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Ann Thorac Surg 2007;83:1121-1127
© 2007 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Sodium–Hydrogen Exchange Inhibition and ß-Blockade Additively Decrease Infarct Size

Peipei Wang, MD, PhDa, Corinne Zaragoza, MSb, William Holman, MDc,*

a Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
b Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama
c Department of Surgery, University of Alabama at Birmingham, Birmingham, Alabama

Accepted for publication October 16, 2006.

* Address correspondence to Dr Holman, Department of Surgery, Room 719, 703 19th St S, Birmingham, AL 35294-0007 (Email: wholman{at}its.uab.edu).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background: Perioperative myocardial infarction adversely affects survival after cardiac operations. In animal studies Na+/H+ exchange inhibitors protect hearts against ischemia–reperfusion injury, but human trials have failed to consistently show beneficial effects. The aim of this study was to investigate whether the combination of the Na+/H+ exchange inhibitor cariporide and the ß-blocker metoprolol additively protects hearts from severe ischemia–reperfusion injury.

Methods: Isolated Langendorff-perfused rat hearts were randomly assigned to a vehicle-treated control group, or groups with 10-minute preischemia infusions of cariporide (10 µmol/L), metoprolol (10 µmol/L), or both cariporide and metoprolol. The hearts were then subjected to 20 minutes of global ischemia followed by 60 minutes of reperfusion. At the end of reperfusion, the hearts were randomly assigned to undergo either infarct size measurements or left ventricular mitochondrial function analyses.

Results: The combination of cariporide and metoprolol limited infarct size significantly compared with control group or cariporide alone (5% ± 1% versus 58% ± 9% or 38.4% ± 4% of risk zone; p < 0.05). Cariporide alone did not reduce infarct size significantly as compared with the control group. As compared with the control group, cariporide and metoprolol decreased mitochondrial calcium content (6.4 ± 1.2 versus 10.2 ± 1.1 nmol/mg protein; p < 0.05), and increased respiratory control ratio (9.5 ± 0.6 versus 5.3 ± 0.7; p < 0.05). However, hearts treated with cariporide or metoprolol alone did not show significant improvement in mitochondrial calcium content (7.8 ± 1.2 and 7.8 ± 1.5 nmol/mg protein) or respiratory control ratio (5.0 ± 0.7 and 7.3 ± 0.7).

Conclusions: The combination of cariporide and metoprolol additively limits infarct size after severe ischemia–reperfusion injury in an isolated rat heart model. Infarct size reduction occurs in association with protection from increased mitochondrial calcium content after reperfusion.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Perioperative myocardial ischemia and infarction may occur as a complication in all types of cardiac operations and remains an important problem in cardiac surgery [1]. For example, during coronary artery bypass grafting, it affects an estimated 13,000 patients annually [2], or 3% to 6% patients undergoing this operation [3]. Clinical studies have shown unequivocally that perioperative myocardial infarction decreases short-term and long-term survival [4]. Thus, it is reasonable to speculate that effective therapy to diminish the impact of perioperative myocardial ischemia will improve survival after cardiac operations.

In 1985, Lazdunski and colleagues [5] suggested that the pH-regulating activity of the Na+/H+ antiporter causes excessive sodium influx during ischemia. The increased sodium influx leads to intramyocyte calcium accumulation by means of Na+/Ca2+ exchange [5]. On the basis of this hypothesis, Na+/H+ exchange (NHE) inhibitors have been used to protect hearts against ischemia–reperfusion (I/R) injury. Animal studies have demonstrated that NHE inhibitors (eg, cariporide, zoniporide, and eniporide) protect hearts against I/R injury by decreasing calcium overload, preserving mitochondrial integrity, decreasing infarct size, and minimizing myocardial stunning [6]. Although the experimental results are compelling, the clinical data are controversial. The GUARDIAN trial (cariporide) [7] and ESCAMI trial (eniporide) [8] failed to improve clinical outcome except in a single subgroup (ie, coronary artery bypass grafting surgery patients in the Guardian trial). In the EXPEDITION trial, the dose and duration of cariporide therapy were associated with an increase in adverse neurologic events compared with the placebo group. The success of NHE inhibitors in experimental studies and the lack of clinically relevant benefits in clinical studies were the stimuli for this study.

