Relative Sensitivity of Different Biological Responses to Small Quantities of Thyroxine and Triiodothyronine

Evans, Edward S.; Rosenberg, Lawson L.; Evans, Alison B.; Koneff, Alexei A.

doi:10.1210/endo-74-5-770

Cited by 37 publications

(21 citation statements)

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“…We chose thyroidectomy to evaluate the importance of TTR-bound T 4 in an acute and extreme condition of thyroid hormone deprivation. Removal of the thyroid gland induces growth arrest (Evans et al 1964) and both the TTR-null and the wild-type mice presented a marked decrease in body weight gain in comparison with their sham-operated counterparts. Two weeks after ablation of the thyroid, TTR-null and wild-type mice showed similar drastic reductions in T 4 and T 3 plasma and tissue levels, which were not further aggravated 3 weeks after thyroid ablation (data not shown).…”

Section: Figurementioning

confidence: 99%

Transthyretin is not necessary for thyroid hormone metabolism in conditions of increased hormone demand

Sousa¹,

Escobar²,

Oliveira³

et al. 2005

Journal of Endocrinology

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Thyroid hormones circulate in blood mainly bound to plasma proteins. Transthyretin is the major thyroxine plasma carrier in mice. Studies in transthyretin-null mice revealed that the absence of transthyretin results in euthyroid hypothyroxinemia and normal thyroid hormone tissue distribution, with the exception of the choroid plexus in the brain. Therefore, transthyretin does not influence normal thyroid hormone homeostasis under standard laboratory conditions. To investigate if transthyretin has a buffer/storage role we challenged transthyretin-null and wild-type mice with conditions of increased hormone demand: (i) exposure to cold, which elicits thermogenesis, a process that requires thyroid hormones; and (ii) thyroidectomy, which abolishes thyroid hormone synthesis and secretion and induces severe hypothyroidism. Transthyretin-null mice responded as the wild-type both to changes induced by stressful events, namely in body weight, food intake and thyroid hormone tissue content, and in the mRNA levels of genes whose expression is altered in such conditions. These results clearly exclude a role for transthyretin in thyroid hormone homeostasis even under conditions of increased hormone demand.

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Section: Figurementioning

confidence: 99%

Transthyretin is not necessary for thyroid hormone metabolism in conditions of increased hormone demand

Sousa¹,

Escobar²,

Oliveira³

et al. 2005

Journal of Endocrinology

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“…By indirect study we have come to the same conclusion [1], In the fasted thyroidectomized rats there is an increase in liver acetyl-CoA and fatty acids and blood ketone bodies and these rats main tain the same levels of liver citrate as when fed [1], all of which would suggest an augmented arrival of fatty acids to the liver from peripheral depots. We do not know how this elevated turnover of lipids in the adipose tissue of the thyroidectomized rats might be driven in vivo, but actually in these animals there is a parallel reduction in the lipolytic hormones such as those secreted by the adenohypophysis [6,7,13,18] and in the antilipolytic hormones such as insulin [1,3,16]. In any event, the ability to mobilize fat stores in the hypothyroid animals, even to a faster rate than in the normals, might play an important role in the hypothyroids metabolic adaptation to fasting which allows them to survive despite the low blood glucose levels that they attain in this situation [1].…”

Section: Adipose Tissue Metabolism In Fasted Thyroidectomized Ratsmentioning

confidence: 99%

Effect of Thyroid Status on Glycerol Metabolism in Adipose Tissue of Fasted Male Rats

Montoya¹,

Herrera²

1974

Horm Res

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We have studied the in vitro metabolism of glycerol by epididymal fat pads from thyroidectomized rats daily injected with either 0, 0.1 or 25 µg of thyroxine and intact controls after a previous fast of 48 h. The tissues coming from the thyroidectomized rats receiving 25 µg of thyroxine produce maximal amounts of glycerol while this parameter does not differ among the other groups. The same is true for the formation of ¹⁴CO₂ from 1–¹⁴C glycerol while the uptake of this and its conversion to ¹⁴C-labelled total lipids is maximal in the thyroidectomized rats no receiving thyroxine, it decreases in those treated with 0.1 µg and it is minimal in those receiving 25 µg and the controls. When proper corrections for the changes in the specific activity of the tracer are carried out it is seen that the rates of lipolysis and those of glycerol uptake and its conversion to lipids are augmented in the thyroidectomized rats receiving 0 or 25 µg of thyroxine, while that of the oxidation of glycerol to C0₂ is only elevated in the second group. The augmented lipolysis in the fasted hypothyroid animals found here is different from studies which omit to take account of the reutilization of glycerol by adipose tissue and can be used to explain the survival of these animals when food is withheld. In some way this could compensate the intense hypoglycemia found in the fasted hypothyroid animals which by itself could be contributing to the adipokinetic effect.

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“…But they could just as well be manifestations of the intense impairment of many of the functions of the anterior pituitary (and of anterior pituitarydependent glands and tissues) which accompanies T in the rat [4,6]. Ob viously, impairment of such important functions could have widespread effects on enzyme activities as well as on hormonal levels.…”

Section: Resultsmentioning

confidence: 99%

Effect of Thyroidectomy and of Several Goitrogens on β-Glucuronidase Activity and Insulin Levels of Rats

Jolin¹,

Núñez²,

Mora³

1972

Horm Res Paediatr

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Thyroidectomized rats present lower plasma β-glucuronidase activity than age-paired controls. A very small daily dose of L-thyroxine (0.2 µg/100 g body wt.) which reinitiated growth in thyroidectomized rats increased their plasma β-glucuronidase activity toward the values of age-paired controls. Hypothyroidism induced by different drugs decreased the plasma activity of the enzyme. Animals on KCI04 had the lowest values and were comparable to those observed in thyroidectomized rats. However rats on PTU and KSCN showed higher values than the KCIO₄ treated rats, although they were lower than those of the controls. The same change to β-glucuronidase was observed in plasma insulin levels.

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Relative Sensitivity of Different Biological Responses to Small Quantities of Thyroxine and Triiodothyronine

Cited by 37 publications

References 0 publications

Transthyretin is not necessary for thyroid hormone metabolism in conditions of increased hormone demand

Transthyretin is not necessary for thyroid hormone metabolism in conditions of increased hormone demand

Effect of Thyroid Status on Glycerol Metabolism in Adipose Tissue of Fasted Male Rats

Effect of Thyroidectomy and of Several Goitrogens on β-Glucuronidase Activity and Insulin Levels of Rats

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