Myocardial electrophysiological properties in the presence of an AT1 angiotensin II receptor antagonist

Introduction Blockade of the AT₁ angiotensin II (Ang II) receptor has been shown to provide antihypertensive effects. However, whether AT₁ Ang II receptor antagonists influence myocardial electrophysiological properties remains unclear.Methods and results Accordingly, atrial and ventricular myocardial electrophysiological properties were examined in adult rat (n=13) and guinea pig (n=9) myocardial preparations in the presence of the specific AT₁ Ang II receptor antagonist, valsartan (CGP 48933; 0.5, 5, or 500 mol/L). These concentrations reflect up to 100 fold higher drug concentrations than those observed in clinical trials. Transmembrane potential data were recorded using standard microelectrode techniques at baseline and following superfusion with valsartan. The lower concentrations of valsartan (0.5 and 5 mol/L) had minimal effects on myocardial electrophysiology. In the presence of 500 mol/L of valsartan, resting membrane potential increased from baseline in both rat (–82.3±4.1 vs –76.8±5.8 mV, p<0.05) and guinea pig (–81.6±2.9 vs –76.9±2.0 mV, p<0.05) atrial myocardium. Action potential duration at 90% repolarization was increased in guinea pig atrial (91.7±1.4 vs 80.0±5.6 ms, p<0.05) and ventricular (131.1±8.1 vs 118.7±8.3 ms, p<0.05) myocardium following exposure to 500 mol/L of valsartan. In a separate series of experiments Ang II (1.0 mol/L) had no effect on atrial or ventricular action potential characteristics in either species.Conclusion Thus, the effects of valsartan, which were observed only at concentrations 100 fold higher than those reported in clinical trials, may be due to non-specific drug interactions with the myocyte sarcolemma.     

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.     

From angiotensin IV binding site to AT4 receptor

One of the fragments of the cardiovascular hormone Angiotensin II incited the interest of several research groups. This 3–8 fragment, denoted as Angiotensin IV (Ang IV) causes a number of distinct biological effects (see Introduction), unlikely to be explained by its weak binding to AT₁ and/or AT₂ receptors. Moreover the discovery of high affinity [¹²⁵I]-Ang IV binding sites and their particular tissue distribution led to the concept of the AT₄ receptor. An important breakthrough was achieved by defining the AT₄ receptor as the membrane-bound insulin-regulated aminopeptidase (IRAP). Crucial for the definition as a receptor the binding of the endogenous ligand(s) should be linked to particular cellular and/or biochemical processes. With this respect, cultured cells offer the possibility to study the presence of binding sites in conjunction with ligand induced signaling. This link is discussed for the AT₄ receptor by providing an overview of the cellular effects by AT₄ ligands.     

At1 Receptor Density Changes During Development of Hypertension in Hyperinsulinemic Rats

In a previous study we showed that the renin-angiotensin system (RAS) plays a role in the etiology of fructose-induced hypertension. To our knowledge, no previous study has evaluated changes in angiotensin II (Ang II) type I receptor (AT₁) density in fructose-fed rats that are insulin resistant and hypertensive. The purpose of this study was to determine the changes in plasma Ang II and AT₁ density associated with the elevation of blood pressure in fructose-treated rats. Male Sprague-Dawley rats were divided into two groups and were fed either normal rat chow or a 60% fructose-enriched diet for four weeks. Plasma Ang II and serum insulin levels of the fructose-treated rats were significantly elevated (p<0.01) by the end of the second week of fructose treatment. Plasma Ang II levels of the fructose-fed rats returned to basal levels by the end of the fourth week of dietary treatment, whereas the serum insulin levels consistently remained elevated. Blood pressure was significantly elevated in the fructose-fed rats within two weeks of fructose treatment. Elevation of blood pressure was associated with left ventricular hypertrophy. Furthermore, there was a significant increase in AT₁ receptor density in the ventricles and a significant decrease in AT₁ receptor density in the aortas of fructose-fed rats at the end of fourth week. There were no significant changes in receptor density in the hypothalami or adrenal glands of fructose-treated rats. These results suggest that chronic fructose treatment activates the renin-angiotensin system, which is manifested by an increase in plasma Ang II, elevation of blood pressure, cardiac hypertrophy, and changes in AT₁ receptor density.     

