Circulating levels of prekallikrein and kallikrein in pregnancy and labor.

Plasma levels of prekallikrein and kallikrein were measured in 147 pregnant women by the chromogenic substrate S2302 method. At the same time, individual fibrinolytic inhibitors (alpha 2-plasmin inhibitor, alpha 1-antitrypsin, alpha 2-macroglobulin, antithrombin-III, and Cl-inactivator) were determined by the radial immunodiffusion method. The plasma levels of prekallikrein increased significantly during pregnancy and thereafter decreased during delivery. In patients with severe toxemia of pregnancy and hydatidiform mole, plasma prekallikrein levels were low, below the normal range. On the other hand, plasma kallikrein concentrations were within non-pregnant levels until the end of pregnancy, but the levels increased just before delivery. Although no significant correlation was found between prekallikrein levels and fibrinolytic inhibitory activity in pregnancy, Cl-inactivator concentrations tended to be low only when the prekallikrein level was high. These changes in the prekallikrein-kallikrein system in late pregnancy may be related to activation of the kinin, which results in labor pain.