Strain differences in age-associated change in testosterone 6β-hydroxylation in Wistar and Dark Agouti rats

Diazepam metabolism in the kidneys of male and female rats of various strains

Previously, we have reported drastic strain differences of diazepam metabolism in the livers of a variety of rat strain. In this study, to characterize strain and sex differences of diazepam metabolism in the kidney, renal microsomal diazepam metabolic activities were determined in the Dark Agouti (DA), Sprague-Dawley (SD), Brown Norway (BN) and Wistar (WS) strains of rat. We found that the major pathway of diazepam metabolism in the kidney was diazepam N-demethylation, which is different from that in the liver, 3-hydroxylation. A Dose-course (12.5-200 muM of diazepam) study revealed that the DA and WS male rats had higher diazepam N-demethylation activity than the SD and BN rats. In contrast to the males, a lower activity of diazepam N-demethylation was observed in female BN rats. By Western blot analysis, constitutive protein expressions of cytochrome P450 (CYP) 2C11, which is responsible for diazepam N-demethylation, were detected in the 4 strain in both the male and female rats, and the BN rats had lower expression levels of CYP2C11 protein. However, we did not observe significant differences in the kinetic parameters of diazepam N-demethylation. Our results suggested that there was a strain difference in CYP-dependent diazepam N-demethylation in the rat kidney, which is different from the finding in liver microsomes.

Strain differences in CYP3A-mediated C-8 hydroxylation (1,3,7-trimethyluric acid formation) of caffeine in Wistar and Dark Agouti rats. Rapid metabolism of caffeine in debrisoquine poor metabolizer model rats

We observed significant strain differences [Dark Agouti (DA) > Wistar] in 1,3,7-trimethyluric acid formation (C-8 hydroxylation) during caffeine metabolism, though not in N-demethylations, in adult male DA and Wistar rats. In contrast, adult female and immature male rats of both DA and Wistar strains did not show significant differences in activity levels of C-8 hydroxylation. Kinetic studies using liver microsomes revealed that adult male DA rats have a larger Vmax for C-8 hydroxylation than do Wistar rats. Troleandomycin (TAO), known as a cytochrome P450 (CYP) 3A inhibitor, and an anti-rat CYP3A2 polyclonal antibody effectively reduced C-8 hydroxylation by rat liver microsomes in a concentration-dependent manner, suggesting that C-8 hydroxylation in rats is mediated largely by an isoform(s) of the CYP3A subfamily. Troleandomycin and the antibody did not inhibit the N-demethylations of caffeine by rat liver microsomes. Treatment of rats with CYP3A inducers caused a marked increase in C-8 hydroxylase activity. These results indicate that the rat CYP3A subfamily is capable of catalyzing C-8 hydroxylation of caffeine as is the case for human CYP3A4. The results of western blotting analysis using anti CYP3A antiserum showed that the staining intensity of the protein band in DA rat liver microsomes was higher than that in Wistar rat liver microsomes. We concluded that marked sex-dependent strain differences in C-8 hydroxylation of caffeine between Wistar and DA rats are due to the differences in the levels of expression of CYP3A in these strains of rats.