胰腺癌细胞系血管紧张素Ⅱ1型受体蛋白表达的研究

目的：探讨血管紧张素Ⅱ1型受体（angiotensin Ⅱ type 1 receptor,AT1）在胰腺癌细胞中的表达。方法：用免疫细胞化学染色检测胰腺癌细胞系SW1990、PaTu8988s和PANC－1中AT1蛋白的表达。结果：胰腺癌细胞系SW1990、PaTu8988s和PANC－1中均有AT1蛋白的表达，结论：AT1在胰腺癌细胞生长中可能发挥重要作用，应用AT1拮抗剂对防治胰腺癌似乎有一定意义。     

Effects of angiotensin II and angiotensin II type 1 receptor blockade on neointimal formation after stent implantation

The prevalence of chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF) increases substantially with age. The coexistence of COPD and CHF is common but often unrecognized in elderly patients. To avoid overlooking COPD in elderly patients with known CHF pulmonary function tests should be routinely obtained. Likewise, to avoid overlooking CHF in elderly patients with known COPD left ventricular (LV) function should be routinely assessed. Plasma brain natriuretic peptide levels are useful to differentiate COPD exacerbation from CHF decompensation in patients presenting with acute dyspnea. Aging exacerbates skeletal muscle alterations that occur in patients with CHF and COPD. Skeletal muscle metabolic alterations and atrophy and the resulting deterioration of functional capacity progress rapidly in elderly patients with COPD and CHF. Physical conditioning reverses rapidly progressing skeletal muscle metabolic alterations and atrophy and promotes independence and life quality in the elderly. Physical conditioning is clearly an essential component of the management of elderly patients with COPD and CHF. The pharmacological management of patients with coexistent COPD and CHF should focus on not depriving these patients from long-term beta adrenergic blockade. Long-term beta adrenergic blockade has been repeatedly shown to improve survival in elderly patients with CHF due to LV systolic dysfunction and, contrary to conventional belief, is well tolerated by patients with COPD.     

原发性高血压患者血管紧张素转化酶和血管紧张素受体基因多态性的研究

目的　探讨血管紧张素转化酶 ( ACE)及血管紧张素 - 1型受体 ( AT1 R)基因多态性与原发性高血压 ( EHT)的关系。方法　应用聚合酶链反应及 PCR加酶解方法检测 1 50例健康人 ( NT)及 1 52例 EHT患者 ACE I/ D基因多态性的 ACE及 AT1 R A1 1 6 6 C突变。结果　 EHT组ACE I/ D基因多态性等位基因频率 I为 0 .50 ,D为 0 .50 ,D等位基因频率及基因型频率显著高于 NT组 ( P<0 .0 5) ;而两者之间的 AT1 R A1 1 6 6 C的C等位基因频率差异无显著性 ( P>0 .0 5)。结论　 ACE基因可能是 EHT的重要遗传因素 ,AT1 R基因 A1 1 6 6 C多态性与 EHT无关     

Central cardiovascular actions of angiotensin II in trout

In mammals, a large body of evidence supports the existence of a brain renin-angiotensin system (RAS) acting independently or synergistically with the endocrine RAS to maintain diverse physiological functions, notably cardiovascular homeostasis. The RAS is of ancient origin and although most components of the RAS are present within the brain of teleost fishes, little is known regarding the central physiological actions of the RAS in these vertebrates. The present review encompasses the most relevant functional data for a role of the brain RAS in cardiovascular regulations in our experimental animal model, the unanesthetized trout Oncorhynchus mykiss. This paper mainly focuses on the central effect of angiotensin II (ANG II) on heart rate, blood pressure, heart rate variability and cardiac baroreflex, after intracerebroventricular injection or local microinjection of the peptide within the dorsal vagal motor nucleus. The probable implications of the parasympathetic nervous system in ANG II-evoked changes in the cardiac responses are also discussed.     

