Investigations into the role of platelet-activating factor in the peri-conception period of the mare.

Investigations show that platelet-activating factor (PAF) is present in the reproductive system of mares, where it plays a significant role in ovulation and early pregnancy by affecting follicular fluid composition and oviductal function.

Background and Purpose of the Study

• PAF is a lipid molecule known to be important in female reproduction and fertility in many mammals.
• PAF has been linked to key reproductive processes such as ovulation and embryo movement but had not been thoroughly studied in horses (mares).
• The study aimed to identify PAF presence in equine reproductive tissues and understand its role during the peri-conception period (time around conception).

Methods Used

• Targeted mass spectrometry combined with chromatographic separation was performed on equine follicular fluid (fluid surrounding the egg in the ovary) to detect and quantify PAF.
• Untargeted high-resolution mass spectrometry-based lipidomic analysis was utilized to measure PAF levels in pre-ovulatory follicles of varying sizes in mares.
• Immunofluorescence staining was conducted to locate the PAF receptor protein in the oviductal (fallopian tube) epithelial cells.
• An equine oviductal epithelial organoid model (a lab-grown mini-organ representative of the oviduct lining) was developed to test PAF effects on the cilia that move embryos through the reproductive tract.

Key Findings

• PAF was quantitatively detected in equine follicular fluid.
• Two molecular species of PAF, termed PAF (14:0) and PAF (16:1), both increased in concentration as the follicles grew larger and closer to ovulation.
• The increase of PAF in follicular fluid suggests that PAF concentration rises as ovulation approaches, implying a role in that process.
• PAF receptors were observed in specific locations of the oviductal epithelial cells—luminal pericellular, apical, and basal aspects—indicating the oviduct is a target tissue for PAF action.
• In the organoid model, adding PAF significantly increased the ciliary beat frequency (CBF), meaning PAF enhances the movement of cilia which helps propel the oocyte and embryo.

Implications and Conclusions

• PAF appears to act locally in the mare’s reproductive tract, helping to regulate ovulation and early embryo transport towards the uterus.
• The increase in PAF within follicular fluid as ovulation nears suggests it could mediate follicular rupture or other ovulation-related events.
• By increasing ciliary beating in the oviduct, PAF likely aids the migration of the oocyte and early embryo, facilitating successful fertilization and early pregnancy establishment.
• This research enhances understanding of equine reproduction and highlights PAF as a potential therapeutic target or biomarker in managing fertility in mares.