In vitro maturation of Mus musculus mice oocytes after hyperosmotic shock induced by vitrification solutions

OBJECTIVE: To evaluate in vitro oocyte maturation rates in embryonic culture medium after induction by hyperosmotic shock caused by exposure to vitrification solutions. METHODS: Bilateral oophorectomy was performed on 20 prepubescent female mice (Swiss). Immature (Prophase I) oocytes (N = 400) were obtained by ovarian dissection, divided into 4 groups, and transferred to culture dishes containing fertilization medium (Sydney IVF Fertilization Medium, Cook(®) Medical). The control group (CG) did not receive treatment, the test groups (G1, G2, G3) were treated with vitrification solution - 2 (VI-2: 14 M sucrose + ethylene glycol and dimethyl sulfoxide) for 30 seconds and subsequently: G1: 30 seconds in devitrification solution - 2 (DV-2: 0.5M sucrose); G2: 60 seconds DV-2; G3: 60 seconds DV-1(1M sucrose) and 180 seconds DV-2. All groups were cultivated for 24 hours in an incubator at 37ºC and 5% CO2 (Thermo model 3110). After this period, we checked their maturation status. RESULTS: Oocytes exposed to VI-2, DV-1 and DV-2 (G3) showed the highest rate of competence in resuming meiosis and reaching the MII stage; however, there was no statistically significant difference (G3 = 50.5% - 49/97; CG = 27.8% - 10/30). CONCLUSIONS: Oocyte exposure to vitrification solutions, in order to cause osmotic shock, did not interfere with the resumption of meiosis in mice oocytes.