CARDIAC RHABDOMYOMA: A Case Report with Reference to Atrial Natriuretic Peptide

An autopsy case of cardiac rhabdomyoma in a male infant is reported. Many nodules of rhabdomyoma were present in all four cardiac chambers and were microscopically composed of ovoid, glycogen-laden cells and typical "spider cells". Atrial natriuretic peptide (ANP) was immunohistochemically demonstrated in both normal myocytes and rhabdomyoma cells of both atria, but not in normal myocytes and rhabdomyoma cells of both ventricles. Ultrastructurally, atrial specific granules were present in atrial rhabdomyoma cells and normal atrial cardiocytes, and these showed ANP immunoreactivity with protein A-gold technique. It could be said that the localization and intracel-Mar distribution of ANP in this cardiac rhabdomyoma were closely similar to those of normal human heart. With regard to the presence of ANP, cardiac rhabdomyoma cells arising in atria seemed to differ from those in ventricles, although many tumor nodules occurred in both atria and ventricles. Furthermore, it seemed that cardiac rhabdomyomas could also be divided into two parts: 1) an atrial part with ANP, and 2) a ventricular part without ANP. Therefore, this study confirms the hypothesis that cardiac rhabdomyoma is a hamartoma rather than a true neoplasm. ACTA PATHOL JPN 38 : 95–104, 1988.     

Comparison of effects of acetylcholine on electromechanical characteristics in guinea-pig atrium and ventricle

The direct negative effects of acetylcholine (ACh) on guinea-pig atria and ventricles were investigated using standard microelectrodes, a force transducer and a video edge-detection system. It was found that: (1) ACh (at 0.001-100 microm) decreased the force of contraction and shortened the action potential duration (APD) in both atria and ventricles in a concentration-dependent manner, and that the atria were more sensitive to ACh than the ventricles; and (2) the direct negative inotropic effect of ACh (1 microm) on an isolated cardiac cell was similar to that on the isolated myocardium. But this effect was not present in all isolated ventricular cells, while all the atrial cells responded to ACh. In conclusion, ACh had direct inhibitory effects on both atrial and ventricular tissue and myocytes, although the effects were greater in atria than in ventricles; and the negative inotropic effect of ACh was closely related to the shortening of the APD.     

Mechanisms of mechanical load-induced atrial natriuretic peptide secretion: role of endothelin, nitric oxide, and angiotensin II

There are three members in the natriuretic peptide hormone family, atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP, brain natriuretic peptide), and C-type natriuretic peptide (CNP), that are involved in the regulation of blood pressure and fluid homeostasis. CNP is found principally in the central nervous system and vascular endothelial cells while ANP and BNP are cardiac hormones. ANP is synthesized mainly in the atria of the normal adult heart, while BNP is produced by both the atria and ventricles. The mechanisms controlling ANP release have been the subject of intense research, and are now fairly well understood. The major determinant of ANP secretion is myocyte stretch. Although much less is known about the factors regulating BNP release from the heart, myocyte stretch has also been reported to stimulate BNP release from both atria and ventricles. However, whether wall stretch acts directly or via factors such as endothelin-1, nitric oxide, or angiotensin II liberated in response to distension has not been established. Recent studies show that by stimulating endothelin type A receptors endothelin plays an important physiological role as a mediator of acute-volume load-induced ANP secretion from atrial myocytes in conscious animals. In fact, endogenous paracrine/autocrine factors liberated in response to atrial wall stretch rather than direct stretch appears to be responsible for activation of ANP secretion in response to volume load, as evidenced by almost complete blockade of ANP secretion during combined inhibition of endothelin type A/B and angiotensin II receptors. Furthermore, under certain experimental conditions angiotensin II and nitric oxide may also exert a significant modulatory effect on stretch-activated ANP secretion. The molecular mechanisms by which endothelin-1, angiotensin II, and nitric oxide synergistically regulate stretch-activated ANP release are yet unclear.     

