Vitrification of cat ovarian tissue: Does fragment size matters?

The aim of the present study was to investigate whether or not the size of the ovarian fragment influences its resistance to cryostorage. For that purpose, ovaries were collected from 34 queens (various breeds, age 1-5 year) by routine ovariectomy, transported to the laboratory and then sectioned in different sizes (3 mm × 3 mm × 3 mm, 5 mm × 3 mm × 3 mm and 7 mm × 3 mm × 3 mm) and randomly assigned to a control (GC3, GC5 and GC7, respectively) or vitrified (GV3, GV5 and GV7, respectively) groups. Vitrified-warmed fragments were evaluated by histomorphology and immunohistochemistry (for apoptotic rates by using cleaved caspase-3). Histological examination reveals that 72.97% of the follicles in GV3 and 72.58% in GV5 were normal while only 42.86% of the follicles in GV7. The main morphological alteration presented in all groups was a detachment of the epithelial cells. Similarly, immunohistochemistry evaluation using caspase 3 revealed a small proportion of apoptotic cells in GV3 (8.43%) while in GV7 30.43% of the cells expressed cleaved caspase-3. These findings indicate that fragments sectioned in 3 mm × 3 mm × 3 mm (27 mm³ ) seem more adequate for perfusion of the cryoprotectant, causing less damage to the cell after vitrification-warming.