Antidepressants and liver tryptophan pyrrolase activity

Abstract

Tricyclic antidepressants were found to diminish liver tryptophan pyrrolase activity in rats. Neuroleptics and anticholinergics, used for comparison, did not change the enzyme activity. No effects of imipramine were observed in vitro nor in adrenalectomized animals. Imipramine did not influence tryptophan or hydrocortisone induction of tryptophan pyrrolase. Antidepressants in doses which lower the enzyme activity also lowered blood plasma concentration of 11-hydroxycorticosteroids. This effect may be responsible for inhibition of tryptophan pyrrolase activity by antidepressants. Inhibitors of monoamine oxidase did not decrease liver tryptophan pyrrolase activity in rats and mice but suppressed tryptophan induction of this enzyme. The possible relations between reduction by antidepressants of liver tryptophan pyrrolase activity and enhanced serotonin synthesis in the central nervous system and the thymoanaleptic effect are discussed.