Angiotensin-(1-7) reduces norepinephrine release through a nitric oxide mechanism in rat hypothalamus

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.

Angiotensin-(1-7) attenuates the negative inotropic response to acetylcholine in the heart

Previous studies have suggested that the Angiotensin-(1-7) [(Ang-(1-7)] can change cardiac function by modulating the autonomic nervous system. However, it is unknown whether the Ang-(1-7) can modulate the effect of acetylcholine (ACh) in ventricular contractility. Thus, this study aimed to investigate whether Ang-(1-7) modifies the amplitude of the cardiac cholinergic effects and if these effects are intrinsic to the heart. In anesthetized Wistar rats, Ang-(1-7) attenuated the effect of ACh in decreasing the left ventricular end-systolic pressure (LVESP), dP/dt_max, and dP/dt_min, but did not modify the hypotensive effect of ACh. Similarly, Ang-(1-7) attenuated the reduction of the LVESP, dP/dt_max, and dP/dt_min evoked by ACh in isolated hearts. These effects were blocked by the Mas receptor antagonist, A-779, but not by the adenylyl cyclase inhibitor MDL-12,330 A. Ang-(1-7) also attenuated the reduction in the maximum contraction and relaxation speeds and the shortening promoted by ACh in isolated cardiomyocytes. These data show that Ang-(1-7) acting through Mas receptor counter-regulates the myocardial contractile response to ACh in an arterial pressure and heart rate-independent manner.

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) and Mas receptor in the brain

The renin-angiotensin system (RAS) is a key regulator of blood pressure and electrolyte homeostasis. Besides its importance as regulator of the cardiovascular function, the RAS has also been associated to the modulation of higher brain functions, including cognition, memory, depression and anxiety. For many years, angiotensin II (Ang II) has been considered the major bioactive component of the RAS. However, the existence of many other biologically active RAS components has currently been recognized, with similar, opposite, or distinct effects to those exerted by Ang II. Today, it is considered that the RAS is primarily constituted by two opposite arms. The pressor arm is composed by Ang II and the Ang II type 1 (AT1) receptor (AT1R), which mediates the vasoconstrictor, proliferative, hypertensive, oxidative and pro-inflammatory effects of the RAS. The depressor arm is mainly composed by Ang-(1-7), its Mas receptor (MasR) which mediates the depressor, vasodilatory, antiproliferative, antioxidant and anti-inflammatory effects of Ang-(1-7) and the AT2 receptor (AT2R), which opposes to the effects mediated by AT1R activation. Central Ang-(1-7) is implicated in the control of the cardiovascular function, thus participating in the regulation of blood pressure. Ang-(1-7) also exerts neuroprotective actions through MasR activation by opposing to the harmful effects of the Ang II/AT1R axis. This review is focused on the expression and regulation of the Ang-(1-7)/MasR axis in the brain, its main neuroprotective effects and the evidence regarding its involvement in the pathophysiology of several diseases at cardiovascular and neurological level.

Angiotensin-(1-7) oral formulation improves physical performance in mountain bike athletes: a double-blinded crossover study

BACKGROUND

The ECA2/Ang-(1-7)/Mas axis is shown to be involved in effects mediated by physical exercise, as it can induce the release of nitric oxide (ON) and bradykinin (BK), which are potent vasodilators. The vasodilating action the NO/BK can contribute to increased metabolic efficiency in muscle tissue and central nervous system. The formulation HPβ-CD-Ang-(1-7) through its mechanisms of action can be a promising supplement to aid in the maintenance and improvement of performance and may also favor recovery during competitions. The premise of this study was to investigate the effects of acute oral supplementation HPβ-CD-Ang-(1-7) on the performance of mountain bike (MTB) practitioners.

METHODS

Fourteen recreational athletes, involved in training programs for at least one year, participated in this crossover design study. Subjects underwent two days of testing with a seven-day interval. HPβ-CD-Ang-(1-7) (1.75 mg) and HPβCD-Placebo were provided in capsules three hours prior to tests. To determine the safety of the HPβ-CD-Ang-(1-7) formulation associated with physical effort, cardiovascular parameters heart rate (HR) and blood pressure (BP) were analyzed. Physical performance was measured using maximal oxygen uptake (VO2), total exercise time (TET), mechanical work (MW), mechanical efficiency (ME), and rating of perceived exertion (RPE). Respiratory exchange coefficient (REC), lactate and non-esterified fatty acids (NEFAs) were measured. Maximal incremental tests were performed on a progressively loaded leg cycle ergometer.

RESULTS

There were no significant differences in terms of HR or BP at rest and maximum effort between the HPβ-CD-Ang-(1-7) and placebo groups. The VO2max showed significant differences (p = 0.04). It was higher in the Ang-(1-7)condition (66.15 mlO2.kg- 1.min- 1) compared to the placebo (60.72 mlO2.kg- 1.min- 1). This was also observed for TET (Ang-(1-7) 39.10 min vs. placebo 38.14 min; p = 0.04), MW (Ang-(1-7) 156.7 vs. placebo 148.2; p = 0.04), and at the lowest RPE (Ang-(1-7) vs. placebo; p = 0.009). No significant differences were observed for REC, NEFAs, or Lactate.

