Atrial natriuretic peptide in a rat model of cardiac failure. Atrial and ventricular mRNA, atrial content, plasma levels, and effect of volume loading

Oryeongsan (Wulingsan) ameliorates impaired ANP secretion of atria from spontaneously hypertensive rats

Oryeongsan (ORS), a herbal medicine formula, has long been used for the treatment of impaired body water balance in Asian countries. Recently, it was shown that ORS administration modulates the renin-angiotensin system (RAS). Purpose of the present study was to determine characteristics of atrial ANP secretion and effects of ORS on the secretion in the atria from spontaneously hypertensive rats (SHR). Normotensive WKY groups (WKY-V, WKY-ORS, WKY-LOS) and hypertensive SHR groups (SHR-V, SHR-ORS, SHR-LOS) treated with vehicle, ORS, and losartan as a positive control group, respectively, were used. Experiments were performed in perfused beating atria (1.3 Hz) allowing atrial distension, acetylcholine (ACh) stimulation, and serial collection of atrial perfusates. The secreted ANP concentration was measured using radioimmunoassay. Interstitial fluid (ISF) translocation was measured using [³H]inulin clearance. Stepwise increase in atrial distension by 1.1, 2.0, and 2.7 cmH₂O above basal distension further increased ANP secretion proportionally in the atria from WKY-V, but the response was significantly suppressed in the atria from SHR-V. Cardiomyocyte ANP release, the first step of atrial ANP secretion, was suppressed in the atria from SHR-V compared to those from WKY-V (-8.02 ± 2.86, -15.86 ± 2.27, and -20.09 ± 3.62%; n = 8, for SHR-V vs. 8.59 ± 2.81, 15.65 ± 7.14, and 38.12 ± 8.28%; n = 8, for WKY-V; p < 0.001 for all stepwise distension, respectively). Chronic treatment with ORS reversed the suppressed ANP release in atria from SHR-ORS group (6.76 ± 3.92, 9.12 ± 2.85, and 28.79 ± 1.79% for SHR-ORS; n = 5 vs. SHR-V; n = 8; p = 0.01, p < 0.001, p < 0.001, respectively). The effects of ORS were comparable to those of losartan. Trans-endocardial translocation of ISF, the second step of atrial ANP secretion was similar in the atria from the hypertensive SHR-V and normotensive WKY-V. ACh-induced ANP secretion and cardiomyocyte ANP release were also suppressed in the atria from SHR-V compared to WKY-V and ORS reversed the suppression. These findings were accompanied with accentuation of the AT₁ receptor expression and suppression of the AT₂/Mas receptor, M₂ mACh receptor and GIRK4, a molecular component of K_ACh channel, expression in the atria from SHR-V. Further, treatment with ORS or losartan reversed the expressions in the groups of SHR-ORS and SHR-LOS. These results show that ANP secretion is suppressed in the atria from SHR in association with accentuation of AT₁ receptor and suppression of AT₂/Mas receptor and K_ACh channel expression. Treatment with ORS ameliorates impaired ANP secretion through improving cardiomyocyte ANP release with modulation of the cardiac RAS and muscarinic signaling. These findings provide experimental evidence which supports the effect of ORS on the regulation of atrial ANP secretion in the atria from SHR.

Physiology of the Right Ventricle Across the Lifespan

The most common cause of heart failure in the United States is ischemic left heart disease; accordingly, a vast amount of work has been done to elucidate the molecular mechanisms underlying pathologies of the left ventricle (LV) as a general model of heart failure. Until recently, little attention has been paid to the right ventricle (RV) and it has commonly been thought that the mechanical and biochemical properties of the RV are similar to those of the LV. However, therapies used to treat LV failure often fail to improve ventricular function in RV failure underscoring, the need to better understand the unique physiologic and pathophysiologic properties of the RV. Importantly, hemodynamic stresses (such as pressure overload) often underlie right heart failure further differentiating RV failure as unique from LV failure. There are significant structural, mechanical, and biochemical properties distinctive to the RV that influences its function and it is likely that adaptations of the RV occur uniquely across the lifespan. We have previously reviewed the adult RV compared to the LV but there is little known about differences in the pediatric or aged RV. Accordingly, in this mini-review, we will examine the subtle distinctions between the RV and LV that are maintained physiologically across the lifespan and will highlight significant knowledge gaps in our understanding of pediatric and aging RV. Consideration of how RV function is altered in different disease states in an age-specific manner may enable us to define RV function in health and importantly, in response to pathology.

Effect of hydrodynamics-based delivery of IL-18BP fusion gene on rat experimental autoimmune myocarditis

Interleukin-18 (IL-18) is a powerful and important cytokine in myocarditis. IL-18-binding protein (IL-18BP), a naturally occurring antagonist of IL-18, is presumed to play a vital regulatory function in IL-18-mediated immune responses. The purpose of this study was to evaluate the alterations of IL-18 and its related protein expressions and the effect of hydrodynamics-based delivery of the IL-18BP gene for treatment of rat experimental autoimmune myocarditis (EAM).Rats were immunized on Day 0 and killed on 2, 3 and 4 weeks to determine IL-18 and its related protein expression and target cells in EAM hearts. On Day 6, rats were injected with a recombinant plasmid encoding IL-18BP-Ig or SP-Ig. On Day 17, rats were detected with echocardiography and then be killed. IL-18BP gene therapy was effective in controlling EAM, as monitored by a decreased ratio of heart weight to body weight, reduced myocarditis areas, reduced expression of atrial natriuretic peptide, brain natriuretic peptide, IL-17, IFN-γ, IL-6 and IL-10. Furthermore, the effect of serum containing IL-18BP on the expression of immune-relevant genes in IL-1α-stimulated NC cells and splenocytes cultured from EAM rats was examined. The results showed that IL-18BP significantly suppressed the expression of IL-17 as well as other proinflammatory genes such as transforming growth factor-β, prostaglandin E2 synthase, cyclooxygenase-2 in IL-1α-stimulated NC cells, and IL-18BP also significantly suppressed the expression of IL-17, IL-17R, IL-21 and IL-17-related transcriptional factor retinoic acid-related orphan nuclear receptor, signal transducer and activator of transcription-3 and Foxp3 in IL-1α-stimulated splenocytes cultured from EAM rats. IL-18 and its related protein played an important role on the development of EAM. IL-18BP effectively prevented progression of EAM by blocking IL-17 and related inflammatory genes expression. This might be a possible mechanism of the amelioration of EAM by IL-18BP treatment.

Metoprolol treatment lowers thrombospondin-4 expression in rats with myocardial infarction and left ventricular hypertrophy

Thrombospondins are matrix proteins linked to extracellular matrix remodelling but their precise role in the heart is not known. In this study, we characterised left ventricular thrombospondin-1 and -4 expression in rats treated with a beta-blocker metoprolol during the remodelling process in response to pressure overload and acute myocardial infarction. Left ventricular thrombospondin-1 and thrombospondin-4 mRNA levels increased 8.4-fold (p < 0.001) and 7.3-fold (p < 0.001) post-infarction, respectively. Metoprolol infusion by osmotic minipumps (1.5 mg/kg/hr) for 2 weeks after myocardial infarction decreased thrombospondin-1 and thrombospondin-4 mRNA levels (55% and 50%, respectively), improved left ventricular function, and attenuated left ventricular remodelling with reduction of left ventricular atrial natriuretic peptide and brain natriuretic peptide gene expression. Thrombospondin-1 and -4 mRNA levels correlated positively with echocardiographic parameters of left ventricular remodelling as well as with atrial natriuretic peptide and brain natriuretic peptide gene expression. Moreover, there was a negative correlation between left ventricular ejection fraction and thrombospondin-1 mRNA levels. In 12-month-old spontaneously hypertensive rats with left ventricular hypertrophy, metoprolol decreased left ventricular thrombospondin-4 levels and attenuated remodelling while thrombospondin-1, atrial natriuretic peptide and brain natriuretic peptide mRNA levels as well as left ventricular function remained unchanged. In metoprolol-treated spontaneously hypertensive rats, thrombospondin-4 gene expression correlated with parameters of left ventricular remodelling, while no correlations between thrombospondins and natriuretic peptides were observed. These results indicate that thrombospondin-1 expression is linked exclusively to left ventricular remodelling process post-infarction while thrombospondin-4 associates with myocardial remodelling both after myocardial infarction and in hypertensive heart disease suggesting that thrombospondins may have unique roles in extracellular matrix remodelling process.

