Increased total and free ionized calcium in a canine model of pigment gallstones

It has been postulated that precipitation of calcium from bile is important in the formation and growth of pigment gallstones, since they contain large amounts of calcium. Therefore we studied biliary total calcium [( Ca]) and free ionized calcium [( Ca++]) concentrations in 12 dogs before and after 6 weeks of a methionine-deficient, high-cholesterol diet. In all dogs pigment gallstones and sludge formed while the animals were on the diet. Although gallbladder function--as assessed by biliary pH, total bile salt, and bile electrolyte concentrations--was minimally altered by the diet, both [Ca] and [Ca++] increased significantly, from 10.16 +/- 0.19 to 13.16 +/- 0.57 mmol/L and 3.02 +/- 0.07 to 3.76 +/- 0.17 mmol/L, respectively. The observed increases in calcium concentrations, and specifically in [Ca++], early during stone formation in this model would increase the likelihood that bile would become saturated with at least one calcium salt and support the hypothesis that calcium is important in pigment gallstone formation.