Abstract: Objective To assess the longterm efficacy of cryopreserved ovarian tissues after heterotopic autologous transplanted in rats. Methods Seventyeight adult Wistar rats were divided into four groups randomly as follows: sham-operated group (group 1,EM>n/EM>=15), freshtransplanted group (group 2,EM>n/EM>=24), frozen-thawed-transplanted group (group 3,EM>n/EM>=24) and ovariectomized group (group 4,EM>n/EM>=15). Fresh and frozen-thawed ovarian tissues of adult rats were autologous transplanted under renal capsule. One third animals of each group were slaughtered and their ovaries and uteruses were removed for morphometric analysis at 5 months after transplantation; one third additional animals were slaughtered at 8 months; and the remaining animals were slaughtered at 10 months. The measurement of serum estradiol (ESUB>2/SUB>) and progesterone (P) concentrations during the estrus stage and vaginal cytology were performed to assess the secretary function of implanted ovarian tissues. Results Both fresh and frozen ovarian grafts survived in all the animal models. In groups 2 and 3, the serum ESUB>2/SUB> and progesterone concentrations during estrus remained comparable to the shamoperated rats’ hormone levels (group1), and significantly higher than the concentrations in group 4 at 5, 8, 10 months respectively (EM>P/EM><0.01). Morphologically, no significant differences were observed in the proportion of each stage of follicles between frozenthawed tissues and fresh ovarian tissues (EM>P/EM>> 0. 05). And the proportion of each stage follicles in both types of grafts was comparable to that in group 1 (P>0.05). The number of primordial follicles in fresh grafts and frozen grafts were significantly less than that in group 1 Grafts in group 2 contained 59.1% of the primordial follicles in sham-operated controls while frozen grafts contained 54.5% at 5 months after implantation. Conclusion Cryopreservation of small pieces of ovarian tissues is feasible for keeping cell viability. After autologous implanted under the renal capsule, the cryopreserved ovarian tissues have no significant morphological changes. The follicles survive and develop well, though th

Key words: Ovary, Autotransplantation, Cryopreservation, Histology, Rat