Role of locally formed angiotensin II and bradykinin in the reduction of myocardial infarct size in dogs

The vagus nerve in cardiovascular physiology and pathophysiology: From evolutionary insights to clinical medicine

The parasympathetic nervous system via the vagus nerve exerts profound influence over the heart. Together with the sympathetic nervous system, the parasympathetic nervous system is responsible for fine-tuned regulation of all aspects of cardiovascular function, including heart rate, rhythm, contractility, and blood pressure. In this review, we highlight vagal efferent and afferent innervation of the heart, with a focus on insights from comparative biology and advances in understanding the molecular and genetic diversity of vagal neurons, as well as interoception, parasympathetic dysfunction in heart disease, and the therapeutic potential of targeting the parasympathetic nervous system in cardiovascular disease.

(Pro)renin Receptor Blockade Ameliorates Cardiac Injury and Remodeling and Improves Function After Myocardial Infarction

BACKGROUND

The (pro)renin receptor [(P)RR] is implicated in the pathogenesis of cardiovascular disease. We investigated the effects of (P)RR blockade after myocardial infarction (MI) in a mouse coronary-ligation model.

METHODS AND RESULTS

Mice underwent sham control surgeries (n = 8) or induction of MI followed by 28 days' treatment with a vehicle control (n = 8) or (P)RR antagonist (n = 8). Compared with sham control subjects, MI + vehicle mice demonstrated reduced left ventricular (LV) ejection fraction (LVEF: P < .001) and fractional shortening (P < .001), and increased LV end-systolic and -diastolic volumes (LVESV: P < .001; LVEDV: P < .001) 28 days after MI. In addition, MI decreased LV posterior wall and septal diameters (both P < .001), increased heart weight-body weight ratios (P < .05), LV collagen deposition, and cardiomyocyte diameter (both P < .001), and up-regulated collagen 1 (P < .01) and β-myosin heavy chain (β-MHC: P < .05) mRNA. Compared with MI + vehicle mice, (P)RR antagonism after MI reduced infarct size (P < .01), improved LVEF (P < .001), fractional shortening (P < .001), and stroke volume (P < .05), and decreased LVESV (P < .001) and LVEDV (P < .001). (P)RR antagonism also reversed MI-induced transmural thinning (P < .001) and reduced LV fibrosis (P < .01), cardiomyocyte size (P < .001), and ventricular collagen 1 (P < .01), β-MHC (P = .06), transforming growth factor β1 (P < .01), and angiotensin-converting enzyme (P < .05) expression.

CONCLUSIONS

The present study found that (P)RR blockade after MI in mice ameliorates infarct size, cardiac fibrosis/hypertrophy, and cardiac dysfunction and identifies the receptor as a potential therapeutic target in this setting.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

The effects of angiotensin II signaling pathway in the systolic response to acute stretch in the normal and ischemic myocardium

Acute myocardial stretch elicits a biphasic increase in contractility: an immediate increase, known as Frank-Starling mechanism (FSM), followed by a progressive increase, regarded as slow force response (SFR). In this study, we characterized the contractile response to acute stretch from 92 to 100% Lmax in rabbit papillary muscles (n=86) under normoxic and ischemic conditions, and its modulation by angiotensin II signaling pathway. Under normoxia, the FSM was independent of Na(+)/H(+)-exchanger, reverse mode of Na(+)/Ca(2+)-exchanger (r-NCX), AT1 receptor, AT2 receptor and PKC. Regarding the SFR, it was mediated by AT1 receptor activation and its downstream effectors PKC, Na(+)/H(+)-exchanger and r-NCX. Ischemia negatively impacted on the FSM and abolished the SFR, with the muscles exhibiting a time-dependent decline in contractility. Under ischemic conditions, FSM was not influenced by AT1 and AT2 receptors or PKC activation. AT1 receptor antagonism rescued the progressive deterioration in contractility, an effect partially dependent on AT2 receptor activation.

Preconditioning of the response to ischemia/ reperfusion-induced plasma leakage in hamster cheek pouch microcirculation

OBJECTIVE

Ischemic preconditioning and some drugs can protect tissues from injury by preserving microcirculation. This study evaluated vascular permeability in a hamster cheek pouch preparation using either short ischemic periods or bradykinin as preconditioning stimuli followed by 30 min of ischemia/reperfusion.

METHOD

Sixty-six male hamsters were divided into 11 groups: five combinations of different ischemic frequencies and durations (one, three or five shorts periods of ischemia, separated by one or five minutes) with 10 min intervals between the ischemic periods, followed by 30 min ischemia/reperfusion; three or five 1 min ischemic periods with 10 min intervals between them followed by the topical application of histamine (2 µM); bradykinin (400 nM) followed by 30 min of ischemia/reperfusion; and three control groups (30 min of ischemia/reperfusion or histamine or bradykinin by themselves). Macromolecular permeability was assessed by injection of fluorescein-labeled dextran (FITC-dextran, MW= 150 kDa; 250 mg/Kg body weight), and the number of leaks/cm2 was counted using an intravital microscope and fluorescent light in the cheek pouch.

RESULTS

Plasma leakage (number of leaks/cm²) was significantly reduced by preconditioning with three and five 1 min ischemic periods, one and three 5 min ischemic periods and by bradykinin. Histamine-induced macromolecular permeability was also reduced after three periods of 5 min of ischemia.

CONCLUSION

Short ischemic periods and bradykinin can function as preconditioning stimuli of the ischemia/reperfusion response in the hamster cheek pouch microcirculation. Short ischemic periods also reduced histamineinduced macromolecular permeability.

The impact of dose of the angiotensin-receptor blocker valsartan on the post-myocardial infarction ventricular remodeling: study protocol for a randomized controlled trial

BACKGROUND

Angiotensin-converting enzyme inhibitors and the angiotensin-receptor blocker valsartan ameliorate ventricular remodeling after myocardial infarction (MI). Based on previous clinical trials, a maximum clinical dose is recommended in practical guidelines. Yet, has not been clearly demonstrated whether the recommended dose is more efficacious compared to the lower dose that is commonly used in clinical practice.

METHOD/DESIGN

Valsartan in post-MI remodeling (VALID) is a randomized, open-label, single-blinded multicenter study designed to compare the efficacy of different clinical dose of valsartan on the post-MI ventricular remodeling. This study also aims to assess neurohormone change and clinical parameters of patients during the post-infarct period. A total of 1116 patients with left ventricular dysfunction following the first episode of acute ST-elevation MI are to be enrolled and randomized to a maximal tolerable dose (up to 320 mg/day) or usual dose (80 mg/day) of valsartan for 12 months in 2:1 ratio. Echocardiographic analysis for quantifying post-MI ventricular remodeling is to be conducted in central core laboratory. Clinical assessment and laboratory test are performed at fixed times.

DISCUSSION

VALID is a multicenter collaborative study to evaluate the impact of dose of valsartan on the post-MI ventricular remodeling. The results of the study provide information about optimal dosing of the drug in the management of patients after MI. The results will be available by 2012.

TRIAL REGISTRATION

NCT01340326.

Effects of captopril and angiotensin II receptor blockers (AT1, AT2) on myocardial ischemia-reperfusion induced infarct size

The renin-angiotensin system (RAS) plays a major role in regulating the cardiovascular system, and disorders of the RAS contribute largely to the cardiac pathophysiology, including myocardial ischemia-reperfusion (MI/R) injury. Two subtypes of angiotensin II (Ang II) receptors have been defined on the basis of their differential pharmacological properties. The current study was undertaken to address the question as to whether the inhibition of the angiotensin converting enzyme (ACE) by captopril and the AT1 and AT2 receptor blockers losartan and PD123319 modulate MI/R-induced infarct size in an in vivo rat model. To produce necrosis, a branch of the descending left coronary artery was occluded for 30 min followed by two hours of reperfusion. ECG changes, blood pressure, and heart rate were measured during the experiment. Captopril (3 mg/kg), losartan (2 mg/kg), and PD123319 (20 μg/kg/min) were given in an IV 10 min before ischemia and were continued during the ischemic period. The infarcted area was measured by TTC staining. The volume of infarct and the risk zone was determined by planimetry. Compared to the control group (55.62±4.00%) both captopril and losartan significantly reduced the myocardial infarct size (30.50±3.26% and 37.75±4.44%), whereas neither PD123319 nor PD123319+losartan affected the infarct size volume (46.50±3.72% and 54.62±2.43%). Our data indicates that captopril and losartan exert cardioprotective activity after an MI/R injury. Also, infarct size reduction by losartan was halted by a blockade of the AT2 receptor. Therefore, the activation of AT2 receptors may be potentially protective and appear to oppose the effects mediated by the AT1 receptors.

