Conversion of endogenous cobalamins into microbiologically-inactive cobalamin analogues in rats by exposure to nitrous oxide.

Rats were exposed to a mixture of oxygen and nitrous oxide (1/1) for up to 18 d. There was a marked fall in both the serum and liver cobalamin levels. There was a significant rise in the concentration of microbiologically-inactive cobalamins in serum 24 h after exposure to N2O. The proportion of microbiologically-inactive cobalamin in liver increased throughout the period of exposure. We were unable to show a similar effect in sera from patients inhaling N2O for 24 h, nor by exposing rat plasma to N2O for 24 h. It was concluded that microbiologically-inactive cobalamins are produced in vivo from endogenous cobalamins and that one form appears to be a product of cobalamin oxidation.