Pathologic consequences of increased angiotensin II activity

Summary Advances in molecular medicine and pharmacology have allowed clinicians to critically reassess the reninangiotensin system. Angiotensin II (AII) participates in the control of cardiovascular function and electrolyte balance, and plays a part in the regulation of cellular oncogenes and the expression of growth factors. The expression of the proteins of the renin-angiotensin system in organs other than the kidneys suggests that these diverse actions are associated with the peptide in the local environment. Tissue reninangiotensin activity has prompted the investigation of alternate pathways for the production of AII and characterization of novel forms of angiotensin peptides that counteract the vasoconstrictor and proliferative actions of AII. The heptapeptide angiotensin-(1–7) appears to be critically involved in regulating the angiotensinogen activity of AII through stimulation of vasodilator prostaglandins and release of nitric oxide. Study in this area has been accelerated by the identification of receptors that convey the actions of angiotensin peptides at the cellular level and the pharmacologic characterization of agents that inhibit the ability of AII to bind to target receptors. The introduction of a new class of orally active AII-receptor blockers has provided a specific test of the role of AII in the development of essential hypertension and the potential for improved therapy for hypertension and cardiac and vascular sequelae.     

Sarcosine1, glycine8 angiotensin II is a functional AT1 angiotensin receptor antagonist

Sarcosine¹, glycine⁸ angiotensin II (SG Ang II) displayed unusual characteristics in early pharmacological studies. It was a potent antagonist of the dipsogenic actions of intracerebroventricularly administered Ang II in the rat, but showed low affinity for bovine cerebellar Ang II receptors. It has recently been shown that SG Ang II binds preferentially to the AT₁ receptor, To determine if SG Ang II is a functional antagonist of the AT₁ receptor-mediated calcium signaling, CHO cells stably transfected with AT₁ receptors were exposed to Ang II in the presence and absence of SG Ang II. At concentrations of 10–100 nM, SG Ang II completely inhibited Ang II-stimulated intracellular Ca²⁺ mobilization in AT_1A and AT_1B receptor-transfected cells. SG Ang II and ¹²⁵I-SG Ang II bound to AT_1A and AT_1B receptor-transfected cells with K _D and K ₁ values of 2–4 nM. In contrast, SG Ang II bound to AT₂ transfected cells with a K ₁ value of 7.86 μM. These results demonstrate that SG Ang II is a selective and functional peptide antagonist of the AT₁ angiotensin II receptor subtype.     

Products of angiotensin I hydrolysis by human cardiac enzymes potentiate bradykinin

Some beneficial effects of ACE inhibitors are attributed to potentiation of bradykinin's actions exerted through its B2 receptor. We investigated them on cultured cells transfected or constitutively expressing both ACE and B2 receptor. The potentiation of bradykinin was indirect and attributed to a crosstalk induced between enzyme and receptor via ACE, a heterodimer formation. While looking for endogenous activators, we investigated the split products of angiotensin I (Ang) Ang 1-9 and 1-7, peptides released by enzymes of human atria and ventricle. Ang 1-9 was liberated by a cathepsin A-type enzyme, Ang 1-7 by a different metallopeptidase-protease. Cathepsin A's presence in heart tissue was shown by deamidating enkephalinamide substrate, by immunoprecipitation and by immunohistochemistry. In immunohistochemistry, cathepsin A was detected in myocytes of atrial tissue. Ang 1-9 and Ang 1-7 potentiated the effect of an ACE-resistant bradykinin analogue on the B2 receptor in transfected cells expressing human ACE and B2, and in human endothelial cells. Ang 1-9 and 1-7 augmented arachidonic acid and NO release by bradykinin. NO liberation by bradykinin from endothelial cells was potentiated at 10nmol/L concentration by Ang 1-9 and Ang 1-7; at higher concentrations, Ang 1-9 was significantly more active. Both peptides had little activity in absence of bradykinin or ACE. Ang 1-9 and 1-7 potentiated bradykinin action on its B2 receptor at much lower concentrations than their IC50 values with ACE. They probably induce conformational changes in the ACE/B2 receptor complex via interaction with ACE.     

