Intracoronary Bradykinin Research Articles

Brief Exposure to Intracoronary Bradykinin at Reperfusion Limits Infarct Size in Isolated Rabbit Hearts by a Mechanism That Involves Both Free Radical Production and PKC

Bradykinin given at reperfusion following ischemia reduces infarct size. We determined if PKC and free radicals, signaling components involved in ischemic postconditioning, are also used by bradykinin. We also determined the minimum bradykinin infusion time required to be protective. Isolated rabbit hearts underwent 30 min coronary branch occlusion followed by 2h of reperfusion. 100 nM bradykinin was included in the perfusate for the first 60 min of reperfusion. Antagonists, when used, were present for the first 20 min of reperfusion. Bradykinin reduced infarct size from 32±4% of the risk zone in control to 11±3% (P<0.05). The scavenger 2‐mercaptopropionyl glycine (MPG), 300 uM, blocked bradykinin's protection (31±4%). The PKC antagonist chelerythrine (2.8 uM) also abrogated protection (29±3%). Infusing bradykinin for 15 min was still protective (17±3%). However, only 7 min of bradykinin did not protect (30±5%). We conclude that, like postconditioning, protection from bradykinin at reperfusion involves both redox signaling and PKC activation. While bradykinin may be too hypotensive to use intravenously, this drug could be given directly into a patient's coronary artery following percutaneous coronary intervention since the heart only needs to be exposed to bradykinin for 15 min. Work funded by NIH grant: HL 020648.

Failure of chronic transmyocardial laser revascularization to alter cardiac nociceptive reflexes: implications for the treatment of angina pectoris

The aim of this study was to assess the delayed effects of transmyocardial laser revascularization (TMLR) on cardiac nociceptors. Experiments were performed in anesthetized dogs 1 month after thoracotomy with either TMLR (n = 17) or sham laser procedure (n = 17). All dogs underwent sinoaortic denervation and vagotomy to isolate the sympathetic afferent system. Left ventricular sympathetic afferents were stimulated by intracoronary bradykinin and transmural myocardial ischemia. Efferent responses were measured by direct recording of renal sympathetic nerve activity. Renal nerve responses to intracoronary bradykinin administered to the laser-treated anterior ventricular wall were not significantly different from those observed from the unlased posterior wall. Anterior transmural ischemia elicited similar renal nerve responses in laser-treated and sham groups. Pathologic analysis showed intact neural structures in the subepicardial regions both near and remote from the lased channels. We conclude that reflexes mediated by left ventricular sympathetic afferents are preserved after chronic TMLR. These findings do not support the neural hypothesis for angina relief.

Cardiac Nociception

Cardiac Nociception

Coronary smooth muscle reactivity to muscarinic stimulation after ischemia-reperfusion in porcine myocardial infarction.

This study tested whether ischemia-reperfusion alters coronary smooth muscle reactivity to vasoconstrictor stimuli such as those elicited by an adventitial stimulation with methacholine. In vitro studies were performed to assess the reactivity of endothelium-denuded infarct-related coronary arteries to methacholine (n = 18). In addition, the vasoconstrictor effects of adventitial application of methacholine to left anterior descending (LAD) coronary artery was assessed in vivo in pigs submitted to 2 h of LAD occlusion followed by reperfusion (n = 12), LAD deendothelization (n = 11), or a sham operation (n = 6). Endothelial-dependent vasodilator capacity of infarct-related LAD was assessed by intracoronary injection of bradykinin (n = 13). In vitro, smooth muscle reactivity to methacholine was unaffected by ischemia-reperfusion. In vivo, baseline methacholine administration induced a transient and reversible drop in coronary blood flow (9.6 +/- 4.6 to 1.9 +/- 2.6 ml/min, P < 0.01), accompanied by severe left ventricular dysfunction. After ischemia-reperfusion, methacholine induced a prolonged and severe coronary blood flow drop (9.7 +/- 7.0 to 3.4 +/- 3.9 ml/min), with a significant delay in recovery (P < 0.001). Endothelial denudation mimics in part the effects of methacholine after ischemia-reperfusion, and intracoronary bradykinin confirmed the existence of endothelial dysfunction. Infarct-related epicardial coronary artery shows a delayed recovery after vasoconstrictor stimuli, because of appropriate smooth muscle reactivity and impairment of endothelial-dependent vasodilator capacity.

