Atrial Natriuretic Factor mRNA Levels Research Articles

NLRP3 inhibition improves heart function in GPER knockout mice

The molecular mechanisms of postmenopausal heart diseases in women may involve the loss of estrogen-deactivation of its membrane receptor, G-protein coupled estrogen receptor (GPER), and subsequent activation of the cardiac NLRP3 inflammasome, a component of the innate immune system. To study the potential effects of cardiac GPER on NLRP3-mediated inflammatory pathways, we characterized changes in innate immunity gene transcripts in hearts from 6-month-old cardiomyocyte-specific GPER knockout (KO) mice and their GPER-intact wild type (WT) littermates using RT2 Profiler™ real-time PCR array. GPER deletion in cardiomyocytes decreased %fractional shortening (%FS) and myocardial relaxation (e′), and increased the early mitral inflow filling velocity-to-early mitral annular descent velocity ratio (E/e′), determined by echocardiography, and increased the mRNA levels of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP), determined by real-time PCR. Of the 84 inflammasome-related genes tested, 9 genes were upregulated, including NLRP3 and IL-18, while 1 gene, IL-12a, was downregulated in GPER KO when compared to WT. The importance of NLRP3 upregulation in GPER KO-induced heart failure was further confirmed by an in vivo study showing that, compared to vehicle-treated KO mice, 8 weeks of treatment with a NLRP3 inhibitor, MCC950 (10 mg/kg, i.p., 3 times per week), significantly limited hypertrophic remodeling, defined by reductions in heart weight/body weight, and improved systolic and diastolic functional indices, including increases in %FS and e′, and decreases E/e′ (P < 0.05). Both ANF and BNP mRNA levels were also significantly reduced by chronic MCC950 treatment. The findings from this study point toward a new understanding for the increased occurrence of heart diseases in women following loss or absence of estrogenic protection and GPER activation that involves cardiac NLRP3 inflammatory pathways.

NF‐қB Activation is Required for Thyroid Hormone Induced Cardiomyocyte Hypertrophy

The nuclear factor NF‐қB promotes inflammatory response and mediates cardiac growth by different hypertrophic stimuli. We have previous results obtained by microarray experiments indicating that thyroid hormone (triiodotyronine, T3) up‐regulates pro‐inflammatory genes. Considering that, we investigated the influence of T3 on NF‐қB signaling and the possible participation of this nuclear factor in cardiomyocyte hypertrophy induced by T3. Primary cultures of neonatal rat ventricular cardiomyocytes were treated with T3 for 10, 30 minutes and 24 hours and the NF‐қB signaling was analyzed by western blot. Also, cardiomyocytes were treated with an inhibitor of NF‐қB (JSH‐23) followed by treatment with T3 for evaluation of mRNA expression of atrial natriuretic factor (ANF) and cell surface area analysis. Data were presented as mean ± SD and were analyzed using one‐way ANOVA and Tukey multiple comparisons test. Values of p&lt;0.05 were considered statistically significant. T3 rapidly increased the nuclear protein expression of NF‐қB without alterations on IKK and IқB expression. The inhibition of NF‐қB reduced both ANF mRNA levels and the surface area of cardiomyocytes compared to T3 treated cells. These results confirm that NF‐қB is required for development of cardiomyocyte hypertrophy by T3. The possible interactions of NF‐қB with genes associated with cardiac growth are being investigated. Financial support: Fapesp (2013/22480‐4 and 2011/23352‐4).

Activation of GPR30 attenuates diastolic dysfunction and left ventricle remodelling in oophorectomized mRen2.Lewis rats

GPR30 is a novel oestrogen receptor expressed in various tissues, including the heart. We determined the role of GPR30 in the maintenance of left ventricular (LV) structure and diastolic function after the surgical loss of ovarian hormones in the female mRen2.Lewis rat, a model emulating the cardiac phenotype of the post-menopausal woman. Bilateral oophorectomy (OVX) or sham surgery was performed in study rats; the selective GPR30 agonist, G-1 (50 µg/kg/day), or vehicle was given subcutaneously to OVX rats from 13-15 weeks of age. Similar to the cardiac phenotype of sham rats, G-1 preserved diastolic function and structure relative to vehicle-treated OVX littermates independent of changes in blood pressure. G-1 limited the OVX-induced increase in LV filling pressure, LV mass, wall thickness, interstitial collagen deposition, atrial natriuretic factor and brain natriuretic peptide mRNA levels, and cardiac NAD(P)H oxidase 4 (NOX4) expression. In vitro studies showed that G-1 inhibited angiotensin II-induced hypertrophy in H9c2 cardiomyocytes, evidenced by reductions in cell size, protein content per cell, and atrial natriuretic factor mRNA levels. The GPR30 antagonist, G15, inhibited the protective effects of both oestradiol and G-1 on this hypertrophy. These data show that the GPR30 agonist G-1 mitigates the adverse effects of oestrogen loss on LV remodelling and the development of diastolic dysfunction in the study rats. This expands our knowledge of the sex-specific mechanisms underlying diastolic dysfunction and provides a potential therapeutic target for reducing the progression of this cardiovascular disease process in post-menopausal women.

