BDL surgery, short for bile duct ligation, is a laboratory procedure performed on mice and rats to deliberately block the flow of bile from the liver. It is not a surgery performed on humans. Researchers use it to create a controlled model of liver disease so they can study how conditions like liver scarring and inflammation develop over time, and test potential treatments.
How the Procedure Works
The common bile duct is the tube that carries bile from the liver and gallbladder down to the small intestine, where bile helps digest fats. In BDL surgery, a researcher makes a small abdominal incision in an anesthetized mouse or rat, locates the common bile duct just above the small intestine, and ties it shut with two tiny silk sutures. The duct is then cut between the two ties, making the blockage permanent. The abdomen is closed, and the animal recovers on a warming pad.
After about five days, researchers can confirm the procedure worked by checking for a visibly swollen gallbladder, since bile has nowhere to go. Blood samples and liver tissue are collected at scheduled time points to track how the liver responds to the obstruction.
Why Researchers Use It
Liver scarring (fibrosis) is a major clinical problem in humans, caused by conditions ranging from chronic hepatitis to alcohol-related liver disease. To develop treatments, scientists need a reliable way to recreate the process in a lab setting. BDL is one of the most widely used models for this purpose, employed in hundreds of laboratories worldwide.
When bile can’t drain normally, it backs up into the liver and triggers a chain reaction: liver cells become damaged, inflammation sets in, and the liver begins producing scar tissue. This mirrors what happens in human diseases where bile flow is obstructed, a condition called cholestasis. The model is popular because the progression is highly predictable, allowing researchers to study specific stages of liver disease at defined time points, from the initial inflammation all the way through to advanced cirrhosis.
What Happens to the Liver After BDL
The trapped bile causes measurable damage almost immediately. Blood levels of bilirubin (the yellow pigment in bile) rise sharply, along with liver enzymes like alkaline phosphatase, both standard markers of bile duct obstruction. These are the same lab values doctors check in humans when they suspect a blocked bile duct.
Over weeks, the liver progresses through recognizable stages of disease. Researchers grade these on a four-stage scale:
- Stage I: Mild changes limited to the areas around the liver’s internal blood vessels (portal tracts)
- Stage II: Those areas expand and begin disrupting surrounding liver tissue
- Stage III: Bands of scar tissue form bridges between portal tracts
- Stage IV: Full cirrhosis
In one study tracking mice for 12 weeks after BDL, normal mice reached an average of stage II disease, while mice lacking a key immune signaling protein progressed further to stage III. This kind of comparison is exactly what the model is designed for: isolating how specific biological pathways contribute to liver scarring.
Beyond the liver itself, the bile obstruction can cause secondary effects similar to those seen in human liver disease, including increased pressure in the vein that carries blood to the liver (portal hypertension), fluid buildup in the abdomen, and an enlarged spleen.
Complete Versus Partial Ligation
The classic version of BDL ties off the entire common bile duct, affecting the whole liver. A newer variation, called partial bile duct ligation (pBDL), blocks only the branch serving the left lobe. This causes cholestasis in just that one section of the liver while leaving the rest functioning normally.
The difference in animal outcomes is significant. In one direct comparison, all 14 mice survived partial ligation, while 5 of 14 had to be euthanized after complete ligation. Animals with complete ligation lost weight continuously and showed increasing signs of distress over time. Those with partial ligation lost weight only in the first few days and then recovered. Their blood chemistry also looked dramatically different: complete ligation caused widespread spikes in liver enzymes, bile acids, and bilirubin, while partial ligation elevated only one enzyme significantly.
The trade-off is scope. Partial ligation produces local inflammation and scarring within the affected lobe, making it useful for studying those processes, but it doesn’t replicate the full systemic effects of cholestasis. Complete ligation remains the standard when researchers need to model the whole-body consequences of severe bile obstruction.
How This Relates to Human Medicine
BDL is not a treatment or diagnostic procedure for people. In human medicine, bile duct obstructions are problems to be solved, not created. They occur when gallstones, tumors, or strictures block bile flow, and the goal is always to restore drainage, typically through endoscopic procedures or surgery.
The value of BDL is entirely in the laboratory. By creating a predictable form of liver injury in animals, it gives researchers a controlled environment to test drugs that might slow or reverse fibrosis, study how individual genes influence liver scarring, and investigate why some livers progress to cirrhosis while others don’t. Many of the insights driving current research into human liver disease trace back to experiments using this model.