Metabolism of lecithin and phosphatidylglycerol in surfactant fraction of the lung.

The metabolisms of lecithin and phosphatidylglycerol in the surfactant and residual fractions of rat lung were compared using the in vitro system where tissue slices and radioactive precursors such as [14C]palmitic acid, [14C]palmitoyl lysolecithin and [14C]stearoly lysolecithin were inculbated. The incorporation of precursors into the residual lecithin proceeded linearly during the incubation time, while the time curve on the incorporation into the surfactant lecithin exhibited a lag period before the incorporation increased significantly. A similar tendency was also observed in the incorporation into phosphatidylglycerol. These findings suggested a precursor-product relationship between the corresponding lipids in both the fractions. The turnover time of lecithin was approx. 340-370 min and that of phosphatidylglycerol was 118 min in the intracellular surfactant fraction. The turnover rates of lecithin and phosphatidlyglycerol were approx. 0.6 and 2 nmoles/g of wet tissue, respectively. The transfer of lecithin from the residual fraction to the surfactant fraction was hardly influenced by the difference of fatty acid moiety at the 2-position of 1-palmitoly-lysolecithin. However, the turnover time of 1-palmitoyl lecithin (360 min) was distinctly shorter than that of 1-stearoly species (730 min). The turnover time of the saturated lecithin was also shown to be 328 min. On the other hand, polyenoic species showed the shorter turnover time; 182 min for the tetraenoic species.