Induction of Mitogen-Activated Protein Kinases Is Proportional to the Amount of Pressure Overload

Pressure overload has been shown to induce mitogen activated protein kinases (MAPKs) and reactivate the atrial natriuretic factor in the heart. To test the sensitivity of these signals to pressure overload, we assayed the activity of MAPKs extracellular signal-regulated kinase, c-Jun N-terminal kinase 1, and p38 in protein lysates from the left ventricle (LV) or white blood cells (WBC) isolated from aortic banded mice with varying levels of pressure overload. In separated mice we measured atrial natriuretic factor mRNA levels by Northern blotting. As expected, a significant induction of atrial natriuretic factor mRNA levels was observed after aortic banding, and it significantly correlated with the trans-stenotic systolic pressure gradient but not with the LV weight:body weight ratio. In contrast, a significant correlation with systolic pressure gradient or LV weight:body weight ratio was observed for all of the MAPK activity detected in LV samples or WBCs. Importantly, LV activation of MAPKs significantly correlated with their activation in WBCs from the same animal. To test whether MAPK activation in WBCs might reflect uncontrolled blood pressure levels in humans, we assayed extracellular signal-regulated kinase, c-Jun N-terminal kinase 1, and p38 activation in WBCs isolated from normotensive volunteers, hypertensive patients with controlled blood pressure values, or hypertensive patients with uncontrolled blood pressure values. Interestingly, in hypertensive patients with controlled blood pressure values, LV mass and extracellular signal-regulated kinase phosphorylation were significantly reduced compared with those in hypertensive patients with uncontrolled blood pressure values. These results suggest that MAPKs are sensors of pressure overload and that extracellular signal-regulated kinase activation in WBCs might be used as a novel surrogate biomarker of uncontrolled human hypertension.

Mitogen-Activated Protein Kinases as Biomarkers of Hypertension or Cardiac Pressure Overload

In hypertension, left ventricular hypertrophy is initially a useful compensatory process that represents an adaptation to increased ventricular wall stress. It is also one of the first steps toward overt clinical disease. Several changes in myocardial structure characterize hypertensive or pressure-overload heart disease that induces myocardial remodeling (eg, enhanced cardiomyocyte growth, excessive cardiomyocyte necrosis/apoptosis, accumulation of interstitial and perivascular collagen fibers, or disruption of the endomysial and perimysial collagen network).1 In the long term, these cellular changes, if untreated, will deteriorate left ventricular function and facilitate the development of heart failure. The growth and survival of adult cardiomyocytes, smooth muscle cells, and macrophages are regulated by extracellular ligands, growth factors, and cytokines that bind to cell-surface receptors and activate intracellular signal transduction cascades. These signaling pathways control essential processes in all eukaryotic cells, including gene transcription, protein translation, cytoskeletal remodeling, endocytosis, cell metabolism, cell proliferation, and survival.2 One of the best-described signal transmission systems activated by pressure overload involves multiple cascades of protein phosphorylation by the mitogen activated protein kinase (MAPK) family, with diverse roles in a broad range of physiological functions.3 The MAPK signaling pathway sequences ultimately result in the dual phosphorylation and activation of terminal kinases, such as p38, c-Jun N-terminal kinases (JNKs), and extracellular signal-regulated kinases (ERK1/2 and ERK5), which are involved in different cellular responses, including pressure-overload–induced cardiac hypertrophy.4 MAPK cascades are triple-kinase pathways that include an MAPK kinase kinase, an MAPK kinase, and a terminal MAPK. MAPK cascades may be …

Selective upregulation of cardiac brain natriuretic peptide at the transcriptional and translational levels by pro-inflammatory cytokines and by conditioned medium derived from mixed lymphocyte reactions via p38 MAP kinase

