 These evaluations indicate that TP receptor antagonists can be more effective than drugs which selectively block the production of TXA2 thromboxane synthase inhibitors.This seemingly paradoxical result may reflect the ability of PGH2, whose production is not blocked by the inhibitors, to substitute for TXA2 in activating TP.Novel TP receptor antagonists that also have activity in reducing TXA2 production by inhibiting cyclooxygenases have been discovered and are in development for testing in animal models.