Regulation of the metabolism of lipid emulsion model lipoproteins by a saturated acyl chain at the 2-position of triacylglycerol

Lipid emulsion particles were prepared by sonicating four different lipid mixtures (triacylglycerol (TAG), 70%; phospholipid, 25%; cholesteryl oleate (CO), 3%; and free cholesterol, 2%), then purified by density gradient ultracentrifugation. For three test mixtures, the TAG contained 50, 75, or 100% 1,3-dioleyl-2-stearylglycerol (OSO) with the remainder being triolein (OOO); 100% triolein in the lipid mixture was used as the control. After intravenous injection of the lipid particles into unanesthetized rats, removal of radioactive TAG fatty acid and CO from plasma was measured for 30 min, then liver and spleen uptakes were measured. When emulsions contained 75% or 100% OSO as TAG, the plasma removal rates of CO were, respectively, 60% or 30% of the rate when the TAG was 100% triolein; smaller recoveries of CO were found in the liver. The clearances of TAG fatty acid did not differ significantly and the recoveries of TAG fatty acid in the organs were not affected by the type of emulsion injected. Remnant particles were derived from donor rats in which uptake was blocked by exclusion of liver and other viscera from the circulation before injection of 100% OOO and 100% OSO emulsions. When injected into recipient intact rats, the removal of remnants from plasma was slower for remnants derived 15 min after injection of 100% OSO emulsions than from 100% OOO emulsions, showing that the slower removal of emulsion CO was due to slower remnant uptake from the plasma with OSO emulsions.(ABSTRACT TRUNCATED AT 250 WORDS)