Decreased platelet alpha-2 adrenoceptor density in major depression: Effects of tricyclic antidepressants and fluoxetine

Background: It has been suggested that major depression is accompanied by a subsensitivity of central α2-adrenoceptors (α2-ARs) and, consequently, by an impaired negative feedback on the presynaptic catecholaminergic neuron, which, in turn, may induce a disinhibition of noradrenergic output and norepinephrine release in response to any activation. Methods: The maximum number of platelet binding sites (Bmax) and their affinity for [³H]- rauwolscine, a selective α2-AR antagonist, were measured in unmedicated and medicated major depressed patients and in normal volunteers. Specific binding was defined as that inhibited by idazoxan, another α2-AR antagonist. Results: Unmedicated major depressed patients had significantly decreased platelet [³H]-rauwolscine binding Bmax values compared to normal volunteers. [³H]-rauwolscine binding K(d) values did not differ significantly between unmedicated major depressed patients and normal controls. [³H]-rauwolscine binding K(d) values were significantly higher in depressed patients treated with tricyclic antidepressants than in unmedicated patients. Subchronic treatment with fluoxetine did not significantly alter either [³H]- rauwolscine binding Bmax or K(d) values. [³H]-rauwolscine binding Bmax values were significantly greater in men than in women. Conclusions: The results suggest that i) major depression is accompanied by decreased platelet α2-AR density; and that ii) subchronic treatment with tricyclic antidepressants, but not fluoxetine, results in a decreased affinity of rauwolscine for platelet α2-ARs.