Fine structure of atrial natriuretic peptide (ANP)-granules in the atrial cardiocytes of the mouse, rat and Mongolian gerbil.

Mouse, rat and Mongolian gerbil atrial and ventricular cardiocytes were examined by immunohistochemistry, and the right atrium including the auricle was examined by transmission electron microscopy. In addition the ANP granules of both right atrial and auricular cardiocytes were analyzed by ultrastructural morphometry. ANP immunoreactivity was detected in the atria of all three species, and the most intensely reacting cardiocytes were localized in the right auricular part of the atrium. These reactions were more prominent in the mouse and rat than in the Mongolian gerbil. ANP immunoreactivity was not detected in the ventricular myocardium of any of the three species, but was occasionally seen in the subendocardium of the ventricular septum. Ultrastructurally, the ANP granules in the auricular and atrial cardiocytes were observed to be variable in size and number, and these granules were located principally in the paranuclear region in association with the Golgi apparatus, and found throughout the sarcoplasmic layers in all three species. The ANP granules were classified into two types: A-granules containing a conspicuous electron-dense core possessing a membrane, and B-granules having profiles with a fibrillogranular, less electron-dense core than the A-granules and an indistinct membrane. The features of these granules were similar in all three species. When examined by ultrastructural morphometry, the number of each type granule and the total number of granules in the right auricular and atrial cardiocytes of the mouse and rat were significantly greater than in the Mongolian gerbil. The total number of granules in the right auricular cardiocytes was significantly greater than in the cardiocytes of the right atrium exclusive of the auricle, however, there was no significant difference between the number of A-granules and B-granules in the three species. The diameter of each type of granule in the right auricular and atrial cardiocytes of the mouse and rat was significantly greater than in the Mongolian gerbil, and the diameter of the A-granules was significantly greater than the diameter of the B-granules in all three species.     

Fine structure of atrial natriuretic peptide (ANP)-granules in the atrial cardiocytes in the hamster, guinea pig, rabbit, cat and dog.

In the hamster, guinea pig, rabbit, dog and cat, the right and left atria and ventricles were examined by immunohistochemistry, and the right auricular cardiocytes were studied by transmission electron microscopy. Moreover, ANP-granules in the cardiocytes were analyzed by ultrastructural morphometry. Immunohistochemically, the most intensely ANP-reactive cardiocytes were localized in the right auricle, particularly more prominent in the hamster and guinea pig than in the rabbit, dog and cat. The immunoreaction in the dog and cat was weaker than that in the rabbit. ANP-immunoreactivity was not detected in the ventricular myocardium of any of all species examined, but was occasionally observed in the subendocardium of the ventricular septum. Ultrastructurally, ANP-granules were localized principally in the perinuclear region associated with the Golgi apparatus and scattered throughout the sarcoplasmic layers. The Golgi apparatus of the cardiocytes was better developed in the hamster and guinea pig than in the rabbit, dog and cat. It was poorly-developed in the dog and cat. By ultrastructural morphometry, the number of granules was greatest in the hamster followed by the guinea pig, rabbit and dog or cat, in this order. On the other hand, the diameter of granules was largest in the guinea pig and reduced via the hamster to the rabbit. The diameter was significantly smaller in the dog than in the rabbit. The diameter of granules of the cat was lay between the rabbit and dog.     

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).     

Atrial natriuretic peptide (ANP)-granules of auricular cardiocytes in aging Mongolian gerbils.

The atrial natriuretic peptide (ANP)-granules of right auricular cardiocytes were studied in aging Mongolian gerbils by immunohistochemistry and transmission electron microscopy, and analyzed by ultrastructural morphometry. Immunohistochemically, the ANP immunoreactions were weaker in 3 and 4-year-old animals than in 90-day-old, 1- and 2-year-old animals. There was no difference in the reaction among 90-day-old, 1 and 2-year-old animals, or between 3 and 4-year-old animals. Ultrastructurally, the morphological features in 1 and 2-year-old animals were similar to those of 90-day-old animals, but distinct in 3 and 4-year old animals by the presence of a few lysosomal structures in the cell. By ultrastructural morphometry, number and diameter of ANP-granules of 3 and 4-year-old animals were significantly smaller than those in the 90-day-old, 1 and 2-year-old. There was no significant difference in number and diameter among the 90-day-old, 1 and 2-year-old, or between the 3 and 4-year-old.     

