Bile acid structure and biliary secretion of cholesterol and phospholipid in the cat

The effect of bile acid structure on biliary lipid composition was studied on the anesthetized bile fistula cat. The sodium salts of taurocholic acid, taurodeoxycholic acid, and taurochenodeoxycholic acid were infused intravenously in 6 animals in random order in a Latin square design. Bile acids were infused for 2 hr at approximately 270 mumoles per hr; each bile acid period was preceded by a 1-hr infusion of isotonic NaCl. Bile samples from the 2nd hr of bile acid infusion, a period of steady bile acid secretion, were compared, and their bile acid, cholesterol, and phospholipid contents were measured. Mean bile acid secretion rates did not differ among the three bile acids, nor did mean phospholipd secretion rates. In contrast, cholesterol secretion was 3 to 4 times greater with the dihydroxy bile acids than with the trihydroxy bile acid, taurocholic acid. It is concluded that bile acid structure is an important determinant of the lipid composition of bile. Further, this comparison of bile acids has dissociated cholesterol from phospholipid secretion, suggesting that bile acids may influence cholesterol and phospholipid secretion independently.