Silymarin- and melatonin-mediated changes in the expression of selected genes in pesticides-induced Parkinsonism

Expression of angiotensin II (Ang II) and its receptors (AT₁/AT₂) is undetected in the mature microglia in normal brain. We report here that the immunoexpression of Ang II and AT₁/AT₂ was altered in activated microglia notably at 1 week in rats subjected to middle cerebral artery occlusion (MCAO). Immunolabeled activated microglia were widely distributed in the infarcted cerebral tissue after MCAO. By enzyme immunoassay, Ang II protein expression levels of the ischemic tissues were decreased drastically at 12 h after ischemia, then rose rapidly at 3 days and 1 week after MCAO when compared with the control. On the other hand, AT₁ and AT₂ receptor mRNA and protein levels were up-regulated after MCAO, peaking at 12 h, but declined thereafter. Expression of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) mRNA and protein levels was concomitantly increased. Edaravone significantly suppressed Ang II and AT₁/AT₂ receptor expression as well as that of TNF-α and IL-1β suggesting that microglia-derived Ang II can act through an autocrine manner via its receptor that may be linked partly to the production of proinflammatory cytokines. We conclude that neuroinflammation in MCAO may be attenuated by Edaravone which acts through suppression of expression of Ang II and its receptors and proinflammatory cytokines in activated microglia.     

ONTOGENY OF ANGIOTENSIN II RECEPTORS

Aside from the well known role of angiotensin II (Ang II) in blood pressure regulation and fluid homeostasis, accumulating evidence suggests that the octapeptide hormone also plays a role in growth and development. There are two major classes of Ang II receptors (AT₁and AT₂) which mediate Ang II action. Both classes are members of the large superfamily of seven transmembrane domain spanning receptors. Fetal tissue express high levels of AT receptors. Throughout fetal and postpartum life, the AT₁and AT₂tissue distribution changes dramatically. The evolution of each receptor type is distinct and varies according to the organ. Thus, the different patterns of temporal expression of each receptor class could be related to various roles that Ang II may play during development.     

Angiotensin II mediates Tyr-dephosphorylation in rat fetal kidney membranes

Angiotensin II (Ang II) elicits a variety of physiological effects through specific Ang II receptors in numerous tissues. In addition, Ang II is a modulator of cellular growth and exerts a positive or negative effect on cell growth depending on which receptor subtype is activated. Expression of the intrarenal AT₂ receptors occurs at its highest levels in the fetal kidney, with a rapid decline after birth. In the present paper, we performed a study on the signaling mechanism of Ang II receptors in rat fetal (E20) kidney, a rich source of AT₂ receptors, where both Ang II receptor subtypes are present. Ang II induces Tyr-dephosphorylation of proteins in rat fetal kidney membranes. The response is dose-dependent, with a reduction of 20% with respect to the control (100%), signal that is completely reversed by Ang II AT₂ competitor PD123319. Orthovanadate, the inhibitor of phospho-Tyr-phosphatases (PTPase), reverts Ang II effect, suggesting the involvement of a protein tyrosine phosphatase. The peptide analog of Ang II, CGP42112, exhibits an agonist effect, which is dose-dependent. Thus, in rat fetal (E20) kidney, the Ang-induced protein Tyr-dephosphorylation of several proteins is mediated by AT₂ receptors, mechanism that involves an orthovanadate sensitive PTPase.     

