Expression and distribution of atrial natriuretic peptide in human hypertrophic ventricle of hypertensive hearts and hearts with hypertrophic cardiomyopathy

More than 50 Years after Konno's Development of the Endomyocardial Biopsy

The endomyocardial biopsy (EMB) method was first developed by Japan's Dr. Souji Konno in 1962. Since then, this technique has been used worldwide in clinical cardiology for the recognition and diagnosis of cardiomyopathies, arrhythmias, and other heart conditions. Many studies relating to the EMB have been published at the global level, including a large review by Cooper, et al.,¹⁾ wherein a limited selection of Japanese papers were cited despite considerable pioneering work on the EMB having been done in Japan. Following this, the Cardiac Biopsy Conference (CABIC) organization, which was founded in Japan in 1979, conducted a nationwide survey of the English language literature on the EMB. Among the collection of 500 studies compiled, approximately 40 abstracts have been selected by the co-editors in CABIC for further discussion. This report aims to supplement Cooper's work and bring to light other prominent contributions of Japanese researchers on the EMB.

Follistatin like 1 Regulates Hypertrophy in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) accounts for ∼50% of all clinical presentations of heart failure, (HF) and its prevalence is expected to increase. However, there are no evidence-based therapies for HFpEF; thus, HFpEF represents a major unmet need. Although hypertension is the single most important risk factor for HFpEF, with a prevalence of 60% to 89% from clinical trials and human HF registries, blood pressure therapy alone is insufficient to prevent and treat HFpEF. Follistatin-like 1 (Fstl1), a divergent member of the follistatin family of extracellular glycoproteins, has previously been shown to be elevated in HF with reduced ejection fraction and associated with increased left ventricular mass. In this study, blood levels of Fstl1 were increased in humans with HFpEF. This increase was also evident in mice with hypertension-induced HFpEF and adult rat ventricular myocytes stimulated with aldosterone. Treatment with recombinant Fstl1 abrogated aldosterone-induced cardiac myocyte hypertrophy, suggesting a role for Fstl1 in the regulation of hypertrophy in HFpEF. There was also a reduction in the E/A ratio, a measure of diastolic dysfunction. Furthermore, HFpEF induced in a mouse model that specifically ablates Fstl1 in cardiac myocytes (cardiac myocyte-specific Fstl1 knockout [cFstl1-KO]) showed exacerbation of HFpEF with worsened diastolic dysfunction. In addition, cFstl1-KO-HFpEF mice demonstrated more marked cardiac myocyte hypertrophy with increased molecular markers of atrial natriuretic peptide and brain natriuretic peptide expression. These findings indicate that Fstl1 exerts therapeutic effects by modulating cardiac hypertrophy in HFpEF.

•

Fstl1, also known as transforming growth factor-β–stimulated clone 36, is an extra-cellular glycoprotein implicated in the pathophysiology of cardiac disease.

•

Fstl1 acts in a noncanonical manner relative to other follistatin family members, but its functions remain poorly understood.

•

Circulating Flst1 levels are increased in humans with chronic stable HFpEF.

•

Fstl1 treatment modulates cardiomyocyte hypertrophy in vitro and in vivo.

•

Cardiac myocyte deletion of Fstl1 worsens the HFpEF phenotype in mice.

•

These studies indicate that Fstl1 may be therapeutically effective in HFpEF by modulating cardiac hypertrophy and improving parameters of diastolic dysfunction.

Atrophic cardiomyocyte signaling in hypertensive heart disease

Cardinal pathological features of hypertensive heart disease (HHD) include not only hypertrophied cardiomyocytes and foci of scattered microscopic scarring, a footprint of prior necrosis, but also small myocytes ensnared by fibrillar collagen where disuse atrophy with protein degradation would be predicted. Whether atrophic signaling is concordant with the appearance of HHD and involves oxidative and endoplasmic reticulum (ER) stress remains unexplored. Herein, we examine these possibilities focusing on the left ventricle and cardiomyocytes harvested from hypertensive rats receiving 4 weeks aldosterone/salt treatment (ALDOST) alone or together with ZnSO₄, a nonvasoactive antioxidant, with the potential to attenuate atrophy and optimize hypertrophy. Compared with untreated age-/sex-/strain-matched controls, ALDOST was accompanied by (1) left ventricle hypertrophy with preserved systolic function; (2) concordant cardiomyocyte atrophy (<1000 μm²) found at sites bordering on fibrosis where they were reexpressing β-myosin heavy chain; and (3) upregulation of ubiquitin ligases, muscle RING-finger protein-1 and atrogin-1, and elevated 8-isoprostane and unfolded protein ER response with messenger RNA upregulation of stress markers. ZnSO₄ cotreatment reduced lipid peroxidation, fibrosis, and the number of atrophic myocytes, together with a further increase in cell area and width of atrophied and hypertrophied myocytes, and improved systolic function but did not attenuate elevated blood pressure. We conclude that atrophic signaling, concordant with hypertrophy, occurs in the presence of a reparative fibrosis and induction of oxidative and ER stress at sites of scarring where myocytes are atrophied. ZnSO₄ cotreatment in HHD with ALDOST attenuates the number of atrophic myocytes, optimizes size of atrophied and hypertrophied myocytes, and improves systolic function.

Resident stem cells in the myocardium of patients with obstructive hypertrophic cardiomyopathy

Interventricular septum myocardium was studied in 40 patients with obstructive hypertrophic cardiomyopathy. Immunohistochemical assay revealed c-kit-positive resident cardiac stem cells in 82.5% patients. The content of the connective tissue and myofibrillar disarray zones and the degree of cardiomyocyte hypertrophy and myolysis were determined. In 30% cases, cardiomyocytes containing atrial natriuretic peptide were detected in the interventricular septum myocardium. The data were compared with clinical and functional parameters of patients. It was found that cardiac stem cells are present in patients, whose myocardium was characterized by increased density of the connective tissue, hypertrophy of mature cardiomyocytes, medium degree of myolysis in them, and accumulation of natriuretic peptide, a cardiac failure marker, in cardiomyocytes.

