EP₄ and EP₂ Receptor Subtypes Involved in Colonic Secretion in Rat

Abstract

Abstract:The study was designed to determine the prostaglandin EP receptor subtypes functionally involved in electrogenic ion secretion in rat colon. With 30 rats, measurements of short circuit current (SCC) and slope conductance were obtained by Ussing chamber technique. Prostaglandin E2 (PGE 2 ) and other EP receptor selective agonists were employed on stripped rat colon pre-treated with indomethacin and theophylline. Receptor-specific agonists were butaprost (EP 2 ), sulprostone (EP 1 and EP 3 ) and PGE 1 alcohol (OH-PGE 1 ) (EP 4 ). GW627368X was used as a specific EP 4 receptor antagonist. Forskolin-induced SCC was used as a control of tissue viability. The mean basal SCC was 24.5 ± 0.9 μ A/cm 2 (range 9.8-45.1), and mean basal slope conductance was 23.7 ± 6.1 mS/cm 2 (range 9.7-39.8). The basal SCC decreased after pre-treatment with indomethacin and increased after pre-treatment with theophylline. PGE 2 , butaprost and OH-PGE 1 stimulated maximal increase in SCC (55.8 ± 4.1, 43.9 ± 3.8 and 93.9 ± 2.7 μ A/cm 2 , respectively), while sulprostone had no apparent effects. GW627368X eliminated OH-PGE 1 -induced SCC and partially PGE 2 -induced SCC, leaving butaprostinduced SCC almost unperturbed. Bumetanide, 20 μ M, inhibited between 40% and 80% of the agonist-induced changes in SCC. In conclusion, compilation of the results on induced SCC by subtype specific receptor agonists for EP receptors and the pattern of induced SCCs inhibited by GW627368X indicate the EP 4 receptor subtype as the major mediator of PGE 2 -induced electrogenic ion secretion with a lesser induction through the EP 2 receptor subtype.Prostaglandins are locally acting paracrine-and autocrinesignalling molecules derived from the metabolism of arachidonic acid by cyclooxygenase enzymes COX-1 and COX-2 (prostaglandin endoperoxide H synthases). Prostaglandins play a significant role in the physiology and pathophysiology of the digestive system affecting water and electrolyte transport, mucus secretion, blood flow and motility [1,2]. Prostaglandin E (PGE) is synthesized in large amounts and widely distributed throughout the gastrointestinal tract [3]. It is also produced in the immune cells in the lamina propria , the submucosa, and to a lesser extent by the intestinal epithelial cells [4]. Prostaglandins, including PGE 2 , are released in colon by a host of primary messengers including signals as increased release of serotonin [5].Prostaglandin E 2 , PGE 2 , may interact with at least four cell surface prostaglandin type E receptors EP 1 , EP 2 , EP 3 and EP 4 which trigger a variety of intracellular responses depending on which G protein they are coupled to [6,7]. The PGE 2 receptors are transmembrane G protein-coupled receptors and it has been established that EP 1 signals are transmitted by increased intracellular Ca 2+ concentrations with activation of phosphorylated protein kinase C [8]. The EP 3 receptor reduces adenylate cyclase activity by stimulating G α -i protein while activation of EP 2 and EP 4 receptor subtypes activate G α -s prot...

Prostaglandin E2-induced colonic secretion in patients with and without colorectal neoplasia

“…This fits with findings in the human duodenum using the same experimental technique [19]. Similar mechanisms appear to be present in rat colon, but in contrast to rats, where EP4 is the major mediator of the PGE 2 response [21], the human colon PGE 2 -induced secretion seems to be induced by all four receptor subtypes, EP4, EP2 and EP1/EP3, Figure 4. This underlines the notable difference of functional EP receptors in some animals as compared to man.…”

“…Indomethacin was always added 15 minutes prior to the addition of EP receptor agonists in order to minimize tissue prostaglandin production. Choices of concentration for the various drugs were based on experience from previous studies [18,21]. Bumetanide was added after EP agonist experiments on the biopsies had been completed.…”

Activation of TRPA1 by luminal stimuli induces EP4-mediated anion secretion in human and rat colon

“…PGE 2 function in the gastrointestinal tract has been well studied in relation to its receptors EP 1 , EP 2 , EP 3 , and EP 4 . In particular, EP 2 and EP 4 , which are coupled to the cAMP pathway, mediate PGE 2 -evoked colonic secretion, but not EP 1 and EP 3 , which are coupled to an intracellular Ca 2ϩ pathway (35). In this study, we have shown that a PGE 2 receptor subtype, EP 4 , is involved in AITC-evoked anion secretion in both human and rat colon (Fig.…”

“…The PGE 2 receptor EP family includes four subtypes, and EP 2 and EP 4 receptors are involved in colonic anion secretion (35). Selective antagonists for EP 1 and EP 2 (AH6809) and for EP 4 (ONO-AE3-208) were used to investigate whether AITC-evoked anion secretion was mediated by EP receptors.…”

Molecular inhibition of prostaglandin E2 with GW627368X: Therapeutic potential and preclinical safety assessment in mouse sarcoma model

“…9 In past few years, there have been number of studies exerting the importance of EP-4 receptor in carcinogenesis. 9 Extensive studies have been conducted on animal models of colon can cer [12][13][14] and various studies also support its role in breast cancer metastasis. [15][16][17][18] However, very few highly potent antagonists are presently available for preclinical and clinical assessment.…”