Numerous studies have shown that ß-blockers reduce mortality after acute myocardial infarction [9], in chronic heart failure patients [10], and after cardiac operations [11]. The protective effect is attributable to multiple mechanisms. Notably, Iwai and associates [12] demonstrated that one of the mechanisms for the protective effect of propranolol is attenuated sodium influx after acute ischemia, with decreased calcium overload and improvement of mitochondrial function.

Previous studies of combined treatments have shown additive protection from I/R injury [13, 14]. Taking the same approach we now ask whether preischemic treatment with a ß-blocker increases the protective effect of NHE inhibitors against I/R injury. The primary end points of this study were infarct size and recovery of myocardial contractile function.

Myocyte survival is crucially dependent on maintaining mitochondrial integrity to provide a continuous supply of adenosine triphosphate (ATP); thus, protection of mitochondrial function is key to determining myocyte functional recovery, apoptosis, or necrosis after I/R injury [15]. As part of this study, we examined mitochondrial protection by measuring changes in the coupling of oxidation and phosphorylation, and in mitochondrial calcium handling.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
These experiments were approved by the University of Alabama—Birmingham Institutional Animal Care and Use Committee. All the procedures adhered to the Guide for the Care and Use of Laboratory Animals (National Academy of Sciences, 1996). Cariporide is a generous gift from Aventis Pharma Deutschland GmbH (Frankfurt am Main, Germany). Metoprolol and other chemicals were purchased from Sigma Chemical Company (St. Louis, MO).

Isolated Heart Preparation
Male Sprague-Dawley rats weighting 300 to 350 g were anesthetized with ketamine (100 mg/kg, intraperitoneally). Hearts were excised quickly and mounted on a modified Langendorff apparatus with the ascending aorta cannulated. Hearts were perfused with Krebs-Henseleit buffer containing (in mmol/L): NaCl, 118; KCl, 4.7; CaCl2, 2.5; MgSO4, 1.2; NaHCO3, 25; KH2PO4, 1.2; and glucose, 11. Buffers were equilibrated with 95%O2 and 5% CO2 (38°C, pH 7.4) and were not recirculated. A balloon filled with saline was gently inserted into the left ventricle through the mitral valve and connected to a pressure transducer for continuous measurements of cardiac function. Perfusion pressure was maintained at 100 mm Hg using a custom-built automated perfusion system capable of delivering either constant perfusion pressure or flow.

Experimental Protocol
All hearts were stabilized for 20 minutes and paced at 330 beats/min. After 10 minutes of preischemia treatment with the assigned drug, the hearts were subjected to 20 minutes of zero-flow global ischemia without pacing followed by 60 minutes of reperfusion. Pacing was restarted for the last 30 minutes of reperfusion.

Hearts were divided into four groups (n = 12 each group; Fig 1): (1) vehicle-treated control (Cont); (2) 10 µmol/L cariporide (Car); (3) 10 µmol/L metoprolol (Met); and (4) cariporide and metoprolol (Car+Met). At the end of reperfusion, hearts were subjected to mitochondrial isolation (n = 6) or infarct size determination (n = 6). The assignment to postreperfusion analysis type was made before the start of the study using a randomized assignment list. We also included another two groups of hearts for mitochondrial function determination: continuous perfusion (n = 6; hearts perfused at a constant pressure of 100 mm Hg for 120 minutes) and nonperfusion (n = 6; hearts harvested with cold buffer flush).


Figure 1
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  		Fig 1. Experimental protocol. Four groups of hearts underwent ischemia–reperfusion protocol with cariporide (Car), metoprolol (Met), and cariporide and metoprolol (Car+Met) pretreatment and without treatment (Cont). One group of hearts was perfused continuously under normoxic condition (CP), and one was assayed without perfusion (NP). The black bars indicate the period of ischemia, and the gray bar indicates the treatment period. (Mito = mitochondrial function assay; TTC = triphenyl tetrazolium chloride staining.)

 
Infarct Size Determination
At the end of 60 minutes of reperfusion and after removing atrial tissue, hearts were frozen and cut into 2-mm slices. The tissue was incubated in 1% triphenyl tetrazolium chloride for 20 minutes at 37°C, and fixed in formalin. The infarct size was presented as a percentage of total ventricular area [13].