Constitutively active calcineurin induces cardiac endoplasmic reticulum stress and protects against apoptosis that is mediated by alpha-crystallin-B

Cardiac-specific overexpression of a constitutively active form of calcineurin A (CNA) leads directly to cardiac hypertrophy in the CNA mouse model. Because cardiac hypertrophy is a prominent characteristic of many cardiomyopathies, we deduced that delineating the proteomic profile of ventricular tissue from this model might identify novel, widely applicable therapeutic targets. Proteomic analysis was carried out by subjecting fractionated cardiac samples from CNA mice and their WT littermates to gel-free liquid chromatography linked to shotgun tandem mass spectrometry. We identified 1,918 proteins with high confidence, of which 290 were differentially expressed. Microarray analysis of the same tissue provided us with alterations in the ventricular transcriptome. Because bioinformatic analyses of both the proteome and transcriptome demonstrated the up-regulation of endoplasmic reticulum stress, we validated its occurrence in adult CNA hearts through a series of immunoblots and RT-PCR analyses. Endoplasmic reticulum stress often leads to increased apoptosis, but apoptosis was minimal in CNA hearts, suggesting that activated calcineurin might protect against apoptosis. Indeed, the viability of cultured neonatal mouse cardiomyocytes (NCMs) from CNA mice was higher than WT after serum starvation, an apoptotic trigger. Proteomic data identified α-crystallin B (Cryab) as a potential mediator of this protective effect and we showed that silencing of Cryab via lentivector-mediated transduction of shRNAs in NCMs led to a significant reduction in NCM viability and loss of protection against apoptosis. The identification of Cryab as a downstream effector of calcineurin-induced protection against apoptosis will permit elucidation of its role in cardiac apoptosis and its potential as a therapeutic target.

Midregional pro-atrial natriuretic peptide: a novel marker of myocardial fibrosis in patients with hypertrophic cardiomyopathy

We aimed to determine the diagnostic performance of biomarkers in predicting myocardial fibrosis assessed by late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) in patients with hypertrophic cardiomyopathy (HCM). LGE CMR was performed in 40 consecutive patients with HCM. Left and right ventricular parameters, as well as the extent of LGE were determined and correlated to the plasma levels of midregional pro-atrial natriuretic peptide (MR-proANP), midregional pro-adrenomedullin (MR-proADM), carboxy-terminal pro-endothelin-1 (CT-proET-1), carboxy-terminal pro-vasopressin (CT-proAVP), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and interleukin-8 (IL-8). Myocardial fibrosis was assumed positive, if CMR indicated LGE. LGE was present in 26 of 40 patients with HCM (65%) with variable extent (mean: 14%, range: 1.3-42%). The extent of LGE was positively associated with MR-proANP (r = 0.4; P = 0.01). No correlations were found between LGE and MR-proADM (r = 0.1; P = 0.5), CT-proET-1 (r = 0.07; P = 0.66), CT-proAVP (r = 0.16; P = 0.3), MMP-9 (r = 0.01; P = 0.9), TIMP-1 (r = 0.02; P = 0.85), and IL-8 (r = 0.02; P = 0.89). After adjustment for confounding factors, MR-proANP was the only independent predictor associated with the presence of LGE (P = 0.007) in multivariate analysis. The area under the ROC curve (AUC) indicated good predictive performance (AUC = 0.882) of MR-proANP with respect to LGE. The odds ratio was 1.268 (95% confidence interval 1.066-1.508). The sensitivity of MR-proANP at a cut-off value of 207 pmol/L was 69%, the specificity 94%, the positive predictive value 90% and the negative predictive value 80%. The results imply that MR-proANP serves as a novel marker of myocardial fibrosis assessed by LGE CMR in patients with HCM.

Hypertrophic and hypertensive hypertrophic cardiomyopathy--a true association?

The cardiomyopathies were previously defined as ''heart muscle diseases of unknown cause'' and were differentiated from specific heart muscle disease with known cause. With increasing understanding of etiology and pathogenesis, the difference between cardiomyopathy and specific heart muscle disease has become indistinct. The term specific cardiomyopathies are used to describe heart diseases that are associated with specific cardiac or systemic disorders. These were previously defined as specific heart muscle diseases. They included ischemic cardiomyopathy, valvular cardiomyopathy, hypertensive cardiomyopathy, inflammatory cardiomyopathy, metabolic cardiomyopathy, general system disease, muscular dystrophies, sensitivity and toxic reactions, and peripartal cardiomyopathy. The cardiomyopathies are therefore classified by the dominant pathophysiology or, if possible, by etiological/pathogenetic factors. Topol in 1985 described a syndrome called hypertensive hypertrophic cardiomyopathy that included severe concentric cardiac hypertrophy, a small left ventricular cavity, and supernormal indexes of systolic function without concurrent medical illness or ischemic heart disease. The aim of this review was to highlighted this syndrome from pathophysiological, clinical, diagnostical view and clear all the possible correlations with genetic, inflammatory, and other markers.

Tachycardia-induced myocardial ischemia and diastolic dysfunction potentiate secretion of ANP, not BNP, in hypertrophic cardiomyopathy

The aim of this study was to investigate what factor determines tachycardia-induced secretion of atrial and brain natriuretic peptides (ANP and BNP, respectively) in patients with hypertrophic cardiomyopathy (HCM). HCM patients with normal left ventricular (LV) systolic function and intact coronary artery (n = 22) underwent rapid atrial pacing test. The cardiac secretion of ANP and BNP and the lactate extraction ratio (LER) were evaluated by using blood samples from the coronary sinus and aorta. LV end-diastolic pressure (LVEDP) and the time constant of LV relaxation of tau were measured by a catheter-tip transducer. These parameters were compared with normal controls (n = 8). HCM patients were divided into obstructive (HOCM) and nonobstructive (HNCM) groups. The cardiac secretion of ANP was significantly increased by rapid pacing in HOCM from 384 +/- 101 to 1,268 +/- 334 pg/ml (P < 0.05); however, it was not significant in control and HNCM groups. In contrast, the cardiac secretion of BNP was fairly constant and rather significantly decreased in HCM (P < 0.01). The cardiac ANP secretion was significantly correlated with changes in LER (r = -0.57, P < 0.01) and tau (r = 0.73, P < 0.001) in HCM patients. Tachycardia potentiates the cardiac secretion of ANP, not BNP, in patients with HCM, particularly when it induces myocardial ischemia and LV diastolic dysfunction.

Neurohumoral profiles in patients with hypertrophic cardiomyopathy: differences to hypertensive left ventricular hypertrophy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) or hypertensive heart disease (HHD) have increased concentrations of various neurohumoral factors. Thus, the aim of the present study was to evaluate the differences in the neurohumoral profiles of HCM and HHD.

