Linolenic Acid Desaturation and Chain Elongation and Rapid Turnover of Phospholipid N - 3 Fatty Acids in Isolated Rat Liver Cells

The desaturation and chain elongation of [1-14C]linolenic acid was studied in isolated liver cells from rats fed a diet deficient in essential fatty acids. 14C-labelled 18:4, 20:3, 20:4, 20:5, 22:5 and 22:6, all n - 3 fatty acids, were formed. In the presence of lactate relatively large amounts of 20:5, 22:5 and 22:6 were formed. 20:5 was mainly present in phospholipids, 22:5 and 22:6 were present in both phospholipids and triacylglycerols. (+)-Decanoylcarnitine and (-)-hydroxycitrate decreased the formation of 20:5, 22:5 and 22:6 and increased the recovery of 18:4. The unchanged 18:3 substrate was also initially rapidly incorporated both in the phospholipids and in the triacylglycerol fraction. During long incubation periods, continued after nearly all the [14C]linolenic acid substrate had been metabolized either by esterification or by oxidation, the phospholipid content of labelled 18:3 and 18:4 decreased while the content of 20:5, 22:5 and 22:6 increased markedly, suggesting a remodeling of the phospholipid n - 3 fatty acid content by a series of deacylations-reacylations. The n - 3 fatty acid pattern in the triacylglycerol fraction changed little. 22:5 and 22:6 appeared in the VLDL fraction secreted by the isolated liver cells.