Implantation is themost critical stage in the establishment of pregnancy. Inmammals, it has been estimated thatbetween 25%and 60%of conceptuses are lost before or at the time of implantation. The objectives of this studywere to investigate the activity of themitochondrial NADH-tetrazoliumreductase, the outgrowth and differentiationof trophoblast cells in in vitro culture of hatched and non hatched blastocyst. Blastocysts were collectedfrom mice cornua utery at day-4 of pregnancy and were divided into 3 groups: blastocysts undergo hatchingwithin 24 hours, 48 hours and non hatching. Embryos were cultured in DMEMmediumin 5%CO2 incubator at37°C for 10 days.The trophoblastsmonolayer were processed forGimsa staining and histochemistry analysisof NADH-tetrazolium reductase activity. The outgrowth of trophoblast cells were measured using eyespiecemicrometer. The results showed that the activity of NADH-tetrazolium reductase of 24 h and 48 h hatchedblastocysts showed higher intensity than the non hatched blastocysts (P<0,05). The trophoblast outgrowthdiameter of 24 h hatched blastocystwas significantly higher than the non hatched blastocyst, but not signifcantlydifferent with the 48 h hatched.Morphology examination using light microscope showed that the trophoblastmonolayer of 24 h hatched blastocyst differentiated into cytotrophoblast, syncytioptrophoblast andspongiotrophoblast after 5 days of in vitro cultured. In conclusion, in in vitro sudy the failure of blastocystsimplantationwas due to the impairment ofNADHdehydrogenase activity in complex Imitochondria and the failureof outgrowth and differentiation of the trofoblast cells.
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