Complementary Effect of Bile Salt Absorption in Terminal Ileum

Abstract

Bile salts is absorbed by intestine via passive transport in all regions of the intestine and via active transport in the ileum. The bile salt concentration in terminal ileum is low, and its active transport is a complementary function in the absorption of bile salt. To demonstrate this phenomenon, either taurocholate (TC) or glycocholate (GC) solution with isotope was placed in the intestine of rat under various concentrations. The amount of bile salt (TC or GC) absorbed in intestine was counted from bile collected in common bile duct by Parkard Tricarb Counter. With the same concentration (10mM) in both jejunum and ileum, the absorption of bile salt by ileum was 7 times more than that by jejunum, no matter in the same rat or the paired one. This showed that absorption was independent in ileum and jejunum, without interference between them. In jejunum, the bile salt being absorbed would increase in amount (4.4 times) with bile salt concentration rising from 10mM to 20mM, and markedly decrease to about zero at concentration as lower as 2mM. In ileum, it would not increase so sensitively with the change of luminal concentration (ratio 1:1.6:0.6 as 10:20:2mM was applied). Therefore, while passive transport does not work at as low concentration as 2mM, the active transport of terminal ileum has complementary effect at lower concentration such as 2mM and absorbs bile salt as complete as possible.