Assay of fractions of bracken fern (Pteris aquilina) for carcinogenic activity.

fractions of bracken fern-fed cattle and of cows bearing spontaneous urinary bladder tumors contained some carcinogenic substance(s) which induced tumors in the bladder of the calf, dog, rat, or mouse and tumors in the skin of mice. It is not known whether this carcinogenic activity is attributable to bracken fern itself or to its metabolites. It has been shown (22) that the carcinogenicity of the crude cycad material and of cycasin in rats depends on an intestinal bacterial flora capable of providing the enzyme @3-glucosidase, necessary for the liberation of the aglycone, methylazoxymethanol. In germ-free rats, cycasin per se, whether present in the intestinal tract or absorbed and excreted, is innocuous. It was desirable to determine whether a similar mechanism operates in the carcinogenicity of crude bracken fern, or whether the fresh bracken fern itself contains the carcinogenic substance before digestion in the animal body. Therefore, it was decided to test fractions of bracken fern for carcinogenic activity on the bladder epithelium of the mouse. The results of these experiments are the subject of this report.