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Circulation. 1997;96:3963-3973

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(Circulation. 1997;96:3963-3973.)
© 1997 American Heart Association, Inc.

Articles

Chronic Endothelin Receptor Blockade Attenuates Progressive Ventricular Dilation and Improves Cardiac Function in Rats With Myocardial Infarction

Possible Involvement of Myocardial Endothelin System in Ventricular Remodeling

Daniela Fraccarollo, PhD; Kai Hu, MD; Paolo Galuppo, PhD; Peter Gaudron, MD; ; Georg Ertl, MD

From the II. Medizinische Klinik, Fakultät für Klinische Medizin Mannheim der Universität Heidelberg, Germany.

Correspondence to Prof Dr Georg Ertl, II. Medizinische Klinik, Fakultät für Klinische Medizin Mannheim der Universität Heidelberg, Theodor-Kutzer Ufer 1–3, 68167 Mannheim, Germany.


*    Abstract
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 *Abstract
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 down arrowMethods
 down arrowResults
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Background Left ventricular dilatation after myocardial infarction is associated with impaired ventricular function and heart failure and has important implications for survival. The purpose of this study was to investigate the role of endothelin-1 (ET-1) in ventricular dilatation and the effects of chronic endothelin receptor blockade by a mixed ETA and ETB receptor blocker (bosentan) on the circulating and cardiac endothelin systems.

Methods and Results Three hours after coronary ligation or sham operation, bosentan (100 mg · kg body wt-1 · d-1) or placebo was given by gavage. Seven days and 8 weeks after surgery, hemodynamic and left ventricular volume studies were performed. Acute bosentan treatment (7 days) had no effects on hemodynamic parameters and early left ventricular dilatation. In the rats with large infarcts, chronic bosentan treatment (8 weeks) versus placebo reduced left ventricular systolic pressure (116±2 versus 125±3 mm Hg, P<.05) and arterial pressure (93±2 versus 103±3 mm Hg, P<.05), improved stroke volume index (0.69±0.06 versus 0.52±0.04 mL/kg, P<.05), and prevented in part the rightward shift of the pressure-volume curve. Chronic bosentan treatment also decreased ET-1 levels (390±33 versus 475±22 pg/g tissue, P<.05) and density of ET-1 receptors (262±24 versus 346±31 fmol/mg protein, P<.05) in left ventricular myocardium.

Conclusions In the present study, a mixed ETA and ETB receptor antagonist (bosentan) partially prevented left ventricular dilatation and improved hemodynamics, suggesting that endothelin plays a role in left ventricular remodeling after myocardial infarction. Supporting this hypothesis, we show inhibitory effects of bosentan on the peripheral and myocardial endothelin system.


Key Words: endothelin • myocardial infarction • receptors


*    Introduction
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 up arrowAbstract
 *Introduction
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 down arrowResults
 down arrowDiscussion
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Myocardial infarction activates compensatory mechanisms that act to maintain cardiac output and peripheral perfusion. These adaptive responses are the results of a complex interplay between hemodynamic, myocardial, and neurohormonal mechanisms.1,2 Hemodynamic and nonhemodynamic influences lead to left ventricular dilation that initially represents an adaptive mechanism to enhance cardiac pumping capability; progressive dilatation, however, may result in a worsening of cardiac performance.3-8 It has been assumed that the beneficial effects of ACE inhibitors in preventing progressive ventricular dilatation are mediated through the reduction of preload and afterload and perhaps specific interference with the cardiac renin-angiotensin system or bradykinin.9-15 Myocardial cell growth promoting effects of angiotensin II as inhibiting effects of bradykinin might contribute to remodeling of the heart and represent sites of action for ACE inhibitors. Because other factors may contribute to cardiac load and promote myocardial cell growth, it appears worthwhile to look for other principles potentially involved in remodeling after MI.

Experimental and clinical studies demonstrated an activation of the endothelin system, like that of the sympathetic and renin-angiotensin systems after MI.16-20 The vasoconstrictor actions of ET-1 and potential positive inotropic and chronotropic effects21-24 may affect the loading conditions of the infarcted heart and contribute to the development of ventricular dilatation and heart failure. Moreover, an increasing number of observations suggest the existence of a myocardial endothelin system and its possible involvement in the pathophysiology of cardiovascular diseases. The production of ET-1 and number of its binding sites are upregulated in the hypertrophied rat heart because of pressure overload25 and in the left ventricle of rats with chronic heart failure.26 The recent evidence that the selective ETA receptor antagonist BQ-123 improves long-term survival in rats with heart failure induced by coronary artery occlusion suggests that endothelin may play a role in myocardial failure.27

However, the role of circulating and cardiac endothelin systems is by far not completely understood in the pathophysiology of postinfarction ventricular dilatation, and no information is available on a right ventricular myocardial endothelin system. Structural left ventricular dilatation after MI is a dynamic time-dependent process involving the infarcted region and the residual viable myocardium.28,29 Ventricular enlargement in the early postinfarction phase is a consequence of thinning and dilatation of the infarct zone, which may progress in severity over time and reach a plateau at 7 days in rats30; in late phases, ventricular enlargement is generated by architectural rearrangements of surviving myocardium. Accordingly, this study investigates the possible involvement of ET-1 in ventricular dilatation by studying the effects of the mixed ETA and ETB receptor antagonist bosentan31 on left ventricular hemodynamics and volume in the acute (7-day) and chronic (8-week) myocardial infarct phases. In addition, we studied the effects of chronic endothelin receptor blockade on the circulating and cardiac endothelin systems and on left ventricular catecholamine content.


*    Methods
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 up arrowAbstract
 up arrowIntroduction
 *Methods
down arrowResults
 down arrowDiscussion
 down arrowReferences
 
MI, Study Protocols, and Dose-Response Data
Left coronary artery ligations were performed in adult female Wistar rats weighing 250 to 300 g (Charles River, Sulzfeld, Germany) by a previously described method.32 Briefly, under ether anesthesia, the thorax was opened, the heart exteriorized, and a ligature placed around the proximal left coronary artery. The heart was returned to its normal position and the thorax closed. Sham-operated rats were treated similarly except that the operative procedure did not produce a detectable MI. Surviving rats were randomly selected for bosentan or placebo treatment and maintained with free access to standard rat chow and water.

Bosentan (100 mg/kg body wt) was prepared fresh every day as a microsuspension in 5% arabic gum and administered by gavage daily for 7 days (acute effects) or 8 weeks (chronic effects), starting 3 hours after coronary artery ligation. After 7 days the animals were assigned to hemodynamic measurements and after 8 weeks were randomly selected for hemodynamic or biochemical study.

