Secretion of very low density lipoproteins enriched in cholesteryl esters by cultured rat hepatocytes during simulation of intracellular cholesterol esterification.

Very low density lipoproteins, newly secreted by cultured rat hepatocytes into a serum-free medium, contain some cholesteryl esters although the percentage of total cholesterol in ester form is less than that in plasma very low density lipoproteins. When acyl CoA:cholesterol acyltransferase activity in hepatocytes was stimulated by the addition of 25-hydroxycholesterol (10 microgram/ml) or mevalonolactone (1 mM), the absolute amount of esterified cholesterol secreted in very low density lipoproteins increased significantly, but the amount of free cholesterol decreased or showed no change. Thus the percentage of very low density lipoprotein cholesterol in ester form increased, in some experiments to as much as 50% of the total. These results provide additional evidence that hepatic acyl CoA:cholesterol acyltransferase plays a role in the generation of some of the cholesteryl ester in newly-secreted lipoproteins. They further suggest that changes in the activity of the enzyme can potentially regulate the fraction of cholesterol secreted in esterified form.