Reduced Bmax of [3H]-imipramine binding to platelets of depressed patients free of previous medication with 5HT uptake inhibitors.

The high-affinity binding sites for [3H]-imipramine (IMI) present in human platelets are associated with the neuronal uptake system for 5HT. It was recently demonstrated that previous antidepressant therapy with drugs which inhibit 5HT uptake could down-regulate [3H]-IMI binding and that this effect could persist up to 1 month after the end of treatment. We therefore re-examined the reported differences in Bmax of [3H]-IMI binding in platelets between control and depressed untreated patients, to evaluate the residual influence of previous antidepressant medication. The saturation characteristics of [3H]-IMI binding were compared in platelets from 17 depressed patients carefully selected according to previous antidepressant therapy and washout period, who were closely matched, for age and sex, with a group of control healthy volunteers. The results reveal a significant decrease by 47% in the Bmax of [3H]-IMI binding in platelets of untreated depressed patients when compared with controls. There was no significant modification of Kd values for platelet [3H]-IMI binding between the depressed and the control groups. Our results support the view that platelet [3H]-IMI binding is a useful tool as a biological marker in depression.