Thromboxane synthetase inhibitors as pharmacological tools: differential biochemical and biological effects on platelet suspensions.

The comparative effects of three so called "thromboxane-synthetase-inhibitors" (imidazole, N-0164, and U-51605) on arachidonate metabolism and on platelet aggregation were studied. All three compounds blocked platelet microsomal thromboxane synthesis from prostaglandin endoperoxides without affecting platelet adenyl cyclase. Imidazole, blocked thromboxane synthesis in intact platelets either from arachidonic acid or PGH2, without affecting aggregation. U-51605 simultaneously inhibited thromboxane synthesis and platelet suspension aggregation. N-0164 inhibited aggregation probably at extracellular sites, at concentrations that did not alter arachidonate or PGH2 metabolism. High concentrations of N-0164 simultaneously inhibited PG cyclo-oxygenase and thromboxane synthetase. The lack of specificity of these compounds requires that other actions of these compound must be considered when they are used as pharmacological tools to inhibit thromboxane synthetase.