Angiotensin and calcium signaling in the pituitary and hypothalamus

1) In the rat pituitary, angiotensin type 1B receptors (AT_1B) are located in lactotrophs and corticotrophs.2) Activation of AT_1B receptors are coupled to G_q/11 (Guanine protein coupled receptor, or GPCR); they increase phospholipase C (PLC) activity resulting in inositol 1,4,5 triphosphate (InsP₃) and diacylglycerol (DAG) formation. A biphasic increase in [Ca²⁺]_itriggered by InsP₃ and DAG ensues.3) As many GPCRs, AT_1B pituitary receptors rapidly desensitize.4) This was observed in the generation of InsP3, the mobilization of intracellular Ca²⁺, and in prolactin release. Both homologous and heterologous desensitization was evidenced.5) Desensitization of the angiotensin II type 1 (AT1) receptor in the pituitary shares similarities and differences with endogenously expressed or transfected AT1 receptors in different cell types.6) In the pituitary hyperplasia generated by chronic estrogen treatment there was desensitization or alteration in angiotensin II (Ang II) evoked intracellular Ca²⁺ increase, InsP3 generation, and prolactin release. This correlates with a downregulation of AT1 receptors.7) In particular, in hyperplastic cells Ang II failed to evoke a transient acute peak in [Ca²⁺]_i, which was replaced by a persistent plateau phase of [Ca²⁺]_i increase.8) Different calcium channels participate in Ang II induced [Ca²⁺]_i increase in control and hyperplastic cells. While spike phase in control cells is dependent on intracellular stores sensitive to thapsigargin, in hyperplastic cells plateau increase is dependent on extracellular calcium influx.9) Signal transduction of the AT1 pituitary receptor is greatly modified by hyperplasia, and it may be an important mechanism in the control of the hyperplastic process.10) In the hypothalamus and brain stem there is a predominant expression of AT_1A and AT₂ mRNA.11) Ang II acts at specific receptors located on neurons in the hypothalamus and brain stem to elicit alterations in blood pressure, fluid intake, and hormone secretion.12) Calcium channels play important roles in the Ang II induced behavioral and endocrine responses.13) Ang II, in physiological concentrations, can activate AT1 receptors to stimulate both Ca²⁺ release from intracellular stores and Ca²⁺ influx from the extracellular space to increase [Ca²⁺]_i in polygonal and stellate astroglia of the hypothalamus and brain stem.14) In primary cell culture of neurons from newborn rat hypothalamus and brain stem, it has also been determined that Ang II elicits an AT1 receptor mediated inhibition of delayed rectifier K(+) current and a stimulation of Ca²⁺ current.15) In primary cell cultures derived from the subfornical organ or the organum vasculosum laminae terminalis of newborn rat pups, Ang II produced a pronounced desensitization of the [Ca²⁺]_i response.16) Hypothalamic and pituitary Ang II systems are involved in different functions, some of which are related. At both levels Ang II signals through [Ca²⁺]_i in a characteristic way.     

Age-Related Changes in Ang II Receptor Localization and Expression in the Developing Auditory Pathway

We studied Ang II receptor localization in different nuclei of the auditory system, by means of binding autoradiography, during brain development. The inferior colliculus (IC), a large midbrain structure which serves as an obligatory synaptic station in both the ascending and descending auditory pathways, exhibited high Ang II AT₂ binding at all ages (P0, P8, P15, P30), being maximal at P15. These observations were confirmed by in situ hybridization and immunofluorescence at P15, demonstrating that AT₂ receptor mRNA localized at the same area recognized by AT₂ antibodies and anti β III–tubulin suggesting the neuronal nature of the reactive cells. Ang II AT₁ receptors were absent at early developmental ages (P0) in all nuclei of the auditory system and a low level was observed in the IC at the age P8. AT₂ receptors were present at ventral cochlear nucleus and superior olivary complex, being higher at P15 and P8, respectively. We also explored the effect of prenatal administration of Ang II or PD123319 (AT₂ antagonist) on binding of Ang II receptors at P0, P8, P15. Both treatments increased significantly the level of AT₂ receptors at P0 and P8 in the IC. Although total binding in the whole IC from P15 animals showed no difference between treatments, the central nucleus of the IC exhibited higher binding. Our results supports a correlation between the timing of the higher expression of Ang II AT₂ receptors in different nuclei, the onset of audition and the establishment of neuronal circuits of the auditory pathway.

     

Central angiotensin II stimulates cutaneous water intake behavior via an angiotensin II type-1 receptor pathway in the Japanese tree frog Hyla japonica

Angiotensin II (Ang II) stimulates oral water intake by causing thirst in all terrestrial vertebrates except anurans. Anuran amphibians do not drink orally but absorb water osmotically through ventral skin. In this study, we examined the role of Ang II on the regulation of water-absorption behavior in the Japanese tree frog (Hyla japonica). In fully hydrated frogs, intracerebroventricular (ICV) and intralymphatic sac (ILS) injection of Ang II significantly extended the residence time of water in a dose-dependent manner. Ang II-dependent water uptake was inhibited by ICV pretreatment with an angiotensin II type-1 (AT₁) receptor antagonist but not a type-2 (AT₂) receptor antagonist. These results suggest that Ang II stimulates water-absorption behavior in the tree frog via an AT₁-like but not AT₂-like receptor. We then cloned and characterized cDNA of the tree frog AT₁ receptor from the brain. The tree frog AT₁ receptor cDNA encodes a 361 amino acid residue protein, which is 87% identical to the toad (Bufo marinus) AT₁ receptor and exhibits the functional characteristics of an Ang II receptor. AT₁ receptor mRNAs were found to be present in a number of tissues including brain (especially in the diencephalon), lung, large intestine, kidney and ventral pelvic skin. When tree frogs were exposed to dehydrating conditions, AT₁ receptor mRNA significantly increased in the diencephalon and the rhombencephalon. These data suggest that central Ang II may control water intake behavior via an AT₁ receptor on the diencephalon and rhombencephalon in anuran amphibians and may have implications for water consumption in vertebrates.     