Role of bradykinin in preconditioning and protection of the ischaemic myocardium.

Since the first description of bradykinin more than 50 years ago (Rocha e Silva et al., 1949), actions of the peptide in a variety of physiological and pathological responses have been extensively researched (reviewed in Bhoola et al., 1992; Wirth et al., 1997; Calixto et al., 2000). In the cardiovascular system, the classical action of bradykinin is vasodilatation, mediated in several vascular beds by the release of nitric oxide (NO) and prostacyclin (Hatta et al., 1997; Wirth et al., 1997). In the heart, exogenously-administered bradykinin is a potent coronary artery vasodilator substance, although the contribution of endogenous bradykinin to the regulation of coronary vascular tone is unclear. Several actions of bradykinin in the heart are of particular interest as they are independent of the vasodilator actions of the peptide. Such actions include the modulation of cell growth and division in the heart and the modulation of myocardial responses to ischaemia-reperfusion. The ability of bradykinin to act as an endogenous cytoprotective mediator in the ischaemic myocardium has received a great deal of attention in recent years. Much of this research on bradykinin has been fuelled by a growing appreciation of ischaemic preconditioning, an adaptive mechanism in which bradykinin plays an important role. This review focuses on the cytoprotective actions of bradykinin in the ischaemic and reperfused myocardium, discusses its role in the ischaemic preconditioning response, and examines the potential for manipulating endogenous bradykinin for therapeutic benefit in myocardial ischaemia.

Cardiac nociceptive reflexes after transmyocardial laser revascularization: Implications for the neural hypothesis of angina relief

Objective: The mechanism by which transmyocardial laser revascularization relieves angina is not understood. One theory is that laser-induced thermal damage to cardiac nerves results in cardiac denervation. This study examined the acute effects of transmyocardial laser revascularization on reflex responses mediated by cardiac nociceptors, the left ventricular receptors with sympathetic afferent fibers that are thought to mediate anginal chest pain. Methods: Experiments were performed in 13 chloralose-anesthetized dogs with sinoaortic denervation and vagotomy. Left ventricular receptors with sympathetic afferent fibers were activated by epicardial and intracoronary bradykinin before and 45 minutes after transmyocardial laser revascularization. Reflex responses elicited by bradykinin were quantitated by direct recording of efferent renal sympathetic nerve activity. Transmyocardial laser revascularization was performed in the open-chest model with a hand-held holmium:YAG laser (2.1-μm wavelength). Results: An average of 44.5 ± 1.0 channels were created. Before transmyocardial laser revascularization, reflex increases in renal sympathetic nerve activity were elicited by both epicardial and intracoronary bradykinin. After transmyocardial laser revascularization, there was no significant attenuation in the reflex responses to either epicardial (before, 66% ± 8%; after, 100% ± 24%; P =.19) or intracoronary (before, 124% ± 37%; after, 108% ± 25%; P =.44) bradykinin. Conclusions: Transmyocardial laser revascularization has no significant short-term effect on reflexes mediated by left ventricular receptors with sympathetic afferent fibers in anesthetized dogs. These results indicate that transmyocardial laser revascularization does not acutely interrupt the afferent nerves, which are believed to transmit the perception of anginal pain.

Effect of acetylsalicylate on cardiac and muscular pain induced by intracoronary and intra-arterial infusion of bradykinin in humans

OBJECTIVESThis study assessed the algesic activity of bradykinin (BK) in humans and the effects of acetylsalicylate on muscular and cardiac BK-induced pain.BACKGROUNDBradykinin is released by the ischemic myocardium and may be involved in the genesis of ischemic pain.METHODSIncreasing doses of BK (from 30 to 960 ng/min) were randomly infused, for periods of 2 min each, into the iliac artery of 10 patients. The same protocol was repeated 30 min after the IV administration of 1 g of acetylsalicylate. In eight other patients with coronary artery disease, the same increasing doses of BK, for periods of 2 min each, were infused into the left coronary artery. The same protocol was repeated 30 min after the IV administration of 1 g of acetylsalicylate. Time to pain onset and maximal pain severity were obtained.RESULTSBefore acetylsalicylate administration, all patients experienced pain during intra-iliac infusion of BK. After acetylsalicylate, eight patients did not experience any pain during BK infusion (p = 0.0014), and in the two remaining patients, time to pain onset and maximal pain severity were similar to those recorded before acetylsalicylate. Before acetylsalicylate administration, all patients experienced pain similar to their habitual angina during intracoronary BK infusion. After acetylsalicylate, six patients did not experience any pain during BK infusion (p = 0.0098), whereas in the two remaining patients time to pain onset and maximal pain severity were similar to those recorded before acetylsalicylate.CONCLUSIONSIntra-iliac infusion of BK causes muscular pain, and its intracoronary infusion in patients with coronary artery disease causes cardiac pain, which is similar to their habitual angina. The BK-induced pain is abolished or reduced by acetylsalicylate, thus suggesting that acetylsalicylate-sensitive mediators, such as prostaglandins, are involved in its pathogenesis.