自发性高血压大鼠右心耳肌细胞特殊颗粒的形态分析和ANP免疫反应强度的观察

本研究运用透射电镜及形态计量学方法结合免疫组织化学技术对成年自发性高血压大鼠（ＳＨＲ）的右心耳肌细胞心房特殊颗粒（ＡＳＧ）和心房利钠肽（ＡＮＰ）的免疫反应强度进行了观察和定量研究。成年自发性高血压大鼠的心肌细胞内,ＡＳＧ数目增加,直径增大,高尔基复合体发达;线粒体轻度肿胀,部分嵴溶解断裂,部分内质网扩张,糖原颗粒增多。ＡＮＰ免疫反应增强与ＡＳＧ数目的增加一致。提示自发性高血压大鼠ＡＮＰ的合成和释放均增加,以维持机体在高血压状态下血压的平衡和内环境的稳定。     

Atrial natriuretic peptide (ANP): a study of ANP and its mRNA in cardiocytes,and of plasma ANP levels in non-obese diabetic mice

Summary Atrial natriuretic peptide (ANP) levels in cardiocytes and plasma were examined by using immunohistochemistry, electron microscopy, and radioimmunoassay in non-obese diabetic mice (NOD). Cardiocyte ANP mRNA expression was measured by the polymerase chain reaction method. ANP immunoreactivity in the auricular cardiocytes was more prominent in hyperglycemic mice (NOD-h) than in normoglycemic mice (NOD-n). Ultrastructural examination showed that auricular cardiocytes of the NOD-h group contained more cytoplasmic granules than cells of the NOD-n group. Ultrastructural morphometry indicated that the number of granules per auricular cardiocyte was significantly larger in the NOD-h group than in the NOD-n group. (P<0.01), whereas the granule diameter was significantly smaller in the NOD-h group (P<0.01). Radioimmunoassay showed that ANP levels in the NOD-h auricular cardiocytes were significantly higher than those in the NOD-n cardiocytes (P<0.01); the opposite was true in plasma. Cardiocyte ANP mRNA expression was lower in the NOD-h group than in the NOD-n group.     

Localization and characterization of atrial natriuretic factor (ANF)-like peptide in the frog atrium

The distribution of ANF was studied in the heart of the frog (Rana ridibunda) using indirect immunofluorescence. ANF-like immunoreactivity was localized mainly in the right and left atrium, most of cardiocytes being intensively labelled. At the electron microscopic level, all secretory granules present in atrial cardiocytes contained ANF immunoreactive material. Using a specific radioimmunoassay, we found higher concentrations of ANF in the left atrium (208 +/- 25 ng/mg protein) than in the right atrium (120 +/- 16 ng/mg protein) whilst in the rat, the right atrium contains the highest ANF concentration. The concentration of ANF in the ventricle was 10 times lower than in the whole atrium (32 +/- 4 ng/mg protein). Sephadex G-50 gel filtration of atrial extracts showed that ANF-like immunoreactivity eluted in three peaks. Most of the immunoreactivity corresponded to high molecular weight material eluting at the void volume while 20% of the material co-eluted with synthetic (Arg 101-Tyr 126) ANF. These results indicate that frog cardiocytes synthetize a peptide which is immunologically and biochemically related to mammalian ANF.     

Atrial-specific granules in the hearts of normal and water-deprived rats

Summary The morphology of atrial-specific granules, which contain atrial natriuretic polypeptide (ANP), was studied in the cardiac tissue of untreated controls and water-deprived rats by means of conventional and immunoelectron microscopy. Immature secretory vesicles or granules appeared to become buded off from the Golgi cisternae and then fused to form specific A-granules. An electron-dense plate with a fuzzy coat was frequently found on the limiting membrane at the end of such fusion. Pale specific B-granules, which were less electron-dense, larger, and more granular than A-granules, were found in small numbers in the left atrial cardiocytes, but rarely in the right ones. Very pale granules with a less granular matrix, considered to be B-type granules which had lost their electron-density, and which had less immunoreactivity for ANP, were numerous in the cardiac tissue after water deprivation. This morphological change, which is interpreted as an indication of granule degradation, was in agreement with the noted increase of natriuretic activity in the atrial tissue of water-deprived specimens.     

