Mixed function oxidases in response to different types of dietary lipids in rats

The influence of dietary lipids on the liver microsomal mixed function oxidase system and on pentobarbital-induced sleeping time was studied in rats. Giving diets containing (g/kg) 150 olive oil, 150 lard or 150 soya-bean oil for 21 d (Expt 1) increased the cytochrome P-450 content in the order: olive oil less than lard less than soya-bean oil. When diets containing (g/kg) 150 lard, 150 soya-bean oil, 150 sardine oil or an equal mixture of 50 of each oil were given for 15 d (Expt 2), the cytochrome P-450 content and aminopyrine N-demethylase activity were significantly higher in the sardine-oil and mixed-oil groups than in the lard group, and the activity of aminopyrine N-demethylase was also significantly higher in the soya-bean oil group compared with the lard group. A significantly higher activity of NADPH-cytochrome c reductase (EC 1.6.2.5) was observed in the sardine-oil group than in the other three groups. Aniline hydroxylase activity and cytochrome b5 content remained unchanged in all the groups. Pentobarbital-induced sleeping time measured on day 15 (Expt 2) varied inversely with the changes in cytochrome P-450 content and aminopyrine N-demethylase activity in the three single-fat groups, but not in the mixed-oil group, reflecting liver microsomal metabolic activity for pentobarbital in vivo. From these results, it appears that high intakes of polyunsaturated fatty acids (18:2n-6, 18:3n-3, 20:5n-3 and 22:6n-3) stimulate the liver microsomal mixed function oxidase system.