Isolation of Mitochondria
Mitochondria were isolated from left ventricular myocardium at the end of reperfusion by a modified method of Palmer and coworkers [16]. In brief, hearts were flushed with ice-cold isolation medium containing sucrose (300 mmol/L), Tris (20 mmol/L), ethylene glycol-is(ß-aminoethyl ether)-N,N'-tetraacetic acid (1 mmol/L), and 0.2% fatty acid-free albumin at pH 7.40. The left ventricle was chopped finely with scissors, then homogenized for 1 minute (Ultra Turrax IKA T18, Wilmington, NC) in 10 mL of isolation medium per gram of tissue. Cell debris was removed by centrifugation for 3 minutes at 600 g (Marathon 21000R, Fisher Scientific, Pittsburgh, PA). The supernatant was then centrifuged at 6000 g for 10 minutes. The resulting mitochondrial pellet was resuspended in 500 µL of isolation medium per gram of tissue and stored on ice for further analysis. Protein concentration was determined by modified Lowry’s method.

Measurement of Mitochondrial Calcium
Extracting total calcium from fresh isolated mitochondria was accomplished by subjecting the samples to nitric acid and lanthanum chloride. The calcium content was measured by using a flame atomic absorption spectrometer (SpectrAA.20 atomic absorption spectrometer, Varian, Palo Alto, CA) and presented as nanomoles per milligram of mitochondrial protein [17].

Measurement of Mitochondrial Oxygen Consumption and Respiration
Immediately after isolation, mitochondrial function was determined at 37°C [18]. In brief, mitochondria at a final protein concentration of approximately 0.18 mg/mL were incubated with the medium containing 20 mmol/L Tris-HCl, pH 7.4, 0.25 mol/L sucrose, 30 mmol/L KH2PO4, and 0.1 mmol/L EDTA. Respiratory complex I activity was determined by adding glutamate (10 mmol/L) and malate (2.5 mmol/L). Adding an additional 50 nmol of adenosine diphosphate (ADP) initiated oxidative phosphorylation. The following variables of mitochondrial function were evaluated: (1) state 3 respiration rate: oxygen uptake during ADP phosphorylation presented as nanomoles of oxygen per minute per milligram of mitochondrial protein; (2) state 4 respiration rate: oxygen uptake in the absence of exogenous ADP; and (3) respiratory control ratio: a ratio of state 3 and state 4 oxygen uptake rates. Respiration measurements were repeated three times. State 3 is an "active" state in which there is rapid electron transfer, oxygen consumption, and rapid ATP synthesis. After conversion of all ADP to ATP, the rates of electron transfer return to the resting state (state 4). Respiratory control ratio, which measures the tightness of coupling between electron transfer and oxidative phosphorylation, is a commonly used term to indicate mitochondrial function of respiration.

Statistical Analysis
Cardiac contractile function was measured by analysis of stored waveform data including measurements of heart rate, coronary flow, peak systolic pressure, end-diastolic pressure (EDP) and maximum and minimum rate of increase of left ventricular pressure (±dP/dt). Infarct area was measured as a percentage of the area at risk, which was the total ventricular area in this study. Intramitochondrial calcium and mitochondrial respiratory function were measured after I/R. All results are shown as mean ± standard error of the mean.

One-way analysis of variance combined with Scheffe’s post hoc test was used to test for differences between groups. Bartlett’s test of sphericity was used to test the significance of correlations. Analysis was performed with the statistical software StatView (Abacus Concepts Inc, Cary, NC). A probability value of less than 0.05 was considered to be significant.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
Cardiac Function Before and After Ischemia–Reperfusion
All hearts were paced at 330 beats/min throughout perfusion except for the 20-minute ischemic period and early reperfusion. Ten minutes of drug pretreatment had no significant impact on cardiac function in all treated groups compared with baseline (data not shown). Preischemic coronary flow, left ventricular developed pressure, and maximum and minimum rate of increase of left ventricular pressure are summarized in Table 1, and EDP is shown in Figure 2. There were no significant differences among groups. Cardiac function was stable during 2 hours of continuous perfusion (data not shown).


