The renin-angiotensin system and experimental heart failure

Experimental studies suggest that the renin-angiotensin system (RAS) and its primary effector peptide, angiotensin II (Ang II), are involved in the pathophysiology of cardiac hypertrophy and failure. All the components required for Ang II production are present in the heart, and cardiac Ang II formation appears to be regulated independent from the circulating RAS. In animal models and in patients with heart failure, the cardiac RAS is activated and, presumably, local Ang II formation is enhanced. Several cardiac cell types express Ang II type 1 (AT1) and/or type 2 (AT2)-receptors and represent potential targets for Ang II-mediated effects. In neonatal cardiac myocytes, Ang II induces a hypertrophic response via the AT1-receptor. Likewise, activation of the AT1-receptor triggers hypertrophy in terminally differentiated cardiac myocytes and in perfused heart preparations. In the neonatal system, Ang II appears to be a major autocrine/paracrine mediator of cardiac myocyte hypertrophy in response to passive mechanical stretch. By contrast, AT1-receptor activation apparently is not required to trigger load-induced hypertrophy in the adult cardiomyocyte. Recent studies suggest that the AT2-receptor opposes AT1-receptor-mediated growth signals in neonatal and in adult cardiac myocytes. Pharmacological studies have established that a blockade of the RAS at the level of the angiotensin-converting enzyme (ACE) or the AT1-receptor ameliorates the remodeling process of the heart and prolongs long-term survival in animal models of cardiac hypertrophy and failure. The therapeutic effects of ACE inhibitors and AT1-receptor antagonists clearly suggest an important role for the ACE-Ang II-AT1-receptor axis in the development of cardiac hypertrophy and failure. It must be kept in mind, however, that these drugs enhance AT2-receptor and B2-kinin receptor-dependent signaling pathways which may contribute significantly to the beneficial effects observed in vivo. Molecular and physiological analyses of transgenic mice with a cardiac-specific overexpression of the AT1 or AT2-receptor confirm that AT1 and AT2-receptor-dependent signaling cascades potently modulate cardiac myocyte function and growth. However, studies in AT1-receptor knockout mice demonstrate that cardiac hypertrophy in response to hemodynamic overload can occur independent from the AT1-receptor. In this paper, we review recent experimental evidence suggesting a critical role for the RAS in cardiac hypertrophy and failure with special emphasis on the putative role of Ang II and Ang II-receptor signaling in cardiac myocytes.     

Insulin-like growth factor-1 attenuates the detrimental impact of nonocclusive coronary artery constriction on the heart.

Coronary artery narrowing (CAN) induces tissue injury, which may involve myocyte necrosis and apoptosis. Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects of myocardial ischemia. On this basis, CAN was produced in female FVB.Igf+/- mice and nontransgenic littermates, and the animals were euthanized 7 days later. CAN consisted of an 82% reduction in the vessel luminal cross-sectional area in both groups of mice. Severe left ventricular dysfunction was present in CAN nontransgenic and transgenic mice, but heart and left ventricular weights increased more in littermates than in FVB.Igf+/- mice. Similarly, the changes in chamber volume and diastolic wall stress were greater in nontransgenic mice. Subacute tissue injury, represented by foci of replacement fibrosis, was 2.6-fold higher in CAN littermates than in FVB.Igf+/- mice. Ongoing myocyte necrosis was 5-fold greater in nontransgenic mice, whereas apoptosis was low and did not differ in the 2 groups of mice. In CAN nontransgenic mice, myocyte necrosis was 12-fold more frequent than apoptosis but, in CAN transgenic mice, these 2 types of cell death were comparable. alpha-Myosin and beta-myosin isoform mRNAs were affected by CAN, but alpha-myosin mRNA was reduced more in nontransgenic mice. In conclusion, myocyte necrosis and replacement fibrosis are the prevailing forms of myocardial damage induced by CAN. Constitutive overexpression of IGF-1 attenuates myocyte necrosis and tissue injury, having no effect on cell apoptosis. These factors limit ventricular dilation, myocardial loading, cardiac hypertrophy, and alterations in alpha- and beta-myosin isoform expression.     

