High survival rate of hamsters given intratracheal instillations of benzo[a]pyrene and ferric oxide and kept on a high beta-carotene diet

The study described in this paper was primarily conducted to identify the cell types involved in the formation, progression and regression of metaplastic changes in the respiratory tract epithelium of hamsters after intratracheal intubations with benzo[a]pyrene. Furthermore, the role of vitamin A and beta-carotene in these processes was studied. In the course of the study a remarkable effect of dietary beta-carotene on survival of hamsters became a subject of investigation. Hamsters were fed diets with various levels of vitamin A or beta-carotene and were treated intratracheally with a suspension of benzo[a]pyrene with ferric oxide in saline. The tumour response of the respiratory tract was very low (2.8%) and hyper- and metaplasia of respiratory epithelium were virtually absent. However, an interesting observation was an exceptionally low mortality of only 2% after 69 weeks in the group of hamsters fed a high beta-carotene diet (1% w/w), whereas in the other groups mortality after 69 weeks amounted to 25%. Although the exact cause of death of most of the hamsters could not be established, a 40% reduction of lipid peroxidation in the livers was found in the high beta-carotene group. Moreover, in this group the degree and incidence of nephrosis and of focal mineralization of kidneys and heart were lower than in the other groups. These favourable effects of the high beta-carotene diet may have contributed to the unusually high survival rate in hamsters fed this diet. Further studies are planned to verify and study this observation.