Immunoreactive atrial natriuretic peptide in the fish heart and blood plasma examined by electron microscopy,immunohistochemistry and radioimmunoassay

Summary The immunoreactivity of atrial natriuretic peptide and ultrastructure of cardiocytes were examined in 5 species each of freshwater and seawater teleosts, as well as in 2 species each of elasmobranchs and cyclostomes. Immunoreactivity was strong in the atria of Cyprinus carpio, Anguilla japonica and Conger myriaster, rather weak in atria of Channa maculata, Lepomis macrochirus, Salmo gairdneri, Oplegnathus fasciatus and Eptatretus burgeri, very weak in atria of Pagrus major, Trachurus japonicus and Triakis scyllia, and not detectable in atria of Hexagrammos otakii, Narke japonica and Lampetra japonica. The immunoreactivity of the atrial cardiocytes was generally stronger in freshwater than seawater fish. Ventricular immunoreactivity was detected only in 7 species, always being weaker than that observed in the atrium. Ultrastructurally, however, secretory granules were found in atria and ventricles of all species examined, being more frequent in the former than the latter. By radioimmunoassay, immunoreactive ANP was detected in the extracts of blood plasma and both atrial and ventricular tissues of all species examined. There were no statistically significant differences in the values between freshwater and seawater species.     

Effects of expansion of blood volume and bilateral vagotomy on specific heart granules and release of atrial natriuretic peptide in the rat

Summary There was no statistically significant difference in basal concentrations of immunoreactive atrial natriuretic peptide (ANP), as assessed by radioimmunoassay, between right and left atrial muscle of control rats; similarly, stereological analysis showed no statistically significant difference in the fractional volume of myocytes occupied by specific heart granules, or in numerical density of granules, between right and left atria. Nevertheless, correlated radioimmunoassay and ultrastructural investigations showed that the major source of elevated plasma levels of ANP after expansion of blood volume was the right atrium. Substantial expansion of blood volume caused an increase in the proportion of peripherally located granules in myocytes of both atria, but reduction in the number of granules and in the concentration and total content of ANP occurred in the right atrium only. Bilateral cervical vagotomy also caused a statistically significant elevation of plasma ANP concentration, accompanied by a statistically significant reciprocal reduction in right atrial ANP content; no statistically significant change occurred in left atrial ANP. When blood volume was expanded after bilateral vagotomy, there was a further statistically significant increase in plasma ANP concentration; this was accompanied by further reduction in right atrial ANP and, moreover, the combined manoeuvre also elicited a statistically significant reduction of ANP in the left atrium. Ultrastructural studies confirmed that, under these conditions, myocytes in both atria showed a marked depletion of specific heart granules.     

Immunohistochemical identification of Purkinje fibers and transitional cells in a terminal portion of the impulse-conducting system of porcine heart

Summary The ultrastructure of porcine ventricular tissue was studied by electron microscopy and immunocytochemical techniques. Electron-dense specific granules were found in both Purkinje fibers and transitional cells in the ventricular walls, and were positively stained by the immunogold staining method using an antiserum against atrial natriuretic polypeptide (ANP). This suggests that both the Purkinje fibers and transitional cells display the same specific granules as atrial cardiocytes containing ANP. These results demonstrate that Purkinje fibers and two types of transitional cells, in addition to the ordinary ventricular cardiocytes, can be identified in porcine ventricular wall tissue.     

Ultrastructure and Atrial Natriuretic Peptide(ANP)-like Immunoreactivity of Cardiocytes in the Larval, Metamorphosing and Adult Specimens of the Japanese Toad, Bufo japonicus formosus

The distribution of an atrial natriuretic peptide (ANP)-like material in the cardiocytes of larval, metamorphosing, and adult specimens (both breeding and non-breeding) of the toad, Bufo japonicus formosus , was studied immunohistochemically, ultrastructurally and immunocytochemically. Histochemically, ANP-immunoreaction was positive in the atrium and ventricle in stage 33 larvae, while negative in the ventricle in stage 40 larvae. In adult toads, the reaction was stronger in the right than in the left atrium but quite weak in the ventricles, particularly those of non-breeding specimens. Electron microscopy indicated a very small number of secretory granules in the atrial and ventricular cardiocytes of embryos as early as the limb-bud stage (stage 28), and as development proceeded, the number of these granules increased rapidly in atrial but not in ventricular cardiocytes. In metamorphosing animals, a small population of larger granules (200–250 nm) was noted next to those of ordinary size (the median, 110 nm) in the same cell. In adult toads, granules of about 120 nm and 200 nm in median size were found in the same cell. Postembedding immunogold staining consistently indicated ANP-immunoreactivity in these granules in atrial and ventricular cardiocytes. The plasma content of immunoreactive ANP was considerably higher in breeding (20.5 ± 5.9 pg/ml) than in non-breeding toads (5.4 ± 1.7 pg/ml). These results are discussed in relation to presently available data on the physiological role of ANP.     

