Enhanced Fe(3+)-reducing capacity does not seem to play a major role in increasing iron absorption in iron-deficient...

Some eucaryotic organisms, including many plants, yeast and mice, have a higher iron uptake during iron deficiency because the capacity to reduce Fe3+ from the environment to Fe2+ is greatly enhanced. To determine whether this occurs in rats, a common experimental model for iron absorption in humans, we compared the in vivo capacity to reduce intraluminal Fe3+ in iron-deficient and normal rats. We also measured potential Fe(3+)-reducing components within the intestinal lumen and on the mucosal surface. Iron-reducing capacity was higher in iron-deficient rats, by a significant (P = 0.026) but modest 20%, in parallel with higher mucosal weight (R2 = 0.501, P = 0.003). In vitro iron reduction by lumen contents was correlated with mucosal weight, even though mucosal tissue was not present in the assays. This capacity was not related to ascorbic acid, glutathione or other nonprotein sulfhydryls. Mucosal ferric reductase activity was higher in iron-deficient rats in parallel with higher tissue weight, but the specific activity did not differ and the higher total activity was not associated with the brush border fraction. The role of endogenous Fe3+ reduction in regulating iron absorption should be investigated in humans and in other experimental models.