Inhibitors of Urokinase-Induced Fibrinolysis in Pregnancy
Pregnancy plasma possesses inhibitory activity against urokinase measured on unheated fibrin plates. Antiurokinase activity in late pregnancy plasma subjected to gel filtration on Sephadex G-200 eluted with the high molecular weight proteins including α2-macroglobulin and, in greater quantity, with albumin. In all non-pregnancy plasmas the high molecular weight inhibitor activity was present in equivalent quantities; the lower molecular weight inhibitor was found in small amounts in only a proportion of plasmas. The anti-urokinase activity of pregnancy plasma could be separated from α1-antitrypsin and α2-antiplasmin by chromatography on DEAE-Sephadex. Within 1 hour of parturition plasma fibrinolytic activity increased and there was substantial reduction in the anti-urokinase activity of the lower molecular weight fractions; no change was seen in the high molecular weight inhibitory activity. It is concluded that anti-urokinase activity in pregnancy plasma resides in a protein distinct from established protease inhibitors; a placental source is postulated.