Effect of nitrous oxide on embryonic macromolecular synthesis and purine levels

Nitrous oxide (N2O), an anesthetic gas, has been implicated as a human teratogen. The mechanism for its developmental toxicant effects is not known but may involve depression of embryonic macromolecular synthesis caused by alterations in precursor concentrations. Such changes might be caused by decreased folate levels. Pregnant rats were exposed to 50% N2O for 24 hours on day 10 of gestation; this is not an anesthetic dose. Embryos were removed immediately after exposure and grown in a rodent whole embryo culture system for 4 hours in medium containing radiolabeled precursors for RNA or protein. Exposure to N2O decreased embryonic DNA and RNA contents but did not alter number of somite pairs or protein content. Such treatment also decreased incorporation of radiolabeled uridine into acid-precipitable RNA. There was no difference between control and treated embryos in the incorporation of radiolabeled leucine into protein. There were also no differences between control and exposed embryos in the level of acid-soluble purines. The lower DNA and RNA contents in N2O-treated embryos are apparently not the result of decreased levels of adenine or guanine.