Modifying effect of vitamin A on benzo[a]pyrene-induced respiratory tract tumours in hamsters.

Groups of 40 hamsters of each sex were fed natural ingredient diets containing 600, 4000 or 100 000 IU vitamin A/kg. After an adaptation period of 170 days on the diets, respiratory tract tumours were induced by intratracheal instillation of benzo[a]pyrene + ferric oxide suspended in saline. Mortality was statistically significantly increased in the high dose group as compared with the mid (control) and low dose group. Microscopy of the respiratory tract did not reveal any significant differences in tumour response between the various dose groups. However, the incidence of preneoplastic respiratory tract lesions was distinctly inversely correlated with the oral vitamin A dose. The serum retinol values were similar in the various dose groups, without any indication of a dose related increase. It was concluded that under the experimental conditions used vitamin A did not influence benzo[a]pyrene-induced respiratory tract cancer in hamsters.