A light microscopic and ultrastructural study on the presence and location of oxytocin in the equine endometrium.

This research investigates the presence and location of the hormone oxytocin in the endometrium (the innermost lining of the uterus) of horses. The research, which examined biopsy specimens collected during the estrus cycle, found that oxytocin was present in the secretory cells of the uterine lumen and the superficial glands and was secreted into the uterine lumen. The findings suggest that oxytocin may play a role in local internal communication within the uterus, impacting contractility and luteolysis in horses.

Methods and Findings

• The researchers conducted a detailed microscopic examination of the equine endometrium, the lining of a mare’s uterus, to locate the hormone oxytocin. They used diverse methods including light microscopy and ultrastructural level studies on endometrial biopsy specimens.
• Their study revealed strong immunostaining that proved the presence of oxytocin in the secretory vesicles of the secretory epithelial cells of the uterine lumen and superficial glands. The secretory cells are the nonciliated type and are responsible for creating and releasing substances.
• The research team applied immunogold labelling, a technique that helps locate protein in a sample. It confirmed that oxytocin was present in the vesicles or pouches of secretory epithelial cells. They also observed that these vesicles were present on the luminal surface, suggesting that oxytocin is secreted into the uterine lumen.
• No oxytocin was found in ciliated epithelial cells of the uterine lumen and endometrial glands, in the stromal cells, or in the basal endometrial glands. Ciliated epithelial cells are those having minute hair-like structures on their surface.

Significance of the Study

• This study is the first of its kind to identify the specific location of oxytocin within the endometrium of any domestic species.
• The findings suggest that oxytocin is not just produced in traditional sites like the hypothalamus and posterior pituitary but also in the endometrium. As oxytocin is known to be involved in uterine contractions and luteolysis (degeneration of the corpus luteum in the ovary), this could have important implications in equine reproductive medicine.
• The identification of the locally synthesised uterine oxytocin could open new paths of research into the autocrine/paracrine control of uterine contractility and luteolysis in horses, potentially changing techniques of mare management in breeding.