Cholecalciferol Vitamin

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

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

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. 

Vaisberg, M.W. et al., Influence of cholecalciferol (vitamin D3) on the course of experimental systemic lupus erythematosus in FI (NZBxW) mice, J. Clin. Lab. Anal., 14, 91, 2000. 

Cholecalciferol (vitamin D-3) differs from calciferol only in the alkyl side-chain, so it was assumed to be in the twisted conformation (75a). In alcoholic solution, vitamin D-3 was irradiated with a mercury arc lamp through a cupric sulphate solution filter to give wavelengths above 250 nm. Six products were isolated. Conformation (75a) could reasonably give rise to the assigned structures (76a), (77a) and (78a) (Scheme 2.3). Photoisomerization could give conformation (75b), which would explain the isolation of (76b), (77b) and (78b). The report is confident on four of the new compounds, but notes that the cyclobutene structures (78a) and (78b) are tentatively assigned [63]. 

The active vitamins are produced by conversion of provitamins by ultraviolet light. Ergosterol, a yeast sterol, is converted to its active form, ergocalciferol (vitamin D2), and 7-dehydrocholesterol, which is found in many natural foods and is also synthesized in man, is converted to cholecalciferol (vitamin D3). Fish liver oils are virtually the only source of vitamin D3 in nature. The most active form of vitamin D3 is 1,25-dihydroxycholecalciferol and this is produced by the hydroxylation of cholecalciferol at position 25 in the liver and then at position 1 in the kidney. 

Vitamin D is commonly found in two forms, both derivatives of steroids. These are known as cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Cholecalciferol is formed directly from the steroid known as 7-dehydrocholesterol by the action of sunlight, or other source of ultraviolet (UV) light, in the skin of humans and other animals. When parents encourage their children to go out and play in the sun, there is good reason for doing so (but avoid sunburn). ... 

Vitamin D hormone is derived from vitamin D (cholecalciferol). Vitamin D can also be produced in the body it is formed in the skin from dehydrocholesterol during irradiation with UV light. When there is lack of solar radiation, dietary intake becomes essential, cod liver oil being a rich source. Metaboli-cally active vitamin D hormone results from two successive hydroxylations in the liver at position 25 ( calcifediol) and in the kidney at position 1 ( calci-triol = vit. D hormone). 1-Hydroxylation depends on the level of calcium homeostasis and is stimulated by parathormone and a fall in plasma levels of Ca or phosphate. Vit D hormone promotes enteral absorption and renal reabsorption of Ca and phosphate. As a result of the increased Ca + and phosphate concentration in blood, there is an increased tendency for these ions to be deposited in bone in the form of hydroxyapatite crystals. In vit D deficiency, bone mineralization is inadequate (rickets, osteomalacia). Therapeutic Liillmann, Color Atlas of Pharmacology... 

The following are recent reviews on the molecular and physical properties of this liver enzyme which converts cholecalciferol (vitamin D3) to 25-hydroxycholecalciferol. 

Vitamin D is a secosteroid present in the diet but is mainly produced non-enzymatically in the skin from cholesterol under the influence of ultraviolet light. Vitamin D synthesis is promoted by PTH. This is vitamin D3 or cholecalciferol. Vitamin D2, ergocalcif-erol is found in vegetables. Both forms of vitamin D... 

Vitamin D preparations that are available include er-gocalciferol (also termed calciferol, or vitamin D2), cholecalciferol (vitamin D3), alfa-calcidol (la-hydroxycholecalciferol) and calcitriol (1,25-hydroxycholcalciferol). 

Vitamin D is the collective term for a group of compounds formed by the action of ultraviolet irradiation on sterols. Cholecalciferol (vitamin D3) and calciferol (vitamin D2) are formed by irradiation of the provitamins 7-dehydrocholesterol and ergosterol, respectively. The conversion to vitamin D3 occurs in the skin. The liver is the principal storage site for vitamin D, and it is here that the vitamin is hydroxylated to form 25-hydroxyvitamin D. Additional hydroxylation to form 1,25-dihydroxyvita-min D occurs in the kidney in response to the need for calcium and phosphate. A discussion of the role of vitamin D in calcium homeostasis is provided in Chapter 66. 

Unlike other vitamins, cholecalciferol (vitamin D3) can be formed from a steroid precursor, 7-dehydrocholesterol (6.7), by the skin when exposed to sunlight with sufficient exposure to the sun, no preformed vitamin D is required from the diet. 

UV light (280-320 nm) causes the photoconversion of 7-dehydrocholesterol to pre-vitamin D3. This pre-vitamin can undergo further photoconversion to tachysterol and lumisterol or can undergo a temperature-dependent isomerization to cholecalciferol (vitamin D3, 6.8). At body temperature, this... 

T FIGURE 10-20 Vitamin D3 production and metabolism, (a) Cholecalciferol (vitamin D3) is produced in the skin by UV irradiation of 7-dehydrocholesterol, which breaks the bond shaded pink. In the liver, a hydroxyl group is added at C-25 (pink) in the kidney, a second hydroxylation at C-1 (pink) produces the active hormone, 1,25-dihydroxycholecalciferol. This hormone regulates the metabolism of Ca2+ in kidney, intestine, and bone, (b) Dietary vitamin D prevents rickets, a disease once common in cold climates where heavy clothing blocks the UV component of sunlight necessary for the production of vitamin D3 in skin. On the left is a 21/2-year-old boy with severe rickets on the right, the same boy at age 5, after 14 months of vitamin D therapy. 

Cholecalciferol [Vitamin D3] (Delta D) [Vitamin/Dietary Supplement] Uses Dietary supl to Rx vit D deficiency Action T Intestinal Ca2+ absorption Dose 400-1000 Int Units/d PO Caution [A (D doses above the RDA), +] Contra T Ca2+, hypervitaminosis, allergy Disp Tabs SE Vit D tox Interactions T Risk of arrhythmias w/ cardiac glycosides X effects w/ cholestyramine, colestipol, mineral oil, orlistat, phenobarbital, phenytoin EMS Can cause vit D tox (Tin serum Ca2+ weakness, AMS, Gl upset and cardiac arrhythmias) OD May cause T risk of vitD tox give IV fluids... 

However, it was not until 1924, when Steenbock and Hess showed that irradiation of certain foods generated protective activity against the disease, that vitamin D (calciferol) was recognized as a second lipid-soluble vitamin. Vitamin D is a family of compounds formed by the irradiation of A5/7-unsaturated sterols such as ergosterol and 7-dehydrocholesterol. The former yields ergocalciferol (vitamin D2) and the latter cholecalciferol (vitamin D3). 

Vitamin D is represented by cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2), which are structurally similar secosteroids derived from the UV irradiation of provitamin D sterols. In vertebrates, vitamin D3 is produced in vivo by the action of sunlight on 7-dehydrocholesterol in the skin. Vitamin D2 is produced in plants, fungi, and yeasts by the irradiation of ergosterol. On irradiation, the provitamins are converted to previtamin D, which undergoes thermal transformation to vitamin D. 

Cholecalciferol (vitamin D3) is derived from cholesterol. How and in which tissue does the conversion occur ... 

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