The effect of repeated human corticotropin-releasing hormone administration on dexamethasone-suppressed pituitary—adrenocortical activity in healthy subjects

A dexamethasone suppression test (DST) using a dosage of 1.5 mg dexamethasone was administered two times in randomized order to 10 healthy male subjects. From 2300 hours to 0700 hours subjects were injected repeatedly with either increasing dosages of human corticotropin-releasing hormone (hCRH) or 0.9% saline. In comparison to saline administration, in which cortisol levels remained suppressed, the time course of cortisol concentrations with hCRH stimulation showed a biphasic secretory pattern. According to a criterion level of a minimum of 40 ng/mL plasma for nonsuppression, the majority of the subjects changed their DST status to nonsuppression with hCRH. Adrenocorticotropic hormone secretion also differed significantly between saline and hCRH administration. During stimulation with hCRH, plasma dexamethasone levels were slightly and nonsignificantly reduced in the morning hours. Our results indicate that repeated dosages of hCRH impair the dexamethasone-induced suppression in man and support an involvement of CRH also in mediation of the DST nonsuppression during depressive illness.