Angiotensin II Activates Programmed Myocyte Cell Deathin Vitro

To determine whether angiotensin II (Ang II) can induce apoptosis of neonatal ventricular myocytes, these cells were exposed to 10⁻⁹MAng II for 24 hin vitroand the effects of this intervention on programmed myocyte cell death were examined by the terminal deoxynucleotidyl transferase assay and DNA gel electrophoresis. Ang II resulted morphologically in a 2.5-fold increase in the percentage of myocytes with double strand cleavage of the DNA and biochemically in the formation of DNA fragments equal in size to mono- and oligonucleosomes. Moreover, Ang II stimulation was characterized by a 37% increase in resting level of intracellular calcium and the activation of calcium-dependent endogenous endonuclease. In contrast, pH-dependent endogenous endonuclease was not enhanced by the addition of Ang II. Ang II-induced DNA damage was inhibited by the AT₁receptor antagonist, losartan. Similarly, the calcium chelator, BAPTA-AM, prevented Ang II-mediated cell death. Conversely, the calcium ionophore, A23187, triggered programmed cell death. Finally, the selective AT₂receptor subtype blocker, PD123319, failed to reduce myocyte apoptosis. In conclusion, ligand binding of AT₁receptors may initiate programmed myocyte cell death via an elevation in cytosolic calcium and the stimulation of calcium-dependent endogenous endonuclease.     

Model of the whole rat AT1 receptor and the ligand-binding site

We present a three-dimensional model of the rat type 1 receptor (AT₁) for the hormone angiotensin II (Ang II). Ang II and the AT₁ receptor play a critical role in the cell-signaling process responsible for the actions of renin–angiotensin system in the regulation of blood pressure, water-electrolyte homeostasis and cell growth. Development of improved therapeutics would be significantly enhanced with the availability of a 3D-structure model for the AT₁ receptor and of the binding site for agonists and antagonists. This model was constructed using a combination of computation and homology-modeling techniques starting with the experimentally determined three-dimensional structure of bovine rhodopsin (PDB#1F88) as a template. All 359 residues and two disulfide bonds in the rat AT₁ receptor have been accounted for in this model. Ramachandran-map analysis and a 1 nanosecond molecular dynamics simulation of the solvated receptor with and without the bound ligand, Ang II, lend credence to the validity of the model. Docking calculations were performed with the agonist, Ang II and the antihypertensive antagonist, losartan.      

Losartan, an antagonist of AT1 receptor for angiotensin II, attenuates lipopolysaccharide-induced acute lung injury in rat

Angiotensin II (Ang II) plays an important role in inflammatory process. Acute lung injury (ALI), an inflammatory disorder of the lung, is commonly associated with endotoxemia; however, the mechanism that endotoxin (lipopolysaccharide, LPS) induces the inflammatory response in ALI is not well defined. Here, we showed, in LPS-induced ALI rat model, that Ang II and Ang II type 1 (AT₁) receptor were significantly increased in lung tissues, compared with those in controls. Meanwhile, nuclear factor (NF)-κB-DNA-binding activity, tumor necrosis factor (TNF)-α mRNA, and pneumocytic apoptosis were significantly increased. Moreover, pretreatment of rats with losartan, an antagonist of AT₁ receptor for Ang II, improved the inflammation, reduced the elevation of Ang II and AT₁ receptor, and inhibited NF-κB-DNA-binding activity, expression of TNF-α mRNA, and pneumocytic apoptosis. The data indicate that Ang II may mediate the inflammatory process in LPS-induced ALI through AT₁ receptor, which can be blocked by losartan.     

