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 LD₅₀ 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 hr to a high level which was maintained for up to 60 hr 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.