Cryopreservation of ovarian cortex is potentially an important tool for the conservation of endangered species. It will allow preserving the large pool of primordial and primary follicles to retrieve fertilizable oocytes in the future. The aim of this study was to evaluate the effects of slow freezing on the morphology and viability of canine follicles after thawing using DMSO or 1,3-propanediol (PROH) as cryoprotectants. Slices of canine ovarian tissue were equilibrated for 20 minutes at 20 °C in minimum essential medium containing either cryoprotectants at 1.5 M, and then frozen by a standardized protocol. Morphology of follicles after thawing was analyzed by means of histology and transmission electron microscopy, and viability was assessed using Trypan blue and fluorescent probes. The exposure of dog ovarian tissue to both cryoprotectants before freezing had no effect on follicular morphology and viability. Also after freezing, follicles remained histologically normal, but transmission electron microscopy revealed damage of ultrastructure in follicles, which were exposed to PROH. Postthaw viability was significantly reduced with 65.7% of the follicles remaining alive in DMSO and 48.7% in PROH. In conclusion, this study demonstrated the survival of canine oocytes within ovarian cortex cryopreserved by slow freezing using 1.5-M DMSO.
Keywords: Dog; Electron microscopy; Histology; Oocyte; Slow freezing; Viability.
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