Changes in the expression of the miu-opioid receptor in the mare oviduct during oestrus and anoestrus.

The research investigates the presence and changes in the expression of the mu-opioid receptor (MOR) in the female horse’s (mare) oviduct during oestrus and anoestrus. It reveals varying expressions of this receptor in different segments of the oviduct and throughout the different phases of the mare’s reproductive cycle.

Research Methods and Findings

• The study involved the use of immunoblotting and immunohistochemistry to examine the presence of the mu-opioid receptor in the mare oviduct both during oestrus (when the mare is sexually receptive) and anoestrus (when sexual activity pauses).
• The researchers discovered through immunoblotting analysis that the MOR protein is expressed in 65, 50, and 30 kDa forms in the infundibulum and ampulla (sections of the oviduct) during both oestrus and anoestrus. However, the 30 kDa form of MOR was absent in the isthmus (another section of the oviduct).
• It was also found that different levels of the MOR protein expression were observed along the ampulla in oestrus and anoestrus.
• The immunohistochemistry technique revealed the presence of MOR in different cells such as the mucosal epithelium, stromal cells, myocytes (muscle cells), and blood vessels. It was shown that ciliated cells (cells with hair-like structures) expressed MOR in the apical cytoplasm and, except for the isthmus of oestrous mares, also in the nucleus.
• In non-ciliated cells, MOR was only discovered in the isthmus segment during oestrus. Stromal cells exhibited varying immunoreactivity during the oestrous and anoestrous phases and across different oviduct segments.
• The study found that myocytes in the ampulla and isthmus’s musculature showed expressions of MOR, with no significant differences between the oestrus and anoestrus phases. Blood vessels in the isthmus myosalpinx of oestrous mares exhibited MOR expression only in endothelial cells and smooth muscle cells.

Conclusion

• The varied expression of MOR was identified in all three segments comprising the mare’s oviduct. Changes in MOR expression were found linked to the mare’s physiological condition, particularly during different phases of its reproductive cycle.
• Overall, this study has contributed significant insights into how MOR protein expression varies in different regions of the oviduct and its association with the mare’s reproductive stages.