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Oxidative and Conjugative Metabolism of Xenobiotics by Livers of Cattle, Sheep, Swine and Rats¹

New Mexico State University^,2, Las Cruces 88003 and and University of Kansas Medical Center^,3, Kansas City 66103

² Dept. Anim. and Range Sci., to whom correspondence should be addressed. Partial support was provided by Contract DE-AC04-76ET33626, U.S. Dept. of Energy, Albuquerque Office, Albuquerque, NM 87115.

Abstract

Homogenate preparations from fresh livers of cattle, sheep, swine and rats were assayed for microsomal cytochrome P-450 content, for mixed-function oxidase activities and for a wide array of conjugative activities using numerous xenobiotic substrates. Results show that hepatic enzymatic capabilities toward xenobiotics do not parallel phylogenetic classifications, thus strengthening the view that most of the comparative data available at present is more descriptive than predictive of relationships among species. Livestock species differed widely from rats in having lower activities of benzo()pyrene hydroxylase, glutathione S-transferase and acetyltransferase toward isoniazid and sulfamethazine and UDP-glucuronosyltransferase toward bilirubin. Acetyltransferase activities toward β-naphthylamine and 2-aminofluorene were not detected in livers of livestock species studied. Cattle livers were remarkably high in activities of styrene oxide hydrolase, ethoxyresorufin O-deethylase, 2-naphthol sulfotransferase and p-aminobenzoic acid acetyltransferase; but notably low in activity of glutathione-S-transferase toward sulfobromophthalein and l,2-dichloro-4-nitrobenzene. Swine livers had low activity of glutathione-S-transferase toward four of six substrates and low acetyltransferase activity toward four of five substrates. Sheep livers generally were higher than cattle livers in sulfo- and UDP-glucuronsyltransferase activities and lower in acetyl- and glutathionyl-S-transferase. Findings emphasize the risk of error in extrapolations among species and in extrapolations among substrates.

¹ Journal Article 1002 of the New Mexico Agr. Exp. Sta. The authors acknowledge important technical contributions by Cathy House, Betty Saggart, Marilyn Ryan and M. J. Harvey.

³ Dept. Pharmacol., Toxicol. and Therap. Partial support was provided by USPHS grants AM14513 and ES01142. John B. Watkins was supported by USPHS grant ES 07079. His present address is Pharmacol. Section, School of Medicine, Indiana Univ. Bloomington, IN 47405.

⁴ Present address: Drug Metabolism Subdivision, Ciba-Geigy Corp., Ardsley, NY 10502.

⁵ Partial support was provided by Gesellschaft fur Strahlen- and Umweltforschung, mbH Munchen, Neuherberg, Fed. Rep. Germany.