U-46619 is a TP receptor agonist that exhibits properties similar to TXA2, inducing platelet aggregation and vascular smooth muscle contraction. 5-trans U-46619 is a minor impurity (2-5%) which is variably present in most commercial preparations of U-46619. The biological activity of 5-trans U-46619 has rarely been tested separately from U-46619 itself. In the only case published to date, 5-trans U-46619 was found to be a about half as potent an inhibitor of PGE synthase as the 5-cis version of U-46619.