Investigations on cyclophosphamide treatment during the preimplantation period. I. Differential sensitivity to maternal cyclophosphamide treatment.

To study the effect of cyclophosphamide (CPA) treatment of pregnant mice during the preimplantation period on different embryonic cells even before implantation, the cell numbers of the immunosurgically isolated inner cell mass (ICM) and the blastocyst total cell number (BTCN) were determined in late blastocysts. In animals treated at 2 P.M. on day 2 of pregnancy a dose-related reduction of the cell numbers was found for both ICM and BTCN in morphologically normal late blastocysts (day 4, 8 A.M.) at CAP doses of 20-60 mg/kg which did not induce embryonic death before implantation but did later during organogenesis. At identical CPA doses the reduction of the cell numbers of the ICM was significantly greater than that of the BTCN. These data provide evidence for a differential sensitivity of the two groups of cells in preimplantation mouse embryos (trophectoderm and ICM) to maternal CPA treatment even before implantation.