Cryopreservation of cat ovarian tissue: post-transplantation effectiveness

The aim of this study was to test three different protocols for cat ovarian tissue cryopreservation and confirm their efficacy by autotransplantation. First, nine pairs of ovaries were obtained after elective ovariohysterectomy in mixed-breed cats. Fragments of ovarian cortex (1x1x5 mm) were subjected to slow freezing with Me2SO 1.5 M, ethylene glycol (EG) 1.5 M or a mixture of both (0.75 M each). All three cryoprotectants showed similar percentages of morphologically normal (MN) follicles at histology (80.56% with EG, 78.7% with Me2SO and 75.87% with EG + Me2SO). After analysis by electron microscopy, the Me2SO protocol showed the best results: absence of oocyte detachment and no cytoplasmic granules or plasmatic membrane rupture. This protocol was selected and autotransplantation was then performed to confirm follicle viability. For this step, four mixed-breed female cats were used. Ovariohysterectomy was performed and fragments of ovarian cortex were subjected to the chosen slow-freezing protocol. After thawing, five fragments were transplanted to the subcutaneous tissue of the donor cats’ dorsal neck. Fragments were removed after 7, 14, 28, 42 or 63 days post-transplantation and processed for histological analysis. The presence of fibrotic tissue after different periods of transplantation was evaluated by Masson’s trichrome staining. The cryopreserved tissue showed 31.3, 3.3 and 26.8% of MN follicles after 7, 14 and 28 days of grafting, respectively, but no MN follicles were observed after 49 or 63 days. Moreover, two antral follicles were detected in one cat after 28 days. Fibrous tissue showed a clear increase mainly after 28, 49 and 63 days of transplantation. In conclusion, despite follicle loss after 49 days probably due to ischemia-reperfusion injury, data from electron microscopy regarding the suitability of Me2SO 1.5 M was confirmed, since MN follicles were present up to 28 days of transplantation. Source of funding: This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).