Activation of Factor XII in Plasma from Rats Pretreated with Tranexamic Acid. Inhibition of a Plasmin‐induced Loss of the Functional Activity of High Molecular Weight Kininogen

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Abstract
Incubation of plasma from rats, pretreated with tranexamic acid (40 mg/100 g) with acetone (23% vol/vol), yielded enzyme preparations in which all the plasminogen present was recovered as plasmin, and as a plasmin-like substance without affinity for Lys-Sepharose. This substance, designated plasmin, was separated from plasmin and kallikrein in a 3-step procedure using columns of Lys-Sepharose, DEAE-Sephadex A-50 and Arg-Sepharose. The ratios of fibrinolytic, caseionlytic, LEe esterase, BAEe esterase and kininogenase activities of plasmin corresponded well with those of rat plasmin and human plasmin. Both rat plasmin and plasmin destroyed the capacity of high MW kininogen (HMWK) to function as a cofactor in the activation of factor XII [FXII] in rat plasma, without causing a corresponding release of the kinin part of the molecule. Rat plasma kallikrein induced full release of kinin from HMWK, but the functional capacity was retained. The reduced extent of activation of FXII observed in plasma from rats injected i.v. with dextran, or rat plasma that was passed through a column with Lys-Sepharose, is due to the loss of functional HMWK caused by plasmin activated in vivo or on the column.

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