ET-receptor antagonism, myocardial gene expression, and ventricular remodeling during CHF in rats (original) (raw)
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Circulation, 1998
Background-To investigate whether endogenous ET-1 participates in an adaptive process of left ventricular hypertrophy (LVH) or a maladaptive process from LVH to congestive heart failure (CHF), we used a Dahl salt-sensitive (DS) rat model, in which systemic hypertension caused compensated concentric LVH at the age of 11 weeks followed by marked LV dilatation and global hypokinesis at the age of 17 weeks. Methods and Results-By specific sandwich enzyme immunoassay, serum and myocardial ET-1 levels at the LVH stage were not elevated compared with age-matched Dahl salt-resistant (DR) rats, despite the marked increase of LV/body weight ratio (LV/BW). However, at the CHF stage, serum and LV ET-1 levels increased by 3.8-fold and 5.4-fold, respectively. LV ET-1 contents had close relationships with the fractional shortening (rϭ0.763) and the systolic wall stress (rϭ0.858) measured by in vivo transthoracic echocardiography. Immunohistochemistry demonstrated that the remarkably increased ET-1 in LV is located mainly in cardiomyocytes. By competitive reverse transcriptase-polymerase chain reaction, LV prepro-ET-1 mRNA levels increased by 4.1-fold in CHF rats. We randomized 11-week-old LVH rats to chronic treatment with the endothelin receptor antagonist bosentan (Bos, 100 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 , nϭ14), the ␣ 1 -receptor antagonist doxazosin (Dox, 1 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 , nϭ12), or vehicle (Cont, nϭ14). Bos treatment did not alter the LV geometry and function at 15 weeks; however, it attenuated the decrease of LV fractional shortening by 51% (PϽ0.01) without reducing the LV/BW at 17 weeks. Conversely, Dox, which decreased the blood pressure to the same extent as Bos, did not affect the progression of LV dysfunction. Bos (93%; PϽ0.0001 versus Cont) but not Dox (42%; Pϭ0.8465 versus Cont) ameliorated the survival rate at 17 weeks (Cont; 36%). Conclusions-The accelerated myocardial synthesis of ET-1 contributes directly to LV contractile dysfunction during the transition from LVH to CHF. Unelevated levels of LV ET-1 at the established LVH stage and lack of effects on LV mass by chronic bosentan treatment suggest that myocardial growth is mediated through alternative pathways. These studies indicate that chronic ET antagonism may provide an additional strategy for heart failure therapy in humans.
Journal of Cardiac Failure, 2002
Background: The ET A and ET B receptors mediate vasoconstriction, aldosterone release, and fibrosis. However, the role of ET B receptors is still controversial because those expressed on endothelial cells also stimulate vasodilatation and may oppose the actions of the ET A receptor. Plasma levels of endothelin-1 (ET-1) are increased in heart failure (HF) and are associated with myocardial dysfunction. The relative efficacy of selective and nonselective ET antagonists in the treatment of HF is unclear. We hypothesized that blockade of ET A receptors may improve cardiac function and prevent left ventricular remodeling in mice with HF, and these effects may be mediated in part by activation of ET B. Methods and Results: A mouse model of chronic HF induced by myocardial infarction (MI) was used. Seven days after MI, mice were divided into vehicle, ET A-ant, or ET A/B-ant groups and treated for 23 weeks. Cardiac function, LV dimensions, and hemodynamics were evaluated in conscious mice before MI and during treatment. Histologic analysis of the heart and liver was performed at the end of the study. HF significantly decreased EF and increased LV dimensions, interstitial collagen fraction (ICF) and myocyte cross-sectional area (MCSA). Both ET A-ant and ET A/B-ant slightly increased EF but had no significant effect on LV dimensions, hypertrophy, or ICF. Both treatments decreased MCSA; however, this was only significant in the ET A/B-ant group. Conclusions: Both selective and nonselective ET-ant have similar slight effects on cardiac function and remodeling. This suggests that (1) ET B receptors do not mediate the beneficial cardiac effects of ET A-ant and (2) blockade of the ET system alone may not provide significant cardioprotection, at least in mice with HF induced by MI.
