Rat small intestinal cytochromes P450 probed by warfarin metabolism.

Small intestinal cytochromes P450 (P450s) provide potential first-pass metabolism of ingested xenobiotics. To investigate this system, this study addresses the procedure for elution of enterocytes from male rat small intestine, histological evaluation of the elution procedure, and assessment of the functional microsomal P450s in small intestine of untreated and induced rats, using warfarin metabolism as a probe. Histologically it was demonstrated that villous enterocytes are initially detached in sheets and are subsequently eluted without clear resolution into villous tip, midvillous, and lower villous cells, contrary to previous reports. Crypt cells are eluted after cells from the villus. The following functional P450s were identified, using stereo- and regioselectivity of warfarin metabolism, in small intestinal microsomes: P4502B1 in untreated rats, P4501A1 in beta-naphthoflavone-induced rats, P4502B1 in phenobarbital-induced rats, and P4503A1/2 in pregnenolone-16 alpha-carbonitrile-induced rats. In contrast to hepatic microsomes from untreated or induced rats, P4502C11 and -2C6 were not present or inducible by these inducing agents in rat intestine. Western immunoblots, warfarin assays, and P450 assays all indicated that beta-naphthoflavone induced P4501A1 in small intestinal villous and crypt cells, but in contrast to the liver neither apo-P4501A2 nor functional P4501A2 was induced.