Sympathetic nervous system overactivity and its role in the development of cardiovascular disease

This review examines how the sympathetic nervous system plays a major role in the regulation of cardiovascular function over multiple time scales. This is achieved through differential regulation of sympathetic outflow to a variety of organs. This differential control is a product of the topographical organization of the central nervous system and a myriad of afferent inputs. Together this organization produces sympathetic responses tailored to match stimuli. The long-term control of sympathetic nerve activity (SNA) is an area of considerable interest and involves a variety of mediators acting in a quite distinct fashion. These mediators include arterial baroreflexes, angiotensin II, blood volume and osmolarity, and a host of humoral factors. A key feature of many cardiovascular diseases is increased SNA. However, rather than there being a generalized increase in SNA, it is organ specific, in particular to the heart and kidneys. These increases in regional SNA are associated with increased mortality. Understanding the regulation of organ-specific SNA is likely to offer new targets for drug therapy. There is a need for the research community to develop better animal models and technologies that reflect the disease progression seen in humans. A particular focus is required on models in which SNA is chronically elevated.

Kallikrein-kinin system: a surgical perspective in post-aprotinin era

Kallikrein-kinin system (KKS) plays an important role in inflammation, ischemia-reperfusion (IR) injury, and development of neoplasia. There is evidence to suggest that KKS plays an important role in organ protection during preconditioning. Aprotinin is a nonspecific serine protease inhibitor, which has been extensively used in cardiac surgery for the control of post operative bleeding. The anti-inflammatory effects of aproprotin are due to its inhibitory effect on the kallikrein-kinin system (KKS). We herein review KKS and its role as applied to the practice of surgery.

Angiotensin II effects on ischemic focal ventricular tachycardia are predominantly mediated through myocardial AT(2) receptor

Ischemic focal ventricular tachycardia (VT) occurs in animals and humans. Angiotensin-converting enzyme inhibitors and receptor blockers reduce sudden death in patients with ischemic heart disease. In our dog model of coronary artery occlusion (CAO), we tested the hypothesis that angiotensin II (AGII) will selectively promote focal VT and that the specific AT(2) blocker PD-123319 (PD), or AT(1) blocker losartan, will affect this VT. Anesthetized dogs (n = 90) underwent CAO, followed by three-dimensional activation mapping of inducible VT. Dogs without VT in 1-3 h after CAO received AGII, and those with VT received either PD or losartan. Focal endocardium excised from ischemic sites was studied in vitro with standard microelectrode. Of 33 dogs with no inducible VT, AGII infusion resulted in sustained VT of only focal Purkinje origin in 13 (39%) compared with 0 of 20 dogs with saline. Of 26 dogs with inducible VT at baseline, given PD, reinduction was blocked in 8 of 10 (P < 0.05) focal VT, but only 1 of 15 with reentry. In contrast, of 11 dogs given losartan, reinduction of either mechanism was not blocked. In vitro triggered activity in Purkinje was blocked by PD in 13 of 19 (P < 0.05), but not by losartan in 8. Also, triggered activity was promoted by AGII, losartan, or the combination in 9 of 12 tissues. AGII promotes only focal, mainly Purkinje ischemic VT. PD, but not losartan, preferentially blocked focal VT, which is likely due to triggered activity due to delayed afterdepolarizations in Purkinje.

Renin: at the heart of the mast cell

Cardiac mast cells proliferate in cardiovascular diseases. In myocardial ischemia, mast cell mediators contribute to coronary vasoconstriction, arrhythmias, leukocyte recruitment, and tissue injury and repair. Arrhythmic dysfunction, coronary vasoconstriction, and contractile failure are also characteristic of cardiac anaphylaxis. In coronary atherosclerosis, mast cell mediators facilitate cholesterol accumulation and plaque destabilization. In cardiac failure, mast cell chymase causes myocyte apoptosis and fibroblast proliferation, leading to ventricular dysfunction. Chymase and tryptase also contribute to fibrosis in cardiomyopathies and myocarditis. In addition, mast cell tumor necrosis factor-alpha promotes myocardial remodeling. Cardiac remodeling and hypertrophy in end-stage hypertension are also induced by mast cell mediators and proteases. We recently discovered that cardiac mast cells contain and release renin, which initiates local angiotensin formation. Angiotensin causes coronary vasoconstriction, arrhythmias, fibrosis, apoptosis, and endothelin release, all demonstrated mechanisms of mast-cell-associated cardiac disease. The effects of angiotensin are further amplified by the release of norepinephrine from cardiac sympathetic nerves. Our discovery of renin in cardiac mast cells and its release in pathophysiological conditions uncovers an important new pathway in the development of mast-cell-associated heart diseases. Several steps in this novel pathway may constitute future therapeutic targets.

Evidence for enhanced eNOS function in coronary microvessels during the second window of protection

Nitric oxide (NO) derived from endothelial NO synthase (NOS) (eNOS) has been identified as a trigger for the second window of protection (SWOP), but its role as a mediator during the SWOP is a matter of debate. Eighteen mongrel dogs were chronically instrumented to measure left ventricular function, coronary blood flow, and wall thickening. Myocardial preconditioning was induced by 10 min coronary artery occlusion. After 24 h of reperfusion (during the SWOP), the hearts were excised. Coronary microvessels were isolated and incubated in presence of 1) the endothelium-dependent agonists carbachol and bradykinin, 2) the calcium ionophore A23187, and 3) the angiotensin-converting enzyme (ACE) inhibitors enalaprilat and ramiprilat. Nitrite, a metabolite of NO, was measured. Under baseline conditions, nitrite production in microvessels from SWOP was 30% higher than that from normal (96 ± 4 vs. 74 ± 3 pmol/mg, P < 0.01, respectively). Nitrite production in response to carbachol, bradykinin, and A23187 was also enhanced in microvessels from SWOP ( P < 0.05). These enhanced responses were abolished by NG-nitro-l-arginine methyl ester (l-NAME) or the endothelial receptor-specific antagonists atropine and HOE-140. The level of eNOS protein in the SWOP myocardium was twofold higher than that in the non-SWOP myocardium. Nitrite production in response to the ACE inhibitors was greater in microvessels from SWOP. These effects were blocked by l-NAME, HOE-140, or dichloroisocoumarin (which inhibits kinin formation). We found that a brief ischemic episode induced delayed, enhanced NO production in coronary microvessels and an upregulation of eNOS protein. These findings suggest that eNOS is a mediator during the SWOP. The ability of ACE inhibitors to enhance NO release during the SWOP points to an additional clinical application for these drugs.

The role of zofenopril in myocardial protection during cardioplegia arrest: an isolated rat heart model

BACKGROUND

Zofenopril has beneficial effects in acute myocardial infarction, and improves the functional recovery after ischemia and reperfusion.

AIM OF THE STUDY

The aim of this study was to investigate the cardioprotective effects of zofenopril, when added to a standard cardioplegic solution or when orally administered as pretreatment.

METHODS

A Langendorff model for isolated rat hearts was employed: three groups of eight hearts each were used, respectively, with plain St. Thomas cardioplegia as control (group A and C), and the same solution added with 12.5 mg of zofenopril (group B). The third group (C) was pretreated for 7days with oral administration of zofenopril (6.5 mg/day). The hearts had a baseline perfusion for 30 minutes with Krebs-Henseleit solution at 37 degrees C, cardioplegia administration for 3 minutes, then 30 minutes of ischemia without any perfusion, and finally 30 minutes of reperfusion with Krebs-Henseleit solution at 37 degrees C.

RESULTS

Left ventricle developed pressure was significantly higher in the reperfusion period only in the pretreated group (group C) with respect to groups A and B (p = 0.016). Similar results were obtained regarding dP/dt curves (p = 0.020). No differences were demonstrated between groups for cellular viability expressed as creatine phospho-kinase (p = ns) and lactate dehydrogenase release (p = ns).

