Plasma melatonin levels in affective states.

Abstract

Melatonin is a major endocrine product of the pineal gland. It is produced at night when noradrenaline acts on beta-adrenergic receptors to stimulate enzymes which catalyse the formation of melatonin from serotonin. It is believed by some that nocturnal melatonin levels reflect beta-receptor function. The melatonin rhythm is also thought to be an indication of circadian rhythmicity. The nocturnal production of melatonin was studied in patients with depression and panic disorder and in control subjects. Midnight concentrations of melatonin in eleven depressed patients were significantly lower than 18 control subjects (27.1 +/- 5.1 pg/ml compared with 51.6 +/- 4.1 pg/ml; p less than 0.02, t-test). These data support previous reports of reduced melatonin synthesis in depressive illness. In the first report of patients with panic disorders, significantly lower midnight levels of melatonin were found compared with controls (28.4 +/- 6.4 pg/ml versus 51.6 +/- 4.1 pg/ml, p less than 0.02, t-test). In subsequent investigations this finding was confirmed, measuring melatonin levels over the initial phase of synthesis (i.e. 20h00 to 24h00). In these samples the melatonin rhythm also seemed to be delayed. These findings are discussed in terms of beta-receptor function and circadian rhythm alterations in affective disorders.