Adição de melatonina ao meio de maturação de oócitos bovinos submetidos ao choque térmico in vitro: efeitos sobre as taxas de produção e qualidade de blastocistos

Abstract

Heat stress increases the production of free radicals, which contributes to a decrease in the quality of oocytes and embryos. Thus, the addition of antioxidants, such as melatonin, to the in vitro maturation medium (IVM), has the potential to reduce damages from high temperatures. Addition of melatonin to the IVM medium of bovine oocytes submitted to heat shock on production rates and blastocyst quality was evaluated. Slaughterhouse derived oocytes were matured under heat shock (12 h at 41.0 o C followed by 12 h at 38.5 o C) in IVM medium without (0M) or with melatonin at 10 -12 ; 10 -9 ; 10 -6 and 10 -3 M concentrations. In the positive (non-stress) control, oocytes were matured in the absence of melatonin under conventional conditions (24 h at 38.5 o C). In the DMSO control oocytes were matured in medium containing 0.46% DMSO (same concentration as the 10 -3 M treatment), under heat shock. Oocytes were randomly assigned to treatments blocked by days of ovarian collection. Greater proportions (P <0.05) of embryos with eight or more cells on day 3 of culture (D3) were observed in the 10 -3 , 10 -6 and 10 -9 M melatonin treatments and non-stress control compared to 10 -12 and 0 M treatments. The proportion of embryos with eight or more cells in D3 was higher (P <0.05) in the DMSO control compared to 10 -9 , 10 -12 e 0 M groups. Blastocyst production on days 7 (D7) and 8 (D8), total number of cells, apoptotic cells to total cell ratio and the proportion of apoptotic cells to the inner cell mass (ICM) (P> 0.05) did not change by the addition of melatonin or DMSO to the IVM medium nor by heat shock (0 M vs non-stress control). The 10 -6 M treatment resulted in a greater proportion (P <0.05) of ICM in relation to total cells compared to 10 -9 , 10 -12 , 0 M and DMSO treatments, but did not differ (P> 0.05) from the 10 -3 M treatment and non-stress control. The greater the melatonin concentration the greater the proportion of embryos with eight or more cells in D3 increased (P <0.05). The proportion of MCI cells increased from 10 -9 M, peaking at 10 -4 M, followed by a reduction at 10 -3 M. In conclusion, the addition of melatonin up to 10 -3 M in the MIV medium of oocytes under heat shock stimulated embryonic development to the 16-cell stage and the proportion of MCI cells was increased by the addition of 10 -4 M melatonin to the IVM medium.