Background and Purpose μ-Opioid receptors, pro-opiomelanocortin and pro-enkephalin are highly expressed in the nucleus tractus solitarii (NTS) and μ receptor agonists given to the NTS dose-dependently increased BP. However, the molecular mechanisms of this process remain unclear. In vitro, μ receptors heterodimerize with α2A-adrenoceptors. We hypothesized that α2A-adrenoceptor agonists would lose their depressor effects when their receptors heterodimerize in the NTS with μ receptors. Experimental Approach We microinjected μ-opioid agonists and antagonists into the NTS of rats and measured changes in BP. Formation of μ receptor/α2A-adrenoceptor heterodimers was assessed with immunofluorescence and co-immunoprecipitation methods, along with proximity ligation assays. Key Results Immunofluorescence staining revealed colocalization of α2A-adrenoceptors and μ receptors in NTS neurons. Co-immunoprecipitation revealed interactions between α2A-adrenoceptors and μ receptors. In situ proximity ligation assays confirmed the presence of μ receptor/α2A-adrenoceptor heterodimers in the NTS. Higher levels of endogenous endomorphin-1 and μ receptor/α2A-adrenoceptor heterodimers were found in the NTS of hypertensive rats, than in normotensive rats. Microinjection of the μ receptor agonist [D-Ala2, MePhe4, Gly5-ol]-enkephalin (DAMGO), but not that of the α2A-adrenoceptor agonist guanfacine, into the NTS of normotensive rats increased μ receptor/α2A-adrenoceptor heterodimer formation and BP elevation. The NO-dependent BP-lowering effect of α2A-adrenoceptor agonists was blunted following increased formation of μ receptor/α2A-adrenoceptor heterodimers in the NTS of hypertensive rats and DAMGO-treated normotensive rats. Conclusions and Implications Increases in endogenous μ receptor agonists in the NTS induced μ receptor/α2A-adrenoceptor heterodimer formation and reduced the NO-dependent depressor effect of α2A-adrenoceptor agonists. This process could contribute to the pathogenesis of hypertension.
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