Thyroxine-Protein Interactions. VII. Effect of Thyroxine Analogs on the Binding of<sup>125</sup>I-Thyroxine to Highly Purified Human Thyroxine-Binding Globulin

Hao, Yu-lee; Tabachnick, Milton

doi:10.1210/endo-88-1-81

Cited by 31 publications

(9 citation statements)

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“…As noted previously (9), the binding capacity of the TBG was less than 1 mole T4 per mole TBG; the maximal T4-binding capacity approached a limiting value of 0.25-0.3 mole T4 per mole TBG.…”

Section: Methodssupporting

confidence: 77%

“…The highly purified human TBG used in these experiments is the same TBG preparation previously described (9,10). As noted previously (9), the binding capacity of the TBG was less than 1 mole T4 per mole TBG; the maximal T4-binding capacity approached a limiting value of 0.25-0.3 mole T4 per mole TBG.…”

Section: Methodsmentioning

confidence: 70%

“…Assay for free and bound T4 in mixtures was done by subjecting solutions to electrophoresis in starch gel at pH 8.6 in 0.03 M borate buffer as described previously (9).…”

Section: Methodsmentioning

confidence: 99%

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Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of¹²⁵I-Thyroxine to Purified Thyroxine-Binding Globulin

Tabachnick

Hao

Korcek

1973

The Journal of Clinical Endocrinology & Metabolism

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The effect of oleate, diphenylhydantoin, and heparin on the binding of 125 I-thyroxine to highly purified human thyroxine-binding globulin (TBG) has been studied. Oleate was about twice as effective as diphenylhydantoin in displacing 125 I-thyroxine from TBG as ascertained by starch gel electrophoresis at pH 8.6. In vitro addition of heparin was relatively ineffective in inhibiting thyroxine (T4) binding to TBG. The possible physiological significance of the results lies in the observation that oleate inhibited T4-binding to TBG at molar ratios to T4 that were well within the normal range (free fatty acid: T4) existing in plasma. (/ Clin Endocrinol Metab 36: 392, 1973) HPHE concentration of free fatty acids (FFA) •*-in human plasma is known to fluctuate widely in response to a variety of dietary and hormonal stimuli. For example, the plasma level of FFA is increased by fasting (1), in uncontrolled diabetes (2), and after administration of epinephrine (1,3), norepinephrine (4), growth hormone (5), and thyroid hormone (6). It has also been shown by Hollander et al. (7) that induction of high FFA levels in human plasma both in vivo and in vitro leads to a rise in the concentration of free thyroxine (T4). The authors (7) attributed the rise in percent free T4 to competition between FFA and T4 for thyroxine-binding sites in plasma. They also suggested that fluctuations in circulating levels of free fatty acids could serve as a regulator of peripheral thyroid hormone action by influencing the binding of thyroxine in plasma (7). Since thyroxine-binding globulin (TBG) is the major T4-binding protein in plasma (8), it was of interest to investigate the effect of a representative fatty acid such as oleate on the interaction of T4 with purified TBG. In addition the effects of diphenylhydantoin and heparin on the binding of T4 to TBG have also been studied.The highly purified human TBG used in these experiments is the same TBG preparation previously described (9,10). As noted previously (9), the binding capacity of the TBG was less than 1 mole T4 per mole TBG; the maximal T4-binding capacity approached a limiting value of 0.25-0.3 mole T4 per mole TBG.Starch hydrolyzed for gel electrophoresis was a product of Connaught Research Laboratories, Toronto, Canada and was purchased from Fisher Scientific Co. 125

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Section: Methodssupporting

confidence: 77%

Section: Methodsmentioning

confidence: 70%

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Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of¹²⁵I-Thyroxine to Purified Thyroxine-Binding Globulin

Tabachnick

Hao

Korcek

1973

The Journal of Clinical Endocrinology & Metabolism

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“…Neither was found. While there is controversy concerning the degree of in vivo binding of T3 to TBG (25)(26)(27)(28), binding of T3 to TBG in vitro is readily demonstrable though the relative affinity of T3 for TBG varies from ',~to Mo of that of T4 in different systems (20,23,29 (23,30,31). T3 binding to albumin is weak and easily interrupted by a variety of materials (23,(31)(32)(33)(34).…”

