Mechanisms responsible for increase in circulating inhibin levels at the time of ovulation in mares.

This research article investigates why inhibin levels in mares surge at the time of ovulation. By using follicular fluid extract, the study finds that the release of these fluids into the abdominal cavity during ovulation triggers the inhibin surge, and that monitoring inhibin pro-alphaC levels could be a useful way to predict ovulation timing.

Overview of Research

• The study focuses on the unusual rise of inhibin levels in mares (adult female horses) at the time of ovulation. Generally, inhibin is a hormone produced by the ovaries that reduces Follicle Stimulating Hormone (FSH) secretion, and its levels drop after ovulation. However, in mares, an unexpected surge in inhibin levels is seen during ovulation.
• The researchers aim to understand the cause of this unusual inhibin surge considering it could offer valuable insights into equine reproductive mechanisms, and potentially serve as a tool for predicting ovulation.

Experimental Process

• To analyze this phenomenon, the researchers injected mares with 50 ml of equine follicular fluid (eFF) during the luteal phase, which is the period after ovulation but before the start of menstruation.
• After the treatment, the researchers analyzed hormone levels in the treated mares and compared them with levels in control mares that weren’t given eFF.

Key Findings

• An hour after eFF treatment, the plasma levels of immunoreactive inhibin and inhibin pro-alphaC (a subunit of inhibin) were significantly higher in treated mares compared to control mares. However, there was no significant change in the levels of estradiol-17beta, another hormone that plays a key role in reproduction.
• The hormone profiles of the eFF-treated mares were found to be similar to those in mares experiencing natural or hCG-induced ovulation, indicating that the eFF injection effectively simulated an ovulation event.
• The study concludes that the inhibin surge observed at ovulation in mares is caused by the release of follicular fluid into the abdominal cavity during follicle rupture (ovulation).
• The research also posits that monitoring the levels of inhibin pro-alphaC in the bloodstream could potentially be used as a method to determine the precise timing of ovulation in mares.