Angiotensin II reduces infarct size and has no effect on post-ischaemic contractile dysfunction in isolated rat hearts

Increased Endogenous Activity of the Renin-Angiotensin System Reduces Infarct Size in the Rats with Early Angiotensin II-dependent Hypertension which Survive the Acute Ischemia/Reperfusion Injury

We investigated the role of the interaction between hypertension and the renin-angiotensin system in the pathophysiology of myocardial ischemia/reperfusion injury. We hypothesized that in the early phase of angiotensin II (ANG II)-dependent hypertension with developed left ventricular hypertrophy, cardioprotective mechanism(s) are fully activated. The experiments were performed in transgenic rats with inducible hypertension, noninduced rats served as controls. The early phase of ANG II-dependent hypertension was induced by five-days (5 days) dietary indole-3-carbinol administration. Cardiac hypertrophy, ANG II and ANG 1-7 levels, protein expression of their receptors and enzymes were determined. Separate groups were subjected to acute myocardial ischemia/reperfusion injury, and infarct size and ventricular arrhythmias were assessed. Induced rats developed marked cardiac hypertrophy accompanied by elevated ANG levels. Ischemia/reperfusion mortality was significantly higher in induced than noninduced rats (52.1 and 25%, respectively). The blockade of AT1 receptors with losartan significantly increased survival rate in both groups. Myocardial infarct size was significantly reduced after 5 days induction (by 11%), without changes after losartan treatment. In conclusion, we confirmed improved cardiac tolerance to ischemia/reperfusion injury in hypertensive cardiohypertrophied rats and found that activation of AT1 receptors by locally produced ANG II in the heart was not the mechanism underlying infarct size reduction.

Cardioprotective effects of Prolame and SNAP are related with nitric oxide production and with diminution of caspases and calpain-1 activities in reperfused rat hearts

Cardiac tissue undergoes changes during ischemia-reperfusion (I-R) that compromise its normal function. Cell death is one of the consequences of such damage, as well as diminution in nitric oxide (NO) content. This signaling molecule regulates the function of the cardiovascular system through dependent and independent effects of cyclic guanosine monophosphate (cGMP). The independent cGMP pathway involves post-translational modification of proteins by S-nitrosylation. Studies in vitro have shown that NO inhibits the activity of caspases and calpains through S-nitrosylation of a cysteine located in their catalytic site, so we propose to elucidate if the regulatory mechanisms of NO are related with changes in S-nitrosylation of cell death proteins in the ischemic-reperfused myocardium. We used two compounds that increase the levels of NO by different mechanisms: Prolame, an amino-estrogenic compound with antiplatelet and anticoagulant effects that induces the increase of NO levels in vivo by activating the endothelial nitric oxide synthase (eNOS) and that has not been tested as a potential inhibitor of apoptosis. On the other hand, S-Nitroso-N-acetylpenicillamine (SNAP), a synthetic NO donor that has been shown to decrease cell death after inducing hypoxia-reoxygenation in cell cultures. Main experimental groups were Control, I-R, I-R+Prolame and I-R+SNAP. Additional groups were used to evaluate the NO action pathways. Contractile function represented as heart rate and ventricular pressure was evaluated in a Langendorff system. Infarct size was measured with 2,3,5-triphenyltetrazolium chloride stain. NO content was determined indirectly by measuring nitrite levels with the Griess reaction and cGMP content was measured by Enzyme-Linked ImmunoSorbent Assay. DNA integrity was evaluated by DNA laddering visualized on an agarose gel and by Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling assay. Activities of caspase-3, caspase-8, caspase-9 and calpain-1 were evaluated spectrophotometrically and the content of caspase-3 and calpain-1 by western blot. S-nitrosylation of caspase-3 and calpain-1 was evaluated by labeling S-nitrosylated cysteines. Our results show that both Prolame and SNAP increased NO content and improved functional recovery in post-ischemic hearts. cGMP-dependent and S-nitrosylation pathways were activated in both groups, but the cGMP-independent pathway was preferentially activated by SNAP, which induced higher levels of NO than Prolame. Although SNAP effectively diminished the activity of all the proteases, a correlative link between the activity of these proteases and S-nitrosylation was not fully established.