Vascular mechanisms involved in angiotensin II-induced venoconstriction in hypertensive rats

To investigate the venoconstrictor effect of angiotensin II (Ang II) in spontaneously hypertensive rats (SHR), we used preparations of mesenteric venular beds and the circular muscle of the portal veins. Vessels were tested with Ang II in the presence or absence of losartan, PD 123319, HOE 140, L-NAME, indomethacin, or celecoxib. In the mesenteric venular bed of SHR, the effect of Ang II (0.1 nmol) was nearly abolished by losartan and enhanced by HOE 140, indomethacin, and celecoxib, while PD123319 and L-NAME had no effect. In portal vein preparations, cumulative-concentration response curves (CCRC) to Ang II (0.1–100 nmol/L) exhibited a lower maximal response (E_max) in SHR compared to Wistar rats. AT₁ receptor expression was similar in the two strains, while AT₂ receptor levels were lower in SHR portal veins when compared to Wistar. In SHR portal veins, losartan shifted the CCRC to Ang II to the right, while indomethacin and HOE 140 increased the E_max to Ang II. PD 123319, celecoxib, and L-NAME had no effect. Taken together, our results suggest that Ang II-induced venoconstriction in SHR is mediated by activation of AT₁ receptors and this effect may be counterbalanced by kinin B₂ receptor and COX metabolites. Furthermore, our data indicate that there are different cellular and molecular mechanisms involved in the regulation of venous tonus of normotensive and hypertensive rats. These differences probably reflect distinct factors that influence arterial and venous bed in hypertension.     

Angiotensin II-dependent growth of vascular smooth muscle cells requires transactivation of the epidermal growth factor receptor via a cytosolic phospholipase A2-mediated release of arachidonic acid

Angiotensin (Ang) II stimulates vascular smooth muscle cell (VSMC) growth via activation of cytosolic phospholipase A₂ (cPLA₂), release of arachidonic acid (ArAc) and activation of mitogen-activated protein kinase (MAPK). The mechanism linking AT₁ receptor stimulation of ArAc release with MAPK activation may involve transactivation of the epidermal growth factor receptor (EGFR). In this study, Ang II increased phosphorylation of the EGFR and MAPK in cultured VSMC and these effects were attenuated by the cPLA₂ inhibitor arachidonyl trifluoromethyl ketone (AACOCF₃), and restored by addition of ArAc. Ang II- or ArAc-induced phosphorylation of the EGFR and MAPK were abolished by the EGFR kinase inhibitor AG1478. Ang II or ArAc also stimulated VSMC growth that was blocked by AG1478 or the MAPK kinase (MEK) inhibitor PD98059. Thus, it appears that the cPLA₂-dependent release of ArAc may provide a mechanism for the transactivation between the AT₁ receptor and the EGFR signaling cascade.     

Angiotensin II induces the production of MMP-3 and MMP-13 through the MAPK signaling pathways via the AT1 receptor in osteoblasts

Angiotensin II (Ang II) plays an important role in the maintenance of bone mass and integrity by activation of the mitogen-activated protein kinases (MAPKs) and by modulation of balance between resorption by osteoclasts and formation by osteoblasts. However, the role of Ang II in the turnover of extracellular matrix (ECM) in osteoid by osteoblasts remains unclear. Therefore, we examined the effect of Ang II on the expression of matrix metalloproteinases (MMPs), plasminogen activators (PAs), and their inhibitors [i.e., tissue inhibitors of metalloproteinases (TIMPs) and PA inhibitor-1 (PAI-1)] using osteoblastic ROS17/2.8 cells. Treatment with Ang II strikingly increased the expressions of MMP-3 and -13 and promoted cell proliferation associated with reduced alkaline phosphatase activity as well as enhanced phosphorylated expression of extracellular signal-regulated kinase (ERK)1/2, p38 MAPK, and stress-activated protein kinases/c-jun N-terminal kinases (SAPK/JNK) in ROS17/2.8 cells. However, Ang II had no effect on the expression of MMP-2, -9, -14, urokinase-type PA, tissue-type PA, TIMP-1, -2, -3, and PAI-1 in cells. Losartan (AT₁ receptor blocker) blocked Ang II-induced expression of MMP-3 and -13, whereas PD123319 (AT₂ receptor blocker) did not completely block these responses. Losartan also blocked the Ang II-induced phosphorylation of ERK1/2, p38 MAPK, and SAPK/JNK. MAPK kinase 1/2 inhibitor PD98059 and JNK inhibitor SP600125 suppressed Ang II-induced expression of MMP-3 and -13. These results suggested that Ang II stimulated the degradation process that occurs during ECM turnover in osteoid by increasing the production of MMP-3 and -13 through MAPK signaling pathways via the AT₁ receptor in osteoblasts. Furthermore, our findings suggest that Ang II does not influence the plasminogen/plasmin pathway in osteoblasts.     

