UMLS:C0004135 - FACTA Search

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The in vivo activation of transcription factors, which is important for cell regulation by gene expression, has not been well examined in myocardial infarcted heart. The purpose of this study was to determine whether myocardial signal transducer and activator of transcription (STAT) pathway is activated as sis-inducing factor (SIF) in infarcted heart, and to assess the angiotensin blockade on SIF activity in ischemic and non-ischemic myocardium of rat. Myocardial infarction was made by ligation of the coronary artery in Wistar rats. In electrophoretic mobility shift assay, myocardial SIF DNA binding activities gradually increased and reached to peak at 1 week in infarcted and non-infarcted regions after myocardial infarction. Imidapril and candesartan cilexitil significantly prevented the increase in SIF DNA binding activity in infarcted and non-infarcted regions. This increased SIF DNA complex was supershifted by specific anti-STAT3 antibody, indicating that increased SIF complex at least contained activated STAT3 proteins in myocardial infarcted heart. Furthermore, immunoprecipitation-Western blot analysis revealed that STAT3 of infarcted and non-infarcted regions were tyrosine-phosphorylated at 1 week after myocardial infarction. Imidapril and candesartan cilexitil prevented the increase in phosphorylated STAT3. Thus, the transcriptional activation of STAT3 through AT1 receptor may be partially involved in cardiac remodeling after myocardial infarction.
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PMID:Angiotensin blockade inhibits SIF DNA binding activities via STAT3 after myocardial infarction. 1065 87

The term ventricular remodeling has been coined to describe the geometrical changes in size and shape of the left ventricle occurring after large myocardial infarcts. We do not exactly know what initiates this process. Slipping of myofilaments following destruction of connective tissue--probably due to metalloproteinase activation--could be the initial event. As a consequence, wall stress is increased triggering deleterious adaptation processes, such as: - intracardiac angiotensin II generation; - cardiac endothelin formation and release; - pro-apoptotic signals for cardiomyocytes; - hypertrophic signals for fibroblasts and cardiomyocytes. This cascade of events is not only observed in the process of remodeling following myocardial infarction but is also operating during the progression of heart failure. Therapeutic principles therefore are similar in both conditions: - reduction of wall stress (pharmacological or mechanical unloading of the heart); - blockade of angiotensin II generation or of AT1-receptors (ACE-inhibitors or AT1 antagonists); - blockade of endothelin receptors (ET(A)-blockers); - blockade of adrenergic receptors (preferably beta1-adrenergic receptor blockers). Better understanding of the molecular mechanisms of the remodeling process already has fueled the search for new therapeutic interventions (such as endothelin receptor blockers, aldosterone antagonists and growth hormone application). Continuous research in this field may be especially rewarding if we will succeed in identifying the very first step in the cascade.
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PMID:Ventricular remodeling after acute myocardial infarction. 1069 91

This article reviews the impressive amount of knowledge accumulated in the last few years on the angiotensin II AT2 subtype receptor. Although still elusive, a large body of experimental evidence strongly suggests that it may play an important role in the adaptive changes of the cardiovascular structures in response to pathological conditions such as myocardial infarction, congestive heart failure or hypertension. The most intriguing aspects of the biology of this receptor, however, appear to be: 1) the regulation of its transcription, which plays an important role in the expression of the protein in adults or in injured tissues; 2) its interaction or "cross-talk" with the predominant angiotensin II receptor, the AT1 subtype, or with the receptors of other growth factors or cytokines; and 3) its connections with the bradykinin/nitric oxide pathways. These aspects may be relevant for the therapeutical use of drugs which antagonize the renin-angiotensin system, such as angiotensin-converting enzyme inhibitors or angiotensin receptor antagonists, as well as for new therapeutic approaches to the treatment of cardiovascular diseases.
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PMID:Angiotensin II AT2 subtype receptors: an emerging target for cardiovascular therapy. 1073 Jun 8