Neuropathic pain attenuates ischemia reperfusion injury through β2-adrenergic pathway

AIMS

The relationship between neuropathic pain and myocardial infarction (MI) was uncertain because of some medication or underlying diseases. This study investigated the impact of neuropathic pain on ischemia reperfusion injury using isolated rat hearts and cardiomyocytes.

MAIN METHODS

Male Sprague-Dawley rats were assigned to the control and allodynia (AL) groups, with the latter subjected to the fifth lumbar spinal-nerve ligation. First, isolated hearts underwent 25-min ischemia and 90-min reperfusion to assess hemodynamic changes and MI area. Second, isolated cardiomyocytes underwent 10-min laser illumination to assess the opening of mitochondrial permeability transition pore (mPTP) and cellular hypercontraction. Lastly, expression of pro-survival kinases was measured in another cardiomyocytes using flow cytometry. AL-treated hearts were concomitantly examined regarding the involvement of β-adrenergic pathways by esmolol (ESM), β1-blocker (100μM, AL+ESM), and ICI118551 (ICI), β2-blocker (50nM, AL+ICI).

KEY FINDINGS

All hemodynamic variables did not change significantly in between-group comparisons except at 30min of reperfusion. MI area decreased remarkably in the AL and AL+ESM groups after 90-min reperfusion. The AL+ICI group significantly increased it as compared with the AL and AL+ESM groups. Similarly, the AL and AL+ESM groups significantly inhibited mPTP opening and cellular hypercontraction, whereas the AL+ICI group reversed these effects. Enhanced expression of pro-survival kinases was observed in the AL and AL+ESM groups, but the AL+ICI group abolished this enhancement.

SIGNIFICANCE

Our findings suggested that neuropathic pain possessed cardioprotective effects through inhibiting mPTP opening. The underlying mechanisms were possibly regulated by β2-adrenergic activation and pro-survival kinase expression in cardiomyocytes.

The differential effects of FTY720 on functional recovery and infarct size following myocardial ischaemia/reperfusion

AIM

The aim of this study was to evaluate the effects of the sphingosine analogue, FTY720 (Fingolimod), on the outcomes of myocardial ischaemia/reperfusion (I/R) injury.

METHODS

Two concentrations of FTY720 (1 or 2.5 µM were administered either prior to (PreFTY), or following (PostFTY) 20 minutes' global (GI) or 35 minutes' regional ischaemia (RI) in the isolated, perfused, working rat heart. Functional recovery during reperfusion was assessed following both models of ischaemia, while infarct size (IFS) was determined following RI.

RESULTS

FTY720 at 1 µM exerted no effect on functional recovery, while 2.5 µM significantly impaired aortic output (AO) recovery when administered prior to GI (% recovery: control: 33.88 ± 6.12% vs PreFTY: 0%, n = 6-10; p < 0.001), as well as before and after RI ( % recovery: control: 27.86 ± 13.22% vs PreFTY: 0.62% ; p < 0.05; and PostFTY: 2.08%; p = 0.0585, n = 6). FTY720 at 1 µM administered during reperfusion reduced IFS (% of area at risk (AAR): control: 39.89 ± 3.93% vs PostFTY: 26.56 ± 4.32%, n = 6-8; p < 0.05), while 2.5 µM FTY720 reduced IFS irrespective of the time of administration ( % of AAR: control: 39.89 ± 3.93% vs PreFTY: 29.97 ± 1.03% ; and PostFTY: 30.45 ± 2.16%, n = 6; p < 0.05).

CONCLUSION

FTY720 exerted divergent outcomes on function and tissue survival depending on the concentration administered, as well as the timing of administration.

