Angiotensin II receptor polymorphisms in hypertension. Pharmacogenomic considerations

Molecular variants of individual components of the renin-angiotensin system (RAS) are thought to contribute to inherited predisposition towards essential hypertension. Polymorphisms in genes of angiotensinogen (AGT), angiotensin I-converting enzyme (ACE) and angiotensin II type 1 receptor (AT-1) have been related to differential responses to antihypertensive drugs. AT-1 receptor mediates the major pressor and trophic actions of angiotensin II (Ang II). At least 14 AT-1 polymorphisms have been described in the gene (AGT1R); in particular the +1166 A/C polymorphism has been associated with the severe form of essential hypertension. A relationship was suggested between this polymorphism and the humoral and renal hemodynamic responses to losartan, an antihypertensive drug acting as an AT-1 blocker. Variability in the individual response to AT-1 antagonists could also be due to variations in the pharmacokinetics of the drugs. This review presents current knowledge on Ang II-receptors and polymorphisms in AGT1R related to cardiovascular disease and antihypertensive therapy.     

Single nucleotide polymorphisms in promoter of angiotensin II type 1 receptor gene associated with essential hypertension and coronary heart disease in Chinese population

AIM: To discover single nucleotide polymorphisms (SNPs) in the promoter region of angiotensin II type 1 receptor (AT1) gene and evaluate their associations with the occurrence of essential hypertension (EH) and coronary heart disease (CHD) in Chinese Han population. METHODS: SNPs detection was performed by PCR-sequencing. The genotype was determined by the same method in a total number of 473 unrelated patients including 160 EH cases, 128 CHD cases, and 185 EH combined with CHD cases as well as 160 healthy controls. RESULTS: Six SNPs were discovered in the promoter region of AT1 gene. -810A/T was almost in completely linkage disequilibrium with -713G/T, -214A/C, -213G/C, and -153A/G polymorphisms. No statistically association was found in our population between -810A/T polymorphism and EH, the association of -810A allele and CHD was of borderline significant (chi2=3.649, P=0.056). However, significant differences of genotype distributions were observed in the EH combined with CHD group (TT=126, TA=51, AA=8) compared with the EH patients (TT=127,TA=26, AA=7, chi2=6.410, P=0.041) and the healthy controls (TT=130, TA=24, AA=6, chi2=7.742, P=0.021). The EH combined with CHD patients had a significantly increased A allele frequency than the normal references (0.181 vs 0.106, chi2=7.690, P=0.006) and the EH subjects (0.181 vs 0.125, chi2=4.119, P=0.042). Hypertensive patients carrying TA genotype (OR=1.977, 95 % CI 1.160-3.354, P=0.011) or A allele (OR=1.548, 95 % CI 1.015-2.361, P=0.043) had an increased risk for CHD morbidity. CONCLUSION: we firstly report that -810A/T polymorphism in the promoter region of AT1 gene might be a genetic risk factor for the pathogenesis of CHD complicated with EH in Chinese Han population.     

血管紧张素Ⅱ受体与高血压性心肌重塑

血管紧张素Ⅱ（angiotensinⅡ,AngⅡ）是肾素-血管紧张素系统（RAS）的效应因子,通过其受体介导生物学效应。放射配基结合分析证实哺乳动物存在AT_1、AT_2受体,大鼠和小鼠AT_1受体存在AT_(1A)、AT_(1B)、和AT(1C)受体亚型。近年来还发现了AT_3和AT_4受体亚型,但结构和功能不清。AT_1受体具有G蛋白耦联受体超家族的特性,有7个螺旋的跨膜段,与其他G蛋白受体有20％～30％同源性,主要分布于成年动物血管、心、肾上腺等;AT_2受体仅有32％氨基酸序列与AT_1受体同源,主要分布于胚胎组织和间质组织。最新研究显示AngⅡ绝大多数生物学效应都是AT_1受体介导的。AngⅡ刺激AT_1受体诱导c-fos、c-jun和c-myc等原癌基因的表达,引起心肌细胞肥大,成纤维细胞增殖和间质胶原沉积,AT_1受体拮抗剂能逆转高血压所致的心肌肥厚,减少胶原积累,AT_2受体拮抗剂无此作用。AT_2受体的生物学效应知之甚少,可能在抑制生长因子引起的细胞增殖、对抗AT_1受体的促细胞有丝分裂作用和诱导细胞凋亡中起作用。心肌组织AT_1和AT_2受体可能共同调节了高血压心肌重塑的发生发展。     

