Effect of beta-mercaptoethanol or epidermal growth factor supplementation on in vitro maturation of canine oocytes collected from dogs with different stages of the estrus cycle.

Abstract

Supplementation of beta-mercaptoethanol (beta-ME) in in vitro maturation (IVM) medium was shown to improve embryo development and quality in several species. Epidermal growth factor (EGF) was also shown to improve IVM of human oocyte and embryo development after in vitro fertilization (IVF). The effect of these two compounds were suggested to be mediated through the synthesis of glutathione (GSH) which is known to play an important role in protecting the cell or embryos from oxidative damage. Thus, it is suggested that supplementation of canine IVM medium with beta-ME or EGF may be of benefit due to its positive role in IVM of various mammalian oocytes and embryo development, including cattle, pigs, rodents and humans. This study investigates the effect of ovarian estrus stage on canine oocyte quality and supplementation of medium with beta-ME or EGF on IVM of canine oocytes. As results, a significantly higher percentage of oocytes progressed to metaphase II (MII) stage in 50 or 100 microM of beta-ME supplemented oocytes collected from the follicular stage. The maturation rate to metaphase I (MI) stage was also significantly higher in oocytes collected from follicular stage and cultured with 25 or 100 microM compared to other experimental groups. After IVM culture, oocytes recovered from dogs with the follicular stage and matured in TCM-199 supplemented with 20 ng/ml EGF yielded better oocyte maturation to MII phase compared to other groups. Taken together, supplementation of beta-ME (50 or 100 microM) or EGF (20 ng/ml) improved IVM of canine oocytes to MII stage.