IRON STATUS ALTERS THE ADSORPTION, UPTAKE, AND ABSORPTION CAPACITIES OF RAT DUODENUM FOR FERROUS AND FERRIC IRON

We employed an in situ technique to determine the duodenal capacity for adsorption, uptake and absorption of free ferrous and ferric iron in both iron-replete and iron-deficient rats. Uptake and absorption capacities were related to luminal iron concentration by a two-component equation representing the simultaneous functioning of two pathways. One component of the equation was analogous to the Michaelis-Menton equation. This component suggested a saturable pathway for uptake of iron bound to mucin in the intestinal mucous layer. The second component of the equation was analogous to second order kinetics. This component suggested non-saturable uptake, perhaps due to the opening of a mucosal barrier, such as the tight junctions between mucosal cells, to diffusion of unbound iron. Iron deficiency caused an increase in the capacity of the saturable components about 5-fold for uptake and about 8-fold for absorption. This change was qualitatively, but not quantitatively, in agreement with the corresponding 20-fold increase of in vivo absorption in rats maintained as cohorts.