Bradykinin protects the rabbit heart after cardioplegic ischemia via NO-dependent pathways

Bradykinin preconditioning improves therapeutic potential of human endothelial progenitor cells in infarcted myocardium

Objectives

Stem cell preconditioning (PC) is a powerful approach in reducing cell death after transplantation. We hypothesized that PC human endothelial progenitor cells (hEPCs) with bradykinin (BK) enhance cell survival, inhibit apoptosis and repair the infarcted myocardium.

Methods

The hEPCs were preconditioned with or without BK. The hEPCs apoptosis induced by hypoxia along with serum deprivation was determined by annexin V-fluorescein isothiocyanate/ propidium iodide staining. Cleaved caspase-3, Akt and eNOS expressions were determined by Western blots. Caspase-3 activity and vascular endothelial growth factor (VEGF) levels were assessed in hEPCs. For invivo studies, the survival and cardiomyocytes apoptosis of transplanted hEPCs were assessed using 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodi- carbocyanine,4-chlorobenzenesul-fonate salt labeled hEPCs and TUNEL staining. Infarct size and cardiac function were measured at 10 days after transplantation, and the survival of transplanted hEPCs were visualized using near-infrared optical imaging.

Results

Invitro data showed a marked suppression in cell apoptosis following BK PC. The PC reduced caspase-3 activation, increased the Akt, eNOS phosphorylation and VEGF levels. Invivo data in preconditioned group showed a robust cell anti-apoptosis, reduction in infarct size, and significant improvement in cardiac function. The effects of BK PC were abrogated by the B2 receptor antagonist HOE140, the Akt and eNOS antagonists LY294002 and L-NAME, respectively.

Conclusions

The activation of B2 receptor-dependent PI3K/Akt/eNOS pathway by BK PC promotes VEGF secretion, hEPC survival and inhibits apoptosis, thereby improving cardiac function invivo. The BK PC hEPC transplantation for stem cell-based therapies is a novel approach that has potential for clinical used.

Signaling pathways of cardioprotective ischemic preconditioning

BACKGROUND

Ischemia/reperfusion (I/R) injury is a major contributory factor to cardiac dysfunction and infarct size that determines patient prognosis after acute myocardial infarction. During the last 20 years, since the appearance of the first publication on ischemic preconditioning (IP), our knowledge of this phenomenon has increased exponentially.

RESULTS AND CONCLUSION

Basic scientific experiments and preliminary clinical trials in humans suggest that IP confers resistance to subsequent sustained ischemic insults not only in the regional tissue but also in distant organs (remote ischemic preconditioning), which may provide a simple, cost-effective means of reducing the risk of perioperative myocardial ischemia. The mechanism may be humoral, neural, or a combination of both, and involves adenosine, bradykinin, protein kinases and K(ATP) channels, although the precise end-effector remains unclear. This review describes different signaling pathways involved in acute ischemic preconditioning in detail.

Calcium-activated potassium channels contribute to human coronary microvascular dysfunction after cardioplegic arrest

BACKGROUND

Cardioplegic arrest (CP) followed by reperfusion after cardiopulmonary bypass induces coronary microvascular dysfunction. We investigated the role of calcium-activated potassium (K(Ca)) channels in this dysfunction in the human coronary microvasculature.

METHODS AND RESULTS

Human atrial tissue was harvested before CP from a nonischemic segment and after CP from an atrial segment exposed to hyperkalemic cold blood CP (mean CP time, 58 minutes) followed by 10-minute reperfusion. In vitro relaxation responses of precontracted arterioles (80 to 180 mum in diameter) in a pressurized no-flow state were examined in the presence of K(Ca) channel activators/blockers and several other vasodilators. We also examined expression and localization of K(Ca) channel gene products in the coronary microvasculature using reverse transcriptase-polymerase chain reaction, immunoblot, and immunofluorescence photomicroscopy. Post-CP reperfusion relaxation responses to the activator of intermediate and small conductance K(Ca) channels (IK(Ca)/SK(Ca)), NS309 (10(-5) M), and to the endothelium-dependent vasodilators, substance P (10(-8) M) and adenosine 5diphosphate (10(-5) M), were significantly reduced compared with pre-CP responses (P<0.05, n=8/group). In contrast, relaxation responses to the activator of large conductance K(Ca) channels (BK(Ca)), NS1619 (10(-5) M), and to the endothelium-independent vasodilator, sodium nitroprusside (10(-4) M), were unchanged pre- and post-CP reperfusion (n=8/group). Endothelial denudation significantly diminished NS309-induced vasodilatation and abolished substance P- or adenosine 5 diphosphate-induced relaxation (P<0.05), but had no effect on relaxation induced by either NS1619 or sodium nitroprusside. The total polypeptide levels of BK(Ca), IK(Ca), and SK(Ca) and the expression of IK(Ca) mRNA were not altered post-CP reperfusion.