CONCLUSIONS

These results suggest that HPβ-CD-Ang-(1-7) improves the physical performance of MTB recreational athletes and could be a promising supplement.

TRIAL REGISTRATION

RBR-2 × 56pw8, registered January 15th, 2021. The study was prospectively registered.

Different reactive species modulate the hypotensive effect triggered by angiotensins at CVLM of 2K1C hypertensive rats

Hypertension is associated with increased central activity of the renin-angiotensin system (RAS) and oxidative stress. Here, we evaluated whether reactive species and neurotransmitters could contribute to the hypotensive effect induced by angiotensin (Ang) II and Ang-(1-7) at the caudal ventrolateral medulla (CVLM) in renovascular hypertensive rats (2K1C). Therefore, we investigated the effect of Ang II, Ang-(1-7), and the Ang-(1-7) antagonist A-779 microinjected before and after CVLM microinjection of the nitric oxide (NO)-synthase inhibitor, (L-NAME), vitamin C (Vit C), bicuculline, or kynurenic acid in 2K1C and SHAM rats. Baseline values of the mean arterial pressure (MAP) in 2K1C rats were higher than in SHAM rats. CVLM microinjection of Ang II, Ang-(1-7), l-NAME, or bicuculline induced decreases in the MAP in SHAM and 2K1C rats. In addition, Vit C and A-779 produced decreases in the MAP only in 2K1C rats. Kynurenic acid increased the MAP in both SHAM and 2K1C rats. Only the Ang-(1-7) effect was increased by l-NAME and reduced by bicuculline in SHAM rats. L-NAME also reduced the A-779 effect in 2K1C rats. Only the Ang II effect was abolished by CVLM Vit C and enhanced by CVLM kynurenic acid in SHAM and 2K1C rats. Overall, the superoxide anion and glutamate participated in the hypotensive effect of Ang II, while NO and GABA participated in the hypotensive effect of Ang-(1-7) in CVLM. The higher hypotensive response of A-779 in the CVLM of 2K1C rats suggests that Ang-(1-7) contributes to renovascular hypertension.

Impact of COVID-19 on Alzheimer's Disease Risk: Viewpoint for Research Action

In the middle of the coronavirus disease 19 (COVID-19) outbreak, the main efforts of the scientific community are rightly all focused on identifying efficient pharmacological treatments to cure the acute severe symptoms and developing a reliable vaccine. On the other hand, we cannot exclude that, in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) positive subjects, the virus infection could have long-term consequences, leading to chronic medical conditions such as dementia and neurodegenerative disease. Considering the age of SARS-CoV-2 infected subjects, the neuroinvasive potential might lead/contribute to the development of neurodegenerative diseases. Here, we analyzed a possible link between SARS-CoV-2 infection and Alzheimer's disease risk, hypothesizing possible mechanisms at the base of disease development. This reflection raises the need to start to experimentally investigating today the mechanistic link between Alzheimer's disease (AD) and COVID-19 to be ready tomorrow.

The depressor axis of the renin–angiotensin system and brain disorders: a translational approach

All the components of the classic renin–angiotensin system (RAS) have been identified in the brain. Today, the RAS is considered to be composed mainly of two axes: the pressor axis, represented by angiotensin (Ang) II/angiotensin-converting enzyme/AT1 receptors, and the depressor and protective one, represented by Ang-(1–7)/ angiotensin-converting enzyme 2/Mas receptors. Although the RAS exerts a pivotal role on electrolyte homeostasis and blood pressure regulation, their components are also implicated in higher brain functions, including cognition, memory, anxiety and depression, and several neurological disorders. Overactivity of the pressor axis of the RAS has been implicated in stroke and several brain disorders, such as cognitive impairment, dementia, and Alzheimer or Parkinson’s disease. The present review is focused on the role of the protective axis of the RAS in brain disorders beyond its effects on blood pressure regulation. Furthermore, the use of drugs targeting centrally RAS and its beneficial effects on brain disorders are also discussed.

Angiotensin-(1-7) attenuates hypertension and cardiac hypertrophy via modulation of nitric oxide and neurotransmitter levels in the paraventricular nucleus in salt-sensitive hypertensive rats

Angiotensin-(1-7) [Ang-(1-7)] is a multifunctional bioactive angiotensin peptide which exerts a cardiovascular protective function mainly by opposing the effects of angiotensin II. We aimed to determine whether brain Ang-(1-7) regulates nitric oxide (NO) and neurotransmitter levels in the hypothalamic paraventricular nucleus (PVN), and influences sympathetic activity, blood pressure and cardiac hypertrophy in salt-sensitive hypertension. Dahl salt-sensitive rats receiving a high-salt (HS, 8% NaCl) or a normal-salt (NS, 0.3% NaCl) diet were treated with an intracerebroventricular (ICV) infusion of Ang-(1-7) for 6 weeks. Seven rats were measured in each group. In comparison with NS rats, HS rats exhibited significantly increased mean arterial pressure, plasma norepinephrine (NE) and cardiac hypertrophy. In addition, HS rats (compared to NS rats) had increased glutamate, NE and tyrosine hydroxylase (TH) expression, and reduced NO levels as well as reduced expression of γ-aminobutyric acid (GABA) and the 67 kDa isoform of glutamate decarboxylase (GAD67) in the PVN. Treatment with ICV infusion of Ang-(1-7) reversed these changes in the salt-sensitive hypertensive rats. The results suggest that the beneficial effects of brain Ang-(1-7) on salt-sensitive hypertension and cardiac hypertrophy are partly due to an elevation in the NO level and restoration of neurotransmitter balance in the PVN.

