Intrafollicular level of steroid hormones and the expression of androgen receptor in the equine ovary at puberty.

The research examines steroid hormone production and the location and expression of androgen receptors within the ovaries of prepubertal and pubertal fillies, with adult mares serving as a control. The main findings indicate that the ovaries of fillies aged six months and onwards can actively produce steroid hormones and that androgen receptors are found in all parts of the equine ovary.

Objective and Methodology

• The researchers aimed to explore the steroid hormone production within the ovarian follicles of prepubertal and pubertal fillies, as well as evaluate the cellular location and expression of androgen receptors (AR) in their ovaries.
• The ovaries of fillies aged 6-18 months were divided into two groups for the purpose of the study. These being: prepubertal (PrP) and ovulating/postpubertal (Ov/pB). Adult mares were also included as a control group.
• Progesterone (P4), testosterone (T) and estradiol (E2) concentrations in the follicular fluid were measured using a method called radioimmunoassay.
• The distribution of AR was examined through immunohistochemistry and the expression of AR protein was determined through the process of Western blot analysis.

Findings

• In the female groups, it was found that estradiol (E2) concentration in follicular fluid of small follicles was low, but increased with the diameter of the follicle, reaching its highest value in preovulatory follicle (pF).
• For prepubertal fillies, the concentration of E2 in larger follicles was comparable to that of postpubertal fillies, but less than half of that found in adult mares.
• Progesterone, testosterone, and estradiol levels were similar between postpubertal fillies and adult mares.
• The localization of AR was predominantly in the cell nuclei and was seen in all types of follicular cells as well as in stroma and luteal cells.
• The specific pattern of staining was dependent on the size of the follicle and the group of females.
• There was stronger nuclear AR staining in smaller antral follicles and in preovulatory follicle (pF) compared to larger follicles.
• AR expression was confirmed in both the prepubertal and adult mare ovarian tissues through Western blot analysis, suggesting that the ovaries of fillies older than six months are capable of producing steroid hormones.

Conclusion

• The results highlight that androgen receptors are present either in the cell nuclei or the cytoplasm of all parts of the equine ovary.
• The researchers posit that the AR expression in follicular and stroma cells potentially indicates the sensitivity of prepubertal ovarian tissue to androgens and underscores the impact of androgens on folliculogenesis and the development of the equine ovary via a receptor-mediated pathway.