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Biological Activity of 24,24-Difluoro-25-Hydroxycholecalciferol in Chicks1

Sumiaki Okamoto2, Connie Smith, Hector F. Deluca3, Sachiko Yamada* and Hiroaki Takayama*

Department of Biochemistry, University of Wisconsin-Madison, College of Agricultural and Life Sciences, Madison, WI 53706 * Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa, JAPAN

The biological activity of subcutaneously injected 24,24-difluoro-25-hydroxycholecalciferol was compared with that of 25-hydroxycholecalciferol in the vitamin D-deficient growing chick. 24,24-Difluoro-25-hydroxycholecalciferol is equal to 25-hydroxycholecalciferol in the stimulation of: 1) growth, 2) intestinal calcium absorption, 3) elevation of serum calcium and serum phosphorus, 4) healing of rachitic cartilage (radiography), and 5) mineralization of rachitic bone (bone ash). The response appears to be linear in the range of 13.0 to 325 pmol daily. Since 24,24-difluorocholecaliferol cannot be 24-hydroxylated to produce either 24,25-dihydroxycholecalciferol or 1,24,25-trihydroxycholecalciferol, while it can be 1{alpha}-hydroxylated to produce 24,24-difluoro-1,25-dihydroxycholecalciferol, these results demonstrate that 24-hydroxylation is not required for the known functions of cholecalciferol in the chick.

KEY WORDS: • vitamin D • calcium • bone calcification • vitamin D metabolites • intestine • vitamin D in chickens

1 This work was supported by a National Institutes of Health Program Project grant no. AM-14881 and a U.S.-Japan Cooperative grant no. INT-8016902 and the Harry Steenbock Research Fund of the Wisconsin Alumni Research Foundation.

2 Present address: First Department of Internal Medicine, Nagasaki University School of Medicine, Nagasaki, 852 Japan.

3 Correspondence may be addressed to H. F. DeLuca; no reprints will be available from the authors.

Manuscript received 31 January 1983.




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