Kinetics of benzene metabolism in rats in inhalation exposure.

Rats inhaling benzene concentrations 400, 800, 2,000, or 4,000 mg m-3 for 6 h excreted similar amounts of phenol in urine; hence benzene metabolism was already capacity-limited at 400 mg m-3. The rate of phenol elimination in the course of 12 h inhalation of benzene, 2,000 mg m-3, was increasing; the in vitro rate of hepatic microsomal benzene metabolism was increasing accordingly. Phenobarbital (PB) pretreatment significantly increased phenol excretion in rats exposed to benzene at 800 mg m-3 and higher concentrations. This effect disappeared during 12 h benzene inhalation, although the in vitro hepatic microsomal benzene metabolism in PB rats was significantly higher than in the controls.