An increase in circulating brain natriuretic peptide (BNP) but not atrial natriuretic factor (ANF) is observed coincident with cardiac allograft rejection that is reversed upon treatment with anti-lymphocyte therapy suggesting that pro-inflammatory cytokines may uniquely modulate BNP gene expression and secretion. This study tested pro-inflammatory cytokines or conditioned medium (CM) derived from mixed– lymphocyte reaction (MLR) cultures in their ability to modulate ANF or BNP mRNA expression, secretion, as well as BNP promoter activity in cultured neonatal rat cardiocytes. IL-1β and TNF-α elicited a significant dose- and time-dependent increase in BNP mRNA, and secretion, whereas, ANF mRNA levels and secretion did not change. IL-1β and TNF-α rapidly increased phosphorylated p38 MAP kinase abundance and activity. Inhibition of p38 MAP kinase with SB203580 abolished IL-1β- and TNF-α-stimulated increase in BNP mRNA, promoter activity and secretion. MLR-CM in 20%, 50% and 100% proportions increased BNP but not ANF secretion. The MLR-induced increases in BNP secretion were completely abolished by SB203580 pre-treatment. These investigations show that exposure of cultured rat cardiocytes to specific pro-inflammatory cytokines as well as MLR-CM results in the only known instance of upregulation of cardiac BNP at the transcriptional and translational levels without a corresponding increase in ANF gene expression. Furthermore, these effects are dependent on signaling by p38 MAP kinase. In all, the findings reveal a unique dis-coordinated expression of BNP and ANF to inflammatory cytokines and offers an opportunity to better understand the differential regulation of these two cardiac-derived endocrine hormones that share receptors as well as biological properties.

Left ventricular unloading alters receptor tyrosine kinase expression in the failing human heart

Background: Experimental and clinical data suggest that the loss of membrane receptor tyrosine kinase (RTK) activity in cardiac myocytes results in increased frequency of apoptotic cell death and progression of heart failure. The goal of our study was to examine the expression characteristics of RTKs in ventricular myocardium obtained from patients before and after mechanical unloading. Methods: We extracted RNA from paired formalin-fixed, paraffin-embedded left ventricular tissue blocks obtained at the time of left ventricular assist device (LVAD) implantation and explantation from a cohort of 36 patients (median age 51 years). The duration of LVAD support ranged from 1 to 314 days (median 95 days), 17 patients had ischemic and 19 non-ischemic cardiomyopathy at the time of LVAD implantation. Using real-time reverse transcription–polymerase chain reaction (RT-PCR) we quantitated transcripts for atrial natriuretic factor (ANF) and tumor necrosis factor-alpha (TNF-α), markers of heart failure, and the RTKs Her2/neu, Her4 and gp130, regulators of cardiac cell survival. Results: In patients undergoing mechanical unloading, ANF and TNF-α mRNA levels were independently suppressed. Her2/neu, along with Her4 was upregulated, mostly in cases of ischemic cardiomyopathy, whereas gp130 levels decreased. Post-LVAD transcript levels of Her2 correlated tightly with gp130 in patients with non-pathologic entry values of gp130. Duration of treatment and age were also determining factors in the change of expression of these genes. Conclusion: Real-time quantitative (Q)-RT-PCR can be used to quantitate gene expression in archival myocardial tissue blocks. Mechanical unloading leads to a re-adjustment of RTK transcript levels, but not their reverting to control values in heart failure patients.

GENETIC VARIABILITY IN FORCED AND VOLUNTARY ENDURANCE EXERCISE PERFORMANCE IN SEVEN INBRED MOUSE STRAINS

PURPOSE: The goal of this study was to characterize the genetic contribution to both forced and voluntary exercise performance and to determine whether performance in these two paradigms is controlled by similar genetic influences. METHODS: Seven inbred mouse strains (Balbc/ByJ, C3H/HeJ, C57BL/6J, DBA/1J, DBA/2J, FVB/NJ, and SW) were assessed for treadmill exercise performance and voluntary wheel performance. Expression of two molecular markers of cardiac hypertrophy (beta myosin heavy chain (β-MyHC) and atrial natriuretic factor (ANF)) was determined for all strains. Cardiac function was assessed via echocardiography and isolated work-performing heart preparations. RESULTS: There were marked strain differences in treadmill exercise performance, with SW and FVB/NJ mice showing elevated performance and C57BL/6J animals showing decreased performance compared to all other strains. Analysis of voluntary free-wheel performance also showed significant strain differences, with SW and C57BL/6J animals showing increased voluntary wheel activity compared to all other strains and DBA/1J animals showing decreased performance compared to all other strains. There was no correlation between treadmill performance and voluntary free-wheel performance. For treadmill and voluntary wheel performance, two estimates of heritability in the broad-sense, the intraclass correlation (rI) and the coefficient of genetic determination (g2) ranged from rI = 0.38 and g2 = 0.24 (average speed on the voluntary wheel) to rI = 0.90 and g2 = 0.82 (treadmill endurance test). DBA/1J and SW mice exhibited significantly greater cardiac contractility than all other analyzed strains while Balbc/ByJ mice exhibited significantly reduced cardiac contractility compared to all other strains. ANF and β-MyHC mRNA levels were significantly elevated in the DBA/2J myocardium compared to all other analyzed strains. CONCLUSIONS: The inbred mouse strains analyzed demonstrate markedly distinct endurance exercise capacities for both treadmill-based and voluntary wheel-based exercise paradigms. For the strains analyzed, treadmill performance did not predict voluntary wheel performance, and there was no correlation across strains between the relative performances for these two distinct exercise paradigms. There were significant strain differences for cardiac gene expression and cardiac function, but there was no significant correlation between any of these measures and either forced or voluntary exercise performance.