Angiotensin II type 2 (AT2) receptor signal and cardiovascular action

Due to the discovery of nonpeptic ligands, the receptors for angiotensin (Ang) II are classified into two subtypes (AT1-R and AT2-R). AT1-R mediates most of the cardiovascular actions of Ang II. AT2-R is expressed at very high levels in the developing fetus. Its expression is very low in the cardiovascular system of the adult. The expression of AT2-R can be modulated by pathological states associated with tissue remodeling or inflammation. In failing hearts or neointima formation after vascular injury, AT2-R is reexpressed in cells proliferating in interstitial regions or neointima and exerts an inhibitory effect on Ang II-induced mitogen signals or synthesis of extracellular matrix proteins, resulting in attenuation of the tissue remodeling. An extreme form of cell growth inhibition ends in programmed cell death, and this process, which is initiated by the withdrawal of growth factors, is also enhanced by AT2-R. Cardiac myocyte- or vascular smooth muscle-specific mice that overexpress AT2-R display an inhibition of Ang II-induced chronotropic or pressor actions, suggesting the role of AT2-R on the activity of cardiac pacemaker cells and the maintenance of vascular resistance. AT2-R also activates the kinin/nitric oxide/cGMP system in the cardiovascular and renal systems, resulting in AT2-R-mediated cardioprotection, vasodilation and pressure natriuresis. These effects, transmitted by AT2-R, are mainly exerted by stimulation of protein tyrosine or serine/threonine phosphatases in a Gi-protein-dependent manner. The expression level of AT2-R is much higher in human hearts than in rodent hearts, and the AT2-R-mediated actions are likely enhanced, especially by clinical application of AT1-R antagonists. Thus, in this review, the regulation of AT2-R expression, its cellular localization, its pathological role in cardiovascular and kidney diseases, and pharmacotherapeutic effects of AT2-R stimulation are discussed.     

Angiotensin II receptor blockers for the treatment of hypertension

The rising incidence of stroke, congestive heart failure (CHF) and end stage renal disease (ESRD) has signalled a need to increase awareness, treatment and control of hypertension. There continues to be a need for effective antihypertensive medications since hypertension is a major precursor to various forms of cardiovascular disease. The renin-angiotensin (AT) aldosterone system (RAAS) is a key component to the development of hypertension and can be one target of drug therapy. Angotensin II (ATII) receptor blockers (ARBs) are the most recent class of agents available to treat hypertension, which work by by inhibiting ATII at the receptor level. Currently, national consensus guidelines recommend that ARBs should be reserved for hypertensive patients who cannot tolerate angiotensin converting enzyme (ACE) inhibitors (ACEIs). ARBs, however, are moving to the forefront of therapy with a promising role in the area of renoprotection and CHF. Recent trials such as the The Renoprotective Effect of the Angiotensin-Receptor Antagonist Irbesartan in Patients with Nephropathy Due to Type 2 Diabetes Trial (IDNT), the Effect of Irbesartan on the Development of Diabetic Nephropathy in Patients with Type 2 Diabetes (IRMA2), and The Effects of Losartan on Renal and Cardiovascular Outcomes in Patients with Type 2 Diabetes and Nephropathy (RENAAL) study have demonstrated the renoprotective effects of ARBs in patients with Type 2 diabetes. The Valsartan Heart Failure Trial (Val-HeFT) adds to the growing body of evidence that ARBs may improve morbidity and mortality in CHF patients. As a class, ARBs are well tolerated and have a lower incidence of cough and angioedema compared to ACEIs. This article reviews the differences among the ARBs, existing efficacy data in hypertension, and explores the role of ARBs in CHF and renal disease.     

