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The induction of hepatic cytochromes P450 and metabolic effects have been examined in male and female Sprague-Dawley rats following treatment with either phenobarbital or 3-methylcholanthrene. Hepatic cytochrome P450 levels were higher in males than in females by ~40%. Treatment of male and female rats with phenobarbital or 3-methylcholanthrene resulted in an ~1.6- and 2-fold increase, respectively, in heptic microsomal cytochrome P450 levels in both sexes, relative to untreated animals. Immunoblot analyses were performed to compare sex-related changes in P450 levels. Hepatic P450IIB1 levels in males were greater than those in females following phenobarbital treatment. 3-Methylcholanthrene-induced male hepatic microsomes exhibited greater levels of P450 IA1 and IA2 than female microsomes, whereas uninduced microsomes from males or females failed to exhibit a band. Mab PCN 2-13-1 against P450IIIA recognized an intense band in uninduced hepatic microsomes from males whereas no band was recognized in uninduced microsomes from female rats. The levels of P450IIIA in males were increased 2 to 3-fold following treatment with phenobarbital, while the increase of IIIA levels in females by phenobarbital was minimal, as monitored by immunoblot analysis. Solid phase radioimmunoassay using monoclonal antibodies supported the results of immunoblot analysis. Phenobarbital treatment caused a 6.5-fold increase in the monoclonal antibody binding to IIB1 in males, whereas treatment of females with phenobarbital resulted in a 12-fold increase of IIB1 binding, relative to respective controls. The relative increase of IA levels by 3-methylcholanthrene was also greater in females than in males (10-vs. 8-fold) although the levels of induced IA were comparable in both sexes, as assessed by radioimmunoassay. Radioimmunoassay also showed that hepatic IIE1 level was 1.5-fold higher in males than in females and that either phenobarbital or 3-methylcholanthrene treatment caused 80% to 40% decrease in IIE1 levels, relative to control, in both sexes. Sex-related metabolic activities were examined in hepatic microsomes. Hexobarbital hydroxylase activity was 2- to 3-fold higher in uninduced microsomes from males than that from females. This hydroxylase activity was increased 2- and 3-fold in males and females, respectively, following phenobarbital treatment, as compared to controls. Addition of anti-P450IIB1 antibody to phenobarbital-induced hepatic microsomes from males and females produced 64% and 84% inhibition of hexobarbital oxidation, respectively. Aryl hydrocarbon hydroxylase activity was increased ~12- and 26-fold in males and females, respectively, following 3-methylcholanthrene treatment relative to controls. The anti-P450IA antibody inhabitable rate of aryl hydrocarbon hydroxylase activity was comparable in both sexes following 3-methylcholanthrene treatmet (~70%). These results demonstrate that levels of hepatic P450IIB1 or P4501A are greater in male than in female for untreated, phenobarbital- or 3-methylcholanthrene treated rats. In addition, the relative increase of P450IIB1 or IA by phenobarbital or 3-methylcholanthrene is more significant in females.
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