Section: Discussionmentioning

confidence: 99%

Triiodothyronine Radioimmunoassay

Lieblich¹,

Utiger²

1972

J. Clin. Invest.

122

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A B S T R A C T Highly specific antisera to triiodothyronine (T3) were prepared by immunization of rabbits with T3-bovine serum albumin conjugates. Antisera with T3 binding capacity of up to 600 ng/ml were obtained. The ability of various thyronine derivatives to inhibit the binding of T3-MI to anti-T3 serum was found to vary considerably. L-Ts, D-T3 and several triiodoanalogues were potent inhibitors of the reaction. Little inhibition of T3-1"I binding was produced by L-thyroxine (T4) or other tetraiodo-analogues, thyronine or iodotyrosines. Chromatography of several T4 preparations indicated that most of their very slight activity could be ascribed to contamination with T3.Successful assay of Ts in serum was accomplished by the addition of diphenylhydantoin to the assay system. Under these circumstances, recovery of Ta added to serum was excellent, and addition of T4 was without significant effect. Serum Ts concentrations in normal subjects averaged 145 ±25 ng/100 ml (SD). Increased concentrations (429 ±146 ng/100 ml) were observed in hyperthyroid patients whereas those with hypothyroidism had serum Ts levels of 99 ±24 ng/100 ml. Elevated Ts concentrations were found also in hypothyroid patients receiving 25 gg or more of T3 daily and in those receiving 300 ,g of T4 daily. Serial measurements of T3 concentrations in subjects after oral T3 administration revealed peak Ta concentrations 2-4 hr after T3 administration. Intramuscular administration of thyrotropin (TSH) resulted in earlier and more pronounced increases in serum T3 than in serum T4 concentrations.Triiodothyronine (T3)1 was recognized to be a biologically active secretory product of the thyroid gland over a decade ago (1). Recent studies have indicated that it is formed extrathyroidally as well (2, 3). Nevertheless, relatively little information concerning the role of Ts secretion in different thyroid disorders has

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“…1,30 Benvenga and Robbins have also demonstrated binding to lipoproteins such as high-density lipoprotein. 32,33 The T 3 affinity for binding to these proteins is approximately one-thirtieth that of T 4, 34 which explains the higher turnover rate of T 3 compared with T 4 .…”

Section: Eliminationmentioning

confidence: 99%

A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism

Colucci¹,

Yue²,

Ducharme³

et al. 2010

European Endocrinology

129

133

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Thyroxine hormone has been recognised since the early part of the nineteenth century and levothyroxine has been available since the mid-nineteenth century as a replacement for deficient thyroid hormones. While levothyroxine remains the staple treatment for hypothyroidism even to this day, its optimal use can be challenging. As is often the case with older drugs, the pharmacokinetics of levothyroxine is often under-appreciated or misunderstood and many factors influence the optimal dosing of levothyroxine. This article will review the pharmacokinetics of levothyroxine in the treatment of hypothyroidism and highlight major concepts that should aid both clinicians and researchers.

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Thyroxine-Protein Interactions. VII. Effect of Thyroxine Analogs on the Binding of¹²⁵I-Thyroxine to Highly Purified Human Thyroxine-Binding Globulin

Cited by 31 publications

References 1 publication

Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of¹²⁵I-Thyroxine to Purified Thyroxine-Binding Globulin

Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of¹²⁵I-Thyroxine to Purified Thyroxine-Binding Globulin

Triiodothyronine Radioimmunoassay

A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism

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Thyroxine-Protein Interactions. VII. Effect of Thyroxine Analogs on the Binding of125I-Thyroxine to Highly Purified Human Thyroxine-Binding Globulin

Cited by 31 publications

References 1 publication

Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of125I-Thyroxine to Purified Thyroxine-Binding Globulin

Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of125I-Thyroxine to Purified Thyroxine-Binding Globulin

Triiodothyronine Radioimmunoassay

A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism

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Product

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Thyroxine-Protein Interactions. VII. Effect of Thyroxine Analogs on the Binding of¹²⁵I-Thyroxine to Highly Purified Human Thyroxine-Binding Globulin

Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of¹²⁵I-Thyroxine to Purified Thyroxine-Binding Globulin

Effect of Oleate, Diphenylhydantoin, and Heparin on the Binding of¹²⁵I-Thyroxine to Purified Thyroxine-Binding Globulin