[The germ-free guinea-pig as an animal model of pigment gallstone].

In the gallbladders of germ-free guinea-pigs, biliary sludge appeared in all 4 two-week-old animals and concrete gallstones appeared at the age of four weeks in all of 9 animals. Qualitative analysis of the gallstones revealed positive bilirubin reactions. Infrared spectrum indicated that the gallstones contained calcium bilirubinate, phosphate and protein. These characteristics are similar to those of gallstones induced in guinea-pigs by partial ligation of the common bile duct without infection. There was no stone in the control group. At the age of four weeks, the indirect reactive bilirubin (IB, represent UCB) concentration in gallbladder bile from germ-free guinea-pigs (0.84 +/- 0.16 mg/dl, n = 8) was higher than that of control animals (0.28 +/- 0.12 mg/dl, n = 9, P less than 0.05); as was the ratio of ionized calcium to total calcium (0.28 +/- 0.04, n = 8, vs 0.16 0.03, n = 7, P less than 0.05). Thus, the characteristics of gallbladder bile in germ-free guinea-pigs (which are susceptible to pigment stones) are consistent with those of bile from human beings with pigment gallstones. Since the presence of intestinal flora is essential for the normal metabolism of bile salts and the regulation of their enterohepatic circulation, the germ-free state of the guinea-pigs must have been responsible for the gallstone formation in these animals. Our experiments have shown that germ-free guinea-pigs provide a useful animal model for investigating the role of intestinal flora and bile salts metabolism in pigment gallstone formation. The gallstone incidence in this animal model is high, and the experimental period is short.