KINETICS OF IRON UPTAKE INVITRO BY HUMAN DUODENAL MUCOSA - STUDIES IN NORMAL SUBJECTS

A method for determining initial rates of unidirectional radio-Fe uptake from a ferric chelate of nitrilotriacetic acid by human duodenal biopsy specimens in vitro was devised. [57Co]cyanocobalamin was used as an extracellular fluid marker and gave results in close agreement with other markers. Uptake was linear for up to 20 min and exhibited saturation kinetics over the concentration range 18-450 .mu.mol/1. In the presence of 2:4 dinitrophenol and fluoride, uptake was reduced by .apprx. 50%, indicating dependence on metabolic energy. Uptake of Fe was markedly diminished at reduced incubation temperatures, demonstrating a high activation energy for the uptake process. Many of the criteria for the demonstration that the initial uptake of Fe depends on an active transport mechanism were fulfilled. The apparent distribution volume of 14C-labelled nitrilotriacetate chelate did not exceed the extracellular fluid space, suggesting that Fe is transferred to specific receptors on the enterocyte. Uptake may be a rate-controlling step for the regulation of net intestinal absorption of Fe in man.