1,25-Dihydroxycholecalciferol: Identification of the Proposed Active Form of Vitamin D$_{3}$ in the Intestine

The major polar metabolite of cholecalciferol (vitamin D$_{3}$) present in chick intestinal mucosa has been chemically characterized by mass spectrometric analysis to have a molecular formula of C$_{27}$H$_{44}$O$_{3}$ and a structure of 1,25-dihydroxycholecalciferol. This compound, which is produced in the kidney from 25-hydroxycholecalciferol, has been previously shown to be from 4 to 13 times as active as cholecalciferol in stimulating intestinal calcium transport. 1,25-Dihydroxycholecalciferol (previously designated metabolite 4B in this laboratory) probably represents the biologically active form of cholecalciferol in the intestine.