Diurnal Variation in Biliary Lipid Composition

Biliary lipid composition was determined on gallbladder bile and on hepatic bile during the diurnal cycle of feeding and fasting in American Indians with and without gallstones and in Caucasian women without gallstones. Fasting hepatic bile was consistently more lithogenic than gallbladder bile or hepatic bile obtained during feeding. Although lithogenicity was greater in Indians, even Caucasian women regularly produce more highly lithogenic bile during the fasting period, apparently because of an uncoupling of cholesterol and bile acid secretion. Although bile acids were sequestered in the gallbladder during late fasting, cholesterol secretion continued somewhat independently of bile acids, thus enhancing lithogenicity. This effect was more pronounced in Indian women, who have reduced pools of bile acids and increased cholesterol secretion. An increasing lithogenicity of hepatic bile throughout fasting might contribute to cholesterol gallstone formation if mixing in the gallbladder is incomplete so that levels of lithogenic bile become segregated.