Evaluation of triiodothyronine (T3) kinetics in normal subjects, in hypothyroid, and hyperthyroid patients using specific antiserum for the determination of labeled T3 in plasma.
Triiodothyronine (T3) kinetics was evaluated using [125I]T3 and the single injection technique; 5 hypothyroid, 6 hyperthyroid patients, and 10 euthyroid control subjects were studied. Plasma-labeled T3 concentration was measured by means of a new method based on extraction of the hormone on Sephadex G-25 columns followed by elution with the specific antiserum. This technique allows a far better separation of the hormonal radioactivity from the labeled iodide produced from T3 catabolism in comparison with the TCA-precipitation-butanol extraction method. The analysis of the experimental data has been performed using non-compartmental treatment (integral approach); results of mono-compartmental analysis of the same data are also reported for comparison. Average metabolic clearance was 15.3 +/- 0.6 (mean + SEM) liters/day/m2 body surface in normal subjects; it was significantly decreased in hypothyroid patients (11.4 +/- 1.1) and significantly increased (33.4 +/- 4.0) in hyperthyroidism. The total plasma equivalent distribution volume was found significantly enlarged in hyperthyroid patients (22.6 +/- 0.9 liters/m2) in respect to that measured in the control group (15.6 +/- 0.4), whereas it was not different from normal value in hypothyroid patients (17 +/- 1.7). Using plasma concentration of native T3, absolute turnover rate and extrathyroidal pool were also estimated; their values were 6.5, 23.7, and 131.7 micrograms/day/m2 and 10.1, 24.2, and 90.6 micrograms/m2, respectively, in hypothyroid, normal, and hyperthyroid groups.
D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000378:metabolism*; D007037:Hypothyroidism / Q000378:metabolism*; D007106:Immune Sera; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism*
D007106:Immune Sera; D014284:Triiodothyronine