Correlation between gallbladder size and release of cholecystokinin after oral magnesium sulfate in man

In order to determine the effect of oral magnesium sulfate on gallbladder contraction and release of cholecystokinin (CCK) in man, magnesium sulfate (25 g in 100 ml distilled water) was given by mouth to five fasting adult male volunteers. Plasma samples were collected for measurement of CCK by a specific radioimmunoassay. Gallbladder volumes were determined from sonograms obtained from a phased-array real-time ultrasound scanner. Basal concentrations of CCK (82.2 +/- 10.1 pg/ml) increased significantly at 20 minutes after oral magnesium sulfate (113.8 +/- 7.1 pg/ml), and reached a maximal value at 50 minutes (150.0 +/- 42.0 pg/ml). The mean basal volume of the gallbladder was 30.8 +/- 5.3 cm(3) and maximum reduction of gallbladder volume (to one third of original) was achieved at 50 minutes after ingestion of magnesium sulfate. Linear regression analysis showed a close correlation (r = -0.9337) between plasma concentrations of CCK and gallbladder size in response to magnesium sulfate. Oral magnesium sulfate also caused a significant increase in serum gastrin (from basal of 51.4 +/- 9.9 pg/ml to 69.8 +/- 15.5 pg/ml at 5 min); there was no significant correlation between gastrin release and gallbladder contraction. This study provides direct evidence that the mechanism of magnesium sulfate-stimulated gallbladder contraction occurs through the release of CCK, and shows a close correlation between CCK release and contraction of the gallbladder.