Dose-response curves for the effect of intravenous ET-1 on arterial blood pressure were constructed for various oral doses of bosentan. Four groups of six rats were studied. Group 1 was treated with vehicle (5% arabic gum) and groups 2, 3, and 4 with bosentan 30, 100, 200 mg/kg body wt, respectively. Six hours later, ET-1 (0.03 to 1 nmol/kg body wt IV) was injected in a cumulative manner. At 100 mg/kg body weight, bosentan significantly inhibited the pressor effect of ET-1 (0.03 to 0.3 nmol/kg body wt). Finally, in another experiment, the duration of the effect of bosentan was tested by measurement of the inhibition of ET-1 action 24 hours after its administration. At a dose of 100 mg/kg body wt administered by gavage, bosentan significantly inhibited the pressor effect of ET-1 (0.03 to 0.1 nmol/kg body wt) (P<.05, n=6). Hemodynamic measurements and sample collection for biochemical study were performed 36 hours after the last administration of bosentan.

Hemodynamic Measurements and Left Ventricular Pressure-Volume Relationship
Hemodynamic studies were performed 7 days or 8 weeks after coronary artery ligation, as described by Pfeffer et al.32 Rats were reanesthetized with ether, tracheotomized, and ventilated. Saline-filled catheters (PE 50) were advanced from the right carotid artery and jugular vein into the left ventricle and right atrium, respectively, and connected via a three-way stopcock to a Millar micromanometer and Statham (P50) transducer. After measurements of left ventricular pressure, the catheter was withdrawn to the aorta and heart rate was calculated from arterial blood pressure tracings. Left ventricular systolic and end-diastolic pressures, mean arterial pressure, and heart rate were measured under light ether anesthesia and spontaneous respiration. During positive-pressure ventilation and after midsternal thoracotomy, an electromagnetic flow probe (2.5 mm ID; Statham, Inc) was placed around the ascending aorta for continuous measurement of aortic blood flow (cardiac output). Stroke volume was calculated as the ratio of cardiac output and heart rate, and total peripheral resistance was calculated as the ratio of the difference between mean systemic and right atrial pressures and cardiac output. All variables derived from aortic blood flow were corrected for body weight. To assess the maximal flow-generating capacity of the heart, warmed (39°C to 40°C) Tyrode's solution was infused into a femoral vein at a rate of 40 mL · kg-1 · min-1 for 45 seconds or until maximal flow was achieved. This infusion produces a rise in cardiac output to peak values, followed by a plateau, despite further elevation of right atrial pressure. Maximum cardiac performance was defined as peak values of cardiac output and stroke volume during this infusion of Tyrode's solution.

Passive pressure-volume curves of the left ventricle were obtained as previously described.10 The heart was arrested by potassium chloride, and a double-lumen catheter (PE 50 inside PE 200) was inserted into the left ventricle via the ascending aorta. The right ventricular free wall was incised to avoid fluid accumulation. The atrioventricular groove was ligated, and isotonic saline was infused at a rate of 0.76 mL/min via one lumen while intraventricular pressure was continuously recorded through the other lumen from negative pressure to 30 mm Hg. Three pressure-volume curves were obtained from each left ventricle within 10 minutes after cardiac arrest.

Biochemical Measurements
Sample Collection
Eight weeks after coronary artery ligation, under anesthesia with sodium pentobarbital (50 mg/kg body wt IP), a blood sample was collected from the abdominal aorta into a chilled tube containing potassium EDTA (2 mg/mL blood). Plasma was separated by centrifugation at 3000g for 10 minutes at 4°C and stored at -80°C. The heart was subsequently removed, rinsed in ice-cold normal saline, and divided into right ventricle and left ventricle, including septum. After infarct size estimation, the scarred area was removed and the tissues were separately weighed and rapidly frozen in liquid nitrogen and stored at -80°C.

Tissue Homogenization
Tissue samples were thawed in ice-cold buffer (10%, wt/vol) containing 50 mmol/L Tris/HCl (pH 7.4), cut into small pieces, and homogenized with a glass Teflon homogenizer. Each tissue homogenate was divided into three aliquots for receptor binding assay and analysis of ET-1 and catecholamine levels, respectively. Tissue homogenate for the binding assay was stored in liquid nitrogen until use. The aliquot for tissue ET-1 determination was quickly diluted 1:1 with ice-cold 2 mol/L acetic acid, and the tissue homogenate for catecholamine measurements was diluted 1:1 with ice-cold 0.4 mol/L perchloric acid containing dihydroxybenzylamine as internal standard.

Plasma and Tissue ET-1
Plasma samples (500 µL) were applied to Sep-Pak C-18 cartridges (Waters Corp) previously washed with 3 mL methanol, 1 mL methanol/water (90/10, vol/vol), and 4 mL methanol/water (5/95, vol/vol). After application of the sample, the cartridge was washed with 10 mL methanol/water (5/95, vol/vol), and the peptides were eluted with 1.5 mL methanol/water (90/10, vol/vol) and 0.5 mL methanol/water/acetic acid (90/9/1 vol/vol/vol). The eluate was dried at 30°C under reduced pressure, reconstituted in 250 µL assay buffer, and subjected to radioimmunoassay. The recovery of the extraction procedure was >85%, as determined by addition of synthetic ET-1 to plasma. Data were not corrected for extraction recovery. Radioimmunoassay was carried out with 125I-labeled ET-1 (DuPont NEN) at a concentration of 4 pg (6000 cpm per tube). A standard curve was constructed by dilution of synthetic ET-1 (Sigma Chemical Co) from 8 to 0.125 pg per tube. Rabbit ET-1 antiserum (RAS 6901, Peninsula Laboratories Europe, Ltd) was incubated with standard or sample for 20 hours at 4°C; 125I-ET-1 was added for a subsequent 20 hours of incubation at 4°C. Bound counts were separated by precipitation at 25°C for 2 hours with goat antirabbit IgG serum (GARGG-500, Peninsula) in conjunction with pretitered normal rabbit serum (NRS-500, Peninsula). After centrifugation at 2000g for 20 minutes at 4°C, the free fraction was aspirated and the pellets were counted in a gamma counter. The detection limit of the assay was 0.2 pg per tube. The anti–ET-1 serum showed cross-reactivity of <7% with ET-3.

Cardiac tissues, which were placed in 1 mol/L acetic acid, were immediately rehomogenized and boiled for 10 minutes. The homogenate was then centrifuged for 20 minutes at 15 000g at 4°C. The supernatant was collected and the extraction performed as described for plasma samples. The eluates reconstituted in assay buffer were subjected to ET-1 ELISA (Amersham International PLC). The assay did not cross-react with ET-3 or big ET-1, and the detection limit was 4 pg per tube.