Angiotensin II upregulates Kv1.5 expression through ROS-dependent transforming growth factor-beta1 and extracellular signal-regulated kinase 1/2 signalings in neonatal rat atrial myocytes

Kv1.5 potassium channel represents a promising target for atrial fibrillation (AF) therapy. During AF, the renin–angiotensin system is markedly activated. Recent evidence indicates that angiotensin II (Ang II) can upregulate Kv1.5 channel, but the mechanism remains unknown. In this study, we report that Ang II-mediated transforming growth factor-beta1 (TGF-β₁)/Smad2/3 and extracellular signal-regulated kinase (ERK) 1/2 signalings are involved in atrial Kv1.5 expression. In neonatal rat atrial myocytes, quantitative PCR and Western blotting revealed that Ang II upregulated TGF-β₁, synapse-associated protein 97 (SAP97) and Kv1.5 expression in a time- and concentration-dependent manner. The Ang II-induced upregulation of Kv1.5, SAP97 and phosphorylated Smad2/3 (P-Smad2/3) were reversed by the Ang II type 1 (AT₁) receptor antagonist losartan, an anti-TGF-β₁ antibody and the ERK 1/2 inhibitor PD98059 but not by the AT₂ receptor antagonist PD123319. mRNA knockdown of either Smad2 or Smad3 blocked Ang II-induced expression of Kv1.5 and SAP97. These data suggest that AT₁ receptor/TGF-β₁/P-Smad2/3 and ERK 1/2 signalings are involved in Ang II-induced Kv1.5 and SAP97 expression. Flow cytometry and Western blotting revealed that losartan and the anti-TGF-β₁ antibody diminished Ang II-induced reactive oxygen species (ROS) generation and that the antioxidants diphenyleneiodonium and N-acetyl cysteine inhibited Ang II-induced expression of P-Smad2/3, phosphorylated ERK (P-ERK) 1/2, Kv1.5, SAP97, suggesting that ROS participate in Kv1.5 and SAP97 regulation by modulating Ang II-induced P-Smad2/3 and P-ERK 1/2 expression. In conclusion, we demonstrate that ROS-dependent Ang II/AT₁ receptor/TGF-β₁/P-Smad2/3 and Ang II/ERK 1/2 signalings are involved in atrial Kv1.5 and SAP97 expression. Antioxidants would be beneficial for AF treatment through inhibiting atrial Kv1.5 expression.     

The Effects of Angiotensin II and Angiotensin-(1–7) in the Rostral Ventrolateral Medulla of Rats on Stress-Induced Hypertension

We have shown that angiotensin II (Ang II) and angiotensin-(1–7) [Ang-(1–7)] increased arterial blood pressure (BP) via glutamate release when microinjected into the rostral ventrolateral medulla (RVLM) in normotensive rats (control). In the present study, we tested the hypothesis that Ang II and Ang-(1–7) in the RVLM are differentially activated in stress-induced hypertension (SIH) by comparing the effects of microinjection of Ang II, Ang-(1–7), and their receptor antagonists on BP and amino acid release in SIH and control rats. We found that Ang II had greater pressor effect, and more excitatory (glutamate) and less inhibitory (taurine and γ-aminobutyric acid) amino acid release in SIH than in control animals. Losartan, a selective AT₁ receptor (AT₁R) antagonist, decreased mean BP in SIH but not in control rats. PD123319, a selective AT₂ receptor (AT₂R) antagonist, increased mean BP in control but not in SIH rats. However, Ang-(1–7) and its selective Mas receptor antagonist Ang779 evoked similar effects on BP and amino acid release in both SIH and control rats. Furthermore, we found that in the RVLM, AT₁R, ACE protein expression (western blot) and ACE mRNA (real-time PCR) were significantly higher, whereas AT₂R protein, ACE2 mRNA and protein expression were significantly lower in SIH than in control rats. Mas receptor expression was similar in the two groups. The results support our hypothesis and demonstrate that upregulation of Ang II by AT₁R, not Ang-(1–7), system in the RVLM causes hypertension in SIH rats by increasing excitatory and suppressing inhibitory amino acid release.     

