Studies on the Metabolism of Very Low Density Lipoprotein Using Pig Liver Perfusion

Abstract

Livers from fasted pigs were perfused with Krebs-Ringer bicarbonate buffer containing glucose, bovine serum albumin, amino acids, and washed human erythrocytes.
Hepatic catabolism of very low density lipoprotein (VLDL) to intermediate density lipoprotein (IDL) or low density lipoprotein (LDL) was investigated by adding ¹²⁵I-VLDL to the perfusate, perfusing livers for 4 hours, and measuring the radioactivity in the IDL and LDL ranges after sequential and rate-zonal ultracentrifugations. It was proved that VLDL had been catabolized neither to IDL nor to LDL by the liver.
Since VLDL was shown not to be catabolized by the liver, it would be proper to consider that VLDL obtained from liver perfusion represent a nascent form of VLDL.
Very low density lipoproteins from 7 liver perfusions were analyzed by laser self-beat spectroscopy. The autocorrelation functions were accurately described by a single exponential which is considered to represent the uniformity of particles. The size of VLDL was calculated by measuring correlation time (τ_c), calculating translational diffusion constant, and putting it into the Stokes-Einstein's equation. The diameter of VLDL synthesized by the perfused liver from fasted pigs was estimated to be 647±39Å.
It was concluded: (1) The liver is not able to catabolize VLDL (2) The nascent VLDLs synthesized by the liver are uniform in size (3) Variable VLDLs which are seen in the circulation are produced during catabolism of these VLDLs by lipoprotein lipase. It was suggested that the size and composition of nascent VLDL, which is synthesized by the perfused liver, may depend on the perfusion and/or animal conditions.