Presence of sucrose in the vitrification solution and exposure for longer periods of time improve post-warming follicle integrity in cat ovarian tissues
Ovarian tissue cryopreservation followed by tissue culture is a promising approach to preserving the fertility of biomedical models and endangered species. The objective of this study was to investigate the impact of exposure time to vitrification solution and presence of sucrose using different exposure temperatures and base media on intra-ovarian follicle integrity. Peripubertal ovarian cortical pieces were obtained by isolating the cortex and dissecting it into 1 × 1 × 0.2 mm3 pieces. The cortical pieces were then exposed to equilibration solution and then vitrification solutions (VS) in one of the conditions mentioned above, plunged directly into liquid nitrogen and stored for ≥24 hr in liquid nitrogen. After thawing, the cortical pieces were cultured in vitro for 0, 1 or 7 days to determine the follicle integrity (through histological assessment) and the ability of the tissue to recover from cryoinjury. Fresh controls maintained a constant level of normal morphology (>60% of the total follicles) throughout the culture period. Cortical pieces exposed to VS with sucrose for 10 min had the highest percentage of normal follicles (approximately 20% after 7 days of culture) throughout the culture period. Other conditions using different base medium, lower exposure temperatures or different thawing methods did not improve the follicle integrity. This protocol provides a solid foundation on which to optimize ovarian tissue cryopreservation in the domestic cat and to investigate the molecular effects of vitrification.