Cardiac Membrane Preparation and ET-1 Receptor Binding Assay
Cardiac membranes were prepared according to the method of Ishikawa et al33 with some modifications. Tissue homogenates were diluted 1:20 with ice-cold buffer (50 mmol/L Tris/HCl, 0.1 mmol/L PMSF, and 0.25 mol/L sucrose, pH 7.4) and centrifuged at 600g for 10 minutes at 4°C. The supernatants were centrifuged at 8400g for 10 minutes at 4°C, decanted, and centrifuged at 105 000g for 60 minutes at 4°C. The resultant pellets were suspended in ice-cold 50 mmol/L Tris buffer containing 10 mmol/L MgCl2, 0.1 mmol/L PMSF, and 0.25 mol/L sucrose (pH 7.4). Protein concentration was determined according to Lowry34 with BSA as standard. A binding assay was performed in binding buffer (50 mmol/L Tris/HCl, 10 mmol/L MgCl2, 0.1 mmol/L PMSF, 0.25 mol/L sucrose, and 0.1% BSA, pH 7.4) with 50 µg membrane proteins per tube in a final volume of 250 µL. Incubation was done at 25°C for 2 hours with increasing concentrations of 125I-ET-1 (8 pmol/L to 0.3 nmol/L) for saturation experiments. After dilution with 4 mL ice-cold binding buffer, bound and free 125I-ET-1 were separated by rapid vacuum filtration through Whatman GF/C filters, followed by three additional washes with 3 mL of binding buffer. The radioactivity of the filters was counted in a gamma counter. Nonspecific binding was defined in the presence of 0.2 µmol/L unlabeled ET-1.

PRA and NT-proANP
PRA was measured by radioimmunoassay of angiotensin I generated after 90 minutes of incubation of the plasma sample at 37°C and pH 6.0 (Sorin Biomedica Diagnostic). NT-proANP was measured by radioimmunoassay (Immunodiagnostic GmbH). The test kit uses a specific antiserum against NT-proANP without extraction and a second antibody for the separation of the antibody bound and free fractions.

Left Ventricular Tissue Catecholamines
Left ventricular tissue homogenates, placed in 0.2 mol/L perchloric acid, were immediately rehomogenized and centrifuged for 15 minutes at 10 000g at 4°C. The supernatant was extracted on aluminum oxide (pH 8.6), and the catecholamines were eluted with 0.1 mol/L perchloric acid (100 µL) and assayed by high-performance liquid chromatography with electrochemical detection. The limit of detection was 2 pg.

Determination of Infarct Size
The left ventricles of hearts included in the hemodynamic study, after pressure-volume curves were made, were infused with a volume of 10% buffered formalin corresponding to pressure of 5 mm{ths}Hg, and the heart (with catheter and closed three-way stopcock) was further fixed in formalin for 24 hours. The right and left ventricles were separated and weighed, and infarct size was quantified histologically by planimetry as previously reported.32 Briefly, the left ventricle was embedded in paraffin, and ten 10-µm thin sections were cut serially from apex to base at 1-mm intervals. Sections were stained with picrosirius red. The boundary lengths of the infarcted and noninfarcted endocardial and epicardial surfaces were traced with a planimeter digital image analyzer (Sony). Infarct size (fraction of the infarcted left ventricle) was calculated as the average of all slices and expressed as a percentage of length.

Because left ventricular myocardium of hearts included in biochemical studies was used for ET-1, catecholamine, and receptor binding assays, infarct size could not be measured histologically. Four longitudinal incisions were made in the left ventricular septum and inferoposterior wall so that endocardial and epicardial surfaces could be pressed flat on glass plates, as previously described by Yamagishi et al.12 A clear macroscopic boundary of scar could be seen, which made the identification of infarcted area reliable. The boundary lengths of the infarcted and noninfarcted epicardial and endocardial surfaces were traced and digitized as described previously for histological slices. This method systematically underestimated infarct size compared with standard histological technique. Because animals were randomly assigned to hemodynamic or biochemical study, "true" infarct size should be similar within various infarct groups.

Statistical Analysis
For hemodynamic and ventricular volume studies, animals with infarcts were classified as small to moderate (5% to 40%) and large (>=40%) infarct groups, and for biochemical studies as small to moderate (5% to 25%) and large (>=25%) infarct groups. For within-treatment comparisons, one-way ANOVA followed by Newman-Keuls test was performed to compare each infarct group with its respective noninfarcted group. Unpaired t test assessed differences between placebo- and bosentan-treated rats within groups with comparable infarct sizes. Correlations were determined by linear regression analysis. These statistical comparisons were performed with the statistical program NCSS, Unisoft. The pressure-volume curves were also examined by a multifactor factorial ANOVA for repeated measures, with group (sham, small to moderate MI, large MI) and treatment (placebo, bosentan) as between factors and pressure at various levels as within factors. This statistical analysis was performed with the statistical program SuperANOVA, version 1.11, Abacus Concepts, Inc. Differences were considered significant at a level of P<.05, and values were expressed as mean±SEM.


*    Results
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 *Results
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Hemodynamic Measurements and Ventricular Volume Studies
Differences in mortality between placebo and bosentan treatment were not found during 7-day and 8-week protocols.

Seven-Day Protocol
Myocardial infarct size distribution was similar in placebo- and bosentan-treated rats (Table 1Down). Body weight and ratio of right ventricular weight/body weight were unchanged by infarction or treatment. The ratio of left ventricular weight to body weight declined in the acute myocardial infarct phase in the rats with large infarcts treated with bosentan.


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  		Table 1. Myocardial Infarct Size Distribution and Ratio of Body Weight to Ventricular Weight in Placebo- and Bosentan-Treated Rats 7 Days After Myocardial Infarction

Left ventricular end-diastolic pressure increased and systolic pressure declined with increasing infarct size. Cardiac and stroke volume indexes decreased with increasing infarct size at rest and during acute volume loading, whereas peripheral resistance increased compared with sham-operated rats. There were no differences between placebo- and bosentan-treated rats (Table 2Down).


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  		Table 2. Hemodynamics in Placebo- and Bosentan-Treated Rats 7 Days After Myocardial Infarction

MI resulted in a rightward shift of the passive pressure-volume curve, indicating an increase of left ventricular volume. No difference was found between placebo and bosentan (Fig 1ADown).



