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

Abstract

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.

In Vitro Metabolism of Palmitic Acid in Human Fetal Tissue

“…The data show that each fetal tissue studied metabolized PA to triglyceride, sterol, sterol ester, phospholipid, and carbon dioxide. These findings are in agreement with data obtained in adult rat tissue in vitro and suggest that fetal FFA are utilized to some extent for energy production and to a large extent for the synthesis of lipids as in adult rat tissue [3,9,16,20].…”

“…These metabolic processes do not differ from those observed in adult rat tissue in vitro [3,9,16,20]. For many years glucose was considered to be the major source of fetal energy [6].…”

“…In each incubated vessel were 4 ml Krebs-Ringer phosphate buffer containing 3% bovine serum albumin fraction V [29] and 1.0-3.0 millimoles FFA extract mixed with 14 C-palmitic acid and 10 millimoles glucose [16]. The FFA extract was prepared by saponification of human adipose tissue [16].…”

“…The FFA extract was prepared by saponification of human adipose tissue [16]. The amount of PA was adjusted in each experiment so that the specific activity of the medium FFA was 15 yuCi/millimole FFA.…”

“…At the end of incubation, each tissue was transferred to cold isotonic saline and washed several times to remove the FFA [16]. Total lipids were then extracted [5].…”