Studies on the regulation of arachidonic acid synthesis in isolated rat liver cells.

Isolated liver cells from rats fed a diet deficient in essential fatty acids were used to study the oxidation, esterification and, especially, the desaturation and chain elongation of [1-14C]linoleic acid. 14C-labelled arachidonic acid (20:4) and smaller amounts of eicosatrienoic acid (20:3) were recovered mainly in the phospholipids, while gamma-linolenic acid (18:3) was found in both the phospholipids and the triacylglycerol fraction. Lactate strongly increased the formation of arachidonic acid, which was found mainly in the phosphatidylcholine and the phosphatidylinositol fractions. Lactate reduced the amounts of gamma-linolenic acid. Glucagon and (+)-decanoylcarnitine reduced the formation of arachidonic acid, and (+)-decanoylcarnitine increased the incorporation of gamma-linolenic acid especially, in the triacylglycerol fraction. Increasing concentrations of the [1-14C]linoleic acid substrate increased the formation of arachidonic acid and of the other chain-elongated or desaturated fatty acids. Lactate also stimulated the formation of arachidonic acid in liver cells from animals fed adequate amounts of essential fatty acids. It is suggested that dietary and hormonal factors which can change the intracellular levels of malonyl-CoA may influence both the ratio of arachidonic acid/gamma-linolenic acid formed and the total amounts of desaturated and chain-elongated fatty acids formed from linoleic acid.