Initial site of bile regurgitation following extrahepatic biliary obstruction in living rats

Background and Aim: The precise mechanism of bile regurgitation from the biliary system to the blood stream still remains to be elucidated. The aim of this study was to examine the initial site of bile regurgitation in vivo after common bile duct (CBD) obstruction by digitally enhanced fluorescence microscopy. Methods: The fluorescence excreted into bile canaliculi after the administration of sodium fluorescein was continuously observed in CBD obstruction, using video-enhanced contrast (VEC) microscopy equipped with a silicon intensified target (SIT) camera. The liver histology and the localization of Mg2+-ATPase were examined by light and electron microscopy. Results: By the continuous recording of canalicular fluorescence, the sequential regurgitation of the fluorescence from the canaliculi to the hepatocyte cytoplasm to the sinusoids was distinctively recognized after CBD obstruction. Bile canalicular fluorescence was enhanced, and then the fluorescence of the hepatocyte cytoplasm increased in intensity, followed by regurgitation of the fluorescence to the sinusoids. These in vivo sequences closely correlated with changes in CBD pressure. In zone 1, canalicular fluorescence focally burst into hepatocyte cytoplasm, thus resulting in the formation of fluorescent cells. By light and electron microscopy, the fluorescent cells were found to correspond to the liver cell injury. The reaction products of Mg2+-ATPase were incorporated into vesicles with a decreased canalicular activity, and then were transported to the sinusoidal surface after CBD obstruction. Conclusions: The initial site of bile regurgitation may be transcellular, and partly involves liver cell injury in zone 1 in extrahepatic biliary obstruction, associated with increased pressure of the biliary system.