Plasma clearance of chylomicrons from butterfat is not dependent on saturation: studies with butterfat fractions and other fats containing triacylglycerols with low or high melting points

Background: Dietary fats influence plasma lipids, and changes in the cleara nce: and metabolism of postprandial lipoproteins can affect atherosclerosis . Butterfat is considered hypercholesterolemic but contains a multitude of constituent fatty acids. Objectives: We determined triacylglycerol and cholesteryl ester clearances of lymph chylomicrons derived from butterfat, fractions of butterfat, and o ther dietary fats. Methods: Radiolabeled lymph chylomicrons resulting from the intestinal abso rption of different fats were reinjected into recipient rats to measure pla sma clearance, plasma clearance of [C-14]triacylglycerol was used as an ind icator of chylomicron lipolysis whereas clearance of [H-3]cholesteryl ester was used as an indicator of chylomicron remnant removal. Results: [H-3]Cholesteryl ester clearance was slower from chylomicrons deri ved from a solid, high-saturated-butterfat fraction than from whole butterf at, but clearance of chylomicrons from other fractions did not correlate wi th the fractions' saturated fatty acid contents. Clearance of cholesteryl e sters in chylomicrons derived from cocoa butter, palm oil, and butterfat wa s slower than clearance of cholesteryl esters in chylomicrons derived from safflower oil. Hepatic uptakes of cholesteryl esters were generally lower f or chylomicrons from all butterfat fractions, cocoa butter, and palm oil. Conclusions: In contrast with minor effects on the lipolysis of chylomicron triacylglycerols, chylomicron remnant removal was strongly influenced by t he type of dietary fat, with slower cholesteryl ester clearances for satura ted fats with higher melting points. However, remnant removal and hepatic u ptake of chylomicrons from whole butterfat and fractions of butterfat were not correlated with fat saturation. The mechanisms of this apparent paradox remain unknown but may be attributable to acyl arrangements ill the lipid classes of chylomicrons that influence the association with apolipoproteins and receptors and hence remnant removal.