Angiotensin II receptor blockers for the treatment of hypertension

The rising incidence of stroke, congestive heart failure (CHF) and end stage renal disease (ESRD) has signalled a need to increase awareness, treatment and control of hypertension. There continues to be a need for effective antihypertensive medications since hypertension is a major precursor to various forms of cardiovascular disease. The renin-angiotensin (AT) aldosterone system (RAAS) is a key component to the development of hypertension and can be one target of drug therapy. Angotensin II (ATII) receptor blockers (ARBs) are the most recent class of agents available to treat hypertension, which work by by inhibiting ATII at the receptor level. Currently, national consensus guidelines recommend that ARBs should be reserved for hypertensive patients who cannot tolerate angiotensin converting enzyme (ACE) inhibitors (ACEIs). ARBs, however, are moving to the forefront of therapy with a promising role in the area of renoprotection and CHF. Recent trials such as the The Renoprotective Effect of the Angiotensin-Receptor Antagonist Irbesartan in Patients with Nephropathy Due to Type 2 Diabetes Trial (IDNT), the Effect of Irbesartan on the Development of Diabetic Nephropathy in Patients with Type 2 Diabetes (IRMA2), and The Effects of Losartan on Renal and Cardiovascular Outcomes in Patients with Type 2 Diabetes and Nephropathy (RENAAL) study have demonstrated the renoprotective effects of ARBs in patients with Type 2 diabetes. The Valsartan Heart Failure Trial (Val-HeFT) adds to the growing body of evidence that ARBs may improve morbidity and mortality in CHF patients. As a class, ARBs are well tolerated and have a lower incidence of cough and angioedema compared to ACEIs. This article reviews the differences among the ARBs, existing efficacy data in hypertension, and explores the role of ARBs in CHF and renal disease.     

Angiotensin II type 1 receptor blockade restores nitric oxide-dependent renal vascular responses in renovascular hypertension

It was previously reported that enhancement of renal vascular responses to angiotensin II in hypertensive rats is related to decreased release of nitric oxide. Thus, it was suggested that impairment of nitric oxide synthesis during development of hypertension is related to a decreased nitric oxide synthase mRNA expression by an angiotensin II-dependent mechanism. The current study evaluated whether the blockade of angiotensin II type 1 receptor during the development of hypertension restored nitric oxide synthase mRNA expression, nitric oxide synthesis, and nitric oxide-dependent modulation of angiotensin II vasoconstrictor effects. It was shown that losartan treatment prevented increased vascular responses to angiotensin II in hypertensive rats and that this effect was associated with restoration of nitric oxide synthase mRNA expression and nitric oxide synthase activity. Furthermore, angiotensin II-dependent nitric oxide release in hypertensive rats was potentiated by losartan treatment. Angiotensin II (1 microg) released renal nitrites by 485 +/- 178, 470 +/- 150, 185 +/- 45, and 515 +/- 100 nmol/ml/30 s in the kidneys from normotensive, losartan-treated normotensive rats, hypertensive, and losartan-treated hypertensive rats, respectively. The data suggest that during development of hypertension, angiotensin II downregulates nitric oxide synthase mRNA expression, blunting nitric oxide vasodilatory tone and increasing vascular sensitivity to vasoconstrictor agents in the renal circulation.     

