Angiotensin-converting enzyme inhibition improves cardiac function. Role of bradykinin

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

Sinapic Acid Attenuates Cardiovascular Disorders in Rats by Modulating Reactive Oxygen Species and Angiotensin Receptor Expression

The main avoidable risk factor for cardiovascular conditions is high blood pressure (hypertension). At global level, hypertension is believed to be responsible for a 54% stroke-related mortality rate and a 47% mortality rate associated with coronary heart disease. It is postulated that sinapic acid (SA) could help in hypertension management because it displays robust antioxidant, antihyperglycemic, and peroxynitrite scavenging effects. To explore this hypothesis, this work examined the effect of SA on oxidative stress and cardiovascular disease in rats with hypertension by comparison against captopril. For this purpose, 50 male rats were used and equally allocated to five groups, namely, normal control, positive control (L-NAME), L-NAME with concomitant captopril administration, L-NAME with concomitant SA administration, and L-NAME with concomitant administration of both SA and captopril. Results showed that, by contrast to control, L-NAME exhibited marked elevation in serum CK-MB, total cholesterol, triglycerides, VLDL-C, LDL-C, Ang II, AT2R, ET-1, and angiopoietin-2; on the other hand, L-NAME exhibited marked reduction in serum HDL-C, superoxide dismutase (SOD) activity, nitric oxide synthase 3 (NOS3), and glutathione (GSH). Furthermore, joint administration of SA and captopril ameliorated hypertension, enhanced cardiovascular function, hindered hyperlipidemia, and decreased oxidative stress and myocardial hypertrophy displayed by rats with hypertension. Based on such findings, better chemopreventive or therapeutic approaches can be devised to manage hypertension and cardiovascular conditions.

Comparative efficacy of empagliflozin and drugs of baseline therapy in post-infarct heart failure in normoglycemic rats

The study aimed to investigate the effects of the sodium-glucose co-transporter 2 (SGLT2) inhibitor empagliflozin on chronic heart failure (HF) in normoglycemic rats. The effects of empagliflozin were compared with the standard medications for HF, e.g., angiotensin-converting enzyme (ACE) inhibitor fosinopril, beta-blocker bisoprolol, and aldosterone antagonist spironolactone. Myocardial infarction (MI) was induced in male Wistar rats via permanent ligation of the left descending coronary artery. One-month post MI, 50 animals were randomized into 5 groups (n = 10): vehicle-treated, empagliflozin (1.0 mg/kg), fosinopril (10 mg/kg), bisoprolol (10 mg/kg), and spironolactone (20 mg/kg). All medications except empagliflozin were titrated within a month and administered per os daily for 3 months. Echocardiography, 24-hour urine volume test, and treadmill exercise tests were performed at the beginning and at the end of the study. Treatment with empagliflozin slowed the progression of left ventricular dysfunction: LV sizes and ejection fraction were not changed and the minute volume was significantly increased (from 52.0 ± 15.5 to 61.2 ± 21.2 ml/min) as compared with baseline. No deaths occurred in empagliflozin group. The 24-hour urine volume tends to be higher in empagliflozin and spironolactone groups than in vehicle and fosinopril group. Moreover, empagliflozin exhibited maximal physical exercise tolerance in comparison with all investigated groups (289 ± 27 s versus 183 ± 61 s in fosinopril group, 197 ± 95 s in bisoprolol group, and 47 ± 46 s in spironolactone group, p = 0.0035 for multiple comparisons). Sodium-glucose co-transporter 2 inhibitor empagliflozin reduced progression of left ventricular dysfunction and improved tolerance of physical exercise in normoglycemic rats with HF. Empagliflozin treatment was superior with respect to physical tolerance compared with fosinopril, bisoprolol, and spironolactone.

A Phytochemical in the Edible Tamogi-take Mushroom (Pleurotus cornucopiae),D-Mannitol, Inhibits ACE Activity and Lowers the Blood Pressure of Spontaneously Hypertensive Rats

D-Mannitol, one of the main phytochemicals of the edible Tamogi-take mushroom (Pleurotus cornucopiae), was found to inhibit an angiotensin I converting enzyme (ACE). The antihypertensive effect of D-mannitol and a hot water extract of Tamogi-take mushroom was demonstrated in spontaneously hypertensive rats (SHR) by oral administration.

Angiotensin-converting enzyme I/D polymorphism is associated with pneumonia risk: a meta-analysis

BACKGROUND

Previous studies examined the association between angiotensin-converting enzyme (ACE) I/D polymorphism and pneumonia, but their results were inconsistent. Thus, a meta-analysis was performed to clarify the effect of ACE I/D polymorphism on pneumonia risk and pneumonia-related mortality.

METHODS

The PubMed, Embase, and Chinese National Knowledge Infrastructure (CNKI) databases were searched for relevant studies published up to 27 April 2013. Data were extracted and pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.

RESULTS

Pooled analysis of 12 case-control studies (1431 cases and 3600 controls) showed that there was a significant association between ACE I/D polymorphism and pneumonia risk in a recessive genetic model (OR = 1.53, 95% CI 1.30-1.80, p < 0.00001). No significant association between ACE I/D polymorphism and mortality was observed (OR = 2.68, 95% CI 0.80-8.90, p = 0.11).

CONCLUSIONS

Our meta-analysis confirmed that ACE I/D polymorphism was associated with pneumonia risk. However, ACE I/D polymorphism was not associated with pneumonia mortality.

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.

Different cross-talk sites between the renin-angiotensin and the kallikrein-kinin systems

Targeting the renin-angiotensin system (RAS) constitutes a major advance in the treatment of cardiovascular diseases. Evidence indicates that angiotensin-converting enzyme inhibitors and angiotensin AT1 receptor blockers act on both the RAS and the kallikrein-kinin system (KKS). In addition to the interaction between the RAS and KKS at the level of angiotensin-converting enzyme catalyzing both angiotensin II generation and bradykinin degradation, the RAS and KKS also interact at other levels: 1) prolylcarboxypeptidase, an angiotensin II inactivating enzyme and a prekallikrein activator; 2) kallikrein, a kinin-generating and prorenin-activating enzyme; 3) angiotensin-(1-7) exerts kininlike effects and potentiates the effects of bradykinin; and 4) the angiotensin AT1 receptor forms heterodimers with the bradykinin B2 receptor. Moreover, angiotensin II enhances B1 and B2 receptor expression via transcriptional mechanisms. These cross-talks explain why both the RAS and KKS are up-regulated in some circumstances, whereas in other circumstances both systems change in the opposite manner, expressed as an activated RAS and a depressed KKS. As the cross-talks between the RAS and the KKS play an important role in response to different stimuli, taking these cross-talks between the two systems into account may help in the development of drugs targeting the two systems.

Cardiac systolic function recovery after hemorrhage determines survivability during shock

BACKGROUND

Small animal model has not been available to study cardiac pathophysiology during hemorrhagic shock. The main purpose of this study, therefore, was to establish earlier differences in left ventricle functional disturbances during hypovolemia comparable in survival and nonsurvival animals. Ventricular pressure-volume relationships have become well established as the most rigorous and comprehensive venue to assess intact heart function.

METHODS

Studies were performed in anesthetized hamsters subjected to a 40% of blood volume hemorrhage to induce the hypovolemic shock. A miniaturized conductance catheter was used to measure left ventricular pressure and volume. Derived from the pressure-volume measurements, cardiac performance was evaluated using systolic and diastolic function indices.