人胚心肌纤维中心房特殊颗粒的分布及心钠素的免疫组化研究

收集胚胎标本共24例（经临床证实孕妇无心血管疾病）,用透射电镜观察各胎龄心脏各部位心肌纤维中心特殊颗粒（ASG）分布及含量变化,同时结合免疫组织化学技术对心脏各部位心肌纤维内心钠素的表达进行研究。结果表明,胚第5周时,心肌纤维便有ASG出现,随着胎龄的增长,心房与心耳的颗粒数量逐渐增多。而心室的颗粒数量却逐渐减少,在同一胎龄,心房内的颗粒数量多于心室,心耳ASG多于心房,免疫组织化学的研究结果表明,胚第7周时,心房与心耳内可出现心钠素样免疫反应阳性的心肌细胞,其阳性反应的变化规律与ASG的变化规律一致。心室中未发现阳性反应。     

Fine structural and immunohistochemical localization of cardiac hormones (ANP) in the right atrium and hypothalamus of the white rat

Atrial natriuretic peptide (ANP) is a polypeptide hormone secreted primarily by atrial myoendocrine cells. It has diuretic, natriuretic and vasorelaxant effects. ANP has been characterized by non-morphological methods in a number of extra-atrial tissues, particularly the hypothalamus, but little is known of the immunohistochemistry of hypothalamic ANP cells in comparison to atrial ones. Although the presence of ANP-producing cells has previously been confirmed in the right atrium of the rat and other vertebrate species, to our knowledge, this is the first study to demonstrate the presence of these cells in the hypothalamus using a purely morphological method such as electron microscopy. The fine structural and immunohistochemical characteristics of right atrial and hypothalamic ANP positive cells were investigated using immunogold labeling with goat anti-alpha-human ANP (1-28) as primary antibody. Atrial ANP cells were characterized by the presence of membrane-bound electrondense spherical or oval granules with a diameter of about 250 nm. The opaque content of the granules is separated from the limiting membrane by a thin electron translucent band about 20 nm wide. Electron dense crystalloid inclusions were evident within the granule matrix of some atrial ANP granules. Hypothalamic ANP granules were membrane-bound larger in diameter (320 nm), and less electron dense, and lacked crystalloid inclusions. Statistical analyses revealed a significant larger diameter and a significant smaller number of hypothalamic ANP granules compared to atrial ones. The significantly greater number of atrial ANP positive granules suggests a greater volume capacity for the atrial ANP positive granules as compared to the hypothalamic ones. This may indicate that ANP is secreted primarily from the right atrium and to a lesser extent from the hypothalamus; and that both atrial and hypothalamic ANP are closely related in chemical nature and immunohistochemical characteristics. This supports the suggestion that ANP may play the dual role of peripheral hormone and a neurotransmitter or neuromediator.     

Immunocytochemical localization of atrial natriuretic factor in the heart and salivary glands

