ToxSci Advance Access published online on May 21, 2007
Toxicological Sciences, doi:10.1093/toxsci/kfm129
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Spatial Distribution of CYP2B1/2 Messenger RNA within the Rat Liver Acinus following Exposure to the Inducers Phenobarbital and Dieldrin
Center for Environmental Health Sciences and Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS, 39762
To whom correspondence should be addressed at Center for Environmental Health Sciences, College of Veterinary Medicine, Wise Center, Mississippi State University, PO Box 6100, Mississippi State, MS 39762-6100. Fax: (662) 325-1031. E-mail: chambers{at}cvm.msstate.edu.
Received May 15, 2007; revision received May 15, 2007; accepted May 16, 2007
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Abstract |
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Traditionally, the liver has been considered a homogeneous organ, but literature suggests that the cytochromes P450 are differentially distributed among the hepatocytes and that the pattern of this distribution is altered by various xenobiotics. In this study, the CYP2B1/2 mRNA in the hepatocytes was compared following treatment of rats with either of two inducers, phenobarbital or dieldrin. Adult male Sprague Dawley-derived rats were treated with either i.p. phenobarbital in saline at 80 mg/kg/day for 5 days or dieldrin in corn oil by oral gavage at 2.5 mg/kg/day for 13 days. Control rats received i.p. saline or p.o. corn oil for the same time. Laser capture microdissection (LCM) followed by duplex QRT-PCR were used to measure the CYP2B1/2 mRNA produced in bands of hepatocytes isolated from 3 locations along the sinusoidal path. The amounts of mRNA present in whole liver subsamples were also analyzed. CYP2B1/2 enzyme activity was determined by assaying 16ß-hydroxytestosterone formation. Whole liver mRNA samples exhibited significant induction in CYP2B1/2 transcript levels: 6-fold for phenobarbital and 2,200-fold for dieldrin. All the LCM band samples also showed significant fold induction in CYP2B1/2 mRNA compared to controls. Dieldrin caused marked increases in CYP2B1/2 mRNA levels in the direction of blood flow through the acinus: periportal, 300-fold; midzonal, 600-fold; and centrilobular, 1,700-fold. A different pattern of induction was observed in the phenobarbital treated rats: periportal, 1,800-fold; midzonal, 8,800-fold; and centrilobular, 1,600-fold. The present study indicates the differences in spatial responses that can be exhibited within the liver following exposure to various xenobiotics. It also indicates the importance of examining xenobiotic metabolism in the liver in light of its non-homogeneous, zoned microenvironment.
Key Words: cytochrome P450 induction; CYP2B1/2; dieldrin; phenobarbital; CYP2B1/2 mRNA; spatial distribution.
Email addresses of additional authors: Dail (dail@cvm.msstate.edu), Burgess (burgess@cvm.msstate.edu), Meek (emeek@cvm.msstate.edu), Wagner (wagner@cvm.msstate.edu) and Baravik (drjeffbaravik@yahoo.com).