Regulation by Calcium of In Vivo Synthesis of 1,25-Dihydroxycholecalciferol and 21,25-Dihydroxycholecalciferol

  1. I. T. Boyle,
  2. R. W. Gray, and
  3. H. F. Deluca*
  1. Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wis. 53706
  2. Department of Medicine, School of Medicine, University of Wisconsin, Madison, Wis. 53706

Abstract

Tritiated 1,25-dihydroxycholecalciferol accumulates in several tissues, to an extent that varies with dietary calcium content, 12 hr after the administration of 325 pmoles of tritiated 25-hydroxycholecalciferol to rats. As the dietary and serum calcium concentrations increase, the amount of 1,25-dihydroxycholecalciferol is diminished and the concentration of 21,25-dihydroxycholecalciferol increases. This correlation is especially evident in rats given vitamin D3. In vitamin D-deficient rats, the repression of 1,25-dihydroxycholecalciferol formation occurs with a diet containing 3% calcium and 20% lactose. The results suggest that the production of 1,25-dihydroxycholecalciferol, believed to be the metabolically active form of vitamin D in the intestine, is responsible for the adaptation of calcium absorption to low dietary concentrations of calcium.

Footnotes

  • ↵ * To whom all inquiries should be addressed. I. T. B. is a Richard Hartenstein fellow and recipient of a Wellcome Research Travel Grant.

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  1. PNAS September 1, 1971 vol. 68 no. 9 2131-2134
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