Angiotensin-(1-7) [Ang-(1-7)] is a multifunctional bioactive angiotensin peptide which exerts a cardiovascular protective function mainly by opposing the effects of angiotensin II.

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.

Brain angiotensin-(1-7)/Mas axis: A new target to reduce the cardiovascular risk to emotional stress

Emotional stress is now considered a risk factor for several diseases including cardiac arrhythmias and hypertension. It is well known that the activation of neuroendocrine and autonomic mechanisms features the response to emotional stress. However, its link to cardiovascular diseases and the regulatory mechanisms involved remain to be further comprehended. The renin-angiotensin system (RAS) plays an important role in homeostasis on all body systems. Specifically in the brain, the RAS regulates a number of physiological aspects. Recent data indicate that the activation of angiotensin-converting enzyme/angiotensin II/AT1 receptor axis facilitates the emotional stress responses. On the other hand, growing evidence indicates that its counterregulatory axis, the angiotensin-converting enzyme 2 (ACE2)/(Ang)iotensin-(1-7)/Mas axis, reduces anxiety and attenuates the physiological responses to emotional stress. The present review focuses on angiotensin-(1-7)/Mas axis as a promising target to attenuate the physiological response to emotional stress reducing the risk of cardiovascular diseases.

Angiotensin-(1-7): beyond its central effects on blood pressure

Angiotensin (Ang) (1-7) is the main component of the depressor and protective arm of the renin-angiotensin system. Ang-(1-7) induces vasodilation, natriuresis and diuresis, cardioprotection, inhibits angiogenesis and cell growth and opposes the pressor, proliferative, profibrotic, and prothrombotic actions mediated by Ang II. Centrally, Ang-(1-7) induces changes in mean arterial pressure and this effect may be linked with its inhibitory neuromodulatory action on norepinephrine neurotransmission. The present review is focused on the role of Ang-(1-7) as a protective agent in the brain.

Chronic oral administration of Ang-(1-7) improves skeletal muscle, autonomic and locomotor phenotypes in muscular dystrophy

Muscular dystrophies are a group of heterogeneous genetic disorders that cause progressive muscle weakness and wasting, dilated cardiomyopathy and early mortality. There are different types of muscular dystrophies with varying aetiologies but they all have a common hallmark of myofibre degeneration, atrophy and decreased mobility. Mutation in Sgcd (sarcoglycan-δ), a subunit of dystrophin glycoprotein complex, causes LGMD2F (limb girdle muscular dystrophy 2F). Previously, we have reported that Sgcd-deficient (Sgcd-/-) mice exhibit AngII (angiotensin II)-induced autonomic and skeletal muscle dysfunction at a young age, which contributes to onset of dilated cardiomyopathy and mortality at older ages. Two counter-regulatory RAS (renin-angiotensin system) pathways have been identified: deleterious actions of AngII acting on the AT1R (AngII type 1 receptor) compared with the protective actions of Ang-(1-7) [angiotensin-(1-7)] acting on the receptor Mas. We propose that the balance between the AngII/AT1R and Ang-(1-7)/Mas axes is disturbed in Sgcd-/- mice. Control C57BL/6J and Sgcd-/- mice were treated with Ang-(1-7) included in hydroxypropyl β-cyclodextrin (in drinking water) for 8-9 weeks beginning at 3 weeks of age. Ang-(1-7) treatment restored the AngII/AT1R compared with Ang-(1-7)/Mas balance, decreased oxidative stress and fibrosis in skeletal muscle, increased locomotor activity, and prevented autonomic dysfunction without lowering blood pressure in Sgcd-/- mice. Our results suggest that correcting the early autonomic dysregulation by administering Ang-(1-7) or enhancing its endogenous production may provide a novel therapeutic approach in muscular dystrophy.

