RATE OF ALTERATION OF HEPATIC MIXED-FUNCTION OXIDASE SYSTEM IN RATS FED DIFFERENT DIETARY FATS

Studies were carried out to evaluate and relate the rate of alteration in mixed-function oxidase system with the changes of the fatty acid c omposition 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 pea nut-rapeseed oil, sunflower oil, or salmon oil. In rats fed a fat-free diet, the cytochrome P-450 concentration and aniline hydroxylase, ami nopyrine N-demethylase, and NADPH-cytochrome-e 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 b( 5) concentration and NADH-cytochrome-b(5) reductase activity were, res pectively, 33 and 43% higher than those of the control group at the sa me time. When rats were fed the sunflower oil diet, the cytochrome P-4 50 concentration and NADH-cytochrome-b(5) reductase activity at 120 da ys were, respectively, 11 and 23% lesser than those of control group. But the cytochrome b(5) concentration was 10% higher than that of the control group. In rats fed the fish oil diet, the cytochrome P-450 con centration and NADPH-cytochrome-c reductase, aniline hydroxylase, and aminopyrine N-demethylase activities at 120 days were, respectively, 3 0, 48, 41, and 31% higher than those of rats fed the control diet. The se enzymes were correlated very well(0.84 < r < 0.93), P < 0.05 with d ietary Sigma polyunsaturated fatty acids (n - 3). The fatty acid compo sition of liver microsomes of rats fed a fat-free diet revealed high l evels of 16:1(n - 7), 18:1(n - 9), and 20:3(n - 9) acids. A dramatic d ecrease 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 we re fed a fish oil diet, the liver microsomes were highly enriched in 2 0:5(n - 3) and 22:6(n - 3) acids and simultaneously there was a decrea se in arachidonic acid. From these findings it is concluded that dieta ry fats induce changes not only in the fatty acid composition of liver microsome lipids, but also in the activities of mixed-function oxidas e system. Also, the results suggest that essential fatty acids might p lay a role in regulating the intrinsic membrane protein activities.