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 pikeEsox luciuswere incubated with radiolabelled linolenic acid ([l‐14C]‐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 time‐course of 24h. The majority of radioactivity from [l‐14C]‐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 [1‐14C]‐18:3(n‐3) was recovered in several hepatocyte PUFA, including 22:6(n‐3), and the Δ6 and Δ5‐desaturation products 18:4(n‐3) and 20:5(n‐3). The presence of radioactivity in C24(n‐3) PUFA may be evidence that the biosynthesis of 22:6(n‐3) in pike proceeds via a pathway independent of Δ4‐desaturation. Analysis by radio gas chromatography revealed that radiolabelled 24:6(n‐3) was present among the desaturation and elongation products of [l‐14C]‐18:3(n‐3). The results establish that, under thein vitroconditions employed, pike hepatocytes are able to convert linolenic acid to 20:5(n‐3) and 22:6(n‐3).