Preserved vasodilator effect of bradykinin in dogs with heart failure

A Novel Approach to Medical Management of Heart Failure With Reduced Ejection Fraction

The advent of newly available medical therapies for heart failure with reduced ejection fraction (HFrEF) has resulted in many potential therapeutic combinations, increasing treatment complexity. Publication of expert consensus guidelines and initiatives aimed to improve implementation of treatment has emphasized sequential stepwise initiation and titration of medical therapy, which is labour intensive. Data taken from heart failure registries show suboptimal use of medications, prolonged titration times, and consequently little change in dose intensity, all of which indicate therapeutic inertia. Recently published evidence indicates that 4 medication classes-renin-angiotensin-neprilysin inhibitors, β-blockers, mineralocorticoid antagonists, and sodium-glucose cotransporter inhibitors-which we refer to as Foundational Therapy, confer rapid and robust reduction in both morbidity and mortality in most patients with HFrEF and that they work in additive fashion. Additional morbidity and mortality may be observed following addition of several personalized therapies in specific subgroups of patients. In this review, we discuss mechanisms of action of these therapies and propose a framework for their implementation, based on several principles. These include the critical importance of rapid initiation of all 4 Foundational Therapies followed by their titration to target doses, emphasis on multiple simultaneous drug changes with each patient encounter, attention to patient-specific factors in choice of medication class, leveraging inpatient care, use of the entire health care team, and alternative (ie, virtual visits) modes of care. We have incorporated these principles into a Cluster Scheme designed to facilitate timely and optimal medical treatment for patients with HFrEF.

Vascular endothelial dysfunction and pharmacological treatment

The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.

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.

Bradykinin restores left ventricular function, sarcomeric protein phosphorylation, and e/nNOS levels in dogs with Duchenne muscular dystrophy cardiomyopathy

AIMS

Cardiomyopathy is a lethal result of Duchenne muscular dystrophy (DMD), but its characteristics remain elusive. The golden retriever muscular dystrophy (GRMD) dogs produce DMD pathology and mirror DMD patient's symptoms, including cardiomyopathy. We previously showed that bradykinin slows the development of pacing-induced heart failure. Therefore, the goals of this research were to characterize dystrophin-deficiency cardiomyopathy and to examine cardiac effects of bradykinin in GRMD dogs.

METHODS AND RESULTS

At baseline, adult GRMD dogs had reduced fractional shortening (28 ± 2 vs. 38 ± 2% in control dogs, P < 0.001) and left ventricular (LV) subendocardial dysfunction leading to impaired endo-epicardial gradient of radial systolic velocity (1.3 ± 0.1 vs. 3.8 ± 0.2 cm/s in control dogs, P < 0.001) measured by echocardiography. These changes were normalized by bradykinin infusion (1 µg/min, 4 weeks). In isolated permeabilized LV subendocardial cells of GRMD dogs, tension-calcium relationships were shifted downward and force-generating capacity and transmural gradient of myofilament length-dependent activation were impaired compared with control dogs. Concomitantly, phosphorylation of sarcomeric regulatory proteins and levels of endothelial and neuronal nitric oxide synthase (e/nNOS) in LV myocardium were significantly altered in GRMD dogs. All these abnormalities were normalized in bradykinin-treated GRMD dogs.

CONCLUSIONS

Cardiomyopathy in GRMD dogs is characterized by profound LV subendocardial dysfunction, abnormal sarcomeric protein phosphorylation, and impaired e/nNOS, which can be normalized by bradykinin treatment. These data provide new insights into the pathophysiological mechanisms accounting for DMD cardiomyopathy and open new therapeutic perspectives.

