Morphologic comparisons among equine endometrium categories I, II, and III, using light and transmission electron microscopy

Objective-To evaluate whether the pathologic changes observed by light micr oscopy in endometrium of categories II and III were reflected by cellular c hanges and to describe differences in the endometrial cell ultrastructure d uring estrus and diestrus. Animals-18 healthy mares. Procedure-Endometrial tissues biopsied during the physiologic breeding seas on were categorized, using light microscopy, and were studied, using transm ission electron microscopy (TEM). Results-Using TEM, glycogen granules were associated with giant mitochondri a for all endometrial types during diestrus. Development of rough endoplasm ic reticulum (RER) and Golgi apparatus suggested protein synthesis in the e ndometrial glands during diestrus. TEM did not reveal major ultrastructural differences, between endometrium of categories I and II. This was unlike d ifferences identified by light microscopy. The most extensive pathologic ch anges were seen in category-III tissue (TEM and light microscopy). Category -III endometria had a large number of light cells with more degenerative st ructures and fewer organelles, and lacked cilia in the lumen of the glands. This tissue had extensive fibrotic tissue in the lamina propria and many i nflammatory cells in most tissue layers. Conclusions-The severe ultrastructural changes may be one of the many facto rs decreasing the fertility of mares with category-III, compared with categ ory-1 and -2, endometrium.