Effects of oleate and compactin on the metabolism and secretion of cholesterol and cholesteryl ester by rat hepatocytes

Abstract

Incubation of rat hepatocytes with oleate for a period of 1 h gave rise to a decrease in the total (esterified plus unesterified) cholesterol associated with very-low-density lipoprotein (VLDL). This effect was no longer apparent after longer incubation periods. The rate of cholesterol biosynthesis decreased during the first hour of incubation in the presence of oleate. After longer incubation periods, however, more cholesterol was synthesised in the presence of oleate than in its absence. The extracellular presence of oleate gave rise to a 2-fold increase in the concentration of cellular cholesteryl ester. Under these conditions cholesteryl ester contributed a larger proportion of the total cholesterol secreted with the VLDL. The cholesteryl ester associated with VLDL was derived predominantly from cholesteryl ester synthesised intracellularly. Inhibition of cholesterol synthesis with compactin did not significantly alter the rate of secretion of VLDL-cholesterol. Newly synthesised non-esterified cholesterol equilibrated with the bulk of pre-existing cellular cholesterol before secretion with the VLDL. This was true irrespective of the rate of endogenous cholesterol synthesis.