Endothelin receptor blockade reduces ventricular dysfunction and injury after reoxygenation

Extracorporeal membrane oxygenation induced cardiac dysfunction in newborn lambs

Extracorporeal membrane oxygenation (ECMO) is routinely used to support cardiopulmonary failure in infants and children. Suboptimal outcomes for primary cardiac support suggest a need for investigation of the impact of ECMO on the heart. Twenty-four newborn lambs received a brief period of ECMO support to investigate the hypothesis that ECMO produces cardiac dysfunction in newborn lamb. Dorset newborn lambs, 4-7 days of age, were exposed to ECMO for 5 min at a 100 ml/kg flow rate and quickly weaned off. Measurements included echocardiographic mean left ventricular (LV) velocity of circumferential fiber shortening corrected for heart rate (mVCFc), LV shortening fraction, and peak systolic wall stress plus hemodynamic measurement of LV maximum rate of pressure change with time (LV dp/dt max), maximum rate of pressure change divided by developed pressure (LV dp/dtP), right atrial pressure, pulmonary capillary wedge pressure, mean pulmonary artery pressure, LV peak and end-diastolic pressure, and aortic pressure. These measures were also obtained after an exposure to 5 min of ECMO and immediate disconnect for 5 min, followed by ECMO administration for 1 h again, followed by discontinuation of ECMO. LV mVCFc is decreased after exposure to 5 min of ECMO support despite a decrease in LV peak systolic wall stress that provides afterload reduction. LV mVCFc is inversely related to peak systolic wall stress at a significance level of p < 0.0001. The time period after initiation of ECMO is a significant factor in the model (p = 0.0097). Time [baseline] was different from the other time points with p = 0.0010. Average mVCFc at baseline is 1.27 ± 0.35 and decreases to 1.01 ± 0.42 after 5 min of ECMO that is then withdrawn. Peak systolic wall stress decreases from 36.0 ± 13.1 at baseline to 29.8 ± 12.1 after 5 min of ECMO. LV dp/dt max decreases from 1,769 ± 453 mmHg/s at baseline to 1,311 ± 513 mmHg/s after exposure to 5 min of ECMO (p = 0.0005). Baseline LV dp/dt max is different from each point after start of ECMO. Diastolic LVdp/dt min increased from -1,340 ± 477 mmHg/s to -908 ± 393 mmHg/s at 5 min. Echocardiographic mVCFc, when considered in isolation or as a function of LV peak systolic wall stress, shows diminished LV function after ECMO. Hemodynamic measurement of LV dp/dt max and LV dp/dt min confirms the observation. Separation of the humoral from mechanical effect of ECMO with the short exposure to the extracorporeal circuit shows that an immediate decrement of LV function occurs at initiation of ECMO, a finding that has not been stressed with previous studies of extracorporeal support. This implies a potentially outcome-limiting deleterious effect for the patient who requires ECMO support for the heart rather than the lungs. We should continue to strive to understand and ameliorate this deleterious effect of the extracorporeal circulation circuit.

Recent advances in the understanding of the role of nitric oxide in cardiovascular homeostasis

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. To date, 3 distinct NOS isoforms have been identified: neuronal NOS (NOS1), inducible NOS (NOS2), and endothelial NOS (NOS3). Biochemically, NOS consists of a flavin-containing reductase domain, a heme-containing oxygenase domain, and regulatory sites. NOS catalyse an overall 5-electron oxidation of one Nomega-atom of the guanidino group of L-arginine to form NO and L-citrulline. NO exerts a plethora of biological effects in the cardiovascular system. The basal formation of NO in mitochondria by a mitochondrial NOS seems to be one of the main regulators of cellular respiration, mitochondrial transmembrane potential, and transmembrane proton gradient. This review focuses on recent advances in the understanding of the role of enzyme and enzyme-independent NO formation, regulation of NO bioactivity, new aspects of NO on cardiac function and morphology, and the clinical impact and perspectives of these recent advances in our knowledge on NO-related pathways.

