METABOLISM OF [1-C-14]DOCOSAHEXAENOATE (22/6N-3), [1-C-14]EICOSAPENTAENOATE (20/5N-3) AND [1-C-14]LINOLENATE (18/3N-3) IN BRAIN-CELLS FROM JUVENILE TURBOT SCOPHTHALMUS-MAXIMUS

The incorporation of [1-C-14]18:3n-3 (LNA) and [1-C-14]-22:6n-3 (DHA), and the metabolism via the desaturase/elongase pathways of [1-14C]LNA and [1-C-14]20:5n-3 (EPA) were studied in brain cells from newly-weaned (1-month-old) and 4-month-old turbot. The rank order of the extent of net incorporation of both LNA and DHA into glycerophospholipids was total diradyl glycerophosphocholines (CPL) > total diradyl glycerophosphoethanol-amines (EPL) > phosphatidylserine (PS) and phosphatidylinositol (PI) and was independent of the polyunsaturated fatty acid added, the age of the fish and the time of incubation. However, the rate of incorporation of LNA into total lipid, CPL, EPL and PS was significantly greater than the rate of incorporation of DHA, and there was a significantly greater amount of DHA incorporated into EPL than LNA. There was no significant difference between the amounts of LNA and DHA incorporated into total lipid, CPL, PS and PI. Therefore, little preferential uptake and incorporation of DHA into brain cells was apparent. In 24-h incubations, on average 1.1% and 8.5% of radioactivity from [1-C-14]LNA and [1-C-14]EPA, respectively, were recovered in the DHA fraction. Therefore, LNA cannot contribute significantly to brain DHA levels in the turbot but EPA can. There were no significant differences between the amounts of radioactivity from either [1-C-14]LNA or [1-C-14]EPA recovered in the individual products/intermediates of the desaturase pathways in brain cells from 30-day-old and 120-day-old turbot.