Abstract
In an attempt to clarify the mechanism of blood flowing in the placental intervillous circulation, we investigated the possibility as to whether the placenta might have an inhibitory effect of platelet aggregation.Materials and Methods: Fresh, full-term placental extracts were prepared by washing several times in 0.01M Tris at 4°C to remove contaminating blood and tissue fluids. Following centrifugation at 3, 000 r. p. m. for 15 minutes, the supernatant fluid was taken and centrifuged again. PRP was prepared by standard techniques. The extract was added to PRP and incubated at 37°C for 3 minutes. The effects of placental extracts on platelet aggregation were measured by using Lumi-aggregometer with inducers such as ADP, collagen, epinephrine and ristocetin. In addition, the inhibitory effects of placental lipids, placental proteins and PGI2 on platelet aggregation were investigated by the same method.Results: 1) The placental extracts inhibited not only the secondary platelt aggregation induced by ADP, but also the release reaction of ATP induced by collagen, epinephrine and ristocetin. 2) The tissue extracts obtained from maternal side and central portion of the placenta also exhibited the strong inhibitory effect of platelt aggregation, but the umbilical cord vessels had little inhibitory effect on secondary aggregation. 3) Tissue extracts of hydatidiform mole showed not only a strong inhibitory effect of secondary aggregation, but also inhibited release reaction by ATP. 4) The inhibitory effect by placental extracts was different from that of PGI2. 5) Furthermore, such inhibitory effects were not demonstrable by placental thromboplastin, hCG, hPL and hSAP, but PP5 as well as PP10 possessed similar properties to an inhibitory effect of platelet aggregation in placental extracts.In conclusion, the placental tissue contains the substance which inhibits the platelet aggregation. Accordingly, such an inhibitory effect might be available for preventing thrombosis formation in the intervillous circulation.
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