CONCLUSIONS

Zofenopril as oral pretreatment showed protective effects in an isolated model of cardioplegic arrest, although improvements in myocardial viability (enzymatic release) could not be demonstrated. Further experimental and clinical evaluations are necessary to assess the direct cardioprotective effect of zofenopril, modifying the length of treatment and the dosage of the drug.

Cumulative effects of AT1 and AT2 receptor blockade on ischaemia–reperfusion recovery in rat hearts

Though ischaemia/reperfusion injury induces renin-angiotensin systemic (RAS) activation and increased heart angiotensin production, the effects of blockade of the two main angiotensin II receptors, AT1 and AT2, are not definitively established. Using a Langendorff heart preparation, effects of Valsartan 10(-7)M (AT1 receptor blocker), PD 123319 10(-7)M (AT2 receptor blocker) or both in the presence of a controlled concentration of angiotensin II (10(-8)M) in order to reproduce systemic RAS activation were studied in adult male Wistar rat hearts submitted to ischaemia/reperfusion. Ischaemia/reperfusion impaired both systolic and diastolic function through a no-reflow phenomenon. Presence of a controlled concentration of angiotensin in the perfusate, enough to produce a significant AT1-induced vasoconstriction before ischaemia, has no relevant influence on ischaemia/reperfusion injury. Only blockade of both AT1 and AT2 receptors significantly improved recovery from ischaemia; better ventricle function paralleled better perfusion. The results suggest that blockade of angiotensin II receptors is cumulative since blockade of AT1 and AT2 receptors is more effective than blockade of just one of them.

Angiotensin II inhibition during myocardial ischemia–reperfusion in dogs: effects on leukocyte infiltration, nitric oxide synthase isoenzymes activity and left ventricular ejection fraction

Leukocyte infiltration and activation in myocardial reperfusion injury may be modulated by nitric oxide synthase isoforms. Angiotensin II influences leukocyte activation directly or by nitric oxide generation mechanisms. The effects of angiotensin II inhibition before reperfusion on myocardial function, leukocyte accumulation and nitric oxide synthase were evaluated on three groups of eight dogs. They were submitted to occlusion of the left anterior descending coronary artery for 90 min, followed by 120 min of reperfusion. The first group received captopril, the second losartan and the third received normal saline solution. Left ventricular ejection fraction significantly improved after reperfusion in the groups under captopril (15+/-5.1%, p=0.029) and losartan (16+/-4.3%, p=0.014) when compared to the control group (7+/-2.5%). Myeloperoxidase activity was significantly lower in captopril group (6.6+/-1.0 U/100 mg, p=0,036) and losartan (6.8+/-1.7 U/100 mg, p=0.044) than in the control group (12.5+/-4.7 U/100 mg). Significant difference on constitutive nitric oxide synthase activity was not observed when all three groups were compared simultaneously (10.1+/-1.8 versus 8.5+/-1.3 versus 7.3+/-1.9 fM/mg/min, p=0.447). Inducible nitric oxide synthase activity was significantly lower in the losartan group (9.0+/-4.1 fM/mg/min) than in the captopril (29.2+/-5.1 fM/mg/min, p=0.0001) and control groups (26.2+/-4.6 fM/mg/min, p=0.0001). Angiotensin II inhibition reduced leukocyte infiltration and improved left ventricular ejection fraction during reperfusion by angiotensin-converting enzyme inhibition or by angiotensin II type 1 receptor blocker. This was observed without influencing the constitutive nitric oxide synthase activity. Only losartan reduced inducible nitric oxide synthase activity but did not influence the leukocyte infiltration and myocardial contractile function.

Protein Kinase C in Cardiac Disease and as a Potential Therapeutic Target

Protein kinase C (PKC) is a member of a large family of serine/threonine kinases that plays an integral role in many of the signaling cascades that govern cellular behavior. As such, it is intricately involved in the processes that mediate disease pathogenesis. Strategies that serve to alter PKC function may prove to be useful in the treatment of numerous disease states. This article reviews the various roles PKC may play in cardiovascular disease, specifically with regard to ischemic heart disease, cardiac hypertrophy, heart failure, hypertension, and atherosclerosis, and suggests the potential for developing therapeutic approaches that can target PKC activity.

Cardioprotective effect of zofenopril in perfused rat heart subjected to ischemia and reperfusion

We investigated the effect of different ACE inhibitors on tissue injury in isolated rat hearts subjected to 30 minutes of ischemia followed by 120 minutes of reperfusion. Zofenoprilat (1-100 microM), but not enalaprilat or lisinopril, significantly reduced infarct size, as estimated on the basis of triphenyltetrazolium chloride staining. The protection was not reproduced by the angiotensin II receptor antagonist irbesartan, and it was partly abolished by the bradykinin receptor antagonist HOE 140. Zofenoprilat molecule contains a sulfhydryl group, and its administration, as compared with enalaprilat or lisinopril administration, was associated with better preservation of protein thiols at the end of ischemia. We conclude that zofenopril has a specific cardioprotective effect, which might be related either to interference with bradykinin metabolism or to preservation of protein sulfhydryl groups.

Bradykinin preconditioning in coronary artery bypass grafting

BACKGROUND

Experimental studies have shown that activation of bradykinin B2 receptor is one of the most important triggers of ischemic preconditioning. However, the effect of exogenous administration of bradykinin in cardiac surgery is not yet known. The present prospective randomized study was designed to investigate the effect of bradykinin pretreatment in patients undergoing elective coronary artery bypass surgery.

METHODS

Forty-one patients with multiple-vessel coronary artery disease and stable angina, admitted for the first time for elective coronary artery bypass surgery, were randomized into control or bradykinin (BK) groups. Patients in the BK group received bradykinin infusion for 7 minutes (total dose 25 microg) before the initiation of cardiopulmonary bypass. Perioperative cardiac specific troponin I (cTnI) and creatine kinase cardiac isoenzyme (CKMB) release and hemodynamics were recorded.

RESULTS

Bradykinin infusion caused acute decrease of blood pressure in most of the cases and the mean minimum mean blood pressure during bradykinin infusion was 72.7% of the original mean blood pressure (MBP) level (74.7 +/- 7.9 vs 54.4 +/- 12.1 mm Hg, p < 0.01). There were no differences in baseline levels of cTnI and CKMB between the groups. The postoperative cTnI levels were lower than 10 ng/mL in most patients in both groups (18 in the BK group and 15 in the control group). There was no difference in cTnI between the groups. However, patients who received bradykinin released significantly less CKMB than did the controls postoperatively (6 hours, BK, 22.1 +/- 9.5 vs control, 23.6 +/- 12.7 U/L; 12 hours, BK, 19.4 +/- 12.4 vs control, 28.7 +/- 23.8 U/L; 24 hours, BK, 21.5 +/- 14.7 vs control, 35.5 +/- 28.9 U/L; 48 hours, BK, 14.4 +/- 7.5 vs control, 23.5 +/- 13.6 U/L; analysis of variance [ANOVA] for repeated measurement, p = 0.036). Maximum CKMB was also lower in the BK group (22.4 +/- 14.4 vs 37.7 +/- 27.5 U/L, p = 0.044). There was no significant difference between the groups in any of the hemodynamic variables.

CONCLUSIONS

Exogenous bradykinin infusion showed weak cardioprotective effect in the low-risk patients undergoing coronary artery bypass surgery but the dose used in the study caused acute decrease of systemic blood pressure.

Reduction of infarct size by orally administered des-aspartate-angiotensin I in the ischemic reperfused rat heart

Occlusion of the left main coronary artery for 45 min caused sizable infarct scarring of the left ventricular wall in the rat heart at 14 days post-reperfusion. Daily oral administration of des-aspartate-angiotensin I (DAA-I) for 14 days attenuated the area of the infarct scar and transmurality. The attenuation was dose-dependent and biphasic; maximum effective dose was 1524 nmol/kg, and doses higher than this were progressively inactive. The exact mechanism of the biphasic attenuation is not known, and receptor down-regulation by internalization, which has been implicated in a similar biphasic nature for the anticardiac hypertrophic action of DAA-I, could be a likely cause. Indomethacin (101 micromol/kg, i.p.), administered sequentially after the daily oral dose of DAA-I (1524 nmol/kg), completely inhibited the attenuation at 14 days post-reperfusion, indicating that prostaglandins may be involved in transducing the attenuation. The present findings support earlier indications that DAA-I exerts protective actions in cardiovascular pathologies in which angiotensin II is implicated. It is suggested that DAA-I exerts the cardioprotective action by acting on the same indomethacin-sensitive angiotensin AT1 receptor. Although similar array of protective actions are also seen with another endogenous angiotensin, angiotensin-(1-7), the present findings demonstrate for the first time the ability of an endogenous angiotensin to reduce the infarct size of an ischemic-reperfusion injured rat heart.