原发性高血压并发脑梗死患者血管紧张素转换酶和血管紧张素受体基因多态性的研究

目的 :探讨血管紧张素转换酶 (ACE)基因及血管紧张素Ⅱ 1型受体 (AT1R)基因A116 6 /C多态性与原发性高血压 (EH)及其并发脑梗死的关系。方法 :应用聚合酶链反应及PCR加酶解方法检测 15 0例健康者 (对照组 )及 15 2例EH无并发症患者 (EH组 )和 80例EH并发脑梗死患者 (EH并发脑梗死组 )ACEI/D基因多态性的ACE及AT1RA116 6C突变。结果 :EH组及EH并发脑梗死组的ACE基因的D等位基因频率为 5 0 %及 4 8% ,明显高于对照组的 33% (P <0 .0 5 )。AT1R基因的C等位基因频率在 3组之间差异无显著性意义 (P >0 .0 5 )。结论 :ACE基因可能是EH及EH并发脑梗死的重要遗传因素 ,而AT1R基因与EH发病及EH患者是否易患脑梗死无关     

血管紧张素Ⅱ受体阻断剂抗肝纤维化的实验研究

目的 探讨血管紧张素Ⅱ１型受体阻断剂对四氯化碳（ＣＣｌ４）诱导的实验性肝纤维化大鼠血清层粘连蛋白等细胞外基质水平的影响。地大鼠肝实质损伤性肝纤维化模型由ＣＣｌ４诱导。５０只雄性ＳＤ大鼠被随机分为５组：对照组、模型组及治疗组（高、中、低剂量组）,每组１０只,除对照组外所有大鼠均给予皮下注射４０％ＣＣｌ４（精制橄榄油配制,每３日１次,共６周）,对照组注射等体积的精制橄榄油。治疗组同时给予血管紧张素Ⅱ受     

SSeCKS gene expression in vascular smooth muscle cells: regulation by angiotensin II and a potential role in the regulation of PAI-1 gene expression

Rat aortic smooth muscle cells (RASM) express the src suppressed C-kinase substrate (SSeCKS), which is thought to be an integral regulatory component of cytoskeletal dynamics and G-protein coupled-receptor signaling modules. The specific sub-classes of growth factor receptors that regulate the genomic changes in SSeCKS expression in smooth muscle cells have not been characterized. In this study we identify SSeCKS as an angiotensin type 1 (AT(1)) receptor-dependent target gene in RASM cells treated with angiotensin II (Ang II). SSeCKS mRNA levels increase up to three-fold relative to the control within 3.5 h of Ang II treatment and are followed by a slight decrease of mRNA relative to the control levels after 24 h of stimulation. SSeCKS gene expression and plasminogen activator inhibitor-1 (PAI-1) gene expression correlate in RASM cells treated with Ang II. By co-transfecting plasmids bearing recombinant-SSeCKS and a PAI-1-promoter/luciferase reporter into Cos-1 cells, we show that alternative forms of recombinant-SSeCKS protein differentially influence PAI-1 promoter activity. These data indicate a biochemical linkage between SSeCKS activity and one or more of the cytoplasmic signaling pathways that are involved in the control of PAI-1 promoter activity. Finally, we show that the alternative forms of recombinant-SSeCKS protein differentially influence cell-spreading when ectopically expressed in ras -transformed rat kidney (KNRK) fibroblasts. Taken together, our data suggest that SSeCKS interacts with intracellular signaling pathways that control cytoskeletal remodeling and extracellular matrix remodeling following Ang II stimulation of the RASM cell.     

Effects of angiotensin receptor blockers on ambulatory plasma Renin activity in healthy, normal subjects during unrestricted sodium intake

BACKGROUND: Plasma renin activity (PRA), measured under controlled conditions, is a marker of the degree and persistence of renin-angiotensin system blockade. METHODS: Two similarly designed five-way crossover studies evaluated angiotensin II type 1 (AT1) receptor blockade-induced changes in PRA in quietly seated, ambulatory volunteers who were ingesting uncontrolled diets. At weekly intervals, PRA was measured during the 24 h after administration of placebo, olmesartan medoxomil (20 or 40 mg), or valsartan (80 or 160 mg) (Study CS866-445), or placebo, olmesartan medoxomil (40 mg), valsartan (160 or 320 mg), or irbesartan (300 mg) (Study CS866-448). The primary end point was change in PRA relative to placebo from predose to 24 h postdose (DeltaPRA24). RESULTS: In the 20 subjects who completed each study, there was a direct relationship between baseline PRA and DeltaPRA24 for all doses. Subjects with low PRA (<0.65 ng/mL/h) exhibited very low absolute increases in PRA. The DeltaPRA(24) increased significantly with olmesartan medoxomil 20 mg (P<.01) and 40 mg (P<.001) and valsartan 160 mg (P<.05) but not with valsartan 80 mg. In the second study (in which baseline PRA was lower), DeltaPRA24 increased with olmesartan medoxomil 40 mg (P<.0001), valsartan 320 mg (P<.01), and irbesartan 300 mg (P<.01) but not with valsartan 160 mg. The DeltaPRA24 was greatest with olmesartan medoxomil 40 mg and was dose-related for olmesartan medoxomil but not for valsartan. CONCLUSIONS: The greater DeltaPRA24 with olmesartan medoxomil 40 mg indicates a more prolonged AT1 receptor blockade than with valsartan 80, 160, or 320 mg or irbesartan 300 mg. A routine, clinic ambulatory PRA level can be used as a biochemical marker of the persistence and degree of AT1 receptor blockade in subjects without suppressed PRA levels.     

