Differential stimulation of hepatic mono-oxygenase and glucuronidating systems in chick embryo and neonatal rat by glucocorticoids.

White Leghorn embryos infused with corticosterone precociously reproduced the hatching surges of hepatic UDPglucuronosyltransferase activity to 2-aminophenol, aminopyrine N-demethylase activity and cytochrome P-450 concentration. Onset of transferase activity followed that of the others by 48 h over hatching and on infusion. Competence of demethylase and transferase to respond to corticosterone appeared over days 12--14. Glucocorticoids are suggested as the natural triggers of both transferase and monooxygenase activities in chick and both processes may share a further control. Exposure of CD rat foetuses at 18 1/2 days to dexamethasone by maternal injection evoked precocious onset of transferase activity to 2-aminophenol but not to bilirubin, nor of demethylase activity or cytochrome P-450 content. Injection of hour-old or infant rats with dexamethasone did reproduce precociously onset of the three latter and stimulated the former. Competence for glucocorticoid response thus appeared before birth for transferase activity to 2-aminophenol and at birth for the others. Onset of transferase following hatching or glucocorticoid lagged behind that of demethylase or cytochrome P-450 by 48 h in chick embryo and 36 h in newborn and infant rats; only in foetal rat was response of transferase rapid to administered glucocorticoid.