TNF-α对培养乳鼠心肌细胞的作用

目的:探讨不同浓度肿瘤坏死因子-α(TNF-α)对培养的乳鼠心肌细胞活力、蛋白合成、分泌AngⅡ及AT1受体表达的影响。方法: 体外培养的SD乳鼠心肌细胞随机分为对照组和不同浓度TNF-α（20、40、60、80、100 μg/L）干预组,用BCA法测定心肌细胞蛋白合成总量,MTT比色法和LDH检测反映心肌细胞的活力,ELISA法检测心肌细胞培养液中AngⅡ的含量,免疫细胞化学染色法检测心肌细胞膜AT1受体表达的变化。结果: TNF-α浓度依赖性地增强乳鼠心肌细胞活力、增加蛋白合成,20、40、60、80 μg/L TNF-α组细胞活力较对照组分别增加1.21（P<0.05)、1.42、1.51和1.73倍（均P<0.01),蛋白合成分别增加27.8%（P<0.05）、38.9%、46%和66.7%（均P<0.01）,而LDH含量差异无显著性。100 μg/L TNF-α组与对照组比较,心肌细胞活力降低18.5%（P<0.01）、蛋白合成降低18.3%（P<0.01）及心肌LDH生成增加1.48倍（P<0.01)。TNF-α浓度依赖性地增加乳鼠心肌细胞AngⅡ分泌,与对照组比较分别增加0.5、1.1、1.6、3和3.6倍（均P<0.01）。TNF-α还具有诱导AT1受体的表达的作用。结论: TNF-α可促进心肌细胞内源性AngⅡ产生,引起心肌细胞活力、蛋白合成改变,AT1受体表达上调,可能介导了心肌肥大、心肌受损等心肌改建的病理生理过程。     

Appraisal of the role of angiotensin II and aldosterone in ventricular myocyte apoptosis in adult normotensive rat

Despite previous observations on isolated ventricular myocytes, there are still few evidences that angiotensin II induces cardiomyocyte apoptosis in vivo. The possibility that aldosterone, the final hormone of the renin-angiotensin-aldosterone system under Ang II control, can stimulate cardiac apoptosis has not yet been explored. Angiotensin II or aldosterone (1mg/kg each) were infused in adult normotensive rats for different times, and the number of apoptotic ventricular myocyte nuclei was quantified by the TUNEL method, along with caspase-3 activation. The role of angiotensin II type 1 receptor in vivo was assessed by selective blockade with valsartan and ex vivo by binding experiments. In addition, myocytes in primary culture were incubated with Ang II or aldosterone in presence of spironolactone. Continuous infusion of Ang II induced a rapid, AT(1)-mediated increase of apoptotic cardiomyocyte nuclei (from 14+/-9 to 188+/-35 TdT-labeled nuclei/10(6) after 3h, P<0.005) and of activated caspase-3, that normalized after 24h. The normalization was associated with a down-regulation of myocardial AT(1) receptors. Aldosterone stimulated cardiomyocyte apoptosis both in vivo and in isolated cells, to a similar extent as Ang II. The maximal apoptotic rate reported here ( approximately 0.02%) and the transient effect of Ang II suggest that myocyte loss by apoptosis is limited in the present model. The data on aldosterone-induced ventricular myocyte apoptosis deserve further attention to delineate the role of aldosterone in cell death and offer possible mechanistic explanations on the benefits afforded by aldosterone receptor antagonists in heart failure.     

Mechanical stretch and angiotensin II differentially upregulate the renin-angiotensin system in cardiac myocytes In vitro.

