Alpha 2-adrenergic receptors in platelet membranes of depressed patients: increased affinity for 3H-yohimbine.

Specific binding to alpha 2-adrenergic receptors was studied in the platelets of 31 patients with major depressive disorder and 18 normal controls using the selective antagonist 3H-yohimbine. Receptor density for depressed patients (Bmax = 88 +/- SD 45.1 fmoles/mg) was not significantly lower than that for controls (124 +/- SD 78.1 fmoles/mg). The affinity of the receptor for yohimbine was significantly greater in depressed patients (Kd = 1.05 +/- SD 0.47 nM) than in controls (Kd = 1.47 +/- SD 0.63 nM). This is consistent with the hypothesis of increased alpha 2-adrenergic receptor sensitivity in depressive disorders. Past studies of alpha 2-adrenergic receptors on platelets are reviewed, and the importance of designing studies with sufficient statistical power is discussed.