test Browse by Author Names Browse by Titles of Works Browse by Subjects of Works Browse by Issue Dates of Works

Advanced Search
& Collections
Issue Date   
Sign on to:   
Receive email
My Account
authorized users
Edit Profile   
About T-Space   

T-Space at The University of Toronto Libraries >
Faculty of Medicine >
Department of Pharmacology and Toxicology >
Department of Pharmacology and Toxicology >

Please use this identifier to cite or link to this item: http://hdl.handle.net/1807/18065

Title: Glucocorticoid and adrenalectomy effects on the rat aryl hydrocarbon receptor pathway depend on the dosing regimen and post-surgical time
Authors: Mullen Grey, Anne K.
Riddick, David S.
Keywords: aryl hydrocarbon receptor
aryl hydrocarbon receptor nuclear translocator
cytochrome P450 1B1
Issue Date: 16-Jul-2009
Publisher: Elsevier
Citation: Chemico-Biological Interactions 182: 148-158 (2009)
Abstract: The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the effects of aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin and 3-methylcholanthrene (MC); the prototypical response is induction of drug-metabolizing enzymes. Factors that regulate AHR levels in vivo are poorly understood and it is also not clear how AHR levels affect aromatic hydrocarbon responsiveness. Our interest in pituitary-dependent regulation of AHR levels was prompted by two findings from our laboratory: (1) hypophysectomized rats have reduced hepatic levels of AHR protein; and (2) glucocorticoids increase AHR expression and aromatic hydrocarbon responsiveness in rodent hepatoma cells. To study whether adrenalectomy and glucocorticoids contribute to hormone-dependent regulation of the hepatic AHR pathway, male adrenalectomized (ADX) or SHAM-ADX rats were treated with dexamethasone (DEX) or vehicle. AHR protein was depleted by 50-60% at four days after ADX, but was not altered by DEX treatment. To assess whether the observed AHR depletion affected aromatic hydrocarbon responsiveness, the induction of hepatic cytochrome P450 1B1 (CYP1B1) mRNA by MC was measured as an AHR-mediated adaptive response. MC-induced hepatic CYP1B1 mRNA was reduced by 50% in ADX rats relative to SHAM-ADX. Exogenous glucocorticoid treatment (DEX – 1.5 mg/kg) induced hepatic AHR nuclear translocator (ARNT) mRNA by up to 9-fold at 3 and 6 h after dosing, with no corresponding change in ARNT protein levels. These data demonstrate that: (1) adrenal-dependent factors contribute to the physiological maintenance of hepatic AHR protein levels; (2) the depletion of hepatic AHR protein in ADX rats coincided with a diminished adaptive response to MC; and (3) exogenous glucocorticoid treatment increases hepatic ARNT mRNA levels regardless of adrenal status. This model is useful for studying the mechanisms of AHR and ARNT regulation and for further characterization of the impact of AHR protein depletion on the response to aromatic hydrocarbons in vivo.
URI: http://hdl.handle.net/1807/18065
ISSN: 1872-7786
Appears in Collections:Department of Pharmacology and Toxicology

Files in This Item:

File Description SizeFormat
MullenGreyCBI09.pdf1.95 MBAdobe PDF

Items in T-Space are protected by copyright, with all rights reserved, unless otherwise indicated.