Iron absorption in mice with altered iron metabolism. (A) Mucosal uptake and (B) mucosal transfer of iron. (C) Iron retention. B6 (▧) and β2m^−/− (□) mice were divided into 6 groups (n = 6 per group) and treated as described in Materials and Methods. Hemolysis was obtained by phenylhydrazine injection of 60 mg/kg body weight. Phlebotomy resulted in 1 mL blood loss from each mouse. The iron-deficient diet contained 6 mg Fe/Kg and the iron-enriched diet contained 2.5% wt/wt carbonyl iron. All other groups were maintained on a standard diet containing 164 mg Fe/kg. Parenteral loading was obtained by injecting 5 mg of iron-dextran. Mucosal uptake was measured at day 1 after the administration of a test dose of ferric iron, and iron retention was measured at day 4. Mucosal transfer of iron was calculated from the ratio IR/MU. The data are presented as the mean ± SEM. ($) Student's t-test for comparison of β2m^−/− mice with B6 mice, same treatment (P < .05). (#) Student's t-test for comparison between untreated (control) and treated mice (P < .05).