Role of angiotensin-(1-7) in the modulation of the baroreflex in renovascular hypertensive rats

Counter-regulatory renin-angiotensin system in hypertension: Review and update in the era of COVID-19 pandemic

Cardiovascular disease is the major cause of mortality and disability, with hypertension being the most prevalent risk factor. Excessive activation of the renin-angiotensin system (RAS) under pathological conditions, leading to vascular remodeling and inflammation, is closely related to cardiovascular dysfunction. The counter-regulatory axis of the RAS consists of angiotensin-converting enzyme 2 (ACE2), angiotensin (1-7), angiotensin (1-9), alamandine, proto-oncogene Mas receptor, angiotensin II type-2 receptor and Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the overactivated RAS. In this review, we summarize the latest insights into the complexity and interplay of the counter-regulatory RAS axis in hypertension, highlight the pathophysiological functions of ACE2, a multifunctional molecule linking hypertension and COVID-19, and discuss the function and therapeutic potential of targeting this counter-regulatory RAS axis to prevent and treat hypertension in the context of the current COVID-19 pandemic.

The Impact of Angiotensin-Converting Enzyme-2/Angiotensin 1-7 Axis in Establishing Severe COVID-19 Consequences

The COVID-19 pandemic has put a tremendous stress on the medical community over the last two years. Managing the infection proved a lot more difficult after several research communities started to recognize the long-term effects of this disease. The cellular receptor for the virus was identified as angiotensin-converting enzyme-2 (ACE2), a molecule responsible for a wide array of processes, broadly variable amongst different organs. Angiotensin (Ang) 1-7 is the product of Ang II, a decaying reaction catalysed by ACE2. The effects observed after altering the level of ACE2 are essentially related to the variation of Ang 1-7. The renin-angiotensin-aldosterone system (RAAS) is comprised of two main branches, with ACE2 representing a crucial component of the protective part of the complex. The ACE2/Ang (1-7) axis is well represented in the testis, heart, brain, kidney, and intestine. Infection with the novel SARS-CoV-2 virus determines downregulation of ACE2 and interrupts the equilibrium between ACE and ACE2 in these organs. In this review, we highlight the link between the local effects of RAAS and the consequences of COVID-19 infection as they arise from observational studies.

Exercise training improves cardiovascular control in sinoaortic denervated SHR by reducing the elevated angiotensin II and augmenting angiotensin-(1-7) availability within autonomic and neuroendocrine PVN nuclei

Previous studies have shown that baroreceptors- and chemoreceptors-denervated SHR exhibit impaired central autonomic circuitry and worsening of the cardiovascular function. It was also known that exercise training (T) ameliorates the autonomic control of the circulation. In the present study we sought to investigate whether sinoaortic denervation (SAD) is able to modify the expression/activity of the renin-angiotensin system (RAS) within brain autonomic areas and the effects induced by T. SHR submitted to SAD or SHAM surgery were trained or kept sedentary (S) for 8 weeks. Femoral artery and vein were chronically cannulated for hemodynamic/autonomic recordings and baroreflex testing (phenylephrine and sodium nitroprusside, i.v). Ang II and Ang (1-7) protein expression (immunofluorescence assays) were quantified within autonomic and neuroendocrine nuclei of the hypothalamic paraventricular nucleus (PVN). SAD-S vs. SHAM-S exhibited large increase in Ang II availability into the ventromedial, dorsal cap and magnocellular PVN nuclei, which are accompanied by augmented sympathetic activity, elevated arterial pressure variability and higher MAP. There was no change in Ang-(1-7) content within these nuclei. In contrast, T largely augmented Ang-(1-7) immunofluorescence in all nuclei, reduced and normalized Ang II availability and ameliorated the autonomic control of the circulation in SAD rats, but did not reduce MAP levels. Data showed that tonic baroreceptors and chemoreceptors' activity is essential to maintain lower Ang II levels within PVN nuclei. In the absence of afferent signaling, exercise training is still efficient to alter Ang II/Ang-(1-7) balance thus improving cardiovascular control even in the presence of high-pressure levels.

The renin-angiotensin system and cardiovascular autonomic control in aging

Aging is the greatest independent risk factor for developing hypertension and cardiovascular-related diseases including systolic hypertension, vascular disease, ischemic events, arrhythmias, and heart failure. Age-related cardiovascular risk is associated with dysfunction of peripheral organ systems, such as the heart and vasculature, as well as an imbalance in the autonomic nervous system characterized by increased sympathetic and decreased parasympathetic neurotransmission. Given the increasing prevalence of aged individuals worldwide, it is critical to better understand mechanisms contributing to impaired cardiovascular autonomic control in this population. In this regard, the renin-angiotensin system has emerged as an important hormonal modulator of cardiovascular function in aging, in part through modulation of autonomic pathways controlling sympathetic and parasympathetic outflow to cardiovascular end organs. This review will summarize the role of the RAS in cardiovascular autonomic control during aging, with a focus on current knowledge of angiotensin II versus angiotensin-(1-7) pathways in both rodent models and humans, pharmacological treatment strategies targeting the renin-angiotensin system, and unanswered questions for future research.

Captopril and losartan attenuate behavioural sensitization in mice chronically exposed to toluene

Inhalants are consumed worldwide for recreational purposes. The main component found in many inhalants is toluene. One of the most deleterious behavioural effects caused by chronic exposure to inhalants is addiction. This response has been associated with activation of the mesolimbic dopaminergic pathway, and it is known that the renin angiotensin system plays a role in the modulation of this dopaminergic system. In the present work, we hypothesize that blockade of the RAS with angiotensin converting enzyme inhibitors or angiotensin II type 1 receptor blockers is able to attenuate the addictive response induced by toluene. We exposed mice to toluene for four weeks to induce locomotor sensitization. In the second phase of the work, captopril or losartan were administered for 20 days. Subsequently, the expression of behavioural sensitization was evaluated with a toluene challenge. To exclude false associations between the observed responses and treatments, motor coordination and blood pressure were analysed in animals treated with captopril or losartan. At the end of the behavioural studies, animal brains were harvested and Ang II/Ang-(1-7) and Ang-(1-7)/Ang II ratios were analysed in the nucleus accumbens (NAc) and prefrontal cortex (PFCx). The results showed that toluene induced behavioural sensitization, while captopril or losartan treatment attenuated the expression of this response. No significant differences were observed in motor coordination or blood pressure. Repeated toluene administration decreased Ang-(1-7)/Ang II ratio in the PFCx. On the other hand, treatment with captopril or losartan decreased the Ang II/Ang-(1-7) ratio and enhanced the Ang-(1-7)/Ang II ratio in the NAc. This work suggests that blockade of RAS attenuates the toluene-induced behavioural sensitization.

Angiotensin-(1-7) Central Mechanisms After ICV Infusion in Hypertensive Transgenic (mRen2)27 Rats

Previous data showed hypertensive rats subjected to chronic intracerebroventricular (ICV) infusion of angiotensin-(1-7) presented attenuation of arterial hypertension, improvement of baroreflex sensitivity, restoration of cardiac autonomic balance and a shift of cardiac renin-angiotensin system (RAS) balance toward Ang-(1-7)/Mas receptor. In the present study, we investigated putative central mechanisms related to the antihypertensive effect induced by ICV Ang-(1-7), including inflammatory mediators and the expression/activity of the RAS components in hypertensive rats. Furthermore, we performed a proteomic analysis to evaluate differentially regulated proteins in the hypothalamus of these animals. For this, Sprague Dawley (SD) and transgenic (mRen2)27 hypertensive rats (TG) were subjected to 14 days of ICV infusion with Ang-(1-7) (200 ng/h) or 0.9% sterile saline (0.5 μl/h) through osmotic mini-pumps. We observed that Ang-(1-7) treatment modulated inflammatory cytokines by decreasing TNF-α levels while increasing the anti-inflammatory IL-10. Moreover, we showed a reduction in ACE activity and gene expression of AT1 receptor and iNOS. Finally, our proteomic evaluation suggested an anti-inflammatory mechanism of Ang-(1-7) toward the ROS modulators Uchl1 and Prdx1.