Pressure overload in vivo results in left ventricular hypertrophy and activation of the renin-angiotensin system in the heart. Mechanical stretch of neonatal rat cardiac myocytes in vitro causes secretion of angiotensin II (Ang II), which in turn plays a pivotal role in mechanical stretch-induced hypertrophy. Although in vivo data suggest that the stimulus of hemodynamic overload serves as an important modulator of cardiac renin-angiotensin system (RAS) activity, it is not clear whether observed upregulation of RAS genes is a direct effect of hemodynamic stress or is secondary to neurohumoral effects in response to hemodynamic overload. Moreover, it is unclear whether activation of the local RAS in response to hemodynamic overload predominantly occurs in cardiac myocytes or fibroblasts or both. In the present study, we examined the effect of mechanical stretch on expression of angiotensinogen, renin, angiotensin-converting enzyme (ACE), and Ang II receptor (AT(1A), AT(1B), and AT(2)) genes in neonatal rat cardiac myocytes and cardiac fibroblasts in vitro. The level of expression of angiotensinogen, renin, ACE, and AT(1A) genes was low in unstretched cardiac myocytes, but stretch upregulated expression of these genes at 8 to 24 hours. Stimulation of cardiac myocytes with Ang II also upregulated expression of angiotensinogen, renin, and ACE genes, whereas it downregulated AT(1A) and did not affect AT(1B) gene expression. Although losartan, a specific AT(1) antagonist, completely inhibited Ang II-induced upregulation of angiotensinogen, renin, and ACE genes, as well as stretch-induced upregulation of AT(1A) expression, it did not block upregulation of angiotensinogen, renin, and ACE genes by stretch. Western blot analyses showed increased expression of angiotensinogen and renin protein at 16 to 24 hours of stretch. The ACE-like activity was also significantly elevated at 24 hours after stretch. Radioligand binding assays revealed that stretch significantly upregulated the AT(1) density on cardiac myocytes. Interestingly, stretch of cardiac fibroblasts did not result in any discernible increases in the expression of RAS genes. Our results indicate that mechanical stretch in vitro upregulates both mRNA and protein expression of RAS components specifically in cardiac myocytes. Furthermore, components of the cardiac RAS are independently and differentially regulated by mechanical stretch and Ang II in neonatal rat cardiac myocytes.     

胰岛素样生长因子和氯沙坦联合治疗心肌梗死的分子机制研究

目的探讨胰岛素样生长因子1(IGF-1)基因转染和氯沙坦联合治疗大鼠急性心肌梗死及其机制。方法构建IGF-1基因的腺病毒重组体(ADV-IGF-1),结扎30只大鼠冠状动脉左前降支,造模急性心肌梗死后,随机分为对照组、腺病毒空载体(ADV)组、ADV-IGF-1组、氯沙坦组和ADV-IGF-1加氯沙坦联合治疗组(联合组),每组6只。后3组在心肌梗死周边区域注射10~(11)pfu/ml ADV-IGF-1 0.1ml和(或)以氯沙坦10 mg/(kg·d)灌胃连续1周,1周后,ELISA法测心肌血管紧张素Ⅱ(AngⅡ)蛋白含量变化;实时荧光定量PCR法检测心肌p53、AngⅡ受体、IGF-1、Bcl-2基因表达;Western blot法检测心肌IGF-1蛋白表达。结果与对照组和ADV组比较,ADV-IGF-1组心肌p53、AngⅡ受体基因表达明显降低,AngⅡ蛋白含量明显降低(P<0.05);氯沙坦组明显上调心肌IGF-1基因表达(P<0.05);联合组p53、AngⅡ受体基因弱表达,Bcl-2强表达(P<0.05)。结论心肌梗死后,心肌特异性过表达IGF-1,下调p53基因表达,继而抑制AngⅡ受体基因表达和AngⅡ产生;氯沙坦干预促进IGF-1基因表达;IGF-1基因转染和氯沙坦联合治疗心肌梗死有协同作用。     

Angiotensin II impairs endothelial progenitor cell number and function in vitro and in vivo: implications for vascular regeneration

Endothelial progenitor cells (EPCs) contribute to endothelial regeneration. Angiotensin II (Ang II) through Ang II type 1 receptor (AT(1)-R) activation plays an important role in vascular damage. The effect of Ang II on EPCs and the involved molecular mechanisms are incompletely understood. Stimulation with Ang II decreased the number of cultured human early outgrowth EPCs, which express both AT(1)-R and Ang II type 2 receptor, mediated through AT(1)-R activation and induction of oxidative stress. Ang II redox-dependently induced EPC apoptosis through increased apoptosis signal-regulating kinase 1, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase phosphorylation; decreased Bcl-2 and increased Bax expression; and activation of caspase 3 but had no effect on the low cell proliferation. In addition, Ang II impaired colony-forming and migratory capacities of early outgrowth EPCs. Ang II infusion diminished numbers and functional capacities of EPCs in wild-type (WT) but not AT(1)a-R knockout mice (AT(1)a(-/-)). Reendothelialization after focal carotid endothelial injury was decreased during Ang II infusion. Salvage of reendothelialization by intravenous application of spleen-derived progenitor cells into Ang II-treated WT mice was pronounced with AT(1)a(-/-) cells compared with WT cells, and transfusion of Ang II-pretreated WT cells into WT mice without Ang II infusion was associated with less reendothelialization. Transplantation of AT(1)a(-/-) bone marrow reduced atherosclerosis development in cholesterol-fed apolipoprotein E-deficient mice compared with transplantation of apolipoprotein E-deficient or WT bone marrow. Randomized treatment of patients with stable coronary artery disease with the AT(1)-R blocker telmisartan significantly increased the number of circulating CD34/KDR-positive EPCs. Ang II through AT(1)-R activation, oxidative stress, and redox-sensitive apoptosis signal-regulating kinase 1-dependent proapoptotic pathways impairs EPCs in vitro and in vivo, resulting in diminished vascular regeneration.     