Alteration of IL-17 related protein expressions in experimental autoimmune myocarditis and inhibition of IL-17 by IL-10-Ig fusion gene transfer

BACKGROUND

T-helper (Th)1/Th2 cytokine balance plays an important role in the pathogenesis of myocarditis. Recently, some studies indicate that interleukin (IL)-17, known as a T cell (Th17)-derived proinflammatory cytokine, is the major mediator of tissue inflammation in inflammatory and autoimmune diseases. Experimental autoimmune myocarditis (EAM) is a T cell-mediated autoimmune disease; however, the pathogenic role of IL-17 in the development of rat EAM remains largely unknown.

METHODS AND RESULTS

In the present study, alterations of IL-17-related protein expressions were investigated and then the effect of hydrodynamic-based delivery of plasmid DNA encoding the IL-10-Ig gene on rat EAM and the effect of IL-10-Ig on IL-17 was evaluated. The results showed that IL-17 was expressed more highly than IFN-gamma expressed by Th1 cells in alphabetaT cells and the peaks of IL-17 related protein expression in the heart were the early phase of EAM. Moreover, we observed that IL-10-Ig gene therapy was effective in controlling EAM and that IL-10-Ig significantly suppressed the expression of IL-17 as well as other proinflammatory cytokines, IL-1beta and TNF-alpha, in IL-1-stimulated splenocytes cultured from EAM rats.

CONCLUSIONS

IL-17 is highly produced by alphabetaT cells in the early phase of EAM hearts and IL-17 inhibition might be a possible mechanism of the amelioration of EAM by IL-10-Ig treatment. These data suggest that IL-17 produced by Th17 plays an important role in the pathogenesis of rat EAM.

Prevention of experimental autoimmune myocarditis by hydrodynamics-based naked plasmid DNA encoding CTLA4-Ig gene delivery

BACKGROUND

Rat experimental autoimmune myocarditis (EAM) is a T cell-mediated disease that resembled the giant cell myocarditis seen in humans. Soluble CTLA4 improves some autoimmune diseases by blocking costimulatory signals on T cell. We investigated the effect of hydrodynamics-based naked plasmid DNA encoding CTLA4-immunoglobulin (Ig) gene delivery.

METHODS AND RESULTS

Lewis rats were immunized with cardiac myosin and treated with hydrodynamic-based transfection, namely a rapid tail vein injection of a large volume of pCAGGS encoding CTLA4-Ig chimera solution on Day 0. The vector-derived CTLA4-Ig mRNA expressions were mainly detected in the liver and plasma CTLA4-Ig protein levels were maintained at about 2 mug/mL during the experiment period. On Day 17, the ratio of heart to body weight, the amount of mRNA of atrial natriuretic peptide, and the inflammatory areas in CTLA4 group were significantly lower than in the control group treated with empty plasmid. Maximum rate of intraventricular pressure rise and decline (dP/dT), minimum dP/dT, left ventricular end-diastolic pressure, and central venous pressure improved significantly after treatment with CTLA4-Ig. On Day 14, expressions of IL-2 in popliteal lymph nodes in the CTLA4-Ig group were significantly lower than in the control group.

CONCLUSION

Hydrodynamics-based transfection of plasmid encoding CTLA4-Ig chimera dramatically prevented EAM.

Activation of protein kinase A by atrial natriuretic peptide in neonatal rat cardiac fibroblasts: role in regulation of the local renin-angiotensin system

There is an inverse relationship between renin and atrial natriuretic peptide (ANP) levels in the plasma. Since both the ANP and renin-angiotensin system (RAS) are upregulated in development and cardiac hypertrophy, we tested whether ANP differentially regulates RAS in cardiac cells. Cardiac fibroblasts isolated from neonatal rats were treated with ANP(1-28), a biologically active fragment of ANP. Renin and angiotensinogen (Ao) mRNA levels were measured by quantitative multiplex RT-PCR and protein levels determined by Western blot analysis. ANP(1-28) increased renin and Ao mRNA levels (737+/-131% and 178+/-51.3%) with EC50 values of 4.12+/-0.3 and 8.67+/-0.22 nmol/L, respectively. At the protein level, secretion of renin and Ao was significantly enhanced resulting in approximately 4-fold increase in ANG II level in the medium. The effect of ANP(1-28) on renin and Ao mRNA expression were reproduced by 8-bromo-cyclic GMP. Inhibition of protein kinase G (PKG) with KT5823 blunted ANP(1-28)-induced upregulation of renin, but not Ao mRNA, while inhibition of protein kinase A (PKA) with KT5720 attenuated the upregulation of both renin and Ao mRNA. These findings suggest that unlike in plasma, ANP positively regulates the RAS in cardiac fibroblasts, which may have a significant role in development of the fetal heart.

Additive improvement of left ventricular remodeling and neurohormonal activation by aldosterone receptor blockade with eplerenone and ACE inhibition in rats with myocardial infarction

OBJECTIVES

We investigated the effects of the aldosterone blocker eplerenone alone and in combination with angiotensin-converting enzyme (ACE) inhibition on ventricular remodeling in rats with left ventricular (LV) dysfunction after extensive myocardial infarction (MI).

BACKGROUND

Adding an aldosterone antagonist to ACE inhibition reduces mortality and morbidity in heart failure.

METHODS

Starting 10 days after MI, rats were treated with placebo, eplerenone (100 mg/kg/day), the ACE inhibitor trandolapril (0.3 mg/kg/day), or a combination of both for nine weeks.

RESULTS

Both monotherapies attenuated the rise in LV end-diastolic pressure (LVEDP) and LV end-diastolic volume (LVEDV) compared with placebo, whereas combined treatment further attenuated LVEDP and LVEDV, significantly improved LV function and reduced plasma norepinephrine levels. The time constant of LV pressure isovolumic decay (tau) was prolonged in placebo MI rats, significantly shortened by eplerenone, and normalized by eplerenone/trandolapril. Increased collagen type I gene expression and collagen content in the noninfarcted LV myocardium from MI placebo rats was attenuated by trandolapril, but almost completely prevented by eplerenone and eplerenone/trandolapril. The addition of eplerenone to ACE inhibition prevented sarcoplasmic-reticulum calcium ATPase downregulation and the increases in LV gene expression of beta-MHC and atrial natriuretic factor more effectively than either monotherapy. Furthermore, combination treatment attenuated the increase in myocardial angiotensin II type 1 receptor expression and increased phosphorylated endothelial nitric oxide synthase protein levels.

CONCLUSIONS

The aldosterone blocker eplerenone improved LV remodeling in rats with LV dysfunction after extensive MI. Combination therapy with an ACE inhibitor substantially potentiates this effect by a complementary prevention of LV fibrosis, cardiac hypertrophy, and molecular alterations.

Hypoxic activation of the atrial natriuretic peptide gene promoter through direct and indirect actions of hypoxia-inducible factor-1

Atrial natriuretic peptide (ANP) is a cardiac peptide, the transcription of which is up-regulated in the ischaemic ventricle. However, the molecular mechanism of ANP induction is unclear. This study demonstrated that ANP mRNA expression in rat ventricular myocardium is induced in an early phase of ischaemia, preceded by hypoxia-inducible factor-1 (HIF-1) alpha expression. The ANP gene was also induced by hypoxia or HIF-1 inducers such as CoCl2 and desferrioxamine in H9c2 and neonatal cardiomyocytes. The 2307 bp 5'-flanking region of the rat ANP gene was cloned and fused to the luciferase gene. Evidence of the promoter activity was only apparent in the myocytes and was induced by hypoxia and HIF-1 inducers. The overexpression of HIF-1alpha markedly enhanced ANP promoter activity, and a dominant-negative isoform completely suppressed it. We demonstrated that the promoter regions are essential for hypoxic ANP induction. One promoter region, containing the HIF-1-binding sequence, is regulated directly by HIF-1. The other region is also activated by HIF-1 despite having no HIF-1-binding sequence. These results suggest that HIF-1 enhances the transactivation of the ANP gene in hypoxic myocytes, implying that stimulation of the ANP promoter by HIF-1 may in fact be responsible for the induction of the ANP gene in ischaemic ventricular myocardium.

