Tritiated imipramine binding distinguishes among subtypes of depression.

We studied 45 depressed patients and 20 healthy controls in order to determine if tritiated imipramine binding distinguished among subtypes of primary major depressive disorder. Mean (+/- standard deviation) values for maximal concentration of tritiated imipramine binding sites on platelet membranes were significantly lower in patients with bipolar and familial pure depressive disease (754 +/- 149 and 870 +/- 241 femtomoles [fmole]/mg of protein, respectively) than in patients with depressive spectrum and sporadic depressive disease (1,236 +/- 241 and 1,188 +/- 325 fmole/mg of protein, respectively), neither of which differed from healthy controls (1,238 +/- 201 fmole/mg of protein). Multiple linear regression analysis revealed that these differences could not be attributed to differences in age, sex, Hamilton Rating Scale score, presence of psychotic features, hospitalization status, or medication history. This association of a biological finding with distinct clinically defined subtypes of depression may lead to a classification of affective disorders useful in further research.