Seasonal hepatic cytochrome P-450 induction in cotton rats (Sigmodon hispidus) inhabiting petrochemical waste sites R.L. Lochmiller a, *, S.T. McMurry a , K. McBee a , D.P. Raerty a , J.W. Lish b , C.W. Qualls Jr. b a Environmental Toxicology Program, Department of Zoology, Oklahoma State University, Stillwater, Oklahoma 74078, USA b Department of Anatomy, Pathology, and Pharmacology, Oklahoma State University, Stillwater, Oklahoma 74078, USA Received 13 May 1998; accepted 14 December 1998 Abstract Wildlife species inhabiting contaminated sites are often exposed to complex mixtures of chemicals that have known eects on physiological and biochemical function. We evaluated the induction of major hepatic cytochrome P-450 isoenzymes through O-dealkylation of various resoru®n ethers in wild cotton rats (Sigmodon hispidus) inhabiting three reference areas and three con- taminated areas at an abandoned oil re®nery Superfund waste site in Oklahoma. Isoenzyme activities were monitored in animals from these sites in summer and winter for 2 years. O-dealkylation of ethoxyresoru®n and methoxyresoru®n was signi®cantly greater (170±180%) in cotton rats from contaminated areas compared to those from reference areas in summer, but not winter. These results indicate that the cotton rat may be a sensitive model species for biomonitoring petrochemical-contaminated ecosystems and demonstrate the importance of multi-season sampling in biomonitoring studies. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Petrochemical contaminants; Sigmodon hispidus; Cytochrome P-450; Wildlife toxicology 1. Introduction Several small mammal species have been used in ®eld studies to monitor exposure and eects of environ- mental contaminants on animal health (for reviews see McBee and Bickham, 1990; Talmage and Walton, 1991; McBee and Lochmiller, 1996). Endpoints in these studies typically were limited to measurement of uptake and accumulation of toxicants in selected tissues. More recently, development of biomarkers in laboratory ani- mals, and to a lesser extent free-ranging wildlife, has led to use of biomarkers in assessment of toxicant-induced alterations in biochemical and physiological function, histology and gross morphology of tissue, chromosome morphology, and population and community dynamics (McBee et al., 1987; Flickinger and Nichols, 1990; Rattner et al., 1993). Evaluation of hepatic cytochrome P-450 induction in wild hispid cotton rats (Sigmodon hispidus) has been suggested as a useful endpoint for biological monitoring of various environmental contaminants (Elangbam et al., 1989). Hepatic microsomes contain multiple cyto- chrome P-450 isoenzymes that possess broad substrate selectivity. The dierent isoenzymes function in the activation and detoxi®cation of various xenobiotics (Ryan et al., 1982; Burke et al., 1985). O-dealkylation of resoru®n ethers (induction of the CYP1A subfamily [classic inducers are 3-methylcholanthrene, b-naphtho- ¯avone]) has been shown to be particularly useful in assessing xenobiotic exposure in wild cotton rats (Novak and Qualls, 1989; Elangbam et al., 1991b; Henneman et al., 1994; Qualls et al., 1998). This study was designed to examine the response and sensitivity of hepatic cytochrome P-450 isoenzyme activities of the cotton rat inhabiting an abandoned petrochemical re®nery contaminated with complex mixtures of or- ganic hydrocarbons and heavy metals. We hypothe- sized that feral cotton rats would be sensitive to con- taminant exposure as re¯ected by elevated hepatic microsomal cytochrome P-450 activity and associated O-dealkylation activities for ethoxyresoru®n and methoxyresoru®n. 0269-7491/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(98)00227-9 ENVIRONMENTAL POLLUTION Environmental Pollution 105 (1999) 191±196 * Corresponding author. Tel.: +1-405-744-9672; fax: +1-405-744- 2478; e-mail: rllzool@okway.okstate.edu.