The interrelationships of the biliary concentrations of bile salts, phospholipids, and cholesterol in the conscious dog were evaluated during complete interruption of the enterohepatic circulation (EHC), partial replacement of the EHC with intravenous taurocholate, or infusions of secretin. EHC interruption in the dog caused a fall in the concentrations and outputs of all three components; cholesterol concentration decreased relatively less than that of bile salts and phospholipids, but in contrast to man, enough of the latter components remained to keep cholesterol solubilized in micelles. Intravenous infusion of taurocholate increased bile salt, cholesterol, and phospholipid outputs. After cessation of the secretin infusion during EHC interruption, bile salt concentration was decreased while phospholipid and cholesterol concentrations were unchanged; outputs of all three components were lower than controls. However, no change in the outputs of these components occurred when secretin was infused together with taurocholate. Regression equations, relating bile salt output to cholesterol and phospholipid output, indicated that during EHC interruption a portion of biliary cholesterol, but not phospholipids, is secreted independently of bile salts. The lack of formation of lithogenic bile with EHC interruption, together with the normally low biliary concentration of cholesterol, may account for the rarity of gallstone formation in the dog.
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