Responses to dietary bile acids in wild-type and Cyp8b1–/– mice. Male animals (n = 4–5 per genotype) were fed the indicated amounts of cholate or chenodeoxycholate (cheno) for a period of 4 days. mRNA levels for CYP7A1 and SHP were determined by real-time PCR. The numbers shown are the averages of triplicate determinations for each mRNA sample. Error bars indicate SEM. In wild-type mice fed 0.1% cholate, the composition of gallbladder bile was 15% muricholates, 78% cholate, 5% deoxycholate, and 2% other; in those fed 0.25% cholate it was 5% muricholates, 73% cholate, 15% deoxycholate, and 7% other. In those fed 0.1% chenodeoxycholate it was 58% muricholates, 13% cholate, 17% chenodeoxycholate, and 12% other, and in those fed 0.25% chenodeoxycholate it was 36% muricholates, 2% cholate, 47% chenodeoxycholate, and 15% other. Bile acid composition was similar in Cyp8b1–/– mice fed the same diets.