Central Administration of Angiotensin-(1-7) Improves Vasopressin Impairment and Hypotensive Response in Experimental Endotoxemia

Angiotensin-(1-7) [Ang-(1-7)]/Mas receptor is a counter-regulatory axis that counteracts detrimental renin-angiotensin system (RAS) effects, especially regarding systemic inflammation, vasopressin (AVP) release, and hypothalamic-pituitary-adrenal (HPA) activation. However, it is not completely understood whether this system may control centrally or systemically the late phase of systemic inflammation. Thus, the aim of this study was to determine whether intracerebroventricular (i.c.v.) administration of Ang-(1-7) can modulate systemic inflammation through the activation of humoral pathways in late phase of endotoxemia. Endotoxemia was induced by systemic injection of lipopolysaccharide (LPS) (1.5 mg/kg, i.v.) in Wistar rats. Ang-(1-7) (0.3 nmol in 2 µL) promoted the release of AVP and attenuated interleukin-6 (IL-6) and nitric oxide (NO) levels but increased interleukin-10 (IL-10) in the serum of the endotoxemic rats. The central administration of Mas receptor antagonist A779 (3 nmol in 2 µL, i.c.v.) abolished these anti-inflammatory effects in endotoxemic rats. Furthermore, Ang-(1-7) applied centrally restored mean arterial blood pressure (MABP) without affecting heart rate (HR) and prevented vascular hyporesponsiveness to norepinephrine (NE) and AVP in animals that received LPS. Together, our results indicate that Ang-(1-7) applied centrally promotes a systemic anti-inflammatory effect through the central Mas receptor and activation of the humoral pathway mediated by AVP.

Effects of aging on the secretory apparatus in the right atrial cardiomyocytes of rats

The cardiac atria secrets polypeptide hormones usually called natriuretic peptides (NPs). These substances play a relevant role in the blood pressure regulation. The objective of the study was to estimate the effects of aging on the secretory apparatus of NPs in cardiomyocytes of the right atrium. Twenty male Wistar rats were studied: 10 young animals aged 3 months old (237 ± 27 g; mean ± SD) and 10 old animals aged 20 months old (450 ± 68 g; mean ± SD). The systolic blood pressure was verified instants before the moment of the euthanasia. Electron micrographs were prepared to quantify the area and density of the NP granules and the relative volumes of the endoplasmic reticulum, Golgi complex, and mitochondria. In addition, the number of pores per 10 μm of karyotheca was another variable evaluated. The significance of the results between the two groups evaluated was analyzed by the Student's t test (p < 0.05). The cardiomyocytes obtained from animals of the old group showed decreased in sectional area and density of secretory granules of NP and lower relative volume of endoplasmic reticulum, Golgi complex, and mitochondria compared with the young rats. Moreover, the quantitative density of nuclear pores was significantly lower compared with the youngers. CONCLUSION: Aging causes hypotrophy of the cardiomyocytes of right atrium, similar to what occurs in ventricular cardiomyocytes.

Ultrastructural effects of diabetes in the right atrium cardiomyocytes of elderly Wistar rats

The present study aimed to evaluate the effects of diabetes on quantitative parameters of right atrial cardiomyocytes of elderly rats. Wistar rats (14 months of age) were divided into two groups: streptozotocin-diabetic rats (DG) and control rats (CG). The groups were sacrificed at 16 months. Ultrafine sections of the right atrium were analyzed by electron microscopy. In elderly diabetic animals, histograms of the frequency distribution of natriuretic peptides according to their size showed increased number of small and medium peptides in relation to large peptides, which increased its numerical density leading to a decrease in the mean diameter of both natriuretic peptides. However, elderly diabetic animals remained normotensive. No significant difference was observed between the groups for the volume density of mitochondria, endoplasmic reticulum, and Golgi apparatus. In conclusion, elderly diabetic rats showed increased functional activity of atrial cardiomyocytes with greater production of natriuretic peptides in association with a quantitative maintenance of cytoplasmic components.

Oral vitamin-A-coupled valsartan nanomedicine: High hepatic stellate cell receptors accessibility and prolonged enterohepatic residence

So far, liver fibrosis still has no clinically-approved treatment. The loss of stored vitamin-A (V_A) in hepatic stellate cells (HSCs), the main regulators to hepatic fibrosis, can be applied as a mechanism for their targeting. Valsartan is a good candidate for this approach; it is a marketed oral-therapy with inverse- and partial-agonistic activity to the over-expressed angiotensin-II type1 receptor (AT1R) and depleted nuclear peroxisome proliferator-activated receptor-gamma (PPAR-γ), respectively, in activated HSCs. However, efficacy on AT1R and PPAR-γ necessitates high drug permeability which is lacking in valsartan. In the current study, liposomes were used as nanocarriers for valsartan to improve its permeability and hence efficacy. They were coupled to V_A and characterized for HSCs-targeting. Tracing of orally-administered fluorescently-labeled V_A-coupled liposomes in normal rats and their fluorescence intensity quantification in different organs convincingly demonstrated their intestinal entrapment. On the other hands, their administration to rats with induced fibrosis revealed preferential hepatic, and less intestinal, accumulation which lasted up to six days. This indicated their uptake by intestinal stellate cells that acted as a depot for their release over time. Confocal microscopical examination of immunofluorescently-stained HSCs in liver sections, with considerable formula accumulation, confirmed HSCs-targeting and nuclear uptake. Consequently, V_A-coupled valsartan-loaded liposomes (VLC)-therapy resulted in profound re-expression of hepatic Mas-receptor and PPAR-γ, potent reduction of fibrogenic mediators' level and nearly normal liver function tests. Therefore, VLC epitomizes a promising antifibrotic therapy with exceptional extended action and additional PPAR-γ agonistic activity.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Brain renin-angiotensin system in the pathophysiology of cardiovascular diseases

Cardiovascular diseases (CVD) are among the main causes of death globally and in this context hypertension represents one of the key risk factors for developing a CVD. It is well established that the peripheral renin-angiotensin system (RAS) plays an important role in regulating blood pressure (BP). All components of the classic RAS can also be found in the brain but, in contrast to the peripheral RAS, how the endogenous RAS is involved in modulating cardiovascular effects in the brain is not fully understood yet. It is a complex system that may work differently in diverse areas of the brain and is linked to the peripheral system by the circumventricular organs (CVO), which do not have a blood brain barrier (BBB). In this review, we focus on the brain angiotensin peptides, their interactions with each other, and the consequences in the central nervous system (CNS) concerning cardiovascular control. Additionally, we present potential drug targets in the brain RAS for the treatment of hypertension.

The Link Between Adipose Tissue Renin-Angiotensin-Aldosterone System Signaling and Obesity-Associated Hypertension

Obese individuals frequently develop hypertension, which is for an important part attributable to renin-angiotensin-aldosterone system (RAAS) overactivity. This review summarizes preclinical and clinical evidence on the involvement of dysfunctional adipose tissue in RAAS activation and on the renal, central, and vascular mechanisms linking RAAS components to obesity-associated hypertension.

