COMPARISON OF SUPEROVULATORY RESPONSE OF MATURE OUTBRED MICE TREATED WITH FSH OR PMSG AND DEVELOPMENTAL POTENTIAL OF EMBRYOS PRODUCED

A superovulatory treatment for mice based on FSH administration was co mpared with a standard one based on PMSG. Our aim was to determine if a mean number of embryos recovered per donor could be increased and if in vitro or in vivo viability was affected by the hormonal treatment used. Thus, female Swiss mice were subjected to 2 superovulatory treat ments, and the 1-cell and 2-cell stage embryos were cultured in 2 diff erent media to the blastocyst stage or were transferred to pseudopregn ant recipients. The data show that despite a lower mating percentage ( 52% with FSH vs 66% with PMSG), the FSH-treated mice provided twice th e number of total embryos (53.4 vs 24.5) with a similar percentage of morphologically normal embryos (74% for FSK vs 69% for PMSG). We also found that in vitro culture results can be influenced by the source of gonadotropins depending on the culture medium used. A culture medium such as CZB which prevents the 2-cell block, provided the same develop mental rates regardless of hormonal treatment used. However, with M-16 medium, which does not prevent this blockage, only 39% of the 2-cell FSH-derived embryos and 49% of the PMSG-derived 2-cell embryos develop ed into blastocysts (P<0.05). FSH-derived embryos resulted in a higher percentage of pregnant recipients (73 vs 56%) than PMSG-derived embry os, but the number of alive fetuses and the number of implantations pe r pregnant recipient was affected only by the kind of culture system u sed before transfer. The results dow that FSH can provide very good su perovulatory response in mice, thus reducing the number of donors need ed for a given experiment and providing embryos of at least the same q uality as those derived from the standard PMSG treatment.