Cholesterol dynamics in rats fed cis- and trans-octadecenoate in the form of triglyceride

The cholesterol dynamics were compared in rats fed diets containing either camellia oil or partially hydrogenated corn oil as a source of cis- and trans-octadecenoate, respectively. The diets contained approximately the same amount of octadecenoic acid, and an equivalent amount of linoleic acid. In rats fed the trans-fat for about 30 days, liver cholesterol levels were clearly low relative to levels in rats fed the cis-fat, while the concentration of serum cholesterol and the distribution of cholesterol in serum lipoproteins were comparable. The activity of hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase and the incorporation of [I-14C]acetate into digitonin-precipitable sterols in the liver homogenate tended to increase in rats fed the trans-fat diet. Cholesterol 7 alpha-hydroxylase activity increased significantly. Cholesterol absorption measured by the dual isotope serum ratio method was markedly lower, and much more radioactivity both from orally and intravenously administered cholesterol was excreted quickly into feces in the trans-fat group, with relatively more excretion in the neutral than in the acidic steroids. Apparent absorption of dietary fat was slightly lower in the trans-fat group. Cholesterol turnover as analyzed according to the two-pool model was much faster in rats fed trans-fat and the pool A size was reduced mainly as a consequence of stimulation of the removal rate from this pool. The intestinal epithelial cells contained relatively more trans-octadecenoate compared to the serum and liver and trans-fat modified the lipid composition specifically. These observations suggest that the changes in cholesterol metabolism due to the ingestion of trans-fat, compared to cis-fat, are as a result of metabolic events in the intestine.