INITIATION AND POSTINITIATION CHEMOPREVENTIVE EFFECTS OF BETA-CAROTENE IN TOAD LIVER CARCINOGENESIS

Hepatocellular carcinoma were recognized in the toad, Bufo viridis, in 14 cases out of 50 by injection of 1 mg 7,12 dimethylbenz(a) anthrace ne (DMBA)/toad twice/week for 12 weeks. In contrast, toads treated wit h DMB at the same dose level and beta-carotene (beta C), 0.05 mg (3 hr prior to the carcinogen)/toad, twice/week for 12 weeks showed no tumo r incidence. However, beta C at the same dose level was less effective when administered 3 hr, after the carcinogen (DMBA). In 8 cases out o f 50 cases neither tumor growth nor neoplastic changes were observed i n toads treated with beta C alone or olive oil. It is concluded that b eta C completely blocked hepatocarcinogenesis in toads when given 3 hr . before initiation.