Metabolism of tritiated vitamin D

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Abstract
Methods of labelling calciferol in specified positions with tritium have been investigated with the purpose of selecting a stable and highly radioactive compound for metabolic studies. [3$\alpha $-$^{3}$H]Ergocalciferol and [24,25,26,27-$^{3}$H$_{9}$]-, [7-$^{3}$H]-, [6-$^{3}$H]- and [1$\alpha $-$^{3}$H]-cholecalciferol have been prepared and the excretion and distribution in the body of vitamin D activity and radioactivity after administration to young rachitic rats has been studied. It is concluded that [1$\alpha $-$^{3}$H]cholecalciferol is a suitable tritium-labelled form of vitamin D for further metabolic studies. The more notable results of the present studies are that much of the tritium from variously tritiated calciferols finds its way into the body water, and that break-down products of calciferol are to be found in the more polar fractions of the extracts of faeces, into which they pass from the bile.