Produção de espécies reativas de oxigênio e criosobrevivência de embriões bovinos pós-vitrificação | Production of reactive oxygen species and cryosurvival of post-vitrification bovine embryos

The reduced survival rate achieved after warming vitrified embryos represents a major problem for the dissemination of the use of cryopreservation. In this context, the objectives of the present study were: (1) to investigate the concentrations of reactive oxygen species and the generation of oxidative stress in fresh and warmed vitrified blastocysts and (2) whether the attenuation of oxidative stress, through post-warming cultivation with (+) and without (-) beta-mercaptoethanol (100 μM), could improve survival (re-expansion and hatching), oxidative index and quality of vitrified embryos. In experiment I, embryos were separated into two groups: fresh embryos (F) and warmed vitrified embryos (V). In experiment II, fresh and vitrified blastocysts were separated into four experimental groups: fresh cultured with antioxidant (F+), fresh cultured without antioxidant (F-), warmed vitrified cultured with antioxidant (V+) and warmed vitrified cultured without antioxidant (V-). The results showed that the concentrations of reactive oxygen species were higher (P<0,05) in vitrified embryos (103,7±8,7 pixels mean) when compared to fresh embryos (57,3±4,2 pixels mean). On the other hand, the rate of re-expansion of the V+ and V- embryos was similar (P>0,05) in all evaluated moments (0 h: V+ = 63,9%, V- = 62,6%; 2 h: V+ = 90,4%, V- = 95,6%; 4 h: V+ = 92,8%, V- = 98,9%). The hatching rate of V+ (49,4%) and V- (48,1%) embryos was similar (P>0,05) to that observed in F- embryos (65.7%). The oxidative index present in the embryos also did not differ between the experimental groups (P>0,05). However, V+ embryos (148,0±7,3) showed a similar total number of cells to F- (158,0±14,5) and F+ (163,2±9,2) embryos, whereas embryos V- (117,4±5,5) had a smaller number of cells (P<0,05) compared to the other experimental groups. It is concluded that vitrification and warming increase the concentrations of reactive oxygen species in vitrified embryos and that, although the attenuation of oxidative stress with beta-mercaptoethanol did not result in better embryonic survival rates, it contributed to improve the total number of cells, an indication of higher quality of vitrified embryos.

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