RESULTS

Thirteen animals were included; all animals survived the hemorrhage. Survival rate after 30 minutes of hypovolemic shock was 61.5%. End-systolic pressure was improved at the late stage of shock in the survival group, whereas no change of this index was found in the nonsurvival group. No significant differences in end-diastolic pressure and relaxation time constant were found between the nonsurvival and the survival groups. Fifteen minutes after the hemorrhage, the stroke work per stroke volume ratio significantly improved in the survival compared with nonsurvival, which also restored blood pressure.

CONCLUSION

The unique advantage of the pressure-volume methodology over all other available approaches to measure cardiac function is that it enables more specific measurement of the left ventricle performance independently from loading conditions and heart rate. Our findings demonstrated that failure to recover cardiac systolic function after hemorrhage, is a major determinant of mortality during hypovolemic shock.

Alterations of cardiac ERK1/2 expression and activity due to volume overload were attenuated by the blockade of RAS

The activities and protein content of extracellular signal-regulated kinase (ERK)1/2 in the heart were measured in rats at 4 and 16 weeks after volume overload due to aortocaval shunt. Protein content of phosphorylated ERK1/2 was increased at both 4 and 16 weeks, whereas protein content of total ERK1/2 was increased only at 16 weeks of inducing volume overload. The ERK1/2 activities, estimated as phospho-Elk-1 content, were also increased at 4 and 16 weeks of inducing volume overload. The increased phosphorylated ERK1/2 and E-26-like (Elk)-1 protein content in 16 weeks failing hearts was much greater than that in 4 weeks hypertrophied hearts. These changes in phosphorylated ERK1/2 and Elk-1 protein content in both 4 and 16 weeks volume overloaded animals were attenuated by treatment with enalapril and/or losartan. The results indicate that activation of ERK1/2 may be involved in the development of cardiac hypertrophy and heart failure due to volume overload, and these changes are partially prevented by blockade of the renin-angiotensin system (RAS).

Additional salutary effects of the combination of exercise training and an angiotensin-converting enzyme inhibitor on the left ventricular function of spontaneously hypertensive rats

OBJECTIVES

To investigate whether the combination of exercise training with the angiotensin-converting enzyme inhibitor lisinopril will have an additional beneficial effect on left ventricular function in spontaneously hypertensive rats.

DESIGN

Twelve-week-old male rats were assigned to treadmill running (Ht-Ex; 20 m/min at 5 degrees grade, 1 h/day, 5 days/week), or lisinopril treatment (Ht-Lis; 15 mg/kg per day by gavage), or treadmill running while treated with lisinopril (Ht-ExLis), and were compared with a sedentary group (Ht-Sed). Age-matched and sex-matched Wistar-Kyoto rats were controls.

METHODS

After 10 weeks of experimentation, left ventricular morphology and function were assessed from M-mode echocardiograms and transmitral Doppler spectra [early (E) and atrial peak velocities (A), their ratio (E/A), and E-wave deceleration time (Edec time) and slope (Edec slope)].

RESULTS

Ht-Sed exhibited prominent concentric left ventricular hypertrophy with systolic and diastolic dysfunctions evidenced by a significantly reduced fractional shortening (%FS) and 'pseudonormalization' of left ventricular filling, characterized by an apparently normal E/A ratio despite an underlying left ventricular relaxation abnormality. Exercise training did not significantly alter left ventricular morphology or function. Lisinopril alone attenuated left ventricular hypertrophy and enhanced diastolic function but had no significant effect on systolic function. Combining exercise training with lisinopril treatment increased %FS by 25%, decreased the E/A ratio and Edec slope by 35% and 37%, respectively, and increased Edec time by 82%.

CONCLUSION

Our results provide experimental evidence that lisinopril administration, when combined with moderate exercise training, is more promising in attenuating cardiac dysfunction than either agent alone in hypertension of a genetic origin.

Both enalapril and losartan attenuate sarcolemmal Na+-K+-ATPase remodeling in failing rat heart due to myocardial infarctionThis article is one of a selection of papers published in the special issue Bridging the Gap: Where Progress in Cardiovascular and Neurophysiologic Research Meet

To investigate the mechanisms underlying the depressed sarcolemmal (SL) Na+-K+-ATPase activity in congestive heart failure (CHF), different isoforms and gene expression of Na+-K+-ATPase were examined in the failing left ventricle (LV) at 8 weeks after myocardial infarction (MI). In view of the increased activity of renin–angiotensin system (RAS) in CHF, these parameters were also studied after 5 weeks of treatment with enalapril (10 mg·kg–1·day–1), an angiotensin-converting enzyme inhibitor, and losartan (20 mg·kg–1·day–1), an angiotensin II type 1 receptor antagonist, starting at 3 weeks after the coronary ligation in rats. The infarcted animals showed LV dysfunction and depressed SL Na+-K+-ATPase activity. Protein content and mRNA levels for Na+-K+-ATPase α2isoform were decreased whereas those for Na+-K+-ATPase α3isoform were increased in the failing LV. On the other hand, no significant changes were observed in protein content or mRNA levels for Na+-K+-ATPase α1and β1isoforms. The treatment of infarcted animals with enalapril or losartan improved LV function and attenuated the depression in Na+-K+-ATPase α2isoform as well as the increase in α3isoform, at both the protein and mRNA levels; however, combination therapy with enalapril and losartan did not produce any additive effects. These results provide further evidence that CHF due to MI is associated with remodeling of SL membrane and suggest that the blockade of RAS plays an important role in preventing these alterations in the failing heart.

ACE inhibitor reduces growth factor receptor expression and signaling but also albuminuria through B2-kinin glomerular receptor activation in diabetic rats

Diabetic nephropathy (DN) is associated with increased oxidative stress, overexpression and activation of growth factor receptors, including those for transforming growth factor-β1 (TGF-β-RII), platelet-derived growth factor (PDGF-R), and insulin-like growth factor (IGF1-R). These pathways are believed to represent pathophysiological determinants of DN. Beyond perfect glycemic control, angiotensin-converting enzyme inhibitors (ACEI) are the most efficient treatment to delay glomerulosclerosis. Since their mechanisms of action remain uncertain, we investigated the effect of ACEI on the glomerular expression of these growth factor pathways in a model of streptozotocin-induced diabetes in rats. The early phase of diabetes was found to be associated with an increase in glomerular expression of IGF1-R, PDGF-R, and TGF-β-RII and activation of IRS1, Erk 1/2, and Smad 2/3. These changes were significantly reduced by ACEI treatment. Furthermore, ACEI stimulated glutathione peroxidase activity, suggesting a protective role against oxidative stress. ACEI decreased ANG II production but also increased bradykinin bioavailability by reducing its degradation. Thus the involvement of the bradykinin pathway was investigated using coadministration of HOE-140, a highly specific nonpeptidic B2-kinin receptor antagonist. Almost all the previously described effects of ACEI were abolished by HOE-140, as was the increase in glutathione peroxidase activity. Moreover, the well-established ability of ACEI to reduce albuminuria was also prevented by HOE-140. Taken together, these data demonstrate that, in the early phase of diabetes, ACEI reverse glomerular overexpression and activation of some critical growth factor pathways and increase protection against oxidative stress and that these effects involve B2-kinin receptor activation.

Effects of angiotensin-converting enzyme inhibitor and exercise training on exercise capacity and skeletal muscle

OBJECTIVE

Physical fitness is closely related with cardiovascular health. We examined the effects of angiotensin-converting enzyme inhibitor, exercise training and their combination on exercise capacity as well as skeletal muscle fiber type and capillarity in spontaneously hypertensive rats (SHR).

