INDUCTION OF NITRIC-OXIDE PRODUCTION BY BOVINE ALVEOLAR MACROPHAGES IN RESPONSE TO PASTEURELLA-HAEMOLYTICA A1

We assessed the kinetics of inducible nitric oxide synthase (iNOS) mRN A expression and production of nitric oxide (NO) in bovine alveolar ma crophages (AMs) stimulated with purified lipopolysaccharide (LPS) from Pasteurella haemolytica strain 12296. The effect of LPS on iNOS gene expression was dose-dependent and was expressed maximally at 24 h afte r stimulation with 10 mu g/ml of LPS. Production of NO measured as sec reted nitrite in supernatants took place in a time and dose-dependent manner with peak production at 24 h after LPS stimulation. Recombinant bovine gamma interferon (rbyIFN) augmented the LPS-induced iNOS gene expression and production of NO. The ability of LPS to induce iNOS gen e expression and NO production either alone or in combination with rby IFN was significantly abrogated by polymyxin B. In addition, the iNOS inhibitor N-G-monomethyl-L-arginine (L-NMMA) significantly inhibited L PS and rbyIFN + LPS induced NO production. Our results also demonstrat ed that NO produced from an exogenous NO donor sodium nitroprusside (S NP), and NO generated from LPS-stimulated AMs (endogenous) caused cyto toxic injury to bovine pulmonary artery endothelial cells in a dose-de pendent manner. The cytotoxic injury caused by NO generated from LPS s timulated AMs was inhibited by polymyxin B or L-NMMA. There was a mark edly increased concentration of nitrite in the lung lavage fluids of c alves following FI haemolytica infection. These findings support a rol e for NO in the pathogenesis of lung injury in bovine pneumonic pasteu rellosis. (C) 1996 Academic Press Limited.