An isolated perfused model for the study of colonic metabolism and transport

The murine colonic perfusion model allows for the examination of absorption, metabolism, and portal transfer by the colon under physiologic conditions. This model was characterized by the use of four radiolabeled compounds: estradiol and Vitamin D3, both physiologically active circulating steroid compounds, and benzo[a]pyrene and N-acetylaminofluorene, xenobiotic carcinogens of the aromatic hydrocarbon and aromatic amide classes, respectively. Hemodynamic parameters and oxygen consumption of the preparation were stable throughout perfusion. Estradiol and N-acetylaminofluorene entered the portal vein at a rate of 2% of the lumenal dose per hour. Benzo[a]pyrene crossed at 0.4% of the lumenal dose per hour. The rate of transfer of Vitamin D3 was negligible. Analysis of the lumenal label revealed only substrate. In all experiments less than 0.02% of the applied substrate remained in the tissue compartment. Analysis of the vascular perfusate demonstrated evidence for sulfates of estradiol and N-acetylaminofluorene. Three conjugate classes were found associated with benzo[a]pyrene, constituting 42% of the portal label. Hydrolysis data suggests the presence of double conjugates of benzo[a]pyrene involving glutathione. In the case of aromatic hydrocarbons, conjugation, particularly thioether formation, implies hydroxylation and epoxide formation. For sulfation an N-acetylamino-fluorene ring or N-hydroxylation is required. The latter process could allow for the delivery of highly carcinogenic N-O sulfates to the liver.