Dietary sodium intake regulates angiotensin II type 1, mineralocorticoid receptor, and associated signaling proteins in heart.

Liberal or high-sodium (HS) intake, in conjunction with an activated renin-angiotensin-aldosterone system, increases cardiovascular (CV) damage. We tested the hypothesis that sodium intake regulates the type 1 angiotensin II receptor (AT(1)R), mineralocorticoid receptor (MR), and associated signaling pathways in heart tissue from healthy rodents. HS (1.6% Na(+)) and low-sodium (LS; 0.02% Na(+)) rat chow was fed to male healthy Wistar rats (n=7 animals per group). Protein levels were assessed by western blot and immunoprecipitation analysis. Fractionation studies showed that MR, AT(1)R, caveolin-3 (CAV-3), and CAV-1 were located in both cytoplasmic and membrane fractions. In healthy rats, consumption of an LS versus a HS diet led to decreased cardiac levels of AT(1)R and MR. Decreased sodium intake was also associated with decreased cardiac levels of CAV-1 and CAV-3, decreased immunoprecipitation of AT(1)R-CAV-3 and MR-CAV-3 complexes, but increased immunoprecipitation of AT(1)R/MR complexes. Furthermore, decreased sodium intake was associated with decreased cardiac extracellular signal-regulated kinase (ERK), phosphorylated ERK (pERK), and pERK/ERK ratio; increased cardiac striatin; decreased endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS (peNOS), but increased peNOS/eNOS ratio; and decreased cardiac plasminogen activator inhibitor-1. Dietary sodium restriction has beneficial effects on the cardiac expression of factors associated with CV injury. These changes may play a role in the cardioprotective effects of dietary sodium restriction.

Caveolin-1 ablation reduces the adverse cardiovascular effects of N-omega-nitro-L-arginine methyl ester and angiotensin II.

Caveolae are the major cellular membrane structure through which extracellular mediators transmit information to intracellular signaling pathways. In vascular tissue (but not ventricular myocardium), caveolin-1 (cav-1) is the main component of caveolae; cav-1 modulates enzymes and receptors, such as the endothelial nitric oxide synthase and the angiotensin II (AngII) type 1 receptor. Evidence suggests that AngII and aldosterone (ALDO) are important mediators of ventricular injury. We have described a model of biventricular damage in rodents that relies on treatment with N-omega-nitro-l-arginine methyl ester (L-NAME (nitric oxide synthase inhibitor)) and AngII. This damage initiated at the vascular level and was observed only in the presence of ALDO and an activated mineralocorticoid receptor (MR). We hypothesize that cav-1 modulates the adverse cardiac effects mediated by ALDO in this animal model. To test this hypothesis, we assessed the ventricular damage and measures of inflammation, in wild-type (WT) and cav-1 knockout (KO) mice randomized to either placebo or L-NAME/AngII treatment. Despite displaying cardiac hypertrophy at baseline and higher blood pressure responses to L-NAME/AngII, cav-1 KO mice displayed, as compared with WT, decreased treatment-induced biventricular damage as well as decreased transcript levels of the proinflammatory marker plasminogen activator inhibitor-1. Additionally, L-NAME/AngII induced an increase in cardiac MR levels in WT but not cav-1-ablated mice. Moreover and despite similar circulating ALDO levels in both genotypes, the myocardial damage (as determined histologically and by plasminogen activator inhibitor-1 mRNA levels) was less sensitive to ALDO levels in cav-1 KO vs. WT mice, consistent with decreased MR signaling in the cav-1 KO. Thus, we conclude that the L-NAME/AngII-induced biventricular damage is mediated by a mechanism partially dependent on cav-1 and signaling via MR/ALDO.

The phenotype and potential origin of nestin+ cardiac myocyte-like cells following infarction.

