Removal of lipid-rich lipoproteins by the liver.
Studies were performed to determine the mechanism of hepatic removal of a cholesterol-rich beta-migrating lipoprotein. This fraction, designated IDLc, was isolated from the serum of cholesterol-fed diabetic rats by ultracentrifugation at d 1.006-1.03 g/ml and contained apoproteins B, E, C, and A-I. When 125I-IDLc (125I-labeled IDLc) was injected into normal chow-fed rats, 40% of the radioactivity was cleared from the plasma within 5 minutes with slight additional removal during the next 25 minutes. The rapid removal phase was due to the clearance of apoB-containing lipoproteins. The slow removal phase was due to transfer of apoA-I and C-apoproteins to HDL which has a considerably slower rate of turnover. The in vivo clearance of total 125I-IDLc radioactivity was enhanced by pretreatment of normal rats with 17 alpha-ethinyl estradiol. This appeared to be associated with lack of transfer of apoA-I and C-apoproteins to HDL, and the removal of these apoproteins along with the apoB-containing lipoproteins. Treatment of rats with 17 alpha-ethinyl estradiol did not result in an increased rate of removal of 125I-IDLc when their livers were perfused and this suggests that the removal of IDLc is not mediated by the LDL (B, E) receptor whose activity is stimulated by estradiol administration.
D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology; D008074:Lipoproteins / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011973:Receptors, LDL; D018110:Receptors, Lipoprotein; D013997:Time Factors
D001053:Apolipoproteins; D008074:Lipoproteins; D011956:Receptors, Cell Surface; D011973:Receptors, LDL; D018110:Receptors, Lipoprotein; C028203:chylomicron receptor; C030104:lipoprotein cholesterol; D004958:Estradiol; D002784:Cholesterol