In vitro studies of duodenal iron uptake in patients with primary and secondary iron storage disease.

Initial rates of iron uptake into fresh specimens of human duodenal mucosa incubated with radio-iron in vitro were examined over a range of physiological iron concentrations. In normal control subjects and patients with iron overload, mucosal iron uptake showed saturation kinetics, thus providing evidence for a carrier-mediated transport process. In five patients with idiopathic haemochromatosis uptake at the lower concentrations of iron was increased up to 80 per cent when compared with 12 control subjects. Uptake at the highest medium iron concentration was not increased. These changes were related to a significant reduction in the apparent affinity constant (Kt) for iron transport and were independent of iron stores. In contrast, the uptake rates in six patients with secondary haemochromatosis were not different from controls except in a subgroup with severe iron-loading anaemias where uptake was modestly enhanced at the higher concentrations only. The studies point to a disorder of mucosal iron transport in idiopathic haemochromatosis which appears to be a primary abnormality rather than a consequence of the iron overload.