Evaluation of hepatobiliary function in the rat by the segmented retrograde intrabiliary injection technique

The mode of transfer of solutes across the biliary tree epithelium in the reabsorptive direction was studied by the segmented retrograde intrabiliary injection (SRII) technique. The principle of the SRII is to deliver an initial "segment" of solution containing a radioactive marker compound into the biliary system through the bile duct cannula and to wash this marker in with 0.9% saline solution in excess of the biliary capacity. Immediately following the SRII, bile flow is restarted and bile is collected to determine the quantity of the marker recovered. The marker compound which was recovered in bile represented that fraction of the solute which was trapped by the biliary epithelium (canaliculus), thus leading to recovery of the compound in bile with the peak concentration located at a position corresponding to the distended biliary tree capacity. With the compounds used, little re-excretion of the systemically absorbed fraction occurred. The filtration process was found to be dependent on the molecular weight of the marker compound, with larger compounds being recovered in bile (retained in the biliary tree) to a greater extent than smaller ones. The equivalent pore radius for this process appeared to be the same as that reported by others for biliary excretion in the orthograde direction. Additional factors such as the volume of the saline wash and the SRII rate were also shown to influence the retention of the marker compound in the biliary system. Another mode of transfer of solutes also took place in the SRII, because even for large molecular weight compounds over 50 per cent was lost from the biliary tree. There was no evidence of any process for excluding this fraction by the biliary tree epithelium. A further study of glucose transport in the biliary tree was suggested.