Combined effect of cadmium and nickel on rat hepatic monooxygenases: possible stimulation of certain cytochrome P-450 isozymes

When male rats were given either a single dose of cadmium (3.58 mg CdCl2.6H2O/kg, i.p.) 72 h prior to sacrifice or a single dose of nickel (59.5 mg NiCl2.6H2O/kg, s.c.) 16 h prior to sacrifice, the activities of ethylmorphine N-demethylase, aminopyrine N-demethylase and aniline 4-hydroxylase, and the levels of cytochrome P-450 and microsomal heme were significantly decreased. Cadmium decreased the cytochrome b5 level significantly, whereas it did not alter the NADPH-cytochrome c reductase activity significantly. In contrast, Ni did not alter the cytochrome b5 level significantly but decreased the NADPH-cytochrome c reductase activity significantly. For the combined treatment, animals received the single dose of nickel 56 h after the single dose of cadmium and then they were killed 16 h later. In these animals ethylmorphine N-demethylase, aminopyrine N-demethylase and NADPH-cytochrome c reductase activities and cytochromes P-450 and b5 levels increased significantly as compared to those of controls, whereas aniline 4-hydroxylase activity and microsomal heme level remained unaltered. In concordance with the increase in the enzyme activities, certain P-450 protein bands were observed to be elevated when studied on SDS-polyacrylamide gel electrophoresis. Furthermore, when the monooxygenase activities and SDS-polyacrylamide gel electrophoresis profiles of combined metal-treated animals were compared with those of the animals treated with classic inducers such as phenobarbital (75 mg/kg i.p., 72, 48 and 24 h prior to sacrifice) and 3-methylcholanthrene (20 mg/kg i.p., 72, 48 and 24 h prior to sacrifice), the combination of metals seemed to have tendency to stimulate certain phenobarbital and 3-methylcholanthrene inducible cytochrome P-450 isozymes.