- 期刊
Complementary Effect of Bile Salt Absorption in Terminal Ileum
末端迴腸在腸道膽鹽吸收之輔助功能
摘要
一般皆認為膽鹽主要吸收是在迴腸，但1983年McClintock與蕭證實空腸之被動運送(passive transport, PT)在膽鹽吸收佔主要地位，雖然迴腸亦有PT之能力，但因空腸內膽鹽濃度高，故吸收總量超過迴腸，而迥腸之主動運送(active transoprt, AT）是在低膽鹽濃度時吸收膽鹽之方法，為補助功能，為證實此構想設計本實驗。膽鹽由空腸與迴腸吸收，經肝臟後，大部份由膽汁排小腸中，完成肝內循環。將標示有放射性元素(上標14)C或(上標3)H之膽鹽，taurocholate (TC)或glycocholate (GC)，以不同濃度注入約10－15公分長的老鼠空腸或末端迴腸，放置30分鐘。腸子所吸收膽鹽之量，可由總膽管收集之膽汁中，計算其放射性元素之量而求得，進而可求得單位腸子所吸收膽鹽之量。以10mM等量之TC注入空腸與末端迴腸中，每公分長度之空腸吸收量只有迴腸之1/7，不論是同隻老鼠或不同隻老鼠之空腸迴腸配對，其結果相同，表示空腸迴腸之吸收不會互相干擾外，同樣10mM濃度，迴腸吸收大於空腸七倍，而用GC10mM同樣濃度，則約為10倍。若空腸內膽鹽濃度為迴腸之10倍，則兩者吸收量近相等。將空腸內濃度降至2mM GC，則吸收約為零。提高迴腸內濃度到20mM GC，其吸收量只增加10mM時的一半而已(194 vs 123μM/cm)。但降低迴腸濃度至2mM時，其吸收量只減少10mM時的40%而已。可知末端迴腸在甚低濃度時，吸收能力仍強，表示當濃度甚低時(2mM)，PT無法勝任（吸收約零），只有迴腸之AT可有效吸收。故迴腸是在甚低濃度時，具有將膽鹽盡量回收之輔助功能。
並列摘要
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.