Action of AD6 (8-monochloro-3-beta-diethylaminoethyl-4-methyl-7-ethoxycarbonylmet hox y coumarin) on human platelets in vitro.

The action of AD6 was tested in vitro on human platelets by measuring beta-thromboglobulin (BTG), platelet factor 4 (PF4) and thromboxane B2 (TXB2) release as well as aggregation. BTG and PF4 release from blood anticoagulated with sodium citrate was inhibited by AD6 during a 3 h incubation. Platelet rich plasma (PRP) was stimulated with ADP, collagen, sodium arachidonate, PAF, A23187 and epinephrine, while resuspended washed platelets (WP) were stimulated by thrombin. AD6 (5-100 microM) inhibited dose dependently aggregation, BTG, PF4 and TXB2 release induced by threshold concentration of all the tested aggregating agents; however AD6 action could be overcome by increasing the concentration of the stimulating agents. After cyclo-oxygenase blockade by acetylsalicylic acid (ASA), PRP was stimulated by a supramaximal concentration of PAF. Under these circumstances we could observe a reversible aggregation and a partial release of BTG and PF4, AD6 was able to further reduce aggregation and release. Cyclic AMP accumulation induced in WP by prostacyclin was not modified by AD6 (100 microM), while theophylline greatly potentiated prostacyclin action. We conclude that AD6 is an inhibitor of platelet activation in vitro. Its mode of action is different from cyclo-oxygenase blockade and provides inhibition of platelet activation by a number of different stimuli.