Central hypotensive effects of neuropeptide y are modulated by endothelial nitric oxide synthase after activation by ribosomal protein S6 kinase

Background and purpose: Neuropeptide Y (NPY) is a 36-amino acid polypeptide found abundantly in the central and peripheral nervous systems. NPY exerts a potent depressor effect via the activation of both Y₁ and Y ₂ receptors in the nucleus tractus solitarii (NTS) of rats. However, the precise mechanisms involved in this NPY-mediated action remained unclear. Experimental approach: Effects of a selective antagonist of Y₁ receptors, a PKC inhibitor, a PI3 kinase inhibitor, a NOS inhibitor, an endothelial NOS (eNOS)-selective inhibitor, a neuronal NOS (nNOS)-specific inhibitor or a MAPK inhibitor, on responses to microinjection of NPY into the NTS of Wistar-Kyoto rats were studied to determine the underlying mechanisms. Blood pressure and heart rate were measured and, in NTS, protein phosphorylation assessed by immunohistochemical techniques. Key results: Unilateral microinjection of exogenous NPY (4.65 pmol/60 nL) into the NTS of urethane-anesthetized Wistar-Kyoto rats markedly decreased blood pressure and heart rate. Microinjection of the Y₁ receptor antagonist BIBP3226 or the G_i/G_o-protein inhibitor, Pertussis toxin, into the NTS attenuated these NPY-induced hypotensive effects. A selective Y₁ receptor agonist increased expression of ERK1/2, ribosomal protein S6 kinase (RSK) and the phosphorylation of eNOS. RSK also bound directly to eNOS and induced its phosphorylation at Ser¹¹⁷⁷. Pretreatment of the NTS with an eNOS inhibitor, but not a nNOS inhibitor, attenuated the NPY-induced hypotensive effects. Conclusions and implications: Together, these results suggested that NPY-induced depressor effects were mediated by activating NPY Y₁ receptor-PKC-ERK-RSK-eNOS and Ca²⁺-eNOS signalling pathways, which are involved in regulation of blood pressure in the NTS.