CONCLUSIONS

Cardioplegic arrest followed by reperfusion after cardiopulmonary bypass causes microvascular dysfunction associated with and likely in part due to impaired function of SK(Ca) and IK(Ca) channels in the coronary microcirculation. These results suggest novel mechanisms of endothelial and smooth muscle microvascular dysfunction after cardiac surgery.

Nitric oxide homeostasis as a target for drug additives to cardioplegia

The vascular endothelium of the coronary arteries has been identified as the important organ that locally regulates coronary perfusion and cardiac function by paracrine secretion of nitric oxide (NO) and vasoactive peptides. NO is constitutively produced in endothelial cells by endothelial nitric oxide synthase (eNOS). NO derived from this enzyme exerts important biological functions including vasodilatation, scavenging of superoxide and inhibition of platelet aggregation. Routine cardiac surgery or cardiologic interventions lead to a serious temporary or persistent disturbance in NO homeostasis. The clinical consequences are "endothelial dysfunction", leading to "myocardial dysfunction": no- or low-reflow phenomenon and temporary reduction of myocardial pump function. Uncoupling of eNOS (one electron transfer to molecular oxygen, the second substrate of eNOS) during ischemia-reperfusion due to diminished availability of L-arginine and/or tetrahydrobiopterin is even discussed as one major source of superoxide formation. Therefore maintenance of normal NO homeostasis seems to be an important factor protecting from ischemia/reperfusion (I/R) injury. Both, the clinical situations of cardioplegic arrest as well as hypothermic cardioplegic storage are followed by reperfusion. However, the presently used cardioplegic solutions to arrest and/or store the heart, thereby reducing myocardial oxygen consumption and metabolism, are designed to preserve myocytes mainly and not endothelial cells. This review will focus on possible drug additives to cardioplegia, which may help to maintain normal NO homeostasis after I/R.

Bradykinin induces microvascular preconditioning through the opening of calcium-activated potassium channels

BACKGROUND

This study was designed to investigate whether the activation of calcium-activated potassium (K(Ca)) or adenosine triphosphate sensitive potassium (K(ATP)) channels are required for bradykinin-induced microvascular preconditioning.

METHODS

Isolated rabbit hearts underwent retrograde perfusion with Krebs-Henseleit buffer (KHB) followed by 60 minutes of ischemic arrest with cold crystalloid cardioplegia (CCCP). Eight CCCP hearts received no pretreatment. Six bradykinin-preconditioned hearts received a 10-minute coronary infusion of 10(-8) mol/L bradykinin-enriched KHB followed by a 5-minute recovery period before CCCP. Six hearts received both 10(-8) mol/L charybdotoxin (a K(Ca) channel blocker) and bradykinin preconditioning. Finally, 6 other hearts received 10(-5 degrees ) mol/L glibenclamide (a K(ATP) channel blocker) to bradykinin-enriched KHB. All hearts were reperfused for 30 minutes with KHB.

RESULTS

Bradykinin preconditioning significantly improved the recovery of left ventricular and microvascular function, as compared with control. On the other hand, bradykinin preconditioning significantly reduced the contractile responses to U46619, a thromboxane A2 analogue. Charybdotoxin significantly inhibited the improved recovery of bradykinin-induced left ventricular and microvascular function. Glibenclamide tended to diminish the bradykinin preconditioning-enhanced recovery of left ventricular function, but failed to affect bradykinin preconditioning-improved recovery of microvascular function.

CONCLUSION

Both K(Ca) and K(ATP) channels were involved partially in bradykinin-induced myocardial preconditioning. However, bradykinin induces microvascular preconditioning through the opening of K(Ca) channels rather than K(ATP) channels.

Bradykinin preconditioning improves the profile of cell survival proteins and limits apoptosis after cardioplegic arrest

BACKGROUND

We hypothesized that preconditioning the heart with bradykinin (BK) would improve the profile of antiapoptotic proteins and inhibit myocardial apoptosis.

