Effect of nitrous oxide on nickel deprivation in rats.

Because nickel may have a biological function in a pathway in which vitamin B12 is important, an experiment was performed to determine the effects of nitrous oxide exposure in rats deprived of nickel. Exposure to nitrous oxide (N2O) causes inactivation of cobalamin and a subsequent decrease in the vitamin B12-dependent enzymes methionine synthase and methylmalonyl CoA mutase. Rats were assigned to dietary groups of 12 in a factorially arranged experiment with dietary variables of nickel (0 or 1 microgram/g) and vitamin B12 (0 or 50 ng/g). After 6 wk, one-half of the rats from each dietary group were exposed to 50% N2O/50% O2 for 90 min/d for the last 28 d of the experiment. Vitamin B12, N2O, or their interaction had numerous effects; classical findings included N2O-induced reduction in plasma vitamin B12 and decreases in the vitamin B12-dependent enzymes. Inactivation of vitamin B12 by N2O, however, did not exacerbate signs of nickel deprivation, possibly because the rats were able to metabolically compensate to N2O exposure.