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  		Table 1 Cardiac Function Before Ischemia and Percent Recovery at the End of Reperfusion
 

Figure 2
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  		Fig 2. Baseline end-diastolic pressure (EDP; black bars), maximum end-diastolic pressure during ischemia (white bars), and end-diastolic pressure at the end of reperfusion (gray bars) are shown. Treatments consisted of giving10 µmol/L cariporide (Car), 10 µmol/L metoprolol (Met), and both (Car+Met) 10 minutes before ischemia. Baseline end-diastolic pressure was less than 5 mm Hg in all hearts, with no significant difference observed among groups. Pretreatment with cariporide and metoprolol decreased end-diastolic pressure during ischemia and at the end of reperfusion significantly compared with the control group and cariporide (n = 12 in each group; *p < 0.05 versus control; {dagger}p < 0.05 versus cariporide).

 
The onset of ischemia led to a cessation of contractile function during the first few minutes in all groups. There was gradually developing cardiac contracture characterized by increasing EDP. Maximum EDP during ischemia is shown in Figure 2 in parallel to preischemic and reperfusion EDP. The combination of cariporide and metoprolol significantly decreased contracture compared with control and cariporide groups. It is generally believed that development of contracture indicates ATP depletion and is associated with irreversible myocardium injury.

Restoration of flow led to rapid recovery of contractile function, but at a lower level than before ischemia. The functional recovery at the end of reperfusion is presented as percentage of its preischemic values in Table 1. All treatments showed improved recovery compared with control, mainly as a result of decreased EDP (Fig 2). The recovery of left ventricular developed pressure and maximum and minimum rate of increase of left ventricular pressure was nominally greater with cariporide and metoprolol as compared with cariporide alone. The change in EDP was significant in the cariporide and metoprolol group compared with the cariporide group.

Mitochondrial Function
Mitochondrial protein yields from left ventricle are presented in Figure 3. There were no significant differences between nonperfused hearts and continuous perfusion hearts. This data indicated that perfusion itself had no impact on mitochondria. Mitochondrial yields from all I/R groups were significantly reduced compared with continuous perfusion hearts, and there were no significant differences between control and treated groups.


Figure 3
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  		Fig 3. Mitochondrial protein yield from left ventricle at the end of ischemia–reperfusion (left) and from nonperfused (NP) and continuously perfused (CP) hearts (right). Perfusion itself has no impact on mitochondrial harvest (n = 6 in each group; #p < 0.05 versus all ischemia–reperfusion groups). (Car = cariporide; Car+Met = cariporide + metoprolol; Cont = control; Met = metoprolol.)

 
By adding an additional 50 nmol of ADP, mitochondrial oxygen consumption (QO2) is activated and is defined as state 3. After conversion of all ADP to ATP, the rates of electron transfer return to the resting state (state 4). In this study, state 3 and state 4 QO2 measurements were repeated three times, and the mean values are presented. Pretreatment with metoprolol alone and the combination of cariporide and metoprolol increased QO2 significantly compared with control. Cariporide alone did not show a beneficial effect (Fig 4A). There were no significant differences in state 4 QO2 (data not shown).


Figure 4
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  		Fig 4. State 3 oxygen consumption (A) and respiratory control ratio (RCR; B). Pretreatment with cariporide and metoprolol (Car+Met) increases respiratory control ratio significantly compared with control (Cont) and cariporide alone (Car; n = 6 in each group; *p < 0.05 versus control; {dagger}p < 0.05 versus cariporide). (CP = continuously perfused; Met = metoprolol; NP = nonperfused.)

 
The ratio of state 3 and state 4 is referred to as the respiratory control ratio, which measures the tightness of coupling between electron transfer and oxidative phosphorylation. Respiratory control ratio was significantly increased in cariporide and metoprolol compared with control and cariporide or metoprolol alone (Fig 4B).

Mitochondrial Calcium Content
Mitochondrial calcium content was dramatically increased in hearts subjected to I/R injury (Fig 5). It increased three to five times as compared with hearts without I/R injury. Cariporide and metoprolol decreased calcium content significantly compared with control. Cariporide or metoprolol alone did not lower mitochondrial calcium content significantly compared with control. Using aggregate data from control, cariporide, metoprolol, and cariporide and metoprolol groups, we asked whether mitochondrial calcium content was correlated with cardiac function at the end of reperfusion. Higher mitochondrial calcium content was associated with higher EDP and less percentage of left ventricular developed pressure recovery (Fig 6; p < 0.05 by Bartlett’s test).