Nestin+ cardiac myocyte-like cells were detected in the peri-infarct/infarct region of the ischemically damaged heart. The present study was undertaken to elucidate the phenotype and potential origin of nestin+ cardiac myocyte-like cells and identify stimuli implicated in their appearance. In the infarcted human and rat heart, nestin+ cardiac myocyte-like cells were morphologically and structurally immature, exhibited a desmin-immunoreactive striated phenotype, expressed the beta(1)-adrenergic receptor, and associated with an aberrant pattern of connexin-43 expression and/or organization. Nestin+ cardiac myocyte-like cells were detected 24 h postischemic injury and persisted in the infarcted rat heart for 9 mo. In the normal rat heart, cardiac progenitor transcriptional factors Nkx2.5/GATA4 were detected in a subpopulation of nestin+ neural stem cells. Following an ischemic insult, nestin+/Nkx2.5+ neural stem cells migrated to the peri-infarct/infarct region and appeared to be in a primordial state of differentiation to a nestin+ cardiac myocyte-like cell. The exposure of adult male rats to normobaric hypoxia (12% O2) for 10 days failed to promote the appearance of nestin+ cardiac myocyte-like cells. Following osmotic pump delivery of isoproterenol to normal adult rats, nestin+ cardiac myocyte-like cells were detected, albeit the response was modest and secondary to tissue loss. Thus ischemia-induced appearance of nestin+ cardiac myocyte-like cells apparently represents an adaptive response to heal the infarcted heart. Nkx2.5/GATA4 expression in a subpopulation of resident neural stem cells provides the appropriate phenotype for their potential differentiation to a nestin+ cardiac myocyte-like cell.

Mineralocorticoid receptor antagonist reduces renal injury in rodent models of types 1 and 2 diabetes mellitus.

To determine whether mineralocorticoid receptor (MR) activation plays a role in diabetic renal injury and whether this role differs in types 1 and 2 diabetes mellitus, we examined the effect of a MR antagonist on renal injury in rodent models of type 1 (streptozotocin-treated rat) and type 2 (db/db mouse) diabetes. We studied three groups of 8-wk-old, uninephrectomized Wistar rats for 4 wk: diabetic streptozotocin- (55 mg/kg) treated rats (n = 11), diabetic streptozotocin-treated rats receiving the MR antagonist eplerenone (n = 15), and nondiabetic rats (n = 9). In addition, we studied three groups of 8-wk-old mice for 16 wk: diabetic db/db mice (n = 10), diabetic db/db mice treated with eplerenone (n = 8), and nondiabetic, db/+ littermates (n = 11). Diabetic rats and mice developed albuminuria and histopathological evidence of renal injury, including glomerular hypertrophy, mesangial expansion, and tubulointerstitial injury as well as increased renal cortical levels of MR protein, MR mRNA, TGFbeta mRNA, and osteopontin mRNA. All of these changes were significantly reduced by treatment with eplerenone except for the elevated MR levels. The beneficial effects of eplerenone were not attributable to changes in blood pressure or glycemia. In summary, MR expression was increased in kidneys of diabetic rodents, and MR antagonists effectively reduced diabetic renal injury irrespective of the species or specific cause of the diabetes. Thus, these data suggest that MR activation is a critical factor in the early pathogenesis of renal disease in both type 1 and type 2 diabetes mellitus.

Vasopeptidase inhibition peri- and post-MI in Zucker insulin resistant rats: effect on MI size, arrhythmias, remodeling, function and fetal gene expression.

