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 a¹⁴C labeled substrate. It was found that 1-¹⁴C-acetate, 1-¹⁴C-laurate, 1-¹⁴C-palmitate, 1-¹⁴C-stearate, 1-¹⁴C-oleate, or U-¹⁴C-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 initial¹⁴C-radioactivity of 1-¹⁴C-acetate, 1-¹⁴C-laurate, 1-¹⁴C-palmitate, 1-¹⁴C-stearate, 1-¹⁴C-oleate, and U-¹⁴C-D-glucose, respectively, were incorporated into phospholipids. Phospholipid fatty acids accounted for 95–96% total phospholipids-¹⁴C when¹⁴C-substrates, other than glucose, were used. For glucose, only 20% phospholipids-¹⁴C was in phospholipid fatty acids. More than 80% phospholipid fatty acids-¹⁴C was in palmitic acid when 1-¹⁴C-acetate and U-¹⁴C-D-glucose were used, while 37, 61, 80, and 94% phospholipid fatty acid-¹⁴C from 1-¹⁴C-laurate, 1-¹⁴C-sterate, 1-¹⁴C-oleate, and 1-¹⁴C-palmitate, respectively were recovered in the original form of the fatty acid used. The newly synthesized phospholipid fatty acid (13–24%) from 1-¹⁴C-laurate, 1-¹⁴C-stearate, and 1-¹⁴C-oleate was palmitic, and 10% of phospholipid fatty acid from 1-¹⁴C-stearate was in oleic acid. Hydrolysis by phospholipase A showed that¹⁴C 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.