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  		Figure 1. Pressure-volume relations 7 days (A) and 8 weeks (B) after MI of placebo- and bosentan-treated sham-operated rats with small to moderate MI and large MI. MI resulted in a progressive rightward shift of the pressure-volume relation, depending on MI size and time after MI. Bosentan treatment partially prevented rightward shift of left ventricular volume in rats with large MI 8 weeks after MI (B) but had no effect 7 days after MI (A). Values are mean±SEM. *P<.05 placebo large MI vs placebo sham, {ddagger}P<.05 bosentan large MI vs bosentan sham, §P<.05 placebo small to moderate MI vs placebo sham, %P<.05 bosentan small to moderate MI vs bosentan sham, {dagger}P<.05 bosentan large MI vs placebo large MI.

Eight-Week Protocol
The infarct size distribution was similar in placebo- and bosentan-treated groups. Body weight and left ventricular weight/body weight ratio were unchanged by infarction or treatment. Right ventricular weight corrected for body weight increased with increasing infarct size and was not significantly different between placebo- and bosentan-treated animals (Table 3Down).


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  		Table 3. Myocardial Infarct Size Distribution and Ratio of Body Weight to Ventricular Weight in Placebo- and Bosentan-Treated Rats 8 Weeks After Myocardial Infarction

The effects of bosentan on hemodynamics 8 weeks after MI are shown in Table 4Down. Left ventricular systolic and mean arterial pressures and heart rate were significantly decreased by bosentan treatment in rats with large infarcts. Left ventricular end-diastolic pressure was increased in rats with large infarcts compared with sham-operated rats, and there were no differences between bosentan-treated and untreated rats. In untreated rats with large infarcts, resting and peak cardiac indexes were significantly lower than in sham-operated rats, and total peripheral resistance index tended to increase. Bosentan prevented the reduction of cardiac index and increase in peripheral resistance in rats with large infarcts. In the animals with large infarcts, stroke volume index was also significantly increased by bosentan versus placebo with rats both at rest and during volume loading.


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  		Table 4. Hemodynamics in Placebo- and Bosentan-Treated Rats 8 Weeks After Myocardial Infarction

A further rightward shift of the left ventricular pressure-volume curve occurred in all infarct-size groups 8 weeks versus 7 days after MI. Bosentan partially prevented the rightward shift of left ventricular volume in rats with large infarcts (Fig 1BUp). The multifactor factorial ANOVA for repeated-measures analysis showed a significant difference between placebo and bosentan in the large MI group (P=.019).

Biochemical Studies
Infarct size, body weights, and heart weights of rats included in the biochemical study are summarized in Table 5Down. The rat subdivision produced groups with similar infarct sizes, scar weights indexed for body weight, and right ventricular weight corrected for body weight, essential for a correct comparison between placebo and bosentan treatment. In placebo and bosentan rats, there was a similar correlation between infarct sizes and scar weight/body weight ratio (placebo, r=.92, P=.0001; bosentan, r=.95, P<.0001). Body weight and left ventricular weight/body weight ratio were unchanged by infarction or treatment. The right ventricular weight corrected for body weight was significantly elevated (compared with noninfarcted rats) in placebo and bosentan rats with large infarcts.


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  		Table 5. Myocardial Infarct Size Distribution and Ratio of Body Weight to Ventricular Weight of Placebo- and Bosentan-Treated Rats From Biochemical Study 8 Weeks After Myocardial Infarction

Endothelin-1
Plasma ET-1 levels as shown in Fig 2Down increased in rats with large infarcts compared with noninfarcted rats and rats with small to moderate infarcts. Bosentan increased plasma ET-1 levels in sham-operated and small to moderate infarct rats but not in rats with large infarcts.



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  		Figure 2. Plasma ET-1 levels 8 weeks after MI of sham-operated rats (placebo, n=6; bosentan, n=10), small to moderate MI rats (placebo, n=12; bosentan, n=8), and large MI rats (placebo, n=10; bosentan, n=9). Values are mean±SEM. *P<.05 vs corresponding value in sham-operated rats, {dagger}P<.05 vs corresponding value in placebo rats with comparable MI size.

ET-1 levels increased in left ventricular myocardium of rats with infarcts compared with sham-operated rats. Left ventricular ET-1 levels were significantly lower in bosentan-treated rats with large infarcts than in untreated rats. In right ventricular myocardium, ET-1 concentration increased with increasing infarct size. There were no differences between left and right ventricular ET-1 (Fig 3Down).



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  		Figure 3. A, ET-1 levels in left ventricular myocardium 8 weeks after MI of sham-operated rats (placebo, n=5; bosentan, n=6), small to moderate MI rats (placebo, n=6; bosentan, n=6), and large MI rats (placebo, n=9; bosentan, n=9). B, ET-1 levels in right ventricular myocardium 8 weeks after MI of sham-operated rats (placebo, n=5; bosentan, n=7), small to moderate MI rats (placebo, n=8; bosentan, n=6), and large MI rats (placebo, n=9; bosentan, n=9). Values are mean±SEM. *P<.05 vs corresponding value in sham-operated rats, {dagger}P<.05 vs corresponding value in placebo rats with comparable MI size.

Left ventricular ET-1 levels (Fig 4Down) significantly correlated with scar weight/body weight ratio. In untreated rats, a correlation was observed between right ventricular ET-1 levels and scar weight/body weight ratio (r=.59, P<.01).



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  		Figure 4. Linear regression plot of relationship between left ventricular ET-1 level and scar weight/body weight ratio (Scar/BW) in placebo- and bosentan-treated rats 8 weeks after MI. ET-1 concentration in left ventricular myocardium exhibited significant positive correlation with Scar/BW.

Endothelin-1 Receptors
The results of ET-1 receptor binding assays are shown in Table 6Down. In placebo-treated rats, left ventricular 125I-ET-1 binding density (Bmax) was increased in rats with large infarcts compared with sham-operated rats, whereas the dissociation constant (Kd) was almost the same. In fact, Scatchard analyses of saturation binding data showed linear plots of similar slope (Kd-1) and different x intercepts (Bmax) from sham and large infarct groups (Fig 5Down). Bosentan treatment for 8 weeks significantly decreased the maximum number of ET-1 receptors in rats with large infarcts compared with placebo-treated rats with comparable infarct size. In the right ventricle, the density of ET-1 receptors was increased in both untreated and bosentan-treated rats with large infarcts compared with sham-operated rats, and the dissociation constant of the various groups of both treated and untreated rats was not altered. The receptor density and the dissociation constant were similar between the left and right ventricles within the various groups of placebo- and bosentan-treated rats (P=NS, paired t test). As with ET-1 cardiac levels, a correlation has been observed between both left and right ventricular receptor density levels and scar weight/body weight ratio (r=.63, P<.001; r=.72, P<.001, respectively).


