Relationship between survival times of rats exposed to lethal level of nitrogen dioxide and arylhydrocarbon hydroxylase activity in lungs

Abstract

A previous paper has shown that survival times of rats exposed to lethal levels of NC₂ were prolonged by administration of enzyme-inducing agents prior to NO₂ exposure, and that the survival time of female rats was longer than that of male rats.

In order to investigate a mechanism on prolongation of survival times by administration of enzyme-inducing agents and on sex-difference, a relationship between survival times and microsomal enzyme activity in lungs of rats administered enzyme-inducing agents was examined. The survival times of rats exposed to 65 ppm NO₂ were prolonged with increase of 3MC doses, and AHH activity in lungs of rats rose with increase of 3MC doses. A significant correlation between the survival time and AHH activity was observed. Induction of AHH activity of female rats administered 3MC was higher than that of male rats. NADPH-dependent cytochrome c reductase activity in lungs of male and female rats did not change with 3MC administration, and a significant relationship between the survival time and NADPH-dependent cytochrome c reductase activity was not observed.

These results suggest that cytochrome p₁-450 system in lung microsomes may have protective action against the toxicity of NO₂.