ROLE OF ACYL-COENZYME-A CHOLESTEROL ACYLTRANSFERASE IN INTRAHEPATIC PROCESSING OF APO-B-LIPOPROTEIN IN SUNCUS

We have previously shown that fatty liver was easily induced in suncus by starvation and that the plasma level of apolipoprotein B (apoB) was very low, We also previously reported that a defect in the assembling process of apo B-containing lipoprotein (very low density lipoprotein, VLDL) may be one of the reasons for the low level of plasma apo B and for induction of fatty liver by starvation in suncus, We also found that hepatic acyl coenzyme A cholesterol acyltransferase (ACAT) activity is very low in the animals, resulting in decreased cholesteryl ester contents in the liver, A deficiency of cholesteryl ester in suncus liver may be one of the reasons for the defect in the assembling process of VLDL, In this study, we investigated the effect of cholesterol-feeding, which induces an increase in triglyceride and cholesteryl ester of the liver as a consequence of the induction of both intestinal and hepatic ACAT activities, on the secretion of VLDL, Although the basal ACAT activity of intestinal mucosa was high, cholesterol-feeding did not induce either an increase in plasma lipid or an increase in intestinal ACAT activities in suncus, The hepatic secretion rate of VLDL was estimated by treatment with Triton WR1339, which is well known to inhibit the catabolism of VLDL, Cholesterol-feeding caused a slight increase in hepatic triglyceride and cholesteryl ester but no increase either in the secretion rate of VLDL or in hepatic ACAT activity, This evidence suggests that either the secretion rate of VLDL is not dependent on absolute hepatic contents of cholesteryl ester, or it is dependent on the level of cholesteryl ester which is produced by hepatic ACAT.