TRANSFERRIN IS NOT INVOLVED IN INITIAL UPTAKE PROCESS OF IRON IN RAT DUODENAL MUCOSA - ULTRASTRUCTURAL-STUDY BY X-RAY-ENERGY SPECTROMETRY

The role of transferrin in iron absorption by the duodenal mucosa in r ats with iron deficiency and controls was evaluated immunohistochemica lly. Ferric iron was administered to each rat using a metallic gastric tube. Transferrin was stained by an immunoperoxidase method and iron with Prussian blue in the same duodenal sections and observed by light microscopy. The localization of transferrin differed from that of fer ric iron both in rats with iron deficiency and in controls. In iron-de ficient rats, transferrin was weakly stained after iron administration but was strongly stained after saline administration. In contrast, in controls, transferrin was weakly stained after saline administration but was strongly stained after iron administration. By electron micros copy, x-ray energy spectrometric analysis of the transferrin-positive areas showed no iron peak. In iron-deficient rats, accumulation of ele ctron-dense transferrin-negative microgranules was observed in some of the duodenal columnar epithelium. X-ray energy spectrometric analysis of this area revealed iron, indicating iron absorption. These results suggest that mucosal transferrin does not act as a shuttle protein in iron absorption via the rat duodenal columnar epithelium, and the fun ction of this protein may be to inform the absorptive cells of the iro n status of the body as observed in other organs.