title: The aryl hydrocarbon receptor pathway and the response to 3-methylcholanthrene are altered in the liver of adrenalectomized rats.
abstract: The aryl hydrocarbon receptor (AHR) is activated by 3-methylcholanthrene (MC), a polycyclic aromatic hydrocarbon, and environmental contaminants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin. Adrenalectomized (ADX) rats have decreased hepatic AHR protein and lower levels of MC-induced CYP1B1 mRNA. To further characterize the effects of decreased AHR protein and the response to MC in ADX rats, we measured AHR-mediated responses in the liver of sham-operated (SHAM) and ADX rats, 6 and 54 h after MC treatment. CYP1A2 mRNA was suppressed by 46 to 60% 4 days after ADX in vehicle-treated animals. AHR mRNA was induced 4-fold 6 h after MC in SHAM rats, but no induction was observed in ADX rats. The MC-induced 7-ethoxyresorufin O-deethylation (EROD) activity in ADX rats was 35% of the activity in the MC-treated SHAM group at 6 h. At 54 h after treatment, the induction of EROD activity by MC was more pronounced in ADX rats than at 6 h. To assess the overall capacity for hepatic P450-mediated metabolism, we measured NADPH-cytochrome P450 oxidoreductase (POR) activity. POR activity was decreased by 50% after ADX. We have shown that the response to MC in ADX rats is suppressed for some, but not all, AHR-mediated responses and that reduced POR activity after ADX could contribute to a decreased capacity for P450-dependent metabolism. The current study contributes to our understanding of how adrenal-dependent factors modulate the AHR pathway and the response to MC in vivo.
authors.affiliation: Department of Pharmacology and Toxicology, Medical Sciences Building, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Mullen Grey
authors.forename: David S
authors.initials: DS
authors.lastname: Riddick
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D000315:Adrenalectomy; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D065633:Cytochrome P-450 CYP1B1; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000235:genetics / Q000378:metabolism; D010078:Oxazines / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*
chemical_list: D000199:Actins; D010078:Oxazines; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D008748:Methylcholanthrene; C007649:ethoxyresorufin; D001189:Aryl Hydrocarbon Hydroxylases; C585499:Cyp1b1 protein, rat; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D065633:Cytochrome P-450 CYP1B1; D009251:NADPH-Ferrihemoprotein Reductase