Bradykinin type-2 receptor expression correlates with age and is subjected to transcriptional regulation

Accumulating work in experimental animals suggests that bradykinin (BK) exerts cardioprotective effects via bradykinin type-2 receptors (BK-2Rs). In human end-stage heart failure, BK-2Rs are significantly downregulated by mechanisms that have remained elusive. Heart tissues from idiopathic dilated cardiomyopathy (IDC; n = 7), coronary heart disease (CHD; n = 6), and normal patients (n = 6) were analyzed by RT-PCR, SSCP, and Western blotting. In normal and IDC hearts, BK-2R expression increased with age, with a lower relative increase in IDC hearts. BK-2R mRNA and protein levels showed a positive linear correlation, suggesting transcriptional regulation. Two known BK-2R promoter polymorphisms, −58T/C and −9/+9, were found to be present in the study population. The allelic frequencies for the C-allele in −58T/C were 0.58 in normal and CHD hearts and 0.81 in IDC hearts. Furthermore, the allelic frequencies for the −9 and +9 alleles were 0.42 and 0.58 in normal hearts and 0.64 and 0.36 in IDC hearts, respectively. All analyzed CHD hearts were homozygous for the −9 allele. Thus, the expression of cardioprotective BK-2Rs in human hearts is increased with age in normal and IDC hearts and may be regulated on the transcriptional level. Moreover, comparison of normal subjects and patients with failing hearts revealed different allelic frequencies in each of two known BK-2R gene polymorphisms.

Theoretical study of the human bradykinin-bradykinin B2 receptor complex

The interaction of bradykinin (BK) with the bradykinin B2 receptor (B2R) was analyzed by using molecular modeling (MM) and molecular dynamics (MD) simulations. A homology model for B2R has been generated and the recently determined receptor-bound solid-state NMR spectroscopic structure of BK (Lopez et al., Angew. Chem. 2008, 120, 1692-1695; Angew. Chem. Int. Ed. 2008, 47, 1668-1671) has been modeled into the binding pocket of the receptor to probe the putative ligand-receptor interface. The experimental hormone structure fitted well into the binding pocket of the receptor model and remained stable during the MD simulation. We propose a parallel orientation of the side chains for Arg1 and Arg9 in BK that is bound to B2R. The MD simulation study also allows the conformational changes that lead to the activated form of B2R to be analyzed. The hydrogen bond between N140 (3.35) and W283 (6.48) is the key interaction that keeps the receptor in its inactive form. This hydrogen bond is broken during the MD simulation due to rotation of transmembrane helix 3 (TM3) and is replaced by a new hydrogen bond between W283 (6.48) and N324 (7.45). We propose that this interaction is specific for the activated form of the bradykinin B2 receptor. Additionally, we compared and discussed our putative model in the context of the structural model of the partially activated rhodopsin (Rh*) and with the known biochemical and structural data.

Angiotensin II type 1 receptor antagonism improves endothelial vasodilator function in L-NAME-induced hypertensive rats by a kinin-dependent mechanism

OBJECTIVE

This study was designed to investigate the ability of a chronic blockade of angiotensin II type 1 receptors with losartan to reverse the endothelial dysfunction present in N-nitro-L-arginine methyl ester (L-NAME)-treated hypertensive rats and the possible dependence of this effect on bradykinin B2-receptor activation.

METHODS

Rats treated with L-NAME alone (60 mg/kg per day for 8 weeks) or with L-NAME + losartan, L-NAME + icatibant (a bradykinin B2-receptor antagonist) and L-NAME + losartan + icatibant were studied. Losartan, icatibant or losartan + icatibant were co-administered with L-NAME during the last 4 weeks of the experiment. Endothelial nitric oxide synthase gene expression in aortic tissues, plasma nitrite/nitrate concentrations, the relaxant effect of acetylcholine on norepinephrine-precontracted aortic rings and 6-keto-PGF1alpha release from aortic rings were used as markers of the endothelial function.

RESULTS

Rats treated with L-NAME alone and L-NAME + icatibant showed, as compared with untreated animals, a clear-cut increase in systolic blood pressure and a decrease of all the markers of endothelial function evaluated. In L-NAME-rats, administration of losartan reduced the systolic blood pressure and restored endothelial nitric oxide synthase gene expression, plasma nitrite/nitrate levels, the relaxant activity of acetylcholine on aortic rings and the generation of 6-keto-PGF1alpha from the aortic tissues. Co-administration of icatibant with losartan blunted the stimulatory effect of losartan on the markers of endothelial function evaluated.

CONCLUSION

These results demonstrated that losartan is capable of reversing the endothelial vasodilator dysfunction in L-NAME-induced hypertensive rats, and that the beneficial effect of losartan is mediated by bradykinin B2-receptor activation.