METHODS AND RESULTS

Plasma concentrations of epinephrine, norepinephrine, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), angiotensin II and endothelin-1 were measured in 40 patients with HCM, 35 with HHD, and 15 controls. Additionally, the concentrations of these neurohumoral factors in the coronary sinus and aortic root were measured in 12 HCM patients and 10 controls. Plasma concentrations of norepinephrine, ANP and BNP were significantly higher in HCM than HHD and controls. In HCM, there was no significant correlation between the left ventricular mass index and any neurohumoral factor. The plasma BNP concentration significantly correlated with left intraventricular pressure gradient in HCM. There were significant differences in the plasma concentrations of ANP and BNP between HCM with and without left ventricular diastolic dysfunction. Transcardiac production of BNP was significantly higher in patients with obstructive HCM than in those with non-obstructive HCM.

CONCLUSIONS

The significant neurohumoral differences between HCM and HHD were the plasma concentrations of norepinephrine, ANP and BNP. In HCM patients, the plasma BNP concentration may reflect the intraventricular pressure gradient and left ventricular diastolic dysfunction whereas the plasma ANP concentration reflects only the left ventricular diastolic dysfunction.

A-type natriuretic peptide level in hypertensive transgenic mice

A-type (atrial) natriuretic peptide (ANP) levels in heart and plasma were examined by immunohistochemistry, electron microscopy, and radioimmunoassay (RIA) in hypertensive transgenic mice (Tsukuba hypertensive mice; THM). Additionally, the ANP mRNA level in the heart was measured using real-time polymerase chain reaction (PCR) assay. The blood pressure and the ratio of heart weight to body weight in THM was significantly higher than those in the control mice (C57BL/6J). The number of ANP-granules and ANP immunoreactivity in the auricular cardiocytes were significantly lower in THM than in the control. Ultrastructurally, the ventricular cardiocytes in the THM occasionally had ANP-like granules, which were not present in the controls. Using RIA, the plasma, auricular, and ventricular ANP concentrations were significantly higher in THM than in the control, but there was no significant difference in plasma cyclic guanosine monophosphate (GMP) concentration between THM and the control. The ANP mRNA levels of the auricular and ventricular cardiocytes in the THM were siginificantly higher than those in the controls. The present study suggested that the ANP release system of the auricular cardiocytes in these transgenic mice is different from normal (control mice).

Immunohistochemistry of atrial and brain natriuretic peptides in control cats and cats with hypertrophic cardiomyopathy

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones involved in electrolyte and fluid homeostasis. Our laboratory has investigated the use of ANP and BNP as diagnostic markers of cardiac disease in cats. We hypothesize that the cardiac distribution of ANP and BNP increases in cats with hypertrophic cardiomyopathy (HCM). Accordingly, we evaluated the immunohistochemical distribution of ANP and BNP in hearts of four cats with naturally occurring HCM relative to five healthy controls. Indirect immunoperoxidase was performed with polyclonal immunoglobulin G against feline ANP (1-28) and proBNP (43-56). In control cats, ANP and BNP immunoreactivity was restricted to the atria. Staining for both peptides was most intense adjacent to the endocardial surface. Auricles stained more diffusely than atria for both peptides. The interstitial capillaries and nerve fibers within the heart were positive only for BNP. Atrial immunoreactivity for ANP and BNP was more diffuse and had a less distinctly layered pattern in HCM than in control cats. Ventricular cardiomyocytes of HCM cats were negative for ANP but stained lightly and diffusely for BNP. The capillaries and nerve fibers remained positive for BNP. We conclude that in cats with HCM, the cardiac distribution of ANP and BNP is more diffuse in the atria and that novel expression of BNP in the ventricular cardiomyocytes occurs.

Ventricular expression of atrial natriuretic peptide in chronic chagasic cardiomyopathy is not induced by myocarditis

BACKGROUND

The ventricles of the normal heart are virtually devoid of atrial natriuretic peptide (ANP). Although ANP occurs in ventricles submitted to elevated wall stress, it is not clear whether ANP expression is affected by myocarditis. We investigated the immunohistochemical expression of ANP in chronic chagasic cardiomyopathy, an inflammatory cardiomyopathy caused by infection with the protozoan Trypanosoma cruzi.

METHODS

Necropsy samples from the left and right ventricles of 16 patients exhibiting chronic chagasic cardiomyopathy were evaluated for myocarditis, fibrosis, T. cruzi parasites and ANP immunoreactivity. The diameters of 50 myocytes per sample were measured.

RESULTS

ANP was present in myocytes of the subendocardial region in 13/16 (81.3%) left and 10/16 (62.5%) right ventricular samples (P=0.25). Myocytes present in the inflammatory foci, near the infiltrating inflammatory cells but distant from the subendocardial region, did not express ANP. Trypanosoma cruzi parasites exhibited intense immunoreactivity for ANP. The mean myocyte diameter and the incidence of myocarditis, fibrosis, and T. cruzi parasites was similar between the left and right ventricular samples. No statistical differences were found between the ANP-positive and ANP-negative cases.

CONCLUSIONS

In chronic chagasic cardiomyopathy, both ventricles exhibit hypertrophy, fibrosis and ANP in the subendocardial region. The inflammatory infiltrate does not induce ANP expression in the myocytes. Regional stress but not myocarditis itself, is probably responsible for ventricular ANP expression in myocarditis.

