Effect of oestradiol on LH secretion and pituitary responsiveness to GnRH in ovariectomized mares.

The research investigated the influence of the hormone oestradiol on the release of luteinizing hormone (LH), and pituitary sensitivity to gonadotropin-releasing hormone (GnRH) in ovariectomized Pony mares, finding that oestradiol significantly increased LH concentrations and the pituitary’s reaction to GnRH.

Methodology

• Ovariectomized Pony mares were treated with varying doses of oestradiol for 10 days, administered at twelve-hour intervals.
• Blood samples were taken regularly throughout the experiment to monitor changes. Extra samples were collected at fifteen-minute intervals during two twelve-hour periods, on the first and last days of the experiment.

Findings

• The study observed a significant effect of oestradiol treatment on the mean daily LH concentrations.
• The increase in LH concentrations showed a clear correlation with the administration of oestradiol, indicating a strong positive feedback effect.
• The heterogeneity in the regression analysis of LH concentrations over time, due to the increasing LH amounts, confirmed the hormone’s influence.

Part Two: Pituitary Sensitivity to GnRH

• The second part of the study aimed to examine how the administration of oestradiol would impact the pituitary’s response to GnRH in the same group of ovariectomized Pony mares.
• This was achieved by administering a large dose of GnRH twice a day on specific days during the oestradiol treatment period.
• Results indicated that LH concentrations increased in oestradiol-treated mares during the treatment period.
• Furthermore, the pituitary’s responsiveness to GnRH also showed a rise, suggesting that oestradiol amplifies the pituitary’s reaction to GnRH.

In conclusion, the research demonstrated that the hormone oestradiol has a significant influence on both the release of luteinizing hormone, and the pituitary’s sensitivity to gonadotropin-releasing hormone in ovariectomized Pony mares.