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 unknown. Therefore, aged rats (24 wk of age) fed a conventional diet were shifted 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-linolenic 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 + linoleic 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. There 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 significantly 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 concentrations of the PLO (25.3) group were consistently higher than those in the other groups. The serum high density lipoprotein cholesterol concentrations of the PEO (0.3) and EPO groups were significantly lower than in the other groups at the end of the 15-wk feeding period. The liver cholesterol concentration of the PLO (25.3) group was significantly higher than those of other groups. There were no significant differences in the hepatic LDL receptor mRNA level among the groups. Hepatic apolipoprotein (apo) B mRNA levels were not affected by the experimental conditions. The fecal neutral steroid excretion of the PLO (25.3) group tended to be low compared to the other groups. The results of this study demonstrate that both n-6 fatty acid and n-3 fatty acids such as gamma-linolenic acid and alpha-linolenic acid inhibit the increase of serum total cholesterol and VLDL + IDL + LDL-cholesterol concentrations of aged rats in the presence of excess cholesterol in the diet compared with dietary saturated fatty acid.