The role of altered extrahepatic biliary function in the pathogenesis of gallstones after vagotomy

Several clinical studies have documented an increased incidence of gallstones after truncal vagotomy. Previous laboratory studies, however, have failed to establish a clear mechanism for this phenomenon. Whereas lithogenic bile is a prerequisite for cholesterol cholelithiasis, gallbladder stasis has also been shown to be a critical factor in stone formation. We tested the hypothesis that truncal vagotomy alters extrahepatic biliary function by performing either sham laparotomy or truncal vagotomy and pyloroplasty in the prairie dog. After operation, animals were fed a trace-cholesterol (nonlithogenic) diet for 3 months. In acute terminal experiments gallbladder bile was collected for determination of lithogenic index (LI). Resistance to flow through the sphincter of Oddi and cystic duct as well as gallbladder compliance were then determined. Sphincter of Oddi resistance was significantly elevated at 3 months after vagotomy (P<0.03). Cystic duct resistance, however, did not change significantly after vagotomy and pyloroplasty. Gallbladder compliance was significantly reduced in vagotomized animals (P<0.03). Gallbladder bile was unsaturated in both sham (LI = 0.47 ± 0.09) and vagotomized animals (LI = 0.52 ± 0.12), and gallstones did not develop in either group. Increased resistance to flow through the sphincter of Oddi after truncal vagotomy may represent the initial step leading to gall bladder dilatation, bile stasis, and, ultimately, gallstone formation.