Angiotensin-(1-7)-Stimulated Nitric Oxide and Superoxide Release From Endothelial Cells

The antithrombotic effect of angiotensin-(1-7) involves mas-mediated NO release from platelets

The antithrombotic effect of angiotensin(Ang)-(1-7) has been reported, but the mechanism of this effect is not known. We investigated the participation of platelets and receptor Mas-related mechanisms in this action. We used Western blotting to test for the presence of Mas protein in rat platelets and used fluorescent-labeled FAM-Ang-(1-7) to determine the specific binding for Ang-(1-7) and its displacement by the receptor Mas antagonist A-779 in rat platelets and in Mas(-/ -) and Mas(+/+) mice platelets. To test whether Ang-(1-7) induces NO release from platelets, we used the NO indicator DAF-FM. In addition we examined the role of Mas in the Ang-(1-7) antithrombotic effect on induced thrombi in the vena cava of male Mas(-/ -) and Mas(+/+) mice. The functional relevance of Mas in hemostasis was evaluated by determining bleeding time in Mas(+/+) and Mas(-/ -) mice. We observed the presence of Mas protein in platelets, as indicated by Western Blot, and displacement of the binding of fluorescent Ang-(1-7) to rat platelets by A-779. Furthermore, in Mas(+/+) mouse platelets we found specific binding for Ang-(1-7), which was absent in Mas(-/ -) mouse platelets. Ang-(1-7) released NO from rat and Mas(+/+) mouse platelets, and A-779 blocked this effect. The NO release stimulated by Ang-(1-7) was abolished in Mas(-/ -) mouse platelets. Ang-(1-7) inhibited thrombus formation in Mas(+/+) mice. Strikingly, this effect was abolished in Mas(-) (/) (-)mice. Moreover, Mas deficiency resulted in a significant decrease in bleeding time (8.50 +/- 1.47 vs. 4.28 +/- 0.66 min). This study is the first to show the presence of Mas protein and specific binding for Ang-(1-7) in rat and mouse platelets. Our data also suggest that the Ang-(1-7) antithrombotic effect involves Mas-mediated NO release from platelets. More importantly, we showed that the antithrombotic effect of Ang-(1-7) in vivo is Mas dependent and that Mas is functionally important in hemostasis.

Sex and the renin-angiotensin system: inequality between the sexes in response to RAS stimulation and inhibition

The purpose of this review is to examine sex differences in response to stimulation and inhibition of the renin-angiotensin system (RAS). The RAS plays a prominent role in the development of chronic renal disease, and there are known sex differences not only in the expression level of components of the RAS but also in how males and females respond to perturbations of the RAS. In men, renal injury increases in parallel with increased activation of the RAS, while in women, increases in ANG II do not necessarily translate into increases in renal injury. Moreover, both epidemiological and experimental studies have noted sex differences in the therapeutic benefits following angiotensin-converting enzyme inhibitor and angiotensin receptor blocker treatment. Despite these differences, RAS inhibitors are the most commonly prescribed drugs for the treatment of chronic renal disease, irrespective of sex. This review will examine how males and females respond to stimulation and inhibition of the RAS, with a focus on renal disease.

On the mechanism of coronary vasodilation induced by angiotensin-(1-7) in the isolated guinea pig heart

Various mechanisms have been postulated to be involved in angiotensin-(1-7)-induced endothelium-dependent vasodilation. Here, we characterized the vasodilator action of angiotensin-(1-7) in the isolated guinea pig heart. Angiotensin-(1-7) (1-10 nmol, bolus) induced dose-dependent increase in the coronary flow. The coronary vasodilation induced by angiotensin-(1-7) was significantly reduced by the nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (L-NAME) (100 microM) and abolished by a B(2) receptor antagonist, icatibant (100 nM). Coronary vasodilation induced by bradykinin (3 pmol, bolus) was inhibited by L-NAME and icatibant to similar extent as that induced by angiotensin-(1-7). Neither the selective AT(2) angiotensin receptor antagonist, PD123319 (1 microM), nor the antagonist of a putative angiotensin-(1-7) receptors, [D-alanine-7]-angiotensin-(1-7) (A-779, 1 microM), influenced the response to angiotensin-(1-7). In conclusion, in the isolated guinea pig heart angiotensin-(1-7) induces coronary vasodilation that is mediated by endogenous bradykinin and subsequent stimulation of nitric oxide release through endothelial B(2) receptors. In contrast to other vascular beds, AT(2) angiotensin receptors and specific angiotensin-(1-7) receptors do not appear involved in angiotensin-(1-7)-induced coronary vasodilation in the isolated guinea pig heart.

Simultaneous analysis of angiotensin peptides by LC-MS and LC-MS/MS: metabolism by bovine adrenal endothelial cells

Liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods were developed to simultaneously determine the concentrations of angiotensin (Ang) II, Ang 1-7, Ang III, and Ang IV in biological samples. The samples were extracted with C18 solid-phase extraction cartridges and separated by a reverse-phase C18 column using acetonitrile in water with 0.1% formic acid as a mobile phase. Ang peptides were ionized by electrospray and detected by triple quadrupole MS in the positive ion mode. (M+3H)(3+) and (M+2H)(2+) ions were chosen as the detected ions in the single ion recording (SIR) mode for LC-MS. The limits of detection (signal/noise [S/N]=3) using SIR are 1 pg for Ang IV and 5 pg for Ang 1-7, Ang III, and Ang II. Multiple reaction monitoring (MRM) mode was used for LC-MS/MS. The limits of detection (S/N =3) using MRM are 20 pg for Ang IV and 25 pg for Ang 1-7, Ang III, and Ang II. These methods were applied to analyze Ang peptides in bovine adrenal microvascular endothelial cells. The results show that Ang II is metabolized by endothelial cells to Ang 1-7, Ang III, and Ang IV, with Ang 1-7 being the major metabolite.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Phosphoinositide hydrolysis increase by angiotensin-(1–7) in neonatal rat brain

