Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

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

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

Modification by bradykinin B2 receptor blockade of protection by pacing against ischaemia-induced arrhythmias

In dogs, rapid cardiac pacing, by way of a pacing electrode in the right ventricle, protects against ventricular arrhythmias when a coronary artery is occluded immediately after cessation of the pacing period. This represents a form of ischaemic preconditioning. The role of bradykinin in mediating the protective effects of rapid cardiac pacing in this model was investigated using a selective antagonist of bradykinin at B2 receptors (icatibant; HOE 140). In the presence of icatibant cardiac pacing (220 beats min(-1)) resulted in more severe ischaemia (as assessed by ST-segment elevation from the pacing electrode at the end of the stimulus) and to a higher incidence of ventricular arrhythmias during the pacing protocol. When the coronary artery was occluded under such conditions the antiarrhythmic protection afforded by cardiac pacing was not seen although other indices of reduced ischaemia severity (epicardial ST-segment mapping; changes in the degree of inhomogeneity of electrical activation within the ischaemic area) were not affected by icatibant treatment. These results suggest that bradykinin is an important trigger mediator involved in the protective effects of cardiac pacing. Whether this is due to the generation of endothelium-derived protective substances (such as nitric oxide and prostacyclin) or whether it results from a direct effect on B2 receptors in cardiac myocytes is unclear.

Effect of neutral endopeptidase 24.11 inhibition on myocardial ischemia/reperfusion injury: the role of kinins

Angiotensin-converting enzyme inhibitors (ACEi) protect the heart against ischemia/reperfusion injury. Part of this cardioprotective effect may be mediated through kinins. Because kinins are also metabolized by neutral endopeptidase (NEP) 24.11 in vivo, we hypothesized that (a) inhibition of NEP-24.11 would afford cardioprotection similar to that of ACEi and potentiate the effect of ACEi; and (b) these effects are mediated by kinins or atrial natriuretic peptide (ANP) or both. In Lewis inbred rats, the left anterior descending coronary artery (LAD) was occluded for 30 min, followed by 120-min reperfusion. Immediately before reperfusion rats received vehicle, the ACEi ramiprilat, the NEP-24.11 inhibitor (NEPi) CGS24592, or both. To test whether the effect of NEPi could be suppressed by blocking kinins or ANP, the kinin-receptor antagonist icatibant or ANP antagonist HS-142-1 was administered before LAD occlusion. In controls, infarct size/risk area was 69 +/- 4%; NEPi reduced this to 24 +/- 4% (p < 0.001) and ramiprilat to 20 +/- 3% (P < 0.001). NEPi did not potentiate the effect of ramiprilat (infarct size/risk area, 18 +/- 4%). The protective effect of NEPi was blocked by icatibant; infarct size/risk area, 61 +/-4%, significantly larger than NEPi along (p < 0.001) but no different from controls. The effect of NEPi was slightly diminished by the ANP antagonist HS-142-1 (infarct size/risk area, 35 +/- 3%; NS vs. NEPi alone). Thus NEP-24.11 participates in catabolism of kinins in the heart; inhibition of NEP-24.11 may increases cardiac kinins, which are responsible for the cardioprotective effect of NEPi.

The cellular basis of angiotensin converting enzyme mRNA expression in rat heart

Angiotensin converting enzyme (ACE) is a key factor in the regulation of two peptide systems: the renin angiotensin system (RAS) and the kinin-kallikrein system (KKS). Since it is involved in the biosynthesis of Angiotensin II (Ang II) as well as in the degradation of bradykinin (BK) it could play an important role in cardiovascular physiology and pathophysiology. ACE is widely expressed in the heart and upregulated in pathophysiological situations such as heart failure and cardiac hypertrophy. In addition, inhibition of ACE has beneficial effects in these conditions. Whereas the regulation of cardiac ACE has been studied extensively, little is known concerning the cellular expression of ACE in cardiac tissue. To define the cellular localization of ACE mRNA expression in the rat heart, we separated coronary microvascular endothelial cells from cardiac myocytes using differential centrifugation and growth on selective media. ACE mRNA expression was measured by a specific polymerase chain reaction assay after reverse transcription (RT-PCR) in different cardiac cells. The studies showed that ACE is differentially expressed in endothelial cells as well as in cardiac myocytes. This differential regulation of ACE in myocytes and non-myocytes may play a role for the diverse actions of the cardiac angiotensin system under physiological and pathological conditions.

