Intralitter variation in murine fetal sister chromatid exchange responses to the transplacental carcinogen ethyl carbamate

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Abstract
Gravid Swiss Webster dams were injected via tail vein with a single (1.1, 2.2, or 3.3 mmol/kg) dose of ethyl carbamate (urethane) on days 13–17 of pregnancy. Relative sister chromatid exchange (SCE) responses in maternal bone marrow vs. individual fetal liver cells were assessed. In addition, in order to evaluate the significance of intralitter variability in fetal SCE responses, SCE in combined (“pooled”) fetal liver tissue preparations were measured and compared with average individual responses. In contrast to maternal responses, average fetal SCE responses to ethyl carbamate varied with gestational age. In addition, significant variation was observed among individual littermate responses at all dose levels. Nonetheless, fetal SCE responses determined from “pooled” tissue preparations provided a valid estimate of average litter responses. Regardless of the method of SCE evaluation in fetal tissue or gestational age, maternal bone marrow exhibited greater sensitivity than fetal liver to SCE induction by ethyl carbamate.