Lipid composition and peroxide levels of mucosal cells in the rat large intestine in relation to dietary fat.

To examine whether dietary fat alters membrane lipid composition and peroxidation of polyunsaturated fatty acids in "non-proliferative" and "proliferative" cells in the large intestine, Sprague-Dawley rats were fed diets providing a polyunsaturated-to-saturated fatty acid ratio of 1.2 or 0.3 at a high or low level of fat intake for a 25-day period. Cell populations were isolated and the effect of dietary fat on membrane polyunsaturated fatty acid content and peroxide levels was determined. Neither fat level nor fatty acid composition of diet influenced total cholesterol, total phospholipids, and percentage of phospholipid classes in membrane phospholipids. Feeding the high fat and/or high polyunsaturated-to-saturated fatty acid ratio diet increased polyunsaturated fatty acid content of mucosal cell phospholipids. Increase in polyunsaturated fatty acid content was paralleled by a decrease in the monounsaturated fatty acid content of mucosal cell phospholipids. Membrane content of total saturated fatty acids was not significantly affected by diet. Variation in phospholipid fatty acid composition between "non-proliferative" and "proliferative" cells was observed. Lipid peroxide levels in mucosal cell lipid fractions were altered by dietary fat treatment. Animals fed high fat diets, compared to groups fed low fat diets, exhibited higher membrane peroxide levels when results are expressed as nmol/mg protein. Higher peroxide levels were observed in mucosal cells for rats fed high polyunsaturated-to-saturated fatty acid ratio diets when results were expressed per nmol of phospholipid. It is concluded that changes in fat level and fatty acid composition of the diet alters the mucosal cell membrane lipid composition in the rat large intestine and influences susceptibility of mucosal cell lipid to peroxidation. Further research is required to delineate which dietary factors--fat level, polyunsaturated-to-saturated fatty acid ratio, or both--have a primary influence on the degree of lipid peroxidation.