Methyl methacrylate toxicity in rat nasal epithelium: investigation of thetime course of lesion development and recovery from short term vapour inhalation

An investigation of the time course of development and recovery of the nasa l lesion induced in rats by inhalation of methyl methacrylate (MMA) was con ducted. Groups of 45 female F344 rats (five animals per time point) were ex posed whole body for 6 hours per day to 0 (control), 110 or 400 ppm MMA for 1. 2, 5, 10 or 28 consecutive days. Additional animals were retained for a period of 4, 13, 24 or 36 weeks following exposure to assess reversibility of any nasal tissue effects. After inhalation of MMA there was damage to t he olfactory epithelium at 110 and 400 ppm. This was apparent following the first day of exposure, but recovery:regeneration was evident during the su bsequent days of the exposure phase of the study. The most severely affecte d section of the nasal passages was that which included the ethmoturbinates . Focal adhesions between the septum and turbinates and between the turbina tes themselves were seen in some animals exposed to 300 ppm MMA at time poi nts after 5 days of exposure. There were no lesions in the squamous, transi tional or respiratory epithelia acid none in control rats. Lesions that dev eloped in rats exposed to 110 ppm MMA subsequently repaired during the expo sure period. At 400 ppm, the majority of the olfactory epithelium had retur ned to normal within 13 weeks of the end of the exposure phase, but minimal respiratory metaplasia remained evident and there were some focal adhesion s between the septum and turbinates and between the turbinates themselves. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.