Abnormal flow-mediated epicardial vasomotion in human coronary arteries is improved by angiotensin-converting enzyme inhibition: A potential role of bradykinin

OBJECTIVESThis study was performed to determine whether angiotensin converting enzyme (ACE) inhibition improves endothelium-dependent flow-mediated vasodilation in patients with atherosclerosis or its risk factors and whether this is mediated by enhanced bradykinin activity.BACKGROUNDAbnormal coronary vasomotion due to endothelial dysfunction contributes to myocardial ischemia in patients with atherosclerosis, and its reversal may have an antiischemic action. Previous studies have shown that ACE inhibition improves coronary endothelial responses to acetylcholine, but whether this is accompanied by improved responses to shear stress remains unknown.METHODSIn 19 patients with mild atherosclerosis, metabolic vasodilation was assessed during cardiac pacing. Pacing was repeated during separate intracoronary infusions of low-dose bradykinin (BK) and enalaprilat. Endothelium-dependent and -independent vasodilation was estimated with intracoronary BK and sodium nitroprusside respectively.RESULTSEnalaprilat did not alter either resting coronary vascular tone or dilation with sodium nitroprusside, but potentiated BK-mediated dilation. Epicardial segments that constricted abnormally with pacing (−5 ± 1%) dilated (3 ± 2%) with pacing in the presence of enalaprilat (p = 0.002). Similarly, BK at a concentration (62.5 ng/min) that did not alter resting diameter in the constricting segments also improved the abnormal response to a 6 ± 1% dilation (p < 0.001). Cardiac pacing-induced reduction in coronary vascular resistance of 27 ± 4% (p < 0.001) remained unchanged after enalaprilat.CONCLUSIONSThus ACE inhibition: A) selectively improved endothelium-dependent but not -independent dilation, and B) abolished abnormal flow-mediated epicardial vasomotion in patients with endothelial dysfunction, in part, by increasing endogenous BK activity.

Simultaneous cardiac and renal sympathetic neural responses to activation of left ventricular sympathetic afferents

In separate sets of experiments, we observed that activation of left ventricular sympathetic afferents by transmural myocardial ischemia (TMI) appeared to elicit greater reflex increases in efferent sympathetic nerve activity (SNA) to the heart than to the kidney. To assess this observation more rigorously, we simultaneously measured changes in cardiac and renal SNA elicited by TMI and by epicardial and intracoronary bradykinin (BK). Experiments were performed in 19 chloralose-anesthetized dogs with sinoaortic denervation and vagotomy. TMI was created by a 2 min complete occlusion of the anterior descending coronary artery while a collateral flow limiting stenosis was present on the circumflex coronary artery. Epicardial BK was applied to small sponges (1 cm 2) which were placed on the anterior wall of the left ventricle. Intracoronary BK was injected into a branch of the anterior descending artery. We observed that mean maximal reflex increases in SNA during TMI and intracoronary BK were significantly greater in cardiac than in renal nerves (TMI; 58±11% versus 36±9%, p=0.01; intracoronary BK; 144±48% versus 77±26%, p=0.05). Epicardial BK elicited reflex increases in cardiac and renal SNA which were not significantly different (167±44% versus 127±36%; p=0.72). Our results indicate that activation of left ventricular sympathetic afferents by TMI and intracoronary BK elicits greater reflex increases in sympathetic outflow to the heart than to other end-organs such as the kidney. We speculate that these augmented excitatory responses are most likely related to engagement of cardio–cardiac spinal sympathetic reflexes during intense stimulation of sympathetic afferent endings.

