EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE AND ITS INVOLVEMENT IN PULMONARY GRANULOMATOUS INFLAMMATION IN RATS

Two types of pulmonary granulomatosis were produced in rats by intratr acheal instillation of zymosan or silica. In both models, immunostaini ng with anti-mt monoclonal antibody for inducible nitric oxide synthas e (iNOS), ANOS11, showed that the intensity of iNOS immunoreactivity i n the inflammatory lesions peaked at 3 days and declined thereafter, I mmunohistochemical double staining and in situ hybridization demonstra ted the expression of iNOS is neutrophils, monocyte-derived macrophage s, and bronchiolar epithelial cells in the pulmonary lesions, Electron spin resonance spectroscopy revealed the production of an excessive a mount of nitric oxide (NO) in the pulmonary lesions, Immunostaining wi th a polyclonal antibody against nitrotyrosine indicated the formation of nitrotyrosine residues in the granulomatous lesions, particularly in the periphery of the lesions, providing indirect evidence for the g eneration of peroxynitrite anion in the zymosan- or silica-instilled l ungs Administration of N-omega-nitro-L-arginine nine methyl ester or S -methylisothiourea sulfate, which significantly suppressed NO producti on, resulted in marked reduction of monocyte/macrophage infiltration a s well as in inhibition of induction of monocyte chemoattractant prote in-1 in the lesions These data indicate that NO and its more reactive product peroxynitrite anion may be important mediators of granuloma fo rmation in the lung.