title: Evidence for predominantly paracellular transport of thyrotropin-releasing hormone across CACO-2 cell monolayers.
abstract: Uptake, transport, and metabolism of tripeptide thyrotropin-releasing hormone were examined in the human intestinal epithelial cell line, Caco-2. A linear relationship between rate and concentration was observed for both the uptake and the transport of thyrotropin-releasing hormone across Caco-2 cell monolayers. Transport of thyrotropin-releasing hormone was not affected by the presence of dipeptide glycylsarcosine, amino acid glycine, tripeptide thyrotropin-releasing hormone free acid as well as active transport inhibitors 2,4-dinitrophenol, sodium azide, ouabain, and amiloride. There was no formation of metabolites during the course of thyrotropin-releasing hormone transport across Caco-2 cells. Incubation of Caco-2 cell homogenate with thyrotropin-releasing hormone, however, showed a time-dependent hydrolysis of thyrotropin-releasing hormone and the formation of thyrotropin-releasing hormone free acid. Increased rate of transport in the presence of EDTA indicates a paracellular passive diffusion as the major route for the transport of TRH. The hydrolytic enzyme present in Caco-2 cells appeared to have little or no access to TRH during the transcellular transport across Caco-2 cell monolayers.
authors.affiliation: Department of Drug Metabolism, Glaxo Inc. Research Institute Research Triangle Park, NC 27709.
authors.forename: L S
authors.initials: LS
authors.lastname: Gan
authors.forename: T
authors.initials: T
authors.lastname: Niederer
authors.forename: C
authors.initials: C
authors.lastname: Eads
authors.forename: D
authors.initials: D
authors.lastname: Thakker
mesh_terms: D019297:2,4-Dinitrophenol; D000230:Adenocarcinoma; D000584:Amiloride / Q000494:pharmacology; D001386:Azides / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003110:Colonic Neoplasms; D004140:Dinitrophenols / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004848:Epithelium / Q000378:metabolism; D005998:Glycine / Q000494:pharmacology; D006801:Humans; D007422:Intestines; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D019810:Sodium Azide; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D014316:Tritium; D014407:Tumor Cells, Cultured
chemical_list: D001386:Azides; D004140:Dinitrophenols; D004151:Dipeptides; D014316:Tritium; C004194:glycylsarcosine; D010042:Ouabain; D013973:Thyrotropin-Releasing Hormone; D000584:Amiloride; D019810:Sodium Azide; D004492:Edetic Acid; D019297:2,4-Dinitrophenol; D005998:Glycine