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

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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 Y(1) and Y(2) receptors in the nucleus tractus solitarii (NTS) of rats. However, the precise mechanisms involved in this NPY-mediated action remained unclear. Effects of a selective antagonist of Y(1) 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. Unilateral microinjection of exogenous NPY (4.65pmol/60nL) into the NTS of urethane-anesthetized Wistar-Kyoto rats markedly decreased blood pressure and heart rate. Microinjection of the Y(1) receptor antagonist BIBP3226 or the G(i) /G(o) -protein inhibitor, Pertussis toxin, into the NTS attenuated these NPY-induced hypotensive effects. A selective Y(1) 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 Ser(1177) . Pretreatment of the NTS with an eNOS inhibitor, but not a nNOS inhibitor, attenuated the NPY-induced hypotensive effects. Together, these results suggested that NPY-induced depressor effects were mediated by activating NPY Y(1) receptor-PKC-ERK-RSK-eNOS and Ca(2+) -eNOS signalling pathways, which are involved in regulation of blood pressure in the NTS.