Prolonged nitrous oxide exposure inhibits settlement of transplanted hemopoietic stem cells in murine spleen.

In order to clarify the mechanism of hemopoietic depression induced by nitrous oxide inhalation, effects of prolonged nitrous oxide exposure on the settlement of transplanted bone marrow cells were investigated. Mice were continuously exposed to mixed gas containing 50% nitrous oxide, 21% oxygen and 29% nitrogen for 7 days and then they were irradiated with 850 rads. By the irradiation, endogenous pluripotent hemopoietic stem cells (CFU-S) almost disappeared in the mice. Normal syngenic murine bone marrow cells were injected intravenously and the numbers of CFU-S, which settled in the bone marrow and spleen 2 hr after injection, were measured. There was no difference of the numbers of CFU-S settled in the bone marrow between nitrous oxide and control gas exposed mice. In contrast, the numbers of CFU-S in the spleen of nitrous oxide exposed mice were approximately 60% of the control. These results and our previous data suggest that hemopoietic inhibitory effects of nitrous oxide in mice are due to a damage of splenic hemopoietic microenvironment, that supports the settlement of hemopoietic stem cells.