Alkaline phosphatase added to capacitating medium enhances horse sperm-zona pellucida binding.

This research investigates the impact of adding alkaline phosphatase, a substance found in horse semen, to a medium used to capacitate, or activate, horse sperm for fertilization. The study reveals this addition can improve sperm’s ability to bind to the oocyte’s zona pellucida, a crucial layer surrounding the egg, and thereby increase the likelihood of successful fertilization.

The Role of Alkaline Phosphatase in Sperm Activity

• The researchers aimed to understand the role of alkaline phosphatase (AP) in stallion sperm activity and interaction with oocytes (female reproductive cells) at varying pH levels. AP is present in male horses’ seminal plasma and spermatozoa, but its function is yet to be fully understood.
• Previous research indicated that sperm-oocyte interaction in horse species is enhanced at slightly basic pH levels. Based on this, the researchers hypothesized that AP might play a significant role in this biological process.

Major Findings from the Experiment

• Stallion spermatozoa were activated using Tyrode’s medium at three different pH levels – 7.4, 8.0, and 9.0 – for 4 hours. This was done with and without the addition of AP to compare the results.
• The researchers found that at a pH of 9.0, AP significantly increased the percentage of living cells with active mitochondria. This indicates that AP can improve the energy production of sperm cells and hence their viability.
• At a pH of 8.0, AP notably reduced the percentage of cells with acrosome damage, demonstrating a potential protective effect of AP on the sperm cells.
• No significant differences were observed in motility parameters, meaning that AP did not make a noticeable difference in the speed or efficiency of sperm movement.

Effects on Sperm-Oocyte Interaction

• The presence of AP led to a significant increase in the number of sperm bound to the oocyte’s zona pellucida at all tested pH levels.
• The zona pellucida is a vitally critical layer surrounding the female reproductive cell, to which sperm must bind for successful fertilization. Therefore, enhancing this binding capacity can increase the success rate of fertilization.

Conclusion

• The study concludes that AP can cause modifications on sperm membranes, boosting their capacity to bind to the zona pellucida of equine oocytes.
• These findings suggest AP could potentially be utilized in reproduction science to increase the success rate of horse breeding programs.