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  		Table 6. Receptor Binding Parameters in the Left and Right Ventricular Myocardium of Placebo- and Bosentan-Treated Rats 8 Weeks After Myocardial Infarction



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  		Figure 5. Scatchard plots of 125I-ET-1 binding to left ventricular membranes of placebo- and bosentan-treated rats with large MI and sham-operated rats 8 weeks after surgery. Plots derived from four representative saturation binding experiments, each performed in duplicate. Kd and Bmax are summarized in Table 6Up.

PRA and NT-proANP
The PRA tended to increase with MI and was unaffected by bosentan therapy. NT-proANP concentration was elevated (compared with noninfarcted rats) in placebo rats with small to moderate and large infarcts and in bosentan-treated rats with large infarcts. There were no differences between untreated and treated rats (Table 7Down).


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  		Table 7. PRA and NT-proANP Concentration of Placebo- and Bosentan-Treated Rats 8 Weeks After Myocardial Infarction

DHPG and NE Ratios
NE levels in left ventricular myocardium were lower in rats with large infarcts than in sham-operated rats in both treatment groups (placebo, 224±18 versus 360±36 ng/g tissue, P<.05; bosentan, 198±20 versus 373±32 ng/g tissue, P<.05). The epinephrine and dopamine levels also decreased, but not significantly, in rats with large infarcts (data not shown). The ratio of the NE metabolite DHPG to NE was elevated in rats with large infarcts compared with sham-operated rats, and chronic bosentan therapy did not alter this ratio (Fig 6Down).



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  		Figure 6. DHPG/NE ratios in left ventricular myocardium 8 weeks after MI of sham-operated rats (placebo, n=5; bosentan, n=9), small to moderate MI rats (placebo, n=7; bosentan, n=5), and large MI rats (placebo, n=7; bosentan, n=6). DHPG/NE ratio was increased in rats with large infarcts and not changed by bosentan. Values are mean±SEM. *P<.05 vs corresponding value in sham-operated rats.


*    Discussion
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 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 up arrowResults
 *Discussion
down arrowReferences
 
This study demonstrates for the first time that chronic treatment for 8 weeks with the mixed ETA and ETB receptor antagonist bosentan prevents progressive left ventricular dilatation and improves cardiac function in rats with large MI. We found that in large infarcts, chronic endothelin receptor blockade reduced left ventricular systolic and arterial pressure and prevented the increase in systemic vascular resistance and a reduction of stroke volume and cardiac index at rest and during volume load. Furthermore, chronic bosentan treatment decreased circulating ET-1 levels and the ET-1 levels and receptor density in left ventricular myocardium. These findings suggest that chronic endothelin receptor blockade improved left ventricular performance via a combined effect on peripheral circulation and on the myocardial endothelin system. Furthermore, this study revealed that blockade of the endothelin system has no effects on development of structural dilatation in the "acute" postinfarction phase, defined in this study as 7 days after MI.

Acute Endothelin Receptor Blockade
Progressive thinning and enlargement of the infarct segment (infarct expansion) associated with cavity enlargement is an event of the first days after MI; dilatation of surviving myocardium follows later.28-29 A variety of interventions have been shown to promote acute cardiac dilatation, such as administration of anti-inflammatory agents and ventricular load, whereas other interventions, such as reperfusion and vasodilatation, reduced shape alterations in the early postinfarction period.5

It has been hypothesized that endothelin receptor blockade can favorably alter the loading conditions on the left ventricle and attenuate ventricular dilatation already in the early stages after infarction. However, in this model, no beneficial effects of bosentan treatment on hemodynamic parameters and early left ventricular dilatation were found. We attribute the failure of bosentan to alter any variable measured in this study to the absence of control of these variables by ET-1 or a lack of activation of the endothelin system during this phase after MI.

Chronic Endothelin Receptor Blockade
We suppose that the favorable effects of bosentan 8 weeks after MI were achieved in part by a reduction of afterload. However, other drugs that reduce afterload but not preload have failed to prevent remodeling.9 The effects of chronic bosentan treatment are similar in part to those of chronic treatment with captopril.9,10 Like the ACE inhibitor, it favorably alters systolic loading conditions on the left ventricle and may thus reduce progressive left ventricular dilation and dysfunction after MI. However, chronic captopril treatment produced a significant decrease in left ventricular end-diastolic pressure,10 with a downward displacement of volume on the pressure-volume relation (less ventricular distension). Similar reduction of end-diastolic pressure was observed by Sakai et al27 for the use of the specific ETA receptor antagonist BQ-123. In contrast, bosentan had no effect on left ventricular filling pressure, and the effect on progressive ventricular enlargement was only the result of an attenuation of the rightward shift of the pressure-volume curve, without a downward displacement of volume in that relation. This shift of the pressure-volume curve occurred at low pressures and therefore suggests a reduction of volume rather than an increase in myocardial stiffness.35 Thus, although ACE inhibitors reduced left ventricular volume in part by a reduction of distending pressure, the effect of bosentan was completely structural, because left ventricular volume was significantly smaller at identical filling pressures. The reason for the different effects of bosentan and BQ-123 remains unclear. It may be due to their different actions on only ETA or on both ETA and ETB receptors, respectively. It may also be due to different protocols in this and the previous study by Sakai et al,27 in which rats were studied for 4 weeks longer and the treatment started 10 days after MI. Sakai et al36 also reported that BQ-123 treatment over a 2-week period did not affect left ventricular end-diastolic pressure.

Bosentan treatment may have reduced heart rate by preventing the positive chronotropic effect of ET-1.22 This may have favorable effects on myocardial energetics and function similar to ß-blocker therapy. However, ß-blockers have rather increased left ventricular dimensions in this or similar models after MI.37 Thus, hemodynamic unloading effects of bosentan do not conclusively explain its substantial reduction of left ventricular volume. However, pressure-volume curves obtained in arrested hearts do not reflect pressure-volume relations of beating hearts. Conclusions on interrelations between in vivo hemodynamics and structure on the basis of this analysis should therefore be drawn with some caution.

The cardiac DHPG/NE ratio provides an index of increased NE turnover and sympathetic activity in rats with chronic left ventricular dysfunction.38 Bosentan treatment did not increase left ventricular DHPG/NE ratio of rats with large infarcts. Therefore, we suppose that its effects were not achieved by an influence on cardiac sympathetic activity.