Treatment of severe pulmonary hypertension: a bradykinin receptor 2 agonist B9972 causes reduction of pulmonary artery pressure and right ventricular hypertrophy

Bradykinin is an important modulator of endothelial cell function and has also a powerful cardioprotective effect. Here we report that treatment of severely pulmonary hypertensive rats (that recapitulate several of the physiological and pathological characteristics of the human pulmonary vascular disease, including dramatic right ventricular hypertrophy, pericardial effusion and death) with a newly synthesized long-acting bradykinin B2 receptor agonist B9972 caused reduction of the pulmonary artery pressure (PAP=51+/-2.0 versus 68+/-2.8 of untreated animals) and of right ventricular hypertrophy (Rv/Lv+S=0.55+/-0.02 versus 0.73+/-0.03 of untreated rats) and activation of Akt. Long-term stimulation with B9972 in our animal model of SPH resulted in decreased expression of the B2 receptor in lung vasculature. Treatment with B9972 decreased the number of plexiform lesions in the lungs by inducing cell apoptosis in the obliterated vessels and by restoring caveolin-1 expression. B9972 also promoted eNOS activation. In vitro B9972 caused activation of caspase-3 as well as Erk and induction of prostacyclin production in rat pulmonary microvascular EC. Taken together our data suggest that a stable bradykinin B2 agonist B9972 demonstrates the capacity to reduce severe pulmonary hypertension, right ventricular hypertrophy and induce apoptosis of hyperproliferative cells in pre-capillary pulmonary arterioles.

Impaired bradykinin response to ischaemia and exercise in patients with mild congestive heart failure during angiotensin-converting enzyme treatment. Relationships with endothelial function, coagulation and inflammation

Inflammation and endothelial dysfunction play important roles in the pathophysiology of congestive heart failure (CHF), and the peptide bradykinin, generated during inflammation, may act as a defence mechanism by inducing vasodilation. Plasma bradykinin levels are increased in experimental heart failure but low in patients with advanced chronic CHF despite treatment with angiotensin-converting enzyme (ACE) inhibitors. It is not currently known how bradykinin behaves in less severe phases of CHF controlled by long-term ACE inhibitor treatment. We studied 10 male patients with clinically stable chronic CHF [New York Heart Association (NYHA) class II] on long-term ACE inhibitor treatment and 10 normal sex- and age-matched control subjects. High performance liquid chromatography/radioimmunoassay methods were used to evaluate plasma levels of bradykinin in relation to an array of parameters of endothelial function, coagulation and inflammation before and after stimuli of forearm arterial occlusion and physical exercise. CHF patients had higher levels of bradykinin (P = 0.008), activated factor XII (P = 0.049), interleukin-6 (P = 0.050) and tumour necrosis factor receptor II (sTNFRII) (P = 0.026) than controls. Arterial occlusion and exercise significantly increased bradykinin and von Willebrand factor levels in controls but not in CHF patients. The increase in brachial artery diameter after arterial occlusion was less in CHF patients (P = 0.036) and inversely related to baseline plasma levels of bradykinin (r = -0.855, P = 0.002) and sTNFRII (r = -0.780, P = 0.008). NYHA class II CHF patients during long-term treatment with ACE inhibitors have increased bradykinin levels and signs of inflammation. They are unable to respond adequately to stimuli of ischaemia and physical exercise which both require vasodilation.

Angiotensin-converting enzyme inhibition and angiotensin AT1-receptor antagonism equally improve endothelial vasodilator function in l-NAME-induced hypertensive rats

