Inhibition of gallbladder emptying decreases cholesterol saturation in bile in the Richardson ground squirrel

Abstract

Impaired gallbladder emptying is frequent in cholesterol gallstone disease as well as in predisposing conditions like pregnancy and obesity. Gallbladder hypomotility is considered a pathogenic factor for gallstone formation, providing the residence time for cholesterol crystal nucleation, but any effect on the enterohepatic circulation of bile acids and subsequently on biliary lipid composition is unknown. Therefore, we studied the effect of prolonged suppression of gallbladder emptying with a cholecystokinin (CCK-A) receptor antagonist on bile formation in Richardson ground squirrels fed a trace versus a 1% cholesterol diet. Biliary lipid secretion was measured directly and bile acid pool size assessed by isotope dilution ([ 14C]-cholic acid). Gallbladder contraction was determined in vitro in response to CCK. The CCK-antagonist (MK-329) greatly inhibited gallbladder contraction in vitro and increased gallbladder fasting volume and bile acid pool size in vivo. It significantly lowered the cholesterol saturation index by 35% and 46% in hepatic bile and by 18% and 28% in gallbladder bile in the trace and cholesterol diet groups, respectively. Bile acid secretion and bile flow doubled with the CCK-receptor antagonist. Chronic CCK receptor antagonist-induced inhibition of gallbladder emptying increases bile acid secretion and thereby decreases cholesterol saturation in bile. Extensive biliary hypomotility thus leads to a more rapid cycling of bile acids by depriving the gallbladder of its function in the enterohepatic circulation.