Recent studies report that the production of ET-1 and its binding sites were increased in the left ventricles of rats 3 weeks after MI.26 In the present study, we show that this increase in ET-1 levels and density of ET-1 receptors in left ventricle is sustained for 8 weeks after MI in a later stage of progressive left ventricular dysfunction. In addition, we find that both are related to infarct size, the degree of left ventricular dysfunction, and activation of other humoral systems represented in this study by PRA and NT-proANP. An increase in ET-1 levels and density of ET-1 receptors was found only in animals with large infarcts, not in animals with small to moderate infarcts. In fact, correlations were found between scar weight and the tissue level of ET-1 and its binding sites, respectively, in both left and right ventricular myocardium. Effects of bosentan were also observed only in rats with large infarcts. These data suggest strongly that an activation of the ET-1 system is a prerequisite for the bosentan effects.

In agreement with previous investigations,20,26 we also observed an increase of plasma ET-1 levels in rats with large infarcts. The increased plasma concentrations in rats with large infarcts may reflect the severity of cardiac dysfunction.26 In addition, impaired pulmonary and renal clearance of ET-1, which might be expected in rats with large MI, may lead to elevated circulating ET-1 levels.20 Sham-operated rats and rats with small to moderate infarcts treated with bosentan had higher ET-1 levels than untreated rats, whereas we did not observe such a difference in rats with large infarcts. Other investigators39 demonstrated that endothelin receptor antagonists increased circulating ET-1 and suggested that this increase was related to displacement of endothelin from the ETB receptor, which is involved in endothelin clearance and an increase of ET-1 gene expression in some vessels. Therefore, it was thought that bosentan enhanced ET-1 production in some vascular tissue of sham-operated rats and rats with small to moderate infarcts but not of rats with severe left ventricular dysfunction. The observation that ET-1 plasma levels in bosentan-treated rats with large infarcts were not different from those of untreated rats was surprising. There is no simple explanation, but indirect mechanisms, such as improvement of left ventricular function and systemic hemodynamics, could have contributed. Recently, Li et al40 demonstrated that plasma ET-1 levels were normalized by cilazapril in spontaneously hypertensive rats treated with N{omega}-nitro-L-arginine methyl ester, and they suggest that the blood pressure–lowering effect of ACE inhibition may reduce ET-1 spillover into the bloodstream.

The finding that vascular endothelin secretion is mainly polar, being directed toward the interstitial region rather than the vascular lumen,41 supports the hypothesis that endothelin acts in a paracrine fashion rather than as a circulating hormone. The marked concentration difference between plasma and tissue levels of endothelin, as our study underlines, provides further evidence for a local role of endothelin. The upregulation of the cardiac endothelin system in rats with large infarcts may represent a neurohumoral compensatory response related to compromised left ventricular function. The vasoconstrictor actions of endothelin in the coronary circulation and a chronic positive inotropic and chronotropic effect21-24 may result in a worsening of cardiac dysfunction. We speculate that bosentan blocked the effects of this neurohormonal system and therefore favorably altered the natural progression of left ventricular dysfunction and dilatation.

ACE inhibitors reduce left ventricular weight in rats with or without MI and independent of infarct size.10 In contrast, bosentan had no effect on left ventricular weight in the present study. In fact, it reduced left ventricular volume in rats with large infarcts while weight remained similar. Although left ventricular hypertrophy was not analyzed on a cellular basis, these data strongly suggest that bosentan did not prevent concentric hypertrophy of surviving myocardium, which was previously shown on the basis of quantitative histomorphology by Olivetti et al.42 Infarct expansion, elongation (eccentric hypertrophy) of muscle fibers, and fiber slippage contribute to left ventricular dilatation after MI. Our data do not suggest that bosentan prevented infarct expansion, because this effect would have shown up at 1 week after infarction. It remains unclear from this study whether bosentan prevented fiber slippage, eccentric hypertrophy, or both.

Several studies9,13-15 indicate that ACE inhibitors and angiotensin type 1 receptor antagonists also prevent right ventricular hypertrophy. These effects were attributed to a reduction of afterload of the right ventricle and inhibition of a hypertrophic effect of myocardial angiotensin II. Chronic endothelin receptor blockade did not prevent the increase of right ventricular weight after MI in our study, in accordance with a lack of bosentan to reduce left ventricular filling pressure. In addition, a direct contribution of endogenous endothelin on right ventricular hypertrophy in this model is unlikely. ET-1 induces hypertrophy of cultured rat cardiomyocytes,43 whereas in vivo, it is involved in monocrotaline-induced pulmonary hypertension44 and in the mechanism of left ventricular hypertrophy during the early phase of pressure overload45 but not in eccentric cardiac hypertrophy induced by volume overload.46 Moreover, the production of ET-1 and its binding sites is upregulated in pressure overload cardiac hypertrophy.25 In this study, we found that in right ventricular myocardium, ET-1 level and the number of ET-1 binding sites were increased in association with the increase of infarct size. The inability of bosentan to maintain inhibitory effects argues against ET-1 being directly causative for right ventricular hypertrophy in this postinfarction phase.

The present study was performed in female rats. Pfeffer et al10 also used female rats to determine the influence of captopril on left ventricular remodeling. Other studies on the effect of ACE inhibitors on ventricular hypertrophy were performed in male rats.13-15 Our results are confined to females, because sex differences have been reported in ventricular hypertrophy.47,48

In conclusion, the present study demonstrates that bosentan treatment had beneficial effects on hemodynamics and left ventricular volume in rats with chronic left ventricular dysfunction after large infarcts. These findings suggest that the effects of ET-1 receptor blockade are related to the extent of left ventricular dysfunction and are apparent only in rats with chronic upregulation of the circulating and cardiac endothelin systems. These observations support the hypothesis that ET-1, in concert with activation of other neurohumoral systems, may contribute after MI in the acute phase to maintain systemic perfusion but may be detrimental in chronic stages of cardiac dysfunction. Conversely, ET-1 antagonists may prove to be useful agents for prevention of progressive left ventricular dysfunction after MI. A combination with an ACE inhibitor could be of specific interest, because bosentan did not reduce left ventricular filling pressure, an effect that is considered important for the action of ACE inhibitors on remodeling.9


*    Selected Abbreviations and Acronyms
 
DHPG = 3,4-dihydroxyphenylethylene glycol
ET-1 = endothelin-1
ETA, ETB = endothelin type A, type B
MI = myocardial infarction
NE = norepinephrine
NT-proANP = N-terminal pro–atrial natriuretic peptide
PRA = plasma renin activity


*    Acknowledgments
 
This study was supported by SFB355, Pathophysiologie der Herzinsuffizienz, Universität Würzburg and the Forschungsfond of the Fakultät für klinische Medizin Mannheim der Universität Heidelberg, Germany. Bosentan was kindly provided by Dr Martine Clozel, Hoffmann-La Roche, Basel, Switzerland. We wish to gratefully acknowledge the technical assistance of Andreas Mangol, Anskar Platte, Oliver Lutz, and Hans-Peter Schepky.


