INCORPORATION OF [H-3] ARACHIDONIC AND [C-14] EICOSAPENTAENOIC ACIDS INTO GLYCEROPHOSPHOLIPIDS AND THEIR METABOLISM VIA LIPOXYGENASES IN ISOLATED BRAIN-CELLS FROM RAINBOW-TROUT ONCORHYNCHUS-MYKISS

The incorporation of [H-3]arachidonate ([H-3]AA) and [C-14]eicosapentaenoate ([C-14]EPA) into glycerophospholipids was studied in isolated brain cells from rainbow trout, a teleost fish whose lipids are rich in (n-3) polyunsaturated fatty acids (PUFAs). EPA was incorporated into total lipid to a greater extent than AA, but the incorporation of both PUFAs into total glycerophospholipids was almost identical. The incorporation of both AA and EPA was greatest into phosphatidylethanolamine (PE). However, when expressed per milligram of individual phosphoglycerides, both AA and EPA were preferentially incorporated into phosphatidylinositol (PI), the preference being significantly greater with AA. On the same basis, significantly more EPA than AA was incorporated into phosphatidylcholine (PC). When double-labelled cells were challenged with calcium ionophore A23187, the H-3 and C-14 released from the cells closely paralleled each other, peaking at 10 min after addition of ionophore. The 12-monohydroxylated derivative was the predominant lipoxygenase product from both AA and EPA with a rank order of 12-hydroxyeicosatetraenoic acid (12-HETE) > leukotriene B4 (LTB4) > 5-HETE > 15-HETE for the AA products and 12-hydroxyeicosapentaenoic acid (12-HEPE) > 5-HEPE > LTB5 > 15-HEPE for EPA products. The H-3/C-14 (dpm/dpm) ratios in the glycerophospholipids, total released radioactivity, and the lipoxygenase products suggested that PC rather than PI was the likely source of eicosanoid precursors in trout brain cells.