Green tea catechins enhance tumor development in the colon without effectsin the lung or thyroid after pretreatment with 1,2-dimethylhydrazine or 2,2 '-dihydroxy-di-n-propylnitrosamine in male F344 rats

Modifying effects of green tea catechins (GTCs) on the post-initiation stag e of colon, lung and thyroid carcinogenesis were examined in F344 male rats . Groups of 20 animals were given subcutaneous injections of 40 mg/kg body wt of 1,2-dimethylhydrazine twice a week for 2 weeks or oral administration of 0.1% 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN) in the drinking water for 2 weeks for initiation. They then received diet containing 1 or 0.1% g reen tea catechin or basal diet alone for 33 weeks. Histopathological exami nation after final sacrifice showed that although total incidence and multi plicity of colon tumors were not significantly different from controls, val ues for colon adenomas were decreased while those for carcinomas and the av erage size of tumors were significantly increased in the 0.1% GTC group. A similar tendency was observed for the 1% GTC group. Incidences and/or multi plicity of lung hyperplasia and tumors, and thyroid lesions did not signifi cantly vary among the DHPN-treated groups. These results indicate that GTCs do not inhibit, but rather may enhance colon carcinogenesis, while not inf luencing lung and thyroid carcinogenesis under the present experimental con ditions. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.