Distribution, progression, and recovery of acute formaldehyde-induced inhibition of nasal mucociliary function in F-344 rats.

A previous report of inhalation exposure of F-344 rats to formaldehyde gas, using a whole-body exposure system, described the induction of regional inhibition of nasal mucociliary function, with a clear concentration-response relationship. A head-only exposure system was subsequently developed in order to facilitate the present study of reversibility of acute effects of formaldehyde on the nasal mucociliary apparatus. This study also included an examination of more extensive areas of the nose than those reported in the previous work. Male F-344 rats were exposed to 2 or 15 ppm formaldehyde gas for 10, 20, 45, or 90 min or 6 hr with recovery groups examined 1 hr after the end of the 90-min and 6-hr exposures. No effects were observed in rats exposed to 2 ppm formaldehyde. In rats exposed to 15 ppm, the extent of formaldehyde-induced inhibition of mucociliary function detected in specific regions of the nose was time dependent, with increasing areas of mucostasis and ciliastasis being induced during a 6-hr exposure period. A 1-hr room-air exposure, following exposure to 15 ppm formaldehyde, resulted in marked recovery of mucociliary function, indicating the value of a head-only exposure system for rapid examination of mucociliary function following exposure. Recovery of mucociliary function occurred especially in the more posterior areas of affected regions of the nose. However, in areas of recovery mucus flow rate was reduced compared to unexposed control rates, indicating incomplete recovery of function in these areas. Regions of formaldehyde-induced inhibition of mucociliary function correlated well with the previously reported distribution of formaldehyde-induced nasal squamous cell carcinomas, with the exception of effects on the medial aspect of the maxilloturbinate. These findings were considered to provide further support for the proposal that both regional exposure and local tissue susceptibility may be responsible for the distribution of formaldehyde-induced nasal squamous cell carcinomas. It was also postulated, on the basis of mucus flow patterns derived from control animals in this study, that flow relationships between nasal mucus and inspired air form a countercurrent system which may optimize clearance of inhaled air contaminants.