Synthesis of cholesterol esters in the plasma and liver of sheep |
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Authors: | R C Noble M L Crouchman J H Moore |
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Affiliation: | (1) The Hannah Research Institute, KA6 5HL Ayr, Scotland;(2) Present address: Unilever Research Laboratory, Welwyn, Herts, England |
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Abstract: | A study was made with sheep on the formation in vitro of long chain fatty acid esters of cholesterol by the lecithin-cholesterol-acyltransferase
system present in the plasma and the acyl CoA-cholesterol-acyltransferase system present in the liver. The rate of cholesterol
esterification in the plasma was 0.024 μmoles/ml/hr. The relative pattern of fatty acids esterified during incubation of the
plasma remained constant over the 8 hr period of incubation and was similar to the fatty acids in the plasma cholesteryl esters
before incubation began and to the fatty acids in the 2-position of the plasma lecithin. The predominant cholesteryl esters
synthesized contained monoenoic and dienoic fatty acids. Unlike the bovine, there was no apparent discrimination in favor
of the 18∶2 containing species of plasma lecithin as donors of fatty acids. This difference could be accounted for by the
similarity in the 18∶2 content of the phospholipids present in the high density (density >1.062 and < 1.21) and the low density
(density > 1.006 and <1.063) lipoprotein fractions of the sheep plasma. The possibility of some discrimination against 20∶4
during cholesterol ester synthesis in the plasma of the sheep cannot be excluded. In the liver, the predominant cholesteryl
esters synthesized contained saturated and monoenoic fatty acids; cholesteryl linoleate was synthesized to a very much less
extent. There was considerable similarity between the composition of the unesterified fatty acid fraction of the liver before
incubation began and the fatty acid composition of the cholesteryl esters synthesized during incubation. Addition of sonicated
suspensions of free fatty acids altered markedly the fatty acid pattern of the cholesteryl esters synthesized by the liver
slices. From the evidence presented it is concluded that the cholesteryl esters in sheep plasma are syntheized mainly by the
plasma lecithin-cholesterol-acyltransferase system. The results are discussed in relation to cholesterol esterification systems
demonstrated in the plasma and liver of monogastric animals. |
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