The differential effects of a selective kappa-opioid receptor agonist, U50488, in guinea pig heart tissues

The differential effects of a selective kappa- (κ-) opioid receptor agonist, U50488, were elucidated by monitoring the contraction of isolated guinea pig atrial and ventricular muscles. In electrically driven left atria, U50488 in nanomolar concentration range decreased the contractile force. Norbinaltorphimine (norBNI), a selective κ-receptor antagonist, and pertussis toxin (PTX) abolished the negative inotropic effect of U50488. In contrast, the inhibitory effect was not affected by the pretreatment of atropine or propranolol. Even though U50488 exerted a negative inotropic effect in the left atrium, it did not affect the contractile force of the right atrium and ventricles paced at 2 Hz. Similarly, the beating rate of the spontaneously beating right atrium was also unaffected by U50488. These results indicate that the activation of κ-opioid receptors can only produce negative inotropic effect in left atria via activation of PTX-sensitive G protein in guinea pigs. The absence of negative inotropic effects in right atria and ventricles suggests that there may be a greater distribution of functional κ-opioid receptors in guinea pig left atria than in right atria and ventricles, and the distribution of the receptors may be species-specific.

Effects of acute angiotensin II on ischemia reperfusion injury following myocardial infarction

Myocardial infarction (MI) induces cardiac remodeling. This may increase the susceptibility of the infarcted heart to subsequent ischemic events. While chronic angiotensin II blockade is cardioprotective post-MI, the acute effects of angiotensin II in ischemia-reperfusion injury (IR) remains unclear. In the present study, we tested whether angiotensin II administration altered recovery of left ventricular (LV) function to IR in hearts from sham and MI rats. Echocardiography, LV pressure-volume relationships, and IR performance were established in subsets of sham (N = 27) and MI hearts (N = 41). IR was conducted in red-cell-perfused Langendorff hearts (60 minutes of low-flow ischemia; 30 minutes of reperfusion) during vehicle or angiotensin II infusions (10(-7) M). MI hearts were dilated and had reduced fractional shortening and blunted systolic elastance (p < 0.05). Despite systolic dysfunction in MI, functional recovery to IR was similar to sham. Angiotensin II significantly worsened IR performance in sham (p < 0.05), but not MI. The effect of angiotensin II on in vitro cardiomyocyte survival under various pH conditions was also tested. Acidosis increased cardiomyocyte death and angiotensin II potentiated this effect. We conclude that IR performance is similar between sham and MI hearts and that MI hearts are resistant to angiotensin II-induced cardiac dysfunction in response to IR.

99mTc-glucarate kinetics differentiate normal, stunned, hibernating, and nonviable myocardium in a perfused rat heart model

PURPOSE

(99m)Tc-glucarate is an infarct-avid imaging agent. However, patients may have mixtures of normal, irreversibly injured, stunned, and hibernating myocardium. The purposes were to determine (99m)Tc-glucarate uptake and clearance kinetics in these four conditions, and its ability to determine the extent of injury.

METHODS

Twenty-two perfused rat hearts were studied: controls (n = 5), stunned (n = 5; 20-min no-flow followed by 5-min reflow), hibernating (n = 6; 120-min low flow at 4 ml/min), and ischemic-reperfused (n = 6; 120-min no-flow followed by reflow). (99m)Tc-glucarate was then infused. Tracer activity was monitored using a NaI scintillation detector and a multichannel analyzer. Creatine kinase, electron microscopy, and triphenyltetrazolium chloride determined viability.

RESULTS

(99m)Tc-glucarate 10-min myocardial uptake was significantly greater in ischemic-reperfused (2.50 +/- 0.09) (cpm, SEM) than in control (1.74 +/- 0.07), stunned (1.68 +/- 0.11), and hibernating (1.59 +/- 0.11) (p < 0.05). Tracer retention curves for ischemic-reperfused were elevated at all time points as compared with the other groups. (99m)Tc-glucarate 60-min myocardial uptake was significantly greater in ischemic-reperfused (7.60 +/- 0.63) than in control (1.98 +/- 0.15), stunned (1.79 +/- 0.08), and hibernating (2.33 +/- 0.15) (p < 0.05). The 60-min well-counted tracer activity ratio of ischemic-reperfused to control was 9:1 and corroborated the NaI detector results. Creatine kinase, triphenyltetrazolium chloride, and electron microscopy all demonstrated significantly greater injury in ischemic-reperfused compared to the other groups. An excellent correlation was observed between viability markers and tracer activity (r = 0.99 triphenyltetrazolium chloride; r = 0.90 creatine kinase).