Cardiac stem cell and myocyte aging, heart failure, and insulin-like growth factor-1 overexpression

To determine whether cellular aging leads to a cardiomyopathy and heart failure, markers of cellular senescence, cell death, telomerase activity, telomere integrity, and cell regeneration were measured in myocytes of aging wild-type mice (WT). These parameters were similarly studied in insulin-like growth factor-1 (IGF-1) transgenic mice (TG) because IGF-1 promotes cell growth and survival and may delay cellular aging. Importantly, the consequences of aging on cardiac stem cell (CSC) growth and senescence were evaluated. Gene products implicated in growth arrest and senescence, such as p27Kip1, p53, p16INK4a, and p19ARF, were detected in myocytes of young WT mice, and their expression increased with age. IGF-1 attenuated the levels of these proteins at all ages. Telomerase activity decreased in aging WT myocytes but increased in TG, paralleling the changes in Akt phosphorylation. Reduction in nuclear phospho-Akt and telomerase resulted in telomere shortening and uncapping in WT myocytes. Senescence and death of CSCs increased with age in WT impairing the growth and turnover of cells in the heart. DNA damage and myocyte death exceeded cell formation in old WT, leading to a decreased number of myocytes and heart failure. This did not occur in TG in which CSC-mediated myocyte regeneration compensated for the extent of cell death preventing ventricular dysfunction. IGF-1 enhanced nuclear phospho-Akt and telomerase delaying cellular aging and death. The differential response of TG mice to chronological age may result from preservation of functional CSCs undergoing myocyte commitment. In conclusion, senescence of CSCs and myocytes conditions the development of an aging myopathy.     

Angiotensin II modulates renal sympathetic neurotransmission through nitric oxide in AT2 receptor knockout mice

OBJECTIVE: Angiotensin (Ang) II enhances renal sympathetic neurotransmission and stimulates nitric oxide (NO) release. The present study investigates whether Ang II-mediated modulation of sympathetic neurotransmission is dependent on NO production in the kidney. AT2 -/y receptor-deficient mice are used to identify the Ang II receptor subtype involved. METHODS: Mice kidneys were isolated and perfused with Krebs-Henseleit solution. Drugs were added to the perfusion solution in a cumulative manner. Release of endogenous noradrenaline (NA) was measured by high-performance liquid chromatography (HPLC). AT1 receptor expression was analysed by real-time polymerase chain reaction (PCR). RESULTS: Ang II (0.01-30 nmol/l) dose dependently increased pressor responses in kidneys of AT2 -/y mice and wild-type (AT2 +/y) mice. Maximal pressor responses and EC50 values for Ang II was greater in AT2 -/y than in AT2 +/y mice. L-NAME (N(omega)-nitro-L-arginine methyl ester; 0.3 mmol/l) enhanced Ang II-induced pressor responses in both strains. In AT2 -/y mice, Ang II-induced facilitation of NA release was more pronounced than in AT2 +/y mice. L-NAME reduced Ang II-mediated facilitation of NA release in both strains. This reduction was more potent in AT2 -/y mice. In kidneys of AT2 -/y mice the AT1 receptor expression was significantly upregulated. CONCLUSION: These results suggest that activation of AT1 receptors by Ang II releases NO in mouse kidney to modulate sympathetic neurotransmission. Since AT1 receptors are upregulated in AT2 -/y mice kidneys, NO-dependent effects were greater in these mice. Thus, NO seems to play an important modulatory role for renal sympathetic neurotransmission.     