Effect of neutral endopeptidase inhibitor on endogenous atrial natriuretic peptide as a paracrine factor in cultured cardiac fibroblasts

1. Cardiac remodelling is a fundamental response to hypertension, myocardial infarction and chronic heart failure, and involves cardiac fibroblast proliferation and production of extracellular matrix components such as collagen. The present study was performed to examine the role of endogenous atrial natriuretic peptide (ANP) as a possible paracrine factor for cardiac fibroblasts, and to examine the effects of three neutral endopeptidase (NEP) inhibitors, thiorphan, phosphoramidon and ONO-BB-039-02 (ONO-BB) on endogenous ANP-induced changes in collagen synthesis by cultured neonatal rat cardiac fibroblasts. 2. Each NEP inhibitor singly had no significant effect on collagen synthesis by cardiac fibroblasts, except for maximum concentration (10(-3) M) of thiorphan. 3. Exogenous ANP inhibited collagen synthesis in a concentration-dependent manner (10(-8) - 10(-6) M). Thiorphan (10(-4) and 10(-3) M) and phosphoramidon (10(-5) and 10(-4) M) enhanced the ANP (10(-7) M)-induced decrease in collagen synthesis. ONO-BB (10(-5) and 10(-4) M) slightly enhanced the ANP-induced decrease in collagen synthesis. 4. Myocyte-conditioned medium (MC-CM), as well as exogenous ANP, inhibited collagen synthesis dose-dependently. The decrease in collagen synthesis at 100% MC-CM was augmented by thiorphan (10(-3) M), phosphoramidon (10(-4) M) and ONO-BB (10(-4) M). 5. HS-142-1, a natriuretic peptide receptor antagonist, significantly reduced the MC-CM plus thiorphan- and MC-CM plus ONO-BB-induced decrease in collagen synthesis, by 92 and 62%, respectively and showed a tendency to attenuate the MC-CM plus phosphoramidon-induced decrease in collagen synthesis by 40%. 6. Our observations suggested that endogenous ANP released from cardiomyocytes inhibited collagen synthesis as a paracrine factor and that NEP inhibitors enhanced the activity of this peptide in cardiac fibroblasts.

Adenosine stimulates ANP expression in cultured ventricular cardiomyocytes

Adenosine protects the ischemic myocardium by coronary vasodilation and the depression of heart rate and contractility, improving myocardial energy balance. Adenosine effects on the myocardium are mediated predominantly by the type A1 receptors. Atrial natriuretic peptide (ANP), a vasodilator and regulator of blood volume, is secreted from either atrial or ventricular myocytes in response to cellular distention. In vivo, adenosine infusion has been shown to induce a rapid increase in plasma ANP, independent of blood pressure. We examined the possibility that adenosine enhances ANP-gene expression in cardiac myocytes. Administration of adenosine (10 microM) to cultured neonatal rat cardiomyocytes led to a 1.7-fold increase (p = 0.014, n = 9) in the abundance of ANP messenger RNA (mRNA) within 30 min, as measured by Northern blot hybridization. No such increase was obtained when adenosine was coadministered with 8-cyclopentyl-1,3dipropylxanthine (CPX, 10 microM), an adenosine A1-receptor antagonist. Our results point at adenosine as regulator of ANP mRNA level in cardiac myocytes.

Pulmonary oligemia in aortic valve disease

PURPOSE

To determine whether the severity of the radiographic appearance of oligemia correlates with the severity of cardiac dysfunction.

MATERIALS AND METHODS

Nine readers graded a set of 25 chest radiographs (15 cases of aortic valve disease [AVD], 10 control cases without AVD) for blood volume and ventricular size. Blood volume was graded on a scale of -3 (severe hyperemia) to 0 (normovolemia) to +3 (severe oligemia). Ventricular size was graded on a scale of 0 (normal) to 3 (massively enlarged). The oligemia and ventricular size grades were added to yield the radiographic severity index. Pulmonary capillary wedge pressure, pulmonary arterial pressure, stroke volume, and cardiac output were measured at the time of catheterization.

RESULTS

The five more experienced readers achieved good nonchance agreement (kappa = 0.48; P < .001). They were unanimous in scoring 12 cases as oligemic; variations occurred only in severity assessments. Oligemia was due to emphysema in one case and to AVD in 11. In oligemic cases, radiographic severity correlated significantly with wedge pressure (r = 0.93, P < .001) and pulmonary arterial pressure (r = 0.93, P < .002).

CONCLUSION

Many cases of AVD show oligemia. The severity of oligemia correlates well with hemodynamic abnormality. Oligemia may be caused by atrial-pulmonary-vascular reflex vasoconstriction, low right ventricular output, and possibly high levels of atrial natriuretic factor.

Expression and distribution of brain natriuretic peptide in human right atria

OBJECTIVES

We investigated expression of brain natriuretic peptide (BNP) as well as atrial natriuretic peptide (ANP) and their genes in human right atria. Their relations with atrial pressure were also examined.

BACKGROUND

The BNP plays a roll in electrolyte-fluid homeostasis such as ANP. The tissue level is reported to be elevated in the failing ventricles. However, expression and transmural distribution of BNP in the atria remain unclear.

METHODS

Expression of ANP and BNP was immunohistochemically investigated in the right atrial (RA) specimens from 21 patients who had undergone cardiac surgery. The mRNA of specimens were quantitatively measured by Northern blot analysis and also evaluated by in situ hybridization. In addition, plasma levels of ANP and BNP were measured in the patients.

RESULTS

The BNP immunoreactivity was diffusely seen in RA tissue of patients with mean RA pressure (mRAP) of 5 mm Hg or more, but it was noted only in the subendocardial half of the atria of those with mRAP less than 5 mm Hg. There was a significant correlation between the incidence of BNP-positive myocytes and mRAP (r = 0.850, p < 0.0001). Conversely, ANP-positive myocytes were found diffusely in all cases. In Northern blot analysis, the mRNAs levels of ANP and BNP in the atrial tissue were positively correlated with the mRAP (ANP, p = 0.775, p < 0.005 and BNP, p = 0.771, p < 0.005). In situ hybridization confirmed these findings. The mRNA levels were significantly correlated to each other (r = 0.845, p < 0.0002). Plasma ANP and BNP levels were elevated in the patients compared with that in controls; however, none were significantly correlated with the mRAP.

CONCLUSIONS

Expression of BNP and BNP mRNA is augmented in the atria with increased pressure, and distributed predominantly in the subendocardial side. The level of BNP mRNA was well correlated with that of ANP mRNA. Thus, these two genes might be commonly regulated in response to atrial pressure.

Atrial natriuretic factor reduces cell coupling in the failing heart, an effect mediated by cyclic GMP

The influence of the atrial natriuretic factor (ANF) on heart-cell communication was investigated in cell pairs isolated from the ventricle of cardiomyopathic hamsters (BIO TO-2; 11 months old), and the results were compared with controls (F1B) of same age. The results indicated that ANF (10(-8) M) added to the bath caused a decline in junctional conductance (gj) of 48 +/- 2% (n = 15) within 90 s. The effect of ANF was suppressed by HS-142-1, a specific antagonist of guanylyl cyclase ANF receptor. Moreover, the decline in gj elicited by ANF was related to the synthesis of cyclic guanosine monophosphate (cGMP). Indeed, dibutyryl-cGMP (10(-4) M) decreased gj by 80 +/- 3.5% (n = 15) within 90 s, and zaprinast, a selective inhibitor of cGMP phosphodiesterase, enhanced the effect of ANF on gj. The possible relationship between ischemia, ANF release, and impairment of cell coupling is discussed.

