The effect of intravenous L-tryptophan on prolactin and growth hormone and mood in healthy subjects.

In order to assess the effects of increased central nervous system serotonergic function in humans on prolactin (PRL), growth hormone (GH) and mood, intravenous L-tryptophan (TRP) was administered to ten healthy subjects. The TRP infusion induced robust increases in PRL in all ten subjects. A significant increase in GH concentration was also observed, although the response was more variable. The subjects reported feeling significantly more high, mellow, and drowsy following the TRP infusion in comparison to placebo. These findings indicate an important role for serotonin in PRL and GH secretion, as well as in mood regulation. The intravenous TRP challenge may be of use in the study of serotonergic function in a variety of neurologic and psychiatric diseases.