Contractile mechanisms of gallbladder filling and emptying in dogs

The mechanisms of gallbladder filling and emptying during the fasting state, postprandial state, and after intravenous administration of cholecystokinin, motilin, and morphine were investigated in conscious dogs.

Bile flow in the cystic and common bile ducts was measured by miniature flow probes.

The gallbladder showed brief alternating excursions of filling and emptying in the fasting and fed state. The emptying excursions exceeded the filling excursions during phase II and for about 4 hours after a meal. The filling excursions exceeded the emptying excursions during phase I, phase III, and the latter half of the postprandial state. Most gallbladder emptying occurred when its pressure was high, and most filling occurred when its pressure was low. The duodenal contractions played a major role in gallbladder filling and emptying during phase III.

Gallbladder filling and emptying are not monotonous during the fasting and postprandial states. The brief alternating excursions of filling and emptying would almost continually mix the concentrated gallbladder bile with the fresh dilute hepatic bile to prevent supersaturation of the gallbladder bile during the fasting state and extend the delivery of a small volume of concentrated gallbladder bile for a period of several hours after a meal.