METHODS

Seven-week-old male SHR were allocated to four groups: sedentary control (C), treatment with perindopril (3 mg/kg per day) (Per), exercise training on a treadmill (EX), and their combination (Per + EX). Following 8-week interventions, rats were submitted to a stepwise exercise test on a treadmill. After experiments, fiber type and capillarity in soleus muscle were examined.

RESULTS

Exercise capacity significantly increased in Per compared with in C. Combination of exercise training and perindopril further increased exercise capacity compared with perindopril alone, whereas there was no significant difference in exercise capacity between EX and Per + EX. Capillary density increased similarly in Per and EX compared with in C. Combination of exercise training and perindopril further increased capillary density compared with exercise training alone. The percentage of type I fiber increased only in Per + EX.

CONCLUSIONS

We found that in growing SHR, chronic treatment with perindopril enhances untrained exercise capacity, while it does not affect acquired exercise capacity as a result of exercise training. We also found that perindopril promotes adaptive changes of skeletal muscle in response to exercise such as increases in capillary density and percentage of type I fiber.

Effect of Ganoderma lucidum on the quality and functionality of Korean traditional rice wine, yakju

The goal of this study was to develop a high value Korean traditional rice wine possessing the pharmaceutical functionality of Ganoderma lucidum. The effects of the fruiting body of G. lucidum on the alcohol fermentation of Korean traditional rice wine, yakju, were investigated. Optimal fermentation conditions for the preparation of G. lucidum-yakju consisted of the koji added at 15% and a fermentation period of 15 d at 25 degrees C. The effects of the amount of G. lucidum added on the acceptability and functionality of G. lucidum-yakju were investigated. G. lucidum GL-1 yakju brewed by adding 0.1% G. lucidum into the mash showed the best acceptability and its angiotensin I-converting enzyme (ACE) inhibitory activity and SOD-like activity were 63% and 42%, respectively, both of which are higher than those of yakju. The high ACE inhibitory activity of G. lucidum GL-1 yakju was found to result from ganoderic acid K in G. lucidum on the basis of physical and spectral data. However, the fibrinolytic activity and antioxidant activity of G. lucidum GL-1 yakju were very low, while tyrosinase inhibitory activity was not determined. From these results, G. lucidum GL-1 yakju may become a new functional Korean traditional rice wine with antihypertensive properties.

Production of Antihypertensive Angiotensin I-Converting Enzyme Inhibitor from Malassezia pachydermatis G-14

To produce a novel antihypertensive angiotensin I-converting enzyme (ACE) inhibitor from yeast, a yeast isolate, designated G-14 showing the highest ACE inhibitory activity was obtained and identified as Malassezia pachydermatis based on morphological, biochemical and cultural characteristics. The maximal extracellular ACE inhibitor production was obtained from M. pachydermatis G-14 when the strain was cultured in YEPD medium containing 0.5% yeast extract, 3.0% peptone and 2.0% glucose at 30℃ for 24 h and the final ACE inhibitory activity was 48.9% under the above condition.

Modification of sarcolemmal Na+-K+-ATPase and Na+/Ca2+exchanger expression in heart failure by blockade of renin-angiotensin system

The activities of both sarcolemmal (SL) Na+-K+-ATPase and Na+/Ca2+exchanger, which maintain the intracellular cation homeostasis, have been shown to be depressed in heart failure due to myocardial infarction (MI). Because the renin-angiotensin system (RAS) is activated in heart failure, this study tested the hypothesis that attenuation of cardiac SL changes in congestive heart failure (CHF) by angiotensin-converting enzyme (ACE) inhibitors is associated with prevention of alterations in gene expression for SL Na+-K+-ATPase and Na+/Ca2+exchanger. CHF in rats due to MI was induced by occluding the coronary artery, and 3 wk later the animals were treated with an ACE inhibitor, imidapril (1 mg·kg−1·day−1), for 4 wk. Heart dysfunction and cardiac hypertrophy in the infarcted animals were associated with depressed SL Na+-K+-ATPase and Na+/Ca2+exchange activities. Protein content and mRNA levels for Na+/Ca2+exchanger as well as Na+-K+-ATPase α1-, α2- and β1-isoforms were depressed, whereas those for α3-isoform were increased in the failing heart. These changes in SL activities, protein content, and gene expression were attenuated by treating the infarcted animals with imidapril. The beneficial effects of imidapril treatment on heart function and cardiac hypertrophy as well as SL Na+-K+-ATPase and Na+/Ca2+exchange activities in the infarcted animals were simulated by enalapril, an ACE inhibitor, and losartan, an angiotensin receptor antagonist. These results suggest that blockade of RAS in CHF improves SL Na+-K+-ATPase and Na+/Ca2+exchange activities in the failing heart by preventing changes in gene expression for SL proteins.

Long-term exercise training and angiotensin-converting enzyme inhibition differentially enhance myocardial capillarization in the spontaneously hypertensive rat

OBJECTIVES

To investigate whether combined treatment with lisinopril, an angiotensin-converting enzyme (ACE) inhibitor and exercise training would have an additive effect in enhancing the capillary supply of the left ventricular (LV) myocardium in spontaneously hypertensive rats (SHR).

DESIGN

Twelve-week-old male SHR were divided into four groups (10-12 each): sedentary, sedentary treated with lisinopril (15-20 mg/kg per day by gavage), exercise trained, and exercise trained while treated with lisinopril. Exercise training consisted of 1 h a day/5 days a week of running on a treadmill.

METHODS

After 10 weeks of experimental protocols, capillary surface density and length density were sterologically determined in 1 mum thick LV tissue samples from perfuse-fixed hearts.

RESULTS

Lisinopril significantly reduced systolic blood pressure (SBP) and LV mass in the sedentary with lisinopril and exercise trained with lisinopril groups but did not affect the heart rate (HR). Exercise training did not reduce SBP or LV mass, but significantly reduced HR in the exercise trained and exercise trained with lisinopril groups. Lisinopril treatment (sedentary with lisinopril), exercise training (exercise) and their combination (exercise trained with lisinopril) significantly increased myocardial capillary surface area density by 26, 38 and 65% and length density by 38, 48 and 67%, respectively.

CONCLUSION

Lisinopril administration and exercise training independently enhanced myocardial capillarization through a reduction of myocardial mass and stimulation of angiogenesis, respectively. A combination of the two treatments enhanced myocardial capillarization more than either intervention alone. This may aid in the restoration of the normal nutritional status of cardiac myocytes compromised by the hypertrophic state of hypertension.

Sarcoplasmic reticulum Ca2+ transport and gene expression in congestive heart failure are modified by imidapril treatment

This study was designed to test the hypothesis that blockade of the renin-angiotensin system improves cardiac function in congestive heart failure by preventing changes in gene expression of sarcoplasmic reticulum (SR) proteins. We employed rats with myocardial infarction (MI) to examine effects of an angiotensin-converting enzyme inhibitor, imidapril, on SR Ca2+ transport, protein content, and gene expression. Imidapril (1 mg·kg−1·day−1) was given for 4 wk starting 3 wk after coronary artery occlusion. Infarcted rats exhibited a fourfold increase in left ventricular end-diastolic pressure, whereas rates of pressure development and decay were decreased by 60 and 55%, respectively. SR Ca2+ uptake and Ca2+ pump ATPase, as well as Ca2+ release and ryanodine receptor binding activities, were depressed in the failing hearts; protein content and mRNA levels for Ca2+ pump ATPase, phospholamban, and ryanodine receptor were also decreased by ∼55–65%. Imidapril treatment of infarcted animals improved cardiac performance and attenuated alterations in SR Ca2+ pump and Ca2+ release activities. Changes in protein content and mRNA levels for SR Ca2+ pump ATPase, phospholamban, and ryanodine receptor were also prevented by imidapril treatment. Beneficial effects of imidapril on cardiac function and SR Ca2+ transport were not only seen at different intervals of MI but were also simulated by another angiotensin-converting enzyme inhibitor, enalapril, and an ANG II receptor antagonist, losartan. These results suggest that blockade of the renin-angiotensin system may increase the abundance of mRNA for SR proteins and, thus, may prevent the depression in SR Ca2+ transport and improve cardiac function in congestive heart failure due to MI.

