Recovery of tissue folates after inactivation of cobalamin by nitrous oxide.  The significance of dietary folate. 
The anesthetic gas, nitrous oxide (N2O), oxidizes the cobalt moiety in the vitamin B12 molecule and in this way inactivates methionine synthetase which requires reduced cobalamin.  In rats this is followed by a disappearance of folates from the tissues, this loss being most marked in the liver.  Returning the animals to a normal atmosphere leads to restoration of most of the pre-N2O folate levels within 5 days.  The plasma folate, which rises on exposure to N2O, falls within several hours.  The restoration of tissue folates does not take place if the rats are placed on a low folate diet after withdrawal from an N2O environment.  Thus the fall in tissue folate levels is due to loss from the body either by excretion or increased catabolism and not to redistribution of folate.  Return of normal folate levels requires a dietary source of folate.