Comparison of angiotensin II type 1 receptor antagonists in the treatment of essential hypertension

Hypertension is a major health problem worldwide, yet remains under-diagnosed and under-treated. Angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]) are highly effective at reducing blood pressure (BP), exhibit renoprotective properties and have placebo-like tolerability. However, it is unclear whether there are clinical differences in efficacy and tolerability between the available ARBs. A review of published, randomized, comparative clinical trials suggests that differences in BP-lowering efficacy and 24-hour BP control may exist between ARBs, although it appears that there is no evidence for important differences in tolerability between ARBs. Few studies have assessed attainment rates for important combined systolic BP (SBP)/diastolic BP (DBP) goals recommended in treatment guidelines. Likewise, few studies have directly compared more than two agents or ARB/hydrochlorothiazide fixed-dose combinations, and most ARBs have not been compared across their full recommended dosage ranges. Overall, there is insufficient weight of evidence to allow definitive conclusions to be drawn regarding the comparative efficacy of the available ARBs. However, newer ARBs (e.g. olmesartan medoxomil and telmisartan) appear to be more effective than older ARBs (e.g. losartan and valsartan) in reducing DBP and/or SBP in some trials. In addition, olmesartan medoxomil treatment regimens resulted in high BP control rates in several trials, but head-to-head trials with other ARBs are required to put these control rates into perspective, especially for SBP control with various agents. The purpose of this review is to present published data from ARB efficacy trials for a comparison of various efficacy parameters among the agents within this drug class.     

Angiotensin type 1 receptor mediates chronic ethanol consumption-induced hypertension and vascular oxidative stress

ObjectivesWe hypothesized that chronic ethanol intake enhances vascular oxidative stress and induces hypertension through renin–angiotensin system (RAS) activation.Methods and resultsMale Wistar rats were treated with ethanol (20% v/v). The increase in blood pressure induced by ethanol was prevented by losartan (10 mg/kg/day; p.o. gavage), a selective AT₁ receptor antagonist. Chronic ethanol intake increased plasma renin activity (PRA), angiotensin converting enzyme (ACE) activity, plasma angiotensin I (ANG I) and angiotensin II (ANG II) levels and serum aldosterone levels. No differences on plasma osmolality and sodium or potassium levels were detected after treatment with ethanol. Ethanol consumption did not alter ACE activity, as well as the levels of ANG I and ANG II in the rat aorta or mesenteric arterial bed (MAB). Ethanol induced systemic and vascular oxidative stress (aorta and MAB) and these effects were prevented by losartan. The decrease on plasma and vascular nitrate/nitrite (NOx) levels induced by ethanol was prevented by losartan. Ethanol intake did not alter protein expression of ACE, AT₁ or AT₂ receptors in both aorta and MAB. Aortas from ethanol-treated rats displayed decreased ERK1/2 phosphorylation and increased protein expression of SAPK/JNK. These responses were prevented by losartan. MAB from ethanol-treated rats displayed reduced phosphorylation of p38MAPK and ERK1/2 and losartan did not prevent these responses.ConclusionsOur study provides novel evidence that chronic ethanol intake increases blood pressure, induces vascular oxidative stress and decreases nitric oxide (NO) bioavailability through AT₁-dependent mechanisms.     

E-选择素基因多态性与新疆哈萨克族原发性高血压的相关性研究

目的探讨E-选择素（E-selectin）基因第2外显子＋G98T和第4外显子＋A561C位点单核苷酸多态性在新疆哈萨克族人群中的分布,并分析E-selectin基因多态性与原发性高血压的相关性。方法采用聚合酶链反应-限制性片段长度多态性（PCR-RFLP）的分析方法,检测了新疆哈萨克族人群无血缘关系的150例原发性高血压患者和150名对照者E-selectin基因＋G98T位点及＋A561C位点多态性,同时用生化分析仪检测相关生化指标。结果①新疆哈萨克族人群中E-selectin基因＋G98T多态性位点存在GG、GT二种基因型,其中以GG基因型发生频率最高（91．3％）,GT基因型频率次之（8．7％）;同时也存在AA、AC二种基因型,其中以AA基因型发生频率最高（88．0％）,AC基因型频率次之（12．0％）;②E-selectinAc基因型在高血压组和对照组间的分布差异存在显著性（X2=5．31,P〈0．025）。结论新疆哈萨克族人群中存在E-selectin＋G98T和＋A561C两位点单核苷酸多态性,其中A561C基因多态性与原发性高血压具有相关性,C等位基因可能是新疆哈萨克族原发性高血压发病的遗传易感基因。     

