Platelet alpha 2-adrenergic receptor sensitivity in major depressive disorder.

We have investigated the functioning of alpha 2-adrenergic receptors in patients with major depressive disorder by measuring the specific binding of 3H-yohimbine, an alpha 2-adrenergic receptor antagonist, to platelet membranes. Bmax and Kd values for platelet 3H-yohimbine binding were normal in unmedicated patients with major depressive disorder, and did not correlate with scores on the Hamilton rating scale for depression. Platelet alpha 2-adrenergic antagonist sites were also unchanged in number or affinity in depressed patients after long-term treatment with a variety of antidepressant medications.