Imidapril treatment improves the attenuated inotropic and intracellular calcium responses to ATP in heart failure due to myocardial infarction

1. Adenosine 5'-triphosphate (ATP) is known to augment cardiac contractile activity and cause an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) in isolated cardiomyocytes. However, no information regarding the ATP-mediated signal transduction in the myocardium in congestive heart failure (CHF) is available. 2. CHF due to myocardial infarction (MI) in rats was induced by the occlusion of the left coronary artery for 8 weeks. The positive inotropy due to ATP was depressed in failing hearts. Treatment of 3 weeks infarcted animals with imidapril (1 mg kg(-1) day(-1)) for a period of 5 weeks improved the left ventricle function and decreased the attenuation of inotropic response to ATP. 3. ATP-induced increase in [Ca(2+)](i) was significantly depressed in cardiomyocytes isolated from the failing heart and this change was partially attenuated by imidapril treatment. However, the binding characteristics of (35)S-labeled adenosine 5'-(gamma-thio) triphosphate in sarcolemma isolated from the failing heart remained unaltered. 4. ATP-induced increase in [Ca(2+)](i) was depressed by verapamil and cibacron blue in both control and failing heart cardiomyocytes; however, the ATP response in the failing hearts, unlike the control preparations, was not decreased by ryanodine. This insensitivity to ryanodine was attenuated by imidapril treatment. 5. Treatment of infarcted rats with enalapril and losartan produced effects similar to imidapril. 6. These findings indicate that the positive inotropic response to ATP and ATP-induced increase in [Ca(2+)](i) in cardiomyocytes are impaired in heart failure. Furthermore, blockade of renin angiotensin system prevented the impairment of the ATP-mediated inotropic and [Ca(2+)](i) responses in the failing heart.

Marinobufagenin may mediate the impact of salty diets on left ventricular hypertrophy by disrupting the protective function of coronary microvascular endothelium

Individuals who eat salty diets and who are "salt-sensitive" tend to have increased left ventricular mass, independent of blood pressure; this phenomenon awaits an explanation. It is clear that local up-regulation of angiotensin II (AngII) production and activity play a key role in the induction of left ventricular hypertrophy (LVH). Recent evidence suggests that a healthy coronary microvascular endothelium opposes this effect by serving as a paracrine source of nitric oxide (NO), a natural antagonist of AngII activity, and that up-regulation of this mechanism can account for the protective role of bradykinin with respect to LVH. The coronary microvasculature also possesses NAD(P)H oxidase activity that can generate superoxide, inimical to the bioactivity of endothelial NO. There is now good reason to believe that the triterpenoid marinobufagenin (MBG), a selective inhibitor of the alpha-1 isoform of the sodium pump, mediates the impact of salty diets on blood pressure; production of MBG by the adrenal cortex is boosted when salt-sensitive animals are fed salty diets. It is hypothesized that coronary microvascular endothelium expresses the alpha-1 isoform of the sodium pump, and that MBG thus can target this endothelium. If that is the case, MBG would be expected to decrease membrane potential in these cells; as a consequence, superoxide production would be up-regulated, NO synthase activity would be down-regulated, and myocardial NO bioactivity would thus be suppressed. This would offer a satisfying explanation for the impact of salt and salt-sensitivity on risk for LVH. If expression of the alpha-1 isoform of the sodium pump is a more general property of vascular endothelium, MBG may suppress NO bioactivity in other regions of the vascular tree, thereby contributing to other adverse effects elicited by salty diets: reduced arterial compliance, medial hypertrophy, impaired endothelium-dependent vasodilation, hypertensive/diabetic glomerulopathy, increased risk for stroke, and hypertension.

Influence of long-term treatment of imidapril on mortality, cardiac function, and gene expression in congestive heart failure due to myocardial infarction

Although it is generally accepted that the efficacy of imidapril, an angiotensin-converting enzyme inhibitor, in congestive heart failure (CHF) is due to improvement of hemodynamic parameters, the significance of its effect on gene expression for sarcolemma (SL) and sarcoplasmic reticulum (SR) proteins has not been fully understood. In this study, we examined the effects of long-term treatment of imidapril on mortality, cardiac function, and gene expression for SL Na+/K+ATPase and Na+–Ca2+exchanger as well as SR Ca2+pump ATPase, Ca2+release channel (ryanodine receptor), phospholamban, and calsequestrin in CHF due to myocardial infarction. Heart failure subsequent to myocardial infarction was induced by occluding the left coronary artery in rats, and treatment with imidapril (1 mg·kg–1·day–1) was started orally at the end of 3 weeks after surgery and continued for 37 weeks. The animals were assessed hemody nam ically and the heart and lung were examined morphologically. Some hearts were immediately frozen at –70 °C for the isolation of RNA as well as SL and SR membranes. The mortality of imidapril-treated animals due to heart failure was 31% whereas that of the untreated heart failure group was 64%. Imidapril treatment improved cardiac performance, attenuated cardiac remodeling, and reduced morphological changes in the heart and lung. The depressed SL Na+/K+ATPase and increased SL Na+–Ca2+exchange activities as well as reduced SR Ca2+pump and SR Ca2+release activities in the failing hearts were partially prevented by imidapril. Although changes in gene expression for SL Na+/K+ATPase isoforms as well as Na+–Ca2+exchanger and SR phospholamban were attenuated by treatments with imidapril, no alterations in mRNA levels for SR Ca2+pump proteins and Ca2+release channels were seen in the untreated or treated rats with heart failure. These results suggest that the beneficial effects of imidapril in CHF may be due to improvements in cardiac performance and changes in SL gene expression.Key words: sarcolemmal Na+/K+ATPase, Na+–Ca2+exchange, sarcoplasmic reticulum, heart failure, ACE inhibition.

Modification of myosin protein and gene expression in failing hearts due to myocardial infarction by enalapril or losartan

The effects of enalapril, an angiotensin converting enzyme (ACE) inhibitor, and losartan, an angiotensin II receptor type I antagonist, were investigated on alterations in myofibrillar ATPase activity as well as myosin heavy chain (MHC) content and gene expression in failing hearts following myocardial infarction (MI). Three weeks after ligation of the left coronary artery, rats were treated with or without enalapril (10 mg/kg/day), and/or losartan (20 mg/kg/day) for 5 weeks. The infarcted animals exhibited an increase in left ventricle (LV) end diastolic pressure and depressed rates of LV pressure development as well as pressure decay. LV myofibrillar Ca2+ -stimulated ATPase activity was decreased in the infarcted hearts compared with controls, MHC alpha-isoform content was significantly decreased whereas that of MHC beta-isoform was markedly increased. The level of MHC alpha-isoform mRNA was decreased whereas that of MHC beta-isoform was increased in the viable infarcted LV. Treatment of animal with enalapril, losartan, or combination of enalapril and losartan partially prevented the MI induced changes in LV function, myofibrillar Ca2+ -stimulated ATPase activity, MHC protein expression and MHC gene expression. The results suggest that the beneficial effects of the renin-angiotensin system blockade in heart failure are associated with partial prevention of myofibrillar remodeling.