*    Footnotes
 
Guest editor for this article was Douglas L. Mann, MD, VA Medical Center, Houston, Tex.

Received April 15, 1997; revision received August 13, 1997; accepted August 21, 1997.


*    References
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  1. Francis GS. Neurohumoral mechanism involved in congestive heart failure. Am J Cardiol. 1985;55:15-21.
  2. Parmley WW. Pathophysiology of congestive heart failure. Am J Cardiol. 1985;55:9-14.
  3. Eaton LW, Weiss JL, Bulkley BH, Garrison JB, Weisfeldt M. Regional cardiac dilatation after acute myocardial infarction. N Engl J Med. 1979;300:57-62.[Abstract]
  4. White HD, Norris RM, Brown MA, Brandt PWT, Whitlock RML, Wild CJ. Left ventricular end-systolic volume as the major determinant of survival after recovery from myocardial infarction. Circulation. 1987;76:44-51.[Abstract/Free Full Text]
  5. Pfeffer MA, Braunwald E. Ventricular remodeling after myocardial infarction. Experimental observations and clinical implications. Circulation. 1990;81:1161-1172.[Abstract/Free Full Text]
  6. Gaudron P, Eilles C, Ertl G, Kochsiek K. Early remodelling of the left ventricle in patients with myocardial infarction. Eur Heart J. 1990;11:139-146.
  7. Gaudron P, Eilles C, Ertl G, Kochsiek K. Compensatory and non-compensatory left ventricular dilatation after myocardial infarction: time course, hemodynamic consequences at rest and exercise. Am Heart J. 1992;123:377-385.[Medline] [Order article via Infotrieve]
  8. Gaudron P, Eilles C, Kugler I, Ertl G. Progressive left ventricular dysfunction and remodeling after myocardial infarction: potential mechanisms and early predictors. Circulation. 1993;87:755-763.[Abstract/Free Full Text]
  9. Raya TE, Gay RG, Aguirre M, Goldman S. Importance of venodilatation in prevention of left ventricular dilatation after chronic large myocardial infarction in rats: a comparison of captopril and hydralazine. Circ Res. 1989;64:330-337.[Abstract/Free Full Text]
  10. Pfeffer JM, Pfeffer MA, Braunwald E. Influence of chronic captopril therapy on the infarcted left ventricle of the rat. Circ Res. 1985;57:84-95.[Abstract/Free Full Text]
  11. Pfeffer MA, Braunwald E, Moyé LA, Basta L, Brown EJ, Cuddy TE, Davis BR, Geltman EM, Goldman S, Flaker GC, Klein M, Lamas GA, Packer M, Rouleau J, Rouleau JL, Rutherford J, Wertheimer JH, Hawkins CM. Effect of captopril on mortality and morbidity in patients with left ventricular dysfunction after myocardial infarction. N Engl J Med. 1992;327:669-677.[Abstract]
  12. Yamagishi H, Kim S, Nishikimi T, Takeuchi K, Takeda T. Contribution of cardiac renin-angiotensin system to ventricular remodeling in myocardial-infarcted rats. J Mol Cell Cardiol. 1993;25:1369-1380.[Medline] [Order article via Infotrieve]
  13. Makino N, Hata T, Sugano M, Dixon IMC, Yanaga T. Regression of hypertrophy after myocardial infarction is produced by the chronic blockade of angiotensin type 1 receptor in rats. J Mol Cell Cardiol. 1996;28:507-517.[Medline] [Order article via Infotrieve]
  14. Bruckschlegel G, Holmer SR, Jandeleit K, Grimm D, Muders F, Kromer EP, Riegger GAJ, Schunkert H. Blockade of the renin-angiotensin system in cardiac pressure-overload hypertrophy in rats. Hypertension. 1995;25:250-259.[Abstract/Free Full Text]
  15. Baker KM, Chernin MI, Wixson SK, Aceto JF. The renin-angiotensin system involvement in pressure-overload cardiac hypertrophy in rats. Am J Physiol. 1990;259:H324-H332.[Abstract/Free Full Text]
  16. Tomada H. Plasma endothelin-1 in acute myocardial infarction with heart failure. Am Heart J. 1993;125:667-672.[Medline] [Order article via Infotrieve]
  17. Omland T, Lie RT, Aakvaag A, Aarsland T, Dickstein K. Plasma endothelin determination as a prognostic indicator of 1-year mortality after acute myocardial infarction. Circulation. 1994;89:1573-1579.[Abstract/Free Full Text]
  18. Ray SG, McMurray JJ, Morton JJ, Dargie HJ. Circulating endothelin in acute ischemic syndromes. Br Heart J. 1992;67:383-386.[Abstract/Free Full Text]
  19. Wei CM, Lerman A, Rodeheffer RJ, McGregor CGA, Brandt RR, Wright S, Heublein DM, Kao PC, Edwards WD, Burnett JC. Endothelin in human congestive heart failure. Circulation. 1994;89:1580-1586.[Abstract/Free Full Text]
  20. Teerlink JR, Loeffler BM, Hess P, Marie JP, Clozel M, Clozel JP. Role of endothelin in the maintenance of blood pressure in conscious rats with chronic heart failure. Circulation. 1994;90:2510-2518.[Abstract/Free Full Text]
  21. Ishikawa T, Yanagisawa M, Kimura S, Goto K, Masaki T. Positive inotropic action of novel vasoconstrictor peptide endothelin on guinea pig atria. Am J Physiol. 1988;255:H970-H973.[Abstract/Free Full Text]
  22. Ishikawa T, Yanagisawa M, Kimura S, Goto K, Masaki T. Positive chronotropic effects of endothelin: a novel endothelium-derived vasoconstrictor peptide. Pflugers Arch. 1988;413:108-110.[Medline] [Order article via Infotrieve]
  23. Li K, Stewart DJ, Rouleau JL. Myocardial contractile actions of endothelin-1 in rat and papillary muscles. Circ Res. 1990;69:301-312.[Abstract/Free Full Text]
  24. Takanashi M, Endoh M, Characterization of positive inotropic effect of endothelin on mammalian ventricular myocardium. Am J Physiol. 1991;261:H611-H619.[Abstract/Free Full Text]
  25. Arai M, Yoguchi A, Iso T, Takahashi T, Imai S, Murata K, Suzuki T. Endothelin-1 and its binding sites are upregulated in pressure overload cardiac hypertrophy. Am J Physiol. 1995;268:H2084-H2091.[Abstract/Free Full Text]
