(a) The fractional absorption of dietary cholesterol in the ABCG5/ABCG8 transgenic mice. A total of six male and six female 9- to 10-week-old transgenic mice and their littermate controls were gavaged with [¹⁴C] cholesterol and [³H] sitostanol. Stool was collected for 3 days, and the ratio of the two isotopes in feces was measured to determine the fractional absorption of cholesterol, as described in Methods. (b) The bile acid pool size in the ABCG5/ABCG8 transgenic and wild-type mice. The content of total bile acids from the small intestine, gallbladder, and liver of chow-fed mice (12–13 weeks old) of the indicated genotype (n = 6 in each group) was determined by extracting the bile acids in ethanol. The bile acids were analyzed using HPLC as described in Methods. (c) The ratios of cholic to muricholic acids in the total bile acid pool. *P < 0.01.