Role of reactive oxygen species in ischemic preconditioning of subcellular organelles in the heart

Ischemic preconditioning (IPC) is an endogenous adaptive mechanism and is manifested by early and delayed phases of cardioprotection. Brief episodes of ischemia-reperfusion during IPC cause some subtle functional and structural alterations in sarcolemma, mitochondria, sarcoplasmic reticulum, myofibrils, glycocalyx, as well as nucleus, which render these subcellular organelles resistant to subsequent sustained ischemia-reperfusion insult. These changes occur in functional groups of various receptors, cation transporters, cation channels, and contractile and other proteins, and may explain the initial effects of IPC. On the other hand, induction of various transcriptional factors occurs to alter gene expression and structural changes in subcellular organelles and may be responsible for the delayed effects of IPC. Reactive oxygen species (ROS), which are formed during the IPC period, may cause these changes directly and indirectly and act as a trigger of IPC-induced cardioprotection. As ROS may be one of the several triggers proposed for IPC, this discussion is focused on the current knowledge of both ROS-dependent and ROS-independent mechanisms of IPC. Furthermore, some events, which are related to functional preservation of subcellular organelles, are described for a better understanding of the IPC phenomenon.

Angiotensin II activates NADPH oxidase in isolated rat hearts subjected to ischaemia-reperfusion

The role of angiotensin II in myocardial ischaemia-reperfusion is not clearly defined. In this respect, the involvement of NADPH oxidase remains to be determined. The aim of this study was 1) to evaluate the cardiac effects of angiotensin AT(1) receptor stimulation in non-ischaemic conditions of perfusion or during ischaemia-reperfusion, and 2) to measure the concomitant activation of NADPH oxidase in isolated rat hearts perfused with angiotensin II and/or Losartan. In non-ischaemic hearts, angiotensin II induced rapid and prolonged vasoconstrictive and negative inotropic effects. Ischaemia-reperfusion increased the mRNA expression of AT(1) and AT(2) receptors. During reperfusion, angiotensin II reduced the incidence of arrhythmias and the lactate dehydrogenase released, and increased NADPH oxidase mRNA expression and enzyme activity. Losartan co-administration totally antagonised the effects of angiotensin II. Our study demonstrates that ischaemia-reperfusion induces adaptative cardiac modifications, which allow exogenously added angiotensin II to stimulate myocardial NADPH oxidase through angiotensin AT(1) receptor activation.

Protection of the cardiovascular system by imidapril, a versatile angiotensin-converting enzyme inhibitor

Imidapril hydrochloride (imidapril) is a long-acting, non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor, which has been used clinically in the treatment of hypertension, chronic congestive heart failure (CHF), acute myocardial infarction (AMI), and diabetic nephropathy. It has the unique advantage over other ACE inhibitors in causing a lower incidence of dry cough. After oral administration, imidapril is rapidly converted in the liver to its active metabolite imidaprilat. The plasma levels of imidaprilat gradually increase in proportion to the dose, and decline slowly. The time to reach the maximum plasma concentration (T(max)) is 2.0 h for imidapril and 9.3 h for imidaprilat. The elimination half-lives (t(1/2)) of imidapril and imidaprilat is 1.7 and 14.8 h, respectively. Imidapril and its metabolites are excreted chiefly in the urine. As an ACE inhibitor, imidaprilat is as potent as enalaprilat, an active metabolite of enalapril, and about twice as potent as captopril. In patients with hypertension, blood pressure was still decreased at 24 h after imidapril administration. The antihypertensive effect of imidapril was dose-dependent. The maximal reduction of blood pressure and plasma ACE was achieved with imidapril, 10 mg once daily, and the additional effect was not prominent with higher doses. When administered to patients with AMI, imidapril improved left ventricular ejection fraction and reduced plasma brain natriuretic peptide (BNP) levels. In patients with mild-to-moderate CHF [New York Heart Association (NYHA) functional class II-III], imidapril increased exercise time and physical working capacity and decreased plasma atrial natriuretic peptide (ANP) and BNP levels in a dose-related manner. In patients with diabetic nephropathy, imidapril decreased urinary albumin excretion. Interestingly, imidapril improved asymptomatic dysphagia in patients with a history of stroke. In the same patients it increased serum substance P levels, while the angiotensin II receptor antagonist losartan was ineffective. These studies indicate that imidapril is a versatile ACE inhibitor. In addition to its effectiveness in the treatment of hypertension, CHF, and AMI, imidapril has beneficial effects in the treatment of diabetic nephropathy and asymptomatic dysphagia. Good tissue penetration and inhibition of tissue ACE by imidapril contributes to its effectiveness in preventing cardiovascular complications of hypertension. The major advantages of imidapril are its activity in the treatment of various cardiovascular diseases and lower incidence of cough compared with some of the older ACE inhibitors.

Effect of ACE-inhibitor ramiprilat and AT1-receptor antagonist candesartan on cardiac norepinephrine release: comparison between ischemic and nonischemic conditions

ACE-inhibitors and AT -receptor antagonists may exert part of their pharmacological actions by interference with angiotensin-and/or bradykinin-mediated prejunctional stimulation of cardiac norepinephrine release. As endogenous formation of angiotensin and bradykinin is increased in ischemia, we investigated the effects of the ACE-inhibitor ramiprilat and the AT -receptor antagonist candesartan on cardiac norepinephrine release in isolated perfused rat hearts, under nonischemic and stop-flow conditions. Exocytotic release of endogenous norepinephrine was induced by electrical field stimulation and measured by HPLC. Paired stimulations were applied in each heart to obtain an intraindividual comparison of the effect of the pharmacological agent on norepinephrine release with the release under baseline conditions. The ACE-inhibitor ramiprilat (0.1-10 nM) and the AT -receptor antagonist candesartan (1-100 nM) were studied during normal flow or in the fourth minute of stop-flow. Under nonischemic conditions, the ACE-inhibitor slightly reduced norepinephrine release at the highest concentration, while the AT -receptor antagonist did not influence norepinephrine release in normoxia. Conversely, both substances significantly increased norepinephrine release during ischemia. Augmentation of norepinephrine release in ischemia by ramiprilat and candesartan was blocked by the bradykinin B -receptor antagonist HOE 140 and, in case of candesartan, by the AT -receptor antagonist PD 123319. The ACE-inhibitor ramiprilat and AT -receptor antagonist candesartan enhance cardiac norepinephrine release selectively in ischemia by stimulating presynaptic bradykinin B -receptors. Regarding the AT -receptor antagonist, AT -receptor activation is also involved in bradykinin-mediated prejunctional stimulation.

Effects of captopril and losartan on myocardial ischemia-reperfusion induced arrhythmias and necrosis in rats

Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 (AT (1)) receptor blockers improve ischemia-reperfusion induced arrhythmias and infarct size in several animal models. However, the effects of pretreatment with ACEIs or AT (1) receptor blockers on acute myocardial infarct size and arrhythmias are controversial. Thus, we sought to assess the comparative effects of pretreatment with ACEI captopril and AT (1)-receptor blocker losartan on myocardial infarct size and arrhythmias in a rat model of ischemia-reperfusion. We randomly assigned 92 male Wistar rats for arrhythmias ( n= 60) and necrosis ( n= 32) experiments. To produce arrhythmia, the left main coronary artery was occluded for 7 min, followed by 7 min of reperfusion and to produce necrosis, the the left main coronary artery was occluded for 30 min, followed by 120 min of reperfusion. Captopril (3 mg kg (-1)) and losartan (0.2 and 2 mg kg (-1)) were given intravenously 10 min before occlusion. Captopril reduced the incidences of ventricular fibrillation (VF) and mortality associated with irreversible VF, whereas the studied doses of losartan did not. Captopril also decreased the number of ventricular beats on reperfusion. Losartan 2 mg kg (-1) reduced both the number of ventricular premature beats and the incidence of ventricular tachycardia (VT) on reperfusion, while losartan at dose of 0.2 mg kg (-1) had no effect on these arrhythmias. Compared to the control group, both captopril and losartan reduced myocardial infarct size in the rat model of ischemia-reperfusion, but this was statistically significant for captopril only. In this experimental model, although captopril did not reduce the incidence of reperfusion-induced VT, it was more effective than the AT (1)-receptor blocker losartan at preventing mortality associated with irreversible VF and to reduce myocardial infarct size in rat model of ischemia-reperfusion.

