Influences on cortisol and noradrenergic turnover of healthy controls and depressed patients during L-tryptophan loading

To investigate the interrelationships between the noradrenergic and serotonergic systems and the hypothalamic-pituitary-adrenal (HPA) axis, we measured the excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG) and free cortisol (UFC) in 24-h urine both before and after loading with 2 g L-tryptophan (L-TRP) orally in 24 healthy controls and 33 depressed patients categorized according to DSM-III. Loading with L-TRP reduced MHPG excretion significantly by 56% in major depressives, whereas in healthy controls and in minor depressives no significant effects were observed. Although basal MHPG did not differ among these study groups, loading with L-TRP resulted in MHPG excretion in major depressives being significantly lower than in healthy controls and minor depressives. Loading with L-TRP increased UFC significantly by 49% only in major depressives with associated features. After L-TRP those patients exhibited significantly increased UFC as compared with all other depressives and controls, whereas basal UFC values did not differ among the study groups. In baseline conditions there were no significant correlations between MHPG and UFC excretion.