Lung as a possible additional target organ for vitamin D during fetal life in the rat.

The presence of specific cytosol binding sites for 1,25-(OH)2D3 was evaluated in rat fetal tissues during the last quarter of gestation (days 17-21). The content of 1,25-(OH)2D3-binding sites was low in intestine, brain, liver, spleen, pancreas, sternum and thymus during the period of gestation studied. It was highest in skeleton (ribs and vertebral bodies), kidney and lung from day 19 onwards. In the cytosol of these latter tissues, a high affinity (Kd 0.7-3.6 X 10(-10) M, low capacity [3H]1,25-(OH)2D3 binding was demonstrated and a distinct 2.9- to 3.5-S [3H]1,25-(OH)2D3-binding component was observed. These findings suggest that fetal lung, skeleton and kidney are possibly major target tissues for 1,25-(OH)2D3.