Demonstration of Direct Effects of Growth Hormone on Neonatal Cardiomyocytes

The cellular and molecular basis of growth hormone (GH) actions on the heart remain poorly defined, and it is unclear whether GH effects on the myocardium are direct or mediated at least in part via insulin-like growth factor (IGF-1). Here, we demonstrate that the cultured neonatal cardiomyocyte is not an appropriate model to study the effects of GH because of artifactual loss of GH receptors (GHRs). To circumvent this problem, rat neonatal cardiomyocytes were infected with a recombinant adenovirus expressing the murine GHR. Functional integrity of GHR was suggested by GH-induced activation of the cognate JAK2/STAT5, MAPK, and Akt intracellular pathways in the cells expressing GHR. Although exposure to GH resulted in a significant increase in the size of the cardiomyocyte and increased expression of c-fos, myosin light chain 2, and skeletal alpha-actin mRNAs, there were no significant changes in IGF-1 or atrial natriuretic factor mRNA levels in response to GH stimulation. In this model, GH increased incorporation of leucine, uptake of palmitic acid, and abundance of fatty acid transport protein mRNA. In contrast, GH decreased uptake of 2-deoxy-d-glucose and levels of Glut1 protein. Thus, in isolated rat neonatal cardiomyocytes expressing GHR, GH induces hypertrophy and causes alterations in cellular metabolic profile in the absence of demonstrable changes in IGF-1 mRNA, suggesting that these effects may be independent of IGF-1.

Cardiovascular effects of combination of perindopril, candesartan, and amlodipine in hypertensive rats.

The combination therapy with ACE inhibitors, angiotensin II type 1 (AT(1)) receptor antagonists, or calcium channel antagonists may exert more beneficial effects on cardiovascular diseases than monotherapy. Perindopril, candesartan cilexetil, or amlodipine alone or the combination of low doses of each agent was administered orally to stroke-prone spontaneously hypertensive rats (SHRSP) for 4 weeks to compare the hypotensive or cardiovascular effects. Although perindopril (2 mg/kg), candesartan cilexetil (2 mg/kg), or amlodipine (3 mg/kg) alone caused comparable hypotensive effects in SHRSP, monotherapy with perindopril or candesartan decreased left ventricular (LV) weight; mRNA levels for atrial natriuretic factor, skeletal alpha-actin, and collagen types I and III; and aortic weight and platelet-derived growth factor-beta receptor tyrosine phosphorylation to a greater extent than monotherapy with amlodipine. Although monotherapy with a low dose (0.2 mg/kg) of perindopril or candesartan cilexetil did not significantly reduce the LV mRNA levels and aortic platelet-derived growth factor-beta receptor phosphorylation of the SHRSP, combination therapy at such a low dose normalized these parameters more potently than the use of amlodipine (3 mg/kg) alone. Although perindopril or candesartan cilexetil alone at 0.05 mg/kg did not decrease the blood pressure of the SHRSP, such a low dose of combination therapy decreased LV weight and atrial natriuretic factor mRNA levels of the SHRSP to a greater extent than amlodipine alone or amlodipine combined with perindopril or candesartan cilexetil. Our results provide evidence that suggests the combination of an ACE inhibitor and an AT(1) receptor antagonist may be more effective in the treatment of cardiac and vascular diseases than the combination of a calcium channel blocker with an ACE inhibitor or an AT(1) receptor antagonist or monotherapy with each agent.

A rapid procedure for the quantitation of natriuretic peptide RNAs by competitive RT-PCR in congenital heart defects.

