GPER-1 agonist G1 induces vasorelaxation through activation of epidermal growth factor receptor-dependent signalling pathway

Objectives The G protein-coupled oestrogen receptor-1 (GPER-1) agonist G1 induces endothelium-dependent relaxation. Activation of the epidermal growth factor (EGF) receptor leads to transduction of signals from the plasma membrane for the release of nitric oxide. We tested the hypothesis that G1 induces endothelium-dependent vasorelaxation through activation of the EGF receptor. Methods Rat aortic rings were mounted in organ baths. After pretreatment with various inhibitors, aortic rings contracted with 11,9-epoxymethano-prostaglandin F_2α or KCl were subjected to relaxation by G1. Key findings G1 induced endothelium-dependent vasorelaxation, which was attenuated by pretreatment with either _L-N^ω-nitroarginine methyl ester (_L-NAME), an inhibitor of nitric oxide synthase, or (3aS,4R,9bR)-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H- cyclopenta[c]quinoline HB-EGF, heparin-binding EGF-like growth factor, a GPER-1 antagonist. Neither a general oestrogen receptor antagonist, ICI 182 780, nor a selective oestrogen receptor-α antagonist, methyl-piperidino-pyrazole dihydrochloride (MPP), had an effect on G1-induced vasorelaxation. However, pretreatment with EGF receptor blockers, AG1478 or DAPH, resulted in attenuated G1-induced vasorelaxation. In addition, pretreatment with Src inhibitor 4-amino-3-(4-chlorophenyl)-1-(t-butyl)-1H-pyrazolo[3,4-d]pyrimidine, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine or Akt inhibitor VIII also resulted in attenuated vascular relaxation induced by the cumulative addition of G1. However, neither phosphatidylinositol-3 kinase inhibitors LY294002 and wortmannin nor an extracellular signal-regulated kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto) butadiene monoethanolate had effect on vascular relaxation induced by the cumulative addition of G1. Conclusions G1 induces endothelium-dependent vasorelaxation through Src-mediated activation of the EGF receptor and the Akt pathway in rat aorta.