[The platelet aggregation inhibiting activity in human placenta--study on the ADP degrading activity of human placental villi].

We studied the platelet aggregation inhibiting activity and ADP degrading activity of human placental villi (tissue culture supernatant) and brush border membrane vesicles (BBMV) and obtained the following results. 1. There existed a platelet aggregation inhibiting activity in tissue culture supernatant of villi (S-villi) but not in that of decidua or amnion. The S-villi inhibited the platelet aggregation induced by ADP, but not that induced by collagen, arachidonic acid or ristocetin. And, there was also ADP degrading activity (ADPase activity) in the S-villi. ADP was quickly degraded by S-villi. When ADP was preincubated with S-villi, the platelet aggregation induced by ADP was completely lost. 2. There was very strong platelet aggregation inhibiting activity in placental BBMV. The BBMV almost completely inhibited the platelet aggregation induced by ADP, collagen, arachidonic acid and ristocetin. And there was very strong ADP degrading activity in the placental BBMV. ADP was quickly degraded by BBMV. When ADP was preincubated with BBMV, the platelet aggregation induced by ADP was completely lost. 3. The enzymatic character (heat stability, enzymatic kinetics, Ca++ dependency and pH dependency) of ADP degrading activity in BBMV was very similar to that in S-villi. 4. The ADP degrading activity of both S-villi and solubilized BBMV were fractionated by anion exchange column chromatography and gel filtration column chromatography in similar patterns, and it was shown that ADP degrading substance of both S-villi and solubilized BBMV had a molecular weight of about 60K.