Aspirin effect on the release of plasminogen activator inhibitors by human platelets.

Intrinsic plasminogen activators (PA) were tested in euglobulins (eug) of platelet poor plasma (PPP) with and without washed platelets (WP), treated or not with urokinase (UK), streptokinase (SK), collagen (Col) and aspirin (ASA) using fibrin plates method. A significant decrease of the fibrinolytic activity related to the presence and number of platelets was observed. We confirm the presence of platelet anti-UK and anti-SK activities. The former appears to be higher than the other activity. Low and high concentrations of Col stimulated the release of plasminogen activator-inhibitors (PA-I) from platelets, and ASA could not modify this release. Besides ASA might inhibit some PA release. The high concentration of Col was capable to release anti-UK and anti-SK activities from platelets and perhaps other intrinsic PA-I. The low concentration of Col was only capable to release intrinsic PA-I, suggesting that anti-UK and anti-SK needed a stronger stimuli to be released than intrinsic PA-I. We must consider the possibility that the PA-I and/or activators could be released by different metabolic pathways other than cyclooxygenase pathway.