title: In vitro synthesis of 1 alpha,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol by isolated calvarial cells.
abstract: The question of whether the skeleton metabolizes 25-hydroxycholecalciferol [25(OH)D3] to more-polar products was studied. Calvarial cells were dispersed from 16-day old chicken embryos by using collagenase and then grown in culture in serum-free medium. Confluent cell cultures were incubated with 7 nM 25(OH)[3H]D3 for 2 hr, and the vitamin D metabolites were then extracted. At least four polar metabolites were produced. Based on separation by Sephadex LH-20 chromatography followed by high-pressure liquid chromatography, two of these metabolites were identified as 1,25-dihydroxycholecalciferol [1,25(OH)2D3] and 24,25-dihydroxycholecalciferol [24,25(OH)2D3]. These metabolites were also produced by cultured kidney cells but not by liver, heart muscle, or skin cells isolated from the same embryos. The specific activities of the calvarial 1- and 24-hydroxylases were similar in magnitude to those in isolated kidney cells. The specific activity of the calvarial 25(OH)D3:1-hydroxylase was inhibited by an 8-hr preincubation with 1,25(OH)2D3, whereas the 24-hydroxylase was enhanced. It is concluded that (i) vitamin D metabolism by isolated cells is organ-specific, (ii) calvarial cells produce active metabolites of vitamin D in significant amounts, (iii) vitamin D metabolism by calvarial cells is regulated by 1,25(OH)2D3, and (iv) locally produced, active metabolites could act locally, thereby adding a new dimension to the regulation of mineral metabolism by vitamin D metabolites.
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000378:metabolism*; D000818:Animals; D001842:Bone and Bones / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D004100:Dihydroxycholecalciferols / Q000096:biosynthesis*; D006887:Hydroxycholecalciferols / Q000096:biosynthesis*; D007700:Kinetics; D013250:Steroid Hydroxylases / Q000378:metabolism*
chemical_list: D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; D013250:Steroid Hydroxylases; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase