An electron microscope study of the endometrium of the rat during delayed implantation

Abstract

The luminal and glandular epithelia of the uterus of the rat during delayed implantation have been studied with the electron microscope, and the fine structure of these tissues has been described in detail. Light microscope histochemical preparations of the uterus have also been examined. The luminal epithelium during delay is characterized by dense lipid deposits below the nuclei of the cells. Very small glycogen bearing granules are scattered along the free surface membranes of the cells under light microscope examination. Electron microscopy reveals cytoplasmic extrusions of the free surface of the cells that correspond in size and position to the glycogen bearing granules observed in the light microscope. The apical cytoplasm is marked by the presence of numerous clear vesicles that have been termed "pinocytotic vesicles." The Golgi apparatus is prominent above the nucleus. Dense inclusion bodies displaying the properties of lysosomes appear in the supranuclear portion of the cell. The gland cells are devoid of lipid. The apical cytoplasm contains fewer pinocytotic vesicles than that of the luminal epithelial cells, and the Golgi apparatus is less well developed. Lysosome-like dense bodies are numerous in the supranuclear region. Enlarged mitochondria occasionally appear below the nuclei of the gland cells. No significant pattern of changes occurs in the fine structure of the luminal and glandular epithelia during the course of the normal ten day period of delay, nor are there any alterations to be observed on the day prior to implantation. No evidence has been found in the fine structure of either the luminal or glandular epithelia of any protein secretory activity during delay. Other than the possible extrusion from the luminal epithelium of cytoplasmic bodies containing glycogen, there appears to be little production of nutrients for the blastocysts resting in the uterine lumen. It is suggested that one of the more important functions of the luminal epithelium may be the regulation of the volume, tonicity, and pH of the luminal fluid.