15-F2t-isoprostane exacerbates myocardial ischemia-reperfusion injury of isolated rat hearts

Reactive oxygen species induce formation of 15-F2t-isoprostane (15-F2t-IsoP), a specific marker of in vivo lipid peroxidation, which is increased after myocardial ischemia and during the subsequent reperfusion. 15-F2t-IsoP possesses potent bioactivity under pathophysiological conditions. However, it remains unknown whether 15-F2t-IsoP, by itself, can influence myocardial ischemia-reperfusion injury (IRI). Adult rat hearts were perfused by the Langendorff technique with Krebs-Henseleit (KH) solution at a constant flow rate of 10 ml/min. 15-F2t-IsoP (100 nM), SQ-29548 (1 μM, SQ), a thromboxane receptor antagonist that can abolish the vasoconstrictor effect of 15-F2t-IsoP, 15-F2t-IsoP + SQ in KH, or KH alone (vehicle control) was applied for 10 min before induction of 40 min of global ischemia followed by 60 min of reperfusion. During ischemia, saline (control), 15-F2t-IsoP, 15-F2t-IsoP + SQ, or SQ in saline was perfused through the aorta at 60 μl/min. 15-F2t-IsoP, 15-F2t-IsoP + SQ, or SQ in KH was infused during the first 15 min of reperfusion. Coronary effluent endothelin-1 concentrations were significantly higher in the group treated with 15-F2t-IsoP than in the control group during ischemia and also in the later phase of reperfusion ( P < 0.05). Infusion of 15-F2t-IsoP increased release of cardiac-specific creatine kinase, reduced cardiac contractility during reperfusion, and increased myocardial infarct size relative to the control group. SQ abolished the deleterious effects of 15-F2t-IsoP. 15-F2t-IsoP exacerbates myocardial IRI and may, therefore, act as a mediator of IRI. 15-F2t-IsoP-induced endothelin-1 production during cardiac reperfusion may represent a mechanism underlying the deleterious actions of 15-F2t-IsoP.

Positive inotropic and negative lusitropic effects of endothelin receptor agonism in vivo

The endothelin (ET) system is involved in the regulation of myocardial function in health as well as in several diseases, such as congestive heart failure, myocardial infarction, and septic myocardial depression. Conflicting results have been reported regarding the acute contractile properties of ET-1. We therefore investigated the effects of intracoronary infusions of ET-1 and of the selective ETBreceptor-selective agonist sarafotoxin 6c with increasing doses in anesthetized pigs. Myocardial effects were measured through analysis of the left ventricular pressure-volume relationship. ET-1 elicited increases in the myocardial contractile status (end-systolic elastance value of 0.94 ± 0.11 to 1.48 ± 0.23 and preload recruitable stroke work value of 68.7 ± 4.7 to 83.4 ± 7.2) that appear to be mediated through ETAreceptors, whereas impairment in left ventricular isovolumic relaxation (τ = 41.5 ± 1.4 to 58.1 ± 5.0 and t1/2= 23.0 ± 0.7 to 30.9 ± 2.6, where τ is the time constant for pressure decay and t1/2is the half-time for pressure decay) was ETBreceptor dependent. In addition, intravenous administration of ET-1 impaired ventricular relaxation but had no effect on contractility. Intracoronary sarafotoxin 6c administration caused impairments in left ventricular relaxation (τ from 43.3 ± 1.8 to 54.4 ± 3.4) as well as coronary vasoconstriction. In conclusion, ET-1 elicits positive inotropic and negative lusitropic myocardial effects in a pig model, possibly resulting from ETAand ETBreceptor activation, respectively.

Endothelin-1 in congenital heart disease

Endothelin-1 (ET-1) is a 21-amino acid polypeptide produced primarily by vascular endothelial cells. First discovered in 1988 as a potent vasoconstrictor, it has subsequently been appreciated to participate in several biologic activities, including vascular smooth muscle proliferation, fibrosis, cardiac and vascular hypertrophy, and inflammation. Increasing data demonstrate alterations in ET-1 signaling in newborns, infants, and children with congenital heart defects that are associated with alterations in pulmonary blood flow. This review outlines the pathophysiologic role of the ET-1 cascade in the development of altered pulmonary vascular tone and reactivity that occurs with congenital heart disease and its repair, following the use of cardiopulmonary bypass. In addition, therapeutic implications for the use of novel ET receptor antagonists will be emphasized.

