Carcinogenicity of Tannin and Tannin-Free Extracts of Bracken Fern (Pteridium aquilinum) in Rats

F344 inbred and Sprague-Dawley noninbred rats were fed a basic diet (groups 1 and 7) or a basic diet supplemented with 0.1% (later. 0.2 and 0.4%) tarinin (group 2) isolated from bracken fern (Pteridium aquilinum) (BF), 33% BF (groups 3 and 6), 2% chloroform fraction of BF (group 4), or 4% tannin-free fraction of BF (group 5). The following incidences of intestinal or bladder tumors were observed: group 1, intestinal and bladder, 0/16; group 2. 0/21; group 7, 0/16; groups 4 and 5, intestinal, 7/15, bladder. 0/15; group 3, intestinal, 19/20, bladder, 12/20; and group 6, intestinal, 22/30. bladder. 15/30. The chloroform- methanol fraction prepared from urine of rats fed BF, chloroform fraction of BF, or tannin-free fraction of BF demonstrated mutagenicity for Salmonella typhimurium TA 100 but not for TA 98. No mutagenicity was detected in other prepared fractions. F344 rats in group 8 received weekly sc injections of tannin solution (0.1 g/kg body wt) for 38 weeks, and 16/20 developed palpable tumors that were malignant fibrous histiocytomas at the injection site. No tumor was present in any rat of control group 9.