METHODS AND RESULTS

Eighteen rabbit hearts were retrogradely perfused with Krebs-Henseleit buffer (KHB). Six control hearts were perfused with KHB for 90 minutes without cardioplegia ischemia. Six hearts were arrested for 30 minutes (37 degrees C) with crystalloid cardioplegia (CCP). Six BK preconditioning (BKPC) hearts received a 10-minute coronary infusion of 10(-8) M BK-enriched KHB followed by a 5-minute recovery period and were then arrested for 30 minutes with CCP. The hearts were reperfused for 30 minutes with KHB. BKPC significantly improved the recovery of left ventricular pressure (73+/-5 versus 51+/-4 mm Hg; P<0.05) and reduced the percentage of myocardial apoptosis (3.4+/-0.3% versus 1.2+/-0.2%; P<0.05) as compared with CCP. There were no significant differences in total protein levels of caspase 3, Bcl-2, Bad, and Bax, among the groups. Both BKPC and CCP induced phosphorylation of Bad at Ser112, but the BKPC group had higher phosphorylated Bad than CCP (4.4+/-0.5 versus 2.0+/-0.3; P<0.05). Both BKPC and CCP alone increased caspase 3 cleavage and activity as compared with controls (P<0.05 and P<0.01, respectively), but BKPC caused less cleavage and activation of caspase 3 than CCP alone (P<0.05).

CONCLUSIONS

BKPC increased Bad phosphorylation, inhibited caspase 3 activation, and limited myocardial apoptosis, which were associated with improvement of left-ventricular performance. These results identify novel molecular mechanisms underlying the protective effects of BKPC during cardiac surgery.

Bradykinin Preconditions Postischemic Arterial Endothelial Function in Humans

BACKGROUND

Arterial endothelial dysfunction is an important mechanism of tissue injury caused by ischemia-reperfusion (I/R). Earlier studies of I/R have shown that intracoronary preinfusion with 2.5-5 microg/mL bradykinin (BK) could alleviate the postischemic myocardial damage. Using an experimental human model of I/R, we investigated whether preceding infusion with BK could prevent the I/R-induced arterial endothelial dysfunction.

METHODS

The left radial artery (LRA) from 16 healthy male adults, 18 to 30 years old, was submitted to I/R by completely occluding the left brachial artery with a pressure tourniquet for 20 minutes (ischemia), followed by its release (reperfusion). Prior to I/R, half of the subjects were randomly assigned to receive either BK (5 microg/mL) or saline, both being infused into the left brachial artery (0.5 mL/min, 10 min). The infusion was followed by a 10-minute drug-free period. The endothelial function of the LRA was studied by measuring the flow-mediated dilation (FMD) at baseline (prior to drug infusion), and at 15 minutes of reperfusion. In addition, baseline radial artery diameter, plasma nitrate, and von Willebrand factor were measured at these time points, and immediately before I/R (pre-I/R).

RESULTS

BK had no effect on the pre-I/R plasma nitrate (p > 0.5 vs. saline) and diameter of LRA (p > 0.5 vs. baseline). At 15 minutes of reperfusion, FMD was significantly decreased in the saline group as compared to baseline (absolute dilation: 0.08 +/- 0.03 vs. 3.02 +/- 0.8 mm, respectively, p < 0.01; percentage dilation: 3 +/- 0.6 vs. 8 +/- 0.6%, respectively, p < 0.001), but it remained unaffected in the BK group (absolute dilation: 3.06 +/- 0.9 vs. 3.27 +/- 0.8 mm, respectively, p > 0.5; percentage dilation: 7 +/- 0.7 vs. 8 +/- 0.8%, respectively, p > 0.5). A similar trend was observed with regard to plasma nitrate, which remained unchanged in the BK group (37.01 +/- 4.14 vs. 39.14 +/- 4.49 micromol/L, p > 0.5) but decreased in the saline group (35.91 +/- 3.03 vs. 28.91 +/- 2.81 micromol/L, p < 0.1).

CONCLUSION

Infusion of BK could protect the arterial endothelial function against I/R injury in humans, possibly in part by preserving the endothelial NO availability. The findings support the use of BK in the prevention of tissue injury due to I/R and might reveal an additional mechanism whereby ACE inhibitors exert their preconditioning effects on myocardium.

