Development of rat one-cell embryos in a chemically defined medium: effects of glucose, phosphate and osmolarity

Rat one-cell embryos recovered from naturally mated females were cultured in modified hamster embryo culture medium 1 without amino acids. In the presence of 0.4 mmol phosphate l-1 (NaH2PO4), no embryos developed beyond the two-cell stage, regardless of the presence of 5.0 mmol glucose l-1. This inhibition was dose dependent at very low concentrations of phosphate in the medium supplemented with 7.5 mmol glucose l-1 and osmolarity adjusted to 244 mosmol; development to the blastocyst stage was not inhibited at 0.001-0.01 mumol phosphate l-1, but development to the morula and four-cell stages was markedly inhibited at 0.1 and 1.0 mumol phosphate l-1. In the medium without phosphate, glucose did not inhibit or promote development to the morula stage, but adequate concentrations of glucose were necessary for the development of morulae to the blastocyst stage; the percentage of one-cell embryos that developed to the blastocyst stage at 7.5 mmol glucose l-1 (67%) and 10.0 mmol glucose l-1 (60%) were not statistically different from the percentage at 5.0 mmol glucose l-1 (46%), but was significantly greater than the percentage at 2.5 mmol l-1 (33%). When osmolarity of the medium with 5.0 mmol glucose l-1 was varied by adjusting the amount of NaCl added, more (82-98%) of the one-cell embryos developed to the four-cell stage at 212-276 mosmol, but development was greatly inhibited at 304 mosmol. Development to the blastocyst stage was largely dependent on osmolarities; at 244 mosmol, 61% of embryos developed to the blastocyst stage, although this percentage was not significantly different from the percentage (43%) at 264 mosmol.