Uptake of 125I-Lys-plasminogen by in vitro thrombi

The specificity, distribution and rate of uptake of radiolabelled 125I-Lys-plasminogen by in vitro thrombi was investigated. 125I-Lys-plasminogen was added to whole blood perfusion mediums containing preformed thrombi and to whole blood prior to thrombus formation. Uptake was assessed by means of radioisotopic analysis and autoradiography. The plasminogen was taken up by thrombi during and after their formation. The largest percentage was in the fibrin component. epsilon-Aminocaproic acid-blocking experiments confirmed the specificity of plasminogen binding to fibrin. Autoradiography of the thrombi revealed plasminogen in the RBC-fibrin part and in platelet-fibrin aggregates. Plasminogen uptake and penetration into preformed thrombi were found to increase as a function of time. However, formation of thrombi from plasminogen-enriched blood was a more effective means for increasing the plasminogen content of thrombi than perfusion of preformed thrombi in a plasminogen-enriched medium, over the time period studied.