Presynaptic regulation of cardiac norepinephrine release in ischemia

In myocardial ischemia presynaptic regulation of norepinephrine release may be altered either by ischemic effects on presynaptic receptor signaling or by ischemia-evoked accumulation of endogenous agonists. Because presynaptic receptors are targets of several drugs. such alterations may have pharmacotherapeutic implications. We investigated the effect of brief ischemic periods on presynaptic regulation of norepinephrine release by alpha2-adrenoceptors, beta2-adrenoceptors, adenosine A1-, angiotensin AT1-, and bradykinin B2-receptors in isolated perfused rat hearts. Exocytotic norepinephrine release was evoked by electrical field stimulation. Paired stimulations were performed to compare the pharmacologic intervention (S2) with the release under baseline conditions (S1), and the effects of receptor agonists and antagonists were compared under nonischemic and stop-flow conditions. In summary. during brief myocardial ischemia, presynaptic modulation of norepinephrine release is differentially regulated. Autoinhibitory alpha2-adrenoceptors lose their activity, whereas stimulatory beta2-adrenoceptors are sensitized. Inhibitory adenosine A1-receptors gain importance during ischemia owing to endogenous adenosine formation. Bradykinin- and angiotensin-mediated stimulation of norepinephrine release is not affected under ischemic conditions.

Angiotensin-converting enzyme inhibition enhances a subthreshold stimulus to elicit delayed preconditioning in pig myocardium

OBJECTIVES

We assessed the effect of angiotensin-converting enzyme (ACE) inhibition in combination with a subthreshold preconditioning (PC) stimulus to elicit delayed preconditioning against infarction in pig myocardium.

BACKGROUND

Bradykinin triggers early PC. Angiotensin-converting enzyme inhibitors increase local bradykinin levels via inhibition of kinin breakdown and have been shown in experimental studies to augment early protection afforded by PC. A role for bradykinin in eliciting delayed PC has not so far been identified.

METHODS

We used a two-day protocol. On day 1 (closed chest), pigs were either sham-operated (group 1) or preconditioned, using balloon catheter inflation of the left anterior descending (LAD) coronary artery, with either a full (4 x 5 min PC, group 2) or subthreshold PC stimulus (2 x 2 min PC, group 3). Additional groups were pre-treated with perindoprilat (0.06 mg/kg i.v.) before sham (group 4) or subthreshold PC (group 5). On day 2 (open chest), all pigs were subjected to 40 min occlusion of the LAD followed by 3 h of reperfusion. Infarct size was determined by tetrazolium staining.

RESULTS

Group 1 had a mean infarct size of 42.8+/-3.2% of the risk zone. Preconditioning with 4 x 5 min reduced the infarct size to 19.5+/-3.9% (p < 0.05). Groups 3 and 4 had infarct sizes not statistically different from group 1. However, combining perindoprilat with subthreshold PC resulted in a significant limitation of the infarction (18.4+/-3.1% p < 0.05), comparable with group 2.

CONCLUSIONS

This is the first study to show that ACE inhibition can augment a mild ischemic stimulus to induce a protected state 24 h later.

Mechanism of the cardioprotective effect of inhibition of the renin-angiotensin system on ischemia/reperfusion-induced myocardial injury

Inhibition of the renin-angiotensin system (RAS) has been shown to be beneficial in providing cardioprotective effects in humans, but the mechanism of these effects is not well understood. In this study, we examined the effects and mechanism of RAS inhibitors on ischemia/reperfusion (IR)-induced myocardial injury in rats. Rats were randomly divided into five groups and treated with vehicle (C), angiotensin converting enzyme inhibitor (ACE-I), angiotensin II type 1 receptor antagonist (AT1-A), angiotensin II type 2 receptor antagonist (AT2-A) or ACE-I plus bradykinin B2 antagonist. Ten minutes after administration, the left main coronary artery was ligated for 45 min, and then reperfused for 120 min. IR-induced cardiomyocyte apoptosis was assessed by terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay and confirmed by typical DNA laddering. Mitogen-activated protein kinase, extracellular signal-regulated protein kinase (ERK) and c-Jun NH2-terminal protein kinase (JNK) activity in the ischemic zone were measured by an in vitro kinase assay. The duration of ventricular tachycardia (VT) during ischemia was reduced by AT2-A and ACE-I, and increased by AT1-A and ACE-I+icatibant. ACE-I and AT2-A reduced apoptosis (by 54% and 53%) and infarct size (by 42% and 41%), while AT1-A increased apoptosis (by 86%) and infarct size (by 45%). These changes were negatively correlated with the change in ERK activity. The effects of ACE-I on apoptosis and infarct size were abolished by the coadministration of icatibant. Apoptosis was correlated with the occurrence of VT (r=0.837, p<0.001). These results suggest that both the accumulation of bradykinin and inhibition of AT2 receptor are cardioprotective against IR injury through the activation of ERK, but not JNK.

Interaction between paracrine tumor necrosis factor-alpha and paracrine angiotensin II during myocardial ischemia

OBJECTIVES

The purpose of this study was to explore interactions between paracrine angiotensin II (Ang-II) and tumor necrosis factor-alpha (TNF-alpha) during myocardial ischemia.

BACKGROUND

Ischemic myocardium releases significant amounts of TNF-alpha. This paracrine release correlated with postischemic myocardial injury. Other studies showed myocardial protection obtained by the use of angiotensin-converting enzyme inhibitors (i.e., captopril) and the Ang-II type 1 receptor antagonist losartan after ischemia. The possibility that these agents decrease TNF-alpha synthesis has not yet been investigated.

METHODS

Using the modified Langendorff model, isolated rat hearts underwent either 90 min of nonischemic perfusion (control group) or 1 h of global cardioplegic ischemia. In both groups, either captopril (360 micromol/liter) or losartan (182.2 micromol/liter) was added before ischemia. The hearts were assayed for messenger ribonucleic acid (mRNA) expression and effluent TNF-alpha levels. In addition, cardiac myocytes were incubated in cell culture with Ang-II.

RESULTS

After ischemia, TNF-alpha mRNA expression intensified from 0.63 +/- 0.06 (control group) to 0.92 +/- 0.12 (p < 0.03), and effluent TNF-alpha levels were 711 +/- 154 pg/ml. The TNF-alpha mRNA expression declined to 0.46 +/- 0.07 (p < 0.01) and 0.65 +/- 0.08 (p < 0.02) in captopril- and losartan-treated hearts, respectively. Effluent TNF-alpha was below detectable levels. Concentrations of TNF-alpha in supernatants of incubated cardiac myocytes treated with 10 and 50 nmol/liter of Ang-II were 206.0 +/- 47.0 pg/ml and 810 +/- 130 pg/ml, respectively (p < 0.004). When pretreated with 700 micromol/liter of losartan, TNF-alpha was below detectable levels.

CONCLUSIONS

This study presents an original explanation for previously reported myocardial protection after ischemia, obtained by the use of captopril and losartan. These drugs reduce TNF-alpha synthesis, providing strong evidence of active interactions between paracrine TNF-alpha and Ang-II in the evolution of the ischemic cascade.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

The renin angiotensin system in bypass graft surgery

The renin angiotensin system is implicated in the development of vein graft disease after coronary artery bypass surgery. Components of this system have been shown to play important roles in determining the short-term and long-term performance of coronary artery bypass grafts. Significant differences exist in the commonly used arterial and venous grafts in angiotensin converting enzyme activity and angiotensin responses. The existence of a dual enzyme pathway in angiotensin II formation has also been demonstrated. Such findings have implications for the use of AT1-receptor antagonists over enzyme inhibitors to improve graft performance and prevent the development of coronary artery bypass graft disease.

