Effects of fatty acid unsaturation on chylomicron metabolism in normal and hepatectomized rats.

Abstract

1. Hepatectomized rats were injected intravenously with doubly labelled ([14C]linoleic acid and [3H]palmitic acid) thoracic duct lymphs from rats fed cream, triolein or corn oil. The disappearance of the radioactive fatty acids of different molecular triacylglycerol species and of phospholipids from plasma was studied.2. 73–93% of the injected triacylglycerols had been cleared from plasma within 15 min. At all stages of lipolysis the 3H/14C ratio of the plasma triacylglycerol was the same as in the injected material. If the cream chyle had been cooled to 4 °C before use there was, however, an enrichment of [3H]palmitic acid and of fully saturated triacylglycerols in the remnant particles formed.3. Only 38–50% of the radioactive chyle phosphatidylcholine was eliminated from plasma in 30 min. At this time most of the remaining phosphatidylcholine was, however, in other lipo‐protein classes than the chylomicron remnants.4. Also in intact rats data were obtained, indicating that the major portion of chylomicron phospholipids is transferred to other serum lipoproteins by exchange or net movement rather than being hydrolysed in the 1‐position by lipoprotein lipase or taken up intact by the liver.5. More of both the labelled fatty acids appeared in liver triacylglycerols in experiments with cream chyle than in experiments with corn oil chyle. Data were obtained suggesting that this may be due to a higher uptake of intact triacylglycerol as remnant particles.6. When linoleic acid is fed as a tracer dose in cream, a high proportion (16–36%) is incorporated into chyle phospholipids.