CHOLESTEROL ESTERS SELECTIVELY DELIVERED IN-VIVO BY HIGH-DENSITY-LIPOPROTEIN SUBCLASS LPA-I TO RAT-LIVER ARE PROCESSED FASTER INTO BILE-ACIDS THAN ARE LPA-I A-II-DERIVED CHOLESTEROL ESTERS/

High-density lipoprotein (HDL) subclass LpA-I has been reported to pro mote cholesterol efflux from mouse adipose cells in vitro, whereas sub class LpA-I/A-II has no effect. To investigate whether the apolipoprot ein composition of HDL plays a role in the selective delivery of chole sterol esters to the liver in vivo, we labelled HDL in its cholesterol ester moiety and separated [H-3]cholesterol oleate-labelled HDL into subclasses LpA-I and LpA-I/A-II by immuno-affinity chromatography. Ser um decay and liver association of LpA-I and LpA-I/A-II were compared f or the apoprotein and cholesterol ester moieties. Both LpA-I and LpA-I /A-II selectively delivered cholesterol esters to the liver with simil ar kinetics. The kinetics of biliary secretion of processed cholestero l esters, initially associated with LpA-I or LpA-I/A-II, were studied in rats equipped with permanent catheters in bile, duodenum and heart. For both LpA-I and LpA-I/A-II, liver association was coupled to bile acid synthesis, with an increase in secretion rate during the night. D uring the first night period, the biliary secretion of LpA-I-derived r adioactivity was significantly greater than for LpA-I/A-II. The data i ndicate that with both LpA-I and LpA-I/A-II selective delivery of chol esterol esters from HDL to the liver occurs, but that cholesterol este rs delivered by LpA-I are more efficiently coupled to bile acid synthe sis.