An inverse correlation between serum levels of desmethylimipramine and melatonin-like immunoreactivity in DMI-responsive depressives

The relationship between plasma levels of the tricyclic antidepressant desmethylimipramine (DMI) and plasma levels of melatonin-like immunoreactivity was studied in 32 endogenously depressed patients. An inverse correlation between plasma levels of DMI and plasma levels of melatonin-like immunoreactivity was found in the group of clinical responders to the chronic administration of the drug. The nonresponders had higher levels of melatonin-like immunoreactivity at comparable levels of DMI. This findings is consistent with the hypothesis that chronic high plasma levels of DMI may down-regulate the β-adrenergic receptors in man. However, some other homeostatic mechanisms may be involved in the clinical response.