title: GPCR dimerization in brainstem nuclei contributes to the development of hypertension.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  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-Ala(2) , MePhe(4) , Gly(5) -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
  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.
authors.affiliation: Institute of Clinical Medicine, National Cheng-Kung University, Tainan, Taiwan; Department of Anesthesiology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan; Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan.
authors.forename: Gwo-Ching
authors.initials: GC
authors.lastname: Sun
authors.forename: Wen-Yu
authors.initials: WY
authors.lastname: Ho
authors.forename: Bo-Rung
authors.initials: BR
authors.lastname: Chen
authors.forename: Pei-Wen
authors.initials: PW
authors.lastname: Cheng
authors.forename: Wen-Han
authors.initials: WH
authors.lastname: Cheng
authors.forename: Mei-Chi
authors.initials: MC
authors.lastname: Hsu
authors.forename: Tung-Chen
authors.initials: TC
authors.lastname: Yeh
authors.forename: Michael
authors.initials: M
authors.lastname: Hsiao
authors.forename: Pei-Jung
authors.initials: PJ
authors.lastname: Lu
authors.forename: Ching-Jiunn
authors.initials: CJ
authors.lastname: Tseng
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000008:administration & dosage / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism*; D019281:Dimerization; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000008:administration & dosage / Q000494:pharmacology; D006973:Hypertension / Q000139:chemically induced / Q000378:metabolism*; D008297:Male; D008845:Microinjections; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D009842:Oligopeptides / Q000378:metabolism; D055503:Protein Multimerization; D051381:Rats; D011918:Rats, Inbred SHR; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009842:Oligopeptides; D018341:Receptors, Adrenergic, alpha-2; D017450:Receptors, Opioid, mu; C105293:endomorphin 1; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-