Active transport of iron by intestine: mucosal iron pools

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Abstract
Methods were developed for the specific estimation of Fe++, Fe+++, Fe59++ and Fe59+++ in homogenates of rat duodenal mucosa and applied to studies of iron transport by everted gut sacs in vitro and duodenal loops in vivo. In the course of active transport in vitro Fe++ is absorbed into a mucosal ferrous pool which turns over relatively rapidly by a) transport of Fe++ to the serosal surface and b) formation of a mucosal Fe+++ pool. The latter turns over more slowly and appears to be a storage depot for excess mineral. When rats are pretreated with oral iron, uptake of Fe++ at the mucosal surface is decreased, diversion of mucosal Fe++ to mucosal Fe+++ is increased, and transport toward the serosal surface is reduced. Corresponding effects, which tend to limit iron absorption in vivo, are observed with duodenal loops. A sensitive hemagglutination-inhibition method was developed to estimate apoferritin in normal rat mucosa, and this protein was detected and quantified. Ferritin could account for only 8.0% of the trivalent mucosal pool and appeared to play an insignificant role in the present studies.