Infusion of Pure Cholecystokinin in Humans: Correlation Between Plasma Concentrations of Cholecystokinin and Gallbladder Size

This study was undertaken to correlate changes in the plasma concentration of cholecystokinin with changes in gallbladder volume, during and after infusion of cholecystokinin in humans. Cholecystokinin-33, 99% pure, was administered intravenously for 1 h at the rate of 0.58 μg/kg · h to 5 fasting adult men. Plasma for radioimmunoassay of cholecystokinin was collected before and during the cholecystokinin infusion, and for 40 additional minutes. Gallbladder volumes were determined from sonograms obtained from a phased-array real-time ultrasound scanner. The mean basal concentration of cholecystokinin in plasma was 88.5 ± 3.9 pg/ml. Mean peak cholecystokinin concentration of 366.2 ± 32.0 pg/ml was achieved 8 min after the start of the infusion. The mean resting gallbladder volume was 23.0 ± 2.9 cm 3 . Maximal gallbladder contraction was achieved at 10 min, at which time the mean gallbladder volume was 3.4 ± 0.5 cm 3 . After the cessation of cholecystokinin infusion, plasma cholecystokinin returned to basal concentrations after 12 min and the gallbladder refilled within 40 min. The correlation coefficients between plasma cholecystokinin and gallbladder size, determined by linear regression analysis, were −0.7649 (p < 0.001) for the contraction phase, −0.5249 (p < 0.01) for the first 12 min of the relaxation phase, and −0.6056 (p < 0.05) for the latter part of the relaxation phase. The clearance rate and the space of distribution of cholecystokinin were 34.8 ml/kg · min and 0.166 L/kg, respectively. Disappearance half-time for plasma cholecystokinin was 3.3 min, and 50% maximum refilling time of the gallbladder was 18.4 min. The study demonstrates close correlation between plasma concentrations of cholecystokinin and gallbladder size. Further, it provides validation for the cholecystokinin radioimmunoassay and suggests that gallbladder contraction, measured by ultrasound, may serve as bioassay for cholecystokinin.