Platelet alpha-adrenergic binding and biochemical responsiveness in depressed patients and controls

In a study of platelet α₂-adrenergic receptor number in depressed patients, binding of tritiated dihydroergocriptine (³H-DHE) to platelet membranes was measured in 23 depressed patients and 51 controls. To examine the functional responsiveness of the platelet α₂-adrenergic receptor, basal cyclic adenosine 3',5'- monophosphate (cAMP) production, prostaglandin E₁ (PGE₁) stimulation of cAMP production, and norepinephrine (NE) inhibition of PGE₁-stimulated cAMP production were measured in 23 depressed patients and 53 control subjects. Finally, plasma NE concentration was measured in 20 patients to explore the possible relationship between this endogenous agonist and platelet α₂-adrenergic receptor function. ³H-DHE binding to platelet membranes was significantly increased in the depressed patients compared to control subjects. Both the PGE₁-stimulated cAMP response and the inhibition of this response by NE were significantly reduced in the depressed patients compared to the control subjects. Thus, an apparent dissociation between α₂-adrenergic receptor binding and functional responsiveness was observed. Plasma NE concentrations were neither significantly different in the depressed patients than in the controls nor correlated with any of the measures of cAMP responsiveness. They were, however, significantly negatively correlated with ³H-DHE binding in depressed patients with adequate PGE₁ stimulation of cAMP production.