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Xenobiotic metabolizing enzyme activities in rat, mouse, monkey, and human testes
K W DiBiasio1, M H Silva, L R Shull
1Department of Environmental Toxicology, University of California, Davis 95616.
Summary
Species differences in testicular xenobiotic metabolism, particularly epoxide hydrolase and glutathione S-transferase activities, may explain varying sensitivities to testicular toxicants. Enzyme levels were generally lower in testes than livers.
Area of Science:
- Toxicology
- Comparative Physiology
- Biochemistry
Background:
- Testicular toxicity susceptibility may depend on xenobiotic metabolism.
- Species-specific differences in testicular xenobiotic-metabolizing enzymes are not well-characterized.
Purpose of the Study:
- To compare xenobiotic-metabolizing enzyme activities in rat, mouse, monkey, and human testes.
- Investigate species variations in enzyme profiles relevant to testicular toxicity.
Main Methods:
- Assayed microsomal epoxide hydrolase (mEH) and cytosolic glutathione S-transferase (cGST) activities.
- Measured ethoxyresorufin O-dealkylase (EROD) and epoxide hydrolase (cEH) in subcellular fractions.
- Compared enzyme activities across rat, mouse, monkey, and human testicular tissues.
Main Results:
- Ethoxyresorufin O-dealkylase (EROD) activity was detected in rat and mouse testes, but not in primate testes.
- Microsomal epoxide hydrolase (mEH) activity was highest in human and mouse testes.
- Cytosolic glutathione S-transferase (cGST) activity was significantly lower in primates compared to rodents.
Conclusions:
- Species-specific differences in testicular xenobiotic metabolism exist.
- Variations in mEH and cGST activities may contribute to differential testicular toxicity sensitivity.
- Testicular enzyme activities are generally lower than hepatic levels, but significant for some enzymes in rodents.