Improved cardiovascular autonomic modulation in transgenic rats expressing an Ang-(1-7)-producing fusion protein

Angiotensin-(1-7) counterbalances angiotensin II cardiovascular effects. However, it has yet to be determined how cardiovascular autonomic modulation may be affected by chronic and acute elevation of Ang-(1-7). Hemodynamics and cardiovascular autonomic profile were evaluated in male Sprague-Dawley (SD) rats and transgenic rats (TGR) overexpressing Ang-(1-7) [TGR(A1-7)3292]. Blood pressure (BP) was directly measured while cardiovascular autonomic modulation was evaluated by spectral analysis. TGR received A-779 or vehicle and SD rats received Ang-(1-7) or vehicle and were monitored for 5 h after i.v. administration. In another set of experiments with TGR, A-779 was infused for 7 days using osmotic mini pumps. Although at baseline no differences were observed, acute administration of A-779 in TGR produced a marked long-lasting increase in BP accompanied by increased BP variability (BPV) and sympathetic modulation to the vessels. Likewise, chronic administration of A-779 with osmotic mini pumps in TGR increased heart rate, sympathovagal balance, BPV, and sympathetic modulation to the vessels. Administration of Ang-(1-7) to SD rats increased heart rate variability values in 88% accompanied by 8% of vagal modulation increase and 18% of mean BP reduction. These results show that both acute and chronic alteration in the Ang-(1-7)-Mas receptor axis may lead to important changes in the autonomic control of circulation, impacting either sympathetic and (or) parasympathetic systems.

EFFECTS OF AEROBIC TRAINING ON THE CARDIOMYOCYTES OF THE RIGHT ATRIUM OF MICE

ABSTRACT Introduction: Polypeptide hormones (natriuretic peptides, NPs) are secreted by the cardiac atria and play an important role in the regulation of blood pressure. Objective: To evaluate the effects of aerobic training on the secretory apparatus of NPs in cardiomyocytes of the right atrium. Methods: Nine-month-old mice were divided in two groups (n=10): control group (CG) and trained group (TG). The training protocol was performed on a motor treadmill for 8 weeks. Systolic blood pressure was measured at the beginning of the experiment (9 months of age) and at moment of the sacrifice (11 months of age). Electron micrographs were used to quantify the following variables: the quantitative density and area of NP granules, the relative volumes of the mitochondria, endoplasmic reticulum, and Golgi complex and the relative volume of euchromatin in the nucleus and the number of pores per 10 µm of the nuclear membrane. The results were compared by Student's t test (p< 0.05). Results: The cardiomyocytes obtained from TG mice showed increased density and sectional area of secretory granules of NP, higher relative volume of endoplasmic reticulum, mitochondria, and Golgi complex compared with the CG mice. Furthermore, the quantitative density of nuclear pores and the relative volume of euchromatin in the nucleus were significantly higher compared with the CG mice. Conclusion: Aerobic training caused hypertrophy of the secretory apparatus in the cardiomyocytes of right atrium, which could explain the intense synthesis of natriuretic peptides in trained mice with respect to the untrained mice.

Angiotensin-(1–7) decreases the expression of collagen I via TGF-β1/Smad2/3 and subsequently inhibits fibroblast–myofibroblast transition

Previous studies have shown that the RAS (renin–angiotensin system) might participate in airway remodelling in asthma. As a main component of the RAS, Ang-(1–7) [angiotensin-(1–7)] has been reported in few studies regarding its protective effect on asthma. However, the functional roles and relevant signalling pathways of Ang-(1–7) have not been well illustrated. In the present study, we analysed the effect of Ang-(1–7) on AngII (angiotensin II)-induced HLF (human lung fibroblast)–MF (myofibroblast) transition by detecting Col-I (collagen type I), TGF-β1 (transforming growth factor-β1) and α-SMA (α-smooth muscle actin) expression. We explored further the possible signalling pathways involved in HLF–MF transition. Our results showed that Ang-(1–7) could down-regulate the expression of Col-I, α-SMA and TGF-β1/Smad2/3 (all P<0.05). A significant decrease was found in phosphorylation of PI3K (phosphoinositide 3-kinase), Akt, p38-MAPK (mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase) signalling pathways during HLF–MF transition (all P<0.05). Our data suggests that Ang-(1–7) decreases the expression of Col-I via TGF-β1/Smad2/3 and subsequently inhibits HLF–MF transition.

Anxiolytic- and antidepressant-like effects of angiotensin-(1–7) in hypertensive transgenic (mRen2)27 rats

Angiotensin-(1–7) [Ang-(1–7)], a counter-regulatory peptide of the renin–angiotensin system (RAS) exerts its effects through the G-protein-coupled receptor Mas, which is expressed in different tissues, including the brain. Ang-(1–7) has a broad range of effects beyond the well-described cardiovascular and renal actions, including the modulation of emotional and behavioural responses. In the present study we tested the hypothesis that Ang-(1–7) could attenuate the anxiety- and depression-like behaviours observed in transgenic hypertensive (mRen2)27 rats (TGRs). We also hypothesized that Ang-(1–7) could be involved in the anxiolytic-like effect induced by ACE (angiotensin-converting enzyme) treatment in these hypertensive rats. Therefore, TGRs and Sprague–Dawley rats were subjected to the Elevated Plus Maze (EPM) test, Forced Swimming Test (FST) and Novelty Suppressed Feeding (NSF). TGRs presented a decreased percentage of entries in the open arms of the EPM test, a phenotype reversed by systemic treatment with enalapril or intracerebroventricular infusion of Ang-(1–7). It is interesting that pre-treatment with A779, a selective Mas receptor antagonist, prevented the anxiolytic-like effect induced by the ACE inhibitor. In the NSF test, TGRs showed increased latency to eating, an indicative of a higher aversion in response to a new environment. These animals also showed increased immobility in the FST. Again, Ang-(1–7) reversed this phenotype. Thus, our data showed that Ang-(1–7) can modulate anxiety- and depression-like behaviours in TGRs and warrant further investigation as a new therapy for certain psychiatric disorders.

Decreased excitability and voltage-gated sodium currents in aortic baroreceptor neurons contribute to the impairment of arterial baroreflex in cirrhotic rats

Cardiovascular autonomic dysfunction, which is manifested by an impairment of the arterial baroreflex, is prevalent irrespective of etiology and contributes to the increased morbidity and mortality in cirrhotic patients. However, the cellular mechanisms that underlie the cirrhosis-impaired arterial baroreflex remain unknown. In the present study, we examined whether the cirrhosis-impaired arterial baroreflex is attributable to the dysfunction of aortic baroreceptor (AB) neurons. Biliary and nonbiliary cirrhotic rats were generated via common bile duct ligation (CBDL) and intraperitoneal injections of thioacetamide (TAA), respectively. Histological and molecular biological examinations confirmed the development of fibrosis in the livers of both cirrhotic rat models. The heart rate changes during phenylephrine-induced baroreceptor activation indicated that baroreflex sensitivity was blunted in the CBDL and TAA rats. Under the current-clamp mode of the patch-clamp technique, cell excitability was recorded in DiI-labeled AB neurons. The number of action potential discharges in the A- and C-type AB neurons was significantly decreased because of the increased rheobase and threshold potential in the CBDL and TAA rats compared with sham-operated rats. Real-time PCR and Western blotting indicated that the NaV1.7, NaV1.8, and NaV1.9 transcripts and proteins were significantly downregulated in the nodose ganglion neurons from the CBDL and TAA rats compared with the sham-operated rats. Consistent with these molecular data, the tetrodotoxin-sensitive NaV currents and the tetrodotoxin-resistant NaV currents were significantly decreased in A- and C-type AB neurons, respectively, from the CBDL and TAA rats compared with the sham-operated rats. Taken together, these findings implicate a key cellular mechanism in the cirrhosis-impaired arterial baroreflex.

