Measurement of respiratory tract ammonia in the rabbit and implications to sulfuric acid inhalation studies.

Ammonia (NH3) in the respiratory tract has the potential to neutralize inhaled acid vapors and aerosols. Levels of exhaled (nasal) NH3 were measured in rabbits at different times on the same day, on different days, and in rabbits in a normal fed state, or in a fasted or fed state in which the teeth were brushed and the mouth cleansed. The variability of NH3 levels within any individual rabbit was found to be of the same order as the variability found between different animals. In addition, rabbits which were fasted and had their teeth brushed exhaled significantly less NH3 than did fed animals. Levels in the former group ranged from 4 to 236 micrograms/m3, while those in the latter group ranged from 10 to 758 micrograms/m3. Although brushing the teeth of fed animals compressed the observable range of NH3 levels (22-404 micrograms/m3), this was not a significant reduction compared to fed, unbrushed animals. Thus, fasting likely minimized foodstuff in the mouth; the latter may contribute to NH3 formation through bacterial degradation, which appears to be a significant source of NH3 exhaled through the nose. The NH3 concentrations observed may produce variable degrees of neutralization of inhaled H2SO4 droplets before they deposit in the lungs.