title: Evidence for carrier-mediated uptake of triiodothyronine in cultured anterior pituitary cells of euthyroid rats.
abstract: T3 uptake and TSH secretion were investigated in anterior pituitary cells isolated from adult fed Wistar rats and cultured for 3 days in medium containing 10% fetal calf serum. TSH release during culture increased linearly with the number of cells in the range of 80,000-800,000 cells/well. Uptake and incubation experiments were performed at 37 C in medium containing 0.5% BSA. Incubation with TRH (0.1 microM) for 2 h stimulated TSH release 2.6-fold, and this effect was partly (approximately 45%) suppressed by preexposure for 2 h to T3 (0.01-1 microM) or T4 (1 microM). Similar concentrations of T3 and T4 reduced the cellular uptake of [125I]T3 (50 pM) during 1 h of incubation by 55%. After 15 min of incubation, [125I]T3 uptake (percent dose) amounted to 1.26 +/- 0.05% (mean +/- SE; n = 9)/500,000 cells. The major part (75%) of the [125I]T3 was found in the extranuclear fraction. Simultaneous incubation with unlabeled T3 (1 or 10 microM) reduced [125I]T3 uptake by 43% (n = 3; P < 0.001) and 52% (n = 6; P < 0.001), respectively. Reduction of the temperature to 20 C diminished the T3-suppressible fraction of [125I]T3 uptake approximately 3-fold. After preincubation (30 min) and incubation (15 min) with monodansylcadaverine (100 microM), the uptake of [125I]T3 was reduced by 32% (n = 3; P < 0.01). When the Na+ gradient was reduced by preincubation and incubation with ouabain (0.5 mM) or monensin (10 or 100 microM), T3 uptake was inhibited by 25% (n = 5; P < 0.01), 37% (n = 6; P < 0.001), and 61% (n = 3; P < 0.001), respectively. It is concluded that 1) T3 is taken up by the pituitary by a carrier-mediated mechanism, and 2) this uptake is at least partly dependent on the Na+ gradient.
authors.affiliation: Department of Internal, Erasmus University Medical School, Rotterdam, The Netherlands.
authors.forename: M E
authors.initials: ME
authors.lastname: Everts
authors.forename: R
authors.initials: R
authors.lastname: Docter
authors.forename: J C
authors.initials: JC
authors.lastname: van Buuren
authors.forename: P M
authors.initials: PM
authors.lastname: van Koetsveld
authors.forename: L J
authors.initials: LJ
authors.lastname: Hofland
authors.forename: M
authors.initials: M
authors.lastname: de Jong
authors.forename: E P
authors.initials: EP
authors.lastname: Krenning
authors.forename: G
authors.initials: G
authors.lastname: Hennemann
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D002478:Cells, Cultured; D005260:Female; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008985:Monensin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D007166:Immunosuppressive Agents; D014284:Triiodothyronine; D010042:Ouabain; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D008985:Monensin; C008542:monodansylcadaverine; D002103:Cadaverine; D013974:Thyroxine