Platelet serotonin transporter function after short-term paroxetine treatment in patients with panic disorder

Dysfunctions in serotonin neurotransmission have been implicated in some psychiatric disorders, and in particular, altered serotonin transporter function has been noted in panic disorder. In this study, the authors compared platelet [3H]serotonin uptake parameters, including maximum velocities (Vmax) and affinity constants (Km), in patients with panic disorder not undergoing treatment (n = 21) and in healthy subjects (n = 20). Vmax and Km values were re-examined after 12 weeks of paroxetine treatment. Values of Vmax and Km were lower in panic disorder patients at baseline than in healthy subjects. After treatment, Km normalized in panic patients, whereas Vmax did not change. A significant inverse correlation was found between increased Km and changes in anxiety levels. These results support a hypothesis of serotonergic transporter abnormalities in panic disorder, and suggest that increased Km values of platelet serotonin transporters parallel clinical improvement after short-term pharmacotherapy in panic disorder.