Angiotensin II type 1 receptor blockade suppresses H2O2-induced retinal degeneration in photoreceptor cells

Exposure to reactive oxygen species (ROS) leads to the development and progression of retinal degenerative diseases. However, the exact mechanisms are not fully understood. In this article, the role of angiotensin II type 1 receptor (AT1R) signaling in H₂O₂-induced retinal damage was examined. Mouse photoreceptor-derived 661?W cells were treated with the AT1R blockers valsartan, losartan and candesartan before exposure to H₂O₂. Cell viability, intracellular ROS level, mitochondrial membrane potential (MMP), cytochrome-c level, DNA fragmentation, caspase activity and gene expression were detected. Pre-treatment of 661?W cells with AT1R blockers significantly decreased H₂O₂-mediated toxicity and reduced the ROS level. In addition, apoptosis-related biochemical indicators showed that pre-incubation of AT1R blockers would elevate the MMP, decrease the release of cytochrome-c and formation of DNA fragmentation, and inhibit activities of caspase-3 and caspase-9 in exogenous H₂O₂-treated 661?W cells. Moreover, treatment with AT1R blockers suppressed the expression of Egr1, Fosl1 and Lox12. These results suggest that AT1R signaling mediates H₂O₂-induced apoptosis, at least partially through generating the ROS and increasing the levels of proapoptotic molecules in 661?W cells. AT1R blockade may provide a new therapeutic approach for preventing oxidative stress-induced retinal neural damage.     

Angiotensin receptor blockers in hypertension and cardiovascular diseases

Angiotensin receptor blockers are the newest class of antihypertensive agents marketed for the treatment of hypertension. There is now an important amount of evidence indicating that this class of drugs exerts beneficial effects in patients with a variety of cardiovascular disorders. Evidence-based medicine includes well controlled studies with mortality and morbidity endpoints in patients with left ventricular dysfunction after a myocardial infarction, congestive heart failure, cerebrovascular disease, type-2 diabetic subjects with renal dysfunction and high-risk hypertensive patients. In addition to these hard endpoints, treatment with angiotensin receptor blockers prevents the development of type-2 diabetes, promotes a more pronounced regression of left ventricular hypertrophy, decreases microalbuminuria and proteinuria in renal patients, ameliorates coronary and peripheral vascular endothelial dysfunction and decreases plasma levels of several markers of vascular inflammation. In summary, angiotensin receptor blockers are antihypertensive drugs with a very good profile in terms of efficacy, tolerability and cardiovascular protection. They represent an important step in the search for the ideal antihypertensive agent.     

Insulin receptor substrate polymorphisms and type 2 diabetes mellitus

Insulin receptor substrate (IRS) molecules are key mediators in insulin signalling and play a central role in maintaining basic cellular functions, such as growth, survival and metabolism. They act as docking proteins for the insulin receptor and a complex network of intracellular signalling molecules containing Src homology 2 (SH2) domains. Four members (IRS-1, IRS-2, IRS-3 and IRS-4) of this family have been identified that differ in tissue distribution, subcellular localisation, developmental expression, binding to the insulin receptor and interaction with SH2 domain-containing proteins. Results from targeted disruption of the IRS genes in mice have provided important clues as to the functional differences among these related molecules and suggest that they play very different roles in vivo. The available data are consistent with the notion that both IRS-1 and IRS-2 are important for insulin action and glucose homeostasis in vivo, whereas IRS-and IRS-4 appear to play a redundant role in the IRS signalling system. Considering their key role in both insulin action and insulin secretion, IRS-1 and IRS-2 molecules have been considered plausible candidate genes involved in the pathogenesis of Type 2 diabetes. Several polymorphisms in the IRS genes have been identified, but only the Gly --> Arg72 substitution of IRS-1, acting with environmental factors, seems to have a pathogenic role in the development of Type 2 diabetes. In contrast, polymorphisms of the other IRS genes do not appear to contribute to Type 2 diabetes.     

