Specific regions in the rat larynx exhibit cellular changes in response to
inhaled xenobiotics. These regions include the base of the epiglottis, ventral
pouch, and medial surfaces of the vocal processes of the arytenoid
cartilages. 1 , 2 In order to collect information on the usefulness of
trimming techniques, the influence of different vehicles, the impact of
different application routes in toxicity studies, and differences between
induced vs. spontaneous lesions, the data obtained from a large number of
inhalation and non-inhalation studies performed in Wistar RCCHanTM:
Wist rats at Harlan Laboratories Ltd Switzerland, all evaluated or reviewed by
the same pathologist, were compiled for a detailed review. The value of
different trimming techniques was deemed to be greatest for transverse and
sagittolongitudinal section techniques, as compared to horizontolongitudinally
section techniques. The comparison of lesions encountered in control rats of
inhalation studies treated with different vehicles did not reveal differences in
the type, distribution pattern, incidence and/or severity of spontaneous
lesions. The types of lesions were also independent of different application
routes in non-inhalation studies compared to inhalation studies. The pattern of
spontaneous lesions in the rodent larynx was determined by degenerative and
inflammatory lesions starting most often in the submucosal glands by desiccated
secretion followed by mineralization and local inflammation or were induced by
impacted foreign bodies. Squamous metaplasia was recorded in the respiratory
epithelium overlaying the ventral gland as a spontaneous lesion in male Wistar
rats from inhalation studies with a maxim of 20.0% in an inhalation oncogenicity
study. Induced metaplastic changes recorded in the larynx were reversible. Other
induced lesions in inhalation studies consisted of submucosal edema, necrosis,
inflammation and/or granuloma. Induced lesions in non-inhalation studies were
found to be exclusively related to reflux laryngitis or food impaction. It is
concluded, that in rodents induced lesions of the larynx differ in type,
distribution pattern, severity and incidence from spontaneous lesions.