This study was undertaken to compare the effects of three major dietary n-3 fatty acids, i.e. α-linolenic acid (C18:3, n-3; LN), eicosapentaenoic acid (C20:5, n-3; EPA) and docosahexaenoic acid (C22:6, n-3; DHA), on liver microsomal mixed-function oxidase activities with and without phenobarbital (PB) induction. Male Sprague-Dawley rats were fed a 5% lipid diet containing either LN, EPA or DHA as major constituent fatty acid (about 40%) of dietary lipids for 15 days. The fatty acid compositions of liver microsomal lipids of each n-3 fatty acid group were characteristically different, particularly in the n-3 fatty acid compositions, but were nearly the same with and without PB treatment. Dietary LN, EPA and DHA did not affect the levels of PB-inducible cytochrome P-450 species nor the activities of aminopyrine N-demethylase and aniline hydroxylase. However, the PB-uninduced constitutive levels of cytochromes P-450 increased in the following order with a slight but significant difference between LN and DHA groups: LN group < EPA group < DHA group. Both the PB-uninduced activities of aminopyrine N-demethylase and aniline hydroxylase changed in a very similar manner to the constitutive levels of cytochromes P-450. These results suggest that the uninduced constitutive level of certain cytochrome P-450 species is modulated differentially by dietary LN, EPA and DHA, whereas dietary LN, EPA and DHA do not affect the PB-inducible levels of cytochrome P-450 species.

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