Periodic gallbladder contraction maintains bile acid circulation during the fasting period: a canine study

Using a canine model we have studied the relationship between the interdigestive cycle in the small intestine, motility changes in the biliary tract and bile acid output into the duodenum from direct hepatic secretion and gallbladder emptying. Under anaesthesia catheters were inserted into the gallbladder, common bile duct and duodenum, and electrodes were attached to the small intestine in five dogs. These animals were subsequently studied conscious and fasting. A double marker technique was used to measure bile acid output from the gallbladder and liver while pressure in the gallbladder and common bile duct and electrical activity in the small intestine were monitored. Four complete interdigestive cycles were recorded in each dog. Output of bile acids from the gallbladder fluctuated with the phases of the cycle: being lowest in phase I (3.9 +/- 0.7 mumol/min); increasing significantly (P less than 0.005) in phase II (9.8 +/- 1.0 mumol/min); remaining elevated in phase III (13.9 +/- 1.7 mumol/min); and falling significantly (P less than 0.05) in phase IV (8.4 +/- 1.8 mumol/min). In contrast, hepatic secretion of bile acids directly into the duodenum remained fairly constant. Intraluminal pressure in the biliary tract paralleled the fluctuation in gallbladder bile acid output, being significantly increased (P less than 0.05) in phases II and III. Periodic contraction of the gallbladder would, therefore, appear to be the principal mechanism for the phasic output of bile during fasting.