The effect of morphine on intestinal ulcer formation and on the degradation of the host defense barrier was studied. Mice receiving morphine (MRM) showed mucosal ulcer formation in the ileum and in the upper third of the colon. In in vitro studies, morphine enhanced apoptosis of cultured human colonic cells (HCC). Nitric oxide synthase (NOS) inhibitors attenuated the proapoptotic effect of morphine. Moreover, morphine stimulated NO generation by HCCs. MRM also showed a breach in the host defense barrier as well as injury to peritoneal macrophages. Although NOS inhibitors completely prevented morphine-induced intestinal ulcer formation, it provided only partial protection against a breach in the host defense barrier and peritoneal macrophage injury. Propranolol did not inhibit the induction of intestinal ulcer formation in MRM; nevertheless, propranolol prevented a breach in the host defense barrier as well as macrophage injury in MRM, whereas hemin exacerbated macrophage injury as well as the breach in the host defense barrier of MRM. These findings suggest that morphine-induced intestinal injury is mediated through NO generation. However, the degradation of the host defense barrier correlates with macrophage injury, but not intestinal injury.
The role of nitric oxide (NO) synthase inhibitors in indomethacin (INDO) -induced enteropathy was investigated in male Sprague-Dawley rats. Rats were subcutaneously administered 5% sodium bicarbonate (controls), two doses of INDO 7.5 mg/kg, and three different inducible NO synthase (iNOS) inhibitors at various concentrations 24 hr, apart; aminoguanidine (AG), guanidinoethyldisulfide (GED), and n-(3-aminomethyl)benzylacetamidine (1400W). Rats were killed four days after the initial injection and small intestinal mucosa was assayed for myeloperoxidase (MPO) activity and iNOS expression by western blot analysis. Serum nitrite/nitrate (NOx) concentration was measured colorimetrically. INDO produced acute ulcers along the mesenteric border from the ileum to proximal jejunum. Rats treated with AG (25 and 50 mg/kg), GED (2.5 mg/kg), and 1400W (0.1 mg/kg) showed decreased total ulcer length and MPO activity by 51, 72, 53, and 61% and by 58, 88, 68, and 70%, respectively, compared to INDO alone. All inhibitors similarly reduced INDO-enhanced serum NOx concentrations to its basal levels. Significant iNOS expression was detected in INDO-treated rats, but the inhibitors did not alter iNOS expression. Our data suggest that NO derived from iNOS may be a key factor in the pathogenesis of acute INDO-induced enteropathy in rats.
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