Hemodynamic effects of phosphodiesterase 5 and angiotensin-converting enzyme inhibition alone or in combination in conscious SHR

The regional hemodynamic responses to continuous 4-day infusion of UK-357,903 [1-ethyl-4-{3-[3-ethyl-6,7-dihydro-7-oxo-2-(2-pyridylmethyl)-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-2-(2-methoxyethoxy)-5-pyridylsulphonyl}piperazine] (266 microg kg(-1) h(-1)) alone and in combination with a low dose of enalapril (10 microg kg(-1) h(-1)) were measured in conscious spontaneously hypertensive rats to test the hypothesis that the renin-angiotensin system may influence the cardiovascular consequences of inhibition of phosphodiesterase 5 (PDE5) by UK-357,903 or vice versa. UK-357,903 alone caused a fall in mean blood pressure (-12.1 mm Hg) associated with vasodilatation in the mesenteric and hindquarters vascular beds. The only way in which the effects of enalapril given alone differed significantly from those of the vehicle was in causing mesenteric vasodilatation, which developed over the 4 days of infusion. UK-357,903 given in combination with enalapril caused hypotension (-17.8 mm Hg) and vasodilatation in the renal, mesenteric, and hindquarter vascular beds. There was evidence of a significant interaction between the effects of the two compounds on renal Doppler shift and vascular conductance with the combined action of the two compounds being greater than the sum of their individual effects. However, although there was a trend for the combination to have greater effects than either of the individual agents on blood pressure and mesenteric vascular conductance, there was no statistical evidence of an interaction. The results indicate that inhibition of the renin-angiotensin system uncovers additional renal vasodilator effects of UK-357,903, and/or inhibition of PDE5 enhances the renal vasodilator effects of angiotensin-converting enzyme inhibition.

Partial prevention of changes in SR gene expression in congestive heart failure due to myocardial infarction by enalapril or losartan

Although activation of the renin-angiotensin system (RAS) is known to produce ventricular remodeling and congestive heart failure (CHF), its role in inducing changes in the sarcoplasmic reticulum (SR) protein and gene expression in CHF is not fully understood. In this study, CHF was induced in rats by ligation of the left coronary artery for 3 weeks and then the animals were treated orally with or without an angiotensin converting enzyme inhibitor, enalapril (10 mg/kg/day) or an angiotensin II receptor antagonist, losartan (20 mg/kg/day) for 4 weeks. Sham-operated animals were used as control. The animals were hemodynamically assessed and protein content as well as gene expression of SR Ca(2+)-release channel (ryanodine receptor, RYR), Ca(2+)-pump ATPase (SERCA2), phospholamban (PLB) and calsequestrin (CQS) were determined in the left ventricle (LV). The infarcted animals showed cardiac hypertrophy, lung congestion, depression in LV +dP/dt and -dP/dt, as well as increase in LV end diastolic pressure. Both protein content and mRNA levels for RYR, SERCA2 and PLB were decreased without any changes in CQS in the failing heart. These alterations in LV function as well as SR protein and gene expression in CHF were partially prevented by treatment with enalapril or losartan. The results suggest that partial improvement in LV function by enalapril and losartan treatments may be due to partial prevention of changes in SR protein and gene expression in CHF and that these effects may be due to blockade of the RAS.

Nephroprotection in Zucker diabetic fatty rats by vasopeptidase inhibition is partly bradykinin B2 receptor dependent

1. Vasopeptidase inhibition (i.e., the simultaneous inhibition of both angiotensin-converting enzyme (ACE) and neutral endopeptidase) can ameliorate diabetic nephropathy. We investigated whether this nephroprotection is mediated by the bradykinin B2 receptor. 2. In all, 43 obese Zucker diabetic fatty (ZDF/Gmi-fa/fa) rats aged 21 weeks were separated into four groups and treated for 26 weeks with either placebo, the bradykinin B2 receptor antagonist icatibant (500 microg kg(-1) day(-1) s.c. infusion), the vasopeptidase inhibitor AVE7688 (45 mg kg(-1) day(-1) in chow), or AVE7688 plus icatibant. Nephropathy was assessed as albuminuria at age 31 and 39 weeks, and by histopathologic scoring at the end of the treatment period. 3. All animals had established diabetes mellitus (blood glucose >20 mmol l(-1)) and marked albuminuria at baseline. Blood glucose was not influenced by any treatment. Icatibant alone did not influence albuminuria (8.6+/-1.6 vs placebo 9.5+/-1.3 mg kg(-1) h(-1)). AVE7688 reduced albuminuria at week 31 markedly to 1.1+/-0.1 mg kg(-1) h(-1) and reduced glomerular and tubulo-interstitial kidney damage at week 47. In the AVE7688 plus icatibant group, proteinuria was significantly higher than in the AVE7688 only group (2.0+/-0.6 mg kg(-1) h(-1)), but still reduced compared to placebo. In addition, icatibant partly antagonized the tubulo-interstitial protection mediated by AVE7688. 4. We conclude that vasopeptidase inhibition provides nephroprotection in rats with type II diabetic nephropathy, which is partly mediated by bradykinin B2 receptor activation.

Marinobufagenin may mediate the impact of salty diets on left ventricular hypertrophy by disrupting the protective function of coronary microvascular endothelium

Individuals who eat salty diets and who are "salt-sensitive" tend to have increased left ventricular mass, independent of blood pressure; this phenomenon awaits an explanation. It is clear that local up-regulation of angiotensin II (AngII) production and activity play a key role in the induction of left ventricular hypertrophy (LVH). Recent evidence suggests that a healthy coronary microvascular endothelium opposes this effect by serving as a paracrine source of nitric oxide (NO), a natural antagonist of AngII activity, and that up-regulation of this mechanism can account for the protective role of bradykinin with respect to LVH. The coronary microvasculature also possesses NAD(P)H oxidase activity that can generate superoxide, inimical to the bioactivity of endothelial NO. There is now good reason to believe that the triterpenoid marinobufagenin (MBG), a selective inhibitor of the alpha-1 isoform of the sodium pump, mediates the impact of salty diets on blood pressure;production of MBG by the adrenal cortex is boosted when salt-sensitive animals are fed salty diets. It is hypothesized that coronary microvascular endothelium expresses the alpha-1 isoform of the sodium pump, and that MBG thus can target this endothelium. If that is the case, MBG would be expected to decrease membrane potential in these cells;as a consequence, superoxide production would be up-regulated, NO synthase activity would be down-regulated, and myocardial NO bioactivity would thus be suppressed. This would offer a satisfying explanation for the impact of salt and salt-sensitivity on risk for LVH. If expression of the alpha-1 isoform of the sodium pump is a more general property of vascular endothelium, MBG may suppress NO bioactivity in other regions of the vascular tree, thereby contributing to other adverse effects elicited by salty diets: reduced arterial compliance, medial hypertrophy, impaired endothelium-dependent vasodilation, hypertensive/diabetic glomerulopathy, increased risk for stroke, and hypertension.

From CONSENSUS to CHARM—how do ACEI and ARB produce clinical benefits in CHF?