Distribution patterns of PCNA and ANP in perinatal stages of the developing rat heart

Distribution patterns of proliferating cell nuclear antigen (PCNA) and atrial natriuretic peptide (ANP) were determined immunohistochemically and morphometrically in atrium and ventriculum of the developing rat heart in different stages of the perinatal period. During the prenatal period, PCNA and ANP were localized in opposite patterns, particularly in trabecular myocytes. A distinct reduction in the percentage of PCNA-positive nuclei was detected starting at day 19 of the prenatal period, and these cells were rarely observed on postnatal days 30 and 60. In cardiomyocytes, a distinct increase in ANP positivity was found, whereas PCNA positivity was very low. It is concluded that PCNA expression gradually decreased from prenatal day 19 onwards, whereas ANP expression increased in atria throughout the prenatal and postnatal periods, except for a decrease in ANP expression in ventricles from prenatal day 21 onwards. The opposite expression patterns of PCNA and ANP in trabecular myocytes of ventricles indicate that ANP may have antimitogenic/antiproliferative effects in trabecular myocytes.     

Reversibility of exercise-induced translocation of Na+-K+ pump subunits to the plasma membrane in rat skeletal muscle

The aim of our study was to clarify whether atrial (ANP) and brain (BNP) natriuretic peptides and the hypotensive peptide adrenomedullin (ADM) are regulated differently in the rat heart in the two-kidney, one-clip model of renovascular hypertension. We assessed messenger ribonucleic acid (mRNA) abundance and distribution of ANP, BNP and ADM in the ventricles and atria of rats after unilateral renal artery stenosis (clipping). Rats were clipped for 6 h or 1, 2 or 4 days and mRNA levels were assessed semiquantitatively in left and right atria and ventricles by RNase protection assay. Left ventricular BNP mRNA up-regulation (4.3-fold after 6 hours) preceded ANP up-regulation (4.5-fold after 1 day) and seemed to be transient, whereas ANP mRNA levels were still elevated at day 4 (2.4-fold vs. sham). The right ventricle and the atria did not participate in these responses. Despite the massive changes of natriuretic peptide mRNAs, ADM mRNA did not change in either the ventricles or the atria. In contrast to ANP and BNP mRNA, which predominate in atrial tissue, mRNA for adrenomedullin is equally distributed in ventricles and atria. Plasma levels of immunoreactive (ir)-ANP and ir-BNP changed in parallel with left ventricular mRNA levels. Our findings suggest that renovascular hypertension induced by clipping the renal artery leads to immediate, but independent, up-regulation of ANP and BNP mRNA in the left ventricle whereas adrenomedullin mRNA is not changed.     

Distribution of atrial natriuretic peptide in the conduction system and ventricular muscles of the human heart

Summary Atrial natriuretic peptide (ANP), a cardiac hormone, is known to be located in the atrial specific granules, but its presence and localization in the ventricular muscle of the human heart has not been examined fully. Using a specific antibody to human ANP, we studied the conduction system and ventricular muscle with immunohistochemical and ultrastructural methods in 30 hearts obtained at autopsy. These included 12 normal and 18 diseased hearts. In the normal hearts, ANP-positive granules, which were regularly observed in the atrial myocytes, were found in small quantities in the cells of the penetrating and branching bundles in 4 of 12, and in the cells of the ventricular free walls in 2 of the 12 hearts. In the diseased hearts, the positivity increased significantly (P<0.05), being found in 13 of 18 (72.2%) conduction systems and 10 of 18 (55.6%) ventricular muscles. The granules were confirmed to be immunoreactive with ANP by ultrastructural examination. Furthermore, the presence of ANP mRNA in the conduction system as well as in the ventricular myocytes was demonstrated by Northern blot hybridization for which we used the complementary DNA of human ANP. Thus, a small quantity of ANP appears to be synthesized and stored in the conduction system and ventricles of some normal hearts. However, ANP was shown to be present in a larger percentage of the diseased hearts.     

