Chloroform in drinking water prevents hepatic cell proliferation induced by chloroform administered by gavage in corn oil to mice

Chloroform administered by gavage in corn oil, but not when administrated in drinking water, has been shown to induce liver cancer in female B6C3F(1) mice and to enhance fell proliferation, Since humans are exposed to chloroform in their linking water, we evaluated whether exposure by this route would interact with the activity of chloroform when administered by gavage in corn oil. Female B6C3F(1) mice were exposed to chloroform in drinking water for 33 days at 0, 300, or 1800 ppm (Experiment 1) or for 31 days at 0, 120, 240, or 480 ppm (Experiment 2) and for 3 days prior to termination also received a daily dose of 263 mg/kg chloroform administered by gavage in corn oil, Exposure to chloroform in drinking water reduced both the hepatotoxicity and the enhanced cell proliferation (bromodeoxyuridine-labeling index and mitotic index) elicited in response to chloroform administered by gavage in corn oil. Hence, chloroform administered in drinking water reduced the activity of chloroform administered by gavage in corn oil, suggesting that it would also reduce the hepatocarcinogenic activity of chloroform administered by gavage. (C) 1997 Society ol Toxicology.