Small intestinal regulation of iron absorption in the rat

Ultrastructural, biochemical, and immunologic studies of the small intestinal mucosa of rats were undertaken to investigate factors associated with the regulation of iron absorption. The quantity of iron within mucosal cells was proportionate to the degree of iron repletion. Although the quantity of iron-binding substances was similar in iron-deficient and iron-loaded animals, the unsaturated iron-binding capacity of mucosal cells varied inversely with the state of iron repletion of animals in ultrastructural, biochemical, and immunologic observations. Although only certain mucosal cells contained iron-binding substances, their number was not increased in iron-deficient animals. Greater quantities of iron and iron-binding substances were observed in duodenal mucosa than in ileal mucosa. These findings are consistent with the hypothesis that the quantity of unsaturated iron-binding substances within intestinal mucosal cells regulates iron absorption. These findings are only partially explained by changes observed in the concentration of ferritin and transferrin within intestinal mucosa and suggest that other iron-binding substances may also participate in the regulation of iron absorption.