Stimulatory Effects of L-5-Hydroxytryptophan on Postdexamethasone β-Endorphin Levels in Major Depression

Recently it has been shown that acute administration of 200 mg L-5-hydroxytryptophan (L-5-HTP) PO may increase post-dexamethasone (DST) adrenocorticotropic hormone (ACTH) and cortisol levels in major, but not minor, depressed subjects. This study aimed to examine the effects of 200 mg L-5-HTP PO on post-DST β-endorphin levels in the same depressed subjects. It was found that in major, but not minor, depressed subjects, L-5-HTP significantly increased post-DST β-endorphin concentrations as compared to placebo. The L-5-HTP-induced post-DST β-endorphin responses were significantly higher in major than in minor depressed subjects. There was a significant and positive relationship between L-5-HTP-induced post-DST β-endorphin and ACTH or cortisol responses. There was a significant and positive relationship between L-5-HTP-induced post-DST β-endorphin values and the Hamilton Depression Rating Scale (HDRS) score. The results show that the acute administration of L-5-HTP may increase the escape of β-endorphin secretion from suppression by dexamethasone in major, but not minor, depression.