Rate of alteration of hepatic mixed-function oxidase system in rats fed different dietary fats

Abstract

Studies were carried out to evaluate and relate the rate of alteration in mixed-function oxidase system with the changes of the fatty acid composition of rat microsomes induced by different dietary lipids. Male weanling rats were fed from day 21 to 120 with a commercial rat diet or a semisynthetic diet containing no fat or 10% fat consisting of peanut–rapeseed oil, sunflower oil, or salmon oil. In rats fed a fat-free diet, the cytochrome P-450 concentration and aniline hydroxylase, aminopyrine N-demethylase, and NADPH–cytochrome-c reductase activities of liver microsomes at 120 days were, respectively, 26, 16, 10, and 24% lesser than those of rats fed the control diet. However, cytochrome b5 concentration and NADH–cytochrome-b5 reductase activity were, respectively, 33 and 43% higher than those of the control group at the same time. When rats were fed the sunflower oil diet, the cytochrome P-450 concentration and NADH–cytochrome-b5 reductase activity at 120 days were, respectively, 11 and 23% lesser than those of control group. But the cytochrome b5 concentration was 10% higher than that of the control group. In rats fed the fish oil diet, the cytochrome P-450 concentration and NADPH–cytochrome-c reductase, aniline hydroxylase, and aminopyrine N-demethylase activities at 120 days were, respectively, 30, 48, 41, and 31% higher than those of rats fed the control diet. These enzymes were correlated very well (0.84 < r < 0.93), P < 0.05 with dietary Σ polyunsaturated fatty acids (n−3). The fatty acid composition of liver microsomes of rats fed a fat-free diet revealed high levels of 16:1(n−7), 18:1(n−9), and 20:3(n−9) acids. A dramatic decrease in 18:2(n−6) and 20:4(n−6) acids was observed. Animals fed a sunflower oil diet showed high levels of 22:4(n−6) and 22:5(n−6), and low levels in monounsaturated fatty acids. However when rats were fed a fish oil diet, the liver microsomes were highly enriched in 20:5(n−3) and 22:6(n−3) acids and simultaneously there was a decrease in arachidonic acid. From these findings it is concluded that dietary fats induce changes not only in the fatty acid composition of liver microsome lipids, but also in the activities of mixed-function oxidase system. Also, the results suggest that essential fatty acids might play a role in regulating the intrinsic membrane protein activities.Key words: cytochrome P-450, cytochrome b5, NADH–cytochrome-b5 reductase, NADPH–cytochrome-c reductase, aminopyrine N-demethylase, aniline hydroxylase, microsomes, rat liver.