Calciferols vitamin ergocalciferol

The term vitamin D is used for a range of compounds which possess the property of preventing or curing rickets. They include ergocalciferol (calciferol, vitamin D ), chole-calciferol (vitamin Dg), dihydrotachysterol, alfacalcidol (la-hydroxycholecalciferol) and calcitriol (1,25-dihydroxycholecalciferol). 

The fat-soluble vitamins can be divided into four different groups, based on biological activity vitamin A (retinol and carotenoids), vitamin D (chole-calciferol and ergocalciferol), vitamin E (tocopherols and tocotrienols), and vitamin K (phylloquinone and menaquinone), all of which may be present in a munber of closely related forms. 

Physiological forms of vitamin D include vitamin D2 (calciferol, ergocalciferol), vitamin D3 (cholecalciferol), phosphate esters of D2, D3, 25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol, and 5,25-dihydroxychole-calciferol. Vitamins D2 and D3 are 9,10-secosteroids that differ stmcturally in the degree of saturation of an... 

Toxicity. Most cases of hypervitaminosis D found in the literature are the consequences of overdosing with either chole-calciferol or ergocalciferol. Toxic concentrations of vitamin D... 

Vitamin D (cholecalciferol ergocalciferol) has its active form as 1,25-dihydroxylchole-calciferol. It is responsible for calcium uptake, and a deficiency of the vitamin results in rickets (in children) and osteomalacia (in adults). The symptoms of both syndromes are soft, pliable bones. High levels of vitamin D are toxic. 

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). 

As a brief introductory summary, vitamin D substances perform the following fundamental physiological functions (1) promote normal growth (via bone growth) (2) enhance calcium and phosphorus absorption from the intestine (3) serve to prevent rickets (4) increase tubular phosphorus reabsorpiion (5) increase citrate blood levels (6) maintain and activate alkaline phosphatase m bone (7) maintain serum calcium and phosphorus levels. A deficiency of D substances may be manifested in the form of rickets, osteomalacia, and hypoparathyroidism. Vitamin D substances are required by vertebrates, who synthesize these substances in the skin when under ultraviolet radiation, Animals requiring exogenous sources include infant vertebrates and deficient adult vertebrates, Included there are vitamin D (calciferol ergocalciferol) and vitamin D< (activated 7-dehydrocholesterol cholecalciferol). 

Vitamin D analogs Calcifediol (Calderol) Calcitriol (Rocaltrol) Dihydrotachysterol (DHT, Hytakerol) Ergocalciferol (Calciferol, Drisdol) Generally enhance bone formation by increasing the absorption and retention of calcium and phosphate in the body useful in treating disorders caused by vitamin D deficiency, including hypocalcemia, hypophosphatemia, rickets, and osteomalacia... 

Cholecalciferol 25-hydroxylase is not restricted to the liver kidneys, skin, and gut microsomes also have a cytochrome P450 -dependent enzyme that catalyzes the 25-hydroxylation of cholecalciferol and la-hydroxycholecalciferol, hut not ergocalciferol. Although there is some evidence that calcitriol can reduce the activity of calciferol 25-hydroxylase, it is not known whether this is physiologically important the major factor controlling 25-hydroxylation is the rate of uptake of cholecalciferol into the liver. It is the fate of calcidiol in the kidneys that provides the most important regulation of vitamin D metabolism (Wikvall, 2001). 

A group of fat-soluble vitamins. Cholecalciferol (vitamin D3) can be obtained from dietary sources and can also be produced in the skin by the action of sunlight on 7-dehydrocholesterol. Another vitamin D (ergocalciferol, vitamin Dj) can be obtained from plants. Cholecalciferol undergoes two hydroxylation steps in the body in its conversion to its active form, 1,25-dihydroxy-cholecalciferol. The C-2S hydroxylation takes place in the liver and this is followed by the C-I hydroxylation which takes place in the kidneys. The rate of synthesis of 1,25-dihydroxychole-calciferol is thought to be controlled by the circulating parathyroid hormone levels. 

CHEMISTRY, METABOLISM, PROPERTIES. Akhough about 10 sterol compounds with vitamin D activity have been identified, only two of these, known as provitamins D or precursors, are of practical importance today from the standpoint of their occurrence in foods—ergocalciferol (vitamin D, calciferol, or viosterol) and cholecalciferol (vitamin D,) the name cholecalciferol of the latter is a reflection of its cholesterol precursor. Because these substances are closely related chemically, the term vitamin D is used collectively to indicate the group of substances that showthis vitamin activity. 

Vitamin D, also called calciferol, is related to the steroids. It arises from A - -un-saturated sterols, the provitamins, by ultraviolet irradiation (cf. the diagram of formulas in Chapt. XIV-4). Thus, vitamin D2 (ergocalciferol) arises from ergos-terol vitamin D3 (cholecalciferol) from A -dehydrocholesteroI. In this connection it is important that A -dehydrocholesterol is concentrated in the skin and therefore exposed to irradiation. 

The mass equivalents of 1 lU for vitamin D is the biological equivalent of 0.025 /rg chole-calciferol/ergocalciferol (1/40 fig exactly). 

Vitamin D is composed of a number of related stmc-tures but the two most prominent members of the family are colecalciferol and ergocalciferol, which is formed from ergosterol rather than 7-dehydrocholesterol. Cole-calciferol is transformed into the most active form of the vitamin, 1,25-dihydroxycholecalciferol, by hydroxylation at the 25 position in the liver and finally at the 1 position in the kidneys. 

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