Cytochrome P450 of small intestinal epithelial cells. Immunochemical characterization of the increase in cytochrome P450 caused by phenobarbital.
We have studied total cytochrome P450 and the major form of cytochrome P450 increased by phenobarbital in small intestinal epithelial cells and livers of male Sprague-Dawley rats. Using an improved method for preparing microsomes from intestinal epithelial cells, we find that concentrations of total cytochrome P450 in intestinal cell microsomes are 10% of those in liver microsomes, and that this percentage is unchanged after phenobarbital treatment. In untreated rats, less than 5% of total cytochrome P450 of liver or intestinal epithelium is the form induced by phenobarbital, as measured by rocket immunoelectrophoresis. In phenobarbital-treated rats, the major phenobarbital-induced form accounts for approximately 50% of the total in both organs. In the small intestine of phenobarbital-treated rats, the concentrations of total cytochrome P450 and of the major phenobarbital-induced form increase concurrently as epithelial cells mature from crypt to upper villus. Concentrations of total cytochrome P450 and of the major phenobarbital-induced form in the proximal two-thirds of the rat small intestine are twofold higher than in the distal third. Immunoblotting performed with a monoclonal antibody to the major phenobarbital-induced form of cytochrome P450 from rat liver revealed a subtle difference between this form in liver and intestine.