Biliary cholesterol and sitosterol secretion. Biliary sterols were analyzed by GC analyses in Abcg8+/+ (n = 4), Abcg8+/- (n = 3) and Abcg8-/- (n = 4) mice following 30-minute bile salt depletion followed by a continuous TUDC infusion as described in Methods. Abcg8-/- mice were unable to secrete cholesterol into bile with forced TUDC administration relative to the wild-type mice (panel a, *P < 0.05). Interestingly, the Abcg8-/- mice were able to still secrete sitosterol (panel b) and campesterol (panel c). Heterozygous mice showed an increased ability to secrete all sterols with forced TUDC administration, although the results were not statistically significant.