Ang-(1-7) activates the NO/cGMP and ATP-sensitive K+ channels pathway to induce peripheral antinociception in rats

Angiotensin-(1-7) is a bioactive component of the renin-angiotensin system that is formed endogenously and induces nitric oxide release in several tissues. The L-arginine/NO/cyclic GMP pathway and ATP-sensitive K+ channels have been proposed as the mechanism of action for the peripheral antinociception of several groups of drug and endogenous substances, including opioids, non-steroidal analgesics, acetylcholine and others. The aim of the present study was to investigate the involvement of the L-arginine/NO/cGMP and KATP+ pathway on antinociception induced by angiotensin-(1-7). Paw pressure in rats was used to induce hyperalgesia via an intraplantar injection of prostaglandin E2 (2 μg/paw). Ang-(1-7) (2, 3 and 4 μg/paw) elicited a local peripheral antinociceptive effect that was antagonized by the nonselective NO synthase (NOS) inhibitor L-NOarg and the selective neuronal NOS (nNOS) inhibitor L-NPA. The selective inhibition of endothelial (eNOS) and inducible (iNOS) NOS by L-NIO and L-NIL, respectively, was ineffective at blocking the effects of a local Ang-(1-7) injection. In addition, the level of nitrite in the homogenized paw tissue, as determined by a colorimetric assay, indicated that exogenous Ang-(1-7) is able to induce NO release. The soluble guanylyl cyclase inhibitor ODQ and the specific blocker of ATP-sensitive K+ channels glibenclamide (40, 80 and 160 μg/paw) antagonized the Ang-(1-7) response. The results provide evidence that Ang-(1-7) most likely induces peripheral antinociceptive effects via the L-arginine/NO/cGMP pathway and KATP+ pathway activation.

Angiotensin peptides and nitric oxide in cardiovascular disease

SIGNIFICANCE

The renin-angiotensin system (RAS) plays an important role in the normal control of cardiovascular and renal function in the healthy state and is a contributing factor in the development and progression of various types of cardiovascular diseases (CVD), including hypertension, diabetes, and heart failure.

RECENT ADVANCES

Evidence suggests that a balance between activation of the ACE/Ang II/AT1 receptor axis and the ACE2/Ang-(1-7)/Mas receptor axis is important for the function of the heart, kidney, and autonomic nervous system control of the circulation in the normal healthy state. An imbalance in these opposing pathways toward the ACE/Ang II/AT1 receptor axis is associated with CVD. The key component of this imbalance with respect to neural control of the circulation is the negative interaction between oxidative and NO• mechanisms, which leads to enhanced sympathetic tone and activation in disease conditions such as hypertension and heart failure.

CRITICAL ISSUES

The key mechanisms that disrupt normal regulation of Ang II and Ang-(1-7) signaling and promote pathogenesis of CVD at all organ levels remain poorly understood. The reciprocal relation between ACE and ACE2 expression and function suggests they are controlled interdependently at pre- and post-translational levels. Insights from neural studies suggest that an interaction between oxidative and nitrosative pathways may be key.

FUTURE DIRECTIONS

The role of redox mechanisms in the control of expression and activity of RAS enzymes and Ang receptors may provide important insight into the function of local tissue RAS in health and disease.

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.

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.

Angiotensin II and angiotensin-1-7 redox signaling in the central nervous system

Reactive oxygen species (ROS) are important intra-neuronal signaling intermediates in angiotensin II (AngII)-related neuro-cardiovascular diseases associated with excessive sympathoexcitation, including hypertension and heart failure. ROS-sensitive effector mechanisms, such as modulation of ion channel activity, indicate that elevated levels of ROS increase neuronal activity. Nitric oxide, which may work to counter the effects of ROS, particularly superoxide, has been identified as a signaling molecule in angiotensin-1-7 (Ang-(1-7)) stimulated neurons. This review focuses on recent studies that have revealed details on the AngII-activated sources of ROS, the downstream redox-sensitive effectors, Ang-(1-7)-stimulated increase in nitric oxide, and the neuro-cardiovascular (patho)physiological responses modulated by these reactive species. Understanding these intra-neuronal signaling mechanisms should provide insight for the development of new redox-based therapeutics for the improved treatment of angiotensin-dependent neuro-cardiovascular diseases.

Angiotensin-(1-7) increases neuronal potassium current via a nitric oxide-dependent mechanism

Actions of angiotensin-(1-7) [Ang-(1-7)], a heptapeptide of the renin-angiotensin system, in the periphery are mediated, at least in part, by activation of nitric oxide (NO) synthase (NOS) and generation NO(·). Studies of the central nervous system have shown that NO(·) acts as a sympathoinhibitory molecule and thus may play a protective role in neurocardiovascular diseases associated with sympathoexcitation, such as hypertension and heart failure. However, the contribution of NO in the intraneuronal signaling pathway of Ang-(1-7) and the subsequent modulation of neuronal activity remains unclear. Here, we tested the hypothesis that neuronal NOS (nNOS)-derived NO(·) mediates changes in neuronal activity following Ang-(1-7) stimulation. For these studies, we used differentiated catecholaminergic (CATH.a) neurons, which we show express the Ang-(1-7) receptor (Mas R) and nNOS. Stimulation of CATH.a neurons with Ang-(1-7) (100 nM) increased intracellular NO levels, as measured by 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM) fluorescence and confocal microscopy. This response was significantly attenuated in neurons pretreated with the Mas R antagonist (A-779), a nonspecific NOS inhibitor (nitro-L-arginine methyl ester), or an nNOS inhibitor (S-methyl-L-thiocitrulline, SMTC), but not by endothelial NOS (eNOS) or inhibitory NOS (iNOS) inhibition {L-N-5-(1-iminoethyl)ornithine (L-NIO) and 1400W, respectively}. To examine the effect of Ang-(1-7)-NO(·) signaling on neuronal activity, we recorded voltage-gated outward K(+) current (I(Kv)) in CATH.a neurons using the whole cell configuration of the patch-clamp technique. Ang-(1-7) significantly increased I(Kv), and this response was inhibited by A-779 or S-methyl-L-thiocitrulline, but not L-NIO or 1400W. These findings indicate that Ang-(1-7) is capable of increasing nNOS-derived NO(·) levels, which in turn, activates hyperpolarizing I(Kv) in catecholaminergic neurons.

