Endogenous prostaglandin E2 accelerates healing of indomethacin-induced small intestinal lesions through upregulation of vascular endothelial growth factor expression by activation of EP4 receptors.

BACKGROUND AND AIMS: The effects of an EP4 agonist/antagonist on the healing of lesions produced by indomethacin in the small intestine were examined in rats, especially in relation to the expression of vascular endothelial growth factor (VEGF) and angiogenesis. METHODS: Animals were given indomethacin (10 mg/kg s.c.) and killed at various time points. To impair the healing of these lesions, a small dose of indomethacin (2 mg/kg p.o.) or AE3-208 (EP4 antagonist: 3 mg/kg i.p.) was given once daily for 6 days after the ulceration was induced, with or without the co-administration of AE1-329 (EP4 agonist: 0.1 mg/kg i.p.). RESULTS: Indomethacin (10 mg/kg) caused severe damage in the small intestine, but the lesions healed rapidly decreasing to approximately one-fifth of their initial size within 7 days. The healing process was significantly impaired by indomethacin (2 mg/kg) given once daily for 6 days after the ulceration. This effect of indomethacin was mimicked by the EP4 antagonist and reversed by co-administration of the EP4 agonist. Mucosal VEGF expression was upregulated after the ulceration, reaching a peak on day 3 followed by a decrease. The changes in VEGF expression paralleled those in mucosal cyclooxygenase-2 expression, as well as prostaglandin E(2) (PGE(2)) content. Indomethacin (2 mg/kg) downregulated both VEGF expression and angiogenesis in the mucosa during the healing process, and these effects were significantly reversed by co-treatment with the EP4 agonist. CONCLUSION: The results suggest that endogenous PGE(2) promotes the healing of small intestinal lesions by stimulating angiogenesis through the upregulation of VEGF expression mediated by the activation of EP4 receptors.

Cyclooxygenase-2/prostaglandin E2 accelerates the healing of gastric ulcers via EP4 receptors.

We examined the involvement of cyclooxygenase (COX)-1 as well as COX-2 in the healing of gastric ulcers and investigated which prostaglandin (PG) EP receptor subtype is responsible for the healing-promoting action of PGE2. Male SD rats and C57BL/6 mice, including wild-type, COX-1(-/-), and COX-2(-/-), were used. Gastric ulcers were produced by thermocauterization under ether anesthesia. Gastric ulcer healing was significantly delayed in both rats and mice by indomethacin and rofecoxib but not SC-560 given for 14 days after ulceration. The impaired healing was also observed in COX-2(-/-) but not COX-1(-/-) mice. Mucosal PGE2 content increased after ulceration, and this response was significantly suppressed by indomethacin and rofecoxib but not SC-560. The delayed healing in mice caused by indomethacin was significantly reversed by the coadministration of 11-deoxy-PGE1 (EP3/EP4 agonist) but not other prostanoids, including the EP1, EP2, and EP3 agonists. By contrast, CJ-42794 (selective EP(4) antagonist) significantly delayed the ulcer healing in rats and mice. VEGF expression and angiogenesis were both upregulated in the ulcerated mucosa, and these responses were suppressed by indomethacin, rofocoxib, and CJ-42794. The expression of VEGF in primary rat gastric fibroblasts was increased by PGE2 or AE1-329 (EP4 agonist), and these responses were both attenuated by coadministration of CJ-42794. These results confirmed the importance of COX-2/PGE2 in the healing mechanism of gastric ulcers and further suggested that the healing-promoting action of PGE2 is mediated by the activation of EP4 receptors and is associated with VEGF expression.

Role of endogenous nitric oxide (NO) and NO synthases in healing of indomethacin-induced intestinal ulcers in rats.

We examined the roles of nitric oxide (NO) and NO synthase (NOS) isozymes in the healing of indomethacin-induced small intestinal ulcers in rats. Animals were given indomethacin (10 mg/kg, s.c.) and killed 1, 4 and 7 days after the administration. Indomethacin (2 mg/kg), N(G)-nitro-L-arginine methyl ester (L-NAME: a nonselective NOS inhibitor: 10 mg/kg) and aminoguanine (a relatively selective iNOS inhibitor: 20 mg/kg) were given s.c. once daily for 6 days, the first 3 days or the last 3 days during a 7-day experimental period. Both indomethacin and L-NAME significantly impaired healing of these lesions, irrespective of whether they were given for 6 days, first 3 days or last 3 days. The healing was also impaired by aminoguanine given for the first 3 days but not for the last 3 days. Expression of iNOS mRNA in the intestine was up-regulated after ulceration, persisting for 2 days thereafter, and the Ca(2+)-independent iNOS activity also markedly increased with a peak response during 1-2 days after ulceration. Vascular content in the ulcerated mucosa as measured by carmine incorporation was decreased when the healing was impaired by indomethacin and L-NAME given for either the first or last 3 days as well as aminoguanidine given for the first 3 days. These results suggest that endogenous NO plays a role in healing of intestinal lesions, in addition to prostaglandins, yet the NOS isozyme mainly responsible for NO production differs depending on the stage of healing: iNOS in the early stage and cNOS in the late stage.

Roles of endogenous prostaglandins and cyclooxygenase isozymes in healing of indomethacin-induced small intestinal lesions in rats.

The role of prostaglandins (PGs)/cyclooxygenase (COX) in the healing of indomethacin-induced small intestinal ulcers was examined in rats. Animals were given indomethacin (10 mg/kg s.c.) and killed 1, 2, 3, 5, and 7 days later. Indomethacin (2 mg/kg), 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC560; COX-1 inhibitor; 3 mg/kg), and rofecoxib (COX-2 inhibitor; 3 mg/kg) were given p.o. once daily for 6 days, during the first 3 days or last 3 days of the experimental period. All COX inhibitors given for 6 days significantly impaired the healing of these ulcers. Healing was also impaired by rofecoxib given for the first 3 days or by SC560 given for the last 3 days. The expression of COX-2 mRNA in the intestine was up-regulated after ulceration, persisting for 3 days and dissipating thereafter. Mucosal PGE2 contents decreased within 3 h after ulceration, recovered 24 h later, and increased above normal 1 approximately 3 days later. The PGE2 content at 4 days after ulceration was decreased by rofecoxib but not SC560, whereas that at 7 days was suppressed by SC560 but not rofecoxib. Vascular content in the ulcerated mucosa decreased when the healing was impaired by COX inhibitors. The deleterious effect of indomethacin on healing was mimicked by a prostacyclin E receptor (EP) 4 antagonist and reversed by coadministration of PGE2 as well as an EP4 agonist. In conclusion, endogenous PGs play a role in the healing of intestinal ulcers through EP4 receptors, yet the COX isozyme involved differs depending on the stage of healing; COX-2 in the early stage and COX-1 in the late stage.