The content of diacylglycerol, triacylglycerol and monoacylglycerol and a comparison of the structural and metabolic heterogeneity of diacylglycerols and phosphatidylcholine during rat lung development.

The content of diacylglycerol in fetal rat lung is approx. 36% of the adult and rapidly increases to adult levels by 1 day after birth. Triacylglycerol content is also low (23%) and increases to adult levels between 1 and 2 days following birth. Monoacylglycerol content is relatively low at all stages of development. The analysis of the molecular species of diacylglycerols showed that the disaturated species accounted for 30-40% of the diacylglycerols and the monoene species 20-28%. Phosphatidylcholine contained 40-45% disaturated and approx. 30% monoene species. The overall pattern of molecular species of phosphatidylcholine was similar to the pattern for diacylglycerol. The in vivo incorporation of [2-3H]glycerol into molecular species of diacylglycerol and phosphatidylcholine in -1-day-fetal (i.e., 1 day before birth) lung showed that the disaturated species of diacylglycerol had the highest incorporation and appeared to have a higher rate of turnover. In contrast, [2-3H]glycerol was incorporated by fetal liver most actively in the monoenoic and dienoic species of diacylglycerol. The relative incorporation of radioactivity into disaturated, monoene and diene species of phosphatidylcholine in fetal lung was very similar to that for the corresponding diacylglycerol species. The rate of the reaction from the disaturated species of diacylglycerol to the disaturated species of phosphatidylcholine, calculated from the in vivo data, was one of the higher rates and indicated considerable potential for the synthesis of disaturated phosphatidylcholine via this route. The overall results suggests that de novo synthesis of disaturated phosphatidylcholine from the disaturated species of diacylglycerol can be a major route for the synthesis of dipalmitoylphosphatidylcholine in fetal lung.