Mortality peri-myocardial infarction (MI) is increased with insulin resistance. As the vasopeptidase inhibitor (VPI) omapatrilat improves insulin sensitivity, it may be beneficial peri-MI in Zucker Insulin Resistant rats (ZIR). ZIR rats (n = 228) received omapatrilat 10 mg/kg/day, 7 days pre-MI, to 38 days post-MI, or control. Twenty-four protocol (n = 72): a subgroup of rats received the kinin receptor antagonist icatibant. Ambulatory ECG recordings, and MI size were evaluated. Thirty-eight-day protocol (n = 156): left ventricular (LV) remodeling, cardiac hemodynamics, morphology, infarct size, and RT-PCR for GLUT-4 and fetal genes were measured. Omapatrilat improved post-MI survival 24 h (62% vs 38%, P = 0.0007) which was maintained 38 days. There was a kinin-induced reduction of ventricular arrhythmias and there appeared to be a kinin-independent reduction in MI size (23.5 +/- 2.4% vs 17.0 +/- 2.2%, P = 0.053) for 24-h post-MI. Omapatrilat reduced but did not prevent LV dilatation, dysfunction, and fetal gene expression 38 days post-MI. Omapatrilat did not prevent reduced cardiac GLUT-4 expression. In ZIR rats, mortality post-MI is reduced by omapatrilat, due and a kinin-dependent reduction in ventricular arrhythmias and possibly a kinin-independent reduction in MI size. Ventricular dilatation, dysfunction, and fetal gene expression are variably attenuated but not prevented.

Effects of the vasopeptidase inhibitor omapatrilat on peri- and postmyocardial infarction in Zucker lean rats.

BACKGROUND: The vasopeptidase inhibitor omapatrilat improves insulin sensitivity and survival following myocardial infarction (MI). It also improves left ventricular (LV) remodelling following MI and reduces MI size. OBJECTIVES: To determine whether improvement in LV remodelling and function is accompanied by a reduction in fetal gene expression of the contractile apparatus, and whether reduction in MI size is accompanied by an increase in the expression of the glucose transporter GLUT-4. METHODS: Eighty-nine rats were pretreated for seven days with omapatrilat 20 mg/kg/day and 91 rats were left untreated. MI was induced in 180 Zucker lean male rats by ligating the left anterior descending coronary artery, and omapatrilat was given for another 38 days in the survivors. After 30 days, echocardiography was performed. At 38 days, hemodynamic measurements were performed, the rats were sacrificed and morphological measurements were done. Using quantitative reverse transcriptase-polymerase chain reaction, gene expression was measured in the LV using transcript levels. RESULTS: Treatment with omapatrilat resulted in improved early (24 h) and late (38 days) survival following MI (50% to 67%, P=0.023, and 44% to 59%, P=0.045, respectively). Omapatrilat treatment reduced MI size and resulted in beneficial ventricular remodelling as reflected by a reduction in cardiac dimensions by echocardiography, and LV and right ventricular hypertrophy, which resulted in borderline hemodynamic improvement. A large MI resulted in an increased expression of beta-myosin heavy chain, alpha-skeletal actin and atrial natriuretic peptide, and a decreased expression of GLUT-4. Omapatrilat treatment did not modify the expression of these genes. CONCLUSIONS: The results suggest that the vasopeptidase inhibitor omapatrilat does not modify fetal gene expression of the contractile apparatus or the expression of GLUT-4 despite reducing cardiac hypertrophy and MI size.

Losartan and acute myocardial infarction in insulin-resistant Zucker fatty rats: reduced ventricular arrhythmias and improved survival.

Insulin resistance (IR) and diabetes increase the risk of acute myocardial infarction (MI). Angiotensin receptor blockers (ARBs) have been shown to reduce the risk of cardiovascular events in patients with hypertension and diabetes, and to be beneficial after a large MI. Whether pretreatment with ARBs is beneficial in acute MI is unknown. We evaluated whether pre-, peri-, and post-MI treatment with the ARB losartan improved the outcome in the IR Zucker fatty rat (ZFR). ZFR (n=264) received either losartan (3 mg/kg daily) or vehicle for 7 d prior to MI. Early (24 h) protocol (n=31): ventricular arrhythmias were evaluated post-MI using continuous ambulatory ECG monitoring. Late (38 d) protocol (n=233): losartan was increased to 10 mg/kg daily 10 d post-MI and to 30 mg/kg daily 20 d post-MI. Blood glucose, cardiac hemodynamics and remodeling, GLUT-4, fetal gene expression, and survival were evaluated. In large-MI rats, losartan improved early survival (43% vs. 27% in controls, p=0.01) and late survival (23% vs.15% in controls, p=0.02). Improved early survival was associated with a reduction in ventricular arrhythmias. Losartan reduced pulmonary congestion, cardiac hypertrophy, and fetal gene expression in the absence of statistically significant changes in ventricular dilatation and hemodynamics. Blood glucose and cardiac GLUT-4 expression did not change with losartan. In IR ZFR, losartan improves post-MI survival, likely as a result of an early reduction in ventricular arrhythmias. There was also an associated reduction in pulmonary congestion, hypertrophy, and fetal gene expression.

