Dietary alpha-linolenic acid lowers postprandial lipid levels with increase of eicosapentaenoic and docosahexaenoic acid contents in rat hepatic membrane.

This study was designed to examine the effects of dietary n-3 and n-6 polyunsaturated fatty acids (PUFA) on postprandial lipid levels and fatty acid composition of hepatic membranes. Male Sprague-Dawley rats were trained for a 3-h feeding protocol and fed one of five semipurified diets: one fat-free diet or one of four diets supplemented with 10% (by weight) each of corn oil, beef tallow, perilla oil, and fish oil. Two separate experiments were performed, 4-wk long-term and 4-d short-term feeding models, to compare the effects of feeding periods. Postprandial plasma lipid was affected by dietary fats. Triacylglycerol (TG) and total cholesterol levels were decreased in rats fed perilla oil and fish oil diets compared with corn oil and beef tallow diets. Hepatic TG and total cholesterol levels were also reduced by fish oil and perilla oil diets. Fatty acid composition of hepatic microsomal fraction reflected dietary fatty acids and their metabolic conversion. The major fatty acids of rats fed the beef tallow diet were palmitic, stearic, and oleic. Similarly, linoleic acid (LA) and arachidonic acid in the corn oil group, alpha-linolenic acid (ALA) and eicosapentaenoic acid (EPA) in the perilla oil group, and palmitic acid and docosahexaenoic acid (DHA) in the fish oil group were detected in high proportions. Both long- and short-term feeding experiments showed similar results. In addition, microsomal DHA content was negatively correlated with plasma lipid levels. Hepatic lipid levels were also negatively correlated with EPA and DHA contents. These results suggest that n-3 ALA has more of a hypolipidemic effect than n-6 LA and that the hypolipidemic effect of n-3 PUFA may be partly related to the increase of EPA and DHA in hepatic membrane.