Infarct scar, a requisite to the rebuilding of necrotic myocardium following myocardial infarction (MI), has long been considered inert. Earlier morphologic studies suggested healing at the infarct site was complete within 6-8 weeks following MI and resultant scar tissue, albeit necessary, was acellular and simply fibrillar collagen. Utilizing molecular and cellular biologic technologies, recent studies indicate otherwise. Infarct scar is composed of phenotypically transformed fibroblast-like cells, termed myofibroblasts (myoFb) because they express alpha-smooth muscle actin (alpha-SMA) and these microfilaments confer contractile behavior in response to various peptides and amines. These cells are nourished by a neovasculature and are persistent at the MI site, where they are metabolically active expressing components requisite to angiotensin (Ang) peptide generation, including converting enzyme, receptors for AngII and transforming growth factor (TGF)-beta1. They continue to elaborate fibrillar type I collagen. Their generation of these peptides contribute to ongoing scar tissue collagen turnover and to fibrous tissue formation of noninfarcted myocardium. Infarct scar contraction accounts for its thinning and its tonus may contribute to abnormal ventricular chamber stiffness with diastolic dysfunction. Infarct scar is a dynamic tissue: cellular, vascularized, metabolically active and contractile. Pharmacologic interventions with angiotensin converting enzyme inhibitor or AT1 receptor antagonist has proven effective in attenuating scar tissue metabolic activity and minimizing adverse accumulation of fibrous tissue in noninfarcted myocardium.
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PMID:Infarct scar: a dynamic tissue. 1077 28

The octapeptide angiotensin II is the major effector of the renin-angiotensin-aldosterone system. Angiotensin II causes a variety of potentially noxious biological effects, such as vasoconstriction, a rise in blood pressure, release of aldosterone, enhancement of the effect of catecholamines, and vascular and myocardial hypertrophy, including remodeling of the heart after myocardial infarction. All of these noxious effects of angiotensin II are mediated by angiotensin II receptors (AT receptors) of the AT1 subtype. The functional effects of AT2 receptors, which have been characterized by means of biochemical techniques, are so far not clearly identified. Stimulation of the AT2 receptor by means of angiotensin II is assumed to counteract vascular/myocardial remodeling and possibly to induce vasodilation. Accordingly, AT1 and AT2 receptors are believed to provoke opposite effects. It has drawn attention that fetal tissues contain a high density of AT2 receptors, which is lowered significantly after birth. The identification and analysis of AT receptors has been greatly stimulated by the development of non-peptidergic AT1 receptor antagonists, of which losartan is the prototype. It is so far unclear whether AT receptors are activated in hypertensive disease. A survey will be made of the hemodynamic effects of AT1 receptor antagonists, their interaction with AT receptors, and the probably important role of the sympathetic nervous system involved in the antihypertensive action of AT receptor antagonists.
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PMID:The role of angiotensin II receptors and their antagonists in hypertension. 1084 96

The aim of the study was to investigate the effect of angiotensin-converting enzyme inhibitor enalapril and non-peptide blocker of AT1 receptors losartan on endothelial function of the shoulder artery in patients with congestive cardiac insufficiency. The examination covered 96 patients (mean age 46.71 +/- 4.13) with stable effort angina (functional class II-III) and circulatory insufficiency (NYHA functional class II-III) having end-diastolic left-ventricular volume > 160 ml, left ventricular ejection fraction < 35%, sinus rhythm, cardiothoracal index > 0.55 units. Patients with fibrillar tachyarrhythmia, high grade blocks, pacemaker migration, artificial pacemaker, myocardial infarction were not included in the trial. The patients were randomized into 3 groups 32 patients each. In addition to basic therapy patients of group 1 received long-acting nitrates, digoxin, aspirin and furosemide; group 2--enalapril in daily dose 10 mg; group 3--losartan in daily dose 25 mg. A course of treatment lasted 12 weeks. Endothelial function was assessed by high resolution echography, dopplerography performed before and after temporary occlusion of the shoulder artery and sublingual nitroglycerin. In patients with cardiac insufficiency, accelerated blood flow in the shoulder artery after its temporary occlusion promoted realization of the vasoconstrictory reaction. This was verified as endothelial dysfunction. In the course of the treatment all the patients achieved insignificant increase of the shoulder artery initial diameter. After sublingual intake of nitroglycerin vasodilation was also insignificant. 12-week enalapril and losartan prevented vasoconstriction in the shoulder artery in response to quicker circulation following arterial occlusion. However, higher maximal flow speed did not correspond to the increment in the artery diameter after the occlusion in any group. The flow-induced vasodilation was more pronounced in the enalapril group. Losartan group had a trend to an increase in the inner diameter of the shoulder artery. It is shown that enalapril and losartan in congestive cardiac insufficiency improves endothelium-dependent vasodilation caused by nitroglycerin. Enalapril demonstrated stronger ability than losartan to reverse endothelial dysfunction in patients with cardiac insufficiency resultant from ischemic heart disease.
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PMID:[Prospects of endothelial dysfunction reversion in patients with congestive heart failure]. 1097 40