Expression of atrial and brain natriuretic peptides and their genes in hearts of patients with cardiac amyloidosis

OBJECTIVES

We investigated the expression of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and their genes in the hearts of patients with cardiac amyloidosis and those with isolated atrial amyloidosis.

BACKGROUND

The expression of ANP and BNP is augmented in the ventricles of failing or hypertrophied hearts, or both. The expression of ANP and BNP in the ventricles of hearts with cardiac amyloidosis, which is hemodynamically similar to restrictive cardiomyopathy, is not yet known. ANP is the precursor protein of isolated atrial amyloid.

METHODS

We analyzed the immunohistocytochemical localizations of ANP and BNP as well as the expression of their mRNAs by in situ hybridization in the myocardium and measured the plasma levels of ANP and BNP in patients with cardiac amyloidosis.

RESULTS

Four of the five right and all six left ventricular endomyocardial biopsy specimens obtained from six patients with cardiac amyloidosis were immunohistochemically positive for both ANP and BNP; none of the biopsy specimens from eight normal subjects were positive for ANP or BNP. All four of the right atria obtained at operation showed positive immunoreactions for both peptides. Electron microscopy identified specific secretory granules in ventricular myocytes of the patients with cardiac amyloidosis, but not in ventricular myocytes from the normal control subjects. Double immunocytochemical analysis revealed the co-localization of ANP and BNP in the same granules and that isolated atrial amyloid fibrils were immunoreactive for ANP and BNP, whereas ventricular amyloid fibrils were negative for both peptides. Both ANP mRNA and BNP mRNA were expressed in the ventricles of the patients with cardiac amyloidosis but not in the normal ventricles. The autopsy study of four patients with cardiac amyloidosis revealed an almost transmural distribution of ANP and BNP, with predominance in the endocardial side. Plasma BNP levels in the patients were markedly elevated ([mean +/- SD] 1,165.1+/-561.2 pg/ml) compared with those in the control subjects (8.9+/-6.0 pg/ml, p < 0.05).

CONCLUSIONS

Expression of ANP and BNP and their genes was augmented in the ventricular myocytes of the patients with cardiac amyloidosis. Both regional mechanical stress by amyloid deposits and hemodynamic stress by diastolic dysfunction may be responsible for the expression of the peptides in patients with cardiac amyloidosis.

Immunohistochemical expression of atrial natriuretic peptide (ANP) in the conducting system and internodal atrial myocardium of human hearts

Expression and distribution of atrial natriuretic peptide (ANP) were studied immunohistochemically in the conducting system and internodal atrial myocardium of 5 adult human hearts. Myocytes from the sinus node and compact atrioventricular node were usually ANP-negative; only a very few cells exhibited ANP immunoreactivity. These ANP-positive myocytes were small and did not appear to be trapped working atrial myocytes which are larger than nodal cells. The transitional cell zones of the sinus node and the atrioventricular node were composed of bundles of ANP-positive myocytes, intermingled with non-reactive myocytes. The internodal atrial myocardium exhibited a comparable intensity of myocyte staining in each case examined. Thus, morphologically distinct connecting pathways between the sinus node and the atrioventricular node with regard to myocyte ANP immunoreactivity could not be demonstrated, reinforcing the notion that they actually do not exist. The penetrating bundle, branching bundle and bundle branches were usually composed of ANP-negative myocytes although some ANP-positive myocytes were observed in the branching bundle and bundle branches in 4 cases. Myocytes from the ventricular conducting tissue presenting ANP immunoreactivity have been designated Purkinje fibers and have been found in several mammalian species.

Ras-dependent pathways induce obstructive hypertrophy in echo-selected transgenic mice

To overcome the genetic and interindividual variability frequently noted in complex phenotypes, we used echocardiographic selection to develop a substrain of myosin light chain (MLC)-Ras (RAS) transgenic mice with an enhanced ventricular hypertrophic phenotype. These echo-selected mice were then compared with wild-type (WT) animals and a pressure overload hypertrophy model (transverse aortic constriction; TAC). Echocardiography demonstrated increased wall thickness in RAS compared with the other groups. We developed novel miniaturized physiological technology to quantitatively identify in vivo intraventricular gradients; increased systolic Doppler velocity was seen in the left ventricle (LV) in 69% of RAS vs. none of WT or TAC. Intracavitary pressure gradients were present in 3 of 10 RAS vs. none of TAC or WT. Passive diastolic LV stiffness was not different among the three groups. Myofibrillar disarray was present in all RAS animals and was significantly more extensive (21.7% area fraction) than in TAC (1.5%) or WT (0.0%). RAS mice had selective induction of natriuretic peptide genes in the LV, a pattern distinct from that induced by pressure overload. Juvenile mortality was significantly increased in the offspring of echo-selected RAS parents. We conclude that adaptation of echocardiography to the mouse permits selection for cardiac phenotypes, and that selectively inbred MLC-Ras transgenic mice faithfully reproduce the molecular, physiological, and pathological features of human hypertrophic cardiomyopathy (HCM). Because previous studies support the concept that hypertrophy in human HCM is secondary to dysfunction created by sarcomeric protein mutations, the current studies suggest that Ras-dependent pathways might play a similar role in forms of human HCM.

Marked expression of plasma brain natriuretic peptide is a special feature of hypertrophic obstructive cardiomyopathy

OBJECTIVES

We examined whether plasma brain natriuretic peptide levels are abnormally elevated in hypertrophic obstructive cardiomyopathy compared with other cardiac diseases.

BACKGROUND

We previously reported that plasma brain and atrial natriuretic peptide levels were elevated in hypertrophic cardiomyopathy.

METHODS

We compared plasma concentrations of brain and atrial natriuretic peptide and hemodynamic and echocardiographic data in 50 patients with hypertrophic obstructive cardiomyopathy (n = 15, mean [+/-SD] intraventricular pressure gradient 37 +/- 16 mm Hg), hypertrophic nonobstructive cardiomyopathy (n = 15), aortic stenosis (n = 10, mean pressure gradient 41 +/- 18 mm Hg) and hypertensive heart disease (n = 10, mean systolic/diastolic blood pressure 203 +/- 16/108 +/- 11 mm Hg, respectively) and 10 normal subjects.

