Fig. 9. Effect of 1,25-dihydroxyvitamin D₃ on in vitro growth of mammary glands from wild-type and Vdr knockout mice. Inguinal mammary gland pairs were removed from wild-type (A,C) and Vdr knockout (B,D) mice pre-treated with estrogen and progesterone for 15 days and placed in organ culture with estrogen, progesterone and lactogenic hormones for 14 days. One gland from each pair was exposed to ethanol vehicle (A,B), while the contralateral gland was exposed to 100 nM 1,25-dihydroxyvitamin D₃ (C,D). Glands were removed from culture, stained and wholemounted after 14 days in vitro growth. Arrows indicate alveolar growth and side branching in A and undeveloped ducts in C. Images are representative of 10 gland pairs per genotype examined. Scale bar: 300 µm.