| Objective:The result of radioimmunoassay manifests that the atrial natriuretic peptide (ANP) is present in the pericardial fluid. Moreover, the level of ANP in the pericardial fluid is about 4 to 100 times than that in the plasma in the physiological or pathological conditions. This great difference of lever indicates that ANP could be directly secreted into the pericardial cavity by the myocardial cells. However, about the physiological and pathological significance of ANP in a high lever in the pericardial fluid is not clear yet. And about its how-to-come and how-to-go problem still lacks the morphological evidences. Therefore, we studied the atrium and pericardium by light microscope (LM) and electron microscope, in order to discuss the releasing pattern and extracellular transport route of the atrial secretory granules (ASG) or ANP, and offer the evidences of the structural foundation and morphology for the how-to-come and how-to-go problem and important significance of ANP in the pericardial fluid. Methods:(1) The right atrial appendage of rabbits and its oppositeportion of the pericardium were stained by hematoxylin-eosin (HE) and 5'-nucleotidase (5'-Nase) staining methods. Then we observed by LM the normal microstructure of the epicardium and pericardium, in which the distribution of the lympgatic vessel was also observed.(2) We observed by transmission electron microscope (TEM) the ultrastructure of right atrial appendage and pericardium and the feature of conjunction between the epithelial cells. And we not only identified the type of the blood capillaries among the myocardial cells, but also observed the ultrastructure and distribution of lymphatic capillaries and ASG.(3) We observed by scanning electron microscopy (SEM) the luminal surface ultrastructure of the epicardium and pericardium. Furthermore, we observed the architecture of the connective tissue fibers under the mesothelial cells of the pericardium, which was macerated with NaOH.Result:(1) The observation of LM indicates that the epicardium is composed of the simple epithelium and subepithelial connective tissue. The myocardium is immediately under the epicardium and the strip-like myocardial cells are seen. The pericardium is composed of the luminal simple epithelium, subepithelial connective tissue and abluminal simple epithelium. The thickness of the connective tissue in the epicardium and pericardium is different from region to region. And in the connective tissue are seen the deep brown lymphatic vessels,whose wall is thin and whose lumen is large and irregular. The lymphatic vessels distribute in the deep layer of the connective tissue in the epicardium and often accompany the blood vessels in the pericardium.(2) The observation of TEM reveals that the interepithelial conjunction of the epicardium is not tight, and that in the cytoplasm of the atrial myocardial cells are there many ASGs, which mainly accumulate near the polarity of the cellular nuclus. ASGs are ovale bodies with homogenous electron-dense content and limiting membrane, under which one could identify thin ring. And their size differs from 100 to 300nm in diameter. Beside the myocardial cells passes a thin myelinated nerve fiber bundle, in which there are a few secretory granules with homogenous electron-dense content, and terminates a unmyelinated nerve ending, in which there are many bright vesicles. We do not observe the synapse-like structure formed by the nerve ending and the myocardial cell. The endothelium of blood capillaries among the myocardial cells is continuous without fenestra. And there is a pericyte that embraces the blood capillary, in which lumen there often are red blood cells. Compared with blood capillaries the interendothelial conjunction of lymphatic capillaries is relatively loose, and the ending-to-ending and overlapping connections could be observed. Lymphatic capillaries generally possess a more irregular and wider lumen than blood capillaries, and their endothelium is relatively attenuated, and their lumens do notcontain red blood cells. In the lumen of the lymphatic capillary could be seen secretory granules with homogenous electron dense content and limiting membrane, and their size is about 700nm. They are in a state of dilation or disaggregation, and the limiting membrane of some secretory granules has deformed and a portion of content has discharged. We often could observe a lot of membranous structure of fragment in the tissue space and the lumen of lymphatic capillaries, and this membranous structure is probably the fragment of limiting membrane remained by secretory granules after emptying their contents. In the pericardium could be seen the submesothelial collagen fiber bundles distributing vertically and horizontally, and also seen a spindle-shaped fibroblast and a longitudinally cutted lymphatic vessel, which is long and narrow, and whose wall is very thin but the nucleate part is relatively thick.(3) The observation of SEM shows that the microvilli of epithelial cells of the epicardium are relatively rich, especially on the cellular edge. Among two or three epithelial cells could be seen many global secretory granules, which are in a state of dilation and satiation, and whose global surface is even, and whose size differs from 1 to 4um in diameter. The epithelial cells in the luminal surface of the pericardium have two types: the cuboidal cell and the squamous cell. The former has a clear big profile. Among three consecutive cuboidal cells exist a triangular pore, whose size is about 5(im. And the latter has relatively rich microvilli and a wave-like edge. On the luminalsurface of the epithelial cells could be seen the milk spots, which is formed by the aggregation of many silent macrophages. The pericardium, which was macerated with NaOH, was also observed in the SEM. All cells were eliminated as result of maceration with NaOH, but the subepithelial collagen fibers remained intact and kept their original architectural feature. A portion of collagen fibers forms a latticed network, which is called maculae cribrosae. And it is composed of the clustered cribriform foramina, which is ellipse- or polygon-shape, and whose size is 10~20um And the rest portion of collagen fibers interlaces tightly. The petty reticular fibers also evenly distribute the surface of the collagen fibers, so they divide the cribriform foramina into many meshes, whose size is 0.5~2um. Conclusion:The structural feature of the auricle and pericardium show:(1) ASG not only distribute in the cytoplasm of the myocardial cells, but also in the exocellular tissue fluid. This finding indicates that the pattern of whole releasing, which is the releasing with granule's limiting membrane, is present when the atrial myocardial cells release ASG.(2) The fact that the ASG could be seen in lumen of the lymphatic vessel among the myocardial cells indicates that it could enter the lymphatic capillary and be transported by the lymphatic system. And ASG are also observed on the surface of the epicardium, which indicates that they could directly enter the pericardial cavity through the epicardium. Then they could... |
PDF Full Text Request