We report an original application of quantitative reverse transcription-polymerase chain reaction (Q.RT-PCR) for the evaluation of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP) and beta-actin mRNA in small atrial samples (10-15 mg). A fixed amount of total RNA was simultaneously reverse transcribed and amplified with dilutions of a competitor RNA fragment used as a control. We constructed a single synthetic RNA competitor for ANF, BNP and beta-actin. The competitors and targets shared the same primer sequences but yielded PCR products of different sizes. We have investigated ANF, BNP and beta-actin gene expression in patients affected by congenital heart defects (CHD) during the surgical correction of the defect. We collected a right atrial sample from each patient before the start of cardiopulmonary bypass. We studied 14 patients affected by tetralogy of fallot (no. 6), complex CHD (no. 4), and ventricular septal defect (no. 4). The results indicate that the Q.RT-PCR represents a simple, highly specific, non radioactive procedure for the quantification of natriuretic peptide gene expression and is particularly suitable for evaluation of gene expression in small myocardial samples. Our data also suggest that: 1) there is a significant relationship between the levels of ANF, BNP and beta-actin mRNA and the type of CHD; 2) the levels of BNP mRNA are more variable than ANF; 3) the beta-actin seems to be unsuitable for normalising cardiac gene expression in CHD because mRNA basal levels of this protein vary greatly among patients with different type of CHD.

Variable renal atrial natriuretic factor gene expression in hypertension.

We have previously established the existence of atrial natriuretic factor (ANF) gene expression within the renal parenchyma. Neither the role nor the regulation of this extracardiac source of ANF is clearly defined. To determine whether renal ANF gene expression, similar to cardiac expression, is linked to the activity of the renin-angiotensin system (RAS), we compared renal ANF gene expression in rats after suprarenal aortic banding, a hypertension model associated with activation of RAS, and in the deoxycorticosterone acetate (DOCA)-salt model, which is characterized by depression of RAS. Renal ANF mRNA was measured with a quantitative competitive reverse transcription polymerase chain reaction method. DOCA-salt hypertension significantly reduced the expression of renal ANF. In contrast, aortic banding significantly increased renal ANF expression. In both cases, ANF gene expression in the heart increased. Ramipril treatment at 10 micrograms/kg of aortic-banded rats, a treatment that specifically affects local RAS but maintains hypertension, normalized renal ANF mRNA levels. Altogether, these results suggest that renal ANF gene expression is modulated by local RAS and is independent of circulating RAS and hypertension per se. The marked decrease of renal ANF mRNA in DOCA-salt hypertension suggests a pathogenic role for renal ANF gene downregulation by decreasing the sodium excretory mechanism mediated by the local expression of ANF acting on receptors found in the inner medullary collecting ducts. In aortic banding, renal ANF gene expression upregulation suggests a local compensatory function consistent with the consensus role of natriuretic peptides in the modulation of RAS, thus ameliorating the sodium-retaining effects of renal underperfusion.

Regulation of aortic atrial natriuretic factor and angiotensinogen in experimental hypertension.

We investigated the relation between atrial natriuretic factor (ANF) gene expression and the status of the renin-angiotensin system (RAS) in aortic tissue in rats made hypertensive by either aortic banding or by deoxycorticosterone acetate (DOCA)-salt administration. These experimental models of hypertension are known to have differences in terms of the status of RAS. ANF messenger RNA (mRNA) levels were measured in aortic tissue by using a newly developed quantitative competitive reverse transcription polymerase chain reaction (QC-RT-PCR) technique. Changes in the proportions of alpha1 and alpha2 isoforms of Na+K+-adenosine triphosphatase (ATPase) mRNA levels were used as indicators of aortic hypertrophy. Treatment with DOCA alone, salt alone, or DOCA-salt for 5 weeks increased aortic-weight/body-weight ratio and aortic angiotensinogen mRNA levels, but did not change alpha1 or alpha2 Na+K+-ATPase mRNA levels. Aortic ANF mRNA levels had a tendency to increase after treatment with DOCA, salt, or DOCA-salt, but this change did not reach statistical significance. Suprarenal aortic banding for 6 weeks or 12 weeks increased aortic-weight/body-weight ratio (12 weeks), decreased alpha2 Na+K+-ATPase and angiotensinogen mRNA levels, but did not affect alpha1 Na+K+-ATPase mRNA levels or ANF mRNA levels. Treatment with ramipril, an angiotensin-converting enzyme (ACE) inhibitor was carried out for 6 weeks just after aortic banding (prevention experiment) or after 6 weeks in rats that were banded for the previous 6 weeks (regression experiment). High-dose ramipril (1 mg/kg)--a treatment known to inhibit both tissue and circulating RAS--normalized aortic-weight/body-weight ratio, and also normalized alpha2 Na+K+-ATPase mRNA levels. Aortic angiotensinogen mRNA levels of banded rats treated with high-dose ramipril was higher than those of the normal control, sham operated, and banded rats. Treatment with high-dose ramipril did not affect alpha1 Na+K+-ATPase mRNA levels or ANF mRNA levels. Low-dose ramipril (10 microg/kg)--a treatment that selectively inhibits tissue RAS--normalized aortic-weight/body-weight ratio but did not normalize alpha2 Na+K+-ATPase mRNA levels (regression experiment) or angiotensinogen mRNA levels (prevention experiment) and did not change either alpha1 Na+K+-ATPase mRNA levels or ANF mRNA levels. The results suggest that, in contrast to previous findings in heart and kidney, the regulation of ANF mRNA levels in aortic tissue is largely independent of pressure load, volume load, and plasma or tissue RAS. It is suggested that any antihypertrophic actions of ANF may be mediated by the increased circulating ANF levels and its interaction with its receptor or through CNP.

