Chemically and enzymatically generated oxidants alter endothelial cell shape, increase macromolecular permeability across endothelial cell monolayers, and increase lung microvascular permeability. We examined the effect of ANP (atrial natriuretic peptide) on oxidant-induced injuries to bovine aortic endothelial cell monolayers and to isolated, perfused rabbit lungs. Treatment of cultured endothelial monolayers with glucose oxidase (1.4 U/ml) caused changes in cell shape characterized by a retraction of cells and the formation of numerous intercellular gaps. Glucose oxidase treatment also caused a reduction in F-actin stress fibers visualized by rhodamine-phalloidin fluorescence. Pretreatment (5 min) of the endothelial monolayers with ANP (10(-7) M) attenuated the oxidant-induced changes in cell shape and reduction in F-actin staining. In addition, ANP significantly (P less than 0.05) reduced increases in endothelial monolayer permeability to albumin resulting from glucose oxidase treatment. Oxidant-induced injury of isolated, perfused rabbit lungs produced pulmonary edema measured as an increase in lung weight. This increase in weight was significantly (P less than 0.05) inhibited by pretreatment of lungs with ANP (10(-7) M). Collectively, these results suggest that ANP may act to preserve endothelial barrier function and reduce edema formation caused by oxidant injury.