The role of antioxidant enzymes in modulating lung airway and vascular diseases will be evaluated. One of the most important findings during the prior funding period of this grant was that the extracellular form of superoxide dismutase (EC-SOD) is a protein uniquely highly expressed in the lung. It was found to be primarily localized in the extracellular spaces surrounding smooth muscle cells in airways and in the pulmonary vasculature. The hypothesis to be tested is that EC-SOD plays a critical role in regulating the activity of nitric oxide (NO.) in the lung. The possible mechanism for EC-SOD regulation of NO. activity involves scavenging O2- and thereby preventing the reaction of O2- with NO.. The distributions and physical relationships of nitric oxide synthase (the enzymatic source of NO.) and EC-SOD in pulmonary airways and in the pulmonary vasculature will be determined. Both in vitro and in vivo animal models will be used to demonstrate the role of EC-SOD in regulating airway and vascular tone in the lung. The Specific Aims are 1) Create tools for the study of EC-SOD in an animal model that will allow the biological function of EC-SOD to be explored, 2) Immunolocalize EC-SOD in airways and pulmonary vasculature, 3) Immunolocalize nitric oxide synthase in airways and pulmonary vasculature, 4) Study the mechanisms of airway bronchomotor tone regulation, and 5) Study the mechanisms of pulmonary vasculature tone regulation. These proposed studies are expected to demonstrate that EC-SOD plays a critical role in regulating both airway and vascular tone in the lung. By demonstrating the physiologic importance of this enzyme, we expect to identify new pharmacologic therapies for the treatment of diseases involving both airway hyperreactivity and pulmonary vascular hyperreactivity.