NITRIC-OXIDE SYNTHASE IN HUMAN AND RAT LUNG - IMMUNOCYTOCHEMICAL AND HISTOCHEMICAL-LOCALIZATION

Nitric oxide synthase (NOS) produces nitric oxide, a mediator of poten tial importance in numerous physiologic and inflammatory processes in the lung. We localized constitutive NOS (c-NOS) and inducible NOS (i-N OS) within lung tissue by immunoperoxidase labeling with specific anti bodies or by histochemical demonstration of the characteristic NADPH d iaphorase activity of NOS. We analyzed human airway (n = 4) or parench yma (n = 10) specimens obtained from uninvolved areas of surgical tumo r resections. We also studied human fetal lung samples (n = 6) and nor mal or inflamed (16 h after intratracheal LPS instillation) rat lung t issue. Immunostaining with anti-c-NOS identified c-NOS antigen in rat lung nerves, endothelium, and airway epithelium. Normal or inflamed ra t macrophages were not stained. Human nerve elements and large-vessel endothelium showed immunostaining with the anti-c-NOS, but no labeling of the airway or alveolar epithelium was seen. Immunostaining with an ti-i-NOS showed strong labeling of rat macrophages after LPS treatment , in vivo or in vitro, while normals were negative. Human alveolar mac rophages were occasionally positive for i-NOS, especially in areas of chronic inflammation, which also showed focal immunolabeling of endoth elium. Uniform labeling of epithelium in large, cartilaginous airways was found with anti-i-NOS in both human bronchi and normal rat trachea samples, suggesting a constitutive role for a NOS that shares epitope (s) with or is highly homologous to the inducible, macrophage type of NOS. Histochemical staining for NADPH diaphorase activity was consiste nt with immunolocalization of NOS antigens. The results indicate that numerous distinct anatomic compartments within human and rat lungs con tain NOS, and suggest a role for NOS activity in pulmonary homeostasis and inflammation.