TGF-beta(1) and prepro-ANP mRNAs are differentially regulated in exercise-induced cardiac hypertrophy

The induction of transforming growth factor (TGF)-beta and prepro-atrial natriuretic peptide (ANP) mRNAs represent hallmark features of pathological cardiac hypertrophy. The present study examined whether this pattern of mRNA expression was conserved in a physiological model of cardiac hypertrophy. To address this thesis, female Sprague-Dawley rats were individually housed and permitted to run freely. Voluntary exercise for 3 and 6 wk resulted in biventricular hypertrophy and increased cytochrome c oxidase activity in the triceps muscle. In the hypertrophied left ventricle, the steady-state mRNA level of the cardiac fetal gene prepro-ANP and the extracellular matrix proteins preprocollagen-alpha(1) and fibronectin were similar in exercise-trained and sedentary rats. By contrast, an increased expression of TGF-beta(1) mRNA was observed, whereas TGF-beta(3) mRNA level was unchanged in the hypertrophied left ventricle of exercise-trained compared with sedentary rats. These data highlight a heterogeneity in the regulation of TGF-beta isoforms, and the increased expression of ventricular TGF-beta(1) mRNA in physiological cardiac hypertrophy may contribute to myocardial remodeling.

Left ventricular aneurysm repair in rats: structural, functional, and molecular consequences

OBJECTIVES

This study examined the effects of aneurysm repair in a rat model of myocardial infarction on functional indices and on the spatiotemporal distribution of cardiac contractile protein and natriuretic peptide messenger RNA.

METHODS

In a rat infarct model, expanded left ventricular aneurysms were plicated 4 weeks after infarction. At 30 weeks, transverse heart sections were taken at 4 levels (apex [level 1] through base [level 4]) and assessed by in situ hybridization histochemistry to determine regional messenger RNA levels of pre-pro-atrial natriuretic peptide, cardiac alpha-actin, skeletal alpha-actin, myosin light chain-2v, and beta-myosin heavy chain.

RESULTS

Rats with plicated left ventricular aneurysms had reduced left ventricular endocardial circumference (19%, P <.005), lower heart weight ratio (31%, P <.05), left ventricular end-diastolic pressures (51%, P <.05), and increased +/-dP/dt (34%-38%, P <.05). Cardiac messenger RNA levels of pre-pro-atrial natriuretic peptide were reduced in the septum (levels 2 and 3), and skeletal alpha-actin levels were reduced in the septum and left ventricular free wall of plicated rats (level 3). beta-Myosin heavy chain levels were markedly reduced in peri-infarct regions of the left ventricular free wall, septum, and right ventricle in plicated rats at level 4, whereas myosin light chain-2v levels were reduced at levels 2 and 4 in the left ventricular free wall and at level 4 in the right ventricle.

CONCLUSIONS

Plication of left ventricular aneurysm after infarction in the rat significantly reduced cardiac hypertrophy, improved cardiac function, and reduced the upregulation of pre-pro-atrial natriuretic peptide and both fetal and adult contractile protein isoforms associated with cardiac hypertrophy.

The neuron-restrictive silencer element-neuron-restrictive silencer factor system regulates basal and endothelin 1-inducible atrial natriuretic peptide gene expression in ventricular myocytes

Induction of the atrial natriuretic peptide (ANP) gene is a common feature of ventricular hypertrophy. A number of cis-acting enhancer elements for several transcriptional activators have been shown to play central roles in the regulation of ANP gene expression, but much less is known about contributions made by transcriptional repressors. The neuron-restrictive silencer element (NRSE), also known as repressor element 1, mediates repression of neuronal gene expression in nonneuronal cells. We found that NRSE, which is located in the 3' untranslated region of the ANP gene, mediated repression of ANP promoter activity in ventricular myocytes and was also involved in the endothelin 1-induced increase in ANP gene transcription. The repression was conferred by a repressor protein, neuron-restrictive silencer factor (NRSF). NRSF associated with the transcriptional corepressor mSin3 and formed a complex with histone deacetylase (HDAC) in ventricular myocytes. Trichostatin A (TSA), a specific HDAC inhibitor, relieved NRSE-mediated repression of ANP promoter activity, and chromatin immunoprecipitation assays revealed the involvement of histone deacetylation in NRSE-mediated repression of ANP gene expression. Furthermore, in myocytes infected with recombinant adenovirus expressing a dominant-negative form of NRSF, the basal level of endogenous ANP gene expression was increased and a TSA-induced increase in ANP gene expression was apparently attenuated, compared with those in myocytes infected with control adenovirus. Our findings show that an NRSE-NRSF system plays a key role in the regulation of ANP gene expression by HDAC in ventricular myocytes and provide a new insight into the role of the NRSE-NRSF system outside the nervous system.

Progressive left ventricular remodeling and apoptosis late after myocardial infarction in mouse heart

We tested the hypothesis that left ventricular (LV) remodeling late after myocardial infarction (MI) is associated with myocyte apoptosis in myocardium remote from the infarcted area and is related temporally to LV dilation and contractile dysfunction. One, four, and six months after MI caused by coronary artery ligation, LV volume and contractile function were determined using an isovolumic balloon-in-LV Langendorff technique. Apoptosis and nuclear morphology were determined by terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) and Hoechst 33258 staining. Progressive LV dilation 1-6 mo post-MI was associated with reduced peak LV developed pressure (LVDP). In myocardium remote from the infarct, there was increased wall thickness and expression of atrial natriuretic peptide mRNA consistent with reactive hypertrophy. There was a progressive increase in the number of TUNEL-positive myocytes from 1 to 6 mo post-MI (2.9-fold increase at 6 mo; P < 0. 001 vs. sham). Thus LV remodeling late post-MI is associated with increased apoptosis in myocardium remote from the area of ischemic injury. The frequency of apoptosis is related to the severity of LV dysfunction.

The natriuretic peptides: physiology and role in left-ventricular dysfunction

The natriuretic peptides (NPs), atrial natriuretic peptide, and brain natriuretic peptide (BNP) have been shown to have important roles in fluid volume homeostasis and blood pressure regulation. In addition, plasma NP levels are elevated in a number of cardiac pathologies and have been used as biochemical markers of left-ventricular dysfunction (LVD) in small- and large-scale clinical studies. In this review, the authors describe NP physiology and summarize the findings of selected studies that have examined the reliability and feasibility of NP measurement in LVD. In particular, BNP is proposed to be a biochemical marker that may provide a useful and inexpensive screening test of LVD. In addition, the authors discuss possible roles of the NPs in the etiology and progression of LVD. The findings of these studies suggest that the NPs may directly contribute to cardiac pathophysiology and LVD progression.

Cytokines and their receptors in cardiovascular diseases--role of gp130 signalling pathway in cardiac myocyte growth and maintenance

Interleukin (IL)-6-related cytokines share gp130 as the signal-transducing protein. Cardiac myocytes produce various kinds of cytokines including IL-6 and cardiotrophin-1. Activation of gp130 transduces hypertrophic and cytoprotective signals in cardiac myocytes via JAK/STAT, MAP kinase and PI-3 kinase pathways. Besides various well-established mechanisms by which cardiac growth and myocardial remodeling are regulated, gp130 signalling may be a newly discovered mechanism that regulates these events in association with cytoprotective effect in myocardial diseases.

