Fate of Tritium-Labeled Vitamin D3 and 25-Hydroxyvitamin D3 in Rabbit Does and Their Pups

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Abstract
Mammary transfer of label from i.p. injected 50 .mu.Ci [1.alpha.,2.alpha.(n)-hydrogen-3]cholecalciferol, and 50 .mu.Ci (26,27-methyl-hydrogen-3)cholecalciferol was studied in nursing rabbits. Does were injected at 3 days postpartum with 1 of the 2 labeled compounds. Pups were killed at either 1, 2, 3, 4 or 5 days after dosing of the does, and does were killed after 5 days. Concentrations of radioactivity were greater in tissues of does dosed with tritiated vitamin D3 than in tissues of those dosed with tritiated 25-hydroxyvitamin D3. Concentrations of radioactivity were greater in maternal tissues than in tissues of pups. On the 5th day following administration of tritiated vitamin D3 or 25-hydroxyvitamin D3, the major portion of the radioactivity in does'' plasma and liver was associated with tritiated 25-hydroxyvitamin D3. In pups from the tritiated vitamin D3 group, the concentration of plasma radioactivity associated with 25-hydroxyvitamin D3 (isolated by high pressure liquid chromatography) increased significantly with time, reaching 85% of the total vitamin D and metabolite radioactivity in the pups at the 5th day. Over 90% of the total recovered plasma radioactivity of pups of the tritiated 25-hydroxyvitamin D3 group was associated with the 25-hydroxyvitamin D3. Much more radioactivity was secreted in the milk of tritiated 25-hydroxyvitamin D3 dosed does than in milk of does dosed with tritiated vitamin D3.

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