Early luteal phase progestin concentration influences endometrial function in pregnant mares.

This study investigates the influence of progestin concentrations in early pregnancy in horses, specifically how varying levels may impact embryo development and the functioning of the uterus. The researchers find that reduced or elevated hormone levels during this stage can significantly affect progesterone receptors in the uterus, impacting overall reproductive health.

Study Objectives and Hypothesis

• The research sought to establish if varying progestin concentrations during the early stages of pregnancy in mares could impact the endometrial function and development of the embryo.
• The hypothesis was that reduced progestin concentrations could potentially affect the downregulation of endometrial progesterone receptors and thus affect the health of the uterus in fertile mares.

Methodology

• The experiment involved eight mares in estrous who were first inseminated then given different hormone treatments to either increase (using altrenogest) or decrease (using cloprostenol) total peripheral progestin concentrations. There was also a control group that received no treatment.
• The altrenogest was administered orally daily from days 5 to 10 after ovulation, and cloprostenol was injected once daily from days 0 to 3 after ovulation.
• On the 14th day following ovulation, the research team collected fluid from the uterus of each mare to analyze free amino acid concentrations. They also performed a biopsy of the uterus to examine the distribution of progesterone receptors.

Results and Findings

• The amount of luminal epithelial cells (cells lining the uterus) staining positive for progesterone receptors varied across treatments. Reduced progestin concentration caused by cloprostenol treatment appeared to delay the downregulation of progesterone receptors until 14 days after ovulation.
• The concentrations of specific amino acids in the uterus, specifically isoleucine and lysine, were influenced by treatment, being lower in mares treated with cloprostenol compared to altrenogest-treated and control mares.
• Pregnancy rate varied slightly among treatments, suggesting that progestin concentrations could potentially impact the reproductive success rate.

Conclusion

• The study concludes that impaired luteal function caused by cloprostenol treatment during the early phase can delay the reduction of progesterone receptors in the uterus, affecting its function. This is reflected in lower concentrations of essential amino acids in the uterus.
• The effects of increased progestin concentrations through altrenogest treatment were not as clear or definitive in healthy mares.