Nitrous oxide reduces growth of experimental rat leukemia.

The ability of nitrous oxide to inhibit the in vivo growth of hematological neoplasms was investigated in a rat model for acute myeloid leukemia (BNML). Nitrous oxide, administered in a concentration of 67% with 33% oxygen, resulted in a reduction of spleen and liver weights of approx. 30%, as compared with leukemic rats kept in ambient air. Peripheral white cell counts were also considerably lower in the treated rats. Plasma levels of vitamin B12 were found to be elevated in untreated leukemia, but fell to about normal levels after nitrous oxide exposure. On the contrary, folic acid levels were low in untreated leukemic rats, and significantly higher in animals exposed to nitrous oxide. The observed effects of nitrous oxide appeared to be dose-dependent. The deoxyuridine suppression test performed with leukemic cells became abnormal after nitrous oxide inhalation, in accordance with the effect on normal bone marrow. These results indicate that the interference of nitrous oxide with vitamin B12-related metabolism, which leads to impairment of de novo thymidine synthesis, has the potency to reduce leukemic proliferation in vivo.