Molecular and functional remodeling of Ito by angiotensin II in the mouse left ventricle

The transient outward potassium current (I_to) in cardiac myocytes is mainly mediated by members of the Kv4 subfamily of voltage-gated potassium channels. Several in vitro studies have shown that angiotensin II (Ang II), which plays an important role in the development of cardiac hypertrophy, rapidly downregulates Kv4.3 mRNA expression. However, it is not clear whether Ang II regulates I_toin vivo and whether this regulation may depend on alterations in Kv4.3 gene expression. To address this question, we determined the effects of acute (24 h) and chronic (14 days) exogenous infusions of Ang II on I_to and the expression of its channel subunits in the mouse left ventricle. Ang II rapidly increased blood pressure and reduced Kv4.2 but not Kv4.3 mRNA levels in the absence of cardiac hypertrophy. In response to chronically elevated Ang II levels cardiac hypertrophy developed, which was associated with a downregulation of Kv4.2 and Kv4.3 mRNA levels, and an upregulation of Kv1.4 mRNA levels. In contrast, neither KChIP2 mRNA levels nor amplitude or macroscopic inactivation kinetics of I_to were affected by the acute or chronic Ang II treatments. Consistent with the unchanged I_to amplitude, Kv4.2, Kv4.3, and KChIP protein expression levels were similar after chronic Ang II and sham treatment. Our findings demonstrate that elevations of Ang II concentrations that induce hypertension and cardiac hypertrophy do not alter the amplitude of I_to in the mouse left ventricle. Furthermore, they suggest that functional expression of cardiac I_to in mice is stabilized by KChIP2.     

Down-regulation of cardiac apelin system in hypertrophied and failing hearts: Possible role of angiotensin II-angiotensin type 1 receptor system

Cardiac apelin has recently been suggested to contribute to the pathophysiology of heart failure (HF) in humans. In animal experiments, its infusion acutely improved systolic as well as diastolic LV function. Although its deficit could critically determine the cardiac dysfunction, its regulatory mechanism is unknown. Accordingly, we investigated the role and regulation of the cardiac apelin system in the diseased heart using Dahl salt-sensitive rats, which show a distinctive transition from compensatory LV hypertrophy (LVH) to HF. In the compensatory LVH stage, apelin and its receptor APJ mRNA showed no change compared with control animals, while these were markedly down-regulated in the HF stage (72% and 57% decrease, respectively). The rats were chronically treated with telmisartan (angiotensin type 1 receptor blocker [ARB], 5 mg/kg/day, n=9), ONO-4817 (matrix metalloproteinase [MMP] inhibitor, 200 mg/kg/day, n=9), bisoprolol (beta blocker, 3 mg/kg/day, n=6) or vehicle (0.5%CMC, n=9) from the LVH stage. Although the functional improvements were similar among the three treated groups 6 weeks after treatment, restoration of cardiac apelin and APJ expression was observed only in the ARB group. Furthermore, in angiotensin II-infused rats, cardiac apelin mRNA was decreased after 24 h of treatment and its restoration was achieved by treatment with ARB. These results indicate that the cardiac apelin system is markedly down-regulated in experimental HF and may be regulated by the angiotensin II-angiotensin type 1 receptor system directly. Inhibition of the renin-angiotensin system may have beneficial effects, at least in part, through restoration of the cardiac apelin system in the treatment of HF.