Angiotensin II enhances endothelin-1-induced vasoconstriction through upregulating endothelin type A receptor

Endothelin-1 (ET-1) is the most potent vasoconstrictor by binding to endothelin receptors (ET_AR) in vascular smooth muscle cells (VSMCs). The complex of angiotensin II (Ang II) and Ang II type one receptor (AT₁R) acts as a transient constrictor of VSMCs. The synergistic effect of ET-1 and Ang II on blood pressure has been observed in rats; however, the underlying mechanism remains unclear. We hypothesize that Ang II leads to enhancing ET-1-mediated vasoconstriction through the activation of endothelin receptor in VSMCs. The ET-1-induced vasoconstriction, ET-1 binding, and endothelin receptor expression were explored in the isolated endothelium-denuded aortae and A-10 VSMCs. Ang II pretreatment enhanced ET-1-induced vasoconstriction and ET-1 binding to the aorta. Ang II enhanced ET_AR expression, but not ET_BR, in aorta and increased ET-1 binding, mainly to ET_AR in A-10 VSMCs. Moreover, Ang II-enhanced ET_AR expression was blunted and ET-1 binding was reduced by AT₁R antagonism or by inhibitors of PKC or ERK individually. In conclusion, Ang II enhances ET-1-induced vasoconstriction by upregulating ET_AR expression and ET-1/ET_AR binding, which may be because of the AngII/Ang II receptor pathways and the activation of PKC or ERK. These findings suggest the synergistic effect of Ang II and ET-1 on the pathogenic development of hypertension.     

Heteromerization of angiotensin receptors changes trafficking and arrestin recruitment profiles

The cardiovascular hormone angiotensin II (AngII) exerts its actions via two G protein-coupled receptor (GPCR) subtypes, AT₁ and AT₂, which often display antagonistic functions. Methodological constraints have so far precluded detailed analyses of the ligand-dependency, cellular localization, and functional relevance of AngII receptor interactions in live cells. In this study, we utilize a protein-fragment complementation assay (PCA) and GPCR-Heteromer Identification Technology (GPCR-HIT) to provide the first detailed investigation of the ligand-dependency and cellular localization of AngII receptor interactions in human embryonic kidney 293 cells. Fluorescent-tagged receptor constructs for PCA and GPCR-HIT displayed normal affinity and selectivity for AngII (AT₁: IC₅₀ = 1.0-1.6 nM; AT₂: IC₅₀ = 2.0-3.0 nM). Well-characterized angiotensin receptor interactions were used as positive and negative controls to demonstrate the sensitivity and specificity of these fluorescence-based assays. We report that AT₁-AT₂ receptor heteromers form constitutively, are localized to the plasma membrane and perinuclear compartments, and do not internalize following AngII stimulation despite arrestin being recruited specifically to the heteromer. Our findings using novel fluorescence-based technologies reveal a previously unrecognized mechanism of angiotensin receptor cross-talk involving cross-inhibition of AT₁ receptor internalization through heteromerization with the AT₂ receptor subtype.     

Angiotensin II and Angiotensin-(1-7) in Paraventricular Nucleus Modulate Cardiac Sympathetic Afferent Reflex in Renovascular Hypertensive Rats

Background

The enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation that contributes to the pathogenesis and progression of hypertension. Activation of AT₁ receptors by angiotension (Ang) II in the paraventricular nucleus (PVN) augments the enhanced CSAR and sympathetic outflow in hypertension. The present study is designed to determine whether Ang-(1-7) in PVN plays the similar roles as Ang II and the interaction between Ang-(1-7) and Ang II on CSAR in renovascular hypertension.

Methodology/Principal Findings

The two-kidney, one-clip (2K1C) method was used to induce renovascular hypertension. The CSAR was evaluated by the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to epicardial application of capsaicin in sinoaortic-denervated and cervical-vagotomized rats with urethane and α-chloralose anesthesia. Either Ang II or Ang-(1-7) in PVN caused greater increases in RSNA and MAP, and enhancement in CSAR in 2K1C rats than in sham-operated (Sham) rats. Mas receptor antagonist A-779 and AT₁ receptor antagonist losartan induced opposite effects to Ang-(1-7) or Ang II respectively in 2K1C rats, but losartan had no effects in Sham rats. Losartan but not the A-779 abolished the effects of Ang II, while A-779 but not the losartan blocked the effects of Ang-(1-7). PVN pretreatment with Ang-(1-7) dose-dependently augmented the RSNA, MAP, and CSAR responses to the Ang II in 2K1C rats. Ang II level, AT₁ receptor and Mas receptor protein expression in PVN increased in 2K1C rats compared with Sham rats but Ang-(1-7) level did not.

Conclusions

Ang-(1-7) in PVN is as effective as Ang II in enhancing the CSAR and increasing sympathetic outflow and both endogenous Ang-(1-7) and Ang II in PVN contribute to the enhanced CSAR and sympathetic outflow in renovascular hypertension. Ang-(1-7) in PVN potentiates the effects of Ang II in renovascular hypertension.