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The natural, active form of vitamin D is calcitriol (1,25-dihydroxycholecalciferol). This molecule and other naturally occurring forms of vitamin D, including its precursors and metabolites, have been modified to synthesize pharmaceuticals with potentially greater, or selective, therapeutic actions. [1] [2] [3] [4]
Paricalcitol (chemically it is 19-nor-1,25-(OH) 2-vitamin D 2. Marketed by Abbott Laboratories under the trade name Zemplar ) is a drug used for the prevention and treatment of secondary hyperparathyroidism (excessive secretion of parathyroid hormone ) associated with chronic kidney failure .
The vitamin D receptor (VDR also known as the calcitriol receptor) is a member of the nuclear receptor family of transcription factors. [5] Calcitriol (the active form of vitamin D , 1,25-(OH) 2 vitamin D 3 ) binds to VDR, which then forms a heterodimer with the retinoid-X receptor .
Calcitriol is a hormone and the active form of vitamin D, normally made in the kidney. [ 8 ] [ 9 ] [ 10 ] It is also known as 1,25-dihydroxycholecalciferol . It binds to and activates the vitamin D receptor in the nucleus of the cell, which then increases the expression of many genes. [ 11 ]
A third important effect of PTH on the kidneys is stimulation of the conversion of 25-hydroxy vitamin D into 1,25-dihydroxy vitamin D (calcitriol). [216] This form of vitamin D is the active hormone which promotes calcium uptake from the intestine via the action of calbindin . [ 218 ]
It is then converted in the liver to calcifediol (25-hydroxycholecalciferol D), which is further converted in the kidney to calcitriol (1,25-dihydroxycholecalciferol D). [4] One of calcitriol’s most important functions is to promote calcium uptake by the intestines. [5] Cholecalciferol is present in food such as fatty fish, beef liver, eggs ...
Alfacalcidol (or 1-hydroxycholecalciferol) is an analogue of vitamin D used for supplementation in humans and as a poultry feed additive.. Alfacalcidol has a weaker impact on calcium metabolism [3] and parathyroid hormone levels [4] than calcitriol; but significant effects on the immune system, including regulatory T cells. [5]
The epidermal strata of the skin. 7-Dehydrocholesterol (7-DHC) is a zoosterol that functions in the serum as a cholesterol precursor, and is photochemically converted to vitamin D 3 in the skin, therefore functioning as provitamin-D 3.