Increased vascular sympathetic modulation in mice with Mas receptor deficiency

INTRODUCTION

The angiotensin-converting enzyme 2 (ACE2)/angiotensin (Ang)-(1-7)/Mas axis could modulate the heart rate (HR) and blood pressure variabilities (BPV) which are important predictors of cardiovascular risk and provide information about the autonomic modulation of the cardiovascular system. Therefore we investigated the effect of Mas deficiency on autonomic modulation in wild type and Mas-knockout (KO) mice.

METHODS

Blood pressure was recorded at high sample rate (4000 Hz). Stationary sequences of 200-250 beats were randomly chosen. Frequency domain analysis of HR and BPV was performed with an autoregressive algorithm on the pulse interval sequences and on respective systolic sequences.

RESULTS

The KO group presented an increase of systolic arterial pressure (SAP; 127.26±11.20 vs 135.07±6.98 mmHg), BPV (3.54±1.54 vs 5.87±2.12 mmHg(2)), and low-frequency component of systolic BPV (0.12±0.11 vs 0.47±0.34 mmHg(2)).

CONCLUSIONS

The deletion of Mas receptor is associated with an increase of SAP and with an increased BPV, indicating alterations in autonomic control. Increase of sympathetic vascular modulation in absence of Mas evidences the important role of Ang-(1-7)/Mas on cardiovascular regulation. Moreover, the absence of significant changes in HR and HRV can indicate an adaptation of autonomic cardiac balance. Our results suggest that the Ang-(1-7)/Mas axis seems more important in autonomic modulation of arterial pressure than HR.

Activation of angiotensin-(1-7)/Mas axis in the brain lowers blood pressure and attenuates cardiac remodeling in hypertensive transgenic (mRen2)27 rats

Activation of the peripheral angiotensin-(1-7)/Mas axis of the renin-angiotensin system produces important cardioprotective actions, counterbalancing the deleterious actions of an overactivity of Ang II/AT1 axis. In the present study we evaluated whether the chronic increase in Ang-(1-7) levels in the brain could ameliorate cardiac disorders observed in transgenic (mRen2)27 hypertensive rats through actions on Mas receptor. Sprague Dawley (SD) and transgenic (mRen2)27 hypertensive rats, instrumented with telemetry probe for arterial pressure (AP) measurement were subjected to 14 days of ICV infusion of Ang-(1-7) (200 ng/h) or Ang-(1-7) associated with Mas receptor antagonist (A779, 1 μg/h) or 0.9% sterile saline (0.5 μl/h) through osmotic mini-pumps. Ang-(1-7) infusion in (mRen2)27 rats reduced blood pressure, normalized the baroreflex control of HR, restored cardiac autonomic balance, reduced cardiac hypertrophy and pre-fibrotic alterations and decreased the altered imbalance of Ang II/Ang-(1-7) in the heart. In addition, there was an attenuation of the increased levels of atrial natriuretic peptide, brain natriuretic peptide, collagen I, fibronectin and TGF-β in the heart of (mRen2)27 rats. Furthermore, most of these effects were mediated in the brain by Mas receptor, since were blocked by its selective antagonist, A779. These data indicate that increasing Ang-(1-7) levels in the brain can attenuate cardiovascular disorders observed in (mRen2)27 hypertensive rats, probably by improving the autonomic balance to the heart due to centrally-mediated actions on Mas receptor.

Protective effects of angiotensin-(1-7) administrated with an angiotensin-receptor blocker in a rat model of chronic kidney disease

AIM

Angiotensin-(1-7) (Ang-(1-7)) opposes angiotensin-II-induced cell growth, matrix accumulation and fibrosis in cardiac tissue. However, the role of Ang-(1-7) in the pathogenesis of renal fibrosis is uncertain. This study observed the effects of Ang-(1-7), on its own or in combination with losartan, an angiotensin-receptor blocker, on five-sixths nephrectomized rats.

METHODS

Male Sprague-Dawley rats underwent five-sixths nephrectomy, and then were either untreated, treated with Ang-(1-7), treated with losartan, or treated with a combination therapy of Ang-(1-7) and losartan. After 8 weeks, renal function was assessed by measuring systolic blood pressure, serum creatinine and proteinuria. The effect of nephrectomy on the renin-angiotensin system was examined by measuring plasma levels of Ang-II and Ang-(1-7). The extent of glomerulosclerosis and tubulointerstitial fibrosis was assessed by periodic acid-Schiff staining and Masson-trichrome staining. The expression of plasminogen activator inhibitor-1, fibronectin and angiopoietins-Tie-2 was investigated by immunohistochemistry and western blot.

RESULTS

In the groups of treated rats, serum creatinine, proteinuria and markers of glomerulosclerosis, such as fibronectin and plasminogen activator inhibitor-1, were ameliorated compared with the untreated, nephrectomized rats. Plasma Ang-(1-7) levels were elevated in all treatment groups, but the plasma Ang-II levels were reduced in the Ang-(1-7)-treated group and the combination therapy group. The ratio of Ang-1/Ang-2 was increased in the combination therapy group compared with two other treatment groups.

CONCLUSION

Ang-(1-7) ameliorated the renal injury of nephrectomized rats. The combination of Ang-(1-7) treatment alongside losartan exerted a superior effect to that of Ang-(1-7) alone on regression of glomerulosclerosis.

ACE2, angiotensin-(1-7) and Mas receptor axis in inflammation and fibrosis

Recent advances have improved our understanding of the renin-angiotensin system (RAS). These have included the recognition that angiotensin (Ang)-(1-7) is a biologically active product of the RAS cascade. The identification of the ACE homologue ACE2, which forms Ang-(1-7) from Ang II, and the GPCR Mas as an Ang-(1-7) receptor have provided the necessary biochemical and molecular background and tools to study the biological significance of Ang-(1-7). Most available evidence supports a counter-regulatory role for Ang-(1-7) by opposing many actions of Ang II on AT₁ receptors, especially vasoconstriction and proliferation. Many studies have now shown that Ang-(1-7) by acting via Mas receptor exerts inhibitory effects on inflammation and on vascular and cellular growth mechanisms. Ang-(1-7) has also been shown to reduce key signalling pathways and molecules thought to be relevant for fibrogenesis. Here, we review recent findings related to the function of the ACE2/Ang-(1-7)/Mas axis and focus on the role of this axis in modifying processes associated with acute and chronic inflammation, including leukocyte influx, fibrogenesis and proliferation of certain cell types. More attention will be given to the involvement of the ACE2/Ang-(1-7)/Mas axis in the context of renal disease because of the known relevance of the RAS for the function of this organ and for the regulation of kidney inflammation and fibrosis. Taken together, this knowledge may help in paving the way for the development of novel treatments for chronic inflammatory and renal diseases.

Effects of ovariectomy on the secretory apparatus in the right atrial cardiomyocytes of middle-aged mice

OBJECTIVE

The aim of the present study was to evaluate the effects of ovariectomy on the secretory apparatus of natriuretic peptides in right atrial cardiomyocytes.

METHODS

Nine-month-old mice underwent bilateral ovariectomy or sham surgery. The blood exam of the ovariectomized mice showed results consistent with castrated females. Systolic blood pressure was measured after ovariectomy (9 mo of age) and at the moment of sacrifice (12 mo of age). Fragments of the right atrium were collected and prepared for electron microscopy examination. The following variables were quantified: the quantitative density and area of the natriuretic peptide granules, the relative volume of euchromatin in the nucleus, the number of pores per 10 μm of the nuclear membrane and the relative volumes of the mitochondria and Golgi complex.

RESULTS

The cardiomyocytes obtained from ovariectomized mice indicated that the quantitative density and the area of secretory granules of natriuretic peptides were significantly lower compared with the sham-operated mice. Furthermore, there was a decrease in the relative volume of euchromatin, a lower density of nuclear pores, and lower relative volumes of the mitochondria and Golgi complex in the ovariectomized mice compared with the sham-operated mice. These findings suggest a pool with a low turnover rate, i.e., low synthesis and elimination of natriuretic peptides.

