Hydrostatic pressure improves in-vitro maturation of oocytes derived from vitrified-warmed mouse ovaries

Cryopreservation has limited successes and in-vitro maturation is used to improve its results. Hydrostatic pressure (HP) plays an important role in follicular development.

This study was designed to examine the effects of HP on in-vitro maturation of oocytes and cell death in cumulus cells derived from vitrified-warmed mouse ovaries.

Preovulatory follicles were harvested from non-vitrified and vitrified-warmed 6-8 week-old female NMRI mouse ovaries and randomly assigned to following groups: non-vitrified (control), non-vitrified with HP exposure (treatment I), vitrified-warmed (treatment II) and vitrified-warmed with HP exposure (treatment III). The follicles of treatments I and III were subjected to HP (20 mmHg) for 30 min and after that all groups were cultured for 24h and assessed for in-vitro maturation of oocytes. The viability and apoptosis of cumulus cells and oocytes were assessed using supravital nuclear staining and TUNEL assay, respectively.

Oocytes harvested follicles in both control and treatment II had a significantly lower percentage of metaphase II oocytes (MII) than the treatment I and III (23.5±3.1, 15.03±4.6 and 32.7±3.2, 25.5±4.6; respectively) (p<0.05). Viability of the cumulus cells reduced in treatment I, II and III (83.4, 83.3 and 77.7%) compared to control (86.9%), (p<0.05). The apoptotic index in cumulus and oocyte complexes in treatments I and III (10.7±0.8 and 15.3±0.8) was higher than in control and treatment II (6.7±0.5 and 9.7±0.5) (p<0.05).

These results demonstrate that HP had a mild effect on cell death incidence in cumulus cells without any effect on oocyte. However, it can be used as a mechanical force to improve in-vitro maturation of oocytes derived from vitrified-warmed mouse ovaries.