Conservation of the Follicular Population in Irradiated Rats by the Cryopreservation and Orthotopic Autografting of Ovarian Tissue

Aim: To preserve the follicular population in rats prior to abdominal irradiation by the orthotopic autografting of ovarian cortical slices (frozen/thawed) in one of two cryoprotective agents (CPAs). The proportion of follicular survival will be quantified at autopsy and a comparison will be made of the two CPAs.

Method: Thirty Wistar rats, aged 38-39 days, were unilaterally ovariectomised. The ovaries of twenty animals were slow-cooled in either 1.5 M dimethylsulphoxide (DMSO; group B) or 1.5 M ethylene glycol (EG; group C). The ovaries of the remaining ten animals (group A) were fixed and histologically examined to determine a fresh follicle count. The contralateral ovary was irradiated with a single dose of 2.5 Gy. Frozen tissue (from groups B and C) was thawed rapidly and autografted into the irradiated ovarian bursa. All animals were mated eighteen days after grafting and were sacrificed eighteen days later. At autopsy, the number of embryos was counted and the ovarian weights recorded, before the tissue was prepared histologically for quantification of follicular survival.

Results: There was no significant difference in the pregnancy rate in the three groups and, although there was a higher number of embryos in the irradiated control group A compared with groups B and C, the difference was not significant. The follicle count in groups B and C was significantly higher than in group A. In group A, the percentage of growing follicles was higher than in groups B and C and the fresh ovary.

Conclusions: Autografting frozen/thawed ovarian tissue preserved a proportion of the follicular population in irradiated rats. There was no significant difference in the numbers of follicles surviving cryopreservation in the two CPAs. Since the irradiated rats were not totally sterilised, we cannot conclude that cryopreserved grafts can restore fertility.