Dietary oxidized linoleic acid modifies lipid composition of rat liver microsomes and increases their fluidity

The effect of dietary oxidized oil on the lipid composition, fluidity and function of rat liver microsomes was studied. Male growing rats were fed diets containing 10 g/100 g of a fresh (control) or oxidized (experimental) linoleic acid-rich preparation for 4 wk. High levels of fluorescent compounds and of thiobarbituric acid reactive substances indicated the occurrence of substantial lipid peroxidation in the microsomes of the experimental rats. The fluidity of the liver microsomes derived from rats fed the experimental diet was significantly higher than that of the membranes of the controls. This was due to profound differences in lipid composition of the liver microsomes, namely, a lower cholesterol to phospholipid molar ratio and a greater arachidonic acid content in the phospholipids of the rats fed the experimental diet. The fluidity differences were accompanied by greater activity of the microsomal enzymes, aldehyde dehydrogenase and NADPH cytochrome C reductase. The study demonstrated that ingestion of oxidized lipids caused profound alterations in membrane composition, fluidity and function. These alterations are likely to be associated with an enhanced cholesterol turnover, as indicated by the greater cholesterol excretion observed for the experimental rats.