Effects of pre-, peri-, and postmyocardial infarction treatment with losartan in rats: effect of dose on survival, ventricular arrhythmias, function, and remodeling.

Angiotensin receptor blockers (ARBs) reduce adverse left ventricular (LV) remodeling and improve LV function and survival when started postmyocardial infarction (MI). ARBs also reduce ventricular arrhythmias during ischemia-reperfusion injury when started pre-MI. No information exists regarding their efficacy and safety when started pre-MI and continued peri- and post-MI. We evaluated whether the ARB losartan improves the outcome when started pre-MI and continued peri- and post-MI. Male Wistar rats (n = 502) were treated for 7 days pre-MI with losartan at a high dose (30 mg.kg(-1).day(-1)), progressively increasing dose (3 mg.kg(-1).day(-1) increased to 10 mg.kg(-1).day(-1) 10 days and 30 mg.kg(-1).day(-1) 20 days post-MI), or no treatment. Ambulatory systolic blood pressure and Holter monitoring were performed for 24 h post-MI. Echocardiography was done 30 days post-MI, and LV remodeling, cardiac hemodynamics, and fetal gene expression were assessed 38 days post-MI. High-dose losartan reduced 24-h post-MI survival compared with the progressive dose and control (21.9% vs. 36.6% and 38.1%, P = 0.033 and P = 0.009, respectively). This was associated with greater hypotension in the high dose and no change in ventricular arrhythmias in all groups. In 24-h post-MI survivors, the progressive dose group had reduced mortality from 24 h to 38 days (8.5% vs. 28.6% for control vs. 38.9% for high dose, P = 0.032 and P = 0.01, respectively). Survivors of both losartan groups demonstrated improved LV remodeling, cardiac hemodynamics, preserved GLUT-4, and reduced cardiac fetal gene expression. Pretreatment with ARBs does not reduce 24-h post-MI ventricular arrhythmias or survival, and high doses increase mortality by causing excessive hypotension. In 24-h post-MI survivors, progressively increasing doses of losartan have multiple beneficial effects, including improved survival.

Comparative effects of a vasopeptidase inhibitor vs. an angiotensin converting enzyme inhibitor on cardiomyocyte apoptosis in rats with heart failure.

