Plasma luteinizing hormone concentration in mares treated with gondotropin-releasing hormone and estradiol.

This study examines the impact of different doses and methods of administering gonadotropin-releasing hormone (GnRH) on luteinizing hormone (LH) levels and ovulation in mares during estrus, and the role of estradiol-17beta (E2-17beta) in LH response to GnRH treatment. It is found that significant increases in LH levels are only seen with the highest dose of GnRH, and that estradiol-17beta appears to enhance this effect, although none of the treatments substantially affect ovulation time.

Overview

The research paper investigates how luteinizing hormone (LH) and ovulation responses were activated through different doses of gonadotropin-releasing hormone (GnRH) in female horses during estrus. It also focuses on studying how Estradiol-17beta (E2-17beta) affects LH reactions to GnRH treatment.

Experimental Design

• To study the influence of different dosages of GnRH on estrous mares, single doses of synthetic GnRH were given to five groups of mares, each group having three mares.
• In the second experiment, GnRH was intravenously infused for 24 hours into a group of six mares to measure the resulting mean plasma LH concentration.
• In a third experiment, three groups of mares were given different treatments. Group H received corn oil and a saline solution; Group I was given corn oil and GnRH, and Group J was administered estradiol-17beta and GnRH.

Findings

• In the first experiment, only mares given the large dose of GnRH showed a significant rise in plasma LH concentration.
• In the second experiment, significant increases in mean plasma LH concentration were recorded 3 and 6 hours post the start of GnRH infusion and it remained steady for the duration of this administration.
• In the third experiment, there were negligible plasma LH responses in mares given only corn oil and a saline solution. However, mares in group J which received E2-17beta and GnRH, exhibited significant increases of plasma LH concentration 1 to 6 hours after GnRH was administered.
• Overall, no substantial changes in ovulation time were observed despite the different treatments across all experiments.

Implications

• The research results delineate the efficient administration and dosage methods of GnRH, necessary to generate a significant LH response.
• The study demonstrates the potential of E2-17beta combined with GnRH in heightening the LH response.
• However, researchers found that these treatments do not significantly alter the time of ovulation, aiding further understanding of the equine reproductive system.