CONCLUSION

(99m)Tc-glucarate activity continually and progressively increased in irreversibly injured myocardium. (99m)Tc-glucarate uptake was strongly correlated with myocardial necrosis as determined by three independent assessments of viability. There were minimal and similar (99m)Tc-glucarate uptakes in control, stunned, and hibernating myocardium.

Effects of postconditioning with N,N,N'N'-tetrakis-[2-pyridylmethyl]-ethylenediamine in isolated rat hearts

Background

It was reported that N,N,N'N'-tetrakis-[2-pyridylmethyl]-ethylenediamine (TPEN), a transition metal chelator, confers cardioprotection against myocardial ischemic injury. In this study, we investigated the effect of TPEN targeting reperfusion period in isolated rat hearts.

Methods

Langendorff perfused rat hearts were subjected to 30 min of regional ischemia and 2 h of reperfusion. Hearts were randomly assigned to either control (n = 9) or 10 µM of TPEN (n = 8) groups. TPEN was perfused for a period of 5 min before and 30 min after reperfusion.

Results

The ratio of infarct area/ischemic area (AN/AR) was significantly reduced in TPEN treated hearts (6.9 ± 1.7%, P < 0.001) compared to control hearts (29.5 ± 3.2%). Recovery of left ventricular developed pressure (LVDP), rate-pressure product (RPP), +dP/dt_max, and -dP/dt_min in the control group after reperfusion were 53.8 ± 6.2%, 51.0 ± 6.3%, 51.9 ± 5.7%, and 51.4 ± 5.7%, respectively, of the baseline levels. In the TPEN group, LVDP, RPP, +dP/dt_max, and -dP/dt_min returned to 58.5 ± 4.6%, 54.8 ± 6.4%, 61.7 ± 4.9%, and 53.4 ± 3.9%, respectively, of the baseline levels. There were no significant differences in the cardiodynamic variables between the two groups (P > 0.05).

Conclusions

Pharmacological postconditioning with TPEN reduces myocardial infarction however, TPEN does not modify post-ischemic systolic dysfunction in isolated rat hearts.

99mTc-sestamibi kinetics predict myocardial viability in a perfused rat heart model

INTRODUCTION

(99m)Tc-sestamibi has been proposed as a viability imaging agent. The purposes of this study were: (1) to determine the relationship between myocardial viability and (99m)Tc-sestamibi kinetics using perfused rat heart models across a full spectrum of viability, (2) to do so under conditions where myocardial flow was controlled and held constant, and (3) to do so using multiple quantitative methods to assess myocardial viability.

METHODS

Twenty-three isolated rat hearts were perfused retrogradely with a modified Krebs-Henseleit (KH) solution. Four groups were studied: controls (C, n = 6), stunned (S, n = 6), ischemic-reperfused (IR, n = 6), and calcium injured (CAL, n = 5). Following a 20-min baseline and subsequent treatment phase, (99m)Tc-sestamibi was infused over 60 min (uptake) followed by 60 min clearance. Treatment phases consisted of 20 min no flow for S, 60 min no flow followed by 60 min reflow for IR, and 10 min infusion of KH solution without calcium followed by 20 min infusion of KH solution with 2 times normal calcium for CAL hearts. Creatine kinase (CK) assay, triphenyltetrazolium chloride (TTC) staining, and transmission electron microscopic (TEM) analysis were used to determine tissue viability.

