Accelerated fetal lung maturation by estrogen is associated with an epithelial-fibroblast interaction

The role of epithelial-mesenchymal interactions in the stimulation of lung development by estrogen is now investigated using organ cultures of lung from male and female fetal rats taken from Days 17 to 21 of gestation. Estradiol at 1 microgram/ml was found to reduce cell proliferation in explants taken during a rapid growth phase (Day 18) and to stimulate surfactant synthesis in both males and females only in Day 20 explants when cell division is much slower. At this time more epithelial cells from estrogen-treated explants contained lamellar bodies, which were also secreted to fill the air sacs. These cultures also showed a significant increase in the frequency of cell-to-cell contacts between epithelial cells and fibroblasts. Uptake of tritiated estradiol by explants increased from Day 18 onward, and by autoradiography, labeling was located predominantly over fibroblasts. Using pure cultures of fetal and adult cells, uptake of labeled estradiol was significantly higher in fibroblasts than in corresponding epithelial cells, and estradiol did not directly enhance palmitate incorporation into epithelial cells. The results suggest that the earlier maturation and increased surfactant synthesis in female fetal lung is related at least in part to enhanced binding of estrogen by the fibroblast with subsequent transfer of a maturation factor to the fetal epithelium.