Histochemical localization of aldehyde dehydrogenase in the respiratory tract of the Fischer-344 rat.

Acetaldehyde, a nasal carcinogen and respiratory tract irritant, is metabolized by aldehyde dehydrogenase. The localization of aldehyde dehydrogenase in individual cells of the nasal passages, trachea, and lungs of the Fischer-344 rat was determined histochemically using a cold glycol methacrylate embedding procedure. Aldehyde dehydrogenase activity was detected principally in the nasal respiratory epithelium, especially in the supranuclear cytoplasm of ciliated epithelial cells while olfactory epithelium was almost devoid of enzyme activity. Epithelial cells of the trachea demonstrated little detectable aldehyde dehydrogenase activity, however, the Clara cells of the lower bronchioles showed remarkably high activity. These results corroborate previous biochemical findings and extend them by histochemically identifying particular aldehyde dehydrogenase-positive cell types within the nasal respiratory epithelium. The distribution of nasal lesions induced by acetaldehyde correlated with regional aldehyde dehydrogenase deficiencies suggesting that regional susceptibility to the toxic effects of acetaldehyde may be due, at least in part, to a lack of aldehyde dehydrogenase in the susceptible regions. Furthermore, aldehyde dehydrogenase activity in the Clara cells indicates a possible site for metabolism of aldehydes which penetrate to the lower airways.