Angiotensin (Ang)-(1-7) is an endogenous peptide hormone of the renin-angiotensin system which exerts diverse biological actions, some of them counterregulate Ang II effects. In the present study potential effect of Ang-(1-7) on phosphoinositide (PI) turnover was evaluated in neonatal rat brain. Cerebral cortex prisms of seven-day-old rats were preloaded with [(3)H]myoinositol, incubated with additions during 30 min and later [(3)H]inositol-phosphates (IPs) accumulation quantified. It was observed that PI hydrolysis enhanced 30% to 60% in the presence of 0.01 nM to 100 nM Ang-(1-7). Neither 10 nM [D-Ala(7)]Ang-(1-7), an Ang-(1-7) specific antagonist, nor 10 nM losartan, an angiotensin II type 1 (AT(1)) receptor antagonist, blocked the effect of 0.1 nM Ang-(1-7) on PI metabolism. The effect of 0.1 nM Ang-(1-7) on PI hydrolysis was not reduced but it was even significantly increased in the simultaneous presence of [D-Ala(7)]Ang-(1-7) or losartan. PI turnover enhancement achieved with 0.1 nM Ang-(1-7) decreased roughly 30% in the presence of 10 nM PD 123319, an angiotensin II type 2 (AT(2)) receptor antagonist. The antagonists alone also enhanced PI turnover. Present findings showing an increase in PI turnover by Ang-(1-7) represent a novel action for this peptide and suggest that it exerts a function in this signaling system in neonatal rat brain, an effect involving, at least partially, angiotensin AT(2) receptors.

Downregulation of angiotensin converting enzyme II is associated with pacing-induced sustained atrial fibrillation

Atrial fibrillation (AF), the most common cardiac arrhythmia, is frequently accompanied by atrial interstitial fibrosis. Angiotensin II (Ang II) dependent signaling pathways have been implicated in interstitial fibrosis during the development of AF. However, Ang II could be further degraded by angiotensin converting enzyme II (ACE2). We examined expression of ACE2 in the fibrillating atria of pigs and its involvement in fibrotic pathogenesis during AF. Nine adult pigs underwent continuous rapid atrial pacing to induce sustained AF and six pigs were sham controls (i.e., sinus rhythm; SR). In the histological examinations, extensive accumulation of extracellular matrix in the interstitial space of the atria, as evidenced by Masson's trichrome stain, were found in fibrillating atria. The relative amount of collagen type I in the atria with AF was significantly increased as compared with that in the SR. Local ACE activity in the fibrillating atria was also markedly higher than that in the SR subjects. ACE2 gene and protein expression in the AF subjects were significantly decreased compared with those in the SR subjects, whereas expression of mitogen-activated/ERK kinase 1/2 (MEK1/2), extracellular signal-regulated protein kinase 2 (ERK2), and activated ERK2 were significantly greater in the AF subjects. We propose that decreasing ACE2 expression during AF may affect the Ang II-dependent signaling pathway. In addition, our results suggest that atrial fibrosis in AF may be induced by antagonistic regulation between ACE and ACE2 expression.

Expression of an angiotensin-(1-7)-producing fusion protein in rats induced marked changes in regional vascular resistance

We have described a transgenic rat line that expresses an angiotensin-(1-7)-producing fusion protein, the TGR(A1-7)3292. In these rats, testis acts as an angiotensin-(1-7) biological pump, increasing its plasma concentration 2.5-fold. In this study, we performed hemodynamic measurements in TGR(A1-7)3292 and age-matched Hannover Sprague-Dawley (SD) control rats, using fluorescent microspheres. Urethane-anesthetized transgenic rats had similar levels of baseline blood pressure (99 +/- 3 mmHg) as did SD rats (101 +/- 3 mmHg). However, pronounced differences were observed in other hemodynamic measurements. TGR(A1-7)3292 rats presented a significant increase in stroke volume (0.29 +/- 0.01 vs. 0.25 +/- 0.01 ml in SD), increased cardiac index (24.6 +/- 0.91 vs. 21.9 +/- 0.65 ml.min(-1).kg) and decreased total peripheral resistance (3.9 +/- 0.13 vs. 4.5 +/- 0.13 mmHg.ml(-1).min.100 g). The increase in stroke volume in transgenic rats may be partially explained by the small decrease in heart rate (326 +/- 7.0 vs. 359 +/- 6.0 beats/min in SD). Strikingly, TGR(A1-7)3292 rats presented a substantial decrease in the vascular resistance in lung, spleen, kidney, adrenals, brain, testis and brown fat tissue with no significant differences in the left ventricle, mesentery, skin, gastrocnemius muscle and white fat tissue. These results corroborate and extend previous results observed after acute angiotensin-(1-7) infusion, showing that chronic increase in circulating angiotensin-(1-7) produces sustained and important changes in regional and systemic hemodynamics. Moreover, our data suggest a physiological role for angiotensin-(1-7) in the tonic control of regional blood flow.

Enalapril and losartan restored blood pressure and vascular reactivity in intrauterine undernourished rats

Epidemiological studies suggest that intrauterine undernutrition plays an important role in the development of arterial hypertension and endothelial dysfunction in adulthood. We have evaluated the effect of the Renin Angiotensin System inhibition on the blood pressure and the mesenteric arteriolar reactivity of the intrauterine undernourished rats. Wistar rats were fed either normal or 50% of the normal intake diets, during the whole gestational period. In this study only the male offspring was used. At 16 weeks of age, the rats were used for the study of blood pressure, microvascular reactivity studied in vivo-in situ to Angiotensin II (Ang II), Bradykinin (Bk) and Acetylcholine (Ach) before and after either losartan (10 mg/kg/15 days) or enalapril (15 mg/kg/21 days) treatment. We also evaluated the mesenteric and plasmatic Angiotensin Converting Enzyme (ACE), renal function, lipid plasmatic content, and insulin and glucose metabolism. Intrauterine undernutrition induced hypertension and increased response of mesenteric arterioles to Ang II and decreased vasodilation to Bk and Ach. The treatments with losartan or enalapril normalized the blood pressure levels and significantly improved the arteriolar responses to Bk, Ach and reduced the response to Ang II. No differences have been detected to ACE activity, renal function, lipid content and insulin and glucose metabolism. This study shows for the first time that Renin Angiotensin System inhibitors can normalize the cardiovascular alterations induced by intrauterine undernutrition.