Antibodies produced in the mouse by repeated intraperitoneal injections of partly purified atrial natriuretic factor (low molecular weight peptide (LMWP) and high molecular weight peptide (HMWP)) have been used to localize these factors by immunohistochemistry (immunofluorescence and immunoperoxidase method) and by immunocytochemistry (protein A-gold technique) in the heart of rats and of a variety of animal species including man and in the rat salivary glands. Immunofluorescence and the immunoperoxidase method gave identical results; in the rat, atrial cardiocytes gave a positive reaction at both nuclear poles while ventricular cardiocytes were consistently negative. The cardiocytes of the right atrial appendage were more intensely reactive than those localized in the left appendage. A decreasing gradient of intensity was observed from the subpericardial to the subendocardial cardiocytes. The cardiocytes of the interatrial septum were only lightly granulated. Sodium deficiency and thirst (deprivation of drinking water for 5 days) produced, as already shown at the ultrastructural level, a marked increase in the reactivity of all cardiocytes from both atria with the same gradient of intensity as in control animals. Cross-reactivity of intragranular peptides with the rat antibodies allowed visualization of specific granules in a variety of animal species (mouse, guinea pig, rabbit, rat, dog) and in human atrial appendages. No reaction could be elicited in the frog atrium and ventricle although, in this species, specific granules have been shown to be present by electron microscopy in all cardiac chambers. With the protein A-gold technique, at the ultrastructural level, single labeling (use of one antibody on one face of a fine section) or double labeling (use of two antibodies on the two faces of a fine section) showed that the two peptides are localized simultaneously in all three types (A, B and D) of specific granules. In the rat salivary glands, immunofluorescence and the immunoperoxidase method showed reactivity exclusively in the acinar cells. The reaction was most intense in the acinar cells of the parotid gland. In the sublingual gland, only the serous cells, sometimes forming abortive "demi-lunes", were reactive. In the submaxillary gland, the reaction was weaker and distributed seemingly haphazardly in the gland. The most constantly reactive cells were localized near the capsule while many cells did not contain visible reaction product.     

Atrial natriuretic peptide in the ventricles of patients with dilated cardiomyopathy and human foetuses

Summary Immunohistochemical examination of atrial natriuretic peptide (ANP) was performed on endomyocardial biopsy specimens from 8 patients with dilated cardiomyopathy (DCM), 10 human foetal hearts obtained from legal abortions, and 8 adult hearts from autopsy control subjects without cardiovascular diseases. The indirect immunoperoxidase method, using specific monoclonal antibody to -human ANP was employed. Immunoreactivity was observed at the light microscope level in the working ventricular cardiocytes of all patients with DCM as dark-brown, granular deposits. Peripheral plasma levels of ANP in these patients were also increased. In control adult hearts without cardiovascular diseases, immunoreactivity was detected both in the atria and in the ventricular impulse-conducting system, although the working ventricular cardiocytes were not immunoreactive. In foetal hearts, immunoreactivity was detected not only in the atria and ventricular impulse-conducting system, but also in the working ventricular cardiocytes. We conclude that ANP is present in the ventricular impulse-conducting system of the human hearts, and that ANP is also present in the working ventricular cardiocytes in patients with DCM as well as in human foetuses.     

Immunohistochemistry and immunocytochemistry of atrial natriuretic polypeptide in porcine heart

Summary Specific granules in porcine hearts were observed in atrial cardiocytes, Purkinje fibers, and transitional cells of the ventricle. These granule-containing cells were immunohistochemically stained by applying the avidin-biotin-peroxidase complex method using an antiserum against -human atrial natriuretic polypeptide (ANP). Immunoelectron microscopy of sections stained using the immunogold method indicated that these specific granules are storage sites of ANP. Furthermore, an impulse-conducting system consisting of immunoreactive cells was clearly distinguishable from nonimmunoreactive ventricular cardiocytes. We conclude that specific-granule-containing cells, i.e., ANP-producing cells, are located in both the atrial walls and the ventricular impulse-conducting system. The presence of ANP may be correlated with impulse conduction.     

Immunocytochemical localization of atrial natriuretic factor in the heart and salivary glands

Summary Antibodies produced in the mouse by repeated intraperitoneal injections of partly purified atrial natriuretic factor (low molecular weight peptide (LMWP) and high molecular weight peptide (HMWP)) have been used to localize these factors by immunohistochemistry (immunofluorescence and immunoperoxidase method) and by immunocytochemistry (protein A-gold technique) in the heart of rats and of a variety of animal species including man and in the rat salivary glands. Immunofluorescence and the immunoperoxidase method gave identical results: in the rat, atrial cardiocytes gave a positive reaction at both nuclear poles while ventricular cardiocytes were consistently negative. The cardiocytes of the right atrial appendage were more intensely reactive than those localized in the left appendage. A decreasing gradient of intensity was observed from the subpericardial to the subendocardial cardiocytes. The cardiocytes of the interatrial septum were only lightly granulated. Sodium deficiency and thirst (deprivation of drinking water for 5 days) produced, as already shown at the ultrastructural level, a marked increase in the reactivity of all cardiocytes from both atria with the same gradient of intensity as in control animals. Cross-reactivity of intragranular peptides with the rat antibodies allowed visualization of specific granules in a variety of animal species (mouse, guinea pig, rabbit, rat, dog) and in human atrial appendages. No reaction could be elicited in the frog atrium and ventricle although, in this species, specific granules have been shown to be present by electron microscopy in all cardiac chambers. With the protein A-gold technique, at the ultrastructural level, single labeling (use of one antibody on one face of a fine section) or double labeling (use of two antibodies on the two faces of a fine section) showed that the two peptides are localized simultaneously in all three types (A, B and D) of specific granules. In the rat salivary glands, immunofluorescence and the immunoperoxidase method showed reactivity exclusively in the acinar cells. The reaction was most intense in the acinar cells of the parotid gland. In the sublingual gland, only the serous cells, sometimes forming abortive demi-lunes, were reactive. In the submaxillary gland, the reaction was weaker and distributed seemingly haphazardly in the gland. The most constantly reactive cells were localized near the capsule while many cells did not contain visible reaction product.     

