Enhancement by bracken of induction of tumours of the upper alimentary tract by N-propyl-N-nitrosourethan.

The effect of bracken on the induction of tumours of the upper alimentary tract by N-propyl-N-nitrosourethan (PNU) was studied in 7-week-old ACI rats. Group I received a solution of 400 pts/10(6) of PNU in their drinking water for 6 weeks; Groups II and III were given PNU as in Group I, and then from 1 week later were fed on diets containing 5 and 30% bracken, respectively, for 33 weeks; Groups IV and V were fed on diets containing 5 and 30% bracken, respectively, for 33 weeks, from 14 weeks after birth. A control group was given basal diet and water only. The experiment was terminated after 40 weeks. The induction of tumours of the upper alimentary tract by PNU was enhanced by bracken diet; i.e. the incidence of pharyngeal tumours in male rats was significantly higher (P less than 0.025) in Group II (10/13) than in Group I (3/13). The incidence and multiplicity of oesophageal tumours in female rats were also higher in Group III than in Group I (P less than 0.025 for incidence; P less than 0.05 for multiplicity). Histologically, the oesophageal tumours in female rats in Groups II and III were not only papillomas but also squamous-cell carcinomas, whereas those in females of Group I were all papillomas. Furthermore, the incidence of tumours of the forestomach in female rats was also higher (P less than 0.05) in Group II (11/13) than in Group I (4/12).