Involvement of different receptor subtypes in prostaglandin E2-induced contraction and relaxation in the lower esophageal sphincter and esophageal body

Abstract

Prostaglandin E2 (PGE2) plays a role in the pathogenesis of gastro-esophageal reflux disease (GERD). There are 4 subtypes of PGE2, PGE2 receptor 1, 2, 3 and 4 (EP 1–4). In GERD patents, PGE2, EP2 and EP4 are upregulated. However, the effects of PGE2 on esophageal motility remain elusive.We examined how PGE2 regulates motility in the porcine circular smooth muscle of the lower esophageal sphincter (LES), and the circular and longitudinal smooth muscle of the esophagus body in organ bath.PGE2 induced tonic relaxation in the LES and circular smooth muscle, but transient contraction in longitudinal smooth muscle. The relaxation of the LES and circular smooth muscle was similar in pattern and mechanism, but was much larger in the LES. The relaxation was completely blocked by a voltage-gated K+ channel blocker or 40 mM K+ depolarization, indicating the involvement of K+ channel. Longitudinal smooth muscle contraction was completely blocked by an L-type Ca2+ channel blocker, showing the contribution of Ca2+ movement. The involvement of the EP receptor in motility was examined with selective receptor agonists and antagonists. Activation of EP2 and EP4 caused relaxation in the LES and circular smooth muscle. Compatible with PGE2, EP2 and EP4 agonists caused more significant relaxation in the LES than in circular smooth muscle. EP1 contributed to the longitudinal smooth muscle contraction.The different effects of PGE2 in the LES, circular and longitudinal smooth muscle contributes to esophageal motility, their impairment might increase the amount and frequency of esophageal reflux.