CONCLUSION

A lack of estrogen caused hypotrophy of the secretory apparatus in right atrial cardiomyocytes that could explain the weak synthesis of natriuretic peptides in mice. Furthermore, one of the mechanisms of blood pressure control was lost, which may explain, in part, the elevated blood pressure in ovariectomized mice.

Angiotensin-converting enzyme 2 and angiotensin 1-7: novel therapeutic targets

Angiotensin-converting enzyme (ACE) 2 and its product angiotensin 1–7 are thought to have effects that counteract the adverse actions of other, better-known renin–angiotensin system (RAS) components

Numerous experimental studies have suggested that ACE2 and angiotensin 1–7 have notable protective effects in the heart and blood vessels

ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the functional importance and signalling mechanisms of angiotensin-1–7-induced actions remain unclear

New pharmacological interventions targeting ACE2 are expected to be useful in clinical treatment of cardiovascular disease, especially those associated with overactivation of the conventional RAS

More studies, especially randomized controlled clinical trials, are needed to clearly delineate the benefits of therapies targeting angiotensin 1–7 actions

Angiotensin-converting enzyme 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of the better-known members of the renin–angiotensin system and might, therefore, be useful therapeutic targets in patients with cardiovascular disease. Professor Jiang and colleagues review the evidence for the potential roles of these proteins in various cardiovascular conditions, including hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes.

The renin–angiotensin system (RAS) has pivotal roles in the regulation of normal physiology and the pathogenesis of cardiovascular disease. Angiotensin-converting enzyme (ACE) 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of other, better known and understood, members of the RAS. The physiological and pathological importance of ACE2 and angiotensin 1–7 in the cardiovascular system are not completely understood, but numerous experimental studies have indicated that these components have protective effects in the heart and blood vessels. Here, we provide an overview on the basic properties of ACE2 and angiotensin 1–7 and a summary of the evidence from experimental and clinical studies of various pathological conditions, such as hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes mellitus. ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the relevant functions and signalling mechanisms of actions induced by angiotensin 1–7 have not been conclusively determined. The ACE2–angiotensin 1–7 pathway, however, might provide a useful therapeutic target for the treatment of cardiovascular disease, especially in patients with overactive RAS.

Angiotensin (1-7) prevents angiotensin II-induced nociceptive behaviour via inhibition of p38 MAPK phosphorylation mediated through spinal Mas receptors in mice

BACKGROUND

We have recently demonstrated that intrathecal (i.t.) administration of angiotensin II (Ang II) induces nociceptive behaviour in mice accompanied by a phosphorylation of p38 mitogen-activated protein kinase (MAPK) mediated through Ang II type 1 (AT1 ) receptors. The N-terminal fragment of Ang II, Ang (1-7), plays a pivotal role in counterbalancing many of the well-established actions induced by Ang II. However, the role of Ang (1-7) in spinal nociceptive transmission remains unclear. Therefore, we examined whether i.t. administration of Ang (1-7) can inhibit the Ang II-induced nociceptive behaviour in mice.

METHODS

In the behavioural experiments, the accumulated response time of nociceptive behaviour consisting of scratching, biting and licking in conscious mice was determined during a 25-min period starting after i.t. injection. The distribution and localization of AT1 or Mas receptors were analysed using a MapAnalyzer and confocal microscope, respectively. Phosphorylation of p38 MAPK in the dorsal spinal cord was measured by Western blotting.

RESULTS

The nociceptive behaviour induced by Ang II was dose-dependently inhibited by the co-administration of Ang (1-7). The inhibitory effect of Ang (1-7) was reversed by the co-administration of A779, a Mas receptor antagonist. Western blot analysis showed that the increase in spinal p38 MAPK phosphorylation following the i.t. administration of Ang II was also inhibited by Ang (1-7), and the Ang (1-7) induced-inhibition was prevented by A779.

CONCLUSIONS

Our data show that the i.t. administration of Ang (1-7) attenuates an Ang II-induced nociceptive behaviour and is accompanied by the inhibition of p38 MAPK phosphorylation mediated through Mas receptors.

Neuromodulatory role of angiotensin-(1–7) in the central nervous system

Ang-(1–7) [angiotensin-(1–7)] constitutes an important functional end-product of the RAS (renin–angiotensin system) endogenously formed from AngI (angiotensin I) or AngII (angiotensin II) through the catalytic activity of ACE2 (angiotensin-converting enzyme 2), prolyl carboxypeptidase, neutral endopeptidase or other endopeptidases. Ang-(1–7) lacks the pressor, dipsogenic or stimulatory effect on aldosterone release characteristic of AngII. In contrast, it produces vasodilation, natriuresis and diuresis, and inhibits angiogenesis and cell growth. At the central level, Ang-(1–7) acts at sites involved in the control of cardiovascular function, thus contributing to blood pressure regulation. This action may result from its inhibitory neuromodulatory action on NE [noradrenaline (norepinephrine)] levels at the synaptic cleft, i.e. Ang-(1–7) reduces NE release and synthesis, whereas it causes an increase in NE transporter expression, contributing in this way to central NE neuromodulation. Thus, by selective neurotransmitter release, Ang-(1–7) may contribute to the overall central cardiovascular effects. In the present review, we summarize the central effects of Ang-(1–7) and the mechanism by which the peptide modulates NE levels in the synaptic cleft. We also provide new evidences of its cerebroprotective role.

Cardiac-autonomic imbalance and baroreflex dysfunction in the renovascular Angiotensin-dependent hypertensive mouse

Mouse models provide powerful tools for studying the mechanisms underlying the dysfunction of the autonomic reflex control of cardiovascular function and those involved in cardiovascular diseases. The established murine model of two-kidney, one-clip (2K1C) angiotensin II-dependent hypertension represents a useful tool for studying the neural control of cardiovascular function. In this paper, we discuss the main contributions from our laboratory and others regarding cardiac-autonomic imbalance and baroreflex dysfunction. We show recent data from the angiotensin-dependent hypertensive mouse demonstrating DNA damage and oxidative stress using the comet assay and flow cytometry, respectively. Finally, we highlight the relationships between angiotensin and peripheral and central nervous system areas of cardiovascular control and oxidative stress in the 2K1C hypertensive mouse.

Brain renin-angiotensin system in the nexus of hypertension and aging

Aging is associated with an imbalance in sympathetic and parasympathetic outflow to cardiovascular effector organs. This autonomic imbalance contributes to the decline in cardiovagal baroreceptor reflex function during aging, which allows for unrestrained activation of the sympathetic nervous system to negatively impact resting systolic blood pressure and its variability. Further, impaired baroreflex function can contribute to the development of insulin resistance and other features of the metabolic syndrome during aging through overlap in autonomic neural pathways that regulate both cardiovascular and metabolic functions. Increasing evidence supports a widespread influence of the renin-angiotensin system (RAS) on both sympathetic and parasympathetic activity through receptors distributed to peripheral and central sites of action. Indeed, therapeutic interventions to block the RAS are well established for the treatment of hypertension in elderly patients, and reduce the incidence of new-onset diabetes in clinical trials. Further, RAS blockade increases lifespan and improves numerous age-related pathologies in rodents, often independent of blood pressure. The beneficial effects of these interventions are at least in part attributed to suppression of angiotensin II formed locally within the brain. In particular, recent insights from transgenic rodents provide evidence that long-term alteration in the brain RAS modulates the balance between angiotensin II and angiotensin-(1-7), and related intracellular signaling pathways, to influence cardiovascular and metabolic function in the context of hypertension and aging.

