Strain Difference of Susceptibility to 4‐Nitroquinoline 1‐Oxide‐induced Tongue Carcinoma in Rats

Strain difference of susceptibility to 4‐nitroquinoline 1‐oxide (4NQO)‐induced squamous cell carcinomas of the tongue among Dark‐Agouti, Long‐Evans, Sprague‐Dawley, ACI/Ms, Fischer 344, Donryu and Wistar/Furth rats was surveyed by evaluating the survival times, incidences and sizes of developed tumors as markers of susceptibility. Administration of 4NQO dissolved in drinking water induced squamous cell carcinomas in various sites of the upper digestive tract mucosa of all the experimental male and female rats of the seven strains. Regarding the mean survival times, Wistar/Furth rats survived much longer than any other strain of rats, and Dark‐Agouti showed the shortest survival. The incidence of large, mass‐type carcinomas of the tongue of Dark‐Agouti rats was higher than in any other strain of rats, while that of Wistar/Furth rats was the lowest. Subsequently the mitotic activity and bromodeoxyuridine incorporation in the tongue epithelium of Dark‐Agouti and Wistar/Furth rats were estimated after a short‐term administration of 4NQO. There was a pronounced difference between the two strains of rats, because the proliferative responses of the tongue epithelium of Dark‐Agouti rats to the 4NQO stimulation were much higher than those of Wistar/Furth rats. These results indicated that there are marked differences in the susceptibility to 4NQO‐induced tongue carcinoma among the seven strains of rats, and that Dark‐Agouti and Wistar/Furth rats could be useful as models of highly and poorly susceptible strains, respectively, for further genetic analysis.