Abstract
The intravascular metabolism of the cholesteryl ester moiety of rat plasma LDL, HDL1, and HDL2 was determined in intact male rats. Biosynthetically labeled lipoproteins were prepared by zonal ultracentrifugation from the plasma of rats injected with [3H]cholesterol. The lipoproteins were concentrated by vacuum ultrafiltration as other procedures were found to alter the biological properties of the lipoproteins. After injection of labeled LDL, [3H]cholesteryl esters remained with the injected lipoprotein and decayed from plasma with a t1/2 of 7-8 hours. [3H]Cholesteryl esters in HDL1 behaved similarly and decayed with a t1/2 of 10.5 hours. With HDL2, however, a different metabolic pattern was observed with intraplasma conversion of some [3H]cholesteryl ester HDL2 particles to HDL1. Since such conversion of HDL2 to HDL1 was not observed after in vitro incubations of rat plasma, this process seems to depend on metabolic events that occur in vivo. [3H]Cholesteryl esters disappeared from HDL2 with a t1/2 of 6-7 hours, while the esters that were transferred to HDL1 decayed with a t1/2 of 10-11 hours, similar to labeled cholesteryl esters injected with HDL1. The study demonstrated that the high apoE content of rat plasma HDL1 is not associated with rapid catabolism of the lipoprotein and that a major source of HDL1 in the rat is the intraplasma conversion of HDL2 particles to HDL1.
Highlights
T h e intravascular metabolism of the cholesteryl ester moiety of rat plasma low density lipoproteins (LDL), high density lipoproteins (HDL), and HDLPwas determined in intact male rats
As most apolipoproteins exchange among lipoproteins, it is uncertain to what extent the plasma decay of a labeled apoprotein does represent that of the whole particle [7]
In a preliminary study we searched for a method to prepare lipoproteins separated by zonal centrifugation that are suitable for metabolic experiments
Summary
T h e intravascular metabolism of the cholesteryl ester moiety of rat plasma LDL, HDL, , and HDLPwas determined in intact male rats. Labeled lipoproteins were prepared by zonal ultracentrifugation from the plasma of rats injected with [‘H]cholesterol. T h e present investigation takes advantage of newly developed techniques to prepare rat plasma lipoproteins [6] and of the absence (or near absence) of core-lipid transfer in this species [6,8,9,10] for studies of lipoprotein metabolism in rats. When rats are injected with radioactive cholesterol, this method yields biosynthetically labeled lipoproteins suitable for metabolic study. With these procedures, we have investigated the intraplasma metabolism of the cholesteryl ester moiety of LDL, HDLl , and HDL2 in the rats. T h e results of these investigations are reported here
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