The relationship between the pineal gland and the pituitary--adrenal axis in health, endocrine and psychiatric conditions.

Evidence is reviewed in favour of a close relationship between the pineal hormone, melatonin and ACTH--cortisol in man. Subgroups of patients with Cushing's disease as well as with major depressive disorder have low levels of nocturnal serum melatonin. Depressed patients with an abnormal dexamethasone suppression test (DST) have lower melatonin levels than do patients with a normal DST. Low melatonin levels may be a genetic trait marker for vulnerability to depression. The mechanism may be related to increased corticotropin-releasing factor (CRF), secondary to hypofunction of a pineal factor which physiologically inhibits CRF.