Immunolocalization of androgen receptors and assesment of steroidogenic activity of the ovaries in prepubertal and pubertal mare

Abstract

The knowledge on steroidogenesis in mare ovaries from birth to sexual maturity is mainly based on the evaluation of the concentration of progesterone (P4) and/or estradiol (E2) in the peripheral blood serum. Steroid hormones are also produced in the adrenal cortex, therefore their concentration in the blood does not directly reflect the steroidogenic activity of the ovaries. Wesson and Ginther [1] observed estrous behaviour in prepubertal fillies after ovariectomy. Sexual behavior of these females was thus induced by estrogens of non-ovarian origin. At the same time aromatase was found in antral follicles of approximately 6 month-old fillies which indicates that their ovaries are able to produce estrogens long before the first ovulation [2]. No information is found in the available literature on the presence of androgen receptors (AR) in the ovaries or the role of androgens in the control of folliculogenesis in the mare. The aim of the study was: i) to evaluate the ability of ovaries in fillies to produce steroid hormones based on the concentrations of E2, P4 and testosterone (T) in follicular fluid (FF), ii) to establish the relation between the physiological state of the follicles and the concentration of steroids in FF including aromatase (P450arom) immunoexpression in granulosa cells (GCs) and the concentrations of E2, and iii) to evaluate the cellular immunolocalization of AR protein in the ovaries of fillies and mares.