Identification and partial characterization of immunoreactive and bioactive atrial natriuretic peptide from eel heart

Summary Cardiocytes positive for human atrial natriurectic peptide (hANP) were identified histochemically in the eel atrium, but they were not found in the ventricule. Secretory granules were frequently observed in atrial cardiocytes by electron microscopy, but the number of such granules was quite small in the ventricle. Immunogold cytochemistry revealed that immunoreactive ANP (IR-ANP) in atrial cardiocytes was localized in these granules. In spite of poor immunostaining of the eel ventricle, an acid extract of the ventricle contained 25±4 ng·g tissue^-1 (n=9) of IR-ANP when the level of IR-ANP was measured by radioimmunoassay (RIA) for hANP. This level was one eight of that measured in atrial extracts (203±13 ng·g tissue^-1, n=9). Plasma contained 116.7±18.6 pg·ml^-1 (n=9) of IR-ANP. An extract of eel hearts decreased arterial pressure in eels and quail as did hANP. The level of ANP in the extract, as measured by an eel vasodepressor bioassay, was much greater than that measured by RIA for hANP. The immunoreactive and bioactive ANP in the heart extract are identical since the vasodepressor activity disappeared after IR-ANP was absorbed by excess antibodies raised against hANP. Chromatography on Sephadex G-75 generated a major peak of IR-ANP at a position that corresponded to a molecular weight of 14 kD and minor peaks at 3–7 kD from both plasma and heart extract. Reverse phase HPLC of plasma and heart extract generated several peaks of IR-ANP at positions more hydrophilic than those of mammalian ANPs. These results show that eel hearts contain immunoreactive and bioactive ANPs which are distinctly different from hANP. These ANPs are synthesized both in the atrium and in the ventricle, and they are secreted into the circulation mostly in the larger molecular form. The atrial ANP may be stored in the granules and secreted upon exposure of eels to certain stimuli, but the ventricular ANP may be secreted constitutively into the circulation without prior storage in the granules.Abbreviations ANP atrial natriuretic peptide - BSA bovine serum albumin - IR-ANP immunoreactive ANP - PBS phosphate-buffered saline - RIA radioimmunoassay     

Localized endocrine conversion of ventricular cardiocytes in ventricular aneurysm

Atrial natriuretic peptide (ANP) is synthesized and stored in the atria of the heart, but not or at very low concentrations in the ventricles. We investigated the occurrence of ANP and its messenger RNA (mRNA) in human ventricular aneurysm where the cardiocytes were physically over-stretched. The techniques of light and electron microscopic immunocytochemistry, and RNA-RNA tissue in situ hybridization were employed. A large amount of ANP immunoreactivity was found in the cytoplasm of the cardiocytes in and around the aneurysm, but not in fibrous scar tissue or in the normal ventricles. Immunoelectron microscopy localized the immunoreactivity mainly to specific secretory granules in the cytoplasm of the cardiocytes. ANP mRNA was also detected in these cardiocytes. The abundance of both was much higher than that found in the hypertrophic ventricles of other types. The highest concentration of ANP immunoreactivity and of ANP mRNA was found in the cardiocytes located at the border zone. The quantities of both ANP and its mRNA decreased in cardiocytes more distant from the lesion. Our findings suggest that human ventricular cardiocytes in and around aneurysm can convert to produce large amounts of the endocrine peptide ANP. This ventricular endocrine conversion was localized and was probably caused by physical over-stretch of the cardiocytes.