title: Nonadditive effects of combined in vivo hepatic microsomal enzyme inducers in the Wistar rat.
abstract: Compounds that are known to increase the hepatic microsomal cytochrome P-450 dependent monooxygenases were administered to adult female rats, alone or in combination, to determine whether their effects on certain substrate oxidations were additive. 3-Methylcholanthrene (3-MC) and pregnenolone-16 alpha-carbonitrile (PCN), known to induce different forms of cytochrome P-450, when administered together increased benzo[a]pyrene oxidation to the same level as observed following 3-MC treatment alone. Phenobarbital (Pb) and PCN when administered concomitantly increased benzo[a]pyrene, amino-pyrine, and ethylmorphine metabolism to the same extent as seen following PCN administration alone. Both compounds are known to induce different forms of cytochrome P-450. Nonadditive effects were also observed with Pb and spironolactone, as well as with Pb and trans-stilbene oxide. Treatment of adult male rats with either PCN or 3-MC resulted in significantly smaller increases in benzo[a]pyrene oxidation than observed in adult female rats. These results suggest that oxidative metabolism in hepatic microsomes is not the sum of activities of a number of cytochrome P-450s, but may represent the activity of a single predominant hemeprotein. In addition, it appears that the oxidation of substrate by a particular cytochrome P-450, in intact microsomes, is greatly influenced by the presence of another form.
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System; D004347:Drug Interactions; D004790:Enzyme Induction / Q000187:drug effects*; D005260:Female; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology*; D010105:Oxygenases / Q000096:biosynthesis*; D010634:Phenobarbital / Q000494:pharmacology; D011285:Pregnenolone Carbonitrile / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013148:Spironolactone / Q000494:pharmacology; D013267:Stilbenes / Q000494:pharmacology
chemical_list: D013267:Stilbenes; D011285:Pregnenolone Carbonitrile; D013148:Spironolactone; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; C025906:stilbene oxide; D010634:Phenobarbital