Cytological and Electron Microscopical Observations on the Vascular System of the Various Organs and Mesentery of Guinea Pigs, with Special Reference to the Endothelial Cells

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Abstract
Healthy matured guinea pigs, of the weight of 300 to 350g, were used for the study. The specimens were taken by clubbing, decapitation, death caused by ether or ravonal narcotism and experimental shock by croton oil. The specimens for light microscope were taken from mesentery, liver, pancreas, spleen, kidney, lung, adrenal gland, thyroid, abdominal aorta and femoral artery and were fixed in LEVI's solution, CHAMPY's solution, ZENKER-formol and 10% formalin. After cutting, in 3 to 4μ paraffin serial sections, they were stained by HEIDENHAIN's iron-hematoxylin (considered to be the most suitable for the observation of the endothelial cells), azan staining, hematoxylin (HANSEN)-eosin staining, thionin staining and PAS reaction. For the electron microscope, small pieces of the mesentery (sacrificed with clubbing) were fixed in 1% osmium tetroxide adjusted to pH 7.4 with veronal-acetate buffer, dehydrated through a series of alcohol, and then embedded in styrene and n-butyl methacrylate (1:1) and epon by KUSHIDA's method. Thin sections were cut on a PORTER BLUM microtome with glass knives, and stained with uranyl acetate, and examined in a HITACHI HU-10 electron microscope at magnification of 1, 000-10, 000. 1. The inner coat, tunica intima, of various organs' arteries and the mesenterial artery are mainly composed of the endothelium, and the tunica media is made up of one or several layers of the smooth muscle cells running circularly. The arteries of large caliber, with 3 or 4 layers of the smooth muscle cells, are small in number, while those of small caliber, with 1 or 2 layers of the smooth muscle cells, are great in number. Glycogen are often noticed in smooth muscle cells, and beside the nucleus 1 or 2 vacuoles are sometimes noticed. The internal elastic membrane, comparatively well developed and stained with PAS reaction and iron-hematoxylin, is observed on the boundary between the tunica intima and media. The wavy running of the lamina elastica interna becomes conspicuous as a result of the contraction of the smooth muscle of the tunica media. In such a case, the endothelial cells take a cylindrical form. 2. In the cytoplasm of the endothelial cells of small arteries of various organs and the mesenterium of the guinea pigs, it has been confirmed that the vacuoles are observed physiologically. a) Liver. Among the interlobular arteries of the GLISSON's capsule, the endothelial cells of comparatively large calibrated arteries, with several layers of the smooth muscle cells of tunica media are mostly low and flat or cubic in shape, and are very scanty of cytoplasm, have no vacuole. Cylindrically shaped endothelial cells, projecting themselves in the blood vessel's lumen, are found in a small number, in which sometimes one or two vacuoles can be seen under the nucleus. The endothelial cells of the interlobular artery of comparatively small caliber, with one or two layers of the smooth muscle cells, are of a cylindrical or cubic shape and are projecting themselves into the arterial lumen in the shape of a dome. Various stages of vacuolation are always observed in their cytoplasm. Firstly, under the nucleus, especially at the basal portion of the cell, small or medium-sized vacuoles make their appearance. They grow up gradually bigger and bigger and fuse with one another. Sometimes the cytoplasm is replaced by vacuoles of various sizes, and can be seen in form of thin layers among the vacuoles. The nucleus is suppressed to the vessel's lumen side and transforms itself under pressure of the vacuoles and sometimes increases in density. The endothelial cells which are intensely vacuolated protracts itself in a shape of a balloon toward the vessel's lumen. Occasions not infrequently arise when the degree of vacuolation differs according to the site of the transverse section of the artery. b) Kidney. Endothelial vacuolation was frequently noticed in interlobar artery

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