Adaption to hyperoxia. Influence on protein synthesis by lung and on granular pneumocyte ultrastructure

We studied the influence of prolonged exposure to hyperoxia (O(2) > 98%) on protein synthesis and on the ultrastructure of the granular pneumocyte. To study protein synthesis, as indicated by l-[U-(14)C]-leucine incorporation into protein, lung slices were incubated with radioactive leucine and a surface-active fraction was obtained by ultracentrifugation of lung homogenates. We found that, following an initial depression in protein synthesis after 48 h of hyperoxia, protein synthesis in rats exposed to oxygen for 96 h rose to greater than control levels. This increase in protein synthesis was noted in whole lung protein and in protein present in the surface-active fraction. Stereologic ultrastructural analysis of granular pneumocytes revealed that the lamellar bodies occupy the same percentage of cytoplasmic volume in oxygen-exposed and control rats after 96 h; a previous study had shown lamellar bodies of oxygen-exposed rats to occupy less volume than those of control rats after 48 h of exposure at which time protein synthesis was also depressed. After 96 h of exposure there is a greater amount of rough endoplasmic reticulum in the granular pneumocytes of oxygen-exposed rats. These studies show that after 96 h of hyperoxia the lung has recovered its ability to synthesize protein including protein in the surface-active fraction and that these biochemical changes are associated with consistent ultrastructural alterations in the granular pneumocyte.