G1 cyclins are involved in the mechanism of cardiac myocyte hypertrophy induced by angiotensin II

The importance of the cell cycle in proliferating cells is well known, but little is known about the role of cell cycle regulatory proteins in cardiac myocytes, which are fully differentiated cells. The present study determined, in vitro, the effect of angiotensin II (Ang II) treatment of neonatal rat cardiac myocytes on protein levels of cyclins and retinoblastoma gene product (pRb) phosphorylation. The role of G1 cyclin/cdk in Ang II-induced cardiac myocyte hypertrophy by overexpressing cdk inhibitor p21Cip1/Waf1 or p16INK4a was also examined using recombinant adenoviral vectors encoding these genes. Western blot analysis revealed that Ang II stimulated cyclin D1, D2, D3 and A protein levels in cardiac myocytes. Moreover, Ang II phosphorylated pRb on serine 780, which is known to occur in mitotic cells during cell cycle progression. Cultured cardiac myocytes treated with Ang II and infected with either control or recombinant adenovirus indicated that expression of p21 and p16 inhibited Ang II-induced cardiac myocyte hypertrophy, [3H]leucine incorporation into total cellular proteins, and skeletal alpha-actin (SK-A) and atrial natriuretic peptide (ANP) mRNA accumulation. Control virus had no effects on these parameters. These results suggest that G1 cyclins play an important role in cardiac myocyte hypertrophy stimulated by Ang II.     

Role of Angiotensin II in Mechanical Stress-Induced Cardiac Hypertrophy

Many lines of evidence have suggested that the renin–angiotensin system plays an important role in the development of cardiac hypertrophy. Pressure overload-induced cardiac hypertrophy is prevented by angiotensin-converting enzyme inhibitors in vivo, and mechanical stretch induces secretion and production of angiotensin II (Ang II) from cardiac myocytes in vitro. Ang II induces cardiomyocyte hypertrophy through the Ang II type 1 (AT1) receptor. All these results suggest that the AT1 receptor-mediated signaling is critical for the development of mechanical stress-induced cardiac hypertrophy. However, we have recently obtained results from AT1 knockout mice suggesting that mechanical stress can induce cardiac hypertrophy without AT1 receptor-mediated Ang II signaling.     

TGF-beta1 and angiotensin networking in cardiac remodeling

The renin-angiotensin system (RAS) and transforming growth factor-beta1 (TGF-beta1) play a pivotal role in the development of cardiac hypertrophy and heart failure. Recent studies indicate that angiotensin II (Ang II) and TGF-beta1 do not act independently from one another but rather act as part of a signalling network in order to promote cardiac remodeling, which is a key determinant of clinical outcome in heart disease. This review focuses on recent advances in the understanding, how Ang II and TGF-beta1 are connected in the pathogenesis of cardiac hypertrophy and dysfunction. Increasing evidence suggests that at least some of the Ang II-induced effects on cardiac structure are mediated via indirect actions. Ang II upregulates TGF-beta1 expression via activation of the angiotensin type 1 (AT1) receptor in cardiac myocytes and fibroblasts, and induction of this cytokine is absolutely required for Ang II-induced cardiac hypertrophy in vivo. TGF-beta induces the proliferation of cardiac fibroblasts and their phenotypic conversion to myofibroblasts, the deposition of extracellular matrix (ECM) proteins such as collagen, fibronectin, and proteoglycans, and hypertrophic growth of cardiomyocytes, and thereby mediates Ang II-induced structural remodeling of the ventricular wall in an auto-/paracrine manner. Downstream mediators of cardiac Ang II/TGF-beta1 networking include Smad proteins, TGFbeta-activated kinase-1 (TAK1), and induction of hypertrophic responsiveness to beta-adrenergic stimulation in cardiac myocytes.     

