Metabolism of Lecithin and Phosphatidylglycerol in Surfactant Fraction of the Lung

Abstract

The metabolisms of lecithin and phosphate-dylglycerol 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] stearoyl lysolecithin were incubated. 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. 340-370min and that of phosphatidylglycerol was 118min in the intracellular surfactant fraction. The turnover rates of lecithin and phosphatidylglycerol were approx. 0.6and 2nmoles/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-palmitoyl-lysolecithin. However, the turnover time of 1-palmitoyl lecithin (360min) was distinctly shorter than that of 1-stearoyl species (730min). The turnover time of the saturated lecithin was also shown to be 328min. On the other hand, polyenoic species showed the shorter turnover time; 182min for the tetraenoic species.