Signal transducer and activator of transcription 3 in the heart transduces not only a hypertrophic signal but a protective signal against doxorubicin-induced cardiomyopathy

The signal transducer and activator of transcription (STAT) 3, a transcriptional factor downstream of several cytokines, is activated by Janus kinase families and plays a pivotal role in cardiac hypertrophy through gp130. To determine the physiological significance of STAT3 in vivo, transgenic mice with cardiac-specific overexpression of the Stat3 gene (STAT3-TG) were generated. STAT3-TG manifested myocardial hypertrophy at 12 wk of age with increased expression of the atrial natriuretic factor (ANF), beta-myosin heavy chain (MHC), and cardiotrophin (CT)-1 genes. The animals were injected i.p. with 15 mg/kg doxorubicin (Dox), an antineoplastic drug with restricted use because of its cardiotoxicity. The survival rates after 10 days were 25% (5/20) for control littermates (WT), but 80% (16/20) for STAT3-TG (P < 0.01). WT showed increased expression of beta-MHC and ANF mRNAs in the hearts 1 day after Dox treatment; this expression peaked at 3 days, suggesting that the WT suffered from congestive heart failure. Although the expression of these mRNAs was elevated in STAT3-TG hearts before Dox treatment, no additional increase was observed after the treatment. Dox administration significantly reduced the expression of the cardiac alpha-actin and Stat3 genes in WT hearts but not in STAT3-TG. These results provide direct evidence that STAT3 transduces not only a hypertrophic signal but also a protective signal against Dox-induced cardiomyopathy by inhibiting reduction of cardiac contractile genes and inducing cardiac protective factors.

Molecular mechanisms of myocardial remodeling

"Remodeling" implies changes that result in rearrangement of normally existing structures. This review focuses only on permanent modifications in relation to clinical dysfunction in cardiac remodeling (CR) secondary to myocardial infarction (MI) and/or arterial hypertension and includes a special section on the senescent heart, since CR is mainly a disease of the elderly. From a biological point of view, CR is determined by 1 ) the general process of adaptation which allows both the myocyte and the collagen network to adapt to new working conditions; 2) ventricular fibrosis, i.e., increased collagen concentration, which is multifactorial and caused by senescence, ischemia, various hormones, and/or inflammatory processes; 3) cell death, a parameter linked to fibrosis, which is usually due to necrosis and apoptosis and occurs in nearly all models of CR. The process of adaptation is associated with various changes in genetic expression, including a general activation that causes hypertrophy, isogenic shifts which result in the appearance of a slow isomyosin, and a new Na+-K+-ATPase with a low affinity for sodium, reactivation of genes encoding for atrial natriuretic factor and the renin-angiotensin system, and a diminished concentration of sarcoplasmic reticulum Ca2+-ATPase, beta-adrenergic receptors, and the potassium channel responsible for transient outward current. From a clinical point of view, fibrosis is for the moment a major marker for cardiac failure and a crucial determinant of myocardial heterogeneity, increasing diastolic stiffness, and the propensity for reentry arrhythmias. In addition, systolic dysfunction is facilitated by slowing of the calcium transient and the downregulation of the entire adrenergic system. Modifications of intracellular calcium movements are the main determinants of the triggered activity and automaticity that cause arrhythmias and alterations in relaxation.

Effect of chronic GH overproduction on cardiac ANP expression and circulating ANP levels

Sodium and water retention are common in acromegaly and upon GH administration. The underlying mechanisms, however, have not been clearly characterized as yet. Therefore, the aim of this study was to examine possible alterations of atrial natriuretic peptide (ANP), an endogenous regulator of volume homeostasis, in response to chronic elevated GH. We used GH-transgenic mice (GH-TM) as a model for chronic hypersomatotropinemia and moreover investigated 7 and 27 week old animals, respectively, in order to discriminate between short and long term effects of GH overexpression. Hematocrit values were reduced in GH-TM compared to control animals and it is known that plasma volume is increased in these animals. Structural lesions of the kidney were found in the GH-TM, however, in the animals studied there were no signs of renal insufficiency as evidenced by serum creatinine and urea levels. The serum concentration of immunoreactive ANP (IR-ANP) determined by RIA was significantly (P < 0.005) elevated in the young GH-TM as compared to control littermates (81.7+/-13.3 vs. 50.9+/-10.8 fmol/ml). The increase in serum IR-ANP of 27 week old GH-TM, however did not reach the level of significance (57.13+/-16.3 vs. 50.25+/-16.4 fmol/ml). Serum samples of control mice as well as of the 7 week old animals mainly contained ANP 99-126, known to be the circulating form of ANP. In contrast, serum of 27 week old GH-TM predominantly showed the cardiac storage form of ANP, ANP 1-126. Cardiac expression of ANP was quantified by Northern blot analysis. mRNA coding for ANP was found 1.2- and 2-fold increased in the atria of 7 and 27 week old GH-TM, respectively. In parallel, a 2.2-fold (7 week) and 2-fold (27 week) increase of IR-ANP was observed in transgenic atria compared to tissue of control animals. In contrast, no significant difference of ANP mRNA expression or of content of IR-ANP was observed in the ventricles of both groups of animals. In conclusion, GH-TM show various alterations in their ANP status suggesting an influence of the peptide on the effect of GH in fluid retention.

Identification of a cis-acting regulatory element conferring inducibility of the atrial natriuretic factor gene in acute pressure overload

To identify the cis-acting regulatory element(s) which control the induction of the atrial natriuretic factor (ANF) gene in acute pressure overload, DNA constructs consisting of promoter elements linked to a reporter gene were injected into the myocardium of dogs, which underwent aortic banding or were sham-operated. Expression of a reporter gene construct harboring the ANF promoter (-3400ANF) was induced 6-12-fold after 7 d of pressure overload. An internal deletion of 556 bp (nucleotide sequence -693 to -137) completely abrogated the inducibility of the ANF reporter gene construct. An activator protein-1 (AP1)-like site (-496 to -489) and a cAMP regulatory element (CRE) (-602 to -596) are located within the deleted sequence. Site-directed mutagenesis of the AP1-like site but not the CRE completely prevented the induction of this construct to acute pressure overload. Further, the AP1-like site was able to confer inducibility of a heterologous promoter (beta-myosin heavy chain) to higher values than controls. Gel mobility shift assay (GMSA) supershift analysis was performed using a radiolabeled probe of the ANF promoter (-506/-483) that included the AP1-like site (ATGAATCA) sequence, as well as a probe converted to contain an AP1 consensus sequence (ATGACTCA). GMSA analysis demonstrated that the ANF AP1-like element could bind both a constitutively expressed factor and the AP1 proteins, and conversion to a true AP1 site increased its affinity for AP1. However, 7 d after the onset of pressure overload, the AP1 proteins were present only at low levels, and the major complex formed by the ANF AP1-like probe was not supershifted by a jun antibody. Using a large animal model of pressure overload, we have demonstrated that a unique cis-acting element was primarily responsible for the overload induction of the ANF gene.

The kallikrein-kinin system in post-myocardial infarction cardiac remodeling

Angiotensin converting-enzyme (ACE) inhibitors attenuate cardiac hypertrophy and prolong survival in animal models and patients after myocardial infarction (MI). Considering the dual function of the ACE, the therapeutic efficacy of ACE inhibitors after MI implicates the renin-angiotensin system and/or the kallikrein-kinin system in the pathophysiology of postinfarction cardiac remodeling. We evaluated the role of kinins, and their potential contribution to the antiremodeling effects of ACE inhibition in this setting. Rats underwent coronary artery ligation followed by chronic B2 kinin receptor blockade with icatibant (HOE 140). Additional groups of MI rats were treated with the ACE inhibitor lisinopril, alone or in combination with icatibant. B2 kinin receptor blockade enhanced the deposition of collagen (morphometric analysis) in the left ventricular interstitial space after MI, whereas markers of cardiomyocyte hypertrophy (left ventricular weights and prepro-atrial natriuretic factor [ANF] expression) were not affected. Chronic ACE inhibition reduced collagen deposition and cardiomyocyte hypertrophy after MI. The inhibitory action of ACE inhibition on interstitial collagen was partially reversed by B2 kinin receptor blockade. However, B2 kinin receptor blockade did not attenuate the effects of ACE inhibition on cardiomyocyte hypertrophy. In conclusion, kinins inhibit the interstitial accumulation of collagen, but do not modulate cardiomyocyte hypertrophy after MI. Kinins contribute to the reduction of myocardial collagen accumulation by ACE inhibition; however, the effects of ACE inhibition on cardiomyocyte hypertrophy are related to reduced generation of angiotensin II.

