Serum melatonin is not affected by glucocorticoid replacement in congenital adrenal hyperplasia

Recently a hypothesis has been proposed suggesting a negative feedback in the regulation of cortisol (F) and melatonin (Mel). To study a possible influence of F on Mel regulation we examined 13 children with congenital adrenal hyperplasia (CAH) on two occasions: once 3 days after cessation of F substitution (group 1; n = 13) and once during treatment with dexamethasone (1 mg/m2/day) and fludrocortisone (0.1 mg/m2/day) (group 2; n = 11) 11 children matched by sex and age served as controls (group 3). While serum 17 OH-progesterone levels, an indicator for the activation of the hypothalamo-pituitary-adrenal axis in CAH, were significantly (P less than 0.001) elevated in untreated patients (group 1), serum Mel levels were not different among the 3 groups nor was the diurnal secretion pattern of Mel affected. Nocturnal serum Mel concentrations, however, correlated with the age of the subjects (r = 0.55, P less than 0.001 at 23.00 h), displaying high values in early childhood that declined with progressing age. The presented data do not support the view of a classical feedback mechanism in the regulation of Mel and F in humans. However, it confirms the description of a tremendous fall of nocturnal Mel concentrations during childhood.