Can the presence of ovarian corpus luteum modify the hormonal composition of follicular fluid in mares?

The hypothesis of this study was to investigate if the presence of corpus luteum (CL) in
one ovary could modify the hormonal content of follicular fluid (FF) in the follicles. Sixty ovaries
were taken after the slaughter of 30 clinically healthy mares. In relation to the sizes, the follicles
were classified into three dierent categories, as small (20–30 mm), medium (31–40 mm) and large
(41 mm). Blood samples were collected from the jugular vein of mares before their slaughter,
and then the FF samplings were extracted from each single follicle. The ovaries that were collected
were classified into two groups, according to the presence (CL-bearing) or absence (non-CL-bearing) of
CL. The serum and FF samples were analysed for progesterone (P4), oestradiol-17 (E2), testosterone
(T), androstenedione (A4) and dehydroepiandrosterone (DHEA). Intrafollicular P4 concentrations
in large follicles of CL-bearing groups were lower than for non-CL-bearing ones. Intrafollicular E2
concentrations increased with the increase of the follicle diameter in both groups, CL-bearing and
non-CL-bearing. However, in the FF with a large and medium follicle size, E2 concentrations were
significantly higher in non-CL-bearing groups than in CL-bearing groups. T and A4 significantly
increased in the large and medium follicle sizes when compared to the small follicle sizes in both
groups, but higher concentrations in the non-CL-bearing group were obtained. Intrafollicular DHEA
significantly decreased with the increase of the follicular diameter in both groups. Steroid hormones
in FF dynamically changed, according to the presence or not of CL in the ovary. This study brings
new knowledge on the role of the CL in the follicular hormonal composition in mares.