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

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

Model proposing the difference of follicle density, number of preantral follicles, and stromal cell density among anestrous (A) and diestrous (B) phases.

<p>The increase of the area of ovarian structures during the diestrous phase due to the presence of large follicle(s) and corpus luteum may increase the ovarian compression and consequently the clustering of preantral follicles and stromal cells per unit area in ovarian fragments harvested by biopsy procedure.</p

Mean (± SEM) percentage of morphologically normal equine preantral follicles according to class distribution in ovarian biopsy fragments collected during anestrous and diestrous phases.

<p>^a,b Within the same follicle class and overall mean, values without a common letter differed (<i>P</i> < 0.05). Because of the low number of primary follicles (n = 5) observed in the anestrous phase, transitional and primary follicles classes were combined.</p

Percentage of morphologically normal equine preantral follicles in biopsy fragments collected during anestrous and diestrous phases, and presence of different ovarian structures (antral follicles and corpus luteum).

<p>Percentage of morphologically normal equine preantral follicles in biopsy fragments collected during anestrous and diestrous phases, and presence of different ovarian structures (antral follicles and corpus luteum).</p

Correlation coefficients between (A) follicle density, (B) number of preantral follicles, and (C) ovarian stromal cell density with area of ovarian structures (antral follicles and corpus luteum).

<p>The association among variables (black line) was evaluated by Spearman correlation [(A): r = 0.21, (B): r = 0.21, (C): r = 0.10; <i>P</i> < 0.05]. Each point on the chart represents one ovarian fragment evaluated.</p

Mean (± SEM) percentage of equine preantral follicles according to class distribution in ovarian biopsy fragments collected during anestrous and diestrous phases.

<p>^a,b Within the same follicle class, values without a common letter differed (<i>P</i> < 0.05). ^‡ Tended to differ from transitional follicles during the same phase (<i>P</i> < 0.09).</p

Mean (± SEM) number of equine preantral follicles in ovarian biopsy fragments collected from left and right ovaries in anestrous and diestrous phases.

<p>Mean (± SEM) number of equine preantral follicles in ovarian biopsy fragments collected from left and right ovaries in anestrous and diestrous phases.</p

Mean (± SEM) number of equine preantral follicles in ovarian biopsy fragments collected during anestrous and diestrous phases.

<p>Mean (± SEM) number of equine preantral follicles in ovarian biopsy fragments collected during anestrous and diestrous phases.</p

Correlation between (A) follicular density and stromal cell density, and (B) number of preantral follicles and stromal cell density.

<p>The association among variables (black line) was evaluated by Spearman correlation coefficient [(A): r = 0.15, <i>P</i> < 0.07; (B): r = 0.16, <i>P</i> < 0.05]. Each point on the chart represents one ovarian fragment evaluated (n = 142).</p