Fertilizability of Superovulated Eggs by Estrous Stage-independent PMSG/hCG Treatment in Adult Wistar-Imamichi Rats

We investigated the fertilization and developmental ability of superovulated eggs obtained from adult Wistar-Imamichi (WI) rats, by using pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) treatment. Female WI rats, 11-13 weeks of age, were divided into four groups by estrous stage (metestrus [ME], diestrus [DE], proestrus [PE], or estrus [E]). PMSG (150 IU/kg) and hCG (75 IU/kg) were injected at an interval of 48 or 55 h and the female rats were mated with mature male rats. The ovulated eggs were collected 20, 24, and 27 h after hCG injection. Regardless of the estrous stage at the time of PMSG injection, the treated rats mated and ovulated similar to the untreated spontaneously ovulated rats (S group). Although the proportion of fertilized eggs in the E- and PE-treated groups was less than the S group 20 h after hCG injection, the proportion was not different among all treated and S groups 24 h after hCG injection. The proportion of fertilized eggs using in vitro fertilization and the proportion of offspring obtained from 2-cell stage embryo transfer did not differ among the treated and S groups. In comparison with PMSG/hCG-treated immature rats, mating and ovulation rate of adult rats were significantly higher. The proportion of fertilized eggs obtained from mated rats did not differ between immature and adult rats. These results demonstrate that adult WI rats are good egg donors for reproductive biotechnological studies using unfertilized or fertilized eggs.