Angiotensin II type 2 receptor vasoactivity in internal mammary arteries of patients with coronary artery disease

BACKGROUND: Several animal studies suggested that the angiotensin II type 2 (AT2) receptor subtype mediates vasodilation, yet the results in human arteries are less well described and more inconsistent. Therefore, we evaluated the role of the AT2 receptor stimulation on the vasotonus of human internal mammary arteries. METHODS: Internal mammary arteries were obtained from 50 patients undergoing coronary bypass surgery. The expression of angiotensin II type 1 (AT1) receptor and AT2 receptor mRNA was determined by using real-time polymerase chain reaction. In addition, angiotensin II and CGP42112A concentration-response curves (concentration range: 10(-10) M to 10(-6) M) were constructed in absence or presence of candesartan (10(-5) M) and/or the AT2 receptor-antagonist PD-123319 (10(-6) M) and/or the alpha receptor antagonist phentolamine. RESULTS: Both AT1 and AT2 receptor protein and mRNA were detected, and higher AT2 receptor mRNA expression levels were associated with increased contractile response to angiotensin II. Angiotensin II caused vasoconstriction up to 41.1 +/- 6.5% of the maximal response to phenylephrine, and PD123319 significantly reduced this response (28.6 +/- 9.6%, P < 0.001). Candesartan completely blocked the angiotensin II-mediated response (1.4 +/- 3.1%, P < 0.001 versus control), and additional blockade of the AT2 receptor with PD123319 did not change this effect (1.8 +/- 5.1%). Phentolamine (10(-5) M) caused attenuation and rightward shift of the angiotensin II concentration response curves. The AT2 receptor agonist CGP42112A did not induce a significant response. CONCLUSION: Although AT2 receptor mRNA is present in human internal mammary arteries, AT2 receptor stimulation does not mediate vasodilation in these arteries.     

Angiotensin II type 1 receptor signalling regulates microRNA differentially in cardiac fibroblasts and myocytes

BACKGROUND AND PURPOSE

The angiotensin II type 1 receptor (AT₁R) is a key regulator of blood pressure and cardiac contractility and is profoundly involved in development of cardiac disease. Since several microRNAs (miRNAs) have been implicated in cardiac disease, we determined whether miRNAs might be regulated by AT₁R signals in a Gαq/11-dependent or -independent manner.

EXPERIMENTAL APPROACH

We performed a global miRNA array analysis of angiotensin II (Ang II)-mediated miRNA regulation in HEK293N cells overexpressing the AT₁R and focused on separating the role of Gαq/11-dependent and -independent pathways. MiRNA regulation was verified with quantitative PCR in both HEK293N cells and primary cardiac myocytes and fibroblasts.

KEY RESULTS

Our studies revealed five miRNAs (miR-29b, -129-3p, -132, -132* and -212) that were up-regulated by Ang II in HEK293N cells. In contrast, the biased Ang II analogue, [Sar1, Ile4, Ile8] Ang II (SII Ang II), which selectively activates Gαq/11-independent signalling, failed to regulate miRNAs in HEK293N cells. Furthermore, Ang II-induced miRNA regulation was blocked following Gαq/11 and Mek1 inhibition. The observed Ang II regulation of miRNA was confirmed in primary cultures of adult cardiac fibroblasts. Interestingly, Ang II did not regulate miRNA expression in cardiac myocytes, but SII Ang II significantly down-regulated miR-129-3p.

CONCLUSIONS AND IMPLICATIONS

Five miRNAs were regulated by Ang II through mechanisms depending on Gαq/11 and Erk1/2 activation. These miRNAs may be involved in Ang II-mediated cardiac biology and disease, as several of these miRNAs have previously been associated with cardiovascular disease and were found to be regulated in cardiac cells.     

