Decrease in the rat bronchial acetylcholinesterase activity after toluene diisocyanate inhalation.

Acetylcholinesterase (AChE) activity was measured in bronchial tissue homogenate and blood from rats subjected to single and repeated 4-h daily inhalation exposure to toluene diisocyanate (TDI) or control atmospheres. A single 4-h exposure to TDI in the concentration range of 0.7-4.3 ppm did not decrease AChE activity in bronchial tissue but a 4-h exposure to 0.6 ppm TDI, or greater, for two consecutive days did reduce this activity (19% to 33% of the controls). Increasing the level of exposure to TDI for two consecutive days from 0.6 to 4.0 ppm and extending the length of exposure to 1.2 ppm TDI from 2 to 4, 9 or 14 days produced no further decrease in bronchial ACHE activity. Throughout these experiments, blood AChE activity remained unchanged. In rats exposed to 0.3 or 1 ppm TDI for 3 weeks, staining of the bronchial smooth muscle for AChE was reduced (36% of the controls) after exposure to 1 ppm TDI. These results support, for the first time, in vivo and localized anti-AChE activity by TDI.