RESULTS

Myocardial peak (99m)Tc-sestamibi uptake (%id) was significantly decreased in IR (4.11 +/- 0.22 SEM; p < 0.05) and CAL (1.07 +/- 0.13; p < 0.05), but not in S (4.88 +/- 0.17) as compared with C (5.99 +/- 0.50). One hour fractional retention was 79.3 +/- 1.9% for C, 80.3 +/- 1.3% for S (p = n.s.), 79.1 +/- 1.8% for IR (p = n.s.), and 14.9 +/- 4.3% for CAL (p < 0.05 compared to all other groups). (99m)Tc-sestamibi absolute retention (%id) 1 h after the end of tracer administration was significantly decreased in IR (3.26 +/- 0.23) and CAL (0.15 +/- 0.02) as compared with both S (3.92 +/- 0.16) and C (4.52 +/- 0.32) (p < 0.05). CK increased significantly from baseline in the IR and CAL hearts. TTC determined percent viability was 100 +/- 0% for C, 98.3 +/- 1.1% for S, 82.8 +/- 2.6% for IR, and 0.0 +/- 0% for CAL. TEM analysis supported these findings. End tracer activity was significantly correlated with TTC determined percentage viable myocardium (r = 0.93, p < 0.05) and CK leak (r = -0.90, p < 0.05).

CONCLUSION

(99m)Tc-sestamibi myocardial activity is significantly reduced in areas of nonviability after 1 h of tracer uptake and 1 h of tracer clearance. There is a linear correlation between myocardial viability, as determined by three independent methods, and tracer activity.

Anandamide reduces infarct size in rat isolated hearts subjected to ischaemia-reperfusion by a novel cannabinoid mechanism

Although the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide share a similar pharmacology, 2-AG reportedly limits myocardial ischaemia-reperfusion injury whereas anandamide does not. We therefore investigated whether or not anandamide reduces infarct size and which, if any, of the known cannabinoid-signalling pathways are involved. Rat isolated perfused hearts were subjected to global, no-flow ischaemia (30 min) and reperfusion (1 h). Agonists were present from 5 min before ischaemia until the end of reperfusion. Antagonists, where used, were present throughout the protocol. Recovery of left ventricular developed pressure and coronary flow was incomplete in control hearts and not significantly affected by any drug treatment. In vehicle-treated hearts, 26+/-3% (n=13) of the left ventricle was infarcted at the end of reperfusion. Infarction of the left ventricle was significantly reduced after 1 microM anandamide (10+/-1%, n=7) or 1 microM methanandamide (12+/-4%, n=6) but not 1 microM HU210. Neither ACPA (1 microM; CB1 receptor agonist) nor JWH133 (1 microM; CB2 receptor agonist), individually or combined significantly affected infarct size. Anandamide (1 microM) did not reduce infarct size in the presence of the CB1 receptor antagonist rimonabant (SR141716A, 1 microM) or the CB2 receptor antagonist, SR144528 (1 microM). Despite sensitivity to CB1 and CB2 receptor antagonists, the infarct-limiting action of anandamide was not mimicked by agonists selective for CB1 or CB2 receptors suggesting the involvement of a novel cannabinoid site of action.

Reversal of hyperglycemic preconditioning by angiotensin II: role of calcium transport

Myocardial cell death is an important contributor to the development of diabetic cardiomyopathy. It has been proposed that diabetes-mediated upregulation of the renin-angiotensin system leads to oxidative stress, the trigger for cardiomyocyte death and contractile dysfunction. However, the adverse effect of ANG II on the diabetic heart may extend beyond the development of the cardiomyopathy. ANG II also alters specific modulators of ischemic injury, such as PKC and calcium transport. Therefore, the present study examined the effect of ANG II on hyperglycemic preconditioning, a glucose-mediated condition associated with the elevation of PKC activity and alterations in calcium transport that render the cell resistant to hypoxia. Exposure of the glucose-treated cell to ANG II during the prehypoxic period blocked glucose-mediated cardioprotection. The reversal of hyperglycemic preconditioning was associated with enhanced accumulation of Ca(2+) during hypoxia, an effect prevented by inhibition of the Na(+)/ H(+) exchanger and the T-type Ca(2+) channel. The inhibitors of hypoxia-mediated Ca(2+) accumulation also blocked the reversal of hyperglycemic preconditioning by ANG II. Thus ANG II and glucose treatment exert opposite actions on the Na(+)/ H(+) exchanger and the T-type Ca(2+) channel. Because those transporters are involved in hypoxia-mediated apoptosis, they are logical candidates for the beneficial effects of high glucose and the adverse effects of ANG II on the hypoxic cardiomyocyte.

