Desaturation and chain elongation of essential fatty acids in isolated liver cells from rat and rainbow trout

Isolated hepatocytes from rainbow trout and rat were incubated with 14C-labeled linoleic acid, linolenic acid, dihomogammalinolenic acid or eicosapentaenoic acid. The most striking difference in the desaturase activity was the lower level of delta 5 desaturase in trout than in rat. No delta 4 desaturation of 22:4(n-6) to 22:5(n-6) was observed in either of the two species, while the conversion of 22:5(n-3) to 22:6(n-3) was significant in both groups and highest in rainbow trout. The chain-elongating activity was remarkably similar in the two species, except for the dead-end elongation which was distinctly more important in fish