Alterations in the mucosal processing of iron in response to very-short-term dietary iron depletion and repletion.

The transfer of control rats to a low-iron diet for only 24 h resulted in a 2-fold increase in iron uptake by brush-border membrane vesicles. Extension of the low-iron feeding period to 72 h or 2 weeks resulted in only small additional increases in iron uptake by vesicle preparations. In contrast, the transfer of iron-deficient rats to a control diet resulted in a progressive decrease in iron uptake by vesicles that reached a level equivalent to that of control rats in 2 weeks. 59Fe labelling of detergent extracts of these vesicle preparations provided evidence for the presence of an iron-binding protein composed of subunits of 52,000 Da. The changes in the 59Fe labelling of this protein component were consistent with the changes observed in iron uptake by intact brush-border membrane vesicles. The 59Fe-labelling profiles of mucosal ferritin and transferrin from a test dose also were changed substantially in response to very-short-term alterations in dietary iron. Even though changes in dietary iron rapidly altered iron uptake by brush-border membrane vesicles and the incorporation of 59Fe from the test dose into mucosal transferrin, changes in the incorporation of 59Fe into mucosal ferritin best reflected the actual changes in the transfer of iron from dose to plasma.

Comparison of changes in uptake and mucosal processing of iron in short and long-term iron depletion.

Thirty minutes following an intragastric dose of [59]Fe, rats subjected to short-term and long-term iron depletion showed a similar increase in [59]Fe in plasma and a similar decrease in the retention of [59]Fe in mucosal cytosol compared to controls. With both low-iron groups, a two-fold increase in [59]Fe uptake by brush-border membrane vesicles and a six-fold reduction in the [59]Fe incorporated into the ferritin of the mucosal cytosol were observed. These studies indicate that short-term exposure to a low-iron diet triggers changes in both the uptake of iron by the brush-border membrane and the processing of iron within the mucosal cell prior to major changes in body iron status.