Cortisol and the dexamethasone suppression test | Corticotropin-releasing hormone and depression | HPA axis pathophysiology in specific mood disorders
The DST, a test originally designed to aid in the diagnosis
of Cushing's syndrome, was one of the first endocrine challenge
tests to be studied in psychiatric patients. Studies of patients
with mood disorders using the DST provided some of the first evidence
of abnormal HPA axis function in depression (Table 45–1).
The DST consists of the administration of a low dose (1 mg) of the
synthetic glucocorticoid dexamethasone at 2300 h followed by measurement
of plasma cortisol concentrations at two or three time points the
following day. Dexamethasone acts at the level of the anterior pituitary
corticotrophs to reduce the secretion of ACTH, resulting in a decrease
in the synthesis and release of cortisol from the adrenal cortex.
Failure to suppress plasma cortisol concentrations after dexamethasone
administration suggests impaired feedback regulation and hyperactivity
of the HPA axis.