Temperature dependence of combined exposure of preimplantation mouse embryos to X-rays and mercury.

Usually preimplantation mouse embryos are cultured in vitro at 37 degrees C. In this study, mouse embryos (starting with the 2-cell stage) were incubated in vitro throughout the preimplantation period at 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38 degrees or 39 degrees C. Embryonic development, in particular hatching of blastocysts (144 h after conception), and cell numbers (at the same time) were analysed. Embryos were exposed to X-rays (1 Gy) or to mercuric chloride (3 microM, 10 microM) or to a combination of the two agents. Control embryos developed rather well in a temperature range of 35 degrees to 38 degrees C. A combined risk greater than expected from the sum of the individual effects was observed only at the optimum temperature (for a combination of 1 Gy + 3 microM) or in the range of the optimum temperature, that is between 36 degrees to 38 degrees C (for a combination of 1 Gy + 10 microM).