INDUCIBLE NITRIC-OXIDE SYNTHASE AFTER SENSITIZATION AND ALLERGEN CHALLENGE OF BROWN-NORWAY RAT LUNG

1 We studied the effects of ovalbumin (OA) sensitization and challenge on inducible nitric oxide synthase (iNOS) gene and protein expression in Brown-Norway rats in vivo. 2 By use of Northern analysis, a 4.4-kb iNOS mRNA transcript was weakly observed in control rat lung but ther e was a 3 fold increase in lungs sensitized to OA alone (P<0.05). In s ensitized rats, four hours after exposure to OA aerosol, there was a 6 fold increase in iNOS mRNA transcript (P<0.05), which returned to bas eline at 24 h. 3 Immunostaining with an anti-mouse INOS antibody revea led some patchy staining of airway epithelium in naive rats. There wer e no changes in sensitized rats exposed to saline, but sensitized and OA-exposed rats showed increased expression in iNOS staining in macrop hages. 4 Electrophoretic mobility shift assays of lung nuclear extract s showed a marked increase in nuclear factor-kappa B (NF-kappa B)-bind ing activity at 2 h after allergen exposure with return to baseline at 6, 12 and 24 h. 5 We concluded that there is increased INOS gene and protein expression associated with increased NF-kappa B DNA-binding in lungs of sensitized and challenged rats. The increase in INOS express ion may underlie the increase in exhaled NO found after allergen chall enge and may contribute to the development of allergen-induced airway hyperresponsiveness.