Synthesis of phospholipids and phospholipid fatty acids by isolated perfused rat lung

Synthesis of phospholipids and phospholipid fatty acids in isolated perfused rat lung was studied. The perfusion fluid was a Krebs‐Ringer bicarbonate buffer containing a 14 C labeled substrate. It was found that 1‐ 14 C‐acetate, 1‐ 14 C‐laurate, 1‐ 14 C‐palmitate, 1‐ 14 C‐stearate, 1‐ 14 C‐oleate, or U‐ 14 C‐D‐glucose was incorporated into tissue lipids in the isolated perfused lung at a rate geeater than that in incubated minced tissue. However, the patterns of the newly synthesized lipids from these two systems were similar. In 1 hr of perfusion, 6.8, 3, 14.5, 7.5, 7, and 2% of the initial 14 C‐radioactivity of 1‐ 14 C‐acetate, 1‐ 14 C‐laurate, 1‐ 14 C‐palmitate, 1‐ 14 C‐stearate, 1‐ 14 C‐oleate, and U‐ 14 C‐D‐glucose, respectively, were incorporated into phospholipids. Phospholipid fatty acids accounted for 95–96% total phospholipids‐ 14 C when 14 C‐substrates, other than glucose, were used. For glucose, only 20% phospholipids‐ 14 C was in phospholipid fatty acids. More than 80% phospholipid fatty acids‐ 14 C was in palmitic acid when 1‐ 14 C‐acetate and U‐ 14 C‐D‐glucose were used, while 37, 61, 80, and 94% phospholipid fatty acid‐ 14 C from 1‐ 14 C‐laurate, 1‐ 14 C‐sterate, 1‐ 14 C‐oleate, and 1‐ 14 C‐palmitate, respectively were recovered in the original form of the fatty acid used. The newly synthesized phospholipid fatty acid (13–24%) from 1‐ 14 C‐laurate, 1‐ 14 C‐stearate, and 1‐ 14 C‐oleate was palmitic, and 10% of phospholipid fatty acid from 1‐ 14 C‐stearate was in oleic acid. Hydrolysis by phospholipase A showed that 14 C from perfused substrates was esterified to both α and β positions of phospholipids. It was found that positional selectivity of phospholipid fatty acids was determined by chain length, degree of unsaturation, and source of fatty acid.