Abstract
The hepatic uptake of high density lipoprotein cholesteryl ester was determine in a nonrecycling isolated rat liver perfusion. High density lipoprotein rich in the E apoprotein (apoE) showed about 10 times more uptake of the ester on a single pass than the bulk of the high density lipoproteins rich in the A-I protein. The apoportein recoveries in the liver paralleled the ester for both lipoproteins. The uptake appeared to occur primarily in the hepatic parenchymal cell. Addition of human C-III-1 apoprotein to the rat apoE-rich high density lipoprotein inhibited the hepatic uptake of its constituents.
Highlights
E apoprotein showed about 10 times more uptake of the ester on a single pass than the bulk of the high density lipoproteins rich in the A-I protein
The C apoproteins of human VLDL were obtained from fasting humans and patients with hyperprebetalipoproteinemia (Type IV) by a conventional method [12] employing alcohol ether delipidation and S-200 Sephacryl (Phannacia, Piscataway, NJ) and DEAE-Sephadex chromatography
The isolated lipothe preferred substrate for biliary excretion. These indirect proteins as well as the C apoproteins were assayed for purity by a kinetic data have notbeen validated by studies which would standard SDS-polyacrylamide technique [13] along with a urea-polymore directly support a preferential hepatic uptake and/or biliary excretion of a particular lipoprotein sterol
Summary
The buffer contained 3 g of bovine albumin (Reheis Chemical Co., Lipoprotein Preparation-Male Sprague-Dawley rats were exsanguinated after an overnight fast,and the blood was collected in buffered (pH 7.4) EDTA, 1mg/ml. An aliquot of the lipid extract was counted in a liquid scintillation spectrometer (Intertechnique, modelFL-4000) under I4C counting conditions Another aliquot of the heptane phase was chromatographed on a neutral lipid thin layer chromatographic system [23]. Along with free cholesterol and cholesteryl ester standards, and the appropriate bands were retrieved from the silicic acid by an Abel extraction [16]with subsequent counting of the octane phase. The free cholesterol and cholesteryl ester bands were isolated from the chromatograms, and the radioactivity was assayed in these compounds as described above. Perfusions using the protein-labeled lipoproteins were performed exactly as described above, but the perfusates, injection solutions, and hepatic tissues were assayed for radioactivity in a y counter (Beckman Biogamma)
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