[The maintenance of placental circulation--the study on the platelet inhibition activity of placental chorioepithelial brush border membrane].

We studied the platelet aggregation inhibiting activity of human placental syncytiotrophoblast brush border membrane vesicles (BBMV) and obtained the following results. 1. There existed a very strong platelet aggregation inhibiting activity in placental BBMV. The BBMV almost completely inhibited the platelet aggregation induced by ADP, arachidonic acid and ristocetin. 2. There existed a very strong ADP degrading activity (ADPase activity) in the placental BBMV. ADP was quickly decomposed to AMP by BBMV. 3. Placental BBMV inhibited platelet TXA2 (TXB2) production. In the 0.04 mg/ml protein concentration of BBMV, platelet TXA2 production was almost completely inhibited. 4. There existed a very strong platelet aggregation inhibiting activity in solved BBMV. Soluble BBMV almost completely inhibited the platelet aggregation induced by ADP and arachidonic acid but did not inhibit the platelet aggregation induced by ristocetin. 5. ADP decomposing activity and platelet TXA2 production inhibiting activity were separated by anion exchange column chromatography of soluble BBMV. 6. When BBMV was treated with ultrasonic waves to destroy the membrane structure, only the activity inhibiting ristocetin-induced platelet aggregation was markedly decreased.