Dextran-induced lowering of parameters of the kallikrein-kinin system in rat plasma

Pretreatment of rats with tranexamic acid inhibited the rapid lowering of the plasma levels of acetone/kaolin-activated prekallikrein proactivator and prekallikrein caused by intravenous injection of dextran, but did not inhibit the reduction in the level of plasminogen, and potentiated the lowering of high molecular weight kininogen. By acetone/kaolin activation of normal rat plasma a mixture of surface-bound factor XIIa and unbound XIIf was obtained, and a BAEe-esterase (MW about 47,000) possessing weak kininogenase activity was present in addition to kallikrein. In activated plasma from dextran-treated rats the cleavage of XIIa was strongly reduced, and the second esterase was almost absent. It is suggested that dextran induces the loss of a plasma factor which is important for the cleavage of factor XIIa in the adopted procedure. This factor was not high molecular weight kininogen, and the lowering of plasminogen was too small to account for the reduction in PKA-activity.