Two decades of research from CONSENSUS to CHARM using modulators of the renin-angiotensin-aldosterone system (RAAS) in chronic heart failure (CHF) patients have shown convincing clinical benefits, but the majority of clinicians prescribing these drugs are still unclear about what mechanisms are responsible for the observed benefits. Of the candidate mechanisms hitherto proposed, there emerges a theme that best fits the spectrum of known factors from pathophysiology of heart failure to how the drugs enhance longevity of patients. This concept can be summarised as follows: after the onset of heart failure, neurohormones are activated resulting in raised levels of angiotensin, aldosterone and catecholamines, which are all known cardiotoxic agents. Cumulatively over time, they are responsible for accelerated cardiomyocyte attrition, manifesting as a faster reduction of cardiac pumping reserve, leading to worsening heart failure, more neurohormonal activation, thus propagating a vicious cycle spiralling towards an earlier fatality. The vicious cycle can be interrupted by dampening the excessive neurohormonal activities, thereby minimising cardiomyocyte losses and preserving cardiac functional reserve for longer. This culminates in maintenance of a reasonable quality of life and enhanced longevity. Such a mechanistic understanding would enable clinicians to have a better perspective on how to apply data from various clinical trials involving these drugs into clinical practice, to optimise and tailor therapy to the individual patient so that each patient can gain maximal benefits.

Isolation and characterization of a novel angiotensin I-converting enzyme inhibitory peptide derived from the edible mushroom Tricholoma giganteum

The fruiting body of Tricholoma giganteum has many pharmaceutical uses and has long been utilized as a home remedy in Asia. This study describes the extraction and characterization of the first angiotensin I-converting enzyme (ACE) inhibitory peptide from T. giganteum. The maximum ACE inhibitory activity (IC50: 0.31 mg) was obtained when the fruiting body of T. giganteum was extracted with distilled water at 30 degrees C for 3 h. After the purification of ACE inhibitory peptides with ultrafiltration, Sephadex G-25 column chromatography, and reverse-phase HPLC, an active fraction with an IC50 of 0.04 mg and a yield of 0.3% was obtained. The ACE inhibitory peptide was a novel tripeptide, showing very low similarity to other ACE inhibitory peptide sequences, and was sequenced as Gly-Glu-Pro. The purified ACE inhibitor from T. giganteum competitively inhibited ACE, and it maintained inhibitory activity even after incubation with proteases. ACE inhibitor from T. giganteum showed a clear antihypertensive effect in spontaneously hypertensive rats (SHR), at a dosage of 1 mg/kg.

Neutral endopeptidase expression in mesangial cells

In the kidney, neutral endopeptidase (NEP) is implicated in the metabolism of several peptides involved in blood pressure and sodium homeostasis control, such as the atrial natriuretic peptide, bradykinin and angiotensin I. Due to its physiological importance in the modulation of pressor responses, the presence of NEP in mouse mesangial cells has been investigated, since these cells control glomerular function and are able to synthesise components of the renin-angiotensin system. A NEP-like activity (NEP-like) that cleaves the fluorogenic substrates Abz-BKQ-EDDnp and Abz-DRRL-EDDnp was purified from mesangial cell lysate by ion-exchange, followed by gel filtration chromatography. The enzyme was able to hydrolyse bradykinin at the G4-F5 peptide bond and was inhibited by thiorphan. A pH study established that enzyme activity was maximal at pH 7.5 and the determined K(m) was 4.86 M using Abz-DRRL-EDDnp as substrate. NEP-like was recognised by monoclonal anti-NEP and had a molecular mass of 95 kDa. The purified enzyme was sequenced and showed similarity with human, rat, mouse and rabbit NEPs. We isolated, for the first time, NEP-like from mesangial cells. This enzyme could have an important role in the renal physiology by its action upon different peptides that are able to alter renal haemodynamics.

Effect of angiotensin AT2 receptor stimulation on vascular cyclic GMP production in normotensive Wistar Kyoto rats

In the present study in normotensive Wistar Kyoto rats (WKY), we investigated whether any angiotensin II (ANG II) increases in vascular cyclic GMP production were via stimulation of AT(2) receptors. Adult WKY were infused for 4h with ANG II (30 ng/kg per min, i.v.) or vehicle (0.9% NaCl, i.v.) after pretreatment with (1) vehicle, (2) losartan (100 mg/kg p.o.), (3) PD 123319 (30 mg/kg i.v.), (4) losartan+PD 123319, (5) icatibant (500 microg/kg i.v.), (6) L-NAME (1 mg/kg i.v.), (7) minoxidil (3 mg/kg i.v.). Mean arterial blood pressure (MAP) was continuously monitored, and plasma ANG II and aortic cyclic GMP were measured at the end of the study. ANG II infusion over 4h raised MAP by a mean of 13 mmHg. This effect was completely prevented by AT(1) receptor blockade. PD 123319 slightly attenuated the pressor effect induced by ANG II alone (123.4+/-0.8 versus 130.6+/-0.6) but did not alter MAP in rats treated simultaneously with ANG II + losartan (113+/-0.6 versus 114.3+/-0.8). Plasma levels of ANG II were increased 2.2-3.7-fold by ANG II infusion alone or ANG II in combination with the various drugs. The increase in plasma ANG II levels was most pronounced after ANG II+losartan treatment but absent in rats treated with losartan alone. Aortic cyclic GMP levels were not significantly changed by either treatment. Our results demonstrate that the AT(2) receptor did not contribute to the cyclic GMP production in the vascular wall of normotensive WKY.

Effects of ACE inhibition on myocardial apoptosis in an ischemia-reperfusion rat heart model

Myocardial ischemia-reperfusion injury involves necrosis and apoptosis. The inhibition of angiotensin-converting enzyme (ACE) has been reported to suppress infarct size. In this study, it was investigated whether an ACE inhibitor affected myocardial apoptosis and apoptosis-related proteins in rats with experimental myocardial infarction. Anesthetized Sprague-Dawley rats were divided into four groups. Group I underwent 30 minutes of left coronary artery occlusion followed by 24 hours of reperfusion (control group); Group II underwent oral administration of the ACE inhibitor quinapril (10 mg/kg/day) before coronary occlusion (quinapril group); Group III underwent administration of the bradykinin B(2)-receptor antagonist Hoe 140 (250 microg/kg/day, subcutaneously) with quinapril (quinapril + Hoe 140 group); and Group IV underwent administration of Hoe 140 alone (Hoe 140 group). After reperfusion, myocardial infarct size was determined by triphenyltetrazolium chloride staining. Myocardial apoptosis was detected immunohistologically using terminal deoxynucleotidyl transferase-mediated nick end labeling staining and DNA electrophoresis. Myocardial caspase-3 activation was analyzed by Western blot and the expressions of Bcl-xL and Bax proteins were detected immunohistochemically. Quinapril significantly reduced the ratio of myocardial infarct size in the ischemic area at risk. In addition, quinapril significantly suppressed the incidence of apoptotic myocytes around the necrotic region (from 18.9 +/- 0.8% to 8.6 +/- 1.0%; P < 0.0001), the intensity of DNA ladder formation, and the activation of caspase-3. Hoe 140 attenuated these protective effects of quinapril. In the immunohistochemical study, Bax and Bcl-xL were expressed in myocytes, and ischemia-reperfusion abolished both proteins in the center region of ischemia. The Bax staining was equally observed among all groups. However, Bcl-xL staining remained in the ischemic area widely after quinapril treatment. In addition, Hoe 140 also depleted this effect of quinapril. These results suggest that inhibition of ACE reduces myocardial infarction and apoptosis via the bradykinin B(2) receptor in part. The antiapoptotic effect of the ACE inhibitor is attributed to the changing expression of Bcl-xL.

Omapatrilat induces profound renal vasodilation but does not affect coronary hemodynamics

BACKGROUND

Omapatrilat has potent enzymatic inhibitory effects on the angiotensin-converting enzyme and neutral endopeptidase. The prolonged effects of this inhibition on systemic and regional hemodynamics, cardiovascular mass, and hydroxyproline concentration in spontaneously hypertensive rats were studied. The contribution of endogenous bradykinin on the cardiovascular actions of omapatrilat in this genetic model of hypertension was also investigated.