Immunocytochemical studies of cardiac myocytes and other non-neuronal cells of the fetal human heart in culture

Summary Non-neuronal cell types present in cultures dissociated from the atria and ventricles of human fetal hearts, from 9 to 21 weeks’ gestation, were studied using phase-contrast optics and immunocytochemistry. All atrial myocytes and many, if not all, ventricular myocytes observed in culture contained atrial natriuretic peptide-like immunoreactivity. Generally, the atrial natriuretic peptide-like immunoreaction in atrial myocytes was more intense and widespread than in ventricular myocytes. Atrial and ventricular fibroblasts expressed extracellular fibronectin-like immunoreactivity. A population of cells with the appearance and growth properties of endothelial cells was observed in both atrial and ventricular cultures, and was classified as endothelioid since their precise origin was not known. Only a subpopulation of these endothelioid cells contained factor VIII-related antigen immunoreactivity, and some cells that did not display the other growth characteristics of endothelial cells were also factor VIII-related antigen immunoreactive in culture. Glial cells were S-100-like immunoreactive; they were usually more numerous in atrial than ventricular preparations. There was no close association between glial cells and neurones in the atrial cultures.     

Localization of NOS-1 in the sarcolemma region of a subpopulation of atrial cardiomyocytes including myoendocrine cells and NOS-3 in vascular and endocardial endothelial cells of the rat heart

Cellular localization patterns of NOS isoforms 1 and 3 (nNOS and eNOS, respectively) in the mammalian heart under basal (non-stimulated) working conditions are still a matter of discussion. Therefore, this issue was reinvestigated in rats using RT-PCR, Western blotting, catalytic histochemistry, immunohistochemistry and image analysis. Tongue and extensor digitorum longus muscles served as positive controls for NOS-1 and NOS-3. RT-PCR revealed NOS-1 mRNA and NOS-3 mRNA in atria and ventricles. Western blotting showed NOS-1 protein in atria and NOS-3 protein in the walls of both heart chambers. Localization of the activity of urea-resistant (and therefore specific) NADPH diaphorase (NADPH-D) and NOS-1 immunohistochemistry showed that NOS-1 is present in the sarcolemma region of a subpopulation of atrial cardiomyocytes but not in working and impulse-conducting cardiomyocytes of atria and ventricles. Atrial natriuretic peptide (ANP) immunohistochemistry revealed that a minority of the NOS-1-expressing atrial cardiomyocytes are myoendocrine cells. eNOS immunostaining was present in endothelial cells of capillaries of the conducting and working myocardium and endocardial cells. Image analysis of the activity of urea-resistant NOS diaphorase showed that NOS-1 activity is lower in the sarcolemma region of atrial cardiomyocytes than in that of tongue and extensor digitorum longus myofibers. These data suggest that, in the non-stimulated rat heart. NOS-1 is expressed in a subpopulation of atrial cardiomyocytes including myoendocrine cells, and that NOS-3 is expressed in the vascular and endocardial endothelium.     

大鼠胚心室肌心房肽样物质定位的研究

本文用免疫组织化学方法研究了大鼠胚(13～19天)心房肽样免疫反应物质在心室肌细胞的定位,并在电镜下观察了大鼠胚心室肌细胞的超微结构。所得结果表明,心房肽类物质不仅存在于心房肌,亦在心室肌细胞内。含心房肽样免疫反应物质的细胞主要位于左心室,尤其是靠内膜侧的小梁状或网格状结构内。左右心室壁内这种细胞很少。心室肌细胞内所含心房肽样免疫反应颗粒的数量较同期心房肌细胞少。在电子显微镜下,见部分心室肌细胞含有与心房特殊颗粒(含心房肽类物质)相似的电子致密颗粒,它们大多靠近高尔基复合体。部分细胞不含这种颗粒,前者可能为心房肽样免疫反应阳性细胞,后者可能为阴性细胞。     

