The biosynthesis of docosahexaenoic acid [22:6(n-3)] from linolenic acid in primary hepatocytes isolated from wild northern pike

Primary hepatocytes from wild northern pike Esox lucius were incubated with radiolabelled linolenic acid ([1-C-14]-18:3(n-3)) to assess their ability to synthesize docosahexaenoic acid [22:6(n-3)]. The distribution of radioactivity in lipid classes and hepatocyte polyunsaturated fatty acids (PUFA) was measured over the lime-course of 24h. The majority of radioactivity from [1-C-14]-18:3(n-3) was recovered in hepatocyte triacylglycerols (TAG) and phosphatidylcholine (PC). The levels of radioactivity in TAG and in most of phospholipids, including PC, increased significantly over the incubation period. Radioactivity from :[1-C-14]-18:3(n-3) was recovered in several hepatocyte PUFA, including 22:6(n-3), and the Delta 6 and Delta 5-desaturation products 18:4(n-3) and 20:5(n-3). The presence of radioactivity in C,, (n-3) PUFA may be evidence that the biosynthesis of 22:6(n-3) in pike proceeds via a pathway independent of Delta 4-desaturation. Analysis by radio gas chromatography revealed that radiolabelled 24:6(n-3) was present among the desaturation and elongation products of [1-C-14]-18:3(n-3). The results establish that, under the in vitro conditions employed, pike hepatocytes are able to convert linolenic acid to 20:5(n-3) and 22:6(n-3). (C) 1995 The Fisheries Society of the British Isles.