METHODS AND RESULTS

Systemic and regional hemodynamics (radionuclide-labeled microspheres), left and right ventricular and aortic masses, and hydroxyproline concentration were determined in 35-week-old spontaneously hypertensive rats after 12 weeks of treatment with omapatrilat (40 mg/kg/day), with and without the bradykinin receptor antagonist icatibant (500 microg/kg/day). Omapatrilat decreased mean arterial pressure, reducing total peripheral resistance as well as decreased left ventricular and aortic mass indices. It also induced a profound renovasodilation associated with a decrease renal vascular resistance that markedly increased renal blood flow. Coronary hemodynamics and left ventricular hydroxyproline concentration remained unaltered. Concomitant blockade of bradykinin receptors partially attenuated the hypotensive effect of omapatrilat and its effect on aortic mass; and icatibant did not influence the renovasodilation.

CONCLUSION

Omapatrilat produced profoundly beneficial effects on systemic and renal hemodynamics, as well as on left ventricular and aortic masses, without any effect on coronary hemodynamics. These effects of omapatrilat on arterial pressure and aortic mass, but not on renal hemodynamics and left ventricular mass, may have been at least partially mediated through the action of bradykinin.

Contribution of bradykinin and nitric oxide to AT2 receptor-mediated differentiation in PC12 W cells

We investigated the effect of angiotensin II on intracellular cyclic GMP content and neurite outgrowth as an indicator of cell differentiation in PC12 W cells. Neurite outgrowth was examined by phase-contrast microscopy. Outgrown neurites were classified as small, medium and large, and were expressed as neurites per 100 cells. Angiotensin II (10-7 m) increased the outgrowth of medium and large neurites by mean +/- SEM 20.2 +/- 2.3 and 6.6 +/- 1.4 compared with 1.66 +/- 0.5 and 0.1 +/- 0.06 neurites per 100 cells in control. Cellular cyclic GMP content increased by 50-250% with angiotensin II at concentrations of 10-6-10-4 m. Both blockade of AT2 receptors and of nitric oxide synthase markedly reduced angiotensin II-induced neurite outgrowth and cyclic GMP production. In contrast, B2 receptor blockade had no effect or even increased these angiotensin II effects. Sodium nitroprusside and 8-bromo-cyclic GMP both mimicked the effects of angiotensin II on cell differentiation. The protein kinase G inhibitor KT-5823 inhibited the neurite outgrowth induced by both angiotensin II and 8-bromo-cyclic GMP. Our results demonstrate that angiotensin II can stimulate cell differentiation in PC12 W cells by nitric oxide-related and cyclic GMP-dependent mechanisms. The effects of angiotensin II on cell differentiation and cyclic GMP production were mediated via the AT2 receptor and further enhanced by bradykinin B2 receptor blockade.

Impact of myocardial angiotensin-converting enzyme activity on coronary vascular resistance and serum brain natriuretic peptide concentration in coronary bypass surgery

Angiotensin-converting enzyme (ACE) inhibitors have cardioprotective effects in animals, but whether that occurs in humans is still controversial. The effect of myocardial ACE activity on coronary vascular resistance during coronary artery bypass surgery and on serum brain natriuretic peptide (BNP) concentration after surgery was studied in myocardial tissue sampled from the right atrium of patients during cardiac surgery (n=20). Tissue enzyme activity (nmol/min per mg protein) was measured using a photometric technique, and the flow rate and pressure upon antegrade infusion of a crystalloid cardioplegic solution was measured for calculating the coronary vascular resistance (mmHg. ml(-1). min(-1)). Serum BNP concentration (pg/ml) was measured on days 0 and 5 after the surgery. Linear regression between tissue ACE activity and coronary vascular resistance (y = 0.46x + 0.56, r=0.85) as well as serum BNP concentration on days 0 (y = 129x + 30, r=0.59) and 5 (y = 347x + 180, r=0.73) after the surgery was significant (x: ACE activity; y: coronary vascular resistance/serum BNP concentration). The results indicate that inhibition of myocardial ACE activity might improve coronary circulation during surgery and hence, cardiac function after surgery.

Inhibition of angiotensin-converting enzyme reduces susceptibility of hypertrophied rat myocardium to ventricular fibrillation

Left ventricular (LV) hypertrophy increases susceptibility to reperfusion arrhythmias and the angiotensin-converting enzyme inhibitor, ramipril, may reduce that susceptibility via regression of LV hypertrophy. Rats (n=12 per group) were subjected to abdominal aortic constriction (AC) or sham-operation (SH) and from 3 to 6 weeks after surgery, 3 AC groups received ramipril (0.01, 0.1, or 1 mg/kg per day p.o.) while the SH and 1 AC group received vehicle. Six weeks after surgery (ie after 3 weeks of treatment), the hearts were excised and subjected to independent Langendorf perfusion of left and right coronary beds. The left coronary bed was then subjected to ischemia (7 min) and reperfusion (5 min). Hypertrophied hearts from the vehicle AC group showed a significant increase in the incidence of reperfusion-induced ventricular fibrillation (VF) compared with control hearts from the SH group (92%* vs 33%: *p<0.05); this difference was abolished by ramipril (42%, 50%, and 42%, at 0.01, 0.1, or 1 mg/kg per day, respectively). The LV weight/body weight ratio was significantly increased in all AC groups (regardless of ramipril treatment) relative to the SH group. At the cellular level, myocyte length was significantly increased in the vehicle AC group, but was normalized by ramipril treatment (1 mg/kg per day). At the molecular level, atrial natriuretic factor (ANF) mRNA expression was also significantly increased in the vehicle AC group, but was again normalized by ramipril treatment (1 mg/kg per day). In conclusion, short-term treatment with ramipril reduced susceptibility to severe ventricular arrhythmias in hypertrophied rat hearts. This protection was achieved in the absence of a significant reduction in LV weight, but was accompanied by regression of myocyte hypertrophy, as reflected by reductions in cell size and ANF expression.

Modification of myosin gene expression by imidapril in failing heart due to myocardial infarction

The beneficial effects of imidapril, an angiotensin converting enzyme (ACE) inhibitor were investigated on changes in myofibrillar ATPase as well as myosin heavy chain (MHC) content and gene expression due to myocardial infarction (MI). Three weeks after occluding the left coronary artery, rats were treated with or without imidapril (1 mg/kg/day), for 4 weeks. The infarcted hearts exhibited depressed rates of left ventricular (LV) pressure development (57+/-2.4% reduction) and pressure decay (55.5+/-1.6% reduction). LV myofibrillar Ca(2+) ATPase activity, unlike that in the right ventricle (RV), was decreased in the infarcted animals compared with controls (6.8+/-0.4 vs 10.3+/-0.6 micromol Pi/mg/hr). MHC alpha-isoform contents were decreased by 47 and 41% whereas those of MHC beta-isoform were increased by 823 and 1200% in the LV and RV due to MI, respectively. MHC alpha-isoform mRNA levels were decreased by 55 and 35% whereas those for MHC beta-isoform were increased by 50 and 30% in the infarcted LV and RV, respectively. Imidapril treatment partially prevented the changes due to MI in LV function (rate of pressure development, 24+/-2.3% reduction and rate of pressure decay, 14+/-1.8% reduction), myofibrillar Ca(2+) ATPase activity (8.2+/-0.7 micromol Pi/mg/hr), MHC protein content (alpha-MHC, 24% reduction and beta-MHC, 525% increase) and MHC gene expression (alpha-MHC, 18% reduction and beta-MHC, 15% increase). The results suggest that the beneficial effects of ACE inhibition on the failing heart are associated with improvements in myofibrillar ATPase activities as well as prevention of changes in MHC isozyme protein contents and their gene expression.

