ULTRASTRUCTURE AS A BASIS FOR DATING OF RAT ENDOMETRIUM

Studies on the endometrial cycle depend upon the precise dating of the cycle stage. In the present paper the generally applied method of vag inal smear was carefully verified through the measurement of the hormo nes relevant to the endometrial cycle. From rats predated through vagi nal smear cytology, the hormone levels of estradiol-17-beta (E(2)) and progesterone (P), luteinizing hormone (LH), and follicle stimulating hormone (FSH) were measured. The values obtained were then compared to the standardized values of our reference curve. Animals with values t hat did not fit within the standard deviation of our reference curve w ere excluded from this investigation. Thus, for the first time exactly dated rat endometrial morphology was studied with electron microscopy . The morphology of the surface epithelium of rat endometrium from all four stages of the cycle is described in detail. In addition, a semiq uantitative morphometric analysis of the following parameters was perf ormed: cell volume, nuclear volume, the volume density of secretory gr anules, digestive vacuoles, mitochondria, Golgi apparatus, rough endop lasmic reticulum, and lipid vacuoles as well as the size of lipid vacu oles. With the cellular content of lipid vacuoles and their diameter, it is possible to differentiate between proestrus/estrus and diestrus I/diestrus II, the latter possessing definitely more and larger lipid vacuoles. During estrus the greatest cytoplasmic volume develops. In a ddition to this, secretory granules are only present during estrus. Fi nally, diestrus I can be well differentiated from diestrus II, because diestrus I exhibits more digestive vacuoles and during diestrus II a high percentage of free ribosomes is present. On the basis of distinct morphological features, described in this paper, it is now clearly po ssible to distinguish between the four different cycle stages. (C) 199 4 Wiley-Liss, Inc.