Circadian rhythm of salivary serotonin in patients with major depressive disorder.

OBJECTIVES: The present study aimed to explore the circadian rhythm of salivary serotonin in patients with major depressive disorder before and after treatment with fluoxetine and its relationship with clinical therapeutic effect.

METHODS: This study investigated salivary serotonin in 13 outpatients with major depressive disorder and age- and sex-matched healthy controls. Depressed patients received six weeks fluoxetine treatment (20 mg/day), saliva was collected before and four weeks after treatment. A total of 8 time-point salivary serotonin was measured across the whole day. Multi-oscillator cosinor model was used to fit the rhythms.

RESULTS: Serotonin concentration in saliva ranged from 0.32 ng/ml to 9.62 ng/ml. Salivary serotonin showed prominent circadian rhythm in 91% depressed patients and 92% healthy subjects. Circadian amplitude tend to be higher after fluoxetine treatment in depressed patients, so as the ultradian cycle amplitude. The serotonin circadian amplitude (After minus Before) was positively correlated with the decrease of Zung Self-Rating Depression Scale(SDS) scores at day 42 whereas there was no such correlation at day 28. There was no significant difference in the parameters of mesor, acrophase, harmonic and area under curve among three groups.

CONCLUSIONS: Salivary serotonin in patients with major depressive disorder showed clear circadian rhythm. The relationship between the increase of salivary serotonin amplitude and clinical response deserve further study.

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