Influence of exogenous and endogenous tissue-type plasminogen activator on the lysability of clots in a plasma milieu in vitro c. zamarron, h. r. lijnen, d. collen

The influence of the fast-acting inhibitor of t-PA on clot lysability by endogenous or exogenous t-PA was investigated by immersing clots prepared from normal or inhibitor-rich plasma (endogenous inhibitor) in normal or inhibitor-rich plasma (exogenous inhibitor). Exogenous t-PA inhibitor efficiently neutralizes clot lysis by both exogenous and endogenous t-PA. Endogenous t-PA inhibitor, however, efficiently neuralizes endogenous t-PA but has little influence on clot lysis by exogenous t-PA. These findings indicate that t-PA inhibitor is not concentrated into a clot and that t-PA inhibitor in plasma efficiently neutralizes t-PA incorporated in a clot.

α2-Antiplasmin depleted plasma clots were more susceptible to lysis by both endogenous and exogenous t-PA than normal clots. Removal of α2-antiplasmin from the surrounding plasma resulted in even shorter lysis times.

It is concluded that not only the concentrations of t-PA and of t-PA inhibitor play a role in the regulation of thrombolysis, but also their distribution between the clot and the surrounding plasma. In addition, α2-antiplasmin counteracts clot lysis significantly.