Nitric Oxide (NO-) is a cell signaling molecule regulating preimplantation embryo development. We have now investigated the role of NO- in culture of bovine embryos in vitro produced, using N-Nitro-L-Arginine Methyl-Ester (L-NAME), an inhibitor of NO- production, and L-arginine (ARG), a precursor for NO-, in different periods of culture (embryo genome activation and compaction). NO- effects were assessed by developmental rates, kinetics of development, embryo quality, and gene expression. Embryos were generated by in vitro maturation and fertilization of oocytes aspirated from abattoir-derived ovaries. In experiment 1, the rates of development were measured in SOFaa in the presence of L-NAME (10mM) in different periods: from day 1st to 4th (LN1-4), from 4th to 8th (LN4-8) and from day 1st to 8th (LN1-8). The NO- inhibition was detrimental from the day 4th of culture (LN4-8 and LN1-8 groups), decreasing the blastocyst hatching (17.3%±13.44 and 13.7%±14.51, respectively, p<0.05). However the most negative effect occurred from the 1st to 8th day of culture which the blastocyst rate was significantly decreased compared to control (29.4%±3.72 vs 47.8%±11.34, respectively, p<0.05). Due to, in experiment 2, ARG (1, 10 and 50mM) was additioned since the 1st day of culture. The blastocyst rates using ARG at 1 and 10mM were similar to control (48%±13.03 e 34.2%±3.92 vs 49.4%±4.82, respectively, p>0.05), but 50mM was found to impair embryo development (10.7%±7.24, p<0.001). In experiment 3, ARG at 1mM was additioned from the 5th to 8th day of culture. The development rates were similar to GLN group (with glutamine only). However, compared to control group (without both aminoacids) ARG addition yielded improved blastocyst hatching (54.8%±6.9 vs 41.4%±11.47, respectively, p<0.05) and embryo quality (84.8%±2.63 vs 52%±8.62, respectively, p<0.05), but not blastocyst rate (49.4%±6.5 vs 49.4%±4.8, respectively, p>0.05). NO- production was positively correlated with blastocyst hatching (R²=96.4%, p<0.001) and embryo quality (R²=75.5%, p<0.05). Additionally, embryos were cultured in the presence of L-NAME and ARG simultaneously (ARG/LN group), from the 5th to 8th day of culture, and OCT-4 and INT-t transcripts were measured by real time PCR. Was found a similar expression of OCT-4 (p>0.05), but a significant decrease of 1.8 and 1.5 fold of INT-t expression related to control groups ARG and Glutamine (p<0.05), respectively. These data provide evidence that NO- contributes to hatching and embryo quality improvement, especially at the period between morula and blastocyst stages. NO- production is required to preimplantational development of bovine embryos in vitro produced and can be mediated by supplementation of medium culture with ARG.
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