Diestrus administration of oxytocin prolongs luteal maintenance and reduces plasma PGFM concentrations and endometrial COX-2 expression in mares.

The research investigates the impact of oxytocin administration on the length of the luteal phase in female horses (mares). The study finds that prolonged oxytocin treatment delays luteolysis (the degradation of the corpus luteum, a structure responsible for progesterone production), reduces plasma PGFM (a prostaglandin metabolite involved in luteolysis) levels, and lessens the expression of cyclooxygenase-2, an enzyme involved in the synthesis of prostaglandins.

Objective of the Research

• The purpose of this research was threefold: first, to assess the effect of different intervals of oxytocin administration on the prevention of luteolysis in mares; second, to investigate the PGF(2α) (Prostaglandin F2 alpha, a component contributing to luteolysis) release in mares experiencing an extended diestrus due to oxytocin treatment; third, to analyze the endometrial expression of oxytocin receptor, estrogen receptor α, and prostaglandin synthesis enzymes following oxytocin administration.

Methodology and Findings

• In the course of the first experiment, mares were administered with oxytocin for different periods after ovulation, while control mares were given sterile saline. An increase in serum progesterone levels until Day 30 post-ovulation defined prolonged diestrus.
• The data indicated that the proportion of mares experiencing extended cycle lengths rose with the number of oxytocin administration days,
• In terms of luteal maintenance, oxytocin-treated mares exhibited it longer than control mares, with the number of mares responding to treatment increasing as oxytocin administration continued past day 8 post-ovulation.
• Moreover, mares that went through prolonged diestrus due to oxytocin had lower plasma PGFM concentrations at Day 16 compared to mares with regular diestrus periods.
• In the second experiment, endometrial biopsies from mares treated with oxytocin had decreased cyclooxygenase-2 expression compared to control mares, as detected by reverse transcription polymerase chain reaction and immunohistochemical staining.

Conclusion

• The research concludes that oxytocin administration can delay luteolysis in mares, with the response rate increasing as the treatment duration extends beyond day 8 post-ovulation.
• In addition, prolonged luteal maintenance in mares is linked with reduced plasma PGFM concentrations and lessened expression of the cyclooxygenase-2 enzyme in the endometrium.