RECOVERY FROM CHANGES IN THE BLOOD AND NASAL CAVITY AND OR LUNGS OF RATS CAUSED BY EXPOSURE TO METHANOL-FUELED ENGINE EXHAUST

One group of male, pathogen-free, Fischer 344 rats was exposed to abou t 17-fold diluted exhaust generated by an M85 methanol-fueled engine ( methanol with 15% gasoline) without catalyst for 8 h, and then the rat es of recovery (rom the resulting increased levels of plasma formaldeh yde and carboxyhemoglobin in their erythrocytes were measured. The car boxyhemoglobin level in the erythrocytes was restored within 4 h, wher eas the plasma formaldehyde level was still elevated after 4 h but was restored to the normal level within 8 h. No methanol or formic acid w as detected in the plasma. Another group of rats was exposed to the sa me dilution of exhaust for 8 h/d for 7 d, and then the recovery from h istopathological damage of the nasal cavity and lungs was also examine d. Hyperplasia/squamous metaplasia and erosion of the respiratory epit helium lining the nasoturbinate, maxilloturbinate, or nasal septum, an d infiltration of neutrophils into the submucosa at level 1 (level of the posterior edge of the upper incisor teeth) were observed immediate ly after the exposure period. Lesions of the respiratory epithelium at level 2 (incisive papilla) were less than those at level 1. Slight le sions at levels 1 or 2 were still noticed 1 wk after exposure, but not 4 wk after exposure. Just after exposure, decreases of Clara cells in the terminal bronchiolus and of cilia in the bronchial/bronchiolar ep ithelium were also observed. Moreover, focal hypertrophy of alveolar w alls and increase of macrophages were observed in parts adjacent to re spiratory bronchiolus. One week after the exposure period, these chang es were no longer seen. These results indicate that changes in the blo od and in the nasal cavity and lungs caused by methanol-fueled engine exhaust are reversible. However, complete recovery from damage of the nasal cavity caused by 7-d exposure to the exhaust takes 4 wk, and rec overy from elevated plasma formaldehyde and erythrocyte carboxyhemoglo bin levels caused by a single 8-h exposure takes 4-8 h.