Follicular viability and histological assessment after cryopreservation of whole sheep ovaries with vascular pedicle by vitrification.

OBJECTIVE: To evaluate a cryopreservation technique by vitrification of whole ovaries with their vascular pedicle in sheep, by using two cryoprotectant solutions.
DESIGN: Animal study.
SETTING: Fertility clinic in a university teaching hospital. ANIMAL(S): Five to 6-month-old ewes. INTERVENTION(S): Whole sheep ovaries with their vascular pedicles were collected at the slaughterhouse and prepared for cryoprotectant toxicity tests and freezing procedures. MAIN OUTCOME MEASURE(S): Follicle viability assessment by trypan blue test and histological examination of ovary and vessel structure. RESULT(S): No statistically significant difference in follicle viability or normal primordial follicle rates were observed between ovaries exposed or nonexposed to cryoprotectant solutions. Nor was any statistically significant difference observed before and after vitrification with the two cryoprotectant solutions. The decrease in the number of primordial follicles was smaller when frozen-thawed ovaries were treated with VS4 solution containing dimethyl sulfoxide, formamide, and propylene glycol. There were fewer nuclear anomalies and general follicular anomalies with the VS4 solution. Pedicle fractures occurred in most ovaries during thawing (11/15). CONCLUSION(S): Cryopreservation of whole ovary by vitrification appears a promising technique in reproductive medicine. The best histologic results were obtained with the VS4 cryoprotectant. Further studies are required to overcome vitrified ovarian vessel fracture.