The presence of the mu-opioid receptor in the isthmus of mare oviduct.

The research focuses on the presence and glycosylation type of the mu-opioid receptor in the isthmus region of a mare oviduct during oestrus.

Objective and Methodology of the Research

• The researchers aimed to determine the presence of the mu-opioid receptor and study the type of glycosylation in the third extra-cellular loop of these receptors in the isthmus region of a mare oviduct during oestrus. The mu-opioid receptor was identified via techniques like immunoblotting and immunohistochemistry, in association with enzymatic (N-glycosidase F and O-glycosidase) and chemical (beta-elimination) treatments.

Results of the Research

• It was revealed that the mu-opioid receptor comprises two peptides with approximate molecular weights of 65 and 50 kDa. Through N-deglycosylation with N-glycosidase F, an additional immunoreactive peptide was noted at around 30 KDa.
• Efforts to cleave O-glycans with O-glycosidase failed in both the applied techniques, indicating that the third extra-cellular loop of the mu-opioid receptor in the mare isthmus oviduct undergoes certain modifications, particularly to the Galbeta(1-3)GalNAc core bound to serine or threonine.
• The mu-opioid receptor was located in the mucosal epithelium, certain stromal cells, muscle cells, and blood vessels using immunohistochemistry. In ciliated cells, the mu-opioid receptor demonstrated N-linked glycans, as the immunoreactivity was absent post N-glycosidase F treatment. However, it was maintained in the apical region after beta-elimination.
• The majority of non-ciliated cells expressed the mu-opioid receptor with both N-linked and O-linked oligosaccharides, as shown by the abolition of immunostaining after N-glycosidase F and beta-elimination. The same expression was noted in stromal cells, endothelial and muscle cells of blood vessels. Myosalpinx myocytes, however, only showed mu-opioid receptor with O-linked oligosaccharides.

Conclusion of the Research

• The results suggest that the mu-opioid receptor might play a role in the production and movement of isthmus lumen content. This would assist in maintaining the optimal condition of the sperm in the mare oviduct.