Male Sprague-Dawley rats given N(omega)-nitro-L-arginine methyl ester (L-NAME) in drinking water for 8 weeks showed: (1) a clear-cut increase in systolic blood pressure; (2) a consistent decrease of endothelial-cell nitric oxide synthase (eNOS) gene expression in aortic tissue; (3) a marked reduction of plasma nitrite/nitrate concentrations; (4) a reduction of the relaxant activity of acetylcholine (ACh, from 10(-10) to 10(-4) M) on norepinephrine-precontracted aortic rings (reduction by 48+/-5%); (5) a marked decrease (-58%) of the basal release of 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) from aortic rings. In L-NAME-treated rats, administration in the last 4 weeks of either the angiotensin-converting enzyme (ACE) inhibitor enalapril (10 mg/kg/day in tap water) or the angiotensin AT(1)-receptor antagonist losartan (10 mg/kg/day in tap water) decreased systolic blood pressure levels, completely restored eNOS mRNA levels in aortic tissue and plasma nitrite/nitrate levels, and allowed a consistent recovery of both the relaxant activity of acetylcholine and the generation of 6-keto-PGF1alpha. Coadministration of icatibant, a bradykinin B(2)-receptor antagonist (200 microg/kg/day), with enalapril blunted the stimulatory effect of the ACE inhibitor on eNOS mRNA expression, circulating levels of nitrite/nitrate, the relaxant activity of ACh and the release of 6-keto-PGF1alpha in L-NAME-treated rats. The generation of 6-keto-PGF1alpha from aortic rings was also decreased in rats coadministered icatibant with losartan. These findings indicate that (1) the ACE inhibitor enalapril and the angiotensin AT(1)-receptor blocker losartan are equally effective to reverse NAME-induced endothelial dysfunction; (2) the beneficial effect of enalapril on the endothelial vasodilator function in L-NAME-treated rats is mediated by bradykinin B(2)-receptor activation; and (3) the enhanced endothelial generation of prostacyclin induced by losartan in L-NAME rats is also mediated by bradykinin B(2)-receptor activation.

Expression of bradykinin receptors in the left ventricles of rats with pressure overload hypertrophy and heart failure

OBJECTIVES

Bradykinin exerts cardioprotective effects through bradykinin type-2 receptors (BK-2Rs). After acute myocardial infarction in rat, the heart adapts by increasing its number of BK-2Rs. However, in human chronic end-stage heart failure, the number of BK-2Rs is significantly decreased. Thus, the presence of a cardioprotective BK-2R signaling system may be critical in the prevention of pressure overload-induced heart failure.

DESIGN

To explain differences in myocardial BK-2R expression during cardiac overload, we studied: (1). spontaneously hypertensive rats (SHRs) of different ages, and (2). normotensive Sprague-Dawley rats subjected to aortic banding or angiotensin II infusion.

METHODS AND RESULTS

The mRNA levels of BK-2Rs were found to be significantly (P < 0.05) increased in the aging (12 and 20-month-old) SHRs (2.9- and 3-fold, respectively). Similarly, in the Sprague-Dawley rats, the expression of BK-2Rs was increased at 12 h (1.8-fold, P < 0.05) and at 3 days (3.1-fold, P < 0.05) after aortic banding, and at 2 weeks (2.2-fold) after angiotensin II infusion. In the 12-month-old SHRs, with compensated left ventricular hypertrophy (no fibrosis or left ventricular dysfunction), the amount of BK-2Rs was also significantly increased (1.8-fold, P < 0.05). However, in the 20-month-old SHRs, with a dramatic increase in fibrosis and development of diastolic dysfunction and heart failure, the amount of BK-2Rs were significantly decreased (63%, P < 0.05) specifically in the cardiac endothelial cells.

CONCLUSIONS

The present results show that, during pressure overload and compensated left ventricular hypertrophy, the expression of BK-2Rs is increased. However, ongoing pressure overload leads to a loss of BK-2Rs with a dramatic increase in left ventricular fibrosis followed by diastolic dysfunction and heart failure.

Down-regulation of cardioprotective bradykinin type-2 receptors in the left ventricle of patients with end-stage heart failure

OBJECTIVES

We sought to study the expression of bradykinin type-2 receptors (BK-2Rs) in patients with heart failure (HF).

BACKGROUND

Recent work in experimental animals has suggested that bradykinin (BK) exerts cardioprotective effects through specific BK-2Rs. However, nothing is known about the regulation of BK-2R expression in the pathogenesis of human HF.

METHODS

Human heart tissue was obtained from excised hearts of patients undergoing cardiac transplantation (n = 13) and from normal hearts (n = 6) unsuitable for donation. The patients had HF due to idiopathic dilated cardiomyopathy (IDC) (n = 7) or coronary heart disease (CHD) (n = 6). Tissue samples from the left ventricles were analyzed by competitive reverse-transcriptase-polymerase chain reaction and Western blotting for the expression of BK-2R messenger ribonucleic acid (mRNA) and protein.