Adenosine A2A Receptor Agonist Improves Cardiac Dysfunction From Pulmonary Ischemia-Reperfusion Injury

BACKGROUND

Ischemia-reperfusion (IR) injury negatively impacts patient outcome in lung transplantation. Clinically, we observed that lung transplant patients with ischemia-reperfusion injury tend to have cardiac dysfunction. Previous studies have shown that ATL-146e (4-{3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl}-cyclohexanecarboxylic acid methyl ester), a selective adenosine A2A receptor agonist, reduces lung inflammation after ischemia-reperfusion. We hypothesized that pulmonary ischemia-reperfusion causes secondary heart dysfunction and ATL-146e will improve this dysfunction.

METHODS

We utilized an in vivo rabbit lung ischemia-reperfusion model. The Sham group underwent 120 minutes single lung ventilation. The IR and ATL groups underwent 90 minutes right lung ischemia with 30 minutes right lung reperfusion. The ATL-146e was given intravenously to the ATL group during reperfusion. Cardiac output and arterial blood gases were monitored, and neutrophil sequestration was measured by myeloperoxidase activity.

RESULTS

Upon reperfusion, cardiac output (mL/min) significantly dropped in the IR and ATL groups. By 15 minutes reperfusion, cardiac output in the ATL group improved significantly over the IR group and remained significant thereafter. Lung myeloperoxidase activity was significantly reduced by ATL-146e. Although never hypoxemic, arterial oxygenation was lower in the IR and ATL groups while central venous pressures and mean arterial pressures were similar among groups. A separate experiment demonstrated that reperfusion with the antioxidant N-(2-mercaptopropionyl)glycine prevented cardiac dysfunction.

CONCLUSIONS

Pulmonary ischemia-reperfusion causes cardiac dysfunction independent of preload, afterload, and oxygenation. The ATL-146e improves this dysfunction presumably by the antiinflammatory effects of adenosine A2A receptor activation on neutrophils. One likely mechanism involves the release of oxidants from the ischemic lung upon reperfusion, which has immediate negative effects on the heart.

The endothelin receptor antagonist decreases ischemia/reperfusion-induced tumor necrosis factor production in isolated rat hearts

Previous studies have shown that endothelin-1 (ET-1) may play a pathophysiological role in myocardial ischemia/reperfusion injury. In the present study, BMS-182874 significantly improved the recovery of cardiac function and reduced the release of CK during reperfusion after ischemia and the content of tumor necrosis factor (TNF-alpha) in myocardial tissues. BMS-182874 also reduced myocardial injury and the increased level of TNF-alpha by exogenous ET-1. These results suggest that the cardioprotective effects of the ET receptor antagonist may be related to inhibition of TNF-alpha production.

Calpain inhibition decreases endothelin-1 levels and pulmonary hypertension after cardiopulmonary bypass with deep hypothermic circulatory arrest*

OBJECTIVE

Cardiopulmonary bypass in infants and children can result in cardiopulmonary dysfunction through ischemia and reperfusion injury. Pulmonary hypertension and injury are particularly common and morbid complications of neonatal cardiac surgery. Inhibition of calpain, a cysteine protease, has been shown to inhibit reperfusion injury in adult organ systems. The hypothesis is that calpain inhibition can alleviate the cardiopulmonary dysfunction seen in immature animals following ischemia and reperfusion with cardiopulmonary bypass.

DESIGN

Animal case study.

SETTING

Medical laboratory.

SUBJECTS

Crossbred piglets (5-7 kg).

INTERVENTIONS

Piglets were cooled with cardiopulmonary bypass to 18 degrees C followed by deep hypothermic circulatory arrest for 120 mins. Animals were rewarmed to 38 degrees C on cardiopulmonary bypass and maintained for 120 mins. Six animals were administered calpain inhibitor (Z-Leu-Leu-Tyr-fluoromethyl ketone; 1 mg/kg, intravenously) 60 mins before cardiopulmonary bypass. Nine animals were administered saline as a control. Plasma endothelin-1, pulmonary and hemodynamic function, and markers of leukocyte activity and injury were measured.