Role of the kallikrein-kinin system in Ang-(1-7)-induced vasodilation in mesenteric arterioles of Wistar rats studied in vivo-in situ

Angiotensin-(1-7) [Ang-(1-7)], exerts a variety of actions in the cardiovascular system, with an important effect being vasodilation. In this work, we investigated the relationship between the vasodilatory activity of Ang-(1-7) and the kallikrein-kinin system. Intravital microscopy was used to study the vasodilation caused by Ang-(1-7) in the mesenteric vascular bed of anesthetized Wistar rats. The topical application of Ang-(1-7) caused vasodilation of mesenteric arterioles that was reduced by A-779, JE 049 and peptidase inhibitors (aprotinin, SBTI, PKSI 527, E-64, PMSF). These results indicated that the vasodilation induced by Ang-(1-7) in the mesenteric arterioles of Wistar rats was heavily dependent on the activation of kallikrein and subsequent kinin formation.

The effect of angiotensin 1-7 on tyrosine kinases activity in rat anterior pituitary

Angiotensin 1-7 (Ang 1-7) is a peptide originated from Ang II. It is known that in vessels Ang 1-7 shows opposite effects to Ang II. Ang 1-7 can modify processes of proliferation. However, Ang 1-7 action in pituitary gland cells was never studied. Moreover, the specific binding sites for Ang 1-7 are still unknown. The aim of this study was to examine the effects of Ang 1-7 on tyrosine kinases (PTKs) activity in the anterior pituitary. The reaction of phosphorylation was carrying out in presence of different concentration of Ang 1-7 and losartan (antagonist of AT1 receptor) and PD123319 (antagonist of AT2). Our results show that Ang 1-7 inhibited activity of PTK to 60% of basic activity. Losartan did not change the Ang 1-7-induced changes in PTKs activity. The presence of PD123319 together with Ang 1-7 caused stronger inhibition PTKs activity than Ang 1-7 alone. These observations suggest that Ang 1-7 binds to the novel, unknown, specific for this peptide receptor.

Angiotensin-(1-7) inhibits angiotensin II-stimulated phosphorylation of MAP kinases in proximal tubular cells

Angiotensin-converting enzyme 2 (ACE2) is a homolog of ACE, which is not blocked by ACE inhibitors. High amounts of ACE2 are present in the proximal tubule, and ACE2 catalyzes generation of angiotensin 1-7 (Ang-(1-7)) by this segment. Ang-(1-7) binds to a receptor distinct from the AT1 or AT2 Ang II receptor, identified as the mas receptor. We studied the effects of Ang-(1-7) on Ang II-mediated cell signaling pathways in proximal tubule. In primary cultures of rat proximal tubular cells, activation of mitogen-activated protein kinases (MAPK) was detected by immunoblotting, in the presence or absence of agonists/antagonists. Transforming growth factor-beta1 (TGF-beta1) was measured by enzyme-linked immunosorbent assay. Ang II (5 min, 10(-7) M) stimulated phosphorylation of the three MAPK (p38, extracellular signal-related kinase (ERK 1/2), and c-Jun N-terminal kinase (JNK)). While incubation of proximal tubular cells with Ang-(1-7) alone did not significantly affect MAPK phosphorylation, Ang-(1-7) (10(-7) M) completely inhibited Ang II-stimulated phosphorylation of p38, ERK 1/2, and JNK. This inhibitory effect was reversed by the Ang-(1-7) receptor antagonist, D-Ala7-Ang-(1-7). Ang II significantly increased production of TGF-beta1 in proximal tubular cells, an effect that was partly inhibited by Ang-(1-7). Ang-(1-7) had no significant effect on cyclic 3',5'-adenosine monophosphate production in these cells. In summary, Ang-(1-7) inhibits Ang II-stimulated MAPK phosphorylation in proximal tubular cells. Generation of Ang-(1-7) by proximal tubular ACE2 could thereby serve a protective role by counteracting the effects of locally generated Ang II.

Simultaneous detection of L-glutamate and nitric oxide from adherently growing cells at known distance using disk shaped dual electrodes

An ex vivo system for simultaneous detection of nitric oxide (NO) and L-glutamate using integrated dual 250 microm platinum disk electrodes modified individually with suitable sensing chemistries has been developed. One of the sensors was coated with an electrocatalytic layer of Ni tetrasulfonate phthalocyanine tetrasodium salt (Ni-TSPc) covered by second layer of Nafion, which stabilises on the one hand the primary oxidation product NO(+) and prevents interferences from negatively charged compounds such as NO(2)(-). For glutamate determination, the second electrode was modified with a crosslinked redox hydrogel consisting of Os complex modified poly(vinylimidazol), glutamate oxidase and peroxidase. A manual x-y-z micromanipulator on top of an inverted optical microscope was used to position the dual electrode sensor at a defined distance of 5 microm from a cell population under visual control. C6 glioma cells were stimulated simultaneously with bradykinin or VEGF to release NO while KCl was used to invoke glutamate release. For evaluation of the glutamate sensors, in some experiments HN10 cells were used. To investigate the sensitivity and reliability of the system, several drugs were applied to the cells, e.g. Ca(2+)-channel inhibitors for testing Ca(2+)-dependence of the release of NO and glutamate, rotenone for inducing oxidative stress and glutamate antagonists for analysing glutamate release. With these drugs the NO and glutamate release was modulated in a similar way then expected from previously described systems or even in-vivo measurements. We therefore conclude that our system is suitable to analyse stress-induced mechanisms in cell lines.