AT1R、ACE基因多态性与东乡族原发性高血压的关系及其对降压药疗效的影响

目的：探讨血管紧张素转换酶（ACE）、血管紧张素Ⅱ（AngⅡ）Ⅰ型受体（ATIR）基因多态性与甘肃东乡族原发性高血压（EH）的关系。对不同基因型患者使用AT1R拮抗剂治疗，观察其疗效。方法：应用聚和酶链反应（PCR）方法检测汉族健康131例、东乡族健康102例、汉族EH198例、东乡族EH115例的AT1RA／C、ACE I／D基因多态性。随机选取60名EH患者，按其基因型分成AA和AC（AA、AC为基因型）两组，使用缬沙坦治疗8周，比较治疗前后血压变化。结果：ACE基因Ⅱ型在汉族EH组明显高于东乡族EH组（P〈0．05），ID基因型在东乡族EH组明显高于汉族EH组（P〈0．01）；AT1R基因AC型汉族EH组明显高于东乡族EH组（P〈0．05）；AA型在东乡族EH组明显高于汉族EH组（P〈0．05）。使用缬沙坦治疗8周，各基因型在治疗后患者血压均下降显著（P〈0．05）。不同基因型之间治疗后比较，降压效果无差异。结论：AT1R基因AA型和ACE基因ID型与东乡族EH有关；ACE基因Ⅱ型和AT1R基因AC型与汉族EH有关，C和D等位基因与汉族和东乡族EH无关。使用缬沙坦对不同基因型患者进行药物治疗，降压疗效相同，说明降压疗效与基因型无关。     

Farnesoid X receptor regulates vasoreactivity via Angiotensin II type 2 receptor and the kallikrein‐kinin system in vascular endothelial cells

Vascular farnesoid X receptor (FXR) ligands have been shown previously to regulate vascular tension. This study investigated whether FXR activation regulates vasoreactivity via the angiotensin II (Ang II) type 2 receptor (AT₂R) and the kallikrein‐kinin system in rat aortic vascular endothelial cells (RAECs). Protein abundances of Ang II type 1 receptor (AT₁R), AT₂R, bradykinin type 1/2 receptor (B₁R, B₂R), small heterodimer partner‐1 (SHP‐1) and the endothelial and inducible NO synthases (eNOS/iNOS) were analysed by Western blotting. Real‐time quantitative polymerase chain reaction was performed to analyse expression of eNOS and iNOS mRNA. Kallikrein activity and bradykinin content were assayed using spectrophotometry and a bradykinin assay kit, respectively. Aortic vasoconstriction and vasodilation were also investigated following FXR activation in the presence or absence of AT₂R and B₂R blockade. It was found that the FXR agonists GW4064 and INT‐747, in a dose‐dependent manner, increased the protein abundance of AT₂R, B₂R and SHP‐1 and decreased that of AT₁R. AT₂R blockade with PD123319 reversed effects of FXR agonists on kallikrein activity and levels of SHP‐1, B₂R and bradykinin. Moreover, it was found that GW4064 and INT‐747 upregulated expression of eNOS and enhanced NOS activity, which attenuated vasoconstriction and induced vasodilation, respectively. These effects were partially reversed by PD123319 and by B₂R blockade with HOE140. The current work suggests that FXR regulates vascular tension by controlling the eNOS‐NO system via activation of a pathway mediated by AT₂R‐B₂R pathway in RAECs.     

Angiotensin type 2 receptor is expressed in human atherosclerotic lesions.

