Garg M L, Sebokova E, Thomson A B, Clandinin M T
Nutrition and Metabolism Research Group, University of Alberta, Edmonton, Canada.
Biochem J. 1988 Jan 15;249(2):351-6. doi: 10.1042/bj2490351.
The effect of feeding semipurified diets enriched in linseed (rich in C18:3, omega 3 fatty acid) or fish (rich in C20:5, omega 3 and C22:6, omega 3 fatty acid) oil with and without cholesterol supplementation on the desaturation of linoleic acid (C18:2, omega 6) by rat liver microsomal fractions was investigated. Animals fed diets supplemented with beef tallow were used as equal-energy controls. Both linseed-oil and fish-oil diets, without added cholesterol, decrease conversion of C18:2, omega 6 fatty acid to gamma-linolenic acid (C18:3, omega 6). Reduction in delta 6-desaturation was significantly greater for animals fed the diet containing fish oil than with animals fed the linseed-oil diet. The major effect of cholesterol supplementation was to decrease the rate of desaturation of C18:2, omega 6, when fed in combination with the beef-tallow diet, whereas delta 6-desaturation was unaffected when cholesterol was fed along with diets high in omega 3 fatty acids (linseed oil or fish oil). The activity of the delta 6-desaturase in vitro is consistent with the fatty acid composition observed for the microsomal membranes on which this enzyme is localized. Dietary linseed oil and fish oil lowered the arachidonic (C20:4, omega 6) acid content of rat liver microsomes, with an accompanying increase in membrane eicosapentaenoic (C20:5, omega 3) and docosahexaenoic (C22:6, omega 3) acid content, in comparison with the group fed beef tallow. Inclusion of cholesterol into the beef-tallow or linseed-oil diets resulted in decreased membrane C20:4, omega 6-fatty-acid content, with concomitant increase in C18:2, omega 6-fatty-acid content. However, addition of cholesterol to the fish-oil diet did not alter the microsomal membrane content of C20:4, omega 6 fatty acid. Thus it is suggested that (1) the decrease in prostaglandin E2, thromboxane and prostacyclin levels generally observed after fish-oil consumption may be at least partly due to inhibition of C20:4, omega 6-fatty-acid synthesis from C18:2, omega 6 fatty acid; and (2) consumption of fish oil prevents the further decrease in C20:4, omega 6-fatty-acid levels by dietary cholesterol that is apparent when cholesterol is fed in combination with diets high in saturated fat or C18:3, omega 3 fatty acid.
研究了在补充或不补充胆固醇的情况下，用富含亚麻籽（富含C18:3，ω-3脂肪酸）或鱼类（富含C20:5，ω-3和C22:6，ω-3脂肪酸）油的半纯化日粮喂养大鼠，对大鼠肝脏微粒体部分中亚油酸（C18:2，ω-6）去饱和作用的影响。以补充牛脂的日粮喂养的动物作为等能量对照。不添加胆固醇时，亚麻籽油和鱼油日粮均会降低C18:2，ω-6脂肪酸向γ-亚麻酸（C18:3，ω-6）的转化。与喂食亚麻籽油日粮的动物相比，喂食鱼油日粮的动物其δ6-去饱和作用的降低更为显著。补充胆固醇的主要作用是，当与牛脂日粮一起喂食时，会降低C18:2，ω-6的去饱和速率，而当胆固醇与富含ω-3脂肪酸（亚麻籽油或鱼油）的日粮一起喂食时，δ6-去饱和作用不受影响。体外δ6-去饱和酶的活性与该酶所在的微粒体膜的脂肪酸组成一致。与喂食牛脂的组相比，日粮中的亚麻籽油和鱼油降低了大鼠肝脏微粒体中花生四烯酸（C20:4，ω-6）的含量，同时微粒体中二十碳五烯酸（C-20:5，ω-3）和二十二碳六烯酸（C22:6，ω-3）的含量增加。在牛脂或亚麻籽油日粮中添加胆固醇会导致微粒体膜中C20:4，ω-6脂肪酸含量降低，同时C18:2，ω-6脂肪酸含量增加。然而，在鱼油日粮中添加胆固醇并不会改变微粒体膜中C20:4，ω-6脂肪酸的含量。因此，有人提出：（1）通常在食用鱼油后观察到的前列腺素E2、血栓素和前列环素水平的降低，可能至少部分是由于抑制了由C18:2，ω-6脂肪酸合成C20:4，ω-6脂肪酸；（2）食用鱼油可防止日粮中的胆固醇使C20:4，ω-6脂肪酸水平进一步降低，而当胆固醇与富含饱和脂肪或C18:3，ω-3脂肪酸的日粮一起喂食时，这种降低是明显的。