Myocardial ANP expression in Pompe's disease: An immunohistochemical study

The expression of atrial natriuretic peptide (ANP) was analyzed in the atrial and ventricular myocardium in three cases of Pompe's disease (glycogen storage disease of the myocardium), using an immunoperoxidase technique. The cytoplasm of almost all atrial myocytes and some subendocardial myocytes from the right and left ventricles were ANP-positive, excluding the typical central vacuole, which was occupied by glycogen. Ventricular ANP expression was usually more prominent in left ventricular samples, and its distribution was similar to that described in dilated, hypertrophic, restrictive, or ischemic heart disease; however, the enlargement of the myocytes in Pompe's disease is not caused by hypertrophy. We conclude that the atrial myocytes in Pompe's disease maintain ANP expression, despite severe cytoplasmic vacuolization. These results suggest that ventricular ANP expression may be related to mechanical stimuli, such as the increase in wall stress, and not directly related to myocyte hypertrophy.     

Ventricular expression of atrial and brain natriuretic peptides in dilated cardiomyopathy. An immunohistocytochemical study of the endomyocardial biopsy specimens using specific monoclonal antibodies.

Although brain natriuretic peptide is expressed in ventricles of failing hearts including dilated cardiomyopathy, its morphological localization is still unclear. In this study, we analyzed the immunohistocytochemical localization of atrial and brain natriuretic peptides in ventricles of dilated cardiomyopathy at both light and electron microscopic levels. Ventricular specimens were obtained by endomyocardial biopsy in 31 patients (26 with dilated cardiomyopathy and 5 controls without any specific cardiac disease). By light microscopic immunohistochemistry using specific monoclonal antibodies, all (26 of 26) of the left ventricular endomyocardial biopsy specimens and 31% (8 of 26) of the right ventricular specimens showed immunoreactivity for both of these natriuretic peptides in dilated cardiomyopathy. In contrast, none of the normal controls showed immunoreactivity for either of these peptides. The percentage of atrial natriuretic peptide-containing or brain natriuretic peptide-containing myocytes in the left ventricular specimens showed an inverse correlation with the left ventricular ejection fraction (r = -0.72 and r = -0.69, respectively). By electron microscopy, we identified specific secretory granules in ventricular myocytes from patients with dilated cardiomyopathy, but not in those from normal controls. Double immunocytochemistry using a two-face immunogold staining method revealed brain natriuretic peptide colocalized with atrial natriuretic peptide in the same ventricular granules. These findings suggest that brain natriuretic peptide is expressed in ventricular myocytes in response to hemodynamic stress in dilated cardiomyopathy. Brain natriuretic peptide may be, at least in part, synthesized simultaneously and secreted together with atrial natriuretic peptide by granules from failing ventricles, although the secretory turnover is different between these two peptides.     

Chimerism of the transplanted heart.

BACKGROUND: Cases in which a male patient receives a heart from a female donor provide an unusual opportunity to test whether primitive cells translocate from the recipient to the graft and whether cells with the phenotypic characteristics of those of the recipient ultimately reside in the donor heart. The Y chromosome can be used to detect migrated undifferentiated cells expressing stem-cell antigens and to discriminate between primitive cells derived from the recipient and those derived from the donor. METHODS: We examined samples from the atria of the recipient and the atria and ventricles of the graft by fluorescence in situ hybridization to determine whether Y chromosomes were present in eight hearts from female donors implanted into male patients. Primitive cells bearing Y chromosomes that expressed c-kit, MDR1, and Sca-1 were also investigated. RESULTS: Myocytes, coronary arterioles, and capillaries that had a Y chromosome made up 7 to 10 percent of those in the donor hearts and were highly proliferative. As compared with the ventricles of control hearts, the ventricles of the transplanted hearts had markedly increased numbers of cells that were positive for c-kit, MDR1, or Sca-1. The number of primitive cells was higher in the atria of the hosts and the atria of the donor hearts than in the ventricles of the donor hearts, and 12 to 16 percent of these cells contained a Y chromosome. Undifferentiated cells were negative for markers of bone marrow origin. Progenitor cells expressing MEF2, GATA-4, and nestin (which identify the cells as myocytes) and Flk1 (which identifies the cells as endothelial cells) were identified. CONCLUSIONS: Our results show a high level of cardiac chimerism caused by the migration of primitive cells from the recipient to the grafted heart. Putative stem cells and progenitor cells were identified in control myocardium and in increased numbers in transplanted hearts.     

