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 eggsobtained 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 ofage, 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 aninterval of 48 or 55 h and the female rats were mated with mature male rats. The ovulatedeggs were collected 20, 24, and 27 h after hCG injection. Regardless of the estrous stageat the time of PMSG injection, the treated rats mated and ovulated similar to theuntreated spontaneously ovulated rats (S group). Although the proportion of fertilizedeggs 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 theproportion of offspring obtained from 2-cell stage embryo transfer did not differ amongthe treated and S groups. In comparison with PMSG/hCG-treated immature rats, mating andovulation rate of adult rats were significantly higher. The proportion of fertilized eggsobtained from mated rats did not differ between immature and adult rats. These resultsdemonstrate that adult WI rats are good egg donors for reproductive biotechnologicalstudies using unfertilized or fertilized eggs.