Congestive heart failure in the elderly

Several aspects of congestive heart failure are discussed in the light of international literature and of recent findings of our group. The annual incidence of heart failure in elderly subjects, aged >or=75y, is 13 to 50/1000, while it is 1.6/1000 in people aged 45-54 y. The prevalence of heart failure is about 3% in subjects aged 45-64% in subjects aged more than 65 y and 10% in subjects aged more than 75 y. These data are confirmed by our population based study in elderly subjects. The etiology of congestive heart failure is similar in elderly and middle-aged patients. However, several anatomo-functional, hormonal and autonomic nervous system changes, typical of congestive heart failure, occur during physiologic ageing processes also. These findings may explain the dramatic evolution of congestive heart failure in elderly patients. Moreover, some features of the elderly - e.g. comorbidity, atypical clinical presentations, loss of autonomy, increased iatrogen risk should be considered. No specific drugs exist for the pharmacologic treatment of heart failure in the elderly, so that the geriatric specificity in the treatment of heart failure can be recognized in the art of drug choice and dosage, to obtain the best results with the least side effects. The multiple etiology of congestive heart failure, the comorbidity, the loss of autonomy and the deterioration of cognitive functions suggest the need for multidimensional approach and continuative intervention in elderly patients with heart disease, and in particular with congestive heart failure. Further studies on disease- and age-related changes are necessary to develop new and more potent strategies to secure 'successful ageing'.

Natriuretic peptides in sheep with pressure overload left ventricular hypertrophy

To examine tissue and plasma atrial (ANP) and brain natriuretic peptide (BNP) responses to left ventricular hypertrophy (LVH) 7 sheep underwent suprarenal aortic banding (20 mmHg initial pressure differential). Median survival time was 15 days. Proximal mean aortic pressure (MAP) increased from 65.1 +/- 5.0 mmHg (baseline) to 111.6 +/- 7.5 mmHg (day 7, p < 0.0001). Distal systolic aortic pressure fell from 85.5 +/- 8.7 mmHg (baseline) to 55.6 +/- 6.4 mmHg (day 7, p = 0.0002). Maximal plasma ANP (26.9 +/- 3.6 vs 10.1 +/- 1.2 pmol/L, p = 0.005) and BNP (15.3 +/- 3.6 vs. 3.5 +/- 1.0 pmol/L, p = 0.006) were recorded at 15 +/- 4.0 days. Coarctation induced rapid increases in PRA and plasma aldosterone and a fall in urinary sodium. Post-mortem examination of hearts confirmed LVH. Compared with controls, tissue ANP concentration was reduced in left atrium (p = 0.04) and LV (p = 0.04). BNP concentration was reduced in left atrium (p = 0.02) but tended to be higher in LV. In conclusion, suprarenal aortic coarctation leads to progressive hypertension resulting in LVH, progressive increases in plasma ANP and BNP and, in most cases, death from heart failure.

Adrenomedullin: changes in circulating and cardiac tissue concentration in Dahl salt-sensitive rats on a high-salt diet

Adrenomedullin (AM), a novel hypotensive peptide, is suggested to be involved in defense mechanisms against hypertension, however, the detail mechanisms have not been clarified. To elucidate whether AM synthesis would be altered in a salt dependent hypertension, we have investigated the AM concentration and AM messenger RNA (mRNA) level in tissues of Dahl salt-sensitive rats on either low- or high-salt intake. The AM concentration in cardiac ventricle of the high-salt group was significantly higher than that of the low-salt group. The plasma AM concentration was also significantly higher in the high-salt group than in the low-salt group. Furthermore, the plasma AM concentration correlated well with the weight of left ventricle. RNA blot analysis revealed that the AM mRNA level in cardiac ventricle of the high-salt group was higher than that of the low-salt group. These results suggest that AM participates in the pathophysiology of salt dependent hypertension and plays a role in cardiac hypertrophy.

Atrial natriuretic peptide accelerates proliferation of chick embryonic cardiomyocytes in vitro

The developing embryonic heart has been reported to contain significant levels of atrial natriuretic peptide (ANP). In this study, the role of ANP in cardiac development was evaluated using cultured cardiomyocytes isolated from chick embryos. We analyzed the effect of ANP on cell number, DNA synthesis, total RNA level, the expression of cell-cycle-specific and sarcomeric proteins, and levels of lactate dehydrogenase and creatine phosphokinase. ANP increased overall DNA synthesis (measured by BrdU incorporation, P < 0.01) and enhanced cell proliferation. Morphologically, the development of the cardiomyocyte network was distinctly enhanced in the ANP-treated cells. Cellular RNA content was elevated; likewise, myosin and tropomyosin biosynthesis was significantly greater in ANP-treated cells. In addition, expression of G1/S-specific protein increased, whereas G2/M-specific protein remained unchanged by ANP treatment. An antibody against ANP and a specific ANP receptor antagonist, HS-142-1, antagonized and/or attenuated the action of ANP on both cell proliferation and protein biosynthesis. These results indicate that ANP accelerates myocardial cell proliferation by enhancing entry into S phase and by increasing DNA synthesis during S phase specifically through receptor mediated pathway. The in vitro effects of ANP on myocardial cell proliferation, together with the elevated levels of ANP seen in vivo during normal heart formation, suggest a possible autocrine function of ANP in embryonic cardiac development.

Atrial natriuretic peptide ANP(1-98) and ANP(99-126) in patients with severe chronic congestive heart failure: relation to echocardiographic measurements. A subgroup analysis from the Cooperative North Scandinavian Enalapril Survival Study (CONSENSUS)

Studies in patients with moderate heart failure have shown a positive relation between atrial size and plasma atrial natriuretic peptide (ANP)(99-126) concentrations; however, the relation of the hormone level and left atrial size and left ventricular function in patients with severe chronic heart failure has not been determined. Fifty-three patients from the Cooperative North Scandinavian Enalapril Survival Study with severe chronic heart failure were evaluated with M-mode echocardiography and determination of plasma concentrations of ANP(99-126). In 35 patients, the plasma level of N-terminal ANP(1-98) was also measured. A significant negative relation was found between ANP(1-98), ANP(99-126), and left atrial diameter (r = -.28, P = .05 and r = -.41, P < .005, respectively). Plasma concentrations of both ANP(1-98) and ANP(99-126) were related to left ventricular systolic function as determined by the systolic time interval index (r = .4, P < .05 and r = .29, P < .05, respectively). A significant improvement of left ventricular systolic function was found in the enalapril group but not in the placebo group. After 6 weeks of therapy, no correlation was found between changes in left atrial size or systolic function or changes in either the ANP(1-98) or ANP(99-126) concentration. The results indicate that high ANP(1-98) or ANP(99-126) plasma concentration is determined by the depressed left ventricular function rather than increased left atrial size in patients with chronic severe heart failure. The findings suggest that the ANP release relation to atrial pressure/atrial size is distorted in severe heart failure.

Rat infarct model of myocardial infarction and heart failure

This review outlines the development and current use of the rat coronary artery ligation model of heart failure. The techniques to ligate the left coronary artery and to obtain morphologic/hemodynamic measurements are described. The authors show how the pathology seen in this model relates to clinical ischemic heart disease. An effort is made throughout the review to relate the changes that occur in this model to clinically relevant observations. For example, the progression to heart failure in these rats is similar to what happens when a patient sustains a large myocardial infarction, survives, but goes on to develop heart failure without another ischemic insult. In both rats and people with large infarctions, the noninfarcted myocardium, even though not damaged at the time of the infarct, cannot compensate sufficiently to prevent the eventual development of heart failure. In addition to being a good approximation of human disease, the responses to pharmacologic interventions, like angiotensin converting enzyme inhibitors, in rats has proved useful in predicting what will happen in humans given the same treatment. More recent data on the molecular control of ventricular remodeling emphasizes how this model will provide important information in the study of integrated physiology by examining biochemical, pharmacologic, and physiologic changes in the same tissue.

