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

Abstract

The metabolism of lecithin and phosphatidylglycerol in the surfactant and residual fractions of rat lung was compared using an in vitro system in which tissue slices and radioactive precursors, e.g., [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 fractions. The turnover time of lecithin was approximately 340-370 min and that of phosphatidylglycerol was 118 min in the intracellular surfactant fraction. The turnover rates of lecithin and phosphatidylglycerol were approximately 0.6 and 2 nmol/g of wet tissue, respectively. The transfer of lecithin from the residual fraction to the surfactant fraction was hardly influenced by the difference in the fatty acid moiety at the 2-position of 1-palmitoyl-lysolecithin. However, the turnover time of 1-palmitoyl lecithin (360 min) was distinctly shorter than that of the 1-stearoyl species (730 min). The turnover time of the saturated lecithin was also shown to be 328 min. Polyenoic species showed the shorter turnover time; for the tetraenoic species it was 182 min.