Immunohistochemical localisation of progesterone and oestrogen receptors at the placental interface in mares during early pregnancy.

The research examines the presence and location of progesterone receptors (PR) and oestrogen receptors (ER) at the placental interface in mares during early pregnancy. The study extends previous research, mapping the receptors from day 20 until day 68 after ovulation, covering important stages in the development of the fetus and its environment.

Objective and Methodology

• The primary aim of the research was to localize the progesterone receptors (PR) and estrogen receptors (ERα) in the equine feto-maternal tissues from day 20 to 68 post-ovulation.
• This period is significant in the horse’s gestational cycle as it entails the fixation of the conceptus, development of endometrial cups, and the attachment and initial interlocking of allantochorion, which forms the placental interface between the maternal and fetal blood supply.

Findings and Observations

• In the early phase of pregnancy, the mares exhibited the same patterns of PR in the endometrium as reported in other mammals. Specifically, there was a loss of PR from the endometrial epithelia but continued presence in stromal cells, which form the connective tissue other than blood cells and fibers.
• The arrangement of ERα, on the other hand, was found in the cytoplasm of endometrial epithelia and occasionally in the nucleus of stromal cells.
• Interestingly, no PR were observed in the fetal tissues, yet ERα was notable in some tissue compartments.
• Significantly, no significant shift in the localization of either receptor was observed throughout the studied period. This is despite the major changes occurring at the placental interface during this time.

Implications of the Research

• The findings indicate that the PR and ERα receptors likely play a crucial role in pregnancy beyond what had been previously documented.
• They are primarily involved in the production of histotroph and growth factors by the endometrium, contributing to stimulation and differentiation of feto-maternal tissues.
• This study provides a better understanding of the hormonal dynamics in horses during early pregnancy and opens up further research opportunities into hormonal functions in mammalian pregnancy.