Histological study of rat ovaries cryopreserved by vitrification or slow freezing and reimplanted in the early or late postmenopausal stage.

PURPOSE To compare two rat ovary cryopreservation techniques (vitrification vs. slow freezing) and two postmenopausal stages (early vs. late) with regard to graft take. METHODS Thirty-three Wistar rats were submitted to bilateral oophorectomy. One ovary was submitted to histological analysis while the other was cryopreserved by slow freezing or vitrification. The cryopreserved ovary was thawed and reimplanted in the greater omentum one week (early menopause) or one month (late menopause) after oophorectomy. One month after ovary reimplantation, the graft take was evaluated macroscopically and histologically. RESULTS Six of the animals were used ascontrols and seven died. The histological findings of 20 animals included atretic follicles (n=4), primordial follicles (n=2), and corpus luteum with primordial follicles (n=3). No ovarian tissue was found in 11 animals. Vitrification resulted in a higher graft take rate than slow freezing (50% vs. 38.5%), but the difference was not statistically significant. However, the graft take rate was 9.3 times higher in the early than in the late postmenopausal stage (61.5% vs. 14.3%) (p=0.043). CONCLUSION Vitrification was superior to slow freezing as ovarian cryopreservation technique, and grafting was significantly more successful when the ovary was reimplanted in the late postmenopausal stage.