Abstract
The results of this experimental pathological investigation of the rat larynx and its response to tobacco smoke exposure, are summarised below: Normal rat larynx Five, ultrastructurally distinct, epithelial types were identified, namely, squamous, squamoid, ciliated, and two cuboidal forms. The distribution of these types generally reflected the likelihood of abrasion or irritation. However, in the lower epiglottis (an apparently vulnerable site) areas of ciliated epithelium were found. Significant differences in mitotic indices were detected between laryngeal regions, which usually correlated with epithelial type. An unusually high mitotic index was found in the ciliated epithelium of the lower epiglottis. Effect of tobacco smoke Epithelial hyperplasia and squamous metaplasia occurred after three days of exposure to smoke. The distribution of these lesions throughout the larynx was non-homogeneous, with the ciliated areas of the lower epiglottis, the cuboidal epithelium cranial to the ventral pouch, and the squamous epithelium over the arytenoid projections as predilection sites. In the respiratory epithelium, squamous transformation was preceded by acute inflammation and degeneration. Simultaneously increased mitoses, basal hyperplasia and squamous differentiation occured and were followed by "slit-formation" and desquamation. In contrast, metaplasia of cuboidal epithelium developed by transformation of the original cells. Continued smoke exposure (up to two years) caused keratinisation and undulation of the epithelia, but no neoplasia. Investigations into the mechanism(s) of smoke-induced changes. A single smoke exposure was found to allow transient penetration of the tracer, horseradish peroxidase, into the intercellular spaces of ciliated epithelium in the lower epiglottis. One exposure also altered the ability of ciliated cells to exclude horseradish peroxidase from their cytoplasm. The application of histamine in vitro, also allowed penetration into the intercellular spaces. The amount of histochemically-demonstrable reduced glutathione was decreased after one smoke exposure, in epithelia which subsequently underwent changes.