Effect of the chronic administration of nitrous oxide 0.5% to gravid rats.

Twenty-four gravid Wistar rats (12 experimental and 12 control) were studied. From day 1 to day 19 of gestation the experimental group was exposed day and night to nitrous oxide 0.5%, while the control group was exposed to air. On day 19 the rats were killed and a detailed examination of the uterus, ovaries and fetuses was undertaken. The fetuses were fixed, cleared and stained with alizarin red, examined for skeletal anomalies and their crown-rump lengths measured. There was a significant decrease in litter size of the dams exposed to nitrous oxide as compared with control (P less than 0.001). Fetal resorption occurred in 10 of the 12 exposed dams. Skeletal anomalies were observed in 9% of the fetuses in the experimental group and there was an overall reduction in their size. None of the above changes were observed in the control.