RESULTS

Plasma brain natriuretic peptide levels were higher in the hypertrophic obstructive cardiomyopathy group (397.1 +/- 167.8 pg/ml*) than in the hypertrophic nonobstructive cardiomyopathy (60.0 +/- 48.1 pg/ml*), hypertensive heart disease (53.9 +/- 31.4 pg/ml*), aortic stenosis (75.4 +/- 54.3 pg/ml*) and normal groups (9.8 +/- 6.4 pg/ml [*p < 0.05 vs. normal group, p < 0.05 vs. hypertrophic obstructive cardiomyopathy group]). Although plasma atrial natriuretic peptide levels were higher in the hypertrophic obstructive cardiomyopathy group than the other patient groups, the brain/atrial natriuretic peptide ratio in the hypertrophic obstructive cardiomyopathy group was higher (4.5 +/- 2.3) than those in the other three patient groups (1.1 to 1.4) and the normal group (0.7 +/- 0.5). Left ventricular end-diastolic pressure and left ventricular end-diastolic volume index were similar among the four patient groups. The interventricular septal thickness and the ratio of interventricular septal thickness to left ventricular posterior wall thickness were similar between the hypertrophic obstructive and nonobstructive cardiomyopathy groups.

CONCLUSIONS

Abnormal elevations of plasma brain natriuretic peptide levels are difficult to explain on the basis of hemodynamic and echocardiographic data and are a special feature of hypertrophic obstructive cardiomyopathy.

Plasma atrial natriuretic peptide is elevated in patients with hypertrophic cardiomyopathy

STUDY OBJECTIVES

To determine if plasma levels of atrial natriuretic peptide are elevated in patients with hypertrophic cardiomyopathy and to determine the relationship of atrial natriuretic peptide to symptoms and echocardiographic indices of left ventricular structure and diastolic function in these patients.

DESIGN

A prospective study in which atrial natriuretic peptide was measured in peripheral venous plasma in 14 patients (age 44 +/- 14 years) with hypertrophic cardiomyopathy and 17 healthy controls. Echocardiography was performed in all cases and 30 controls to examine indices of left heart structure and function. All patients underwent clinical evaluation.

RESULTS

The concentration of atrial natriuretic peptide was significantly higher in patients with hypertrophic cardiomyopathy than controls, (17.86 +/- 8.72 vs. 6.22 +/- 3.26 pmol/l, P = 0.0001). Diastolic dysfunction was observed in 11 of 14 patients with hypertrophic cardiomyopathy. No correlation was demonstrated between atrial natriuretic peptide levels and the degree of diastolic dysfunction, septal or free wall thickness, left atrial size, degree of mitral regurgitation or New York Heart Association functional class.

CONCLUSIONS

Plasma levels of atrial natriuretic peptide are elevated in patients with hypertrophic cardiomyopathy but do not correlate with symptoms or echocardiographically-derived indices of left ventricular structure or diastolic function.

Tumour necrosis factor is expressed in cardiac tissues of patients with heart failure

Tumour necrosis factor (TNF), a cytokine produced mainly by macrophages, has also been found in vascular smooth muscle cells. Elevated serum levels of TNF have been reported in various cardiac diseases, especially congestive heart failure (CHF). Although the myocardium produces several cytokines, the expression of TNF in human cardiac tissue has not yet been demonstrated. We examined TNF expression in right atrial (RA) specimens obtained from 15 patients during cardiac surgery with immunohistochemistry using an anti-human TNF monoclonal antibody, enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (RT-PCR). TNF immunoreactivity was found only in cardiac myocytes and some vascular smooth muscle cells of small vessels of specimens from patients with severe CHF (3/5), and not in those from patients without severe CHF (0/10). ELISA of four RA specimens revealed that RA tissues from two patients with severe CHF contained more TNF than did those from two patients without severe CHF (3.1 and 4.7 pg/mg vs. 0.1 and 0.3 pg/mg). RT-PCR revealed TNF mRNA in all seven cases we examined. It was concluded that TNF mRNA is expressed by atrial tissue. The production of immunoreactive TNF-like peptides by myocytes and vascular smooth muscle cells is augmented in patients with severe CHF.

Atrial natriuretic factor secretion: a role for atrial systolic ejection force?

The increase in plasma concentration of atrial natriuretic factor in heart transplant patients has not been fully elucidated. Besides an eventual pressure or volume overload leading to passive atrial distension, the atrial tension developed during atrial systole, or atrial ejection force, which may be increased by the transplantation procedure, is an important determinant of atrial natriuretic factor release. We therefore determined the plasma concentration of atrial natriuretic factor and the maximal atrial ejection force in 15 heart transplant patients and 8 controls, matched for age and body mass. Atrial ejection force, as defined as the force exerted by the left atrium to accelerate blood into the left ventricle during atrial systole, was obtained using combined two-dimensional imaging and doppler echocardiography. Serum creatinin concentrations, heart rate [91.9 (SD 13.2) vs 71.8 (SD 10.9) beats.min-1], mean arterial blood pressure [103.9 (SD 9.8) vs 87.4 (SD 5.8) mmHg, 13.85 (SD 1.31) vs 11.65 (SD 0.77) kPa], left ventricular posterior wall thickness and interventricular septum thickness were higher in heart transplant patients compared to controls. Plasma concentration of atrial natriuretic factor was also elevated in heart transplant patients [63.9 (SD 18.1) vs 34.0 (SD 3.2) pg.ml-1; P < 0.001]. In contrast, although the left atrial area was greater in heart transplant patients [28.2 (SD 4.8) vs 15.8 (SD 2.5) cm2; P < 0.001], mitral area, transmitral Doppler A-wave maximal velocity and atrial ejection force were similar in transplant and in control patients [7.7 (SD 3.5) vs 8.9 (SD 2.8) kdyn, 77 (SD 35) vs 89 (SD 28)mN]. No significant correlation was observed between concentration of atrial natriuretic factor and atrial ejection force, either in heart transplant patients or in controls. Thus, the elevated plasma concentration of atrial natriuretic factor observed in these heart transplant patients was multifactorial in origin, and was considered to depend upon an hypersecretion rather than upon a decreased clearance rate. Moreover, it is suggested that the atrial ejection force was unlikely to have participated in this enhanced release of atrial natriuretic factor.