MEASUREMENTS AND MAIN RESULTS

Calpain inhibition prevented the increased pulmonary vascular resistance seen in control animals (95.7 +/- 39.4 vs. 325.3 +/- 83.6 dyne.sec/cm, respectively, 120 mins after cardiopulmonary bypass and deep hypothermic circulatory arrest, p = .05). The attenuation in pulmonary vascular resistance was associated with a blunted plasma endothelin-1 response (4.91 +/- 1.72 pg/mL with calpain inhibition vs. 10.66 +/- 6.21 pg/mL in controls, p < .05). Pulmonary function after cardiopulmonary bypass was better maintained after calpain inhibition compared with controls: Po2/Fio2 ratio (507.2 +/- 46.5 vs. 344.7 +/- 140.5, respectively, p < .05) and alveolar-arterial gradient (40.0 +/- 17.2 vs. 128.1 +/- 85.2 mm Hg, respectively, p < .05). Systemic oxygen delivery was higher after calpain inhibition compared with controls (759 +/- 171 vs. 277 +/- 46 mL/min, respectively, p < .001). In addition, endothelial nitric oxide synthase activity in lung tissue was maintained with calpain inhibition.

CONCLUSIONS

The reduction in plasma endothelin-1 and maintenance of lung endothelial nitric oxide levels after cardiopulmonary bypass and deep hypothermic circulatory arrest with calpain inhibition were associated with reduced pulmonary vascular resistance. Improved gas exchange and higher systemic oxygen delivery suggest that calpain inhibition may be advantageous for reducing postoperative cardiopulmonary dysfunction commonly associated with pediatric heart surgery and cardiopulmonary bypass.

Protection against ischemia/reperfusion injury in cardiac and renal transplantation with carbon monoxide, biliverdin and both

Both carbon monoxide (CO) and biliverdin, products of heme degradation by heme oxygenase, have been shown to attenuate ischemia/reperfusion (I/R) injury. We hypothesized in this study that dual-treatment with CO and biliverdin would induce enhanced protective effects against cold I/R injury. Heterotopic heart and orthotopic kidney transplantation were performed in syngeneic Lewis rats after 24-h cold preservation in UW solution. While monotherapy with CO (20 ppm) or biliverdin (50 mg/kg, ip) did not alter the survival of heart grafts, dual-treatment increased survival to 80% from 0% in untreated recipients, with a significant decrease of myocardial injury and improved cardiac function. Similarly, dual-treatment significantly improved glomerular filtration rates of renal grafts and prolonged recipient survival compared to untreated controls. I/R injury-induced up-regulation of pro-inflammatory mediators (e.g. TNF-alpha, iNOS) and extravasation of inflammatory infiltrates were significantly less with dual-treatment than untreated controls. In addition, dual-treatment was effective in decreasing lipid peroxidation and improving graft blood flow through the distinctive action of biliverdin and CO, respectively. The study shows that the addition of byproducts of heme degradation with different mechanisms of action provides enhanced protection against transplant-associated cold I/R injury of heart and kidney grafts.

Sildenafil citrate alleviates pulmonary hypertension after hypoxia and reoxygenation with cardiopulmonary bypass

BACKGROUND

Sudden reoxygenation of hypoxic neonates undergoing cardiac operation exacerbates the systemic inflammatory response to cardiopulmonary bypass secondary to reoxygenation injury, worsening cardiopulmonary dysfunction. Reports suggest sildenafil decreases pulmonary hypertension and may affect myocardial function. Sildenafil's efficacy for treating postbypass cardiopulmonary dysfunction remains unknown.

STUDY DESIGN

Fourteen neonatal piglets (5 to 7 kg) underwent 90 minutes of hypoxia, 60 minutes of reoxygenation with cardiopulmonary bypass, and 120 minutes of recovery. Six animals received 50 mg oral sildenafil and eight received saline at hypoxia. Data are presented as mean +/- SD.

