Stimulation of LH, FSH, and luteal blood flow by GnRH during the luteal phase in mares.

The research article investigates the effect of the hormone GnRH on the concentrations of LH, FSH, and progesterone, as well as blood flow to the CL ovary in mares during the luteal phase of their reproductive cycle.

Introduction and Methodology

This study was designed to explore the impact of varying doses of GnRH (Gonadotropin-releasing hormone) on certain hormone levels and blood flow in mares. GnRH is a hormone that triggers the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which regulate the reproductive cycle. The timing of this investigation was set to occur on Day 10 of the reproductive cycle, where Day 0 was the ovulation day.

• The study groups consisted of a control group receiving no GnRH (n=9), a group receiving 100 μg of GnRH (n=8), and another receiving 300 μg of GnRH (n=9).
• Hormonal concentrations of LH, FSH, and progesterone (P4), and blood flow to the CL (Corpus Luteum) ovary were measured at multiple intervals post-treatment: 0 hour (at the time of treatment), 0.25, 0.5, 1, 2, 3, 4, and 6 hours.
• Blood flow was measured using spectral Doppler ultrasonography to assess resistance to blood flow in an ovarian artery before entry into the CL ovary.
• An operator, who was uninformed about the mare identity, hour, or treatment dose, estimated the percentage of the CL with color Doppler signals of blood flow from videotapes of real-time color Doppler imaging.

Results and Findings

• The study found that concentrations of LH and FSH increased significantly at hour 0.25, and subsequently decreased over hours 1 to 6; however, the P4 concentration was not changed due to the treatment.
• The resistance to blood flow decreased between hours 0 and 1, with a greater decrease observed for the 100-μg dose than the 300-μg dose.
• The percentage of CL with blood flow signals increased significantly between hours 0 and 1 without any significant difference between the 100- and 300-μg doses.

Conclusion

The results support the hypothesis that GnRH increases LH concentration and vascular perfusion of the CL ovary, and enhances CL blood flow during the luteal phase; nevertheless, P4 concentration remained unaffected. This implies GnRH has a role in regulating blood flow and certain hormone concentrations during the luteal phase of the reproductive cycle in mares.