Expression of inducible nitric oxide synthase (iNOS) in rat intestinal mucosa by indomethacin

Abstract

Nitric oxide (NO) is an ubiquitous mediator of numerous physiological processes in the gastrointestinal tract. The relatively large concentrations of NO produced by iNOS are potentially damaging to tissue. We previously showed in a rat model of acidosis (Gastroenterology 116:A782, 1999) that NO production causes intestinal damage using myeloperoxidase (MPO) activity as an index of inflammatory response. Studies have suggested that iNOS activity is increased in animal models of intestinal inflammation and in patients with Crohn's disease or ulcerative colitis. Indomethacin (INDO)-induced enteropathy in rats resembles Crohn's disease. AIM: To evaluate iNOS expression in the development of INDO-induced small intestinal injury in rats. METHODS: Enteropathy was induced in male Sprague-Dawley rats by 2 subcutaneous injections of INDO (7.5mglkg body weight) 24 h apart. Control rats received only 5% sodium bicarbonate. Rats maintained on pelletized rat chow and tap water, were sacrificed at 3, 4, 8 and 14 days after INDO injection. The small bowel from pylorus to ileocecal junction was removed for iNOS expression, ulcer measurement and MPO assay. Mucosal extracts were obtained for iNOS expression by Western blotting using an iNOS-specific antibody. RESULTS: Acute confluent linear and oval ulcerations were found along the antimesenteric border from ileum to proximal jejunum at 3 days and were maximum at 4 days. Ulcers were rarely found in the duodenum. Ulcerations were almost healed at 8 and 14 days. Total ulcer length (rnm, n = 8) was 81.6 :!: 13.4, 215.9 :!: 20.5, 69.4 :!: 6.5 and 43.1 :!: 14.7 at 3, 4, 8 and 14 days, respectively. MPO activity increased significantly by 95, 116,88 and 39% at 3, 4, 8 and 14 days, respectively, compared to control value (273 :!: 23 U/min/g of tissue, n = 4). MPO activity also decreased significantly at 14 days compared to 3, 4 and 8 days (P < 0.05). Expression of iNOS was identified in mucosal extracts of INDO-treated rats at 3 and 4 days but not at 8 and 14 days. iNOS expession was undetectable in control mucosa. CONCLUSION: INDO treatment increases iNOS expression in small intestinal mucosa as early as 3 and 4 days with concomitant increased ulcer length and MPO activity. Our data suggest that NO produced by iNOS may contribute to the development of ulceration and inflammation in INDOinduced enteropathy .