Protection by carbon tetrachloride against the toxic effects of dimethylnitrosamine in mice

A single intraperitoneal dose of carbon tetrachloride (CCl4), from 0-004 to 0-5 ml/kg, protected male mice against the toxic effects of dimethylnitrosamine (DMN). The LD20 of DMN was increased by a factor of about 4-2 with the highest dose of CCl4 and by a lesser factor with lower doses. The increase in LD50 correlated with a decrease in DMN-demethylase activity in the liver of CCl4 treated mice. These effects commenced within 10 min of administration of CCl4, increased very rapidly for 12 h to a high level which was maintained for up to 60 h, after which the LD50 of DMN and the level of DMN-demethylase returned slowly to normal only in 5 or 6 days. The administration of CCl4 reduced the acute hepatonecrotic action of DMN.