title: Kinetics of thyroxine (T(4)) and triiodothyronine (T(3)) transport in the isolated rat heart.
abstract: The dynamics and kinetics of thyroid hormone transport in the isolated rat heart were examined using the modified unidirectional paired tracer dilution method. The uptake of (125)I-thyroxine ((125)I-T(4)) and (125)I-triiodothyronine ((125)I-T(3)) from the extracellular space into heart cells was measured relative to the extracellular space marker (3)H-mannitol. The thyroid hormone maximal uptake was 54.4 % for (125)I-T(4) and 52.15 % for (125)I-T(3). The thyroid hormone net uptake was 25.69 % for (125)I-T(4) and 25.49 % for (125)I-T(3). Backflux from the intracellular space was 53.17 % for (125)I-T(4) and 61.59 % for (125)I-T(3). In the presence of unlabelled thyroid hormones, (125)I-T(4) and (125)I-T(3) maximal uptakes were reduced from 10.1 to 59.74 % and from 34.6 to 65.3 %, respectively, depending on the concentration of the unlabelled hormone, suggesting a saturable mechanism of the thyroid hormone uptake by the heart cells, with K(m(T4))= 105.46 microM and the maximal rate of (125)I-thyroid hormone flux from the extracellular space to heart cells (V(max(T4))) = 177.84 nM min(-1) for (125)I-T(4) uptake, and K(m(T3)) = 80.0 microM and V(max(T3)) = 118.5 nM min(-1) for (125)I-T(3) uptake. Experimental Physiology (2001) 86.1, 13-18.
authors: Institute of Physiology, Faculty of Medicine, University of Kragujevac, Kragujevac, Yugoslavia.
authors: M
authors: M
authors: Rosic
authors: S
authors: S
authors: Pantovic
authors: A
authors: A
authors: Lucic
authors: N
authors: N
authors: Ribarac-Stepic
authors: I
authors: I
authors: Andjelkovic
mesh_terms: D000818:Animals; D001692:Biological Transport; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013974:Thyroxine / Q000493:pharmacokinetics*; D014284:Triiodothyronine / Q000493:pharmacokinetics*
chemical_list: D014284:Triiodothyronine; D013974:Thyroxine