Utilization of fatty acids by rat liver slices as a function of medium concentration

¹ Laboratory of Metabolism, National Heart Institute, National Institutes of Health, Bethesda, Maryland

The rate of incorporation of palmitate-1-C¹⁴ into neutral lipids and phospholipids of rat liver slices in vitro and its conversion to C¹⁴O₂ were shown to increase markedly as the free fatty acid (FFA) concentration of the medium was increased. Incorporation into lipids and conversion to C¹⁴O₂ proceeded linearly with time over 60 min. The incorporation of glycerol-1,3-C¹⁴ into neutral lipids also increased as the FFA concentration of the medium was increased but incorporation into phospholipids was unchanged. It is concluded that high FFA concentrations cause a true increase in rate of neutral lipid synthesis by liver slices. The associated increase in incorporation of labeled palmitate into phospholipids most likely reflects the higher specific radioactivity of the precursor pool of FFA and/or an exchange reaction rather than a true increase in net synthesis. A method for recovering tissue FFA quantitatively is described. Normal liver was found to contain 0.40–0.87 µEq FFA/g wet wt. The composition of this tissue FFA fraction is presented.

Key Words: fatty acid esterification and oxidation • lipid metabolism • palmitate-1-C¹⁴ • glycerol-1,3-C¹⁴ • neutral lipid synthesis • glyceride synthesis • fatty livers • effect off asting on hepatic glyceride synthesis • fatty acid oxidation, liver • glycerol utilization, liver • glycerol oxidation, liver • glyceride synthesis, liver • phospholipid synthesis, liver • free fatty acids of liver, concentration and composition

Submitted on July 15, 1963