title: Chylomicrons or their remnants penetrate rabbit thoracic aorta as efficiently as do smaller macromolecules, including low-density lipoprotein, high-density lipoprotein, and albumin.
abstract: BACKGROUND
  The aortic accumulation of chylomicrons, low-density lipoprotein (LDL), high-density lipoprotein (HDL) and albumin were compared in normal New Zealand White rabbits.
  
  
  METHODS
  Lipoproteins and albumin were labelled with radioiodinated tyramine cellobiose (TC) to avoid potential oxidative modification of lipoproteins and as a marker of intracellular degradation. In preliminary experiments it was established that TC labelling did not alter the kinetic properties of lipoproteins in vivo. Importantly, radiolabelled apolipoproteins did not transfer significantly between plasma lipoproteins. Therefore, aortic radioactivity following infusion of TC-radiolabelled lipoproteins was considered to be indicative of lipoprotein accumulation.
  
  
  RESULTS
  In conscious rabbits, net aortic accumulation of chylomicrons or their remnants was similar to those of LDL, HDL and albumin up to 2 h after infusion, despite rapid clearance from plasma. When accumulation was calculated on the basis of mean arterial exposure to allow for the differences in plasma clearance, the accumulation of aortic chylomicrons/remnants was substantially greater than that of LDL, HDL or albumin. Qualitatively similar results were obtained in rabbits that were functionally eviscerated to slow clearance of chylomicron remnants. Chylomicrons/remnants did not appear to efflux from aortic tissue as rapidly as did LDL or other plasma lipoproteins. Autoradiographic analysis showed that the primary site of lipoprotein accumulation was within medial smooth muscle cells.
  
  
  CONCLUSIONS
  Our data demonstrate that chylomicrons/remnants accumulate in arterial blood vessels more rapidly than does LDL, suggesting that dietary lipoproteins may be directly involved in the pathogenesis of atherosclerosis.
authors.affiliation: Department of Physiology, University of Western Australia.
authors.forename: J C
authors.initials: JC
authors.lastname: Mamo
authors.forename: J R
authors.initials: JR
authors.lastname: Wheeler
mesh_terms: D000418:Albumins / Q000493:pharmacokinetics; D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism*; D001161:Arteriosclerosis / Q000378:metabolism; D001345:Autoradiography; D002475:Cellobiose; D002914:Chylomicrons / Q000493:pharmacokinetics*; D005260:Female; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL / Q000493:pharmacokinetics*; D008077:Lipoproteins, LDL / Q000493:pharmacokinetics*; D046911:Macromolecular Substances; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D014018:Tissue Distribution; D014439:Tyramine
chemical_list: D000418:Albumins; D002914:Chylomicrons; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D046911:Macromolecular Substances; C038394:tyramine-cellobiose adduct; D002475:Cellobiose; D014439:Tyramine