Effects of the antiglucocorticoid RU 486 on the initiation of ultrastructural type-II cell differentiation in fetal rat lung.

The possible early role of endogenous glucocorticosteroids on the further ultra-structural development of the fetal rat lung epithelium was investigated in vitro using a potent antiglucocorticoid drug, RU 486. Lung primordia were explanted on day 13 of gestation and cultured for 4-6 days in the presence of fetal calf serum, with or without RU 486 in excess. The results obtained show that osmiophilic lamellar bodies specific for morphologically differentiated type-II cells did appear in a number of epithelial cells, even though the glucocorticosteroids possibly present in the culture medium, or transferred at explantation were antagonized by RU 486. The number of lamellar bodies stored in these pneumocytes was not different from that in controls. In contrast, their total surface area per cell profile was transiently decreased. Taken together the reported data strongly suggest that endogenous glucocorticosteroids are not necessary for the initiation of type-II cell differentiation.