Atrial amyloid deposits in the failing human heart display both atrial and brain natriuretic peptide-like immunoreactivity

Atrial amyloid deposits are common in the ageing human heart and contain alpha-atrial natriuretic peptide (proANP99-126) immunoreactivity. However, atrial myocytes secrete both amino and carboxy terminal fragments of the ANP prohormone (proANP1-126) and also express an homologous, but separate brain natriuretic peptide (BNP). Characteristic amyloid deposits were identified in the atria of 9/22 patients (26-63 years of age) with end-stage heart failure. Amyloid fibrils displayed immunoreactivity for both amino and carboxy terminal fragments of proANP1-126 and for the distinct BNP sequence. As in other endocrine organs, both mature and precursor peptide sequences appear to be constituents of amyloid fibrils. Whilst immunoreactivity for cardiac peptide hormones is co-localized in atrial amyloid deposits, it is uncertain whether the increase in natriuretic peptide expression which accompanies cardiac failure contributes to the incidence of isolated atrial amyloidosis.     

Case report of a heart transplantation in a 16-year-old male

We examined ultrastructural changes and did immunohistochemical studies of atrial natriuretic peptide (ANP) in biopsied samples obtained from the heart of a 16-year-old Japanese boy with dilated cardiomyopathy and from the transplanted donor heart. In the right ventricle of the diseased heart, a small number of atrial granules containing ANP were found in the perinuclear area of the cardiomyocytes and near areas lacking some myofibrils. Although no evidence of rejection was seen in the right ventricle of the transplanted donor heart under the light microscope, electron microscopy revealed moderate degeneration of cardiomyocytes and injuries to capillary endothelial cells. We did not find atrial granules, although the serum ANP level was elevated. These data suggest that the ultrastructural changes in the transplanted heart were related to a mild rejection, the effects of cyclosporin, or the effects of a domino heart transplantation from a patient with cystic fibrosis. Because of the absence of atrial granules in the right venticle, it is postulated that the high serum ANP level may be attributed to merely an increased secretion of ANP from atrial granules in the atria, without secretion of ANP in the ventricles.     

Effect of ryanodine on atrial natriuretic peptide secretion by contracting and quiescent rat atrium

To elucidate the mechanism involved in the release of atrial natriuretic peptide (ANP), we studied the importance of ryanodine-sensitive Ca²⁺ release in stretch-secretion coupling. The experiments were made with a left atrial preparation, where the stretch of myocytes was induced by changing the intra-atrial pressure. When external pacing was not applied, the atrial preparation was not spontaneously contracting, and it was therefore possible to investigate the secretory mechanism in the quiescent atrium. The superfusate was collected in 2-min fractions and assayed for ANP immunoreactivity. Filtration analysis revealed that the major fraction in the superfusate in all experimental situations had a similar molecular weight as the ANP 1–28. Ryanodine (1.0 M and 0.1 M) inhibited stretch-stimulated ANP secretion dose dependently both in paced and nonpaced atrium, but did not have any effect on basal secretion. The present results support the notion that intracellular Ca²⁺ transients from the intracellular stores are essential for stretch-stimulated ANP secretion, independently from excitation and contraction. Basal ANP secretion is not inhibited by blocking ryanodine-sensitive Ca²⁺ channels, either in contracting or in non-contracting atria. In addition our results confirm that the principal stimulus for ANP secretion in response to atrial distension is the stretch of myocytes. Length shortening of myocytes is not essential for ANP release.     

