Patterns of gallbladder contraction induced by a meal or cerulein were examined by means of real-time ultrasonography in conscious dogs. The postprandial gallbladder emptying was characterized by two parameters of the power-exponential function: the gallbladder half emptying time T1/2 = 47.3 +/- 4.7 min and the curve shape parameter S = 0.866 +/- 0.036. Cerulein infused at stepwise increasing rates of 0.7, 2.2, 7.4, 22.2, and 66.5 pmol/kg/hr, administered each for 10 min, evoked a gallbladder contraction to 87.4 +/- 3.8%, 66.7 +/- 2.4%, 44.5 +/- 1.5%, 25.9 +/- 2.1%, and 11.9 +/- 2.0% of the basal volume, respectively. The dependence of the gallbladder emptying on the dose of cerulein was described by the equation of linear regression y - 21.33 [ln(dose + 1)] + 95.81 (r = -0.963, P < 0.001). Accordingly, the cerulein dose required to evoke a 50% reduction of the gallbladder volume amounted to 7.6 pmol/kg/hr (95% confidence interval: 6.8-8.6 pmol/kg/hr). A plateau at the level of about 44% of the basal gallbladder volume characterized the time-course of the gallbladder emptying between 20 and 60 min of the infusion at a constant rate of 7.4 pmol/kg/hr. On the other hand, the 1-hr infusion of 22.2 pmol/kg/hr evoked a continuous decrease in the gallbladder volume with a nadir of 10.2 +/- 0.7% achieved at 60 min. Refilling of the gallbladder, contracted after a 1-hr infusion of cerulein, was complete within 30 and 60 min after the end of infusion for rates of 7.4 pmol/kg/hr and 22.2 pmol/kg/hr, respectively. The time course of the gallbladder filling after cessation of 1-hr infusion of cerulein at 7.4 pmol/kg/hr was described by the equation of linear regression of relative gallbladder volumes vs time: y = 1.732x + 48.61 (r = 0.739, P < 0.001). Refilling of the gallbladder was faster during the first 30 min (y = 2.191x + 7.13, r = 0.885, P < 0.001) and slower between 30 and 60 min (y = 1.218x + 74.97, r = 0.533, P < 0.001) after the end of a 1-hr infusion of cerulein at a rate of 22.2 pmol/kg/hr.