Development of Rat Embryos at the 1- and 2-Cell Stage in Modified HECM-1 Medium after Exposure to a Medium that Contained Phosphate.

The development of rat embryos after exposure to a medium that contained phosphate was examined. After exposure to a medium that contained phosphate, embryos were washed 10 times in watch glasses with 1 ml of modified HECM-1. Then they were rinsed 8 times with 100-μl droplets of the same medium in an attempt to bring the concentration of phosphate after washing below 1.0 fM. After exposure for 0, 10 and 20 min to Ca2+-Mg2+ and substrate-free Dulbecco's Phosphate Buffered Saline (D-PBS (-)), the development rates of 1-cell embryos to the blastocyst stage were 44%, 39% and 52%, respectively, and the mean numbers of blastomeres in the blastocysts were 20.0 17.7 and 19.4, respectively. After exposure for 0, 30 and 60 min to mHECM-1 supplemented with 1.19 mM KH2PO4, the development rates to the blastocyst stage from the 1-cell stage were 47%, 60% and 55%, respectively, and mean numbers of blastomeres in the blastocysts were 16.3, 16.6 and 15.5, respectively. By contrast, 93% to 100% of 2-cell embryos developed to the blastocyst stage. In each six experiments, the development of embryos after breif exposure to phosphate was not significantly different from the group witout exposure. When 2-cell embryos were exposed to phosphate for 15 h and 18 h, the rate of development to blastocysts decreased markedly to 60% and 22%, respectively. Embryonic development was completely inhibited by exposure to phosphate for more than 21 h.