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After oral administration of 500 mg KFe[Fe(CN)6] labelled with 59Fe either in the ferric or ferrous position and with 14C in the cyanide group only 0.22% of the FeII and less than 0.04% of the FeIII were absorbed in three male volunteers. Only 2 mg non-complex bound 14C-labelled cyanide (0.03 mg CN-/kg body wt) were absorbed from 500 mg [14C]KFeHCF, which is about a factor of 20-100 below the lethal dose in humans (0.5-3.5 mg CN-/kg body wt). Therefore, iron(III) hexacyanoferrates(II) can be considered as safe antidotes, i.e. for inhibiting the intestinal absorption of radiocaesium or for accelerating the excretion of already absorbed 134/137Cs in the case of a severe nuclear accident.

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Abstract. The intestinal absorption of 59Fe from a diagnostic 10 ~mole (0.56 rag) 59Fe~+ test dose and 5 mg Fe equivalents of SgFe-labeled pork, hog liver and hemoglobin was measured with a 4 z geometry whole-body radioactivity detector with liquid organic scintillator and the results compared with the stainable amounts of diffuse cytoplasmatie (non-heine) storage iron in the bone marrow macrophages, serum iron concentrations and total iron-binding capacity, erythropoietic activity and other hematological parameters. Children with mild hypochromic, microcytie anemia due to heterozygous fl.thalassemia absorbed normal amounts of 5~ from the diagnostic dose of 59Fe~+ if their bone marrow macrophages contained normal or mildly increased amounts of diffuse cytoplasmatie storage iron. Depleted iron stores also caused increased absorption of diagnostic 59Fe in children with heterozygous fl-thalassemia, so that prelatent iron deficiency can be diagnosed by measurement of increased iron absorption.The diagnostic 5~Fe~+ absorption was increased to 70--100% in children with homozygous fl-thalassemia when it was measured 64--300 days after the last blood transfusion. Since all these children contained normal to increased amounts of diffuse cytoplasmatie storage iron in the bone marrow macrophages, the high intestinal iron absorption was not caused, as is usual, by depleted iron stores but coincided with considerable hyperplasia of ineffective erythropoiesis demonstrated by the increased numbers of normoblasts in the bone marrow and peripheral blood during a period of severe anemia. Blood transfusions which elevate the hemoglobin levels from 4--5 g/100 ml to 8.5--9.9 g/100 ml and suppress the erythroblastic hyperplasia in the bone marrow also reduce the increased absorption of inorganic and food iron to normal values. Interruption of blood transfusions always results in the next erythroblastic hyperplasia and a simultaneous increase of intestinal iron absorption. Mild hyperplasia of the erythropoietic system such as is observed in megaloblastic anemia due to vitamin-B~ deficiency or in hereditary spherocytosis is not sufficient to increase iron absorption. Anemia per se does not increase iron absorption, as is borne out by the observation that patients with severe aregenerative anemia or megaloblastic anemia absorb 5aFe~+ according to their normal iron stores * Supported in part by a research grant of "Deutsche Forschungsgemeinschaft".

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