Effect of luteinizing hormone overstimulation on equine follicle maturation.

This research examines the impact of overstimulation with luteinizing hormone (LH) on the maturation of equine follicles, with the findings suggesting that high LH levels can lead to changes in the follicular fluid that potentially disrupt normal follicle development and ovulation.

Research Purpose and Hypothesis

• This study aimed to investigate the effects of high levels of luteinizing hormone (LH) on the development and ovulation of follicles in mares.
• The researchers hypothesized that an early rise in LH levels during a follicular wave could disrupt the normal maturation of follicles, leading to ovulatory dysfunction.

Methods Used

• The researchers conducted two experiments using a two treatment groups of mares—one receiving daily administration of equine LH (eLH) and the other a saline solution (control).
• In both experiments, follicles larger than 10mm were obliterated at the midpoint of the estrous cycle.
• Upon reaching a dominant follicle size of greater than 32mm, an ovulatory dose of hCG was administered.

Findings

• Both experiments found that eLH treatment did not significantly impact the ovulatory response or progesterone levels in the post-treatment luteal phase.
• The administration of eLH stimulated a rise in circulating LH, comparable to levels after PGF(2α) injection. However, PGF(2α) or eLH neither significantly affected follicle growth nor the overall number of follicles following ablation.
• Nevertheless, there were noticeable differences in the levels of androstenedione and insulin-like growth factor I, with the preovulatory follicle in the eLH and PGF(2α) groups having lower androstenedione and higher insulin-like growth factor I levels.
• Moreover, the levels of prostaglandin E2 in preovulatory follicles exhibited a downward trend in the eLH and PGF(2α) treatment groups.

Conclusions

• The study concluded that while exposure to high LH levels did not directly impact ovulation, it did induce changes in the follicular fluid, potentially disrupting normal follicle and/or oocyte maturation.
• The implications of the use of PGF(2α) for fertility control in farm animals require further studies due to its potential to interfere with normal follicle development and ovulation.