Cardiovascular Research, 2002
Objective: To characterize the cardiac angiotensin and endothelin (ET) system in compensated left ventricular hypertrophy due to long standing arterial hypertension and to assess the role of angiotensin and ET converting enzymes in mediating the observed changes of angiotensin and ET levels, respectively. Methods: We studied the left ventricular renin-angiotensin system (RAS) and ET system in 20-week-old male transgenic hypertensive TG(mREN2)27 rats, a model of the monogenic renin-dependent form of severe hypertension. Age-matched Sprague-Dawley rats served as controls. Results: TG(mREN2)27 rats exhibited left ventricular hypertrophy without signs of congestion. Transgene overexpression led to an activation of the tissue RAS with increased angiotensin II levels in spite of unchanged angiotensin converting enzyme (ACE) activity and ACE mRNA levels. ET-1 production was markedly increased in TG(mREN2)27 rats indicating that the ET-system was activated. Cardiac ET-1 in TG(mREN2)27 originated most likely from increased preproET-1 production because preproET-1 mRNA levels were increased but ET converting enzyme gene expression and activity were unchanged. Furthermore, ET-1 binding sites were significantly increased in TG(mREN2)27 rats without changes in K values and ET / ET receptor D A B ratios. ET receptor gene expression was not altered whereas ET receptor mRNA levels were up-regulated twofold in TG(mREN2)27 A B rats suggesting that ET and ET receptor expression may be regulated differentially. Conclusions: Cardiac ET and angiotensin systems A B are co-activated in compensated cardiac hypertrophy before onset of heart failure, and thus may be involved in the mechanism by which cardiac remodelling and progression of left ventricular dysfunction occur in TG(mREN2)27 rats.
Circulation, 2001
Background-In view of their mutual crosstalk, the roles of angiotensin II (Ang II) and endothelin-1 (ET-1) in the myocardium are assumed to be synergistic and supplemental. Methods and Results-In the phase of compensated left ventricular (LV) hypertrophy of Dahl salt-sensitive rats, Ang II peptide and the ACE mRNA in the LV were increased by 1.6-and 3.8-fold, respectively. In contrast, ET-1 peptide and the preproET-1 mRNA remained unchanged. In subsequent congestive heart failure (CHF), Ang II and ACE mRNA did not show further increases. But ET-1 and the mRNA were increased de novo by 5.3-and 4.1-fold, respectively. In ascending aorta-banded rats, the local activations of Ang II and ET-1 also showed a differential time course between LV hypertrophy and CHF. Long-term treatments of Dahl salt-sensitive rats with temocapril (an ACE inhibitor) and with bosentan (a mixed ET receptor blocker) equally improved long-term survival. Temocapril reduced the LV/body weight ratio and ameliorated LV fractional shortening. Conversely, although bosentan equally improved fractional shortening, it did not reduce the increase in LV mass. Combined treatment with these 2 drugs further ameliorated the animal's survival without additional decreases in systolic pressure.
Basic Research in Cardiology, 2002
Intervention with selective endothelin (ET) A receptor antagonists within 24h after myocardial infarction (MI) in rats has been reported to aggravate left ventricular (LV) remodeling. In contrast, beneficial effects are reported when initiation of treatment is delayed 7 days or more after MI. However, bosentan, a mixed ET A /ET B receptor antagonist with low affinity for the ET receptors, has been shown to exert beneficial effects independent of the time point of initiation of treatment after MI. The aim of the present study was to investigate to what extent early intervention with a mixed ET A /ET B receptor antagonist with higher affinity at the ET receptors (SB 209670) would also exert beneficial effects on postinfarction LV remodeling. After ligation of the left coronary artery, rats were randomized to treatment with SB 209670 (6.25 mg·kg -1 SC b.i.d., n = 10) or vehicle (n = 12) for 26 days, starting 48h after MI. Treatment with SB 209670 adversely affected the postinfarction remodeling process causing further dilatation of the LV (LV end-diastolic diameter: 10.4 ± 0.5 vs 9.1 ± 0.2 mm; LV end-systolic diameter: 8.5 ± 0.4 vs 7.2 ± 0.2 mm, P < 0.05). However, SB 209670 did not significantly affect infarct size, compensatory cardiac hypertrophy, nor the myocardial mRNA levels of procollagen type I and III, and prolyl 4-hydroxylase and lysyl oxidase, 2 important enzymes affecting collagen secretion, stability and functionality. In addition, SB 209670 had no significant effects on LV collagen cross-linking or extent of fibrosis. Thus, our data demonstrate that early intervention with a potent, mixed ET A /ET B receptor antagonist after MI may promote dilatation of the LV without significant alterations of infarct size and extracellular matrix composition. Our data support the notion that the timing of initiation of ET receptor antagonism after MI is critical and that potent ET receptor antagonists may be harmful during the first few days after MI.
