The influence of bile on the bioavailability of polynuclear aromatic hydrocarbons from the rat intestine.

The mechanisms governing absorption of polynuclear aromatic hydrocarbons (PAHs) are important since these carcinogenic compounds occur as solutes in dietary lipids. These highly lipophilic compounds are well absorbed in the intestine. Bile salt micellar solubilization probably facilitates their transport across the unstirred water layer to the enterocytes. To study the role of bile in the intestinal absorption of PAHs, conscious rats with bile duct and duodenal catheters were given isotopically labelled 2,6-dimethylnaphthalene (DMN), phenanthrene, anthracene, 7,12-dimethylbenzanthracene (DMBA), and benzo[alpha]pyrene (BP); the recovery of radioactivity in bile and urine was measured. The PAHs were given intraduodenally in corn oil with or without exogenous bile. Cumulative recovery of radiolabel in bile and urine over 24 h was used to assess the efficiency of absorption of the hydrocarbons with and without bile. The following values for absorption without bile (as percentage of absorption with bile) were obtained: DMN, 91.6%; phenanthrene, 96.7%; anthracene, 70.8%; DMBA, 43.4%; BP, 22.9%. The values for anthracene, DMBA, and BP were significantly less than 100% (P less than 0.05); the values for DMN and phenanthrene were not significantly different from 100%. The dependence of the tricyclic compound anthracene (a structural isomer of phenanthrene) on bile for its absorption correlates with its lower water solubility. These results are consistent with the concept that the unstirred water layer presents a significant barrier to the absorption of this group of compounds and that micellar solubilization facilitates the uptake process.