Venticular expression of atrial and brain natriuretic peptides in patients with myocarditis

We analyzed the ventricular expression of atrial and brain natriuretic peptides (ANP and BNP) in patients with myocarditis. Immunohistochemical analysis of endomyocardial biopsy specimens showed ANP and BNP immunoreactivity in the early myocarditis group (ANP in 4/10 and BNP in 3/10) and the late myocarditis group (ANP and BNP in 4/10), but not in the controls (0/8). Hemodynamic parameters, such as left ventricular volume indexes, pulmonary capillary wedge pressure, and left ventricular end-diastolic pressure, were higher and the cardiac index and ejection fraction were lower in the patients positive for ANP and/or BNP. Histological changes, including myocyte size, cellular necrosis, inflammatory infiltrates and fibrosis, were more severe in the immunohistochemically positive biopsy specimens. In the autopsy hearts, ANP- or BNP-positive myocytes were noted in the chronic myocarditis or postmyocarditis group, but not in acute fulminant myocarditis or in normal controls. Both ANP and BNP were predominantly localized in the residual myocytes edging the myocardial lesions, and also in the myocytes just beneath the left ventricular endocardium. This study demonstrated augmented ventricular ANP and BNP expressions in patients with myocarditis, and suggested that regional stress is important in the augmentation of these peptides as well as hemodynamic stress.

Divergent pathways mediate the induction of ANF transgenes in neonatal and hypertrophic ventricular myocardium

To determine whether similar or divergent pathways mediate atrial natriuretic factor (ANF) induction in neonatal and hypertrophied adult ventricular myocardium, and to assess whether studies using an in vitro model system of hypertrophy have fidelity to the in vivo context during pressure overload hypertrophy, we generated transgenic mice which harbor either 638 or 3,003 bp of the rat ANF 5' flanking region ligated upstream from a luciferase reporter. Luciferase activity in the ventricles of day 1 transgenic neonates was 8-24-fold higher than the levels expressed in the ventricles of adult mice. Adult mice expressed the luciferase reporter in an appropriate tissue-specific manner. Transverse aortic constriction of adult mice harboring ANF reporter transgenes demonstrated no significant increase in reporter activity in the ventricle. These findings demonstrate that distinct regions of the ANF 5'-flanking region are required for inducible expression of the ANF gene in the hypertrophic adult ventricle compared with those required for atrial-specific and developmentally appropriate expression in the intact neonatal heart. Furthermore, the cis regulatory elements necessary for induction of ANF expression in endothelin-1 or alpha 1-adrenergically stimulated cultured neonatal ventricular myocytes are not sufficient for induction in the in vivo context of pressure overload hypertrophy.

Atrial natriuretic peptide and its potential role in pharmacotherapy

Atrial natriuretic peptide (ANP) is a 28 amino-acid polypeptide secreted into the blood by atrial myocytes after atrial pressure and distension. Although its role in humans is not clear, it can produce a variety of physiologic effects including vasodilatation, natriuresis, and suppression of the renin-angiotensin-aldosterone axis. These actions are potentially useful in a variety of pathologic states such as hypertension and congestive heart failure, and diverse methods to augment the effects of ANP in these states have been devised. The results are exciting and, despite some problems, may lead to the pharmacologic use of enhancement of ANP actions in several clinical disorders.

Increased plasma atrial natriuretic peptide levels after heart transplant: relation to ventricular expression and severity of rejection

To determine whether elevated plasma atrial natriuretic peptide (ANP) levels observed after cardiac transplant are related to ventricular ANP expression and/or the severity of rejection, 59 ambulatory patients with cardiac transplant underwent hemodynamic evaluation, endomyocardial biopsy, and plasma ANP sampling. Forty-two of the 59 patients had right ventricular (RV) biopsy specimens immunohistochemically stained for the presence of ANP. Plasma ANP levels were elevated (p < 0.0001) in transplant patients (172 +/- 12 pg/ml) compared to normal subjects (36 +/- 4 pg/ml). Sixty-four percent of transplant patients showed stainable RV ANP on endomyocardial biopsy. There was no significant difference in plasma ANP levels between patients with or without RV ANP. The degree of RV staining did not correlate with plasma ANP levels, degree of rejection, mean atrial or systemic pressures, or specific immunosuppressive regimen. Plasma ANP levels were higher in patients with moderate or severe rejection (237 +/- 17 pg/ml) compared to patients with mild or no rejection (163 +/- 12 pg/ml; p 0.03), but there was significant overlap of values. These data suggest that ventricular ANP secretion may account for some of the increase in plasma ANP levels in cardiac transplant patients. However, increased plasma ANP levels in some transplant patients who have no RV ANP and the lack of correlation between the amount of stainable RV ANP and plasma ANP levels suggest that other mechanisms are also likely responsible for plasma ANP elevations in this setting.

Prognostic significance of N-terminal pro-atrial natriuretic factor (1-98) in acute myocardial infarction: comparison with atrial natriuretic factor (99-126) and clinical evaluation

OBJECTIVE

To evaluate the prognostic significance of plasma N-terminal pro-atrial natriuretic factor (1-98) concentrations measured in the subacute phase after acute myocardial infarction, and to compare the predictive value of measurement of N-terminal pro-atrial natriuretic factor (1-98) with the measurement of atrial natriuretic factor (99-126) and with clinical assessment of the degree of heart failure.

DESIGN

Prospective observational.

SETTING

Norwegian central hospital.

PATIENTS

139 patients (mean (SD) age 66.9 (11.1) years, 71.2% males) with acute myocardial infarction. Patients in cardiogenic shock or with severe heart failure (New York Heart Association class IV) were excluded.

MAIN OUTCOME MEASURE

Cardiovascular death within 12 months.

RESULTS

During the follow up period 15 patients died. In a univariate Cox proportional hazards model N-terminal pro-atrial natriuretic factor (1-98) was significantly related to mortality (p = 0.0003). In a multivariate model the prognostic value of N-terminal pro-atrial natriuretic factor (1-98) was better than that of atrial natriuretic factor (99-126) and clinical assessment of heart failure (N-terminal pro-atrial natriuretic factor (1-98), p = 0.0003; atrial natriuretic factor (99-126), p = 0.4513; heart failure, p = 0.0719). The odds ratio estimate of patients in whom plasma concentrations of N-terminal pro-atrial natriuretic factor (1-98) were greater than 2000 pmol/l was 25 (95% confidence interval 2.8-225.0) compared with patients with plasma concentrations less than 1000 pmol/l.