Unchanged cardiac angiotensin II levels accompany losartan-sensitive cardiac injury due to nitric oxide synthase inhibition

Chronic nitric oxide synthase (NOS) inhibition results in hypertension and myocardial injury. In a rapid and severe model of chronic NOS inhibition, we determined the role of angiotensin II in these effects by using angiotensin II receptor blockade and by measuring cardiac angiotensin II concentrations before and during development of cardiac damage. Rats received either no treatment, the NOS inhibitor Nomega-nitro-L-arginine (L-NNA; 500 mg/l), the angiotensin AT(1) receptor antagonist losartan (400 mg/kg chow), or L-NNA plus losartan for 21 days. In the second protocol, five groups of rats received L-NNA (500 mg/l) for 0, 4, 7, 14 and 21 days, respectively. L-NNA increased systolic blood pressure (SBP) (227+/-8 versus 143+/-6 mm Hg; P<0.01), heart weight index (0.44+/-0.02 versus 0.32+/-0.01; P<0.01) and induced coronary vasculitis and myocardial necrosis. Co-treatment with losartan prevented all changes. L-NNA during 4 days decreased cardiac angiotensin II (23+/-4 versus 61+/-15 fmol/g; P<0.05). Although after 7 days, fresh infarcts and after 14 days organized infarcts were present, cardiac angiotensin II was only slightly increased after 21 days (100+/-10 fmol/g; P<0.05). In conclusion, losartan-sensitive cardiac damage due to chronic NOS inhibition is not associated with primary increase of cardiac angiotensin II, suggesting that chronic NOS inhibition increases cardiac sensitivity for angiotensin II.

Selective activation of E-type prostanoid(3)-receptors reduces myocardial infarct size. A novel insight into the cardioprotective effects of prostaglandins

Prostaglandins (PGs) and other eicosanoids are members of a large family of lipid mediators (autacoids). In 1978, Lefer and colleagues (Science 200, 52-55 [1978]) reported that prostacyclin reduces the myocardial tissue injury caused by coronary artery occlusion and reperfusion in the cat. Since this discovery, more than 50 papers have reported on the cardioprotective effects of vasodilator PGs, including prostacyclin. The cardioprotective effects of PGs are due in part to (1) a reduction in afterload, (2) an increase in coronary blood flow, (3) the inhibition of platelet function, and (4) the inhibition of the activation and extravasation of polymorphonuclear granulocytes. All of these effects are secondary to the activation of EP (E-type prostanoid)(2)-receptors, which activate G(s)-protein and, hence, adenylate cyclase. In addition, the protection of organs such as the heart by PGs has been attributed to a cytoprotective effect of these agents, the mechanism of which is largely unknown. We recently have discovered that certain E-type PGs, which do not activate EP(2)-receptors, also reduce myocardial infarct size, without causing a fall in blood pressure (EP(2)-receptor-mediated effects). Having provided a brief introduction into the role of eicosanoids in ischaemia-reperfusion injury of the heart, this review focuses on the recent discovery that selective agonists of EP(3)-receptors reduce myocardial infarct size, without causing haemodynamic side effects. The mechanisms of the cardioprotective effects of these agents are discussed, as are the therapeutic implications.

Cardioprotection after angiotensin II type 1 blockade involves angiotensin II type 2 receptor expression and activation of protein kinase C-epsilon in acutely reperfused myocardial infarction in the dog. Effect of UP269-6 and losartan on AT1 and AT2-receptor expression and IP3 receptor and PKCepsilon proteins

To determine whether cardioprotection after chronic angiotensin II (Ang II) type 1 (AT(1)) receptor blockade involves Ang II type 2 (AT(2)) receptor expression and protein kinase C-epsilon (PKC(epsilon)) activation, we measured in vivo haemodynamics and left ventricular (LV) remodelling and dysfunction (echocardiogram/ Doppler) and ex vivo AT(1)/AT(2)-receptor expression, IP(3)R (1, 4, 5-inositol trisphosphate type 2 receptor) and PKC(epsilon) proteins in dogs with acutely reperfused (90 minutes ischaemia, 90 minutes reperfusion) myocardial infarction (MI) following seven days of AT(1)-receptor blockade with oral losartan or UP269-6. The animals were randomised to sham; sham + losartan or UP269-6; MI alone; MI + losartan; MI + UP269-6. More marked AT(1)-receptor blockade with UP269-6 (greater inhibition of Ang II pressor responses) was associated with a smaller increase in preload, less systolic and diastolic dysfunction, less infarct expansion, and smaller LV diastolic and systolic volumes. However, both AT(1)-receptor antagonists decreased infarct size. Importantly, MI decreased AT(1)-receptor and AT(2)-receptor expression while MI after AT(1)-receptor antagonism increased AT(1)-receptor (mRNA, not protein) and AT(2)-receptor (mRNA and protein) expression as well as IP(3)R and PKC(epsilon) proteins and cyclic guanosine 3', 5' monophosphate (cGMP). These results suggest that cardioprotection induced by chronic AT(1)-receptor antagonism involves enhanced AT(2)-receptor expression and possibly downstream signalling through IP(3)R, PKC(epsilon) and cGMP.

Force-length relationship in dogs as a measure of protective effect of imidapril on regional myocardial ischemia and reperfusion injury

Our laboratory previously reported that the end-systolic force-length relationship of the left ventricle provides a better method of evaluating myocardial contractile properties than the left ventricular end-systolic pressure-volume relationship, because it avoids deficiencies of the latter parameter such as dependence of its slope (E(max)) on the volume intercept (V(0)). The slope (E(c)) of the left ventricular end-systolic force-length relationship represents the contractility of functioning myocardium, while its length intercept (L(0)) reflects the length of non-functioning myocardium. However, the effect of regional myocardial ischemia on these parameters, as evaluated by the force-length relationship, remains unknown. To clarify the effects of regional ischemia and angiotensin-converting enzyme inhibition on the myocardium during ischemia-reperfusion, the changes in E(c) and L(0) were determined in anesthetized open-chest dogs. (1) Control group (n=26): Before and after 15 min of complete coronary artery occlusion, as well as after 15 min of reperfusion, left ventricular pressure and volume were simultaneously recorded during inferior vena cava occlusion. The left ventricular force-length relationship was obtained from the pressure and volume of three cylindrical segments of the ventricle, and E(c) and L(0) were calculated. (2) Imidapril group (n=14): Imidaprilat (1 microg/kg/min) was continuously infused from 30 min before ischemia to the end of the experiment, and the same procedures were followed as in the control group. Fourteen out of the 26 dogs (54%) in the control group died of reperfusion-induced ventricular arrhythmias, while only two of the 14 dogs (14%) in the imidapril group did so (P<0.05). In the control group, E(c) was increased during ischemia and remained at the same level after reperfusion. However, E(c) was not altered in the imidapril group. Although L(0) was increased during ischemia and decreased after reperfusion in both groups, the percent increase of L(0) in the imidapril group was significantly smaller than in the control group (8% vs. 32%, P<0.05). With the improvement of these indices, the bradykinin concentration of coronary venous blood increased in the imidapril group (P<0.01). These findings suggest that regional myocardial ischemia increased the average contractility of overall functioning myocardium despite the increased non-functioning myocardium. Moreover, imidapril has a cardioprotective effect against ischemia-reperfusion injury by decreasing infarct size, and through the antiarrhythmic effect and the reversal of increased overall contractility.

