Fetal lung in organ culture. III. Comparison of dexamethasone, thyroxine, and methylxanthines

Exposure of explants of fetal rat lung to dexamethasone, thyroxine, or the methylxanthines, aminophylline and caffeine, resulted in a significant increase in the rate of choline incorporation into all the choline-containing phospholipids. Dexamethasone, aminophylline, or caffeine treatment also resulted in an increase in the percentage of radioactivity from [3H]acetate in the surfactant-associated phospholipids, disaturated phosphatidylcholine, and phosphatidylglycerol and a corresponding decrease in the membrane phospholipids. Exposure to thyroxine had different effects. Only aminophylline and caffeine produced an increase in the rate of incorporation of acetate into phospholipid. Differences were also observed in the activities of enzymes of phospholipid synthesis. The activity of cholinephosphate cytidylyltransferase was increased by dexamethasone and that of choline kinase and lysolecithin acyltransferase by aminophylline. Thyroxine had no effect on any of the enzymes examined. All these agents produced a significant decrease in lung glycogen content and a small decrease in the protein-to-DNA ratio. These data indicate that corticosteroids, thyroxine, and the methylxanthines act directly on the fetal lung, but produce different effects and presumably act via different mechanisms.