1,25-Dihydroxycholecalciferol: A Potent Stimulator of Bone Resorption in Tissue Culture

1,25-Dihydroxycholecalciferol (DHCC), isolated from kidney homogenates incubated with 25-hydroxycholecalciferol (HCC), stimulated the release of previously incorporated 45 Ca from fetal rat bones in organ culture, at concentrations of 10 -10 to 10 -8 M . The dose response curves for 1,25-DHCC and 25-HCC, the parent compound, are parallel, but 1,25-DHCC is about 100 times as potent on a weight basis. Brief exposure to maximum doses of either agent leads to prolonged bone resorption.