Optimal Conditions for Successful In Vitro Fertilization and Subsequent Embryonic Development in Sprague-Dawley Rats

The present study was conducted to determine the optimal conditions for successful in vitro fertilization (IVF) in SpragueDawley (SD) rats. The IVF of oocytes from SD and Wistar rats was compared in different fertilization media (mR1ECM, IVF-20, and modified Krebs-Ringer bicarbonate solution [mKRB]), and IVF conditions were then optimized for oocytes of the SD strain. Results showed that in mR1ECM medium, fertilization rates were markedly lower in SD rats (15%) than in the Wistar strain (73%), although this response was significantly improved by increasing the NaCl concentration. In addition, fertilization rates in SD rats were higher in modified IVF-20 (73%) than in IVF-20 (18%) and mKRB (53%). In contrast, fertilization rates in Wistar rats were higher in IVF-20 and modified IVF-20 than in mKRB (78%, 74%, and 36%, respectively). Further investigation concerning the effects of the NaCl supplementation (10– 40 mM) in IVF-20 on the fertilization of oocytes in the SD strain indicated that significantly higher percentages of oocytes were fertilized in IVF-20 supplemented with 30 mM NaCl (66%) and developed to the blastocyst stage (47%) in vitro. After transfer, embryos derived from this IVF system developed to term at a percentage comparable to that of in vivo-fertilized controls. In conclusion, differences exist in optimal IVF conditions between rat strains, and a modified culture medium has been successfully developed for assessment of the developmental competence of oocytes in SD rats.