Imidazoline and α2a-adrenoceptor binding sites in postmenopausal women before and after estrogen replacement therapy

Background: Platelet α2A-adrenoceptors (α2AAR) and imidazoline binding sites (subtype I1) have been proposed as peripheral markers of brain stem receptors that mediate sympathetic outflow and are reported to be elevated in major depression. Methods: In our study, p[125I]-iodoclonidine was used to assess platelet α2AAR and I1 binding sites in healthy postmenopausal women (n = 34) compared with healthy women of reproductive age (n = 26). Receptor determinations were repeated in 19 postmenopausal women following 59–60 days of estrogen replacement therapy (ERT; 0.1 mg estradiol transdermal patches). Results: I1 binding sites were twofold higher in platelets of postmenopausal women compared with women of reproduction age but were down-regulated (normalized) after 59–60 days of ERT. All other binding parameters, including platelet α2AAR density, were not different between groups nor were they changed after ERT. Platelet I1 densities after 59–60 days of ERT were positively correlated with plasma luteinizing hormone concentrations. Conclusions: It is suggested that increased imidazoline binding sites might be associated with mood and behavioral changes in postmenopausal women.