Effect of specific antagonists on PAF-induced platelet aggregation and release of plasminogen activator

We investigated the inhibitory effects of two synthetic phospholipids KO-286,001 and KO-286,006 on the platelet-activating factor (PAF) induced release of plasminogen activator (PA) in the isolated pig ear preparation as well as aggregation of pig platelets. The action was compared with that of the natural PAF antagonist BN 52021. The activator release induced by 5 x 10(-9) mol/l PAF was inhibited by 10(-6) mol/l KO-286,006, whereas BN 52021 and KO-286,001 had no effect. All three PAF antagonists tested inhibited the aggregation in a dose-dependent manner. Comparison of the IC50 values confirmed the considerably lower inhibitory action of BN 52021 and KO-286,001. Our results suggested that similar receptor sites are involved in both PAF activities tested and furthermore, that are species differences in the inhibition of PAF effects.