Objective: We aimed to evaluate the role and the relations between peripheral platelet serotonin content, blood plasma serotonin concentration and the function of platelet α2-adrenergic receptors (α2-AR) as potential state or trait biomarkers for recurrent depressive disorder (RDD).
Methods: 26 drug-free patients with life-long RDD and 31 healthy controls were included in the study. Several methodological improvements in blood collection and platelet isolation were implemented following the present standards in Haematology and Light transmission aggregometry.
Results: Our results have shown lower platelet serotonin content, higher plasma serotonin concentration and desensitization of platelet α2-AR in patients with RDD. The variables were found heterogeneous and mainly influenced by the clinical characteristics of the current episode. High amplitude of the α2-AR correlated with severe anxious symptoms and high platelet serotonin content (as well as low plasma serotonin levels) were associated with psychotic symptoms.
Conclusions: The evaluated peripheral markers reflect only state (but not trait) abnormalities in patients with current severe episode of RDD. The observed peripheral α2-AR and serotonin abnormalities are mutually not related and they are probably triggered by different mechanisms.
Keywords: Serotonin; life-long depression; platelets; recurrent depression; state markers; α2-AR.