Transgenic expression of replication-restricted enteroviral genomes in heart muscle induces defective excitation-contraction coupling and dilated cardiomyopathy.

Numerous studies have implicated Coxsackievirus in acute and chronic heart failure. Although enteroviral nucleic acids have been detected in selected patients with dilated cardiomyopathy, the significance of such persistent nucleic acids is unknown. To investigate the mechanisms by which restricted viral replication with low level expression of Coxsackieviral proteins may be able to induce cardiomyopathy, we generated transgenic mice which express a replication-restricted full-length Coxsackievirus B3 (CVB3) cDNA mutant (CVB3DeltaVP0) in the heart driven by the cardiac myocyte-specific myosin light chain-2v (MLC-2v) promoter. CVB3DeltaVP0 was generated by mutating infectious CVB3 cDNA at the VP4/VP2 autocatalytic cleavage site from Asn-Ser to Lys-Ala. Cardiac-specific expression of this cDNA leads to synthesis of positive- and negative-strand viral RNA in the heart without formation of infectious viral progeny. Histopathologic analysis of transgenic hearts revealed typical morphologic features of myocardial interstitial fibrosis and in some cases degeneration of myocytes, thus resembling dilated cardiomyopathy in humans. There was also an increase in ventricular atrial natriuretic factor mRNA levels, demonstrating activation of the embryonic program of gene expression typical of ventricular hypertrophy and failure. Echocardiographic analysis demonstrated the presence of left ventricular dilation and decreased systolic function in the transgenic mice compared with wild-type littermates, evidenced by increased ventricular end-diastolic and end-systolic dimensions and decreased fractional shortening. Analysis of isolated myocytes from transgenic mice demonstrate that there is defective excitation-contraction coupling and a decrease in the magnitude of isolated cell shortening. These data demonstrate that restricted replication of enteroviral genomes in the heart can induce dilated cardiomyopathy with excitation-contraction coupling abnormalities similar to pressure overload models of dilated cardiomyopathy.

Dissociation of cardiac hypertrophy, myosin heavy chain isoform expression, and natriuretic peptide production in DOCA-salt rats

We examined the relationship between cardiac hypertrophy, myosin heavy chain (MHC) isoform expression, and production of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) before and after the development of DOCA-salt hypertension. DOCA-salt rats exhibited significant left ventricular hypertrophy at the prehypertensive stage (1 week of treatment), without MHC isoform switch or change in natriuretic peptide gene expression. In the hypertensive stage (5 weeks of treatment), pronounced left ventricular hypertrophy was observed, and this was characterized by an increase in beta-MHC protein, resulting in a switch from 90% alpha-MHC to 51% alpha-MHC and 49% beta-MHC. ANF and BNP mRNA levels and peptide content were significantly increased at this stage. Unexpectedly, the MHC isoform switch was evident in the non-hypertrophied right ventricle to the same degree as in the left ventricle. Natriuretic peptide production was also increased in the right ventricle at 5 weeks of treatment, but to a lesser degree than in the left ventricle. In contrast, in the hypertrophied left atrium there was no MHC isoform switch, while ANF and BNP mRNA levels were augmented. Plasma ANF was significantly increased in the prehypertensive stage; this was accompanied by a partial depletion of atrial ANF stores. Plasma BNP was increased only in the hypertensive stage, reflecting an increase in ventricular BNP synthesis and secretion. These results suggest that 1) cardiac hypertrophy, MHC isoform expression, and stimulation of natriuretic peptide production are processes that may be dissociated from each other; 2) increases in plasma ANF without a concomitant increase in plasma BNP reflect atrial hemodynamic overload, while increases in both ANF and BNP in plasma are associated with ventricular hypertrophy; and 3) there exist differences in the storage, secretion, and processing patterns of ANF and BNP in the atria.

