Effects of combined administration of L-tryptophan and tricyclic antidepressants on alpha 2- and beta-adrenoceptors and monoamine levels in rat brain.

In order to test whether co-administration of a serotonin precursor with antidepressant drugs could potentiate the effects of the antidepressants on monoamines or adrenoceptors in rat brain, L-tryptophan (20 mg/kg) was administered to rats daily for 7 or 15 days, either alone or in combination with desipramine (10 mg/kg) or amitriptyline (10 mg/kg). After treatment with L-tryptophan for 7 days, increases were observed in rat hypothalamic and frontal cortex 5-hydroxy-3-indoleacetic acid levels as well as in hypothalamic dopamine and nucleus accumbens 3,4-dihydroxyphenylacetic acid levels. After 15 days, hippocampal beta-adrenoceptor density was found to be decreased. There was no evidence of potentiation of desipramine or amitriptyline action when L-tryptophan was administered in combination with the antidepressants. On the contrary, the antidepressants appeared to interact with L-tryptophan to reduce its effects.