Role of kinins in chronic heart failure and in the therapeutic effect of ACE inhibitors in kininogen-deficient rats

Using Brown Norway Katholiek (BNK) rats, which are deficient in kininogen (kinin precursor) due to a mutation in the kininogen gene, we examined the role of endogenous kinins in 1) normal cardiac function; 2) myocardial infarction (MI) caused by coronary artery ligation; 3) cardiac remodeling in the development of heart failure (HF) after MI; and 4) the cardioprotective effect of angiotensin-converting enzyme inhibitors (ACEI) on HF after MI. Two months after MI, rats were randomly treated with vehicle or the ACEI ramipril for 2 mo. Brown Norway rats (BN), which have normal kininogen, were used as controls. Left ventricular (LV) end-diastolic volume (EDV), end-systolic volume (ESV), end-diastolic pressure (EDP), and ejection fraction (EF) as well as myocardial infarct size (IS), interstitial collagen fraction (ICF), cardiomyocyte cross-sectional area (MCA), and oxygen diffusion distance (ODD) were measured. We found that 1) cardiac hemodynamics, function, and histology were the same in sham-ligated BN and BNK rats; 2) IS was similar in BN and BNK; 3) in rats with HF treated with vehicle, the decrease in LVEF and the increase in LVEDV, LVESV, LVEDP, ICF, MCA, and ODD did not differ between BNK and BN; and 4) ACEI increased EF, decreased LVEDV and LVESV, and improved cardiac remodeling in BN-HF rats, and these effects were partially blocked by the bradykinin B(2) receptor antagonist icatibant (HOE-140). In BNK-HF rats, ACEI failed to produce these beneficial cardiac effects. We concluded that in rats, lack of kinins does not influence regulation of normal cardiac function, myocardial infarct size, or development of HF; however, kinins appear to play an important role in the cardioprotective effect of ACEI, since 1) this effect was significantly diminished in kininogen-deficient rats and 2) it was blocked by a B(2) kinin receptor antagonist in BN rats.

The effects of Z13752A, a combined ACE/NEP inhibitor, on responses to coronary artery occlusion; a primary protective role for bradykinin

The effects on the responses to coronary artery occlusion of a combined ACE/NEP inhibitor (Z13752A) were examined in anaesthetized dogs. A 1 h infusion of Z13752A (128 microgram kg(-1) min(-1) intravenously) decreased arterial blood pressure (by 11+/-3%; P<0. 05) and increased coronary blood flow (by 12+/-4%, P<0.05). There were no other significant haemodynamic changes. Z13752A inhibited both NEP and ACE enzymes both in dog plasma and in tissue (lung ACE; kidney NEP). Pressor responses to angiotensin I in vivo were inhibited and systemic vasodilator responses to bradykinin were potentiated. When the left anterior descending coronary artery was occluded for 25 min, Z13752A markedly reduced the severity of the resultant ventricular arrhythmias. No ventricular fibrillation (VF) occurred (compared to 7/16 in the controls; P<0.05), and ventricular tachycardia (VT) was reduced (VT in 2/9 dogs treated with Z13752A cp. 16/16 of controls; episodes of VT 0.2+/-0.1 c.p. 10.7+/-3.3; P<0. 05). Reperfusion of the ischaemic myocardium led to VF in all control dogs but occurred less frequently in dogs given Z13752A (survival from the combined ischaemia-reperfusion insult 67% c.p. 0% in controls; P<0.05). Z13752A reduced two other indices of ischaemia severity; epicardial ST-segment elevation and inhomogeneity of electrical activation. These protective effects of Z13752A during ischaemia and reperfusion were abolished by the administration of icatibant (0.3 mg kg(-1), i.v.) a selective antagonist of bradykinin at B(2) receptors; the ischaemic changes in dogs given both icatibant and Z13752A were similar to those in the controls. We conclude that this ACE/NEP inhibitor is effective at reducing the consequences of coronary artery occlusion in this canine model and that this protection is primarily due to potentiation of released bradykinin. British Journal of Pharmacology (2000) 129, 671 - 680

Participation of angiotensin II and bradykinin in contractile function in dog stunned myocardium

We examined the effects of enalapril and 4'-[(1, 4'-dimethyl-2'-propyl-[2,6'-bi-1H-enzimidazole]-1'-yl)methyl]-[1, 1'-biphenyl]-2-carboxylic acid (BIBR-277), an angiotensin II receptor antagonist, on contractile dysfunction in the stunned myocardium. Dogs were subjected to 20-min ligation of the coronary artery, followed by 60-min reperfusion. Saline, enalapril (1 mg/kg or 3 mg/kg), or BIBR-277 (3 mg/kg) was injected i.v. 10 min before ligation. D-Arginyl-L-arginlyl-L-prolyl-trans-4-hydroxy-L-prolylglycyl -3-(2-thi enyl)-L-alanyl-L-seryl-D-1,2,3, 4-tetrahydro-3-isoquinolinecarbonyl-L-(2alpha, 3beta, 7abeta)-octahydro-1H-indole-2-carbonyl-L-arginine (Hoe-140), a bradykinin B(2) receptor antagonist, at 300 microg/kg was injected i. v. 10 min before drug injection. Contractile function was assessed on the basis of percentage segment shortening (%SS). ATP levels were measured in 60-min reperfused hearts. %SS significantly decreased during ischemia, and recovered during reperfusion, although the %SS was significantly less than the pre-ischemic level. Both enalapril at either dose and BIBR-277 significantly enhanced %SS recovery during reperfusion, an effect which was associated with a tendency toward energy preservation. Hoe-140 completely abolished the effect of enalapril at either dose, while it did not modify that of BIBR-277. Inhibition of angiotensin II formation and bradykinin breakdown may be separately related to the improvement of myocardial stunning.

Structure of a kallikrein-like enzyme and its tissue localization in the dog

We previously purified a kallikrein-like enzyme from the dog heart and demonstrated that it is not only able to form kinins but can also convert angiotensin (Ang) I to Ang II. The aim of the present study was to clarify the structure and tissue localization of this enzyme. Western blot analysis of various canine tissues was performed with antiserum against the purified dog heart enzyme. The purified enzyme was subjected to a determination of its amino acid composition and a sequence analysis. Western blotting indicated that this enzyme was present in the heart, aorta, kidney, pancreas, lung, liver, spleen, small intestine, and skeletal muscle. The amino acid composition of the enzyme was different from that of dog urinary kallikrein. Amino acid sequence analysis indicated that it is likely to be N-terminally blocked. The present study showed that this kallikrein-like enzyme is different from previously reported kallikrein and is distributed not only in the heart, but also in other tissues such as the aorta, kidney, lung, liver, spleen, small intestine, and skeletal muscle. This enzyme may exert local effects by generating kinins and Ang II.

Cardioprotective effects of the aminopeptidase P inhibitor apstatin: studies on ischemia/reperfusion injury in the isolated rat heart

Aminopeptidase P and angiotensin-converting enzyme (ACE) are responsible for the metabolism of exogenously administered bradykinin in the coronary circulation of the rat. It has been shown that ACE inhibitors decrease cytosolic enzyme release from the ischemic rat heart and reduce reperfusion-induced ventricular arrhythmias by increasing endogenous levels of bradykinin. It was hypothesized that the aminopeptidase P inhibitor apstatin could do the same. In an isolated perfused rat heart preparation subjected to global ischemia and reperfusion, both apstatin and ramiprilat (an ACE inhibitor) significantly decreased creatine kinase (CK) and lactate dehydrogenase (LDH) release. The difference between the postischemia and preischemia levels of released CK was reduced 68% by apstatin and 68% by ramiprilat compared with control. The corresponding reductions in LDH release were 74% for apstatin and 81% for ramiprilat. A combination of the inhibitors was not significantly better than either one alone. Apstatin and ramiprilat also significantly reduced the duration of reperfusion-induced ventricular fibrillation by 69 and 61%, respectively. The antiarrhythmic effect of apstatin was reversed by HOE140, a bradykinin B2-receptor antagonist, suggesting that apstatin is acting by potentiating endogenously formed bradykinin. The results demonstrate that the aminopeptidase P inhibitor apstatin is cardioprotective in this model of cardiac ischemia/ reperfusion injury.