ACE2/ANG-(1-7)/Mas pathway in the brain: the axis of good

The last decade has seen the discovery of several new components of the renin-angiotensin system (RAS). Among them, angiotensin converting enzyme-2 (ACE2) and the Mas receptor have forced a reevaluation of the original cascade and led to the emergence of a new arm of the RAS: the ACE2/ANG-(1-7)/Mas axis. Accordingly, the new system is now seen as a balance between a provasoconstrictor, profibrotic, progrowth axis (ACE/ANG-II/AT(1) receptor) and a provasodilatory, antifibrotic, antigrowth arm (ACE2/ANG-(1-7)/Mas receptor). Already, this simplistic vision is evolving and new components are branching out upstream [ANG-(1-12) and (pro)renin receptor] and downstream (angiotensin-IV and other angiotensin peptides) of the classical cascade. In this review, we will summarize the role of the ACE2/ANG-(1-7)/Mas receptor, focusing on the central nervous system with respect to cardiovascular diseases such as hypertension, chronic heart failure, and stroke, as well as neurological diseases. In addition, we will discuss the new pharmacological (antagonists, agonists, activators) and genomic (knockout and transgenic animals) tools that are currently available. Finally, we will review the latest data regarding the various signaling pathways downstream of the Mas receptor.

Angiotensin-(1-7) ameliorates myocardial remodeling and interstitial fibrosis in spontaneous hypertension: role of MMPs/TIMPs

Angiotensin-(1-7) displays antihypertensive and antiproliferative properties although its effect on cardiac remodeling and hypertrophy in hypertension has not been fully elucidated. The present study was designed to examine the effect of chronic angiotensin-(1-7) treatment on myocardial remodeling, cardiac hypertrophy and underlying mechanisms in spontaneous hypertension. Adult male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were treated with or without angiotensin-(1-7) or the angiotensin-(1-7) antagonist A-779 for 24 weeks. Mean arterial pressure, left ventricular geometry, expression of the hypertrophic markers ANP and β-MHC, collagen contents (type I and III), collagenase (MMP-1), matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of MMPs-1 (TIMP-1) were evaluated in WKY and SHR rats with or without treatment. Our data revealed that chronic angiotensin-(1-7) treatment significantly suppressed hypertension, left ventricular hypertrophy, expression of ANP and β-MHC as well as myocardial fibrosis in SHR rats, the effects of which were nullified by the angiotensin-(1-7) receptor antagonist A-779. In addition, angiotensin-(1-7) treatment significantly counteracted hypertension-induced changes in the mRNA expression of MMP-2 and TIMP-1 and collagenase activity, the effects of which were blunted by A-779. In vitro study revealed that angiotensin-(1-7) directly increased the activity of MMP-2 and MMP-9 while decreasing the content of TIMP-1 and TIMP-2. Taken together, our results revealed a protective effect of angiotensin-(1-7) against cardiac hypertrophy and collagen deposition, which may be related to concerted changes in MMPs and TIMPs levels. These data indicated the therapeutic potential of angiotensin-(1-7) in spontaneous hypertension-induced cardiac remodeling.

Angiotensin-converting enzyme 2: central regulator for cardiovascular function

Angiotensin-converting enzyme 2 (ACE2) is a new component of the renin-angiotensin system (RAS). Accumulating evidence shows that ACE2 provides protective effects in peripheral tissues and has great potential for the treatment of RAS-related diseases. The role of ACE2 in the central nervous system is not well established. However, in recent years, much more progress has been made on the studies of this carboxypeptidase in the central regulation of blood pressure and cardiovascular function in general. It has been shown that brain ACE2 interacts with the other components of the RAS (ACE, angiotensin II, and angiotensin II type 1 receptor), protects baroreflex and autonomic function, stimulates nitric oxide release, reduces oxidative stress, and prevents the development of or attenuates hypertension. These data support the critical role of ACE2 in the central regulation of cardiovascular function. This review summarizes recently published data on the central effects of ACE2 in the regulation of cardiovascular function.

