Journal of Lipid Research, Vol 28, 162-172, Copyright © 1987 by Lipid Research, Inc.
Hepatic metabolism and secretion of a cholesterol-enriched lipoprotein fraction
BG Stone, D Schreiber, LD Alleman and CY Ho
A potentially important source of cholesterol secreted in bile is
cholesterol-rich lipoproteins. However, the fate of the cholesterol carried
in these lipoproteins after hepatic uptake has not been investigated. We
harvested an apoE- and cholesterol-rich lipoprotein fraction (d 1.02-1.06
g/ml) from hypercholesterolemic rats and examined the acute effects of
these lipoproteins on hepatic cholesterol metabolism, very low density
lipoprotein (VLDL) secretion, and biliary lipid secretion. Administration
of a lipoprotein bolus (20 mg of cholesterol) to rats resulted in a
significant decrease in 3-hydroxy-3- methylglutaryl coenzyme A reductase
activity and a significant increase in acyl-coenzyme A:cholesterol
acyltransferase activity over controls at 1 hr. Hepatic cholesteryl ester
content increased 400% with no change in hepatic free cholesterol content
or biliary cholesterol secretion. These cholesterol-rich lipoproteins
delivered in the isolated perfused liver effected a fivefold increase in
hepatic VLDL secretion with no change in composition. Therefore,
cholesterol-rich lipoproteins do not acutely alter biliary cholesterol
secretion. Rather, the majority of the cholesterol delivered to the liver
in these lipoproteins is either esterified and stored as cholesteryl ester
or resecreted as free and esterified cholesterol in hepatic VLDL.