Yoshiro Iga

Molecular Exchange between Blood and in vitro Thrombi

Uptake of radioiodinated Lys-plasminogen (125I-PLG), albumin (125I-ALB), and tritiated water (3H-H2O) by in vitro thrombi and interchange of these molecules with blood in an in vitro perfusion system were investigated. The radioisotopes were taken up by thrombi either by incorporation during formation in radiolabelled blood or by perfusion of preformed nonradioactive thrombi in radiolabelled blood. Release of the radioisotopes into a perfusion medium of nonradiolabelled blood was then monitored over a 120-min period. The small molecules of 3H-H2O were rapidly released from the thrombi and achieved equilibrium with the perfusion medium by 120 min in that the specific radioactivity (cpm/mg) of the thrombi equalled that of the medium. The larger molecules of 125I-PLG and 125I-ALB were more slowly released and did not reach equilibrium with the perfusion medium over the period studied. Release of 125I-ALB was intermediate between that of 3H-H2O and 125I-PLG. The greater retention of 125I-PLG by the thrombi was consistent with the high binding affinity of plasminogen for fibrin. The demonstrated movement of these radioisotopes between medium and thrombus suggests that thrombi exist in blood in a dynamic state of flux, exhibiting a fluid exchange of molecules between the interstitial compartment of the thrombus and blood.

Kinetics of urokinase-induced thrombolysis in a biphasic in vitro system

The role and effect of added lys-plasminogen (lys-PLG) on urokinase-induced thrombolysis in an in vitro biphasic system were investigated. The kinetics of lysis of whole blood thrombi was followed in perfusion mediums of normal plasma, PLG-deficient plasma and normal saline using a high and a low concentration of urokinase (UK). The lysis of standard whole blood thrombi in whole blood perfusion mediums to which had been added UK alone or UK plus lys-PLG was compared to whole blood thrombi enriched with lys-PLG by incorporation during thrombus formation or by adsorption during perfusion. In addition, the kinetics of lysis of PLG-deficient fibrin thrombi perfused in PLG-deficient plasma or normal saline was studied when lys-PLG had been added to the thrombus, to the perfusion medium or to both thrombus and medium. In PLG-deficient plasma from which plasmin inhibitors had not been removed, thrombolysis was minimal even at a high concentration of UK. This effect could be neutralized, and to some extent, regulated, by lys-PLG enrichment of the medium. Both PLG-incorporated and PLG-adsorbed whole blood thrombi gave initial and sustained acceleration of UK-induced lysis in comparison with standard nontreated thrombi. It is concluded that in a blood-thrombus biphasic thrombolytic system induced by UK, there is interaction between the phases, and that PLG in both phases influences thrombolysis.