165 EFFECTS OF GLUCOSE CONCENTRATIONS ON IN VITRO DEVELOPMENT AND THE INTRACELLULAR OXIDATIVE STATE OF IN VITRO-PRODUCED PORCINE EMBRYOS

Abstract

The present study was conducted to elucidate the effects of glucose addition during Days 0 to 2 (the day of in vitro fertilization was defined as Day 0) on the developmental competence, intracellular reactive oxygen species (ROS) level, and glutathione (GSH) concentration of in vitro-produced pig embryos. Zygotes were obtained as reported previously (Kikuchi et al. 2002 Biol. Reprod. 66, 1033-1041), and cultured in NCSU-37 supplemented with 1.5, 3.5, 5.5, 10, and 20 mM glucose (glucose groups) or in NCSU-37 supplemented with 0.17 mM pyruvate and 2.73 mM lactate (Pyr/Lac group) from Days 0 to 2. Subsequently, embryos in all groups were then cultured in NCSU-37 added with 5.5 mM glucose until Day 6. Data were analyzed by ANOVA and are presented as percentage for blastocyst rate and as mean � SEM for blastocyst cell number. The blastocyst rates and blastocyst cell numbers in glucose groups were significantly lower compared to those in the Pyr/Lac group (blastocyst rate: 5.2, 13.8, 12.6, 16.3, and 13.5%, respectively, vs. 26.3%); blastocyst cell number: 41.8 � 3.2, 41.6 � 2.3, 42.2 � 3.2, 43.0 � 3.3, and 39.2 � 2.8, respectively, vs. 52.7 � 4.1). The ROS levels of Day 1 embryos were significantly higher when they were exposed to glucose, whereas the ROS levels of Day 2 embryos were higher only in the 1.5 mM and 3.5 mM glucose groups, compared to levels in embryos in Pyr/Lac group. There were no differences in the GSH concentrations of Day 1 embryos among the glucose groups and the Pyr/Lac group. Of Day 2 embryos, the GSH concentration was significantly lower only in 1.5 mM glucose group, compared to that in embryos in the Pyr/Lac group. These results indicate that (1) the presence of glucose during the first 2 days of culture causes a decrease in the development of in vitro-produced embryos to the blastocyst stage, which might be related to the rise in ROS generation in Day 1 embryos; and (2) except for the 1.5 mM glucose group, the ability of Day 2 embryos in glucose groups to maintain GSH concentration at levels needed for their development might provide them with preferable intracellular conditions for the development to the blastocyst stage.