Development of resistance to chloroform toxicity in male BDF1 mice exposed to a stepwise increase in chloroform...

To investigate the development of resistance to chloroform toxicity, a 4-week inhalation study was conducted in which BDF1 male mice were exposed to a low level of chloroform for an initial two-week period, and thereafter the exposure concentration was increased for a second two-week period. The animals were exposed to inhalation of chloroform vapor 6 hr per day, 5 days per week, with clinical observation and measurement of body weight conducted. These results demonstrate that pre-exposure to chloroform at a low dose level induced resistance to a higher dose of chloroform in male mice. This resistance was dependent on the pre-exposure concentration.