Background: The study aim was to assess whether the incorporation of myo-inositol (MI) into culture medium could improve oocyte maturation in vitro.
Methods and results: We performed a controlled prospective study using female ICR strain mice superovulated with pregnant mare's serum gonadotrophins. Cumulus-enclosed germinal vesicle (GV) oocytes were randomly cultured in medium with or without MI supplementation. The kinetics of GV breakdown after 4 h of incubation was significantly higher in oocytes incubated with 30 mmol/l of MI than in controls (P < 0.001). Accordingly, this concentration of MI was used for subsequent experiments. The proportion of metaphase II oocytes achieved after 24 h of culture, their fertilization and cleavage rates were significantly higher in the MI-treated group (P < 0.01, P < 0.05, P < 0.05 respectively). This group also demonstrated significant improvement in postimplantation development after transferring the 2-cell embryos to pseudopregnant mice. Confocal microscopy revealed spontaneous intracellular Ca(2+) oscillations within competent GV oocytes and treatment with MI caused an earlier onset of these Ca(2+) signals.
Conclusions: Our results suggest that MI may affect meiotic progression of mouse GV oocytes possibly by enhancing the intracellular Ca(2+) oscillations. Supplementation of MI in culture medium may be useful for human oocyte maturation.