THE SIGNIFICANCE OF TRANSFERRIN FOR INTESTINAL IRON-ABSORPTION

  • 1 January 1983
    • journal article
    • research article
    • Vol. 61  (2) , 283-290
Abstract
A mechanism is proposed by which apotransferrin is secreted from mucosal cells, loaded with Fe in the intestinal lumen and then the intact complex is taken into the cell. Within the cell, Fe is released and transferred to the blood stream, whereas Fe-free transferrin returns to the brush border to be recycled. This hypothesis was investigated by measuring intestinal absorption of radio-Fe and 125I-labeled plasma transferrion using tied-off gut sequments in normal and Fe-deficient rats. There was no absorption of diferric transferrin from the ileum, but high absorption from the duodenum and jejunum segments. Jejunal absorption occurred as a function of the dose offered and showed saturation kinetics. In normal animals, 4 .mu.g of the 50 .mu.g of transferrin Fe was absorbed over 1 h. In Fe-deficient animals, mean values as high as 13 .mu.g were observed. Radio-Fe content of the jejunal mucosa bore a linear relatinship to the dose administered and was inversely proportional to the amount of Fe entering the plasma. Recycling of transferrin was indicated by the presence of labeled apotransferrin in the lumen, first observed between 15-60 min after the injection of diferric transferrin. A high resistance of diferric transferrin and apotransferrin to proteolytic degradation within the gut lumen was demonstrated. Comparative studies with lactoferrin and ferritin disclosed poor availability of their Fe for absorption. The small amount that was absorbed did not relate to the Fe status of the recipient animal. These studies support the role of mucosal transferrin as a shuttle protein for Fe absorption.