VIABILITY OF SMALL PREANTRAL OVARIAN FOLLICLES FROM DOMESTIC CATS AFTER CRYOPROTECTANT EXPOSURE AND CRYOPRESERVATION

About 1500 preantral follicles can be recovered from a single cat ovar y by mechanical dissection. This is a potentially rich source of genet ic material if ova could be preserved and grown in vitro, especially f rom rare or endangered species that die abruptly or are ovariectomized for medical reasons. The aims of this study were to examine cryoprote ctant toxicity and then the potential of successfully cryopreserving p reantral cat follicles. In the initial toxicity trial, isolated cat fo llicles (40-90 mu m) were exposed to dimethylsulfoxide, glycerol, 1,2- propandiol or ethylene glycol at 0 degrees C for 15 min. Follicle viab ility was assessed by supravital staining using a combination of Trypa n blue and Hoechst 33258 at 0 h, and after 18 h and 1 week of culture. Percentages of follicles with intact oocytes and granulosa cells were similar (P > 0.05) among control (no cryoprotectant), dimethylsulfoxi de, 1,2-propandiol and ethylene glycol treatments at all time points, but were reduced (P < 0.05) after glycerol exposure. On the basis of t his finding, dimethylsulfoxide and 1,2-propandiol were used to cryopre serve intact follicles, and post-thaw viability was assessed by suprav ital staining and 5-bromo-2'-deoxyuridine uptake into oocytes and gran ulosa cells during culture. Of control (noncryopreserved) follicles, 3 1.4%+/-2.9%, 18.8%+/-1.9% and 16.2%+/-1.6% were intact after 0 h, 18 h and 1 week of culture, respectively. Uptake of 5-bromo-2'-deoxyuridin e occurred in approximately 20% of follicles at all time points. On th e basis of the presence of both a healthy oocyte and granulosa cells, cryopreservation in dimethylsulfoxide or 1,2-propandiol allowed approx imately 19% of follicles to survive. Approximately 10% demonstrated cl ear evidence of cell activity that was sustainable for I week. In conc lusion, the cat ovary contains a population of: preantral follicles th at are not adversely affected by short-term exposure to most conventio nal cryoprotectants. Furthermore, there is a subpopulation of these fo llicles capable of surviving cryopreservation, remaining structurally intact and physiologically active after thawing.