[Recent advances on the "active" vitamin D: 1alpha,25-dihydroxicholecalciferol (author's transl)]

The researches on the mode of action of vitamin D have shown that vitamin D3 in animals is not utilized as such but after Hydrosylation of carbon 25 in the liver and of carbon 1 in the kidney. 1alpha,25-dihdroxycholecalciferol (1alpha,25-(OH)2D3) is the active on two target organis the intestin and bones, acting as a steroid hormone. In the intestin it controls the syntesis of a specific calcium binding protein (CaPB) responsable for calcium absorption. At the bone level it act on the deposition of calcium salts, and whenever necessary on its mobilization. Therefore 1alpha,25(OH)2D3 is active part of the calcium homeostatic system in the organism together with specific hormones such as parathyroid hormone and calcitonin.