Effect of phenobarbital, dichlorodiphenyltrichloroethane, and polychlorinated biphenyls on diethylnitrosamine-induced hepatocarcinogenesis.

Studies were made in rats on the tumor-enhancing effect of phenobarbital, dichlorodiphenyltrichloroethane (DDT), and polychlorinated biphenyls (PCB), singly and in combination, after exposure to diethylnitrosamine (DEN). In sequential exposure to one of these three chemicals after DEN, liver tumor production was markedly enhanced by PCB, and moderately by phenobarbital sodium, but minimal by DDT. In combined administration of two to three of them, PCB took a dominant role in tumor enhancement, but their overall tumor enhancement did not exceed that of PCB alone.