Thromboxane A,(TxA,) is an extremely unstable natural product with potent vasoconstricting, bronchoconstricting, and platelet aggregating activities., It has been implicated in the etiology of a variety of disorders including vasospasm, stroke, ischemia, and myocardial infar~ tion.~ The biosynthesis of TxA2 from arachidonic acid is blocked by classical nonsteroidal antiinflammatory drugs which prevent the formation of its precursors ...