CONCLUSIONS

These results suggest that determination of plasma N-terminal pro-atrial natriuretic factor (1-98) in the subacute phase of myocardial infarction may provide clinically relevant prognostic information that is superior to that obtained from atrial natriuretic factor (99-126) measurements and clinical evaluation.

Myocardial expression of atrial natriuretic factor gene in early stages of hamster cardiomyopathy

Ventricular cardiomyocytes represent the most important source of atrial natriuretic factor (ANF) in pathological conditions such as congestive heart failure (CHF). It has been suggested that in cardiomyopathic Syrian hamster ventricles the ANF gene can be reactivated during the hypertrophic stage occurring before heart failure. The present study was undertaken to investigate ANF gene expression during early stages of myocardial damage and its distribution throughout atrial and ventricular myocardium in UM-X7.1 cardiomyopathic Syrian hamsters (CMPH) before hypertrophy and cardiac failure occur. Atria, right and left ventricles, and interventricular septum of hearts of 20-23 days old (young) and 90-95 days old (adult) CMPH were studied. The absence of hypertrophy and cardiac failure was preliminarly ascertained by microscopic and hemodynamic evaluation. ANF-mRNA as well as tissue and plasma immunoreactive ANF were assayed. Moreover, ANF secretion pattern was evaluated by immunocytochemical techniques. Young and adult CMPH hearts were in the necrotic stage of myocardial disease, as demonstrated by histopathological evaluation and by decreased wet weights (mg/g body weight) of different heart regions. Hemodynamic assessment showed no significant changes of left ventricular end-diastolic pressure (LVEDP) and a decrease of the left ventricular peak systolic pressure (LVSP) and +dP/dt. Plasma immunoreactive ANF (IR-ANF) levels were higher in young (3-fold) and adult (6-fold) CMPH than in age-matched normal hamsters. A reduced IR-ANF concentration (per milligram protein) was observed in both young and adult cardiomyopathic atria in respect to healthy controls, whereas a higher IR-ANF concentration was present in ventricles. A 3-fold, 6-fold and 20-fold increase of IR-ANF concentration was found in right ventricular free-wall (RV), left ventricular free-wall (LV) and interventricular septum (IVS), respectively. Northern-blot analysis confirmed that IVS was the major site of ventricular ANF-mRNA transcription in both young and adult CMPH. ANF-mRNA was increased also in atria where a faster peptide secretion can be hypothesized to lower tissue IR-ANF concentration. ANF secretion in ventricular myocardium was achieved via constitutive pathway as demonstrated by immunocytochemistry. Different patterns of ANF gene reactivation occur in CMPH myocardium before intraventricular pressure increases and structural hypertrophic modifications are detectable. The extent of ANF gene reactivation in CMPH ventricles parallels the severity of necrotic damage. Moreover, ANF gene expression is heterogeneously distributed throughout the myocardium, suggesting that interventricular septum, the ontogenically youngest heart region, might preserve foetal characters which can be rapidly reactivated in pathological conditions.

Synthesis and distribution of atrial natriuretic peptide (ANP) in hearts from normal dogs and those with cardiac abnormalities

The cardiac distribution of immunoreactive atrial natriuretic peptide (IR-ANP) and ANP-specific mRNA was studied in 35 normal dogs and 44 dogs with primary and secondary heart abnormalities. According to clinical and pathological findings the dogs were assigned to seven groups: Group 1, normal young dogs (< 12 months); Group 2, normal adult dogs (> 12 months); Group 3, low to moderate hypertrophy; Group 4, severe hypertrophy; Group 5, dilated cardiomyopathy; Group 6, renal failure with secondary left ventricular hypertrophy; and Group 7, other heart abnormalities. In comparison with hearts of normal dogs, the amount of IR-ANP and ANP-specific mRNA was reduced in the atria and increased in the ventricles of dogs with hypertrophy and cardiomyopathy. The immunoreactivity in normal canine atria was far lower than in control rats and hamsters. The pattern of ventricular immunoreactivity was faint and patchy. Only in a few ventricular localizations of three dogs of Group 5 and one dog of Group 6 was there a granular pattern suggesting the presence of secretory granules. A state of intense secretory stimulation in cardiomyopathy was indicated by electron microscopy. Due to its low concentration and localized pattern, however, IR-ANP does not seem to be a reliable marker for the presence of hypertrophic or cardiomyopathic changes in dogs.

Disturbed secretion of atrial natriuretic peptide in patients with persistent atrial standstill: endocrinologic silence

Persistent atrial standstill is a very rare pathophysiologic condition whose diagnosis is established when both electrical and mechanical silence of the atria are confirmed. To test the hypothesis that secretion of atrial natriuretic peptide is disturbed in patients with persistent atrial standstill, the response of atrial natriuretic peptide secretion and other neurohormonal factors during exercise was investigated in three patients with a rate-responsive ventricular demand (VVI) pacemaker implanted for confirmed persistent atrial standstill. The results were compared with those observed in eight normal subjects and patients with a rate-responsive VVI (Group A) or atrial demand (AAI) (Group B) pacemaker implanted for confirmed sick sinus syndrome. Patients in Group A displayed significant elevation of alpha-human atrial natriuretic peptide secretion both before and during exercise (122.5 +/- 14.8 and 207.5 +/- 8.3 pg/ml, respectively) compared with those in Group B (55 +/- 14.1 and 116.4 +/- 51.5 pg/ml, respectively) and the normal subjects (18.9 +/- 9.8 and 30.8 +/- 19.2 pg/ml, respectively). This indicated development of a nonphysiologic increase in atrial volume or pressure overload, or both, in rate-responsive VVI pacing because of lack of atrioventricular synchrony. However, patients with persistent atrial standstill had undetectable (less than 10 pg/ml) or almost undetectable secretion of atrial natriuretic peptide as well as lower levels of cyclic guanosine monophosphate in the circulation both before and during exercise. Changes in plasma catecholamines during exercise were similar in patients with persistent atrial standstill compared with the other groups. This study indicates that "endocrinologic silence" accompanies electrical and mechanical silence of the atria, which may constitute a third diagnostic clue to persistent atrial standstill.