Die Oberfläche des Endokards des Rattenherzens. Rasterelektronenmikroskopische Untersuchungen

Abstract Introduction : The difficulties in the observation of the inner surface of blood vessels and heart mainly arise from the known preparation techniques („Hautchen“, replicas, surface light microscopy, freeze etching). Scanning electron microscopy may overcome some of these difficulties because of its great depth of focus and the possibility to study large surface areas. Material and Methods: 12 adult male Wistar rats were fixed by in vivo perfusion via the abdominal aorta with 3% glutaraldehyde + 3% saccharose +3% dextran (15–20,000 m.w.) in phosphate buffer (0.1 m, pH 7.2) under ether anesthesia. The perfusion pressure was 100–120 mm Hg. Tissue dehydration was performed through a graded alcohol series followed by drying in a vacuum chamber. After this the hearts were dissected and the specimens were coated with 100 A carbon and 300 A gold. They were observed with the JSM-U3 (Jeol) and the Stereoscan (Cambridge). The number of the endothelial cell nuclei of the middle part of the septum (fig. 1–3) and of the latero-anterior wall of the left ventricle (fig. 4), the lateral wall of the right ventricle, the right atrium, and of the tricuspid, mitral, and aortic (fig. 10–12) valves have been determined in relation to a standard sur/face area of 10,000 μ 2 . The results were examined with the multiple comparison test of Scheffe (see table). It is suggested that a more active or passive motility of the heart structures results in a denser population of their endothelial cells. Results and Discussion: In some areas the endothelial cell borders are seen as a network of slightly elevated rims which correspond to the light microscopic lines after silver impregnation of the vessel endothelium (fig. 4). Some endothelial cells, especially on the aortic valves, possess microvilli or wart-like processes (fig. 6, 11). The endothelium of the aortic valves may have pseudopode-like protrusions of the cytoplasm, too (fig. 12). The relief of the subendothelial connective tissue fibers and myocardial fibers can be detected through the thin cytoplasm of the endothelial cells (fig. 2, 3, 7, 9). The myocardial fibers exhibit their cross-banding if the connective tissue is very thin (fig. 3). The connective tissue fibers may be devided into thin (less than 0.5 μ in diameter; fig. 3) and thick (1–1.5 μ in diameter; fig. 7, 9) fibers which are probably solitary reticulum or collagen fibers respectively bundles of them. The fiber direction varies in relation to the blood stream or to the myocardial fibers in different localizations (fig. 3, 7, 9). Thus, not only tension forces but also some other factors may influence the position of the endocardial fibers. Some bands consisting of crossly arranged rolls (fig. 2, 3) may be the effect of shrunk elastic fibers.