Platelet-dependent granulocyte activation in vitro: effect of ticlopidine.

The presence of platelets or platelet release products is known to augment the injury of endothelial cells caused by stimulated neutrophils (PMN leukocytes). In our in vitro studies, platelet-rich or platelet-poor plasma (PRP or PPP) was placed in one compartment and a PMN suspension in the other of a modified Boyden chamber divided by a dialysis membrane. The addition of the aggregating substance (ADP, collagen) to PRP but not to PPP was followed by PMN activation as shown by enzyme release and O-2 generation. The in vivo treatment with ASA completely prevented the platelets from triggering PMN activation. The in vitro addition of a thromboxane synthetase inhibitor (imidazole 10(-3) M) or a lipoxygenase inhibitor (NDGA 10(-6) M) did not show any effect on platelet-dependent PMN activation, thus suggesting that neither TxA2 nor lipoxygenase by-products are involved. Finally, in vitro and in vivo treatment with ticlopidine blunted the stimulating activity of the platelets on PMN. Our data further support the hypothesis that a sequential platelet-PMN interaction may occur, and that the therapeutic effect of some antiplatelet drugs may be partly due to a protective effect against platelet-dependent PMN-mediated vascular damage.