Lipid metabolism in rabbit lungs

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Abstract
The incorporation of palmitate-3H into phospholipids and neutral lipids by alveolar slices from rabbit lung rose with increasing medium palmitate concentration, but glycerol-U-14C incorporation was inadequate to account for all of the palmitate-3H esterified. The highest specific activities with respect to palmitate-3H were found in the triglycerides, diglycerides, and phosphatidylcholine fractions, although that of the phosphatidyl-N,N-dimethylethanolamine was greatest in the early stages of incubation. Incubation of slices with the labelled precursors for 5 min followed by a chase of 175 min resulted in a rapid drop in the specific activity of the phosphatidyl-N,N-dimethylethanolamine and diglycerides with concomitant increases in phosphatidylcholine and triglycerides. However, the radioactivity of the lecithin was too great and the specific activity of the phosphatidylethanolamine too low for the methylation pathway to be of importance in the synthesis of lecithin.Lysophosphatidylcholine could be converted to phosphatidylcholine by lung slices but its addition did not increase the esterification of palmitate. Methionine-methyl-14C was incorporated into phospholipids only slightly, phosphatidylserine having the highest specific activity.Following the intravenous injection of the labelled precursors, half the radioactivity in the lung was found in the phosphatidylcholine fraction of the alveolar tissue, little radioactivity being found in the bronchiolar tissue and the alveolar cell-free saline washings. The highest specific activities were found in the triglycerides and phosphatidylcholine fractions in all three tissue components.

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