Interaction in the cerebral metabolism of the biogenic amines. Effect of phenelzine on this interaction.

1. Chronic administration of phenelzine to dogs caused the concentrations of homovanillic acid (HVA) in c.s.f. from both the lateral ventricle and cisterna magna to fall to new low levels at which they were maintained.2. After 10-12 days treatment with phenelzine the caudate nucleus had elevated concentrations of dopamine and 3-methoxytyramine and lowered concentrations of 3,4-dihydroxyphenylacetic acid and HVA.3. Intravenous administration of tryptophan to dogs pretreated with phenelzine caused in c.s.f. an increase in the concentrations of HVA and in the caudate nucleus a decrease in dopamine concentration and an increase in the concentrations of its metabolites, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid and HVA.4. A model is proposed for the cerebral metabolism of dopamine and some of the points at which tryptophan and its metabolites may interact with dopamine metabolism are discussed.