Effects of active immunization against gonadotropin releasing hormone on gonadotropin secretion after ovariectomy and testosterone propionate administration to mares.

The research demonstrates that active immunization against gonadotropin releasing hormone (GnRH) in mares affects secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), particularly following ovariectomy or the administration of testosterone.

Research Methodology

• The study was conducted on ten lighthorse mares, five of which were immunized against GnRH conjugated with bovine serum albumin (BSA).
• The other five mares, which were immunized against BSA alone, served as a control group.
• Immunizations started on November 1, while the ovariectomy (removal of ovaries) was carried out in June.
• Following the ovariectomy, all mares were treated with testosterone propionate (TP) from day 50 to day 59.

Results of Immunization against GnRH

• On the day of ovariectomy, the concentration of LH was found to be lower in GnRH-immunized mares than in BSA-immunized mares. The hormone was typically non-detectable in mares immunized against GnRH.
• Moreover, FSH concentration was also reduced by 50% in GnRH-immunized mares.
• Contrarily, plasma concentrations of LH or FSH did not increase post-ovariectomy in GnRH-immunized mares unlike in BSA-immunized mares.

Response to GnRH Analog and Testosterone Treatment

• The study found that the LH response to the GnRH analog (with less than .1% cross-reactive with GnRH antibodies) was reduced by 97% in GnRH-immunized mares compared to BSA-immunized mares.
• FSH response remained the same in both groups.
• Treatment with TP created a significant effect in BSA-immunized mares: it reduced the LH response and increased the FSH response to GnRH analog whereas it had no discernible effect on the response of either gonadotropin in GnRH-immunized mares.

Conclusion

The study concludes that active immunization against the gonadotropin releasing hormone, GnRH, in mares significantly influences the secretion of two principal hormones – LH and FSH – following specific biological processes such as ovariectomy and testosterone administration. This finding may open potential lines of inquiry in hormone regulation and reproductive function in lighthorse mares and possibly in other species.