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Biological Activity of 24,25-Dihydroxycholecalciferol in Chicks and Rats¹

Department of Biochemistry, University of California, Riverside, Riverside, California 92502

The ability of 24R,25- and 24S,25-dihydroxycholecalciferol to stimulate intestinal calcium transport and bone calcium mobilization in chicks was measured. Enhancement of intestinal calcium transport by 325 or 130 nmoles of either compound was maximal by 24 hours. The effects of these compounds on bone calcium mobilization were also maximal by 24 to 36 hours. When lower doses were tested, 2 nmoles of the 24R,25-dihydroxycholecalciferol significantly stimulated intestinal calcium transport, whereas 130 nmoles of the S isomer were required for a significant response. Neither steroid had a significant effect on bone calcium mobilization when doses of less than 130 nomles were given. When chicks received orally 32.5, 325 or 1,625 pmoles of 24R,25-dihydroxycholecalciferol daily from hatching for 4 weeks, several parameters showed a dose-related response. These included growth, serum calcium, bone ash, renal 25-hydroxycholecalciferol-1-hydroxylase and intestinal vitamin D-dependent calcium binding protein. Rats given 32.5 to 1,625 pmoles of 24R,25-dihydroxycholecalciferol for 3 or 6 weeks were equivalent to vitamin D-treated controls in terms of growth and serum calcium levels. It is concluded that within the lower dose ranges (2 to 30 pmoles) the R isomer of 24,25-dihydroxycholecalciferol is more active in stimulating intestinal calcium transport than the S isomer but that neither compound increases bone calcium mobilization at these dose levels. Also, the rat is more responsive in terms of growth and serum calcium, to small daily doses of 24R,25-dihydroxycholecalciferol than is the chick.

KEY WORDS: • 24,25-dihydroxycholecalciferol • 1,25-dihydroxycholecalciferol • calcium • vitamin D₃

¹ This work was supported in part by United States Public Health Service Grants AM-09012, AM-14,750, and AM-04052.

² Recipient of United States Public Health Service Career Research Development Award 1-ROK-AM-13654.

³ Department of Physical Biology, New York State Veterinary College, Cornell University, Ithaea, N.Y., 14950; Present address: Baylor College of Dentistry, Dallas, Texas.

⁴ Medical and Research Services, VA Wadsworth Hospital and the Department of Medicine, UCLA School of Medicine, Los Angeles, Calif., 90073.

Manuscript received 26 September 1975.

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				H. Henry and A. Norman Vitamin D: two dihydroxylated metabolites are required for normal chicken egg hatchability Science, September 1, 1978; 201(4358): 835 - 837. [Abstract] [PDF]