Altered Expression of Endothelin Receptors in Failing Human Left Ventricles
Journal of Molecular and Cellular Cardiology, 2002
Background: Endothelin signaling is activated in failing human hearts, and may contribute to progressive myocardial dysfunction and remodeling. However, the behavior of endothelin receptor systems (ET A and ET B ) in failing human hearts is not well understood. Methods and Results: 125 [I]-endothelin-1 binding assays conducted in the presence of a non-hydrolyzable guanine nucleotide to uncouple agonist binding demonstrated that membranes prepared from nonfailing left ventricles (LVs) exhibit a mixed pattern of ET A ($60%) and ET B ($40%) receptor protein expression. Chronic LV failure from either idiopathic dilated (IDC) or ischemic (ISC) cardiomyopathy was accompanied by a signi®cant (P , 0.001) increase in ET A receptor density, to $80% of the total population, and a signi®cant (P , 0.02) decrease in ET B receptor density. Ribonuclease protection assays demonstrated an increase in ET A mRNA abundance in IDC and ISC LVs, and a signi®cant (P , 0.04) increase in ET B mRNA abundance in ISC LVs. Enzyme-linked immunoabsorbent assays demonstrated a signi®cant increase in tissue immunoreactive endothelin-1 concentration in IDC (P 0.01) and in IDC ISC LVs (P 0.02), but receptor subtype protein or mRNA level was not signi®cantly correlated with tissue ET-1 across all LVs. In situ reverse-transcription polymerase chain reaction in LV sections demonstrated that in both failing and nonfailing LVs the ET A gene is expressed in cardiac myocytes, vascular smooth muscle and endothelium; the ET B gene is expressed in cardiac myocytes, ®broblasts and endothelium; and the prepro-endothelin-1 gene is expressed in myocytes and interstitial cells. Conclusions: In chronically failing human LVs, ET A receptor density is increased to become the dominant subtype while ET B receptor density is decreased. The ET A , but not the ET B density change is accompanied by cognate regulation of mRNA abundance. Both receptor genes and prepro-endothelin-1 are expressed in cardiac myocytes. Finally, based on a lack of correlation with endothelin-1 tissue levels, it is unlikely that the failure-related changes in ET A and ET B receptor protein and mRNA expression result from homologous regulation by agonist exposure.
Increased cardiac expression of endothelin-1 mRNA in ischemic heart failure in rats
Cardiovascular Research, 1997
Plasma endothelin (ET) concentrations are increased in heart failure. The aims of the present study were to investigate to what extent cardiac ET mRNA expression is induced in ischemic heart failure and whether there may be compensatory downregulation of myocardial mRNA levels for the ET, and ET, receptor subtypes. Methods: In rats with ischemic heart failure (left ventricular end-diastolic pressure > 1.5 mmHg) due to left coronary artery ligation, Northern blot analyses were performed on mRNA isolated from cardiac tissues. Results: A substantial upregulation was revealed in all chambers of the failing hearts. Up to 27-fold upregulation (mean 10.6 f 4.0, P = 0.002) of left ventricular ET-l mRNA levels was measured 1 week after myocardial infarction, whereas only a modest upregulation was detected after 6 weeks (mean 2.7 + 0.5, P < 0.05). Ribonuclease protection assay revealed 2.8 + OA-fold higher levels of ET-l n-RNA in the left ventricular area subjected to myocardial infarction compared to the non-infarcted tissue after 1 week. Left ventricular ET-l mRNA correlated significantly with left ventricular end-diastolic pressure after 1 week (r* = 0.86, P = 0.007). The ET, and ET, receptor mRNA levels tended to increase 1 week after myocardial infarction although these changes were not statistically significant. Conclusions: Cardiac ET-l mRNA levels are increased in ischemic heart failure and correlate significantly with left ventricular end-diastolic pressure 1 week after myocardial infarction. The increase in cardiac ET-l mRNA is not accompanied by a decrease in ET receptor mRNA.
Journal of Molecular and Cellular Cardiology, 2001
ET-1) levels and ET receptor expression are increased in congestive heart failure (CHF). In order to determine whether this results in increased responsiveness of ET-A or ET-B receptors to ET-1, we evaluated the contractile effects of ET-1 in isolated papillary muscles isolated from hearts of control rats and from rats 4 weeks post myocardial infarction (MI) having received no therapy or chronic quinapril therapy. The ET-1 dose-response was biphasic in normal muscles. The use of the selective ET-A receptor antagonist BQ123 and the selective ET-B receptor antagonist BQ788 revealed that the initial decrease in tension was the result of ET-B receptor stimulation. Blockade of nitric oxide (NO) production with L-NAME abolished the initial decrease in tension. MI resulted in CHF that was partially reversed by quinapril. In MI, the positive inotropic effects of ET-1 were enhanced due to the loss of the initial ET-B receptor mediated decrease in tension, as well as an increase in the positive inotropic effects of ET-A receptors. This was associated with an increase in ET-A and ET-B receptor mRNA and a decrease in cardiac ecNOS protein. Four weeks of therapy with quinapril attenuated the positive inotropic effects of ET-1 and prevented the increase in ET-A receptor mRNA. Although quinapril did not restore the effects of ET-B receptor stimulation or prevent the increase in ET-B mRNA, it did restore cardiac ecNOS protein expression. Thus, the inotropic response to ET-1 is biphasic due to an overall positive inotropic effect of ET-A receptor stimulation and an ET-B receptor mediated decrease in contractility at low ET-1 concentrations which appears to be mediated by cardiac ecNOS (NO). In post-MI CHF, responsiveness to ET-A receptors increases and the ET-B mediated negative inotropic response is lost despite an increase in both receptor subtypes. Quinapril therapy attenuates these effects and normalises cardiac ecNOS protein.