Canine common duct and gallbladder bile contain antinucleating factors that inhibit CaCO3 precipitation

We performed studies involving large incremental additions of calcium to bile to examine the degree of CaCO3 supersaturation that can be achieved in bile, as compared with that in simple NaCl-NaHCO3 solutions. The addition of CaCl2 to bile increased total and free ionized calcium by from four to 12 times their original values and by from two to three times the highest concentrations encountered in bile in vivo. The increase in [Ca++] resulted in fourfold to 12-fold increases in the saturation indexes of bile, with the saturation index reaching as high as 73.4 in a common duct sample. Despite the markedly elevated CaCO3 saturation indexes, evidence of CaCO3 precipitation was not observed in either common duct or gallbladder bile over a 24-hour period. For comparison, calcium added to NaCl-NaHCO3 solutions resulted in the precipitation of CaCO3 within 4 hours if saturation indexes were greater than 12. These results indicate that native bile contains potent antinucleating factors that markedly inhibit CaCO3 precipitation, and they confirm our previous in vivo observations in canine common duct bile.