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Patent ductus arteriosus (PDA) is common in premature infants. Cyclooxygenase inhibitors such as indomethacin, which inhibit prostaglandin E 2 (PGE 2 ) synthesis, are currently the sole treatments for patients with PDA. Their efficacy are, however, frequently limited, and adverse effects are problematic. Because the PGE 2 -specific receptor EP4 selectively expresses in rat ductus arteriosus (DA), it is hypothesized that EP4 inhibition would promote DA closure with fewer side-effects.Methods and Results:A new chemical compound EP4 antagonist, RQ-15986 (renamed from CJ-042794), was used. Whether RQ-15986 selectively contracted the DA was examined by measuring the isometric tension of rat DA ex vivo at embryonic day 19 (e19) and e21. RQ-15986 at a dose of 10 -6 mol/L increased the isometric tension of the DA up to 44.8±6.2% and 69.1±12.9% to the maximal KCl-induced tension at e19 and e21 respectively. The effect of RQ-15986 on rat DA in vivo was also tested by using a rapid whole-body freezing method. RQ-15986 inhibited PGE 1 -induced DA dilatation in neonatal rats. Furthermore, RQ-15986 contracted the DA in a dose-dependent manner, and the constriction was greater at e21 than at e19. Moreover, RQ-15986 did not contract the aorta or the marginal artery of the colon.

Prostaglandin E<sub>2</sub> Receptor EP4 Inhibition Contracts Rat Ductus Arteriosus