Heavy metals and enzyme induction.

In experiments on male albino rats it was established that single toxic doses of heavy metal salts inhibited to a different extent the enzyme-inducing action of phenobarbital and methylcholanthrene as determined by ethylmorphine-N-demethylase, respectively aniline hydroxylase activity. The majority of salts (of Cu, Co, Cd, Pb, Ni, Zn and Hg) inhibited more strongly the enzyme induction produced by methylcholanthrene as compared with that caused by phenobarbital. Subtoxic doses of Co, Cd, Zn and Ni salts given daily with the drinking water for 30 days shortened the hexobarbital sleeping time and increased the ethylmorphine-N-demethylase activity and cytochrome P-450 content in the liver microsomes. This suggests an enzyme-inducing action of these heavy metal salts at oral administration in subtoxic doses. Cu, Bi, Sn, Pb did not produce enzyme induction. The changes in the three indices of the As and Hg action were not consistent in our experiments.