Developmental changes in steroidogenesis by equine preovulatory follicles: effects of equine LH, FSH, and CG.

This research investigates the changes in steroid production by preovulatory follicles in horses, focusing on their response to different hormones. It found differing responses depending on the stage of the estrus cycle and the type of hormone applied.

Research Methodology and Treatment

• The researchers cultured pieces of follicle wall (FW), containing theca cells and attached granulosa cells, from equine preovulatory follicles during various stages of estrus: late diestrus (14th day of cycle), early estrus (1st-2nd day), and late estrus (4th or 5th day).
• These follicle wall pieces were then cultured either with or without the hormones equine LH (Luteinizing Hormone), FSH (Follicle Stimulating Hormone), combination of LH and FSH, or CG (Chorionic Gonadotropin).
• The follicular fluid from presumptive ovulatory follicles and the medium from the FW cultures were analyzed for their content of three steroids: progesterone, androstenedione, and estradiol-17 beta.

Test Results and Observations

• After 72 hours of culture, the cumulative secretion of all three steroids was significantly lower in FW isolated during late diestrus than compared with early or late estrus.
• The maximal progesterone secretion was observed with FW from late estrus, whereas maximal androstenedione and estradiol secretion occurred with FW from early estrus.
• In opposition to the in vitro results, concentrations of progesterone in the follicular fluid were not different among stages of follicular development. Androstenedione and estradiol reached their maxima in late estrous follicles.
• The hormones LH, FSH, or a combination of both, had their greatest stimulating effect on steroidogenesis when applied to FW from late diestrus.
• Equine LH and FSH also increased androstenedione secretion by follicles obtained during both diestrus and estrus. However, estradiol secretion had a quicker loss of responsiveness to the stimulation of LH and FSH. They stimulated estradiol secretion by FW from late diestrous follicles, but did not stimulate FW from early or late estrous follicles.
• Equine CG appeared less effective as a stimulator of steroidogenesis in vitro when compared with LH and FSH.

Overall Conclusion

• This work suggests that the ability of equine preovulatory follicles to produce steroids and respond to hormonal stimulation changes throughout the estrous cycle. This knowledge contributes to a better understanding of equine reproduction, potentially supporting the development of more effective breeding practices.