Alpha 2-adrenoceptor levels on platelets of patients with major depressive disorders.

3H-p-Aminoclonidine binding to platelets of patients with primary, unipolar major depressive disorder was compared to that of a normal healthy control population. The variances of platelet alpha 2-adrenoceptor Kd and Bmax values in patients were significantly greater than in the control group. No significant difference could be demonstrated between the Kd values of the two different groups, but the Bmax value of the depressed group was significantly lower than that of controls. We propose that an abnormal platelet alpha 2-adrenoceptor density may be used as a biological marker for major depressive disorder.