Bradykinin as an endogenous myocardial protective substance with particular reference to ischemic preconditioning--a brief review of the evidence

The present brief review summarizes the evidence for the possibility that endogenously released bradykinin plays a major role in protecting the heart against the consequences of acute myocardial injury. This evidence includes the facts that kinins are generated under myocardial ischemia; that when they are administered, they are cardioprotective (e.g., antiarrhythmic); that drugs that enhance the release of bradykinin from the ischemic heart reduce the ischemic injury and, conversely, drugs that block bradykinin receptors attenuate the reduction in ischemic injury resulting from the release of, or administration of, bradykinin. The possible mechanism of bradykinin in the cardioprotection afforded by ischemic preconditioning is summarized. Ischemic preconditioning can be defined as the marked reduction in the severity of ischemic changes that result from coronary artery occlusion when that occlusion is preceded by brief periods of myocardial ischemia, either regional or global, induced, for example, by complete or partial coronary artery occlusion or by rapid ventricular pacing. The possible mechanisms of cardioprotection elicited by bradykinin (and ischemic preconditioning) are summarized. The most likely is the generation of cyclic GMP within the ischemic myocardium following bradykinin-stimulated nitric oxide generation and release from endothelial cells.

Role of the cardiac renin-angiotensin system in human heart failure

The local effects of angiotensin II (ANG II) on the heart may play an important role for the pathophysiology of cardiovascular disease. Numerous in vitro studies have demonstrated that angiotensin II has distinctive cellular effects in the cardiovascular system which are independent from its effects on blood pressure. These have led to the hypothesis that activation of the angiotensin system in the heart could be of functional relevance for the adaptive processes in several cardiovascular disorders such as cardiac hypertrophy heart failure. This concept has been further supported by clinical studies showing the beneficial effects of angiotensin-converting enzyme inhibitors in these circumstances. In order to study the gene regulation of renin-angiotensin system components in cardiac disorders we investigated the gene expression of angiotensin converting enzyme in human heart failure. Results showed that the enzyme is activated locally in this condition, supporting previous studies in animals. Taken together with recent evidence from genetic studies linking the enzyme to myocardial infarction and cardiac hypertrophy, our findings are in support of the notion that angiotensin converting enzyme plays a central role in cardiovascular physiology and pathophysiology.

Intracoronary infusion of bradykinin: effects on noradrenaline overflow following reperfusion of ischemic myocardium in the anesthetized dog

OBJECTIVE

The aim of this study was to investigate the effects of intracoronary bradykinin (BK) infusion on noradrenaline release and ventricular arrhythmias induced by coronary occlusion and reperfusion in the anesthetized dog.

METHODS

14 anesthetized adult mongrel dogs of either sex underwent a 60 min occlusion of the left anterior descending coronary artery (LAD) followed by a 30-min reperfusion period. BK (1 ng.kg-1.min-1, n = 7), or its vehicle (Lactate Ringer, n = 7), infusions just distal to the left coronary ostium started 15 min before the LAD occlusion and were maintained throughout the experimental period. An epicardial vein, running parallel to the LAD was cannulated to enable the biochemical determinations. The effects of BK on ventricular arrhythmias, cardiac noradrenaline and lactate releases and creatine kinase activity were assessed.

RESULTS

BK significantly reduced the amount of noradrenaline released at reperfusion by ischemic myocardium (from 82.1 +/- 31.7 to 11.9 +/- 9.6 ng.min-1), as well as plasma creatine kinase activity at 30 min of reperfusion. This is accompanied by a significant reduction in the incidence of reperfusion-induced sustained ventricular tachycardia.

CONCLUSION

This suggests that the protective effect of bradykinin against reperfusion-induced sustained ventricular tachycardia could be associated with a reduction in cardiac noradrenaline release.

Bradykinin, coronary artery disease and gastro-oesophageal reflux

Gastro-oesophageal reflux and coronary artery disease frequently coexist. Stimulation of myocardial vagal receptors impairs lower oesophageal sphincter (LOS) function and may explain this link. This study examined the role of bradykinin, produced in increased quantities by the ischaemic myocardium, in activating this reflex. Thirteen dogs had patches soaked in bradykinin 100 micrograms/ml and saline applied sequentially to the left ventricular epicardium. Eleven of these animals were further divided into two subgroups: group 1 animals (six dogs) had the above sequence repeated after obliteration of sympathetic afferent fibres with phenol and those in group 2 (five animals) underwent sequential intravenous and intra-atrial injection of bradykinin 0.2 micrograms/kg. Epicardial bradykinin produced a fall in mean(s.e.m.) LOS tone from 13.3(1.3) to 6.0(0.5) sphinctometer units (P < 0.002), accompanied by a reduction in mean(s.e.m.) arterial pressure from 95(4) to 83(5) mmHg (P < 0.002). Destruction of sympathetic afferent fibres did not alter the LOS effect. Intra-atrial, but not intravenous, bradykinin reproduced the LOS effect; this suggests a cardiac origin. Myocardial release of bradykinin may play a role in producing transient LOS relaxation, predisposing to gastro-oesophageal reflux.

Role of kinins and nitric oxide in the effects of angiotensin converting enzyme inhibitors on neointima formation

Marked neointima formation occurs after balloon injury to the intima of rat arteries. Angiotensin II has been implicated as a growth factor in this process, since angiotensin converting enzyme (ACE) inhibitors block neointima formation after injury. However, ACE is an important kininase, and its inhibitors may act in part by a kinin-mediated mechanism. Kinins are also known to stimulate synthesis of endothelium-derived relaxing factor/nitric oxide (EDRF/NO) and prostacyclin, both of which have antigrowth effects. To determine whether the effect of ACE inhibitors on neointima formation is due to blockade of angiotensin II synthesis alone and/or inhibition of kinin inactivation, we followed two approaches. First, we compared the inhibition of neointima formation induced by the AT1-type angiotensin II receptor antagonist losartan with that caused by the ACE inhibitor ramipril. We also studied whether a kinin receptor antagonist, Hoe 140, blocks the effect of two different ACE inhibitors, ramipril and enalapril, on neointima formation. In addition, we studied whether the effect of ramipril is blocked by an NO synthesis inhibitor, N omega-nitro-L-arginine-methyl ester (L-NAME). Although both ramipril and losartan significantly reduced neointima formation, ramipril had a more marked effect (p < 0.05 for ramipril versus losartan). The kinin antagonist Hoe 140 reduced the inhibitory effect of ramipril and enalapril by 73% and 62%, respectively. The remaining effect of the ACE inhibitors was now similar to that of losartan. Inhibition of neointima formation by ramipril was also blocked by the NO synthesis inhibitor L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effects of bradykinin on the ischaemic heart: implication of the B1 receptor

