An ADPase-like substance in placental extracts

The inhibitory effect of human placenta on ADP-induced platelet aggregation was examined. Placental extracts were purified by chromatography and gel filtration. The eluted fractions were subjected to affinity chromatography with Bestatin AH-Sepharose to obtain a more purified substance. A substance markedly inhibited platelet aggregation induced by ADP, and also exhibited high placental leucine aminopeptidase (P-LAP) activity. Preincubation of sample with ADP abolished the platelet aggregatory effect. Thin-layer chromatography (TLC) analysis revealed that the substance hydrolyzed ADP to AMP. The potent anti-platelet aggregating activity of placental extracts appears to be due to ADPase-like action. This action may be one of the controlling factors of hemostasis in fetoplacental circulation.