Effect of suppression of FSH with a GnRH antagonist (acyline) before and during follicle deviation in the mare.

This research examines the role of the hormone FSH in early ovary follicle development in mares, using a hormone inhibitor called Acyline. The study found alternating dependencies in growth on FSH at different stages of follicle development.

Experiment One: Understanding Acyline’s Effects

• The first part of this study involved testing different dosage levels of Acyline on mares. A dose of 3 mg per mare showed a suppression in FSH and follicle responses to exogenous GnRH — a hormone that stimulates the release of FSH and LH.
• In comparison, no dosage and 1 mg dosage produced different results, suggesting that Acyline effectively hampers FSH and follicle responses to exogenous GnRH in high dosages.

Experiment Two: Investigating FSH Concentration after Follicle Ablations

• This experiment induced high FSH concentrations by sequentially removing all follicles larger than or equal to 6 mm on the 10th and 13th days after the mares’ ovulation.
• Researchers found that a single treatment with Acyline led to a more significant decrease in plasma FSH levels than a treatment with charcoal-extracted follicular fluid (a source of the hormone inhibin) or estrogen.
• The findings suggested no significant difference in the suppression of FSH between a group treated solely with Acyline and a group treated with a combination of Acyline, inhibin, and estrogen.

Experiment Three: Observing the FSH’s Surge’s Effects on a New Follicular Wave

• The third experiment involved ablating all follicles on day 10 to induce an FSH surge and a new follicular wave.
• Acyline treatment on day 10 resulted in an immediate decrease in FSH levels, but it did not significantly affect the emergence of a new follicular wave or the growth of follicles of 7 to 11 mm in size on days 11-13.
• Acyline intervention on day 15, a day before expected follicle deviation and after the FSH surge’s peak, led to an immediate FSH decrease and cessation of follicle growth.
• This indicates that follicle growth in the initial two days following wave emergence is independent of FSH levels, contrasting with the growth dependency on FSH seen during the decline in FSH surge and before follicle deviation.

Conclusion

• The whole research suggests that at different stages of early follicle development, the follicles rely on the hormone FSH to varying extents.
• The findings may aid in understanding more about equine reproduction and fertility and could possibly be utilized in treatment practices in the future.