We tested the hypothesis that a combination of angiotensin-converting enzyme inhibitor (ACEi) and angiotensin II type 1 receptor antagonist (AT1-ant) may have an additive cardioprotective effect in mice with heart failure (HF), because these two agents could have other mechanisms of action besides interrupting the renin-angiotensin system. ACEi prevent degradation of bradykinin. During treatment with AT1-ant, increased angiotensin II could activate AT2 receptors, with an antitrophic effect. To test this hypothesis, we used a mouse model of HF induced by myocardial infarction. Seven days after surgery, mice were divided into six groups and treated for 23 weeks: (a) sham ligation; (b) HF-vehicle; (c) HF-ACEi; (d) HF-AT1-ant; (e) HF-ACEi + AT1-ant (half dose of each); and (f) HF-ACEi + AT1-ant (full dose of each). Cardiac function was evaluated in conscious mice during the treatment period. The HF-vehicle group showed significantly decreased left ventricular (LV) ejection fraction (EF), shortening fraction (SF), and cardiac output (CO) and increased LV dimensions, interstitial collagen, and myocyte cross-sectional area (MCSA) compared with controls. Treatment with ACEi or AT1-ant significantly increased EF, SF, and CO and decreased LV dimensions and MCSA in mice with HF. However, a combination of these drugs did not improve cardiac function more than ACEi or AT1-ant alone. We concluded that ACEi and AT1-ant have similar cardioprotective effects and may reach maximal effect when given individually; thus no further improvement can be achieved with combined therapy in mice with HF.
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PMID:Effects of ACE inhibitor, AT1 antagonist, and combined treatment in mice with heart failure. 1102 48

There have been many studies concerning the hemodynamics and physiological mechanisms in ischemic heart disease, little is known about molecular mechanisms during myocardial ischemia in in vivo study. As the signal transduction pathway responsible for myocardial hypertrophy and apoptosis, janus kinase (JAK) and signal transducers and activators of transcription (STAT) are suggested to play an important role. However, whether in vivo activation of JAK-STAT pathway occurs during myocardial ischemia is still unknown. The purpose of this study was to determine whether myocardial JAK or STAT is activated in ischemic heart, and to evaluate the angiotensin blockade on the pathway. Myocardial infarction was produced by ligation of the coronary artery in Wistar rats. After myocardial ischemia, we analysed both activated levels and total amounts of JAK1, JAK2, STAT1 and STAT3 by Western blot analyses at 0, 5, 15, 30, 60, 120 and 240 min. Compared with JAK activities at 0 min, JAK1 activities were significantly increased at 60 and 120 min (3.0- and 3.7-fold, respectively, P<0.01). JAK2 and STAT1 activities of ischemic myocardium were unchanged through the time course. STAT3 activities were increased at 5 min (3.3-fold, P<0.01) and markedly enhanced at 30, 60 and 120 min (4.6-, 7.7- and 8.7-fold, respectively, P<0.01). Pretreatment with imidapril (ACE inhibitor) and candesartan cilexitil (AT1 receptor antagonist) significantly prevented the increase in the phosphorylation of JAK1 at 120 min and STAT3 at 30 and 120 min. Sis-inducing factor (SIF) DNA complex was supershifted by specific anti-STAT3 antibody, indicating that increased SIF complex at least contained activated STAT3 proteins in ischemic myocardium. Imidapril and candesartan cilexitil inhibited the activation of SIF DNA binding at 1 day after coronary ligation. In conclusion, we showed that JAK1 and STAT3 were activated by ischemia from the basal activities in in vivo rat myocardial ischemia model. Imidapril and candesartan cilexitil prevented the increase in phosphorylated JAK1 and STAT3, thereby suggesting that angiotensin II, especially angiotensin II type I receptor, partially mediates activation of myocardial JAK-STAT pathway in acute myocardial ischemia.
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PMID:Myocardial ischemia activates the JAK-STAT pathway through angiotensin II signaling in in vivo myocardium of rats. 1116 35

