ROLE OF NITRIC-OXIDE ON EOSINOPHILIC LUNG INFLAMMATION IN ALLERGIC MICE

Nitric oxide (NO) is an important mediator of inflammatory reactions a nd may contribute to the lung inflammation in allergic pulmonary disea ses. To assess the role of NO in pulmonary inflammation, we studied th e effect of four nitric oxide synthase (NOS) inhibitors, N-nitro-L-arg inine methyl ester (L-NAME), aminoguanidine, N-G-monomethyl-L-arginine (NMMA) and L-N-6-(1-Iminoethyl) lysine (L-NIL), on the influx of eosi nophils into the bronchoalveolar lavage (BAL) fluid and lung tissue of antigen-challenged allergic mice. We also analyzed lung tissues for t he presence of steady state mRNA for inducible nitric oxide synthase ( iNOS) and iNOS protein. Furthermore, BAL fluid and serum were analyzed for their nitrite content. B6D2F1/J mice were sensitized to ovalbumin (OVA) and challenged with nerosolized OVA. The NOS inhibitors were gi ven 0.5 h before and 4 h after the antigen challenge. OVA challenge in duced a marked eosinophilia in the BAL fluid and lung tissue 24 h afte r challenge. The OVA-induced pulmonary eosinophilia was significantly reduced by L-NAME(IO and 50 mg/kg, intraperitoneally [i.p.]). The inac tive isomer, D-NAME (50 mg/kg, i.p.) had no effect. When mice were tre ated with L-NAME (20 mg/kg, i.p.) and an excess of NOS substrate, L-ar ginine (200 mg/kg, i.p.), the OVA-induced pulmonary eosinophilia was r estored. Treatment with aminoguanidine (0.4-50 mg/kg, i.p.) also reduc ed the pulmonary eosinophilia. Treatment with NMMA (2-50 mg/kg, i.p.) partially reduced the eosinophilia, but L-NIL (10-50 mg/kg, i.p.), a s elective iNOS inhibitor, had no effect. L-NAME had no effect on the re duction of eosinophils in the bone marrow following OVA challenge to s ensitized mice. OVA challenge to sensitized mice had no effect on iNOS protein expression or iNOS mRNA in the lungs or on the levels of nitr ite in the BAL fluid. These results suggest that NO is involved in the development of pulmonary eosinophilia in allergic mice. The NO contri buting to the eosinophilia is not generated through the activity of iN OS nor does NO contribute to the efflux of eosinophils from the bone m arrow in response to antigen challenge. It is speculated that after an tigen challenge, the localized production of NO, possibly from pulmona ry vascular endothelial cells, is involved in the extravasation of eos inophils from the circulation into the lung tissue.