Platelet [3H]-imipramine binding according to DSM-III subtypes of depression

The question of the previously reported changes in the density of high-affinity binding sites for [3H]-imipramine (IMI) in platelets from depressed patients was reexamined among the different diagnostic subtypes of depression according to the DSM-III classification and taking into account the possible influence of the low-affinity binding site. Using a least-square computer-assisted analysis, a precise determination of the [3H]-IMI binding parameters exclusively in relationship to the high-affinity site was performed in 46 untreated depressed patients and compared to 35 healthy controls. The results revealed a clear and highly significant 22% decrease in the maximal density (Bmax) of [3H]-IMI binding in all of the depressed patients compared to controls with no change in affinity values. Considering the diagnostic subgroups, we found that all the bipolar patients, the depressed as well as the euthymic or manic ones, had very low Bmax values and that some of them also exhibited an unusual low-affinity binding. Mean Bmax of the unipolar and dysthymic patients significantly decreased when compared to controls, although the Bmax values showed a large variability. Only dysthymic patients presented Bmax values which were significantly associated to symptom severity as assessed by the Hamilton Depression Rating Scale scores. Our results confirm the lower density of platelet [3H]-IMI binding in affective disorders, particularly in bipolar patients, and also suggest that this biological parameter is a trait marker in bipolar depression and a state marker in dysthmic disorder.