Hepatic cholesterol synthesis was studied in rats after consuming diets of varying neutral lipid and cholesterol content. Cholesterol synthesis was evaluated by measuring 3-hydroxy-3-methylglutaryl-CoA reductase and by determining the rate of 3H-labeled sterol production from [3H]mevalonate. Results were correlated with sterol balance data and hepatic lipid content. Hepatic cholesterol synthesis was relatively great when cholesterol was excluded from the diet. The source of neutral dietary lipids, saturated vs. unsaturated, produced no change in hepatic sterol synthesis. Values for fecal sterol outputs and hepatic cholesterol levels were also similar in rats consuming either saturated or unsaturated fats. When 1% cholesterol was added to the diet, hepatic cholesterol synthesis was suppressed but the degree of suppression was greater in rats consuming unsaturated vs. saturated fats. This was associated with greater accumulation of cholesterol in livers from rats consuming unsaturates and a reduction in fecal neutral sterol output in this group as opposed to results from rats on saturated fats. Cholesterol consumption also altered the fatty acid composition of hepatic phospholipids producing decreases in the percentages of essential polyunsaturated fatty acids. It is concluded that dietary cholesterol alters cholesterol and fatty acid metabolism in the liver and that this effect is enhanced by dietary unsaturated fats.

Animals↗

PubMed1978

Effect of diester and diether phosphatidylcholine on intestinal absorption of neutral and acidic sterols.

The effects of nondigestible diether phosphatidylcholine on intestinal absorption of cholesterol and dihydroxy and trihydroxy conjugated bile salts were studied in bile fistula rats using radioactive substrates. No inhibition of absorption of either dihydroxy or trihydroxy bile salts was observed. Nondigestible phospholipid did, however, significantly inhibit cholesterol absorption. Under control conditions with natural phosphatidylcholine in the intestinal perfusate, absorption of cholesterol was significantly greater when infused with taurocholate (TC) as compared to results obtained after infusion with taurochenodeoxycholate (TCD). Studies were repeated using radioactive rat liver phosphatidylcholine to determine whether the observed decrease in cholesterol absorption could be correlated with a decrease in digestion and absorption of rat liver phosphatidylcholine. No evidence was found for decreased absorption of this phospholipid when given with TCD. It is concluded that less cholesterol is absorbed in the presence of TCD as compared to TC, but the mechanism for this remains unexplained.

Animals↗

PubMed1978