Differential 3H-imipramine platelet binding in patients with panic disorder and depression.

3H-Imipramine (3H-IMI) binding to platelet membranes was measured in 19 patients with agoraphobia with panic attacks, 9 patients with major depression, and 22 healthy subjects. In comparison to healthy subjects, the maximal number of binding sites (Bmax) was significantly decreased in depressed patients but not in panic disorder patients, and the apparent affinity of binding was slightly decreased in depressed patients but not in panic disorder patients. The Bmax and Kd of 3H-IMI platelet binding did not differ between panic disorder patients with and without a history of a major depressive episode. Thus, 3H-IMI platelet binding is clearly different in patients with panic disorder compared to those with an active depression. Because 3H-IMI binding is associated with the serotonin reuptake site in platelet and brain membranes, these findings give further support to abnormalities in serotonergic function in patients with major depression.