RESULTS

In both the IDC and CHD hearts, the level of BK-2R mRNA expression was found to be significantly lower (30% and 38% of control values, respectively) than that in normal hearts. Correspondingly, the BK-2R protein level was significantly reduced in both the IDC and CHD hearts (45% and 62% of control values, respectively) and apparently involved all myocardial cell types. The down-regulation of BK-2R expression in failing hearts did not correlate with decreased cellularity or with the expression pattern of other members of the G-protein-coupled receptor superfamily. However, BK-2R down-regulation in the failing hearts was associated with a decrease in endothelial nitric oxide synthase in both IDC (53% of control value) and CHD (43% of control value) hearts.

CONCLUSIONS

These results are the first to suggest that a loss of BK-2Rs is involved in the pathogenesis of human HF.

Reduced coronary vasodilator responses to amlodipine in pacing-induced heart failure in conscious dogs: role of nitric oxide

1. This study examined whether NO is involved in the in-vivo coronary vasodilator effects of amlodipine (a calcium channel blocker) and whether heart failure (HF) alters the coronary responses to amlodipine. 2. Nine conscious dogs were chronically instrumented to measure circumflex coronary blood flow (CBF) and coronary diameter (CD). Drugs were administered directly into the circumflex artery through an indwelling catheter to avoid systemic changes. HF was induced by right ventricular pacing (240 b.p.m., 3 weeks). 3. Compared with control (C), in HF, coronary responses to acetylcholine (1 - 10 ng kg(-1)) were reduced while responses to nitroglycerin (0.1 - 0.5 microg kg(-1)) were unchanged. In C, amlodipine (30 - 150 microg kg(-1)), increased dose-dependently CBF and CD. After LNA (a NO synthase inhibitor, 2 mg kg(-1)), amlodipine produced less increases in CBF and CD (+121+/-26 ml min(-1) and +76+/-35 microm versus +196+/-40 ml min(-1) and +153+/-39 microm respectively for 150 microg kg(-1) amlodipine alone, both P<0.05). In HF, the coronary responses to amlodipine were reduced (150 microg kg(-1) of amlodipine increased CBF and CD +121+/-23 ml min(-1) and +77+/-21 microm respectively, both P<0.05). After LNA, the CBF responses to amlodipine tended to be reduced (+94+/-19 ml min(-1) at 150 microg kg(-1)) but CD responses were significantly reduced (+41+/-16 microm, P<0.05). The supplementation with L-arginine did not enhance the coronary responses to amlodipine. 4. These results indicate that, in conscious dogs, NO participates in the coronary responses to amlodipine and in HF, the coronary responses to amlodipine are reduced, which is related to a reduced NO production.

Changes in pain perception during treatment with angiotensin converting enzyme-inhibitors and angiotensin II type 1 receptor blockade

OBJECTIVES

Besides the well-known role of the angiotensin system in blood pressure control, an interaction of angiotensin and pain perception has been suggested. This study sought to investigate whether an angiotensin converting enzyme inhibitor, which facilitates bradykinins, algesic peptides, and/or an AT1 receptor antagonist may modify hypertension-related hypoalgesia in humans. The study was approved by the ethical committee of our Department.

METHODS

A total of 22 hypertensive patients were submitted to dental pulp stimulation to obtain the dental pain threshold and tolerance, and to 24 h blood pressure monitoring together with a control group of 55 normotensives. Then the hypertensives were randomized to enalapril or losartan treatment and were re-evaluated (dental pain perception and ambulatory monitoring) after 8 weeks of the first treatment and after an additional 8 weeks of the second treatment.

RESULTS

Untreated hypertensives showed a reduced perception to painful stimuli when compared with normotensives. A significant reduction of both pain threshold and tolerance was observed during the anti-hypertensive treatments (Friedman test: P = 0.007 and P = 0.006, respectively). Pain sensitivity was similar during the two treatments and it did not differ from pain sensitivity values of normotensive controls. ANCOVAs were computed to evaluate the relationship between anti-hypertensive agents and pain sensitivity, after controlling for blood pressure. A 24 h mean pressure served as covariate, removing any effect of blood pressure; a significant difference was observed entering both pain threshold and tolerance as dependent variables (F = 5.28, P = 0.0076; F = 8.16, P = 0.0007, respectively).

