Effects of selective cyclooxygenase-2 inhibitors on alkaline secretory and mucosal ulcerogenic responses in rat duodenum

Abstract

Effects of the selective cyclooxygenase-2 (COX-2) inhibitors such as NS-398 and nimesulide on duodenal HCO 3 − secretory and ulcerogenic responses to mucosal acidification were examined in rats, in comparison with indomethacin, a nonselective COX inhibitor. Duodenal HCO 3 − secretion in anesthetized rats was increased in response to mucosal acidification. The increased HCO 3 − response to acid was significantly suppressed by pretreatment with indomethacin (10 mg kg −1, s.c.), while both NS-398 and nimesulide (10 mg kg −1, s.c.) had no effect on this response. The luminal release of prostaglandin E2 (PGE2) was increased during and after mucosal acidification, and this response was significantly inhibited by indomethacin but not NS-398 or nimesulide. Indomethacin provoked hemorrhagic lesions in the duodenum when acid hypersecretion was concomitantly induced by histamine (8 mg kg −1 hr −1, i.V.), while either NS-398 or nimesulide did not cause damage in the duodenum. Either of these drugs had no effect on histamine-induced acid secretion. On the other hand, both NS-398 and nimesulide showed a significant suppression against carrageenan-induced rat paw edema, similar to indomethacin. The present study supports a mediator role for endogenous PGs in duodenal HCO 3 −1 secretion in response to mucosal acidification and suggests that COX-1 but not COX-2 is a key enzyme in regulating this process and maintaining the mucosal integrity against acid in the duodenum.