Hepatic and intestinal formation of polar sterols in vivo in animals fed on a cholesterol-supplemented diet.

In rats fed on a diet containing 1% cholesterol for 24 h, the decrease in hepatic non-saponifiable lipid synthesis, cholesterogenesis and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was accompanied by an increase in the proportion of newly synthesized polar sterols in vivo. In these animals there was also a strong inverse correlation between the proportion of polar sterols in the non-saponifiable lipid and hepatic HMG-CoA reductase activity. A similar correlation was not observed in animals fed on a normal diet. Cholesterogenesis in the intestine was not as sensitive to inhibition by dietary cholesterol as was that in the liver, and there was no increase in the polar-sterol content of the newly synthesized non-saponifiable-lipid fraction.