U-51605 is a stable analog of the endoperoxide prostaglandin H (PGH). It is an inhibitor of both prostacyclin (PGI) and thromboxane (TX) synthases with more selectivity towards PGI synthase. U-51605 is also a partial agonist at TP receptors. In human foreskin fibroblasts, U-51605 inhibits PGI synthase at a concentration of 2.8 µM, whereas, human platelet TX synthase is inhibited at a concentration of 5.6 µM. At concentrations up to 1 µM, U-51605 reduced the release of prostacyclin in SHR aorta elicited by the calcium ionophore A-23187 with no effect on TXA production and yet significantly increased PGE and PGF release.
U-51605 is a platelet aggregation inhibitor and inhibits thromboxane synthesis. U-51605 is also a prostaglandin I2 synthase inhibitor and can inhibit the retinal vasodilation response induced by NO donors (such as NOR3).