Effect of hypertension on angiotensin-(1–7) levels in rats with different angiotensin-I converting enzyme polymorphism

To determine circulating angiotensin-(1-7) [Ang-(1,7)] levels in rats with different angiotensin converting enzyme (ACE) genotypes and to evaluate the effect of hypertension on levels of this heptapeptide, plasma levels of angiotensin II (Ang II) and Ang-(1-7) were determined by HPLC and radioimmunoassay in (a) normotensive F0 and F2 homozygous Brown Norway (BN; with high ACE) or Lewis (with low ACE) rats and (b) in hypertensive F2 homozygous male rats (Goldblatt model). Genotypes were characterized by PCR and plasma ACE activity measured by fluorimetry. Plasma ACE activity was 2-fold higher (p < 0.05) in homozygous BN compared to homozygous Lewis groups. In the Goldblatt groups, a similar degree of hypertension and left ventricular hypertrophy was observed in rats with both genotypes. Plasma Ang II levels were between 300-400% higher (p < 0.05) in the BN than in the Lewis rats, without increment in the hypertensive animals. Plasma Ang-(1-7) levels were 75-87% lower in the BN rats (p < 0.05) and they were significantly higher (p < 0.05) in the hypertensive rats from both genotypes. Plasma levels of Ang II and Ang-(1-7) levels were inversely correlated in the normotensive rats (r = -0.64; p < 0.001), but not in the hypertensive animals. We conclude that there is an inverse relationship between circulating levels of Ang II and Ang-(1-7) in rats determined by the ACE gene polymorphism. This inverse relation is due to genetically determined higher ACE activity. Besides, plasma levels of Ang-(1-7) increase in renovascular hypertension.

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.

Biomedical aspects of targeted delivery of drugs to pulmonary endothelium

Drug targeting to selected subcellular compartments of the pulmonary endothelium may optimise treatment of many diseases. This paper describes endothelial determinants that are potentially useful for such targeting, including endothelial ectopeptidases, cell adhesion molecules and novel candidates identified by high-throughput methods, as well as the means to achieve optimal subcellular targeting of drugs in the endothelium that have been explored in cell culture and animal studies. Criteria for determining the applicability for targeting include accessibility, specificity, safety and subcellular precision. The effects of endothelial delivery of therapeutic agents, including the effects mediated by the intervention in the function of the target determinants, must be characterised in the context of given pathological conditions.

Physiologically relevant measurements of nitric oxide in cardiovascular research using electrochemical microsensors

Nitric oxide (NO) plays an important role in the regulation of blood flow. Pharmacological tools and a series of other techniques have been developed for studying the NO/L-arginine pathway, but it has proved difficult to make a quantitative link between effect and tissue NO concentration. NO microsensors have been applied with success for the measurement of NO in suspensions of mitochondria and cells, such as platelets and leukocytes, and in cell cultures, which together with other interventions or measurements are particularly useful for the examination of cell signalling related to the NO/L-arginine pathway. In isolated vascular segments, studies using the NO microsensor have defined the relationship between NO concentration and relaxation and revealed residual NO release in the presence of NO synthase inhibitors. Moreover, simultaneous measurements of NO concentration and vasorelaxation in isometric preparations have shown that agonist-induced relaxation is L-arginine dependent and NO release is reduced in hypertension. By placing NO microsensors in catheters, it is possible to measure NO in the living animal and man. This approach has been applied for the measurements of NO concentration in relation to increases in flow, erection, in conditions of hypoxia, and in endotoxemia. However, further methodological development of NO microsensors is necessary to avoid the influence of changes in temperature, pH and oxygen on the measurements.

Pharmacological concentration of angiotensin-(1-7) activates NADPH oxidase after ischemia-reperfusion in rat heart through AT1 receptor stimulation

The cardiovascular role of angiotensin-(1-7), especially in the functional and metabolic alterations associated with ischemia-reperfusion (IR), is still not clearly defined. Our objective was to evaluate the cardiac effects of angiotensin-(1-7), the receptors involved, and their relationships with NADPH oxidase activation under non-ischemic conditions and, during an ischemia-reperfusion sequence. Isolated perfused rat hearts underwent 45 min of non-ischemic perfusion, or 30 min of global ischemia followed by 30 min of reperfusion. Angiotensin-(1-7) and/or AT1 receptor blocker losartan or angiotensin-(1-7) receptor antagonist (D-Ala7)-angiotensin-(1-7) were perfused. Our results showed that angiotensin-(1-7) was without effect at low concentrations (10(-10) to 10(-7) M). At a pharmacological concentration, 0.5 microM angiotensin-(1-7) induced vasoconstriction, which was antagonised by losartan. After ischemia, we noted a partial recovery of functional parameters, which was not modified by any of the treatments. The expression of AT1 receptor mRNA was increased by ischemia-reperfusion, except in (D-Ala7)-angiotensin-(1-7) treated hearts. Angiotensin-(1-7) further increased the AT1 expression. NADPH oxidase activity was enhanced in 0.5 microM angiotensin-(1-7)-treated hearts subjected to ischemia-reperfusion, this effect was totally reversed by losartan. This is the first time that it has been shown that, in the heart, angiotensin-(1-7) at pharmacological concentration activates NADPH oxidase, an enzyme thought to be involved in several angiotensin II effects.

Angiotensin-(1-7) and its receptor as a potential targets for new cardiovascular drugs

The identification of novel biochemical components of the renin-angiotensin system (RAS) has added a further layer of complexity to the classical concept of this cardiovascular regulatory system. It is now clear that there is a counter-regulatory arm within the RAS that is mainly formed by the angiotensin-converting enzyme 2-angiotensin (1-7)-receptor Mas axis. The functions of this axis are often opposite to those attributed to the major component of the RAS, angiotensin II. This review will highlight the current knowledge concerning the cardiovascular effects of angiotensin-(1-7) through a direct interaction with its receptor Mas or through an indirect interplay with the kallikrein-kinin system. In addition, there will be a discussion of its role in the beneficial effects of angiotensin-converting enzyme inhibitors and angio-tensin receptor type 1 (AT1) antagonists, and the potential of this peptide and its receptor as a novel targets for new cardiovascular drugs.

