Induction of cytochrome P-450 mRNA in rainbow trout: in vitro translation and immunodetection.
The time course of induction of the rainbow trout microsomal hepatic monooxygenase (MO) system was examined by determination of levels of mRNA and corresponding levels of catalytic activity. Animals were pretreated with beta-naphthoflavone (beta-NF, ip, 100 mg/kg) and terminated at 0, 2, 6, 18, and 48 hr postinjection. Levels of mRNA were determined by immunoprecipitation of in vitro translation products. Levels of mRNA coding for the cytochrome P-450 LM4b isozyme were maximally increased (13-fold) at 18 hr and had decreased almost to pretreatment levels by 48 hr post-treatment. This was in contrast to the catalytic activity in which ethoxyresorufin-O-deethylase (EROD) and ethoxycoumarin-O-deethylase (ECOD) were significantly elevated at both 18 hr (25- and 5-fold, respectively) and 48 hr (46- and 8-fold, respectively). Pretreatment with beta-NF (ip, 100 mg/kg) or 2,4,5,2',4',5'-hexachlorobiphenyl (6-CB, ip, 150 mg/kg) for 18 hr resulted in significant differences in levels of mRNA in only the beta-NF-treated group. The LM2 P-450 isozyme could not be detected by immunoprecipitation with anti-LM2 IgG in trout treated with these same inducers. The results suggest a difference between the time course of induction of the mRNA for cytochrome P-450 LM4b isozyme and the induction of catalytic activity. Under the detection system utilized, the results suggest that the phenobarbital-like inducer, 6-CB, does not induce cytochrome activity nor does it induce the mRNA for cytochrome P-450 LM4b isozyme.
Haasch
M L
ML
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee 53226.
Kleinow
K M
KM
Lech
J J
JJ
D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D007163:Immunosorbent Techniques; D007527:Isoenzymes / Q000235:genetics; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D010634:Phenobarbital / Q000494:pharmacology; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D012016:Reference Values; D012487:Salmonidae / Q000235:genetics*; D013997:Time Factors; D014337:Trout / Q000235:genetics*; D019324:beta-Naphthoflavone
D001571:Benzoflavones; D007527:Isoenzymes; D012333:RNA, Messenger; D008748:Methylcholanthrene; D019324:beta-Naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital