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Nutritional Effectiveness of 1,25-Dihydroxycholecalciferol in Preventing Rickets in Chicks¹

Department of Biochemistry, College of Medicine, The University of Arizona, Tucson, Arizona 85724

1,25-Dihydroxycholecalciferol, the apparent active form of vitamin D₃ (cholecalciferol) which mediates calcium translocation in bone and intestine, has been tested for its nutritional efficacy in preventing rickets. Chicks were fed a vitamin D-deficient diet and received oral supplements of 1,25-dihydroxycholecalciferol, 25-hydroxycholecalciferol or cholecalciferol for 3 weeks. Growth, plasma calcium concentration, calcium absorption and percentage bone ash were determined; sections of tibia were examined microscopically for evidence of rickets, 1,25-Dihydroxycholecalciferol displayed an effectiveness similar to 25-hydroxycholecalciferol, with both metabolities being between 1.5 and 2.2 times as active as cholecalciferol with respect to stimulation of weight gain and maintenance of plasma calcium levels. The antirachitic potency of 1,25-dihydroxycholecalciferol in chicks is estimated to be 1.3 times that of cholecalciferol. Thus, 1,25-dihydroxycholecalciferol was found to be more potent than the parent sterol in terms of supporting normal calcium and bone metabolism, and the metabolite alleviated all signs of rickets. These data substantiate the conclusion that 1,25-dihydroxycholecalciferol is the hormonal form of vitamin D and indicate that other metabolites of the vitamin are not required for the regulation of calcium metabolism and prevention of bone disease.

KEY WORDS: • 1,25-dihydroxycholecalciferol • vitamin D₃ • rickets

¹ This research was supported by United States Public Health Service Grant AM15781 and General Research Support Grant no. 5-S01 RR05675 to the University of Arizona College of Medicine.

Manuscript received 5 September 1972.