Secretion of cholesteryl-ester-rich lipoproteins by the perfused livers of rabbits fed a wheat-starch-casein diet.

Rabbits fed a cholesterol-free semi-synthetic wheat-starch-casein diet had a high plasma cholesterol concentration; most of the cholesterol was associated with low-density lipoproteins (LDL). Chemical analyses of plasma lipoproteins revealed that very-low-density lipoproteins (VLDL), intermediate lipoproteins and LDL from casein-fed rabbits contained more cholesteryl ester than that of lipoproteins isolated from chow-fed animals. The fatty acid composition of cholesteryl esters of plasma lipoproteins showed that there were higher contents of oleic acid than linoleic acids in lipoproteins from casein-fed rabbits. Lipoproteins isolated from liver perfusates of casein-fed rabbits had higher cholesteryl oleate content than lipoproteins from chow-fed rabbit liver perfusates. There was a marked increase in secretion of apolipoproteins from perfused livers of casein-fed rabbits. We conclude that the high levels of plasma cholesterol in casein-fed rabbits are of hepatic origin and that one of the hypercholesterolemic actions of dietary casein in rabbits is the induction of hepatic synthesis and secretion of cholesteryl-ester-rich lipoproteins.