Inhibin secretion in the stallion.

This research study investigates the secretion of the hormone inhibin in stallions, which plays an important role in their reproductive system. The study concludes that inhibin, produced mainly by Leydig and Sertoli cells in the testes of a stallion, is a valuable indicator of reproductive activity, changing with the breeding seasons.

Study Methodology

• The study utilized a heterologous radioimmunoassay (RIA) for detecting immunoreactive-inhibin levels in the plasma and testicular homogenates of stallions. This RIA was based on a bovine one and thereby validated.
• The biocapacity of the equine testicular inhibin was also analysed by conducting an assay to gauge the suppression of Follicle-Stimulating Hormone (FSH) secretion from rat anterior pituitary cells.
• Moreover, to trace the testicular cell responsible for the secretion of inhibin, the researchers performed localisation of inhibin in the testis by applying an immunohistochemical method. This method employed a polyclonal antibody against (Tyr30)-porcine inhibin alpha(1-30) NH2.

Findings and Observations

• The RIA showed reliable dose-response curves for both the bovine inhibin standard and the diluted samples of stallion plasma and equine testicular homogenates.
• The findings from the bioassay conducting FSH inhibition also matched the RIA results. The response of stallion plasma and equine testicular homogenates against the bovine inhibin standard was found to be analogous.
• The histological examination revealed that significant immunopositive staining for inhibin was present in the Leydig cells of the testes. Although Sertoli cells also stained positively, the reaction was weaker compared to the Leydig cells. Thus, both Leydig and Sertoli cells in stallions were recognized as potential sources of testicular inhibin.
• The plasma concentrations of inhibin, testosterone, and oestradiol-17beta in stallions precipitously decreased following bilateral gonadectomy. Following this decrease, there was an increase in FSH and LH (luteinizing hormone) concentrations in the plasma. This indicates that the majority of circulating inhibin observed in stallions originates from the testes.

Conclusions

• The study concludes that the main source of inhibin in stallions is the testes, specifically the Leydig and Sertoli cells.
• There was a clear rise in plasma inhibin concentrations detected during the natural breeding season. Similar seasonal fluctuations were noticed in plasma concentrations for testicular steroid hormones and pituitary gonadotrophins, demonstrating a clear correlation with inhibin.
• Overall, the study suggests that plasma inhibin levels could serve as an effective gauge of reproductive activity in stallions, considering these levels fluctuate in unison with their breeding seasons.