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Vol. 31, Issue 5, 612-619, May 2003
Laboratories of Biochemistry, School of Veterinary Medicine,
University of Pennsylvania, Philadelphia, Pennsylvania
Numerous studies, usually limited to male rodents, have reported an
inverse relationship between the age of the animal and the activities
of various multi-cytochrome P450-dependent drug-metabolizing enzymes. It has been suggested that the aging-induced decline in
hepatic drug-metabolizing capacity is solely a male phenomenon. That
is, whereas the levels of male-specific isoforms of P450 decline with
senescence, the female-dependent isoforms remain unchanged in females
and even increase in male liver. In addition to their baseline
activities, induction levels of hepatic monooxygenases have also been
reported to decrease with aging. To examine aging- and sex-dependent
effects on drug metabolism at a more molecular level, we measured the
expression (mRNA, protein, and/or catalytic activity) of a near dozen
constitutive and inducible isoforms of P450 in 5-and 23-month-old male
and female Sprague-Dawley rats. Moreover, we investigated the induction
effects of low concentrations of phenobarbital known to reveal gender
differences and the threshold sensitivities of both constitutive and
inducible isoforms. With the exception of male-specific CYP2C11 (whose
expression declined ~70% in aged male rats), we observed little
senescence-associated reduction in either preinduction or induction
levels of CYP2B1, CYP2B2, CYP3A1, CYP3A2, CYP2C6, CYP2C7, CYP2C12, and
CYP2C13 in either male or female rats. Moreover, the sexually dimorphic
expression levels apparent at 5 months of age persisted in the old rats.
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