We have demonstrated that placental protein (PP 5) first detected by Bohn (1972) shows the same inhibitory effect on platelet aggregation as found in the isolation process of human placental extracts by our previous report. In this report, coagulation and fibrinolytic activities on placental platelet aggregation inhibitor (PPAI) and placental protein (PP 5) were examined. Materials and Methods: The microsomal fraction with an inhibitory effect of platelet aggregation was obteined from human placental extracts. The supernatant fraction concentrated by a column of Bio-beads SM-2 was isolated by gelfiltration on Sephadex G-150 or G-100. PP 5 was measured by RIA using a double antibody method. Antiplasmin and placental UK inhibitor (Kawano) activities were assayed by the chromogenic substrates, S-2251 and S-2444, respectively. Results: 1) PPAI consists of two types of proteins with molecular weights of 78, 000 and 112, 000. 2) Although PPAI appeared relatively the shortened clotting time, it showed neither antiplasmin activity nor UK inhibitory effect. 3) PP 5 had relatively prolonged APTT and thrombin time, but it was found to inhibit the activity of plasmin. 4) Although PP 5 showed no UK inhibitory activity, it was detectable that PP5 is mixed into the placental UK inhibitor (Kawano) by SDS-PAGE method.
In conclusion, it is suggested that PPAI and PP 5 might contribute the homeostasis of fluidity of blood in the placenta.