17OH-progesterone response to acute dexamethasone administration in congenital adrenal hyperplasia.

Glucocorticoid-related changes in 17OH-progesterone (17P) concentrations were studied in 13 patients receiving treatment for 21-hydroxylase deficiency congenital adrenal hyperplasia (CAH). Blood spot and saliva 17P levels were elevated, with or without loss of diurnal rhythm, within 24 h of stopping maintenance glucocorticoid therapy. A single dose of dexamethasone (0.01 mg/kg) given either intravenously or orally at 09.00 h resulted in rapid onset of complete pituitary-adrenal suppression characterised by a prompt and exponential fall in 17P levels (first-order elimination half-life, mean 2.87 h, range 1.98-3.98 h). Concentrations of 17P remained low throughout the day until the onset of an abrupt nocturnal rise, which occurred between 24.00 and 05.00 h. There were individual differences in both the rate of fall and the timing of the nocturnal rise in 17P levels which may partly explain the need to vary individual steroid requirements in the treatment of CAH.