Metabolism of iodinated high density lipoproteins in the rat: II. Autoradiographic localization in the liver

Abstract

The fate of rat high density lipoproteins labeled in their protein moiety with 125I was studied in the intact rat and in perfused rat liver. 6 h following injection, 15% of the injected material was recovered in the liver, 85–93% of which were trichloro-acetic acid precipitable. Following solubilization of liver lipoproteins with sodium cholate, 34% of the labeled lipoprotein was recognizable by a specific antibody, 1 h after injection, and this declined to 19% at 6 h. The localization of the labeled lipoprotein in the liver was studied with radioautography and the radioautographic reaction was seen predominantly over parenchymal cells; some Kupffer and endothelial cells were also labeled. A similar localization was found irrespective of injected dose (up to 8 mg). Electron microscopic radioautography showed the presence of silver grains over various cytoplasmic organelles, but concentration of grains, as expressed by grain density, was found only over dense bodies, many of which could be classified as secondary lysosomes. This localization, together with loss of antigenic determinants and the appearance of trichloroacetic acid-soluble label in the bile, was interpreted as showing that in the rat the liver is participating actively in the catabolism of high density lipoproteins of serum.