The Inhibition by Plasma of Urokinase and Tissue Activator-Induced Fibrinolysis in Pregnancy and the Puerperium

Evaluation of the fibrinolytic system in full-term neonates

Plasminogen activity and antigen, euglobulin fibrinolytic activity, tissue-type plasminogen activator activity and antigen urokinase-type plasminogen activator antigen, plasminogen activator inhibitor-1 activity and antigen, plasminogen activator inhibitor-2 antigen, tissue-type plasminogen activator/plasminogen activator inhibitor complexes, alpha 2-antiplasmin, histidine-rich glycoprotein, and fibrinogen/fibrin degradation products were measured in blood samples taken from the umbilical vein of 100 healthy full-term newborns. Results were compared with a control group of 30 healthy adults. The overall fibrinolytic activity assessed on fibrin plates was significantly increased (P < 0.002). We also observed high tissue-type plasminogen activator activity levels (P < 0.001), whereas urokinase-type plasminogen activator antigen levels were lower than in adults. There was a significant reduction in plasminogen activity and antigen (P < 0.0001), plasminogen activator inhibitor-1 activity (P < 0.05), alpha 2-antiplasmin (P < 0.0001), and histidine-rich glycoprotein (P < 0.0001), whereas plasminogen activator inhibitor-2, tissue-type plasminogen activator/plasminogen activator inhibitor complexes and fibrinogen/fibrin degradation products did not differ between groups. We conclude that in the newborn there is increased fibrinolytic activity, mainly due to increased plasminogen activators and reduced fibrinolysis inhibition, without systemic fibrinolysis and fibrinogenolysis.

Fibrinolysis and factor XIII in women with spontaneous abortion

In the present study, parameters of the fibrinolytic system and factor XIII were determined in 26 women with spontaneous abortion and in 21 women with intact pregnancies to gain insight into the role of fibrinolysis in spontaneous abortion. Both groups of women did not significantly differ from each other in age or weeks of pregnancy. There were no differences in euglobulin lysis time (ELT), tissue plasminogen activator (t-PA) antigen, and plasminogen activator inhibitor type 1 (PAI-1) antigen between the study group and the control group. Factor XIII activity was significantly decreased in patients during abortion. In the present study, changes of fibrinolytic parameters measured in teh cubital vein blood of patients with abortion were not observed although local changes in fibrinolytic activity had been associated with spontaneous abortion. The pathophysiological role of the decrease in factor XIII activity observed in the present study remains to be elucidated.

Fibrinolysis during normal human pregnancy: complex inter-relationships between plasma levels of tissue plasminogen activator and inhibitors and the euglobulin clot lysis time

Although it has been previously considered that blood fibrinolytic capacity is reduced during pregnancy, this has been disputed. Also the mechanisms underlying any change in fibrinolysis in pregnancy require clarification. We have therefore measured the plasma activity of tissue plasminogen activator (t-PA) and inhibitors (t-PAi) and the concentration of the pregnancy specific inhibitor (PA12) antigen, as well as the euglobulin clot lysis time (ECLT) during normal pregnancy. Plasma concentrations of fibrinogen, plasminogen, fibrin(ogen) degradation products (FDP) and cross-linked products (D-dimer) were also monitored. We confirm a marked reduction of the fibrinolytic activity of the plasma euglobulin fraction from the second trimester, and a parallel reduction in t-PA and increase in t-PAi activities, with rapid return to non-pregnant levels post-partum. In contrast, PAI2, whilst undetectable in non-pregnant control plasma, was already measurable in the first trimester, increased through pregnancy, and remained at a high concentration up to at least 48 h post-partum. Fibrinogen and plasminogen concentrations rose progressively through pregnancy and FDP and D-dimer were frequently detectable in late pregnancy plasma. Changes in the ECLT and plasma t-PA and t-PAi activities in pregnancy cannot therefore be directly related to the concentration of PAI2 antigen. Also, despite the apparent marked reduction in fibrinolytic capacity fibrin(ogen) breakdown products are frequently present in increased plasma concentrations in late pregnancy.

Plasma fibrinolysis during and after normal childbirth

A detailed sequential study of plasma fibrinolytic components in 42 healthy women during and after childbirth showed that striking changes occurred within minutes of placental separation. Significant increases in overall fibrinolytic activity were detected 15 min after delivery. During this period statistically significant increases in tissue plasminogen activator levels were noted but were overshadowed by a dramatic decrease in the level of plasminogen activator inhibitor (PAI). A 10-fold fall in PAI was noted by days 3-5 post-partum, suggesting that the placenta is the major source of PAI detectable at the end of pregnancy and during labour. Persisting slightly elevated levels of PAI were detected for the first few days post partum. This may be due to increased production of normal 'endothelial' PAI in response to the vascular trauma incurred by placental separation, and in response to uterine vascular changes immediately post-partum.

