TOXICOLoGY AND APPLIED PHARMACOLOGY 94,246-253 (1988) Induction of Cytochrome P-450 mRNA in Rainbow Trout: In Vitro Translation and lmmunodetection MARY L. HAASCH, KEVIN M. KLEINOW,’ AND JOHN J. LECH Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and NIEHS Biomedical Center, Milwaukee, Wisconsin 53226 Received September IO, 1987; accepted February 25,1988 Induction of Cytochrome P-450 mRNA in Rainbow Trout: In Vitro Translation and Immu- nodetection. HAASCH, M. L., KLEINOW, K. M., AND LECH, J. J. (1988). Toxicol. Appl. Pharma- col. 94,246-253. The time course of induction of the rainbow trout microsomal hepatic mono- oxygenase (MO) system was examined by determination of levels of mRNA and corresponding levels of catalytic activity. Animals were pretreated with &naphthollavone (b-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 cyto- chrome 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 activ- ity in which ethoxyresorufin-O-deethylase (EROD) and ethoxycoumarin-Odeethylase (ECOD) were significantly elevated at both 18 hr (25- and 5-fold, respectively) and 48 hr (46- and 8-fold, respectively). Pretreatment with @-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 fi- NF-treated group. The LM2 P-450 isozyme could not be detected by immunoprecipitation with anti-LMz 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 induc- tion of catalytic activity. Under the detection system utilized, the results suggest that the pheno- barbital-like inducer, 6-CB, does not induce cytochrome activity nor does it induce the mRNA for cytochrome P-450 LMdb isozyme. o 1988 Academic press. ~nc. It has been shown that a variety of chemi- cals induce hepatic microsomal cytochrome P-450 in many species. These agents are generally divided into two broad categories, thatis, a PB-type, e.g., phenobarbital, di- chlorodiphenyltrichloroethane (DDT), and noncoplanar polychlorinated (brominated) biphenyls (PCB or PBB isomers) and a 3- MC-type, e.g., 3-methylcholanthrene, ,& naphthoflavone (/3-NF), 2,3,7,8-tetrachloro- dibenzo-p-dioxin (TCDD), polycyclic aro- ’ Present address: Department of Veterinary Physiol- ogy, Pharmacology and Toxicology, Room 2427, School of Veterinary Medicine, Louisiana State University, Ba- ton Rouge, LA 708038420. matic hydrocarbons (PAH), and coplanar PCB or PBB isomers. It is now recognized that this classification is not all inclusive as multiple isozymes of cytochrome P-450 have been demonstrated which are neither pre- cisely “3-MC-type” nor “PB-type” (Nebert, 1979). The evidence available (Elcombe and Lech, 1979; Forlin, 1980; Vodicnik et al., 198 1, 1984; Eisele et al., 1984; Kleinow et al., 1986) strongly suggests that rainbow trout, unlike rats which respond to both types of in- ducers, are refractive to the PB-type of induc- ing agents. Insights into this difference be- tween induction in rats and in rainbow trout may lead to a better understanding of the ge- netic regulation of chemical biotransforma- 0041-008X/88 $3.00 Copyright 0 1988 by Academic Press, Inc. 246 All ri!&ts of reproduction in any form reserved.