1. We studied the role of bradykinin (BK) and its active metabolite Des-Arg9-BK on noradrenaline release in association with the incidence of ventricular arrhythmias at reperfusion of the ischaemic myocardium. 2. Experiments were performed in Langendorff perfused isolated hearts of rats subjected to 30 min no flow followed by 5 min reperfusion. The electrocardiogram was monitored continuously and noradrenaline was measured in the effluent as well as in the myocardial tissue. 3. In untreated hearts, cumulative noradrenaline overflow following global ischaemia reached 226 +/- 35 pmol g-1 of heart (n = 8, P < 0.05) during the 5 min of reperfusion along with ventricular tachycardia and/or fibrillation. A decrease in myocardial noradrenaline (-31%) was also observed. 4. Bradykinin perfused at concentrations between 0.01 and 1 microM, 10 min before flow was stopped and at reperfusion, inhibited noradrenaline overflow in a concentration-dependent manner. At a concentration of 1 microM, bradykinin completely abolished noradrenaline overflow. For the same concentration of bradykinin, myocardial noradrenaline contents were significantly higher (n = 5-8, P < 0.05). Ventricular fibrillation but not ventricular tachycardia was also prevented. 5. Des-Arg9-BK (0.1 microM) in the same experimental conditions had similar effects. While Hoe 140, a selective antagonist at B2 receptors, did not abolish the effects of bradykinin, Lys [Leu8] Des-Arg9-BK, an antagonist at B1 receptors, abolished the effects of both Des-Arg9-BK and bradykinin. 6. These results suggest that the cardioprotective action of bradykinin in the preparation may be mediated partially by an inhibitory effect on noradrenaline liberation which could be mediated by the activation of B1 receptors.

Local intracoronary infusions of bradykinin profoundly reduce the severity of ischaemia-induced arrhythmias in anaesthetized dogs

Bradykinin in a dose (25 ng kg-1 min-1) which did not alter coronary flow, or saline, were infused into a small branch of the left anterior descending coronary artery in dogs anaesthetized with chloralose and urethane, for 10 min prior to coronary artery occlusion and throughout the 25 min occlusion period. The degree of inhomogeneity of conduction and epicardial ST-segment changes were measured in the ischaemic zone with a composite electrode. In control dogs, coronary artery occlusion led to severe arrhythmias with an incidence of ventricular fibrillation of 47% and tachycardia of 80% and with a mean of 528 +/- 140 ventricular premature beats. In marked contrast, those dogs administered bradykinin had no ventricular fibrillation or tachycardia and the number of premature beats was significantly less (53 +/- 19). ST-segment changes were also much less in these dogs. These results raise the possibility that bradykinin might contribute to the protective effects of preconditioning and acts as an 'endogenous myocardial protective substance'.

New, long-acting, potent bradykinin antagonists

1. Three new bradykinin (BK) antagonists, D-Arg0-Hyp3-Thi5-D-Tic7-Oic8-BK (compound I), D-Arg0-Hyp3-D-Tic7-Oic8-BK (compound II), and Arg(Tos)1-Hyp3-Thi5-D-Tic7-Oic8-BK (compound III), were tested against the effects of BK in 9 bioassay preparations including visceral smooth muscles, vasoconstriction, plasma protein extravasation, release of prostaglandin E2, bronchoconstriction, and stimulation of afferent C-fibre nociceptors. In some of these tests the effects of the new compounds were compared with those of the antagonist D-Arg0-Hyp2-Thi5,8-D-Phe7-BK (compound IV), described by Stewart & Vavrek (1987). 2. For all bioassays the general rank order of potency of the compounds was found to be I greater than II greater than III much greater than IV. The new antagonists were long-acting; in some bioassays their effects outlasted the duration of the experiment. 3. The inhibitory effects of the new BK antagonists were specific for BK; actions of noradrenaline, angiotensin II, acetylcholine or histamine were unaffected by the antagonists. They did not stimulate the release of histamine or prostaglandins. An agonistic effect was observed only with very high concentrations of compounds I and II in the plasma protein extravasation test. 4. The long duration of action of the new BK antagonists is probably due to a high and long-lasting affinity to the BK receptors. A high resistance of the antagonists to enzymatic destruction may be another reason. 5. The new BK antagonists will be valuable tools for the investigation of the pathophysiological role of BK. In addition they may offer a potential for therapeutic applications.