RESULTS

Sildenafil prevented the high pulmonary vascular resistance observed in controls (controls baseline 81 +/- 37 dynes. s/cm(5) versus recovery 230 +/- 93 dynes. s/cm(5), p = 0.004; sildenafil baseline 38 +/- 17 dynes. s/cm(5) versus recovery 101 +/- 60 dynes. s/cm(5), p = 0.003). Despite lower pulmonary vascular resistance after sildenafil, arterial endothelin-1 (ET-1) was increased in both groups (control baseline 1.3 +/- 0.5 pg/mL versus recovery 4.5 +/- 3.7 pg/mL, p = 0.01; sildenafil baseline 1.3 +/- 0.3 pg/mL versus recovery 9.8 +/- 4.9 pg/mL, p = 0.003). Intravenous nitric oxide (NO) levels were preserved after sildenafil treatment (sildenafil baseline 340 +/- 77 nM versus recovery 394 +/- 85 nM). IV NO levels in controls were decreased when compared with baseline (control baseline 364 +/- 83 nM versus recovery 257 +/- 97 nM, p = 0.028). Although levels of exhaled NO decreased in both groups, the sildenafil-treated animals had higher levels of exhaled NO when compared with controls at the end of recovery (0.6 +/- 0.4 parts per billion versus 1.8 +/- 0.9 parts per billion, respectively, p = 0.029).

CONCLUSIONS

Sildenafil alleviated pulmonary hypertension after reoxygenation with cardiopulmonary bypass. Despite increased ET-1 levels, pulmonary vascular resistance was lower with sildenafil treatment, suggesting sildenafil's effect on the pulmonary vasculature is capable of countering vasoconstriction by ET-1. Further study into the role of sildenafil in perioperative therapy and its interactions with ET-1 are warranted.

Differentiated and dose-related cardiovascular effects of a dual endothelin receptor antagonist in endotoxin shock

OBJECTIVE

To evaluate the effects of endothelin receptor antagonism on cardiac performance in endotoxin shock.

DESIGN

Prospective, experimental study.

SETTING

A university-affiliated research institution.

SUBJECTS

Domestic anesthetized landrace pigs.

INTERVENTIONS

Thirty-seven pigs were anesthetized and subjected to echocardiography, coronary sinus catheterization, and monitoring of central and regional hemodynamics in order to assess cardiac performance. All animals received endotoxin for 5 hrs. Twenty pigs served as endotoxin controls. Tezosentan, a dual endothelin-A and -B receptor antagonist, was administered during established endotoxemic shock. Seven pigs received an infusion of tezosentan of 1 mg x kg(-1) x hr(-1) (tezo1), and an additional ten pigs received a higher dose of 10 mg x kg(-1) x hr(-1) (tezo10).

MEASUREMENTS AND MAIN RESULTS

Endotoxemia evoked a state of shock with pulmonary hypertension and metabolic acidosis. A decrease in stroke volume and coronary perfusion pressure as well as an increase in troponin I was also noted. Tezosentan administration resulted in a significant increase in cardiac index, stroke volume index, left ventricular stroke work index, and left ventricular end-diastolic area index. Decreases in systemic and pulmonary vascular resistance indexes were also evident after intervention. This was achieved without changes in heart rate or systemic arterial or pulmonary artery occlusion pressures in tezo, animals compared with controls. In addition, metabolic variables were improved by tezosentan. These effects were sustained only in the tezo, group. In the higher dosage, tezosentan resulted in a deterioration of cardiac performance and 50% mortality rate. The endotoxin-induced increase in troponin I was attenuated in the tezo, group compared with controls.

CONCLUSIONS

In this porcine model of volume-resuscitated, endotoxemic shock, endothelin-receptor blockade with tezosentan improved cardiac performance. However, the effect was not sustained with higher doses of tezosentan, possibly due to reduced coronary perfusion pressure. These findings show differentiated, dose-dependent effects by dual endothelin receptor blockade on endotoxin-induced cardiovascular dysfunction.

Preoperative glucocorticoids decrease pulmonary hypertension in piglets after cardiopulmonary bypass and circulatory arrest

BACKGROUND

Glucocorticoids during cardiopulmonary bypass benefit pediatric patients undergoing repair of congenital heart defects and are routine therapy, but underlying mechanisms have not been fully examined. The hypothesis was that glucocorticoids could improve cardiopulmonary recovery after cardiopulmonary bypass and deep hypothermic circulatory arrest.

METHODS

Crossbred piglets (5 to 7 kg) were cooled with cardiopulmonary bypass, followed by 120-min deep hypothermic circulatory arrest. Animals were then warmed to 38 degrees C, removed from bypass, and maintained for 120 min. Methylprednisolone (60 mg/kg) was administered in the cardiopulmonary bypass pump prime (intraoperative glucocorticoids) or 6 hours before bypass (30 mg/kg) in addition to the intraoperative dose (30 mg/kg; preoperative and intraoperative glucocorticoids). Controls (no glucocorticoids) received saline.