Apoptosis is involved in ventricular remodeling after myocardial infarction (MI). We investigated the effects of the vasopeptidase inhibitor (VPI) omapatrilat on cardiomyocyte apoptosis and compared it to the angiotensin converting enzyme inhibitor (ACEI) captopril in the rat post-MI model and in cultured neonatal rat cardiomyocytes. Wistar males rats surviving 4 h post-MI were assigned to omapatrilat (40 or 80 mg/kg/day), captopril (160 mg/kg/day) or no treatment. After 56 days, hemodynamic measurements were performed (n = 96) and rats were sacrificed. One group had assessment of cardiac remodeling and detection of DNA fragments by in situ end labelling method (ISEL), while the other had morphologic measurements and DNA laddering assessed. In addition, cultured neonatal rat cardiomyocytes (n = 6) were treated for 72 h with vehicle, captopril or omapatrilat in the presence or absence of the apoptosis inducing agent H2O2. Omapatrilat and captopril resulted in similar improvements of hemodynamic measurements, ventricular weight and dilatation, cardiac fibrosis and myocardial cell cross-section in large MI rats. Omapatrilat increased scar thickness more than did captopril. All sham-operated groups had little evidence of apoptosis. In the large MI group, there was a significant increase in ISEL-positive cells in the control (0.095 +/- 0.016%) and captopril (0.124 +/- 0.024%) groups in comparison with control sham-operated (0.006 +/- 0.006%), but this increase was limited to the peri-MI area. Omapatrilat (0.012 +/- 0.012% for both doses) prevented the increase in apoptosis in the peri-MI area. Also, omapatrilat but not captopril reduced DNA laddering in large MI. Moreover, in cultured neonatal rat cardiomyocytes, omapatrilat but not captopril reduced apoptosis as assessed by DNA laddering. The VPI omapatrilat, with its combination of NEP and ACE inhibition, suppresses cardiomyocyte apoptosis post-MI and in neonatal cultured rat cardiomyocytes more than the ACEI captopril, but this does not result in significant hemodynamic or morphologic differences between omapatrilat and captopril.

Meta-analysis of the effects of endothelin receptor blockade on survival in experimental heart failure.

BACKGROUND: Although an initial study of endothelin receptor blockade reported positive findings, subsequent experiments and clinical trials in humans found little or no benefit. METHODS: We applied meta-analytic methods to assess the methodologic rigor of preclinical studies of endothelin blockade and to quantitatively evaluate the totality of evidence regarding the effect of endothelin receptor blockers in experimental heart failure. A total of 396 animals were assigned to control and 594 were assigned to experimental therapy in the pooled analysis. Of the 9 studies identified, no study reported a priori sample size justification. Although there was a tendency to increased mortality with early administration (relative risk 1.39, P=.15) and decreased mortality with late administration (relative risk 0.85, P=.6), in the overall analysis, there was no significant evidence of benefit or harm (relative risk 1.03, P=.9). Studies with a small sample size had estimated effects that tended to deviate further from the pooled estimate of all studies. CONCLUSIONS: Consideration of mortality effects in the totality of studies revealed no significant effect of endothelin antagonists in animal models of experimental heart failure. Given the potential for between-study variability, reliance on studies with small sample size may lead to unrealistic expectations when extrapolating preclinical experimental results to future research.

Vasopeptidase inhibitor omapatrilat induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats: Studies comparing a vasopeptidase inhibitor, angiotensin-converting enzyme inhibitor, and angiotensin II type I receptor blocker.

BACKGROUND: ACE inhibitors (ACEIs) improve insulin resistance and prevent type 2 diabetes, possibly mediated by inhibition of bradykinin (BK) degradation. The vasopeptidase inhibitor omapatrilat (OMA) raises BK to a greater extent than ACEIs by dual enzyme inhibition, whereas its insulin-sensitizing effects and mechanisms have not been investigated. METHODS AND RESULTS: We compared the insulin-sensitizing effects of OMA, ramipril (an ACEI), losartan (an angiotensin II type 1 receptor blocker), and placebo by 2-step euglycemic hyperinsulinemic clamp in insulin-resistant Zucker fatty rats (n=6 to 7 in each group). OMA resulted in a lower rate of endogenous glucose production than placebo at baseline (35+/-5 versus 54+/-4 mmol x kg(-1) x min(-1), P<0.01), greater suppression of endogenous glucose production by low-dose insulin (73+/-11% versus 27+/-18%, P<0.05), and greater glucose disposal at high-dose insulin (135+/-5 versus 92+/-4 mmol x kg(-1) x min(-1), P<0.01). Ramipril tended to improve insulin sensitivity, but losartan did not. OMA significantly increased 2-deoxyglucose uptake by myocardium, fat, and skeletal muscle. Ramipril increased 2-deoxyglucose uptake only by some skeletal muscles, but losartan did not. The insulin-sensitizing effects of OMA were blocked significantly by HOE-140 (a BK, B2 receptor antagonist) and NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) in all tissues except myocardium. CONCLUSIONS: OMA induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats. This effect is greater than that of ramipril and probably occurs at least in part via stimulation of the B2 receptor. OMA has the potential for greater type 2 diabetes prevention than ACEI.

