Blunted ACTH and cortisol response to afternoon tryptophan infusion in euthymic bipolar patients

The serotonin precursor tryptophan was used to test neuroendocrine responses in remitted bipolar patients and controls. Tryptophan was administered in the afternoon when spontaneous cortisol secretion is lower than in the morning. Following pilot studies at various doses, 50 mg/kg L-tryptophan was given i.v. over 20 min to 11 patients and 14 controls. Controls demonstrated cortisol release, whereas the response curve for patients was indistinguishable from placebo. Differences between groups were significant at 15, 30, and 45 min. Changes in adrenocorticotropic hormone were consistent with those in cortisol. Prolactin and growth hormone levels increased in both patients and controls following tryptophan. Higher doses caused gastrointestinal upset in some subjects.