Nickel carbonyl inhibition of phenobarbital induction of hepatic cytochrome P-450.

Administration of phénobarbital (7.5 mg/100 gm) to rats for 2 days increased the mean concentration of hepatic cytochrome P-450 from 2.1 ±0.5 units to 5.1 ±0.8 units, and increased the mean hepatic weight from 4.4 ±0.3 percent of body weight to 5.0 ± 0.4 percent. Phénobarbital induction of cytochrome P-450 and phénobarbitalstimulation of hepatic enlargement were blocked by injection of nickel carbonyl (2 mg Ni/100 gm). For example, in phenobarbital-treated rats which received nickel carbonyl 24 hr before sacrifice, the mean con centration of hepatic cytochrome P-450 was 2.5 ±0.7 units and the mean hepatic weight was 4.4 ±0.4 percent of body weight. Nickel carbonyl did not alter the levels of cytochrome P-450 or the relative hepatic weights in noninduced rats, or in rats which received daily injections of phénobarbitalfor 1 week or longer.