Cardiovascular actions of angiotensin-(1-7)

Angiotensin-(1-7) (Ang-(1-7)) is now considered to be a biologically active member of the renin-angiotensin system. The functions of Ang-(1-7) are often opposite to those attributed to the main effector component of the renin-angiotensin system, Ang II. Chronic administration of angiotensin-converting enzyme inhibitors (ACEI) increases 10- to 25-fold the plasma levels of this peptide, suggesting that part of the beneficial effects of ACEI could be mediated by Ang-(1-7). Ang-(1-7) can be formed from Ang II or directly from Ang I. Other enzymatic pathways for Ang-(1-7) generation have been recently described involving the novel ACE homologue ACE2. This enzyme can form Ang-(1-7) from Ang II or less efficiently by the hydrolysis of Ang I to Ang-(1-9) with subsequent Ang-(1-7) formation. The biological relevance of Ang-(1-7) has been recently reinforced by the identification of its receptor, the G-protein-coupled receptor Mas. Heart and blood vessels are important targets for the formation and actions of Ang-(1-7). In this review we will discuss recent findings concerning the biological role of Ang-(1-7) in the heart and blood vessels, taking into account aspects related to its formation and effects on these tissues. In addition, we will discuss the potential of Ang-(1-7) and its receptor as a target for the development of new cardiovascular drugs.

Nanomolar level of ouabain increases intracellular calcium to produce nitric oxide in rat aortic endothelial cells

Changes in [Ca(2+)](i) across the cell membrane and/or the sarcoplasmic reticulum regulate endothelial nitric oxide (NO) synthase activity. In the present study, we investigated the effect of ouabain, a specific inhibitor of Na(+)/K(+)-ATPase, on NO release and [Ca(2+)](i) movements in cultured rat aortic endothelial cells (RAEC) by monitoring NO production continuously using an NO-specific real-time sensor and by measuring the change in [Ca(2+)](i) using a fluorescence microscopic imaging technique with high-speed wavelength switching. The t((1/2)) (half-time of the decline of [Ca(2+)](i) to basal levels after stimulation with 10 micro mol/L bradykinin) was used as an index of [Ca(2+)](i) extrusion. A very low concentration of ouabain (10 nmol/L) did not increase the peak of NO production, but decreased the decay of NO release and, accordingly, increased integral NO production by the maximal dose-response concentration induced by bradykinin. The same dose of ouabain affected [Ca(2+)](i) movements across the cell membrane and/or sarcoplasmic reticulum induced by bradykinin with a time-course similar to that of NO release. Moreover, the t((1/2)) was significantly increased. Pretreatment of RAEC with Na(+)-free solution, an inhibitor of the Na(+)/Ca(2+) exchanger, and nickel chloride hexahydrate prevented the effects induced by bradykinin and ouabain. These observations using real-time recording indicate that a small amount of ouabain contributes to the bradykinin-stimulated increase of NO production through inhibition of plasma membrane Na(+)/K(+)-ATPase activity and an increase in intracellular Na(+) concentrations. The membrane was then depolarized, leading to a decline in the bradykinin-stimulated increase in [Ca(2+)](i) by forward mode Na(+)/Ca(2+) exchange to prolong the Ca(2+) signal time. From these results, we suggest that nanomolar levels of ouabain modulate [Ca(2+)](i) movements and NO production in RAEC.

The suitability of iodinated Angiotensin-(1–7) peptides as pharmacological tools

INTRODUCTION

The heptapeptide Angiotensin-(1-7) [(Ang-(1-7)] is a biologically active component of the Renin-Angiotensin System. Pharmacological studies often involve Ang-(1-7) radioactively labelled with (125)I. Given the small size of the original peptide, we investigated whether introduction of a rather bulky iodine label interferes with the biological activity of Ang-(1-7).

METHODS

Ang-(1-7) was labelled with nonradioactive iodine with the chloramine-T method. The reaction products were separated on HPLC and analysed with mass spectrometry. The products were tested for biological activity in two ways: The ability of labelled Ang-(1-7) to block Ang II-induced contraction in rat aortic rings was tested in an organ bath setup. The affinity of labelled angiotensin for ACE in rat plasma was examined in vitro.

RESULTS

Iodination of Angiotensin-(1-7) resulted in two main products: monoiodinated and diiodinated Ang-(1-7) that could be easily separated on HPLC. In an organ bath experiment, monoiodinated Ang-(1-7) blocked Ang II responses identical to the native compound, whereas diiodinated Ang-(1-7) had lost its ability to block Ang II responses. Likewise, monoiodinated Ang-(1-7) had retained its affinity for ACE, while the affinity of diiodinated Ang-(1-7) was greatly reduced.

DISCUSSION

Monoiodinated Ang-(1-7) has a biological activity identical to the native compound, whereas this is lost in diiodinated Ang-(1-7). Therefore, only the monoiodinated radioactive form seems suited for pharmacological studies.

Endothelial dysfunction in congestive heart failure: ACE inhibition vs. angiotensin II antagonism

BACKGROUND

Endothelial dysfunction of the vasculature contributes to the elevated peripheral resistance and reduced myocardial perfusion in congestive heart failure (CHF). The present study systematically investigated the effect of angiotensin II (AT(1))- receptor blockade on vascular superoxide (O(2)(-)) production and endothelial dysfunction.

METHODS AND RESULTS

Vasodilator responses and O(2)(-) production were determined in aortic rings from Wistar rats with experimental CHF 10 weeks after extensive myocardial infarction and compared with sham-operated animals (Sham). Rats were either treated with placebo (P), with the AT(1)-receptor antagonist Irbesartan (50 mg kg(-1) day(-1)) or with the ACE inhibitor Trandolapril (0.3 mg kg(-1) day(-1)). In CHF-P, endothelium-dependent, acetylcholine-induced relaxation was significantly attenuated compared with Sham-P. Chronic treatment with Trandolapril or Irbesartan significantly improved endothelium-dependent relaxation. Aortic O(2)(-) formation was markedly increased in CHF, and was not significantly affected by Trandolapril treatment, while it was reduced by Irbesartan. eNOS expression was reduced in CHF and normalised by both treatments.

CONCLUSION

Endothelial vasomotor function in CHF rats was normalised by long-term treatment with an ACE inhibitor or an AT(1)-antagonist. Reduced aortic eNOS expression was normalised by both treatments, whereas aortic superoxide formation was only reduced by the AT(1)-antagonist Irbesartan.

