title: Role of the kidney in the plasma clearance of angiotensinogen in the rat: plasma clearance and tissue distribution of 125I-angiotensinogen.
abstract: We studied the tissue distribution and plasma clearance of angiotensinogen (AGN) in rats following an i.v. injection of 125I-labeled AGN. The plasma clearance rate of [125I]AGN fits a two-compartment model with half-lives of 10.2 +/- 1.5 min and 4.1 +/- 0.5 h in non-treated rats, and the half-life of slower phase significantly increased to 10.2 +/- 1.1 h following bilateral nephrectomy. Radioactivity was predominantly distributed in the kidneys (4.9%), and to a lesser extent in the liver (1.8%), testis (1.2%), spleen (0.61%), heart (0.35%), lung (0.18%), thymus (0.03%) and brain (0.03%). The subcellular distribution of radioactivity in the kidney was 64% in the soluble fraction and 33% in the crude mitochondrial-lysosomal fraction. Sodium dodecylsulfate-polyacrylamide gel electrophoresis revealed that the radioactivity in the soluble fraction consisted of proteins corresponding to intact [125I]AGN, whereas the mitochondrial-lysosomal fraction contained additional radioactive proteins with molecular weights between 18,000 and 29,000. When isolated kidney cells were incubated with [125I]AGN at 0 degree C, the radioactive binding was saturable and specific with a Kd value of 4.8 x 10(-11)M, whereas incubation at 37 degrees C resulted in the appearance of degraded products of [125I]AGN in the medium. These results suggested that circulating AGN is cleared mainly by the kidneys via receptor-mediated endocytosis, which may play an important role in regulating plasma level of AGN.
mesh_terms: D000808:Angiotensinogen / Q000097:blood* / Q000493:pharmacokinetics*; D000818:Animals; D002478:Cells, Cultured; D007275:Injections, Intravenous; D007457:Iodine Radioisotopes; D007668:Kidney / Q000502:physiology*; D008297:Male; D009392:Nephrectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D007457:Iodine Radioisotopes; D000808:Angiotensinogen