PLASMA-LIPOPROTEINS AFTER TRIGLYCERIDE CLEARANCE IN CHOLESTEROL-FED RATS

The clearance of particulate triglyceride from the plasma of cholester ol-fed rats with appreciable stores of hepatic cholesterol ester produ ces a substantial increment in plasma cholesterol. Most of this plasma cholesterol increment arises from existing tissue sources. The increm ent begins from 4 to 6 h after clearance and is due to the appearance of larger cholesterol-rich, triglyceride-poor, beta migrating lipoprot eins, which are isolated in the d < 1.063 fraction with an apoprotein (Apo) content consisting primarily of Apo E and smaller amounts of Apo B. A concurrent decrease in a lipoproteins occurs with the beta lipop rotein increment. Within 1 d of clearance the beta lipoproteins fall a nd alpha lipoproteins increase. The increase in total plasma Apo E and Apo B initially parallels that of the cholesterol, but it persists ev en when cholesterol falls. A modest decrease in plasma Apo A1 was obse rved during the time alpha lipoproteins declined. A significant increa se in plasma lecithin cholesterol acyl transferase preceded the increa se in beta lipoprotein cholesterol. This enzyme increment was absent i n rats with little lipoprotein response despite increased hepatic chol esterol. In vivo inhibition of this enzyme with dithionitrobenzoic aci d virtually eliminated the postclearance hypercholesterolemia. Plasma particulate triglyceride clearance induces an increase in beta lipopro teins. Coupling of this clearance and hepatic lipoprotein secretion oc curs by an unknown mechanism modulated b lecithin cholesterol acyl tra nsferase.