Cholecalciferol

See also 7-Dehydrocholesterol Cholecalciferol. [VITAMINS - VITAMIN D] (Vol 25) -See also 22,23-Dihydroergosterol. [VITAITINS - VITAMIN D] (Vol 25)... 

Fig. 2. Homeostatic control of blood Ca " level where PTH is parathyroid hormone [9002-64-6], CC, cholecalciferol, ie, vitamin D HCC, hydroxycholecalciferol DHCC, dihydroxycholecalciferol CaBP, calcium-binding protein NAD PH, protonated nicotinarnide-adenine dinucleotide...

Metabolites of vitamin D, eg, cholecalciferol (CC), are essential in maintaining the appropriate blood level of Ca ". The active metabolite, 1,25-dihydroxycholecalciferol (1,25-DHCC), is synthesized in two steps. In the fiver, CC is hydroxylated to 25-hydroxycholecalciferol (25-HCC) which, in combination with a globulin carrier, is transported to the kidney where it is converted to 1,25-DHCC. This step, which requites 1-hydroxylase formation, induced by PTH, may be the controlling step in regulating Ca " concentration. The sites of action of 1,25-DHCC are the bones and the intestine. Formation of 1,25-DHCC is limited by an inactivation process, ie, conversion of 25-HCC to 24,25-DHCC, catalyzed by 24-hydroxylase. 

In 1949 the World Health Organization adopted the biological activity of 1 mg of an oil solution containing 0.025 p.g of crystalline D as the analytical standard for vitamin D. This standard was discontinued in 1972. USP uses crystalline cholecalciferol as a standard (80). Samples of reference standard may be purchased from U.S. Pharmacopeia Convention, Inc., Reference Standards Order Department, 12601, Twinbrook Parkway, Rockville, Maryland 20852. One international unit of vitamin D activity is that activity demonstrated by 0.025 ]1 of pure crystalline (7 -vitamin D. One gram of vitamin D3 is equivalent to 40 x 10 lU or USP units. The international chick unit (ICU) is identical to the USP unit. 

The standard chemical and biological methods of analysis are those accepted by the JnitedStates Pharmacopeia XXIII as well as the ones accepted by the AO AC in 1995 (81—84). The USP method involves saponification of the sample (dry concentrate, premix, powder, capsule, tablet, or aqueous suspension) with aqueous alcohoHc KOH solvent extraction solvent removal chromatographic separation of vitamin D from extraneous ingredients and colormetric deterrnination with antimony trichloride and comparison with a solution of USP cholecalciferol reference standard. 

Year Source Cod-hver oil, /L Ergocalciferol (crystalline vitamin D2), /g Cholecalciferol D /g... 

Fat-Soluble Retinol (vitamin A) Ergocalciferol (vitamin Dg) Cholecalciferol (vitamin Dg) n-Tocopherol (vitamin E) Vitamin K ... 

FIGURE 18.37 (a) Vitamin D3 (cholecalciferol) is produced in the skin by the action of sunlight on 7-dehydrocholesterol. The successive action of mixed-function oxidases in the liver and kidney produces 1,25-dihydroxyvitamin D3, the active form of vitamin D. 

Summary term for a number of steroid hormones and their precursors with differentiation-inducing activity in many tissues. As regards bone, three components are relevant cholecalciferol ( vitamin D ) 25-hydroxyvi-taminD3 (calcidiol) and 1,25-dihydroxy vitamin D3 (calcitriol). The latter is the biologically active form and increases both intestinal calcium absoiption and bone resorption. Vitamin D preparations are widely used for the treatment of osteoporosis. Daily supplementation with vitamin D reduces bone loss in postmenopausal women and hip fractures in elderly subjects. 

Alkaloids (codeine, brucine), phenothiazines (promethazine), sulfonamides (sulfathiazole), vitamins (axerophthol, cholecalciferol)... 

Cholesterol, mostly esterified, is utilized in the buildup of cell biomembranes. Besides, cholesterol is a precursor to biologically important steroid compounds bile acids (in liver), steroid hormones (in adrenal cortex, male and female sexual glands, and placenta), and vitamin D3, or cholecalciferol (in skin). 

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