
For clinical use, a recombinant preparation of the tissue plasminogen activator alteplase was obtained. The drug is administered intravenously with acute myocardial infarction caused by coronary thrombosis, with pulmonary arterial thromboembolism. Rapidly metabolized in the liver. Despite the fact that alteplase has little effect on the circulating plasmogen in the blood, it often causes hemorrhagic complications. Unlike streptokinase does not have antigenic properties.