Reciprocal changes in vasoactive hormones in the rat myocardial infarction model of heart failure

The purpose of this study was to determine (1) if there is a relationship between the changes in the plasma levels of atrial natriuretic peptide (ANP) and plasma renin activity (PRA) as rats compensated from 3 days to 6 weeks after coronary ligation and (2) if these changes are related to myocardial infarction (MI) size. Arterial blood was drawn twice from 34 conscious rats (control, n = 10; small MI, n = 10; large MI, n = 14). Histologic MI size correlated better with ANP 3 days (r = .72, P < .001) than with ANP 6 weeks after MI (r = .39, P = .021). The reverse was true for an electrocardiographic index of MI size that used the sum of the Q waves minus the sum of the R waves in leads I, aVL, and V5. Atrial natriuretic peptide at 3 days was increased in both MI groups and was highest in the large MI group (control, 25.6; small MI, 41.0; large MI, 58.6 pM). Atrial natriuretic peptide decreased significantly from 3 days to 6 weeks in the large MI group and normalized in the small MI group (control, 25.0; small MI, 26.4; large MI, 44.4 pM). Plasma renin activity was not elevated at either time. However, the change in ANP from 3 days to 6 weeks in the MI rats was negatively related to the change in PRA (r = .48, P = .016). Atrial natriuretic peptide levels early after MI may be a good predictor of infarct size. The pattern of ANP and PRA changing in opposite directions over time suggest a counterregulatory link between these two systems.

Differential regulation of natriuretic peptide receptor messenger RNAs during the development of cardiac hypertrophy in the rat

The heart expresses the three natriuretic peptide receptors (NPR), namely NPR-A, NPR-B, and NPR-C. We have examined the temporal relationship between the expression of mRNA transcripts for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and their receptors in the heart during the development of cardiac hypertrophy in the aortovenocaval fistula rat. Messenger RNAs were measured by cDNA amplification. Progressive cardiac hypertrophy was accompanied by increased ANP mRNA prevalence throughout the heart and increased BNP mRNA in the left atrium. The most striking observation was the gradual disappearance of NPR-C transcripts (the putative "clearance" receptor) in all chambers; this was in marked contrast to the increase in mRNA levels for NPR-A and NPR-B (the guanylyl cyclase-linked receptors). Our observations have important therapeutic implications if the transcript changes are mirrored at the receptor protein level because (a) the apparent down-regulation of NPR-C may enhance the local action of natriuretic peptides on the heart, and (b) the loss of NPR-C, particularly if it is widespread, may reduce the rate of elimination of the natriuretic peptides, restricting the therapeutic potential of specific NPR-C ligands designed to reduce peptide clearance.

Concurrent neutral endopeptidase and ACE inhibition in experimental heart failure: renal and hormonal effects

Neutral endopeptidase (NEP) inhibitors have been shown to strengthen the effects of endogenous atrial natriuretic peptide (ANP). It has been well documented that angiotensin I-converting enzyme (ACE) inhibitors act beneficially in chronic congestive heart failure (CHF). In the present study, renal and hormonal effects of SCH 34826, an orally active NEP inhibitor, were studied in a coronary-ligation model of experimental CHF in the rat. The effects were compared to those of captopril. The drugs were also administered in combination. In anaesthetized rats with CHF, SCH 34826 (90 mg kg-1 sc) elevated plasma ANP from 382 +/- 85 to 658 +/- 120 ng l-1 compared with vehicle (p = 0.002). In sham-operated control rats, plasma ANP also increased slightly from 52 +/- 6 to 70 +/- 9 ng l-1 (p = 0.05). Plasma renin activity did not change in either group. When given orally for 36 h (90 mg kg-1 b.i.d.), SCH 34826 enhanced natriuresis in controls but not in rats with CHF. Captopril (0.2 mg ml-1 in drinking water) enhanced natriuresis in CHF rats and both natriuresis and kaliuresis in controls. When SCH 34826 and captopril were combined, natriuresis was potentiated in control rats as compared with captopril alone; in rats with CHF, however, a brisk kaliuresis was seen. The excretion of cyclic guanosine monophosphate was enhanced in CHF rats by 52% during treatment with SCH 34826 but not with captopril or combination of the two drugs. Moreover, captopril suppressed aldosterone excretion both in CHF rats and controls when administered alone but not when combined with SCH 34826.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of atrial natriuretic factor in impaired sodium excretion of normocapnic and hypercapnic patients with chronic obstructive lung disease

To investigate the mechanisms of sodium retention in patients with chronic obstructive lung disease (COLD), we examined the renal and hormonal responses to volume expansion with isotonic saline and to infusion of atrial natriuretic factor (ANF) in 10 hypercapnic (PaCO2 52 +/- 2 mm Hg) and 12 normocapnic patients (PaCO2 39 +/- 1 mm Hg). Sodium excreted within 4 h of loading (expressed as % sodium load) was 23.5 +/- 2.5% (p < 0.05) in normocapnic and 8.5 +/- 1.5% (p < 0.001) in hypercapnic patients, compared with 32.5 +/- 3.0% in 11 age-matched control subjects. Sodium excretion and renal blood flow correlated negatively with arterial PCO2 and positively with FEV1. Basal plasma ANF concentrations were 72 +/- 5 pg/ml in controls, 100 +/- 14 pg/ml in normocapnic patients, and 230 +/- 52 pg/ml in hypercapnic patients (p < 0.001). Plasma renin activity and aldosterone did not differ between groups. In response to volume expansion, plasma ANF increased in both normocapnic and controls (with a greater increase in normocapnic patients) but remained unchanged in hypercapnic patients. Exogenous ANF increased glomerular filtration rate, renal plasma flow, natriuresis, and diuresis in both groups of patients. Patients with COLD have depressed renal function that appears unrelated to activation of the renin-angiotensin-aldosterone system. An increased secretory response of ANF to volume expansion may help to maintain volume homeostasis in normocapnic patients, while a blunted secretory response of ANF may contribute to sodium retention in hypercapnic patients.

Systemic and regional hemodynamic effects of perindopril in experimental heart failure

The effects of converting-enzyme inhibition by perindoprilat (0.5 mg/kg, intravenously, short-term administration) or perindopril (2 mg/kg, orally, long-term administration once a day for 21 days) on systemic and regional hemodynamics were studied on a new rat model of heart failure, which was induced by microembolization of coronary vessels by 15 microns plastic microspheres. Cardiac output and regional blood flows were measured by microsphere technique; the tone of the venous vessels was determined as mean circulatory filling pressure in conscious, freely moving rats. Perindoprilat evoked a much more prominent increase in kidneys, adrenal glands, intestine, and skin blood flows in embolized rats than in sham-operated rats. The differences between the effects of long-term treatment with perindopril in sham-operated and embolized rats were highly significant. Mean circulatory filling pressure was decreased by short-term and long-term administration of an angiotensin-converting enzyme inhibitor. It is concluded that venous vessels could be one of the target sites for the effects of perindopril-like drugs.

Chronic ethanol ingestion modifies the renin-aldosterone axis independent of alterations in the regulation of atrial natriuretic peptide

Using an animal model, we have investigated the effects of chronic ethanol ingestion on the regulation of atrial natriuretic peptide (ANP) synthesis and release. Male Sprague-Dawley rats were maintained for 6 weeks on a liquid diet of ethanol (up to 20% v/v) as part of a 2% solution of calf milk replacer. Weight-matched controls received an equal volume of ethanol-free solution, and normal animals drank ad libitum. All animals received rat chow throughout the experiment. This model produced physiologically relevant levels of blood ethanol, as concentrations at the time of sacrifice were 171.98 +/- 39.26 mg/dl. Plasma renin activity was significantly elevated in response to ethanol treatment, whereas circulating aldosterone concentration was reduced. No alterations in the plasma or atrial tissue levels of ANP were evident, although we did observe a significant increase in the ventricular tissue levels of ANP from 45.1 to 71.8 ng/g as a consequence of ethanol treatment. Levels of both atrial and ventricular ANP mRNA were not different between alcohol-treated and liquid-restricted control animals, although both groups showed significant increases in the amount of transcript in comparison with rats drinking ad libitum. No significant increases in either arterial blood pressure or heart/body weight ratio were observed for ethanol-treated rats. These results suggest that modifications in the renin-aldosterone axis can occur independently of alterations in the regulation of ANP under the influence of chronic ethanol ingestion.

