THE METABOLISM OF 22-5(-6) AND OF DOCOSAHEXAENOIC ACID [22-6(-3)] COMPARED IN RAT HEPATOCYTES

Elevated levels of 22:5(-6), which is the elongated and desaturated pr oduct of arachidonic acid, is induced by selective n - 3 fatty acid de ficiency, especially in brain cortex. Less elongation and desaturation of 20:4(-6) than of 20:5(-3) has been found in intact rat liver cells in previous studies and is probably the main reason why so little 22: 5(-6) is found under adequate nutritional conditions, The present stud y compares the metabolism of 22:5(-6) with the metabolism of 22:6(-3), the main n - 3 fatty acid in mammals. Freshly isolated rat liver cell s were incubated with [1-C-14]22:5(-6) and [1-C-14]22:6(-3). Oxidation and esterification in triacylglycerols, diacylglycerols and phospholi pids were studied. The phospholipid classes were separated and the dif ferent molecular species identified. Rats with essential fatty acid de ficiency were compared with control rats. 22:5(-6) was found to be a g ood substrate for membrane phospholipid biosynthesis and was conserved well in the phospholipid fraction of the rat liver cells for more tha n 3 h of incubation. More 22:5(-6) was esterified in the total phospho lipid fraction acid less was incorporated in triacylglycerols than obs erved with 22:6(-3) in hepatocytes from control animals. This was not the case in animals with essential fatty acid deficiency. 22:5(-6) was esterified to a greater extent in phosphatidylcholine than 22:6(-3) i n control cells bur not in essential fatty acid deficiency cells. More 22:5(-6) was coupled with 18:0 in the sn - 1 position of the phosphol ipid molecular species than 22:6(-3) was in control cells.