In vivo incorporation of tritium from 3H2O into pulmonary lipids of meal-fed and starved rats.

In vivo fatty acid synthesis, as measured by tritium incorporation from 3H2O into fatty acids, was examined in the lungs of meal-fed and starved rats. In meal-fed animals, 74% of the radioactivity isolated from pulmonary lipids was found in the phospholipid fraction, with phospholipid fatty acids accounting for approximately 89% of total radioactivity in this fraction. Starving rats for 72 h markedly reduced in vivo 3H2O incorporation into pulmonary lipids. Intraperitoneal injection of (-)-hydroxycitrate prior to 3H2O administration also markedly reduced isotope incorporation into pulmonary lipid fractions of fed rats. These studies demonstrated net in vivo synthesis of fatty acids in pulmonary tissue of rats using a method that is not complicated by potential differences in metabolic pool sizes or peculiarities of specific carbon substrate sources. Synthesis of fatty acids in vivo was affected by the nutritional state of the animal and citrate appears to be a significant source of cytoplasmic acetyl-CoA for de novo pulmonary lipogenesis in the fed rat.