Intravenous L-5-Hydroxytryptophan in Normal Subjects: An Interdisciplinary Precursor Loading Study

L-5-hydroxytryptophan ethylester (Ro 3-5940), a new soluble form of this serotonin precursor, was administered to 26 healthy, non-depressed subjects after premedication with the peripheral decarboxylase inhibitor benserazide (Ro 4-6402) in a total of 51 infusions. Those conditions were chosen for the main trial which in a pre-trial investigation had proved to combine minimal side effects with clear central effects in particular the observed marked mood elevation after 1-5HTP. Using these standardized conditions of application, an interindividually similar pattern of the time course of substance effects could be shown, and convincing evidence was deducible for an objective mood elevating effect of 1-5HTP infusion. Amongst the most impressive results was the parallelity of the time course of mood changes and concomitant changes in serum growth hormone levels. Especially emphasized are the important questions of effectivity, specificity and clinical practicability or safety, which are essential for any precursor study. Arguments are presented supporting the assumption that primarily serotoninergic changes underlie these mood effects. In our opinion this mode of i.v. application of 1-5HTP represents a practicable strategy for investigating biochemical hypotheses as to serotonin mediated normal and deviant human behaviour, especially in affective disorders.