1,25-Dihydroxyvitamin D3 target cells in rat mammary gland.

In autoradiograms of mammary glands of rats on days 18 and 20 of pregnancy and day 6 of lactation after injection of 3H 1,25-(OH)2 vitamin D3, a nuclear concentration of radioactivity is observed in alveolar and ductal cells, as well as in cells of the epidermis of the nipple. Myoepithelial cells and connective tissue cells do not concentrate the hormone in their nuclei. The nuclear radioactivity appears specific, since 1,25-(OH)2 vitamin D3 but not 25-(OH)2 vitamin D3 prevents the uptake. The results suggest the existence of nuclear receptors for 1,25-(OH)2 vitamin D3 in mammary tissues and thus complements previous biochemical evidence showing the presence of cytoplasmic receptors for the hormone in mouse mammary glands; in addition, our results allow the identification of the cell types possessing the receptors.