Central angiotensin-(1-7) improves vagal function independent of blood pressure in hypertensive (mRen2)27 rats

Hypertensive transgenic (mRen2)27 rats with overexpression of the mRen2 gene have impaired baroreflex sensitivity for heart rate control and high nicotinamide adenine dinucleotide phosphate oxidase and kinase-to-phosphatase signaling activity in medullary tissue compared with normotensive Hannover Sprague-Dawley control rats. They also exhibit insulin resistance at a young age. To determine whether blocking angiotensin II actions, supplementing angiotensin-(1-7), or scavenging reactive oxygen species in brain differentially alters mean arterial pressure, baroreflex sensitivity, or metabolic function, while altering medullary signaling pathways in these animals, we compared intracerebroventricular infusions of the angiotensin II type 1 receptor antagonist candesartan (4 μg/5 μL/h), angiotensin-(1-7) (0.1 μg/5 μL/h), a reactive oxygen species scavenger tempol (25 μg/5 μL/h), or artificial cerebrospinal fluid (5 μL/h) for 2 weeks. Mean arterial pressure was reduced in candesartan-treated rats without significantly improving the vagal components of baroreflex function or heart rate variability. In contrast, angiotensin-(1-7) treatment significantly improved the vagal components of baroreflex function and heart rate variability at a dose that did not significantly lower mean arterial pressure. Tempol significantly reduced nicotinamide adenine dinucleotide phosphate oxidase activity in brain dorsal medullary tissue but had no effect on mean arterial pressure or autonomic function. Candesartan tended to reduce fat mass, but none of the treatments significantly altered indices of metabolic function or mitogen-activated protein kinase signaling pathways in dorsal medulla. Although additional dose response studies are necessary to determine the potential maximal effectiveness of each treatment, the current findings demonstrate that blood pressure and baroreflex function can be essentially normalized independently of medullary nicotinamide adenine dinucleotide phosphate oxidase or mitogen-activated protein kinase in hypertensive (mRen2)27 rats.

Chronic infusion of angiotensin-(1-7) into the lateral ventricle of the brain attenuates hypertension in DOCA-salt rats

Angiotensin-(ANG)-(1-7) is known by its central and peripheral actions, which mainly oppose the deleterious effects induced by accumulation of ANG II during pathophysiological conditions. In the present study we evaluated whether a chronic increase in ANG-(1-7) levels in the brain would modify the progression of hypertension. After DOCA-salt hypertension was induced for seven days, Sprague-Dawley rats were subjected to 14 days of intracerebroventricular (ICV) infusion of ANG-(1-7) (200 ng/h, DOCA-A7) or 0.9% sterile saline. As expected, on the 21st day, DOCA rats presented increased mean arterial pressure (MAP) (≈40%), and impaired baroreflex control of heart rate (HR) and baroreflex renal sympathetic nerve activity (RSNA) in comparison with that in normotensive control rats (CTL). These changes were followed by an overactivity of the cardiac sympathetic tone and reduction of the cardiac parasympathetic tone, and exaggerated mRNA expression of collagen type I (≈9-fold) in the left ventricle. In contrast, DOCA rats treated with ANG-(1-7) ICV had an improvement of baroreflex control of HR, which was even higher than that in CTL, and a restoration of the baroreflex control of RSNA, the balance of cardiac autonomic tone, and normalized mRNA expression of collagen type I in the left ventricle. Furthermore, DOCA-A7 had MAP lowered significantly. These effects were not accompanied by significant circulating or cardiac changes in angiotensin levels. Taken together, our data show that chronic increase in ANG-(1-7) in the brain attenuates the development of DOCA-salt hypertension, highlighting the importance of this peptide in the brain for the treatment of cardiovascular diseases.

Therapeutic targeting of the angiotensin-converting enzyme 2/Angiotensin-(1-7)/Mas cascade in the renin-angiotensin system: a patent review

INTRODUCTION

The renin-angiotensin system (RAS) is a main therapeutic target for cardiovascular diseases. Within the last two decades, novel components of the RAS have been discovered, opening new opportunities to interfere with its activity. Angiotensin(Ang)-(1-7) is synthesized by angiotensin-converting enzyme 2 (ACE2), and interacts with the G-protein-coupled receptor Mas. The axis formed by ACE2/Ang-(1-7)/Mas represents an endogenous counter regulatory pathway within the RAS.

AREAS COVERED

In this review, the authors discuss patents and recent initiatives to develop therapeutic strategies based on the ACE2/Ang-(1-7)/Mas axis.

EXPERT OPINION

Many publications and patents support a strategy to interfere with the activity of the RAS by stimulating its counter-regulatory axis mainly in two different ways: i) To increase the activity of ACE2, which will impact the system by increasing the inactivation of Ang II and the production of Ang-(1-7); ii) To stimulate Mas, taking advantage of nanostructured formulations of the natural peptide or analogues of Ang-(1-7). Although the preclinical studies are compelling, the possible impact of these novel therapeutic tools for the treatment of cardiometabolic diseases will only be known after completion of the ongoing clinical studies.

Chronic activation of endogenous angiotensin-converting enzyme 2 protects diabetic rats from cardiovascular autonomic dysfunction

In this study, we evaluated whether the activation of endogenous angiotensin-converting enzyme 2 (ACE2) would improve the cardiovascular autonomic dysfunction of diabetic rats. Ten days after induction of type 1 diabetes (streptozotocin, 50 mg kg(-1) i.v.), the rats were treated orally with 1-[(2-dimethylamino)ethylamino]-4-(hydroxymethyl)-7-[(4-methylphenyl) sulfonyl oxy]-9H-xanthene-9-one (XNT), a newly discovered ACE2 activator (1 mg kg(-1) day(-1)), or saline (equivalent volume) for 30 days. Autonomic cardiovascular parameters were evaluated in conscious animals, and an isolated heart preparation was used to analyse cardiac function. Diabetes induced a significant decrease in the baroreflex bradycardia sensitivity, as well as in the chemoreflex chronotropic response and parasympathetic tone. The XNT treatment improved these parameters by ≈ 76% [0.82 ± 0.09 versus 1.44 ± 0.17 Ratio between changes in pulse interval and changes in mean arterial pressure (ΔPI/ΔmmHg)], ∼85% (-57 ± 9 versus -105 ± 10 beats min(-1)) and ≈ 205% (22 ± 2 versus 66 ± 12 beats min(-1)), respectively. Also, XNT administration enhanced the bradycardia induced by the chemoreflex activation by v 74% in non-diabetic animals (-98 ± 16 versus -170 ± 9 Δbeats min(-1)). No significant changes were observed in the mean arterial pressure, baroreflex tachycardia sensitivity, chemoreflex pressor response and sympathetic tone among any of the groups. Furthermore, chronic XNT treatment ameliorated the cardiac function of diabetic animals. However, the coronary vasoconstriction observed in diabetic rats was unchanged by ACE2 activation. These findings indicate that XNT protects against the autonomic and cardiac dysfunction induced by diabetes. Thus, our results provide evidence for the viability and effectiveness of oral administration of an ACE2 activator for the treatment of the cardiovascular autonomic dysfunction caused by diabetes.

New cardiovascular and pulmonary therapeutic strategies based on the Angiotensin-converting enzyme 2/angiotensin-(1-7)/mas receptor axis

Angiotensin (Ang)-(1–7) is now recognized as a biologically active component of the renin-angiotensin system (RAS). The discovery of the angiotensin-converting enzyme homologue ACE2 revealed important metabolic pathways involved in the Ang-(1–7) synthesis. This enzyme can form Ang-(1–7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1–9) with subsequent Ang-(1–7) formation. Additionally, it is well established that the G protein-coupled receptor Mas is a functional ligand site for Ang-(1–7). The axis formed by ACE2/Ang-(1–7)/Mas represents an endogenous counter regulatory pathway within the RAS whose actions are opposite to the vasoconstrictor/proliferative arm of the RAS constituted by ACE/Ang II/AT₁ receptor. In this review we will discuss recent findings concerning the biological role of the ACE2/Ang-(1–7)/Mas arm in the cardiovascular and pulmonary system. Also, we will highlight the initiatives to develop potential therapeutic strategies based on this axis.