Effects of the insurmountable angiotensin AT1 receptor antagonist candesartan and the surmountable antagonist losartan on ischemia/reperfusion injury in rat hearts

Two angiotensin AT1 receptor antagonists with different receptor binding characteristics, candesartan (insurmountable antagonism) and losartan (surmountable antagonism), were compared as regards their effects on angiotensin II-induced vasoconstriction and on myocardial ischemia/reperfusion injury. In isolated rat hearts perfused under constant flow, it was found that at equipotent concentrations candesartan (10 nM) and losartan (3 microM) almost completely inhibited the angiotensin II-induced increase in coronary perfusion pressure. However, if a washout period was introduced before the angiotensin II challenge, the effect of losartan quickly vanished, while that of candesartan remained. In hearts subjected to 25 min of global ischemia and 45 min of reperfusion, pre-treatment with candesartan (10 nM) or losartan (3 microM) immediately prior to ischemia improved the recovery of left ventricular developed pressure as compared to the effect of vehicle (69 +/- 3.2 and 64 +/- 2.3 vs. 44 +/- 6.2%, respectively; mean +/- S.E.M, P < 0.05). When ischemia was initiated following 30 min of washout after drug administration, the recovery of left ventricular developed pressure was higher in the candesartan group (73 +/- 3.2%, P < 0.05), but not in the losartan group (63 +/- 2.8%), than in the vehicle group (58 +/- 4.8%). The cumulative creatine kinase release during the first 30 min of reperfusion in the washout experiments was lower in the candesartan group (28.5 +/- 2.30 U, P < 0.05), but not in the losartan (40.8 +/- 6.73 U) group, than in the vehicle group (48.1 +/- 4.35 U). No significant difference between groups in left ventricular end-diastolic pressure and coronary perfusion pressure was found. The present results demonstrate that angiotensin AT1 receptor antagonists at equipotent concentrations could differ in their cardioprotective effects in hearts subjected to ischemia/reperfusion. It is suggested that the insurmountable AT1 receptor characteristics of candesartan could provide more persistent cardioprotection than the surmountable receptor characteristics of losartan.

EXP3174, the AII antagonist human metabolite of losartan, but not losartan nor the angiotensin-converting enzyme inhibitor captopril, prevents the development of lethal ischemic ventricular arrhythmias in a canine model of recent myocardial infarction

OBJECTIVES

The antiarrhythmic efficacies of the competitive angiotensin II (AII) antagonist losartan, losartan's more potent noncompetitive AII antagonist human metabolite EXP3174 and the angiotensin-converting enzyme inhibitor captopril were assessed in a canine model of recent myocardial infarction.

BACKGROUND

Multiple hemodynamic and electrophysiologic effects of AII may contribute to cardiac electrical instability. In the recent Losartan Heart Failure Study, Evaluation of Losartan in the Elderly (ELITE), a 722-patient trial primarily designed to assess effects on renal function, an unexpected survival benefit was observed with losartan compared with captopril, with the lower mortality using losartan primarily confined to a reduction in sudden cardiac death.

METHODS

Intravenous losartan (1 mg/kg + 0.03 mg/kg/min), EXP3174 (0.1 mg/kg + 0.01 mg/kg/min), captopril (1 mg/kg + 0.5 mg/kg/h) or vehicle were infused in anesthetized dogs with recent (8.1 +/- 0.4 days) anterior myocardial infarction. Electrolytic injury of the left circumflex coronary artery to induce thrombotic occlusion and posterolateral ischemia was initiated 1 h after the start of treatment.

RESULTS

Losartan, EXP3174 and captopril elevated plasma renin activities and comparably and significantly reduced mean arterial pressure. No significant electrocardiographic or cardiac electrophysiologic effects were noted with any treatment. Incidences of acute posterolateral ischemia-induced lethal arrhythmias were: vehicle, 7/9 (77%); losartan, 6/8 (75%); EXP3174, 2/8 (25%; p < 0.05 vs. vehicle control); captopril, 7/10 (70%). There were no among-group differences in time to onset of acute posterolateral ischemia or underlying anterior infarct size.

CONCLUSIONS

EXP3174, but not losartan nor captopril, reduced the incidence of lethal ischemic ventricular arrhythmia in this preparation. The antiarrhythmic efficacy of EXP3174 may be due to an attenuation of deleterious effects of local cardiac AII formed during acute myocardial ischemia or, alternatively, a non-AII-related activity specific to EXP3174. These findings suggest that in humans, metabolic conversion of losartan to EXP3174 may afford antiarrhythmic protection.

Myocardial bradykinin production during coronary balloon angioplasty in humans

BACKGROUND

Recent studies have implicated the peptide bradykinin as a potential trigger of ischaemic preconditioning, the phenomenon whereby a brief episode of myocardial ischaemia induces an increased tolerance to subsequent more prolonged ischaemia. Brief myocardial ischaemia occurring during percutaneous transluminal coronary balloon angioplasty in humans is reported to be capable of inducing preconditioning.

DESIGN

We studied the intracardiac production of bradykinin in eight patients (seven men, mean age 53.5 years) undergoing elective percutaneous transluminal coronary angioplasty for a single left anterior descending coronary artery stenosis. Paired blood samples were obtained from the coronary sinus and the proximal aorta at baseline, immediately before balloon deflation after a 2-min inflation, and at 1, 3 and 5 min post deflation. Bradykinin levels were measured by radioimmunoassay.

RESULTS

There was no significant change either in aortic or coronary sinus bradykinin levels at any time point.

CONCLUSIONS

Intracardiac production of bradykinin is unlikely to be a trigger for ischaemic preconditioning after brief myocardial ischaemia in humans.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

A role for the renin-angiotensin system in the evolution of cardiac memory

INTRODUCTION

We studied the role of the cardiac renin-angiotensin II system in the genesis of cardiac memory, in which T wave changes induced by ventricular pacing (VP) accumulate and persist during subsequent sinus rhythm.

METHODS AND RESULTS

Anesthetized dogs were instrumented via a thoracotomy and three 20-minute runs of VP were interspersed with periods of normal sinus rhythm sufficient to permit T wave recovery to 90% of control. Memory was quantified as the change (delta) in T wave vector angle showing accumulation over the three monitoring periods. In five control dogs T wave vector = -27 +/- 49 degrees, and this shifted by 104 degrees (P < 0.05) over the three postpacing recovery periods. In seven dogs infused with the receptor blocker saralasin, five infused with the angiotensin-converting enzyme inhibitor captopril, and four infused with the tissue protease inhibitor chymostatin, there were significant reductions in the incidence and the accumulation of memory. In four other experiments, we used isolated, blood-perfused canine hearts to demonstrate that VP used to induce memory alters the contractile pattern of the left ventricle.

CONCLUSIONS

We propose that the alteration in myocardial stretch induced by pacing activates angiotensin II synthesis by cardiac cells. We propose, further that the endogenous cardiac renin-angiotensin II system (blocked by saralasin, captopril and by chymostatin) is an important contributor to the induction of memory.

Infarct size reduction by AT1-receptor blockade through a signal cascade of AT2-receptor activation, bradykinin and prostaglandins in pigs

OBJECTIVE

We studied the effect of the angiotensin II type 1 (AT1)-receptor antagonist candesartan on infarct size resulting from regional myocardial ischemia in pigs.

BACKGROUND

The effects of AT1-receptor blockade on infarct size in different species remain controversial and its potential cardioprotective mechanisms are still unclear. In pigs, infarct development closely resembles that observed in humans.

METHODS

A total of 62 enflurane-anesthetized pigs underwent a protocol of 90-min low-flow ischemia and 120-min reperfusion. Systemic hemodynamics (micromanometer), regional myocardial function (sonomicrometry), regional myocardial blood flow (microspheres) and infarct size (TTC [triphenyl tetrazolium chloride]-staining) were determined.

RESULTS

Left ventricular peak pressure decreased with candesartan (1 mg/kg i.v.) from 97+/-2 standard error of the mean (SEM) to 86+/-5 mm Hg and was then readjusted by aortic banding. In placebo pigs (n=9), infarct size was 21.8+/-4.8% of the area at risk. Candesartan (n=7) reduced infarct size to 9.7+/-2.5% (p < 0.05). Pretreatment with the AT2-receptor antagonist PD123319 (3 microg/kg/min intracoronarily [i.c.]; n=8), the bradykinin B2-receptor antagonist HOE140 (0.01 microg/kg/min i.c.; n=8) or the cyclooxygenase inhibitor indomethacin (10 mg/kg i.v.; n= 8) per se did not affect infarct size but did abolish the reduction of infarct size achieved by candesartan (PD123319 + candesartan (n=7): 23.2+/-4.7%; HOE140 + candesartan (n=7): 18.2+/-4.0%; indomethacin + candesartan (n=8): 21.1+/-5.2%). Hemodynamics, regional myocardial blood flow during ischemia and the area at risk were comparable among all groups of pigs.

CONCLUSIONS

Reduction of infarct size by the AT1-receptor antagonist candesartan in pigs involves angiotensin II type 2 receptor (AT2) activation, bradykinin and prostaglandins.