Effect of vitrification method on survivability, follicular growth and ovulation of preantral follicles in mice

Abstract

This study was designed to compare the survival rates, follicular growth rates, and ovulation rates of vitrified preantral follicles (PF) from ovaries with those isolated from a vitrified ovarian cortical strip. Mouse ovaries were divided into three groups: those not treated by vitrification of the PF (control), those treated by vitrification of the PF isolated from the ovaries (group I), and those treated by vitrification of ovarian tissue followed by PF isolation (group II). The group I samples were exposed to equilibration solution (EG-20) for 5.0 min plus vitrification solution (EFS-40) for 0.5 min, while the group II samples were exposed to EG-20 for 10.0 min plus EFS-40 for 2.0 min, before vitrification. They were subsequently placed on an electron microscope grid, and submerged immediately in liquid nitrogen. After thawing, the survival rate and the growth rate of the follicles were evaluated every 2 days. In the in vitro condition, the follicles grew and developed into antral follicles in groups I and II. The survival rate of the group I samples was higher than that of the group II samples during the in vitro culture (P<0.05). The growth rates of the follicles in group I were higher than those in group II after day 6 (P<0.05). The ovulation rate of the samples in group I was higher than that of group II (P<0.05). These results demonstrated that direct PF vitrification appeared to be better than vitrification of the PF isolated from ovarian tissue.