RESULTS

Pulmonary vascular resistance in controls increased from a baseline of 152 +/- 40 to 364 +/- 29 dynes. s/cm(5) at 2 hours of recovery (p < 0.001). Intraoperative glucocorticoids did not alleviate the increase in pulmonary vascular resistance (301 +/- 55 dynes. s/cm(5) at 2 hours of recovery, p < 0.001). However, animals receiving pre and intraoperative glucocorticoids had no increase in pulmonary vascular resistance (155 +/- 54 dynes. s/cm(5)). Plasma endothelin-1 in controls increased from 1.3 +/- 0.2 at baseline to 9.9 +/- 2.0 pg/mL at 2 hours recovery (p < 0.01), whereas glucocorticoid-treated animals had lower endothelin-1 levels (4.5 +/- 2.1 pg/ml, preoperative and intraoperative glucocorticoids; 4.9 +/- 1.7 pg/mL, intraoperative glucocorticoids) at the end of recovery (p < 0.05). Intracellular adhesion molecule-1 in lung tissue was lower in animals receiving pre and intraoperative glucocorticoids (p < 0.05). Myeloperoxidase activity was elevated in control lungs at 2 hours of recovery compared with glucocorticoid-treated groups (p < 0.05). Inhibitor kappaBalpha, the inhibitor of nuclear factor-kappaB, was higher in lungs of animals receiving glucocorticoids compared with controls (p < 0.05).

CONCLUSIONS

Glucocorticoids prevented pulmonary hypertension after cardiopulmonary bypass and deep hypothermic circulatory arrest, which was associated with reduced plasma endothelin-1. Glucocorticoids also reduced pulmonary intercellular adhesion molecule-1 and myeloperoxidase activity. Inhibition of nuclear factor-kappaB, along with reduced neutrophil activation, contributed to glucocorticoid alleviation of pulmonary hypertension after cardiopulmonary bypass and deep hypothermic circulatory arrest.

Direct inhibition of the sodium/hydrogen exchanger after prolonged regional ischemia improves contractility on reperfusion independent of myocardial viability

BACKGROUND

A mechanism for myocardial dysfunction after ischemia and reperfusion is Na(+)/H(+) exchanger activation. Although past in vivo models of limited ischemia and reperfusion intervals demonstrate that Na(+)/H(+) exchanger inhibition confers myocardial protection when administered at the onset of ischemia, the effect of Na(+)/H(+) exchanger inhibition on myocardial function after prolonged ischemia and reperfusion remains unknown. This investigation tested the hypothesis that Na(+)/H(+) exchanger inhibition instituted at reperfusion and after prolonged coronary occlusion in pigs would influence myocardial contractility independent of myocardial viability.

METHODS

A coronary snare and sonomicrometry crystals were placed in pigs (n = 21, 32 kg). Coronary occlusion was instituted for 120 minutes followed by reperfusion for 180 minutes. At 105 minutes of ischemia, pigs were randomized to ischemia and reperfusion only (saline solution, n = 11) or Na(+)/H(+) exchanger inhibition (HOE-642, 3 mg/kg intravenously, n = 10). Myocardial injury was determined by tissue staining and measurement of plasma myocyte-specific enzymes. Myocardial contractility was determined by calculation of the regional end-systolic pressure-dimension relation (millimeters of mercury per centimeter) and by assessment of interregional shortening.

RESULTS

Infarct size was not different between groups (39% +/- 6%, P =.26). Moreover, at 180 minutes of reperfusion, plasma troponin-I and creatine kinase MB values had increased to identical levels in the ischemia and reperfusion-only and Na(+)/H(+) exchanger inhibition groups (300 +/- 35 and 50 +/- 6 ng/mL, respectively). At 90 minutes of ischemia, regional end-systolic pressure-dimension relation decreased from baseline (5.7 +/- 0.5 versus 2.7 +/- 0.3, P <.05) in the area at risk. By 30 minutes of reperfusion, regional end-systolic pressure-dimension relation decreased further in the ischemia and reperfusion-only group (1.6 +/- 0.2, P <.05), but improved with Na(+)/H(+) exchanger inhibition (4.4 +/- 0.7, P <.05).

