Influence of cycle stage, age and endometrial biopsy score on oxytocin receptor distribution and gene expression in the cervix and uterus of non-pregnant mares.

This research explores the influence of various factors on the distribution and gene expression of oxytocin receptors in non-pregnant horses, shedding light on the primary causes of certain fertility issues in mares. The study finds no correlation between mare age, endometrial biopsy score and oxytocin receptor gene expression, suggesting other factors may contribute to delayed uterine clearance.

Study Details and Methodology

• The investigation delved into areas such as PBIE (Persistent breeding-induced endometritis) and DUC (delayed uterine clearance), both related to mare subfertility.
• 27 non-pregnant mares of different ages (17 were 2-9 years old and 10 were more than 10 years old) were examined using immunohistochemistry and QRT-PCR (Quantitative Reverse-Transcription Polymerase Chain Reaction) techniques.

Oxytocin Receptor Distribution and Expression

• Oxytocin receptors were concentrated in endometrial luminal and glandular epithelia, transmural vascular endothelium, sub-epithelial and peri-glandular stromal cells, and myometrial smooth muscle cells in the uterus and cervix.
• The OR distribution pattern was consistent in the uterus and cervix, except for the absence of glandular epithelium in the cervix.
• The highest OR labeling intensity was consistently observed in the vascular endothelium.
• QRT-PCR revealed a higher OR gene expression in the myometrium compared to the cervix and the endometrium, but there was no significant difference in OR gene expression between the cervix and the endometrium.

Oxytocin Receptor Gene Expression in Different Phases

• The study found that oxytocin receptor gene expression was notably higher during the non-luteal phase in both combined uterine tissues (endometrium and myometrium) and in the myometrium.
• Importantly, neither the mare’s age nor the endometrial biopsy score influenced the distribution of oxytocin receptors or OR gene expression in the animals.

Implications of the Findings

• The lack of any significant correlation between a mare’s age or endometrial biopsy score and OR gene expression suggests that other factors are likely influential in the occurrence of DUC.
• Evidently, the oxytocin receptors and their gene expression are unlikely to be associated with DUC, thus opening the path for more research in determining the exact factors contributing to mare subfertility.