Brain derived neurotrophic factor and neurotrophin-4 employ different intracellular pathways to modulate norepinephrine uptake and release in rat hypothalamus

Classical actions of the neurotrophin family are related to cellular survival and differentiation. Moreover, acute effects of neurotrophins have been reported. Although neurotrophins effects on synaptic transmission at central nervous system level have been largely studied, acute effects of neurotrophins on hypothalamic noradrenergic transmission are still poorly understood. Thus, we have studied the effects of the neurotrophin family members nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neurotrophin-4 (NT-4) on norepinephrine (NE) neuronal uptake and its evoked release, as well as the receptor and the intracellular pathways involved in these processes in rat hypothalamus. Present results indicate that BDNF increased NE uptake and decreased its evoked release through a mechanism that involve Trk B receptor and phospholipase C. Moreover, NT-4, also through the Trk B receptor, decreased NE uptake and its evoked release by activating phosphatidylinositol 3-OH-kinase. These effects were observed in whole hypothalamus as well as in the anterior hypothalamic zone. On the other hand, NGF did not modify noradrenergic transmission. In conclusion, we showed for the first time that BDNF and NT-4 activate two different intracellular signalling pathways through a Trk B receptor dependent mechanism. Furthermore, present findings support the hypothesis that BDNF and NT-4 acutely applied, could be considered as modulators of noradrenergic transmission and thus may regulate hypothalamic physiological as well as pathophysiological responses.

Angiotensin-converting enzyme 2 in the brain: properties and future directions

Angiotensin (Ang)-converting enzyme (ACE) 2 cleaves Ang-II into the vasodilator peptide Ang-(1-7), thus acting as a pivotal element in balancing the local effects of these peptides. ACE2 has been identified in various tissues and is supposed to be a modulator of cardiovascular function. Decreases in ACE2 expression and activity have been reported in models of hypertension, heart failure, atherosclerosis, diabetic nephropathy and others. In addition, the expression level and/or activity are affected by other renin-angiotensin system components (e.g., ACE and AT1 receptors). Local inhibition or global deletion of brain ACE2 induces a reduction in baroreflex sensitivity. Moreover, ACE2-null mice have been shown to exhibit either blood pressure or cardiac dysfunction phenotypes. On the other hand, over-expression of ACE2 exerts protective effects in local tissues, including the brain. In this review, we will first summarize the major findings linking ACE2 to cardiovascular function in the periphery then focus on recent discoveries related to ACE2 in the CNS. Finally, we will unveil new tools designed to address the importance of central ACE2 in various diseases, and discuss the potential for this carboxypeptidase as a new target in the treatment of hypertension and other cardiovascular diseases.

Immunofluorescence localization of the receptor Mas in cardiovascular-related areas of the rat brain

The G protein-coupled receptor Mas was recently described as an angiotensin-(1–7) [ANG-(1–7)] receptor. In the present study we evaluated the anatomical localization of Mas using immunofluorescence in the central nervous system of adult male Wistar rats. An abundant labeling was found in the hippocampus, amigdala, anterodorsal thalamic nucleus, cortex, and hypoglossal nucleus. More importantly, a dense ANG-(1–7) receptor Mas immunoreactivity was observed in cardiovascular-related areas of the medulla and forebrain, shown in several previous studies as sites for the action of ANG-(1–7) in the brain. A strong staining was found in the nucleus of the solitary tract, caudal and rostral ventrolateral medulla, inferior olive, parvo and magnocellular portions of the paraventricular hypothalamic nucleus, supraoptic nucleus, and lateral preoptic area. Furthermore, Mas staining was predominantly present in neurons. At the medullary sites, a specific and high-intensity binding for rhodamine-ANG-(1–7) was also shown. The specific ANG-(1–7) binding was completely displaced by the anti-Mas antibody or by the ANG-(1–7) antagonist, A-779. The data presented provide the first anatomical basis for the physiological role of ANG-(1–7)/Mas axis in the modulation of different cardiovascular functions and give new insights for clarifying the role of ANG-(1–7) in the central nervous system.

Involvement of angiotensin-(1-7) in the hypothalamic hypotensive effect of captopril in sinoaortic denervated rats

The role of anterior hypothalamic angiotensin-(1-7) (Ang-(1-7)) on blood pressure regulation was studied in sinoaortic denervated (SAD) rats. Since angiotensin-converting enzyme inhibitors increase endogenous levels of Ang-(1-7), we addressed the involvement of Ang-(1-7) in the hypotensive effect induced by captopril in SAD rats. Wistar rats 7 days after SAD or sham operation (SO) were anaesthetized and the carotid artery was cannulated for monitoring mean arterial pressure (MAP). A needle was inserted into the anterior hypothalamus for drug administration. Intrahypothalamic administration of Ang-(1-7) (5 pmol) was without effect in SO rats but reduced MAP in SAD rats by 15.5+/-3.2 mm Hg and this effect was blocked by 250 pmol [D-Ala(7)]-Ang-(1-7), a Mas receptor antagonist. Angiotensin II (Ang II) induced an increase in MAP in both groups being the effect greater in SAD rats (DeltaMAP=15.8+/-1.4 mm Hg) than in SO rats (DeltaMAP=9.6+/-1.0 mm Hg). Ang-(1-7) partially abolished the pressor response caused by Ang II in SAD rats. Whilst the captopril intrahypothalamic injection did not affect MAP in SO animals, it significantly reduced MAP in SAD rats (DeltaMAP=-13.3+/-1.9 mm Hg). Either [D-Ala(7)]-Ang-(1-7) or an anti-Ang-(1-7) polyclonal antibody partially blocked the MAP reduction caused by captopril. In conclusion, whilst Ang-(1-7) does not contribute to hypothalamic blood pressure regulation in SO normotensive animals, in SAD rats the heptapeptide induces a reduction of blood pressure mediated by Mas receptor activation. Although Ang-(1-7) is not formed in enough amount in the AHA of SAD animals to exert cardiovascular effects in normal conditions, our results suggest that enhancement of hypothalamic Ang-(1-7) levels by administration of captopril is partially involved in the hypotensive effect of the ACE inhibitor.

