UPTAKE OF LACTOFERRIN BY THE LIVER .1. ROLE OF THE RETICULOENDOTHELIAL SYSTEM AS INDICATED BY BLOCKADE EXPERIMENTS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 50  (3) , 323-328
Abstract
When 125I-labeled human [milk] lactoferrin was injected i.v. into mice it was rapidly taken up by the liver, where 75% of the dose was recovered after 15 min. The inhibition curve with unlabeled lactoferrin showed that the fates of labeled and unlabeled protein were similar and that the uptake capacity was saturable by milligram quantities of protein per gram of liver; this suggests the existence of numerous specific binding sites. The presence of these sites on the RES was indicated by the blocking effect of dextran sulfate and latex particles. Fucoidin (fucan sulfate), which is used in the study of receptors specific for fucose, inhibited the uptake of goat red blood cells as well as lactoferrin. Therefore, the inhibition exerted by fucoidin on the uptake of lactoferrin could be mediated by blockade of the RES and not necessarily by competition for fucose receptors. The report by others that lactoferrin was taken up by a fucosyl receptor on hepatocytes is incorrect. The competition curve obtained when mouse lactoferrin was injected with its human homologue indicated that both proteins reacted with the same binding sites. However, a significant part of mouse lactoferrin was taken up by the kidneys. Hepatic and renal uptakes were both reduced by prior injection of dextran sulfate.