Tritiated imipramine binding to platelets in manic subjects

We studied 21 patients with bipolar affective disorder and 25 healthy controls in order to determine if tritiated imipramine binding to platelets distinguished the manic from the depressed phase of bipolar disorder. Depressed patients had a significantly lower mean Bmax value (754 +/- 149 fmole/mg protein) than the manic and control groups (1112 +/- 248 and 1237 +/- 201 fmole/mg protein, respectively), which did not differ from each other. These differences could not be attributed to differences in age, sex, menopausal status, the presence of psychotic features or medication history among the subject groups. These findings confirm that decreased imipramine binding to platelets is a state marker for bipolar depression and not a trait marker of bipolar disorder.