title: Weanling, but not adult, rabbit colon absorbs bile acids: flux is linked to expression of putative bile acid transporters.
abstract: Intestinal handling of bile acids is age dependent; adult, but not newborn, ileum absorbs bile acids, and adult, but not weanling or newborn, distal colon secretes Cl(-) in response to bile acids. Bile acid transport involving the apical Na(+)-dependent bile acid transporter (Asbt) and lipid-binding protein (LBP) is well characterized in the ileum, but little is known about colonic bile acid transport. We investigated colonic bile acid transport and the nature of the underlying transporters and receptors. Colon from adult, weanling, and newborn rabbits was screened by semiquantitative RT-PCR for Asbt, its truncated variant t-Asbt, LBP, multidrug resistance-associated protein 3, organic solute transporter-alpha, and farnesoid X receptor. Asbt and LBP showed maximal expression in weanling and significantly less expression in adult and newborn rabbits. The ileum, but not the colon, expressed t-Asbt. Asbt, LBP, and farnesoid X receptor mRNA expression in weanling colon parallel the profile in adult ileum, a tissue designed for high bile acid absorption. To examine their functional role, transepithelial [(3)H]taurocholate transport was measured in weanling and adult colon and ileum. Under short-circuit conditions, weanling colon and ileum and adult ileum showed net bile acid absorption: 1.23 +/- 0.62, 5.53 +/- 1.20, and 11.41 +/- 3.45 nmol x cm(-2) x h(-1), respectively. However, adult colon secreted bile acids (-1.39 +/- 0.47 nmol x cm(-2) x h(-1)). We demonstrate for the first time that weanling, but not adult, distal colon shows net bile acid absorption. Thus increased expression of Asbt and LBP in weanling colon, which is associated with parallel increases in taurocholate absorption, has relevance in enterohepatic conservation of bile acids when ileal bile acid recycling is not fully developed.
authors.affiliation: Department of Physiology and Biophysics, University of Illinois, Chicago, Illinois 60612, USA.
authors.forename: Dirk
authors.initials: D
authors.lastname: Weihrauch
authors.forename: Jainuch
authors.initials: J
authors.lastname: Kanchanapoo
authors.forename: Mei
authors.initials: M
authors.lastname: Ao
authors.forename: Roli
authors.initials: R
authors.lastname: Prasad
authors.forename: Pawinee
authors.initials: P
authors.lastname: Piyachaturawat
authors.forename: Mrinalini C
authors.initials: MC
authors.lastname: Rao
mesh_terms: D000375:Aging / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis; D003106:Colon / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D005260:Female; D007408:Intestinal Absorption / Q000502:physiology*; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis; D027361:Organic Anion Transporters / Q000096:biosynthesis; D029363:Organic Anion Transporters, Sodium-Dependent / Q000096:biosynthesis; D011817:Rabbits; D018160:Receptors, Cytoplasmic and Nuclear; D027981:Symporters / Q000096:biosynthesis; D014157:Transcription Factors / Q000096:biosynthesis; D014886:Weaning; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D001647:Bile Acids and Salts; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D027361:Organic Anion Transporters; D029363:Organic Anion Transporters, Sodium-Dependent; D018160:Receptors, Cytoplasmic and Nuclear; D027981:Symporters; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C037643:bile acid binding proteins; C071908:sodium-bile acid cotransporter; C114462:multidrug resistance-associated protein 3