Maximum nocturnal serum melatonin level (MTmax) in relation to some clinical variables was studied in 32 patients with a major depressive episode and in 33 healthy subjects with reference to the outcome of the dexamethasone suppression test (DST). Significant regressions were found between MTmax levels and clinical rating scores in CPRS, interpreted as retardation symptoms. Four healthy subjects with disposition for dysthymic reactions had subnormal MTmax levels, which differed from MTmax levels in subjects without such disposition. Patients but not the healthy subjects, who reported parental loss before 17 years of age, had subnormal MTmax levels and differed from patients with no reported parental loss. Patients with no reported suicidal behaviour in clinical history had significantly lower MTmax levels than patients with reported suicide attempts. No relations were found between low MTmax levels and diagnoses, duration of illness, reported inheritance for depressive illness or sleep disturbances. A hypothetical low melatonin syndrome in depression is proposed: low nocturnal melatonin, abnormal dexamethasone suppression test, disturbed 24-h rhythm of cortisol, less pronounced daily and annual cyclic variation in depressive symptomatology.

A double-blind study of the tryptophan depletion (TD) challenge was performed on a sample consisting of 20 patients with a major depressive disorder in clinical remission after citalopram treatment. TD was induced by the intake of 43 g of an amino acid mixture containing the five large neutral amino acids. The control group received the same mixture, to which 2.3 g tryptophan had been added. Five of the 12 challenged patients showed a worsening of depressive symptoms during the day of the test. In contrast, there was no mood alteration in the eight control patients. Baseline cortisol levels were significantly higher in responders to TD compared to those in non-responders and controls. Platelet serotonin-receptor function and plasma prolactin levels were correlated. There was a significant positive correlation in the baseline data between rated mood state and plasma cortisol and a significant inverse correlation between related mood state and plasma tryptophan concentration. Thus low mood appeared to be associated with low serotonin precursor availability as well as with high cortisol levels.

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