title: Xenobiotic metabolizing enzyme activities in rat, mouse, monkey, and human testes.
abstract: The capacity of the testis to metabolize xenobiotics has been proposed to play a role in the susceptibility of different species to testicular toxicity. Since species differences in testicular xenobiotic metabolizing enzyme activities are not well documented, the primary objective of the present study was to compare enzyme activities in subcellular fractions prepared from rat, mouse, monkey, and human testes. In microsomal fractions, enzyme activities measured were pentoxyresorufin O-dealkylase (PROD), ethoxyresorufin O-dealkylase (EROD), and epoxide hydrolase (mEH). In cytosolic preparations, epoxide hydrolase (cEH) and glutathione S-transferase (cGST) activities were measured. PROD activity was not detectable in any of the species studied, while it was readily detected in liver microsomes used as a positive control. Although EROD activity was low, it was measurable in testicular microsomes from rat and mouse, but not monkey or human. No marked species differences in cEH activity were found. In contrast, mEH activity was low in the monkey, intermediate in the rat, and highest in the human and mouse. cGST activity was significantly lower in the two primate species compared with the rat and the mouse. The levels of activity of the xenobiotic metabolizing enzymes studied were generally more than an order of magnitude lower in the testis as compared to the liver. However, in rat and mouse, the levels of mEH and cGST activities in testis were relatively similar to hepatic levels. Overall, these data indicate that species differences in capacity to metabolize xenobiotics may play a role in differential sensitivity to testicular toxicants.
authors.affiliation: Department of Environmental Toxicology, University of California, Davis 95616.
authors.forename: K W
authors.initials: KW
authors.lastname: DiBiasio
authors.forename: M H
authors.initials: MH
authors.lastname: Silva
authors.forename: L R
authors.initials: LR
authors.lastname: Shull
authors.forename: J W
authors.initials: JW
authors.lastname: Overstreet
authors.forename: B D
authors.initials: BD
authors.lastname: Hammock
authors.forename: M G
authors.initials: MG
authors.lastname: Miller
mesh_terms: D000328:Adult; D000818:Animals; D019363:Cytochrome P-450 CYP1A1; D019362:Cytochrome P-450 CYP2B1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D004851:Epoxide Hydrolases / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008253:Macaca mulatta; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008862:Microsomes, Liver / Q000201:enzymology; D010088:Oxidoreductases / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013045:Species Specificity; D013347:Subcellular Fractions / Q000378:metabolism; D013737:Testis / Q000201:enzymology*; D015262:Xenobiotics / Q000378:metabolism*
chemical_list: D015262:Xenobiotics; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019363:Cytochrome P-450 CYP1A1; D019362:Cytochrome P-450 CYP2B1; D005982:Glutathione Transferase; D004851:Epoxide Hydrolases