Changes in equine endometrial oestrogen receptor alpha and progesterone receptor mRNAs during the oestrous cycle, early pregnancy and after treatment with exogenous steroids.

This study focuses on the changes in estrogen and progesterone receptor mRNAs in the uterine lining of horses, and how these changes are influenced by the reproductive cycle, early stages of pregnancy, and treatment with external hormones. Notably, it reveals that the amount of these mRNAs varies in correlation with the hormone environment in the uterus, and that this mechanism can be affected by the duration of progesterone dominance.

Study Overview

• The research consists of two separate experiments, with common focus on changes in mRNA of estrogen and progesterone receptors (ER alpha and PR).
• The subject matter was centered around the equine endometrium – the inner lining of a mare’s uterus.
• The driving factor behind the research included hormonal changes throughout the oestrus cycle, early stages of pregnancy, and the impact of externally administered steroids.

Experiment 1

• Biopsies were taken from non-mated mares in heat and 5, 10, and 15 days after ovulation. In pregnant mares, samples were taken 10, 15, and 20 days post-ovulation.
• The results showed significant overall effects of the day post-ovulation on the abundance of ER alpha and PR mRNAs in the endometrium.
• The amounts of ER alpha mRNA decreased at day 10 of pregnancy, while PR mRNA was reduced at day 5 in non-mated mares and day 15 in pregnant mares.

Experiment 2

• This study sought to determine the impact of externally administered steroids on the endometrium’s ER alpha and PR mRNA levels.
• Biopsies were obtained from 19 mares not in heat who had been treated with a control, oestradiol (estrogen), progesterone, or estrogen followed by progesterone for varying lengths of time.
• The treatment using steroids impacted the levels of ER alpha mRNA, with a higher amount seen in the group treated only with estrogen compared to those treated with a long-term combination of estrogen and progesterone.
• Importantly, this aspect of the study demonstrated that the period of dominance by progesterone can influence ER alpha gene expression.

Conclusion

• The study clearly shows changes in the amounts of steroid receptor mRNA paralleling fluctuations in the hormone environment within the uterine endometrium throughout the cycle and in early pregnancy.
• Moreover, it is suggested that factors beyond the investigated steroids could also influence ER alpha and PR gene expression in the equine uterine endometrium.