Reaction of hemoglobin with nitric oxide and nitrogen dioxide in mice

The reaction of hemoglobin with NO and NO2 was compared in mice exposed to these cases. Nitrosyl hemoglobin (NOHb) and methemoglobin (MetHb) were determined simultaneously by electron spin resonance spectrometry at -140 degrees C. In mice exposed to 40 ppm NO, NOHb became constant (0.7%) in 30 min and declined rapidly with a half-life of several minutes when the mice were removed to room air. An increase of MetHb (5%) was also caused by exposure to NO and the time course was almost the same as that of NOHb. Exposure to 40 ppm NO2 produced only NOHb (0.2%); MetHb did not increase. The time course of NOHb was identical to that observed with NO exposure. Dose-effect relationships were determined with both gases at concentrations ranging from 20 to 80 ppm. A linear relationship could be observed between the concentrations of the gases and NOHb, but NO produced more NOHb than did NO2. There was an exponential increase of MetHb, particularly at high concentrations of NO.