Effect of psychotrophic drugs on [14C]tryptophan metabolism in cultured rat pineal gland.

A potentiated production of [14C]melatonin ([14C]Mt) with a simultaneous decline in [14C]serotonin ([14C]5-HT) conversion to its final metabolite [14C]5-hydroxyindole acetic acid ([14C]5-HIAA) was recorded in a rat pineal medium cultured with [14C]tryptophan and either a neuroleptic [haloperidol (HAL) or chloropromazine (CPZ)] or an antidepressant [desipramine (DIP)] drug. A difference between the pharmacological groups of drugs was evident only in [14C]5-HT levels, which were found significantly elevated in the presence of the neuroleptic HAL and reduced in the presence of the tricyclic antidepressant DIP. A parallel trend was observed in norepinephrine (NE)-induced [14C]tryptophan metabolism in the pineal culture medium. All three drugs tested brought about further enhancement of NE-induced synthesis of MT; HAL produced an elevated, but DIP a reduced, level of [14C]5-HT, compared to the NE-induced value.