Atrial natriuretic peptide and circadian blood pressure regulation: clues from a chronobiological approach

A critical review of the data available in the literature today permits a better understanding of the multiple actions of atrial natriuretic peptide (ANP) on the cardiovascular system. Moreover, the results of chronobiological studies suggest a role for this peptide in the determination of the circadian rhythm of blood pressure (BP). ANP can affect BP by several mechanisms, including modification of renal function and vascular tone, counteraction of the renin-angiotensin-aldosterone system, and action on brain regulatory sites. A series of interrelated events may follow from very small changes in the plasma levels of ANP. The endpoints are blood volume and BP reduction, but they are rapidly offset (mainly by reactive sympathetic activation) as soon as blood volume or pressure is threatened. The circadian rhythms of BP and ANP are antiphasic under normal conditions and in essential hypertension. The loss in the nocturnal decrease of BP is accompanied by a comparable loss in the nocturnal surge of ANP in hypertensive renal failure and hypotensive heart failure. In the latter condition, BP and ANP variabilities correlate significantly both before and after therapy-induced functional recovery, independently of the mean BP levels. Autonomic function modulates the secretion of ANP, which seems more apt to determine only transient changes in BP levels, as suggested by the short half-life of the peptide and the buffering role of its clearance receptors. There is now sufficient evidence that ANP contributes to short-term control over BP and electrolyte balance, in contrast and in opposition to the renin-angiotensin-aldosterone system, which is involved primarily in long-term BP control. By interfering with other well-established neurohormonal factors, ANP appears to be an additional modulator of the circadian rhythm of BP.

Ventricular remodeling after myocardial infarction. Experimental and clinical studies

Changes of ischemic myocardium following coronary occlusion, including active and passive functions, and adaptive changes of non-ischemic surviving myocardium have been summarized under the term "left ventricular remodeling" post myocardial infarction. An increase in left ventricular volume may be a consequence, and associated with an adverse prognosis. Although left ventricular dilatation may increase stroke volume and, thus, be compensatory at first, in about one-fifth of patients it ultimately results in progressive dysfunction and heart failure. Major determinants of this process are time, infarct size, infarct location, global left ventricular function assessed 4 days after infarction by radionuclide ejection fraction and right heart catheter (stroke volume), and morphology of the infarct-associated coronary artery. The surviving myocardium hypertrophies and may also dilate structurally. Depression of left ventricular ejection fraction chronically after the infarct is due to deterioration of wall motion of chamber segments initially classified normal by radionuclide analysis. Biochemical changes may also occur, including reduction of phosphocreatine, prolongation of time to peak Cai2+, and changes in myosin isoforms. Systemic or local humoral factors may be involved in these changes, however, clear evidence is still lacking. Perfusion of surviving myocardium may be altered under various conditions due to morphologic and functional changes of coronary vasculature. Successful prevention of heart failure and death by angiotensin converting enzyme inhibitors in asymptomatic patients with left ventricular dysfunction post-myocardial infarction has supported the pathophysiologic concepts of remodeling.

Changes in plasma atrial natriuretic peptide concentration during heart transplantation

Examination of changes in plasma atrial natriuretic peptide (ANP) concentrations during heart transplantation may provide important information about factors influencing plasma ANP in patients with severe heart failure. Serial changes in plasma ANP during heart transplantation, and atrial content of ANP in native and donor atria, were measured in 12 patients. Preoperative plasma ANP was elevated in all patients (387 +/- 77 pg/mL), whereas atrial content of ANP in native atria was reduced (0.36 +/- 0.082 micrograms/mg protein). Preoperative plasma ANP did not correlate with hemodynamics, but was negatively correlated with creatinine clearance (r = -0.76, P < .01). Intraoperative plasma ANP prior to transplantation was strongly correlated with intraoperative plasma ANP after transplantation (r = 0.84, P < .001). Although postoperative plasma ANP was reduced from preoperative plasma ANP by 75%, these two measurements were also significantly correlated (r = 0.70, P < .02). Postoperative plasma ANP was not correlated with hemodynamics, but was negatively correlated with both creatinine clearance (r = -0.65, P < .05) and content of ANP in the native atria (r = -0.75, P < .01). Multiple linear regression analysis suggested that up to 85% of the variability of early postoperative plasma ANP could be accounted for by the variability in these latter two parameters. The decrease in native atrial ANP content, in the context of elevated plasma ANP concentration, is consistent with prior animal studies suggesting that severe heart failure induces cellular adaptations favoring accelerated ANP synthesis and secretion (with resultant reduction in tissue content).(ABSTRACT TRUNCATED AT 250 WORDS)

Diminished release of atrial natriuretic factor in calves with a total artificial heart

Venous hypertension after total artificial heart (TAH) replacement, a common problem in humans as well as experimental animals, is thought to be related to reduced release of atrial natriuretic factor (ANF) due to atrial damage. To verify this hypothesis, we stimulated the release of ANF in 6 calves before (-7 days) and after TAH replacement (+25, +50, +80, and +100 days) by the rapid (+ = 10 min) infusion of 2 L of Ringer's solution. In normal calves (-7 days) this procedure induced a rise in plasma concentration of ANF from 18.5 +/- 12 to 31.6 +/- 12 pmol/L (p < 0.05). After TAH the ANF release continuously decreased (analysis of variance, p < 0.02). Thus, ANF increased by 9.8 +/- 9.3, 6.8 +/- 17.5, 0.4 +/- 5.2, and 0.5 +/- 3.2 pmol/L at days 25, 50, 80, and 100, respectively. The central venous pressure increased by 3.4 +/- 1.5 mm Hg (before TAH) and by 6 +/- 2.9 mm Hg (after TAH) during this procedure. A decrease in plasma concentrations of aldosterone, most likely due to extracellular volume expansion and a decrease in total protein plasma concentrations and in hematocrit due to the dilution of blood, was seen in each experiment. Necropsy demonstrated massive atrial dilatation and myocardial dystrophy with atrial fibrosis. ANF granules were present to a small extent in every calf. We conclude that rapid intravenous infusion is an adequate stimulus to release ANF in normal calves. After TAH implantation the release of ANF by high venous pressure declines although ANF granules are still present in the damaged atrial stumps. Therefore, the loss of stimulated ANF could contribute to the observed increase in venous pressure in TAH calves although other pathophysiologic mechanisms cannot be excluded.

Plasma concentration of atrial natriuretic peptide at admission and risk of cardiac death in patients with acute myocardial infarction

OBJECTIVE

To compare the concentration of plasma atrial natriuretic peptide in patients with acute myocardial infarction with a healthy population and to determine whether a raised concentration of plasma atrial natriuretic peptide at admission was a predictor of mortality after acute myocardial infarction.

DESIGN

Patients with acute myocardial infarction were divided into a group with no congestion (class I) and a group with congestion (class II-IV) according to their highest Killip classification in the first 24 hours after infarction. The concentration of plasma atrial natriuretic peptide was measured at admission. On the basis of the concentration of atrial natriuretic peptide measured in the healthy population, patients were separated into two groups: a group with a high (greater than 200 pg/ml) and a group with a low concentration of atrial natriuretic peptide (less than or equal to 200 pg/ml). The patients were followed for three years.

PATIENTS

55 patients admitted to the coronary care unit within 12 hours of the appearance of symptoms of acute myocardial infarction were compared with 51 healthy individuals.

MAIN OUTCOME MEASURES

Plasma atrial natriuretic peptide, Killip class, mortality.

RESULTS

The patients had significantly higher concentrations of atrial natriuretic peptide than the healthy controls. Furthermore, patients with congestion had a significantly higher concentration of atrial natriuretic peptide than the uncongested group of patients. Total mortality was 34.5%. In the group with a low concentration of atrial natriuretic peptide the mortality was only 13.6%, whereas mortality was significantly higher (48.5%) in the group with a high concentration.

CONCLUSIONS

The measurement of atrial natriuretic peptide separated the patients into low and high risk groups after acute myocardial infarction.

