Plasma melatonin during desmethylimipramine treatment: evidence for changes in noradrenergic transmission.

Plasma melatonin was used to determine overall beta-adrenergic transmission through pineal neuro-effector junctions during desmethylimipramine (DMI) treatment in 10 normal subjects. Changes in plasma melatonin indicated that an initial increase in noradrenaline (NA) transmission produced by DMI was counteracted by adaptive changes which restored transmission to normal by the third week of treatment. A 'rebound' increase in NA transmission was seen on DMI withdrawal. The results suggest that the adaptive changes which occur in NA synapses during DMI treatment do not, as has been proposed, decrease NA transmission below normal levels, but instead restore homeostasis in the presence of the drug.