Activator Inhibitor 1 : Development of a Radioimmunoassay and Observations on Its Plasma Concentration During Venous Occlusion and After Platelet Aggregation

To study the effect of plasminogen activator inhibitors (PAl) on fibrinolysis it is essential to be able to specifically measure these proteins in plasma. To this end PAl-i was purified from cortisol-stimulated HT 1 080 fibrosarcoma cells and antisera raised in rabbits. The immunologic relationship of the purified inhibitor to PAl-i in plasma and platelet extracts was established by immunoblotting and regular and reverse fibrin zymography. Furthermore. the purified product could be immunoprecipitated with antibodies to human or bovine endothelial cell-derived PAl-i. A radioimmunoassay was developed that measures both free and tissue-type plasminogen activator (t-PA)-bound PAl-i in plasma and has an effective range of 8 to 250 ng/mL. PAl-i antigen levels showed a twofold increase after 20 minutes of venous occlusion, partially due to hemoconcentration. Approximately one quarter of PAl-i before and after venous occlusion is derived from platelets.