Quinaprilat reduces myocardial infarct size involving nitric oxide production and mitochondrial KATP channel in rabbits

This study examined whether quinaprilat, an angiotensin-converting enzyme inhibitor, reduces the infarct size, and investigated the mechanisms for its infarct size-reducing effect, in rabbits. Japanese white rabbits underwent 30 min of ischemia and 48 h of reperfusion. Quinaprilat (100 microg/kg/h or 300 microg/kg/h for 70 min, IV) was administered 20 min before ischemia with or without pretreatment with Nomega-nitro-l-arginine methyl ester (l-NAME) (10 mg/kg, IV, a nitric oxide synthase inhibitor), 5-hydroxydecanoic acid sodium salt (5-HD) or posttreatment with 5-HD (5 mg/kg, IV, a mitochondrial KATP channel blocker). The area at risk as a percentage of the left ventricle was determined by Evans blue dye and the infarct size was determined as a percent of the area at risk by triphenyl tetrazolium chloride staining. Using a microdialysis technique, myocardial interstitial levels of 2,5-dihydroxybenzoic acid (2,5-DHBA), an indicator of hydroxyl radicals, and NOx, an indicator of nitric oxide, were measured before, during, and after 30 min of ischemia. Quinaprilat significantly reduced the infarct size in a dose-dependent manner (30.1 +/- 3%, n = 10, and 27.6 +/- 2%, n = 7, respectively) compared with the control (46.5 +/- 4%, n = 10). The infarct size-reducing effect of quinaprilat was completely blocked by pretreatment with l-NAME (43.8 +/- 2%, n = 8) and 5-HD (50.1 +/- 3%, n = 8) and posttreatment with 5-HD (50.3 +/- 2%, n = 8), respectively. Quinaprilat did not affect the myocardial interstitial 2,5-DHBA level but significantly increased the NOx level during ischemia and reperfusion. Quinaprilat reduces myocardial infarct size involving NO production and mitochondrial KATP channels in rabbits without collateral circulation.

Myocardial kinetics of Tc-99m glucarate in low flow, hypoxia, and aglycemia

BACKGROUND

Technetium-99m glucarate is a myocardial infarct-avid imaging agent. Recent conflicting and inconclusive reports have suggested that the agent may be taken up by ischemic but viable myocardium. The purposes of this study were (1) to determine conclusively whether there is Tc-99m glucarate uptake in ischemic viable myocardium and (2) to investigate the potential mechanisms for such uptake by studying components of ischemia, namely, low flow, hypoxia, and aglycemia.

METHODS AND RESULTS

Rat hearts were isolated and perfused in a modified Langendorff preparation with a crytalloid perfusate. Tc-99m glucarate was studied in control (n = 6), low-flow (n = 5), hypoxic (n = 5), and aglycemic (n = 5) conditions. The experimental protocol consisted of 20-minute baseline (12 mL/min flow) and 20-minute treatment (low flow at 1 mL/min, hypoxia, or aglycemia), followed by tracer uptake (20 minute) and washout (20 minutes). Activity was monitored with a sodium iodide detector. The tracer was delivered continuously over a 20-minute uptake period. The injected dose was 150 micro Ci (5.6 MBq). Hemodynamics were monitored throughout. Triphenyltetrazolium chloride staining was used to assess myocardial viability. There was no evidence of myocardial necrosis. Low flow tended to delay tracer uptake compared with control for the first 10 minutes, but this did not reach statistical significance. Low flow increased end fractional retention significantly compared with control (mean +/- SEM, 59.0% +/- 0.9% peak vs 41.2% +/- 1.4%, respectively; P <.05). Hypoxia resulted in a trend toward increased uptake; however, this was significant only at one early time point during the uptake phase. Retention in the hypoxia group was similar to control. Tc-99m glucarate uptake was significantly increased in aglycemia from 16 minutes to peak compared with control (1.36% +/- 0.71% injected dose per gram vs 0.91% +/- 0.37% injected dose per gram, respectively; P <.05). Aglycemia produced significantly higher end fractional retention compared with control (51.6% +/- 1.8% peak vs 41.2% +/- 1.4%, respectively; P <.05).

