title: Macromolecular transport across the rabbit proximal and distal colon.
abstract: BACKGROUND
  Although many studies have investigated macromolecular uptake in the stomach and small intestine, little is known about macromolecular uptake in the colon.
  
  
  OBJECTIVE
  To investigate the mechanisms involved in the transport of large antigenically intact macromolecules across the proximal and distal colonic epithelium in the rabbit.
  
  
  METHODS
  The mucosal to serosal movement of bovine serum albumin (BSA) was examined in modified Ussing chambers under short circuited conditions. The mucosal surface was exposed to varying concentrations of BSA, and after a 50 minute equilibration period, the mucosal to serosal flux of immunologically intact BSA was determined by ELISA. Total BSA flux was determined by the transport of radiolabelled 125I-BSA.
  
  
  RESULTS
  Intact BSA transport in proximal and distal colonic tissue showed saturable kinetics. Intact BSA transport in the proximal and distal segment was 7% and 2% of the total 125I-BSA flux respectively. Immunologically intact BSA transport in the distal segment was significantly less than that in the proximal segment. Intact BSA transport in the proximal colon was significantly reduced following treatment with sodium fluoride, colchicine, and tetrodotoxin. Cholinergic blockade had no effect on the uptake of intact BSA.
  
  
  CONCLUSIONS
  The findings indicate that the transport of intact macromolecules across the proximal and distal large intestine is a saturable process. Further, intact BSA transport in the proximal colon is an energy dependent process that utilises microtubules and is regulated by the enteric nervous system.
authors.affiliation: Gastrointestinal Research Group, University of Calgary, Alberta, Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Hardin
authors.forename: M H
authors.initials: MH
authors.lastname: Kimm
authors.forename: M
authors.initials: M
authors.lastname: Wirasinghe
authors.forename: D G
authors.initials: DG
authors.lastname: Gall
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D003078:Colchicine / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D005260:Female; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism; D046911:Macromolecular Substances; D008297:Male; D011817:Rabbits; D012710:Serum Albumin, Bovine / Q000493:pharmacokinetics*; D012969:Sodium Fluoride / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D012710:Serum Albumin, Bovine; D013779:Tetrodotoxin; D012969:Sodium Fluoride; D003078:Colchicine