Effects of pre-, peri-, and postmyocardial infarction treatment with omapatrilat in rats: survival, arrhythmias, ventricular function, and remodeling.

We showed previously that the vasopeptidase inhibitor (VPI) omapatrilat improves peri-myocardial infarction (MI) survival, but the mechanisms involved and whether these effects are sustained remained to be determined, and are the subject of this study. Rats (n = 272) received omapatrilat (20 mg x kg-1x day-1) starting 7 days before MI and continued peri- and post-MI, or no treatment (control). One group of rats had continuous ambulatory ECG and blood pressure recordings started 6 h before MI and continued until 24 h after MI, when survival was evaluated, and the rats were killed, and MI size was evaluated. A second group had left ventricular (LV) remodeling evaluated by echocardiography at 30 days and, at 38 days, had cardiac hemodynamics and morphology done and survival evaluated. Survival 24 h after MI (n = 255) improved with omapatrilat (60% vs. 46% for control; P = 0.0378). Over the next 37 days, there was no further improvement with omapatrilat but the early benefit was sustained. Omapatrilat reduced MI size 24 h after MI (36 +/- 2 vs. 42 +/- 2 mm2 for controls; P = 0.034). Omapatrilat reduced ventricular arrhythmia score 1-12 h after MI. Omapatrilat decreased blood pressure, but not during the first 24 h after MI. Omapatrilat reduced LV diastolic and systolic dimensions and LV and right ventricular weights compared with control large MI, indicating a decrease in reactive hypertrophy. Improvement in cardiac remodeling was accompanied by improved cardiac hemodynamics. Thus this study indicates that pre-, peri-, and post-MI treatment with the VPI omapatrilat is beneficial in survival, ventricular arrhythmias, LV remodeling, and cardiac function.

Effect of chronic treatment with bovine recombinant growth hormone on cardiac dysfunction and lesion progression in UM-X7.1 cardiomyopathic hamsters.

In view of the potentially beneficial effect of GH on ventricular function of humans suffering from idiopathic dilated cardiomyopathy, we undertook a study to evaluate the optimal time to initiate treatment with GH and its duration in UM-X7.1 cardiomyopathic hamsters (CMH). GH (1 mg/kg.d) therapy was initiated either in the early or late (30 and 160 d old, respectively) phases of the disease and continued until death at 240 d of age. Age- and sex-matched Golden Syrian hamsters (GSH) were used as controls. Basal IGF-1 levels in serum were reduced by nearly half in CMH compared with GSH but were increased within a physiological range in male hamsters. In contrast, female hamsters presented elevated basal serum IGF-1 levels that were not further elevated by GH administration, as reported in experimental models and humans. Accordingly, the present study will focus on the effects of GH therapy on cardiac performance in male hamsters. GH did not improve ventricular function when starting at a late stage of the disease compared with CMH controls. Maximum rate of left ventricular pressure development decreased by approximately 64% in CMH treated early with recombinant bovine GH. Ventricular dysfunction was associated with morphologic indices of hypertrophy, ventricular dilatation, and extensive fibrosis. Mortality was strikingly increased in GH-treated CMH for 210 d (four males and eight females), as opposed to four females (and no male) in the vehicle-treated group. These results suggest that chronic treatment with recombinant bovine GH in CMH, starting at an early stage of lesion development, is associated with a reduced cardiac performance at the terminal stage of the disease.

Angiotensin receptor blockers: powerful evidence with cardiovascular outcomes?

