Biliary lipid metabolism in the pregnant baboon

The serum cholesterol value, bile acid pool size and kinetics as well as lipid composition of gallbladder bile have been studied in seven baboons during nine pregnancies. During pregnancy, the per cent decrease in the average serum cholesterol value ranged from 25.6 to 74.4 per cent, mean 54.5 +/- 14.3 per cent, compared with that of antepartum averages. In seven of the nine pregnancies, chenodeoxycholic acid pool size decreased in the range of 40.1 to 86.6 per cent. In two pregnancies, the pool size of this bile acid was essentially unchanged. Total bile acid pool size also decreased from a mean of 990 +/- 260 milligrams antepartum to 520 +/- 200 milligrams in the third trimester, p less than 0.01. With regard to the cholesterol, phospholipid and bile salt content of gallbladder bile, cholesterol value decreased from an antepartum mean of 19.1 +/- 3.9 to 14.1 +/- 4.5 micromoles per milliliter in the third trimester. As a consequence, the lithogenic index of gallbladder bile decreased during pregnancy. The changes in chenodeoxycholic and total bile acid pool size are qualitatively similar to those reported by other investigators following the administration of estrogens to both baboons and other animal species. In the pregnant baboon, the decrease in pool size and in synthesis rate of bile acids is accompanied by a decrease in the cholesterol content of gallbladder bile. These changes in the lipid content of gallbladder bile are reflected in a decrease in the mean lithogenic index. These data suggest that the baboon may be an inappropriate model for studies of the relationship of pregnancy to cholesterol cholelithiasis in humans. In the baboon, both serum and biliary cholesterol values decrease during pregnancy. In humans, serum cholesterol levels increase during pregnancy. If the content of biliary cholesterol is a reflection of the serum concentration of this lipid, as has been suggested in recent studies, human bile may be more lithogenic during pregnancy. Additional studies are necessary to define the role of gallbladder contractility and bile stasis to gallstone formation during pregnancy.