Increased cardiac weight in interleukin-6 transgenic mice with viral infection accompanies impaired expression of natriuretic peptide genes

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) regulate cardiac hypertrophy. We investigated ventricular alterations of ANP and BNP in interleukin-6 (IL-6) transgenic mice (TG) and wild type (WT) mice with or without viral infection. The ANP and BNP mRNA/GAPDH mRNA ratios in the ventricles of IL-6 TG mice were twice that of WT mice, but were not increased significantly by viral inoculation. In WT mice, both ANP and BNP responses were significantly increased in the ventricles of mice 10 days after encephalomyocarditis (EMC) viral inoculation. Cardiac weight in IL-6 TG mice was significantly greater than in WT 10 days after viral inoculation. Left ventricular wall thickness and the diameter of ventricular myocytes also were greater in IL-6 TG than WT after viral infection. Primary cultures of neonatal rat cardiac myocyte showed that IL-6 increased ANP and BNP mRNA expression in a dose-responsive fashion. In summary, overexpression of ANP and BNP occurs in the ventricles of IL-6 TG mice, along with increased cardiac weight after infection with EMC virus, and impaired responses in the expression of ANP and BNP.     

Identification and distribution of atrial natriuretic polypeptide in ventricular myocardium of humans with myocardial infarction

The expression of atrial natriuretic polypeptide (ANP) in the ventricles of human hearts with myocardial infarction (MI) was studied immunohistochemically. Immunoreactive myocytes were identified in the ventricular tissues of all of 16 hearts with old MI (both with and without heart failure) and in all five hearts with subacute MI, but not in any of the eight hearts without MI nor in the five with acute MI. In the nonfailing hearts with MI, ANP positive myocytes surrounded the areas of infarction, and were also seen in the subendocardium of the infarcted segment. In the failing hearts with MI, ANP expression was noted in the whole ventricular subendocardial region, in addition to the border of infarcts. The sites of ANP expression corresponded well to those of marked stress attributable to tissue shrinkage or fibrosis due to MI, haemodynamic overload, or both. It thus appears that ANP expression is augmented in human hearts with MI regardless of the presence or absence of heart failure, and it is suggested that regional mechanical stress on the ventricular myocardium, as well as haemodynamic overload, may be very closely associated with ventricular ANP expression.     

Membrane systems of guinea pig myocardium: ultrastructure and morphometric studies

The structure and quantitative contribution of membrane systems (transverse-axial tubular system [TATS] and sarcoplasmic reticulum [SR]) have been investigated in the heart of the adult guinea pig. Although previous quantitative studies have been made of guinea pig myocardium, this is the first such study that has utilized tissue in which membrane system elements were clearly identified by selective staining (in this case by the osmium-ferrocyanide [OsFeCN] postfixation method). Both membrane systems are highly developed in ventricular cells, but a TATS is essentially absent from atrial myocytes. The ventricular TATS consists principally of large-bore elements which may be oriented transversely, axially, or obliquely, making numerous anastomoses with one another to form a highly interconnected system of extracellular spaces that penetrate to all myoplasmic depths of the ventricular cell. The cell coat that lines the lumina of these tubules is structured, containing fibrillar structures that run along the length of the tubule. The volume fraction (VV) of the ventricular TATS is low (2.5-3.2%), in consideration of the qualitative prominence of the TATS in these cells. The relative total population of sarcoplasmic reticulum is higher in the atria (VV of 10-11%) than in the ventricles (VV of ca. 8%). In all guinea pig myocytes, several major structural divisions of SR can be discerned, which include network SR, junctional SR, corbular SR, and cisternal SR. Junctional SR (J-SR) in the atrial cells is limited almost exclusively to peripheral saccules of junctional SR (PJSR), whereas both interior J-SR and PJSR are present in the ventricle. Two distinct morphological types of PJSR appear in atrial cells, including both flattened and distended saccules, the latter resembling PJSR of lower vertebrate heart. Spheroidal bodies of SR with opaque contents (corbular SR) are prominent at or near Z-line levels of the sarcomeres of atrial and ventricular cells. Cisternal SR is likely a subset of network SR, but some examples appear related to rough endoplasmic reticulum. An overall impression obtained from this study is that guinea pig atria are composed of structurally primitive cells, whereas the ventricular cardiac muscle cells are more highly developed entities.