Molecular species profiles of acidic phospholipids in lung fractions of adult and perinatal rabbits.

The molecular species of phosphatidylglycerol (PG) and phosphatidylinositol (PI) in pulmonary surfactant and membrane fractions of adult and perinatal rabbit lungs were analyzed by high-performance liquid chromatography of the dinitrobenzoyl derivatives of the diacylglycerols (DGs), derived from the two acidic phospholipids. The PG in both surfactant and membrane fractions of adult lungs consisted mainly of the 16:0/16:0 species, followed in order by 16:0/18:1 and 16:0/18:2 species. In contrast, the prominent molecular species of PI in the membrane fractions were 18:0/20:4 and 16:0/18:1, while surfactant PI consisted mainly of 16:0/18:1 and 16:0/18:2, containing only 3% of 16:0/16:0. In the perinatal rabbit lungs, a compositional change between surfactant PG and PI was found, i.e., an increase in PG and a decrease in PI. The molecular species compositions of PG and PI in the perinatal lungs were generally the same as those observed in the adult lungs. It should, therefore, be noted that the species profiles of surfactant PG and PI, particularly in the content of 16:0/16:0 and 18:0/20:4, are not similar, but distinctly different from each other in both adult and developing lungs. Therefore, the present results strongly suggest two possibilities; (1) both acidic phospholipids which appear in pulmonary surfactant may originate from different pools of CDP-DGs having different molecular species; and/or (2) surfactant PG and PI may be synthesized by individual enzymes having different substrate specificities for different CDP-DGs in alveolar type II cells.