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.

Regulation of Cardiovascular Control Mechanisms by Angiotensin-(1–7) and Angiotensin-Converting Enzyme 2

Among the molecular forms of angiotensin peptides generated by the action of renin on angiotensinogen (Aogen), both angiotensin II (Ang II) and the amino terminal heptapeptide angiotensin-(1–7) [Ang-(1–7)] are critically involved in the long-term control of tissue perfusion, cell-cell communication, development, and growth. Whereas an impressive body of literature continues to uncover pleiotropic effects of Ang II in the regulation of cell function, research on Ang-(1–7) has a shorter history as it was only 16 yr ago that a biological function for this heptapeptide was first demonstrated in the isolated rat neuro-hypophysial explant preparation (1). On the contrary, the synthesis of angiotonin/ hypertensin (now Ang II) was first obtained in 1957 (2), three decades ahead of the discovery of Ang-(1–7) biological properties.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

The endothelium-dependent vasodilator effect of the nonpeptide Ang(1-7) mimic AVE 0991 is abolished in the aorta of mas-knockout mice

Recently, we demonstrated that the endothelium-dependent vasodilator effect of angiotensin(1-7) in the mouse aorta is abolished by genetic deletion of the G protein-coupled receptor encoded by the Mas protooncogene. To circumvent the limitations posed by the possible metabolism of Ang(1-7) in this vessel, in this work we studied the mechanism underlying the vasorelaxant effect of AVE 0991, a nonpeptide mimic of the effects of Ang(1-7), using wild-type and Mas-deficient mice. Ang(1-7) and AVE 0991 induced an equipotent concentration-dependent vasodilator effect in aortic rings from wild-type mice that was dependent on the presence of endothelium. The vasodilator effect of Ang(1-7) and AVE 0991 was completely blocked by 2 specific Ang(1-7) receptor antagonists, A-779 and D-Pro-Ang(1-7), and by inhibition of NO synthase with L-NAME. Moreover, in aortic rings from Mas-deficient mice, the vasodilator effect of both Ang(1-7) and AVE 0991 was abolished. In contrast, the vasodilator effect of acetylcholine and substance P were preserved in Mas-null mice. In addition, the vasoconstriction effect induced by Ang II was slightly increased, and the vasodilation induced by the AT2 agonist CGP 42112A was not altered in Mas-deficient mice. Our results show that Ang(1-7) and AVE 0991 produced an NO-dependent vasodilator effect in the mouse aorta that is mediated by the G protein-coupled receptor Mas.

Angiotensin-(1–7) inhibits the angiotensin II-enhanced norepinephrine release in coarcted hypertensive rats

Since it has been suggested that angiotensin (Ang) (1-7) functions as an antihypertensive peptide, we studied its effect on the Ang II-enhanced norepinephrine (NE) release evoked by K+ in hypothalami isolated from aortic coarcted hypertensive (CH) rats. The endogenous NE stores were labeled by incubation of the tissues with 3H-NE during 30 min, and after 90 min of washing, they were incubated in Krebs solution containing 25 mM KCl in the absence or presence of the peptides. Ang-(1-7) not only diminished the K+-evoked NE release from hypothalami of CH rats, but also blocked the Ang II-enhanced NE release induced by K+. Ang-(1-7) blocking action on the Ang II response was prevented by [D-Ala7]Ang-(1-7), an Ang-(1-7) specific antagonist, by PD 123319, an AT2-receptor antagonist, and by Hoe 140, a B2 receptor antagonist. Ang-(1-7) inhibitory effect on the Ang II facilitatory effect on K+-stimulated NE release disappeared in the presence of Nomega-nitro-L-arginine methylester and was restored by L-arginine. Our present results suggest that Ang-(1-7) may contribute to blood pressure regulation by blocking Ang II actions on NE release at the central level. This inhibitory effect is a nitric oxide-mediated mechanism involving AT2 receptors and/or Ang-(1-7) specific receptors and local bradykinin generation.

Effects of angiotensin-(1-7) and other bioactive components of the renin-angiotensin system on vascular resistance and noradrenaline release in rat kidney

OBJECTIVE

Angiotensin (Ang) is broken down enzymatically to several different metabolites which, in addition to Ang II, may have important biological effects in the kidney. This study investigates the role of Ang metabolites on vascular resistance and noradrenaline release in the rat kidney.

