Prostacyclin (PGI
2) is a potent vasorelaxant and inhibitor of platelet aggregation. It mediates its actions by binding to a specific G protein-
coupled receptor, the IP receptor, on the surface of endothelial cells, arterial smooth muscle, and platelets.
1 The IP receptor also participates in signal transduction of the pain response, cardioprotection, and inflammation.
2,3,4,5 MRE-
269 is the active form of the prodrug NS-
304. It is a potent and selective agonist for the human IP receptor with a K
i value of 20 nM.
6 In contrast to PGI
2, which has a half-
life of 30 seconds to a few minutes
in vivo, plasma concentrations of MRE-
269 remain near peak levels for more than eight hours in rats and dogs.
6 Unlike the PGI
2 analogues, beraprost and iloprost, MRE-
269 lacks high affinity for the EP
3 receptor.
7 As a result, MRE-
269 induces vasodilation equally in large and small pulmonary arteries, whereas vasodilation of small arteries by beraprost and iloprost is reduced
via EP
3-
mediated vasoconstriction.
7