Cyclic changes of the canine endometrial surface: An electron-microscopic study

The endometrial surface morphology of 38 dogs during different stages of the estrous cycle was investigated with scanning electron microscopy. The cell surface altered from convex in proestrus and estrus to very variable in early metestrus, flattened in late metestrus and became completely plane in anestrus. Microvilli were numerous and long in proestrus and in estrus, became short and variable in number in early metestrus, decreased further in length in late metestrus and became very short and rare in anestrus. The variable appearance in early metestrus was not influenced by changing the osmolarity of the fixative and might be a physiological process. The number of glandular openings showed little variability throughout the estrous cycle. Ciliated cells were rare but present in all cycle stages except in late metestrus. However, in the latter cycle stage and in anestrus rare single strands were noted. Transmission electron microscopy was used to determine the inner structure of these strands. Microtubuli were detected in transversal and longitudinal sections but without the 9 + 2 arrangement which is characteristic for cilia. The nature and function of these structures remain unclear. Copyright (C) 2003 S. Karger AG, Basel.