Regional myocardial effects of intracoronary bradykinin in conscious dogs

This study examined in conscious dogs, the coronary and regional myocardial effects of bradykinin (BK) administered by intracoronary route and their modulation by an angiotensin-converting enzyme inhibitor. Eleven dogs were chronically instrumented with a left ventricular (LV) micromanometer, a circumflex coronary catheter, a flow probe, and ultrasonic crystals in the LV posterior wall. In the absence of systemic hemodynamic changes, BK (0.1-10 ng/kg i.c.) produced dose-dependent increases in coronary blood flow velocity (CBFV) and in LV posterior end-diastolic wall thickness (EDWT) but produced no change in LV regional myocardial function as assessed by LV posterior systolic wall thickening. The increases in LV EDWT and CBFV were linearly correlated. The BK B2 antagonist (HOE 140) abolished the effects of BK. Intracoronary enalaprilat (0.75 mg) extended the duration of the effect of BK on CBFV without modification of peak responses and induced a further increase in LV posterior EDWT but no change in LV regional myocardial function. Thus, in conscious dogs, the vasodilator effect of intracoronary BK alone or modulated by enalaprilat is not associated with changes in LV regional myocardial function.

Coronary and contractile effects of intracoronary bradykinin and their modulation by ACE inhibitor in normal conscious dogs

Coronary and contractile effects of intracoronary bradykinin and their modulation by ACE inhibitor in normal conscious dogs

Role of kinins in the pathophysiology of myocardial ischemia. In vitro and in vivo studies.

In ischemia, the heart generates and releases kinins as mediators that seem to have cardioprotective actions. Kinin-generating pathways are present in the heart. Kininogen, kininogenases, kinins, and B2 kinin receptors can be measured in cardiac tissue. Kinins are released under conditions of ischemia. In anesthetized rats and dogs with coronary artery ligation and in human patients with myocardial infarction, kinin plasma levels are increased. In isolated rat hearts, the outflow of kinins is enhanced during ischemia but markedly attenuated after deendothelialization, pointing to the coronary vascular endothelium as the main possible source. Kinins administered locally exert beneficial cardiac effects. In isolated rat hearts with ischemia-reperfusion injuries, perfusion with bradykinin (BK) reduces the duration and incidence of ventricular fibrillation, improves cardiodynamics, reduces release of cytosolic enzymes, and preserves energy-rich phosphates and glycogen stores. In anesthetized animals, intracoronary BK is followed by comparable beneficial changes and limits infarct size. Inhibition of breakdown of BK and related peptides induces beneficial cardiac effects. Treatment with ACE inhibitors such as ramipril increases cardiac kinin levels and reduces post-ischemic reperfusion injuries in isolated rat hearts and infarct size in anesthetized animals. The importance of an intact endothelium that continuously generates kinins is supported by observations that basal and ramipril-induced release of kinins and PGI2 is markedly reduced after deendothelialization of isolated hearts. Blockade of B2 kinin receptors increases ischemia-induced effects. Endothelial formation of NO and PGI2 by ACE inhibition is prevented by the specific B2 kinin receptor antagonist icatibant. In isolated hearts, ischemia-reperfusion injuries deteriorate with icatibant, which also abolishes the cardioprotective effects of ACE inhibitors and of exogenous BK. Infarct size reduction by ACE inhibitors and by BK in anesthetized animals is reversed by icatibant. Kinins contribute to the cardioprotective effects associated with ischemic preconditioning because preconditioning or BK-induced antiarrhythmic and infarct size-limiting effects are attenuated by icatibant. In conclusion, kinins may act as mediators of endogenous cardioprotective mechanisms. Kinins are generated and released during ischemia, with subsequent formation of PGI2 and NO probably derived mainly from the coronary vascular endothelium. Their cardioprotective profile resembles that of ACE inhibitors.

744-2 Effects of Intracoronary Bradykinin on the LV Pressure-Volume Relation and Coronary Blood Flow in Anesthetized Dogs

