Catabolism of HDL1 cholesteryl ester in the rat. Effect of ethinyl estradiol treatment

The present study was performed in control and ethinyl estradiol-treated ra ts in order to determine the mechanisms involved in the catabolism of HDL1 cholesteryl ester. Ligand blottings on liver membranes showed that purified HDL1,containing about 70 % apolipoprotein E and 10 % apolipoprotein Al, bi nd to the LDL receptor (130 kDa) and not to HB2 (100 kDa) or SR-BI (82 kDa) , candidate HDL receptors. Immunoblots showed that the treatment increased the hepatic level of the LDL receptor five- to ten-fold, strongly decreased that of SRBI and did not change that of HB2. An in vivo kinetic study show ed that the turnover of HDL1 cholesteryl ester is more rapid in treated tha n control rats. The liver participation (60 %) in this clearance was not mo dified by the treatment. Therefore, it can be concluded that the catabolism of HDL1 cholesteryl ester, in control as in treated rats, is essentially e nsured by the uptake of entire particles in the hepatocytes via LDL recepto rs. (C) Academie des Sciences/ Elsevier, Paris.