Post-initiation inhibitory effects of green tea catechins on 7,12-dimethylbenz[a]anthracene-induced mammary gland carcinogenesis in female Sprague-Dawley rats

The dose-dependence of green tea catechin (GTC) effects on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary gland carcinogenesis were investigated in female Sprague-Dawley rats. Groups of 20 6-week-old rats were treated with dietary 1, 0.1 or 0.01% GTC for 2 weeks and then basal diet alone for 35 weeks. At the end of week 1, they received a 25 mg/kg body weight intragastric dose of DMBA. Further groups of 20 7-week-old rats each were given an intragastric dose of 25 mg/kg body weight DMBA, and starting 1 week after DMBA treatment they were placed on diet containing 1, 0.1 or 0.01% GTC or basal diet alone for 35 weeks. Control rats were given 1% GTC or basal diet alone. The final incidences and multiplicities of mammary tumors were not significantly different between the groups treated with GTC at the same time as DMBA, compared to the DMBA alone control group. On the other hand, the final multiplicities of mammary tumors in groups treated with 1% GTC (P < 0.05) or 0.01% GTC (P < 0.01), but not 0.1% GTC, after DMBA treatment were significantly decreased as compared to the control value. These results indicate that whereas GTC may inhibit mammary carcinogenesis in the post-initiation stage, the effect is weak and not dose-dependent. (C) 1997 Elsevier Science Ireland Ltd.