  26. Sakai S, Miyauchi T, Sahurai T, Kasuya Y, Ihara M, Yamaguchi I, Goto K, Sugishita Y. Endogenous endothelin-1 participates in the maintenance of cardiac function in rats with congestive heart failure: marked increase in endothelin-1 production in the failing heart. Circulation. 1996;93:1214-1222.[Abstract/Free Full Text]
  27. Sakai S, Miyauchi T, Kobayashi M, Yamaguchi I, Goto K, Sugishita Y. Inhibition of myocardial endothelin pathway improves long-term survival in heart failure. Nature. 1996;384:353-355.[Medline] [Order article via Infotrieve]
  28. Weisman HF, Healy B. Myocardial infarct expansion, infarct extension, and reinfarction: pathophysiologic concepts. Prog Cardiovasc Dis. 1987;30:73-110.[Medline] [Order article via Infotrieve]
  29. McKay RG, Pfeffer MA, Pasternak RC, Markis J, Come PC, Nakao S, Alderman JD, Ferguson JJ, Safian RD, Grossman W. Left ventricular remodeling after myocardial infarction: a corollary to infarct expansion. Circulation. 1986;74:693-702.[Abstract/Free Full Text]
  30. Hochmann JS, Bulkley BH. Expansion of acute myocardial infarction: an experimental study. Circulation. 1982;65:1446-1450.[Abstract/Free Full Text]
  31. Clozel M, Breu V, Gray GA, Kalina B, Loeffler BM, Burri K, Cassal JM, Hirth G, Moeller M, Neidhart W, Ramuz H. Pharmacological characterization of bosentan, a new potent orally active non-peptide endothelin receptor antagonist. J Pharmacol Exp Ther. 1994;270:228-235.[Abstract/Free Full Text]
  32. Pfeffer MA, Pfeffer JM, Fishbein MC, Fletcher PJ, Spadaro J, Kloner RA, Braunwald E. Myocardial infarct size and ventricular function in rats. Circ Res. 1979;44:503-512.[Abstract/Free Full Text]
  33. Ishikawa T, Li L, Shinmi O, Kimura M, Yanagisawa M, Goto K, Masaki T. Characteristics of binding of endothelin-1 and endothelin-3 to rats hearts: developmental changes in mechanical responses and receptor subtypes. Circ Res. 1991;69:918-926.[Abstract/Free Full Text]
  34. Lowry OH, Roseborough NJ, Farr AL, Randall RJ. Protein measurement with the Folin reagent. J Biol Chem. 1951;193:265-275.[Free Full Text]
  35. Fletcher PJ, Pfeffer JM, Pfeffer MA, Braunwald E. Left ventricular diastolic pressure-volume relations in rats with healed myocardial infarction: effects on systolic function. Circ Res. 1981;49:618-626.[Abstract/Free Full Text]
  36. Sakai S, Miyauchi T, Sahurai T, Yamaguchi I, Kobayashi M, Goto K, Sugishita Y. Pulmonary hypertension caused by congestive heart failure is ameliorated by long-term application of an endothelin receptor antagonist. J Am Coll Cardiol. 1996;28:1580-1588.[Abstract]
  37. Fishbein MC, Lei LQ, Rubin SA. Long-term propranolol administration alters myocyte and ventricular geometry in rat hearts with and without infarction. Circulation. 1988;78:369-375.[Abstract/Free Full Text]
  38. Howes LG, Hodsman GP, Maccarone C, Kohzuki M, Johnston CI. Cardiac 3,4-dihydroxyphenylethylene glycol (DHPG) and catecholamine levels in a rat model of left ventricular failure. J Cardiovasc Pharmacol. 1989;13:348-352.[Medline] [Order article via Infotrieve]
  39. Loeffler BM, Breu V, Clozel M. Effect of different endothelin receptor antagonists and of the novel non-peptide antagonist Ro 46-2005 on endothelin levels in rat plasma. FEBS Lett. 1993;333:108-110.[Medline] [Order article via Infotrieve]
  40. Li JS, Deng LY, Grove K, Deschepper CF, Schiffrin EL. Comparison of effect of endothelin antagonism and angiotensin-converting enzyme inhibition on blood pressure and vascular structure in spontaneously hypertensive rats treated with N{omega}-nitro-L-arginine methyl ester. Hypertension. 1996;28:188-195.[Abstract/Free Full Text]
  41. Wagner OF, Christ G, Wojta J, Vierhapper H, Parzer S, Nowotny PJ, Schneider B, Waldhausl W, Binder BR. Polar secretion of endothelin-1 by cultured endothelin cells. J Biol Chem. 1992;267:16066-16068.[Abstract/Free Full Text]
  42. Olivetti G, Capasso JM, Meggs LG, Sonnenblick EH, Anversa P. Cellular basis of chronic ventricular remodeling after myocardial infarction in rats. Circ Res. 1991;68:856-869.[Abstract/Free Full Text]
  43. Ito H, Hirata Y, Hiroe M, Tsujino M, Adachi S, Takamoto T, Nitta M, Taniguchi K, Marumo F. ET-1 induces hypertrophy with enhanced expression of muscle specific genes in cultured neonatal rat cardiomyocytes. Circ Res. 1991;69:209-215.[Abstract/Free Full Text]
  44. Miyauchi T, Yorikane R, Sakai S, Sakurai M, Okada M, Nishikibe M, Yano M, Yamaguchi I, Sugishita Y, Goto K. Contribution of endogenous endothelin-1 to the progression of cardiopulmonary alterations in rats with monocrotaline-induced pulmonary hypertension. Circ Res. 1993;73:887-897.[Abstract/Free Full Text]
  45. Ito H, Hiroe M, Hirata Y, Fujisaki H, Adachi S, Akimoto H, Ohta Y, Marumo F. Endothelin ETa receptor antagonist blocks cardiac hypertrophy provoked by hemodynamic overload. Circulation. 1994;89:2198-2203.[Abstract/Free Full Text]
  46. Yorikane R, Sakai S, Miyauchi T, Sahurai T, Goto K. Possible involvement of endothelin-1 in cardiac hypertrophy. Drug Res. 1994;44:412-415.[Medline] [Order article via Infotrieve]
  47. de Simone G, Devereux RB, Roman MJ, Ganau A, Chien S, Alderman MH, Atlas S, Laragh JH. Gender differences in left ventricular anatomy, blood viscosity and volume regulatory hormones in normal adults. Am J Cardiol. 1991;68:1704-1708.[Medline] [Order article via Infotrieve]
  48. Cabral AM, Vasquez EC, Moyses MR, Antonio A. Sex hormone modulation of ventricular hypertrophy in sinoaortic denervated rats. Hypertension. 1988;11(suppl I):I-93-I-97.



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