Unconjugated bilirubin, and the hydrolysis of conjugated bilirubin, in gallbladder bile of patients with cholelithiasis

Abstract

To assess the role in pigment gallstone formation of hydrolysis of conjungated (CB) to unconjugated (UCB) bilirubin, 52 samples of human gallbladder bile were aspirated at laparotomy. On each bile sample, the concentrations of CB and UCB were determined, using a new thin layer chromatographic method, and the rate of hydrolysis of CB to UCB was measured during incubation at 37 °C, performed under nitrogen and in the dark to prevent oxidation of the bile pigments. Nine control biles without gallstones contained no more than 1.87 mg per dl of UCB (less than 1.2% of total bilirubin), and showed no significant hydrolysis of CB to UCB. Among 24 biles containing cholesterol gallstones, only 3 showed significant hydrolysis of CB, and only 1 of these exhibited increased concentrations of UCB. By contrast, 10 of 19 biles containing pigment precipitates or gallstones revealed increased concentrations of UCB and/or significant hydrolysis of CB to UCB. Biles containing pigment calculi were best distinguished by their supersaturation with the poorly soluble, nonionized form of UCB at the measured bile acid concentration of each sample. Total bilirubin concentrations were not elevated except in 4 of the 5 biles containing pigment precipitates. Among 15 biles cultured both aerobically and anaerobically, only 2 grew any bacteria (Escherichia coli), and there was no relationship between the presence of bacteria and hydrolysis of CB to UCB. It is concluded that some UCB is normally secreted into bile, and that hydrolysis of CB, and excessive concentrations of UCB, especially its nonionized form, are associated with pigment gallstones, although related to factors other than bacterial infection.