Nitrous oxide alters body laterality in rats

Seventy timed-pregnant Sprague-Dawley rats were exposed to either air (control) or 75% nitrous oxide (N2O) for 24 hours on day 8 of gestation. Four rats from each group were killed on days 11-16, 18, and 20, and laparotomy was performed. The viability of the embryos/fetuses was determined, as was the side of tail flexion on days 11 and 12, the direction from which the umbilical artery emerged from the body on days 13 and 14, the side of the body facing the placenta on days 15 and 16, and the side to which the aortic arch curved on days 18 and 20. Mean mortality rate in the control group was 8.9 +/- 6.1% (+/- S.D.), and there were no control embryos/fetuses with altered laterality except the 9% that faced left on day 16. In contrast, N2O treatment on day 8 of gestation resulted in significantly increased mortality (40.8 +/- 3.3%) beginning on day 14 of gestation and increased incidence of altered laterality overall (31.3%) and at all stages of development. The mechanisms underlying these events remain to be defined, as do the implications of our findings for pregnant surgical patients and occupationally exposed workers.