title: Regulation by calcium of in vivo synthesis of 1,25-dihydroxycholecalciferol and 21,25-dihydroxycholecalciferol.
abstract: Tritiated 1,25-dihydroxycholecalciferol accumulates in several tissues, to an extent that varies with dietary calcium content, 12 hr after the administration of 325 pmoles of tritiated 25-hydroxycholecalciferol to rats. As the dietary and serum calcium concentrations increase, the amount of 1,25-dihydroxycholecalciferol is diminished and the concentration of 21,25-dihydroxycholecalciferol increases. This correlation is especially evident in rats given vitamin D(3). In vitamin D-deficient rats, the repression of 1,25-dihydroxycholecalciferol formation occurs with a diet containing 3% calcium and 20% lactose. The results suggest that the production of 1,25-dihydroxycholecalciferol, believed to be the metabolically active form of vitamin D in the intestine, is responsible for the adaptation of calcium absorption to low dietary concentrations of calcium.
mesh_terms: D000818:Animals; D001345:Autoradiography; D001835:Body Weight; D001842:Bone and Bones / Q000032:analysis; D002118:Calcium / Q000097:blood; D002136:Calcium, Dietary; D002762:Cholecalciferol / Q000008:administration & dosage / Q000032:analysis / Q000096:biosynthesis* / Q000097:blood; D002852:Chromatography, Ion Exchange; D006887:Hydroxycholecalciferols / Q000096:biosynthesis / Q000378:metabolism; D007413:Intestinal Mucosa / Q000032:analysis; D007668:Kidney / Q000032:analysis; D008297:Male; D010758:Phosphorus / Q000097:blood; D051381:Rats; D013057:Spectrum Analysis; D013997:Time Factors; D014316:Tritium; D014808:Vitamin D Deficiency / Q000378:metabolism
chemical_list: D002136:Calcium, Dietary; D006887:Hydroxycholecalciferols; D014316:Tritium; D002762:Cholecalciferol; D010758:Phosphorus; D002118:Calcium