Abstract: Homoeriodictyl-7-O-β-D-glycoside, a flavonoid compound isolated from the Chinese medicinal herb, viscum coloratum inhibited platelet aggregation induced by platelet-activating factor(PAF), but it had no inhibitory activity on adenosine diphosphate-induced platelet aggregation. In the present study, we intended to get an insight into the mechanism of its anti-PAF action. Using [³H]PAF receptor binding assay we found that the compound exhibited inhibitory activity. The inhibitory rate was 18.5%, 28.4%, 58.7%, 78% and 78%, respectively, at concentrations of 10^-8, 10^-7, 10^-6, 10^-5 and 10^-4 mol·L^-1, There was a visible dose-effect relationship as well as a correlation between different concentrations and their inhibitory rates (γ = 0.985, P<0.05) when the dose was equal to or less than 1×10^-5 mol·L^-1, and its IC50 was 8.0×10^-7 mol·L^-1. The inhibitory rate didn't increase with increasing concentration of the compound when it went beyond 1×10^-5 mol·L^-1 indicating competitive inhibition of binding of [³H]PAF to PAF receptor reached saturation.

Key words: Homoeriodictyol-7-O-β-D-glycoside, Platelet-activating factor antagonist, Platelet-activating factor receptor, Platelet aggregation