Fasting has been associated clinically with the development of gallbladder sludge and pigment gallstones, both of which are composed primarily of calcium bilirubinate. Although fasting has been demonstrated to increase the cholesterol saturation of bile, its effect on biliary calcium and bilirubin has not been investigated. We, therefore, tested the hypothesis that short-term fasting would increase gallbladder bile calcium and bilirubin levels. Fifteen prairie dogs were studied. Seven animals were not fasted, whereas eight were fasted for 16 hr prior to acute experiments. Gallbladder and hepatic bile samples were obtained and analyzed for calcium, bilirubin, pH, and biliary lipids. Gallbladder bile ionized calcium levels were significantly increased in fasted animals (1.7 ± 0.2 mM) compared to those in nonfasted animals (1.1 ± 0.1 mM). Similarly, total calcium (4.3 ± 0.5 mM vs 2.3 ± 0.3 mM), total bilirubin (63 ± 12 μM vs 29 ± 8 μM), and bilirubin monoglucuronide (58 ± 10 μM vs 22 ± 8 μM) were significantly increased in the fasted group. Fasted animals were also noted to have an increased biliary cholesterol saturation index (0.57 ± 0.04 vs 0.36 ± 0.03) and decreased biliary pH (6.9 ± 0.1 vs 7.6 ± 0.1). These data indicate that in the prairie dog short-term fasting results in significant alterations in gallbladder bile composition. The increased concentrations of gallbladder calcium and bilirubin observed in these experiments may account, in part, for the formation of pigment gallstones and gallbladder sludge seen clinically with prolonged fasting.
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