TYPE-II PNEUMOCYTES SECRETE VITAMIN-E TOGETHER WITH SURFACTANT LIPIDS

Lung surfactant is exposed to strongly oxidizing conditions. We examin ed the hypothesis that in lung, lipophilic antioxidants are secreted t ogether with surfactant to counteract the peroxidation of surfactant c onstituents. Lung lavage and the subfractions of the alveolar surfacta nt contain the lipophilic antioxidants vitamin E, vitamin A, and plasm alogens. The specific radioactivity of vitamin E isolated from serum, lung homogenate, lamellar bodies, and lung lavage increased linearly u p to 3 h after intraperitoneal application of [H-3]tocopherol. [H-3]to copherol was secreted in situ together with [C-14]palmitic acid-labele d phospholipid in response to isoproterenol. Type II cells cultured in presence of [H-3]tocopherol or of [H-3]cholecalciferol and [C-14]palm itic acid responded to isoproterenol by a time-dependent increase in s ecretion of [H-3]tocopherol and of C-14-labeled phospholipids but not of [H-3]cholecalciferol. The isoproterenol-stimulated secretion of [H- 3]tocopherol and of C-14-labeled phospholipids by type 11 cells is inh ibited by surfactant protein A. We conclude that the alveolar surfacta nt contains lipophilic antioxidants as integral constituents. [H-3]toc opherol seems to be secreted together with surfactant.