Tritiated imipramine binding to platelets is decreased in patients with agoraphobia

Controversy exists regarding the relationship between anxiety states and major depression. We studied the binding of tritiated imipramine to platelet membranes in order to determine if patients with agoraphobia and panic attacks differed from depressed subjects or healthy volunteers on this biological parameter. Mean (+/- SD) Bmax and Kd values were significantly lower in patients with agoraphobia and panic attacks (787 +/- 276 fmole/mg protein and 0.35 +/- 0.14 nM, respectively) than in healthy volunteers (1237 +/- 201 fmole/mg protein and 0.71 +/- 0.37 nM, respectively). In addition, patients with agoraphobia and panic attacks had binding parameters that were similar to those of patients with bipolar or familial pure depressive disorder, but significantly lower than those of patients with depressive spectrum or sporadic depressive disorder. These findings have implications for both the nosology and pathophysiology of anxiety disorders.