Changes in tone of canine gallbladder measured by an electronic pneumatic barostat.

We developed an electronic pneumatic barostat to measure changes in gallbladder muscle tone in vivo independent of biliary flow dynamics. Dogs were prepared with a gallbladder cannula for insertion of barostat balloon and an inflatable balloon-occluder around the cystic duct. The barostat was validated to maintain a constant pressure of 2 +/- 0.4 (SE) mmHg within a plastic balloon of "infinite" compliance that filled the gallbladder lumen; changes in balloon volume reflected changes in wall tone because intraluminal pressure was kept constant. Gallbladder tone, as measured by the barostat balloon volume, varied cyclically with the duodenal migrating motor complex and decreased by 28 +/- 8% (P less than 0.05) at the time of phase III in the stomach and duodenum. Superimposed rapid changes in barostat volume occurred during phase III. The barostat response to motilin mimicked events during spontaneous phase III; in contrast, the response to cholecystokinin octapeptide (CCK-OP) was greater (volume decrease = 53 +/- 12%) and no phasic changes occurred. Two distinct patterns of gallbladder contraction were demonstrated: a basal tone increase with superimposed phasic contractions observed during phase III and after motilin, and a basal tone increase without phasic activity that occurs after CCK-OP.