1,25-dihydroxycholecalciferol: identification of the proposed active form of vitamin D3 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)0(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.