dihydroxycholecalciferol

dihydroxycholecalciferol /di·hy·droxy·cho·le·cal·cif·e·rol/ (-ko″le-kal-sif´ĕ-rol) a group of active metabolites of cholecalciferol (vitamin D3). 1,25-Dihydroxycholecalciferol (1,25-dihydroxyvitamin D3 or calcitriol) increases intestinal absorption of calcium and phosphate, enhances bone resorption, and prevents rickets, and, because of these activities at sites distant from the site of its synthesis, is considered to be a hormone. See also calcitriol.

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dihydroxycholecalciferol

a group of active metabolites of cholecalciferol (vitamin D₃) numbered according to the carbon atom(s) on which a hydroxyl group is substituted. 1,25-Dihydroxycholecalciferol (calcitriol) is the most active derivative; the 25-hydroxylation occurs in the liver under the influence of substrate concentration whereas the second 1-hydroxylation occurs in the kidney mitochondria under regulation by parathyroid hormone in response to decreases in plasma calcium concentration. 1α,25-Dihydroxycholecalciferol acts like a steroid hormone stimulating calcium absorption from the small intestine and calcium mobilization from bone.