We previously reported (Arch. Toxcol. 1998, 72, 492-498) that the differential decrease in the levels of hepatic cytochrome P450 (CYP) isozymes in rats was observed 24 hr after intracerebroventricular (icv) injection of bacterial lipopolysaccharide (LPS) at the dose ineffective (0.1 µg) when injected intraperitoneally (ip). Among CYP isozymes we examined, the male specific CYP isozyme, CYP2C11 was most severely affected by icv injection of LPS. In this study, we examined the gene expression of

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... YP2C11, the total P450 contents, the CYP2C11-dependent activity of imipramine N-demethylase (IMND) and protein of CYP2C11 10 hr after icv or ip injections of LPS. Intracerebroventricular injection of LPS significantly decreased the level of CYP2C11 mRNA (to 63% of saline icv control), the total P450 contents (to 70% of saline icv control), the IMND activity (to 74% of saline icv control), but not protein of CYP2C11 in rat liver. In contrast, ip injection of LPS at the same dose as icv did not significantly affect these parameters. Since CYP is a heme protein, we also measured the activity of heme oxygenase (HO) using the same rat liver microsomes. The HO activity was increased to 166% by icv injection of LPS and 135% by ip injection of LPS compared to corresponding saline control. It is suggested that icv injection of LPS down-regulates the expression of CYP2C11 at transcriptional level and that both the decrease in CYP2C11 mRNA and the increase in heme degradation may be involved in the decreased level of protein and activity of CYP2C11 by icv injection of LPS in rat liver.-KEY WORDS: CYP2C11, cytochrome P450, intracerebroventricular, lipopolysaccharide, messenger RNA.