Figure 5
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  		Fig 5. Mitochondria calcium contents at the end of ischemia–reperfusion (left) and from nonperfused (NP) and continuously perfused (CP) hearts (right). Ischemia–reperfusion increases mitochondria calcium contents greatly compared with nonischemic hearts, but the increase is significantly reduced by metoprolol and cariporide pretreatment (Car+Met; n = 6 in each group; *p < 0.05 versus control; #p < 0.05 versus all ischemia–reperfusion groups). (Car = cariporide; Cont = control; Met = metoprolol.)

 

Figure 6
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  		Fig 6. Correlation of mitochondria calcium contents with end-diastolic pressure (EDP; A) and percentage of left ventricular developed pressure recovery (% LVDP; B) at the end of reperfusion (n = 6 rats in each group; p < 0.05).

 
Infarct Size
In this study 6 hearts from each group were studied with triphenyl tetrazolium chloride staining at the end of 60 minutes of reperfusion. Infarct size was presented as a percentage of total ventricular area (Fig 7). Treatment with cariporide alone did not show a protective effect. Metoprolol decreased infarct size significantly compared with control. With combined treatment, infarct size was additively decreased (p < 0.05 versus control, cariporide, and metoprolol).


Figure 7
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  		Fig 7. Infarct size presented as percentage of total ventricular area at the end of reperfusion (n = 6 in each group; *p < 0.05 versus control; {dagger}p < 0.05 versus cariporide). (Car = cariporide; Met = metoprolol.)

 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
Since 1985 numerous experimental studies have demonstrated that NHE inhibition protects hearts against I/R injury. However clinical trials have not proven safety and efficacy. It is possible that a combination of NHE inhibitors and another drug with complementary mechanisms of action will amplify the beneficial effects of NHE inhibitors at a lower dose and duration of treatment. In the present study we asked whether combining pretreatment with the NHE cariporide and the ß-blocker metoprolol improves cardiac protection against I/R injury. It appears that combined treatment with cariporide and metoprolol improves mitochondrial function at the end of 60 minutes of reperfusion. Moreover, the combination of treatments increased mitochondrial ADP-activated state 3 oxygen consumption, improved coupling of electron transfer to oxidative phosphorylation, and reduced mitochondrial calcium content. This improvement in mitochondrial function was associated with a decrease in infarct size.

As pointed out by Bolli and colleagues [19], cardioprotection in the setting of acute myocardial infarction, cardiac surgery, and cardiac arrest is at a crossroads; investigators need to translate experimental interventions into clinical practice. The strategy used in this study was to combine treatments that have independent mechanisms of action but that share a common end point (eg, mitochondrial protection) to provide a clinically relevant improvement. Using a similar strategy our group previously demonstrated that NHE inhibition combined with an ATP-sensitive potassium-channel opener improves recovery of contractile function after I/R injury [13].

Elucidation of the crucial role for mitochondria in I/R can be traced back almost four decades to Jennings and associates [20]. It was subsequently addressed by Ganote and coworkers [21], who observed that mitochondrial function after I/R is a critical factor in myocardial dysfunction and recovery. From this information, it is reasonable to speculate that better protection of mitochondria will lead to improved recovery of cardiac function after I/R injury. In this study, we included measurements that defined mitochondrial function. Complex I, as the first step in the mitochondrial respiratory chain, plays an important role in the maintenance of proton transfer and ATP production. The activity of complex I is inhibited in cardiac I/R injury [22]. In this study, state 3 QO2 was restored to preischemic levels with cariporide and metoprolol as well as with metoprolol pretreatment. Similar values of state 3 QO2 in the continuous perfusion and nonperfused groups indicate that normoxic perfusion itself has no adverse effect on the heart, and confirms that the differences in this study were caused by I/R injury and the interventions.

The present study further showed that mitochondrial respiratory control ratio was significantly improved by cariporide and metoprolol, but not by cariporide or metoprolol alone. This observation demonstrates that mitochondria electron transfer and oxidative phosphorylation are preserved by cariporide and metoprolol pretreatment, which is a key step to increase ATP synthesis. Electron transfer and oxidative phosphorylation in the mitochondria respiratory chain are steps that involve mitochondrial complexes from I through V. It is possible that more than one site was impaired during I/R but protected by cariporide and metoprolol. However, there is evidence to show that complex I and mitochondrial membranes are the specific targets of I/R injury [23]. Our data show that complex I state 3 QO2 was decreased to about 50% of nonischemic levels at the end of reperfusion in control hearts, which is in agreement with previous findings [23]. State 3 QO2 was restored to more than 90% of nonischemic levels with cariporide and metoprolol pretreatment.

