Several recent clinical and laboratory observations suggest that impaired gallbladder emptying is important in the pathogenesis of cholesterol cholelithiasis. However, the exact mechanism by which gallbladder stasis occurs in the majority of patients who form gallstones has not been clear. We tested the hypothesis that impaired gallbladder emptying antedates cholelithiasis and results from increased resistance to bile flow. Using the prairie dog gallstone model, resistance to flow through the cystic duct (CD) and sphincter of Oddi (SO) was measured in control and cholesterol-fed animals. Prairie dogs were fed either a control (trace cholesterol) or a 0.4% cholesterol-enriched diet known to induce gallstones in 6 weeks. Resistance across the CD and SO was measured at 4 weeks (pregallstone) and 16 weeks (gallstone). Resistance was measured by infusing lactated Ringer's solution through the CD and SO at four separate flow rates while gallbladder and distal common bile duct pressures were recorded. Resistance to flow through the cystic duct increased prior to gallstone formation and continued to increase during the 16 weeks of cholesterol feeding. In comparison, sphincter of Oddi resistance remained normal despite chronic exposure to lithogenic bile and formation of stones within the gallbladder. The increased cystic duct resistance observed prior to gallstone formation provides a mechanism for diminished gallbladder emptying and suggests an etiological role for increased cystic duct resistance in the pathogenesis of cholesterol gallstones.
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