Effects of diets enriched in n-6 or n-3 fatty acids on cholesterol metabolism in older rats chronically fed a cholesterol-enriched diet

Hypocholesterolemic effects in older animals after long-term feeding are un known. Therefore, aged rats (24 wk Of age) fed a conventional diet were shi fted to diets containing 10% perilla oil [PEO; oleic acid + linoleic acid alpha -linolenic acid; n-6/n-3, 0.3; polyunsaturated fatty acid/saturated fatty acid (P/S), 9.6], borage oil [oleic acid + linoleic acid + alpha -lin olenic acid; n-6/n-3, 15.1; P/S, 5.3], evening primrose oil (EPO; linoleic acid + gamma -linolenic acid; P/S, 10.5), mixed oil (MIO; oleic acid + lino leic acid + gamma -linolenic acid + alpha -linolenic acid; n-6/n-3, 1.7; P/ S, 6.7), or palm oil (PLO; palmitic acid + oleic acid + linoleic acid; n-6/ n-3, 25.3; P/S, 0.2) with 0.5% cholesterol for 15 wk in this experiment. Th ere were no significant differences in the food intake and body weight gain among the groups. The liver weight in the PEO (n-6/n-3, 0.3) group was sig nificantly higher than those of other groups in aged rats. The serum total cholesterol and very low density lipoprotein (VLDL) + intermediate density lipoprotein (IDL) + low density lipoprotein (LDL)-cholesterol concentration s of the PLO (25.3) group were consistently higher than those in the other groups. The serum high density lipoprotein cholesterol concentrations of th e PEO (0.3) and EPO groups were significantly lower than in the other group s at the end of the 15-wk feeding period. The liver cholesterol concentrati on of the PLO (25.3) group was significantly higher than those of other gro ups. There were no significant differences in the hepatic LDL receptor mRNA level among the groups. Hepatic apolipoprotein (apo) B mRNA levels were no t affected by the experimental conditions. The fecal neutral steroid excret ion of the PLO (25.3) group tended to be low compared to the ether groups. The results of this study demonstrate that both n-6 fatty acid and n-3 fatt y acids such as gamma -linolenic acid and cx-linolenic acid inhibit the inc rease of serum total cholesterol and VLDL + IDL + LDL-cholesterol concentra tions of aged rats in the presence of excess cholesterol in the diet compar ed with dietary saturated fatty acid.