The distribution kinetics of triiodothyronine: studies of euthyroid subjects with decreased plasma thyroxine-binding globulin and patients with Graves' disease

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Abstract

The kinetics of distribution of 3,3′,5-triiodo-L-thyronine (T3) have been studied employing both a single-injection and a continuous infusion of T3-131I. External monitoring of radioactivity in the liver during the infusion permitted estimation of the hepatic distribution volume (VH) and the one-way hepatic clearance (CH) of the hormone. Among 10 euthyroid control subjects, VH averaged 2.07 liters ±0.50 (SD), and the mean value for CH, 231 ml of plasma per min (±64). In three euthyroid men whose plasma showed decreased binding capacity by thyroxine-binding globulin (TBG) abnormally high VH and CH values were found, the increase in CH being proportional to the decrease in binding activity by plasma proteins. Among all 13 subjects, there was a high correlation (+ 0.86) between CH and the proportion of free hormone in plasma, measured in vitro.

Authors

Ralph R. Cavalieri, Martin Steinberg, Gilbert L. Searle