Iron absorption in the iron-deficient rat.

Iron absorption in the iron-deficient rat was compared with that in the normal rat to better understand the regulation of this dynamic process. It was found that: Iron uptake by the iron-deficient intestinal mucosa was prolonged as a result of slower gastric release, particularly when larger doses of iron were employed. The increased mucosal uptake of ionized iron was not the result of increased adsorption, but instead appeared related to a metabolically active uptake process, whereas the increased mucosal uptake of transferrin iron was associated with increased numbers of mucosal cell membrane transferrin receptors. Mucosal ferritin acted as an iron storage protein, but its iron uptake did not explain the lower iron absorption in the normal rat. Iron loading the mucosal cell (by presenting a large iron dose to the intestinal lumen) decreased absorption for 3 to 4 days. Iron loading of the mucosal cell from circulating plasma transferrin was proportionate to the plasma iron concentration. Mucosal iron content was the composite of iron loading from the lumen and loading from plasma transferrin versus release of iron into the body. These studies imply that an enhanced uptake-throughout mechanism causes the increased iron absorption in the iron-deficient rat. Results were consistent with the existence of a regulating mechanism for iron absorption that responds to change in mucosal cell iron, which is best reflected by mucosal ferritin.