Angiotensin receptor blockers (ARBs) were developed to better antagonize the effects of chronic overactivation of angiotensin II. In clinical studies, ARBs have consistently been shown to be more tolerable than angiotensin-converting enzyme inhibitors (ACEis). Although many studies evaluating the benefits of ARBs in clinical practice are underway, relatively little information exists as to their benefits concerning cardiovascular events. In heart failure patients with ACEi intolerance, ARBs may improve survival. In patients who can tolerate an ACEi, ARBs reduce hospitalization. Due to a possible detrimental interaction when an ARB is added to the treatment of patients already taking an ACEi and a beta-blocker, the use of ARBs in such heart failure patients is not generally indicated. ARBs also preserve renal function and may reduce cardiovascular events in patients with pre-existing renal dysfunction and type 2 diabetes. However, there is no convincing evidence that ARBs improve the survival of these patients. Thus, ARBs should be used on their own merits and should not be used as substitutes for ACEis in this patient population. Studies to establish the status of ARBs in the treatment and prevention of cardiovascular diseases are ongoing, but until they are completed, care should be taken in extrapolating the effects of ARBs to those of ACEis.

Cardioprotective effects of vasopeptidase inhibitors.

In all cardiovascular disease, there is an imbalance between vasoconstrictor and vasodilator systems that favours vasoconstriction. Angiotensin-converting enzyme (ACE) inhibitors help to redress this imbalance. ACE inhibitors reduce angiotensin II and, by blocking the metabolism of bradykinin, ACE inhibitors upregulate nitric oxide and prostacycline. Neutral endopeptidase (NEP) is the major enzymatic pathway for the degradation of natriuretic peptides and adrenomedullin, and is a secondary enzymatic pathway for the degradation of kinins. Thus, inhibition of NEP increases levels of natriuretic and vasodilatory peptides. Vasopeptidase inhibitors (VPIs), by simultaneously inhibiting ACE and NEP, reduce vasocontriction and enhance vasodilation; thus, they improve local blood flow, and improve sodium and water excretion. In addition, they likely reduce growth, fibrosis, coagulability, adhesive molecule expression and monocyte adhesion, and inflammation in the vasculature and the heart. In clinical studies, they have proven to be very effective in treating hypertension. The major side effect of the drugs appears to be angioedema. Thus, VPIs are promising new drugs for the treatment of cardiovascular diseases.

Comparison of the effects of an angiotensin-converting enzyme inhibitor and a vasopeptidase inhibitor after myocardial infarction in the rat.

OBJECTIVES: The goal of this study was to compare the effects of the vasopeptidase inhibitor omapatrilat and the angiotensin-converting enzyme inhibitor (ACEI) captopril in the postmyocardial infarction (MI) rat model. BACKGROUND; The cardioprotective effects of ACEIs after MI are thought to be partially due to an increase in bradykinin (BK). Vasopeptidase inhibitors inhibit both ACE and neutral endopeptidase (NEP), further reduce BK metabolism and increase natriuretic peptides, which may result in better cardioprotective effects than with ACEIs after MI. METHODS: Myocardial infarction was induced in 514 Wistar male rats by ligation of the anterior coronary artery. Rats surviving 4 h after MI (n = 282) were assigned to omapatrilat (40 or 80 mg/kg/day), captopril (160 mg/kg/day) or no treatment. After 56 days, neurohumoral, hemodynamic, ventricular remodeling, morphometry, immunohistochemistry and cardiac cytokine expression were measured. RESULTS: Omapatrilat and captopril resulted in similarly improved survival, cardiac hemodynamics and reduced cardiac fibrosis and hypertrophy after MI. The pattern of left ventricular (LV) remodeling differed, omapatrilat causing less attenuation of the rightward shift of the LV pressure-volume relation at lower filling pressures than captopril. Both interventions reduced messenger ribonucleic acid expression of the profibrotic cytokine transforming growth factor-beta(1); neither effected the anti-inflammatory cytokine interleukin-10, and only captopril reduced the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Expression of TNF-alpha was in cardiomyocytes. Both medications reduced circulating endothelin-1, angiotensin II and catecholamines, but only omapatrilat increased atrial natriuretic peptides. CONCLUSIONS: This study indicates that both omapatrilat and captopril markedly improve post-MI survival, cardiac function and cardiac remodeling in the rat. It would appear that the addition of NEP inhibition to those of ACEIs does not result in significant further benefit after MI.

