Dissolution Rates of Model Gallstones in Human and Animal Biles and Importance of Interfacial Resistance

Cholesterol monohydrate dissolution kinetics in human gallbladder bile were studied to determine the magnitudes of the in vitro dissolution rates, the rate resistances in human gallbladder bile, and the extent that the interfacial resistance is the rate-determining factor. Dissolution rate studies also were conducted using human duodenal bile and animal bile for comparison. The dissolution rate resistance, R, ranged from 104sec/cm for chicken bile to 104–106sec/cm for human bile. Interfacial resistance was the rate-determining factor for essentially all results. Where chemical composition data were obtained, the R values for the human bile samples were consistent with predictions made from the simulated bile studies. In two human gallbladder specimens having low bile acid-lecithin molar ratios (i.e., 2.9 and 2.3), very high R values of 1.9×105 and 4.1×106sec/cm were found. These values were in good agreement with the findings in the simulated bile studies and suggest that stone dissolution in patients with low bile acid–lecithin ratios may proceed very slowly, even when the bile is highly undersaturated with respect to cholesterol.