Peptidase activities in rats treated chronically with N-nitro-l-arginine methyl ester (L-NAME)

The chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension. This inhibition of NO production results in activation of the renin-angiotensin system, with increased activity of the carboxypeptidase angiotensin I-converting enzyme (ACE). Since chronic NO inhibition increases ACE activity, we hypothesized that this inhibition could also affect the activities of other peptidases involved in cardiovascular functions. To test this possibility, we examined the activities of aminopeptidase M (APM), dipeptidyl peptidase IV (DPP IV), metalloendopeptidase 24.15 (MEP 24.15) and neutral endopeptidase 24.11 (NEP 24.11) in rat brain, heart, kidney, liver, lung and thoracic aorta. Male Wistar rats were treated chronically with L-NAME (80mgkg(-1) per day) administered in the drinking water for 4 weeks and their organs then removed and processed for the determination of peptidase activities. Treatment with L-NAME did not significantly alter the activities of the four peptidases in brain, heart, kidney, liver and lung. In contrast, in aorta, the activity of APM was slightly but significantly reduced whereas those of DPP IV and MEP 24.15 were markedly enhanced; NEP 24.11 was not detected in this tissue. Immunoblotting for DPP IV and MEP 24.15 showed increased expression in aortic tissue. Neither L-NAME (1-100microM) nor the NO donors sodium nitroprusside and 3-morpholinosydnonimine (SIN-1; 1-100microM) had any consistent effect on the activity of recombinant MEP 24.15 or renal DPP IV. The importance of MEP 24.15 in peptide metabolism was confirmed in pentobartibal-anesthetized rats pretreated with the MEP 24.15 inhibitor N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Aib-Tyr-p-aminobenzoate (JA2), which significantly potentiated the hypotensive response to bradykinin. The altered peptidase activities seen in aorta may contribute to modulating vascular responses in this model of hypertension.

Levels of plasma angiotensin-(1-7) in patients with hypertension who have the angiotensin-I-converting enzyme deletion/deletion genotype

In patients with hypertension who have the DD-ACE genotype (higher angiotensin-converting enzyme [ACE] activity), plasma levels of angiotensin-(1-7) are 4 times lower than in patients with the II-ACE genotype (lower ACE levels). Angiotensin II levels are similar in both groups.

The kallikrein-kinin and the renin-angiotensin systems have a multilayered interaction

Understanding the physiological role of the plasma kallikrein-kinin system (KKS) has been hampered by not knowing how the proteins of this proteolytic system, when assembled in the intravascular compartment, become activated under physiological conditions. Recent studies indicate that the enzyme prolylcarboxypeptidase, an ANG II inactivating enzyme, is a prekallikrein activator. The ability of prolylcarboxypeptidase to act in the KKS and the renin-angiotensin system (RAS) indicates a novel interaction between these two systems. This interaction, along with the roles of angiotensin converting enzyme, cross talk between bradykinin and angiotensin-(1-7) action, and the opposite effects of activation of the ANG II receptors 1 and 2 support a hypothesis that the plasma KKS counterbalances the RAS. This review examines the interaction and cross talk between these two protein systems. This analysis suggests that there is a multilayered interaction between these two systems that are important for a wide array of physiological functions.

Biphasic effects of angiotensin (1-7) and its interactions with angiotensin II in rat aorta

Using isolated rat aortic rings perfused with Krebs-Henseleit saline, the vascular effects of angiotensin (1-7) (Ang [1-7]) and its interactions with angiotensin II (Ang II) were investigated. Ang (1-7) induced endothelium-dependent relaxation and vasodilating effects in preparations precontracted with phenylephrine. Without preconstriction, Ang (1-7) at high doses (10(-6) 10(-5) M) produced either a significant inhibition of Ang II-induced vasoconstriction or a non-tachyphylactic vasopressor response. While losartan inhibited the vasoconstriction induced by Ang (1-7), A779 blocked only its relaxation. Unlike losartan, blockade of AT(2)-receptors with PD 123319 had no effect. Taking into account the biphasic effects of angiotensin (1-7), we propose that it is one of the active components of the renin-angiotensin system, which is involved as a modulator both in the counter-regulatory actions of Ang II and in the self-regulation of its own vasodilating effects.

Systemic and regional hemodynamic effects of angiotensin-(1-7) in rats

The systemic and regional hemodynamics effects of ANG-(1-7) were examined in urethane-anesthetized rats. The blood flow distribution (kidneys, skin, mesentery, lungs, spleen, brain, muscle, and adrenals), cardiac output, and total peripheral resistance were investigated by using fluorescent microspheres. Blood pressure and heart rate were recorded from the brachial artery. ANG-(1-7) infusion (110 fmol x min(-1) x 10 min(-1) iv) significantly increased blood flow to the kidney (5.10 +/- 1.07 to 8.30 +/- 0.97 ml x min(-1) x g(-1)), mesentery (0.73 +/- 0.16 to 1.17 +/- 0.49 ml x min(-1) x g(-1)), brain (1.32 +/- 0.44 to 2.18 +/- 0.85 ml x min(-1) x g(-1)), and skin (0.07 +/- 0.02 to 0.18 +/- 0.07 ml x min(-1) x g(-1)) and the vascular conductance in these organs. ANG-(1-7) also produced a significant increase in cardiac index (30%) and a decrease in total peripheral resistance (2.90 +/- 0.55 to 2.15 +/- 0.28 mmHg x ml(-1) x min x 100 g). Blood flow to the spleen, muscle, lungs, and adrenals, as well as the blood pressure and heart rate, were not altered by the ANG-(1-7) infusion. The selective ANG-(1-7) antagonist A-779 reduced the blood flow in renal, cerebral, mesenteric, and cutaneous beds and blocked the ANG-(1-7)-induced vasodilatation in the kidney, mesentery, and skin, suggesting a significant role of endogenous ANG-(1-7) in these territories. The effects of ANG-(1-7) on the cerebral blood flow, cardiac index, systolic volume, and total peripheral resistance were partially attenuated by A-779. A high dose of ANG-(1-7) (11 pmol x min(-1) x 10 min(-1)) caused an opposite effect of that produced by the low dose. Our results show for the first time that ANG-(1-7) has a previously unsuspected potent effect in the blood flow distribution and systemic hemodynamics.

