Angiotensin-(1–7) in Paraventricular Nucleus Modulates Sympathetic Activity and Cardiac Sympathetic Afferent Reflex in Renovascular Hypertensive Rats

et al. (2012) Angiotensin-(1-7) in Paraventricular Nucleus Modulates Sympathetic Activity and Cardiac Sympathetic Afferent Reflex in Renovascular Hypertensive Rats. PLoS ONE 7(11): e48966. doi:10.1371/journal.pone.0048966 Angiotensin-(1-7) in Paraventricular Nucleus Modulates Sympathetic Activity and Cardiac Sympathetic Afferent Reflex in Renovascular Hypertensive Rats Ying Han 0 Hai-Jian Sun 0 Peng Li 0 Qing Gao 0 Ye-bo Zhou 0 Feng Zhang 0 Xing-Ya Gao 0 Guo-Qing Zhu 0 Luis Eduardo M. Quintas, Universidade Federal do Rio de Janeiro, Brazil 0 Key Laboratory of Cardiovascular Disease and Molecular Intervention, Department of Physiology, Nanjing Medical University , Nanjing, Jiangsu , China Background: Excessive sympathetic activity contributes to the pathogenesis and progression of hypertension. Enhanced cardiac sympathetic afferent reflex (CSAR) is involved in sympathetic activation. This study was designed to determine the roles of angiotensin (Ang)-(1-7) in paraventricular nucleus (PVN) in modulating sympathetic activity and CSAR and its signal pathway in renovascular hypertension. Methodology/Principal Findings: Renovascular hypertension was induced with two-kidney, one-clip method. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in sinoaortic-denervated and cervicalvagotomized rats with anesthesia. CSAR was evaluated with the RSNA and MAP responses to epicardial application of capsaicin. PVN microinjection of Ang-(1-7) and cAMP analogue db-cAMP caused greater increases in RSNA and MAP, and enhancement in CSAR in hypertensive rats than in sham-operated rats, while Mas receptor antagonist A-779 produced opposite effects. There was no significant difference in the angiotensin-converting enzyme 2 (ACE2) activity and Ang-(1-7) level in the PVN between sham-operated rats and hypertensive rats, but the Mas receptor protein expression in the PVN was increased in hypertensive rats. The effects of Ang-(1-7) were abolished by A-779, adenylyl cyclase inhibitor SQ22536 or protein kinase A (PKA) inhibitor Rp-cAMP. SQ22536 or Rp-cAMP reduced RSNA and MAP in hypertensive rats, and attenuated the CSAR in both sham-operated and hypertensive rats. Conclusions: Ang-(1-7) in the PVN increases RSNA and MAP and enhances the CSAR, which is mediated by Mas receptors. Endogenous Ang-(1-7) and Mas receptors contribute to the enhanced sympathetic outflow and CSAR in renovascular hypertension. A cAMP-PKA pathway is involved in the effects of Ang-(1-7) in the PVN. - Funding: This work was supported by Chinese National Natural Science Fund (81100182 & 31171095), Natural Science Foundation from Department of Education of Jiangsu Province (11KJB310002 & 10KJB310004), Science and Technology Foundation from Nanjing Medical University (2010NJMUZ23), and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Sympathetic activity is enhanced in patients with essential [1] or secondary hypertension [25] and various hypertensive models [610]. Excessive sympathetic activity contributes to the pathogenesis of hypertension and progression of organ damage [1113]. Intervention of the sympathetic activation is considered to be an antihypertensive strategy [1416]. Cardiac sympathetic afferent reflex (CSAR) is known as a positive-feedback, sympathoexcitatory cardiovascular reflex [17,18]. Previous studies in our lab have shown that the CSAR is enhanced in renovascular hypertensive rats [6,19] and spontaneously hypertensive rats (SHR) [10], which contributes to the sympathetic activation and hypertension [20,21]. Paraventricular nucleus (PVN) is an important component of the central neurocircuitry of the CSAR [22] and plays a major role in the integration of sympathetic outflow and cardiovascular activity via projections to the intermediolateral column (IML) of the spinal cord and the rostral ventrolateral medulla (RVLM) [23]. Angiotensin (Ang)-(17) is known as an important biological active peptide of reninangiotensin system (RAS) family. Angiotensinconverting enzyme 2 (ACE2) hydrolyzes Ang II or Ang I to Ang(17). Many of Ang-(17) effects are primarily mediated by Mas receptors [24] and are selectively blocked by its specific antagonist D-Alanine-Ang-(17) (A-779) [25]. Ang-(17) immunoreactive staining is present in the PVN [26] including parvocellular and magnocellular subdivisions [27]. The endogenous Ang-(17) level in the hypothalamus of rats is comparable to Ang I and Ang II [28]. The Mas receptors are expressed predominantly in the mouse and rat brain and particularly in the forebrain [29]. It has been reported that blockade of endogenous Ang-(17) by microinjection of A-779 into the PVN reduces renal sympathetic tone in normal rats [30]. Ang-(17) level in hypothalamus is increased in aortic coarctation-induced hypertensive rats [31]. However, it is not known whether Ang-(17) in the PVN is Systolic blood pressure (SBP), mean arterial pressure (MAP) and heart rate (HR) were measured with a pressure transducer in the right carotid artery under anesthesia. Values are expressed as mean 6 SE. * P,0.05 compared with the Sham rats. doi:10.1371/journal.pone.0048966.t001 involved in the excessive sympathetic activation and the enhanced CSAR in hypertension. It has been found that activation of Mas receptors by Ang-(17) increases intracellular cAMP level and activates protein kinase A (PKA), while inhibition of either adenylyl cyclase (AC) or PKA activity attenuates Ang-(17)-induced ERK1/2 activation in glomerular mesangial cells [32]. Ang-(17) inhibits vascular growth through the prostacyclin-mediated production of cAMP and activation of cAMP-dependent PKA [33]. These results show that the cAMP-PKA signaling pathway is involved in the activity of Ang-(17) and Mas receptors in some peripheral tissues. However, whether cAMP-PKA pathway in the PVN is involved in the CSAR and sympathetic activation and the effects of Ang-(17) in hypertension is not understood. The present study was designed to determine whether Ang-(17) in the PVN contributed to the enhanced CSAR and sympathetic activation, and whether the cAMP-PKA pathway in the PVN was involved in the effects of Ang-(17) in hypertension. Materials and Methods Experiments were carried out in male SpragueDawley rats. The procedures were approved by the Experimental Animal Care and Use Committee of Nanjing Medical University (No. 20110316) and complied with the Guide for the Care and Use of Laboratory Animals (NIH publication no. 8523, revised 1996). The rats were kept in a temperature-controlled room on a 12 h 12 h lightdark cycle with free access to standard chow and tap water. Renovascular hypertensive model Goldblatt two-kidney one-clip (2K1C) method w (...truncated)