Receptor-independent low density lipoprotein transport in the rat in vivo. Quantitation, characterization, and metabolic consequences

J Clin Invest. 1985 Sep;76(3):1113-22. doi: 10.1172/JCI112066.

Abstract

Receptor-independent low density lipoprotein (LDL) transport plays a critical role in the regulation of plasma cholesterol levels; hence, these studies were done to characterize this process in the tissues of the rat. High rates of receptor-independent clearance were found in the spleen, but other organs, like liver, gastrointestinal tract, and endocrine glands manifested lower clearance rates that varied from 3 to 9 microliter/h per g, while the rates in nervous tissue, muscle, and adipose tissue were less than 1 microliter/h per g. Receptor-dependent uptake was much higher in liver (85 microliter/h per g) and adrenal gland (219 microliter/h per g), but was also low in most other tissues. At normal plasma LDL concentrations, 67% of the receptor-dependent transport in the whole animal was accounted for by LDL uptake in the liver. In contrast, the receptor-independent uptake found in the whole animal took place in many organs, including skeletal muscle (20%), liver (16%), small bowel (15%), skin (10%), and spleen (7%). Furthermore, in liver, the rate of cholesterol synthesis could be varied 11-fold, yet the rate of receptor-independent LDL clearance remained constant at approximately 8 microliter/h per g. When the circulating levels of LDL were systematically increased, receptor-independent LDL clearance also remained constant, so that hepatic LDL-cholesterol uptake by this mechanism increased linearly, from 1 to 20 micrograms/h per g, as the plasma LDL-cholesterol level was increased from 10 to 250 mg/dl. Finally, when equal amounts of LDL-cholesterol were delivered into the liver by either the receptor-dependent or receptor-independent mechanism, there was significant suppression of cholesterol synthesis and an increase in cholesteryl esters. Thus, in any situation in which receptor-dependent LDL degradation is lost, cholesterol balance in the whole animal and across individual organs is maintained by receptor-independent mechanisms, although when the new steady state is achieved, circulating levels of LDL must necessarily be very much increased.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport, Active
  • Cholesterol, LDL / metabolism
  • Dexamethasone / pharmacology
  • Endocrine Glands / metabolism
  • Female
  • Humans
  • Kinetics
  • Lipoproteins, LDL / metabolism*
  • Liver / metabolism
  • Metabolic Clearance Rate / drug effects
  • Methylation
  • Rats
  • Rats, Inbred Strains
  • Receptors, Cell Surface / analysis
  • Receptors, Cell Surface / drug effects
  • Receptors, Cell Surface / metabolism*
  • Receptors, Lipoprotein
  • Sucrose / metabolism

Substances

  • Cholesterol, LDL
  • Lipoproteins, LDL
  • Receptors, Cell Surface
  • Receptors, Lipoprotein
  • Sucrose
  • Dexamethasone