The balance between the production of tumor necrosis factor-alpha and interleukin-10 determines tissue injury and lethality during intestinal ischemia and reperfusion

A major goal in the treatment of acute ischemia of a vascular territory is to restore blood flow to normal values, i.e. to "reperfuse" the ischemic vascular bed. However, reperfusion of ischemic tissues is associated with local and systemic leukocyte activation and trafficking, endothelial barrier dysfunction in postcapillary venules, enhanced production of inflammatory mediators and great lethality. This phenomenon has been referred to as "reperfusion injury" and several studies demonstrated that injury is dependent on neutrophil recruitment. Furthermore, ischemia and reperfusion injury is associated with the coordinated activation of a series of cytokines and adhesion molecules. Among the mediators of the inflammatory cascade released, TNF-alpha appears to play an essential role for the reperfusion-associated injury. On the other hand, the release of IL-10 modulates pro-inflammatory cytokine production and reperfusion-associated tissue injury. IL-1beta, PAF and bradykinin are mediators involved in ischemia and reperfusion injury by regulating the balance between TNF-alpha and IL-10 production. Strategies that enhance IL-10 and/or prevent TNF-alpha concentration may be useful as therapeutic adjuvants in the treatment of the tissue injury that follows ischemia and reperfusion.

Bradykinin Preconditioning Preserves Coronary Microvascular Reactivity During Cardioplegia–Reperfusion

BACKGROUND

Alterations of microvascular reactivity reduce myocardial perfusion after ischemic cardioplegia. We hypothesized that bradykinin preconditioning (BKPC) would preserve endothelium-dependent microvascular responses and improve myocardial function after cardioplegic ischemia-reperfusion.

METHODS

Rabbit hearts were perfused with Krebs-Henseleit buffer (KHB). The hearts were arrested for 60 minutes with moderately cold (25 degrees C) crystalloid cardioplegia (MCCP, n = 8) or with cold (0 degrees to 4 degrees C) crystalloid cardioplegia (CCCP) (n = 6). The BKPC hearts received a 10-minute coronary infusion of 10(-8) M BK-enriched KHB, followed by a 5-minute recovery period, and then were arrested for 60 minutes with MCCP (BKPC + MCCP, n = 8) or with CCCP (BKPC + CCCP, n = 6). The hearts were reperfused for 30 minutes with KHB. Six control hearts were perfused with KHB for 90 minutes without cardioplegia-ischemia. Left ventricle performance was measured, and in vitro relaxation responses of precontracted coronary arterioles (internal diameter, 80 to 150 mum) were obtained in a pressurized no-flow state.

RESULTS

Ischemic arrest with MCCP or CCCP markedly reduced endothelium-dependent relaxation to adenosine 5'-diphosphate, substance P, and calcium ionophore (A23187). Both MCCP and CCCP significantly enhanced contractile responses to U46619 (10(-7) M), a thromboxane A2 analogue, compared with control (p < 0.05). In contrast, BKPC significantly improved the recovery of endothelium-dependent relaxation to adenosine 5'-diphosphate, substance P, and A23187 compared with MCCP or CCCP, respectively. BKPC reduced the contractile responses to U46619 compared with MCCP or CCCP. BKPC also improved postischemic performance compared with MCCP or CCCP alone (p < 0.05).

CONCLUSIONS

BKPC preserves endothelium-dependent microvascular responses and prevents the hypercontractility to U46619. These effects may provide increased coronary perfusion and prevent arteriolar spasm after open heart surgery. They suggest that BK preconditions the coronary microvasculature during cardiovascular surgery.

Pharmacological Preconditioning With Bradykinin Affords Myocardial Protection Through NO-dependent Mechanisms

Bradykinin (BK) is one of the triggers of ischemic preconditioning. Protein kinase C (PKC) and mitochondrial ATP-dependent potassium (K(ATP)) channels are central factors in cardioprotection afforded by BK. However, the role of nitric oxide (NO) in the early phase protection of preconditioning with BK is not well understood. We assessed the signaling pathway of the early phase protection of pharmacological preconditioning afforded by BK. Isolated perfused rat hearts (n = 8/group) were subjected to 30-minute global ischemia and 50-minute reperfusion. Left ventricular systolic pressure (LVSP) was recorded prior to the global ischemia and at the end of reperfusion. Preconditioning with BK was induced by two cycles of 5-minute infusion of BK (0.5 micromol/L) and 5-minute washout prior to the global ischemia. To examine participants in the signaling pathway, 5-hydroxydecanoate (5-HD, 200 micromol/L), chelerythrine (CH, 5 micromol/L), or N(omega)-nitro-L-arginine methyl ester (L-NAME, 50 mmol/L) was added to the perfusate for 5 minutes prior to the infusion of BK. Pharmacological preconditioning by BK improved postischemic recovery of LVSP (+ 45.1% versus control, P < 0.01). Protection by BK was abolished by coadministration of CH, 5-HD, or L-NAME. BK affords myocardial protection in the early phase of pharmacological preconditioning through a pathway that includes endogenous NO, PKC, and mitochondrial K(ATP) channels.

