Molecular mechanisms of peripheral N-Methyl-D-Aspartate receptor mediated pressor response.

摘要

The primary goal of this study was to characterize the N-Methyl-D-Aspartate (NMDA) receptor within the cardiovascular system and elucidate the molecular mechanisms involved in peripheral NMDA receptor-mediated pressor response. The central hypothesis of this study was "peripheral NMDA receptor signaling plays a pivotal role in the acute cardiovascular effects of ethanol". The data provide the first evidence that peripheral NMDAR activation mediates dose-dependent pressor responses in conscious, unrestrained rats. The results indicated that the pressor response was peripherally mediated because it persisted following ganglionic blockade with hexamethonium, and was attenuated by NMDAR antagonists, AP-5 or R-(+)-HA-966. Ex vivo studies revealed enhanced nitric oxide (NO) and reactive oxygen species (ROS) generation in vascular tissues collected at the peak of the NMDAR-mediated pressor response. The in vivo findings using selective pharmacological interventions, corroborated with complementary ex vivo and in vitro studies supported a causal role for nNOS-(NO)-dependent ROS generation in the NMDA-evoked pressor response. Additional studies tested the hypothesis that NMDAR-mediated enhancement of vascular phosphatidylinositol 3-kinase (PI3K)/Akt-protein kinase C (PKC) signaling underlies nNOS and NADPH oxidase (Nox) activation leading to NO and ROS generation and ultimately the pressor response. The pharmacological and ex vivo findings demonstrated that these interventions significantly attenuated the increases in blood pressure and vascular NO production evoked by peripheral NMDAR activation. NMDA-mediated increases in vascular Nox activity, and the abrogation of this increase in apocynin, wortmannin or chelerythrine pretreated rats was observed. These findings suggested that the vascular PI3K/Akt-PKC signaling cascade partially mediates nNOS (NO) and Nox (ROS) activation, which leads to the peripheral NMDAR-mediated pressor response. Further, the present study yields new insight into acute ethanol-induced modulation of peripheral (vascular) NMDAR signaling in conscious rats. Our pharmacological findings indicate that ethanol has the ability to attenuate the peripheral NMDAR-mediated responses and the ex vivo studies provided support for the involvement of oxidative stress (ROS) in peripheral NMDA-evoked pressor responses. Despite the ability of ethanol to increase vascular ROS, pretreatment with ethanol attenuated the NMDA-evoked oxidative stress and the associated pressor response. Finally, in the presence of partial peripheral NMDAR blockade with AP-5, ethanol produced a modest hypotensive response. These findings support a protective role for ethanol against NMDA-mediated oxidative stress. Collectively, these studies provide insight into identifying signaling pathway(s) triggered by peripheral NMDAR in conscious animals and potential contribution of NMDAR signaling to the acute cardiovascular effects of ethanol.