Changes in Bile Flow and Composition Induced by Radiographic Contrast Materials

The hepatic excretion of radiographic contrast materials has a major impact on the composition and volume of bile. One obvious effect is the presence of the contrast agent in bile at a concentration that is determined by the rate of hepatic excretion, the rate of basal bile flow, and the rate of bile flow induced by the biliary excretion of the contrast agent. The magnitude of the choleretic response associated with the biliary transfer of contrast materials varies over a wide range. Iopanoic acid does not increase bile flow, while RCK-136, an experimental contrast material that is similar to iopanoic acid chemically (both are triiodophenyl alkanoates), is a potent choleretic, generating 44 μl of bile for each μmol excreted into bile. In distinction, the contrast materials in another chemical class, the dimers of triiodobenzoic acid, increase bile flow, but over a narrow range (20–25 μl/μmol). The changes in bile flow and composition accompanying the administration of iodoxamate, one of the compounds of the dimer type, were compared to the choleresis induced by taurocholate. The additional bile flow was canalicular in origin in both instances, but the electrolyte composition of the bile was different. Bicarbonate concentration in the iodoxamate-induced increment of bile was nearly twice the concentration of bicarbonate in bile stimulated by taurocholate (52.3 and 25.3 mEq/l, respectively). This suggests a canalicular mechanism for iodoxamate-stimulated bicarbonate entry into the bile. The characteristics of bile induced by iodoxamate were also compared to bile associated with a variety of other choleretic agents, including diethyl maleate, DBcAMP, SC2644, and secretin. Only SC2644 stimulated canalicular bile flow with a high bicarbonate concentration similar to iodoxamate.