Cryopreservation of a whole ovary as a strategy for restoring ovarian function

Purpose: To evaluate whether a total ovary can successfully be cryopreserved and thawed under maintenance of high proportions of structurally normal primordial follicles. Methods: Porcine ovaries were explanted immediately after slaughtery. Ten ovaries were cooled to -196degreesC using cryoprotective solution and a computer-controlled freezing technique. Five contralateral ovaries were fixed with formalin for histological examination, the five remaining ovaries were directly plunged in liquid nitrogen. After three weeks of storage, frozen ovaries were thawed and examined by light and electron microscopy. Viability was assessed by evaluation of intact primordial follicles with respect to cellular and intracellular structures. Results: Histological viability of primordial follicles in computer-frozen ovaries was 84.4% (76.1-90.6%), as compared to non-frozen control samples (92-100%; mean 97.6%) and to ovaries plunged in liquid nitrogen without cryoprotection 21.1% (4.5-35.0%). Conclusions: Cryopreservation of whole ovaries may present a feasible way to maintain high numbers of viable primordial follicles in ovarian tissue retransplantation.