Alteration in phospholipid content of lung of adult rats treated with methylprednisolone of high doses.

The effect of methylprednisolone (MP) of high dosage on not only surfactant lipids but also other phospholipid components of adult rat lungs was studied. In spite of the decrease in body weight after one and two intraperitoneal injections of MP of 50 and 100 mg/kg, the increase in content of phospholipids of post-lavaged lung tissue, alveolar white layer, and alveolar macrophages occurred. Although the phospholipid content in the lung tissue and white layer started to decrease by following MP treatment of higher doses, its amount in the white layer and macrophages continued to increase by 25 mg/kg of MP. These changes in the phospholipid content with MP treatment was mainly a consequence of the changes in the content of phosphatidylcholine, especially disaturated phosphatidylcholine, as a main component of lung surfactant. The changes in percentages of other phospholipid components, except for phosphatidylglycerol among total phospholipid in the white layer were not significant. Changes in the content and composition of phospholipid of the isolated epithelial type II cells from adult rat lung after one and two injections of MP (50 mg/kg) were similar to those shown in the lung tissue. Our results indicate that, in the adult rat lung, not only the biosynthesis of phospholipid including surfactant lipids but also its secretion into alveolar space are greatly stimulated by administration of MP of high doses.