Dexamethasone increases the activity but not the amount of choline-phosphate cytidylyltransferase in fetal rat lung.

The activity of choline-phosphat e cytidylyltransferase is increased by glucocorticoids in late gestation fetal lung in association with increased phosphatidlyleholine biosynthesis. Previous indirect data had suggested that the stimulator~ effect of the hormone was due to activation of existing enzyme rather than synthesis of new cytidylyltransferase protein. Using a rabbit antibody raised against purified rat liver choline-phosphat e cytidylyltransferase, we have now quantitated the amount of the enzyme in fetal rat lung explants cultured with and without dexamethasone. Our results show that the hormone increased the activity of the enzyme but not the amount of cytidylyltransferase protein. Thus the stimulatory effect of dexamethasone on cytidyW.yltransferase is due to activation of existing enzyme rather than induction of enzyme synthesis.