Fetal rat lung maturation: initiation and modulation.

The purpose of this study was to determine whether a rise in the level of circulating hormones is responsible for initiating fetal lung maturation. Explants of 13- to 20-day fetal rat lung were cultured in a constant chemically defined medium containing 0 or 1% serum. Growth, morphological maturation, and two biochemical markers of lung development, disaturated phosphatidylcholine (DSPC) synthesis and specific nuclear glucocorticoid binding, showed evidence of continuing development in culture. There is normally a marked increase in DSPC content and in the rate of choline incorporation into DSPC after 20 days gestation. Regardless of the gestational age of the fetal lungs used, there was a similar increase in culture at an equivalent gestational age of 20 days (e.g., 14-day lung after 6 days, 16-day lung after 4 days). Removal of 50 or 75% of the lung mesenchymal tissue at the initiation of the culture period did not prevent the increase in choline incorporation. Since the culture environment was constant and contained virtually no hormones, we conclude that the stimulus for the initiation of fetal lung maturation is most likely located in the lung tissue itself. The role of circulating hormones is probably later modulation of the maturational process.