Fate of Isotopically Labeled Cholecalciferol and 25-Hydroxycholecalciferol in Sheep

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Abstract
The fate of tritiated 25-hydroxycholecalciferol administered i.m. is compared in two groups of sheep raised in confinement or outdoors. The uptake of radioactivity was more rapid by the indoor than the outdoor sheep. The assessment of radioactivity in plasma and tissues of outdoor sheep dosed with tritiated 25-hydroxycholecalciferol or with equivalent amounts of tritiated cholecalciferol revealed that plasma and tissue radioactivity were substantially higher in sheep dosed with tritiated 25-hydroxycholecalciferol than in sheep dosed with tritiated cholecalciferol. Three days after the administration of tritiated cholecalciferol virtually all plasma radioactivity was associated with 25-hydroxycholecalciferol. [Evaluation of vitamin D status in ruminants was discussed.].