METHODS AND RESULTS

In rat isolated kidney Ang I, Ang II, Ang III, Ang IV and des-Asp-Ang I induced pressor responses and enhanced noradrenaline release to renal nerve stimulation (RNS) in an concentration-dependent manner, with the following rank order of potency (EC(50)): Ang II >or= Ang III > Ang I = des-Asp-Ang I > Ang IV. All effects were blocked by the AT(1)-receptor antagonist EXP 3174 (0.1 micromol/l) but not by the AT(2)-receptor antagonist PD 123319 (1 micromol/l). Angiotensin-converting enzyme (ACE) inhibition by captopril (10 micromol/l) abolished the effect of Ang I and des-Asp-Ang I but had no influence on the effect of the other metabolites. Ang-(1-7) blocked the effects of Ang I and Ang II, being 10 times more potent against Ang I than Ang II. The selective Ang-(1-7) receptor blocker d-Ala7-Ang-(1-7) (10 micromol/l) did not influence the inhibitory effects of Ang-(1-7). Ang-(1-7) (10 micromol/l) by itself had no influence on vascular resistance and RNS-induced noradrenaline release.

CONCLUSION

Ang I, Ang II, Ang III, Ang IV and des-Asp-Ang I regulate renal vascular resistance and noradrenaline release by activation of AT(1) receptors. In the case of Ang I and des-Asp-Ang I this depends on conversion by ACE. Ang-(1-7) may act as a potent endogenous inhibitor/antagonist of ACE and the AT(1)-receptors, respectively.

Enhancement of phosphatidylcholine biosynthesis by angiotensin-(1-7) in the rat renal cortex

In the present paper, we investigated the effect of angiotensin-(1-7) (Ang-(1-7)) on phospholipid biosynthesis in the rat renal cortex. A significant increase in phosphatidylcholine (PC) labeling was observed when cortical slices, prelabeled with [32P]orthophosphate, were incubated for 30 min in the presence of Ang-(1-7) (1 pM to 100 nM). Neither the phospholipase C inhibitors, neomycin or db-cAMP nor the protein kinase C inhibitors, chelerythrine or H7, modified the stimulatory effect induced by 0.1 nM Ang-(1-7). The enhancement of PC biosynthesis caused by 0.1 nM Ang-(1-7) was unmodified by either losartan, an AT(1) receptor antagonist, or (1-[[4-(dimethylamino)-3-methylphenyl]methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazol[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate) (PD 123319), an AT(2) receptor antagonist, but was partially blocked by [D-Ala(7)]Ang-(1-7), an Ang-(1-7) specific antagonist. However, losartan potentiated the effect of 100 nM Ang-(1-7) on PC biosynthesis. Losartan by itself increased the de novo synthesis of PC. These results suggest that the Ang-(1-7)-mediated increase in PC biosynthesis is independent of AT(1) and AT(2) receptor activation but mediated by a specific Ang-(1-7) receptor. This mechanism is independent of phospholipase C and PKC activation.

Angiotensin II type 2 receptors: signalling and pathophysiological role

The signalling mechanisms and biological significance of the angiotensin II type 2 receptor have long been unknown. In recent years, studies, first in cell culture models but now increasingly also in vivo, have shed some light on the molecular events occurring after a stimulation of the receptor with its ligand as well as on its physiological effects and its significance for pathophysiological processes. There is increasing evidence that the angiotensin II type 2 receptor is involved in different pathophysiological processes, such as myocardial infarction, heart and kidney failure, and stroke.

Angiotensin-(1-7) does not affect norepinephrine neuronal uptake or catabolism in rat hypothalamus and atria

1. Since we previously reported that angiotensin-(1-7) [Ang-(1-7)] increases or inhibits norepinephrine (NE) release in rat atria or hypothalamus, respectively, the present work was undertaken to investigate the effect of the heptapeptide on NE neuronal uptake and metabolism in atria and hypothalamus isolated from rats. 2. Ang II (1-10 microM) caused a decrease in neuronal NE uptake in both atria and hypothalami isolated from rats. On the contrary, tissues incubated with [3H]NE in the presence of 0.1-10 microM Ang-(1-7) showed no modification in [3H]NE content with respect to the control group, suggesting that the heptapeptide did not modify [3H]NE neuronal uptake. 3. To study the effect of the heptapeptide on NE catabolism, monoamine-oxidase (MAO) and catechol-O-methyltransferase (COMT) activities were determined. Pretreatment of the tissue with Ang-(1-7) (0.1-1.0 microM) showed a tendency to diminish MAO activity in rat atria, while no significant changes were observed in hypothalamic MAO activity. Moreover, the heptapeptide (0.1-1.0 microM) did not affect central COMT activity with respect to the control group. 4. Present results allow us to conclude that Ang-(1-7) interacts with noradrenergic neurotransmission by increasing or inhibiting NE release at the peripheral and central levels, respectively, without affecting either the neurotransmitter neuronal uptake or catabolism.