AT1 blockade prevents glucose-induced cardiac dysfunction in ventricular myocytes: role of the AT1 receptor and NADPH oxidase

Enhanced tissue angiotensin (Ang) II levels have been reported in diabetes and might lead to cardiac dysfunction through oxidative stress. This study examined the effect of blocking the Ang II type 1 (AT1) receptor on high glucose-induced cardiac contractile dysfunction. Rat ventricular myocytes were maintained in normal- (NG, 5.5 mmol/L) or high- (HG, 25.5 mmol/L) glucose medium for 24 hours. Mechanical and intracellular Ca2+ properties were assessed as peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR90), maximal velocity of shortening/relengthening (+/-dL/dt), and intracellular Ca2+ decay (tau). HG myocytes exhibited normal PS; decreased +/-dL/dt; and prolonged TPS, TR90, and tau. Interestingly, the HG-induced abnormalities were prevented with the AT1 blocker L-158,809 (10 to 1000 nmol/L) but not the Janus kinase-2 (JAK2) inhibitor AG-490 (10 to 100 micromol/L). The only effect of AT1 blockade on NG myocytes was enhanced PS at 1000 nmol/L. AT1 antagonist-elicited cardiac protection against HG was nullified by the NADPH oxidase activator sodium dodecyl sulfate (80 micromol/L) and mimicked by the NADPH oxidase inhibitors diphenyleneiodonium (10 micromol/L) or apocynin (100 micromol/L). Western blot analysis confirmed that the protein abundance of NADPH oxidase subunit p47phox and the AT1 but not the AT2 receptor was enhanced in HG myocytes. In addition, the HG-induced increase of p47phox was prevented by L-158,809. Enhanced reactive oxygen species production observed in HG myocytes was prevented by AT1 blockade or NADPH oxidase inhibition. Collectively, our data suggest that local Ang II, acting via AT1 receptor-mediated NADPH oxidase activation, is involved in hyperglycemia-induced cardiomyocyte dysfunction, which might play a role in diabetic cardiomyopathy.     

Cardiac hypertrophy is associated with decreased eNOS expression in angiotensin AT2 receptor-deficient mice

Angiotensin II receptors play an essential role in cardiovascular physiology and disease. The significance of angiotensin type II (AT2) receptors in cardiac disease still remains elusive. Thus, we tested in gene-targeted mice whether AT2 receptors modulate cardiac function and remodeling after experimental myocardial injury. To generate myocardial infarcts of reproducible size, a cryolesion was generated at the free wall of the left ventricle of wild-type mice (Agtr2+/Y) and mice carrying a deletion of the AT2 receptor gene (Agtr2-/Y). Postinjury remodeling was followed up for 4 weeks after cryoinjury. The cryoprocedure led to an increased heart weight/body weight ratio and heart weight/tibia length ratio in AT2-deficient mice compared with control mice. Morphometric analysis revealed a significant increase in myocyte cross-sectional area after cardiac injury (infarct vs sham Agtr2+/Y, +53%; vs Agtr2-/Y, +95%). Expression of endothelial nitric oxide synthase (eNOS) was significantly lower in hearts from Agtr2-/Y than from Agtr2+/Y mice. eNOS downregulation was accompanied by a decrease in cardiac cGMP levels in Agtr2-/Y mice. In isolated murine cardiomyocytes, angiotensin II induced eNOS expression through AT2 receptors, and inhibition of NO production by NG-nitro-l-arginine methyl ester abolished the antihypertrophic effect of AT2 on cardiac myocytes. Our results demonstrate in a genetic mouse model that angiotensin II AT2 receptors exert an antihypertrophic effect in cardiac remodeling after myocardial cryoinjury and link the expression of cardiac eNOS to AT2 receptor activation.     

Hemodynamic effects of vasorelaxant compounds in mice lacking one, two or all three angiotensin II receptors

The renin-angiotensin system (RAS) has a vital role in regulating the cardiovascular system. The primary effector of the RAS is the octapeptide angiotensin (Ang) II, a potent regulator of blood pressure and water homeostasis. Ang II mediates its functions through the stimulation of two distinct receptors, AT(1) (two subtypes in rodents (AT(1a) and AT(1b))) and AT(2). It was shown that in addition to Ang II, shorter fragments of Ang are also biologically active. Ang-(1-7) came into focus because it opposes many of the detrimental effects of Ang II. However, it is still controversial whether Ang II receptors are involved in Ang-(1-7)-mediated signaling. To characterize the impacts of Ang II receptors on Ang-(1-7)-stimulated vascular relaxation, the effects of acute infusion of the three vasorelaxant compounds, that is, Ang-(1-7), bradykinin (BK) and acetylcholine (ACh), on heart rate (HR) and mean arterial pressure (MAP) were investigated in mice deficient for one, two or all three Ang II receptors. Ang-(1-7) and BK reduced MAP in wild-type, AT(1a)/AT(1b)-deficient and AT(2)-deficient mice. Although the change in absolute MAP values in the hypotensive triple knockouts (KO) could not be further reduced by both peptides, the percent change in MAP was comparable between the triple KO and wild-type mice. Both peptides did not alter the HR in all four genotypes. ACh significantly reduced absolute MAP values in all four genotypes with a similar percentage of reduction. In contrast to Ang-(1-7) and BK, ACh significantly reduced HR without genotypic differences. Our results generate proof that Ang-(1-7)-induced effects on MAP are mediated by a receptor that is independent of AT(1) and AT(2).     