Can angiotensin-converting enzyme inhibitors reverse atherosclerosis?

Angiotensin II, a potent vasoconstrictor, is mainly present in the vascular endothelium. Multiple studies have confirmed that angiotensin-converting enzyme (ACE) inhibitors, which block the formation of angiotensin II, lower blood pressure and also improve heart failure. These agents not only have beneficial hemodynamic effects but also bestow additional benefits on vascular function and prevent clinical cardiovascular events in patients at risk for coronary artery disease. These latter benefits may represent effects of ACE inhibitors on local endocrine pathways, inflammatory processes, and atherosclerosis taking place within the arterial wall. Current evidence suggests that, although ACE inhibitors may not substantially reverse atherosclerotic plaque already present, they may slow the progression of such atherosclerotic lesions. In addition, by modulating inflammatory pathways within and adjacent to the atherosclerotic lesion, they may stabilize an unstable plaque and therefore decrease the risk of plaque rupture and its complications.

Effects of angiotensin II on vascular endothelial cells: formation of receptor-mediated reactive nitrogen species

Angiotensin II (ANG II) participates in many cardiovascular disease states, but the mechanisms involved are not completely defined. Doses of ANG II that do not affect blood pressure significantly can still cause early changes in vascular endothelial performance and cell-specific protein 3-nitrotyrosine formation (protein-3NT, marker of peroxynitrite formation) in vivo. Here, we have tested the hypothesis that ANG II induces endothelial cell peroxynitrite (ONOO-) formation in vitro, and investigated the mechanisms involved. Endothelial cells were incubated with ANG II (1nM-250 microM), and protein nitration was assessed by immunoblotting. ANG II caused concentration-dependent increases in protein-3NT above detectable basal control levels, at concentrations greater than 100nM. This response was inhibited significantly by co-incubation with losartan or diphenyleneiodonium chloride. Endothelial cell lysates incubated with nitrated protein standards demonstrated significant protein-3NT modification activity only in the presence of serum. However, endothelial cell lysates did not modify the free amino acid form of 3NT (free-3NT) in identical experimental conditions, assessed by capillary electrophoresis. Finally, free-3NT was cytotoxic to cultured endothelial cells (fitted LC(50)=98 microM). These data demonstrate that stimulation of angiotensin receptor subtype 1 by ANG II can cause increased endothelial cell protein nitration in vitro in the absence of other cell types or stimuli, at concentrations that are pathophysiologically relevant. Furthermore, endothelial cells selectively modified nitrated protein tyrosine residues only in the presence of a cofactor(s), and did not modify the free modified amino acid. Protein nitration may be a regulated endothelial signaling process, while free-3NT may be toxic to endothelial cells.

Characterization of angiotensin-(1-7) receptor subtype in mesenteric arteries

Mesenteric arteries from male Sprague-Dawley rats were mounted in a pressurized myograph system. Ang-(1-7) concentration-dependent responses were determined in arteries preconstricted with endothelin-1 (10(-7)M). The receptor(s) mediating the Ang-(1-7) evoked dilation were investigated by pretreating the mesenteric arteries with specific antagonists of Ang-(1-7), AT(1) or AT(2) receptors. The effects of Ang-(3-8) and Ang-(3-7) were also determined. Ang-(1-7) caused a concentration-dependent dilation (EC(50): 0.95 nM) that was blocked by the selective Ang-(1-7) receptor antagonist D-[Ala(7)]-Ang-(1-7). Administration of a specific antagonist to the AT(2) receptor (PD123319) had no effect. On the other hand, losartan and CV-11974 attenuated the Ang-(1-7) effect. These results demonstrate that Ang-(1-7) elicits potent dilation of mesenteric resistance vessels mediated by a D-[Ala(7)]-Ang-(1-7) sensitive site that is also sensitive to losartan and CV-11974.

Angiotensin-(1-7) inhibits angiotensin II-induced signal transduction

The inhibitory effects of angiotensin-(1-7) on angiotensin II-induced vasoconstriction, growth of vascular smooth muscle cells, stimulation of protein kinase C, extracellular signal-regulated kinases (ERK), and angiotensin subtype 1 receptor (AT1) and subtype 2 receptor (AT2) mRNA expression were investigated. The hemodynamic effects of angiotensin-(1-7) were measured in Wistar rats. Vasoconstriction was measured using aortic rings. DNA synthesis or protein synthesis was measured in cultured vascular smooth muscle cells using [3H] thymidine or [3H] leucine incorporation, respectively. Angiotensin II stimulated protein kinase C and ERK1/2 were measured by Western blot analysis using phosphospecific protein kinase C and ERK1/2 antibodies. AT1 and AT2 receptor mRNA expression was measured using reverse-transcription polymerase chain reaction. Infusion of angiotensin II significantly increased whereas infusion of angiotensin-(1-7) had no effects on mean arterial blood pressure in Wistar rats. Angiotensin-(1-7) dose-dependently showed partial antagonism on angiotensin II-induced contraction of aortic rings. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced DNA synthesis and protein synthesis. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced activation of protein kinase C and ERK1/2. The administration of angiotensin-(1-7) showed partial antagonism on angiotensin II-induced downregulation of AT1 receptor mRNA expression, whereas AT2 receptor mRNA expression was unchanged. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced intracellular signal transduction and may play a crucial role in the adaptation process of AT1 receptors to sustained stimulation of angiotensin II.

Oxygen-dependent signaling in pulmonary vascular smooth muscle

The pulmonary circulation constricts in response to acute hypoxia, which is reversible on reexposure to oxygen. On exposure to chronic hypoxia, in addition to vasoconstriction, the pulmonary vasculature undergoes remodeling, resulting in a sustained increase in pulmonary vascular resistance that is not immediately reversible. Hypoxic pulmonary vasoconstriction is physiological in the fetus, and there are many mechanisms by which the pulmonary vasculature relaxes at birth, principal among which is the acute increase in oxygen. Oxygen-induced signaling mechanisms, which result in pulmonary vascular relaxation at birth, and the mechanisms by which chronic hypoxia results in pulmonary vascular remodeling in the fetus and adult, are being investigated. Here, the roles of cGMP-dependent protein kinase in oxygen-mediated signaling in fetal pulmonary vascular smooth muscle and the effects of chronic hypoxia on ion channel activity and smooth muscle function such as contraction, growth, and gene expression were discussed.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.

