PATHOLOGY OF THE OROPHARYNGEAL CAVITY IN 6 STRAINS OF RATS - PREDISPOSITION OF FISCHER-344 RATS FOR INFLAMMATORY AND DEGENERATIVE CHANGES

The sagittolongitudinal histopathological evaluation of the oropharyng eal cavity in 6 strains of rats revealed a clear predisposition of the Fischer 344 strain for degenerative and inflammatory lesions in this region. A degeneration and calcification predominantly of the laryngea l cartilage is evident in 72%, granulomas of the seromucinous glands i n 38%, and an inflammation with bacterial colonies or plant material i n the basal part of the laryngotracheal junction in 26% of the Fischer 344 rats. The incidences of these types of lesions were negligible in the other rat strains evaluated. The comparison of control Fischer 34 4 rats from 2 carcinogenicity studies (untreated group; gavaged group with water, pH 10; gavaged group with propylene glycol/methocel) showe d an influence of the gavage technique with the solvent on the surviva l rate in the female Fischer 344 rats. The lower survival rate was acc ompanied by the occurrence of food impaction in the oropharyngeal cavi ty. This increased mortality in female Fischer 344 rats was also assoc iated with a degeneration of the laryngeal cartilages, whereas the for mation of granulomas and inflammation seemed to have no direct relatio nship to the mortality. The gavage technique with the applied solvent was an enhancing factor in the female Fischer 344 rats on mortality, o n cartilage degeneration, but not on inflammatory changes. In contrast to the females, male Fischer 344 rats had a higher incidence of granu lomas and inflammation, which, however, did not influence the survival rate. In conclusion, Fischer 344 rats, especially the female sex, exp osed to chronic daily irritation by gavage, are predisposed to have a high mortality rate in chronic toxicologic tests. An explanation lies in the disposition of the Fischer 344 rat to a high incidence of carti lage degeneration, which presumably leads to a dysfunction of the lary nx.