Expression of cyclooxygenase (COX)-1 and COX-2 in adaptive cytoprotection induced by mild stress

Abstract

Prostaglandins (PG) derived from COX-1 play an important role in the maintenance of mucosal integrity but the role of COX-2-derived products in mucosal defence mechanism has not been fully explained. Mild stress is known to prevent gastric mucosal lesions induced by severe stress via the phenomenon of adaptive cytoprotection but it remains unknown which COX is involved in this adaptation. In this study, the mucosal expression of COX-1 and COX-2 was examined and the inhibitors of these enzymes were used to determine the contribution of these enzymes in adaptive cytoprotection induced by mild stress. Male Wistar rats were exposed to mild water immersion and restraint stress (WRS) at various time intervals ranging from 5 min up to 2 h followed 1 h later by exposure to severe 3.5 h WRS with or without pretreatment with: 1) NS-398 (10 mg.kg –1 i.g.), a selective COX-2 inhibitor; 2) resveratrol (5 mg.kg –1 i.g.), a selective COX-1 inhibitor; 3) meloxicam (2 mg.kg –1 i.g.), preferential COX-2 inhibitor; and 4) indomethacin (5 mg.kg –1 i.p), non-selective inhibitor of COX. The number of WRS lesions was counted, gastric blood flow (GBF) was measured by H 2-gas clearance technique, mucosal biopsy samples were taken for the assessment of PGE 2 by radioimmunoassay, and the expression of COX-1 and COX-2 mRNA by RT-PCR. WRS for 3.5 h produced numerous gastric lesions, decreased GBF by 48% and inhibited formation of PGE 2 by 68% as compared to intact mucosa. Exposure to mild WRS during 5–30 min by itself failed to affect mucosal integrity but significantly attenuated gastric lesions induced by exposure to severe 3.5 h stress; the maximal protective effect being achieved with mild WRS during 15 min. This protective effect was accompanied by the rise in GBF and the generation of PGE 2 in the gastric mucosa. After extension of mild WRS from 15 min up to 1 or 2 h before more severe 3.5 h WRS, the loss of cytoprotective effect of mild WRS against severe stress accompanied by significant fall in the GBF were observed. Pretreatment with NS-398 (10 mg.kg –1 i.g.) that failed to affect mucosal PGE 2 generation, reduced significantly the protection and accompanying rise in GBF produced by mild WRS, whereas resveratrol partly reduced the protection and the rise in GBF induced by mild WRS. Meloxicam or indomethacin significantly inhibited PGE 2 generation and completely abolished the hyperemia and protection induced by mild WRS against more severe stress. The protective and hyperemic effects of mild WRS were completely restored by the addition of 16,16 dm PGE 2 (5 μg.kg –1 i.g.) to NS-398 or resveratrol, while the deleterious effects of meloxicam and indomethacin were significantly attenuated by the concomitant treatment with this PGE 2 analogue. We conclude that PG derived from both, COX-1 and COX-2 appear to be involved in adaptive cytoprotection developed in response to mild stressors.