Increase in urinary beta-phenylethylamine preceding the switch from mania to depression: a "rapid cycler".

beta-Phenylethylamine (PEA), an endogenous amphetamine-like substance, is known to increase central catecholamine metabolism and has been hypothesized to have an etiological importance in affective disorders. A case of a "rapid cycler" who showed increased PEA excretion before the switch from mania into depression was reported. In order to evaluate whether the patient's cycle of moods could be prevented by modulating PEA metabolism, carbidopa (peripheral dopa decarboxylase inhibitor) and safrazine (monoamine oxidase inhibitor) were administered during the manic and depressive periods of the patient, respectively. Carbidopa exacerbated the manic symptoms, although it decreased PEA excretion. Safrazine induced the increase of PEA without any beneficial effect on the depressive symptoms. These findings may suggest that PEA plays the role of a biochemical trigger in the switch mechanism of a rapid cycler, especially in the switch from mania to depression.