Dual ACE and NEP inhibitor MDL-100,240 prevents and regresses severe angiotensin II-dependent hypertension partially through bradykinin type 2 receptor

OBJECTIVE

To investigate the effects of the dual angiotensin-converting enzyme (ACE) + neutral endopeptidase (NEP) inhibitor, MDL-100,240 (MDL), on hypertension and cardiovascular damage in male heterozygous transgenic Ren2 rats.

METHODS

Blood-pressure-matched 5-week-old transgenic rats were allocated to receive a placebo, MDL (40 mg/kg body weight) or ramipril (5 mg/kg body weight) for 8 weeks. During the last 4 weeks, the bradykinin B2 receptor antagonist, icatibant (0.5 mg/kg body weight), was also administered subcutaneously via osmotic minipumps to 50% of the transgenic rats receiving MDL or ramipril. We measured blood pressure, heart weight, structural changes in the aorta and small resistance mesenteric arteries, and the plasma concentrations of adrenomedullin, aldosterone, atrial natriuretic peptide and cGMP. To verify if MDL could regress long-standing hypertension and full-blown cardiovascular damage, 3-month-old transgenic rats received MDL subcutaneously (3 and 10 mg/kg body weight, osmotic minipumps) for 4 weeks.

RESULTS

Compared with placebo, MDL decreased blood pressure (P < 0.001) and prevented left ventricular hypertrophy (P < 0.001), being as effective as ramipril. Hypertrophy and dilatation of the aorta and hypertrophy of the resistance arterioles were all prevented by MDL. Plasma aldosterone was decreased by MDL (P < 0.001), but not by ramipril. Icatibant blunted the decrease in blood pressure (P < 0.001), decreased cGMP concentrations and blunted the decrease in cross-sectional area of the resistance arteries in MDL-treated, but not in ramipril-treated, transgenic rats. In 3-month-old transgenic rats, MDL normalized blood pressure, regressed left ventricular hypertrophy and decreased adrenomedullin concentrations.

CONCLUSIONS

The dual ACE+NEP inhibitor MDL prevented and regressed severe hypertension and cardiovascular damage, even in this model of severe angiotensin II-dependent hypertension with pronounced cardiovascular damage. Enhancement of the effects of bradykinin has a role in such favourable outcomes.

Effects of adrenomedullin on hypertrophic responses induced by angiotensin II, endothelin-1 and phenylephrine

We examined whether adrenomedullin (AM), a vasoactive peptide with significant expression and binding sites in the heart, modulates the hypertrophic response in cultured neonatal rat ventricular myocytes. Myocyte hypertrophy was induced by treating the cells with angiotensin II (Ang II), endothelin-1 (ET-1) or alpha-adrenergic agonist, L-phenylephrine (PHE). All treatments resulted in a hypertrophic response as reflected by increased protein synthesis and expression of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) genes. AM treatment resulted in a complete inhibition of the Ang II-induced increase in ANP and BNP gene expression and secretion. In contrast, no inhibitory effect was seen in either ET-1-induced natriuretic peptide gene expression or PHE-induced ANP and BNP gene expression and secretion. AM had only a modest effect on basal levels of natriuretic peptide secretion and gene expression. When AM mRNA levels in isolated neonatal rat myocytes treated for 48 h with Ang II, ET-1 or PHE were measured, only Ang II induced a consistent increase in AM gene expression. These results indicate that AM is not invariably associated with attenuation of the hypertrophic response but its effect is dependent on the stimulus activating myocyte hypertrophy. AM may form an important autocrine/paracrine growth-inhibitory loop in Ang II-induced myocyte hypertrophy.

Effects of ANG II on bradykinin receptor gene expression in cardiomyocytes and vascular smooth muscle cells

Bradykinin has vasodilatory and tissue-protective effects exerted via its B(2) type receptor, whereas the B(1) receptor is constitutively absent but inducible by inflammation and toxins. In previous studies, we found that B(2) receptor gene knockout mice exhibit overexpression of the B(1) receptor, which assumes a vasodilatory function and is further upgraded in renovascular hypertension. The present study was designed to explore the effects of excess angiotensin II (ANG II) on B(1) receptor and B(2) receptor gene expression in mouse cardiomyocytes and rat vascular smooth muscle cells (VSMC) in vivo (after a 3-day infusion of 30 ng/min ANG II in 11 wild-type and in 13 genetically engineered mice with deleted B(2) receptor gene) and in vitro (ANG II added in rat VSMC culture in the presence or absence of AT(1) or AT(2) receptor antagonist). Expression of B(1) and B(2) receptor mRNA was assessed by reverse transcriptase-polymerase chain reaction. ANG II infusion caused upregulation by 30% of the already significantly overexpressed B(1) receptors in cardiomyocytes of the B(2) receptor gene knockout mice, but in the wild-type mice it upregulated only the B(2) receptor mRNA by 47%. The addition of ANG II in VSMC culture produced a time-dependent induction of B(1) and upregulation of B(2) receptor gene expression, maximal at 3 h (by fivefold), declining almost to baseline by 24 h. The addition of losartan completely blocked this effect, whereas the AT(2) blocker PD-123319 made no difference, indicating that this is an AT(1)-mediated effect of ANG II. The data indicate that excess ANG II in subpressor doses in vivo upregulates expression of the B(2) receptor, but in its absence, the already overexpressed B(1) receptor is further upregulated, evidently assuming a counterregulatory response; in vitro, it transiently upregulates both bradykinin receptors.

Negative inotropic effect of bradykinin in porcine isolated atrial trabeculae: role of nitric oxide

OBJECTIVES

To investigate whether bradykinin affects cardiac contractility independently of its effects on coronary flow and noradrenaline release, and whether such inotropic effects, if present, are mediated via nitric oxide (NO).

METHODS

Right atrial trabeculae were obtained from 35 pigs, suspended in organ baths and attached to isometric transducers. Resting tension was set at approximately 750 mg and tissues were paced at 1.5 Hz. Tissue viability was checked by constructing a concentration response curve (CRC) to noradrenaline. Next, CRCs were constructed to bradykinin, either under baseline conditions or after pre-stimulation with the positive inotropic agent forskolin (1 or 10 micromol/l), in the absence or presence of the bradykinin type 2 (B2) receptor antagonist D-Arg [Hyp3-Thi5, d-Tic7, Oic8]-bradykinin (Hoe 140) (1 micromol/l), the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) (100 micromol/l) and/or the NO scavenger hydroxocobalamin (200 micromol/l).

RESULTS

Bradykinin exerted a negative inotropic effect, both with and without forskolin pre-stimulation, reducing contractility by maximally 22 +/- 3.6% (mean +/- SEM) and 23 +/- 3.6%, respectively (pEC50 8.37 +/- 0.23 and 8.62 +/- 0.22, respectively). L-NAME reduced this effect in pre-stimulated, but not in unstimulated, trabeculae. Hoe 140 and hydroxocobalamin fully blocked the inotropic effect of bradykinin.

CONCLUSIONS

Bradykinin induces a modest negative inotropic effect in porcine atrial trabeculae that is mediated via B2 receptors and NO. The inconsistent results obtained with L-NAME suggest that it depends on NO synthesized de novo and/or NO from storage sites.