Effects of gomisin A on hepatocarcinogenesis by 3'-methyl-4-dimethylaminoazobenzene in rats.

We examined the effects of gomisin A on tumor promotion in the liver after a short-term feeding of 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB) to rats, compared with the effects of phenobarbital. Male Donryu rats were fed ad libitum a diet containing 0.06% 3'-MeDAB and 0.03% or 0.01% gomisin A or water containing 0.05% phenobarbital. Gomisin A and phenobarbital did not cause any proliferative and neoplastic lesions by themselves in 40 weeks of feeding. Altered foci in the liver increased with a peak at 12 weeks after the rats were fed 3'-MeDAB. Gomisin A decreased the number of hepatic altered foci such as the clear cell and basophilic cell type foci in the early stages. Phenobarbital enhanced neoplastic alterations so that the number and size of the foci were much larger in the phenobarbital-combined group than in the 3'-MeDAB-control group. Thus, phenobarbital acted as a promoter of cells initiated by 3'-MeDAB; on the other hand, gomisin A showed a weak suppressive effect on tumor promotion.