Abstract
Early histological changes in the mucosa of the respiratory system were examined in Brown Norway (BN) and Fischer 344 (F344) rats exposed to aerosol inhalation of 1% formaldehyde (HCHO) solution of 3 or 5 days. Treatment-related clinical signs suggestive of respiratory disorders were more obviously observed in F344 rats than in BN rats. In F344 rats, mucosal changes were found in the nasal cavity and trachea. They were initiated by degeneration and/or desquamation of epithelial cells with inflammation and then followed by stratification or squamous metaplasia of epithelial cells. The incidence and extent of these lesions were increased with duration of exposure. On the other hand, similar but less severe changes were observed restricted to the nasal mucosa in BN rats. The degree of epithelial damage was consistent with that of mucosal inflammation, and squamous cell metaplasia occurred only in the portion where severe mucosal lesions preexisted. The present study confirms that BN rats are less sensitive to HCHO inhalation than F344 rats.
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