Effect of side of the corpus luteum and pregnancy on estrogen and progesterone receptor expression and localization in the endometrium of mares.

This research explores how the location of the corpus luteum (a structure in the ovary) affects hormonal receptor expression and localization in the uterine lining of horses, both cyclic and pregnant. It specifically focuses on how estrogen receptor α (ERα) and progesterone receptor (PR) expression and localization vary, if at all, depending on the relative position of the corpus luteum and whether or not the mare is pregnant.

Methodology

• The study involves healthy cyclic and pregnant mares 13 days after ovulation, the time of the formation of corpus luteum.
• The collected samples included endometrium (uterine lining inside the uterus), using a transcervical biopsy method, in relation to the side where the corpus luteum is located.
• Blood samples were also taken on a daily basis from day 0 to the day of biopsy to test for 17β-estradiol (E2) and progesterone (P4) – the hormones associated with cycles and pregnancy.
• The researchers evaluated hormone receptor expression by relying on the process of immunohistochemistry (a staining process to detect proteins) and transcript expression (presence of mRNA indicating gene expression) through real-time RT-PCR method.

Findings

• Estradiol and progesterone levels in the blood were found to be unaffected by the horses’ reproductive status.
• The portion of the uterus contralateral (opposite to) the corpus luteum had more cells expressing ERα than the ipsilateral (same side as) horn.
• Progesterone receptor expression showed no differences based on the location of the corpus luteum.
• In general, ERα staining was low and was not significantly affected by pregnancy.
• However, pregnant mares displayed lower protein expression of PR.
• There was also a trend towards the contralateral horn presenting higher expression of ERα mRNA and PR mRNA.
• Pregnant mares displayed lower relative expression of ERα mRNA.
• An interaction was noted between reproductive status and the side of corpus luteum, affecting PR mRNA expression. Lower PR mRNA content was observed in the ipsilateral horn in pregnant mares compared to cyclic mares.

Significance

• This study is notable as it is the first time that research has described the behavior outlining the effects of the location of corpus luteum on the steroid hormone receptors in the endometrium of mares.
• The findings could help in better understanding of the reproductive biology in mares, which could further help in equine breeding management and possibly also have implications for human reproductive health understanding.