The role of platelet cyclooxygenase and lipoxygenase pathways in tumor cell induced platelet aggregation.

Walker 256 carcinosarcoma cells induce the aggregation of rat platelets and concomitant production of eicosanoid metabolites (e.g., 12-hydroxyeicosatetraenoic acid, thromboxane A2). Cyclooxygenase inhibitors, but not lipoxygenase inhibitors, were able to inhibit platelet aggregation induced in vitro by low concentrations of agonists. At high agonist concentrations, neither cyclooxygenase nor lipoxygenase inhibitors affected platelet aggregation; however the combination of both inhibitors resulted in inhibition of aggregation. Also, a low concentration of agonist induced minimal eicosanoid metabolism, whereas a high concentration resulted in increased eicosanoid metabolism. These inhibitors, at the doses tested, did not inhibit protein kinase C activity.