Misoprostol is a prostaglandin E1 (Item No. 13010) analog with agonist activity mediated by EP2, EP3, and EP4 receptors.{2313,1754,1752,1611} It has been shown to inhibit the formation of gastric lesions in rats (ED50 = 0.31 μg/kg),{1754} inhibit superoxide generation in human neutrophils (EC50 = 0.35 μM),{1752} and relax fetal rabbit ductus arteriosus (EC50 = 0.36 nM){1611} in a concentration dependent manner. Misoprostol is commonly used in clinical medicine for the prevention of peptic ulcer disease. It has also been used in conjunction with mifepristone (RU-486; Item No. 10006317) for the oral induction of first trimester abortion. Misoprostol contains a C-1 methyl ester and is readily absorbed and rapidly hydrolyzed in humans to the active free acid.{2313}