Placental circulation, especially circulation in choriodecidual space in normal and toxemia of pregnancy was investigated from the view point of coagulation and fibrinolysis. Main results obtained were as follows:
1) No endothelial cells could be observed at least on the surface of villi.
2) Antithrombin III (AT-III) and α2 plasmin inhibitor (α2-PI) were decreased in plasma obtained from uterine vein during cesarean section.
3) Two potent proteins which inhibited platelet aggregation (placental platelet aggregation inhibitor: PPAI) and prolonged blood coagulation time (placental coagulation inhibitor: PCI) were found in microsomal fraction of placental homogenate.
4) PCI was purified by several steps of column chromatography. Molecular weight and pI of PCI were estimated to be 29,000 daltons and 4.2-4.4, respectively.
5) Histochemical study of PCI revealed that it was distributed syncytiotrophoblast in the placenta.
6) In the coagulation cascade, thrombin and factor Xa formation were inhibited by PCI when reacted with phospholipid and Ca2+, but essentially no inhibition was observed without phospholipid.
7) In toxemia of pregnancy, AT-III was decreased and α2-PI plasmin complax was increased as severity increased.
8) The amount of PCI in the placenta of toxemia was significantly increased but thrombomodulin activity was almost similar to that of normal pregnancy.