Signaling mechanisms for the activation of an embryonic gene program during the hypertrophy of cardiac ventricular muscle

To study the signaling mechanisms which mediate ventricular hypertrophy, we utilized the induction of the ANF gene as a marker of the hypertrophic response. The induction of the atrial natriuretic factor gene (ANF) is one of the most conserved features of ventricular hypertrophy, occurring in multiple species (mouse, rat, hamster, canine, and human) in response to diverse stimuli (hormonal, mechanical, pressure/volume overload, genetic, IHSS, hypertension, etc.). The ANF gene is expressed in both the atrial and ventricular compartments during embryonic development, but shortly after birth ANF expression is down-regulated to negligible levels in the adult myocardium. Since the reactivation of ANF gene expression in the hypertrophied ventricle is a hallmark of the activation of an embryonic gene program, it has also become of interest to determine if similar mechanisms activate ANF expression during hypertrophy and the initial stages of cardiogenesis. A combination of cotransfection, microinjection, and transgenic approaches has been coupled to well characterized cultured cell systems and in vivo murine models employing normal and transgenic mice. The microinjection of oncogenic RAS proteins into living myocardial cells does not lead to the activation of cell proliferation, but activates ANF gene expression, as assessed by immunofluorescence. Co-transfection of mutant and wild-type RAS expression vectors with a ANF-luciferase fusion gene supports a direct effect of activated RAS on ANF gene transcription. Co-transfection of a dominant negative RAS vector effectively inhibits the induction of the ANF gene during alpha adrenergic mediated hypertrophy of ventricular muscle cells, thereby establishing that a RAS-mediated pathway is required for ANF induction.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired response of atrial natriuretic factor to blood volume expansion in acute right ventricular infarction

To assess the role of atrial natriuretic factor (ANF) in right ventricular (RV) infarction, 30 patients with inferior wall acute myocardial infarction (15 with RV involvement) and normal left heart filling pressures were studied 39 +/- 12 hours after the onset of symptoms. Serial measurements of cardiac output, right atrial, pulmonary artery and pulmonary wedge pressures, as well as plasma ANF, plasma renin activity, plasma aldosterone and vasopressin were obtained before and 30 minutes after acute volume expansion to raise wedge pressure greater than or equal to 20 mm Hg. Baseline mean right atrial pressure and plasma ANF levels were greater in patients with than without RV infarction (8 +/- 3 vs 5 +/- 2 mm Hg; p less than 0.0001, and 4.6 +/- 2.9 vs 2.7 +/- 1.5 fmol/ml; p less than 0.05, respectively). There were no differences in other baseline hemodynamic or humoral parameters between both groups. After volume expansion, pulmonary wedge pressure was similar in both groups, but right atrial pressure increased to higher levels in patients with RV infarction (19 +/- 2 vs 14 +/- 2 mm Hg; p less than 0.0001). Despite this greater stimulus for ANF secretion, the increase in plasma ANF was less pronounced in patients with RV infarction (63 +/- 81 vs 455 +/- 417%; p less than 0.002), especially among those with paroxysmal supraventricular tachyarrhythmias. Thus, despite higher baseline plasma levels of ANF, response to volume loading is markedly attenuated in patients with RV infarction complicating an inferior wall acute myocardial infarction.

Enhanced cardiac angiotensinogen gene expression and angiotensin converting enzyme activity in tachypacing-induced heart failure in rats

The aim of the study was to analyze changes in myocardial angiotensinogen gene expression and myocardial angiotensin converting enzyme activity in slowly progressing low-output failure. In adult, male Wistar rats, acute ventricular tachypacing by 610 to 620 impulses per minute lowered end-diastolic external diameter of the left ventricle by 2.6% (p less than 0.01), but did not lower cardiac output or abolish coronary reserve, since left-ventricular subendocardial blood flow of paced rats increased under dipyridamole (2 mg/kg i.v.) by 56% (p less than 0.01). Systemic neuroendocrine activation and ventricular dilation without enlargement of ventricular mass developed subsequent to chronic tachypacing, but left-ventricular diameter during pacing never exceeded the value of sham rats on sinus rhythm. After 2 weeks, cardiac output was lowered by 14% (p less than 0.001), cardiopulmonary blood volume was elevated by 30% (p less than 0.001), and angiotensinogen mRNA and angiotensin converting enzyme activity in ventricular myocardium were doubled. We conclude that conditions for an enhanced intracardiac angiotensin II-formation developed in tachypacing-induced heart failure, but that enhanced systolic wall stress or myocardial ischemia are not required for this activation of the local cardiac renin-angiotensin system.

Prolonged neutral endopeptidase inhibition in heart failure

We studied the hormonal, renal and hemodynamic effects of prolonged treatment with SCH 39370, a new neutral endopeptidase (NEP) inhibitor, in experimental congestive heart failure (CHF). Coronary-ligated CHF rats and sham-operated controls received vehicle or SCH 39370 30 mg/kg s.c. twice daily for six days. In rats with heart failure, SCH 39370 elevated the high plasma atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) levels 2-fold both initially and at the end of the experiment. Initially, water balance was more negative in SCH 39370-treated CHF rats than in those treated with vehicle. In all SCH 39370-treated rats, ANP, cGMP and electrolyte excretion and diuresis were pronounced for 6 h after injection but attenuated thereafter. Blood pressure and pulse remained unchanged. On reverse phase high performance liquid chromatography (HPLC), ANP-(99-126) appeared to be the only circulating form of ANP in rats with heart failure. Three forms have been discovered in patients with heart failure. HPLC revealed only intact ANP in plasma of rats with heart failure during SCH 39370 treatment. NEP inhibitors may provide a new tool for treating chronic heart failure.

Atrial natriuretic peptide response to cardioversion of atrial flutter and fibrillation and role of associated heart failure

Plasma atrial natriuretic peptide (ANP) concentrations were measured before and 1 hour after cardioversion in 40 patients (27 with atrial flutter and 13 with atrial fibrillation) admitted for elective cardioversion. Fourteen (11 with atrial flutter and 3 with atrial fibrillation) had clinical evidence of congestive heart failure (CHF). Conversion to sinus rhythm was successful in 39 patients. The mean ANP concentration in the entire group decreased after cardioversion from 38 +/- 4 to 17 +/- 2 pmol/liter (p less than 0.001). In the subgroup with CHF, the ANP level, which was not significantly higher than that in the group without CHF, decreased from 47 +/- 8 to 19 +/- 3 pmol/liter (p less than 0.01). Neither mode of cardioversion (spontaneous 1, pharmacologic 2 and direct-current countershock 36) nor associated CHF influenced ANP response to cardioversion. One patient with atrial flutter and "failed cardioversion" had unchanged ANP level. The decrease after cardioversion in ANP concentration correlated with its control level (r = 0.88, p less than 0.001) but not with the decrease in heart rate. The ANP level in patients with atrial fibrillation was 45 +/- 9 vs 38 +/- 5 pmol/liter in those with atrial flutter (difference not significant). Arrhythmia duration, left atrial size, and ventricular rate or arterial blood pressure did not correlate with ANP concentration in any subgroup. It is concluded that (1) the ANP level is elevated comparably in patients with both atrial flutter and fibrillation regardless of the presence or absence of CHF; and (2) the level decreases, independent of the mode of cardioversion or presence of CHF, promptly after successful cardioversion.

Consistent changes in the circadian rhythms of blood pressure and atrial natriuretic peptide in congestive heart failure

We demonstrated in previous works that the circadian rhythms of blood pressure (BP) and atrial natriuretic peptide (ANP) are antiphasic in normal subjects and in essential hypertension. The aim of the present study was to assess the circadian rhythms of BP and ANP in 20 patients with stable congestive heart failure (CHF), divided into two groups of 10 according to their New York Heart Association functional class. A matched control group of 10 normal volunteers was also studied. Noninvasive BP monitoring at 15-min intervals was performed for 24 h. Peripheral blood samples were also obtained at 4-h intervals starting from 08:00 h. The mean (+/- SEM) circadian mesors of ANP plasma levels were 13.4 +/- 1.7 pmol/L in the control group, 28.6 +/- 2.4 pmol/L in the group of 10 patients in class II, and 81.5 +/- 12 pmol/L in the group of 10 patients in class III-IV. In normal subjects, plasma ANP concentration was highest at 04:00 h (21.5 +/- 2.7 pmol/L) and lowest at 16:00 h (8.8 +/- 2.4 pmol/L; p less than 0.01). Both groups of patients with CHF showed no significant circadian change in the plasma levels of ANP and also a significantly blunted circadian rhythm of BP. Cosinor analysis confirmed the loss of the circadian rhythms of ANP and BP in CHF patients. Our findings support the existence of a causal relationship between the circadian rhythms of ANP and BP.