Different effects on the expression of CYP7 and CYP27 in rabbit liver by cholic acid and cholestyramine.

It was recently reported that both cholesterol 7 alpha-hydroxylase CYP7 and sterol 27-hydroxylase CYP27 are subject to negative feedback control by bile acids in isolated rat hepatocytes and rat liver (Twisk et al., (1995) Biochem. J. 305, 505-511; Vlahcevic et al. XIII International Bile Acid Meeting, September 30-October 2, 1994, Abstract 17). In the present work a series of experiments was performed to study whether there is a coordinate regulation of CYP7 and CYP27 also in rabbit liver. Treatments of rabbits with cholic acid or cholestyramine resulted in marked suppression and induction, respectively, of CYP7 mRNA. In contrast, there were no significant effects on the CYP27 mRNA expression, amount of CYP27 protein or mitochondrial 27-hydroxylase activity. Thus, there is an apparent difference between rat and rabbit with respect to regulation of CYP27 by bile acids. It is concluded that, in rabbit, there is little or no coordinate regulation of CYP7 and CYP27 at a transcriptional level, and that CYP27 is not subject to a negative feedback control by bile acids neither at a transcriptional nor at a posttranscriptional level.