Bradykinin preconditioning in coronary artery bypass grafting

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Role of bradykinin B2 and B1 receptors in the local, remote, and systemic inflammatory responses that follow intestinal ischemia and reperfusion injury

The administration of bradykinin may attenuate ischemia and reperfusion (I/R) injury by acting on B(2)Rs. Blockade of B(2)R has also been shown to ameliorate lesions associated with I/R injury. In an attempt to explain these contradictory results, the objective of the present work was to investigate the role of and interaction between B(1) and B(2) receptors in a model of intestinal I/R injury in mice. The bradykinin B(2)R antagonist (HOE 140) inhibited reperfusion-induced inflammatory tissue injury and delayed lethality. After I/R, there was an increase in the expression of B(1)R mRNA that was prevented by HOE 140. In mice that were deficient in B(1)Rs (B(1)R(-/-) mice), inflammatory tissue injury was abrogated, and lethality was delayed and partially prevented. Pretreatment with HOE 140 reversed the protective anti-inflammatory and antilethality effects provided by the B(1)R(-/-) phenotype. Thus, B(2)Rs are a major driving force for B(1)R activation and consequent induction of inflammatory injury and lethality. In contrast, activation of B(2)Rs may prevent exacerbated tissue injury and lethality, an effect unmasked in B(1)R(-/-) mice and likely dependent on the vasodilatory actions of B(2)Rs. Blockade of B(1)Rs could be a more effective strategy than B(2) or B(1)/B(2) receptor blockade for the treatment of the inflammatory injuries that follow I/R.

Bradykinin induces mitochondrial ROS generation via NO, cGMP, PKG, and mitoKATP channel opening and leads to cardioprotection

Bradykinin (BK) mimics ischemic preconditioning by generating reactive oxygen species (ROS). To identify intermediate steps that lead to ROS generation, rabbit cardiomyocytes were incubated in reduced MitoTracker Red stain, which becomes fluorescent after exposure to ROS. Fluorescence intensity in treated cells was expressed as a percentage of that in paired, untreated cells. BK (500 nM) caused a 51 +/- 16% increase in ROS generation (P < 0.001). Coincubation with either the BK B2-receptor blocker HOE-140 (5 microM) or the free radical scavenger N-(2-mercaptopropionyl)glycine (1 mM) prevented this increase, which confirms that the response was receptor mediated and ROS were actually being measured. Closing mitochondrial ATP-sensitive K+ (mitoKATP) channels with 5-hydroxydecanoate (5-HD, 1 mM) prevented increased ROS generation. BK-induced ROS generation was blocked by Nomega-nitro-m-arginine methyl ester (m-NAME, 200 microM), which implicates nitric oxide as an intermediate. Blockade of guanylyl cyclase with 1-H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10 microM) aborted BK-induced ROS generation but not that from diazoxide, a direct opener of mitoKATP channels. The protein kinase G (PKG) blocker 8-bromoguanosine-3',5'-cyclic monophosphorothioate (25 microM) eliminated the effects of BK. Conversely, direct activation of PKG with 8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphate (100 microM) increased ROS generation (39 +/- 15%; P < 0.004) similar to BK. This increase was blocked by 5-HD. Finally, the nitric oxide donor S-nitroso-N-acetylpenicillamine (1 microM) increased ROS by 34 +/- 6%. This increase was also blocked by 5-HD. In intact rabbit hearts, BK (400 nM) decreased infarction from 30.5 +/- 3.0 of the risk zone in control hearts to 11.9 +/- 1.4% (P < 0.01). This protection was aborted by either 200 microM m-NAME or 2 microM ODQ (35.4 +/- 5.7 and 30.4 +/- 3.0% infarction, respectively; P = not significant vs. control). Hence, BK preconditions through receptor-mediated production of nitric oxide, which activates guanylyl cyclase. The resulting cGMP activates PKG, which opens mitoKATP. Subsequent release of ROS triggers cardioprotection.