Atrial natriuretic factor significantly contributes to the mineralocorticoid escape phenomenon. Evidence for a guanylate cyclase-mediated pathway.

The mechanism underlying the mineralocorticoid escape phenomenon remains unknown. To assess the possible contribution of natriuretic peptides to mineralocorticoid escape, rats were injected with 5 mg deoxycorticosterone acetate for 3 d. Plasma atrial natriuretic factor (ANF) rose to twice basal levels and atrial ANF content decreased significantly by 24 h of treatment. This coincided with renal escape and with a significant increase in urinary cGMP excretion. Plasma ANF remained elevated and atrial ANF content continued to decline by 48 and 72 h while atrial ANF mRNA levels increased significantly only at 72 h. Plasma brain natriuretic peptide did not increase during escape although atrial brain natriuretic peptide mRNA levels increased significantly. Chronically administered HS-142-1 (HS), a specific antagonist of the guanylate cyclase-coupled natriuretic peptide receptors, significantly and dose-dependently impaired the escape phenomenon. The highest dose of HS completely suppressed the increase in urinary cGMP. Despite the continued suppression, partial escape was observed by the end of the observation period. HS alone influenced neither plasma nor tissue or urine parameters. These findings show that despite activation of atrial ANF, blockade of the guanylate cyclase-coupled natriuretic peptide receptors impairs the ability of the kidney to escape the Na+ retaining effect of excess mineralocorticoid in a dose-dependent fashion. Later-acting, unknown mechanisms eventually come into play to mediate the escape phenomenon through a guanylate cyclase-independent pathway. Therefore, ANF of cardiac origin appears to be a major factor initiating mineralocorticoid escape through a guanylate cyclase-dependent pathway.

Myocardial expression of a constitutively active alpha 1B-adrenergic receptor in transgenic mice induces cardiac hypertrophy.

Transgenic mice were generated by using the alpha-myosin heavy chain promoter coupled to the coding sequence of a constitutively active mutant alpha 1B-adrenergic receptor (AR). These transgenic animals demonstrated cardiac-specific expression of this alpha 1-AR with resultant activation of phospholipase C as shown by increased myocardial diacylglycerol content. A phenotype consistent with cardiac hypertrophy developed in adult transgenic mice with increased heart/body weight ratios, myocyte cross-sectional areas, and ventricular atrial natriuretic factor mRNA levels relative to nontransgenic controls. These transgenic animals may provide insight into the biochemical triggers that induce hypertrophy in cardiac disease and serve as a convenient experimental model for studies of this condition.

Selective changes in natriuretic peptide and early response gene expression in isolated rat atria following stimulation by stretch or endothelin-1

Important physiological and pathophysiological conditions are associated with changes in secretion and synthesis of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP). The aim of this study was to examine the effects of mechanical stretch and endothelin-1 on ANF and BNP secretion and gene expression in isolated adult rat atria, as paradigms for mechanical and endocrine stimulation of atrial tissue. The expression of the early response genes c-fos, c-jun, Egr-1, and c-myc was also studied, since their protein products may be involved in controlling natriuretic peptide gene expression. Isolated rat atria were stimulated by stretch (5 g) or endothelin-1 (10(-7) M) for 30 min, 2 h, or 4 h. ANF and BNP secretion was measured by radioimmunoassay, and relative mRNA levels were determined by northern blotting. Atrial stretch resulted in an immediate 1.8-fold increase in ANF release, which returned to basal levels after 160 min. Endothelin-1 caused a gradual increase in ANF release, up to 2.3 times basal levels, and thereafter returned towards basal levels. BNP secretion was increased threefold by endothelin-1, and remained significantly raised for 90 min. BNP mRNA levels were transiently increased by 33% after 2 h of endothelin-1 stimulation. Stretch increased c-fos mRNA levels (+55%) and Egr-1 mRNA levels (+70%) after 2 h, and increased c-myc mRNA levels (+69%) after 4 h. Endothelin-1 increased Egr-1 mRNA levels up to +767% after 4 h. Endothelin-1 stimulates BNP secretion from rat atria; this is followed by an increase in BNP mRNA levels. Conversely, acute secretion of ANF by stretch or endothelin-1 is not accompanied by changes in ANF mRNA levels. Atrial stretch results in changes in the expression of the early response genes c-fos, Egr-1, and c-myc, while endothelin-1 stimulates Egr-1 expression. The specific changes in natriuretic peptide and early response gene expression reveal distinct mechanisms of modulation of atrial gene expression by mechanical and endocrine stimuli.