Role of angiotensin-(1-7) in rostral ventrolateral medulla in blood pressure regulation via sympathetic nerve activity in Wistar-Kyoto and spontaneous hypertensive rats

Angiotensin (Ang)-(1-7) Ang-(1-7) is formed from angiotensin II by angiotensin-converting enzyme 2 (ACE2) and modulates the renin-angiotensin system. We evaluated whether the Ang-(1-7)-Mas axis in the rostral ventrolateral medulla (RVLM) contributes to neural mechanisms of blood pressure (BP) regulation. We microinjected Ang-(1-7), Ang-(1-7)-Mas receptor antagonist A-779, and ACE2 inhibitor DX600 into the RVLM of anesthetized Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHRs). Unilateral Ang-(1-7) microinjection induced a significantly greater increase in AP (arterial blood pressure) in SHR than in WKY. Bilateral A-779 microinjection induced a significantly greater decrease in AP and renal sympathetic nerve activity in SHR than in WKY. Bilateral DX600 microinjection induced a significantly greater decrease in AP in SHR than in WKY. Our results suggest that endogenous Ang-(1-7) in the RVLM contributes to maintain AP and renal sympathetic nerve activity both in SHR and WKY and that its activity might be enhanced in SHR.

Angiotensin peptides and central autonomic regulation

Aging, hypertension, and fetal-programmed cardiovascular disease are associated with a functional deficiency of angiotensin (Ang)-(1-7) in the brain dorsomedial medulla. The resulting unrestrained activity of Ang II in brainstem regions negatively impacts resting mean arterial pressure, sympathovagal balance, and baroreflex sensitivity for control of heart rate. The differential effects of Ang II and Ang-(1-7) may be related to the cellular sources of these peptides as well as different precursor pathways. Long-term alterations of the brain renin-angiotensin system may influence signaling pathways including phosphoinositol-3-kinase and mitogen-activated protein kinase and their downstream mediators, and as a consequence may influence metabolic function. Differential regulation of signaling pathways in aging and hypertension by Ang II versus Ang-(1-7) may contribute to the autonomic dysfunction accompanying these states.

Angiotensin-converting enzyme inhibition changes the metabolic response to neuroglucopenic stress

Neuroglucopenia induced by 2-deoxy-D-glucose (2DG) activates hypothalamic glucoreceptors leading to increased hepatic glucose production and insulin inhibition. This response is similar to what is observed with intravenous injection of angiotensin II (Ang II). However, the involvement of an angiotensin-converting enzyme inhibitor on neuroglucopenia has not been investigated. The aim of this study was to determine the effects of chronic enalapril treatment on plasma glucose, insulin and lipid levels in response to neuroglucopenia. Male Holtzman rats (120-170 g) were chronically treated with enalapril (10 mg/kg per day) in the drinking water for two weeks. On the day of experiment the animals received an i.v. enalapril final dose one hour before the neuroglucopenic stress by 2DG infusion (500 mg/kg), and blood samples were drawn before and 5, 10, 20, 30 and 60 minutes following infusion. The hyperglycaemic response to 2DG was not significantly changed by enalapril treatment. The enalapril-treated group exhibited a peak of plasma insulin higher than controls. Plasma triglyceride showed a significant increase only in the enalapril group after neuroglucopenic stress (p < 0.05).These data show that chronic enalapril treatment changes insulin and triglyceride responses to neuroglucopenia, suggesting an effect on glucose-induced insulin secretion and the storage of triglycerides.

Hydrogen sulfide inhibits plasma renin activity

The development of renovascular hypertension depends on the release of renin from the juxtaglomerular (JG) cells, a process regulated by intracellular cAMP. Hydrogen sulfide (H2S) downregulates cAMP production in some cell types by inhibiting adenylyl cyclase, suggesting the possibility that it may modulate renin release. Here, we investigated the effect of H2S on plasma renin activity and BP in rat models of renovascular hypertension. In the two-kidney-one-clip (2K1C) model of renovascular hypertension, the H2S donor NaHS prevented and treated hypertension. Compared with vehicle, NaHS significantly attenuated the elevation in plasma renin activity and angiotensin II levels but did not affect plasma angiotensin-converting enzyme activity. Furthermore, NaHS inhibited the upregulation of renin mRNA and protein levels in the clipped kidneys of 2K1C rats. In primary cultures of renin-rich kidney cells, NaHS markedly suppressed forskolin-stimulated renin activity in the medium and the intracellular increase in cAMP. In contrast, NaHS did not affect BP or plasma renin activity in normal or one-kidney-one-clip (1K1C) rats, both of which had normal plasma renin activity. In conclusion, these results demonstrate that H2S may inhibit renin activity by decreasing the synthesis and release of renin, suggesting its potential therapeutic value for renovascular hypertension.

Angiotensin-(1-7) antagonist, A-779, microinjection into the caudal ventrolateral medulla of renovascular hypertensive rats restores baroreflex bradycardia

In the present study we evaluated the effect of caudal ventrolateral medulla (CVLM) microinjection of the main angiotensin (Ang) peptides, Ang II and Ang-(1-7), and their selective antagonists on baseline arterial pressure (AP) and on baroreceptor-mediated bradycardia in renovascular hypertensive rats (2K1C). Microinjection of Ang II and Ang-(1-7) into the CVLM of 2K1C rats produced similar decrease in AP as observed in Sham rats. In both Sham and 2K1C, the hypotensive effect of Ang II and Ang-(1-7) at the CVLM was blocked, for up to 30 min, by previous CVLM microinjection of the Ang II AT1 receptor antagonist, Losartan, and Ang-(1-7) Mas antagonist, A-779, respectively. As expected, the baroreflex bradycardia was lower in 2K1C in comparison to Sham rats. CVLM microinjection of A-779 improved the sensitivity of baroreflex bradycardia in 2K1C hypertensive rats. In contrast, Losartan had no effect on the baroreflex bradycardia in either 2K1C or Sham rats. These results suggest that Ang-(1-7) at the CVLM may contribute to the low sensitivity of the baroreflex control of heart rate in renovascular hypertensive rats.

Angiotensin-(1-7) and baroreflex function in nucleus tractus solitarii of (mRen2)27 transgenic rats

BACKGROUND

Endogenous angiotensin (Ang)-(1-7) enhances, while Ang II attenuates, baroreceptor sensitivity (BRS) for reflex control of heart rate (HR) in Sprague-Dawley (SD) rats. In (mRen2)27 renin transgenic rats [(mRen2)], there is overexpression of the mouse Ren2 gene in brain, leading to elevated Ang II and reduced Ang-(1-7) in brain medullary, and associated with hypertension and impaired BRS.

METHODS

We therefore tested the contribution of endogenous Ang-(1-7) to BRS for control of HR and responses to cardiac vagal chemosensitive afferent fiber activation (CVA) with phenylbiguanide (PBG) in anesthetized SD and (mRen2) 27 rats before and after bilateral nucleus of the solitary tract (nTS) injection of the Ang-(1-7) receptor antagonist (D-Ala7)-Ang-(1-7).

