Fetal lung disaturated phosphatidylcholine. Ostensible increase following exposure to dexamethasone

Fetal rat lung removed at 15 days gestation and placed in organ culture incorporates choline into phosphatidylcholine. Addition of 10(-9) M dexamethasone resulted in increased rates of choline incorporation per micrograms protein after both 6 and 12 days culture. This concentration of dexamethasone did not increase tissue phosphatidylcholine or disaturated phosphatidylcholine. Thus, at a culture time when dexamethasone had a significant effect on choline incorporation, there was no change in either the total phospholipid or disaturated phosphatidylcholine content of the lung tissue. The transplacental administration of dexamethasone decreased fetal lung DNA and phospholipid content. At the mid-range dosage tested (400 micrograms), dexamethasone depressed DNA (51%) appreciably more than total phosphatidylcholine (28%) and disaturated phosphatidylcholine (33%). These results show that the hormone does not increase the total amount of surfactant per lung. The increased disaturated phosphatidylcholine per mg DNA results in an ostensible beneficial effect of dexamethasone on surfactant and may reflect an increased proportion of Type II cells in fetal lung both in vitro and in vivo following hormone exposure. Disaturated phosphatidylcholine per Type II alveolar cell is no doubt increased but the trade-off is fewer total cells in the lung.