Inhibition of Tissue Plasminogen Activator Activity by Aspirin In Vivo and Its Relationship to Levels of Tissue Plasminogen Activator Antigen, Plasminogen Activator Inhibitor, and Their Complexes

The observation that aspirin inhibits the increment in tissue plasminogen activator ft-PA) activity induced by venous occlusion of the forearm became controversial with the publication of several nonconfirmatory studies. The current study was performed to confirm the original observation and determine the mechanism by which aspirin suppresses the incremental t-PA activity induced by venous occlusion. Aspirin (650 mg/d X 2) caused no change in resting levels of t-PA antigen (t-PA:Ag) or activity, plasminogen activator inhibitor 1 antigen (PAl-i :Ag), or activity or t-PA-PAI-1 complexes. In contrast. aspirin reduced the increments induced by venous occlusion as follows: t-PA:Ag by 45% (P = .001 ); t-PA activity (euglobulin lysis time, ELT) by 43% (p = .006); and t-PA activity (alpha2-plasmin inhibitor-plasmin complexes. PIPC) by 41%