Relationship between endometrial oxytocin receptors and oxytocin-induced prostaglandin F2 alpha release during the oestrous cycle and early pregnancy in pony mares.

The research article investigates the interaction between endometrial oxytocin receptors, plasma oxytocin concentrations, and prostaglandin F2 alpha (PGF2 alpha) release in horses during their oestrous cycle and early pregnancy, and suggests an embryo-derived factor that may disrupt this interaction during early pregnancy.

Background

• The research is set against the backdrop of the mares’ oestrous cycle and early pregnancy stages, focusing on key hormones and compounds including oxytocin, oxytocin receptors, and PGF2 alpha.
• Researchers aimed to investigate the changes in the onset of oxytocin release, plasma oxytocin concentrations, and PGF2 alpha release during different stages of the mares’ reproductive cycle.

Methodology

• Researchers observed 18 pony mares at different stages of their reproductive cycle: days 8, 12, and 14 after ovulation, days 12 and 14 of early pregnancy, and during oestrus.
• They conducted endometrial biopsies and closely tracked the concentrations of oxytocin and PGF2 alpha in the mares’ blood over a 15-minute period following the biopsy.
• The biopsy specimens were examined for their oxytocin receptor densities.

Findings

• A key finding was that the biopsy procedure swiftly stimulated oxytocin release in all mares, regardless of their reproductive stage.
• Interestingly, the researchers noticed the maximum increase in plasma oxytocin on day 12 in both pregnant and non-pregnant mares, while the minimum increase was on day 8.
• In nonpregnant mares, the concentration of plasma PGF2 alpha rose consistently over the 15-minute timeframe.
• Endometrial oxytocin receptor concentration was observed to be lowest in mares during oestrus and highest in nonpregnant mares on day 14 post-ovulation.
• The density of oxytocin receptors in pregnant mares was similar to nonpregnant mares on day 12 post-ovulation but notably reduced on day 14.

Conclusion

• The research thus established a correlation between oxytocin and PGF2 alpha release in nonpregnant mares, implying that oxytocin might trigger the release of PGF2 alpha via oxytocin receptors.
• However, this interaction was disrupted during early pregnancy, indicating the involvement of an embryo-derived factor that suppresses PGF2 alpha release despite oxytocin and its receptor densities being normal.
• However, the exact nature of this embryo-derived factor and how it influences this interaction during early pregnancy is a subject for future research.