Systemic and Intrafollicular Androgen Concentrations in Cycling Mares

Abstract

The evidence that androgens regulate the folliculogenesis supports the hypothesis that intrafollicular testosterone (T), androstenedione (A4) and dehydroepiandrosterone (DHEA) could be modified along follicular growth. The objective of this study was to evaluate the changes and related relationships between systemic and intrafollicular T, A4 and DHEA in post-deviation and impending ovulation follicles. Sixty ovaries were taken after the slaughter of 30 clinically healthy mares. In according to the sizes, the follicles were classified in 3 different categories, as small (20-30 mm), medium (31-40 mm) and large (≥ 41 mm), and the follicular fluid (FF) samplings were extracted from each single follicle. Intrafollicular concentrations of T, A4, and DHEA were significantly higher than systemic ones. Intrafollicular and systemic T and A4 concentrations were strongly and positively correlated, and DHEA negatively. A4 was the predominant androgen in FF. T and A4 were positively and DHEA negatively correlated with the follicular diameter. T and A4 significantly increased in large and medium than small follicle sizes. DHEA was significantly higher in small than medium and large follicle size. The increase of intrafollicular androgens suggests the presence of androgenic environment based in the biotransformation of DHEA in A4 and later in T in the follicles, and the progressive oestradiol-17β (E2) production with the advance of follicular growth. The evidence of significant correlations between systemic and intrafollicular androgens considerably helps to understanding more deeply the role of these steroids in the physiology of follicular development in the mare, adding a new segment of scientific literature.