INVESTIGATION OF A ROLE FOR REDUCTION IN FERRIC IRON UPTAKE BY MOUSE DUODENUM

Fe-59 uptake rates by mouse duodenal fragments incubated in vitro were markedly reduced by non-permeable reagents, ferricyanide (oxidising agent) and ferrozine (Fe2+ chelator), in the medium; ferrocyanide had no effect. Reduction of Fe3+, as reflected by an increase in ferrozine-(Fe2+)-chelatable iron, was observed in the presence of the tissue fragments. The generation of Fe2+ occurred linearly with time, was independent of the medium ferrozine concentration, and was not due to release of reducing factors from the duodenal fragments. Fe3+-reducing activity was mainly present on the mucosal surface and was localised primarily to the proximal region of the small intestine. Changes in Fe3+ reduction rates closely parallelled the changes in duodena Fe-59 uptake, when metabolic inhibitors or modulators of membrane potential were included in the medium. Thc enhancement in duodenal mucosal Fe-59 uptake in chronic hypoxic and iron-deficient mice parallelled the changes in the tissue reduction of medium Fe3+. Moreover, the rates of reduction were quantitatively similar to rates of uptake. These observations indicate that a sequential reduction and uptake process operates for Fe3+ uptake in mouse duodenum.