Adenosine triphosphate is synthesized by mitochondrial ATP synthase (F1F0 ATPase) through the driving force of proton influx. Under certain pathologic circumstances, eg, cardiac I/R injury, F1F0 ATPase can be switched to ATP hydrolysis instead of ATP synthesis [24], and it is estimated that 50% to 80% of ATP consumed during severe ischemia might be attributed to mitochondrial ATP hydrolysis [25]. Although in this study myocardial ATP content was not measured, it is reasonable to speculate that improving the coupling of mitochondrial electron transfer and oxidative phosphorylation by cariporide and metoprolol can push F1F0 ATPase toward ATP synthesis during reperfusion. This speculation is supported by a study reporting that protection of mitochondria is associated with increased cellular ATP content and reduced cell injury at the end of reperfusion [26]. Moreover, inhibition of complex I increases free radical generation after I/R injury, which may cause additional cell injury [27]. We believe that increased ATP production and inhibition of free radical generation may be involved in the protective effect of cariporide and metoprolol, produced by mitochondrial complex I protection.

In addition to providing ATP, mitochondria also play a critical role in maintaining calcium homeostasis, especially during I/R [28]. Calcium overload is known as one of the most important factors contributing to I/R injury. In this study we found that mitochondrial calcium was increased in control hearts compared with hearts with cariporide and metoprolol pretreatment. Our data indicate that mitochondrial calcium overload is associated with an increase of EDP at the end of reperfusion. Furthermore, decreased mitochondrial calcium content was associated with better functional recovery. This finding is corroborated by previous studies showing that calcium overload inhibits complex I activity directly [29] and prevention of mitochondrial calcium overload attenuates I/R injury [30].

The mitochondrial transition pore is a nonspecific pore that exists between the inner and outer mitochondrial membranes. The mitochondrial transition pore remains closed under normal condition, but it opens under conditions of high calcium, high intracellular phosphorus, low ATP, and low glucose, all of which may be present in I/R injury [31]. Opening of the mitochondrial transition pore causes mitochondrial outer membrane rupture and collapse of the inner membrane potential, which leads to the release of proapoptotic molecules (eg, cytochrome c) and reverses net ATP synthesis to ATP consumption [32]. Protection of mitochondria is therefore key for myocyte functional recovery and minimizing apoptosis or necrosis after I/R injury [15]. Inhibition of mitochondrial transition pore opening at the time of reperfusion attenuates calcium overload and may limit the death of myocytes [33]. Thus, stabilization of the mitochondrial transition pore may be an important mechanism for the protective effect of cariporide and metoprolol.

Our data showed a decrease in infarct size for the cariporide and metoprolol group; however, cardiac systolic recovery was not significantly improved at the end of reperfusion. Similar phenomena have been reported previously. Ischemic preconditioning and pharmacologic preconditioning reduce infarct size, but do not improve systolic cardiac function at the end of reperfusion in isolated hearts [34]. It was also reported that trimetazidine, a peroxisome proliferator–activated receptor antagonist, decreases infarct size without improved functional recovery after I/R injury [35]. Ranolazine, an inhibitor of the late sodium channel, similarly decreases infarct size without improving maximum and minimum rate of increase of left ventricular pressure in an in vivo study [36].

In summary, this study demonstrates that combining treatment with the NHE inhibitor cariporide and the ß-blocker metoprolol additively improves mitochondrial function and limits infarct size after severe I/R injury in an isolated rat heart model. The improvements in mitochondrial oxygen consumption and coupling of proton transfer to phosphorylation were associated with decreased mitochondrial calcium content, which may be related to stabilization of the mitochondria transition pore. Combined prophylactic treatment with ß-blockers and NHE inhibitors, if confirmed in a large animal model of regional ischemia, may substantially decrease the morbidity and mortality currently associated with perioperative myocardial ischemia and infarction in cardiac surgery.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
We thank Stanley Digerness, PhD, and Connie McLernon for technical and administrative support. This work was supported by NIH grant R01 HL66015.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

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Steven Anderson
Ann. Thorac. Surg. 2007 83: 1128. [Extract] [Full Text] [PDF]



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Ann. Thorac. Surg., March 1, 2007; 83(3): 1128 - 1128.
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