Gonadotrophin subunit and GnRH receptor gene expression in the pars distalis of the equine pituitary.

The study investigates how changes in seasons affect the reproductive hormones in horses, specifically looking into the levels of gonadotrophin subunits and gonadotropin-releasing hormone receptor (GnRH-R) mRNA in horses’ pituitary glands during breeding and non-breeding seasons.

Research Aim and Methodology

• The research aimed to understand how photoperiod-driven changes in a horse’s fertility are regulated on a hormonal level.
• To achieve this, the researchers examined the gene expression of gonadotrophin subunits and GnRH receptor mRNA in the pituitary glands of Thoroughbred horses. This was done during both breeding (BS) and non-breeding (NBS) seasons.
• The prevalence of gonadotrophins (hormones that promote growth and function of the gonads) in a region of the pituitary gland known as the pars distalis was also studied.
• The methods of investigation included Northern analysis for measuring mRNA content and immunohistochemistry for assessing the number of LH-gonadotrophs. This was done in mares who were sexually active during the breeding season, sexually inactive during the non-breeding season, and also in castrated male horses (geldings).
• Three subunit mRNAs namely common alpha, LHbeta and FSHbeta along with GnRH-R mRNA were the primary targets of this analysis.

Findings of the Study

• In mares, the pituitary content of FSHbeta mRNA was significantly higher in the non-breeding season, while the content of the common alpha-subunit mRNA was significantly higher during the breeding season.
• GnRH-R and LHbeta mRNA abundance weren’t affected by changing seasons.
• Although the total number of LH-gonadotrophs remained the same in both seasons, the proportion of LH cells in relation to other cells was higher in the breeding season, caused by an increased number of non-gonadotroph cells during the non-breeding season.
• In geldings, no significant seasonal effects on any of these variables were detected.
• The results demonstrated clear seasonal effects on the gene expression of common alpha-subunit and FSHbeta in the mare’s pituitary gland, without any detectable changes in the content of LHbeta or GnRH-R mRNA.

Significance of the Study

• This research contributes to a deeper understanding of how horses’ fertility is regulated by hormonal changes in response to changing photoperiods.
• This knowledge can potentially improve current animal breeding practices by aligning them better with the natural hormonal cycles of the species.