Respiratory responses in the lower respiratory tract of Sprague-Dawley rats to formaldehyde inhalation.

This study was conducted to determine the characteristic response of Sprague-Dawley rats to formaldehyde (HCHO) challenges to the lower respiratory tract, and whether these response patterns are altered in rats that have received repeated exposures to HCHO. Male Sprague-Dawley rats were exposed to 0, 0.5, or 15 ppm HCHO for 6 hours/day, 5 days/week, for 8 or 16 weeks. Both naive rats and rats repeatedly exposed to HCHO were then administered 30 ppm HCHO test challenges by tracheal exposure, with the minute volume, respiratory rate, and tidal volume responses monitored. The pulmonary response of naive rats to HCHO tracheal challenge involved the correlation of minute volume and tidal volume depression, while respiratory rate was either unaffected or slightly increased. This was also the response pattern for rats that received 8 weeks of repeated exposure to HCHO. The only significant difference in respiratory response patterns between naive and pre-exposed animals existed in a slight increase in the respiratory rate compensatory response in the rats pre-exposed for 16 weeks to 15 ppm. There was substantial recovery of initially depressed respiratory parameters during the tracheal challenge in both naive and pre-exposed rats. The characteristic pulmonary response to HCHO in the lower respiratory tract demonstrated for Sprague-Dawley rats was thus similar to patterns of lower respiratory response to HCHO reported for other rodent species.