title: Catabolism of homologous and heterologous hemopexin in the rat and uptake of hemopexin by isolated perfused rat liver.
abstract: Iodinated hemopexin (Hx) from three different species, rabbit, human and rat, was injected into rats and its clearance from the plasma measured. Rabbit, human and rat apo-Hx were cleared from the plasma with a T 1/2 of 20--31 h, 31--32 h, and 48--60 h respectively. Heme injection (10 mg/kg) after equilibration of the protein immediately accelerates elimination of the hemopexins of all three species (T 1/2 of 4.5 to 10 h). This indicates that the two heterologous hemopexins maintain their function in heme transport. The T 1/2 of rabbit and human Hx return to pre-heme injection values 16 to 20 hours after the injection of heme. For rat Hx, however, the T 1/2, which was 54 +/- 3.5 h before heme injection, was reduced to 25 +/- 1.3 h 20 hours after heme injection. Administration of 1.2--1.3 mg of protoporphyrin IX or uroporphyrin III, after equilibration of iodinated rat Hx, did not change the T 1/2 of the protein, whereas the same amount of coproporphyrin III significantly reduced its T 1/2 from 54 +/- 3.5 to 37 +/- 0.4 h. In addition, the uptake of rat apo-Hx, heme-Hx and albumin by rat liver tissue was measured in an isolated liver perfusion system using radioiodinated proteins screened in vivo. The uptake of apo-Hx by the liver after 2 h (46.8 ml/100 g) was less than that of heme-Hx (67.3 ml/100 g). The amount of apo-Hx and heme-Hx associated with the liver, relative to that circulating in the perfusate, was greater than that of albumin (12.1 ml/100 g). These results are considered to represent selective uptake of Hx by the liver induced by its interaction with heme.
mesh_terms: D000818:Animals; D001692:Biological Transport; D003306:Coproporphyrins / Q000494:pharmacology; D006418:Heme / Q000378:metabolism / Q000494:pharmacology; D006466:Hemopexin / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000378:metabolism*; D010477:Perfusion; D011524:Protoporphyrins / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D014578:Uroporphyrins / Q000494:pharmacology
chemical_list: D003306:Coproporphyrins; D011524:Protoporphyrins; D014578:Uroporphyrins; D006418:Heme; D006466:Hemopexin