CONCLUSIONS

Na(+)/H(+) exchanger inhibition instituted at reperfusion improved contractility independent of myocardial viability as assessed by absolute infarct size and myocyte-specific enzyme release. Thus, modulation of Na(+)/H(+) exchanger activity in the setting of prolonged ischemia and reperfusion may hold therapeutic potential.

Gene expression profile after cardiopulmonary bypass and cardioplegic arrest

OBJECTIVE

This study examines the cardiac and peripheral gene expression responses to cardiopulmonary bypass and cardioplegic arrest.

METHODS

Atrial myocardium and skeletal muscle were harvested from 16 patients who underwent coronary artery bypass grafting before and after cardiopulmonary bypass and cardioplegic arrest. Ten sample pairs were selected for patient similarity, and oligonucleotide microarray analyses of 12,625 genes were performed using matched precardiopulmonary bypass tissues as controls. Array results were validated with Northern blotting, real-time polymerase chain reaction, in situ hybridization, and immunoblotting. Statistical analyses were nonparametric.

RESULTS

Median durations of cardiopulmonary bypass and cardioplegic arrest were 74 and 60 minutes, respectively. Compared with precardiopulmonary bypass, postcardiopulmonary bypass myocardial tissues revealed 480 up-regulated and 626 down-regulated genes with a threshold P value of.025 or less (signal-to-noise ratio: 3.46); skeletal muscle tissues showed 560 and 348 such genes, respectively (signal-to-noise ratio: 3.04). Up-regulated genes in cardiac tissues included inflammatory and transcription activators FOS; jun B proto-oncogene; nuclear receptor subfamily 4, group A, member 3; MYC; transcription factor-8; endothelial leukocyte adhesion molecule-1; and cysteine-rich 61; apoptotic genes nuclear receptor subfamily 4, group A, member 1 and cyclin-dependent kinase inhibitor 1A; and stress genes dual-specificity phosphatase-1, dual-specificity phosphatase-5, and B-cell translocation gene 2. Up-regulated skeletal muscle genes included interleukin 6; interleukin 8; tumor necrosis factor receptor superfamily, member 11B; nuclear receptor subfamily 4, group A, member 3; transcription factor-8; interleukin 13; jun B proto-oncogene; interleukin 1B; glycoprotein Ib, platelet, alpha polypeptide; and Ras-associated protein RAB27A. Down-regulated genes included haptoglobin and numerous immunoglobulins in the heart, and factor H-related gene 2, protein phosphatase 1, regulatory subunit 3A, and growth differentiation factor-8 in skeletal muscle.

CONCLUSIONS

By establishing a profile of the gene-expression responses to cardiopulmonary bypass and cardioplegia, this study allows a better understanding of their effects and provides a framework for the evaluation of new cardiac surgical modalities directly at the genome level.

The therapeutic potential of endothelin-1 receptor antagonists and endothelin-converting enzyme inhibitors on the cardiovascular system

Clinical trials have established bosentan, an orally active non-selective endothelin (ET) receptor antagonist, as a beneficial treatment in pulmonary hypertension. Trials have also shown short-term benefits of bosentan in systemic hypertension and congestive heart failure. However, bosentan also increased plasma levels of ET-1, probably by inhibiting the clearance of ET-1 by endothelin type B (ET(B)) receptors, and this may mean its effectiveness is reduced with long-term clinical use. Preliminary data suggests that selective endothelin type A (ET(A)) receptor antagonists (BQ-123, sitaxsentan) may be more beneficial than the non-selective ET receptor antagonists in heart failure, especially when the failure is associated with pulmonary hypertension. Experimental evidence in animal disease models suggests that non-selective ET or selective ET(A) receptor antagonism may have a role in the treatment of atherosclerosis, restenosis, myocarditis, shock and portal hypertension. In animal models of myocardial infarction and/or reperfusion injury, non-selective ET or selective ET(A) receptor antagonists have beneficial or detrimental effects depending on the conditions and agents used. Thus clinical trials of the non-selective ET or selective ET(A) receptor antagonists in these conditions are not presently warranted. Several selective endothelin-converting enzyme inhibitors have been synthesised recently, and these are only beginning to be tested in animal models of cardiovascular disease, and thus the clinical potential of these inhibitors is still to be defined.