Effect of hyperoxia on the composition of the alveolar surfactant and the turnover of surfactant phospholipids, cholesterol, plasmalogens and vitamin E.

Experimental and clinical studies have provided evidence for the involvement of oxygen free radicals in development of acute and chronic lung diseases. Hyperoxia is very often an indispensable therapeutic intervention which seems to impose oxidative stress on lung tissue. We measured the effect of hyperoxia (80% O2 for 20 h) (1) on the lipid composition of pulmonary surfactant treated in vitro, (2) on surfactant lipid synthesis and secretion of type II pneumocytes in primary culture, (3) on the lipid composition and on the SP-A content of rat lung lavages and (4) on the turnover of phospholipids, cholesterol, plasmalogens and vitamin E in type II pneumocytes, lamellar bodies and lavages of adult rat lungs. (1) Hyperoxia of lung lavages in vitro reduces the vitamin E content significantly but does not change the relative proportion of PUFA or the content of plasmalogens. (2) Hyperoxia does not affect the biosynthesis or secretion of surfactant lipids and plasmalogens by type pneumocytes in primary culture. (3) Hyperoxic treatment of rats increases the SP-A content and reduces the vitamin E content significantly but does not change the concentration of other lipid components of lung lavage. (4) The vitamin E turnover, measured in type II pneumocytes, lamellar bodies and lung lavages, is increased 2-fold in these fractions. In contrast, the turnover of surfactant cholesterol and surfactant lipids does not change. (5) Hyperoxia caused an increase of the vitamin E uptake by type II pneumocytes resulting in a vitamin E enrichment of lamellar bodies. From these results we conclude that type II pneumocytes are able to regulate the turnover of lipophilic constituents of the alveolar surfactant independently of each other. Hyperoxia caused type II pneumocytes to increase the vitamin E content of lamellar bodies. The lipid and SP-A content of alveolar fluid can be regulated independently each other.