1a,25-dihydroxyvitamin

Vitamin D3 is transported to liver where it undergoes a hydroxylation at C-25 into 1a,25-dihydroxyvitamin D3 (calcitriol) (Fig. 64). In the kidney, it undergoes further hydroxylations at different sites, depending on the serum Ca + concentration. The most biologically active metabolite of vitamin D3 is calcitriol, which plays important roles in the regulation of calcium and phosphorus metabolism. It is used for treating bone diseases, but is also involved in the cell proliferation and the inducement of cell differentiation [151]. 

Calcitroic acid 1al24l25-Trihydroxyvitamin D3 1a,25-Dihydroxyvitamin D3 25-Hydroxyvitamin D3... 

Nogawa K, Tsuritani I, Kido T, Honda R, Yamada Y, Ishizaki M. Mechanism for bone disease found in inhabitants environmentally exposed to cadmium decreased serum 1a,25-dihydroxyvitamin D level. Int Arch Occup Environ Health 1987 59 21-30. Nogawa K, Kobayashi E, Yamada Y, Honda R, Kido T, Tsuritani I. Ishizaki M. Parathyroid hormone concentration in the serum of people with cadmium-induced renal damage. Int Arch Occup Environ Health 1984 54 187-193. 

Therapeutic Function Calcium regulator Chemical Name 9,10-Secocholesta-5,7,10(19)-triene-1,3,25-triol Common Name 1a,25-Dihydroxvcholecalciferol 1a,25-dihydroxyvitamin D3 Structural Formula ... 

Figure 4 A schematic representation of the origin of vitamin D3 and its metabolism in the liver by the hepatic vitamin D-25-hydroxylase. Once formed, the 25-hydroxyvitamin D3 (25(OH)D3> is metabolized by either a 25(OH)D-1a-hydroxylase or a 25(OH)D-24-hydroxylase. 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) can either go to its target tissues to carry out its biologic functbn(s), or it can be metabolized in its side-chain and degraded to calcitroic add. (Reproduced with permissbn from Holick MF (1995) Vitamin D Photobiology, Metabolism, and Clinical Applications. In DeGroot U etal. (eds.) Endocrinology, 3rd edn, pp. 990-1013. Philadelphia W.B. Saunders.)...

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