Beneficial effects of long-term use of the antioxidant probucol in heart failure in the rat.

BACKGROUND: Congestive heart failure (CHF) is a disease that is characterized by progressive left ventricular (LV) dysfunction and dilatation. Oxidative stress is thought to contribute to the progression of CHF, and antioxidants have been shown to have beneficial effects when started early after myocardial infarction (MI). In this study, we tested whether the powerful antioxidant probucol would attenuate progression of CHF once it was established after MI in the rat. METHODS AND RESULTS: Ligation of a coronary artery was used to create an MI in rats (n=266). Survivors were then randomized 20 days after MI to either probucol 61 mg. kg(-1). d(-1) or vehicle and followed up for a total of 100 days after MI. Studies of cardiac hemodynamics, LV remodeling, cardiac apoptosis and morphology, systemic neurohumoral activation, oxidative stress, and renal function were then evaluated. Probucol improved LV function (LV maximum rate of pressure rise from 3103 to 4250 mm Hg/s, P<0.05, and LV end-diastolic pressure decrease from 28 to 24 mm Hg, P<0.05), reduced pulmonary weights, prevented right ventricular systolic hypertension, and preserved renal function compared with vehicle. Probucol also prevented LV dilatation, prevented wall thinning (1.70 versus 1.42 mm, P<0.05), reduced cardiac fibrosis and cardiac apoptosis, attenuated increased myocardial cell cross-sectional area, and increased scar thickness. CONCLUSIONS: In chronic CHF, probucol exerts multiple beneficial morphological effects that result in better LV remodeling and function, reduced neurohumoral activation, and preserved renal function.

Effects of captopril and omapatrilat on early post-myocardial infarction survival and cardiac hemodynamics in rats: interaction with cardiac cytokine expression.

The purpose of this study was to evaluate and compare the effects of simultaneous angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) inhibition by the vasopeptidase inhibitor omapatrilat (10 and 40 mg x kg(-1) x day(-1)) with those of the selective ACE inhibitor captopril (160 mg x kg(-1) x day(-1)) on survival, cardiac hemodynamics, and cytokine mRNA expression in left ventricular (LV) tissues 4 days after myocardial infarction (MI) in rats. The effects of the co-administration of both B1 and B2 kinin receptor antagonists (2.5 mg x kg(-1) x day(-1) each) with and without omapatrilat were also evaluated to assess the role of bradykinin (BK) during this post-MI period. Both omapatrilat and captopril treatments improve early (4 days) post-MI survival when started 4 h post-MI. The use of kinin receptor antagonists had no significant effect on survival in untreated MI rats and omapatrilat-treated MI rats. This improvement in survival with omapatrilat and captopril is accompanied by a reduced LV end-diastolic pressure (LVEDP) and pulmonary congestion. The use of kinin receptor antagonists had little effect on cardiac hemodynamics or morphologic measurements. Acute MI significantly increased the expression of cardiac cytokines (TNF-alpha, TGF-beta1, and IL-10). Captopril significantly attenuated this activation, while omapatrilat had variable effects: sometimes increasing but generally not changing activation depending on the cytokine measured and the dose of omapatrilat used. The co-administration of both kinin receptor antagonists attenuates the increase in expression of cardiac TNF-alpha and TGF-beta1 after omapatrilat treatment. Taken together, these results would suggest that despite very marked differences in the way these drugs modified the expression of cardiac cytokines, both omapatrilat and captopril improved early (4 days) post-MI survival and cardiac function to a similar extent.