Cat ovarian follicle ultrastructure after cryopreservation with ethylene glycol and dimethyl sulfoxide.

Ovarian tissue cryopreservation is a promising technique for fertility maintenance. The aim of this study was to compare the morphology of domestic cat ovarian follicles after tissue cryopreservation with ethylene glycol (EG) and dimethyl sulfoxide (Me2 SO). Ovaries from healthy adult cats undergoing elective ovariohysterectomy were used. Eight fragments were obtained from each pair of ovaries: two were used as fresh controls; three were submitted to fresh perfusion toxicity test and perfused with M199, 10% fetal calf serum and 0.4% sucrose containing Me2 SO 1.5 M, EG 1.5 M or Me2 SO 0.75 M + EG 0.75 M; and the remaining three fragments were perfused as described and submitted to slow freezing. After 45 days of cryopreservation, the samples were thawed, fixed and processed for light and transmission electron microscopy (TEM). The percentages of morphologically normal follicles identified by light microscopy were higher in the control group (94.45%) in comparison to the frozen groups (80.56% with EG, 78.7% with Me2 SO and 75.87% with EG + Me2 SO). The fresh perfused tissue showed no statistical difference compared to control or frozen samples. The TEM analysis showed less damage in the ultrastructure of follicles from the Me2 SO group in comparison with the EG and Me2 SO + EG groups. According to the morphological analysis, 1.5 M Me2 SO is the best cryoprotectant for cryopreservation of domestic cat ovarian tissue regarding the morphology of preantral follicles after thawing. Further studies regarding the viability of these follicles should be performed.