Ultrastructural and histological characteristics of the equine endometrium at day 5 post ovulation

Rapid endometrial adaptations occur with the embryo entering the uterus to create a receptive uterine environment, which is essential for the conceptus' development. The aim of this study was to demonstrate ultrastructural and histological changes of the endometrium at day 5 after ovulation in cyclic and inseminated mares. Mares were daily examined by transrectal palpation and ultrasonographic examination of the reproductive tract until ovulation was detected. In the first cycle, endometrial biopsies from 10 cyclic mares (Cyclic group) were collected on day 5 post-ovulation. In the second cycle, the same mares were inseminated with fresh semen from a fertile stallion (Inseminated group). Intrauterine biopsies were collected on day 5 post-ovulation, and according to sampling moment, inseminated mares were subdivided into two subgroups, those sampled at day 5-5.5 (n = 5) and those sampled at day 5.5-6 (n = 5). Biopsy samples were analyzed through scanning electron microscopy and light microscopy. Inseminated group presented an increase in glandular diameter, decrease in ciliated cell population, and an increase in lymphocyte population, compared to Cyclic group. No differences were observed between both experimental groups in number of micro-ciliated polygonal cells, percentage of flat or protruded cells in the epithelium, amount of secretion over the epithelium, glandular density, glandular luminal diameter, height of the glandular epithelium, amount of intraglandular secretion, blood vessel diameter and number of eosinophils and neutrophils. No differences in any of the variables were detected between subgroups from inseminated mares. These facts lead to the hypothesis that there is some sort of signaling to prepare and adapt the uterus to maintain pregnancy even before embryo arrival. There is also evidence to support an alternative hypothesis suggesting that all of the above mentioned are inflammatory events, resulting from a previous inflammation due to residual seminal effects. The results here presented lead to the conclusion that significant ultrastructural and histological changes of the endometrium occur on day 5 post ovulation in inseminated mares.

50 Equine uterine fluid proteome on the fifth day after ovulation

The characterisation of the uterine proteome before the entry of the embryo to the uterus is essential to know the factors involved in the physiological events of gestation. The objective of the study was to compare, by a proteomics approach, the uterine lumen of cyclic and inseminated mares on Day 5 after ovulation. Samples of endometrial secretion were collected over 2 cycles during Day 5 post-ovulation. The first cycle constituted the cyclic group (n=10), and in the following cycle, the same mares were inseminated and considered as the inseminated group (n=8). All samples were subjected to polyacrylamide gel electrophoresis with sodium sulfate in gels of 12.5%. A total of 107 spots were visualised by 2-dimensional polyacrylamide gel electrophoresis with sodium sulfate. Eight selected spots were extracted, digested by trypsin, and analysed by mass spectrometry for protein identification. Selected spots were considered representative of the differentially expressed proteins when it was shown that the intensity of the spots between the groups in the study was significantly different and considering that the protein was present in at least 50% of the gels (P<0.05). Student’s t-test was used to compare the relative percentage of expression of the spots. Four different proteins were identified by MASCOT (http://www.matrixscience.com/) and validated by the application SCAFFOLD, version 3.6.4 (http://www.proteomesoftware.com/products/scaffold/). In this study, ceruloplasmin was the main protein identified in the equine endometrium on Day 5 after ovulation. The results demonstrated statistically significant changes in ceruloplasmin expression for the inseminated group in comparison with the cyclic group (P=0.036). Our findings suggest that the increase of ceruloplasmin expression in the uterine fluid represents preparation of the endometrial for implantation and development of a potential equine embryo. The comparison of the proteic expression from the endometrium of cyclic and inseminated mares before the embryo moves into the uterus enhances understanding of the processes associated with conceptus-endometrium interaction during the maternal recognition period in the mare.