Angiotensin-(1-7) stimulates oxidative stress in rat kidney

The effect of two different doses of angiotensin-(1-7) and angiotensin II on the oxidative stress generation was analyzed in rat kidney. Animals were injected intraperitoneally with a single dose of angiotensin-(1-7) or angiotensin II (20 or 50 nmol/kg body weight) and killed 3 h after injection. Production of thiobarbituric acid reactive substances (TBARS), measured as indicator of oxidative stress induction, was significantly increased in rat kidney after Ang-(1-7) administration up to 30% and 50% over controls, at 20 and 50 nmol/kg, respectively. Reduced glutathione (GSH), the most important soluble antioxidant defense in mammalian cells, showed a significant decrease of 13% and 20% at 20 and 50 nmol/kg of angiotensin-(1-7), respectively. When the antioxidant enzyme activities were determined, it was found that catalase activity was not altered by the assayed angiotensin-(1-7) doses while superoxide dismutase and glutathione peroxidase activities were significantly reduced by injection of 20 nmol/kg (34% and 13%, with respect to controls) and 50 nmol/kg of angiotensin-(1-7) (54% and 22%, respectively). In contrast, angiotensin II injections did not produce significant changes neither in TBARS levels nor in soluble and enzymatic defense parameters at the two doses used in this work. These results suggest that angiotensin-(1-7) is undoubtedly related to oxidative stress induction.

Effects of angiotensins on day-night fluctuations and stress-induced changes in blood pressure

In this study we evaluated by telemetry the effects of ANG II and ANG-(1-7) infusion on the circadian rhythms of blood pressure (BP) and heart rate (HR) and on the cardiovascular adjustment resulting from restraint stress in rats. ANG II or ANG-(1-7) or vehicle were infused subcutaneously for 7 days. Restraint stress was carried out before, during, and after infusion at 7-day intervals. Parallel with an increase in MAP, ANG II infusion produced an inversion of MAP circadian rhythm with a significant MAP acrophase inversion. It also produced bradycardia during the first 3 days of infusion. Thereafter, HR progressively increased, reaching values similar to or above those of the control period at the end of the infusion period. HR circadian variation was not changed by ANG II infusion. Strikingly, ANG II significantly attenuated the increase in MAP induced by restraint stress without altering the HR response. ANG-(1-7) infusion produced a slight but significant decrease in MAP restricted to the daytime period. No significant changes in the MAP acrophase were observed. In addition, ANG-(1-7) infusion produced a small but significant sustained bradycardia. ANG-(1-7) did not change cardiovascular responses to restraint stress. These data indicate that ANG II can influence the activity of brain areas involved in the determination of stress-induced or circadian-dependent variations of blood pressure without changing HR fluctuations. A significant modulatory influence of ANG-(1-7) on basal MAP and HR is also suggested.

Angiotensin-(1-7) is involved in the endothelium-dependent modulation of phenylephrine-induced contraction in the aorta of mRen-2 transgenic rats

1. The contribution of the local vascular production of angiotensin-(1-7) [Ang-(1-7)] to the control of alpha-adrenergic-induced contractions in the aorta of Sprague-Dawley (SD) and TGR(mRen-2)27 [mRen-2] rats was studied. 2. In mRen-2 rats, contractile responses to phenylephrine were diminished as compared to control SD rats in endothelium containing but not in endothelium-denuded vessels. L-NAME increased contractile responses to phenylephrine in mRen-2 rats and, after nitric oxide synthase blockade, responses to phenylephrine became comparable in both strains. 3. Inhibition of angiotensin-converting enzyme (ACE) by captopril potentiated contractile responses in mRen-2 rats and diminished contractile responses in SD rats, both effects being dependent on the presence of a functional endothelium. The effect of captopril in mRen-2 rats was abolished in vessels pre-incubated with Ang-(1-7). 4. Blockade of Ang-(1-7) and bradykinin (BK) receptors by A-779 and HOE 140 respectively, increased phenylephrine-induced contraction in mRen-2, but not in SD rats. This effect was seen only in endothelium-containing vessels. 5. Angiotensin II AT(1) and AT(2) receptor blockade by CV 11974 and PD 123319 did not affect the contractile responses to phenylephrine in aortas of transgenic animals but diminished the response in SD rats. This effect was only seen in the presence of a functional endothelium. 6. It is concluded that the decreased contractile responses to phenylephrine in aortas of mRen-2 rats was dependent on an intact endothelium, the local release and action of Ang-(1-7) and bradykinin.

Effect of angiotensin-(1-7) on jejunal absorption of water in rats

The effect of angiotensin-(1-7) on jejunal water absorption in rats was investigated. The jejunal sac of anesthetized rats was filled with two ml of tyrode solution containing 3.7 MBq of tritiated water. A femoral vein was cannulated for administration of peptides and drugs. Infusion of Ang-(1-7) at the dose of 0.7 ng/kg.min produced a significant increase in jejunal water absorption compared to control (32% increase). The Ang-(1-7) antagonist A-779 abolished the effect of Ang-(1-7) on water absorption. A reduction of the Ang-(1-7) effect was also produced by treatment with the AT(1) receptor antagonist, losartan or the AT(2) receptor antagonist, PD123.177. The increase in jejunal water absorption produced by Ang-(1-7) was blocked by the nitric oxide synthase inhibitor, L-NAME and by indomethacin. These data suggest that the effect of Ang-(1-7) on the jejunal loop is mediated by activation of a multiple angiotensin receptors and/or by an atypical angiotensin receptor. Furthermore, the effect of Ang-(1-7) on jejunal water absorption is mediated by nitric oxide and by a cyclooxygenase-dependent mechanism.