Platelet alpha 2 adrenoreceptors are decreased in number after antidepressant therapy.

Specific binding of 3H-clonidine to alpha 2 adrenoreceptors upon human blood platelet membranes is increased in patients with major depressive disorder (endogenous depression). Specific binding of 3H-yohimbine to the platelet adrenoreceptor is not altered in endogenously depressed patients. Other psychiatric disorders are not associated with alterations in the specific binding of either 3H-clonidine or 3H-yohimbine. In patients with severe congestive heart failure or with symptomatic coronary artery disease the number of platelet alpha 2 adrenoreceptors is actually decreased. Treatment of endogenously depressed patients with tricyclic antidepressants, lithium salts or electroconvulsive therapy results in a decrease in the number of alpha 2 adrenoreceptors on blood platelet membranes. These studies suggest that a supersensitivity of the alpha 2 adrenoreceptor might exist in patients with endogenous depression and that effective forms of therapy lead to a decrease in the number of neural alpha 2 adrenoreceptors which is reflected by a decrease in the number of these receptors upon blood platelet membranes.