BEHAVIORAL, NEUROENDOCRINE AND BIOCHEMICAL EFFECTS OF DIFFERENT DOSESOF 5-HTP IN PANIC DISORDER

To investigate the role of serotonin (5-HT) in the pathophysiology of panic disorder (PD) a challenge test with L-5-hydroxytryptophan (5-HTP ) was conducted. Seven patients suffering from PD and seven healthy co ntrols received an i.v. challenge with 10 mg, 20 mg and 40 mg 5-HTP an d placebo in random order on four different occasions. Before, during and until 2 h after 5-HTP administration anxious and depressive sympto matology was assessed. In addition, plasma levels of 5-HTP. cortisol, and 5-HIAA were measured at several timepoints. During and after infus ion of placebo or any of the different dosages of 5-HTP, none of the p atients or controls experienced a panic attack or showed an increase i n anxiety or depressive symptoms. There was a dose-related increase in side effects, like nausea, dizziness and fatigue. Only infusion with 40 mg 5-HTP led to an increase in plasma cortisol in both patients and controls. The observed increase in plasma cortisol level was higher f or patients compared to controls only at 30 min after infusion. In con clusion, stimulation of the serotonergic neuronal system by three diff erent dosages of 5-HTP did not induce panic or anxiety in PD patients and healthy controls. The 5-HT hypersensitivity hypothesis of PD could not be confirmed in the present study.