HEPATIC-UPTAKE AND INTESTINAL-ABSORPTION OF BILE-ACIDS IN THE RABBIT

The existence of transporters for bile acids (BA) in liver and intesti ne has been well documented, but information is still needed as to the ir respective transport capacity. In the present investigation, we com pared the hepatic and intestinal transport rates for BA, using perfuse d livers and intestines. The livers and intestines were separately per fused and dose-response curves (0.25-10 mM) for tauroursodeoxycholate, taurocholate and taurodeoxycholate were obtained. The intestinal and mesenteric concentration and bile acid pattern were also evaluated in six non-fasting rabbits. Taurocholic, tauroursodeoxycholic and taurode oxycholic acid ileal absorption showed saturation kinetics in the inte stine as in the liver; the maximal uptake velocity for each bile acid in the liver was tenfold higher than the respective maximal transport velocity in the intestine; the Km values obtained in the liver were of the same order of magnitude, i.e. in the millimolar range. Taurocholi c, tauroursodeoxycholic and taurodeoxycholic acid transport difference s in the liver paralleled those in the intestine. Although the intesti ne was not homegeneously filled, the bile acid concentration in the il eal content fell into the range of the Km for the three studied bile a cids, while the portal blood total bile acid concentration was inferio r to the observed Kms of liver uptake. Therefore, both the hepatic and intestinal systems do not operate at their maximal transport rates at the prevailing concentrations in portal blood and luminal content, an d the hepatic transport occurs at its highest efficiency (below the Km values) in physiological conditions.