The Mare Model to Study the Effects of Ovarian Dynamics on Preantral Follicle Features

Abstract

Ovarian tissue collected by biopsy procedures allows the performance of many studies with clinical applications in the field of female fertility preservation. The aim of the present study was to investigate the influence of reproductive phase (anestrous vs. diestrous) and ovarian structures (antral follicles and corpus luteum) on the quality, class distribution, number, and density of preantral follicles, and stromal cell density. Ovarian fragments were harvested by biopsy pick-up procedures from mares and submitted to histological analysis. The mean preantral follicle and ovarian stromal cell densities were greater in the diestrous phase and a positive correlation of stromal cell density with the number and density of preantral follicles was observed. The mean area (mm2) of ovarian structures increased in the diestrous phase and had positive correlations with number of preantral follicles, follicle density, and stromal cell density. Biopsy fragments collected from ovaries containing an active corpus luteum had a higher follicle density, stromal cell density, and proportion of normal preantral follicles. In conclusion, our results showed: (1) the diestrous phase influenced positively the preantral follicle quality, class distribution, and follicle and stromal cell densities; (2) the area of ovarian structures was positively correlated with the follicle and stromal cell densities; and (3) the presence of an active corpus luteum had a positive effect on the quality of preantral follicles, and follicle and stromal densities. Therefore, herein we demonstrate that the presence of key ovarian structures favors the harvest of ovarian fragments containing an appropriate number of healthy preantral follicles.

Regional distribution and integrity of equine ovarian pre‐antral follicles

“…Perhaps some paracrine factors may be involved, besides aspects related to possible differences in the blood distribution in the ovarian parenchyma, like suggested by Alves et al. (). Our study did not cover such aspects, but it is known that hormones, growth factors and gases can impact follicular degeneration (Araujo et al., ).…”

“…More recently, a new hypothesis was presented to elucidate the uneven distribution of follicles in the equine species. According to Alves et al (2016), there is a variation in follicle quality, class distribution and follicle and stroma cell densities. These recent publications portray the growing interest of the scientific community in the mapping of the equine follicles.…”

Can the Presence of Ovarian Corpus Luteum Modify the Hormonal Composition of Follicular Fluid in Mares?

“…In the present study, no differences between the follicular diameters of CL-bearing and non-CL-bearing ovaries were obtained. During diestrus, in the presence of CL, multiple structures, such as small, medium antral and preovulatory follicles, can be present in the ovary of the mare [30]. Due to the great heterogenicity of follicle sizes that can occur even in mares for which the phase of the estrous cycle is unknown [31], one can presume not to expect significant differences between follicle sizes in CL-bearing and non-CL-bearing groups.…”

The development and integrity of equine pre‐antral follicles cultured in vitro with follicle‐stimulating hormone (FSH) supplementation

“…In other words, the in vitro development of follicles in ovarian fragments could be influenced by the origin of the samples. We formed this hypothesis based on the recent data from Alves et al (2016), who showed changes in follicular activity and distribution according to the phase of the mare's oestrous cycle. In this way, we can hypothesize that the previous stage of ovarian activity may interfere with the in vitro follicular growth, including the response to FSH, which might explain the different results for the in vitro culture of the follicles in mares and other species with reproductive seasonality.…”