National and international societies have issued guidelines on the management of heart failure: The European Society of Cardiology, WHO, ACC/AHA Task Force Report, US Department of Health and Human Services, German Society of Cardiology. The therapeutic approaches to heart failure have undergone considerable changes during the last few years. The guidelines have to be updated almost yearly due to new results from prospective randomized studies. Although an agreement could be reached with respect to general measures and drug treatment, no agreement on mechanical devices, pacemakers and surgical interventions has been reached. The basis for medical treatment of chronic heart failure depends on diuretics, digitalis, ACE inhibitors, and beta-blockers. Calcium antagonists and other positive inotropic drugs, other than digitalis, should be avoided as far as possible. Thiazides, loop diuretics and aldosterone antagonists are needed for acute and chronic treatment of heart failure, alone or in combination (diuretic resistant heart failure!). Digitalis glycosides are needed in patients with atrial fibrillation with a fast ventricular rate or atrial flutter and in patients with systolic dysfunction, large hearts and symptomatic failure class NYHA III and IV. However, digitalis does not convert atrial fibrillation to sinus rhythm. Today there is no question that ACE inhibitors improve the prognosis of all patients with heart failure in all stages, if ejection fraction is reduced. Therefore, most patients after myocardial infarction or after having experienced pump failure due to myocarditis or cardiomyopathy are treated with ACE inhibitors and diuretics. The beneficial effects of ACE inhibitors seem to be most pronounced the worse the situation is. Relative risk reductions (mortality!) between 10% and 40% have been published depending on the severity of symptomatic left ventricular dysfunction. Those patients with high absolute risk have more to gain than those with low risk for any given "risk reduction", of course. Recent studies also indicate that most high risk cardiac patients profit from ACE inhibitors even if pump function is normal (i.e., patients with coronary heart disease, diabetes mellitus, cerebral vascular disease, hypertension) (15). AT1 antagonists can substitute for ACE inhibitors, if the latter are not tolerated due to cough. Up to now, beta-blocking agents apart from diuretics seem to be the best investigated drugs in heart failure. Large controlled studies with bisoprolol, carvedilol and metoprolol in addition to diuretics, digitalis and ACE inhibitors convincingly yielded positive results in chronic left ventricular failure patients. Reduction of mortality by 35% and even of sudden cardiac deaths by 40% have been proven beyond doubt. Thus, heart failure patients today should also receive beta-blocking agents in all stages of the disease. In the era of controlled prospective studies (evidence-based medicine), physicians are well advised to use only drugs that have been proven beneficial in large controlled studies.
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PMID:The management of heart failure--an overview. 1119 49

Blockade of the renin-angiotensin system by angiotensin converting enzyme (ACE) inhibitors has an established role in the management of hypertension, heart failure, patients post-myocardial infarction and renal impairment. The mechanism of action of angiotensin II antagonists offers the potential of more complete blockade of angiotensin II, selective inhibition of the AT1 receptor and specificity for the renin-angiotensin system. Whether these mechanistic differences enhance the clinical potential of these drugs remains to be established. Preliminary evidence suggests that ACE inhibitors and angiotensin II antagonists have similar antihypertensive, haemodynamic and nephroprotective effects. Several major outcome trials with angiotensin II antagonists are underway and these should determine the eventual clinical potential of this class. Early results suggest equivalence with ACE inhibitors but further direct comparisons are needed. Angiotensin II antagonists have one undisputed advantage--excellent tolerability. Given the continuing under-use of ACE inhibitors because of concerns about adverse effects, this property alone may prove decisive in ensuring that angiotensin II antagonists yield the full clinical potential from blockade of the renin-angiotensin system.
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PMID:Clinical potential: angiotensin converting enzyme inhibitor or angiotensin II antagonist? 1145 Dec 17

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