RESULTS

(mRen2) 27 rats exhibited a approximately 50% impairment in BRS as compared with SD (P < 0.05). (D-Ala7)-Ang-(1-7) attenuated BRS by approximately 50% in SD rats, but was without effect in (mRen2) 27 rats. (D-Ala7)-Ang-(1-7) did not alter the responses to CVA by PBG (iv bolus) in either strain. There were no differences in the depressor effects of Ang-(1-7) injected into the nTS, nor were levels of mRNA different for angiotensin-converting enzyme, angiotensin-converting enzyme 2, neprilysin, or the mas receptor in medullary tissue from SD versus (mRen2)27 rats.

CONCLUSION

Endogenous Ang-(1-7) does not provide tonic input in the nTS to modulate BRS for control of HR in (mRen2)27 rats, which may contribute to impairment of BRS in these animals.

Baroreflex control of heart rate and renal sympathetic nerve activity in rats with low brain angiotensinogen

The main objective of the present study was to evaluate baroreceptor control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in transgenic rats (TG) with low angiotensinogen production in glial cells, TGR(ASrAogen)-680. In addition, the sympathetic and vagal autonomic tonus to the heart was investigated. As previously shown, TG rats presented a lower arterial pressure (AP) and HR. However, TG rats had decreased AP variability during the night (8.9+/-0.4 mmHg vs 9.8+/-0.3 mmHg, in SD) accompanied by an increase in HR variability (39+/-1 beats/min vs 35+/-1 beats/min, in SD) and augmented locomotor activity during the night (3.5+/-0.3 counts/min vs 2.5+/-0.2 counts/min, in SD). In addition, TG rats presented increased baroreflex sensitivity for the RSNA (slope of line that correlates decreases in RSNA and increases in AP=1.36+/-0.18 vs 0.77+/-0.1, in SD) and an increased sensitivity for both the baroreflex bradycardia (0.79+/-0.04 ms/mmHg vs 0.52+/-0.04 ms/mmHg, in SD) and tachycardia (1.46+/-0.1 ms/mmHg vs 0.93+/-0.01 ms/mmHg, in SD). Further, TG rats had increased vagal tonus (25+/-3 beats/min vs 11+/-4 beats/min in SD) without significant change in the sympathetic tonus to the heart. These results confirm and extend previous observations showing that glial angiotensinogen, the main source of brain RAS peptides, importantly modulates sympathetic tonus, at least to the renal nerve, and vagal tonus to the heart.

Differential regulation of the renin-angiotensin system by nicotine in WKY and SHR glia

Given that (1) the renin-angiotensin system (RAS) is compartmentalized within the central nervous system in neurons and glia (2) the major source of brain angiotensinogen is the glial cells, (3) the importance of RAS in the central control of blood pressure, and (4) nicotine increases the probability of development of hypertension associated to genetic predisposition; the objective of the present study was to evaluate the effects of nicotine on the RAS in cultured glial cells from the brainstem and hypothalamus of Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Ligand binding, real-time PCR and western blotting assays were used to compare the expression of angiotensinogen, angiotensin converting enzyme, angiotensin converting enzyme 2 and angiotensin II type1 receptors. We demonstrate, for the first time, that there are significant differences in the basal levels of RAS components between WKY and SHR rats in glia from 1-day-old rats. We also observed that nicotine is able to modulate the renin-angiotensin system in glial cells from the brainstem and hypothalamus and that the SHR responses were more pronounced than WKY ones. The present data suggest that nicotine effects on the RAS might collaborate to the development of neurogenic hypertension in SHR through modulation of glial cells.

Nicotine modulates the renin-angiotensin system of cultured neurons and glial cells from cardiovascular brain areas of Wistar Kyoto and spontaneously hypertensive rats

Considering the importance of the renin-angiotensin system (RAS) for the central control of blood pressure and that nicotine increases the probability of development of hypertension associated to genetic predisposition, our aims are (1) to determine RAS in cultured neurons and glia from the brainstem and hypothalamus of spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats; (2) to analyze the possibility of nicotine to interact with brain RAS; and (3) to hypothesize any contribution of nicotine and RAS to the development of neurogenic hypertension. This study demonstrated physiological differences in RAS between cultured neuronal and glial cells from the brainstem and hypothalamus of SHR and WKY neonate rats. Our study also featured evidences of direct modulation of the RAS by nicotine in neurons and glia of brainstem and hypothalamus, which seems to be differential between the two rat strains. Such modulation gives us a clue about the mechanisms possibly involved in the genesis of neurogenic hypertension in vivo, for example, increase in angiotensin II type 1 receptor binding and decrease in angiotensin-converting enzyme 2. In conclusion, we demonstrated that neuronal and glial RAS from the brainstem and hypothalamus of SHR differ from WKY rats and nicotine differentially modulates the brain RAS in SHR and WKY.

Liver fibrosis: a balance of ACEs?

There is an increasing body of evidence to suggest that the RAS (renin–angiotensin system) contributes to tissue injury and fibrosis in chronic liver disease. A number of studies have shown that components of a local hepatic RAS are up-regulated in fibrotic livers of humans and in experimental animal models. Angiotensin II, the main physiological effector molecule of this system, mediates liver fibrosis by stimulating fibroblast proliferation (myofibroblast and hepatic stellate cells), infiltration of inflammatory cells, and the release of inflammatory cytokines and growth factors such as TGF (transforming growth factor)-β1, IL (interleukin)-1β, MCP (monocyte chemoattractant protein)-1 and connective tissue growth factor. Furthermore, blockade of the RAS by ACE (angiotensin-converting enzyme) inhibitors and angiotensin type 1 receptor antagonists significantly attenuate liver fibrosis in experimental models of chronic liver injury. In 2000 ACE2 (angiotensin-converting enzyme 2), a human homologue of ACE, was identified. ACE2 efficiently degrades angiotensin II to angiotensin-(1–7), a peptide which has recently been shown to have both vasodilatory and tissue protective effects. This suggests that ACE2 and its products may be part of an alternate enzymatic pathway in the RAS, which counterbalances the generation and actions of angiotensin II, the ACE2–angiotensin-(1–7)–Mas axis. This review focuses on the potential roles of the RAS, angiotensin II and ACE2 in chronic liver injury and fibrogenesis.

Evidence for a role of AT(2) receptors at the CVLM in the cardiovascular changes induced by low-intensity physical activity in renovascular hypertensive rats

In the present study, we evaluated the involvement of the rennin-angiotensin system (RAS) in the control of the blood pressure (BP), baroreceptor-mediated bradycardia and the reactivity of caudal ventrolateral medulla (CVLM) neurons to Ang II and to AT(2) receptor antagonist in sedentary or trained renovascular hypertensive rats. Physical activity did not significantly change the baseline mean arterial pressure (MAP), heart rate (HR) or the sensitivity of the baroreflex bradycardia in normotensive Sham rats. However, in 2K1C hypertensive rats, physical activity induced a significant fall in baseline MAP and HR and produced an improvement of the baroreflex function (bradycardic component). The microinjections of Ang II into the CVLM produced similar decreases in MAP in all groups, Sham and 2K1C, sedentary and trained rats. The hypotensive effect of Ang II at the CVLM was blocked by previous microinjection of the AT(2) receptors antagonist, PD123319, in all groups of rats. Unexpectedly, microinjection of PD123319 at the CVLM produced a depressor effect in 2K1C sedentary that was attenuated in 2K1C trained rats. No significant changes in MAP were observed after PD123319 in Sham rats, sedentary or trained. These data showed that low-intensity physical activity is effective in lowering blood pressure and restoring the sensitivity of the baroreflex bradycardia, however these cardiovascular effects are not accompanied by changes in the responsiveness to Ang II at CVLM in normotensive or hypertensive, 2K1C rats. In addition, the blood pressure changes observed after AT(2) blockade in 2K1C rats suggest that hypertension may trigger an imbalance of AT(1)/AT(2) receptors at the CVLM that may be restored, at least in part, by low-intensity physical activity.