Objective: To study the effects of simulated microgravity on mammalian fertilization and preimplantation embryonic development in vitro with the use of a horizontal clinostat device. Design: Controlled animal study. Setting: Research laboratory at a university medical school. Animal(s): B6D2F1 (C57BL/6 x DBA/2) and ICR mice between 8 and 10 weeks old. Intervention(s): The first experiment was performed to investigate whether gravity is required for fertilization in vitro under three conditions: clinostat rotation, rotational control, and stationary control. In the second experiment, one-cell embryos were cultured under each condition and their morphology and viability were assessed at 96 hours. Main Outcome Measure(s): The fertilized numbers and embryonic numbers at the morula and blastocyst stages were recorded in each condition. Result(s): In the first experiment, there were no statistically significant differences in the efficiency of achieving normal fertilization in vitro among the conditions. In the second experiment, there was a statistically significant decrease in the number of embryos reaching the morula and blastocyst stages after 96 hours in culture under clinostat rotation. Conclusion(s): These results suggest that the process of fertilization in vitro is not sensitive to the gravitational vector. However, the possibility exists that the frequency of early embryonic lethality is increased by microgravity. (Fertil Steril(R) 2000;74:1142-7. (C) 2000 by American Society for Reproductive Medicine).
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