Comparative analysis of two cryopreservation systems of ovarian tissues in female Wistar rats

The aim of this study was to determine the most efficient protocol for cryopreservation of ovarian tissue using the automatic Freeze Control® system and to test two different cooling curves combined with two different cryoprotectants: dimethyl sulfoxide (DMSO) and ethylene glycol (EG).

In this study, 20 female Wistar rats underwent bilateral oophorectomy. The ovaries were divided into two groups: one cryopreserved in 1.5M DMSO and the other in 1.5M EG. Two cooling curves, slow (1h 50min) and rapid (35min) were analyzed. Tissue samples were frozen, thawed, fixed, and stained with hematoxylin and eosin to analyze oocyte integrity. Follicular analysis was performed under optical microscopy (400x magnification) and preantral follicles were classified as primordial or primary according to developmental stage. ANOVA was performed, and Tukey's test was used for comparison between means, with P<0.05 defined as significant.

In cryopreserved tissue, the follicles with preserved integrity in each ovary were 79% primordial and 29% primary. In non-frozen (control) tissue, all follicular types were observed (primordial, primary, secondary, preantral, and antral). Reversible changes included cytoplasmic vacuolization and irregular cell outline. Irreversible changes included pyknosis. EG was more efficient than DMSO, preserving a greater number of viable primordial and primary follicles. Comparison of both cooling curves revealed no statistically significant differences between them.

The EG is more effective as a cryoprotectant than DMSO for obtaining higher viable numbers of primordial and primary follicles from rat ovarian tissue. Further studies are needed to demonstrate ovarian functionality, such as detection of hormone levels.