P-24: The Effect of Oocyte Activation with DTT on Development of Ovine Embryos in ICSI

Background: The objective of the current study was to determine the effect of activation of injected oocytes with dithiothreitol on development of ovine embryos derived from in vitro-matured oocytes and intracytoplasmic sperm.The injected oocytes with non-treated sperm were activated with 1) ionomycin (Io) + 6-dimethylaminopurine (6-DMAP) 2) DTT, 3) DTT+ ionomycin (I)+6-DMAP. Materials and Methods: Within 1 hour after injection, the injected oocytes (ICSI groups) were activated as the following groups: I) Exposure to 5µM ionomycin in H-SOF with 1% FBS for 5 minutes, culture in IVF-SOF for 3 hours to allow extrusion of the second polar body, and then exposure to 1.9 mM 6-DMAP prepared in H-SOF at 39ºC, 5% CO2 in air for 3 hours; II) Exposure to 2 mM DTT in H-SOF at 38.5ºC for 20 minutes and washed twice (10 minutes each) in H-SOF; III) Exposure to 2 mM DTT in H-SOF at 38.5 ºC for 20 minutes and washed twice (10 minutes each) in H-SOF accomplished with ionomycin followed 3 hours later by 6-DMAP. After activation, oocytes were washed in HSOF and placed into 20 µl drops of IVC. Results: The cleavage rates in those activated with DTT (n=78) was lower (p<0.05) than those activated with either ionomycin (Io) + 6-dimethylaminopurine (6-DMAP)(n=277) or DTT+I+6-DMAP (n=74) (30.8 % versus 78.3% and 89.2 % respectively) and also the blastocyst rates in those activated with DTT was lower (p<0.05) than those activated with either ionomycin (Io) + 6-dimethylaminopurine (6-DMAP) or DTT+I+6-DMAP(0 % vs. 17% and 9.5% respectively). Conclusion: Moreover, DTT was not effective on oocyte activation compared with Io+6-DMAP after ICSI.