Abstract
Our previous studies showed that intravenous injection of tissue plasminogen activator (TPA) from pig heart to albino rats causes lysis of artificial clots in v.jugularis. This is concomitant with a short-term increase in the fibrinolytic activity (FA) of the euglobulin fraction of blood plasma. The other components of the fibrinolytic system remain thereby unchanged.We tested the state of the fibrinolytic system at increasing concentrations of TPA and under varying conditions. A repeated (2-fold) injection of TPA did not further increase FA. When TPA was injected 4 times, the antiactivator and the level of TPA in the plasma of test and control animals decreased. This can be due to exhaustion of endogenous plasminogen activator as a stress response to repeated fixation of animals for intravenous injection of TPA. Injection of the same amount of TPA for 5 days caused no significant changes in FA. After a single injection of a 5-fold amount of TPA the changes were more noticeable; fibrinogen concentration was slightly decreased, whereas plasma recalcification time was increased. Thus, administration of exogenous TPA causing clot lysis has no prolonged effect on FA, which can be either due to its rapid release from the blood stream or to its binding to blood proteins.
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