Respiratory effects of trimellitic anhydride aerosols in mice

Groups of mice were exposed to trimellitic anhydride (TMA) aerosols for 30 min at concentrations ranging from approximately 2 to 150 mg/m3. The sensory and pulmonary irritating properties of TMA were assessed during these exposures. Sensory irritation, as evidenced by a lenghthening of the time of expiration (TE), was not evoked in any exposure. However, TMA aerosols evoked other rapid, reversible alterations of respiratory cycle timing, suggestive of pulmonary irritation. The time of inspiration (TI) and expiration (TE) decreased as TMA exposure concentration was increased. Also, characteristic pauses (i.e., apneic periods) occurred between breaths. The length of these pauses (TP) increased as TMA exposure concentration was raised. Respiratory frequency (f) was dependent upon the magnitude of increase in TP. At lower TMA concentrations, TP was short and f was elevated, whereas at higher concentrations, TP was long and f was reduced. Interestingly, there was no other evidence of pulmonary irritation besides the alterations in respiratory cycle timing. Histopathological evaluation of the respiratory tracts of TMA-exposed animals revealed no changes from those of controls. Finally, there was no evidence of cumulative or delayed pulmonary effects in mice repeatedly exposed to TMA aerosols. These acute changes in respiratory cycle timing may have occurred as a result of stimulation of vagal nerve endings along the conducting airways and in the deep lung, directly produced by TMA aerosols.