Carbohydrate diet-induced calcium bilirubinate sludge and pigment gallstones in the prairie dog

Epidemiologic studies suggest that consumption of diets rich in carbohydrates may, in part, be responsible for the increasing incidence of pigment gallstone disease. The mechanism by which these dietary components lead to pigment stone formation remains obscure. Furthermore, investigative efforts in this area have been hampered by the lack of a suitable animal model. The present study was undertaken to study the role of complex carbohydrates in pigment gallstone formation in the prairie dog. Two groups of eight animals each were maintained on either a control, nonlithogenic chow, or a high carbohydrate (35% sucrose, 32% rich starch) diet for 2 months. Neither crystals nor gallstones were observed in any of the control animals. All of the carbohydrate fed animals (P < 0.005 vs control) had calcium bilirubinate crystals and sludge, while microscopic, black stones were present in six of these eight animals (P < 0.05 vs control). Although hepatic bile bilirubin was unchanged in the carbohydrate-fed group, these animals had a significant increase in hepatic bile calcium (P < 0.005) and phospholipids (P < 0.005) when compared to controls. Carbohydrate-fed animals also had a significant increase in gallbladder bile concentrations of phospholipids (P < 0.001), calcium (P < 0.001), unconjugated (P < 0.005), conjugated (P < 0.005), and total bilirubin (P < 0.001) as compared to controls. These data indicate that in the prairie dog, carbohydrate feeding results in (1) increased biliary concentrations of phospholipids, calcium and bilirubin, and (2) formation of calcium bilirubinate crystals, sludge and microscopic gallstones. Furthermore, these findings suggest that the carbohydrate-fed prairie dog provides a suitable model for studying pigment gallstone disease.