PROSTAGLANDIN EP RECEPTORS AND THEIR ROLES IN MUCOSAL PROTECTION AND ULCER HEALING IN THE GASTROINTESTINAL TRACT

Endogenous prostaglandins (PGs) play an important role in modulating the mucosal integrity and various functions of the alimentary tract, and E type PGs are most effective in these actions PGE(2) protects against acid reflux esophagitis and affords gastric cytoprotection against ethanol and indomethacin. These effects are mimicked by EP1 agonists and attenuated by an EP1 antagonist Adaptive cytoprotection induced by mild irritants is also attenuated by the EP1 antagonist as well as indomethacin. PGs contribute to capsaicin-induced gastric cytoprotection, yet this effect is mitigated by indomethacin and sensory deafferentation but not the EP1 antagonist. Similarly, PGE(2) does not exhibit gastric cytoprotection in EP1-receptor knockout mice, while capsaicin-induced protection is observed in animals lacking either EP1 receptors but disappears in IP-receptor knockout mice In the duodenum, acid perfusion produces damage in animals lacking EP3 receptors. The protective effect of PGE(2) on indomethacin-induced small intestinal damage is mimicked by both EP3 and EP4 agonists. PGE(2) also shows a healing-promoting effect on gastric ulcers as well as intestinal lesions via the activation of EP4 receptors. The underlying mechanisms of these actions of PGE(2) in the stomach, duodenum, or small intestine are related to inhibition of stomach contraction (EP1), stimulation of duodenal HCO3- secretion (EP3/EP4), or suppression of bacterial invasion due to inhibition of intestinal contraction (EP4) and stimulation of mucus secretion (EP3/EP4) respectively, although the mechanisms related to the esophageal protection remain unknown. Furthermore, the healing-promoting effect is associated with the stimulation of angiogenesis via an increase in VEGF expression (EP4).