Inhibition of rat fetal methionine synthase by nitrous oxide. An in vitro study.

The effect of in vitro exposure to nitrous oxide on rat fetal and maternal methionine synthase activity was investigated. Enzyme solutions were prepared from livers of fetuses and mothers on day 19 of gestation and exposed to air, 50% oxygen or 50% nitrous oxide in oxygen for periods up to 24 h. Normal activity of methionine synthase in the fetus was about 65% of that in the mother. Activity decreased by about 25% over 24 h when the enzyme was incubated at 37 degrees C in the presence of either air or 50% oxygen. Nitrous oxide produced a time-dependent decrease in activity which generally was similar for both fetal and maternal enzyme. After 24 h exposure to nitrous oxide, activity has decreased to 14 and 17% of fetal and maternal control values, respectively.