The rapid inhibition of urokinase by plasma from pregnant women at risk for abruptio placenta

Rapid inhibition of urokinase in plasma obtained from women in the third trimester of pregnancy was assessed by the addition of 75 IU urokinase per ml plasma, and measurement of residual urokinase activity with PyroGlu-Gly-Arg-pNA after 5 minutes incubation at 37 degrees C. The urokinase inhibitory capacity was markedly increased for the pregnant women compared to non-pregnant controls. Alpha 1-antitrypsin, alpha 2-macroglobulin and alpha 2-antiplasmin did not account for the activity. Inhibition was higher for women with multiple gestations or macrosomia (n = 11) compared to normal pregnant women (n = 35) suggesting that the placenta contributes significantly to the measured activity. Inhibition was lower for women with hypertension (n = 33) compared to the normal pregnant women. Although the etiology for this difference is unclear, the decreased inhibitory activity may contribute to the increased risk for placental abruption that is observed for this group of women.

Plasminogen activator inhibitors in plasma and platelets from patients with recurrent venous thrombosis and pregnant women

Using affinity chromatography on lysine Sepharose 4B, a fast-acting tissue plasminogen activator inhibitor (t-PAI) was partially purified from t-PAI-rich plasma from patients with recurrent DVT. Its inhibition of tissue plasminogen activator (t-PA) was demonstrated in functional assays and its reaction with 125I-t-PA was analyzed by autoradiography following SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). When the t-PAI was mixed with an equimolar concentration of t-PA at 37 degrees C, the half-life of free one-chain and two-chain 125I-t-PA was 1.8 and 0.8 min, respectively. The rate of complex formation between 125I-t-PA and t-PAI was similar both in patient plasma, pregnancy plasma and platelet lysates made from platelet-rich normal, patient and pregnancy plasma. The molecular weights of the complexes between t-PA and the inhibitors in patient plasma and in the different platelet lysates were identical, while that of the inhibitor complex formed in pregnancy plasma was found slightly higher by SDS-PAGE indicating that the pregnancy plasma t-PAI differs from the fast-acting t-PAI found in plasma from thrombotic patients and in platelet lysates.

Different types of plasminogen activator inhibitors in plasma and platelets in pregnant women

The content of tissue plasminogen activator inhibitor (t-PA-I), and of specific pregnancy plasma-PA-I reacting with antibodies to placental-PA-I, was measured in platelet-poor plasma (PPP), platelet-rich plasma (PRP), serum and platelet lysate, both from pregnant women and healthy non-pregnant (male or female) controls. Inhibitory activity was much higher in PPP from pregnant women than in PPP from controls, though it was comparable in platelet lysates both from pregnant women and from controls. The specific pregnancy Plasma-PA-I was present in high concentration in pregnancy PPP, but absent in PPP from the controls and also absent in platelet lysates from both pregnant women and controls. The results show that the specific pregnancy plasma-PA-I is not identical to either the PA-I in platelet lysate or to the PA-I in PPP from non-pregnant controls.

Isolation of a new specific plasminogen activator inhibitor from pregnancy plasma

A specific plasminogen activator inhibitor was isolated from the plasma of pregnant women by matrix-bound, cross reacting monoclonal antibodies against placental plasminogen activator inhibitor. The pregnancy plasma plasminogen activator inhibitor (PP-PA-I) was found to be immunologically different from the inhibitor produced by endothelial cells. Its molecular weight was 70 000 daltons. It formed complexes with urokinase (u-PA) and with plasminogen activator of the tissue type (t-PA), similar to those formed by the placental plasminogen activator inhibitor (PI-PA-I). It did not inhibit plasmin. For measuring PP-PA-I, an enzyme-linked immunosorbent assay (ELISA) was designed using monoclonal and polyclonal antibodies against the placental inhibitor. Concentrations of PP-PA-I increased successively during pregnancy, and fell sharply after delivery. This inhibitor could not be detected in normal non-pregnancy plasma. The results indicate that the inhibitor isolated from pregnancy plasma is responsible for the depressed fibrinolytic activity during pregnancy, and that the placenta is the source of the inhibitor.