CONCLUSIONS

Tc-99m glucarate myocardial retention is increased in the setting of ischemia, even in the absence of necrosis. This increased retention is not due to hypoxia. Furthermore, the retention is only partially explained by tissue hypoglycemia. Thus low flow per se appears to have a role in this increased retention, probably as a result of delayed flow-dependent washout.

Angiotensin II activates NADPH oxidase in isolated rat hearts subjected to ischaemia-reperfusion

The role of angiotensin II in myocardial ischaemia-reperfusion is not clearly defined. In this respect, the involvement of NADPH oxidase remains to be determined. The aim of this study was 1) to evaluate the cardiac effects of angiotensin AT(1) receptor stimulation in non-ischaemic conditions of perfusion or during ischaemia-reperfusion, and 2) to measure the concomitant activation of NADPH oxidase in isolated rat hearts perfused with angiotensin II and/or Losartan. In non-ischaemic hearts, angiotensin II induced rapid and prolonged vasoconstrictive and negative inotropic effects. Ischaemia-reperfusion increased the mRNA expression of AT(1) and AT(2) receptors. During reperfusion, angiotensin II reduced the incidence of arrhythmias and the lactate dehydrogenase released, and increased NADPH oxidase mRNA expression and enzyme activity. Losartan co-administration totally antagonised the effects of angiotensin II. Our study demonstrates that ischaemia-reperfusion induces adaptative cardiac modifications, which allow exogenously added angiotensin II to stimulate myocardial NADPH oxidase through angiotensin AT(1) receptor activation.

Angiotensin-(1-7) improves the post-ischemic function in isolated perfused rat hearts

We evaluated the effects of angiotensin-(1-7) (Ang-(1-7)) on post-ischemic function in isolated hearts from adult male Wistar rats perfused according to the Langendorff technique. Local ischemia was induced by coronary ligation for 15 min. After ischemia, hearts were reperfused for 30 min. Addition of angiotensin II (Ang II) (0.20 nM, N = 10) or Ang-(1-7) (0.22 nM, N = 10) to the Krebs-Ringer perfusion solution (KRS) before the occlusion did not modify diastolic or systolic tension, heart rate or coronary flow (basal values for Ang-(1-7)-treated hearts: 0.72 +/- 0.08 g, 10.50 +/- 0.66 g, 216 +/- 9 bpm, 5.78 +/- 0.60 ml/min, respectively). During the period of occlusion, the coronary flow, heart rate and systolic tension decreased (values for Ang-(1-7)-treated hearts: 2.83 +/- 0.24 ml/min, 186 +/- 7 bpm, 6.95 +/- 0.45 g, respectively). During reperfusion a further decrease in systolic tension was observed in control (4.95 +/- 0.60 g) and Ang II-treated hearts (4.35 +/- 0.62 g). However, in isolated hearts perfused with KRS containing Ang-(1-7) the further reduction of systolic tension during the reperfusion period was prevented (7.37 +/- 0.68 g). The effect of Ang-(1-7) on the systolic tension was blocked by the selective Ang-(1-7) antagonist A-779 (2 nM, N = 9), by the bradykinin B2 antagonist HOE 140 (100 nM, N = 10), and by indomethacin pretreatment (5 mg/kg, ip, N = 8). Pretreatment with L-NAME (30 mg/kg, ip, N = 8) did not change the effect of Ang-(1-7) on systolic tension (6.85 +/- 0.61 g). These results show that Ang-(1-7) at low concentration (0.22 nM) improves myocardial function (systolic tension) in ischemia/reperfusion through a receptor-mediated mechanism involving release of bradykinin and prostaglandins.