P-37: The Effect of Extracellular Calcium Concentration on the In vitro Maturation of Mouse Oocytes after Mechanical Stimulation by Hydrostatic Pressure

Background: Oocyte maturation is usually defined as the period of progression from the first to the second meiotic arrest and involves coordinated nuclear and cytoplasmic modification. Ca2+ signals are known as important regulators of oocyte maturation. Extracellular Ca2+ is important for first polar body formation, normal meiosis kinetics, and for preserving the chromosome and spindle configuration which is normally maintained between MI and MII. Hydrostatic pressure as a physical factor plays physiological roles in the reproduction system. Hydrostatic pressure allows Ca2+ to enter gamets and embryos and causes non-specific permeabilization of plasma membrane to Ca2+. In this study we investigated the role of extracellular Ca2+ on hydrostatic pressure inducing oocyte maturation in mouse. Materials and Methods: Six to 8-week-old female NMRI mice were used in this study. The ovaries were collected in α-MEM culture medium and oocytes were retrieved from ovaries. They were divided in experiment and control groups. In experiment group, oocytes were transferred to pressure chamber and subjected to 10 mmHg pressure for 10 minutes. Oocytes without exposure to pressure were considered as control. Oocytes from two groups were cultured in T6 culture medium prepared with different concentration of calcium 0, 0.4, 0.8 and 1.7 mM (treatments I, II, III and IV; respectively), supplemented with 5 IU/ml HCG for in vitro maturation. Oocytes were cultured for 48 hours and the in vitro maturation of oocytes was assessed. Results: After 48 hours of in vitro maturation, in experiment and control groups treatments I, II, III, IV the percentage of MII oocytes was %6.0, %10.3, %12.5, %37.0 and 3.0%, 7.0%, 8.0%, 15.0% respectively. Oocyte maturation rate in experiment group was higher than control group (p<0.05). Oocyte maturation rate was increased by increasing the extracellular calcium concentration during the maturation period (p<0.05). Conclusion: Our data suggests that hydrostatic pressure enhances oocyte maturation. It is concluded that improving in oocyte maturation rate could be in correlation with increasing in extracellular calcium concentration.