The effect of 5-bromodeoxyuridine on cell division and differentiation of preimplantation mouse embryos.

Mouse embryos exposed to concentrations of 5-bromodeoxyuridine (BUdR) ranging from 0-01 to 1-0 mug/ml in vitro for two days from the 8-cell stage exhibit a concentration-dependent decrease in the frequency of normal blastocysts and decrease in average cell number per embryo. A 20-h exposure was adequate to achieve the full BUdR response. Both effects were eliminated in the presence of excess thymidine. Autoradiographs demonstrated that BUdR[3H] was incorporated into DNA during the first and second day of culture. Thus, BUdR appears to act through incorporation into DNA; and, in this system, cell division is at least as sensitive to BUdR as is differentiation.