OBJECTIVE: Expression of the angiotensin type 2 receptor (AT2-receptor) occurs in many animal models of atherosclerosis. However, its expression in human plaques and its functional role remains undetermined. This study examined AT2-receptor expression in human atherosclerotic plaque and also explored its potentially important functional role in atherosclerosis. MATERIAL AND METHODS: We analysed carotid atherosclerotic plaques obtained from 14 Caucasian patients who had previously undergone endarterectomy for symptomatic carotid artery stenosis. Half of all subjects received treatment with an angiotensin receptor blocker (ARB) (n=7); the remaining subjects received no intervention in the renin-angiotensin system (n=7). Immunohistochemistry measured tissue expression of smooth muscle cells (a-actin), macrophages (CD68 antibody), collagen (picro-sirius), and AT2-receptor (AT2-receptor antibody). RESULTS: AT2-receptor expression occurred consistently in all specimens. Although cellular localisation varied, AT2-receptor expression levels correlated with macrophage levels (p<0.01). Compared to conventional treatment, ongoing ARB treatment affected neither AT2-receptor levels nor plaque composition. CONCLUSIONS: AT2-receptor is expressed in human atherosclerotic plaque. Furthermore, we detected no functionally important role of AT2-receptor expression and found no evidence that ARB treatment regulates AT2-receptor expression.     

Angiotensin II receptor blockade and ventricular remodelling.

Cardiac remodelling is the expression of molecular, cellular and interstitial changes in response to cardiac injury, manifesting as adverse alterations in the size, shape and function of the ventricle. Several clinical studies have documented significant elevations in the levels of renin, angiotensin II (Ang II) and aldosterone attending acute myocardial infarction and/or congestive heart failure. Similar to catecholamines, markedly elevated activity of the renin-angiotensin-aldosterone system (RAAS) is associated with poor prognosis. The effects of Ang II upon cardiac tissue are related to two primary receptors, Ang II type 1 (AT1) and Ang II type 2 (AT2). The AT1-receptor appears to mediate many of the deleterious effects of chronic RAAS activity, while the AT2-receptor is increasingly shown to have potential cardioprotective effects. Attenuating the deleterious effects of sustained Ang II stimulation can be achieved by direct inhibition of angiotensin- converting enzyme (ACE) and/or direct antagonism of AT receptors. ACE inhibition reduces left ventricular (LV) volumes, retards the progression of LV dilatation and hypertrophy and increases systolic function in systolic dysfunction. By blocking at the receptor level, Ang II receptor blockers (ARBs) provide an alternative and more direct approach to inhibiting the effects of Ang II; however, data relating to their effects upon ventricular remodelling, whether used in isolation or in combination with ACE inhibitors (ACE-Is), are less convincing. Data arising from several recent clinical trials suggest that simultaneous use of ACE-Is and ARBs maybe of more benefit in attenuating ventricular remodelling than either agent alone.     

Functional comparison of the antagonistic properties of some Angiotensin II type 1 receptor blockers on the contraction elicited by Angiotensin II and thromboxane A2 on human saphenous veins

We previously described on human vascular preparations that, in addition to its antagonistic properties on Angiotensin II type 1 (AT1) receptor, losartan could also inhibit the contraction elicited by the stable thromboxane A2 mimetic U46619. The present study was designed (1) to investigate, in human vascular preparations (the saphenous veins) whether these antagonistic properties on thromboxane A2/prostaglandin H2 (TP) receptor were shared by some other AT1 receptor antagonists (irbesartan and valsartan) and the active metabolite of losartan EXP3174, and (2) to compare their antagonistic properties on TP receptors to their antagonistic properties on AT1 receptors. In the presence of indomethacin (10 microM) and Nomega-nitro-L-arginine (100 microM), irbesartan, valsartan, and EXP3174 induced a rightward shift of U46619- and angiotensin II-induced contraction. The inhibitory effect of irbesartan, valsartan, and EXP3174 on U46619-induced contraction was significant from 100 microM while their inhibitory effect on the contraction elicited by angiotensin II was significant from 1 nM. With regard to the plasma therapeutic concentrations of irbesartan, valsartan, and EXP3174, these data suggest that TP receptor blockade does not account for the antihypertensive effects of these AT1 receptor blockers.