The effects of formaldehyde gas in a flow-through rat tracheal implant system

A flow-through rat tracheal implant system is described which permits the quantitative and repetitive exposure of respiratory epithelia to test gaseous substances. To investigate the acute toxicity of formaldehyde gas with this new system, open-ended rat tracheal implants were exposed to the gas for 1 h twice a week for up to 8 weeks. The formaldehyde gas was gene-rated from paraformaldehyde, mixed with humidified air and introduced into the lumens of the tracheal implants through microbore tubing. Concentrations of 4.1 +/- 0.9, 8.1 +/- 1.2 or 12.7 +/- 1.5 ppm, were introduced into the trachea by passing an airstream moving at 50, 225 or 475 ml/min, respectively, over the paraformaldehyde heated to 42 degrees C. These formaldehyde concentrations induced mucociliary hypertrophy and increasing amounts of atrophic, transitional and metaplastic epithelia in the tracheal mucosa.