CONCLUSIONS

Both the angiotensin converting enzyme inhibitor enalapril and the AT1 receptor blocking agent losartan acted similarly on pain threshold and tolerance, pain sensitivity being increased during the two anti-hypertensive treatments. The blood pressure reduction during drug assumption could not account for the pain sensitivity changes observed. The latter may be due to a specific pharmacodynamic mechanism mediated through angiotensin II AT1 receptors.

Alterations of endothelium-dependent and -independent regulation of coronary blood flow during heart failure

Conflicting data concerning the changes in basal coronary blood flow and nitric oxide (NO)-releasing capacity in chronic heart failure may be due to different phases or duration of heart failure. To investigate endothelium-dependent and -independent regulation of coronary blood flow in different phases of heart failure, coronary pressure-flow relationships during long diastole were obtained before and after rapid pacing of 3 and 5 wk at 240 beats/min in 12 or 6 dogs. Neither basal coronary blood flow nor the slope of coronary pressure-flow relationships changed; however, zero-flow pressure increased slightly after rapid pacing. Intracoronary injection of N(G)-nitro-L-arginine methyl ester decreased coronary blood flow at a perfusion pressure of 50 mmHg by approximately 20% at baseline, 55% after 3 wk of rapid pacing, and 20% after 5 wk of rapid pacing. Acetylcholine-induced increase in coronary blood flow was maintained for 3 wk but was finally attenuated after 5 wk of rapid pacing. In contrast, the coronary blood flow response to adenosine gradually decreased with time. These results suggest that basal coronary blood flow is maintained until the late stage of heart failure, presumably by an increases in NO production during the early stage and then by other vasodilatory substances during the late stage, and that endothelium-dependent vasodilation via exogenously administered acetylcholine in resistance vessels is not necessarily impaired in the early stage despite the gradual reduction of endothelium-independent vasodilation via adenosine in chronic heart failure.

Bradykinin for the treatment of cardiovascular disease

Bradykinin is a vasoactive kinin known to be involved in many biologic processes. Levels of bradykinin have been shown to be elevated in a number of cardiac diseases. It is thought that these elevated levels play a protective role in cardiovascular diseases. Preliminary studies have demonstrated that bradykinin may have beneficial effects on a wide spectrum of cardiovascular disorders. Though much study is still required, bradykinin augmentation represents an exciting new target for the treatment of cardiovascular disease.

Increased bradykinin levels accompany the hemodynamic response to acute inhibition of angiotensin-converting enzyme in dogs with heart failure

To determine the short-term effects of angiotensin-converting enzyme (ACE) inhibition on hemodynamics and circulating levels of norepinephrine, angiotensin, and bradykinin, responses to enalaprilat and perindoprilat were examined at doses of 0.03, 0.3, and 1 mg/kg in permanently instrumented conscious dogs with pacing-induced heart failure (right ventricular pacing, 240-250 beats/min, 3 weeks). All doses of the two inhibitors produced similar decrease in mean aortic pressure and increase in cardiac output. Neither inhibitor affected plasma norepinephrine level. Both compounds induced a similar 60-80% decrease in blood angiotensin II level, a similar two- to eightfold increase in blood angiotensin I level, and a 80-95% decrease in the angiotensin II/angiotensin I ratio. There were also a fourfold to 10-fold increase in blood bradykinin-(1-9) level, a twofold increase in blood bradykinin-(1-7) level, and a 70-85% decrease in bradykinin-(1-7)/bradykinin-(1-9) ratio. In addition, the changes in total peripheral resistance induced by the two ACE inhibitors were weakly but significantly correlated with the changes in blood angiotensin II or blood bradykinin-(1-9). Thus whatever the specificity of enalaprilat and perindoprilat, both inhibitors produced similar acute hemodynamic effects in dogs with heart failure, which was associated with marked decrease in circulating angiotensin II level and increase in bradykinin-(1-9) level. This study, which measures for the first time in heart failure the blood bradykinin level after ACE inhibitors, indicates, in concert with angiotensin II reduction, a role for increased bradykinin-(1-9) level in mediating short-term hemodynamic effects of ACE inhibition in this model of heart failure.