Differentiation of the pulmonary surfactant system. Disaturated phosphatidylcholine accumulation in fetal rat lung in vivo and in vitro.

Fetal rat lung was placed in organ culture at 15 days gestation (22 days total gestation period), before biochemical and morphological development of the pulmonary surfactant system. At the fifth day of culture numerous Type II cells containing lamellar bodies were present as determined by electron micrography. Phospholipid accumulation in the cultures increased abruptly beginning at 6 days in culture. The phospholipid which accumulated between the sixth and twelfth culture days was composed of 21--27% disaturated phosphatidylcholines. Both the percent of disaturated phosphatidylcholines in the phospholipid fraction and the qualitative pattern of accumulation as a function of time were similar to observations for fetal rat lung developing in vivo. The data presented provide evidence for development of the pulmonary surfactant system in organ culture in vitro.