Brain natriuretic peptide is induced by alpha 1-adrenergic agonists as a primary response gene in cultured rat cardiac myocytes

To better understand the molecular basis for increased atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) expression during overload-induced cardiac hypertrophy, we studied the induction of the genes in primary myocardial cells by the alpha 1-adrenergic agonist, phenylephrine (PE), a potent hypertrophic agent. PE augmented the transcription of both genes to similar extents, although the time course of mRNA accumulation differed. Increases in ANF mRNA were evident only after 6-8 h of PE exposure, when transcript levels were 2-4-fold over control. However, similar increases in BNP mRNA were observed as soon as 1 h of PE exposure. Moreover, while ANF mRNA levels continued to increase through 24 h of PE treatment, maximal levels of BNP mRNA (8-10-fold over control) were observed at 4 h, after which transcript levels declined to about 3-fold over control. The early induction of the BNP mRNA by PE was independent of protein synthesis, whereas the late induction of both genes required protein synthesis. Interestingly, the early BNP induction was only partially blocked by the transcription inhibitor, actinomycin D, indicating that, in part, the inductive effects of PE might be the result of transcript stabilization. Indeed, the BNP transcript, which was shown to possess a half-life of less than 1 h in control cells, was stabilized by the addition of PE, while the ANF transcript possessed a half-life of at least 24 h under all conditions. These data indicate that the induction of BNP by alpha 1-adrenergic agonists has characteristics of both a primary and secondary response gene, while ANF is a typical secondary response gene. Moreover, alpha 1-adrenergic stimulation enhances BNP expression through both transcriptional activation and transcript stabilization, while ANF expression is enhanced primarily transcriptionally.

Alterations in cardiac gene expression during the transition from stable hypertrophy to heart failure. Marked upregulation of genes encoding extracellular matrix components.

The failing heart is characterized by impaired cardiac muscle function and increased interstitial fibrosis. Our purpose was to determine whether the functional impairment of the failing heart is associated with changes in levels of mRNA encoding proteins that modulate parameters of contraction and relaxation and whether the increased fibrosis observed in the failing heart is related to elevated expression of genes encoding extracellular matrix components. We studied hearts of 18- to 24-month-old spontaneously hypertensive rats with signs and symptoms of heart failure (SHR-F) or without evidence of failure (SHR-NF) and of age-matched normotensive Wistar-Kyoto (WKY) rats. Compared with WKY rats, SHR-NF exhibited left ventricular (LV) hypertrophy (2.2-fold) and right ventricular (RV) hypertrophy (1.5-fold), whereas SHR-F were characterized by comparable LV hypertrophy (2.1-fold) and augmented RV hypertrophy (2.4-fold; all P < .01). Total RNA was isolated from ventricles and subjected to Northern blot analysis. In SHR-F hearts, the level of alpha-myosin heavy chain mRNA was decreased in both ventricles to 1/3 and 1/5 of the SHR-NF and WKY values, respectively (both P < .01). Levels of beta-myosin heavy chain, alpha-cardiac actin, and myosin light chain-2 mRNAs were not significantly altered in hearts of SHR-NF or SHR-F. Levels of alpha-skeletal actin were twofold greater in SHR-NF hearts compared with WKY hearts and were intermediate in SHR-F hearts. Levels of atrial natriuretic factor (ANF) mRNA were elevated threefold in the LV of SHR-NF (P < .05) but were not significantly increased in the RV of SHR-NF compared with WKY rats. During the transition to failure (SHR-F versus SHR-NF), ANF mRNA levels increased an additional 1.6-fold in the LV and were elevated 4.7-fold in the RV (both P < .05). Levels of sarcoplasmic reticulum Ca(2+)-ATPase (SRCA) mRNA were maintained in the LV of hypertensive and failing hearts at levels not significantly different from WKY values. In contrast, the level of RV SRCA mRNA was 24% less in SHR-NF compared with WKY rats, and during the transition to failure, this difference was not significantly exacerbated (29% less than the WKY value). The levels of fibronectin and pro-alpha 1(I) and pro-alpha 1(III) collagen mRNAs were not significantly elevated in either ventricle of the SHR-NF group but were fourfold to fivefold higher in both ventricles of SHR-F (all P < .05).(ABSTRACT TRUNCATED AT 400 WORDS)