Role of AT2 receptors in the cardioprotective effect of AT1 antagonists in mice

Angiotensin II (Ang II) acts mainly on two receptor subtypes: AT1 and AT2. Most of the known biological actions of Ang II are mediated by AT1 receptors; however, the role of AT2 receptors remains unclear. We tested the hypothesis that the cardioprotective effects of AT1 receptor antagonists (AT1-ant) after myocardial infarction (MI) are partially mediated by activation of AT2 receptors; thus in AT2 receptor gene knockout mice (AT2-/Y), the effect of AT1-ant will be diminished or absent. MI was induced by ligating the left anterior descending coronary artery. Four weeks later, AT2-/Y and their wild-type littermates (AT2+/Y) were started on vehicle, AT1-ant (valsartan, 50 mg/kg per day), or ACE inhibitor (enalapril, 20 mg/kg per day) for 20 weeks. Basal blood pressure and cardiac function as well as remodeling after MI did not differ between AT2+/Y and AT2-/Y. AT1-ant increased ejection fraction and cardiac output and decreased left ventricular diastolic dimension, myocyte cross-sectional area, and interstitial collagen deposition in AT2+/Y, and these effects were significantly diminished in AT2-/Y. ACE inhibitors improved cardiac function and remodeling similarly in both strains. We concluded that (1) activation of AT2 during AT1 blockade plays an important role in the therapeutic effect of AT1-ant and (2) the AT2 receptor may not play an important role in regulation of cardiac function, either under basal conditions after MI remodeling or in the therapeutic effect of ACE inhibitors.     

Angiotensin II enhances noradrenaline release from sympathetic nerves of the rat prostate via a novel angiotensin receptor: implications for the pathophysiology of benign prostatic hyperplasia

The renin-angiotensin system (RAS) is present in the human prostate and may be activated in benign prostatic hyperplasia (BPH), possibly contributing to the pathophysiology of this disorder by enhancing local sympathetic tone and cell growth. The functional role of the RAS in the prostate, however, is unknown. The present study was undertaken to determine whether angiotensin (Ang) II enhances sympathetic transmission in the prostate. The neuronal stores of the rat prostate were labelled with [(3)H]noradrenaline (NA). Ang II and Ang I enhanced [(3)H]NA release in a concentration-dependent manner. The Ang II receptor subtype 1 (AT(1) receptor) antagonist losartan and the AT(2) receptor antagonist PD123319 inhibited this facilitatory effect of Ang II and Ang I, whereas the other AT(2) receptor antagonist, CGP42112, was without effect. Bradykinin also increased [(3)H]NA release, which was inhibited by the B(2) receptor antagonist Hoe140. The angiotensin-converting enzyme inhibitor captopril inhibited the effect of Ang I, but potentiated that of bradykinin. Interestingly, captopril alone produced an increase in [(3)H]NA release which was inhibited by Hoe140. Losartan, but not PD123319 or CGP42112, inhibited [(125)I]-Ang II binding in Chinese hamster ovary cells transfected with the AT(1a) or AT(1b) receptor. In contrast, in cells expressing the AT(2) receptor, PD123319 and CGP42112, but not losartan, inhibited [(125)I]-Ang II binding. In conclusion, Ang II enhances the release of NA from sympathetic nerves of the rat prostate via a novel functional receptor distinct from the cloned AT(1a), AT(1b) or AT(2). These data provide direct evidence in support of a functional role for the local RAS in modulating sympathetic transmission in the prostate, which may have important implications for the pathophysiology of BPH.