Effects of hard metal on nitric oxide pathways and airway reactivity to methacholine in rat lungs

To examine whether the development of hard metal (HM)-induced occupational asthma and interstitial lung disease involves alterations in nitric oxide ( NO) pathways, we examined the effects of an industrial HM mixture on NO pro duction, interactions between HM and lipopolysaccharide (LPS) on NO pathway s, and alterations in airway reactivity to methacholine in rat lungs. HM (2 .5 to 5 mg/100 g intratracheal) increased NO synthase (NOS; EC 1.14.23) act ivity of rat lungs at 24 h without increasing inducible NOS (iNOS) or endot helial NOS (eNOS) mRNA abundance or iNOS, eNOS, or brain NOS (bNOS) protein s. The increase in NOS activity correlated with the appearance histological ly of nitrotyrosine immunofluorescence in polymorphonuclear leukocytes (PMN ) and macrophages. Intraperitoneal injection of LPS (1 mg/kg) caused up-reg ulation of iNOS activity, mRNA, and protein at 8 h but not at 24 h. HM at 2 .5 mg/100 g, but not at 5 mg/100 g, potentiated the LPS-induced increase in NOS activity, iNOS mRNA, and protein. However, HM decreased eNOS activity at 8 h and eNOS protein at 24 h. Whole body plethysmography on conscious an imals revealed that HM caused basal airway obstruction and a marked hyporea ctivity to inhaled methacholine by 6-8 h, which intensified over 30-32 h. H M-treatment caused protein leakage into the alveolar space, and edema, fibr in formation, and an increase in the number of inflammatory cells in the lu ngs and in the bronchoalveolar lavage. These results suggest that a HM-indu ced increase in NO production by pulmonary inflammatory cells is associated with pulmonary airflow abnormalities in rat lungs.