The effect of insulin deficiency on the metabolism of lipid emulsion models of triacylglycerol-rich lipoproteins in rats

Abstract

Groups of control rats and rats made insulin deficient by treatment with streptozotocin were injected intravenously (IV) with triacylglycerol-cholesteryl oleate-cholesterol-phospholipid emulsions designed to model the composition of triacylglycerol-rich lipoproteins. Insulin deficiency decreased the removal rates of emulsion triacylglycerol and cholesteryl ester whether fed a regular diet or a high-fat diet. Injection of heparin to stimulate the action of lipoprotein lipase increased the removal rates in both control and insulin-deficient rats, but control values were not restored by heparin given to insulin-deficient rats and compared with controls the difference due to insulin deficiency persisted. When emulsions were injected into functionally hepatectomized insulin-deficient rats the removal of the emulsion triacylglycerols was faster than in controls. Preformed remnants made in functionally hepatectomized donor rats were removed less rapidly after plasma injection into insulin-deficient rats than in control rats. If the remnants were isolated from the plasma by ultracentrifugation this effect disappeared. An emulsion with a supra-physiological content of unesterified cholesterol had increased efficiency of removal of emulsion core lipids from the plasma of insulin-deficient rats, but had negligible influence in control rats. These effects correlated with changes in the apolipoproteins associated with the lipid particles. Compared with control rat plasma, more of apolipoproteins AI and AIV and less of apolipoprotein E isoforms associated with emulsions exposed to insulin-deficient rat plasma.