Growth and metabolism of preimplantation mouse embryos cultured in phosphate-buffered medium.

Abstract

Summary. The development of two-cell, eight-cell and morula stages of the mouse embryo in phosphate-buffered medium incubated aerobically was limited to that which occurred during the initial 24 hr of culture. Fewer embryos developed in phosphate- than in bicarbonatebuffered medium. More two-cell embryos developed in 4 mm- than in 1 mm-phosphate-buffered medium but there was no difference in the number of eight-cell embryos and morulae developing in either concentration. Addition of oxaloacetate or malate to phosphate-buffered media did not improve development. With incubation periods of 2 to 12 hr, two-cell embryos were more susceptible to phosphate than eight-cell embryos. Culture for 24 hr in phosphate-buffered medium resulted in a reduced incorporation of pyruvate and lactate carbon into the acidsoluble fraction of embryos at all stages of development. In embryos cultured from the two-cell and eight-cell stage, incorporation of substrate carbon into protein and, to a lesser extent, RNA and DNA was also depressed after culture in phosphate-buffered medium. This reduced synthetic activity could result in less ATP utilization and may be responsible in part for the higher levels of ATP found in embryos at these stages after culture in phosphate- as compared to bicarbonate-buffered medium. At the morula stage, macromolecular synthesis was not affected by culture in phosphate-buffered medium and the ATP levels in these embryos were similar to those in embryos developing in bicarbonate-buffered medium. The oxidation of pyruvate by embryos also indicated that the utilization rather than the production of ATP was more affected by culture in phosphate- than in bicarbonate-buffered medium.