Ileal resection-induced gallstones: altered bilirubin or cholesterol metabolism?

Ileal resection has been shown to increase the risk of cholelithiasis. Earlier studies in humans suggested that ileal resection increases the cholesterol saturation index. Recent data from patients on long-term parenteral nutrition and from animals, however, have suggested that ileal resection predisposes to pigment gallstone formation. We therefore tested the hypothesis that ileal resection alters bile calcium and bilirubin metabolism without affecting the cholesterol saturation index. Adult male prairie dogs underwent either sham laparotomy (eight prairie dogs) or ileal resection (16 prairie dogs). All animals were fed a trace cholesterol (nonlithogenic) diet before and for 4 weeks after operation. Pigment gallstones were present in 44% of the ileal-resected animals and in none of the sham animals (p less than 0.05). Calcium bilirubinate crystals were present in 94% of the ileal-resected animals and in none of the sham animals (p less than 0.01). Gallbladder bile calcium (25.6 +/- 2.4 versus 17.2 +/- 1.1 mg/dl; p less than 0.05) and total bilirubin (29.3 +/- 4.0 versus 9.4 +/- 1.8 mg/dl; p less than 0.01) concentrations were significantly greater in ileal-resected animals. The cholesterol saturation index of gallbladder bile, however, was no different in ileal-resected (0.53 +/- 0.04) and in sham-operated animals (0.50 +/- 0.04). Although initial studies suggested that the cholesterol saturation index of hepatic bile was increased after ileal resection, a second set of experiments demonstrated that this phenomenon resulted from washout of bile salts that were already in extremely low concentrations in hepatic bile. We conclude that alterations in bilirubin, but not cholesterol, metabolism result in pigment gallstone formation after ileal resection.