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Plasma Concentrations of 1,25-Dihydroxyvitamin D, 1,24R,25-Trihydroxyvitamin D₃, and 1,25,26-Trihydroxyvitamin D₃ After Their Administration to Dairy Cows

National Animal Disease Center, Agricultural Research Service, US Department of Agriculture, Ames, IA 50010

M. R. Uskokovic and J. J. Partridge

Chemical Research Department, Hoffmann-La Roche, Inc., Nutley, NJ 07110

ABSTRACT

Intramuscular administration of 1,25 (R or S),26-trihydroxyvitamin D₃ to dairy cows resulted in significant elevation of 1,25-dihydroxyvitamin D₃ concentration in blood plasma. The increase of 1,25-dihydroxyvitamin D₃ in plasma paralleled the increase of 1,25,26-trihydroxyvitamin D₃. We also found that intramuscular 1,25-dihydroxyvitamin D₃ administration to dairy cows significantly elevated plasma 1,24,25-trihydroxyvitamin D₃. These data suggest possible impairment of 1,25-dihydroxyvitamin D₃ metabolism during the presence of pharmacologic concentrations of 1,25,26-dihydroxyvitamin D₃ in plasma. In addition, the 24-hydroxylation of 1,25-dihydroxyvitamin D₃ to 1,24,25-trihydroxyvitamin D₃ appears to be an important route for further metabolism of 1,25-dihydroxyvitamin D₃ in dairy cows.

¹ Agricultural University of Norway, Department of Animal Nutrition, P. O. Box 25, 1432 ÅS-NLH, Oslo, Norway.

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