Autoradiographic localization of 1,25-dihydroxyvitamin D3 in rat placenta and yolk sac

After injection of 3H-1,25-(OH)-vitamin D3 into rats on days 18 and 20 of pregnancy, autoradiograms of placenta and fetal membranes show nuclear concentration of radioactivity in certain cells. This nuclear concentration is abolished when unlabeled 1,25-(OH)2-vitamin D3, but not 25-(OH)-vitamin D3, is injected prior to the labeled hormone. Nuclear labeling is observed in epithelial cells of visceral yolk sac and amnion, and in certain trophoblasts in basalis and labyrinth. The results suggest the presence of a specific receptor-like binding for 1,25-(OH)2-vitamin D3 and thus involvement of the target cells in calcium regulatory mechanisms during development.