Endometrial prostaglandin synthases, ovarian steroids, and oxytocin receptors in mares with oxytocin-induced luteal maintenance.

The research article investigates the effects of continuous administration of oxytocin on the luteal phase in mare reproduction. The study focuses specifically on the impact of oxytocin on the maintenance of the luteal phase and the expression of important proteins involved in hormone regulation, contributing new insights into ovarian hormone and oxytocin receptor behavior in the process.

Objective of the Study

• The main aim of the study was to understand how sustained oxytocin administration impacts the maintenance of the luteal phase in mares – a biological stage crucial to pregnancy.
• Additionally, the researchers analyzed the endometrial expression of several proteins involved in hormone production and regulation (PTGS2, AKR1C3, PTGES, PTGIS, OXTR, PGR, ESR1, ESR2) in mares with luteal maintenance after chronic oxytocin administration.

Methodology

• The study was performed with two groups of mares. The control group (C group) received 6mL of saline, whereas the test group (OXT group) received 60 units of oxytocin every 12 hours, from days 7 to 14 post ovulation.
• Endometrial biopsies were conducted on the C group on day 10 and on the OXT group on day 24. The researchers monitored the time it took for luteolysis (the degradation of the corpus luteum) to occur in each group.

Findings

• Among the mares in the OXT group, 67% experienced luteal maintenance. The researchers identified changes in the transcription (a key process in gene expression) of several genes in these mares, compared to the control group. In terms of protein expression, the study detected an increase in oxytocin receptors (OXTRs) and a decrease in estrogen receptors (ESR2).
• A higher concentration of progesterone was found in the control group on biopsy day.
• The study also found a differential spatial location of OXTRs and progesterone receptors (PGRs), localized in diverse endometrium layers.

Implications

• The article suggests that extended luteal function, seen in mares treated with oxytocin, might be connected to the different expression patterns of OXTR and PGR in the endometrium.
• The observed decrease in ESR2 likely contributes to the maintenance of PGR in luminal and glandular epithelium. Furthermore, it may attenuate the transcriptional activity of ESR1 in the mare endometrium.
• The discovery adds to the body of knowledge related to the endometrial expression of ovarian steroids and oxytocin receptors, particularly regarding pharmacologically induced luteal maintenance in mares.