Acute antihypertrophic actions of bradykinin in the rat heart: importance of cyclic GMP

The antihypertrophic action of angiotensin (Ang)-converting enzyme (ACE) inhibitors in the heart is attributed in part to potentiation of bradykinin. Bradykinin prevents hypertrophy of cultured cardiomyocytes by releasing nitric oxide (NO) from endothelial cells, which increases cardiomyocyte guanosine 3'5'-cyclic monophosphate (cyclic GMP). It is unknown whether cyclic GMP is essential for the action of bradykinin, or whether findings in isolated cardiomyocytes apply in whole hearts, in the presence of other cell types and mechanical/dynamic activity. We now examine the contribution of cyclic GMP to the antihypertrophic action of bradykinin in cardiomyocytes and perfused hearts. In adult rat isolated cardiomyocytes cocultured with bovine aortic endothelial cells, the inhibitory action of bradykinin (10 micromol/L) against Ang II (1 micromol/L)-induced [3H]phenylalanine incorporation was abolished by the soluble guanylyl cyclase inhibitor [1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L). In Langendorff-perfused rat hearts, Ang II (10 nmol/L)-induced increases in [3H]phenylalanine incorporation and atrial natriuretic peptide mRNA expression were prevented by bradykinin (100 nmol/L), the NO donor sodium nitroprusside (3 micromol/L), and the ACE inhibitor ramiprilat (100 nmol/L). The acute antihypertrophic action of bradykinin was accompanied by increased left ventricular cyclic GMP, and the ramiprilat effect was attenuated by HOE 140 (1 micromol/L, a B2-kinin receptor antagonist) or [1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (100 nmol/L). In conclusion, bradykinin exerts a direct inhibitory action against the acute hypertrophic response to Ang II in rat isolated hearts, and elevation of cardiomyocyte cyclic GMP may be an important antihypertrophic mechanism used by bradykinin and ramiprilat in the heart.

Bradykinin elicits "second window" myocardial protection in rat heart through an NO-dependent mechanism

Bradykinin is an important endogenous mediator exerting acute protective effects in the ischemic myocardium. The aims of this study were to investigate whether exogenously administered bradykinin could evoke delayed myocardial protection and to determine whether any protection observed might be dependent on nitric oxide (NO) generation. Conscious rats received bradykinin (40 microg/kg iv) or saline, preceded 15-20 min earlier by the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg ip) or saline. Twenty-four hours later, hearts were Langendorff perfused and subjected to 35 min of regional ischemia and 120 min of reperfusion. Infarct size was assessed using tetrazolium staining and expressed as a percentage of the risk zone. Bradykinin pretreatment reduced the infarct-to-risk ratio from 53.5 +/- 3.2% to 29.1 +/- 4.7% (P < 0.01). The administration of L-NAME before bradykinin abrogated the delayed protection (infarct size 52.3 +/- 5.0%) but alone did not influence infarct size (53.5 +/- 4.8%). These results are the first to demonstrate that bradykinin can evoke a delayed ("second window") enhancement of myocardial tolerance to ischemia, an action that is dependent on the early generation of NO.

Bradykinin B2 receptor is involved in the late phase of preconditioning in rabbit heart

Activation of bradykinin B2 receptor has been shown to confer short-term cardioprotection against a prolonged ischemic insult. The present study was designed to delineate the role of B2 receptor in the late phase of ischemic preconditioning. Anesthetized, open chest, male rabbits were assigned to 1 of 6 groups (n=8/group). Ischemic preconditioning was elicited by four 5-min occlusion periods interspersed with 10 min of reperfusion. To test the role of B2 receptors, rabbits were pretreated with specific receptor antagonist, HOE-140 (1 microgm/kg IV bolus), 15 min prior to ischemic preconditioning. Additionally, two separate groups of animals were treated by intra-atrial infusion with either bradykinin (0.05 microg/kg/min for 15 min) or saline. Twenty-four hours later, the animals were subjected to 30 min of ischemia and 3 h of reperfusion. Infarct size was determined by tetrazolium staining. Ischemic preconditioning reduced infarct size from 43.09+/-4.66 to 20.65+/-1.87 (% risk area, P<0.05), which was blocked by HOE-140 as indicated by increase in infarct size (36.72+/-4.04%, P<0.05). HOE-140 treatment had no significant effect on infarct size in the sham group. Similarly, intra-atrial infusion of bradykinin caused decrease in the infarct size from 52.36+/-2.17% in the saline control group to 22.83+/-1.71% (P<0.05). The degree of infarct limitation with bradykinin was comparable to ischemic preconditioning (20.65+/-1.87%v 22.83+/-1.71%, P>0.05). For the first time, these results provide evidence for the involvement of B2 receptor in the genesis of late phase of ischemic preconditioning.