Influence of vitrification techniques and solutions on the morphology and survival of preantral follicles after in vitro culture of caprine ovarian tissue

The objective was to compare the efficiency of various vitrification techniques and solutions for preserving morphology and viability of preantral caprine follicles enclosed in ovarian tissue. Fragments of ovarian cortex were cryopreserved by conventional vitrification (CV) in French straws, vitrification in macrotubes (MTV), or solid-surface vitrification (SSV). Six solutions containing 6 M ethylene glycol, with or without sucrose (SUC; 0.25 or 0.50 M) and/or 10% fetal calf serum (FCS) were tested (Experiment I). After 1 wk, samples were warmed and preantral follicles were examined histologically. To evaluate follicular viability (Experiment II), ovarian fragments were vitrified with the three techniques listed above, in a solution containing 0.25 M SUC and 10% FCS. After warming, follicles were assessed by the trypan blue dye exclusion test. In Experiment III, preantral follicles enclosed in ovarian tissue were vitrified using the protocol which yielded the highest percentage of viable preantral follicles (SSV with 0.25 M SUC and 10% SFB). After warming, the preantral follicles enclosed in ovarian tissue were cultured in vitro and then, were analyzed by histology and fluorescence microscopy (calcein-AM and ethidium homodimer-1). Every vitrification protocol significantly reduced the percentages of morphologically normal follicles relative to the control (88.0%); however, the addition of 0.25 M SUC and 10% FCS to the vitrification solution improved preservation of follicular morphology (67.4, 67.4, and 72.0% for CV, MTV, and SSV, respectively). Although follicular viability after SSV (80.7%) did not differ from that in fresh (non-vitrified) ovarian tissues (88.0%), after in vitro culture, percentages of viable follicles were significantly reduced (70.0%). Percentages of morphologically normal follicles after in vitro culture of vitrified ovarian tissue were similar (76.0%) to those in ovarian cortex fragments cultured without previous vitrification (83.2%). In conclusion, SSV using a solution containing 0.25 M SUC and 10% FCS, was the most efficient method for vitrifying caprine ovarian tissue.