Myocardial bradykinin (BK) levels increase during ischemia. BK modulates cardiac efferent nerves and affects cardiovascular hemostasis possibly via BK receptors (B 1 or B 2 ). We examined the effects of BK on the end-systolic LV pressure-volume relation (ESPVR; conductance catheter method) and blood flow (BF; electromagnetic flow probe) in 6 open-chest, instrumented dogs. BK (0.01-1.0 nMlkg) was injected into the circumflex artery while LV pressure-volume loops and BF were continuously monitored without and with BK B 2 -receptor blockade with HOE-140 (HOE; 4.5 nM/kg; i.v. ). At baseline before HOE, LV systolic pressure, stroke volume, end-systolic volume, the slope of the ESPVR ( Ees ), dP/dt max and BF were 104 ± 10 mmHg, 14 ± 3 mL, 24 ± 4 mL, 2.9 ± 1.4 mmHg/mL, 1440 ± 62 mmHg/sec, and 33 ± 12 mL/min, respectively. With intracoronary BK, Ees increased in a dosedependent manner (6.9 ± 2.4 mmHg/mL at 1.0 nM/kg, p ) ≤ 0.05): BF was higher than baseline despite lower LV pressure. After HOE, LV systolic pressure increased (p ≤ 0.01), stroke volume decreased (P ≤ 0.011 and BF was unchanged. HOE blocked the dose-dependent BK-mediated hypotension and coronary vasodilatation but had no effect on peak reactive hyperemia following a 20 sec coronary occlusion (120 ± 47 vs 113 ± 41 mL/min; p = NS); BF repayment time decreased significantly (47 ± 4 vs 39 ± 5 sec). 1) BK augments LV contractility, 2) HOE blocks BK-mediated increases in LV contractility, and 3) HOE does not affect peak reactive hyperemia but reduces repayment time. Thus, BK lowers LV pressure and volume but increases BF secondary to augmented LV contractility. These effects may be receptor-mediated since they were significantly attenuated after BK B 2 receptor blockade.

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

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

Distribution of left ventricular sympathetic afferents demonstrated by reflex responses to transmural myocardial ischemia and to intracoronary and epicardial bradykinin.

Stimulation of left ventricular (LV) receptors with sympathetic afferents generally results in reflex sympathoexcitatory responses. Stimulation of LV receptors with vagal afferents results in reflex sympathoinhibitory responses. Vagal afferents are known to be preferentially distributed to the inferoposterior (IP) wall of the LV. We tested the hypothesis that there is also a preferential distribution of LV sympathetic afferents. We measured reflex responses to stimulation of sympathetic afferents located in the anterior and IP LV: We used myocardial ischemia and chemical stimuli to increase the activity of the sensory endings in 15 chloralose-anesthetized, mechanically ventilated dogs with sinoaortic denervation and vagotomy. Reflex responses were assessed by direct recordings of efferent renal sympathetic nerve activity (RSNA). In nine dogs, maximal RSNA changes elicited by transmural anterior myocardial ischemia (22.6 +/- 3.9% increase from baseline nerve traffic) were not significantly different from maximal RSNA changes observed during transmural IP ischemia (27.1 +/- 4.4%). Similar changes in mean arterial and left atrial pressures were noted during transmural anterior and IP ischemia. In eight dogs, maximal changes of RSNA elicited by epicardial or intracoronary bradykinin to the anterior LV were not significantly different from those observed during bradykinin to the IP LV (anterior epicardial bradykinin, 76.7 +/- 11.7%; IP epicardial bradykinin, 72.2 +/- 10.0%; anterior intracoronary bradykinin, 84.6 +/- 21.0%; IP intracoronary bradykinin, 88.8 +/- 17.3%). We conclude that cardiac receptors with sympathetic afferents are distributed equally to the IP and anterior regions of the LV.

Bradykinin-induced coronary chemoreflex in the dog.

The injection of 1.0 μg of bradykinin into the left coronary artery of anaesthetized dogs produces a simultaneous decrease in blood pressure and heart rate and also a less pronounced decrease in respiratory rate and amplitude. These effects are quite similar, although less intense, to those evoked by equivalent doses of veratrine. Moreover, there is no tachyphylaxis if the interval between injections is kept around 10 min. The cardiovascular changes are proportional to the dose of bradykinin up to 4.0 μg; with increasing doses only the hypotensive action is increased. Smaller doses of bradykinin are only effective in the presence of the bradykinin-potentiating-factor, BPF10 (1.0 mg/kg). The bradycardia, but not the hypotension, is potentiated by neostigmine (0.5 mg), and abolished by atropine (1.0 mg/kg). Cervical bilateral vagotomy abolishes the bradycardia and reduces the hypotension elicited by intracoronary bradykinin. When injected into the right atrium bradykinin causes hypotension and an increase in heart rate, even in the presence of BPF10. It is concluded that bradykinin induces a coronary chemoreflex when injected into the coronary artery of the dog.