Susceptibility of Rat Preneoplastic Hepatocytes to Liver-tumor Promoters : Effects of Phenobarbital and Ethyl-α-p-chlorophenoxyisobutyrate on Phalloidin Sensitivity

The effects of the liver-tumor promoters phenobarbital (PB) and ethyl-α-p-chlorophenoxyisobutyrate (CPIB) on phalloidin sensitivity of normal and preneoplastic hepatocytes were examined. Hepatocytes were isolated by a collagenase perfusion method from rats fed either 0.05% PB or 0.25% CPIB for 14 weeks, and from those treated for 12 weeks with these agents followed by 2-week withdrawal of the agents. Preneoplastic hepatocytes were isolated from enucleated nodules induced by the Solt-Farber method in the livers of rats, either treated or not treated with PB or CPIB. The phalloidin sensitivity of hepatocytes of the rats treated with PB or CPIB deceased, showing 73 to 90% of the control value in the former and 88 to 97% in the latter, depending on the concentration of phalloidin. After the 2-week withdrawal of the agents, the sensitivity recovered completely. The sensitivity of the preneoplastic hepatocytes of rats treated with PB or CPIB were far less sensitive to phalloidin than the untreated preneoplastic cells. The sensitivity was 28 to 54% in the preneoplastic cells of PB-treated and 54 to 59% in the cells of CPIB-treated rats compared to the values in the untreated preneoplastic cells. After the 2-week withdrawal of PB or CPIB, the sensitivity increased but was not completely recovered. Thus, preneoplastic hepatocytes were more susceptible to PB and CPIB than normal hepatocytes. Histological examinations showed that PB and CPIB promoted preneoplastic lesions in the livers. The enhanced susceptibility is suggested to be responsible for the promotion of hepatocarcinogenesis