Ralph Green

Body iron excretion in man: a collaborative study.

Abstract A collaborative study was undertaken in an attempt to document obligatory iron losses in adult male subjects, using a variety of isotopic and chemical methods. Total body excretion was measured in four groups of subjects by injecting Fe 55 intravenously and following the decline in red cell activity over several years. Calculated daily iron losses were as follows: Seattle white subjects (group I) 0.95 mg. (±0.30); Venezuelan Mestizos (group II) 0.90 mg. (±0.31); Johannesburg Bantu (group III) 2.42 mg. (±1.09); Durban Indians (group IV) 1.02 mg. (±0.22); and Durban Bantu (group V) 2.01 mg. (±0.94). The higher values in the Bantu subjects were ascribed to the greater than normal iron stores in this population group. That losses in the Durban Indian subjects, who were working in an extremely hot and humid environment, were not greater than those in the white subjects suggests that excessive sweating does not represent a major route for iron excretion. The results of isotopic experiments to determine the quantities of iron lost via the gastrointestinal tract suggested a daily loss of approximately 0.1 mg. within desquamated mucosal cells and 0.4 mg. in blood. Chemical analyses of bile indicated a mean daily content of 0.26 mg. However, it was not possible to establish what proportion of this iron is reabsorbed into the body. Direct chemical measurements of iron in urine revealed a mean daily content of approximately 0.1 mg.; this quantity did not seem to be influenced by the size of the body stores. The amount of iron taken up daily from the plasma by eccrine skin at normal transferrin saturations was between 0.2 and 0.3 mg. When the transferrin saturation was high this figure rose to between 0.6 and 0.7 mg. In a final analysis, the calculated iron losses from individual compartments were added together and compared with those obtained in the long-term excretion study. Agreement was close in all but the Bantu groups. Even when maximum figures for individual compartmental losses were used, the figures were still lower than those obtained for total excretion. These discrepancies may reflect methodologic errors but it is equally possible that subjects with overload lose iron in ways other than those examined in the present study, such as bile and/or iron-loaded reticuloendothelial cells shed into the lumen of the gastrointestinal tract.

Clinical studyBody iron excretion in man: A collaborative study

Abstract A collaborative study was undertaken in an attempt to document obligatory iron losses in adult male subjects, using a variety of isotopic and chemical methods. Total body excretion was measured in four groups of subjects by injecting Fe 55 intravenously and following the decline in red cell activity over several years. Calculated daily iron losses were as follows: Seattle white subjects (group I) 0.95 mg. (±0.30); Venezuelan Mestizos (group II) 0.90 mg. (±0.31); Johannesburg Bantu (group III) 2.42 mg. (±1.09); Durban Indians (group IV) 1.02 mg. (±0.22); and Durban Bantu (group V) 2.01 mg. (±0.94). The higher values in the Bantu subjects were ascribed to the greater than normal iron stores in this population group. That losses in the Durban Indian subjects, who were working in an extremely hot and humid environment, were not greater than those in the white subjects suggests that excessive sweating does not represent a major route for iron excretion. The results of isotopic experiments to determine the quantities of iron lost via the gastrointestinal tract suggested a daily loss of approximately 0.1 mg. within desquamated mucosal cells and 0.4 mg. in blood. Chemical analyses of bile indicated a mean daily content of 0.26 mg. However, it was not possible to establish what proportion of this iron is reabsorbed into the body. Direct chemical measurements of iron in urine revealed a mean daily content of approximately 0.1 mg.; this quantity did not seem to be influenced by the size of the body stores. The amount of iron taken up daily from the plasma by eccrine skin at normal transferrin saturations was between 0.2 and 0.3 mg. When the transferrin saturation was high this figure rose to between 0.6 and 0.7 mg. In a final analysis, the calculated iron losses from individual compartments were added together and compared with those obtained in the long-term excretion study. Agreement was close in all but the Bantu groups. Even when maximum figures for individual compartmental losses were used, the figures were still lower than those obtained for total excretion. These discrepancies may reflect methodologic errors but it is equally possible that subjects with overload lose iron in ways other than those examined in the present study, such as bile and/or iron-loaded reticuloendothelial cells shed into the lumen of the gastrointestinal tract.

Tissue vitamin B-12 assay by a radioisotope dilution technique

A method is described for the measurement of vitamin B-12 (B-12) in solid tissues by radioisotope dilution (RID) assay. The method is a modivication using double extraction of a serum B-12 RID assay which uses chicken serum as the B-12 binder. The method was developed and tested using human and bat liver specimens. Double extraction was shown to be more efficient than single extraction, and resulted in complete release of endogenous liver [57Co] B-12 administered to bats. Results using the RID assay in 16 humans and 17 bat liver specimens were compared with those obtained using the Lactobacillus leichmannii microbiological assay. Correlation was good, but the RID assay gave higher results using the microbiological assay appear to be due to inadequate extraction of B-12 from tissues.

Comparison of results of microbiologic and radioisotopic assays for serum vitamin B12 during pregnancy

The serum vitamin B12 level falls progressively during pregnancy, when measured either by microbiologic assay or by a radioisotope dilution technique. The concentration of the vitamin assayed by radioisotope dilution was consistently higher than the value obtained by microbiologic assay. This discrepancy was greatest in early pregnancy and decreased as the duration of pregnancy increased. These results add further evidence to the hypothesis that changes in serum binders for vitamin B12 are of major significance in the pathogenesis of the observed fall in serum levels of the vitamin during pregnancy.