Dietary iron levels and hypoxia independently affect iron absorption in mice

The effect of dietary iron levels on the hypoxic response of iron absorption was investigated by feeding mice diets of different iron composition and determining iron absorption. Eight groups of mice were fed a purified diet consisting of casein, corn oil and sucrose with vitamins and iron-free mineral supplements. Groups A-D were fed a nonpurified diet until 6 wk old and then switched to purified diet for 4 d. Groups E-H were fed purified diet for 4 wk from weaning. Groups C, D, G and H were exposed to hypoxia (53.3 kPa) for the last 3 d of the study. Groups A, C, E and G received the low iron purified diet (<1 mg iron per kg); the other groups received the same diet supplemented with 62 mg/kg iron as FeCl3 x 6H2O. Hypoxic exposure raised iron absorption (P < 0.001) by a similar proportion (2.5- to 5.0-fold) in all mice but did not affect duodenal nonheme iron levels. Low iron diet feeding raised iron absorption but reduced duodenal and liver nonheme iron levels. In a second experiment, mice fed nonpurified diet were divided into four groups and exposed to normal atmosphere or hypoxia (53.3 kPa) with or without dosing with 100 microg iron by stomach tube 1 h before determining iron absorption. There was no effect of iron dosing on iron absorption at either pressure. The data suggest that the control of iron absorption by tissue oxygen acts through a mechanism independent of the control exerted by dietary or mucosal iron levels.