Background: Hypersensitivity of brain serotonin receptors has been proposed as a causal mechanism in the pathophysiology of panic disorder. This theory can be tested, using serotonergic stimulation of the HPA axis. Up to now, plasma cortisol has generally been used as the outcome measure in such studies. Assessment of salivary cortisol is a non-invasive alternative to measure HPA axis activity.
Method: Salivary cortisol levels were measured in 24 panic disorder patients and 24 healthy volunteers, following ingestion of 200 mg L-5-hydroxytryptophan or placebo.
Results: A significant rise in cortisol was observed in both patients and controls following ingestion of L-5-hydroxytryptophan. No such effects were seen in the placebo condition.
Conclusion: The results show that L-5-hydroxytryptophan stimulated salivary cortisol is a useful probe of serotonin function in healthy volunteers as well as panic disorder patients, and provide some evidence against a serotonin receptor hypersensitivity in panic disorder.