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In order to better understand physiological changes during the different stages of the oestrous cycle, immunohistochemistry was used in the present study to investigate the distribution of oestrogen receptor alpha (ER alpha) as well as the proliferative marker Ki-67, in the sow uterus during the oestrous cycle. Uterine samples were collected from multiparous sows with normal reproductive performance at selected stages of the oestrous cycle: at late dioestrus (d 17), prooestrus (d 19), oestrous (d 1), early dioestrus (d 4) and dioestrus (d 11-12), respectively. The tissue samples were fixed in 10% formaldehyde, embedded in paraffin and subjected to immunohistochemistry using monoclonal antibodies against ER alpha (C-311) and Ki-67 (MM-1). In general, the immunostaining of both ER alpha and Ki-67 was confined to nuclei of the target cells. Variations were seen, not only at the different stages of the oestrous cycle, but also in the different tissue compartments of the uterus. In the epithelia, the strongest ER alpha staining and highest amount of positive Ki-67 cells were found at early dioestrus. In the myometrium, the highest levels of staining of both ER alpha and Ki-67 positive cells were found at pro-oestrus and oestrus. For the proliferative marker, Ki-67, no positive cells were found at dioestrus and late dioestrus in the epithelium and myometrium. In the connective tissue stroma (subepithelial layer), the highest number of ER alpha positive cells were found at oestrus, which was significantly different compared with other stages (p< or = 0.05), whereas the levels of Ki-67 positive cells were relatively low and did not differ between the stages examined. Significant correlations between the number of ER alpha positive cells in the stroma and Ki-67 positive cells in the epithelia were observed. This suggests indirect regulatory mechanisms on epithelial proliferation via ER alpha in the stroma. In conclusion, these findings in the sow uterus show that the presence of ER alpha as well as Ki-67 protein varies not only between different stages of the oestrous cycle but also between different tissue compartments of the uterus. These findings indicate various regulatory mechanisms and stress the importance of localising ER alpha and proliferating cells in different uterine tissues.

Physiological changes in the sow uterus involve the regulation by progesterone and its receptor proteins (PR). Therefore, the aim of the present study was to investigate the localization of PR during different stages of the oestrous cycle and in inseminated sows during early pregnancy by use of immunohistochemistry. Uterine samples were collected from cyclic and inseminated sows at different stages of the oestrous cycle and early pregnancy. The samples were fixed in 10% formaldehyde and embedded in paraffin. Immunohistochemistry was done by use of a mouse monoclonal antibody to PR. The highest PR immunostaining in the surface epithelium was observed at oestrus/5 -6 h after artificial insemination (AI) and early dioestrus/70 h after AI. In the glandular epithelium, the highest level of PR was found at oestrus with the lowest at late dioestrus/d 19. Higher levels of PR were observed in inseminated groups compared with cyclic sows. In the myometrium, a high level of PR was found at oestrus, while stromal PR cells were constantly present throughout the oestrous cycle and at different stages of early pregnancy. In conclusion, this study shows that the immunopresence of PR in the sow uterus differed between uterine compartments at the same reproductive stage. Differences were also found for some uterine compartments between cyclic and inseminated/early pregnant sows. The relatively consistent immunostaining of PR in the stroma strengthens a stromal role in the regulation of physiological activities in the sow uterus during the oestrous cycle as well as early pregnancy.