16,16-dimethyl prostaglandin E2 inhibits indomethacin-induced small intestinal lesions through EP3 and EP4 receptors

We evaluated the effect of various PGE analogs specific to EP receptor subtypes on indomethacin-induced small intestinal lesions in rats and investigated the relationship of EP receptor subtype with the PGE action using EP receptor knockout mice. Animals were administered indomethacin subcutaneously, and they were killed 24 hr later. 16,16-dimethyl prostaglandin E-2 (dmPGE(2)) or various EP agonists were administered intravenously 10 min before indomethacin. Indomethacin caused hemorrhagic lesions in the rat small intestine, accompanied with an increase in intestinal motility and the number of enteric bacteria as well as iNOS and MPO activities. Prior administration of dmPGE(2) dose-dependently prevented intestinal lesions, together with inhibition of those functional changes. These effects of dmPGE(2) were mimicked by prostanoids (ONO-NT-012 and ONO-AEI-329), only specific to EP3 or EP4 receptors, although the intestinal motility was inhibited only by ONb-AEI-329. Intestinal mucus secretion and fluid accumulation were decreased by indomethacin but enhanced by dmPGE(2), ONO-NT-012, and ONO-A-EI-329 at the doses that prevented intestinal lesions. Indomethacin also caused intestinal lesions in both wild-type and knockout mice lacking EP1 or EP3 receptors, yet the protective action of dmPGE(2) was observed in wild-type and EP1 receptor knockout mice but not the mice lacking EP3 receptors. These results suggest that the intestinal cytoprotective action of PGE(2) against indomethacin is mediated by EP3/EP4 receptors and that this effect is functionally associated with an increase of mucus secretion and enteropooling as well as inhibition of intestinal hypermotility, the former two processes mediated by both EP3 and EP4 receptors, and the latter by EP4 receptors.